This example models moist air flow in a vehicle heating, ventilation, and air conditioning (HVAC) system. The vehicle cabin is represented as a volume of moist air exchanging heat with the external environment. The moist air flows through a recirculation flap, a blower, an evaporator, a blend door, and a heater before returning to the cabin. The recirculation flap selects flow intake from the cabin or from the external environment. The blender door diverts flow around the heater to control the temperature.
The model can be simulated in two modes: predefined system inputs or manual system inputs. For predefined system inputs, the control settings for the HVAC system is specified in a signal builder block. For manual system inputs, the control settings can be adjusted at run time using the dashboard controls.
The heater core and the evaporator are basic implementations of heat exchangers using the e-NTU method. They are custom components based on the Simscape™ Foundation Moist Air library.
This figure shows a psychrometric chart for the moist air inside the cabin. It is based on the ASHRAE Psychrometric Chart No. 1 and is used to convey thermodynamic properties of moist air, such as dry-bulb temperature, web-bulb temperature, relative humidity, humidity ratio, enthalpy, and volume. The trajectory of the state of the cabin moist air during simulation is plotted on the chart.
This plot shows rate of condensation in the evaporator when the air conditioning is turned on.