Bethel Evangelical Church, Coventry
Planning Application Supporting Document
Sustainable Energy Statement
MCA Consulting Engineers Ltd
17/18 Newhouse Business Centre
Old Crawley Road: Faygate
West Sussex RH12 4RU
Tel: 01293 851490 Fax: 01923 852156 Email: [email protected]
Nov 2011
Table of Contents
1.0
Introduction ....................................................................................................................................................4
1.1
General .......................................................................................................................................................4
1.2
Executive Summary ....................................................................................................................................4
2.0
Policy & Guidance ...........................................................................................................................................4
3.0
Development Overview ..................................................................................................................................5
3.1
Building Description....................................................................................................................................5
3.2
Landscape & Topography ...........................................................................................................................5
3.5
Site Constraints...........................................................................................................................................5
4.0
Energy Assessment .........................................................................................................................................6
4.1
Energy Requirements .................................................................................................................................6
4.2
Energy Efficiency Measures ........................................................................................................................7
4.2.1
Insulation Standards. ..........................................................................................................................7
4.2.2
Space Heating. ....................................................................................................................................7
4.2.3
Limiting the Risk of Summer Overheating ..........................................................................................8
4.2.4
Air Permeability and Ventilation ........................................................................................................8
4.2.5
Thermal Bridging ................................................................................................................................9
4.2.6
Lighting and Appliances ......................................................................................................................9
4.3
Energy Use and CO2 Emissions Following Efficiency Measures..................................................................9
5.0
Renewable Energy Requirements ............................................................................................................... 10
6.0
Consideration of Renewable Energy & Low Carbon Technologies ............................................................. 11
6.1
Biomass.................................................................................................................................................... 11
6.2
Solar Thermal........................................................................................................................................... 13
6.3
Solar Photovoltaic (P.V.) .......................................................................................................................... 13
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6.4
Wind Turbines ......................................................................................................................................... 14
6.5
Micro Hydro-electric Systems ................................................................................................................. 15
6.6
Heat Pumps ............................................................................................................................................. 15
6.6.1
Ground Source Heat pumps ............................................................................................................ 16
6.6.2
Air Source Heat pumps .................................................................................................................... 17
6.7
7.0
Combined Heat and Power (CHP) Systems ............................................................................................. 18
Review of Renewable Energy Options......................................................................................................... 19
7.0.1
Biomass Heating .............................................................................................................................. 19
7.0.2
Air Source Heat Pump...................................................................................................................... 19
7.0.3
Solar Photovoltaic (PV) .................................................................................................................... 20
7.1
Energy Calculations ................................................................................................................................. 20
7.2
Energy Summary...................................................................................................................................... 20
8.0
Conclusion and Recommendations ............................................................................................................. 21
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1.0 Introduction
1.1
General
This Energy Statement has been prepared by MCA Consulting Engineers Ltd. on behalf of C.P.L.
Chartered Architects, in support of the planning application for the extension of Bethel Evangelical
Church, Coventry.
1.2
Executive Summary
This document will present a detailed report on how the proposed development will achieve the
following:

A reduction in energy consumption of 14% from Building Regulations minimum standard baseline
by energy efficiency measures alone.

A reduction in CO2 emissions of 8% from Building Regulations minimum standard baseline by
energy efficiency measures alone.

Photovoltaic (P.V.) to supply 12% of proposed building’s energy demand from renewable sources.

Photovoltaic (P.V.) to provide additional 22% reduction in CO2 emissions over and above efficiency
measures alone
The report also presents an additional statement on measures employed to support the sustainable
drainage and water use of the site and recommends the use of a green roof system where feasible.
2.0 Policy & Guidance
This statement is based on ‘Delivering a More Sustainable City’ Supplementary Planning Document
adopted in January 2009 by Coventry City Council for ‘major proposals’ as the total floor space exceeds
1,000sq.m. The statement included a hierarchy of key policy documents including the Energy
Performance of Buildings Directive 2006 and the Conservation (Natural Habitats) Regulations 1994 in the
European Context; various national policies for sustainability, and the West Midlands Regional Spatial
Strategy 2004, Phase II 2007 and the West Midlands Regional Sustainability Framework 2006.
Coventry City Council requires that all planning applications where the total floor area exceeds
1,000sq.m. (proposal is for 1,430sq.m.) should carry out a sustainability appraisal.
