Ventilation Schedule

Hi All,

We were digging a big down into ventilation operation. From extracting the hourly OA ventilation rates, it appears to us that by default the ventilation is happening 24/7.

export_variableto_csv_report_AirSystemOutdoorAirMassFlowRate_Hourly.csv (342.2 KB)

Initially we thought to tie the ventilation to the occupancy schedule, but that would really function as a ‘too good to be true’ DCV since it will be operating on a fractional schedule the same way the occupancy is.

So we have created logic in our script to generate a custom ventilation schedule that turns on and off the ventilation based on the setpoints/setbacks.

Wondering if this makes sense to you and if there is an easier way to do this in HB or a way of altering the default assumption for ventilation.

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That depends on what Program you are simulating. Some of them have ventilation schedules associated with them but most do not, meaning that the outdoor air is always always at the specified max flow rate.

Using a ventilation schedule is a perfectly fine way to vary the outdoor air flowing through the HVAC and all of the relevant HVAC system templates will respect it (except for the HeatCool HVAC Templates, which do not support ventilation).

You can also use the dcv_ input that’s on the relevant HVAC components to automatically set the outdoor air to fluctuate based on the occupancy schedule. I don’t know why this seems “too good to be true” since this is essentially what happens with most DCV systems using CO2 sensors. But I don’t know what your specific case is here or if your DCV system is using some strategy other than CO2 monitoring.

Lastly, you can specify a doas_avail_sch_ for all of the DOAS system templates, which can be used to shut off the DOAS completely when the space is unoccupied. Whereas the two strategies above will only change the amount of outdoor air mixed into the supply air stream and not change the behavior of the fans, this last strategy will also shut off the fan, allowing you to conserve fan energy in this case.