Comparison of Calculation Methods of Renewable Energy Generated by Electric Heat Pumps

Heat pumps are widely used in buildings due to high energy performance and environmental-friendliness. 2010/31/EU Directive of the European Parliament and Council requires assessing the consumption of primary energy generated from renewable sources when calculating the energy performance of buildings. However, the equation given in the 2009/28/EU Directive and guidelines 2013/114/EU of the European Commission does not take into account the amount of energy supplied by electric heat pumps into buildings. The paper presents the method that does not assess the energy input of primary sources for transforming electric power and for this reason, the calculations result in a lesser amount of energy than the ones obtained by the method of 2013/114/EU Directive. The calculation results proved that using merely heat pumps in nearly zero-energy buildings will not ensure the necessary amount of energy from renewable primary energy sources. Hence, to ensure the lacking amount of energy other renewable energy sources, such as solar panels, wind power plants, hydro power plants, biofuel, etc. are necessary to use.


Introduction
and drying, as well as cooling, drying and heating by comparing the potential of such hybrid systems in saving primary energy with a traditional air heat pump system (Gea et al. 2011).Balta assess the exergetic energy released in the building from a primary energy source, which is the method applied in the premises heated by a geothermal heat pump (Balta et al. 2008).Moreover, Huchtemann compares highly efficient condensing boilers to heat pumps, assess the efficiency of various types of fuel used, and the factors of primary energy and CO 2 emission conversion (Huchtemann et al. 2012).
Similarly, by comparing two systems for heating water, namely a heat pump combined with water heating solar panels, and a gas boiler, Tagliafico estimates the possibility to save primary energy.The research has been performed on pools, but most of the criteria and results of the analysis are valid for buildings in need of hot water as well (Tagliafico et al. 2012).Further, Tagliafico also examines a heat pump combined with solar panels and used for heating a variety of water types (Tagliafico et al. 2014).Zhaon analyses heating and cooling systems including a heat pump with a gas-driven engine, and propose using residual heat from the engine to reach higher primary energy coefficients (Zhaon et al. 2011).Lee compares two types of heat pumps (fed on electricity and gas) (Lee et al. 2012).Teng assess the influence of gas turbine capacity of an absorption heat pump and the strategy of its use on the consumption of primary energy in a building (Teng et al. 2014).
A new method of assessment is presented by Zhang who analyses the seasonal primary energy indicator of a gas-driven heat pump of a water heater (Zhang et al. 2014).Elgendy analyses the characteristics of a gas-driven heat pump with an integrated heat recovery/regeneration subsystem, focusing on the temperature of outflowing water, heating capacity and primary energy coefficients (Elgendy et al. 2014).
In regard to the primary energy efficiency criterion, Wu compare an electric soil heat pump with absorption soil heat pump, and estimate the influence of thermal imbalance of soil on energy efficiency indicators.In their further research (Wu et al. 2013), Wu analyses a combined heating/cooling/hot water preparation system with a geothermal absorption heat pump used in cold climate zones.During the simulation, the imbalance of soil has been diminished and a part of recovered condensation/absorption heat used to produce hot water by a heat pump.Thus, such a combined system improves the efficiency of primary energy consumption (Wu et al. 2014).
The possibility of using heat compensation equipment with a thermo siphon in case of heating buildings by soil heat pumps in cold climate zones is discussed by You who claims that longterm exploitation of a heat pump reduces its efficiency due to soil cooling down (You et. al. 2014).Havelsky uses primary energy indicators to analyse cogeneration system connected to heat pumps (Havelsky 1999).Hebenstreit looks at the operating input, primary energy consumption efficiency, and greenhouse gas emission to study the possibility of using a heat pump in an active condensation system by regenerating heat from biomass-driven boilers (Hebenstreit et. al. 2014).Yang considers potential and efficiency of a heat pump in ventilating and heating a greenhouse by the use of redundant thermal air energy formed therein (Yang et al. 2013).A hybrid heating system composed of a sewage thermal energy-driven heat pump and a gas boiler is analyzed by Li who examine its optimal operation strategy in order to reduce annual energy need (Li et al. 2013).
Bayera assess the pumps in respect of the reduction of CO 2 emission (Bayera et al. 2012).They presuppose that electric power generation, becoming more ecological in the future, will lead to the increased efficiency of the pumps.Having compared various types of heat pumps and their operational principles, Sarbu states that better heat pump efficiency indicators are reached by combining heating and cooling as well as increasing the amount of renewable energy in the total of electric power used (Sarbu et al. 2014).The comparison of a heat pump to a gas boiler is presented by Cabrol taking into account CO 2 emission (Cabrol et al. 2012).They claim that increasing the mass of the building or installing additional heat insulation enables reaching an acceptable thermal comfort level during the heating season even if the air heat pump is not operating at maximum capacity.Rosiek estimates the amounts of primary energy consumption and CO 2 emission by comparing different building cooling; heating and electric power generation systems based on the combination of renewable energy sources with traditional systems (Rosiek et al. 2013).
The presented work analyzed existing and developing systems and methodologies of consumed and generated energy by heat pumps.The objectives are to propose the methodology evaluating renewable energy generated by electric heat pump while considering factors such as the primary renewable and non-renewable energy, efficiency of heat pumps, the proportion of primary renewable energy in a building's overall energy consumption.
The efficiency of traditional heat sources (gas, solid fuel, electric boilers, etc.) is defined by the useful efficiency coefficient η H.eq , the value of which shows the ratio of the amount of thermal energy produced by a heat source to the amount of thermal energy present in the energy source (gas, solid fuel, electricity, etc.) used to produce heat.Thus, the dimension of the coefficient stands as "the amount of thermal energy/ "the amount of thermal energy".
The efficiency of an electric heat pump is assessed by a seasonal performance factor η SPF that defines the ratio of the amount of thermal energy produced by a heat pump to the amount of electricity used by the pump to produce that energy.η SPF dimension can be expressed as "the amount of thermal energy"/ "the amount of electricity".The η SPF value of a heat pump is estimated by testing in accordance with the LST EN 15450:2008(2008) Standard.If the value of useful efficiency of electricity generation η el is known (i.e. the ratio between the generated amount of electric power and the amount of energy in the energy sources used to produce that energy), the value of electric heat pump coefficient η H.eq can be estimated as follows:

