Commercial Buildings
Special Working Group
Current Standard Solutions for Buildings
Report 2010
Commercial Buildings SWG
Current Standard Solutions
Executive Summary
As an initiative within the Energy Agreements Programme, SEI have launched Special Working
Groups which are formed by groups of member companies in conjunction with SEI. This report is an
outcome of the ‘Commercial Buildings Special Working Group’ charged with considering ways to
reduce the energy consumption of Commercial Buildings. The report focuses on “Current Standard
Solutions for Buildings and Considerations when Retrofitting Buildings”. Bearing in mind that most
member companies have a number of existing buildings that could be classified as ‘Commercial
Buildings’ under their ownership, there is particular focus on the retrofitting opportunities and
operational improvements that can be made with regard to the different technologies.
Further reason to focus on existing buildings lies in the fact that the current economic climate implies
that most short to medium term work will lie in the refurbishment/upgrading of existing buildings.
Also with the emergence of energy management systems and associated standards such as I.S. EN
16001:2009, the improvement of operational procedures, as well as the documentation requirements
of those procedures is also likely to be an area of growing relevance to many companies.
Whenever a building is being refurbished/upgraded presents an opportunity for building-services
engineers to add value and reduce energy costs and carbon emissions through energy efficient
measures. With increased awareness of the importance of energy efficiency in buildings, not only to
reduce carbon emissions but also to meet regulatory and planning requirements, the refurbishment
of building services is a very important subject.
In the past many energy management programs have concentrated on the acquisition of energy and
installing energy-efficient technologies, with less emphasis placed on efficient operation. This is most
likely the result of efficient operation being the least understood component of an energy
management program. Yet this component can offer high potential for savings with little or no
capital outlay and hence is addressed within this guideline.
Participating companies in this Special Working Group spanned a range of sectors including, retail, IT,
dairy and commercial and were a combination of privately owned and semi state companies.
Technical descriptions of reviewed technologies have been kept short and precise. This guideline has
instead focused on two aspects of the reviewed technologies, namely;
•
•
Suitability as a retrofit technology
Optimisation from an operational perspective
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Table of contents
Executive summary .............................................................................................................................................................. 2
1.
Introduction .............................................................................................................................................................. 6
2.
Building Fabric ......................................................................................................................................................... 8
2.1.
Thermal Comfort ..................................................................................................................................................... 8
2.2.
Thermal Envelopes ................................................................................................................................................. 9
2.2.1. Insulation ................................................................................................................................................................. 10
2.2.2. Windows and Doors ............................................................................................................................................ 11
2.2.3. Air tightness ........................................................................................................................................................... 11
2.2.4. Thermal Bridges .................................................................................................................................................... 11
2.3.
Heat Losses and Gains ........................................................................................................................................ 13
2.3.1. Reducing Unwanted Heat Gain....................................................................................................................... 13
2.3.2. Thermal Mass ......................................................................................................................................................... 13
3.
Heating Systems ................................................................................................................................................... 15
3.1.
Fossil Fuel Boilers ................................................................................................................................................. 15
3.1.1. Atmospheric boilers ............................................................................................................................................ 15
3.1.2. Forced/induced-draught boilers .................................................................................................................... 15
3.1.3. Condensing boilers.............................................................................................................................................. 15
3.1.4. Dual-fuel boilers ................................................................................................................................................... 16
3.2.
Biomass Boilers ..................................................................................................................................................... 17
3.3.
Air or Ground Source Heat Pumps ................................................................................................................. 19
3.4.
Radiant Heating .................................................................................................................................................... 21
3.5.
CHP ............................................................................................................................................................................ 22
3.6.
Solar .......................................................................................................................................................................... 24
3.6.1. Solar Air Heating ................................................................................................................................................... 24
3.6.2. Solar Water Heating ............................................................................................................................................ 25
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4.
Cooling ..................................................................................................................................................................... 28
4.1.
Vapour Compression Chillers........................................................................................................................... 29
4.2.
Absorption Cooling ............................................................................................................................................. 31
4.3.
Evaporative Cooling ............................................................................................................................................ 34
4.4.
Free Cooling ........................................................................................................................................................... 36
4.4.1. Water Side Free Cooling .................................................................................................................................... 37
4.4.2. Air Side Free Cooling ........................................................................................................................................... 37
5.
Air Conditioning ................................................................................................................................................... 40
5.1.
Constant Volume .................................................................................................................................................. 40
5.2.
Variable Air Volume ............................................................................................................................................. 42
5.3.
Chilled Ceilings...................................................................................................................................................... 43
5.4.
Split Systems .......................................................................................................................................................... 44
5.5.
Room Based Heat Pumps .................................................................................................................................. 45
5.6.
Variable Refrigerant Flow (VRF)....................................................................................................................... 46
5.7.
Mechanical Ventilation and Energy Recovery ........................................................................................... 47
5.7.1. Thermal Wheel ...................................................................................................................................................... 47
5.7.2. Run-Around Loop................................................................................................................................................. 48
5.7.3. Air-to-Air Plate Heat Exchanger ...................................................................................................................... 49
5.7.4. Heat Pipe ................................................................................................................................................................. 49
5.8.
Natural Ventilation ............................................................................................................................................... 50
5.8.1. Single-sided ventilation ..................................................................................................................................... 51
5.8.2. Cross ventilation ................................................................................................................................................... 51
5.8.3. Stack ventilation ................................................................................................................................................... 51
5.8.4. Stack/wind ventilators ........................................................................................................................................ 51
6.
Lighting .................................................................................................................................................................... 53
6.1.
Lighting Terminology ......................................................................................................................................... 53
6.2.
Control ..................................................................................................................................................................... 56
6.3.
Recommended Fittings...................................................................................................................................... 56
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7.
Controls.................................................................................................................................................................... 59
7.1.
Control Terminology ........................................................................................................................................... 60
7.2.
Control algorithms ............................................................................................................................................... 62
7.2.1. Controlling by time.............................................................................................................................................. 62
7.2.2. Controlling by occupancy ................................................................................................................................. 63
7.2.3. Controlling by condition ................................................................................................................................... 63
7.3.
BMS and M&T ......................................................................................................................................................... 65
7.4.
Wireless Sensors and Meters ............................................................................................................................ 67
7.5.
Individualised Workspace Control ................................................................................................................. 69
8.
Retro Commissioning ......................................................................................................................................... 71
8.1.
Overview ................................................................................................................................................................. 71
8.2.
The Retro-commissioning process ................................................................................................................ 72
8.3.
Summary ................................................................................................................................................................. 73
9.
Under Utilised Technologies ............................................................................................................................ 74
9.1.
Photovoltaic ........................................................................................................................................................... 74
9.2.
Fuel Cells.................................................................................................................................................................. 75
9.3.
Wind .......................................................................................................................................................................... 77
9.4.
Ground Coupled (Air) Heating / Cooling ..................................................................................................... 81
9.5.
Thermal Storage Aquifers ................................................................................................................................. 82
10.
Conclusions ............................................................................................................................................................ 85
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1. Introduction
The Energy Agreements Programme is aimed at the largest energy users interested in taking a strong,
strategic and systematic approach to energy management. Firms agree to implement the new
Energy Management Standard, IS EN 16001, and to pursue an aggressive programme of energy
efficiency action and investment. In return, SEI offers relationship support, advice and networking.
The primary aim of the agreements programme is pooling energy efficiency knowledge, increasing
cost competitiveness and reducing energy consumption.
As an initiative within the Energy Agreements Programme, SEI have launched Special Working
Groups which are formed by groups of member companies in conjunction with SEI. A programme of
work is determined by the Group which may consists of shared studies, self-assessments,
identification of energy saving projects, grouped special investigations, published guidelines and
recommendations to the wider group of Energy Agreements participants.
This particular Special Working Group’s focus is on the energy consumption of Commercial Buildings
and ways to minimise the same. As part of the output from this group, this report considers “Current
Standard Solutions for Buildings and Considerations when Retrofitting Buildings”.
As mentioned the member companies involved have all indicated a commitment to implementation
of the new Energy Management Standard, IS EN 16001. This brings a requirement to pursue both
energy efficiency improvement projects and also demonstrate and document improved operational
procedures. With that in mind the focus of this report gives specific reference to these retrofit
considerations and to improved operational procedures. Thus as each of the technologies are
described, a section entitled “Retrofit and Operational Considerations” pays particular attention to
these aspects.
A breakdown of the energy consumption of a typical commercial building is illustrated in Figure 1
Figure 1 Energy Use Breakdown for a Typical Commercial Building (Source SEI, Building Energy
Manager’s Resource guide)
Those end users highlighted in Figure 1 form the basis of the systems considered in this report.
Clearly the majority of energy can be attributed to Heating, Ventilation and Air Conditioning (HVAC)
which therefore forms the basis of the report i.e. Chapters 2, 3, 4 and 5. Chapter 6 considers Lighting;
another significant energy consumer as shown in Figure 1 and Chapter 7 considers controls which
again are related to the technologies considered in the preceding chapters 2-6. Chapter 8 then
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consider retro commissioning, of particular relevance to the theme of this guideline, and finally
Chapter 9 reviews some of the technologies not being fully utilised in the Irish market.
The ethos of concentrating on the most significant energy consumers is aligned with the
methodologies promoted by energy management standards such as IS EN 16001 and should be a
concept familiar to the member companies.
The guideline itself is not intended to replace or reiterate the work of existing available
documentation such as that from CIBSE (Chartered Institute for Building Services Engineers), BSRIA
(The Building Services Research and Information Association), the Carbon Trust and ASHRAE
(American Society for Heating and Refrigeration Engineers). For that reason technical descriptions
are kept to a minimum with the emphasis as mentioned on the retrofit and operational consideration
of each technology.
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2. Building Fabric
This section considers the significant influence of a building’s fabric on its energy consumption and
suggests means by which to reduce unwanted heat loss/gain.
Heat is lost/gained from buildings through the fabric of the building itself (roof, walls, floor,
windows and doors) and through infiltration of air via any holes and gaps. Unwanted fabric heat
loss/gain can be addressed by shading or improving insulation. Ventilation heat loss can only be
reduced by minimising infiltration of cold air: construction needs to be airtight, with controlled
ventilation supplying adequate fresh air, possibly with a heat recovery system to reduce the heat loss
even further. Airtight construction requires good design and close attention to detail during
construction. As insulation standards have improved , the issue of ventilation heat loss has become
relatively more significant.
2.1.
Thermal Comfort
Human thermal comfort is defined by ASHRAE (American Society for Heating, Refrigeration and Air
Conditioning Engineers) as the state of mind that expresses satisfaction with the surrounding
environment. Maintaining thermal comfort for occupants of buildings or other enclosures is one of
the important goals of HVAC design engineers.
Figure 2 Heat Exchange Between People and Their Surroundings (Source BSRIA Illustrated Guide to
Mechanical Building Services)
The term ‘thermal comfort’ describes a person’s psychological state of mind and is usually referred to
in terms of whether someone is feeling too hot or too cold. Thermal comfort is very difficult to define
because you need to take into account a range of environmental and personal factors when deciding
what will make people feel comfortable. The best that you can realistically hope to achieve is a
thermal environment that satisfies the majority of people in the workplace, or put more simply,
‘reasonable comfort’.
As engineers we concentrate on getting the materials, design, location and shading of the building as
suitable as possible for likely future climate conditions, and allowing future occupants sufficient
controls to adjust environmental conditions as they see fit.
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Design conditions for a space usually specify the required environmental factors, such as air
temperature, humidity requirements etc.
For certain applications, such as for the production of pharmaceuticals, it may be essential to
maintain relatively specific temperature and humidity levels. This can be expensive from an energy
perspective.
For most building it is acceptable for internal conditions to vary within acceptable limits. Therefore,
for buildings such as offices, the internal conditions may be specified as requiring a resultant
temperature of 20°C ±2.
If humidity control is required, such as in a fully air-conditioned building, it is typically specified as
needing to maintain a level of relative humidity (RH) between an upper and lower limit, for example
40% - 60%RH. In temperate climates such as Ireland, humidity levels in buildings with only a comfort
cooling system will generally stay within the limits of comfort which are approximately between 30%
- 70% RH and thus humidity control in Irish commercial buildings is discouraged.
Retrofit and Operational Considerations
The specification of environmental condition requirements of a space can have significant
energy consumption implications.
Allowing temperature set points to drift within an acceptable band can reduce the energy
implications of providing the required environment.
Humidity control is expensive from an energy perspective and should rarely be required in
the Irish climate (for thermal comfort reasons).
It is worthwhile reviewing control setpoints to seek immediate energy saving opportunities
by relaxing the environmental condition specifications in an area.
2.2.
Thermal Envelopes
The building envelope is a critical component of any facility since it protects the building occupants
and plays a major role in regulating the indoor environment. Consisting of the building's foundation,
walls, roof, windows, and doors, the envelope controls the flow of energy between the interior and
exterior of the building. A well designed envelope allows the building to provide comfort for the
occupants and respond efficiently to heating, cooling, ventilating, and natural lighting needs.
For a new project, opportunities relating to the building envelope begin during the pre design phase
of the facility. An optimal design of the building envelope may provide significant reductions in
heating and cooling loads—which in turn can allow downsizing of mechanical equipment.
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With regard to existing buildings there are practical limits to what can be done to improve the
building envelope, however improvements can still be made. Reducing outside air infiltration into the
building by improving building envelope tightness is usually quite feasible. Extra insulation can
typically be added in roof spaces with little difficulty. Windows and wall insulation can be upgraded
during more significant building improvements and renovations.
Recommendations with regard to upgrading the thermal envelope via improved building
components are now considered with respect to;
•
•
•
•
Insulation
Windows and Doors
Air tightness
Thermal Bridges
2.2.1.
Insulation
One of the key challenges in upgrading overall insulation levels in dwellings is to choose from the
wide variety of materials available on the marketplace. Above all, the insulation has to be appropriate
to its application. Some insulation products are suited to use for fill in cavity walls, for example,
whereas others are not. Some are load-bearing for use under concrete floors whereas others are ‘soft’
and better suited to fitting in the attic space. Some products have very low thermal conductivity
values ((λ) lambda values) - which means they have high insulating properties and can provide a
higher level of insulation for a given thickness compared to lesser performing products. Insulation
types will also vary on price, fire safety issues and amount of processing and / or chemicals involved
in their manufacture.
Dependent on the overall retrofit strategy, the additional insulation might be placed on the outside
of the structural building shell (sometimes referred to as ‘outsulation’), the inside (so-called ‘drylining’) and/or within the construction envelope (eg. filling the external and internal blockwork or, in
the case of timber frame between the wall studs).
The location of insulation relative to the structural envelope can have a significant influence on
thermal bridges. External insulation, for example, is typically the most effective in reducing thermal
bridges, whereas internal insulation would be the least effective from a thermal bridge reduction
perspective.
The following Table 1 illustrates the suitability of different insulation types for various applications.
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Table 1 Application of Different Insulation Types (Source: Retrofitted Passive Homes, SEI publication)
2.2.2.
Windows and Doors
The greatest heat losses in a building typically occur through windows and doors. The joints between
windows and doors to walls and floors have to be sensibly detailed. Ideally, an external insulation
layer would be used to overlap the window or door frame by at least 65mm in order to reduce
potential thermal bridges to a minimum. Furthermore those joints have to be vapour proof on the
inside and weather proof externally.
2.2.3.
Air tightness
Limiting building air leakage, infiltration or air permeability and maximizing building air tightness is
essential to having an energy efficient, comfortable and durable building. The air tightness of any
building can be tested using a standard blower door test.
The test should ideally be carried out once the airtight layer has been completed but while it is still
exposed, including most especially the taped joints between the windows and doors to the building
envelope as well as joints between different elements of the dwelling (ceiling, walls and floors).
