A COMPARATIVE ASSESSMENT OF FUTURE HEAT AND POWER SOURCES
FOR THE UK DOMESTIC SECTOR
Jeremy Cockroft, Nick Kelly#
Energy Systems Research Unit, University of Strathclyde, Glasgow, G1 1XJ
#
Corresponding Author e-mail: nick@esru.strath.ac.uk tel: +44(0)141 548 2854 fax: +44(0)141 5525105
ABSTRACT
In 2003 the UK government announced its aspiration for a 60% reduction in CO 2 emissions by 2050
relative to 1990 levels. To achieve this radical target action is required across all sectors of the economy
to significantly reduce energy demand and to increase the supply of energy from zero or low carbon
sources. Focusing on the domestic sector, where energy consumption is currently rising, technologies
such as fuel cells, Stirling and internal combustion engine micro-CHP and heat pumps are often cited as
the means to reduce carbon emissions. However there is much uncertainty as to the potential
environmental benefits (if any) of the aforementioned technologies when set against a picture of changing
energy supply and demand. The paper describes an analysis in which the performance of these four
different technologies mentioned above was compared against a common datum of energy supply from
condensing gas boilers and grid electricity for a number of scenarios. The aim of the analysis was to
determine if significant CO2 savings could be made and the minimum thermodynamic performance
criteria that these technologies must attain if they are to yield any environmental benefits. The main
finding of the work is that air source heat pumps yield significantly more CO2 savings than any of the
other technologies examined.
KEYWORDS
heat pumps, fuel cells, cogeneration, modelling, housing, emissions
INTRODUCTION
2003 saw the publication of the United Kingdom’s Energy White Paper [1], the core of which was the
aspiration for a 60% reduction in greenhouse gas emissions by 2050 compared to 1990 values. To achieve
this goal the UK will need to implement radical changes in the means by which energy is supplied and
used. Focusing on the domestic sector the large scale deployment of embedded renewable technologies
such as photovoltaics (PV) and micro wind power, micro combined heat and power (μ-CHP) coupled
with greatly improved energy efficiency is seen as a means of combating increasing energy demand and
reducing carbon emissions. The transition towards low carbon housing is of particular interest to
researchers from many disciplines in that the effective integration of renewables and micro power
technologies and improving energy efficiency will require significant changes from a technical, economic
and social perspective given that the provision of heat and (particularly) power from local sources will
involve a radical shift away from the energy supply systems in common use today. Significant resources
are being targeted in this area with several large scale research projects underway examining issues
ranging redesigning dwellings for low carbon emissions [2] to the integration of micro-power within the
electricity supply infrastructure [3]. Surprisingly, despite these research efforts there is currently little
published literature on the likely effect of deploying new heat and power sources on UK domestic CO2
emissions.
With regards to energy efficiency, the energy profile of the domestic sector is changing, driven by
conflicting trends. Positive drivers for change include the development of more energy efficient and
responsive environmental conditioning equipment. Additionally, new legislation is also being designed to
drive down energy demands, for example, the European Energy Performance in Buildings Directive
(EBPD) [4] introduces mechanisms such as energy labelling and performance benchmarking for
buildings. Counteracting these positive trends are increased expectations for occupant comfort (e.g.
increased internal temperatures and demand for hot water); increased demand for electronic equipment; a
growing market for domestic air-conditioning; changing demographics (e.g. an ageing population,
reducing family sizes, increasing numbers of single-person households); behavioural patterns and socioeconomic developments (e.g. increased working-from-home): all are acting to increase domestic energy
consumption [5].
Given this complex and changing picture of domestic energy supply and demand driven by social change,
legislation and many other factors it is difficult to determine exactly what impact the introduction of new
heat and power technologies into the domestic sector will have.
In this paper a simulation-based approach is adopted to assess the performance of new domestic energy
