Coil Load Calculation Example

Determine the minimum cooling coil load and required chilled water flow for a system serving an office space with a sensible cooling load of 30,800 Btu/h and a latent load of 13,500 Btu/h. Indoor design conditions are 75°F/50% RH, and Outdoor design conditions are 85°F DB/70oF WB. The minimum ventilation air is 25% of the total supply air which is delivered at 55°F. The fan selected is a 70% efficient "drawthrough" arrangement, and delivers air at 4.0 inches total pressure. No manufacturer’s coil data is available. Assume 10°F chilled water temperature rise through the coil.

RSH = 1.08 x CFM x ∆T

CFM = RSH / (1.08 x ∆T)

CFM = 30,800 / [1.08 (75 - 55)]

CFM = 1425 SHR = 30,800 / (30,800 + 13,500) = 0.70