Cooling and Heating Equations

Latent and sensible cooling and heating equations - in imperial units

Sensible Heat

The sensible heat in a heating or cooling process of air can be expressed as

h_s = 1.08 q dt         (1)

where

h_s = sensible heat (Btu/hr)

q = air volume flow (cfm, cubic feet per minute)

dt = temperature difference (^oF)

Latent Heat

The latent heat due to moisture in the air can be expressed as:

h_l = 0.68 q dw_gr         (2)

or

h_l = 4,840 q dw_lb         (3)

where

h_l= latent heat (Btu/hr)

q = air volume flow (cfm, cubic feet per minute)

dw_gr = humidity ratio difference (grains water/lb dry air)

dw_lb = humidity ratio difference (lb water/lb dry air)

Total Heat - Latent and Sensible Heat

Total heat due to both temperature and moisture can be expressed as:

h_t = 4.5 q dh         (4)

where

h_t= total heat (Btu/hr)

q = air volume flow (cfm, cubic feet per minute)

dh = enthalpy difference (btu/lb dry air)

Total heat can also be expressed as:

h_t = h_s + h_l

    = 1.08 q dt + 0.68 q dw_gr         (5)

Example - Heating Air

An air flow of one cfm is heated from 32 to 52^oF. Using (1) the sensible heat added to the air can be expressed as:

h_s = 1.08 (1 cfm) ((52 ^oF) - (32 ^oF))      

    = 21.6 (Btu/hr)

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