European Commission
Intelligent Energy Programme
Training module for installation contractors
MANUAL FOR THE TRAINER
Energy+ Pumps Project
Authors: Tommaso Toppi,
Nicola Labanca,
eERG – Politecnico di Milano
Energy+ Pumps Project
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Energy+ Pumps Project
INDEX
INDEX ........................................................................................................................................................................3
Introduction.................................................................................................................................................................4
Aim of the module..............................................................................................................................................4
Structure of the module......................................................................................................................................4
Training material ................................................................................................................................................4
Environmental issues..................................................................................................................................................5
The Greenhouse effect .......................................................................................................................................5
Reduction of electricity consumption to prevent climate change ...................................................................7
Pump basics.................................................................................................................................................................8
The Energy+ Pumps Project ....................................................................................................................................10
Saving potential of energy efficient pumps in Europe and the Energy+ Pumps Project .....................................10
Pumps energy efficiency and energy labels............................................................................................................13
The Europump label and energy efficiency class determination.......................................................................13
The Europump label – examples of application .................................................................................................16
How pump energy efficiency may be increased .....................................................................................................19
Energy+ pump specifications (when can a pump be Energy+?) .......................................................................22
Main features of Energy+ pumps (mainly VSD) ...............................................................................................23
Variable Speed Drivers ....................................................................................................................................23
Permanent Magnet Motors ..............................................................................................................................24
Energy and economic savings yielded by Energy+ pumps ...................................................................................25
The saving calculation tool ......................................................................................................................................27
Description of the calculation spreadsheet .........................................................................................................27
ENERGY+ models against traditional models...............................................................................................27
ENERGY+ models against a specific model..................................................................................................31
LCA results ...........................................................................................................................................................37
Example 1 (“Energy+ models versus a generic traditional model” sheet selected).....................................37
Example 2 (“Energy+ models versus a generic traditional model” sheet selected).....................................37
Example 3 (“Energy+ models versus a specific model” sheet selected) ......................................................37
Energy savings due to circuit design and pump sizing ..........................................................................................39
Pump sizing...........................................................................................................................................................39
Circuit loss reduction ...........................................................................................................................................39
Distributed pressure losses ..............................................................................................................................39
Local pressure losses........................................................................................................................................41
References .................................................................................................................................................................43
The sole responsibility for the content of this document lies with the authors. It does not represent the opinion of the
European Communities. The European Commission is not responsible for any use that may be made of the information
contained therein.
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Energy+ Pumps Project
Introduction
Aim of the module
The training material prepared is directed to installers of circulating pumps for heating systems and is focused
on pumps with a flow rate < 1,85m3/h as used in apartments, single family houses and small flats.
Installer may have lack of knowledge about energy efficiency benefits and how they can be achieved by
installing energy efficient pumps. Thanks to the present training module, pump installers may:
•
•
•
Get information about new and efficient products
Have the opportunity to offer to their customers a better service and a more valuable product (i.e. with
lower whole life costs) and, at the same time, install relatively more expensive solutions.
Get useful instruments to present energy efficient pumps to their customers.
Structure of the module
The following topics will be addressed within the training module:
•
•
•
•
•
•
Relevance of the energy efficiency issue for the society and the end-users;
Energy labels for pumps and how to use them to compare different pump models performances;
Energy saving potential for pumps in Europe;
Energy and economic savings yielded by energy efficient pumps;
Presentation of a calculation tool to estimate the savings generated by energy efficient pump models;
Basics on pump sizing and hydraulic circuit design.
Training material
The material prepared consists of the followings:
•
•
•
The present manual that the trainer may want to use to improve his/her knowledge about the topics to
be addressed within the training module..
A Power point presentation (to be used during the module) referring to the topics described in detail in
this guide.
A calculation tool that installers may use to explain the advantages of energy efficient pumps to endusers.
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Energy+ Pumps Project
Environmental issues
The Greenhouse effect1
The greenhouse effect is generated by the sun infrared radiation that warms the Earth’s surface. This name
comes from an analogy with the warming effect typically observed within greenhouses. It was first discovered
by Joseph Fourier in 1824 and investigated via quantitative estimates by Svante Arrhenius in 1896.
The Earth's average surface temperature of 15 °C is about 33 °C warmer than it would be without the
greenhouse effect. Most of the energy coming to the Earth from the Sun is made of visible wavelength
radiation and infrared wavelengths that are near the visible spectrum (also known as "near infrared" radiation).
The Earth reflects about 30% of the incoming solar radiation. The remaining 70% is absorbed and warms the
ground, the atmosphere and the oceans. The Earth is in a steady state and its average temperature does not
hence vary sensibly as the absorbed solar radiation is very closely balanced by the energy radiated back to
space in the infrared wavelengths. The infrared photons emitted by the surface are mostly absorbed in the
atmosphere by greenhouse gases and clouds and do not escape directly to space. The greenhouse effect is
nothing but such trapping of the sun infrared radiation by greenhouse gases in the atmosphere (e.g. water
vapor, carbon dioxide, nitrous oxide, methane, etc.).
Let’s now try to explain this phenomenon with simpler words. Have you ever seen a greenhouse? Most
greenhouses look like a small glass house. Greenhouses are used to grow plants, especially in the winter.
Greenhouses work by trapping heat from the sun. The glass panels of the greenhouse let in light but keep heat
from escaping. This causes the greenhouse to heat up, much like the inside of a car parked in sunlight, and
keeps the plants warm enough to live in the winter.
The Earth’s atmosphere is all around us. It is the air that we breathe. Greenhouse gases in the atmosphere
behave much like the glass panes in a greenhouse. Sunlight enters the Earth's atmosphere, passing through the
blanket of greenhouse gases. As it reaches the Earth's surface, land, water, and biosphere absorb the sunlight’s
energy. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into
space, but much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat
up.
1
Most of the information reported in this section are taken from http://www.epa.gov/climatechange/ and
http://science.house.gov/resources/climate_change_faq's.htm
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Energy+ Pumps Project
Figure 1 – the Greenhouse effect
The greenhouse effect is a very important physical phenomenon. Without the greenhouse effect, the Earth
would not be warm enough for humans to live. But if the greenhouse effect becomes too strong, it could make
the Earth uncomfortably warmer. Even a little extra warming may cause problems for humans, plants, and
animals.
Some greenhouse gases such as carbon dioxide occur naturally and are emitted to the atmosphere through
natural processes and human activities. Other greenhouse gases are created and emitted solely through human
activities.
The main greenhouse gases that enter the atmosphere because of human activities are:
•
•
•
•
Carbon Dioxide (CO2): Carbon dioxide enters the atmosphere through the burning of fossil fuels
(oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of other chemical
reactions (e.g., manufacture of cement). Carbon dioxide is also removed from the atmosphere (or
“sequestered”) when it is absorbed by plants as part of the biological carbon cycle.
Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil.
Methane emissions also result from livestock and other agricultural practices and by the decay of
organic waste in municipal solid waste landfills.
Nitrous Oxide (N2 O): Nitrous oxide is emitted during agricultural and industrial activities, as well as
during combustion of fossil fuels and solid waste.
Fluorinated Gases: Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic,
powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases
are sometimes used as substitutes for ozone-depleting substances (i.e., CFCs, HCFCs, and halons).
These gases are typically emitted in smaller quantities, but as they are powerful greenhouse gases,
they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).