Research problem definition
(1) The efficiency of an electric heat pump is assessed by a seasonal performance factor ηSPF that defines the ratio of the amount of thermal energy produced by a heat pump to the amount of electricity used by the pump to produce that energy.ηSPF dimension can be expressed as "the amount of thermal energy"/ "the amount of electricity".The ηSPF value of a heat pump is estimated by testing in accordance with the LST EN 15450:2008(2008) Standard.If the value of useful efficiency of electricity generation ηel is known (i.e. the ratio between the generated amount of electric power and the amount of energy in the energy sources used to produce that energy), the value of electric heat pump coefficient ηH.eq can be estimated as follows: If (1-ηH.eq)>0, the value of (1-ηH.eq)indicates the amount of thermal energy present in the energy source (gas, solid fuel, etc.) that was not converted into thermal energy by that source.
(1-ηH.eq)<0 suggests that more thermal energy was produced while transforming the energy of a source into thermal energy than the amount of energy initially held by the energy source.In such a case, a part of energy is generated from renewable energy rather than the thermal energy initially present in the source.As follows, the value of (ηH.eq-1) defines the part of thermal energy that may be ascribed to the thermal energy generated from renewable sources and initially present in the traditional source (gas, solid fuel, etc.).
The guidelines of the European Commission 2013/114/EU, specifying the requirement of the EU Directive 2009/28/EU to calculate the part of renewable energy generated using different technology-based heat pumps, provides a statistical method with the following equation: (2) here: Eusable, the amount of energy suitable for use and supplied by heat pumps is estimated by equation (3): (3) here: HHP -the equivalent amount of hours of a heat pump operating at full load (h); Prated -capacity of a heat pump of the respective type (kWh).
To perform statistical calculations the HHP values have to be estimated in accordance with the data given in the guidelines 2013/114/EU of the European Commission that are linked to the climate conditions of the respective EU member state.Thus, depending on the climate conditions and the type of a heat pump, fixed HHP values unrelated to the energy needs of a building were determined If (1-η H.eq )>0, the value of (1-η H . eq ) indicates the amount of thermal energy present in the energy source (gas, solid fuel, etc.) that was not converted into thermal energy by that source.
(1-η H . eq )<0 suggests that more thermal energy was produced while transforming the energy of a source into thermal energy than the amount of energy initially held by the energy source.In such a case, a part of energy is generated from renewable energy rather than the thermal energy initially present in the source.As follows, the value of (η H.eq-1 ) defines the part of thermal energy that may be ascribed to the thermal energy generated from renewable sources and initially present in the traditional source (gas, solid fuel, etc.).
The guidelines of the European Commission 2013/114/EU, specifying the requirement of the EU Directive 2009/28/EU to calculate the part of renewable energy generated using different technology-based heat pumps, provides a statistical method with the following equation: here: E usable , the amount of energy suitable for use and supplied by heat pumps is estimated by equation ( 3): (2) The efficiency of an electric heat pump is assessed by a seasonal performance factor ηSPF that defines the ratio of the amount of thermal energy produced by a heat pump to the amount of electricity used by the pump to produce that energy.ηSPF dimension can be expressed as "the amount of thermal energy"/ "the amount of electricity".The ηSPF value of a heat pump is estimated by testing in accordance with the LST EN 15450:2008(2008) Standard.If the value of useful efficiency of electricity generation ηel is known (i.e. the ratio between the generated amount of electric power and the amount of energy in the energy sources used to produce that energy), the value of electric heat pump coefficient ηH.eq can be estimated as follows: If (1-ηH.eq)>0, the value of (1-ηH.eq)indicates the amount of thermal energy present in the energy source (gas, solid fuel, etc.) that was not converted into thermal energy by that source.
(1-ηH.eq)<0 suggests that more thermal energy was produced while transforming the energy of a source into thermal energy than the amount of energy initially held by the energy source.In such a case, a part of energy is generated from renewable energy rather than the thermal energy initially present in the source.As follows, the value of (ηH.eq-1) defines the part of thermal energy that may be ascribed to the thermal energy generated from renewable sources and initially present in the traditional source (gas, solid fuel, etc.).
The guidelines of the European Commission 2013/114/EU, specifying the requirement of the EU Directive 2009/28/EU to calculate the part of renewable energy generated using different technology-based heat pumps, provides a statistical method with the following equation: (2) here: Eusable, the amount of energy suitable for use and supplied by heat pumps is estimated by equation (3): (3) here: HHP -the equivalent amount of hours of a heat pump operating at full load (h); Prated -capacity of a heat pump of the respective type (kWh).
To perform statistical calculations the HHP values have to be estimated in accordance with the data given in the guidelines 2013/114/EU of the European Commission that are linked to the climate conditions of the respective EU member state.Thus, depending on the climate conditions and the type of a heat pump, fixed HHP values unrelated to the energy needs of a building were determined here: H HP -the equivalent amount of hours of a heat pump operating at full load (h); P rated -capacity of a heat pump of the respective type (kWh). (3) The efficiency of an electric heat pump is assessed by a seasonal performance factor ηSPF that defines the ratio of the amount of thermal energy produced by a heat pump to the amount of electricity used by the pump to produce that energy.ηSPF dimension can be expressed as "the amount of thermal energy"/ "the amount of electricity".The ηSPF value of a heat pump is estimated by testing in accordance with the LST EN 15450:2008(2008) Standard.If the value of useful efficiency of electricity generation ηel is known (i.e. the ratio between the generated amount of electric power and the amount of energy in the energy sources used to produce that energy), the value of electric heat pump coefficient ηH.eq can be estimated as follows: If (1-ηH.eq)>0, the value of (1-ηH.eq)indicates the amount of thermal energy present in the energy source (gas, solid fuel, etc.) that was not converted into thermal energy by that source.
(1-ηH.eq)<0 suggests that more thermal energy was produced while transforming the energy of a source into thermal energy than the amount of energy initially held by the energy source.In such a case, a part of energy is generated from renewable energy rather than the thermal energy initially present in the source.As follows, the value of (ηH.eq-1) defines the part of thermal energy that may be ascribed to the thermal energy generated from renewable sources and initially present in the traditional source (gas, solid fuel, etc.).
The guidelines of the European Commission 2013/114/EU, specifying the requirement of the EU Directive 2009/28/EU to calculate the part of renewable energy generated using different technology-based heat pumps, provides a statistical method with the following equation: (2) here: Eusable, the amount of energy suitable for use and supplied by heat pumps is estimated by equation (3): (3) here: HHP -the equivalent amount of hours of a heat pump operating at full load (h); Prated -capacity of a heat pump of the respective type (kWh).
To perform statistical calculations the HHP values have to be estimated in accordance with the data given in the guidelines 2013/114/EU of the European Commission that are linked to the climate conditions of the respective EU member state.Thus, depending on the climate conditions and the type of a heat pump, fixed HHP values unrelated to the energy needs of a building were determined in the corresponding climate zones.The 2010/31/EU Directive requires estimating the energy performance of buildings in regard to the primary energy input, whereas equation ( 2