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3.0 Development Overview
3.1
Building Description
The building is located in Spon End, close to the ring road in Whoberley Ward, postcode CV1 3HB to the
east of the Spon End viaduct and immediately adjacent to one of the major trunk roads into the
Coventry city centre. The existing buildings are shown on the Location Plan, Drawing No. CV.08/001 and
all are proposed to be demolished. The proposal is to redevelopment the entire site possibly in two
phases as funding permits and comprises a new entrance foyer, a two storey octagonal building, with
curtain glazing and a low pitched roof, a new main hall with a curved green roof, and a two storey
mainly brick teaching and meeting rooms particularly enclosing a landscaped secure garden area
situated at the rear of the site. The majority of glazing is located on the south west, north west and
north east elevations. The plan and proposed elevational treatment is shown, Drawings Nos.
CV.10/101-107 attached as Appendix A.
3.2
Landscape & Topography
The site is located within an urban environment and within an area of archaeological interest being the
site of medieval housing remnants of which can be seen on the north side of Spon End. The site slopes
upwards from pavement level approximately 80.800 to 82.840 towards the Southern boundary with
residential properties facing onto Broomfield Place.
3.5
Site Constraints
The Planners have indicated their preference for any new development to be moved closer to the
pavement line in order to restore an active frontage to this part of Spon End. The height of any new
development has also be limited to two storeys to avoid overlooking properties to the south and the
eaves height of the proposed new hall has been kept as low as possible to avoid obscuring light to
windows on the west elevation of the Dyers Arms.
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4.0 Energy Assessment
4.1
Energy Requirements
The estimated annual energy demand and consequent CO2 emission rates, for the proposed
development has been estimated using ‘Dynamic Simulation Modelling’ performed using approved
National Calculation Methodology Software.
The National Calculation Method for the EPBD (Energy Performance of Buildings Directive) is defined by
the Department for Communities and Local Government (DCLG). The procedure for demonstrating
compliance with the Building Regulations for buildings other than dwellings is by calculating the annual
energy use for a proposed building and comparing it with the energy use of a comparable ‘notional’ or
‘base-line’ building. Both calculations make use of standard sets of data for different activity areas and
call on common databases of construction and service elements.
A preliminary assessment has been used to establish a baseline energy demand for the development
and to demonstrate the savings that will result from energy conservation measures. The software used
in this example was ‘Virtual Environment 6.4.0.1’ produced by Integrated Energy Solutions Ltd. (IES)
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4.2
Energy Efficiency Measures
The following energy efficiency measures illustrate a possible route to the required reductions in energy
demand and CO2 emissions:
4.2.1
Insulation Standards.
The building will incorporate enhanced insulation in the building envelope (walls, roofs, floors and
glazing) to achieve average U‐values better than those required by Part L2 (2010) of the UK Building
Regulations. These are likely to include:
• Low Emissivity (Low E) glazing with a U‐value of 1.54 W/m²K
• Wall U‐values will be improved to 0.17 W/m²K
• Ground Floor U‐values will be improved to 0.13 W/m²K.
• Roof U‐values will be improved to 0.16W/m²K
4.2.2
Space Heating.
The space heating requirement of the development will be reduced by the fabric measures detailed
above.
In addition, it is intended to take advantage of solar gain where practicable, to further reduce the space
heating demands of the building. Orientation will therefore be taken into account in the layout of the
development. The building will be orientated to have glazed elevations facing East and West to take
advantage of early morning and late afternoon winter sunshine and subsequent solar gains. (These are
the times of day and the times of year when a large proportion of heating is required). Furthermore,
where practicable, the internal layout of the building will be such that the most utilised areas will be
designed to benefit from a greater amount of solar gain than the less utilised and more utilitarian areas
which do not have the same heating requirement and can be located where there is less solar gain.
It should be noted that the effects of solar gain cannot be allowed to go un-checked. Excessive gains can
cause problems with high summer time temperatures within the building and therefore measures will
be incorporated into the building design to mitigate the effects of excessive summer time solar gains.
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4.2.3
Limiting the Risk of Summer Overheating
At this stage it is not proposed to provide any mechanical cooling to the building, however more
detailed analysis of the building during the latter stages of the design process may result in some active
cooling being required. However it is proposed to reduce the need for active cooling as far as possible at
this stage of the design process.
