Enthalpy - Honeywell Design and Application Technical Reference Manual

Section 2 - Enthalpy Theory And Controllers
The measure of heat used in the United States
today is the British Thermal Unit or BTU. This
is the amount of heat required to raise the
temperature of one pound of water by one
degree Fahrenheit. A metric unit is the joule.
There are 1055 joules per BTU.
Sensible Heat
Heat that changes the temperature of the air
without changing its moisture content or dew
point temperature is sensible heat. Heat
added by a heating coil is sensible heat. Heat
removed by a cooling coil that remains dry is
also sensible heat.
30 BTU/LB
69.7 k-J/kg
25 BTU/LB
58 k-J/kg
20 BTU/LB
46.4 k-J/kg
15
BTU/LB
34.8 k-
J/kg
40 F 50 F
4 C
35 F 45 F
2 C 7 C
63-8594-02 Honeywell Economizers
45 BTU/LB
104.5 k-J/kg
40 BTU/LB
92.8 k-J/kg
35 BTU/LB
81.4 k-J/kg
60 F 70 F
10 C 16 C 21 C
55 F 65 F
13 C 18 C
DRY BULB TEMPERATURES

Enthalpy

Latent Heat
Heat required to change water to vapor
(steam) without change in temperature or
pressure is latent heat. It is also called heat of
vaporization. When water is vaporized the
latent heat passes into the air, and when vapor
condenses, latent heat is removed.
Total Heat (Enthalpy)
The sum of sensible and latent heat and is
commonly referred to as enthalpy. Enthalpy is
often referred to as the total heat content of
the air.
50 BTU/LB
116 k-J/kg
80 F 90 F
27 C 32 C
75 F 85 F
24 C 29 C
26
100 F 110 F
38 C 43 C
95 F 105 F 115 F
35 C 41 C 46 C
120 F
49 C
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