SEasonal PErformance factor and MOnitoring for heat pump systems in the building sector SEPEMO-Build Benchmarking method of seasonal performance D4.4. Benchmarking method of seasonal performance under consideration of boundary conditions. Author(s) Andreas Zottl, Roger Nordman, Marek Miara Date of delivery: 2012-04-02 Contract Number IEE/08/776/SI2.529222 The sole responsibility for the content of this document lies with the authors. It does not necessarily reflect the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information contained therein.
Transcript
SEasonal PErformance factor and MOnitoring for heat pump systems in the building sector
SEPEMO-Build
Benchmarking method of seasonal performance D4.4. Benchmarking method of seasonal performance under
consideration of boundary conditions.
Author(s) Andreas Zottl, Roger Nordman, Marek Miara
Date of delivery: 2012-04-02
Contract Number IEE/08/776/SI2.529222
The sole responsibility for the content of this document lies with the authors. It does not necessarily reflect the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information contained therein.
SEPEMO-Build report
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1 Foreword ............................................................................................................................. 3 2 Nomenclature ..................................................................................................................... 3 3 Limitations of SPF .............................................................................................................. 4 4 Benchmark methodology .................................................................................................. 6 4.1 Primary energy ratio PER ...................................................................................................... 7 4.1.1 Primary Energy demand ..................................................................................................... 7 4.1.2 Final Energy ........................................................................................................................ 8
4.1.3 Primary energy factor pf ..................................................................................................... 8
4.1.4 Heat pump systems - SPF .................................................................................................. 9 4.1.5 Backup systems - AE .......................................................................................................... 9 4.1.6 PER – monovalent and monoenergetic systems ............................................................... 10 4.1.7 PER – bivalent systems .................................................................................................... 10 4.2 Carnot efficiency .................................................................................................................. 10 4.2.1 Carnot Efficiency for Heat Pump unit ................................................................................ 10 4.2.2 Carnot Efficiency for Heat Pump systems ......................................................................... 11 4.3 Specific energy demand ...................................................................................................... 12 4.3.1 Specific heating demand ................................................................................................... 12 4.3.2 Specific electric energy demand ....................................................................................... 13 4.4 Domestic hot water ratio ...................................................................................................... 13 4.5 Heat pump energy supply ratio ............................................................................................ 13 5 Benchmark Example ........................................................................................................ 14 5.1 Example calculation – additional system electric backup ..................................................... 14 5.1.1 Data from field measurement & meta data ........................................................................ 14 5.1.2 SPF calculation ................................................................................................................. 14 5.1.3 PER calculation ................................................................................................................. 15 5.1.4 Carnot efficiency calculation .............................................................................................. 16 5.1.5 Specific energy demand calculation .................................................................................. 16 5.1.6 DHWR calculation ............................................................................................................. 16 5.1.7 HPESR calculation ............................................................................................................ 17 5.2 Summary Example – electric backup ................................................................................... 17 5.1 Comparison SPF / PER with different additional systems .................................................... 18 6 Literature .......................................................................................................................... 20
SEPEMO-Build report
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1 Foreword The deliverable “D4.4 Benchmarking method of seasonal performance under consideration of boundary conditions” presents a methodology for benchmarking the seasonal performance under consideration of the boundary conditions the system is running. For a better interpretation of the heat pump performance, SPF does not give the whole picture. Additional parameters should be used to point out the operating conditions of the system:
- PER – primary energy ratio - Specific Energy Demand - Carnot Efficiency - DHWR - Domestic hot water ratio - HPSR - Heat pump energy supply ratio
2 Nomenclature
