Supply Air Flow Rate
When the sensible heat loss and supply air temperature in winter are known then the mass flow rate of air is calculated from the following formula:
Hs = ma x Cp ( ts - tr )
where:
Hs = Sensible heat loss (kW)
ma = mass flow rate of air (kg/s)
Cp = Specific heat capacity of humid air (approx.1.01 kJ/kg degC)
tr = room temperature (oC)
ts = supply air temperature (oC) ..............therefore:
ma = Hs / Cp ( ts - tr )
ma = 18 / 1.01 (32.5 - 21)
ma = 18 / 11.615
ma = 1.55 kg/s
Heater Battery Output
The heater battery output is as follows:
H reheater battery = ma ( hS - hM)
where:
H reheater battery = Reheater battery output (kW)
ma = mass flow rate of air (kg/s)
hS = specific enthalpy at condition S (kJ/kg)
hM = specific enthalpy at condition M (kJ/kg)
The specific enthalpies at points S and M are shown on the psychrometric chart below.