Latent Heat Load

Calculates the hidden heat required for a phase change at constant temperature. Used in boilers (supplied by fuel) and cooling towers (paid by evaporation).

$$Q=m\times h_{fg}$$

Variables

Symbol	Meaning	Unit
Q	Heat for phase change	BTU
m	Mass or mass flow rate	lb (or lb/unit time)
$h_{fg}$	Latent heat of vaporization (about 970 for water at atmospheric pressure)	BTU/lb

Worked example

Vaporizing one pound of water: Q = 1 lb x 970 BTU/lb = 970 BTU, nearly seven times the 140 BTU needed to bring it to a boil.

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Part of The Blueprint of Water