SH space heating [-] DHW domestic hot water [-] HP heat pump [-] CU Cooling unit [-] SPF i Seasonal performance factor (Index: H for heating, C for cooling) [-] COP Coefficient of performance [-] EER Energy efficiency ratio [-] SEER Seasonal energy efficiency ratio [-] For heating mode: Q H_hp quantity of heat of the HP in SH operation [kWh] Q W_hp quantity of heat of the HP in DHW operation [kWh] Q HW_bu quantity of heat of the back-up heater for SH and DHW [kWh] E S_fan/pump electrical energy use of the HP source: fan or brine/well pump for
SH and DHW [kWh]
E B_fan/pump electrical energy use of the heat sink (building): fans or pumps for SH and DHW
[kWh]
E bt_pump electrical energy use of the buffer tank pump [kWh] E HW_hp electrical energy use of the HP for SH and DHW [kWh] E HW_bu energy use* of the back-up heater for SH and DHW [kWh] *for additional heating other then electrical back up heater the energy
content of the fuel demand has to be taken
3 Limitations of SPF Seasonal performance factor, SPF is not the only measure to check that a heat pump system is working properly. In this section, some examples are chosen to illustrate this fact. Therefore, there is a need to have additional benchmarking key numbers to facilitate system performance analysis. The following operating situations illustrate why SPF alone cannot be judged alone in order to understand heat pump performance:
• Part load operation in an oversized system • (Full load operation in an undersized system) Large share of backup in an undersized system
Large share of DHW to space heating (typical for low energy buildings) Many of the heat pumps on the market today are capacity controlled. This type of heat pump has a capacity vs. part load ratio that increases at part load, Figure 1,[4]. The heat pump is normally designed to fit the nominal capacity to match the building heat demand on the coldest day, or at the bivalent point in the case of heat pumps with backup systems. By designing this way, the heat pump will operate in part load capacity most of the time, resulting in much higher COP/SPF than expected from the design point of view. Similarly, in an undersized system, the heat pumps will operate at nominal full capacity for a very large portion of the time. The heat pump performance is then good, but the potential is misused. In heat pumps with integrated electric backup, the SPFH3 according to “Concept for Evaluation of SPF“, [2] will be very low. Also in buildings with very low specific energy use, the Overall SPF of the heat pump system can be poor, see Figure 2. The reason for this is simply that the share of domestic hot water production is large. This production is generally made at an elevated temperature compared to space heating, thus resulting in lowered COP. These observations makes it clear that even in well insulated buildings in the future, there could be reasons that SPF will be lower that is actually found in installations today. There is hence a need for alternative or complementary benchmarking key numbers. We propose a set of such in this report.
For cooling mode:
Q C produced cooling energy of the CU for cooling [kWh] E S_fan/pump electrical energy use of the CU- heat sink: fan or brine/well pump [kWh] E B_fan/pump electrical energy use of the building fans or pumps [kWh] E CU electrical energy use of the CU [kWh] E bt_pump electrical energy use of the buffer tank pump [kWh]
Figure 1. Part load factor vs, Part load Ratio [4].
Figure 2. SPF vs. Specific heat demand for a number of monitored heat pumps. [Source: M. Miara Fraunhofer ISE]
4 Benchmark methodology The efficiency of heat pumps systems represented as SPF is mainly influenced by the operating conditions and the set system boundaries for calculating the SPF. Therefore it is important to define minimum results for field trials in order to get a hint under which conditions the heat pump was operated. Furthermore it is necessary to calculate the SPF according to different system boundaries display the impact of the auxiliaries integrated in the system. The IEE project SEPEMO-Build deals with these two main points in the “Concept for Evaluation of SPF“, [2] and the “Field Measurement Guideline”, [1]. According to the calculated SPF of D4.2 it is necessary to evaluate data about the boundary conditions of the system. Such boundary conditions are also the heat source temperature and the heat sink temperature. In addition the operational hours of the compressor and the auxiliary devices have influence on the SPF. This data are also a basis for development of quality characteristics for heat pump systems. Therefore for data presentation the minimum results according to [1] should be used (Table 1).
minimum results Electric energy input – total kWh Electric energy input backup heater kWh Electric energy input pumps/fans heat source side kWh Electric energy input pumps/fans heat sink side kWh Energy output heating / cooling kWh Energy output DHW kWh SPF2 - SPF3 - Average supply temperature heat sink* °C Average return temperature heat sink* °C Average supply temperature DHW* °C Average return temperature DHW* °C Average supply temperature heat source* °C Average return temperature heat source* °C Average outdoor temperature* °C Average indoor temperature* °C *during operation of the unit
Table 1: Minimum results
Additional to these defined minimum results the calculation methodology for benchmarking the systems focuses on metadata from the buildings and systems to specify the building quality where the system is integrated by at least showing the specific heating energy demand and specific electrical energy demand of the system. In a next step the PER together with the SPF can be calculated to compare the systems concerning there primary energy efficiency. Finally the Carnot efficiency can be used for showing the quality of the system under investigation.
4.1 Primary energy ratio PER The comparison of different SPF according to different system boundaries have been defined in the SEPEMO Deliverable D4.2 [SEPEMO D4.1, 2011]. Additionally to the comparison of the SPF the systems should be analysed according there primary energy efficiency, the so called primary energy ratio PER. The PER points out how much usable energy can be generated per primary energy input (Equation 1).