2.2.4.
Thermal Bridges
There are two types of thermal bridges, namely
• Repeating thermal bridges
• Linear thermal bridges.
Repeating thermal bridges would include studs or rafters in the insulation layer or indeed wall ties in
masonry construction. Repeating thermal bridges are usually accounted for within the normally
quoted U-values for walls, roofs and ground floors.
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Linear thermal bridges, on the other hand, can be found at junctions of internal and external walls, at
the eaves where there is little or no space for insulation and even around opes for windows and
doors.
These bridges were not accounted for at all until they were recognised in recent versions of the
building regulations. The calculation of thermal bridges can be quite complex.
Retrofit and Operational Considerations
Thermal bridges can result from internal insulation, for example at external/internal
wall junctions. Additional insulation will therefore be needed at these locations.
A room which is internally insulated will heat up much quicker due to the avoidance of
having to heat up massive external walls. However the advantages of such massive
external walls (e.g. storing solar energy in the daytime and dampening diurnal load
variations) is also lost.
The key principle behind external insulation is to completely wrap around the entire
structural building envelope thereby significantly reducing the thermal bridges which
can otherwise arise where external walls and foundations connect to internal walls and
the floor slab.
If external insulation is being proposed for a cavity wall construction, then it would be
imperative to also fill the cavity with insulation in order to avoid thermal looping
occurring from the ‘cold’ unheated cavity through the internal block leaf to the inside of
the building.
Cavity wall insulation in Ireland is now commonplace and involves filling the cavity
between the inner and outer leaf of concrete blocks with appropriate insulation
material.
The proper installation of cavity insulation can be proven by using a thermal imaging
camera which will immediately highlight parts of the construction that have not been
fully insulated.
As the U-value of windows, e.g. double glazing / triple glazing improve, the glass will let
through less solar and light gains in addition to typically reduced glazing areas due to
increased frame, mullion and stanchion proportions. Generally however, improved Uvalues will provide a net decrease in energy consumption.
With regard to testing for air tightness in a retrofit situation the timing of carrying out
the air tightness test is very important in the overall retrofit procedure. It is important to
carry out the test prior to the completion of final finishes so that if the test results show
leakages then any gaps or cracks in the airtight layer can be precisely located and
accessed for repairs
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2.3.
Heat Losses and Gains
Heat is lost/gained from buildings through the fabric of the building itself (roof, walls, floor,
windows and doors) and through infiltration of air via any holes and gaps. Unwanted fabric heat
loss/gain can be addressed by shading or improving insulation. Ventilation heat loss can only be
reduced by minimising infiltration of cold air as discussed previously.
2.3.1.
Reducing Unwanted Heat Gain
Cooling loads that need to be removed by a natural/mechanical ventilation can be reduced by the
introduction, or improvement, of solar shading. The appropriate shading device will depend on
climate, building use and the source of the light to be excluded (high or low angle direct sunlight,
diffuse sky light or perhaps reflected light from paving on the street outside).
The key objective must be to prevent solar gain from entering the building in the first place. A range
of shading options are possible:
• Structural overhangs (including light shelves) and awnings
• Deep window reveals
• External blinds
• Double-skin facades
• Solar shading (fixed or solar tracking)
• Films
• Coated glazing (where windows are being replaced)
• Mid-pane blinds
• Internal blinds.
Interior shades protect occupants against the immediate effects of direct sunlight and against glare.
However infra-red radiation still penetrates the glazing most of it is trapped in the room and must be
dissipated by ventilation or mechanical cooling. Mid-pane blinds are often a useful compromise and
despite a higher capital cost tend to require less maintenance and cleaning.
Horizontal shading elements are effective in reducing peak summer solar gain where high solar
attitudes are experienced, primarily on southern facades. Vertical elements are effective for
restricting solar gain to facades subject to lower solar attitudes (in the east and west elevations).
Fixed external shading devices include permanent facade features such as overhangs and window
reveals. Unlike external blinds, the shading effect cannot be adjusted and the obstruction to daylight
is permanent.
2.3.2.
Thermal Mass
Exposed thermal mass can be used to reduce peak temperatures and improve thermal stability. This
is particularly common in many new buildings designed for natural ventilation. Exposed concrete,
masonry or other thermal mass present, has the ability to store and release heat (depending on its
temperature relative to the surrounding air) and can therefore be used with a night cooling regime to
reduce daytime peaks.
Cooler thermal mass will cool the air in the space by natural convection as it moves across the surface.
The lower surface temperature also introduces a radiant cooling effect, reducing the perceived
temperature by an appreciable amount especially when the exposed mass is overhead.
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Night cooling involves using the ventilation system to remove heat gains that have built up during
the preceding day. By allowing cool night air to flow through a building, the heat is removed from
the buildings fabric (commonly referred to as flushing the building). The fabric will be cool by the
start of the following day, thus having capacity to absorb heat build up in the building. Night cooling
techniques are most effective when a thermally heavyweight structure is exposed to enable heat
transfer. The external temperature on a typical summer night will typically drop by at least 8oC from
the daytime maximum. Flushing a building with this colder air discharges the heat stored in the fabric
from the previous day, enabling the thermal capacity to subsequently operate effectively to absorb
heat and hence reduce daytime peak temperatures.
Retrofit and Operational Considerations
Solar shading can be relatively easily retrofitted to buildings to reduce cooling loads. If
cooling loads are significantly reduced, a review (downsizing) of cooling plant might be
feasible/warranted.
Where office IT loads are so high, as such, that they cannot be removed by natural
ventilation, office equipment should be grouped and served by dedicated heat
rejection plant. Providing a single room for fax machines, photocopying and printing
machines etc means that this room only may require mechanical cooling, rather than
the entire office space. Better still simple extraction may suffice.
The removal of a suspended ceiling may reveal the underside of the floor slab above,
and increase the height of the room to provide a useful warm air reservoir above the
occupied zone. Daylight penetration can also be improved, especially if advantage is
taken of the extra height to increase the height of the windows in a retrofit scenario.
It has been shown that as little as 100 mm of concrete can be sufficient to provide good
damping of the diurnal temperature swing when used with night cooling
Night cooling strategies require consideration to be given to the appropriate inlet and
outlet vent design, size and location as well as the shape of the building and the
location and shape of adjacent buildings. Inlet and outlet vents should encourage air
flow over the exposed surfaces.
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3. Heating Systems
In Irish buildings heating energy consumption can be one of the biggest energy consumptions in a
building. A brief technical description of commonly encountered heating systems follows.
3.1.
Fossil Fuel Boilers
There is a wide range of fossil fuel boilers which can be divided between the atmospheric type (no
fan) and forced/induced draught boilers which incorporate a fan. These and other classifications are
described in the following subsections.
3.1.1.
Atmospheric boilers
These typically comprise a cast-iron sectional boiler with an atmospheric burner, i.e. combustion
gases rise up the chimney by convection and combustion air is entrained from around the boiler.
Given that no fan assistance is provided, atmospheric boilers are very quiet in operation.
Figure 3 Modular Atmospheric Gas Boiler Installation
3.1.2.
Forced/induced-draught boilers
A forced-draught boiler incorporates a fan to force combustion air into the boiler and drive the
combustion gases up the chimney. Dependent on whether the fan is pushing or pulling the air up
the chimney classifies the boiler as forced-draught or Induced-draught respectively. An example of a
forced draught boiler is shown in Figure 4.
3.1.3.
Condensing boilers
Condensing boilers recover waste heat from the hot flue gases, and are thus more efficient than
conventional boilers. Capital costs are higher, but relatively short pay-back periods are possible.
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Figure 4 Forced Draught Condensing Gas Boiler Installation
3.1.4.
Dual-fuel boilers
A dual-fuel boiler is capable of using two types of fuel such as gas and oil, which consequently
improves flexibility and reliability.
Retrofit and Operational Considerations
Retrofit to a condensing boiler is a good option usually offering reasonable payback.
Weather compensation should be employed to reduce the supply temperature of the boiler
when there is a reduced heating requirement. This will in turn reduce unwanted heat loss
from the boiler and distribution system.
Modular boiler systems are encouraged, this is an array of boilers linked together, this
enables boilers to operate closer to full load improving efficiency, than were a single boiler
operating at a low load.
Regular maintenance of boilers is important to ensure they are operating efficiently.
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3.2.
Biomass Boilers
Biomass is any plant-derived organic material that renews itself over a short period. Biomass energy
systems are based on either the direct or indirect combustion of fuel's derived from such plant
sources.
The most common form of biomass is the direct combustion of wood in treated or untreated forms.
Potential wood fuel sources are wide ranging and include solid wood, wood off-cuts, woodchips,
pellets and briquettes.
Figure 5 Biomass Boiler with Related Plant (Source BSRIA Illustrated Guide to Renewable
Technologies)
Features of a good large-scale biomass boiler include the following:
•
•
•
Thermal efficiency greater than 85%
Automatic cleaning of the boiler heat-exchanger and automatic ash removal
Remote monitoring of the boiler operating parameters.
Biomass boilers are not suited to a significantly modulating load and could therefore be considered
to meet the building's base heating load (ensuring the boiler runs consistently at full load).
Thereafter a small conventional boiler can be employed to meet peak demands. In this scenario care
needs to be taken with the design and specification of the control system, which will be required to
manage two boilers with very different operating characteristics.
Other considerations include types of biomass materials. Biomass should be selected for its local
availability as well as for its combustion characteristics. Alternative sources of supply are also very
important.
Biomass material such as wood chips can be used directly or converted into pellets. Although the
latter have the advantage of higher calorific values due to the lower moisture content, they are much
more expensive. Relatively dry fuel-sources have significant advantages such as; smaller boiler plant
requirements; less fuel storage requirements, and less chance of the fuel composting during storage.
Various methods are available to transport the fuel from the storage facility to the biomass boiler;
these include:
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•
•
•
•
•
•
Gravity feed or chute
Screw-type auger feed
Conveyor belt
Pneumatic blower
Bucket conveyor
Front loader bucket grab
Retrofit and Operational Considerations
Biomass boilers can deliver temperatures comparable with traditional boilers and are
therefore suitable as a replacement option of traditional boilers.
Biomass boilers start-up times are longer and heat retention within the boiler means
that heat is transferred to the heated medium for a considerable period after boiler
shutdown.
Although most biomass boilers are designed to allow modulation of the boiler output
down to typically 30% of the maximum output, they are not best suited to frequent
modulation.
For efficient, low emission combustion, biomass needs to be burned rapidly and at a
high temperature. One approach to achieving optimum performance is to incorporate
a buffer tank into the system. A large volume of water is used as a thermal store
between the boiler and the load side of the heating system. When the load decreases
the temperature of the water in the tank rises and when the load subsequently
increases there is a store of hot water to satisfy demand until the boiler output rises.
The on-site biomass storage facility may need to hold considerable volumes of fuel
depending on the boiler capacity and rate of use. The main purpose of the store will be
to keep the biomass dry and protected from rain and groundwater.
Typical storage facilities include bunkers or silos. Ventilation will be required in order
to keep the biomass dry and possibly to aide further drying. In addition, the ventilation
helps prevent composting of the biomass and the formation of moulds, the spores from
which can present a health risk.
The amount of biomass material to be delivered and the delivery mechanism will
depend on the size of the biomass storage facility. Biomass can be delivered to the
storage facility by: manually tipping, tipping from a truck, or pumping wood pellets
through a tube or pipe.
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3.3.
Air or Ground Source Heat Pumps
Heat pumps work like a refrigerator, moving heat from one place to another. To move heat takes
energy, either electrical (vapour compression heat pumps) as shown in Figure 6 or thermal energy
(absorption heat pumps).
The essential components of a heat pump are heat exchangers (through which energy is extracted
and emitted) and a means of pumping heat between the exchangers. The effectiveness of the heat
pump is measured by the ratio of the heating capacity to the effective power input, usually known as
the coefficient of performance (COP). Up to five units of heat can be provided for one unit of
electrical energy used.
In a vapour compression cycle, as shown in Figure 6, the working fluid evaporates by extracting heat
from a low temperature source (ground or air): the vapour is compressed mechanically and
condenses back into a liquid state giving up its latent heat as useful heat. The liquid then expands
through a valve causing a drop in pressure and partial vaporisation before re-entering the evaporator
for the cycle to be repeated.
Figure 6 Schematic of Ground Source Heat Pump Components
The vapour compression cycle is by far the most common cycle for commercial heat pump
equipment. Its disadvantages are the need for high capacity compressors and the sensitivity of the
output to the evaporator temperature. This means that compression heat pumps, although well
suited to low temperature heating systems (such as underfloor heating) have poor COPs when used
with conventional hydronic heating systems with higher temperatures requirements of 60oC or
higher.
Air or Ground source heat pumps have a number of environmental and operational
advantages. These are:
•
•
•
•
•
Long life expectancy (typically 20-25 years and up to 50 yeais for the ground coil)
Low noise
Low maintenance costs
No combustion or explosive gases within the building
No flue or ventilation requirements
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The ground collector for a ground source heat pump may be installed vertically or horizontally. The
choice of a vertical or horizontal system depends on the available land, local soil type and the
topographical features.
Retrofit and Operational Considerations
Air source heat pumps can find the coldest Irish days difficult to provide for. Such heat
pump’s efficiency shows significant seasonal variation.
An air or ground heat pump operates most effectively when the temperature difference
between the heat source and distribution system is small. Thus heat distribution
systems need to be low temperature and therefore large surface area (e.g. underfloor
heating systems).
With regard to retrofit the large surface area required for the heat distribution system
(e.g. underfloor heating systems) and the disruption to land external to the dwelling
during installation (in the case of ground source) means that air or ground heat pumps
are commonly not suitable as a retrofit option.
With underfloor heating systems, a long on-time is required to ensure an adequate
indoor temperature. This is not well suited to intermittently occupied buildings.
Convective radiators that operate at low distribution temperatures can offer a solution.
With ground source heat pumps although horizontal collectors are generally cheaper to
install, vertical collectors provide better efficiencies due to the higher temperature at
greater depths.
With ground source heat pumps, because of the large size of systems serving
commercial buildings, horizontal ground collectors are not suitable and instead
multiple boreholes will be required for vertical collectors. Ground collector loops are
increasingly being incorporated into the foundation piles of buildings.
The reversible nature of air or ground source heat pumps means that cooling duties
during summer months can be met either partially or fully.
Air or ground source heat pumps return optimum efficiency when operated on a
continuous basis. Systems are best suited to buildings that have a continuous heating
or cooling load.
Consider using an air or ground source heat pump to match the building base heating
or cooling load and use other technologies to meet peak loads. This will allow the heat
pump to operate for longer periods of time, enhancing the efficiency.
The use of weather compensation control for space heating system will help reduce the
heating system flow temperature and therefore increase the efficiency of the air or
ground source heat pump.
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3.4.
Radiant Heating
Radiant heating systems are typically used in buildings housing large volume rooms such as
warehouses, industrial units and sports halls. There are two key reasons for this:
• Radiant heating is suited to buildings with tall spaces, such that the heaters can be located at high
level and provide a radiant output in a downwards direction into the occupied area.
•
Radiant heaters warm people directly without heating the air within a space. This enables an
acceptable level of comfort to be maintained with a relatively low air temperature. This is an efficient
way to heat commercial/industrial buildings which have large volumes of air that would need to be
heated if heated by more traditional warm air systems.
Figure 7 Schematic of Radiant Heating (Source BSRIA Illustrated Guide to Mechanical Building
Services)
Radiant heating can be directly gas-fired, electric or fed by a hot water system.