), given in
To perform statistical calculations the H HP values have to be estimated in accordance with the data given in the guidelines 2013/114/EU of the European Commission that are linked to the climate conditions of the respective EU member state.Thus, depending on the climate conditions and the type of a heat pump, fixed H HP values unrelated to the energy needs of a building were determined in the corresponding climate zones.The 2010/31/EU Directive requires estimating the energy performance of buildings in regard to the primary energy input, whereas equation ( 2), given in 2013/114/EU, enables estimating "the part of renewable energy generated by heat pumps" that is related neither to the requirements of the 2010/31/EU Directive nor the LST EN 15450:2008 Standard.Equation (3) cannot be applied for calculating primary energy since the physical meaning of its multiplier is as follows: In equation ( 4), thermal and electric power cannot be taken as the same, because the latter is generated from the energy of a primary energy source (gas, oil, solid fuel, etc.).Yet, electricity in not a primary energy source that is used in heat pumps to produce thermal energy.To generate electric power the EU member states use less than a half of energy available in primary energy sources.
According to the data provided in the guidelines 2013/114/EU of the European Commission, the average value of useful efficiency of electricity generation η el makes up 0.455 in the EU member states.Consequently, if thermal and electric power were handled identically, then the impact of energy from renewable sources used in heat pumps on the calculation of the amount of energy generated from renewable sources would be reduced by 2.2 times (1/0.455=2.2) in equation ( 4).
In that case, the calculation using equation (1) would result in an increased amount of thermal energy produced from renewable sources than it should actually be. (4) Prated -capacity of a heat pump of the respective type (kWh).
To perform statistical calculations the HHP values have to be estimated in accordance with the dat given in the guidelines 2013/114/EU of the European Commission that are linked to the clima conditions of the respective EU member state.Thus, depending on the climate conditions and th type of a heat pump, fixed HHP values unrelated to the energy needs of a building were determine in the corresponding climate zones.The 2010/31/EU Directive requires estimating the energ performance of buildings in regard to the primary energy input, whereas equation ( 2 To calculate the amount of renewable and non-renewable energy supplied to a building by electric heat pumps, the following energy balance condition was composed: "the total amount of thermal energy supplied to the building systems" = "the amount of thermal energy generated using electric power and supplied to the building systems" + "the amount of thermal energy generated using renewable energy sources and supplied to the building systems".