Equation 1
Figure 3 shows the different boundaries for characteristic factors for benchmarking the systems according to primary energy, final energy, usable energy, SPF, PEF and PER. In the next chapters the needed parameters for calculating the PER are described.
Figure 3. Boundaries for characteristic factors
4.1.1 Primary Energy demand The annual PE demand can be calculated on the basis of the final energy and PE factor fp of the different energy carriers of the different systems (Equation 2).
Equation 2
[-] AE[kWh]energy usable[kWh]energy final systemsupback =
]-[ SPF[kWh]energy usable]kWh[energy final pumpsheat =
[kWh]energy final[kWh]energy primaryf =p
4.1.2 Final Energy The final energy consumption of the different heating systems will be calculated based on the measured usable energy and the different efficiencies of the systems. For the backup heating systems the annual efficiency (AE) will be taken for the calculation (Equation 3).
Equation 3
The final energy for heat pumps will be calculated with the seasonal performance factor SPF (Equation 4). As the SPF is >1 the final energy demand will be smaller than the usable energy demand.
Equation 4
4.1.3 Primary energy factor pf
The PE factor pf is defined as PE demand per final energy (Equation 5).
Equation 5
According to EN 15603:2008 [5] the PE is described as energy that has not been subjected to any conversion or transformation process. The PE includes non-renewable energy and renewable energy. If both are taken into account it can be called total PE [5]. For the calculation according D4.3 the PEFT will be used. Table 2 shows the PEFT and PEFR of the selected energy carriers for calculating the PE demand of the different heating systems. Since the EN 15603 data are relatively old, we have used the data from Eurostat, also shown in Table 3.
Primary energy factor
Non-renewable (Resource)
Total, EN15603
Fuel oil 1,35 1,35
Natural gas 1,36 1,36
Anthracite 1,19 1,19
Electricity Mix UCPTE 3,14 3,31
Table 2: PE factors [5, 8]
One reason that emission data from different sources differ are the use of different system boundaries. It is a problem that the process many times is treated as a black box which makes it difficult for the user to know what sub processes, efficiency values, allocations etc. the data set is based on. In Table 3 below data from three different sources, EN 15603 [5], GEMIS 4.7 [8] and Eurostat are compared. As can be seen the values from GEMIS are in general some percent lower than EN 15603. Especially for electricity there is a big difference between the two data sources. Eurostat is reporting 2,2 as the primary energy factor for electricity in 2011, and have by definition 1 as PE factor for fossil fuels.
EN 15603 GEMIS 4.7 EUROSTAT
Primary energy factor (Total)
Primary energy factor (Total)
Primary energy factor (Total)
Fuel oil 1,35 1,19 1
Natural gas 1,36 1,15 1
Coal 1,19 1,10 1
Electricity Mix (EU) 3,31 2,65 2,2
Table 3: Comparison of PEF from three different data sources
4.1.4 Heat pump systems - SPF The heat pump performance has to be calculated according to the system boundary SPFH1-4 in D4.2 [2] with the measured data collected during the field measurements.
4.1.5 Backup systems - AE The calculation of the performance of the backup heating systems using electricity, gas or solar thermal heating is done with the annual efficiency AE of the different systems (Table 4)
Fuel Efficiency Data source Electric back up 1,00 [7, Table A6] Gas boiler 0,86 [7, Table A6] Solar thermal 40,00 assumption
Table 4: annual efficiency of common systems
PEFSPF
[kWh]energy primary[kWh]energy usablePER ==
nn11 f energy final...f energy finalenergy usable
[kWh]energy primary[kWh]energy usablePER
pp ×++×==
21
1Carnot T-T
TCOP =
Carnot
realCarnot COP
COP=ε
4.1.6 PER – monovalent and monoenergetic systems For systems using only one energy carrier (e.g. electrical energy) for operating the heat pump and an electric backup heater the PER is directly calculated with the evaluated SPF and the PEF of the energy source (Equation 6).
Equation 6
4.1.7 PER – bivalent systems For combined systems (e.g. heat pump and gas boiler) the primary energy of the different systems is calculated based on the final energy of the systems and the PEF of the energy sources. Equation 7 illustrates the calculation of the PER of the whole bivalent system.