During the past century humans have substantially added to the amount of greenhouse gases in the atmosphere
by burning fossil fuels such as coal, natural gas, oil and gasoline to power our cars, factories, utilities and
appliances. The added gases — primarily carbon dioxide and methane — are enhancing the natural
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Energy+ Pumps Project
greenhouse effect, and likely contributing to an increase in global average temperature and related climate
changes.
Carbon dioxide (CO2) is emitted in a number of ways. It is emitted naturally through the carbon cycle and
through human activities like the burning of fossil fuels. Within the carbon cycle billions of tons of
atmospheric CO2 are removed from the atmosphere by oceans and growing plants, also known as ‘sinks,’ and
are emitted back into the atmosphere annually through natural processes also known as ‘sources.’ When in
balance, the total carbon dioxide emissions and removals from the entire carbon cycle are roughly equal.
Since the Industrial Revolution in the 1700’s, human activities, such as the burning of oil, coal and gas, and
deforestation, have increased CO2 concentrations in the atmosphere. In 2005, global atmospheric
concentrations of CO2 were 35% higher than they were before the Industrial Revolution.
The burning of fossil fuels and biomass (i.e. living matter such as vegetation) has also resulted in emissions of
aerosols that absorb and emit heat, and reflect the light.
The addition of greenhouse gases and aerosols has changed the composition of the atmosphere. The changes
in the atmosphere have likely influenced temperature, precipitation, storms and sea level (IPCC, 2007).
However, these features of the climate also vary naturally, so determining which fraction of the climate
changes are due to natural variability versus human activities is challenging.
Reduction of electricity consumption to prevent climate change
Electricity production is an important source of CO2 emissions. In fact, a great share of the world electricity
production (65%) is based on power plants where fossil fuels are burned, as showed in figure 2.
Figure 2 – world production of electricity by fuel
Coal
39%
Others
2%
Nuclear
17%
Natural gas
19%
Hydro
16%
Oil
7%
Source: OECD/IEA World Energy Outlook 2004
As shown in the graph, about 65% of the world electricity production comes from fossil fuel. Therefore, there
is evidence that an important way to reduce CO2 emissions is the reduction of electricity demand.
In Europe, in the last decade several campaigns have been established in order to meet the target of a
progressive reduction of energy consumption. Among these campaigns an important role can be played by the
Energy+ Pumps project aiming at leading a market transformation towards new and very energy-efficient
pump technologies for circulators in heating systems (see below).
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Energy+ Pumps Project
Pump basics2
The pumps used for domestic heating systems are usually centrifugal pumps. A centrifugal pump works on the
principle of conversion of the kinetic energy of a flowing fluid (velocity pressure) into static pressure. This
action is described by the Bernoulli's principle. The rotation of the pump impeller accelerates the fluid as it
passes from the impeller eye (centre) and outward through the impeller vanes to the periphery, as shown in
figure 3. As the fluid exits the impeller, a proportion of the fluid momentum is then converted to (static)
pressure. Typically the volute shape of the pump casing, or the diffuser vanes assist in the energy conversion.
The energy conversion results in an increased pressure on the downstream side of the pump, causing flow.
Figure 3 – scheme of a centrifugal pump
Pump curves
Pump manufacturers provide performance characteristics called pump characteristic curves. They are a
graphical representation of the relationship between the variables involved in pumping:
•
•
•
Head (H)
Flow (Q)
Power
In Figure 4 a typical characteristic curve of the head versus flow for a centrifugal pump is shown.
2
Most of the information reported in this section is taken from http://www.pumpsolutions1corp.com/index.php/Centrifugal_Pumps
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Energy+ Pumps Project
Figure 4 – pump characteristic curve: head versus flow
Sometimes the manufacturers provide also curves where the power consumption (P1) and the efficiency (Eta)
of the pump are represented. Such curves typically look like the one shown in Figure 5.
Figure 5 – pump characteristic curve with power consumption and efficiency versus flow
Every centrifugal pump may be characterized by a specific characteristic curve, depending on its size,
rotational speed and impeller as well as overall pump design.
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Energy+ Pumps Project
The Energy+ Pumps Project
The Energy+Pumps Project is co-financed by the European Commission through the Energy Intelligent
Europe (EIE) programme with the purpose to lead a market transformation towards new and very energyefficient pump technologies for small and medium size circulators in domestic heating systems.
The project promotes pumps and boilers whose technical specifications satisfy rather stringent energy
performance constraints. The main goal is that of aggregating demand for such boilers and pumps in order to
stimulate their supply by manufacturers.
Project target groups are hence boiler manufacturers as well as pump manufacturers. The lists of Energy+
boilers with the efficient pumps integrated and of the Energy+ stand-alone pumps are regularly published on
the Energy+ Pumps Project website at www.energypluspumps.eu. On this website it is also possible to find
information about the project participants and the project events organized, including the Energy+ awards
competition dedicated to the most energy efficient pumps and condensing boilers and the best Energy+
promotion campaign.
The project is expected to contribute to bringing small-scale Energy+ circulators to the market for single or
double homes and flats from all major manufacturers, and to reducing the price premium over conventional
electronically controlled circulators for that market to less than 50%.
The circulator is one of the largest electricity consumers in the household. In the Central and Northern
European climate zones, the electricity consumption of a household heating system circulator may be as high
as 500 to 600 kWh/year, which is comparable to the average electricity consumption of a fridge-freezer, or the
lighting system.
The total electricity consumption of circulators in European household central heating systems is estimated to
be of 50 TWh per year, which makes it comparable to the total electricity consumption of household washing
machines in the EU.
Compared with the total electricity consumption in Europe, which amounts to about 3000 TWh per year,
household circulation pumps in central heating systems represents a share of about 2%.
These data show how important an energy saving policy focused on circulators may be.
Presently Energy+ Pumps have higher prices compared to traditional pumps mostly because Energy+ pump
production levels are by far lower than those of less efficient pumps.
This is also due to the fact that circuit pumps are one of the least known electricity consumers. Small
circulators in particular are typically seen as low cost products. The end-users are usually not aware about the
energy saving potential of energy efficient pumps as well as they typically ignore that new higher efficiency
circulation pumps may have payback times of the order of one to three years, depending on usage.
Saving potential of energy efficient pumps in Europe and the
Energy+ Pumps Project
A conservative estimate is that the buyers aggregated by the Energy+ project might purchase 10 000 Energy+
pumps during the project duration (i.e. between January 2006 and December 2008); this would save 2,5
million kWh per year. If Energy+ pump market share will achieve 5 % at the end of the project, energy
savings for 100 GWh/year will be yielded by Energy+ products sold in 2008.
In a long term scenario, if the Energy+ pumps became the new technology standard for circulators, they
would save about 1 % of current EU 25 electricity consumption, i.e. 250 kWh/year per unit. Considering that
about 100 million units are installed in the EU, this means that 30 TWh/year or more could be saved. The
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Energy+ Pumps Project
project will provide a major contribution towards achieving this objective, and particularly towards
accelerating the underlying market transformation. It will thus contribute to decrease energy supply
dependence and to reduce CO2 emissions. Electricity savings for 30 TWh per year would indeed reduce CO2
emissions by over 10 million tons per year.
