Cooling and Heating Equations
Latent and sensible cooling and heating equations  imperial units
Sensible Heat
The sensible heat in a heating or cooling process of air (heating or cooling capacity) can be calculated in SIunits as
h_{s} = c_{p} ρ q dt (1)
where
h_{s} = sensible heat (kW)
c_{p} = specific heat of air (1.006 kJ/kg ^{o}C)
ρ = density of air (1.202 kg/m^{3})
q = air volume flow (m^{3}/s)
dt = temperature difference (^{o}C)
Or in Imperial units as
h_{s} = 1.08 q dt (1b)
where
h_{s} = sensible heat (Btu/hr)
q = air volume flow (cfm, cubic feet per minute)
dt = temperature difference (^{o}F)
Latent Heat
Latent heat due to the moisture in air can be calculated in SIunits as:
h_{l} = q ρ h_{we }dw_{kg} (2)
where
h_{l} = latent heat (kW)
ρ = density of air (1.202 kg/m^{3})
q = air volume flow (m^{3}/s)
h_{we} = latent heat evaporization water (2454 kJ/kg  in air at atmospheric pressure and 20^{o}C)
dw_{kg} = humidity ratio difference (kg water/kg dry air)
 estimate humidity with the Mollier diagram
Latent evaporation heat for water can be calculated as
h_{we} = 2494  2.2 t (2a)
where
t = evaporation temperature (^{o}C)
Or for Imperial units:
h_{l} = 0.68 q dw_{gr} (2b)
or
h_{l} = 4840 q dw_{lb} (2c)
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)

1 grain = 0.000143 lb = 0.0648 g
 Psychrometric chart
Total Heat  Latent and Sensible Heat
Total heat due to both temperature and moisture can be expressed in SI units as:
h_{t} = q ρ dh (3)
where
h_{t} = total heat (kW)
q = air volume flow (m^{3}/s)
ρ = density of air (1.202 kg/m^{3})
dh = enthalpy difference (kJ/kg)
 estimate enthalpy with the Mollier diagram
Or  in imperial units:
h_{t} = 4.5 q dh (3b)
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} (4)
Example  Heating Air
An air flow of one cfm is heated from 32 to 52^{o}F. Using (1) the sensible heat added to the air can be expressed as:
h_{s} = 1.08 (1 cfm) ((52 ^{o}F)  (32 ^{o}F))
= 21.6 (Btu/hr)
Sensible Heat Load and Required Air Volume Chart
Sensible heat load and required air volume to keep the temperature constant at various temperature differences between make up air and room air:
Latent Heat Load and Required Air Volume Chart
Latent heat load  humidifying and dehumidifying  and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below:
SHR  Sensible Heat Ratio
The Sensible Heat Ratio can be expressed as
SHR = h_{s} / h_{t} (6)
where
SHR = Sensible Heat Ratio
h_{s} = sensible heat
h_{t} = total heat (sensible and latent)
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