Equation 7
4.2 Carnot efficiency The Carnot efficiency is the relation between the efficiency under real conditions and the theoretically maximum reachable efficiency.
4.2.1 Carnot Efficiency for Heat Pump unit The theoretical performance of heat pumps is often referred to the COPCarnot (Equation 9). Together with the measured COPreal, εCarnot is calculated according Equation 9. This parameter enables benchmarking the system and analysing if the heat pump unit is operating properly.
Equation 8
Equation 9
Figure 4 presents the COP for an ideal heat pump as a function of temperature lift, where the temperature of the heat source is 0°C. In addition the range of actual COPs for various types and sizes of real heat pumps at different temperature lifts is shown. The Carnot-efficiency varies from 0.3 to 0.5 for small electric heat pumps and 0.5 to 0.7 for large, very efficient electric heat pump systems.
21
1Carnot T-T
TSPF =
Carnot
C1 / H1SPF-Carnot SPF
SPF=ε
Figure 4: Carnot Efficiency [3]
Modern heat pump units for single family houses should reach the following εCarnot depanding on the heat source:
• outside air εCarnot = 0,40 • ground εCarnot = 0,45 • ground water εCarnot = 0,50
4.2.2 Carnot Efficiency for Heat Pump systems The calculation of the Carnot Efficiency based on SPF (Equation 11) for analysing heat pumps systems has to be slightly adopted as the calculation parameters will change from COP to SPF. For the calculation the average temperatures measured during operation of the unit have to be considered (Equation 10).
Equation 10 T1… average supply temperature heat sink during heat pump operation T2… average supply temperature heat source during heat pump operation
Equation 11
[m²] area /cooledheated[kWh]energy usabledemand heating specific =
As the Carnot Efficiency is defined for the refrigeration cycle, SPFH1/C1 according to SEPEMO Deliverable D4.2 [2] has to be used for calculating εCarnot-SPF (Figure 5).
Figure 5: System boundary SPFH1 and SPFC1 [2]
The advantages of presenting the data of SPFH3/C3 in combination with the Carnot Efficiency are:
showing the quality/efficiency of the heat pump unit during operation using εCarnot-SPF as characteristic factor for showing the performance of the heat pump
unit proving the operating conditions without showing operating temperatures e.g.:
high SPFH3/C3 + average εCarnot-SPF: average heat pump unit efficiency + good system integration
low SPFH3/C3 + average εCarnot-SPF: average heat pump unit efficiency + poor operating conditions for the heat pump
4.3 Specific energy demand The specific energy demand is based on the measured usable energy delivered by the heat pump system to the building, the final energy demand of the heat pump system and heated/cooled building area. Using specific values makes it possible to compare the energy demand of different system independently of the capacity of the system.
4.3.1 Specific heating demand The specific heating demand is calculated with the yearly usable energy delivered from the heating system to the building in relation to the heated / cooled area (Equation 12).
Equation 12
[m²] area /cooledheated[kWh]energy finaldemandenergy electric specific =
[ ][kWh] energy usable energy usable
[kWh] energy usable% DHWRDHWSH
DHW
+=
[ ][kWh] energy usable energy usable
[kWh] energy usable% HPESR
buhp
hp
+=
4.3.2 Specific electric energy demand The specific electric energy demand is calculated with the yearly final energy needed for operating the heating system in relation to the heated / cooled area (Equation 13).
Equation 13
4.4 Domestic hot water ratio The heat pump system operates for domestic hot water (DHW) preparation and space heating mode based on the application and the thermal building quality. Depending on the supply temperature for space heating, the DHW preparation will have an influence on the SPF. Therefore the domestic hot water ratio DHWR is calculated to shows how much of the useable energy is used for DHW production (Equation 14).
Equation 14
4.5 Heat pump energy supply ratio For bivalent heat pump systems the heat pump energy supply ratio HPESR is calculated according to Equation 15, to show how much of the usable energy is supplied by heat pump and the backup heater.
Equation 15
5 Benchmark Example The benchmark example illustrates the different steps needed to get the characteristic figures described in chapter 4 for analysing the heat pump systems including the operating boundary conditions of the system.
5.1 Example calculation – additional system electric backup In the next steps an example calculation of a ground coupled heat pump system using an electric backup heater as additional heating system is done to show how to proceed with the benchmark methodology.
5.1.1 Data from field measurement & metadata Table 5 lists the minimum results needed for benchmarking, based on D4.1 and additionally the metadata concerning the heated / cooled area of the building.
