HVAC control and natural ventilation

[DavidS]

Hi all,

I am modelling a convention hall with AHU units for heating and cooling using ApacheHVAC. We also have natural ventilation for cooling.
To save energy, the priority is to have only natural ventilation (AHUs are OFF) as long as the comfort temperature is reached (Ta<24°C).
When this condition is not met, the AHU units turn on to cool the building.

I have set all the parameters in MacroFlo without problem. The AHU units are also properly modelled in ApacheHVAC.
My problem is the following: how can I properly model the control of the AHU units depending on the natural ventilation in MacroFlo?

Any input would be greatly appreciated.

Thanks in advance,

David

[bbrannon4]

There is a prototype system you can reference, but I generally do it two ways. One way is to put controllers that measure the OA air (or whatever other temperature you are controlling off of) and then use them in an AND connection with your system airflow controllers. This should have the opposite logic of your nat vent controller (ie when conditions are appropriate, natvent = 1 and HVAC operation = 0.

I've also had luck controlling the HVAC passively such that the macroflo openings control based on the outdoor and indoor temperatures to only open when appropriate which means they will only ever lower or eliminate the heating/cooling loads and so the system will turn off by itself. This doesn't work in the real world, but it generally works for me in the model since it's idealized. Of course if you are switching to adaptive comfort when in nat vent mode, this won't work.