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PART 5. Equations. HVAC EQUATIONS, DATA, AND RULES OF THUMB. 5.01 Cooling and Heating Equations. HS = 1.08 × CFM × ∆T. HS = 1.1 × CFM × ∆T. HL = 0.68 × CFM × ∆WGR. HL = 4840 × CFM × ∆WLB. HT = 4.5 × CFM × ∆h. HT = HS + HL. H = U × A × ∆T. HS HS SHR = = HT HS + HL. TU/HR LB. HFG. HS HL HT ∆T. ∆WGR. ∆WLB. ∆h. CFM. U.
Specific Heat Ratio of air at temperatures ranging -40 - 1000 degC (-40 - 1500 degF) at standard atmospheric pressure - Imperial and SI Units.
It is important to use the correct procedure for estimating heat gain or heat loss. Two groups—the Air Conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)—publish calculation procedures for sizing central air conditioners.
Latent Heat: LH = 3.0 Q∆w. where heat is in W = ∆t temperature difference, K or °C = ∆h enthalpy difference, kJ/kg ∆w = moisture concentration, g/kg dry air = Q flow rate of air, L/s. Pump or Fan Power. P = Q h.
STANDARD AIR = .24 Specific Heat (BTU’s needed to raise 1 lb. 1 degree) SENSIBLE HEAT FORMULA (Furnaces): BTU/hr. – Specific Heat X Specific Density X 60 min./hr. = X CFM X ∆T
SENSIBLE HEAT FORMULA (Furnaces): BTU/hr. – Specific Heat X Specific Density X 60 min./hr. = X CFM X ∆ T.24 X .075 X 60 X CFM X ∆ T = 1.08 X CFM X ∆ T ENTHALPHY = Sensible heat and Latent heat TOTAL HEAT FORMULA (for cooling, humidifying or dehumidifying) BTU/hr. = Specific Density X 60 min./hr. X CFM X ∆ H = 0.75 x 60 x CFM x ∆ H ...
Specific heat (C) is the amount of heat required to change the temperature of a mass unit of a substance by one degree. Isobaric specific heat (Cp ) is used for air in a constant pressure (ΔP = 0) system. I sochoric specific heat (Cv ) is used for air in a constant-volume (isovolumetric or isometric) closed system. Note!