The condition may be put into an equation as follows:
Solution to the problem In equation ( 4), thermal and electric power cannot be taken as the same, because the latter is generated from the energy of a primary energy source (gas, oil, solid fuel, etc.).Yet, electricity in not a primary energy source that is used in heat pumps to produce thermal energy.To generate electric power the EU member states use less than a half of energy available in primary energy sources.According to the data provided in the guidelines 2013/114/EU of the European Commission, the average value of useful efficiency of electricity generation ηel makes up 0.455 in the EU member states.Consequently, if thermal and electric power were handled identically, then the impact of energy from renewable sources used in heat pumps on the calculation of the amount of energy generated from renewable sources would be reduced by 2.2 times (1/0.455=2.2) in equation ( 4).In that case, the calculation using equation (1) would result in an increased amount of thermal energy produced from renewable sources than it should actually be.

Solution to the problem
To calculate the amount of renewable and non-renewable energy supplied to a building by electric heat pumps, the following energy balance condition was composed: "the total amount of thermal energy supplied to the building systems" = "the amount of thermal energy generated using electric power and supplied to the building systems" + "the amount of thermal energy generated using renewable energy sources and supplied to the building systems".The condition may be put into an equation as follows: Hence, the amount of thermal energy from renewable energy sources used in a building may be estimated in such a manner: Similarly, the energy supplied to a building from electric heat pumps is expressed as in equation ( 7): 1 presents the comparison of the calculations performed using equations ( 2) and ( 7).The analysis discusses the calculation results of thermal energy produced using renewable sources in electric heat pumps per one kWh of thermal energy supplied by the pumps to the building systems.Hence, the amount of thermal energy from renewable energy sources used in a building may be estimated in such a manner: In equation ( 4), thermal and electric power cannot be taken as the same, because the latter is generated from the energy of a primary energy source (gas, oil, solid fuel, etc.).Yet, electricity in not a primary energy source that is used in heat pumps to produce thermal energy.To generate electric power the EU member states use less than a half of energy available in primary energy sources.According to the data provided in the guidelines 2013/114/EU of the European Commission, the average value of useful efficiency of electricity generation ηel makes up 0.455 in the EU member states.Consequently, if thermal and electric power were handled identically, then the impact of energy from renewable sources used in heat pumps on the calculation of the amount of energy generated from renewable sources would be reduced by 2.2 times (1/0.455=2.2) in equation ( 4).In that case, the calculation using equation (1) would result in an increased amount of thermal energy produced from renewable sources than it should actually be.

Solution to the problem
To calculate the amount of renewable and non-renewable energy supplied to a building by electric heat pumps, the following energy balance condition was composed: "the total amount of thermal energy supplied to the building systems" = "the amount of thermal energy generated using electric power and supplied to the building systems" + "the amount of thermal energy generated using renewable energy sources and supplied to the building systems".The condition may be put into an equation as follows: Hence, the amount of thermal energy from renewable energy sources used in a building may be estimated in such a manner: Similarly, the energy supplied to a building from electric heat pumps is expressed as in equation ( 7): Table 1 presents the comparison of the calculations performed using equations ( 2) and ( 7).The analysis discusses the calculation results of thermal energy produced using renewable sources in electric heat pumps per one kWh of thermal energy supplied by the pumps to the building systems.
Similarly, the energy supplied to a building from electric heat pumps is expressed as in equation ( 7): In equation ( 4), thermal and electric power cannot be taken as the same, because the latter is generated from the energy of a primary energy source (gas, oil, solid fuel, etc.).Yet, electricity in not a primary energy source that is used in heat pumps to produce thermal energy.To generate electric power the EU member states use less than a half of energy available in primary energy sources.According to the data provided in the guidelines 2013/114/EU of the European Commission, the average value of useful efficiency of electricity generation ηel makes up 0.455 in the EU member states.Consequently, if thermal and electric power were handled identically, then the impact of energy from renewable sources used in heat pumps on the calculation of the amount of energy generated from renewable sources would be reduced by 2.2 times (1/0.455=2.2) in equation ( 4).In that case, the calculation using equation (1) would result in an increased amount of thermal energy produced from renewable sources than it should actually be.

