Sensible Heat Load Equation

[chadinsk]

Can anyone tell me why the temperature difference in the equation for ventilation sensible heat gain, q=1.08xCFMx(To-Ti), uses indoor air temperature (ie 75) rather than the temperature leaving the coil (ie 55)?

 

[imok2]

For Ventilation sensible heat gain

You use the air off the coil and the OSA temp to calculate the total Ventilation sensible cooling load
Assume the temperature at the cooling coil to be 55ºF. OSA Temp = 95*F and 300 CFM OSA
QS = 1.08 x CFM x ?T (Interior Design Temp – Cooling Coil Temp)
= 1.08 x 300 CFM x (95ºF – 55ºF)
= 12,960Btu/hr

For latent heat
Q latent = 4840 x CFM x ?w

Q latent = 4840 x CFM x ?w
= 4840 x 300 CFM x (0.029 – 0.009)
= 29,040 Btu/hr
Total heat = sensible + Latent heat

 

[DRWeig]

Good on ya, imok2.

The formula chadinsk used is a good approximation if the ventilation air is only tempered to room conditions before introduction (as in separate ducting from the cooling system), in which case the air leaving the coil is approximately equal to room temperature.

If you're cooling it, imok2's answer is right -- it's a coil load.

Goober Dave