topic Re: Air balance schedule "improper use of boolean expressions" in Revit MEP Forum

Air balance schedule "improper use of boolean expressions"

eruesswickG7LDL — Thu, 24 Apr 2025 13:45:09 GMT

Im creating an air balance schedule and hitting the wall. Using spaces for schedule. Ive created a field for AIA ACH where I manually input the number of air changes. Trying to use that in a formula to calculate AIA CFM (Volume * AIA ACH/60) and get "improper use of boolean expressions". Did anyone figure out how to do this or a work around? Thank you in advance.

Re: Air balance schedule "improper use of boolean expressions"

iainsavage — Thu, 24 Apr 2025 14:06:13 GMT

Although it says its improper use of boolean expressions, I wonder if its actually due to inconsistent units.

Your CFM test will have units of cfm, your volume is cf but your ACH is I assume a unitless number, as is your numerator (60).

So in terms of units you have cfm = cf which is obviously wrong. You would need to include minutes in your numerator to end up with cfm = cfm e.g. Volume*AIA ACH/60 minutes.

At least, I think that might be your problem but maybe someone else can help more.

Re: Air balance schedule "improper use of boolean expressions"

HVAC-Novice — Thu, 24 Apr 2025 15:33:07 GMT

What are all the units in your equation? Volume should be ft³. And you want to get ft³/minute.

is "AIA ACH" just a number (unitless)?

Re: Air balance schedule "improper use of boolean expressions"

eruesswickG7LDL — Tue, 29 Apr 2025 14:35:33 GMT

I should have clarified. Im doing hospital design with designated minimum air changes per hour. Yes, the AIA ACH is a unitless number

Re: Air balance schedule "improper use of boolean expressions"

HVAC-Novice — Tue, 29 Apr 2025 14:51:34 GMT

@eruesswickG7LDL wrote:
I should have clarified. Im doing hospital design with designated minimum air changes per hour. Yes, the AIA ACH is a unitless number

Divide volume by "1 ft³" and multiply the result by "1 cfm" make sure the numbers are correct (doing the 60-conversion correctly etc. ) . Basically with any equation, manually calculate and see if it works correctly. Especially with made-up unitless numbers.

Re: Air balance schedule "improper use of boolean expressions"

eruesswickG7LDL — Wed, 30 Apr 2025 09:13:34 GMT

This worked! Huge thanks.