Solution to the problem
To calculate the amount of renewable and non-renewable energy supplied to a building by electric heat pumps, the following energy balance condition was composed: "the total amount of thermal energy supplied to the building systems" = "the amount of thermal energy generated using electric power and supplied to the building systems" + "the amount of thermal energy generated using renewable energy sources and supplied to the building systems".The condition may be put into an equation as follows: Hence, the amount of thermal energy from renewable energy sources used in a building may be estimated in such a manner: Similarly, the energy supplied to a building from electric heat pumps is expressed as in equation ( 7): Table 1 presents the comparison of the calculations performed using equations ( 2) and ( 7).The analysis discusses the calculation results of thermal energy produced using renewable sources in electric heat pumps per one kWh of thermal energy supplied by the pumps to the building systems.
Table 1 presents the comparison of the calculations performed using equations ( 2) and ( 7).The analysis discusses the calculation results of thermal energy produced using renewable sources in electric heat pumps per one kWh of thermal energy supplied by the pumps to the building systems.
The amount of thermal energy from renewable sources used in buildings obtained following equation ( 1) is from 1.43 to 4.96 times higher (Table 1, column 5) than that obtained by equation ( 7).This is because equation (1) does not take into account the thermal energy of energy sources used to generate electricity.If the thermal energy used by energy sources to generate electric power is not estimated, the value of the ratio between "renewable/non-renewable thermal energy" achieved using low-efficiency heat pumps (η SPF =2.5) is 1.5, and when η SPF =5, the value makes up as much as 4.0 (Table 1, column 9).Analogous calculation by equation ( 7) demonstrates that the value of the ratio "renewable/non-renewable thermal energy" makes up as little as from 0.138 to 1.275 (Table 1, column 8).
The calculation of renewable/non-renewable primary energy of electric heat pumps is related to the values of primary energy factors from electric power.The estimation of these values takes into account the amount of renewable/non-renewable primary energy used by all energy sources to generate electricity, renewable/non-renewable primary energy input for energy transportation, and primary energy losses in electricity networks.In this case, the values of primary energy factors cover not only energy sources, but also the value of useful efficiency of electricity generation η el and the losses in electricity transportation.The Lithuanian normative documents in construction assume that for the calculation of electric power input in buildings electric power supplied from electricity networks is f PRr =0 and f PRn =2.8.
The amount of non-renewable primary energy supplied to the building systems by heat pumps used therein to generate thermal energy from electric power may be estimated as follows: (8) pumps (ηSPF =2.5) is 1.5, and when ηSPF =5, the value makes up as much as 4.0 (Table 1, column 9).Analogous calculation by equation ( 7) demonstrates that the value of the ratio "renewable/nonrenewable thermal energy" makes up as little as from 0.138 to 1.275 (Table 1, column 8).
The calculation of renewable/non-renewable primary energy of electric heat pumps is related to the values of primary energy factors from electric power.The estimation of these values takes into account the amount of renewable/non-renewable primary energy used by all energy sources to generate electricity, renewable/non-renewable primary energy input for energy transportation, and primary energy losses in electricity networks.In this case, the values of primary energy factors cover not only energy sources, but also the value of useful efficiency of electricity generation ηel and the losses in electricity transportation.The Lithuanian normative documents in construction assume that for the calculation of electric power input in buildings electric power supplied from electricity networks is fPRr =0 and fPRn =2.8.
The amount of non-renewable primary energy supplied to the building systems by heat pumps used therein to generate thermal energy from electric power may be estimated as follows: here: EElectricity_total -total amount of electricity, consumed by heat pumps.
tems, includes the renewable primary energy of electric power consumed in the pumps and the energy of renewable sources, calculated by equation ( 7).This amount may be estimated as follows: Table 2 Primary energy supplied from electric heat pumps calculated according to equations ( 10) and ( 11) here: E Electricity_total -total amount of electricity, consumed by heat pumps.
E Electricity from ren source (HYDRO, PV, WIND) -amount of electricity from renewable sources (hydro, PV, wind).
The amount of renewable primary energy, supplied by electric heat pumps to the building sys- (11 electricity networks is fPRr =0 and fPRn =2.8.
The amount of non-renewable primary energy supplied to the building systems by heat pump therein to generate thermal energy from electric power may be estimated as follows:

(
The amount of renewable primary energy, supplied by electric heat pumps to the building sy includes the renewable primary energy of electric power consumed in the pumps and the ene renewable sources, calculated by equation ( 7).This amount may be estimated as follows: ( here: fel.PRn -non-renewable primary energy factors from electric power (unit), which is ac here as fel.PRn =2.8 in calculating; fel.PRr -renewable primary energy factors from electric power (unit).In the present calculatio accepted that fel.PRr =0, but renewable energy sources may also be used for generating electrici for this reason, fel.PRr may be >0.For example, if electricity from hydro power plants is used fel.PRr =1, fel.PRn =0.5.Electricity from PV power plant is used, then fel.PRr =1, fel.PRn =0.7; elec from wind power plant is used, then fel.PRr =1, fel.PRn =0.3; fHP.PRr -renewable primary energy factors from heat pumps (unit).According to the determined by the LST EN 15450:2008 Standard, renewable primary energy fHP.PRr =1.
Table 2 provides the calculation results of primary energy per one kWh to the amount of th energy supplied by heat pumps to the building systems; i.e. when Eusable=1 kWh, accord equations ( 10) and ( 11).generate electricity, renewable/non-renewable primary energy input for energy transportation, and primary energy losses in electricity networks.In this case, the values of primary energy factors cover not only energy sources, but also the value of useful efficiency of electricity generation ηel and the losses in electricity transportation.The Lithuanian normative documents in construction assume that for the calculation of electric power input in buildings electric power supplied from electricity networks is fPRr =0 and fPRn =2.8.
The amount of non-renewable primary energy supplied to the building systems by heat pumps used therein to generate thermal energy from electric power may be estimated as follows: here: EElectricity_total -total amount of electricity, consumed by heat pumps.EElectricity from ren source (HYDRO, PV, WIND) -amount of electricity from renewable sources (hydro, PV, wind).
The amount of renewable primary energy, supplied by electric heat pumps to the building systems, includes the renewable primary energy of electric power consumed in the pumps and the energy of renewable sources, calculated by equation ( 7).This amount may be estimated as follows: (11) here: fel.PRn -non-renewable primary energy factors from electric power (unit), which is accepted here as fel.PRn =2.8 in calculating; fel.PRr -renewable primary energy factors from electric power (unit).In the present calculations it is accepted that fel.PRr =0, but renewable energy sources may also be used for generating electricity and for this reason, fel.PRr may be >0.For example, if electricity from hydro power plants is used, then fel.PRr =1, fel.PRn =0.5.Electricity from PV power plant is used, then fel.PRr =1, fel.PRn =0.7; electricity from wind power plant is used, then fel.PRr =1, fel.PRn =0.3; fHP.PRr -renewable primary energy factors from heat pumps (unit).According to the order determined by the LST EN 15450:2008 Standard, renewable primary energy fHP.PRr =1.
Table 2 provides the calculation results of primary energy per one kWh to the amount of thermal energy supplied by heat pumps to the building systems; i.e. when Eusable=1 kWh, according to equations ( 10) and ( 11).Table 2.Primary energy supplied from electric heat pumps calculated according to equations ( 10) and ( 11 here: f el.PRn -non-renewable primary energy factors from electric power (unit), which is accepted here as f el.PRn =2.8 in calculating; f el.PRr -renewable primary energy factors from electric power (unit).In the present calculations it is accepted that f el.PRr =0, but renewable energy sources may also be used for generating electricity and for this reason, f el.PRr may be >0.For example, if electricity from hydro power plants is used, then f el.PRr =1, f el.PRn =0.5.Electricity from PV power plant is used, then f el.PRr =1, f el.PRn =0.7; electricity from wind power plant is used, then f el.PRr =1, f el.PRn =0.3; f HP.PRr -renewable primary energy factors from heat pumps (unit).According to the order determined by the LST EN 15450:2008 Standard, renewable primary energy f HP.PRr =1.
Table 2 provides the calculation results of primary energy per one kWh to the amount of thermal energy supplied by heat pumps to the building systems; i.e. when E usable =1 kWh, according to equations ( 10) and ( 11).
The calculations show that when f el.PRn =2.8, f el.PRr =0 and η el =0.455, the ratio of renewable and non-renewable energy supplied by electric heat pumps to a building E PRr /E PRn =1 can only be achieved when heat pumps η SPF ≥5 (Table 2, line 5).
The calculation of renewable and non-renewable energy ratio by equation ( 2 cover not only energy sources, but also the value of useful efficiency of electricity generation ηe and the losses in electricity transportation.The Lithuanian normative documents in construction assume that for the calculation of electric power input in buildings electric power supplied from electricity networks is fPRr =0 and fPRn =2.8.
The amount of non-renewable primary energy supplied to the building systems by heat pumps used therein to generate thermal energy from electric power may be estimated as follows: here: EElectricity_total -total amount of electricity, consumed by heat pumps.EElectricity from ren source (HYDRO, PV, WIND) -amount of electricity from renewable sources (hydro, PV wind).
The amount of renewable primary energy, supplied by electric heat pumps to the building systems includes the renewable primary energy of electric power consumed in the pumps and the energy of renewable sources, calculated by equation ( 7).This amount may be estimated as follows: (11) here: fel.PRn -non-renewable primary energy factors from electric power (unit), which is accepted here as fel.PRn =2.8 in calculating; fel.PRr -renewable primary energy factors from electric power (unit).In the present calculations it is accepted that fel.PRr =0, but renewable energy sources may also be used for generating electricity and for this reason, fel.PRr may be >0.For example, if electricity from hydro power plants is used, then fel.PRr =1, fel.PRn =0.5.Electricity from PV power plant is used, then fel.PRr =1, fel.PRn =0.7; electricity from wind power plant is used, then fel.PRr =1, fel.PRn =0.3; fHP.PRr -renewable primary energy factors from heat pumps (unit).According to the order determined by the LST EN 15450:2008 Standard, renewable primary energy fHP.PRr =1.
Table 2 provides the calculation results of primary energy per one kWh to the amount of therma energy supplied by heat pumps to the building systems; i.e. when Eusable=1 kWh, according to equations ( 10) and (11).Table 2.Primary energy supplied from electric heat pumps calculated according to equations ( 10) and ( 11    Such a striking distinction in the calculation results obtained by equations ( 2) and ( 7) poses a question on the difference between the assessments of renewable energy generated by a heat pump for heating a building according to 2013/114/EU Directive and the method proposed in this paper.
For the present analysis, a low thermal capacity single-flat building with 100 m² of heated area satisfying the requirements of B energy performance label (according to STR 2.01.09:2012) was selected; the building has the following parameters: _ energy input for heating: 383•A p -0,22 =383•100 -0,22 = 139 kWh/m² annually; _ soil-water heat pump with η SPF =3.5; _ average temperature of premises during heating season: 20 ºC; _ average outdoor temperature during heating season: 0.6 ºC' _ duration of heating season: 220 days.
To generate (139 kWh/m²)*(100 m²)=13900 kWh of energy annually a 7 kW capacity heat source should be in operation at full capacity and optimal performance for (13900 kWh)/(7 kW)=1986 h.However, the heat pump does not operate at full capacity during the whole operational period, which is why the actual operational period becomes longer.In Table 1, the 2013/114/EU method provides for 1.25 times higher heat pump operational cost for cold climate zones making up 2470 h in total.Therefore, according to this method, the amount of renewable energy generated by the heat pump annually is as follows: (12) ηEER target value of 2.8 are usually used, whereas soil pumps with ηEER target value of 3.8, an water pumps with ηEER target value of 4.3 are rarely used for the same purpose.In this case, th ratio EPRr/EPRn=1 can be achieved by using the pumps of considerably higher ηEER values.
Such a striking distinction in the calculation results obtained by equations ( 2) and ( 7) poses question on the difference between the assessments of renewable energy generated by a heat pum for heating a building according to 2013/114/EU Directive and the method proposed in this paper.
For the present analysis, a low thermal capacity single-flat building with 100 m² of heated are satisfying the requirements of B energy performance label (according to STR 2.01.09:2012) wa selected; the building has the following parameters: -energy input for heating: 383•Ap -0,22 =383•100 -0,22 = 139 kWh/m² annually; -soil-water heat pump with ηSPF =3.5; -average temperature of premises during heating season: 20 ºC; -average outdoor temperature during heating season: 0.6 ºC' -duration of heating season: 220 days.
To generate (139 kWh/m²)*(100 m²)=13900 kWh of energy annually a 7 kW capacity heat sourc should be in operation at full capacity and optimal performance for (13900 kWh)/(7 kW)=1986 h However, the heat pump does not operate at full capacity during the whole operational period which is why the actual operational period becomes longer.In Table 1, the 2013/114/EU metho provides for 1.25 times higher heat pump operational cost for cold climate zones making up 2470 in total.Therefore, according to this method, the amount of renewable energy generated by the hea pump annually is as follows: According to equation ( 7), if the heat pump supplied 17290 kWh of thermal energy annually, th following results of renewable energy calculation would be obtained: The results of the analysis showed that the 2013/114/EU method for renewable energy calculatio does not take into account the primary energy input for transforming electric power.Therefore, th calculated amount of renewable energy generated by heat pumps is higher than it should be.