In the EU Save II Project Promotion of Energy Efficiency in Circulation Pumps, especially in Domestic
Heating Systems3 the effects of introducing higher efficiency circulation pumps in the EU15, both for new and
replacement installations, have been modelled in more details. The project has elaborated different reduction
scenarios:
•
•
ETP: Economically justified (to the consumer) and Technically feasible (by manufacturer) Potential
scenario; in this case, the most efficient pumps are also the products that would have the minimum
life cycle cost to the consumer (MLCC);
Policy scenarios: realistic scenarios which take into account that efficient pumps will penetrate in the
market only if specific policies are implemented; depending on the kind of policies put in places, the
Scenario 1 and the Scenario 2 are considered.
All of these scenarios assume an energy efficiency installation improvement. None of such scenarios consider
the effects of installation of heating systems which do not require a circulation pump and the possible effects
due to future heating demand reduction.
The ETP scenario assumes that all pumps (both stand alone and integrated into the boilers) newly installed or
replaced are at the ETP installation level. Such ETP level is assumed to happen at 100% by 2005. This is a
hypothetical scenario used to describe the highest economic savings which can be achieved by improving the
efficiency of the pumps alone, without including the effect of lower use of pumps (through lower temperature
requirements, or better insulation, or even change of heating system type).
If all pumps on the market are at this economically efficient level by 2005, then consumption will decline with
respect to the reference case (RC), as shown in the graph in Figure 6.
Since pump mean lifetime is about 13 years the full effect of this potential increase in efficiency would not be
seen until 2020 circa.
These theoretical energy savings assume purchase cost, production availability, and installer knowledge were
not restraining issues. In practice the ETP scenario will not be realised without intervention by policy makers.
The main reasons for this are lack of information, insufficient market demand and absence of regulation
incentivising these higher efficiency products.
To realise the ETP scenario, or bring about higher efficiency pumps, information on energy efficient pumps
would need to be more transparent. A mandatory A-G labelling scheme would be likely to enable this.
Subsequent to a labelling scheme a minimum efficiency standard with a sufficient lead-time should be
introduced to eliminate the less efficient pumps.
Moreover, besides a labelling system some form of financial incentives to install higher efficiency pumps
would be needed.
Finally, additional training for installers on energy efficiency should be introduced – both for initial training
and as part of continued professional development.
Circulation pump electricity consumption development under the Scenario 1 is shown in the graph below,
describes the maximum likely effect of the above policy measures, assuming that the ETP level is reached by
2011 only for standalone circulation pumps. If similar parallel measures are also taken for boilers, and the
ETP level is reached by 2011 also for boilers, the maximum likely effect on energy consumption is that shown
as Scenario 2.
3
see http://gasunie.eldoc.ub.rug.nl/FILES/root/2001/2906182/2906182.pdf for more information
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Energy+ Pumps Project
Figure 6 – Electricity consumption by EU circulation pumps under Reference Case (RC), ETP, Scenario 1 and Scenario 2
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Energy+ Pumps Project
Pumps energy efficiency and energy labels
The Europump label and energy efficiency class determination
An A-G Energy labeling scheme for circulators is presently implemented in Europe and is based on a
classification scheme developed by Europump. Such scheme addresses all circulators for heating systems,
which fulfill all of the following requirements:
•
•
•
•
•
Stand alone (not an integral part of a boiler)
Motor integrated into the pump
Wet runner (glandless)
Centrifugal pumping
PL < 2 500 W
Stand alone circulators with pump and motor integrated are circulators which are sold as a separate products
and not as an integral part of, for example, a boiler. Wet runner means that the rotor is running in the pumped
fluid. Only circulators with a power input PL < 2500 W (for every head) and based on centrifugal pumping
principle are addressed.
It’s important to notice that the Europump label scheme (although imitating the EC energy label scheme
design) is not an official European energy label and that it has been introduced by manufacturers on a
voluntary basis. Therefore, label exhibition is not mandatory (e.g. as currently happening with refrigerators),
and the EEI calculation method has been decided by the manufacturers.
Circulators are labeled based on a so called Energy Efficiency Index (EEI).
The EEI is calculated as
EEI =
PL ,avg
Pref
[!]
Where:
•
•
PL,avg: is the average compensated power input, i.e. a weighted average power input based on a yearly
load profile and compensated for control error;
Pref: reference power input of a standard circulator at a specific size.
PL,avg is calculated as the weighted average of power consumption at different flow levels.
In particular, the power consumption is measured at a flow rate equal to 25%, 50%, 75% and 100% of the
nominal flow and weighted over the running hours at each flow rate.
The EEI calculation method will be further explained by examples in the next chapter. Hereunder further
information about how Pref and the pump maximum power input are calculated are provided.
The circulator power consumption depends both on the hydraulic power and the size of the circulator. The
reference power input for a circulator of a given size is calculated based on an empirically derived relation
between hydraulic power and maximum power input. Such relation has been calculated based on data
available for the majority of circulators on the market in a given year.
The maximum hydraulic power is the point where the factor Q*H (i.e. the flow rate multiplied by the pump
head) is maximum. At this operating point the maximum power input is measured according to the norm
EN 1151.
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Energy+ Pumps Project
In Figure 7 it is shown how the points of maximum hydraulic power and maximum power input are
individuated on the pump curves.
Figure 7 – points of maximum hydraulic power and maximum power input
In figure 8 the relation between maximum hydraulic power and maximum power input for the majority of
circulators on the market in 2002 is shown.
Figure 8 – power input reference versus hydraulic power
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Energy+ Pumps Project
Once the pump maximum hydraulic power has been estimated, Pref may be calculated analytically based on
best fit curve of the market data represented in Figure 8.
The formula below represents a linear approximation of the best fit curve. .
In such formula the maximum hydraulic power is defined as:
Where:
•
•
•
Q : The flow in m3/h
H : The pressure in m
2.73 is the conversion factor between the different unit of measures used to express the power.
However the linear relation gives unrealistic reference power input for small pumps with a hydraulic power
less than 20 [W].
Therefore the reference power calculation is mostly performed via the following better analytical
approximation of the best fit curve:
This function is calibrated so that the reference power input of a pump with a hydraulic power of 1 W is 20 W,
which is a more realistic value. The effect of this change is negligible for hydraulic powers above 20 W.
The EEI calculated as above described is used to define A-G circulator energy efficiency classes and
individuate the energy efficiency class of a specific pump model. Energy efficiency classes reported on the
Europump label are defined on the basis of the energy efficiency index as indicated in the Table 1 below.
Table 1 - Calibration of EEI to A-G energy label
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Energy+ Pumps Project
This calibration implies that average circulators on the market in 2002 belong to the “D” or “E” energy
efficiency class (EEI=1.00). “A” class circulator average power input is at least 60% lower compared to the
average power input of EEI=1 circulators with the same maximum hydraulic power..
Although the energy label is calibrated over the average circulator available on the market in 2002 a
considerable amount of savings can be achieved by replacing all existing circulators with “A” labeled ones
still today.
Figure 9 – Europump label
As shown in the above figure the label reports only information on pump energy efficiency class which is
related to its average power consumption. Pump yearly energy consumption depends on several factors that
are, among others, specific for the country, the building and the circuit in which the pump is installed. The
influence of such factors on the pump annual energy consumption is so high that any indication on the label
about pump average annual consumption in given standard conditions would be of no use.