Retrofit and Operational Considerations
A building can be pre-heated far more rapidly than is possible with a warm air system.
Air movement is not required to distribute heat throughout the space.
High-level mounting of heating equipment frees up floor space and reduces risk of damage.
Regular maintenance is essential to such systems.
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3.5.
CHP
Combined heat and power (CHP) or co-generation, is the simultaneous generation of heat and
electrical power from the same source. CHP systems can be used in applications were there is a
demand for heating in addition to the electricity generated.
A CHP unit comprises an engine or turbine in which fuel is combusted. The mechanical power
produced by the engine is used to generate electricity using an integral electrical generator. The heat
emitted from the engine or turbine (waste heat) is then used to provide space heating or domestic
hot water. The waste heat can also be used to provide space cooling when passed through an
absorption chiller.
Figure 8 Schematic of a CHP System
CHP systems are traditionally defined according to their electrical output. The terminology for the
different sizes is shown in the following table.
Terminology
Micro CHP
Mini CHP
Small Scale CHP
Medium Scale CHP
Large Scale CHP
Electrical Output
< 5 kWe
5 – 500 kWe
500 kWe – 5 MWe
50 MWe
50+ MWe
Table 2 CHP Classification (Source BSRIA Illustrated Guide to Renewable Technologies)
The environmental benefits associated with a CHP system are to do with the increased energy
efficiency which results from the use of the heat produced by the CHP unit. This heat is wasted in
conventional electricity power stations. By using this waste heat, a CHP unit can achieve efficiencies
of around 80%. Furthermore, because the electricity is generated on-site, the transmission losses
associated with conventional centralised generation and distribution via the national grid do not
occur.
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CHP uses a variety of different technologies to act as the engine or turbine, with a variety of fuels also
in use. These include reciprocating engines, steam turbines, gas turbines and combined-cycle
systems. Reciprocating engines are commonly used for smaller CHP systems (such as micro, mini and
small scale CHP).
The thermal efficiency of a CHP unit will depend on what portion of the rejected heat can be captured
and utilised. The two main sources of rejected heat are the exhaust gases and engine water jacket. A
shell and tube heat-exchanger is typically used to recover heat from the exhaust gas of the engine or
turbine, while a plate heat-exchanger is used to recover heat from the engine jacket.
An automatic control system is usually provided to safely stop and start the CHP unit and to modulate
the heat and electrical power output to meet the building or facility’s load demands. The control
system can also be used to monitor the operating conditions and performance of the CHP unit.
The use of tri-generation can greatly improve the usefulness, applicability and cost effectiveness of a
CHP unit. Tri-generation involves the use of waste heat to generate chilled water via an absorption
cycle (Section 4.2).
Retrofit and Operational Considerations
CHP can be powered using biofuels
High operating efficiencies can be achieved if heat generated is fully utilised
CHP can improve the quantity of the mains power supply by stabilising supply currents
and voltages
Requires predictable and relatively constant loads for optimum performance.
Requires full use of generated heat for optimum efficiency
Requires regular planned maintenance
Typically, to be cost effective, CHP systems will require to be operated for a minimum of
four to five thousand hours per annum.
Most suitable to sites with a year round heat demand example, swimming pools, leisure
facilities, hospitals, universities etc. CHP systems are commonly retrofitted into these
facilities after careful analysis of loads and savings achievable from a CHP system.
CHP can be provided on an own and operate basis or on some form of Energy Service
Company contract where the system is independently owned and operated with the
end user merely paying for energy used. Such contracts need to be carefully
negotiated, analysed and agreed.
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3.6.
Solar
The analysis of solar heating has been broken up to separately consider solar air heating and solar
water heating.
3.6.1.
Solar Air Heating
Solar air systems collect solar energy to heat air. The air can be used to pre-heat ventilation air, heat
air inside a building, or less often to heat water. A basic system comprises a solar collector and a hot
air distribution system. The solar collectors can be purpose-built panels or a glazed cavity over an
existing facade.
Solar heating of ventilation air can be achieved by passing outside air intended for ventilation
purposes through a collector. The air is heated and supplied to the occupied space. This is the
simplest form of solar air heating and the least expensive to install. Costs can be reduced if the
system is used to supplement or replace an existing ventilation system in a retrofit scenario, in which
case the existing air distribution system can be used (Figure 9).
Figure 9 Schematic of a Solar Air System
This type of system can be used in conjunction with thermal mass storage. For example, the heated
air can be passed through the internal building fabric. This approach is advantageous in applications
where the demand for heating is later than the peak thermal gain to the collector.
An alternative system uses a cavity collector, in which heated air from a collector is circulated through
the cavities in the building envelope. The buffer of heated air reduces the heat loss through the
building envelope and in turn reduces the demand for space heating.
Variations can involve the use of glazed roof areas, transparent insulations, sunspaces, glass facades
and perforated air collectors on walls, all of which can act as solar collectors.
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Retrofit and Operational Considerations
Air solar collectors heat up quickly due to the low heat capacity of air.
Low heat capacity has fan power implications in that large volumes of air need to be
transferred to meet heating loads.
The solar collectors can be an integral part of the building fabric
No problems associated with water leaks, corrosion or freezing when dealing with solar
air heating as compared to solar water heating.
Can be used in conjunction with a conventional ventilation system (important from a
retrofit perspective), for instance to pre-heat ventilation air.
The ideal orientation for a solar air-heating system is due south as this provides
maximum potential solar gain. However, a southeast or south-west orientation will also
provide worthwhile solar gain.
For open loop systems (where the solar-heated air is supplied directly to the occupied
space) care is required to avoid draughts at times of insufficient solar heating.
Supplementary heating capacity should be made available in order to further heat the
air during these periods.
Conversely summer bypasses should be provided to avoid excessively hot air being
supplied to the occupied zones during summer conditions.
3.6.2.
Solar Water Heating
Solar water heaters are reliable and their use is widespread, they use the energy from the sun to heat
water. Solar heating systems use a heat collector that is usually mounted on a roof in which a fluid is
heated by the sun. This fluid is used to heat water that is stored in either a separate hot water cylinder
or in a twin-coil hot water cylinder (the second coil is used to provide additional heating from a boiler
or other heat source).
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Figure 10 Solar Hot Water Panel Array
A controller compares the temperature of the fluid in the collectors with the temperature of the water
in the cylinder and activates a circulating pump whenever the fluid in the collectors is hotter. A
conventional heating system can be used to boost the stored hot water when required.
Solar collectors can be categorised into the following types:
• Glazed flat-plate collectors
• Evacuated tube-collectors
• Unglazed plastic or low temperature collectors.
Evacuated tube-collectors are the most efficient of these systems and unglazed plastic or low
temperature collectors are the least efficient.
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Retrofit and Operational Considerations
Solar water heating can be used in dwellings, and commercial and public buildings
where there is a demand for domestic hot water (DHW). Solar water heating can be
applied to many building types including, offices, sports complexes, hotels, and
hospitals.
Systems without thermal buffer stores, are the simplest type of system for commercial
and public buildings. The design is similar to that used in a domestic application.
Supplementary heating is provided by a boiler or other heat source, and this is also
used to perform thermal disinfection to help prevent Legionnaires' disease.
Thermal stores can be used to store partially heated water before supplying it to the
DHW storage tank. Such buffer tanks avoid storing large amounts of water at high
temperatures with consequent high thermal losses. This approach provides a higher
system utilisation with auxiliary heating only used in the DHW storage tank.
Solar thermal systems can be combined with recirculation hot water systems
commonly found in large commercial and public buildings.
The efficiency of the system will be improved if a larger hot water storage cylinder is
installed (larger compared with a cylinder used with a conventional hot water heating
system).
Optimum performance will result where collectors are oriented due south and inclined
at an angle of 30-40o. In practice this is not normally achievable; however a south-east
to south-west orientation and an elevation of between 10o and 60o will suffice.
Energy savings will be maximised in buildings with high domestic hot water demands
that occur during the day. This allows a match between demand and solar supply
Maintenance requirements are generally low but an annual maintenance check should
be performed to ensure that the collector surfaces are clean, that there is no corrosion,
and that sensors and fixings are properly in place.
Mounting of the solar collectors on the building facade is possible, although the annual
irradiance received will be greatly reduced compared with a roof-mounted collector.
One possibility is to incorporate collectors into sunshades, therefore providing a more
effective slope.
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Commercial Buildings SWG
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4. Cooling
Having the capacity to cool is central to most air-conditioning systems. To do this refrigeration
equipment, commonly referred to as a chiller plant is used. Chilled water is typically distributed to
heat exchangers, or coils, in air handling units, or other types of terminal devices which cool the air in
its respective space(s), and then the chilled water is re-circulated back to the chiller to be cooled
again. These cooling coils transfer sensible heat and latent heat from the air to the chilled water, thus
cooling and usually dehumidifying the air stream.
Some smaller chillers provide refrigerant directly to a cooling coil in an air handling unit and
consequently avoid the need for a chilled water circuit (often referred to as a DX system). The chiller
and air handling unit in a DX system can be purchased as an integrated unit, (Section 5.4 and 5.6).
In order for a chiller to cool the water used in the air-conditioning system it must first extract heat
from the water and then get rid of it, this can be achieved in several ways. The simplest approach is to
combine the heat rejection system and chiller into a single unit called a packaged chiller. This is
located outside and incorporates one or more fans which draw fresh air through the unit to carry
away the heat.
Large chillers commonly found in commercial buildings will often have a separate heat rejection
system linked by pipework, enabling the chiller to be located in a plant room and the heat rejection
system outside.
The heat rejection system can take several forms. The most efficient is the
evaporative cooling tower which uses the cooling effect of evaporating water to boost the cooling
provided by fresh air.
A more widely used system for providing separate heat rejection is the dry cooler. This consists of a
unit containing one or more fans which drive fresh air across a serpentine coil. The coil contains hot
water from the chiller which is cooled and pumped back to the chiller. Alternatively, the coil can
contain hot refrigerant directly from the refrigeration process, which is cooled in the same way and
then travels back to the chiller.
Figure 11 Heat Rejection Plant of a Chiller
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4.1.
Vapour Compression Chillers
A vapour-compression water chiller comprises the 4 major components of the vapour-compression
refrigeration cycle (compressor, evaporator, condenser, and some form of metering device). These
machines can implement a variety of refrigerants. Most often, pure water is actually chilled, but this
water may also contain a percentage of glycol and/or corrosion inhibitors; other fluids such as thin
oils can be chilled as well.
Figure 12 Vapour Compression Chiller Plant
A chiller can cool a very large building or complex, and can make use of cooling towers to increase
their effectiveness. There are four types of compressors used in vapour compression in water chillers reciprocating compression, scroll compression, screw-driven compression, and centrifugal
compression are mechanical compression types.
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Retrofit and Operational Considerations
Reduce condensing temperatures and increase evaporating temperatures (chilled water set point)
as much as possible to reduce the energy consumption of the plant.
If a current chiller is oversized consider a smaller chiller that might manage the full load for most
of the year (as with boilers a modular approach is advised).
Legislative requirements to replace R22 or similar refrigerants may be a good opportunity for
chiller replacement. Care is needed to consider incoming legislation when selecting a new
refrigerant (reference SEI document produced by the refrigeration special working group entitled
“Refrigerants Choice, Regulatory Requirements and Energy Efficiency”).
Maintenance of evaporator and condenser is important to minimise fouling.
Evaporative condensers are the best performing, from an energy efficiency perspective, followed
by water cooled and lastly air cooled. Evaporative condensers can cool towards ambient wet bulb
while air cooled condensers can only cool the refrigerant towards ambient dry bulb temperature
(usually 3-4oC degrees higher than ambient wet bulb in Ireland).
Condensing temperatures should be optimised (i.e. varied and minimised) based on the ambient
conditions at the time.
An evaporator in the form of a plate heat exchanger can save energy over a shell and tube
evaporator by allowing a closer approach temperature to be achieved between the refrigerant
and the water being cooled.
The chiller should have good efficiency at full load as well as at part load conditions. This is
particularly true if it is expected that there will be times when only half the design cooling load is
required. This can be achieved by modular design or by using a chiller with two compressors
capable of working independently or together. From a performance point of view, the chiller in
that case will be most efficient at 50% capacity. This is because at this point, only one compressor
is operating and the evaporator and condenser are twice the size normally used for the
compressor size.
Heat recovery from the chillers is an option that should only be considered as long as it is not at
the expense of chiller efficiency. Increasing condensing temperatures to provide for increase heat
recovery would only be economical if electricity costs are low and alternative fuel costs are high.
In a direct expansion system an Electronic Expansion Valve (EEV) replaces the
conventional thermostatic expansion valves (TEV) which require a minimum pressure
differential across the compressor to operate and hence limit the chillers ability to
reduce the condensing pressure in winter resulting in increased energy usage.
Variable speed drives are available on centrifugal and screw compressor.
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Commercial Buildings SWG
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4.2.
Absorption Cooling
In an absorption chiller a heat source is used to drive the cooling process as opposed to an electric
motor as in the previous, more common, vapour-compression chiller.
In a conventional mechanical vapour-compression chiller (Section 4.1) the refrigerant evaporates at a
low pressure and produces a cooling effect. A compressor is then used to compress the vapour to a
higher pressure where it condenses and releases heat. In an absorption chiller the compressor is
replaced by a chemical absorber, generator and a pump, as shown in Figure 13. The pump consumes
much less electricity than a comparable compressor (approximately nine percent of that for a vapour
compression plant). The majority of the energy required to drive the cooling process is provided by
the external supply of heat.
Absorption cycles use two fluids: the refrigerant and the absorbent. The most common fluids are
water for the refrigerant and lithium bromide for the absorbent. These fluids are separated and recombined in the absorption cycle. The low-pressure refrigerant vapour is absorbed into the
absorbent releasing heat. The liquid refrigerant/absorbent solution is then pumped to a generator
with high operating pressure. Heat is then added at the high-pressure generator which causes the
refrigerant to desorb from the absorbent and vaporise. The vapours flow to a condenser, where heat
is rejected and condensed to a high-pressure liquid. The liquid is then throttled through an
expansion valve to the lower pressure in the evaporator where it evaporates by absorbing heat. This
absorbing of heat is used to provide a useful cooling effect. The remaining liquid absorbent in the
generator passes through a valve where its pressure is reduced and is then re-combined with the low
pressure refrigerant vapours returning from the evaporator. The cycle is then repeated.
Absorption chillers can be classified based on the type of heat source, the number of effects and the
chemicals used in the absorption process. Indirect-fired absorption chillers use waste/rejected heat
(typically steam, hot water or hot gases) from another process to drive the absorption process.
Direct-fired chillers include an integral burner, usually operating on natural gas.
Retrofit and
Operational
Consideratio
ns
Figure 13 Absorption Chiller (Source BSRIA Illustrated Guide to Renewable Technologies)
31
Reduce
condensing
temperatures
and increase
evaporating
temperaturs
(chilled water set
Commercial Buildings SWG
Current Standard Solutions
In a single-effect absorption chiller the heat released, during the chemical process of absorbing
refrigerant vapour into the liquid stream, is rejected as waste heat. In a double-effect absorption
chiller some of this rejected heat energy is used to generate high-pressure refrigerant vapour. Using
this heat of absorption reduces the demand for heat and boosts the chiller system efficiency.
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Commercial Buildings SWG
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Retrofit and Operational Considerations
Most of the considerations given with regard to vapour compressions chillers are still
valid with respect to absorption chillers (minimising evaporating temperatures etc.).
The refrigerants used with respect to absorption chillers do not damage the
atmosphere and have no global warming potential (unlike some refrigerants used in
vapour compression chillers which have very high global-warming potential).
