How much capacity needed to cool airflow
How much capacity needed to cool airflow
(OP)
Forgive me if I do not ask this correctly, thermal topics are not by best.
I want to put a heat exchanger in an air duct. If I know the airflow and humidty of the airflow, how do I determine how much heat I need to pull from the air to cool it from 77 deg to 70 degrees?
Thank you.
Les Strickland
Fort Worth, TX
I want to put a heat exchanger in an air duct. If I know the airflow and humidty of the airflow, how do I determine how much heat I need to pull from the air to cool it from 77 deg to 70 degrees?
Thank you.
Les Strickland
Fort Worth, TX





RE: How much capacity needed to cool airflow
RE: How much capacity needed to cool airflow
As Yeldud says, psycrometric chart is easiest for this. However, if you're only interested in reducing temperature and not humidity (ie sensible cooling) then cooling duty is:
Q = M x C x (t1 - t2)
Q = Duty (kW)
C = Specific Heat Capacity (approx 1.012 kJ/kg Kelvin)
t1 = On coil temperature (Kelvin)
t2= = Off coil temperature (K)
M = Mass flow rate of air = volume flow x density (density approx 1.17 kg / m3)
Sorry for my units but the equation will of course hold true using F and CFM, you will need to adjust the specific heat capacity and density figures accordingly.
Cheers,
Graham.
RE: How much capacity needed to cool airflow
Latent heat in btu/hr = CFM x 4840 x (W2-W1)
Where W1 = entering humidity in lb water vapor/lb dry air
W2 = leaving humidity in "ditto"
Total heat in btu/hr = Sens heat + Latent Heat
Gpm of cooling water needed = Total heat in btu per hr/(500 x (t1-t2))
Where t1 = °F entering water temperature
t2 = °F leraving water temperature