Knowledgebase
How to model walk in cooler, freezer or cold room
Posted by Andy Tindale on 10-Aug-22 06:06 PM

It is possible to model freezer zones in DesignBuilder, but it is important to ensure that the temperature of the supply air is set to a very low value to cool the air below zero.

If you are using Simple HVAC then take these steps:

- Reduce the cooling supply air temperature in the Cooling design calculation options to -99°C.
- Reduce the supply air temperature under Cooling on the HVAC tab in the freezer zones to -99°C.
- Switch off Heating on the HVAC tab.
- Switch off Mechanical ventilation on the HVAC tab.
- On the Activity tab, set the cooling setpoint and setback temperatures to the required freezer zone air temperature.
- Set the cooling operation schedule to 'On' at HVAC tab so that it always operates.

Note: You will need DesignBuilder version 7.1 to allow you to set negative room temperatures at the HVAC tab.
For earlier versions, you will need to create a copy of the HVAC template, set up the negative temperatures, and apply the new HVAC template.


With Detailed HVAC then the solution will be:

- On the Activity tab, set the cooling setpoint and setback temperatures to the required freezer zone air temperature.
Add a PTHP zone unit to the HVAC zone group. These units can cool down spaces below 0ºC.

- Then set the units (Fan + DX Coil) characteristics in a way that it won't consume any energy.

Fan unit:



PTHP DX Cooling coil:



Note that "All 0" curves have all their coefficients set to 0. This means that the curve output is always 0.

The final results shows that freezer temperature is quite well maintained (there are some peaks, probably caused by sizing) and the PTAC does not consume any energy:





Following these steps allow you to cool zones down to very low temperatures.

Updated 10.Aug.2022