Absorption chillers are ideal where waste heat is available for example if coupled with a
CHP plant. The available heat source will determine the type of an absorption chiller
that is suitable for a specific application, and give an indication of the potential
efficiencies achievable.
The heat rejection from an absorption chiller will be greater than a conventional chiller
with the same cooling capacity. This will require larger heat rejection units (such as dry
air-coolers or wet cooling towers) for absorption chillers. The associated space and
weight constraints on some sites may be an issue.
Absorption chillers are slower to start-up than mechanical vapour compression chillers.
They are also slower to respond to changing loads. For large systems a buffer tank may
be required to increase the inertia for the chilled water circuit. The frequent starting
and stopping of absorption chillers should be avoided.
Absorption chillers have few moving parts and have correspondingly lower
maintenance requirements compared to conventional chillers. Maintenance costs can
be lower than conventional chillers.
An absorption chiller can be used to meet the base-load cooling demand in a building,
while peak cooling loads can be met by a conventional chiller. This approach can be
advantageous because conventional chillers usually cost less than an equivalent
absorption chiller. Their use can therefore be cost effective for limited running hours.
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Commercial Buildings SWG
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4.3.
Evaporative Cooling
The evaporative cooling process is based on the latent heat absorbed by water when it evaporates.
By taking this heat from the air this process in turn cools a flow of air. This process of water
evaporating into the air takes place only when there is a difference between wet-bulb temperature
and dry-bulb temperature of the air. For that reason the greater this temperature difference
(between wet and dry bulb), the more effective evaporative cooling that can occur.
There are two principal methods of evaporative cooling
Direct evaporative cooling
Indirect evaporative cooling
•
•
The direct evaporative cooling takes place when supplied air is cooled through direct contact with
water, either via contact with wetted materials or direct water spray into the airstream. This process
involves heat and mass transfer and reduces the dry-bulb temperature of the supplied air stream, as
well as increases its humidity (Figure 14). In this process, the energy in the air does not change.
Warm dry air is changed to cool moist air.
The indirect method uses the evaporatively cooled outside or exhaust airflow and the air-to-air heat
exchanger, where it releases its cooling energy into the supplied airstream on the other, dry side of
the heat exchanger. This process involves only sensible heat transfer, as no moisture is passed onto
the primary, supplied airstream. The evaporative cooling of the secondary airflow (outside or exhaust
air) can be achieved by direct evaporative methods, however this cooled moist air never comes in
direct contact with the conditioned environment (Figure 15).
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Figure 14 Evaporative Cooling Process – Psychrometric Chart
34
Commercial Buildings SWG
Current Standard Solutions
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Figure 15 Indirect Evaporative Cooling with Air-to-Air Heat Exchanger
To increase evaporative cooling effectiveness, the indirect-direct two-stage systems can be
introduced. The first stage includes the indirect cooler that pre-cools the air without adding moisture
to it, while the second stage involves direct evaporative cooler that further reduces supply air
temperature but also increases its’ humidity. There is less added moisture in the two-stage process
when compared with a single-stage direct evaporative cooling, due to already pre-cooled air that
cannot hold as much moisture and requires less humidity to achieve expected cooling temperature.
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Figure 16 Two Stage Evaporative Cooling
35
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'(#
Commercial Buildings SWG
Current Standard Solutions
Retrofit and Operational Considerations
Areas where humidity control is not important can be cooled by direct or indirect
evaporative coolers.
Moisture sensitive spaces that require lower or closely controlled humidity levels can be
cooled using the indirect method only
The direct evaporative cooling is simpler and less expensive, but it is most suitable for
hot and dry climates, meanwhile the indirect method can also be successfully
implemented in more humid climates. Therefore in Ireland the indirect evaporative
cooling would be the most suitable method and could reduce energy consumption of
an associated cooling system.
There are indirect evaporative coolers that can be used on the fresh air supply side, this
system can work as a pre-cooler to the existing refrigeration system. This indirect
evaporative pre-cooling of the primary airstream does not bring any additional
moisture into the airstream and reduces sensible load of the cooling coil and
compressor, allowing for downsizing of the refrigeration equipment and savings in
energy use with respect to operational costs.
Evaporative cooling as a pre cooling mechanism in an AHU would be a reasonably
straight forward retrofit on an existing AHU particularly where the fresh air intake or
return air duct runs from an outside roof, this should have a reasonably short payback
providing the AHU handles a sufficiently large amount of air.
4.4.
Free Cooling
The aim of free cooling is to minimise or eliminate the need for provision and operation of a
refrigeration/cooling system. Free cooling is an energy efficient method of cooling a medium (usually
air or water) without using mechanical refrigeration. Free cooling uses a combination of technology
application and favourable outside weather conditions to achieve cooling with little or no use of
electrical or heat energy. Ireland’s climate is characterised by weather conditions that are particularly
suitable for the utilisation of free cooling opportunities.
Depending on the application and other factors such as weather conditions and cooling demand,
free cooling can be used to completely offset the requirement for mechanical refrigeration or it can
be used to compliment mechanical refrigeration by reducing the load on the refrigeration plant.
Evaporative cooling discussed previously could have been considered a form of free cooling.
36
Commercial Buildings SWG
Current Standard Solutions
Free cooling techniques considered in the following subsections are broken down into;
•
•
Water side free cooling
Air side free cooling
4.4.1.
Water Side Free Cooling
Water side free cooling refers to the use of free cooling techniques that reduce or offset the load on
chilled water installations. Water side free cooling utilizes a cooling tower’s evaporative cooling
capacity to directly or indirectly produce chilled water for use in cooling applications. The
temperature of cooling tower water varies with ambient wet bulb temperature. Water side free
cooling is best suited for climates with wet bulb temperatures below 13°C for 3,000 or more hours a
year. Ireland typically has a wet bulb temperature below 13°C for over 6,300 hours of the year and an
average wet bulb temperature in the region of 9.3°C, which indicates that water side free cooling is
available for a significant portion of the year.
Free cooling mode is activated once the ambient wet bulb temperature is low enough to ensure the
cooling tower can provide chilled water at the required temperature. Changeover between free
cooling and mechanical refrigeration can be fully automated and controlled by the Building
Management System (BMS) or a dedicated field controller. Once in the free cooling mode, the
temperature of the chilled water can be controlled by the cooling tower fans, via variable speed
drives that can provide close temperature control.
Water side free cooling can be divided into two categories:
•
•
Direct Waterside Free Cooling
Indirect Waterside Free Cooling
Both method essentially involve turning off mechanical refrigeration plant and bypassing it such that
cooling is done directly by a cooling tower that under normal running conditions rejects heat from
the condenser of the mechanical refrigeration plant.
The direct water side free cooling uses the cooling water to feed directly into the chilled water loop to
provide cooling whenever favourable weather conditions are present.
Indirect systems, which tend to be more suitable for retrofit scenarios, also use the cooling ability of
the cooling tower loop, but in this case to cool chilled water in the chilled water loop to within a few
degrees of the ambient wet bulb temperature by use of a heat exchanger. Thus in this case the free
cooling energy is passed onto the receivers indirectly through a secondary loop. In indirect water side
free cooling system the chilled and cooling water loops are hydraulically separated.
4.4.2.
Air Side Free Cooling
Mechanical ventilation systems (Chapter 5) either provide supply air using a mixture of fresh outside
air and recirculated air or 100% fresh outside air. The decision whether to use a 100% fresh air system
or a mixing system should take into consideration the potential for air side free cooling.
In general, air side free cooling techniques can provide free cooling during the warmer months of the
year as well as heat recovery during the colder months of the year. In fact in the Irish climate, some of
the air side free cooling techniques are actually chosen based on their heat recovery capabilities as
opposed to their free cooling potential.
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The most common type of air side free cooling seen in Ireland is the mixing of fresh air and
recirculated air in a constant volume system. This is achieved by the use of modulating dampers that
are provided on the outside air intake ductwork, exhaust air ductwork and recirculation ductwork.
These dampers modulate to achieve the correct mixture of fresh air and recirculated air based on a
control strategy to achieve desired supply conditions. Recirculation systems are a very effective
means of both free cooling and heat recovery. Depending on the outside air conditions this type of
system can reduce or eliminate the requirement for boilers or mechanical refrigeration systems. This
type of system is also commonly referred to as a mixing box or an air side economiser.
Figure 17 Schematic of a Mixing Section in an AHU
The fresh air dampers and exhaust air dampers operate in sequence such that they are always open
an equal amount and the recirculation air damper modulates based on the position of these dampers
to ensure that a relatively constant volume of air is being maintained in the system, i.e. when fresh air
damper is open at 30%, then the recirculation air damper must be open at 70% to provide for the
remaining part of the supplied flow rate, and as a result the exhaust air damper would also be open at
30%.
The fresh air damper has a minimum setting. This minimum setting is usually based on a fixed volume
of fresh air per person or as a percentage of the overall supply. This can often be set too high based
on an overestimated level of occupancy in the space leading to excessive amounts of cold fresh air
being introduced into the system during winter. In such a scenario CO2 monitoring can be integrated
into the system to control the amount of fresh air supplied (Chapter 7).
Full fresh air systems can utilise some sort of energy exchange device to avail of free cooling and such
methods are investigated in the following Chapter 5.
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Retrofit and Operational Considerations
Ireland averages 6,400 hours at or below 13°C per year which gives a significant
opportunity to utilise free cooling for 73% of the time. The opportunities for free cooling
are extremely under utilised at present.
Indirect waterside free cooling is more likely to be a suitable water side free cooling
mechanism with respect to a retrofit as this only requires some by pass piping and a
plate heat exchanger, and will have no impact on the user side.
Incorrectly operating mixing dampers on Air Handling Unit’s (AHU’s) is one of the most
commonly found energy saving opportunities in carrying out HVAC energy audits. Such
faults can have significant energy implications. These dampers should be the subject of
a maintenance check/routine.
AHU’s with fixed proportions of fresh and recirculated air can be easily retrofitted to
incorporate automated motorised dampers to optimise free heating and cooling.
Payback is likely to be short, especially where the control functionality, i.e. a Building
Management System (BMS), already exists.
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5. Air Conditioning
The most common types of air-conditioning system can been be classified as follows;
Centralised air
•
•
•
Constant volume (CV)
Variable air volume (VAV)
Displacement ventilation
Partially centralised air/water systems
•
•
•
•
Fan coils
Chilled beams
Chilled ceilings
Room based heat pumps
Local systems
•
•
Split units
Variable refrigerant flow (VRF)
Centralised air system’s have all the plant located in a single area, for example in a basement or roof
top plant room. Air Handling Unit’s (AHU’s) condition the air which is then supplied by ductwork to
the spaces within the building. The AHU’s will typically contain heating and cooling coils (served by
boilers and chillers respectively) filters, possibly a humidifier, and fans to move the air.
In partially centralised air/water systems, most of the cooling/heating is carried out within the
occupied space by individual room units such as fan coils. These spaces are individually supplied with
hot/chilled water from a central plant area via a pipework system. Centralised plant also supplies
fresh air through out the building by means of ductwork. However the size of the ductwork
installation and associated air handling plant is smaller than that required by the centralised air
system, because air is only required for ventilation and consequently the high volume of air necessary
in fully centralised systems, to provide the building's heating/cooling, is avoided.
Finally local systems are not linked to any centralised plant and only provide conditioning in the
immediate space where they are located. They may or may not provide ventilation depending on
their level of complexity. One such system is a variable refrigerant flow system (Section 5.6).
5.1.
Constant Volume
Constant volume systems provide a fixed volume of air at a temperature and humidity required by
the space being served. They are best suited to supplying single areas or zones with similar loads.
They are not generally suitable for serving multiple zones with varying heating and cooling
requirements. A work around can be to utilise re-heaters in each zone, thereby providing local
control. However, this approach is generally wasteful of energy, due to resulting simultaneous
heating and cooling.
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Figure 18 Schematic of a Simple Constant Volume Air Conditioner (Source BSRIA Illustrated Guide
to Mechanical Building Services)
A common application of constant volume systems is to provide fresh air in partially centralised
air/water systems such as fan coil or chilled beam installations. In this instance, the constant volume
system provides fresh air for ventilation and may meet a small proportion of the heating or cooling
load, but the primary heating and cooling requirement is met by the room units, such as fan coils or
chilled beams.
Retrofit and Operational Considerations
Constant volume systems can be used for single zone applications, where only one set of
internal conditions need to be satisfied.
Constant volume systems are simple and relatively easy to maintain.
Where constant volume systems are in place the potential to reduce air flow rates should
be analysed as this can lead to significant energy savings. A reduction in air flow of 20%
will lead to 20% savings in heating, cooling, humidifying and dehumidifying and 50%
savings in fan power requirements based on the cube law.
Correctly operating mixing sections are important to the efficient operation of constant
volume systems.
CV systems can also be retrofitted to act as VAV system, however if serving areas of similar
load requirements a once off reduction in air volumes will a much easier retrofit.
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5.2.
Variable Air Volume
Variable Air Volume (VAV) air-conditioning can satisfy the individual cooling requirements of multiple
zones. In these systems air is supplied at a constant temperature from central plant to one or more
VAV terminal units in each zone. The VAV terminal unit contains a damper controlled by temperature
in the zone which regulates the amount of air entering the zone in response to the need for cooling.
Figure 19 Schematic of a Simple VAV System (Source BSRIA Illustrated Guide to Mechanical Building
Services)
The advantage of the VAV system is its ability to simultaneously provide the required level of cooling
to any number of zones within a building. These systems can boast energy efficient operation as a
result of their ability to operate the main supply/extract fan(s) at reduced speeds for much of the year,
when the overall volume of air required by the various zones is low (fans are generally the most
significant user of energy in a centralised air system). This is typically achieved by a Variable Speed
Drive (VSD) on the fan controlled by static pressure in the distribution duct. When the cooling load is
low, the VAV terminal unit will throttle the supply air down to a minimum level of around 40% of the
maximum volume.
Most types of VAV terminal unit can incorporate a heating device which can boost the temperature of
the supply air if conditions within the zone require it.
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Retrofit and Operational Considerations
In VAV systems the air flow must not drop below a minimum requirement (usually 40% of
max flow). This is to ensure sufficient ventilation with fresh air and that the velocity of air
leaving the diffuser does not drop too low causing the coanda effect (which causes the air to
move along the underside of the ceiling) to be lost, leading to cold draughts. It is, therefore,
particularly important that VAV systems are designed and commissioned (and maintained) to
a high standard to ensure satisfactory control can be achieved.
5.3.
Chilled Ceilings
Chilled ceilings can essentially take two forms;
•
•
Chilled Beams
Chilled Ceilings
Chilled beams are mounted at high level within a space and cool the surrounding air causing it to
travel downwards, due to its negative buoyancy into the occupied space below. They comprise long
rectangular units containing a finned tube through which chilled water is pumped. The beams are
typically arranged at regular intervals above, or partly below, a false ceiling, requiring a minimum
ceiling void depth of around 300mm. The type of chilled beam described here is sometimes referred
to as a passive beam. Active chilled beams are also available, which incorporate small fans to assist air
movement.
Figure 20 Schematic of a Chilled Beam
Chilled ceilings are mounted at high level within a space and provide a combination of radiant and
convective cooling to the space below. Each unit typically comprises a small bore chilled water pipe
arranged in a serpentine pattern and attached to the upper surface of a thin metallic ceiling panel.
Alternatively, the pipe may be embedded within the panel. The panel is cooled through contact with
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the chilled-water pipework and in turn cools the space with a combination of convective and radiant
output (up to 40% radiant).
A key benefit of chilled ceilings is that they can be accommodated in a very shallow ceiling void and
are therefore suited to buildings with minimal floor to ceiling heights. However, they offer a limited
cooling output which can preclude them from use in environments with moderate to high heat gains.
