Heat Pump

A heat pump is a device that uses work to transport environmental heat into heat at a useful temperature level. In our model, we have electric heat pumps available as a technology.

The heat pump technology models a small to medium size heat pump located in a building.

The power available to the heating system is given by the electric input power multiplied with the coefficient of performance (COP). .. math:: P_text{out} = text{COP} cdot P_text{elec}

Our model contains a module for the detailed modeling of the COP based on properties of the building and the heat pumps. For this, there are plenty of parameters in the input file.

For Swiss municipalities, the heat pump is usually already deployed in some buildings, since it is an often encountered technology. Therefore, an additional replacement capex can be defined. If heat pumps reach the end of their life, this replacement capex defines how much it costs to replace it with a new heat pump, without redoing any of the ancillary installations.

Attribute	Description	Standard value	Unit	Data type
deployment	If set to ‘true’, the technology will be considered in the energy system model (this does not necessarily mean it will be used). Only relevant for optimisation.	True	—	bool
kW_th_max	Maximum thermal capacity (i.e. heat output).	inf	kW	str
co2_intensity	Carbon-dioxide intensity of technology output (annual average value).	0 *(emissons allocated to electricity tech)*	kg CO2/kWh	float
lifetime	Expected lifetime of technology before replacement is required.	25	years	int
interest_rate	Interest rate for computing levelised costs (if required).	0.025	—	float
capex	CAPEX cost of technology per unit of capacity (new installations).	6000	CHF/kWp	float
capex_one_to_one_replacement	CAPEX cost of technology per unit of capacity (when device has reached the end of life).	2000	CHF/kWp	float
maintenance_cost	OPEX cost of technology.	10	CHF/kWp/year	float
fixed_demand_share	If set to ‘True’, a fixed share (per timestep) of the total heat demand will be served by this tech. Only relevant if Optimisation is activated.	False	—	bool
fixed_demand_share_val	The share (per timestep) of the total heat demand served by this technology. Only relevant if fixed_demand_share == True and if Optimisation is activated.	0	—	float
only_allow_existing	If set to ‘True’, only the existing (allready installed) capacity can be used. Only relevant if Optimisation is activated. CAREFUL: Avoid conflict with fixed_demand_share.	False	—	bool
cop_mode	Method for estimating the COP timeseries. Options are: “from_file”, “constant”, “from_file_adjusted_to_spf”, “location_based”. “location_based” is an intricate algorithm taking into account building and heat pump properties as well as the local weather (detailed description below). “constant” means that a constant COP is used. “from_file” means means that a timeseries loaded from a given file is used. “from_file_adjusted_to_spf” means that a timeseries loaded form a file is is scaled s.t. a given value for the seasonal performance factor (SPF) is reached	location_based	—	str
cop_timeseries_file_path	Path to COP timeseries file for mode “form_file” and “from_file_adjusted_to_spf”	<path>	<path>	str
cop_constant_value	Constant COP value to use if cop_mode=constant	3.5	—	float
spf_to_target	Seasonal performance factor (SPF) to which the COP is adjusted in the mode from_file_adjusted_spf	3.5	—	float
quality_factor_ashp_new	Quality factor for new ASHPs for mode “location_based”.	0.4	—	float
quality_factor_ashp_old	Quality factor for old ASHPs for mode “location_based”.	0.4	—	float
quality_factor_gshp_new	Quality factor for new GSHPs for mode “location_based”.	0.48	—	float
quality_factor_gshp_old	Quality factor for old GSHPs for mode “location_based”.	0.48	—	float

The relationship between the in- and outflows is given by

\[\mathtt{v\_h\_hp} = \mathtt{COP} \cdot \mathtt{u\_e\_hp}\]

The symbols and names of the flows are

u_h_hp	Environmental Heat Inflow Heat pump
u_e_hp	Inflow Electricity
v_h_hp	Outflow Heat

COP modes

There are several ways to set the COP of the heat pumps.

In the mode “constant”, a constant, user-defined COP is used.

In the mode “from_file”, a timeseries provided by the user as file is used.

In the mode “from_file_adjusted_to_spf”, a timeseries provided by the user is used but using the demand profile, it is scaled such that the SPF reaches a user-defined value.

In the mode “location_based”, a COP model taking into account many properties of the building stock and location is used. This model is described further below.

“location_based” COP mode

The “location_based” COP mode is the standard COP mode. It calculates a COP timeseries based on the properties of the individual buildings, the quality_factors specified in the input file, the local weather and internal parameters defined in the corresponding code file.

For each building, the algorithm assign probabilities for several properties for space heating

1. Is the heat dissipator radiator- or underfloor-heating-based

2. Is the heat pump air-source or ground-source.

3. Does the heat pump already exist or is it a new device to be installed by the optimizer.

4. Which heating curve construction period is used.

and for domestic hot water-heating

1. Is the heat pump air-source or ground-source.

2. Does the heat pump already exist or is it a new device to be installed by the optimizer.

For each building, we assign a construction year. This year is the GBAUJ from the RBD if it is defined. Otherwise, the construction period (GBAUP) is used and the central year of the construction period is assigned as construction year.

The share of radiators is assumed to be 100% until 1970. From then on, it rises by 1.66% per year until reaching 100% in 2030. The year here is the construction year of the building.

The share of ASHPs is assumed to be 66% for existing installations (34% GSHP), while for new installations, 72% ASHPs and 28% GSHPs is assumed. These percentages are based on the statistics for sold heat pumps by the FWS (FWS, 2025). For existing installations, this is only used if the heat source is not specified in the RBD.

Whether the heat pump already exists is based on the RBD-information (FSO, 2025).

For the definition of the heating curve construction period, we rely on the information sheet “Heizkurve richtig einstellen” by the Swiss Federal Office of Energy (SwissEnergy, 2022).

For air-source heat pumps, the outdoor temperature is used as source temperature. For ground-source heat pumps, a simple harmonic function is used as source temperature, with a mean value of 5°C and an amplitude of 3°C, where the lowest point is reached at the end of February.

For the domestic hot water, a constant temperature of 55°C is assumed.

The COP is then calculated based on the Carnot efficiency of a perfect heat pump, capping the efficiency at 20. This value is then corrected by the quality_factor provided by the user.

\[\begin{split}COP_{Carnot} = \\frac{T_{cond}}{T_{cond} - T_{evap}}\end{split}\]

where temperatures are in kelvin and refer to the condenser (output) and evaporator (source) sides of the heat pump.

This efficiency is then different for newly installed HPs than for the existing ones. Usually the existing HPs profit from being in more modern buildings, which yields lower heating water temperatures and thereby higher efficiencies, but their efficiency is reduced by the age of the existing heat pumps, which have lower device-level efficiencies, and by the fact that new buildings have a higher share of DHW, which is hotter than heating water.

References

SwissEnergy (2022, August 29). Set the heating curve correctly Federal Office of Energy. https://pubdb.bfe.admin.ch/en/publication/download/9982

FWS (2025). Jahres-Statistiken & Marktzahlen FWS Fachvereinigung Wärmepumpen Schweiz. https://www.fws.ch/statistiken/

Federal Statistical Office (FSO). (2025). Federal register of buildings and dwellings (RBD). https://www.bfs.admin.ch/bfs/en/home/registers/federal-register-buildings-dwellings.html