Free-cooling: Mechanical ventilation

jverschuere · Posts: 1

Could someone please advice how to model a mechanical free cooling? I would like to model a mechanical ventilation of 4arch/h only if the outside temperature is 5°C below the inside temperature.
For natural ventilation this is easy to set. How do you set the delta 5°C with mechanical ventilation?

Many thanks, Joost

Andy Tindale · Posts: 1196 Location: Stroud

Joost,

You can approximate the situation you describe using Simple HVAC and setting the following:

Activity tab
- Mechanical vent setpoint temperaure Max In-out deltaT = 5
- Mech vent cooling setpoint temperature 18degC
- Cooling setpoint temperature 26degC

HVAC Tab
- Mech vent on
- Outside air mech vent definition method = 1-By zone
- Outside air mech vent ac/h = 4
- Cooling on

I suggest you set up a simple model and play with the setpoints and look carefully at output every timestep to understand the operation of the system. I couldn't find a way to ensure that free cooling never operates while cooling operates but this should not be too significant as the Max In-out deltaT = 5 setting prevents mech vent while inside air is less tahn 5degC warmer than outside air.

I hope it helps.

Andy

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