Table 5: Example measurement results
5.1.2 SPF calculation According to deliverable D4.2 the SPF depending on the different system boundaries is calculated based on the measurement results in Table 5.
Q H_hp [kWh] 7500 Q W_hp [kWh] 2500 Q HW_bu [kWh] 1000 E S_fan/pump [kWh] 350 E B_fan/pump [kWh] 300 E HW_hp [kWh] 2200 E HW_bu
[kWh] 1000 Average supply temperature heat sink* °C 37,8 Average return temperature heat sink* °C 33,6 Average supply temperature heat source* °C 7,9 Average return temperature heat source* °C 4,1 Average outdoor temperature* °C 5,2 Average indoor temperature* °C 20,5 heated / cooled area m² 160 *during operation of the unit
5,4_
__1 =
+=
hpHW
hpWhpHH E
QQSPF
9,3_/_
__2 =
+
+=
hpHWpumpfanS
hpWhpHH EE
QQSPF
1,3__/_
___3 =
++
++=
buHWhpHWpumpfanS
buHWhpWhpHH EEE
QQQSPF
7,2/___/_
___4 =
+++
++=
pumpfanBbuHWhpHWpumpfanS
buHWhpWhpHH EEEE
QQQSPF
5.1.3 PER calculation The PER is calculated for the different system boundaries SPFH1-SPFH4 according Equation 7. For calculating the primary energy the PE factors pf in Table 2 are used (e.g.: .f elp− = 3,31).
37,1f[kWh]energy primary
[kWh]energy usablePER._
__1 =
×
+==
−elphpHW
hpWhpHH E
QQ
( ) 18,1f
PER._/_
__2 =
×+
+=
−elphpHWpumpfanS
hpWhpHH EE
QQ
( ) 94,0ff
PER._._/_
___3 =
×+×+
++=
−− elpbuHWelphpHWpumpfanS
buHWhpWhpHH EEE
QQQ
( ) 86,0ff
PER._./__/_
___4 =
×+×++
++=
−− elpbuHWelppumpfanBhpHWpumpfanS
buHWhpWhpHH EEEE
QQQ
However, by using the GEMIS fp-el of 2.65, and Eurostat value of 2,2, different PER’s are achieved. The same pattern of PER decrease when expanding the system boundary can be seen independent of the data source, but important to note is the absolute values that shows for GEMIS and Eurostat that the useful energy supplied by heat pump is larger than the primary energy input.
43,040,1050,4
SPFSPF
Carnot
C1 / H1SPF-Carnot ===ε
40,109,78,37
8,3715,273T-T
TSPF21
1Carnot =
−+
==
=
++==
m²kWh 69
area /cooledheated[m²] area /cooledheated[kWh]energy usabledemand heating specific ___ buHWhpWhpH QQQ
==
+++=
==
m²kWh 24
area /cooledheated
[m²] area /cooledheated[kWh]energy finaldemandenergy electric specific
/___/_ pumpfanBbuHWhpHWpumpfanS EEEE
[ ] [ ]% 32[kWh] energy usable energy usable
[kWh] energy usable% DHWR
___
__
DHWSH
DHW =++
+=
+=
buHWhpWhpH
buHWhpW
QQQQQ
EN 15603 data source GEMIS data source Eurostat data source PERH1 1,37 1,71 2,06 PERH2 1,18 1,47 1,78 PERH3 0,94 1,17 1,41 PERH4 0,86 1,07 1,29
5.1.4 Carnot efficiency calculation εCarnot-SPF is calculated based on the minimum results defined in SEPEMO D4.1 [1] and Equation 10 and Equation 11.
T1… average supply temperature heat sink during heat pump operation T2… average supply temperature heat source during heat pump operation
5.1.5 Specific energy demand calculation The specific energy demands for heating and for operating the system are calculated according to Equation 12 and Equation 13.
5.1.6 DHWR calculation For calculating the DHWR, Equation 14 is used to get information on the ratio of domestic hot water operating mode of the heat pump system.
[ ] [ ]% 91[kWh] energy usable energy usable
[kWh] energy usable% HPESR
___
__
buhp
hp =++
+=
+=
buHWhpWhpH
hpWhpW
QQQQQ
5.1.7 HPESR calculation Equation 15 is used for pointing out the HPESR to show the ratio of heating demand is covered by the heat pump system without additional heating system.
