Once the cold season is hot water or steam is supplied to the heating coils in the AHU. This coil heats the leaving the AHU, sending warm air to all of the rooms.. The coil consists of a copper header supplying steam to a copper tube which passes through a continuous aluminium fin for added heat transfer surface area

HEATING COIL CALCULATION
When a certain volume of air passes a heating
coil, air temperature is increased from t1 to t2.
This process takes place at constant air
humidity. The effect of the heating coil is
calculated as follows:
Q = L . 1.2 .D t [kW], where:

L = air flow rate, [m3/s]
D t = increase in temperature across the coil,
[ºC]
Example on calculation of required heating coil
effect:
t1 = 0° C, RH = 50%
t2 = 20° C
L = 1.4 m3/s
Q = 1.4 . 1.2 . 20 = 34 kW
Air velocity
The air velocity across the heating coil is
calculated as follows:

L

v = L [m/s], where: V = A
A

L = air flow rate m3/s
A = gross area m2

Water volume
To calculate pressure drop on the water side
of the heating coil and determine the size of
the shunt valve, the water volume in a heating
coil must be given.

This is calculated as follows:

q = Q [kg/s], where
Cp.D t

Q = heating coil effect, [W]
t = temperature increase of water through the
heating coil, [° C]
Cp = 4.175 j/kg° C at a water temperature of
50° C