Conclusions
All renewable energy sources contain some non-renewable energy and for this reason, th requirement of the 2010/31/EU Directive, stating that more than a half of the amount of energy use by nearly zero-energy buildings should come from renewable energy sources, can only be related t the amounts of renewable and non-renewable primary energy used in the buildings, rather tha According to equation ( 7), if the heat pump supplied 17290 kWh of thermal energy annually, the following results of renewable energy calculation would be obtained: ηEER target value of 2.8 are usually used, whereas soil pumps with ηEER target value of 3.8, an water pumps with ηEER target value of 4.3 are rarely used for the same purpose.In this case, th ratio EPRr/EPRn=1 can be achieved by using the pumps of considerably higher ηEER values.Such a striking distinction in the calculation results obtained by equations ( 2) and ( 7) poses question on the difference between the assessments of renewable energy generated by a heat pum for heating a building according to 2013/114/EU Directive and the method proposed in this paper.
For the present analysis, a low thermal capacity single-flat building with 100 m² of heated are satisfying the requirements of B energy performance label (according to STR 2.01.09:2012) wa selected; the building has the following parameters: -energy input for heating: 383•Ap -0,22 =383•100 -0,22 = 139 kWh/m² annually; -soil-water heat pump with ηSPF =3.5; -average temperature of premises during heating season: 20 ºC; -average outdoor temperature during heating season: 0.6 ºC' -duration of heating season: 220 days.
To generate (139 kWh/m²)*(100 m²)=13900 kWh of energy annually a 7 kW capacity heat sourc should be in operation at full capacity and optimal performance for (13900 kWh)/(7 kW)=1986 h However, the heat pump does not operate at full capacity during the whole operational period which is why the actual operational period becomes longer.In Table 1, the 2013/114/EU metho provides for 1.25 times higher heat pump operational cost for cold climate zones making up 2470 in total.Therefore, according to this method, the amount of renewable energy generated by the he pump annually is as follows: The results of the analysis showed that the 2013/114/EU method for renewable energy calculatio does not take into account the primary energy input for transforming electric power.Therefore, th calculated amount of renewable energy generated by heat pumps is higher than it should be.

