Here's how you calculate:
q: heat transfer rate, Btu/h
Trt: Room temperature, F
Tst: Supply Air temperature, F
V: Air flow rate, ft3/m
q= 1.085 x V x (Trt - Tst)
Metric form:
q: Watts
V: L/s
Trt, Tst: C
q = 1.2 x V x (Trt - Tst)
Note this calculation is based on sensible heat and it is used for dry bulb temperature while not taking into consideration the latent loads or moisture sources.