AIR MIX SELECTION

[stern]

Hello everyone,

I have the following problem, outside air x conditions and its required 90% return air and 10% outside air to heat a building.

Is there a rule of thumb on what conditions to consider for indoor air( return) to calculate the mix?

I need to determine the BTU/hr required and need a practical method to handle air mixes.

Thank you

 

[quark]

Yes, there is a thumbrule, but the problem is we can't differentiate it from a standard procedure, because both are same.

Check thread403-299263 for the procedure and download Psychro07.zip from

http://www.hvacware.net/engrproj.html.

The fourth worksheet is about mixing calculations.

 

[stern]

Thank you quark,

I see the calculator and its easy to use when you have both air stream conditions.

The problem is when you dont have the return air measurements, I suppose we have to assume these conditions but Im not sure.

Am I wrong?

 

[quark]

You are right. Return conditions are conditions required in the control space (plus duct heat gain, which can be ignored for the sake of preliminary calculations).