Appendix 1: Formulas

Following is a list of formulas and equations in the order that they appear in the
book, with a description of each:

P = (GPM / Cv) squared

Pressure (in PSI), expressed as a function of flow and Cv (valve coefficient.

MAT = {(RAT x %RA) + (OAT x %OA)} / 100

Mixed Air Temperature, expressed as a function of return air temperature and
percentage, and outside air temperature and percentage.

%OA = {(MAT – RAT) / (OAT – RAT)} x 100

Percentage of Outside Air, expressed as a function of mixed air, return air,
and outside air temperatures.

BTUH = 1.08 x CFM x delta T

Airside Heat Transfer Equation

BTUH = 500 x GPM x delta T

Waterside Heat Transfer Equation

BTUH = KW x 3410

Conversion of kilowatts to BTUH

KW = BTUH / 3410

Conversion of BTUH to kilowatts

PSI = ft. hd. / 2.31

Conversion of “feet of head” to PSI

Practical Controls Book Excerpts