Heat pump

There are a multitude of different heat pumps available in the Hysopt optimisation software.

1. Air source vs. Ground source heat pump (under construction)

2. Heat pump booster

3. Gas absorption heat pump

4. Heat pump for heating and cooling

5. Reversible heat pump

6. Polyvalent four-pipe heat pump

In the following page, all the information given will be focused on the air source heat pump, but a lot of information will translate for the other heat pumps as well.

The basic block for the air source heat pumps includes 3 nodes: A hydronic connection, an activation signal (where the modulation can also be connected if needed), and a connection for the temperature on the evaporator side. more information on this here.

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Input parameters

Input parameters in the base circuit   

The parameters of design conditions need to be defined in the Base circuit itself:

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With an Air source heat pump for instance, the manufacturer typically gives the thermal power with the following quotation "A7/W35" which means an (A) air temperature of 7°C (evaporator side) and a (W) water temperature of 35°C (condenser side). For a GSHP on the other hand, the quotation is typical "G0/W35".

These reference evaporator and condenser temperature are therefore important to set the correct thermal power and should be locked. When designing your own size, these values are also important to make a correct selection of heat pump size.

The values in the COP - and power table are scaled with respect to these parameters, enabling the model to calculate the condenser heat and the electrical power consumption.

Evaporator temperature

The evaporator temperature is defined as an input signal. This temperature is different for air source (ASHP) and ground source heat pumps (GSHP). Air source vs. Ground source heat pump (under construction)

This parameter does not apply for a heat pump booster. Heat pump booster

Tables

The Hysopt software determines the heat flow and the electrical power consumption of the heat pump using COP- and power tables. The data required for these tables can be found in the manufacturer's technical brochures. This procedure is used to parameterize the heat pump and booster heat pump for dynamic simulation.

Technical brochure example for a typical heat pump where COP changes based on evaporator (-5,0,2,10,15°C) and condenser (35,45,55,60°C), as well as thermal power (Vermogen) and Electrical power (Elektr. opgenomen vermogen).

Please note that some technical brochures only mention the heat flow and not the electrical power. The latter can be determined using the following formula:

Hysopt requires these table values to be provided in CSV format, the template tables can be downloaded from Hysopt. It is also possible to upload your own tables.

When you open the downloaded COP table, you find a list of COP values (4th column) for a combination of different values of the inflow temperature of the evaporator (1st colomn), the outflow temperature of the condenser (2nd column) and the modulation signal (3th column). The power table contains a list of electrical power values and is constructed the same way as the COP table.

Both of these tables can be modified to match the technical performance of a specific heat pump. Below you can see a completed COP table and power table according to the manufacturing datasheet above.

COP table example

Power table example

The process of changing the power and COP tables is similar as the efficiency lookup tables in the boiler BC. A step-by-step guide on changing the tables can be found here: Changing boiler efficiency (with templates) .

Modulation signal

The lowest modulation value specified in the COP table has to correspond with the minimum modulation of the heat pump. This value should be found in the manufacturing datasheet of the heat pump.

Some heat pumps only have a few discrete operating points, while other heat pumps are able to operate over a continues operating range. For simulation, the user needs to make an external control loop that is connected to the activation signal port of the heat pump that will mimic this exact behaviour. Model templates for controlling a heat pump are given in the inspiration library (Heat Pumps).

Compressor configuration

Heat pumps have either compressors which are controlled with a variable speed drive (VSD) or have 1 or more compressor stages which are controlled with an on/off system. It is possible to choose this configuration in the heat pump block. If the implemented heat pump has an internal VSD, the minimal modulation percentage of the VSD drive should also be added as an input.

For a fixed speed heat pump, the amount of stages can be chosen. For example, a 2 stage heat pump will cycle between it’s full design load and half of the design load based on the existing thermal load of the system.

During cycling from a compressor stage to the next, the compressor’s thermal output is increased linearly in a period of 5 minutes in order to simulated compressor start-up time. This ramp up is only implemented when an extra compressor stage is started and not when a compressor stage is stopped.

Heat pump thermal loses

The Hysopt Optimiser allows to take thermal losses into account. The thermal losses depend on the condenser thermal UA-value, the condenser capacitance and the ambient temperature. To adjust these parameters make sure to turn on the simulation layer.

The condenser thermal UA-value and the condenser capacitance are parameters that can be adjusted in the Base circuit.

The ambient temperature that is used for thermal losses in heat pumps depends on how you configure the heat pump:

• If you assign the heat pump to a zone (see Zone library | Assign base circuits and pipes to a zone), then the temperature of the zone is used

• If you did not assign the heat pump to a zone, then the environment temperature is used (which can be specified as a parameter in the Base Circuit). If you leave this parameter empty, then the outside temperature is used (which is the default setting).
  
  

Heat pump KV-value condenser

The KV-value parameter is used to design a pressure drop over the condenser heat pump side.

If the actual KV value isn't known, the user can click on the "pencil" icon which results in a calculation popup window. In the popup window, the user can calculate the KV value by entering the pressure drop and flow rate (and if needed, the brine, mixture and reference temperature). This option is preferred when the information on the heat pump is known. However, the user can also let the software automatically calculate the KV value depending on the design flow rate by using the other tab and entering the estimated pressure drop over the heat pump.

Heat pump Condenser capacitance

Besides the above-mentioned parameters, the user can also adjust the heat pump capacitance (water content and mass of steel).

If the heat pump capacitance isn't known but the water content and mass of steel is known, the user can click on the "pencil" icon and enter these aspects into the capacitance calculator. The average flow temperature and type of refrigerant can also be changed. Next, click on the “Calculate”-button in order to calculate the capacitance.