Openings Sizing for Natural Ventilation

[alinlis]

Hello,

How do you determine the opening and ridge vent size for Natural Ventilation in a building?

Great appreciated.

 

[YuriB]

Empirically ?

 

[cdxx139]

architects usually size thses, so there might be something in the local building code for minimum sizing requirements

knowledge is power

 

[Waramanga]

if its just for code compliance then see you local building regulations, if you are doing a thermal 'chimney' sort of arrangement then get your physics books out and then take a wild guess.

 

[willard3]

Calculating draft pressures is pretty easy if you know density differences with temperature and height.

 

[Waramanga]

the draft pressures are pretty straight forward but the real trick is integrating it all into the building and avoiding water and dust ingress, providing access for maintenance, allowing for wind effects, maintaining a reasonable thermal envelope, avoiding condensation on louvres etc. It seems all pretty easy but I have personally seen millions of dollars of natural ventilation decommissioned due to all of the above. Be very careful!

 

[KiwiMace]

ASHRAE handbook has a formula for this.

 

[marcoh]

Most ridge ventilator suppliers should have some guidance based on height and temperature.

The theoretical calculations are not diffucult, and fairly sure there are some Ashrae guides or similar. The real challenge is that the ventilation is very dependant on (1) internal heat gain, and (2) much more on wind pressure which you cannot control.

Other issues to consider is that you are working with very small pressure differentials, and makeup/relief air into the space is very important.