How to control the house temperature using a fan system?

I am modeling a fan system that is able to reduce the temperature of the house when it exceeds a certain set temperature.

The idea is to use the difference between the set temperature and the house temperature to tune and control whether the fan system comes on to cool down the house temperature in case it's too high and vice versa. It should be able to control and maintain a certain temperature in the house.

This is where I am stuck, I don't know how to control the house temperature to a desired set temperature using the fan system.

Attached is the simulink file.

All the help is appreciated thanks.

[John D'Errico]

Why would a fan be able to control the teperature of a house? Sorry, but your goal is a bit strange.

Consider a case where the outside temperature is 35 degrees C, and the internal temperature is 30 degrees C.

Now using only a fan, tell us what mechanism you would use to reduce the internal temperature of the house below the current 30 degrees C.

Similarly, suppose the outside temp is 10 degrees. Explain how you would use a fan to increase the internal house temperature above that point.

Until you explain what mechanism you would use (one that does not contradict the laws of thermodynamics) you cannot perform this task.

[hunter manana]

Lets say the say the set internal temperature is 25 degrees C, when the internal temperature temperature is 30 degrees C, the fan will extract the hot air from inside until the temperatures drop to 25 degrees C. When the temperatures are lower, the stored heat during the day for instance will be used to increase the temperatures to 25 degrees C.

[DGM]

If the indoor temperature is decreasing naturally, it's because heat is being lost to the outdoors. Ventilation only accelerates the process. It's not clear to me where you're storing heat otherwise, but then again, I can't open the .slx file. Latest version of simulink I have installed is R2015b.

Answer 1

[Sam Chak]

Hi @hunter manana

I'm unsure of how your house temperature control mechanism works. But if based on the thermal dynamics provided, then this is probably how the math produces magic (see User-defined parameters section). I also do not know how your PID works. Perhaps you can translate the given math into something that your PID control block recognizes.

tspan  = linspace(0, 1, 10001);
T0     = 30;    % Initial house temperature
[t, T] = ode45(@odefcn, tspan, T0);

% Solution Plot
plot(60*t, T, 'linewidth', 1.5), 
ylim([18 32]), grid on, 
xlabel('Time / min'), ylabel('Temperature / °C')
yline(23, '--', '23°C', 'LabelVerticalAlignment', 'Bottom')

% Ordinary Differential Equation function
function Tdot = odefcn(t, T)    % (T = Thouse)

    % Thermal Resistance of the House
    Req   = 0.0000004;  % C/J-hr
    
    % Mass of air present in the house
    M     = 5987.7684;  % kg
    
    % Specific heat capacity of air
    c     = 1005.4;     % J/kg-C
    
    % Outside temperature (assumed to be measurable)
    Tout  = 23 + 5*sin(2*pi/24*t);
    
    % User-defined parameters (set the values as indicated, the rest are 'laws')
    ts    = 20/60;      % desired settling time (hr)    <-- set this one
    k     = 5/ts;       % thermal control rate          <-- maybe related to the heater's capacity
    Tref  = 23;         % reference temperature         <-- and this one
    Tgain = (- Req*M*c*k*(T - Tref) + T - Tout)/Req;
    
    % Thermal dynamics
    Tloss = (T - Tout)/Req;
    Tdot  = (Tgain - Tloss)/(M*c);

end