Retrofit and Operational Considerations
Both chilled beams and chilled ceilings require a separate ventilation system to supply
fresh air to the space.
They provide a quiet, draught-free operation
They operate with high chilled water temperatures, offering the potential for sources of
chilled water other than chillers, such as rivers, cooling towers, dry coolers and ground
water
Maintaining a chilled-water temperature above 14-15°C is essential to avoid condensation
forming on the beams.
The cooling capacity of both systems is reasonably limited, not suitable for high heat gain
environments.
These systems have minimal maintenance requirements.
5.4.
Split Systems
Split systems provide a convenient packaged way to air-condition small buildings or specific areas
within a building. These systems are quick to install with minimal disruption to building occupants.
Another key benefit of split systems is that they do not require any form of centralised plant space
within the building, making them convenient for retrofit purposes.
Split systems are made up of two basic components: one or more indoor room cooling units, and an
outdoor refrigeration unit which dumps heat taken from the building. The indoor and outdoor units
are linked by pipes which transport refrigerant between the units.
Advanced split systems can operate as a heat pump and can therefore provide heating as well as
cooling by reversing the refrigeration process. The benefit of this is that the system can provide a
complete heating and cooling solution (Section 5.5).
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Retrofit and Operational Considerations
Relatively quick and easy to install
Only suitable for relatively small spaces
Typically only re-circulate room air and cannot provide ventilation
Can only service a single internal zone; systems with multiple indoor units cannot provide
simultaneous heating and cooling in different areas.
Typically require a specialist service engineer for repairs and maintenance.
5.5.
Room Based Heat Pumps
Ground source heat pumps have been discussed earlier (Section 3.3) and room based heat pumps
apply the same refrigeration principles to split systems to enable them to heat or cool as required.
Individual units, which can be floor standing or concealed in a void, are all linked by a piped water
circuit that runs around the building. Each unit operates independently and is able to heat or cool
the air in it’s area. This is achieved by means of a small heat pump in the unit which takes low grade
heat from the water circuit and uses it to heat the room. To cool the room, the heat pump works in
reverse to remove heat from the space and transfer to the water circuit.
A key benefit of this type of system is the ability to save energy by transferring heat from an area
where it is not needed to an area where it is by virtue of the piped water system.
45
Air movement is not required to distribute heat throughout the space.
Overall reliability is good, as the cooling process is spread across many room units and the
failure of a single unit does not have a major impact.
Room units can require specialist maintenance
Commercial Buildings SWG
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Such systems can be relatively easily installed (only require piping not ducting) as a retrofit
to improve thermal comfort.
5.6.
Variable Refrigerant Flow (VRF)
A Variable Refrigerant Flow (VRF) air conditioning system is similar to the previously described split
systems. However unlike the split systems these systems have the ability to provide heating or
cooling simultaneously to each of the indoor units (similar to the room based heat pump systems).
VRF systems do not however have individual heat pumps for each area and instead contain
microprocessor-based electronics, which ensure efficient operation. Central to VRF control is their
ability to automatically vary refrigerant flow from the outdoor unit in response to the heating/cooling
load of the building.
Figure 21 Schematic of a VRF System
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Again relatively quick and easy to install
Capable of providing simultaneous heating and cooling in a very energy efficient manner.
Only re-circulate room air and cannot provide ventilation
Significant amount of refrigerant passes through occupied spaces. This could potentially
cause a problem if a leak occurs.
Typically require a specialist service engineer for repairs and maintenance.
The system must be installed to a high standard to ensure good performance and reliability
5.7.
Mechanical Ventilation and Energy Recovery
As has been discussed in this chapter a supply and extract ventilation system typically comprises a
central air handling unit (AHU), containing separate supply and extract fans, air filters and heating
and cooling coils, as well as ductwork used to supply and extract air to and from the building.
To save energy in cold weather, some systems are designed to re-circulate a portion of the warm
extracted air back into the supply, which cuts down the amount of fresh air that must be heated, such
set ups were discussed in section 4.4.2. Alternatively, where extracted air cannot be put back into the
space, a heat recovery device can he incorporated into the AHU. This takes heat from the exhaust air
and transfers it back into the supply air without mixing the two air streams. This can be important in
some industrial processes, swimming pools etc. where extract air must not be re-introduced into the
space. Various heat recovery mechanisms are possible and these are discussed in the following
subsections.
Air-to-air heat recovery systems are primarily used on 100% fresh air systems to reclaim heat that
would otherwise be rejected to atmosphere. This can help reduce winter fuel consumption costs (or
summer cooling costs) but there is a price to be paid with additional fan power and maintenance.
There are four main HVAC air-to-air recovery devices:
•
•
•
•
Thermal wheel
Run-around coil
Plate heat exchanger
Heat pipe
5.7.1.
Thermal Wheel
Thermal Wheels or Rotary Heat Exchangers can be delivered either as hygroscopic (sensible and
latent recovery) or non-hygroscopic (sensible recovery only) wheels. Both types of thermal wheel
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transfer the sensible energy from the exhaust air to the supply air, which means that heat is generally
transferred in winter, and cooling transferred in summer. The hygroscopic wheel not only recovers
the sensible energy in both summer and winter mode but also transfers the moisture, providing
humidification in winter time and dehumidification in summer time. Both wheels provide a reduction
in the capacity of cooling and heating required as well as the actual cooling and heating energy used.
Figure 22 A Thermal Wheel
5.7.2.
Run-Around Loop
These comprise finned-tube copper coils located in supply and exhaust air streams connected by
pipework through which water or antifreeze solution is pumped. Typical thermal effectiveness is 5565% depending on the number and spacing of coil rows and the prevailing temperatures.
When an additional loop is added after the cooling/dehumidification coil, the heat recovery from the
exhaust air can provide some of the required energy to re-heat the overcooled air.
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Figure 23 Run-around Energy Recovery Loop (with additional Dehumidification Re-heat Loop)
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5.7.3.
Air-to-Air Plate Heat Exchanger
Air-to-air plate heat exchangers consist of plates within main air streams providing cross- or counter
flow of supply and exhaust air. Typically they are constructed of aluminium sheets and provide only
sensible energy recovery.
Figure 24 Cross and Counter Flow Heat Exchangers
5.7.4.
Heat Pipe
Heat pipes allow the transfer of sensible energy only. In their simplest form, a sealed tube (usually
copper) is evacuated and charged with a refrigerant. Heat transfer occurs without the need for any
energy input. In operation, heat is absorbed from the warm air stream in the evaporator section,
boiling the refrigerant. Due to its elevated vapour pressure, the vapour inside the heat pipe moves to
the cooler condenser section of the heat pipe, carrying with it the absorbed heat. As the vapour
reaches the condensing area of the heat pipe, heat is released to the cooler air and the vapour
condenses. The liquid returns by gravity or capillary action by means of a “wick” to repeat the process
almost immediately. The entire heat transfer process occurs with a very small temperature difference
along the pipe.
Figure 25 Heat Pipe System with Indirect Evaporative Cooling
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Retrofit and Operational Considerations
With mechanical ventilation the volume of air entering/leaving a building can be controlled
and the ability to recover heat ensures good energy efficiency.
Mechanical ventilation systems can lend themselves to be used for night-time cooling.
With regard to the heat recovery mechanisms, it can be difficult to get payback on these as
retrofits, however they should be designed into any new systems.
Choice of heat recovery mechanism must be carefully made to consider implications such
as the potential for cross contamination, for instance ruling out thermal wheels (which can
lead to some cross contamination) or direct recirculation.
Most heat recovery mechanisms are seasonally reversible, providing preheating in winter
and pre-cooling in summer.
5.8.
Natural Ventilation
Natural ventilation is a cheaper (from an energy perspective) ventilation system than mechanical
ventilation. Both methods can also be combined, known as mixed mode systems. The choice of
ventilation systems is largely dependent on the following factors:
•
•
•
•
Predicted heat gains to the space.
Occupant usage patterns.
External noise levels and air quality.
The need to remove contaminated air.
Natural ventilation is basically air that enters a building by natural means. Typical mechanisms of air
movement are temperature difference and/or wind.
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Figure 26 Illustration of Natural Ventilation
The most basic natural ventilation system is the provision of openable windows which can be
manually operated or automated based on certain control criteria, such as, wind speed, solar gain,
time of day, weather conditions etc. More generally types of natural ventilation include;
•
•
•
•
Single-sided ventilation
Cross ventilation
Stack ventilation
Stack/wind ventilators
5.8.1.
Single-sided ventilation
Single sided ventilation refers a space primarily ventilated by wind entering one or more openings
within a single external wall. This method will only work for narrow-plan offices.
5.8.2.
Cross ventilation
Cross ventilation is a very effective way to achieve a good rates of ventilation. This system can be
used in relatively deep-plan offices. Wind drives air through open windows on the windward side of
the building and open windows on the opposite (leeward) side allow stale air to escape.
5.8.3.
Stack ventilation
Stack ventilation is based on warm buoyant air rising upwards in a building and exiting through high
level openings. The air displaced from the building by this system allows cooler fresh air to be drawn
into the building through low level openings. A benefit of stack ventilation is that the temperature
difference between the inside and outside of a building is the driving force and thus it can provide
ventilation on hot still days when there is little or no wind.
5.8.4.
Stack/wind ventilators
Ventilators combine the benefits of stack ventilation and wind. With such ventilators wind from any
direction strikes louvres on the ventilator(s) and is channelled down into the occupied space. At the
same time, warm room air rises up and is exhausted from the building on the down wind side of the
ventilator(s). Most buildings require multiple stack ventilators to ensure adequate ventilation.
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Retrofit and Operational Considerations
Natural ventilation systems require careful design and educated users to operate them
efficiently.
Simulation models are particularly useful in the design of natural ventilation systems to
assess the most suitable method of natural ventilation to apply to a building.
It is important to assess air quality and noise issues before designing a natural ventilation
system.
Natural ventilation is not usually suitable as a retrofit.
Mechanical ventilation systems can be combined with natural ventilation to provide a
mixed mode ventilation system.
When the weather permits, the combination of wind and stack effect provides enhanced
ventilation performance. Such simultaneous cross ventilation and stack ventilation is
particularly effective.
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6. Lighting
Lighting can account for up to 40% of buildings electricity consumption and is therefore worth due
consideration in seeking to minimise the energy consumption of an existing building from an
operational or retrofit viewpoint. The following sections will introduce lighting technologies and
advice on the best approaches to retrofit for energy efficiency while maintaining/improving the
quality of the lit environment.
6.1.
Lighting Terminology
Lighting systems are made up of three basic components:
•
•
•
Lamp — the source of the light, for example, the bulb.
Luminaire — a light fitting that incorporates the lamp.
Controls — manual or automatic switching equipment, which operates the lighting system.
With regard to lamps the light from each type of lamp can be defined in terms of colour, brightness
and warmth. Lamps can also be compared by their efficiency and life. There are three categories of
lamp which create light differently:
•
•
•
filament lamps
discharge lamps
light emitting diodes (LED)
In filament lamps the filament has high resistance to electricity and light is produced when this
filament gets so hot it glows. This is a fundamentally inefficient method of producing light and it in
fact produces more heat than light. This is the way all ‘traditional’ tungsten light bulbs work. To their
advantage all filament lamps will reach maximum light output the instant they are switched on,
provide good quality, accurate colour rendering and can be dimmed. However, they are expensive to
run, produce high levels of unwanted heat and have high maintenance costs on account of their
relatively short 1,000-hour lamp life.
In discharge lamps electricity creates a charge which, when applied to a gas filled lamp at the correct
voltage, causes the gas to emit energy in the form of light primarily with some heat and noise also
being produced. To obtain and maintain the correct voltage, additional control gear called a ballast is
needed. This is how most non-tungsten lights work including fluorescent, sodium metal halide and
mercury. Fluorescent lamps have 4-10 times the efficacy (a measure of light output per Watt input) of
incandescent lamps and can last up to 18 times longer. Compact fluorescent lamps (CFLs) often look
like standard tungsten filament lamps, but work much the same way as fluorescent strip lighting, in
that they require an electronic ballast to start and the inside of the tube is coated with phosphor that
gives off the light. Triphosphor versions of both CFL’s and fluorescents are available, which are more
efficient, have a longer life and maintain their light output levels better than ‘standard’
halophosphate lamps. Lastly with regard to discharge lamps special ballasts can be employed so they
can be dimmed.
Light emitting diodes (LEDs) can be very efficient, relying on a pure semi-conductor to emit light (but
not heat or noise) as a response to an electric current. LEDs present advantages of lower energy
consumption, long lifetime, improved robustness, smaller size, faster switching, and greater durability
and reliability. However current (bearing in mind this is a fast moving market) LED products for
general lighting are more expensive to buy than fluorescent lamp sources of comparable output.
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In considering which lamps to use, one will need to be aware that certain lamps will require particular
kinds of luminaire, and many lamps can be greatly enhanced by efficient luminaires. A luminaire’s
efficiency is measured by its light output ratio (LOR). This is the ratio of the luminaire’s light output to
the light output of the bare lamp, or lamps. Various other terminology is used to describe lamps and
knowledge of this terminology is important in making the correct choice of lamp and fitting for an
area. Other terminology includes the following;
Illuminance — the measurement of light falling on a surface, lumens/m2.
Colour temperature — a measure of the colour appearance of a light source ranging from ‘warm’
light (for example, the light a candle produces) through to ‘cool’ light (for example, a bright white
fluorescent light). This is measured in Kelvin (K). Lamps below 3,300K are classed as ‘warm’ whilst
those above 5,300K are ‘cold’, see Figure 27.
Colour rendering — the ability of a lamp to show surface colours accurately, measured in Ra. The
lower a lamp’s Ra value relative to an ‘excellent’ value of 100, the poorer the lamp’s colour rendering
ability.
Efficacy — the amount of light provided relative to the amount of energy used, measured in lumens
per Watt once the lamp has reached full brightness. The higher the value the more light is gained for
the same energy.
Lamp life — how long the lamp should last in operating hours.
Warm up — the time it takes for a lamp to reach 80% of maximum output from cold.
Re-strike — time taken for a warm discharge lamp to reach 80% of maximum light output when
power is interrupted.
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Figure 27 Colour Temperature of different Lamps (Source UK Carbon Trust Lighting Technology
Overview CTV021)
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6.2.
Control
The most energy efficient of lamps will waste energy if lights are on when they are not required.
There are various types of control available to help maintain correct lighting levels and provide
optimum light output whilst minimising energy consumption. Controls will be more specifically
discussed in Chapter 7 but a brief introduction to some controls specific to lighting are given here.
To meet the differing needs of large work spaces zones can be created where separate lighting
controls are installed. This allows lights to be switched off in certain areas independently. Zoning
provides closer, more efficient lighting control which can both improve local conditions and save on
operational costs. Zoning should be considered for an area when there are:
•
•
•
Different occupancy patterns
Different lighting requirements depending on the task being carried out
Different levels of daylight provision within a building.
Zoning could also allow switching lights off that are close to windows whilst dimming those further
in to provide adequate light levels. This enables occupants to make the most of natural daylight
without leaving those spaces further away from windows in shadow. As a result, less lighting is used
which again reduces energy consumption. Furthermore heat generated by the lights will also be
reduced and, therefore, less cooling is required for the space.
A seven-day timer will allow users to determine different operating times for lighting throughout the
week, however for lighting occupancy sensors will typically offer a better solution. A scenario where
timers are more suitable than occupancy sensors would be in the case of slow response lighting such
as that usually found mounted at heights. These take time to warm up (and cool down) so should not
be switched on and off too often during building occupation. Timers in this case can ensure the
lights are turned off outside of core business hours. In this instance the timer could be over-ridden by
an occupancy sensor to prevent a safety issue.
