Calculating cooling requirements for a greenhouse
- Thread starter carlo987
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- aircon cooling greenhouse heat
kratos015
Well-Known Member
Unfortunately cooling calculations for outdoor grows aren't quite as black and white as indoor calculations. There are way too many variables to account for.
Is the greenhouse going to be sealed with visqueen/plastic or simply covered with shade cloth? Will you be relying on misters, an evap cooler/wall, or simply ventilation? What are the hottest temps you deal with? What's your humidity and therefore wet bulb temps?
If you're only relying on ventilation, that's easy to calculate because it's the same thing as indoors. However if you're looking for cooling solutions then you'll have a tough time cooling a greenhouse unless your humidity is below 20% or so, give or take.
If you live somewhere where the humidity is under 20% AND the greenhouse is perfectly sealed (i.e using visqueen and not shadecloth), look into building an evaporative cooling wall. Grab yourself a submersible pump and put it in a reservoir, attach the pump to pvc piping and drill holes in the pvc pipe so that water is dripping onto the aspen pads in between the studs of your greenhouse. Seal the greenhouse as best as you can and get some strong ventilation fans to take advantage of negative air pressure that will force air through your pads and cool the greenhouse. Humidity is rarely above 10-15% where I live, so my greenhouse is anywhere between 60-90 degrees depending on the outdoor temps and humidity.
If you have high humidity (anything over 35%) then things get a bit tricky as you'll pretty much only have ventilation and/or shade cloth to rely on. If it were me growing in high humidity then I'd have ventilation fans set up around the greenhouse and use nothing but shadecloth. The shadecloth will drop temps by ~5-10 degrees and the ventilation will ensure that the air/humidity is constantly being moved out of the greenhouse. I'd also grab strains that are specifically suited to harsh outdoor growing conditions and make absolutely zero attempts to grow anything finicky.
Is the greenhouse going to be sealed with visqueen/plastic or simply covered with shade cloth? Will you be relying on misters, an evap cooler/wall, or simply ventilation? What are the hottest temps you deal with? What's your humidity and therefore wet bulb temps?
If you're only relying on ventilation, that's easy to calculate because it's the same thing as indoors. However if you're looking for cooling solutions then you'll have a tough time cooling a greenhouse unless your humidity is below 20% or so, give or take.
If you live somewhere where the humidity is under 20% AND the greenhouse is perfectly sealed (i.e using visqueen and not shadecloth), look into building an evaporative cooling wall. Grab yourself a submersible pump and put it in a reservoir, attach the pump to pvc piping and drill holes in the pvc pipe so that water is dripping onto the aspen pads in between the studs of your greenhouse. Seal the greenhouse as best as you can and get some strong ventilation fans to take advantage of negative air pressure that will force air through your pads and cool the greenhouse. Humidity is rarely above 10-15% where I live, so my greenhouse is anywhere between 60-90 degrees depending on the outdoor temps and humidity.
If you have high humidity (anything over 35%) then things get a bit tricky as you'll pretty much only have ventilation and/or shade cloth to rely on. If it were me growing in high humidity then I'd have ventilation fans set up around the greenhouse and use nothing but shadecloth. The shadecloth will drop temps by ~5-10 degrees and the ventilation will ensure that the air/humidity is constantly being moved out of the greenhouse. I'd also grab strains that are specifically suited to harsh outdoor growing conditions and make absolutely zero attempts to grow anything finicky.
carlo987
Active Member
Thanks, for the reply. I'm planning a geothermal cooling system for the greenhouse.
https://www.rollitup.org/t/geothermal-climate-battery-and-fan-sizing.994869/
Humidity outside is between 30-40% max, which I'm not too worried about, but evaporative coolers are def a no go!
It is a closed greenhouse. Shadcloth is not an option, we have on average >3000w/m2, but not that many sun hours.
Using the geothermal piping I know, that the I can easily cool the greenhouse by recirculating the air 5 to 10 times per hour. I was just interested how it usually works, if one were to do it with an AC. How one would size it?
https://www.rollitup.org/t/geothermal-climate-battery-and-fan-sizing.994869/
Humidity outside is between 30-40% max, which I'm not too worried about, but evaporative coolers are def a no go!
It is a closed greenhouse. Shadcloth is not an option, we have on average >3000w/m2, but not that many sun hours.
Using the geothermal piping I know, that the I can easily cool the greenhouse by recirculating the air 5 to 10 times per hour. I was just interested how it usually works, if one were to do it with an AC. How one would size it?
kratos015
Well-Known Member
I'll be honest with you, I was going to point out the underground system (didn't even remember the name..) but I didn't think you were in a huge enough set up to even entertain the idea/expenses involved. That being said, if you're involved with projects of that kind of scale then I unfortunately have no experience to be of any use to you. Totally out of my element!
In my research on this in the past, I don't recall there being any mention of an AC being used. I thought these worked by taking advantage of the natural hot and cool air from the Earth, I believe the temperature differences create a vacuum and this is what's responsible for regulating the temps? I just remember reading that, but definitely could be wrong. I wish I could be of more help to you.
carlo987
Active Member
Always happy about people trying to sincerely help. It is the intention that counts. Yes, no AC will be used. I was just wondering how one were to calculate it, if one were to use an AC. It is fairly easy to find calculations on heating requirements, but sadly none on cooling requirements.