This will initially be achieved through the specification of non‐mechanical measures such as good
thermal insulation and air tightness. Where appropriate, solar control glazing will be installed. The areas
of South facing glazing will be reduced in comparison with that proposed for the East and West
Elevations. In Addition the larger areas of glazing will incorporate ‘Brise Soleil’ shading so as to reduce
the solar gain from the higher sun angles experienced during the middle part of the day during the
summer months. All windows will be fitted with blinds to allow further reductions in solar gain wherever
necessary.
A number of large deciduous trees are already established across the site and these will be protected
and preserved during the build process. These trees allow localised cooling through evapotranspiration –
energy which would otherwise heat the local atmosphere is instead used evaporating water, thus
helping to reduce any ‘urban heat island’ effect. Deciduous trees provide shading in the summer and,
through the loss of their leaves, still allow solar gain to occur in the winter.
Open‐able windows will be installed wherever practical within the building to allow the natural
ventilation. These will enable cross‐ventilation, convective‐ventilation and night purging.
4.2.4
Air Permeability and Ventilation
Air permeability standards will conform to Approved Document Part L accredited details. These details
incorporate an improvement over Building Regulation (2010) requirements by reducing air leakage loss
and convective bypass of insulation. An improvement of design air permeability rate from 10m³/hm² to
less than 5m³/hm² will further reduce space heating requirements.
The increase in the air tightness of the building introduces the need to provide more fresh air to the
building occupants by artificial means. This in itself can increase the energy demands from the building
through the need to incorporate mechanical ventilation plant. However it also provides an opportunity
to incorporate heat recovery ventilation systems.
The majority of heat recovery ventilation systems incorporate Air to Air Plate Heat Exchangers or
Recuperators as they are also known. These are an extremely effective way of reducing the heating (or
cooling) loads from HVAC systems. A reduced heating or cooling load equates to lower energy
consumption and reduced carbon emissions. Heat recovery rates in excess of 90% can be achieved
under favourable conditions with the majority of systems consistently achieving heat recovery
efficiencies of 70% or more.
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Open‐able windows will also be installed wherever practical within the building to allow the natural
purge ventilation.
4.2.5
Thermal Bridging
In well insulated buildings, as much as 30% of heat loss can occur through thermal bridges, which occur
when highly conductive elements (e.g. metals) in the wall construction enable a low resistance escape
route for heat. It is proposed that the development will meet Accredited Construction Details for
thermal bridges.
4.2.6
Lighting and Appliances
Approximately 90% of internal light fittings will be dedicated for the installation of energy efficient
lighting. External lighting will also be low energy lighting and controlled through PIR sensors, or daylight
cut-off devices. Kitchen and other pre‐installed appliances will be A or A+ rated for energy efficiency.
In addition the use of natural light will be maximised wherever possible through the use of high level
windows and roof-lights.
It is difficult to design and construct any building to reduce the unregulated electricity demands because
this is almost entirely dependent on the occupants of the building and can vary substantially. However,
the Applicant is committed to ensuring that all efforts are made to enable the people utilising the
building to minimise their unregulated electricity consumption.
4.3
Energy Use and CO2 Emissions Following Efficiency Measures
The impact of the efficiency measures proposed in Section 4.2 is summarised in Table 1 (below), which
details the total energy demand for the notional building and compares this with the energy demand
and CO2 emissions for the proposed – ‘as designed’ building. These figures are drawn from N.C.M.
calculations the results of which are shown in greater detail in Appendix B.
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Table 1
Heating
Hot Water
Lighting
Aux (Unregulated)
TOTAL
Notional (Baseline)
Design (Actual)
Energy
Carbon
Energy
Carbon Dioxide
(kWh/m².yr)
Dioxide
(kWh/m².yr) (kg CO2/m².yr)
(kg
CO2/m².yr)
30.30
6.00
19.24
3.81
13.62
2.70
15.39
3.05
9.04
4.67
12.02
6.21
4.43
2.29
2.63
1.36
57.38
15.66
49.28
14.43
The above figures are subject to final design detail and verification.
5.0 Renewable Energy Requirements
It is the requirement of the Coventry City Council Planning Authority that at least 10% of any of the
development’s annual energy requirements are provided from onsite renewable sources.
Based on the NCM Figures outlined in section 4 above, the development at Bethel Evangelical Church
will require the following level of renewable energy production.