Another time control application for lighting is the use of time delay switches installed in storerooms
and cupboard spaces that are infrequently occupied. These switches will automatically turn lights off
after a given period of being continuously on. These can be used to prevent lights being left on
accidentally.
Occupancy sensors help to ensure lights only operate when there is somebody there to require them.
Sensors can achieve savings of up to 30% on lighting costs.
Light sensors, or ‘photocells’ can be used to switch off artificial lighting when there is sufficient
natural daylight. As daylight hours vary throughout the year, sensors help to provide closer control
and thus offer substantial savings. They can be particularly useful for external lighting and can pay
back their costs in less than a year. Both occupancy and daylight controls can be combined with time
switches to provide even bigger savings however such combined controls have additional cost
implications.
6.3.
Recommended Fittings
The following Table 3 makes some general recommendations on suitable lamps for differing
applications.
Internal
Space Use
Recommended Lamp Type
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External
Offices
Triphosphor tubular fluorescent, compact fluorescent, low voltage
tungsten halogen (use sparingly)
Factories
Triphosphor tubular fluorescent, high pressure sodium, metal
halide, inductive
Hotels
Triphosphor tubular fluorescent, compact fluorescent, low voltage
tungsten halogen (use sparingly), LED
Hospitals
Triphosphor tubular fluorescent, compact fluorescent
Retail
Metal halide, white sodium, compact fluorescent, low voltage
tungsten halogen (use sparingly), LED
Leisure
Triphosphor tubular fluorescent, compact fluorescent, metal halide,
inductive
Emergency Directional
LED
Car parks
High pressure sodium, metal halide, compact fluorescent
Multi-storey car parks
Triphosphor tubular fluorescent, compact fluorescent, metal halide,
high pressure sodium
Floodlighting
Metal halide and high pressure sodium
Feature
Metal halide, high
fluorescent, LED
Sports facilities
Metal halide (4,000K+)
pressure
sodium,
triphosphor
tubular
Table 3 Suitable Lamps for Differing Applications (Source UK Carbon Trust Lighting Technology
Overview CTV021)
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Retrofit and Operational Considerations
Check lux levels needed for different areas and compare to actual measurements made
with a lux level meter. Caution is advised here, be careful not to reduce light levels to a
level below those required by safety regulations, or to the detriment of staff’s ability to
perform tasks.
When considering lamp types, choose the most efficient (highest efficacy) to meet but
not exceed general lighting needs (such as brightness or colour) and regulations (such
as health and safety). Lamp life should also be considered and related to this
maintenance costs.
Reduction in lighting energy costs can be achieved by;
• Lowering light levels.
• Making use of natural lighting.
• Reducing the number of lights.
• Housekeeping – switching off lights when not needed (aide the process by
labelling switches).
• Using blinds to optimise daylight by redirecting it away from work areas and
onto the ceiling or higher walls, thus brightening the space while eliminating
glare.
• Involving staff by running training in best practice and controls so that they
can achieve comfortable and efficient conditions for themselves.
• Implementing a cleaning schedule for windows, skylights, luminaires and
sensors.
• Checking sensors regularly.
• Maintaining equipment by developing maintenance schedules for lighting
equipment.
• Replacing blackened, flickering, dim or failed lamps immediately.
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Whenever changing equipment from a maintenance perspective this is the opportune
time to consider if there is a more energy efficient alternative available.
Note florescent tubes that are not working should be replaced or removed, because
regardless of the lamp the ballast will still consume up to 25% of the lamp energy for
mains frequency lighting and about 10% of the lamp energy for high frequency
lighting.
Replace all traditional (tungsten) light bulbs with Compact Fluorescent Lamps (CFL’s).
For a similar light output these use only 20-25% of the energy and last up to 8 times
longer.
T-12 fluorescent tubes can be retrofitted with more energy efficient T-8’s or T-5’s which
are the most energy efficient. This can be achieved by replacing the entire fitting
including luminaire or by using an add-on retrofit to the existing fitting. If replacing
the entire fitting, new improved luminaires combined with higher efficacy tubes may
allow for an overall reduction in the number of fittings.
Triphosphor coating should be specified on all new fluorescent tubes as it provides a
more natural, brighter light for the whole life of the tube.
High frequency fittings reduce the energy use and heat output of discharge lamps.
They can also eliminate flicker and hum, extend lamp life and allow dimming.
7. Controls
This section considers the main energy saving opportunities relating to building controls. Some of
the main types of building controls are discussed and the associated energy saving opportunities are
examined. Significant energy savings can be achieved by most organisations by simply installing
controls where they are not currently present and ensuring that they are set, operated and
maintained correctly.
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Controls manage the operation of all types of building services, such as:
•
•
•
•
•
Heating and hot water
Ventilation (through the use of fans and ductwork)
Cooling and air conditioning
Lighting
Windows and shading devices.
Aside from the capabilities of controls associated with these systems, there are a number of other
factors that need to be considered. These include where the control hardware is located, how
controls are set, and when/how often they are checked. Getting these additional factors correct can
have a major impact on the performance of building services.
Correctly installed and operated building controls can have a range of benefits. They can:
•
•
•
•
•
•
Minimise the energy consumption of associated services.
Improve comfort for building users.
Prevent the unwanted or out-of-hours operation of equipment.
Limit excessive wear and tear on building systems and plant.
Minimise maintenance, repair and replacement costs.
Reduce the need for cooling by minimising the unwanted heat gains associated with the use
of controlled equipment such as lighting, fans and motors.
Three main types of control considered here are;
Controlling by time
Time controls vary in complexity from simple 24 hour on/off timers, to sophisticated seven-day
timers, which allow for control to be set for individual days of the week. Upgrading existing time
controls to enable services to be switched on and off to better match daily and weekly requirements
can result in substantial savings.
Controlling by occupancy
Building services can be turned off or adjusted for intermittently occupied spaces such that services
switch off when nobody is around. Occupancy controls are generally used for quick response
services like lighting and individual ventilation fans. They are rarely appropriate for slower response
services like heating and cooling across an entire building.
Controlling by condition
Building services can be controlled by environmental conditions such as temperature (for heating,
and cooling systems), day-lighting (for lighting and shading systems), humidity (for ventilation
systems and air conditioning systems), and carbon dioxide levels (for ventilation systems).
The three types of control mentioned here can be combined, to provide optimum conditions and
control. In larger buildings with interacting services, controls are sometimes brought together in a
Building Energy Management System (BMS or BEMS), discussed in Section 7.3.
7.1.
Control Terminology
A control system essentially consists of three basic elements:
• a sensor
• a controller
• a controlled device.
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The sensor measures a variable, such as temperature in Figure 28, this temperature value is
transmitted to the controller. The controller then uses the measured temperature to compute an
output signal, which is transmitted to the controlled device. When this output signal is transmitted,
the controlled device changes the output of the load.
Figure 28 Schematic of Control System (Source UK Carbon Trust Building Controls Technology
Overview CTV032)
In Figure 28 the controller is attempting to maintain room temperature at a set point. A low room
temperature results in increased output from the heater, which in turn raises the room temperature.
This increase is detected by the sensor and transmitted to the controller, which will reduce the output
of the load accordingly. This type of system is known as a closed loop control system. In that it allows
the control to receive feedback.
Conversely an open loop is a control system that does not respond to its own actions, such as a
heating system controlled only by an on/off timer. This type of basic control can result in poor use of
services, higher energy consumptions and an uncomfortable internal environment.
Most successful control strategies have an open loop element dictating whether the closed loop
system should be enabled. For example, setting the thermostat to only operate within occupied
hours, using a timer.
Some more sophisticated closed loop control systems include:
• Proportional control
• Proportional plus integral plus derivative (PID) control
Proportional control alters how the service responds in proportion to the needs of the space. For
example, proportional control of a heating system will ensure a greater response when the internal
temperature is well below the desired set point. The response will reduce as the internal space moves
towards the set point, which in turn reduces the likelihood of the heating system overshooting
control temperatures. Improved temperature control, fewer temperature fluctuations and reduced
energy consumption result.
Proportional plus integral plus derivative (PID) control rectifies the scenario whereby proportional
control can result in a system taking an excessively long time to reach a set point as response is
reduced to prevent the system overshooting. PID controllers ensure faster response times and
minimal overshoot.
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Finally load control refers to when a system has a fluctuating heating demand, it may be efficient to
install load controls to the boilers. These are commonly used to control the loading of multiple boilers
in order to reduce the need to fire all of them at times of low demand. Two such types of control
include:
• Fixed priority strategy
• Rotate strategy
Fixed priority strategy identifies a priority for each heating load, allowing the system to drop the least
important loads at times of higher demand than supply. For instance, this may mean that hot water
provision takes priority over space heating (even if the thermostat is calling for heat) until the water
requirements have been met.
Rotate strategy is the most common strategy for multiple boiler installations of similar output and
efficiency, as it allows boilers to be rotated to match heating demand. Regular rotation of boilers
extends their working life and ensures all are equally used.
7.2.
Control algorithms
Complex control strategies will usually have a control algorithm that dictates how and in what
circumstances the controls will operate. The subject of control algorithms is vast and for the
purposes of this guideline three types of control algorithm will be considered broken down
according to:
•
•
•
Controlling by time
Controlling by occupancy
Controlling by condition
7.2.1.
Controlling by time
Using timers to control building services can have a significant impact on the energy used.
Commonly utilised time controllers are described in this subsection.
Time switches are simple controls that switch services on and off in response to programmed time
settings. They are most appropriate for heating, ventilation and cooling systems.
An optimum start controller can also be used for heating. Such controllers learn how quickly the
building reaches the desired temperature and brings the heating on at just the right time to achieve
the correct temperature as people arrive. Installing these controls typically results in heating
switching on later on mild days, due to shorter warm-up times. In addition, optimum stop control is
used to switch the heating off as early as possible without compromising comfort conditions during
occupied times.
Boost or advance controls are used almost exclusively in heating systems and are invaluable in
providing additional service without the need to override existing time controls. Therefore, in normal
heating and hot water circuits, the boost control will switch the hot water circuit on for a limited time
period (usually one hour) outside its normal time control settings, allowing for the provision of
additional hot water or space heating. By not having to override existing time controls there is no
danger of a temporary measure (and its associated additional energy consumption) being
unintentionally left on/set up.
In general override facilities are on controls are discouraged wherever possible, to prevent services
from being permanently left on. Training of staff is important to prevent such incidents. Settings
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should be reviewed every month as part of a maintenance/operational procedure to check that they
are correct. This practice would be encouraged by Energy Management Standards such as IS EN
16001.
7.2.2.
Controlling by occupancy
Occupancy sensors can help to ensure that building services only operate when there is somebody
present.
These types of controls are mainly used in lighting systems, though they can also be used for fastresponse ventilation or extract systems. Heating and cooling systems tend to be too slow in their
response to be effectively controlled by occupancy sensors. That said occupancy sensors could, in
that case, be employed to instigate a set back level of HVAC.
Occupancy control can:
• Prevent unwanted operation or control systems out-of-hours
• Extend the life of services and reduce maintenance, repair and replacement costs.
There are four types of sensing technology available and these can be adjusted to increase or reduce
sensitivity to suit a particular application:
Passive infrared (PIR) sensors are the cheapest and most common sensors and can only ‘see’ in an
unobstructed, direct line of sight. PIR sensors are appropriate in areas with little or no obstructions,
such as in small offices and conference rooms.
Ultrasonic sensors emit and receive high frequency sound waves. These devices can pick up smaller
degrees of motion and can detect movement outside their line of sight, but can be more expensive
than PIR sensors. Ultrasonic sensors, are suitable in larger areas such as open plan offices, conference
rooms and unusually shaped spaces.
Microwave sensors generate and receive microwaves and operate by sensing changes in reflective
frequency. Microwave sensors are very sensitive and can provide good directional and spatial
coverage. They are commonly used for automatic door control.
Audio sensors contain a microphone that picks up sound. They are fairly inexpensive, are unaffected
by obstructions and do not rely on movement to be activated. Their main problem is that they cannot
differentiate between internal and external noise.
Combined or hybrid sensors offer greater accuracy and improved response by combining some of
the above technologies into one sensor. However, this can increase purchase costs making them less
viable for smaller spaces.
User interactive control systems also fall into the category of occupancy based control but these are
discussed separately in Section 7.5.
7.2.3.
Controlling by condition
Energy savings and improved occupant comfort can be achieved through monitoring and adjusting
building services in response to internal conditions. The conditions that are usually controlled are:
•
•
Temperature — used to control heating, cooling and ventilation
Daylight levels — used to control lighting
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•
•
Humidity — used to control air conditioning
Carbon dioxide levels — used to control ventilation.
These are now briefly discussed.
Room thermostats positioned in an appropriate location can provide overall temperature control of
an area so that it reflects the activity taking place in the space. In a radiator-based heating system,
thermostatic radiator valves (TRVs) offer control. A TRV is a simple control valve with an air
temperature sensor, used to control the heat output from a radiator by adjusting water flow.
Thermostats and sensors should not be influenced by draughts or heat sources such as sunlight,
radiators or office equipment. These factors create a false local temperature and may result in over or
under heating a building.
Reducing temperatures in heating systems during milder weather can reduce costs by minimising
unwanted heat loss from the system. This is done with the installation of weather compensation
controls which measure the external temperature and adjust the circulating temperature accordingly.
Light sensors or ‘photocells’ (previously mentioned in Chapter 6) are most commonly used to control
artificial lighting according to available natural daylight. In the most basic form photocells can
control light system to an on/off basis. However they can also be used where high-frequency
fluorescent lighting is installed, to dim the light output to maximise the benefit from the available
daylight, thereby minimising the energy consumption of the lighting.
Humidity control is achieved through a ‘humidistat’ controlling heating, ventilation or cooling
services.
Ventilation speeds can be regulated to meet requirements based on the levels of carbon dioxide in
the air, which can be used as an indication of occupancy levels. Connecting carbon dioxide sensors to
variable speed ventilation fans results in airflow dropping when there is less demand for fresh air.
Lowering ventilation rates saves energy in two ways: first by reducing the ventilation fan speed;
second through lowering heating/cooling requirements (see section 5.2).
Some areas in large buildings require different levels of heating, lighting, cooling and ventilation. A
solution to this is to create ‘zones’ in the building where separate time, temperature and occupancy
controls are installed for individual areas. Zoned areas will provide closer, more efficient control.
Zoning should be considered when there are:
•
•
•
Different occupancy patterns
Different temperature requirements
Different activities taking place
An interlocking control switches off building services when triggered and can be used to minimise
the risk of two systems operating in competition, for instance a radiator heating system and air
conditioning cooling system. Simple interlock controls are relatively cheap to install and can be
effective in achieving energy savings
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Retrofit and Operational Considerations
If a building houses activities that abide to a regular schedule it may be worth
considering devices that offer control by time.
One should consider profiling or measuring of certain building characteristics such as
temperature to determine if an opportunity exists for optimum control devices, i.e. is a
building getting to the required temperature for 07:20 but typically not occupied until
08:30?
Are certain areas only intermittently occupied in which case there may be an
opportunity for control by occupancy for services to these areas.
If there are complaints about conditions determine what factors are affecting these
conditions (e.g. temperature, humidity, fresh air, light) and consider control by the
appropriate condition.
It is very important that interlocking controls are used to prevent scenarios where
systems fight each other. For instance an air conditioning unit trying to achieve 20oC and
a radiator system trying to achieve 21 oC. Interlocking controls can prevent such a
scenario.
7.3.
