The air system in this simulation is relatively simple. When heating or cooling is required, a thermostat control signal will enable the fan which draws conditioned air from the buidling. The room air then passes over the heating/cooling coil of the heat pump; which then heats or cools the air (taking into account both the sensible and latent considerations).
The heating/cooling capacity of the heat pump is a function of the air flow rate, the air temperature, the water flow rate, and the water temperature. The capacity will be read from a look-up table and used to determine the exiting air conditions from the heat pump.
The air leaving the heat pump passes over the auxiliary heating coil, which is controlled by the thermostat based on the room temperature, and is returned to the building. Duct losses (both pressure and temperature) are ignored in this simulation (although they easily could be calculated).