Table 2
Total Floor Area of Development:
Annual Energy Consumption Rate:
Total Annual Energy Consumption:
10% Annual Energy Provision
required from renewable sources:
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1,430 m²
49.28 kWh/m².yr
70,470 kWh
7,047 kWh
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6.0 Consideration of Renewable Energy & Low Carbon Technologies
Renewable energy should not be confused with energy efficiency. Renewable energy is the supply of
energy to buildings in the form of heat and electricity from sources which are not depleting the limited
resources of the Earth. This obviously involves the use of solar, wind and energy from the sea or other
water borne sources, but also includes energy from organic material where new crops can be grown to
replace those used in the production of energy. This specifically includes biomass systems whether
burning wood fuel, energy crops such as Miscanthus, willow and chestnut coppice, organic waste
products (e.g. coconut and peanut husks), and waste wood from shipping pallets, furniture production
or waste timber from sawmills and building sites.
It can also include the production of energy from bio-digester systems using many forms of waste
material, where the anaerobic decomposition of organic products produces methane, which is used to
power boilers or electricity generation systems.
Renewable energy does not include systems which can be more energy efficient than conventional
systems, but which still use fossil fuels. This includes combined heat and power systems (CHP), rain
water harvesting and grey water recycling. This is not to negate the use of this type of equipment, but to
ensure that terminology is correctly applied.
It should be noted that, although arguably not a purely renewable energy source, in December 2008 The
European Union ruled that technologies that exploit "ambient heat contained in water, air or the
ground", such as ground or air source heat pumps, would be classified as renewable.
6.1
Biomass
Biomass is a very well advanced form of renewable energy and requires little maintenance, other than
the removal of ash. It works by the combustion of fuel from organic sources to produce heat. Systems
can be either ‘dry’ or ‘wet’. The energy conversion of dry biomass involves heat, whereas wet biomass
involves fermentation or anaerobic digestion. Common applications for the latter include large industrial
schemes or developments in rural areas with easy access to a source of biological waste and where
neighbouring properties will not be affected (possible problems with noxious odours). Wet systems are
likely to be unsuitable for this proposed development.
Dry biomass differs from other forms of renewable energy in that the fuel is grown rather than
harnessed and it gives off carbon dioxide when burnt. However the fuels are treated as carbon neutral
because the carbon released on combustion is only that which was absorbed during crop growth. There
are currently 3 different types of biomass system: those designed to produce electricity only, those
designed to produce electricity and heat (combined heat and power (CHP) plants) – both of these
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primarily utilise gaseous or liquid bio fuels. The third type is that designed for heat production only –
biomass boilers – which primarily burn solid biomass (e.g. wood chip and pellets). From a planning
perspective each system is similar and produces the same amount of waste products.
It is important to understand that modern biomass boilers are not to be confused with the idea of log
stoves. They are modern sophisticated machines, totally automatic, reliable and with very high
efficiencies. Most good boilers have direct operating efficiencies of up to 90% when operating on good
quality fuel, which can be higher than similar commercial gas and oil fired plant of similar outputs. They
are used extensively throughout much of Europe, and in Austria, approx 50% of the country is heated
from wood fired systems, most of them being part of district heating systems. Solid fuel Biomass boilers
tend to have a longer life expectancy than comparable fossil fuelled boilers, and need little maintenance
other than ash removal. All Biomass plant require fuel storage areas adjoining them, where good road
access is permissible, allowing for fuel deliveries from tankers and/or tipper lorries. The size of the fuel
storage area depends on the type of fuel being used, space available and the permissible frequency of
fuel deliveries.
The use of a biomass boiler at this development would provide all the energy requirements for both
heating and hot water production; with the bulk of the associated CO2 emissions from traditional
sources being eliminated. However incorporating biomass technologies into the proposed development
is not considered feasible at this stage. The current design proposals do not incorporate sufficient plant
space to house a suitably sized biomass boiler. In addition the large fuel storage volumes and unique
delivery management procedures are further constraints affecting the feasibility of biomass systems at
this site. Further design development may realise space within the proposed building; alternately, a
location on the site for a freestanding boiler house may be found.
Due to the urban location of the development, the issue of particulate emissions and compliance with
the clean air act will need careful consideration. Under the Clean Air, Act local authorities may declare
the whole or part of their district to be a ‘smoke control zone’. It is an offence to emit smoke from a
chimney of a building, from a furnace or from any fixed boiler if located in a designated smoke control
area.
