Natural ventilation with HB 1.3

Hi everyone,

I have quite a simple project. It is about a shoebox, with a glass roof that is naturally ventilated, the indoor temperature should not go beyond 30 degrees. Therefore when the temperature outdoors is above 30 degrees the operable windows closed and the cooling system starts.
The main issue comes when I try to change the outdoor maximum temperature for ventilation to a lower value, lets say 25 degrees and the cooling load doesn’t change, i was expecting to get different values, since the windows will only be open when outdoor temperature is bellow 25. I am quite confuse and I don’t understand where is my mistake. Does anyone have the same issue, did you figure out the problem?
PC Greenhouse (565.5 KB)


Hey @Julioamodia89 ,

With one look at your model, I can see what’s wrong. You don’t have any height difference across the windows of your room and the one window that you have is oriented straight up in a way that can catch wind-driven cross ventilation:

So you effectively have zero buoyancy driven natural ventilation and zero wind driven ventilation.

If you are really trying to model the tiny amount of airflow that you would have through an arrangement like this, you could use the AirflowNetwork instead of the default simpler airflow models. This would at least allow you to account for buoyancy driven flow of the infiltration through the walls and then up through the open skylight.

But, generally speaking, this is a poor ventilation design. I would recommend using a sawtooth or other design for the greenhouse if you want to use the roof for ventilation. Or you should at least account for the slope of the roof that you’ll need for drainage so that you have some height difference across the roof to drive buoyancy-driven flow.

Yes, that seems to be it.
Thank you for your help @chris

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