Chiller Sizing Information
No matter what your application, there is a single formula for determining the size of chiller you need. Before you begin, you must know three factors:
The incoming water temperature
The chill water temperature you require
The flow rate

General sizing formula:
1.Calculate Temperature Differential (ΔT°F) ΔT°F = Incoming Water Temperature (°F) - Required Chill Water Temperature
2.Calculate BTU/hr. BTU/hr. = Gallons per hr x 8.33 x ΔT°F
3.Calculate tons of cooling capacity Tons = BTU/hr. ÷ 12,000
4.Oversize the chiller by 20% Ideal Size in Tons = Tons x 1.2
4.You have the ideal size for your needs

For example, what size chiller is required to cool 40GPM from 70°F to 58°F?
1.ΔT°F = 70°F - 58°F = 12°F
2.BTU/hr. = 40gpm x 60 x 8.33 x 12°F = 239,904 BTU/hr.
3.Ton Capacity = 239,904 BTU/hr. ÷ 12,000 = 19.992 Tons
4.Oversize the chiller = 19.992 x 1.2 = 23.9904
5.A 23.9904 or 25-Ton chiller is required