Heat Pump

Description

The HeatPump asset models a four-port water-to-water heat pump that extracts heat from a primary circuit and delivers it to a secondary circuit. In the thermal network, the primary side acts as a heat sink and the secondary side acts as a heat source. The asset therefore couples two hydraulic circuits through an energy balance, while electrical power provides the difference between heat extracted on the primary side and heat delivered on the secondary side.

The asset is mapped from ESDL HeatPump objects. The coefficient of performance is read from the ESDL COP property, and an optional electrical power limit is read from the ESDL power property. During simulation, the controller provides temperatures and heat-demand setpoints for both sides of the asset.

Parameters

Parameter	Description	Unit	ESDL Asset Property
coefficient_of_performance	Ratio of delivered secondary heat to electrical input power		COP
maximum_electrical_power	Upper bound on electrical input power, if configured	W	power
temperature_in_primary	Primary-side inlet temperature	K	not mapped from ESDL; set by controller
temperature_out_primary	Primary-side outlet temperature	K	not mapped from ESDL; set by controller
temperature_in_secondary	Secondary-side inlet temperature	K	not mapped from ESDL; set by controller
temperature_out_secondary	Secondary-side outlet temperature	K	not mapped from ESDL; set by controller

Controlled Parameters

The controller provides setpoints for both hydraulic sides of the heat pump:

Signal	Description	Unit
primary_temperature_in	Primary-side inlet temperature	K
primary_temperature_out	Primary-side outlet temperature	K
primary_heat_demand	Requested heat extraction on the primary side	W
secondary_temperature_in	Secondary-side inlet temperature	K
secondary_temperature_out	Secondary-side outlet temperature	K
secondary_heat_demand	Requested heat delivery on the secondary side	W
set_pressure	Flag that determines whether the secondary side is pressure-controlled or mass-flow-controlled

The secondary-side setpoints are applied first. If a maximum electrical power is configured, the requested secondary heat output can be capped before the corresponding primary-side heat extraction is determined.

Additional simulation outputs

In addition to the default per-port outputs for mass flow, pressure, temperature, and volume flow, the heat pump asset provides the following additional outputs:

Signal	Description	Unit
heat_power_primary	Heat power on the primary side [1]	W
heat_power_secondary	Heat power on the secondary side [2]	W
electricity_consumption	Electrical input power [3]	W

[1]

The primary-side heat power is calculated from the solved primary mass flow and the internal-energy difference between primary outlet and inlet.

[2]

The secondary-side heat power is calculated from the solved secondary mass flow and the internal-energy difference between secondary outlet and inlet.

[3]

Electrical input power is reported as the absolute difference between the absolute primary-side and secondary-side heat powers.

Physics and Assumptions

The heat pump couples a cold primary side to a hot secondary side through an energy-transfer model. The secondary side represents the useful heat delivered to the network. The primary side represents heat extracted from a source circuit. Electricity supplies the remaining energy needed to raise heat from the primary temperature level to the secondary temperature level.

COP-based coupling

The model uses the coefficient of performance, \(COP\), to define the ratio between extracted primary heat and delivered secondary heat:

\[Q_{hot} = Q_{cold} + W_{el}\]

\[COP = \frac{Q_{hot}}{W_{el}}\]

Combining these relations gives:

\[\frac{Q_{cold}}{Q_{hot}} = 1 - \frac{1}{COP}\]

The solver uses the ratio \(c = Q_{cold}/Q_{hot} = 1 - 1/COP\) as the heat-transfer coefficient between the primary and secondary sides.

where:

\(Q_{hot}\)	Heat delivered on the secondary side [W]
\(Q_{cold}\)	Heat extracted on the primary side [W]
\(W_{el}\)	Electrical input power [W]
\(COP\)	Coefficient of performance [-]

Mass flow

For each side, the requested heat transfer is translated into a mass flow using the prescribed inlet and outlet temperatures:

\[\dot{m} = \frac{Q}{c_p (T_{out} - T_{in})}\]

where:

\(\dot{m}\)	Mass flow rate [kg/s]
\(Q\)	Requested heat transfer on the selected side [W]
\(c_p\)	Specific heat capacity at the mean fluid temperature [J/(kg K)]
\(T_{in}\)	Inlet temperature on the selected side [K]
\(T_{out}\)	Outlet temperature on the selected side [K]

On the primary side, the resulting mass flow is used to initialize the heat-transfer balance. On the secondary side, the asset either prescribes mass flow directly or prescribes pressure, depending on set_pressure.

Electrical power cap

If maximum_electrical_power is configured, the requested secondary heat output is limited so that

\[|W_{el}| \leq W_{el,max}\]

which implies

\[|Q_{hot}| \leq COP W_{el,max}\]

When this cap is active, the secondary heat-demand request is reduced before the corresponding primary-side demand is derived.

Heat powers and electricity consumption

After solving, the reported heat powers are evaluated from mass flow and internal-energy difference on each side:

\[Q_{primary} = \dot{m}_{primary} (u_{out,primary} - u_{in,primary})\]

\[Q_{secondary} = \dot{m}_{secondary} (u_{out,secondary} - u_{in,secondary})\]

The electrical input power is then reported as:

\[W_{el} = \left| |Q_{primary}| - |Q_{secondary}| \right|\]

These outputs are useful for checking whether the simulated heat pump is operating near its intended COP and electrical-power limit.

Assumptions

• The heat pump is represented as a steady-state coupling between a primary and secondary circuit.

• The coefficient of performance is constant during a timestep.

• Prescribed inlet and outlet temperatures are used directly; no internal refrigerant cycle is modeled.

• Dynamic compressor behavior, cycling, and start-up effects are not modeled.

• The secondary side can be operated either with prescribed mass flow or prescribed pressure.

• Fluid properties are represented through temperature-dependent water properties used elsewhere in the simulator.

Limitations

• No explicit refrigerant thermodynamics, compressor map, or part-load efficiency curve.

• No defrost behavior, auxiliary electric heater, or minimum on/off time logic.

• No explicit thermal losses to the surroundings.

• The COP does not vary with source temperature, sink temperature, or operating point within the asset model.

• The documentation describes the four-port HeatPump asset; the separate two-port AirToWaterHeatPump asset follows different behavior and should be documented separately.

See Also

• Heat Exchanger — Related four-port heat transfer asset (passive coupling)

• Air To Water Heat Pump — Two-port heat pump variant

• ProductionCluster — Simple heat source model

References

References

(No references listed.)