BMS and M&T
Many of the controls and functions described within this guide can be integrated into a single
Building Energy Management System (BEMS or BMS). A BEMS offers closer control and monitoring of
building services performance, including heating, cooling, ventilation and lighting, showing data on a
computer screen in real time. This allows settings to be viewed and changed quickly and easily. BEMS
also offer a transparent view of where energy is being consumed in a building, thus helping to
identify areas of focus from an energy saving opportunities perspective. This is particularly relevant
for larger buildings with energy bills in excess of €15,000, and in these cases a BEMS is likely to offer
an appropriate and cost-effective solution to control and energy saving opportunity identification.
A typical BEMS architecture is illustrated in Figure 29. Intelligent controllers, or ‘outstations’ monitor
conditions throughout the building and determine the operation of boilers, pumps, fans, motors and
lighting in response to changing conditions such as time, temperature and light levels. A system can
begin with a single controller and be ‘added to’ over time as more controllers are introduced. With
recent advances in technology, access to various networks at remote geographic locations can be
achieved through the use of modems, IT networks and the internet. Many systems now make use of
computer interfaces and so, many aspects of their operation are intuitive to users who are familiar
with web-based software.
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Figure 29 Building Energy Management System
As shown in Figure 29 BEMS consist of:
• Hardware, such as sensors, actuators and controllers.
• Software, including programs set up to deliver the control strategy.
• A network or networks, as well as interfaces with other systems, such as the operator’s PC,
fire alarms and security systems.
Sensors provide information to the BEMS on their surroundings. There are three principal types:
• Digital inputs to show on or off status.
• Analogue inputs to provide values for certain variables.
• Pulse inputs these act as counters.
Actuators are the action element of the system and fall into two categories:
• Digital outputs to switch equipment on or off.
• Analogue outputs adjust devices to a specific position.
Controllers (or outstations) are the basic building blocks of a BEMS. These include:
• Internal clocks and microprocessors
• Integral power supplies
• Interfaces to sensors and actuators
The main advantage of a BEMS installation is the ease with which users can review the performance
of controls and conveniently make adjustments. Other advantages include:
• Close control of environmental conditions, providing more comfort for building occupants.
• Energy saving control functions which will reduce energy bills.
• Ability to log and archive data for energy management purposes.
• Provision of rapid information on plant status.
• Automatic generation of alarms to warn appropriate personnel of equipment failure or
condition changes.
• Identification of both planned and reactive maintenance requirements (for example, systems
can record the number of hours that motors have run, or identify filters on air supply systems
which have become blocked).
• Ease of expansion.
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Retrofit and Operational Considerations
Retrofitting a BMS to a building is most likely justifiable for buildings with energy costs
in excess of €15,000 per annum.
Alternatively an M&T (Monitoring and Targeting) System could be installed but this only
reports energy consumption, it has no control functionality. It can none the less identify
energy saving opportunities.
In developing BMS control logic one should remember the following rules;
-
Only supply building services where there is a demand
React to external temperatures and light levels (where appropriate) by
adjusting internal settings
Except if controlling humidity never operate heating and cooling in the
same place at the same time
Control separate zones with different needs independently
Provide necessary heating or cooling with minimal boiler or chiller
capacity.
Training of staff in the operation of a BMS is fundamental to its successful application.
To optimise internal conditions and make ongoing savings, BMS’s need to be regularly
maintained, this is a cost that must be considered in deciding whether to purchase a
BMS.
With regard to commissioning and operation, when new controls have been installed,
ensure that the contractor or supplier clearly explains how to set and use the new
system.
Keep a record of control settings and display these near to the controls themselves so
that they can be returned to their optimum settings if temporarily adjusted.
Regularly check control set points are correct and have not been inaccurately adjusted.
BMS vendors can provide a range of sophisticated control routines for variable supply
temperature control, adjusted fan speed for VAV systems etc. the level of complexity
incorporated in the control logic should be applicable to the scale of the building and
the level of in house maintenance available. Control logics not fully understood by the
owners can ultimately end up costing energy due to misuse.
7.4.
Wireless Sensors and Meters
Today, wireless technology is evolving rapidly. Reliability, battery life, and cost have improved to the
point where wireless is a practical alternative to traditional sensors in common applications. Retrofits
are among the most beneficial applications of wireless zone sensors based on the significantly
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reduced installation costs due to no wiring requirements. Other examples where wireless sensors
should be considered include;
•
•
•
•
•
•
Difficult construction materials such as stone, brick, glass, or concrete block.
Historic properties or listed buildings, since many present preservation restrictions.
Atriums, where wiring is unfeasible.
Spaces that undergo frequent reconfiguration, or renovations such as leased properties,
offices, and retail space.
Precise temperature control properties where wireless can increase the chances for optimal
sensor placement
Fast-track projects encountering occupancy deadline pressure
With a rapid adoption curve and resulting economies of scale, the cost of wireless solutions for BMS,
including sensors, is expected to continue to decline. At the same time, investment in new wireless
developments is high. The industry is investing in solutions that make integration easy. In addition,
interoperable solutions like ZigBee™ wireless protocols and power harvesting are likely to bring open,
interoperable, and battery free wireless solutions in the not so distant future.
Retrofit and Operational Considerations
Wireless zone sensors are a viable alternative to wired sensors in retrofit applications
today. When retrofitting and wiring costs are expensive (e.g. it requires running wiring
in conduits on the surface of walls or opening up existing walls), wireless systems
should be assessed as an alternative.
The cost avoidance for wiring will most likely be the key selling point of wireless
technology.
Consider investing in a wireless network that covers the entire building. Once you have
a wireless network, the incremental cost of additional sensors is only the cost of the
sensor and very little set up cost. Note older buildings with considerable thermal mass
may require a number of repeaters around the building.
Always consider the extendibility of the wireless network.
As a building undergoes internal changes, you may need to add a repeater to cover
newly constructed space.
Wireless technologies should be easily extendable by adding additional repeaters and
sensors with minimal setup.
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7.5.
Individualised Workspace Control
Productivity is directly affected by environmental conditions of individual workspaces and the overall
quality of the office environment. Dissatisfaction with environmental conditions, such as air quality,
temperature and light levels can have a negative impact on job satisfaction. As mentioned in Section
2.1, no matter how well designed and implemented a system is, it cannot meet the needs every
individual so where possible/necessary individualised control in the form of user interactive controls
can be employed.
User interactive control systems provide individual control of building systems, such as air flows, light
levels and localised heating, as illustrated in Figure 31.
Figure 30 Illustration of Individualised Workspace Control (Source Johnson Controls, Personnel
Environments)
In such systems control is usually provided to the user though an electronic system, for example,
through PCs or telephones. The main benefits in using interactive control systems are:
•
•
•
The user feels in control of their environment
Telephone and PC-based systems can enable individual desk control
Considerable energy savings are achievable with unpredictable occupancy levels by linking
occupancy sensors which turn off all systems when a workspace is unoccupied for a certain
length of time.
Occupant information and training is extremely important with regard to user interactive control
systems. The way occupants use controls depends on their understanding of how they work and
whether they believe the controls help to enhance their environment. Controls which dictate to
occupants are likely to be overridden or bypassed which negates any savings. To reduce the
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possibility of this occurring, it is important that staff understand how controls function in their work
area, so that they have full control of their environment. A basic action is to label controls with the
preferred settings, so users can return them to their correct settings if they have been adjusted.
Retrofit and Operational Considerations
Staff productivity can be hampered by dissatisfaction with environmental conditions.
Local workspace control can be utilised to offer additional energy savings and workplace
comfort/satisfaction.
Retrofit to individualised workspace control should allow for reduction of central plant
requirements (air conditioning, ventilation, lighting etc.) servicing the area.
If staff are given control of their own conditions these controls must be introduced with
sufficient training.
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8. Retro Commissioning
8.1.
Overview
Retro-commissioning refers to the commissioning of existing buildings. It involves a systematic
investigation process for optimizing building performance by identifying and implementing
relatively low-cost operational and maintenance improvements. Retro-commissioning will analyse
the original design intent of the facility and then determine if it is in alignment with the building’s
current needs.
Retro-commissioning isolates problems that occurred at the time of construction, similarly to
new commissioning, but it also identifies problems/changes that have occurred during the course of
the building’s life, and suggest solutions where such problems/changes have had a detrimental affect
on energy consumption. For instance if a laboratory with strict environmental conditions in terms of
temperature and relative humidity requirements has been converted into office space, it is commonly
found that no adjustment of the tight HVAC control regime (and associated energy costs) has
accompanied the change of use.
Benefits resulting from Retro-commissioning can include;
!
!
!
!
!
Reduced energy costs
Identification of low-cost operational and maintenance improvements
Saving opportunities with short pay-back time
Extended equipment life
Improved worker productivity
In the past many energy management programmes have concentrated on the acquisition of energy
and installing energy-efficient technologies, with less emphasis placed on efficient operation. This is
most likely the result of efficient operation being the least understood component of an energy
management programme. Yet efficient operation can offer high potential for savings with little or no
capital outlay.
The current economic climate implies that most short to medium term work will lie in the retrocommissioning of existing buildings. Furthermore with the emergence of energy management
systems and associated standards such as I.S. EN 16001:2009, the improvement of operational
procedures, as well as the documentation requirements of the same procedures (as promoted by
retro-commissioning) is likely to be an area of growing interest to many companies.
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8.2.
The Retro-commissioning process
The principal differences between commissioning as applied to a new build and commissioning of an
existing building are highlighted in the following table.
New Building
Have access to the project design.
Existing Building
Typically difficult to find information re design
intent.
Difficult to determine the current system
performance. Renovations may have changed
the use and configuration of systems.
Must define desired goals for the current system
performance, and get the system performance to
meet these.
Sole responsibility for arranging all testing.
Plans and specifications detail what is expected
in system performance.
Design Engineer has the responsibility for
determining system solutions when problems
arise.
Contractors typically required to provide system
testing.
Systems are new and generally in good working
order.
Systems have not been operated and maintained
under occupied conditions by O&M staff.
The processes for commissioning are well
defined.
Systems are often older and in poor condition.
The systems operational intent may have been
altered by O&M staff.
The processes are job dependent and are based
on the basic principles of the commissioning
process.
The owner may more easily measure the results
of the building retro commission process.
The owner pays for the commissioning with the
expectation that he will receive the benefits from
the process which is hard to document.
Table 4 Traditional Commissioning v’s Retro-commissioning
Retro-commissioning can be applied to a building that has not previously been commissioned. The
process is systematic and ensures that individual systems and processes operate correctly. Retrocommissioning also optimises, from an energy and reliability perspective, how the myriad of systems
within a building operate together in a combined manner. This is an area not covered in traditional
commissioning as this tends to concentrate on the operation of individual systems.
When retro-commissioning is carried out it will typically concentrate upon the main energy
consumers within a building and thus will typically include the following:
! HVAC
! Building Management Systems
! Controls systems
! Lighting Systems
! Chillers systems (Distribution and generation)
! Boilers (Distribution and generation)
Controls, mechanical systems and HVAC systems are typically the more closely examined systems in
retro-commissioning projects, as they will normally represent the largest energy consumers and also
potentially the more critical parts of a buildings infrastructure.
Retro-commissioning projects involve planning, investigation, implementation and hand over
phases. These can typically be broken down into the following:
1.
Arrange and co-ordinate all system testing.
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2.
3.
4.
5.
6.
7.
8.
Determine the desired system operating conditions, including heating and cooling loads, air
and water flows, and required ventilation rates.
Evaluation of system performance compared to desired performance.
Formulate solutions to bring system performance in alignment with desired conditions.
Estimate solution costs.
Estimate benefits of each solution and prioritise in accordance with economic and
environmental benefits.
Execute acceptable solutions.
Repeat system tests to confirm performance is as expected.
The emphasis on verification of savings is important to develop a belief in the process which can help
to integrate retro-commissioning as a routine business procedure for companies, perhaps by
embedding retro-commissioning into the companies overall energy management system.
8.3.
Summary
When applied appropriately, retro-commissioning surpasses quick-fix solutions to systematically
optimize building systems so that they operate efficiently and effectively, often eliminating the need
for costly capital improvements.
Some buildings represent higher potential beneficial gains from the retro-commissioning process.
These buildings include;
! High energy usage buildings.
! Highly regulated indoor environments.
! Buildings with multiple and complex systems interacting together.
Conversely retro-commissioning is typically not a major advantage where systems are outdated and
are liable to be replaced in the short term.
In essence much of the guidance given throughout this report under the description of “Retrofit and
Operational Considerations” would be typical retro-commissioning type recommendations.
Related to retro-commissioning is the process of continuous commissioning. Continuous
commissioning, however, more rigorously addresses the issue of persistence. A key goal is to ensure
that building systems remain optimized continuously. To achieve this, continuous commissioning
requires benchmarking pre- and post-energy use via metering equipment that is permanently
installed. Data are then continuously gathered and compared against the post commissioning
benchmarks to ensure that the building systems function optimally throughout their lives. Again
continuous commissioning can be introduced as part of energy management system.
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9. Under Utilised Technologies
This chapter considers technologies that, despite being proven technologies and gaining significant
market penetration in other countries have, as yet, not been implemented to similar extents in
Ireland.
9.1.
Photovoltaic
Photovoltaics (PV) convert light directly into electricity. Photovoltaics come in many different types,
although the majority are made from silicon-based materials. They can be categorised into:
! crystalline silicon cells
! thin film cells
Crystalline cells can be either mono crystalline (single-crystalline) or poly crystalline. Mono crystalline
silicon cells are the most efficient of the PV technologies with a conversion efficiency of 15-18% (the
amount of available solar energy converted to electricity) while poly crystalline cells have a typical
efficiency of 13-16%.
Thin-film cells are composed of photoactive semiconductors applied as a thin homogeneous layer to
a substrate (usually glass). Thin-film cell types include amorphous silicon, cadmium telluride and
copper indium diselenide, with efficiencies for these materials ranging from 5 - 9.5%. Thin film cells
are cheaper to produce than crystalline cells.
To protect the cells against mechanical stress, weathering and humidity, the cell strings are
embedded in a transparent bonding material that also isolates the cells electrically. A typical PV cell
will produce a voltage of around 0-5 V. In order to generate a higher voltage, a number of cells are
connected in series to form a PV module. The modules are then connected together to create a
photovoltaic array.
Figure 31 Photovoltaic Array
PV arrays produce DC electricity that can be used directly by DC motors in fans or pumps, or
alternatively for charging batteries. However, in most instances the DC power will be converted to
AC power using an inverter.
PV systems can be grid-connected or standalone. Grid-connected PV systems are connected to the
public grid and use an inverter to convert the DC PV array output to the AC required by the grid.
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Stand-alone systems use batteries that are charged during times with no or low loads, while at times
with no or low solar radiation the loads are met by discharging the batteries. A charge controller is
used to regulate the charge/discharge of the batteries. As is the case with grid-connected systems an
inverter is used to convert from DC to AC electrical supply.
PV systems can be incorporated into buildings in a number of ways including:
• Sloping and flat roofs
• Building facades
• Glass roof structures
• Solar shading devices.
Retrofit and Operational Considerations
For optimum results, roof mounted PV arrays should face between south-east and
south-west and at an elevation of between 30-40o
The building should be free from shading (PV performance can be significantly affected
even if panels are only partially shaded).
Check whether DC loads will be present in the building. It may be possible to power
some DC plant directly from the PV arrays.
Additional equipment and permission will be typically be required if seeking connection
to the gird for export.
Efficiency of PV cells falls as their temperature rises. They will therefore need sufficient
ventilation cooling behind the PV array (this is particularly true if integrating into the
building fabric).
Cleaning and maintenance of PV arrays is vital, ease of access needs to be considered.
