We have a 1500 sq ft green house in Arizona, the inside is hitting around 125 F. This greenhouse was built in the 1980s. It is a full fiberglass exterior. (If you touch it you itch) We would really like to bring the temperature down to make it usable. We are installing 2 12 inch exhaust fans this weekend. We keep the windows and 2 doors open for heat release with no change. As far as sealing the green house it has just corrugated fiberglass on the eaves. We get a significant about of wind here and attaching a keeping a shade cloth on would be really hard.
Any advice to pull the temp down and get this thing usable?
by Cannavis
19 Comments
You need waaaay bigger exhaust and intackr fans. 12in ain’t gunna do anything for that size. You also need shade cloths. Look into swamp coolers as well
There is a greenhouse like that at one of the garden nurseries here in Texas. It’s covered in shade cloth and has two GIANT swamp coolers on it and it’s still upwards of 100F in there on hot days.
Giant shade cloth
Ridge vent along the entire length to vent the heat out, in addition to making the end walls able to roll up for a cross draft… might bring you down under 100f with your 12in fans in push/pull configuration.
You need roof windows/openings or bigger exhausts (or active ones with a fan) at the gable. And more lower intakes. Try to create a chimney effect. You really need air flow and air exchange in there, also against humidity peaks.
I’m in southern AZ, and it’s a much smaller greenhouse (8′ x 14′), but can reach 130º+ in summer if I’m not cooling it. I grow cactus/succulents exclusively, so I try to keep it under 110º, which is done with a combination of the following:
I have the greenhouse lined with 50% shade cloth on the roof, 30% shade cloth on the sides. I line it on the insides, same as you would, due to the wind we get here. It doesn’t keep heat out as well but it still helps. Also prevents plant burning.
4x roof vents, and usually have the doors open all day. Fans.
Swamp cooler. Critical in summer. Shaves off 10-15º. In something as big as yours, you could install a water wall (essentially a giant swamp cooler built into the wall).
https://preview.redd.it/c8jvvo2hm0rg1.jpeg?width=1079&format=pjpg&auto=webp&s=850ea0bca330efa4f4ec572725de0b0c1dca9c73
With a building as large as this, I’d consider an evaporative cooling wall, and big exhaust fans.
Have you considered adding more thermal mass with a water feature or containers?
You, sir, need a retracting shade controlled by a temperature delta range.
Install your shade cloth on the inside instead of on the outside. That would take care of your wind problem. A color other than black, maybe wheat, might work best. That’s what was advised for me in zone 8b.
I built a homemade swamp cooler from YouTube instructions done by a guy in Arizona using a box fan, an evaporative pad, and a tank (I’m now using a trash can on wheels). In a pinch, you might could try that and strategically set several around. They do work very well, and help raise the humidity level which is helpful on days when our humidity is low.
Be careful adding swamp coolers… If you do add them keep them away from your plants..
My friend added one, and it caused powdery mildew.
You need some big ass fans moving that air around
Evaporative wet wall on one end (easily diy’d, see YouTube) and large exhaust fans on the opposite end. The fans will turn on and draw hot dry air through the evaporative wall and cool it significantly while exhausting out the hot air.
I don’t think 2 12″ exhaust fans will help all that much with such a large space. [This](https://www.acfgreenhouses.com/greenhouse-fan-calculator.aspx) calculator can help you determine the size of fans you need but considering you’re in AZ and can’t use shade cloth (which helps a TON by the way) I would size up their fan recommendation.
Replace fibergless with insect screen ( mesh 50 )
It seems like shade cloth is pretty unanimous, I will look into the evaporative wet wall as well thank you everyone who reached out!
https://www.farmstandapp.com/177231/6-best-greenhouse-shading-paints-for-intense-sunlight-that-prevent-leaf-scorch/
I have not used one before since I use cloth but maybe greenhouse shade paint on the outside?
Mount 30-50% shade cloth on those rafters inside flat.
Mount large 24-48″ fans at both ends at the peak of the roof to pull the heat from between the shade cloth and the roof. Make one wall, the hot side, almost entirely exhaust fans. Make the other end wall wet walls pulling cool air in. Mount t misters on those rafters every other one and then hang oscillating fans on the other rafters, approx 10′ apart on center. Cheap? No.
Effective? Very.
Call Rimol Greenhouses. They’ll help you design an exhaust system and/or shade and/or evap system for this, and do it correctly.
Are all of these photos from the same building?