5.2 Summary Example – electric backup Table 6 sums up the calculated characteristic figures using the benchmark methodology. The electric backup heater has a big influence on the efficiency of the system as SPFH2 to SPFH3 decreases for 21 % and also the PERH3 goes down to 0.94. The Carnot Efficiency εCarnot-SPF of 0.43 means that the heat pump unit is operating properly, but the system integration could be improved due to a SPFH3 of 3.1, which should be higher for ground coupled heat pump systems. Together with Table 5 the results show that the operating conditions are fine, but that the performance could be improved by a reduced back up heater operation as the HPESR ends up at 91%.
- 0,94 PERH4 - 0,86 εCarnot-SPF - 0,43 specific heating demand kWh/m² 69 specific electric energy demand kWh/m² 24 DHWR % 32 HPESR % 91
5.1 Comparison SPF / PER with different additional systems Further to the example calculation the sensitivity of the PER depending on the used energy carrier is analysed based on 3 different additional heating systems (electric, gas and solar thermal). For calculating the SPF and PER the methodology and factors described in chapter 4 together with the example results in Table 5 are used. Table 7 lists the energy in- and output of the system for calculating SPF and PER for different system boundaries.
Table 7: Energy in- and output of the system for different additional heating systems
Depending on the efficiency of the additional heating systems the SPFH3 and SPFH4 are increasing or decreasing (Table 8). The additional solar thermal system offers a big increase of the SPF, due to low electric energy demand for using solar thermal energy.
Table 8: SPF for different additional heating systems
additional electric heating
additional gas heating
additional solar heating
Q H_hp [kWh] 7500 7500 7500 Q W_hp [kWh] 2500 2500 2500 Q HW_bu [kWh] 1000 1000 1000 E S_fan/pump [kWh] 350 350 350 E B_fan/pump [kWh] 300 300 300 E HW_hp [kWh] 2200 2200 2200 E HW_bu
[kWh] 1000 1176** 25***
* efficiency gas boiler 85 % ** measured fuel demand 121 m³ gas, calorific heat of gas 9,7 kWh/m³
*** electric energy demand of the circulating pump in the solar system
Table 9 shows the results of calculating the PER for different additional heating systems depending on the defined system boundaries. The PER is directly influenced by the efficiency of the additional heating system and the PE factors pf of the energy carrier in Table 2. Therefore the PERH3 of an
additional heating using gas is higher (better) than a system using electric energy, as pf for electric energy according to EN15603 is 3 times higher than for gas (Table 2). By using the corresponding values according to GEMIS, additional heating proves better than gas backup. This example shows that there is need for a trustworthy value of the pf values, and that they properly account for the increasing share of RES electricity generation in Europe. additional electric
Table 9: PER for different additional heating systems
6 Literature
1. “Guideline for heat pump field measurements for hydronic heating systems The guideline contains information on what to measure in order to calculate SPF and about the required measurement quality”, Andreas Zottl, Roger Nordman, Michel Coevoet, Philippe Riviere, Marek Miara, Anastasia Benou, Peter Riederer, Kajsa Andersson, Markus Lindahl, Deliverable D4.1. / D2.3 in the Project IEE SEPEMO-Build, 2011
2. Concept for evaluation of SPF - Version 2.1 A defined methodology for calculation of the
seasonal performance factor and a definition which devices of the system have to be included in this calculation. Heat pumps with hydronic heating systems”, Andreas Zottl, Roger Nordman, Michel Coevoet, Philippe Riviere, Marek Miara, Anastasia Benou, Peter Riederer, Deliverable D4.2. / D2.4 in the Project IEE SEPEMO-Build, 2010
4. “PERFORMANCE EVALUATION OF AN AIR-TO-AIR HEAT PUMP COUPLED WITH TEMPERATE AIR-SOURCES INTEGRATED INTO A DWELLING”, Bruno Filliard, Alain Guiavarch, and Bruno Peuportier, Eleventh International IBPSA Conference, Glasgow, Scotland, July 27-30, 2009
5. EN 15603, 2008: Energy performance of buildings ― Overall energy use and definition of
energy ratings, 2008
6. “Evaluation method for comparison of heat pump systems with conventional heating systems - Concept for evaluation of CO2-reduction potential”, Andreas Zottl, Markus Lindahl, Roger Nordman, Philippe Rivière, Marek Miara, 2011, Deliverable D4.3 in the Project IEE SEPEMO-Build, 2010
