Cooling and Heating Equations
Latent and sensible cooling and heating equations - in imperial units
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Sensible Heat
The sensible heat in a heating or cooling process of air can be expressed as
hs = 1.08 q dt (1)
where
hs = 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:
hl = 0.68 q dwgr (2)
or
hl = 4,840 q dwlb (3)
where
hl= latent heat (Btu/hr)
q = air volume flow (cfm, cubic feet per minute)
dwgr = humidity ratio difference (grains water/lb dry air)
dwlb = 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:
ht = 4.5 q dh (4)
where
ht= 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:
ht = hs + hl
= 1.08 q dt + 0.68 q dwgr (5)
Example - Heating Air
An air flow of one cfm is heated from 32 to 52oF. Using (1) the sensible heat added to the air can be expressed as:
hs = 1.08 (1 cfm) ((52 oF) - (32 oF))
= 21.6 (Btu/hr)
Sensible Heat Load and Required Air Volume Chart
Sensible heat load and required air volume to keep temperature constant at various temperature differences between entering air and room air are indicated in the chart below:
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:
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Related Topics
- Air Conditioning - Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort
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Related Documents
- Air Heating Systems - Using air to heat buildings - temperature rise diagram
- Changing Air Condition by Heating, Cooling, Mixing, Humidifying or Dehumidifying Processes - Basic air condition processes - heating, cooling, mixing, humidifying and dehumidifying by adding steam or water - psychometric diagrams and the Mollier charts
- Cooling Loads - Latent and Sensible Heat - Latent and sensible cooling loads to consider in design of HVAC systems
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