supply systems and quantify any resulting environmental benefits. Key questions to be answered include
the following. What levels of performance will be required to produce tangible environmental savings?
What impact will energy efficiency have on the viability of these technologies? How do they compare to
each other and conventional alternatives? This paper sets out to examine these issues within the context of
changing energy supply and demand characteristics (e.g. increased production of electricity from
centralised renewable sources such as wind and tidal power and improved domestic energy efficiency).
NEW DOMESTIC HEAT AND POWER TECHNOLOGIES
Many new technologies are emerging as potential low carbon heat and/or power sources for the domestic
sector, which could be considered as a direct replacement for the domestic boiler. Some of the main
examples include: air-source heat pumps; micro-CHP featuring internal combustion engines (ICE),
micro-CHP featuring Stirling Engines, proton exchange membrane fuel cells (PEM) and solid oxide fuel
cells (SOFC).
Air Source Heat Pumps: while ground source heat pumps have traditionally had a higher coefficient of
performance (COP) [6], the capital cost associated with their installation and the lack of availability of
land for the evaporator coils in urban areas coupled with ready availability of other fuel sources such as
coal, oil and latterly natural gas has meant that the number of ground source heat pumps (GSHPs)
installed in the UK is very small [7]. The technology behind air source heat pumps (ASHPs) has been
significantly improved in recent years and COPs of more than 3 have been reported in tests and field trials
(e.g. [8]). ASHPs potentially have a much greater market potential than GSHPs in the UK due to the fact
that they are more easily retro-fitted and could be seen as a direct replacement for the gas boilers that are
the main heat source for around 80% of the UK’s homes 9]. There is currently one major field trial of
ASHP’s underway in the UK1 and several others planned.
Stirling Engine Micro-CHP: in the UK there is significant interest in the use of this technology to replace
domestic boilers. There are currently several large scale field trials underway, however given the near-tomarket status of the technology, performance data from these trials is limited. Useful information on insitu-performance is available from studies conducted by NRCan [10], where overall device efficiencies of
1
Undertaken by West Lothian Council
over 80% have been reported. Heat to power ratios are of the order of 12:1 and consequently the electrical
power output from these units is low (<1kW).
ICE Micro-CHP: Several internal combustion engine (ICE) combined heat and power (CHP) devices,
specifically targeted at the domestic sector have recently appeared on the market. These devices are
usually scaled down versions of larger units and are designed to run on natural gas and have sizes ranging
in size 1-4kW of electrical output. Some limited performance data is available from the manufacturers,
with heat to power ratios of around 3:1 and overall efficiencies of 85% being reported [11].
Fuel Cells: two fuel cell technologies are of interest with regards to domestic heat and power
applications: the proton exchange membrane (PEM) and the solid oxide fuel cell (SOFC). SOFCs offer a
higher-grade source of heat for the production of steam, high-pressure hot water or low-pressure hot
water. Moreover their high operating temperature (800-1000oC) leads to high electrical efficiencies, with
45% electrical efficiency and an overall efficiency of around 85% being reported (Sulzer Hexis, 2005).
The high operating temperature also means that reforming of hydrocarbon fuels (e.g. natural gas) to
produce the hydrogen needed to power these units can be done internally [13].
While the previous three technologies could be described as market ready, the prospect of heat and power
from domestic fuel cells is still several years away. The US DOE published cost targets for stationary fuel
cells, with a target of $750/kW by 2010. At these levels the technology would be competitive with
alternative technologies, however current costs are significantly greater than this at over $2000/kW [14].
ANALYSIS
In this paper the environmental performance of the low carbon technologies mentioned above is analysed
using computer simulation; the approach adopted is to calculate their CO2 emissions when supplying heat
and power to three characteristic UK dwellings for a number of different scenarios and comparing these
emissions to the conventional alternative, e.g. a boiler and grid electricity. The three characteristic UK
dwellings considered in the simulations were:

an apartment with a total floor area of 68m2;

a terraced dwelling with a floor area of 90m2; and

a ‘semi-detached’ dwelling with a floor area of 87m2 .
In the simulations two different demand and supply scenarios are considered; these correspond, very
roughly, to the current situation in 2005 and a more energy efficient scenario in 2020. For the 2005
demand scenario the buildings are assumed to be poorly insulated and have poor air tightness (1.5 air
changes per hour): typifying the performance of many current UK dwellings. For the second more energy
efficient demand scenario the buildings are insulated to current UK building regulations [15, 16], while
air tightness has been significantly improved such that infiltration is restricted to 0.5 air changes per hour.
In both cases the buildings are subject to intermittent occupancy, which represents occupation by a
working family. In all cases the living space in each dwelling was heated to 21 oC, while the other spaces
were heated to 18oC, temperatures which are typical of UK dwellings [9]
The complementary supply scenarios are as shown in table 1. The first reflects the make up of the UK
electricity supply at present and the other represents the envisaged supply in 2020 [17].
Table 1 Electricity Supply Make up (%)
Source
2005
2020
Coal
33.0
12.0
Oil
0.6
0.4
Gas
33.9
48.2
Nuclear
24.6
5.8
Hydroa
0.9
0.6
Other RE
4.4
12.4
Importsb
2.6
20.3
CO2 ‘coefficient’ of grid
0.42
0.30
electricity kg CO2/kWh
a
pumped storage bFrench
electricity
Notice that the envisaged change in the supply make up reduces the CO 2 coefficient for grid electricity by
approximately 28% by 2020.
A total of 24 scenarios are analysed (2 demand/supply combinations x 3 dwellings x 4 micro generation
sources); each of the low carbon technologies is in turn subjected to up to 6 variations in electrical and
thermal efficiency leading to a total of 124 different analyses. Specifically, the variations made are: (1)
the thermal efficiency is increased while the electrical efficiency is held constant: effectively increasing
the overall efficiency and the heat to power ratio of the device; (2) the electrical efficiency of the device is
increased while the thermal efficiency is held at the rated value: decreasing the heat to power ratio while
increasing the overall efficiency. For the air source heat pump only the COP is varied.
The calculation of each building’s annual CO2 emissions2 for each combination required the development
of a customised calculation tool. The tool uses hourly time-varying electrical, space heating and hot water
demand profiles, details of the prevailing electricity generation mix (shown in table 2) coupled with
models of the micro-generation and conventional heat and power technologies to calculate the hourly CO 2
emissions associated with heating and powering the dwellings over the course of a year.
The ESP-r building simulation tool [18] is used to calculate the time-varying space heating demands for
each dwelling type. In ESP-r the geometry of the building, fabric, systems and occupant activity are
described in a mathematical model. Solution of this model with real climate data and user defined control
criteria yields the building’s time-varying mass, energy flows and state variables (e.g. temperature,
pressure, etc.) over a simulated period.
UK standard electricity profiles3 describing the daily variations of household electricity demand were
modified for each dwelling: each profile was scaled according to the floor area and number of occupants.
For the 2020 scenario electricity consumption patterns are assumed to follow the current trend: increasing
at 2% per year [5], hence demand in 2020 is 30% greater than the 2005 case. Note that DTI projections
assume that overall electricity demand will increase by 36% over the whole economy by 2020.
Hot water demand profiles are calculated based on an assumption of 36 litres of hot water usage per
person per day [21]; this figure is based on data from 1997. Typical profiles of hot water consumption
have two distinct demand peaks; in the morning and again in the evening [22]. A combination of the
