Exhaust fans versus 'normal' fans?

[daemondamian]

Hi folks,
must an exhaust fan be used for moving air out of a greenhouse?

Why can't a normal fan be used but facing out from the outside of the GH- wouldn't that be drawing in air from inside the GH and blowing it out?

When I say normal fan I mean this - the main round fan blades and front and back grill -which is either on a bracket or stand.

I have looked at all the calculations- trying to get the right cfm but nothing I've found comes close to what it seems I'll need for removing the air volume per minute [see below for my 'GH' dimensions] plus it's measured in litres per minute here in Australia.

I can easily can get a pretty big normal type fan and sit it in the timber frame- fill in around it. Otherwise the exhaust types fans I could get are:

EZI AIR 4 POLE INLINE FAN 300MM 240V 65W 380L/S

SKYWIDE 250MM AXIAL INLINE DUCT FAN 4 POLE 65W
Flow Rate L/Sec: 110 approx



SPECTRUM HGT-30 AXIAL INLINE FAN 300MM BLACK 65W 380L/S

SPECTRUM CUSTOMLINE C200 CENTRIFUGAL FAN 150WATT 220L/S

or

Easy Duct Thermal Transfer System
55 litres per second

Damian.

Extra info:
I'm in the process of setting up a new area for my Pleurothallidinae & Oncidinae alliance plants which is approximately 5 metres long by 2.5 metres wide [actually it's wider at one point and tapers thinner towards the other end] by 2.8 metres high.

On one end wall I'm putting in an evaporative cooler [with the back of it actually exposed outside so as to draw in new air] sitting on the bench and I have a big 3 speed tilt adjustable wall mounted oscillating fan [maybe 40cm?].

On the other end wall I am considering putting in a fan that would draw out hot air in summer and in conjuction with the evaporative cooler keep temperatures lower and humidity higher.

The setup is actually on the east side of my house [I'm in Australia]- house on one side [brick, two big windows] and solid fence on the other side- I've just put up some timber framing, polyflute, clear plastic, shadecloth etc put the area does stay much cooler than my other little shed where I've been growing everything.