Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
There is a neat trick that uses zone exhaust fans to help balance air system flows when using ZoneMixing. The volume of return air flow can be deprecated using Fan:ZoneExhaust. That is the air leaving the sending zone as transfer air can subtracted from the air returning to its air handler. Set the flow rates to be same in the ZoneMixing and Fan:ZoneExhaust objects, but don't consume power in the exhaust fan. The sending zone may not really have exhaust fans but this trick allows capturing the reduced return air flow in the air handler.
Depending on what is happening in the zone receiving the transfer air, you can control the split between a real exhaust fan and the air handler return in the Fan:ZoneExhaust using the field Balanced Exhaust Fraction Schedule. I don't think you can force more return air than enters the receiving zone via the air system supply air, but if you really have exhaust then it need not deprecate return air flow when all the exhaust should be transfer air.