2
Note that this paper will specifically avoid addressing criteria for economic viability for a number of reasons. Firstly, many low
carbon technologies are currently at the prototype and early deployment stages and so the eventual cost of these units is hard to
predict. Secondly, the technologies’ economic viability is heavily dependent upon the cost of fuel (gas and electricity), which is
currently in a state of flux in the UK (e.g. [19, 20]) with fuel process rising above inflation in the period 2003-5. Price increases may
make technologies such as micro-power more attractive, but for micro-CHP in particular many other factors come into play: for
example the electricity/gas price differential is crucial. Current UK price trends may not be advantageous if gas prices continue to
rise and electricity prices remain comparatively low. Finally, unless there are demonstrable environmental benefits from new
domestic energy technologies then the economic arguments become irrelevant, as there will be no environmental impetus to install
these technologies in dwellings.
3
http://www.electricity.org.uk
global consumption data and profile information is used to generate the demand profiles for these
simulations. The profiles are scaled according to the number of occupants in the dwelling.
Figures 1 and 2 show the simulated heat, electrical and hot water demands from the 2005 and 2020
scenarios from the apartment dwelling for a winter day in January. The graphs show total demand (kW)
and its constituents at each hour. Note the dramatic reduction in the space heating energy requirement
(and hence total demand) caused by the improvements in insulation and air tightness.
Given the high-level nature of this study and the distinct lack of suitable models of micro power devices 4,
some simple parameterised models of the generation components were used in this analysis. The
parameters used for each model are those that dictate the basic performance in relation to supplying the
calculated demands. Sensitivity analysis on these key parameters (table 2) gives an approximate
indication of the minimum performance criteria needed for each low carbon technology to yield a CO2
saving compared to the provision of heat from a condensing gas boiler (efficiency 91% 5) and electricity
from the grid. In each case the micro-generation device was sized to be capable of meeting the maximum
thermal demand (space heating and power) from the building being analysed. Control of the each device
was assumed to be on/off. Hence if the hourly load is less than the device capacity, the device will cycle
between zero and full output, operating on full load for a fraction of the hour f.
Table 2 Technology Performance Variables
Technology
Variables
Air Source Heat Pump
COP
Fuel Cell, Stirling and
electrical efficiency, thermal
ICE Micro-CHP
efficiency, overall efficiency,
H:P ratio
In the analysis an assumption made was that any surplus electrical output from the fuel cell, Stirling
engine or ICE engine is exported back to the grid. Note however that exported power is not included in
the CO2 saving calculation: exporting power from a large number of micro-generators could eventually
4
The lack of models for micro-power devices, specifically for building simulation tools is being addressed within the International
Energy Agency’s (IEA) Energy Conservation in Building and Community Systems (ECBCS) Annex 42 [23].
http://www.cogen-sim.net
5
www.sedbuk.com
lead to a larger generator ceasing operation, operating at part load or could displace renewable electricity,
hence it is difficult to determine if a CO2 saving (or penalty) results from power export.
For cogeneration devices, the CO2 saving, S (kg CO2/annum) at each hour of the year is calculated by
subtracting the emissions associated with provision of heat and power the cogeneration device and any
impoted electricity from the emissioms associated with suppying a heat from a condensing boiler and all
electricity from grid. For the Stirling, ICE and SOFC units, the saving is calculated using the following
equation:
Q

