How to automatically vent Free, or Cheap

I've got my greenhouse build underway here in Ozarks. Its 100 ft. from house and I've got a temp adjustable switch for fan. I have some screened widows out of an Rv that can be manually opened. I want some way to vent automatically that I can fabricate or adapt form something I can salvage. I've seen those fancy store bought vents. Nice but too much. I thought of making of finding a vent that would open with the air pressure from fan, and that I could somehow protect from wind. Once it got hot here I was planning on rolling up plastic on one side of greenhouse so I'm thinking I only would need this in spring and fall.

Have heard of non-powered automatic vents. Are these the store bought ones you're mentioning?

The automatic non-powered ones are like cylinders of wax, when it gets hot enough for the wax to melt then the windows open. You can sometimes buy replacement-cylinders for not too expensive, and fit them onto your own windows/vents.

I use a solar panel, old car battery and a fan with a thermostat on it... but I think that probaly cost me more (if I hadn't scrounged the parts anyway) than getting the wax cylinders.

Tim Malacarne wrote:Have heard of non-powered automatic vents. Are these the store bought ones you're mentioning?

Yes-- There are several companies selling what looks like the same thing. Look on Amazon. Have some sort of wax inside cylinder. I'm going to search for replacement cylinders. Wonder what wax this is. I think for now I'm going to just use the manually operated vents till I come up with free parts or better idea.

Charli Wilson wrote:The automatic non-powered ones are like cylinders of wax, when it gets hot enough for the wax to melt then the windows open. You can sometimes buy replacement-cylinders for not too expensive, and fit them onto your own windows/vents.
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I found replacement cylinders at about 1/2 of price for new whole unit. Also found a new unit for about $16 at I think it was Harbor Freight. Reading the reviews I saw the expected lack of quality but one fella took his apart after it stopped working. He found poor workmanship left burrs which destroyed the o-rings. Then he put light weight oil inside to replace the oil which was in there. He said it worked after that. Was this just warm melted wax and not really oil. I did see references in adds to just having oil inside.
I'm still thinking about the electric cylinders I found at I think it was Surplus Supply in Nebraska
If i can find an old car hood cylinder I'll see what i can do in way of experiment. In your normal cylinder there is nothing but a honed smooth cylinder and o-ring mounted piece holding rod. I was looking up the thermal expansion of oil but the math made me want to wait till later.

We vent manually, and at this time of year, that works OK... The WX the last few days has been sunny and highs in the low 40's 2 days running. It gets to about 70 in the coldframe, that's about "it." The beds are warming nicely, and we've been cutting the lettuce and spinach I sowed in October or November..... Gotta water out there about once a week....

I put one of those spinning attic turbine vents you see on top of mine. It spins and pulls air out at the slightest wind or if the heat starts to build up the hot air will start it spinning on its own. I have two lower vent that open automatically like the ones you talk about above. When the turbine is spinning and the two lower one are open it really moves the air. As the greenhouse cools the lower vents close and the top one continues to spin which vents some but not as much. I have a door built for the spinner made of 2 inch foam board. I stick it in the vent from the bottom at night in case the wind kicks up so the spinner wont suck out all my warm air. I also stick the door in in the winter durring the very coldest months and just let the two bottom vents do there thing. The system works very well and requires no power and very little attention.

I think you are looking for these. The principle is when the internal fluid is heated naturally by the greenhouse, it expands causing a hydraulic force which lifts a window. Very durable, good brands last many years, cheap and there are many models in the market. Repairs after a few years are conducted simply by replacing a simple o-ring and refilling the reservoir. Again, very cheap and sustainable.

Those are exactly what I have down low. The problem is they only move about an 1 1/2 so they wont open a window very far. Also they have a small amount of power to lift and close. I think mine were rated at 15 lbs. So you will need a lot of them if this is your only ventalation and it is sunny and hot out side. That is why I added the spinner.

Only problem I see with spinners is thermal loss during winter. They work great during the summer though. A remedy would be to have the option to close off the spinners during the winter months.

Amedean Messan wrote:Only problem I see with spinners is thermal loss during winter. They work great during the summer though. A remedy would be to have the option to close off the spinners during the winter months.

If you notice in my reply, I close it every night for about 6 months a year. I keep it closed for 3 months in the winter even during the day. and keep it open for the summer even at night. It does work well. Thanks

if you live in an windy area, you may have to set them up to open into the greenhouse.
i have seen a few blown off in my area because they open up to the wind.

It was recently discovered that fishing thread can be tightly wound and then heat treated to memorize the shape. This process turns simple fishing line into a really strong artificial muscle which contracts and expands depending on ambient heat loads.

http://singularityhub.com/2014/03/10/superstrong-artificial-muscles-developed-from-fishing-line-and-sewing-thread/

Because heat is the triggering element which controls the expansion and contraction and because this is so simple and most likely DIYable, I can see this replacing somewhat expensive or bulky vent controls.

Just a thought and something I want to try when I start developing my own greenhouse blueprints for scalability on my own land.

Cheers.

That was an awesome article. Thanks for sharing that, Chael.

There was a youtube video shown in it, shown below, which gives an idea of how it works.