Matching Fan Flow Rate to Varying Fresh Air Requirement

This is a generally-applicable method to make fan flow rates match a zone’s fresh air requirement, when this requirement varies from hour to hour.

Step 1/3

In the zone, set the fresh air rate to one of the hourly options.

Note that you will need to ensure that the internal conditions for the zone are set up appropriately; if this means you have to edit the TBD file, you must then re-simulate it and reload the TSD into TPD.

See Fresh Air Rate

Step 2/3

Attach a controller to the fans which will always return a signal of zero.

For example, you could use an external controller which only returns a non-zero signal at extreme temperatures which are never reached in the weather file.


Step 3/3

For the fans, set the minimum flow rate to the attached zone fresh air rate with a minimum design flow fraction of zero.



The controller will force the fan to use its minimum flow source on every hour, which will be the varying hourly fresh air rate from the zone.