With the introduction of the ‘Renewable Heat Incentive’ tariff by the UK Government in October 2011
may result in the use of a biomass system being a sound financial investment with tariff payments being
assured for up to twenty years; allowing the relatively high cost of installation to be offset or ‘paid back’
within a relatively short period.
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6.2
Solar Thermal.
Solar Thermal Collectors are recognised as amongst the most cost effective renewable energy systems,
using the sun’s energy to heat water directly through solar collection panels. Collectors, in the form of
flat plates or airtight (evacuated) tubes can be mounted on south facing roofs or can be set onto a
freestanding tilted frame on a flat roof. However, flat plate collectors in the UK can be susceptible to
frost. Evacuated tube collectors on the other hand do not require protection against the frost and are
generally more efficient in collecting energy on colder days. They are therefore more suited to the UK
climate.
There is some scope for installing an evacuated tube system at St. Johns Church, although their use may
be restricted due to the erratic nature of the hot water requirements of the building. Solar thermal
systems are best suited to regular (Daily) hot water demands. Long periods with no hot water use can
result in the systems ‘stagnating’ (overheating). Installation is also dependant upon a number of factors
which can only be properly assessed at the detailed design stage. Factors include the appearance of the
collectors and their associated impact upon the adjacent Listed Buildings. In order to be effective, the
majority of collectors need to be inclined at an angle of 30-40 degrees, depending on latitude, and
orientated to face due south.
Given that the design of the buildings has still to be been finalised, it is not known to what extent this
can be achieved at the site. Current design proposals indicate relatively flat roof areas which would
require the collectors to be mounted on support frames, further impacting on the visual appearance of
the building. Due to the unpredictable nature of the hot water demand and the likely visual impact of a
solar thermal system on this site, its incorporation into the overall services strategy, although technically
feasible, is considered unlikely.
6.3
Solar Photovoltaic (P.V.)
Solar photovoltaic systems (PV) operate in a similar way to solar hot water systems in that they are
designed to convert energy from the sun into electricity. This energy is converted at source into the
voltages and A.C. Frequencies used in the UK, and becomes an alternative source of electrical energy
within the building.
PV Cells can be mounted to the exterior of buildings on south facing roofs or walls and can be mounted
at virtually any angle from vertical (on walls) to horizontal (on flat roofs). They can also be integrated
into the fabric of new buildings in place of roofing materials, cladding or glazing. These can have an
aesthetic advantage in giving a roof a more uniform appearance than with a surface mounted solar
collector.
Traditionally the high installation cost and relatively low energy yields from P.V. systems have deemed
them to be uneconomical, with ‘payback period being far in excess of the useful lifespan of the plant.
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However, with the introduction of the ‘Feed In Tariffs’ by the UK government in April 2010, the returns
on investment have improved dramatically and PV systems are now considered to be a sound financial
investment as well as a way of producing ‘clean’ electricity.
With the proposed building having relatively flat roofs the installation of roof integrated PV systems is
the most likely scenario and the appearance of a PV roof could complement the modern appearance of
the building. The likely yield from a PV system on the proposed building will be examined in later
sections of this report.
6.4
Wind Turbines
The principle of harnessing wind power is well established in the UK with access to over 40% of the total
European wind resource. Until recently developments have been concentrated within coastal regions;
however technological advances mean that wind power is viable in many urban locations.
Wind turbines are a means of capturing the power within a moving air mass (wind) and converting it into
electricity. Various designs are now available, ranging from small scale mounted turbines suitable for
individual dwellings through to large commercial turbines which can generate enough energy for major
development projects.
Most wind turbines are horizontal-axis, propeller type systems. A horizontal-axis wind turbine consists of
a rotor, a generator, a mainframe and sometimes, a tail. The rotor captures the kinetic energy of the
wind and converts it into rotary motion to drive the generator. The rotor usually consists of two or three
blades. A three-blade unit can be a little more efficient and will run smoother than a two-blade rotor,
but they also cost more. The blades are usually made from either wood or composite materials
(Fibreglass or carbon fibre) because these materials have the necessary combination of strength and
flexibility. Vertical-axis turbines can also be employed and although they are less susceptible to
turbulence and sudden changes in wind direction, their efficacy is still un-proven and consequently are
more expensive and less common.