S   TH  G  Ei  E 
 B

 QTH  EOM 

 G  EiM  E 
 

M



(1)
Equation 1 can be re-arranged to give
QTH  EOM
Q
S   TH 
M
 B
 Ei  EiM  E


 G


(2)
Where
EiM  Ei  EOM
EiM  Ei
E OM  E i
(3)
E OM  E i
Equation 1 can therefore be expressed as:
QTH  EOM
Q
S   TH 
M
 B
 EOM  E EO  Ei



 G

(4)
M
In the case of the air source heat pump, the CO2 savings for each hour of the year are calculated by
subtracting the emissions associated with the electricity used by the heat pump from the emissions
associated with supplying heat from a boiler:

 
S  QTH  G  E 
 B COP 
(5)
Balance of plant and distribution system losses are assumed to contribute to the heating of the dwelling
and so the efficiencies of these subsystems are not included in the calculations.
RESULTS
Figure 3 shows the predicted CO2 savings from all of the simulations conducted for the 2005 demand
scenario. Figure 4 shows the results for the simulations conducted for the 2020 scenario. Importantly the
figures show that in certain cases micro-generation and heat pump devices show a negative carbon
saving.
For both the 2005 and 2020 scenarios the air source heat pump (ASHP) shows the greatest potential CO2
savings. The savings are greatest with the 2005 electricity supply mix and demand level; the reason for
this is that the high heat demands for the 2005 scenario afford the air source heat pump (ASHP) the
greatest potential to offset CO2 emissions: the greater the amount of heat produced by the ASHP the
greater the CO2 saving compared to a conventional boiler. For the ASHP each kWh of heat produced
saves s (kg/CO2):

 
s   G  E 
  B COP 
(6)
Inspection of equation 5 indicates that for the air source heat pump (ASHP), the potential CO 2 savings per
kWh of heat supplied actually increase as the carbon dioxide emissions factor of electricity (E) reduces.
Examining the curves displayed in figures 7 and 8 it can be deduced that with the 2005 fuel mix a
minimum COP of around 2.0 is required to achieve CO 2 savings, while with the 2020 fuel mix this is
reduced to 1.4; these values can also be determined from equation 5 by setting s to 0 and rearranging for
the COP.
Figures 4 and 5 show that for the ASHP and the Stirling engine units, the magnitude of potential CO2
savings decreases from 2005-2020 due to the fact that the amount of heat supplied to each of the
dwellings decreases significantly (50-60%); this reduction in heating energy requirement does not affect
the SOFC and ICE micro-CHP devices as dramatically as electricity consumption increases significantly,
hence the CO2 saving potential of these two technologies deceases only slightly with the 2020 demand
scenario and fuel mix.
Figure 5 shows the CO2 savings from the SOFC, ICE and Stirling engine micro generation units plotted
against overall efficiency for the 2005 scenario. Shaded areas have been added to indicate the envelope of
operation examined in the simulations. These areas indicate the rough efficiencies required of these
technologies to enable them to make positive CO2 savings: for all three technologies an overall efficiency
of more than 85% is required.
Figure 6 shows the same technologies for the 2020 scenario. Again shaded areas have been added
indicating that for the SOFC and ICE units an overall efficiency of over 80% would be required to make
CO2 savings, while for Stirling engines over 85% would be required.
Interestingly Figures 5 and 6 show that Stirling engine units become less environmentally viable with the
more energy efficient 2020 scenario, while the viability of ICE and SOFC units improve; notice the
shaded areas for the ICE and SOFC units move upwards in the 2020 graph while the shaded area for the
Stirling engine moved downward. There are several reasons for this change in viability. Firstly, the little
electricity displaced by the Stirling engine has a lower carbon content in the 2020 scenario, reducing the
potential for savings. Secondly the total amount of electricity which can be displaced is reduced as the
reduction in space heating demands reduces the engine’s potential running time. Finally the change in
heating and electricity demand characteristics with the reduction in heat demands and increase in
electrical power loads alters the three buildings’ heat to power ratios (5:1 → 3:1), moving the ratios
further away from that of the Stirling engine (12:1). Conversely, this heat to power ratio now closely
matches those of the SOFC and the ICE CHP units (3:1); this results in almost all of the electricity
produced by these two units being used internally, displacing grid electricity. For the 2005 scenario, much
of the electricity being produced by the SOFC and ICE CHP devices was exported, resulting in fuel use
for no tangible CO2 saving.
Figure 7 shows that for an ASHP COP of around 3, a COP which is already being achieved [8], savings
of between 500-800kg per annum or, approximately, a 20% reduction in CO2 emissions are achieved.
The Stirling engine, SOFC and ICE micro-CHP cannot achieve this magnitude of emissions saving.
CONCLUSIONS
The main findings from this exploratory simulation-based analysis are:

Of the four micro heat and power technologies examined, air source heat pumps (ASHP) offer the
greatest potential for significant CO2 emissions reductions compared to a condensing boiler and grid
electricity.

