Heating Coil or Dry Cooling Coil - Commissioning-hvac.org

Heating Coil or Dry Cooling Coil
Jean Lebrun
University of Liège
The model proposed here can be used in both heating and cooling regime, providing that
the coil stays dry.
The secondary fluid is called “refrigerant”, but the heat flow rate is taken as positive in
heating mode.
The coil is supposed to behave as a counter-flow heat exchanger.
Laminar and turbulent regimes are considered on air and “refrigerant” sides respectively.
The output variables are the coil heating (or cooling) power and the exhaust temperatures
of both fluids (air and refrigerant).
The parameters are the specific heat of the refrigerant, the nominal flow rates of both
fluids and the three nominal thermal resistances (air side, metal and refrigerant side).
The input variables are the supply conditions on both sides of the coil.
This gives the following information flow diagram:
The first equations are based on two simple heat balances:

Then, the effectiveness is defined as for a classical counter-flow heat exchanger:
The thermal resistances are calculated by reference to their values in nominal conditions: