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Greenhouses & Garden Structures

Exhaust fan opinion needed

16 years ago

Whenever I see pictures of an exhaust fan, it is usually installed at the back of the greenhouse. I got a 16 inch exhaust fan and 2 16 inch motorized shutters. Is there any reason anyone knows why I couldn't put the fan over my door. The door faces south and the shutters will be on the wall facing north. I'm thinking they would be drawing in cooler air from the north.

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Comments (8)

User
16 years ago
The air on the north outside the GH is the same temp as the air on the south, so from that POV, it doesn't make any difference.

The principle consideration should be the prevailing winds. Southern winds tend to blow warmer air, and on those days with warmer air, exhausting the GH will be more important. You don't want the GH exhaust system trying to move air against the current of the prevailing wind.

SB
ole_dawg
16 years ago
Prevailing winds change with the season in many places. It would be difficult for me to decide which way the wind will blow as we seem to get it from all directions. Yesterday from the North and today from the West.

1eyedJack and the Dawg
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mudhouse_gw
16 years ago
Mine is on the back (east) wall, and that worked fine since most our winds are from the west. If it works out for your prevailing breezes, oraylawson put his exhaust fan over his 10x12 HFGH doors:
oraylawson's photos

Also, I think I remember a comment from Laserfan a while back, saying he was going to install his fan over the doors too, due to the direction of his prevailing wind.
C Schaffner
Original Author
16 years ago
Ahhh, prevailing winds. I think ours come from the west. We are on the coast.
our greenhouse is right behind our house on the south side, the east side is a tall bank. I'm hoping it will work okay. Thanks for the links to oraylawson's fan. It looks similar, except I have 2 smaller intake shutters.
We are putting the shutters on the north side at the bottom. It sure looks cool. I can't wait until it's done.
laserfan
16 years ago
>We are putting the shutters on the north side at the bottom.

I put our intake shutter low on the back wall also, with the fan above the door. Thought maybe the air lower-to-the-ground might be a little cooler (fat chance here where yesterday it was 100F already).

BTW when mounting our fan above the door, I made the lower support (piece of angle iron) wide enough to span to those supports that reach all-the-way to the floor. Maybe a little less stress on the door span that way.
rjinga
15 years ago
I think that I may put mine above the door in the space where the center panel blew out recently..since I"ve scoured the area and cannot find it...it creates the perfect space!!!

I will have to close up the pointed top most part and hope I can find a fan that fits exactly into that space :) I'll start looking now.

Seems here the strongest winds come from the West, and my door entry is facing east, so it would seem reasonable to be sucking out hot air and spitting it out in the direction the wind already is blowing :)
dcarch7 d c f l a s h 7 @ y a h o o . c o m
15 years ago
In general, it is very difficult to guess/predict how wind current works as it blows over a structure, especially with trees and buildings around it. Aerodynamics is complicated.

ThatÂs why tall building designs are frequently put thru wind tunnel in model form. Even with powerful computer software, airplane designs are also tested in wind tunnels.

I tend to think you would first measure temperature distribution inside your greenhouse, and then the fan should be installed as near the hottest point as possible.

If you are really into it, make a simple scaled cardboard model, go to an air conditioning supply house or go to a model train hobby store and buy some smoke making chemical. Using a fan, and observe how the airflow works with your model.

dcarch
C Schaffner
Original Author
15 years ago
Thanks so much for all your help. The fan and shutters are in. We just need to hook them up.

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