Unless run at very high efficiencies (for the 2005 scenario) all the micro generation and heat pump
devices analysed might operate with negative carbon savings: the SOFC, ICE and Stirling engine
units need to operate with overall efficiencies of more than 85% to make tangible carbon savings,
while the ASHP needs to operate with a COP of more than 2.

The SOFC, ICE micro-CHP and Stirling engine devices cannot attain the same magnitudes of carbon
savings as the ASHP.

A reduction in the CO2 emissions coefficient of grid electricity increases the potential for CO 2
savings from the ASHP; however reduced heat demands due to improved fabric and air tightness
reduce the overall magnitude of potential savings.

The current UK trend towards greater electricity consumption and improved insulation in buildings
significantly alters heat and power demand characteristics, reducing the heat to power ratio and
improving the environmental viability of solid oxide fuel cells and internal combustion engine based
micro-CHP, but reducing the potential for CO2 savings from Stirling engine based micro-CHP.
FURTHER WORK
While this study provides useful insight into the basic viability of each of the four technologies analysed,
more detailed work is required in the following areas prior to drawing final conclusions:

Assessment of the impact of the balance of plant (BOP) including energy storage, more complex
control strategies, coupled with time-varying device efficiencies and possibly sub-hourly time steps
will require the development of detailed micro generation technology models for use in building
simulation tools. Work in the area of profiles and development of building simulation models of
micro-generation is currently being undertaken within an International Energy Agency project
sponsored within its implementing agreement in Energy Conservation in Building and Community
Systems.[21]

A fixed CO2 emissions coefficient was assumed in this paper, however in reality this will vary over
time as different central power sources come on and off line during the day. So the timing of power
displacement/export from micro-cogeneration in relation to the variation in the electricity supply mix
and its impact on CO2 savings requires investigation.

