Help! Greenhouse too hot

daisychain01(zone 3)May 15, 2010

Our school greenhouse was built without proper ventilation and with our early spring this year, temps are hitting 110 F and higher. I was able to move some of the plants out into a light filled hallway for the weekend, but those pesky students return on Monday and I'll have to move them back to the greenhouse.

It is a permanent glass structure built onto the side of a classroom on the second floor of our school. It's wonderful until late April/early May. There are blinds that I can close on the wall windows, but the blinds on the roof windows won't close because of gravity (some genius must have been in charge of the design).

I've been trying to think of ideas and done a little research. I'm thinking shade cloth attached to the roof blinds with clothes pins? Some sort of water cooling system?

Anyone have any other brilliant ideas? Cost is, of course, a factor.

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imstillatwork(8-9 Oregon Coast / Ca Border)

cheapest will be shade cloth, but put it on the outside if possible. Shade cloth on the inside provides shade, yes, but the heat will be an issue still if the cloth is on the inside. You need to be able to vent that hot air. How about 2 cheap box fans (wal-mart, etc). both in the doorway. One on the floor blowing in, one up high blowing out. It might help, but it is far, far from optimal. You NEED shade cloth AND ventilation.

    Bookmark   May 16, 2010 at 1:04AM
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daisychain01(zone 3)

Thanks so much for the response.

I don't think I can get the shade cloth on the outside (greenhouse is on the 3rd floor not 2nd as I said above), but what if I put it very close to the glass on the inside.

I can probably do the box fans. I'll try one I have at home first. There is a fan installed in the wall at one end, but because it is off of a classroom, the teacher needs to turn off the fan when she's teaching (too noisey).

I can get the shade cloth for free from a supplier that supports our garden club so I'll try that. Why do you say it's best if it's outside?

    Bookmark   May 17, 2010 at 1:36PM
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We have Shade cloth on the inside of our glass and it works just fine. We use Aluminet cloth so it reflects some heat as well. Are there any vents in the glass roof or near the peak of the roof? If not then yes vents or fans will be a must this time of year on a sunny day. We run misting too, but without venting or fans it does more to raise humidity than cool.

You will need to move air, so maybe a quieter exhaust fan or even passive roof vents would help. The two box fan idea may work, but you'll also be dumping a lot of hot air and moisture into the hallway, not to mention the noise they may cause.

Shade cloth and misting would help, but without venting or exhaust fans it will be a tough fight.

    Bookmark   May 17, 2010 at 2:22PM
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ykerzner(9 TX)

When using ventilation of any sort, try to position fans so that they produce a rotation of air inside the greenhouse. As fuzzymoto said, without venting it will be a very tough fight. The greenhouse I use is also attached to a building, albeit a biology building at a university. "Some genius" must've designed this one too, since while there are two vents (side and ridge), there's no space for an exhaust fan. This means I have to work with shade cloth and fans, like you. If you have low humidity, you may want to try to rig up a swamp cooler-type system. Otherwise, the more fans, the merrier. Make sure to position them where they will be most effective, yet won't damage plants.

    Bookmark   May 17, 2010 at 2:50PM
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Mine GH used to get in the 100's here recently. I actually ran a test the other day and put a garden hose in there with a misting nossel. This little test dropped the temp quite a bit. With the correct placement of the misting heads and more of them, this would be a great system to cool the inside. You can find them pretty cheap online for the low-pressure types that hook up to the common garden hose. I plan on buying one with a timer within the next month. I plan on misting for 1-2 mins, every 10-20 mins. I will post some pics and results when I have get the money and buy one ;)

    Bookmark   May 19, 2010 at 12:35PM
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White paint on the inside of the glass - I forget the name but it's made specifically for the purpose.

The problem with shadecloth on the inside is that the heat has already come through the glass. It's better than nothing.

And see if you can get some vents installed in a couple of the windows.

    Bookmark   May 20, 2010 at 10:47AM
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Our Aluminet works great on the inside of the glass and it will last a lot longer on the inside. Youc an build a misting system for cheap from drip irrigation parts too.

    Bookmark   May 20, 2010 at 11:05AM
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"Shade" cloth, including Aluminet, has two functions. Inside the greenhouse, it is to hold heat inside during cold nights. Outside, it reflects heat (and light), lowering inside greenhouse temperatures. The reduced light reaching the plants can be a problem with this product, especially for fruiting crops such as tomato, cucumber, pepper, etc. Imstillatwork is correct that to reduce heat inside the greenhouse, the proper location is on the roof, outside the greenhouse.

    Bookmark   May 20, 2010 at 9:21PM
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stressbaby(z6 MO)

Some locations do not allow shade cloth outside...maybe height, maybe wind...I agree with fuzzy, Aluminet is the choice in this case.

    Bookmark   May 20, 2010 at 9:40PM
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Either way...whatever works best for you. We love having it inside, especially when we put the solar pool cover on the outside in winter. We also currently have toms, cukes, peppers and many others all doing fact our cukes are almost reaching the roof of our GH already.

    Bookmark   May 21, 2010 at 2:46PM
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