Conclusions
All renewable energy sources contain some non-renewable energy and for this reason, th requirement of the 2010/31/EU Directive, stating that more than a half of the amount of energy use by nearly zero-energy buildings should come from renewable energy sources, can only be related t ηEER target value of 2.8 are usually used, whereas soil pumps with ηEER target value of 3.8 water pumps with ηEER target value of 4.3 are rarely used for the same purpose.In this case ratio EPRr/EPRn=1 can be achieved by using the pumps of considerably higher ηEER values.Such a striking distinction in the calculation results obtained by equations ( 2) and ( 7) po question on the difference between the assessments of renewable energy generated by a heat p for heating a building according to 2013/114/EU Directive and the method proposed in this pap For the present analysis, a low thermal capacity single-flat building with 100 m² of heated satisfying the requirements of B energy performance label (according to STR 2.01.09:2012) selected; the building has the following parameters: -energy input for heating: 383•Ap -0,22 =383•100 -0,22 = 139 kWh/m² annually; -soil-water heat pump with ηSPF =3.5; -average temperature of premises during heating season: 20 ºC; -average outdoor temperature during heating season: 0.6 ºC' -duration of heating season: 220 days.
To generate (139 kWh/m²)*(100 m²)=13900 kWh of energy annually a 7 kW capacity heat s should be in operation at full capacity and optimal performance for (13900 kWh)/(7 kW)=19 However, the heat pump does not operate at full capacity during the whole operational pe which is why the actual operational period becomes longer.In Table 1, the 2013/114/EU m provides for 1.25 times higher heat pump operational cost for cold climate zones making up 24 in total.Therefore, according to this method, the amount of renewable energy generated by the pump annually is as follows: The results of the analysis showed that the 2013/114/EU method for renewable energy calcul does not take into account the primary energy input for transforming electric power.Therefor calculated amount of renewable energy generated by heat pumps is higher than it should be.

Conclusions
All renewable energy sources contain some non-renewable energy and for this reason requirement of the 2010/31/EU Directive, stating that more than a half of the amount of energy The results of the analysis showed that the 2013/114/EU method for renewable energy calculation does not take into account the primary energy input for transforming electric power.Therefore, the calculated amount of renewable energy generated by heat pumps is higher than it should be.
), given i 2013/114/EU, enables estimating "the part of renewable energy generated by heat pumps" that related neither to the requirements of the 2010/31/EU Directive nor theLST EN 15450:200given in the guidelines 2013/114/EU of the European Commission conditions of the respective EU member state.Thus, depending on t type of a heat pump, fixed HHP values unrelated to the energy needs in the corresponding climate zones.The 2010/31/EU Directive re performance of buildings in regard to the primary energy input, w 2013/114/EU, enables estimating "the part of renewable energy gen related neither to the requirements of the 2010/31/EU Directive n

Table 1
EElectricity_total -total amount of electricity, consumed by heat pumps.EElectricity from ren source (HYDRO, PV, WIND) -amount of electricity from renewable sources (hydr wind).

Table 2 .
Primary energy supplied from electric heat pumps calculated according to equation and(11) ) ) given in the 2009/28/ EU Directive and the guidelines 2013/114/EU of the European Commission (Table 1, column 9) is different from the calculation results of renewable/non-renewable energy ratio presented herein (Table 2, column 5) by 4 to 14 times. )

Table 3
gives the 2011 data on the f PRn values of electric power used for calculation in the building standards of some EU members.The pumps that are most often used to heat buildings and water are soil-water heat pumps with η SPF target value of 4.0 for new buildings in Central Europe.Table4gives the calculation results of E PRr /E PRn (per 1 kWh of thermal energy supplied by heat pumps to the building systems, by formulas/equations (8) and (9)) in electric heat pumps with η SPF = 4 in the EU members given in Table3and Lithuania, as well as the η SPF values of electric heat pumps that enable achieving E PRr /E PRn =1 in the mentioned coun-

Table 3 f
PRn values of electric power in the building standards of the EU members To perform the calculation the average value of useful efficiency of electricity generation η el that makes up 0.455, and f el.PRr =0 was applied.As the data in Table4shows, in all the countries discussed except Sweden, the ratio of thermal energy supplied by electric heat pumps to a building E PRr /E PRn =1 can be achieved by very high-efficiency pumps with η SPF value varying between 4.8 and 5.2, while in Sweden the same ratio can be reached with pumps having η SPF =4.2.Analogous results were obtained having performed calculations on electric heat pumps applied for cooling buildings.In this case, the value η SPF was replaced

Table 4
EER in the calculations in Table2.To cool a building air-air electric heat pumps with η EER target value of 2.8 are usually used, whereas soil pumps with η EER target value of 3.8, and water pumps with η EER target value of 4.3 are rarely used for the same purpose.In this case, the ratio E PRr /E PRn =1 can be achieved by using the pumps of considerably higher η EER values.
According to equation (7), if the heat pump supplied 17290 kWh of thermal energy annually, th following results of renewable energy calculation would be obtained: