mixed condition
mixed condition
(OP)
Dear Braintrust,
I am trying to understand the best way to find a mixed condition (ie temperature, enthalpy, etc.). When for example...return air is mixed with outside air. A text I am studying says you can find this by the following equation:
mixed temp. condition=(OATemp*CFMOA+RETTemp*CFMRET)/CFMT
CFMT=CFMOA+CFMRET
I get mixed results when I solve by this approach...ie I don't get the right answer according to other textbooks I am studying.
Please help.
I am trying to understand the best way to find a mixed condition (ie temperature, enthalpy, etc.). When for example...return air is mixed with outside air. A text I am studying says you can find this by the following equation:
mixed temp. condition=(OATemp*CFMOA+RETTemp*CFMRET)/CFMT
CFMT=CFMOA+CFMRET
I get mixed results when I solve by this approach...ie I don't get the right answer according to other textbooks I am studying.
Please help.





RE: mixed condition
your formula is correct, I used 200 CFM OA at 95*F and 1600 CFM RA at 75*F = (19000)+ (120,000)/1800 CFM = 139,000/1800 = 77.22*F
RE: mixed condition
Regards,
RE: mixed condition
The easiest way is to go to the Trane website:
http://www.trane.com/commercial/software/index2.asp?fla...
There's a "Web Psychrometrics" section, which has a mixed air calculator.
---KenRad
RE: mixed condition
RE: mixed condition
http://pmilligan.net/pmtherm.htm
Install it (v 1.23). Go to "Psychro" on the menu bar, then "PsychroCalc." You can enter conditions in boxes 1 & 2 and calculate the result in 3 with "Processes."
RE: mixed condition
PS: PMTherm requires the file vbrun300.dll to work and there is also a link available.
Regards,
RE: mixed condition
calculate drybulb temperature with it, either use a psychrometric chart or use one of the many software
utilities already mentioned in previous replies.
When using the psychrometric chart draw a stright line between the outside air and the return air conditions.
Then calculate the percentage of outside air, measure
the line that you have drawn and take the percentage of distance from the return air point using the outside air
percentage distance.