Vehicle Climate Control System

This model interfaces simulates the working of a climate control system in a car.

The Climate Control System

The user can enter the temperature value they would like the air in the car to reach by double clicking on the USER SETPOINT IN CELSIUS Block and entering the value into the dialog box. The EXTERNAL TEMPERATURE IN CELSIUS can also be set by the user in a similar way. The numerical display on the right hand side of the model shows the reading of a temperature sensor placed behind the driver's head. This is the temperature that the driver should be feeling. When the model is run and the climate control is active, it is this display box whose value changes showing the change of temperature in the car.

The Stateflow Controller

The control of the system is implemented in Stateflow. Double clicking on the Stateflow chart will show how this supervisory control logic has been formulated.

Heater and Air Conditioner Models

The Heatermodel was built from the equation for a heater exchanger shown below:

Tout = Ts - (Ts-Tin)e^[(-pi.D.L.hc)/(m_dot.Cp)]

where



In addition, the effect of the heater flap is taken into account. Similar to the operation of the blower, the greater the temperature difference between the required setpoint temperature and the current temperature in the car, the more the heater flap is opened and the greater the heating effect.

The Air Conditioner: The final temperature to exit from the A/C is calculated as follows:

y.(w.Tcomp) = m_dot.(h4-h1)

where



Here we have bang-bang control of the A/C system where the temperature of the air that exits the A/C is determined by the engine speed and compressor torque.

Heat Transfer in the Cabin

The temperature of the air felt by the driver is effected by :

The above effects are inputs into the thermodynamic model of the interior dynamics of the cabin. The temperature of the air exiting the vents is taken into account by calculating the difference between the vent air temperature and the current temperature inside the car and multiplying it by the fan speed proportion (mass flow rate). 100W of energy is added per person in the car. Lastly, the difference between the temperature of the outside air and the interior air temperature is multiplied by a lesser mass flow rate to account for the air radiating into the car from the outside.

The output of the interior dynamics model is fed to the display block as a measure of the temperature read by a sensor which is placed at the back of the driver's head.