The Europump label – examples of application
In the following example the energy performances of different circulators installed in a given heating system
are compared based on the energy efficiency classes reported on the energy label. Energy consumption and
savings are calculated assuming that pumps are properly sized and set.
Obviously energy consumption and savings vary a lot among installations and depends on several factors (e.g.
circulator age, running hours, building envelope, etc.). Therefore the estimates below should be considered as
just indicative. However actual energy consumption and savings would typically be higher than the estimated
ones as the pumps usually installed are typically oversized or not properly set.
The typical heating system considered for the calculations has the following features:
•
•
•
•
•
heat load: 15 kW
flow temperature: 75 °C
return temperature: 60 °C
pump flow (at the point of maximum hydraulic power): 860 l/h
pump head (at the point of maximum hydraulic power): 2 m
Calculations are based on a heating season of 285 days, which is a typical heating season in central Europe,
assuming that the heating system works for 24 hours per day.
Four different circulator options are considered:
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Energy+ Pumps Project
1. A “C” class constant speed circulator set on speed 2 (mid setting), which is 1-10 years old.
2. A new “B” class constant speed circulator set on speed 2 (mid setting).
3. A high efficiency “A” class circulator operating at constant speed and set at speed 2 (mid setting).
Notice that also circulators with variable speed drives may function at constant speed when e.g.
uncertainty about boiler minimum flow rate exists.
4. The last option is an “A” class circulator operating at variable speed.
In Table 3 the annual energy consumption of the different circulator options is estimated for “average”
circulator models representing each option. The load profile considered for the estimation (see Table 2
reported below) is the same used to calculate the EEI whereby the energy efficiency class reported on the
Europump label is established. Notice that such a profile implies that circulators operate at 100 % of the flow
for only 6 % of the time and are below 50 % for nearly 80 % of the time. These numbers result from a series
of assumptions made about the variation of the outdoor temperature and the characteristics of the heating
system.
Table 2 – standard load profile used in the Europump label
Flow (as % of
the maximum
flow)
100%
75%
50%
25%
Time in %
(Europump)
6
15
35
44
In case of the “C” class pump in the example, the energy consumption results the following:
E (yearly ) = E (@100% ) + E (@ 75% ) + E (@ 50% ) + E (@ 25% ) = 287
kWh
year
Where:
days
hours
kWh
! 24
= 18
day
year
day
year
days
hours
kWh
E (@ 75% ) = P(@ 75% ) ! t% ! days ! hours
= 44 W ! 15% ! 285
! 24
= 45
day
year
day
year
days
hours
kWh
E (@ 50% ) = P(@ 50% ) ! t% ! days ! hours
= 42 W ! 35% ! 285
! 24
= 101
day
year
day
year
days
hours
kWh
E (@ 25% ) = P(@ 25% ) ! t% ! days ! hours
= 41 W ! 44% ! 285
! 24
= 123
day
year
day
year
E (@100% ) = P(@100% ) ! t% ! days ! hours
= 44 W ! 6% ! 285
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Energy+ Pumps Project
In the table 3 below calculation outcomes for each average model representing each of the four options
mentioned are summarized.
Table 3 - Yearly energy consumption of different circulator options in a specific system
Load profile
Flow [%] Time [%]
100
6%
75
15%
50
35%
25
44%
Old fixed speed
circulator
labelled: C
P1 [W] E [kWh]
44
18
44
45
42
101
41
123
287
New fixed speed
circulator
labelled: B
P1 [W] E [kWh]
34
14
33
34
32
77
31
93
218
Fixed speed
circulator
labelled: A
P1 [W] E [kWh]
25
10
25
26
25
60
25
75
171
Variable speed
circulator
labelled: A
P1 [W] E [kWh]
19
8
15
15
11
26
9
27
77
The table indicates that a high efficiency circulator only draws 9 W at 25% of the load, whereas the
corresponding fixed speed circulator draws 41 W. Most circulators installed today draw between 60 –100 W
at 25 % of the load.
The bottom line of the table shows the yearly energy consumption in bold letters. A high efficiency circulator
in variable speed mode consumes only 77 kWh per year against 287 kWh per year consumed by a class C
circulator, which is a saving of 73 %.
These results are also summarized in the Figure 10 below.
Figure 10 – comparison between the annual energy consumption for the circulators considered
350
300
287
[kWh/year]
250
218
200
171
150
100
77
50
0
Old fixed speed
circulator
New fixed speed
circulator
High efficiency
fixed speed
circulator
High efficiency
variable speed
circulator
The results obtained indicate that the highly efficient variable speed circulators have a yearly energy
consumption which is about 26% of the consumption of the old constant speed circulator. Moreover, it can be
noticed that the variable speed circulator consumes less than a half of the energy used by the highly efficient
constant speed circulator. This confirms that the energy savings which can be obtained with a variable speed
drive pump are really high.
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Energy+ Pumps Project
How pump energy efficiency may be increased4
Pump energy efficiency may decrease for several reasons. Among these, one of the most important is the
wrong sizing of the pump itself.
Pump efficiency can decrease significantly when the pump is operating away from the designed Best
Efficiency Point (BEP). For example, over-specifying the duty when choosing a pump to install will mean
much increased energy costs.
However it should be admitted that pumps are not made to standard duties, which makes comparing
efficiencies less simple than with other products (e.g. motors).
For example a manufacturer of pumps with a high BEP may lose out to another manufacturer of a less
efficient BEP pump, depending on where the actual duty point requested lies within the performance curves of
the pumps.
In order to cover a much wider range of duties a same pump will usually be offered with different impellers or
with different speed motors.
Besides the wrong sizing, another important aspect that must be considered is that pump performances and
efficiency deteriorates over time. Pumps incur in corrosion, abrasion, erosion and ageing.
Deterioration over time depends on the material chosen for the pump itself, but also on the operating mode
and whether the pump is operating in the right range (determined by the minimum allowable flow rate,
maximum allowable flow rate and temperature range) or not. If pumps are operating outside the point of best
efficiency not only the efficiency decreases, but shafts and bearings are subject to higher forces and the
chance of a breakdown becomes extremely high.
Pump operation in partial load condition (which is, as seen in the previous chapter, really frequent), is
typically obtained by throttling the flow through a valve. But deliberately restricting the system flow is by far
worst than matching the pump and the actual system requirements.
In fact, a valve causes a pressure loss in the circuit, with additional ware, and reduces system efficiency (see
Figure 11).
4
Most of the information reported in this section were taken from Efficiency Characteristics of Centrifugal Pumps, guide prepared by
the EU SAVE Pump Study Group
19
Energy+ Pumps Project
Figure 11 – effect on head, power and efficiency due to pump throttling
As already mentioned pump manufacturers often offer the same pump with different motor options to allow
the same pump to be used over a much wider range of duties. For instance, changing from the most common
4-pole motor to a faster 2-pole motor will enable the same pump to deliver twice as much peak flow and 4
times head (the effect of running a pump with 4 or 2 pole motors is the same of running at 50% and 100%
speeds as shown in Figure 12).
Variable Speed Drives allow a pump to operate efficiently over a wide range of speeds and hence duties (see
Figure 12) without changing its motor; this means that pumps equipped with VSD are able to maintain a high
efficiency even in partial load mode. This kind of pumps is therefore particularly useful in systems where
there is a wide variation in demanded flow.