The accuracy of using hourly profiles in estimating CO2 savings, particularly in the analysis of
micro-CHP has been called into question recently [24]. Work is therefore required in gathering
characteristic sub-hourly profiles of both hot water and especially power consumption for different
user types.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the help of John Lightfoot of Marstair Ltd. for the provision of air
source heat pump performance data.
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[1] Department of Trade and Industry (DTI), Energy White Paper, The Stationary Office, London, 2003
[2] Boardman B, Brave New World, Article on the ‘40% House Project’, Tbe Guardian, March 30, 2005
[3] Kuri B, Li F, "Distribution network planning considering generation uncertainties from renewables",
3rd IEE International Conference on Reliability of Transmission and Distribution Networks (RTDN
2005), London, 2005.
[4] European Parliament, Directive 2002/91/EC of The European Parliament and of the Council, Official
of The European Communities pp L 1/65 – L1/71, 2002.
[5] Department of Trade and Industry (DTI), Energy Consumption in the United Kingdom, The
Stationary Office, London, 2003.
http://www.dti.gov.uk/energy/inform/energy_consumption/ecuk.pdf.
[6] Berntsson T, Heat Sources – Technology Economy and Environment, International Journal of
Refrigeration, vol 25, pp428-438, Elsevier Science, Amsterdam, 2002.
[7] Rawlings R H D, 1999, Ground Source Heat Pumps – a Technology Review, The Building Services
Research and Information Association, Technical Note TN 18/99.
[8] Marcic M, Long Term Performance of Central Heat Pumps in Slovenian Homes, Energy and
Buildings, vol 36, pp185-193, Elsevier Science, Amsterdam, 2002.
[9] Utley J I, Shorrock L, Brown J H F, Domestic Energy Fact File: England, Scotland, Wales and
Northern Ireland, BRE Report, BRE Bookshop, London, 2001.
[10] Entchev E, Gusdorf J, Swinton M, Bell M, Szadkowski F, Kalbfleisch W, Marchand R, Microgeneration Technology Assessment for Housing Technology, Energy and Buildings, vol 36, pp 925-931,
Elsevier Science, Amsterdam, 2004
[11] Honda Motor Co. Ltd., Press Release, October 20, 2004.
http://world.honda.com/news/2004/c041020.html
[12] Sulzer Hexis Ltd., 1kW fuel cell product performance data sheet, 2005.
http://www.hexis.com/eprise/SulzerHexis/Sites/Fuelcell/HXS1000/Performance.html
[13] Hoogers G (editor), Fuel Cell Technology Handbook, CRC Press, Boca Raton, 2004.
[14] US Department of Energy (DOE), Hydrogen, Fuel Cells and Infrastructure Technologies
Programme, Report No. DOE/GO-102003-1741. 2005
http://www.eere.energy.gov/hydrogenandfuelcells/mypp
[15] Office of the Deputy Prime Minister (ODPM), Building Regulations Part L (Conservation of Fuel
and Power), The Stationary Office, London, 2004.
http://www.odpm.gov.uk/ stellent/ groups/ odpm_control/ documents/ homepage/ odpm_home_page.hcsp
[16] Scottish Building Standards Agency, The Scottish Building Standards Technical Handbook
(Domestic), The Stationary Office, London, 2004.
http://www.sbsa.gov.uk/tbooks.htm
[17] Department of Trade and Industry (DTI), 2004, Updated Energy Projections, Working Paper.
http://www.dti.gov.uk/energy/sepn/uep.pdf.
[18] Clarke J A, Energy Simulation in Building Design, Butterworth-Heinemann, Oxford, 2001.
[19] BBC Online, News Article, 2004
http://news.bbc.co.uk/1/hi/business/4271723.stm
[20] Department of Trade and Industry (DTI), 2005, Quarterly Energy Prices,
http://www.dti.gov.uk/energy/energy_prices/index.shtml
[21] European Commission, 2005, ATLAS Information Base.
http://europa.eu.int/comm/energy_transport/atlas/homeeu.html.
[22] Fairey P and Parker D S, 2004 ,A Review of Hot Water Draw Profiles Used in Performance
Analysis of Residential Domestic hot Water Systems, Florida Solar Energy Centre, Report FSEC-RR-5606, University of Central Florida.
[23] Beausoleil-Morrison, FC+COGEN-SIM The Simulation of Building-Integrated Fuel Cell and Other
Cogeneration Systems, IEA Annex 42 Text, Natural Resources Canada, 2004.
[24] Hawkes A, Leach M, 2005, Impact of Temporal Precision in Optimising Modelling of microCombined Heat and Power, Energy, 30, Elsevier Science, Amsterdam 1759-1779.
NOMENCLATURE
Thermal demand (kWh)
QTH
G
E
Ei
Eo

Natural gas CO2 emissions coefficient
(kg CO2/kWh)
Grid electricity emissions coefficient
(kg CO2/kWh)
Electricity import (kW)
Electricity export (kW)
Efficiency
Subscripts
B
Boiler
E
Electricity
G
Gas
M
Micro-generation
Electricity and Heating Loads 2005
6
5
4
kW
Electricity
3
Water
Space Heat
2
1
23
21
19
17
15
13
11
9
7
5
3
1
0
Time (hrs)
Figure 1 Total Demand January Day 2005 Scenario.
Electrical and Heating Loads 2020
6
5
4
Water
Space Heat
2
1
23
21
19
17
15
13
11
9
7
5
3
0
1
kW
Electricity
3
Time (hours)
Figure 2 Total Demand January Day 2020 Scenario.
Figure 3 CO2 Savings from 2005 Simulations.
Figure 4 CO2 savings from 2020 Simulations.
Figure 5 Efficiency vs CO2 savings 2005.
Figure 6 Efficiency vs CO2 Savings 2020.
Figure 7 ASHP COP vs CO2 Savings 2005.
Figure 8 ASHP COP vs CO2 Savings 2020.