Cooling/Heating Systems - Page 18

EVAPORATIVE COOLER SELECTION TABLE

Hastings evaporative coolers reduce the dry bulb temperature of the intake or outside air from 87 to 92 percent of the wet bulb depression. The percentage is shown as efficiency in the selection table above. As evaporative cooling is essentially adiabatic with no change in total heat, the wet bulb temperature will remain constant through the cooling process. Discharge dry bulb temperature can be determined by applying FORMULA A.

A practical method of determining the required evaporative cooler air supply is the employment of air change calculations as shown in FORMULA B. Excessive interior heat loads and humid conditions having low design wet bulb depressions will require more air changes and, in turn, a larger air quantity. It is important that evaporative coolers not be undersized. Also room air should not be circulated through the evaporator and all air from the evaporative cooler must be exhausted.

FORMULA A

Evaporative cooler leaving air dry bulb can be calculated from formula:

T2 Tl (Tl - T3)(E)

Where

T2 = Leaving dry bulb

T1 = Entering dry bulb

T3 = Entering wet bulb

E = Efficiency

FORMULA B

Evaporative cooler size for summer operation can be determined from CFM required by a two step process:

((1) Minutes per air change =( Design dry bulb - Design wet bulb) / 10

(2) CFM required = Building volume in cubic feet / Minutes per air change