20
Energy+ Pumps Project
Figure 12 – Effect of speed reduction on pump performances
In the Figure 13 below the points where the pump works when the flow is throttled by a valve are marked in
red are. If a variable speed drive is used the pump works according with the points marked in green: power
consumption is lower and the efficiency is higher.
21
Energy+ Pumps Project
Figure 13 – Effect of speed reduction on pump performances
Energy+ pump specifications (when can a pump be Energy+?)
As explained in the previous chapters, the overall objective of the Energy+ Pumps project is a market
transformation towards new very energy-efficient pump technologies – i.e. the Energy+ pumps – for
circulators in heating systems. A new technology of pumps with electronically commutated (EC) motor
pumps, e.g. with permanent magnet motors, is available now and represents one possible way to achieve a
reduction in circulator annual electricity use by 60 % or more.
Market barriers to a wider diffusion of these efficient pumps do exist and include a high initial price due to
low production numbers, low customer interest leading to the fact that not the final customer but installation
contractors or even boiler manufacturers usually choose the pump and vendors sell them on the base of
product price only.
Only one manufacturer (Biral) had until recently introduced the new pump technology in the market for single
or double family homes and flats. Such pump technology uses only 5 to 30 Watts instead of the 40 to 120
Watts that traditional circulators usually need. Other big manufacturers have developed the technology ready
for market entry but were so far afraid to launch their products in the power range below 300 W, since they
were not sure to be able to sell them. This is a notable difference to the market for medium-sized circulators
(200 to 400 Watts of input power, for office and other larger buildings), for which the major manufacturers
(Grundfos, Wilo, Biral; KSB may follow) all have a range of EC motor pumps on the market. The reason is
that this is a market of institutional buyers that specify the pumps themselves and are used to economic
calculations, hence easier to convince than the single homeowner.
The Energy+ Pumps project therefore mainly targets the market for the small-scale circulators.
Boilers that have the new EC motor pumps built in are fully integrated into the project, since in this case, the
boiler manufacturer chooses the pump and there is no pump choice for the installation contractor or the buyer
of the boiler.
Energy+ specifications that energy+ products have to comply with have been defined by the project
consortium based also on a market survey.
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Energy+ Pumps Project
In case of Energy+ circulators an upper limit of 300W on the maximum power input has been established.
Such limit allowed addressing small sized circulators for apartments, single family houses and small flats but
also medium-sized circulators for multi-family houses and smaller non-residential buildings.
In order to define the energy efficiency of stand-alone circulators, the project applies the load profile and
classification of the Europump Labelling Scheme. The minimum energy efficiency required for an Energy+
pump is that established for Europump Label Class A products.
Heating units (gas boilers, oil boilers, premanufactured district heating substations, heat pumps) with a high
thermal energy efficiency are also included in the project, so the specifications for Energy+ boilers have been
defined too.
The minimum energy efficiency required for Energy+ boilers relates both to the boiler thermal energy
efficiency and the circulator energy efficiency.
In order to get the Energy+ label, gas and oil boilers have to be condensing boilers. Moreover, the maximum
allowed internal hydraulic resistance of a condensing boiler at nominal flow rate must be limited to 50 mbar to
avoid a forced circulation inside the boiler.
Regarding the circulator energy efficiency, the manufacturer of the heating unit has to declare that the unit has
a circulator built in or packaged that would qualify for Europump Label Class A if run and controlled like a
stand-alone circulator.
Main features of Energy+ pumps (mainly VSD)
There are several pump features which may be improved in order to achieve high performances. The most
important and generally used in the Energy+ pumps are:
•
•
•
Variable Speed Driver (VSD)
Permanent magnet motor
Improved rotor in order to decrease fluid dynamic losses
Variable Speed Drivers5
Variable speed drives allow loads driven by AC induction motors (such as fans and pumps) to operate in a
wide range of speeds compared to the motor fixed speed 6. VSDs are also called variable-frequency drives,
adjustable-speed drives, variable-frequency inverters, or frequency converters.
VSD installations can increase energy efficiency (in some cases energy savings can exceed 50%), improve
power factor and process precision, and provide other performance benefits such as soft starting and overspeed capability. They also can eliminate the need for expensive and energy-wasting throttling mechanisms
such as control valves and outlet dampers.
VSDs can provide significant savings in applications such as variable air volume air conditioning systems,
chilled water pumping, exhaust air systems (such as dust extraction, paint shop exhaust and fume cupboards),
refrigeration systems, some modern compressors (including air and refrigeration compressors)
Full load operation
VSDs provide considerable energy savings by optimizing the system, not by improving the actual efficiency
of the motor in isolation (as an energy efficient motor retrofit would). In fact, a VSD system is about 4% to
5
Most of the information reported in this section were taken from
http://www.synergy.net.au/Business_Segment/Energy_Management/Variable_Speed_Drives.html
23
Energy+ Pumps Project
6% less efficient at full load than an induction motor alone, due to the losses in the VSD itself. However, as
the power consumption at partial load is far lower than in the systems without a VSD, it doesn’t take much
operation at reduced load to save more energy than is lost at full load. Average loading as high as 90% can
justify a VSD retrofit for high-duty applications.
Low speed operation
Most induction motors can operate with modern VSDs through moderate speed ranges (around 30% to 100%
speed). Sustained operation at low speeds and, in particular, high load at low speeds may require a special or
larger drive and special measures to cool the motor.
AC induction motors operate hotter with a VSD because of harmonics, impurities in the electric power they
provide to the motor and also the slower rotating speed of the motor's integral cooling fans. This is usually not
a problem if speeds are continuously above 40% or where there are brief periods of slow-speed operation.
However, if the motor is not specifically designed for operating with a VSD, prolonged operation at or below
about 30% speed, especially when driving significant loads, can cause rapid and potentially damaging heat in
some motors.
Harmonics and power factor
Although they can improve displacement power factor (DPF), modern VSDs also create harmonics, which
reduce real power factor. For instance, while a VSD can improve DPF to close to 1.0, the harmonics generated
by the VSD can cause the real power factor to decline to between 0.75 and 0.80. These harmonic currents
(most often the fifth and seventh harmonics) tend to exacerbate resistance losses and can even negate the
benefits of improved DPF.
To minimize this problem, more and more VSD manufacturers are packaging harmonics-mitigating
equipment (such as line reactors or isolation transformers) with drives. This lets users enjoy the full benefits
of power factor improvement. What’s more, this added equipment can significantly reduce the impact of
VSD-generated harmonics on other electronic equipment.
VSDs located too far from motor
Pulse-width modulated drives can cause significant damage to motors if the length of cable between the VSD
and the motor exceeds 15 to 30 meters. (The number seems to differ by manufacturer.) Using pulse-width
modulated VSDs on older motors with long cable runs may shorten the life of the motor.
These are the general features of a variable speed driver device when connected to an existing motor. In the
case of Energy+ pumps the VSD is specifically designed for the motor and it’s integrated into the pump
vessel. This technical solution allows avoiding some of the problems we have just discussed about the use of a
VSD and makes the coupling of the pump to the rest of circuit absolutely identical to that of a traditional
pump. Indeed no additional electric connections and no additional elements compared with a traditional pump
are required when installing Energy+ pumps with an integrated VSD.
