Bug in Simulating Automatic Climate Control Systems simulink example

Hello,

I just noticed that in the Simulink example “Simulating Automatic Climate Control System” there seems to be an issue with the thermodynamic model. For instance, if I set the User Setpoint temperature to 25 °C and the external temperature to –20 °C, the heater does not turn on, which clearly indicates a problem.

Link to the demo: https://ch.mathworks.com/help/simulink/slref/simulating-automatic-climate-control-systems.html

Answer 1

[Sam Chak]

Hi @Tommaso

The reason the heater does not turn on is that the thermometer clearly indicates the initial air temperature in the car is 25.5°C, which exceeds the user setpoint of 25.0°C. I believe that if the temperature drops below 25.0°C, the heater will activate.

[Tommaso]

The thing is that the temperature never drops below 25.5. The power generated by the occupants is much higher than the power lost between the internal and external temperatures (see summation before internal dynamics). As a result, even under these conditions, the car will (counterintuitively) still need AC

[Sam Chak]

Hi @Tommaso

You need to investigate:

Is 25.5°C the equilibrium temperature of the thermal system when the setpoint is 25.0°C?

If the setpoint is adjusted to 27.0°C while the current temperature is 25.5°C, does the heater turn on?

Additionally, if the number of occupants remains the same while the heater and air conditioning are disabled, does the temperature rise?

One more point to consider is that there is usually a deadband for heating to prevent excessive energy waste from On/Off cycles. Does 25.5°C fall within the range of temperatures at which the heater does not respond?

[Tommaso]

Yes it's 25.5°C, when you increase that the setpoint we the heater will turn for few instants. I think there is a wrong scaling factor. Physically doesn't make sense that when the temperature outside is -20 the heater doesn't get turn on.

[Sam Chak]

Have you observed a temperature drop when the heater and air conditioning are completely disabled or disconnected? Logically, since the outdoor temperature is –20°C, the indoor temperature is expected to decrease.

[Tommaso]

No the internal power heat from the passengers is way higher... I am pretty sure there is a missing scale coeffieint in the simulation

[Sam Chak]

At this point, the best course of action is likely to contact technical support to report the bug you discovered.

https://www.mathworks.com/support/contact_us.html