This chapter details the different ways of modelling a heat pump system within Sympheny. This includes the consideration of the low-temperature source, which availability will influence the operation of the heat pump.

This chapter starts with the modelling of the basic systems (heat pump, chiller and their aggregation, reversible heat pump). In this case, no maximal availability of the low temperature heat source will be considered. This hypothesis generally applies to air-source heat pump.

In a second section, the different possibilities of modelling two temperature levels with a standard heat pump are shown. The chosen solution will depend on the users and on their project. It is also possible to model all the possibilities and to let Sympheny calculate the optimal solution.

In the last sections, heat pump applications where a special attention must be taken in the low temperature source are detailed: heat pump on groundwater, heat pump on geothermal heat and heat pump on wastewater.

- Standard Heat Pump

This heat pump model is working on a low-temperature source called ‘heat ambient’. This can be understood as being any type of source, e.g. air or water. In this simple case, the heat intake from the ambient heat is not limited. It is therefore more coherent to consider this technology as an air-source heat pump. In the case of a heat pump working on groundwater, river water, geothermal heat or wastewater, the availability of the low temperature source must generally be accounted for (refer to the relevant sections).

Please note that the temperature levels and COP selected here are only meant as examples.

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Set-up summary

Energy Carriers

Energy Demands


Supply technologies

Heat pump HP




Primary Input

Heat ambient




Heat 70-80°C



(primary) Output

Set-up Implementation 

When defining a heat pump in Sympheny, the following steps must be done:

  • Defining the energy carriers necessary (as displayed in the table under the first row of the ‘set-up summary’ section).

  • Defining the inputs of the heat pump (in this case, electricity, and heat ambient) within the imports & exports tab.

The heat pump itself is defined within the Supply technologies tab.
The COP can be flexibly adapted by the user as well as the input ratios.

It is important to make sure that the correct primary input is selected (electricity in the case of a heat pump). Indeed, the efficiency of the output is calculated based on the primary input.

Optionally, for a more detailed modelling, the output efficiency can be entered with monthly efficiencies, by activating the time-varying efficiency toggle.

A common pitfall is missing to fill in one of the entries: technology names, hub, setting the check for primary input /output or entering the lifetime. If any of these entries is missing, the ‘save’ button is unavailable.

To be able to save the technology, verify that you have all these entries set up. Per technology, there must be one primary input and one primary output (except in the exception where the technology has no input, in which case, no primary input is needed).

- Modelling multiple temperature levels with a standard heat pump

The modularity of Sympheny allows the users to define their systems in a very flexible way. This section shows the different options for modelling two temperature levels with heat pumps. The standard example is the one of a residential building where heating and domestica hot water (DHW) are required, each of them at a different temperature level (medium temperature (MT) for heating and high temperature (HT) for DHW).

Different modelling options are possible:

  • 2 Heat pumps in parallel

  • 2 Heat pumps in series

  • 1 Heat pump with two modes

  • 1 Heat pump for HT and a heat exchanger / mixer


- 2 Heat pumps in parallel

In this variant, the two heat pumps can operate totally separately. Therefore, no storage is required for the energy balance to hold. The efficiency of the heat pump HT (High temperature) reflects the higher temperature delta and is accordingly lower than the efficiency of the heat pump MT (‘medium temperature’).

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- 2 Heat pumps in series

When the heat pumps are operating in series, a storage is required, to make sure that both demands (heating and DHW) can be supplied simultaneously, without requiring a heat pump of unnecessarily large capacity. As the heat pump HT is now operating on medium temperature heat, its COP is higher than for the version described above, where the heat pumps operate in parallel.

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- 1 Heat pump with two modes

The case of a heat pump with two modes is similar to the case of two heat pumps in parallel. By using the modes, the software will only consider the costs once (as it is the same machine). Within Sympheny’s modelling, the modes can operate simultaneously during the same hour. If a capacity limit is set, this is valid for the sum of both modes over the hour.

For a realistic operation, it is therefore strongly advised to integrate a heat storage (at least for one of the temperature levels).

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Modes are set within the definition of the supply technology. To enter a second mode, press ‘new mode’:

This will create a second field for entering the technology’s second mode of operation. In this case, both modes are very similar: the only variation is the type of output (high temperature or medium temperature heat) and the corresponding COP (entered as a percentage).

Modes of a technology can be spotted by their names in the system diagram: each mode has its mode number appended to the name of the technology (e.g. ‘Heat pump HT 1’ and ‘Heat pump HT 2’) are the operation modes of one single technology.

- 1 Heat pump for HT and a heat exchanger / mixer

Finally, there is also the possibility to model a heat pump producing high temperature, which is then mixed / dissipated to another medium to create lower temperature. In this case, the production of medium temperature heat will not beneficiate from a higher COP (as was the case in the other options described above). A storage is also necessary for the energy balance to hold in case of simultaneous demand of heating and DHW.

Video Tutorial