Using a number of smaller inverters, each serving a PV sub-array, has the advantage of
providing greater security of supply and lower load losses.
9.2.
Fuel Cells
Fuel cells are energy conversion devices that produce electricity from the energy contained in a fuel.
Like batteries, they produce direct current (DC) electricity; but, like engines, they are refuelled (by
filling a fuel tank), rather than being recharged with electricity.
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Fuel cells can be very efficient at converting chemical energy contained in a fuel into electricity. This
means that up to two-thirds of the energy contained in a fuel (sometimes more) can be recovered as
electricity, the rest being converted to heat.
Fuel cells can be used in a very wide range of applications where they can convert energy more
efficiently than current technologies. The main obstacle to their uptake has been the high cost of fuel
cell models with acceptable performance and durability.
The simplest fuel that can be fed into a fuel cell is hydrogen, as all fuel cells will readily react this fuel
with oxygen (usually from the air) to produce electricity (water and heat are also released in the
process). Other fossil (e.g. petrol, natural gas) and renewables (e.g. biodiesel, biogas) fuels can also be
fed to fuel cells, either directly, or after being converted to hydrogen by a fuel processing device (also
called a reformer).
The basic components of a fuel cell are shown in Figure 32, and comprise; an electrolyte, an anode,
and a cathode. Gaseous fuels are fed continuously to the anode while an oxidant (oxygen from the
air) is fed continuously to the cathode. The anode and cathode are separated by the electrolyte. Ions
flow through the electrolyte between the anode and cathode. Electrons generated at the anode flow
through an external load to the cathode, completing the electrical circuit. Although all forms of fuel
cells use similar technologies, there are differences between the various types.
Figure 32 Schematic of a Fuel Cell
Each fuel cell produces in the order of 1V, which is too small for practical applications. In order to
provide a useful voltage a number of cells are connected together in a stack. A stack typically
comprises over 100 cells.
Fuel cells produce zero emissions (at the point of use) when running on pure hydrogen. However,
most building applications to date have involved the use of carbon based fuels (primarily natural gas)
requiring the use of a reformer. A consequence of the reforming process is the emission of carbon
dioxide, although emissions are still lower than conventional combustion processes due to the
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higher operating efficiency of the fuel cell (40% - 50% efficiency for electrical power generation).
Using a fuel cell for on-site generation of electricity also reduces transmission losses associated with
the delivery of electricity over electrical distribution networks or a grid. Lastly efficiencies can be
even higher where use is made of the waste heat generated.
As mentioned fuel cells generate DC electrical power. In order to produce useful AC power for
building services applications, fuel cells need to incorporate power conditioning equipment. The
power conditioning equipment comprises invertors for DC to AC conversion, current, voltage and
frequency control, and the ability to step the voltage up or down through a transformer depending
on required voltage. Controls are also required to regulate the real power output by controlling the
fuel rate and electrical output.
Retrofit and Operational Considerations
The most effective applications will use 100% of the thermal and electrical output of the
fuel cell. The more site energy that is displaced by the fuel cell, the higher the energy
savings and hence the shorter the payback period.
There are still some issues regarding the combining of fuel cells, particularly with
controls, this is partly due to difficulties with synchronising the units.
The temperature of the waste heat from different types of fuel cells varies widely, the
operating temperatures being between 80oC for the phosphoric acid fuel cell up to
1000oC for the solid-oxide fuel cell. This means that the appropriate fuel cell type should
be used dependent on the temperature of heat required.
The demand profile for heat is important. Not only does the flow rate vary when a fuel
cell is running at part load, but also the fuel cell has a finite number of cycles before the
cell stack needs to be replaced. The fuel cell should therefore be matched to the load
profile of the building, or even sized to the thermal base load of the building, with the
possible inclusion of thermal storage devices to enable the fuel cell to be switched on
and off as little as possible.
Fuel cells can have reasonably significant space requirements.
Proximity to the relevant building services plant room is generally the best location. As
the electrical and thermal interfaces are not always next to each other, it is usually more
important to locate the fuel cell nearest the thermal interface.
Noise levels associated with fuel cells tend to be minimal.
9.3.
Wind
Wind turbines convert the kinetic energy of wind into mechanical energy that is in turn converted to
electricity. Turbines are available in a range of sizes and designs and can provide electrical power
either directly to a load or via a battery system.
Wind turbines can generally be located as;
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•
•
Free standing
Building mounted
Where space is available surrounding a building, a free-standing turbine can be considered. The ideal
site for a wind turbine is on a smooth, rounded and exposed hilltop, away from obstructions. In
reality it is unlikely that these conditions will be met, however where possible the wind turbine
should be located clear of large obstacles particularly in the path of the prevailing wind.
Free-standing wind turbines are supported using a tower. Turbine performance improves with
height as wind velocity is usually proportional to height. Turbines should ideally be mounted nine
metres above any obstruction that is within 100 m.
Where space constraints inhibit the use of a free-standing turbine, a building mounted turbine can be
employed usually on the building's roof. The performance of a roof mounted turbine will be
reduced, compared with a freestanding turbine, due to the building obstructing the airflow. In
addition, the turbulent airflow will adversely affect the operational life of the turbine through
increased vibration.
Figure 33 Building Mounted Wind Turbine
There are two basic groups of wind turbines: horizontal-axis design and vertical-axis design.
Horizontal-axis wind turbines are the most common type and can range in size from a few hundred
watts to several megawatts. This type of turbine has a horizontal rotor shaft and generator typically
located at the top of a tower. Propeller-type blades are used and these are orientated into the wind,
using a wind vane (yaw control) for small turbines, or wind sensors used in conjunction with
servomotors for larger turbines. A turbine system will include the following:
•
•
A rotor, or blades, which convert the wind's energy into rotational shaft energy
A nacelle containing a drive train, usually including a gearbox (some turbines operate
without a gearbox)
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•
•
A tower to support the rotor and drive train
Electronic equipment such as controls, electrical cables, ground support equipment, and
inter-connection equipment.
Vertical-axis turbines have a rotor shaft orientated vertically. This avoids the need for a tower and the
generator is located at ground level. Another advantage is that no yaw mechanism is required to turn
the rotor into the wind. However the disadvantages of vertical axis turbines are that the efficiencies
are lower and they are not self-starting.
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Retrofit and Operational Considerations
Wind energy systems employing batteries have costs incurred due to the typically large
number of batteries required, also these batteries have a finite life (6-10 years) and they
require an enclosed location provided with sufficient ventilation and temperature
control.
Wind turbines can also be connected to the public electricity supply network. This
allows any spare electricity generated by the wind turbine to be exported to the grid.
Grid-connected systems need to be synchronised with the public electricity supply.
Approval from the local distribution network operator must also be obtained.
Although wind turbines incorporate an AC generator that can be connected to the
public network, sonic turbines likely to be used in building applications can generate
DC electricity to charge batteries.
The installation of a wind turbine to a building may have insurance premium
implications. The consequences of a catastrophic failure of the wind turbine should be
considered.
The power available from the wind is a function of the cube of the wind speed. This
means that a 20% increase in wind speed will almost double the power available.
Wind increases in speed with height because of the reduced drag of the land. Small
increases in turbine height can produce significantly increased power output.
An increase in rotor diameter will result in an increased power output. The output is
related to the square of the rotor diameter. Doubling the diameter of the rotors will
result in a quadrupling of the power output.
Ideally, turbines should be located clear of obstructions with a minimum distance
between obstructions and the turbine of 10 times the height of the obstruction. The
presence of obstructions will reduce the air speed and result in turbulence that can
damage or limit the lifespan of the turbine.
Building augmented wind turbines are turbines that are located such that the building
structure is used to alter and augment the wind flow to produce higher wind velocities
and less turbulent conditions.
A minimum average wind speed of around 6 m/s is required for turbines
In urban areas wind speed is likely to be reduced compared to rural areas. This will in
turn greatly reduce the power output of an urban wind turbine
Potentially damaging air turbulence is more likely in urban areas
Building mounted wind turbines will have potential structural, vibration and noise
implications
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9.4.
Ground Coupled (Air) Heating / Cooling
Although ground source heat pumps (discussed in section 3.3) are a form of ground coupled
heating/cooling here we are considering the less utilised technology of ground-coupled air systems.
Ground coupled air systems are primarily used for pre-conditioning outdoor air prior to additional
heating and cooling. Ground coupled air systems typically comprise a length of underground piping.
The piping is connected to an outdoor air intake and to the building ventilation system at the other
end (Figure 34). During the summer, heat transfer to the surrounding ground cools warm outside
air, while during the winter, cold outside air is warmed.
The cooled air can also be used for cooling the building's thermal mass within the building structure.
The cooling/heating effect provided by the thermal mass of the ground can significantly reduce (or
even remove) the need for mechanical cooling or space heating.
Figure 34 Schematic of Ground Coupled Cooling
The effectiveness of a ground-coupled system is dependant on a range of factors including the
following:
•
•
•
•
•
•
•
Ground or soil temperature
Soil type and thermal conductivity
Soil moisture levels; wet and heavy soils are an advantage in terms of thermal performance
Length of pipe or ducts
Air temperature
Mass flow-rate of air and air velocity
The amount of air turbulence at the inside surface of pipe or duct.
The performance of the ground-coupled system will be enhanced if the tubes or ducts are below the
water table and further enhanced if flowing ground water is present. This will require careful
selection and on-site assembly of the tubes to avoid significant water penetration. Interlocking
concrete pipes or galvanised steel spiral drainage sections offer the best opportunity' of achieving a
watertight system.
The distribution ductwork should be large enough to allow access for inspection and cleaning. The
pipes are inclined towards the intake to ensure that condensate and any ground water can drain off.
Because the pipes are difficult to replace, long life (>50 years) materials should be used.
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Retrofit and Operational Considerations
The system can be used to cool the supply air entering a building in summer, or to
preheat air in the winter.
Avoid air intakes over areas exposed to direct sunshine or macadamised surfaces.
Placement of vegetation around the intake can reduce intake temperatures.
Coarse filters can be fitted to remove large particulates, with fine filters in the air
handling unit downstream of the earth duct.
At a soil depth of between 2 - 5 m, the ground temperature is relatively stable at around
13°C all year round. Performance of the system will be improved at greater depths but
this will incur greater excavation costs.
To limit the pressure drops in the piping network, the air velocity in the pipe should be
about 2 m/s.
The optimum pipe length is a function of pipe diameter and air velocity.
Creating and maintaining turbulent airflow along the duct length can increase heat
transfer by between 3-8°C for an incoming air temperature range of -l°C to 5°C.
Pipes should be installed 1 m apart. This distance prevents mutual interference
between pipes.
Minimising fan power consumption will enhance the energy performance of the
system.
Labyrinths for the underground pipe run are more expensive than earth tubes, but
payback can still be within 10 years.
Access should be provided for inspection and cleaning
9.5.
Thermal Storage Aquifers
Ground water cooling through the use of aquifers makes use of the relatively stable ground/water
temperature. Aquifers are water yielding rock strata. The cold water in aquifers can be used to
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provide space cooling within buildings or as a source of heat for preheating ventilation air. Water
from aquifers can be pumped directly or indirectly to cooling systems and used as a heat source or
sink for heat pumps (discussed in section 3.3).
There are two types of aquifer-based systems:
•
•
open loop
closed-loop.
Open loop ground water cooling systems comprise two boreholes; a cold well and a warm well.
When cooling is required in the building, water is extracted from one part of the aquifer system (the
cold well) and transferred to a heat exchanger then returned to the aquifer at a different location (the
warm well). On the secondary (building) side of the heat exchanger the water is cooled then
supplied to provide a cooling effect in the building.
Typically, ground water can be extracted at a temperature of around 6-10°C giving a chilled water
supply temperature from the heat exchanger of approximately 120C (allowing for heat transfer
efficiencies). Where additional cooling is required, this water can be further cooled using mechanical
vapour compression or absorption cooling techniques. The supply of chilled water from the heat
exchanger can also be used to provide condenser cooling.
During the heating season, the flow of water can be reversed with water extracted from the warm
well and returned, via the heat exchanger, to the cold well. In this scenario the supply of water from
the heat exchanger can be used to preheat ventilation air. Further heating can be produced if the
water is used as a heat source for a heat pump.
Closed-loop systems on the other hand do not extract water from the aquifer. They comprise a
continuous loop of piping that is installed underground. Water is circulated through the loop and
into the building where it can be used for space cooling. As with ground source heat pumps there
are tow types of closed-loop systems; vertical boreholes and horizontal loops.
Vertical loops provide better performance than horizontal loops because of the lower and more
stable aquifer temperature associated with the greater depth, however installation costs are higher.
As ground water will not be directly used, closed-loop systems tend to have fewer operational issues,
although the coefficient of performance will be slightly lower. Unlike open systems approval for
water extraction is not required from the Environmental Protection Agency (EPA) in the case of
closed loop systems.
Surface water cooling is another form of using a naturally occurring thermal aquifer. Surface water
cooling involves pumping water from the sea, lakes or water courses and using it to provide some or
all of a building's cooling requirements. Such systems are open loop, where water is extracted,
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passed through a heat exchanger then returned to the water source. As before on the secondary
(building) side of the heat exchanger the resulting cooled water can be used tor a range of cooling
purposes and during the winter the water can be used to pre-heat ventilation air.
Figure 35 Schematic of Surface Water Cooling
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If there is a low temperature difference between the aquifer and the water in the loop,
the cooling output will be low. In this case output can be increased through the use of
a heat pump.
For open loop systems cold and warm wells should be between 100 and 150m apart.
While capital costs are relatively high, energy operating costs are low compared to
conventional HVAC approaches.
For open loop systems favourable ground conditions for aquifers are of sand or bedded
porous and permeable calcareous rock, such as chalk and carboniferous limestone,
bounded by tight layers of clay or similar materials (for thermally balanced two-bore
system). Geological surveys will be required.
Open-loop systems can be susceptible to blockages caused by silt and corrosion, from
dissolved salts. Filtration of the extracted water will be required along with possible
water treatment.
For closed loop systems vertical loops are inserted as U-tubes into borehole; then
backfilled with high thermal conductivity grout.
The thermal performance of a closed loop system will be less than that of an open loop
system.
No environment agency approval is required for closed loop systems as water is not
extracted from the aquifer.
Aquifer cooling or surface water cooling could also be used as a constant temperature
heat source or sink for a heat pump.
Surface water cooling can be used for supplying cooling, via a heat exchanger, to fan
coils, chilled ceilings etc. or to pre cool return chilled water prior to further cooling by
other techniques.
Effective direct surface water cooling occurs only when the intake temperature from
the water source is below 10°C. Although water will be cooler at greater depths, this
will require greater pump energy.
The viability of a proposed surface water cooling system will depend on the proximity
of the building to the cold water source.
Filtration will be required for surface water cooling to prevent fouling of the heat
exchanger.
10.
Conclusions
As discussed at the outset it has not been the intention of this guideline to replace existing
documentation that describes in detail all those technologies considered in this report. For that
reason technical descriptions have been kept short and precise, with the user advised to seek further
material where necessary. This guideline has tried instead to highlight two aspects of these existing
technologies, namely;
•
•
Suitability as a retrofit technology
Optimisation from an operational perspective
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This approach has been arrived at on the basis that the guideline is targeted at companies seeking
accreditation to the IS EN 16001 energy management standard. This energy management standard
lays down the requirement to review both energy efficiency projects that might take the form of
retrofits/upgrades but also to improve, document and understand the operational traits of a
buildings plant.
The guideline has drawn from the experience of the author in highlighting commonly found energy
saving opportunities related to specific technologies and also emphasized compatibility issues that
can occur when different technologies are combined or used in unsuitable replacement scenarios.
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