AIR HANDLING
COOLING COILS
Cooling Coil in the Main Air Handling Unit (AHU)
AHU cooling coil can use chilled water or refrigerant as
direct expansion system.Chilled water temperature varies
between 57'C.Refrigerant temperatures at direct expansion
systems can be as low as 2' C.
COOLING COIL
In calculating the required cooling effect, it is
important to consider that part of the effect is
used to separate the water (latent heat) and
the remaining effect to lower the air
temperature (sensible heat). It is therefore
necessary to incorporate enthalpy differences
in the calculations to absorb the latent heat
part. The cooling effect is calculated as
follows:
Q = L . 1.2 . D h[kW], where:
L = air flow rate, [m3/s]
h = enthalpy difference for air through the coil,
[kJ/kg]
Example on calculation of cooling coil effect:
L = 1.4 m3/s
t1 = 25ºC, RH = 50%
t2 = 12ºC, RH = 100%
Enthalpy can be obtained from tables or
simply from a Mollier diagram:
h1 = 50 kJ/kg
h2 = 33 kJ/kg
Q = 1.4 . 1.2 . (50  33) = 28.56 kW
