Air To Water Heat Pump Example

This example illustrates some of the main steps involved in setting up an ASHP system. It is based on the Small Office example file and involved loading a default ASHP template and modifying the model to achieve a high-performance low temperature ASHP system with gas-fired boiler supplementary heating.

1. Load the base Small Office example model.

2. Set the Detailed HVAC model option.

3. Load the ASHP Air-to-water Heat Pump, Series Boiler, Water Convector Detailed HVAC template.

This provides a high temperature air to water heat pump with gas boiler supplementary heater.

4. Run the Heating design calculations to obtain the total design heating capacity of the system.

5. Now change the default high temperature model loaded from the template to use low temperature outlet from the HP. Edit the Air to water heat pump coil and select the ASHP LowT COPFT and ASHP LowT Heating CAPFT performance curves. The curves section of the dialog should similar to the screenshot below.

5. Edit the Air to water heat pump coil and:

Enter the Rated heating capacity of the ASHP. Enter 90% of the design heating load (we will rely on the gas boiler to boost overall system capacity to achieve the full capacity).

6. Edit the Air to water heat pump and:

Create and select a new schedule for the Compressor setpoint temperature schedule based on LowT heat pump water supply temperature: Always 55.00.

Ensure that the Minimum inlet air temperature for compressor operation is set to -10°C to allow operation on cold days but prevent operation on days colder than -10°C.
Change the Deadband temperature difference to 2°C.

7. Edit the Water heater and:

Change the Air to water heat pump Tank volume to 0.25m3.
Change the Indirect water heating recovery time to 0.2hrs

9. Edit the boiler and change the capacity of the boiler to provide the remaining 10% of the design heating load.

10. Check that the SPM downstream of the supply side of the HX is controlling supply water temperature to 55°C.

11. Change the Pressure rise of the ASHP fan to be 100Pa.