Enthalpy combines the heat in the air's temperature with the heat locked in its water vapor. Total coil load in Btu per hour is roughly 4.5 times cfm times the enthalpy drop across the coil. Enthalpy economizers compare outdoor and return air enthalpy rather than just temperature, so they don't bring in cool but very humid air that would add load.
Enthalpy drops from 30 to 23 across the coil at 2,000 cfm, that's about 63,000 Btu, call it five tons.
Also heard as
- h
- total heat
- heat content
Related terms
Sensible heat
Heat that changes the air's temperature, which you can read on a thermometer.
Latent heat
Heat tied up in moisture, added or removed when water evaporates or condenses without changing air temperature.
Economizer
Dampers and controls that bring in cool outdoor air for free cooling instead of running compressors.
Wet bulb
The temperature a wet-wicked thermometer reads in moving air, lowered by evaporation in proportion to how dry the air is.