A wind turbine must have a clear shot at the wind to perform efficiently. Turbulence, which reduces
performance and "works" the turbine harder than smooth air, is at its highest close to the ground and
diminishes with height. Also, wind speed increases with height above the ground. As a general rule of
thumb, a wind turbine should be installed on a tower such that it is at least 10 m above any obstacles
within 100m; small turbines are typically installed on shorter towers than larger turbines. A 1 kW turbine
is often, for example, installed on a 9 to15 m. tower, while a 10 kW turbine will usually need a tower of
25 to 36 m. It is not recommended to mount wind large turbines on smaller residential buildings
because of the inherent problems of turbulence, noise, and vibration.
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The Town Centre location of the proposed development means that it would prove difficult to harness
sufficient wind energy to meet the needs of the development. The high density of the surrounding
buildings, obstruct air patterns and reduces the energy of the wind and the efficiency of the turbine. The
size of the turbine required is also likely to detract unacceptably from the townscape and generate a
significant amount of noise, both of which prejudice local residential amenity.
For these reasons, other forms of renewable energy technologies are considered more appropriate for
the proposed development.
6.5
Micro Hydro-electric Systems
Micro hydro systems use water power as the source of generating electricity. The requirements are a
suitable supply of fast moving water with sufficient difference in elevation across the site to enable the
system to work effectively.
Due to there being no suitable water courses on the site, the use of this technology can be completely
discounted.
6.6
Heat Pumps
This is the generic term given to a range of machines, which convert virtually unlimited quantities of low
grade heat energy in the surrounding environment (Air, Ground and Water), into high grade energy
suitable for use in heating systems. Therefore “air to water” heat pumps take energy from the air, and
use that to heat water, whereas “ground to water” heat pumps take energy from pipes buried in the
ground, and heat water to a level suitable for heating buildings.
The machines work on the opposite principle to air conditioning units, in that instead of taking heat from
a space, and rejecting that to the atmosphere, they take energy from the atmosphere or ground, and
reject that into the space.
The machines use fluids which have a boiling point below 0°C, so that there is sufficient energy in the
atmosphere, even at low temperatures to boil the refrigerant, and create the heating process. Similarly
with pipes buried in the ground, where temperatures several metres down are at a constant
temperature of around 10 - 12°C throughout the year.
The efficiency of the machines is called the “Coefficient of Performance” (C.O.P.), and is the energy
output of the machine, divided by the electrical energy required to operate it. Typically, ground source
heat pumps have C.O.P.’s between 3.0 and 4.0, which mean for every kW of electrical motor power
used, 3 to 4kW of heat are produced. This means than running costs are 25% to 33% of a straight
forward electrical system at around 3.0 to 4.0p/kWh, which makes them slightly cheaper than oil or gas
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to operate. Air to Air heat pumps have variable C.O.P.’s because of the variations in ambient air
temperature and vary from as high as 4.0 to as little as 1.0.
6.6.1
Ground Source Heat pumps
A few meters below the surface, the ground maintains a constant year-round temperature of 11-12°C.
Although the ground temperature may not necessarily be higher than ambient air temperature during
much of the year, it is more stable compared to the wide temperature range of ambient air. This makes
system design more robust.
Ground Source heat pump ‘collectors’ consist of pipe work that can be buried horizontally in the form of
‘slinkies’ or vertically in ‘bore holes’, depending on the space available. When using vertical, bore-hole,
ground source systems, care needs to be taken when the system is used for heating or cooling only, to
avoid sub-cooling the ground. Test holes would need to be drilled to assess the thermal characteristics
of the ground and to confirm the number of boreholes required. Boreholes would normally be around
100m deep and 120mm diameter, and each borehole will typically have a “U” tube inserted. This is filled
with a water and glycol solution, and then the borehole is backfilled, and the pipes connected to a
common header.
The nature of the site at Bethel Evangelical Church does not allow for extensive ground works beyond
the extent of the proposed building due to the risk of damaging historical and potentially valuable
archaeology, therefore although potentially suitable for a building of this type the site constraints are
too prohibitive to allow this technology to be exploited.
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6.6.2
Air Source Heat pumps
Air-source heat pumps are similar in operation to ground-source heat pumps, except that heat is
extracted from the external air rather than the ground. The main advantage of air-source heat pumps
over ground-source heat pumps is their lower installation cost. A ground-source heat pump requires a
network of underground coils that is used to extract heat from the ground. By comparison, air-source
heat pumps extract the heat directly from the outside air and so avoid these potential problems.