Permanent Magnet Motors
A second important technical solution often adopted by Energy+ pumps is represented by permanent magnet
motors. A permanent magnet motor has rotor structure that includes magnetically permeable backing material
attached to magnets for enhancing flux density distribution. A plurality of permanent magnets are
circumferentially distributed about an axis of rotation and adjacent magnets successively alternating in
magnetic polarity. Permanent magnets allow, among others, avoiding the use of the brushes typically used to
create rubbing electric contacts so reducing the energy losses due to contact friction.
24
Energy+ Pumps Project
Energy and economic savings yielded by Energy+ pumps
Choosing an Energy+ pump instead of a traditional pump may give both energy and economic savings.
The amount of the annual energy savings mainly depends on the number of yearly running hours: the more the
running hours, the more the savings that will be achieved by replacing a traditional pump with an efficient
one.
The average number of running hours changes widely with the country considered and depends on the climate
as well as the control strategy adopted in the building where the pump is installed. In Table 4 the estimated
average number of annual running hours for some European countries is showed.
Table 4 – running hours per country for different type of control systems
Country
Austria
Belgium
Czech Repulic
Finland
France
Germany
Greece
Italy
Spain
Boiler not
controlled
5730
4590
5573
8420
4014
5415
2410
3146
2254
Boiler
controlled
3858
3091
3753
5670
2703
3647
1623
2119
1518
Boiler
E-controlled
5109
4093
4969
7508
3579
4829
2149
2806
2010
In such table mean values are reported, so the actual number of running hours for a particular pump can be
different.
The table indicates that the number of yearly running hours is much higher in the Northern countries, where
the heating season is longer (often the heating system are used also during summer days) and the heating
systems usually run for 24 hours per day, than in Southern countries. In these countries the heating season is
indeed shorter and the heating systems does not run overnight.
The economic savings yielded by Energy+ pumps derives from the energy savings yielded during pump
lifetime times the electricity price minus the extra-price of Energy+ pumps with respect to traditional pumps.
Whereas the Energy+ pump purchase price does not vary that much across Europe, the electricity price may
vary more sensibly over the European territory.
A simplified calculation, made by using average values for the pump prices 7, gives for Italy the following
results:
•
•
•
Energy savings: 165 kWh/year
Economic savings: 17,9 !/year
Pay back time: 5,1 years
7
The calculation is made by comparing an Energy+ pump model sold in Italy (WILO Stratos ECO 25/1-3; purchase price 267 Euros;
flow rate at operating point of maximum hydraulic power 1.85 m3/h) with an equivalent traditional pump model (estimated purchase
price 129 Euros)
25
Energy+ Pumps Project
Along the 15 years of life time assumed the total economic savings (not actualized) amount at about 268 ! and
the CO2 emissions avoided amount at about 1,31 tons. This means that the choice of an Energy+ pump can
give advantage not only for the environment, but also for the purchaser: the savings achieved along the years
compensate widely the higher purchase price. The Figure 14 below indicates how the costs due to pump
purchase and operation vary with time for the two models considered in the above calculation.
Figure 14 – Purchase costs plus operation costs for an Energy+ and a traditional pump model
700
600
[!]
500
400
300
200
Payback time
100
0
1
3
5
7
9
11
13
15
year
Traditional pump
Energy+ pump
26
Energy+ Pumps Project
The saving calculation tool
Description of the calculation spreadsheet
A calculation spreadsheet has been designed in order to provide installation contractors with an easy to use
tool to estimate energy and economic savings which can be obtained by installing Energy+ pumps. Such
spreadsheet is provided to the installers attending the training module in such a way they can learn to use it
proficiently thanks to the explanations given by the installer trainer.
The estimates reported in the spreadsheet rely on a database which contains information about the Energy+
pumps available on the market, the electricity price in the various countries considered, the estimated average
number of running hours in each of these countries and other information serving to calculate the energy and
economic savings yielded by Energy+ pump models.
Energy and economic savings can be calculated in two different ways: according to a simplified approach
whereby a comparison with a traditional average pump is performed and according to a more specific
approach whereby a given Energy+ pump model is compared with a specific pump model indicated by the
calculation tool user.
ENERGY+ models against traditional models
The calculation spreadsheet is provided with a sheet named “Energy+ MODELS VS. TRADITIONAL
MODELS” that may be used to roughly estimate the energy and economic savings which is possible to
achieve thanks to the installation of an Energy+ Pump compared to a default traditional pump.
The estimate mentioned may be performed by the following steps.
Step 1
Select the country to which the calculation has to be referred (the software will automatically give the price of
the electricity immediately after country selection).
27
Energy+ Pumps Project
1
Step 2
Select the type of control system for the regulation of the operating mode of the boiler which is installed in the
plant. Three possibilities are given: boiler not controlled, boiler controlled and boiler E-controlled
(electronically controlled). This choice determinates the number of pump running hours assumed for the
calculation.
2
28
Energy+ Pumps Project
Step 3
Select pump flow rate; this will allow the software to select the pumps which fit your requirements form the
Energy+ Pumps database. hree different range are proposed:
• 0 - 1,85 m3/h
• 1,85 - 2,35 m3/h
• >2,35 m3/h
3
Once the flow rate is selected, the software automatically provides the list of the Energy+ pumps available
within that specific flow rate.
Step 4
Select one of the Energy+ pumps displayed by flagging the related row on the left of the pump name (see
figure below). The calculation tool will then estimate economic and energy savings attributable to the selected
pump and will display them in the bottom part of the sheet.
29
Energy+ Pumps Project
4
5
Step 5
In particular yearly energy savings, economic savings after 15 years of functioning and payback time are
showed in the bottom part of the spreadsheet 8. On the right part calculation results are displayed graphically:
the red line represents the total cost (investment cost plus energy cost) for a traditional pump as a function of
time, whereas the green line represents the total cost for an Energy+ Pump. The pay back time is given at the
straight line intersection point and represents the time after which the total cost for a Energy+ pump becomes
lower than the total cost of the equivalent traditional pump.
Traditional pumps considered are equivalent to the selected Energy+ pump from the point of view of the
hydraulic power and of the flow rate.
8
No discount rates are considered in the calculations made.
30
Energy+ Pumps Project
ENERGY+ models against a specific model
A second calculation sheet named “ENERGY+ VS A SPECIFIC MODEL” may be used to compare Energy+
model performance with a specific alternative and equivalent model that may be considered for installation.
Indeed such calculation sheet gives the opportunity to consider the specifications of an “ad hoc” traditional
pump, which might be the pump normally used by the installer, for the comparison. Once the data of the
traditional pump are uploaded, the software returns a list of equivalent Energy+ pumps which might be used
instead of the traditional pump itself.
Step 1 and 2
As in the previous sheet, country and boiler control system have to be selected first. Country selection allows
the calculation tool to retrieve the related electricity price, whereas control mode selection allow to retrieve
the number of operating hours used for the saving estimation.
1
31
Energy+ Pumps Project
2
Step 3
Once the country and the control mode have been selected, traditional pump specifications have to be added.
Such specification data relate to:
• The name of the traditional pump (optional)
• The flow rate in m3/h at the maximum hydraulic power
• The head in metres at the maximum hydraulic power
• The power consumption at 100% of the flow rate
• The power consumption at 75% of the flow rate
• The power consumption at 50% of the flow rate
• The power consumption at 25% of the flow rate
• The purchase price of the pump
Most of the above technical data may be derived by the pump technical specifications usually provided by the
pump manufacturer. In case such technical data are not explicitly provided, they can be approximately
estimated by referring to the graphs representing respectively the pump head and the pump power input vs. its
flow rate.
