Opening Windows and "shield roof"

Carlos · Posts: 25

Hi all, two more questions:

1) I have a house with high inside temperatures (about 5ºC above outdoors, and outside its about 30ºC).

I want to open the windows by night for night natural ventilation cooling. In Openings Tab I set Operation "%glazing area opens" as 50% (since the windows only open to the half) and operation schedule to be on daily from 9pm to 6am.

In Activity Tab -> Ventilation Setpoint Temperatures -> Natural Ventilation I set Nat Vent Cooling as 0ºC, so it works all the time, independently of the inside temperature.

In the main Building Model Options, it is set as Natural Ventilation: Calculated, so, in HVAC Tab, Natural Ventilation is not activated.

Is it right??? the windows are oppening at night? Because I ran the simulation and the disconfort increased (a little) instead of decreasing.

2) I don't know if it is called 'shield roof'. It's a inclined roof with voids and holes so that air enters from one side, absorbs the heat from the radiation and then gets out from the other roof's side, and new fresh air enters.

I tried to simulate it. Since I cannot make holes to the inside of a roof, I set the roof as a 1cm width. Then I built a narrow block (17cm) over, so that it had a zone (unoccupied, with holes in two of the 'external walls') acting as the shield roof of the real zone.

When I do it, I have a ceiling, a roof, 4 walls... and a fifth wall called "Downward facing external wall" that faces directly to the ceiling, as if it were a kind of floor. Besides I dont' know what it is, it occupies space destinated to the actual void.

That downward wall itsn't there when the first roof (the one of 1cm) is completely horizontal, but when it has a slope, even as minimal as 1º, the downward wall shows up.

The Construction is 'Separated'.

Thanks,

Carlos

Laurent_Support · Posts: 292 Location: Vincennes

Hello Carlos,

About night natural ventilation, you must have check On the natural ventilation box in the HVAC tab to activate the calculation (whatever option you chosen in Model Options).

You will see external air curve from outside to zones and between zones in your outputs if settings are Ok.

For your ventilated roof, I think the difficulty is to estimate a correct air flow between the construction layers.... a CFD problem.
My idea (as is) should be to model the roof as usual. Then add thin blocks (their thickness should be the air gap) on each roof surface. Set the correct construction layers into this block and finally choose an air change rate to make the air circulation sufficient to bring heat away.

This is only a first idea not complete but I hope could make you come up with your problem.

Regards,

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