A potential downside of using air as a heat source is the heat pump's coefficient of performance (C.O.P.).
During the heating season the outside air temperature is often less than the ground temperature (at a
depth at which heat is extracted by a ground-source heat pump). This lower temperature has the effect
of reducing the C.O.P. Some manufacturers of air-source heat pumps quote C.O.P.’s of four or more, but
this data should be treated with caution. However they can be useful when air conditioning is required,
when the same machine can be ‘reversed’ and used for cooling in the summer, and heating in the
winter.
For an air-to-water heat pump ‘Standard’ C.O.P.’s are expressed under conditions of 7°C outdoor air
temperature (source temperature). At external air temperatures lower than this, the C.O.P. will fall, as
will the heating output of the heat pump. Depending on the application this reduction may be
significant, such as during a cold winter morning when building pre-heat is needed.
A further factor influencing the C.O.P. of a heat pump is the output temperature (the temperature of the
supplied heated air or circulated water within the building). For an air-to-water heat pump ‘Standard
C.O.P.’s are expressed under conditions of return and flow temperature of 40°C and 45°C respectively.
The Table below gives typical annual C.O.P.’s for a range of output flow temperatures for correctly sized
heat pumps. The installation of under sized air source heat pumps can result in C.O.P.’s of less than 1
due to the consumption of electricity to defrost the outdoor units during periods of cold weather.
Table 3
Temperature
Output (°C)
35
45
55
Operating
C.O.P.
3.5
3.0
2.5
The use of air source heat pumps could be considered for this development but great care would need
to be taken in the sizing of the units and the design of the heating systems within the building. The
positioning of the outdoor units will have to be carefully considered to minimise the visual impact of
what could be potentially large and noisy items of plant. The use of air source heat pumps would best be
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considered in conjunction with summer time cooling however for the purposes of this report the
contribution to the heating load only shall be considered.
6.7
Combined Heat and Power (CHP) Systems
Strictly speaking, CHP is not renewable energy, but it is often included in this field by planners and
similar authorities because of its apparent efficient use of energy. CHP typically operates by producing
electricity by conventional methods such as gas turbines or diesel generators, and reclaiming much of
the waste heat contained in the exhaust gases. Because electricity generation is very inefficient, most of
the energy used to produce electricity is wasted through the exhaust gases, so this sounds a very
interesting proposition. With efficient CHP machines, approx 3kW to 4kW of heat are reclaimed for
every 1kW of electricity produced, unfortunately, in order to enjoy the benefits of this system, there
must be a demand for that heat at all times.
If the electrical requirement is fairly constant, which it is for most developments, and the machine is
sized to meet that load, there has to be a demand for 3 or 4 times that in heat to be used throughout
the year. This is rarely the situation, and typically for most buildings, for many months in the year, there
is very little heating requirement. The cost of generating electricity from a CHP system where no waste
heat is used is greater than buying electricity directly from the grid, and therefore this is not a viable
option. It is possible to size CHP systems on the minimum heating load to ensure that the system will
always operate efficiently, but as the electrical production will often be quite modest, it will require
supplementing with grid delivered electricity, which limits the overall cost benefits.
CHP has been discounted for this development due to the relatively low and in consistent heat loads.
CHP works best where there is a constant demand for the waste heat, and this can be found in Sports
centres or other buildings with large hot water loads, or where cooling is required, which can be
provided from absorption chillers which are driven from the waste heat. They can be effective as a part
load supply, but the extra capital cost needs to be weighed against the savings available.
Unfortunately, the cost of electricity in the UK is not sufficiently higher than the cost of the primary fuels
required to run the CHP machines to make them commercially beneficial in part load applications.
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7.0 Review of Renewable Energy Options.
Three technologies have been identified as potentially feasible for the Bethel Evangelical Church site,
these are:

Biomass heating

Air source heating

Solar photovoltaic (PV)
Whereas biomass and air source heating can be designed to meet 100% of the heating requirements of
the building; the solar technology can only be employed to a limited extent due to the limited roof
space. However it is still felt that PV would the most appropriate for this development due to its ease of
incorporation into the current design proposal. In addition PV systems have proven to be financially
viable through the introduction of the Feed In Tariff although recent tariff reviews have extended
payback periods and reduced income streams considerably.
