High-Temperature Heat Pump – Polysun Guide

High-temperature heat pumps (HTHPs) are gaining traction in modern energy engineering. This trend is driven by building retrofits requiring hihg flow temperatures on one hand, and industrial process heat applications on the other.

This article provides a step-by-step guide to simulating an HTHP within Polysun. The technical foundation relies on an expanded CSV data profile. Unlike the standard model, this advanced profile explicitly incorporates the temperature differentials across both the evaporator and the condenser. Consequently, the software interpolates performance data, allowing users to map operating behavior with high accuracy.

Thermodynamic Modeling of the Heat Pump

Accurately mapping the thermodynamic behavior of an HTHP up to 144°C across its entire operating range requires the evaluation of four critical variables:

• Evaporator Temperature ( \(T_V​\) ): This variable represents the temperature of the selected thermal source (e.g., groundwater, brine, or ambient air).
• Condenser Outlet Temperature ( \(T_K​\)​ ): This represents the flow temperature of the hydronic heating system. For high-temperature heat pumps, this value typically sits significantly above 55°C.
• Evaporator Temperature Differential (ΔV): This defines the thermal fluid temperature split (delta) between the inlet and outlet on the source side.
• Condenser Temperature Differential (ΔK): This index defines the fluid temperature split between the inlet (return) and outlet (flow) on the sink side (heating circuit).

High-Temperature Heat Pump: Expanding the Standard Model

Accounting for individual temperature differentials empowers engineers to determine operational setpoints with pinpoint accuracy. This capability proves advantageous when dealing with variable volume flows or highly fluctuating temperature splits.

The Standard Model Limitation

In the standard model, the simulation engine operates using fixed, non-editable temperature differentials. Therefore, adjusting the model to non-standard operating conditions is highly restricted.

Adjustable Temperature Differentials in HTHP Systems

Users can activate the extension of the standard model by simply importing an expanded CSV profile. This updates the standard heat pump model with user-definable temperature differentials.

Depending on the chosen heat pump configuration, the software unlocks the following parameters:

• Brine/Water and Water/Water Heat Pumps: Users can set both ΔV (evaporator side) and ΔK (condenser side).
• Air/Water Heat Pumps: For these systems, users only configure ΔK (condenser side). The column for the evaporator delta (ΔV) is automatically omitted from the profile. This occurs because the ambient air temperature dictates the evaporator conditions directly, meaning no primary-side temperature split needs to be defined.

Note: Utilizing this expanded modeling approach is highly recommended for plants operating outside standard nominal rating points—specifically those dealing with highly dynamic volumetric flow rates or high temperature lifts.

CSV Profile Structure for HTHP Systems

Users define the operational data points within a profile file. The CSV layout for high-temperature heat pumps features two additional columns dedicated to temperature differentials.

The complete CSV syntax is structured as follows: #LoadStage[0-1];Evaporator[°C];Condenser[°C];Delta_V[K];Delta_K[K];ThermalCapacity[W];ElectricalPower[W]

Column Name	Technical Meaning	Value Range / Engineering Notes
LoadStage	Part-load ratio modulation	0 = System Off, 1 = Full Load operation
Evaporator	Source-side inlet temperature	Stated in °C (e.g., source groundwater temperature)
Condenser	Sink-side outlet temperature (Flow)	Stated in °C (Typical HTHP range: 70–100°C)
Delta_V	Evaporator temperature differential	Source split in Kelvin (Inlet minus Outlet)
Delta_K	Condenser temperature differential	Sink split in Kelvin (Flow minus Return)
ThermalCapacity	Net thermal energy output	Expressed in Watts (positive integers)
ElectricalPower	Compressor electrical power consumption	Expressed in Watts (positive integers)

Sample Data Entries for a Water/Water High-Temperature Heat Pump

#HP_Model_Identifier;;;;
#LoadStage[0-1];Evaporator[°C];Condenser[°C];Delta_V[K];Delta_K[K];ThermalCapacity[W];ElectricalPower[W]
0.2;-20;35;3.0;5.0;8024.2;3040.1
0.3;-15;55;2.5;4.8;12500.0;4960.0
0.6;0;70;2.0;6.0;21000.0;9100.0
1.0;5;80;1.8;7.2;35000.0;16500.0

Sample Data Entries for an Air/Water High-Temperature Heat Pump

#HP_Model_Identifier;;;;
#LoadStage[0-1];Evaporator[°C];Condenser[°C];Delta_K[K];ThermalCapacity[W];ElectricalPower[W]
0.25;-20;35;5.0;4687.5;1521.2
0.5;-20;35;5.0;9375.0;3042.3
0.75;-20;35;5.0;14062.5;4563.5
1.0;-20;35;5.0;18750.0;6084.7

Critical Simulation and Calculation Insights

There are three fundamental thermodynamic laws to follow when dealing with High Temperature Heat Pumps:

• Thermal Source Boundaries: The evaporator temperature must always remain below the condenser temperature due to basic laws of thermodynamics.
• Temperature Splits: Higher fluid temperature deltas (Temperature lift) generally result in a lower Coefficient of Performance (COP). Polysun maps this accurately by evaluating the explicit performance curves provided in the CSV profile.
• Data Interpolation: User does not need to populate a data point for every conceivable operating point. Polysun interpolates within the available data points.

Reference Layouts for High-Temperature Heat Pump Design

Polysun contains the following schematics for High-Temperature Heat Pumps. They can be expanded, and modified, by doing so users can identify the optimal heat pump size.

61a: Air-to-water high-temperature heat pump in existing buildings

61b: Industrial process with high-temperature heat pump

61c: High-temperature local heating network with CHP and high-temperature heat pump

61d: Parallel high-temperature heat pumps for process heat

Additional schematics for the layout of heat pumps with buffer tanks can be found in our software, or in this blog article describing six proven and reliable schematics.