32
Energy+ Pumps Project
3
The figure below reports these two graphs in case of a typical traditional pump and the text hereunder briefly
describes how such graphs may be used to get the technical data needed.
The pump flow rate and the head at the maximum hydraulic power may be estimated by using the first out of
the two graphs below representing the pump head vs. its flow. Indeed the point of maximum hydraulic power
is where the flow multiplied by the head reaches the maximum value (see the red bullet point on the graph). A
proxy of the flow rate at the maximum hydraulic power Q@ max may be calculated by considering two curve
end points (e.g. the points P1 and P2 in the first graph below) and by applying the formula:
Q@ max =
1 ! Q1 # H 2 $ Q2 # H1 "
&
2 %'
H 2 $ H1
(
The pump head at the maximum hydraulic power (Hmax) will then correspond to the pump head at Qmax and
may be retrieved by using the graph mentioned9.
The power consumption at the different flow rates may be found by using the second graph as follows: 100%
of the flow corresponds to the right end of the line, whereas the points related to a flow rate of 75%, 50% and
25% may be determined by dividing the whole flow rate range into four parts, as shown in the example below.
9
By substituting letters with numbers in the formula above, it may be estimated that for the example represented Qmax =
"*[(0,8*3,3-1,0*0,8)/(3,4-1,6)]=1,9 m3/h. The curve on the first graph indicates that the pump head (Hmax) corresponding to Qmax is
about 2,4 m.
33
Energy+ Pumps Project
Figure 15 – determination of main pump parameters
P1(Q1; H1) = (0,8 ; 3,3)
PM(QM; HM) = (1,9 ; 2,4)
P2(Q2; H2) = (2,8 ; 1,0)
34
Energy+ Pumps Project
The software will then calculate the Europump energy efficiency class for the traditional pump specified
based on data provided. Calculation results are displayed on the spreadsheet as indicated in the figure below
(notice that data retrieved from the two graphics above correspond to a class D pump).
Step 4 and 5
Once the specifications of the traditional pump considered have been added, it is possible to obtain the list of
equivalent Energy+ pumps which can be used in place of the traditional pump. The Energy+ pumps retrieved
by the software tool will have a flow rate and a head similar to the traditional pump used for the confrontation.
In order to obtain such a list the user has to click on the red arrow highlighted in the figure below. Upon red
arrow clicking the list is automatically uploaded and an Energy+ pump can be selected in order to evaluate the
economic and energy savings which is possible to obtain with respect to the specific traditional pump initially
considered.
35
Energy+ Pumps Project
4
5
Step 6
Once a given Energy+ pump has been selected by flagging the cell on the left side of its displayed name, the
software tool calculates the yearly energy savings, the economic savings and the payback time and displays
such numbers graphically on the sheet right bottom side.
6
In the spreadsheet database the most relevant information about the Energy+ Pumps currently available on the
market are included. More detailed information about these models may be found on the project website at
www.energypluspumps.eu. Energy+ model lists will be continuously updated until project termination on
December 2008.
36
Energy+ Pumps Project
Three buttons have been added on the top right of each out of the two calculation spreadsheets. By these
buttons the user can:
•
•
•
CLEAN spreadsheet contents: by this button all the data inserted by the user are deleted and the sheet
is ready for a new calculation;
PRINT PREVIEW: by this button the sheet print preview is provided;
PRINT: by this button it is possible to print out all the data reported on the spreadsheet.
LCA results
In this paragraph some example of the results which are obtainable from the spreadsheet are shown.
Example 1 (“Energy+ models versus a generic traditional model” sheet selected)
Input Data:
•
•
•
Country: Germany
Boiler operating mode: E- controlled
Flow rate range: 0-1,85 m3/h
Energy+ Pump selected: Grundfos Alpha2 25/40
Output data:
•
•
•
Energy savings: 284 kWh/year
Economic savings after 15 years: 607 !
Payback time: 3,1 years
Example 2 (“Energy+ models versus a generic traditional model” sheet selected)
Input Data:
•
•
•
Country: Belgium
Boiler operating mode: Controlled
Flow rate range: 1,85 – 2,35 m3/h
Energy+ Pump selected : KSB Riotronic
Output data:
•
•
•
Energy savings: 214 kWh/year
Economic savings after 15 years: 314 !
Payback time: 5,8 years
Example 3 (“Energy+ models versus a specific model” sheet selected)
Input Data:
•
Country: Italy
37
Energy+ Pumps Project
•
•
•
Boiler operating mode: Not controlled
Flow rate range: > 2,35 m3/h
Traditional pump model: Wilo TOP 25/1-7
o flow rate in m3/h at the maximum hydraulic power: 5,2 m3/s
o head in metres at the maximum hydraulic power: 3,8 m
o power consumption at 100% of the flow rate: 200 W
o power consumption at 75% of the flow rate: 190 W
o power consumption at 50% of the flow rate: 180 W
o power consumption at 25% of the flow rate: 160 W
o purchase price of the pump: 431,57
Energy+ Pump selected: Wilo Stratos 25/1-6
Output data:
•
•
•
Energy savings: 291 kWh/year
Economic savings after 15 years: 649 !
Payback time: 1,4 years
38
Energy+ Pumps Project
Energy savings due to circuit design and pump sizing
Choosing to install an energy efficient pump into a heating system circuit may lead to energy consumption
reduction. However, there are other additional measures which can be implemented when designing the
heating system circuit and which can give a considerable contribution to reduce energy consumption as well.
Among these measures, the most important are:
•
•
Correct pump sizing (an oversized pump may work at low energy efficiency rates and hence consume
more energy than needed);
Reducing pressure losses in the circuit through a correct choice of the pipe diameter and through an
optimized design of the circuit.
Pump sizing
Usually installers choose oversized pumps in order to prevent possible malfunctioning due to possible
underestimates of the heating system circuit’s maximum load conditions. But choosing an oversized pump
may decrease the pump efficiency and determine higher energy consumption.
An oversized traditional pump operates as described in the previous chapters where pump operation at partial
load conditions as been discussed: the system will have to be continuously regulated by a throttling valve
which introduces in the circuit an additional pressure loss; such additional pressure loss adds to the other
losses all along the circuit and causes the efficiency losses already described in the previous sections.
It has to be noticed that in case of slightly oversized pumps with VSDs the energy consumption at partial load
conditions is still much lower than traditional pumps’ energy consumption because of higher flexibility of
such models.
Circuit loss reduction
The energy to be provided by the heating system circulator is linked to the circuit losses so. When the pressure
losses along the heating system circuit increase, the energy to be provided by the pump increases too.
The pressure losses occur all along the circuit pipes due to friction or flow local disturbances caused by e.g.
valves or pipe angularities.
Distributed pressure losses
The general formula which expresses the pressure loss !H for an incompressible fluid circulating in a pipe is
the Darcy-Weisbach formula:
!H = f
L w2
[m]
D 2g
Where:
•
L is the length of the circuit in meters
39
Energy+ Pumps Project
•
•
•
•
w is the speed of the water inside the pipe in m/s
D is the diameter of the pipe in meters
g is the standard gravity (9,81 m/s2)
f is the friction coefficient, depending on the Reynolds number and on the roughness factor "
The Darcy-Weisbach formula can also been written as:
!Q"
L #% A $&
'h = f
D 2g
2
Where:
• Q is the flow in m3/s
• A is the section of the pipe in m2
By analyzing the Darcy-Weisbach it is possible to notice that, once the flow is fixed, the pressure losses
depend by the following parameters:
•
•
•
Length of the pipe: in order to decrease the pressure losses and the energy consumption, the length of
the circuit should be decrease as much as possible. This can be achieved during the circuit design
phase, once the position of the different elements of the circuits (e.g. boiler, radiators, collectors, etc.)
is established and the path for the pipes connecting the different elements is decided.
Friction coefficient; the friction coefficient depends, as already mentioned, on the value of the
Reynolds number, by which the flow conditions inside the pipes are characterized, and on the ratio
"/D, as showed in the Moody diagram in Figure 16. Pipes with low "/D ratio (i.e. pipes with a smooth
internal surface and a large diameter) have to be chosen to decrease the pressure losses in the circuit .
The friction coefficient depends on the Reynolds number only in case of laminar flow or not
completely developed turbulent flow, whereas it is not influenced by the Reynolds number when the
flow is completely turbulent.
Pipe diameter: the influence of the pump diameter over the pressure losses may be quantified by the
Darcy-Weisbach formula, whereby the pressure loss can be written as:
!
# Q
2
#
!Q"
D2
#
%
L w2
L # A$
L#
(h = f
= f & ' = f & 4
D 2g
D 2g
D
2g
2
"
$
$
$$
2
' = f LQ
D 2g
1
L Q2
=
8
f
D4
D 5 %2 g
%2
16
Such formula shows that the pressure loss depends inversely on the fifth power of the pipe diameter; this
meaning that also very small variations in the diameter can produce important variations in the pressure loss
and that, in particular, a small diameter increase may strongly reduce the pressure loss.
The friction factor in the formula above is also affected by the pipe diameter. In general, and notably in case
of turbulent flow, a reduction in the pump diameter causes an increase in the friction factor. Therefore the
pressure loss will generally depend inversely on a power of the pipe diameter higher than the fifth.
40
Energy+ Pumps Project
Figure 16 – Moody diagram
Reynolds number R = VD/! (V in m/s; D in m; ! in m2/s)
Summarizing the most important parameters which should be considered to reduce pressure losses are the pipe
length and diameter.
The pipe length should be reduced as far as possible during the circuit design phase, while the diameter will
be chosen by taking into account that a smaller diameter means lower pipe purchase prices and lower space
encumbrance, whilst an higher diameter means lower pressure losses and lower energy costs.
Moreover it should also be taken into account that the choice of higher pipe diameters also means lower water
velocities and when the water velocity inside the pipes decreases, pipe erosion and noise are reduced too.
Local pressure losses
Pressure losses may occur in specific regions of the heating circuit, whereas some circuit elements (e.g.
curves, valves or pipe section variations) modify the flow. Usually local pressure losses are negligible
compared with friction induced pressure losses in case of high length pipes, but in case of relatively short
circuits, or in case of circuits with low friction induced pressure losses, they may become important for the
overall circuit balance.
Local pressure losses depend on local turbulences which develop every time the module or the direction of the
velocity of the fluid which circulates into the system vary; in such zones of turbulence energy is dissipated
and the pressure drops. Although local pressure drops are confined in a small part of the circuit, they may
affect the fluid flow far away from the point where they are generated downstream the heating circuit.
41
Energy+ Pumps Project
The most common examples of heating circuit local pressure losses are does induced by reduction or increase
of the pipe cross-section, curves, valves and valve gate.
Variations in the pipe cross-section
The sudden variation of cross-section causes a separation of the fluid vein from the pipe surface with the
resulting formation of vortexes which dissipate energy.
In the case of an increase in the pipe cross section, the fluid vein expands, the flow lines diverge and favor the
formation of vortexes in the expanding fluid;
Instead, in the case of a reduction in the flow section, the flow lines converge and prevent the formation of
vortexes. However the energy losses occur anyway during the expansion phase that takes the fluid from the
contracted vein section to the full section.
In both cases the energy losses my be reduced by using pipe fittings which permit to vary the cross section
gradually.
Curves
Pressure losses may happen also within pipe curves because the fluid is forced to modify his rectilinear
motion; in this case the fluid change of direction causes energy dissipations which are higher when the bend
radius is smaller.
Valves and valve gates
In most of the hydraulic circuits valves or valve gates are used to regulate the fluid flow within the circuit.
These components cause a pressure drop and their installation depends on the circuit regulation needs. Such
needs may be reduced by using pumps with variable speed drives. Indeed, in case of constant speed pumps the
only way to reduce the flow rate is the increase of the circuit head, which can be obtained only by valves
which cause a pressure drop.
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Energy+ Pumps Project
References
•
EPA – Environmental Protection Agency – United States; http://www.epa.gov/climatechange/
•
National Land and Water Information Service – Canada
•
IPCC Fourth Assessment Report: Climate Change 2007
•
Efficiency Characteristics of Centrifugal Pumps. Guide prepared by the EU SAVE Pump Study
Group
•
Jorge L. Parrondo, Sandra Velarde, Carlos Santolaria, Universidad de Oviedo, Gijón, Spain Development of a predictive maintenance system for a centrifugal pump, 1998
•
Europump - INDUSTRY COMMITMENT to improve the energy performance of stand-Alone
Circulators through the setting-up of a Classification Scheme in relation to Energy Labelling, 2005
•
Bidstrup, N., van Elburg, M. and Lane, K. – Promotion of Energy Efficiency in Circulation Pumps
especially in Domestic Heating Systems, Study under SAVE II programme, June 2001
•
Technical and economic data provided by pump manufacturers: Calpeda, DAB, Ebara, Grundfos,
KSB, Nocchi, Wilo
•
http://www.synergy.net.au/Business_Segment/Energy_Management/Variable_Speed_Drives.html
•
http://www.pumpsolutions1corp.com/index.php/Centrifugal_Pumps
43
Energy+ Pumps Project
44
Technology Procurement for very Energy Efficient Circulation Pumps
www.energypluspumps.eu
The Energy+ Pumps project is being conducted under the auspices of the Intelligent Energy-Europe programme of the
European Commission. Energy+ Pumps project partners: Germany – Wuppertal Institute for Climate, Environment and
Energy (project coordinator), – DENA, German Energy Agency, Austria – A.E.A., Austrian Energy Agency; Italy – eERG,
Politecnico di Milano, Belgium – VITO, Flemish Institute for Technological Research, Greece – CRES, Centre for Renewable
Energy, Spain – ESCAN S.A., Czech Republic – SEVEn, Energy Efficiency Center; Finland – MOTIVA, Energy Information
Centre for Energy Effi ciency and Renewable Energy Sources, France – ADEME, French Agency for the Environment and
Energy Management, Switzerland – Arena. Financial contributions by: Deutsches Bundesministerium für Wirtschaft und
Technologie (BMWI), Ministerium für Wirtschaft, Mittelstand und Energie des Landes Nordrhein-Westfalen (MWME),
Österreichisches Bundesministerium für Land- und Forstwirtschaft, Umwelt- und Wasserwirtschaft (BMLFUW), Comunidad de
Madrid and Ministry of Trade and Industry in Finland.