There is a requirement to improve on building regulations carbon emissions (Building Emissions Rate BER) by providing 10% of the buildings expected energy requirements from renewable sources. The
estimated energy yield and CO2 savings for each technology can now be calculated and compared with
the 10% renewable energy requirement.
7.0.1
Biomass Heating
A well designed Biomass boiler system will be able to provide 100% of the total annual space heating
and hot water energy requirements for the development.
7.0.2
Air Source Heat Pump
A well used ‘rule of thumb’ is that an efficiently designed Air Source Heat pump will be able to provide
approximately 80% of the total annual space and hot water heating energy requirements at a C.O.P. of
2.5. The remaining 20% of energy requirements will usually be provided from various sources; either use
a small gas fired boiler to provide the shortfall in energy provision. Or run the heat pump at lower
efficiencies in order to produce higher temperatures along with the use of electric immersion heaters to
‘top up’ the hot water requirements. However for the purposes of this report it shall be assumed that
the shortfall will be provided by the originally NCM assumed HVAC System (Gas fired boiler).
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7.0.3
Solar Photovoltaic (PV)
The contribution to the energy demand from the building will be directly dictated by the space available
for the installation of the PV system, the orientation and angle of the roof to be used and the type of PV
modules being installed.
Approximate Total Flat Roof Area: 438sq.m. (excluding the curved roof over the main hall)
Approximate Maximum PV system size: 10kWp (Based on a flexible PV roof integrated system)
The potential annual energy yields from these systems were calculated using the ‘Photovoltaic
Geographic Information System’ published by the ‘European Commission – Joint Research Centre’ and
are detailed in Appendix C.
7.1
Energy Calculations
Full details of the calculations for the energy and CO2 figures shown in Table 4 are subject to detailed
design and verification.
Table 4
RENEWABLE
TECHNOLOGY
ENERGY PROVIDED/
DISPLACED BY
TECHNOLOGY
(kWh)
BIOMASS
HEAT PUMP
PHOTOVOLTAIC (PV)
7.2
49,329
23,959
8,456
% OF BUILDINGS
TOTAL ENERGY USE
DISPLACED BY
TECHNOLOGY
70
34
12
CO2 EMISSIONS
DISPLACED BY
TECHNOLOGY
(kg CO2)
8,966
-344
4,472
% OF BUILDINGS
TOTAL CO2 EMISSIONS
DISPLACED BY
TECHNOLOGY
44
-2
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Energy Summary
The figures summarised in Table 1 (Section 4.3) indicate that through energy efficiency measure alone,
energy consumption can be reduced by over 14% and CO2 emissions by almost 8%.
The figures given in Table 4 clearly show that it is feasible to reduce (or ‘displace’) in excess of 10% of on
site energy consumption through the use of renewable and low carbon energy technology
It is of note that the negative figures given for the air source heat pump in Table 4 indicate a net
increase in CO2 emissions. This is due to the technology being used to replace a gas fired heating system.
Although the overall energy consumption of the site is being reduced, some of the CO2 emissions from
the gas fired plant are being replaced by emissions from grid supplied electricity which has a far higher
emission rate than natural gas for a given energy content.
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8.0 Conclusion and Recommendations
For the Bethel Evangelical Church development, passive design measures have been identified to help to
reduce the energy consumption and associated CO2 emissions. After reducing energy consumption,
options for further reducing or offsetting energy use and associated CO2 emissions, through the use of
onsite renewable energy systems have been identified.
The scheme complies with the energy efficiency and renewable energy policies, as required by Coventry
City Council.
Although the incorporation of a biomass heating system would produce the largest energy yield from
renewable sources and create the greatest savings in CO2 emissions, the constraints of the proposed
building design and the limitations of the site as outlined in section 6.1, would make this option
impractical without major redesign of the development.
The installation of a roof integrated Photovoltaic system would be the most cost effective and least
disruptive way of incorporating renewable energy into the design of the proposed building and is
strongly recommended; allowing the requirement for 10% of energy from renewable sources to be met.
Recent developments in materials technology allow P.V. collectors to be incorporated into the flexible
waterproof membranes used to cover the roofs of modern buildings such as this. Producing renewable
electricity with virtually no visual or structural impact on the building
The advised option will be considered at the detailed design and construction stages and adequate
provisions made to ensure that these CO2 reduction targets are met. The figures in this report are based
on preliminary analysis only, and further detailed studies will be required before specifying any of the
potential systems.
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