Setting up a custom greenhouse

[jmmehler]

So one of the newest members of our society, had a custom green house built (before she joined our society). While the builders had no formal experience with greenhouses, she lives just around the corner from me, and has asked me for help in establishing it, and indoctrinating her in the world of orchids. I hope to share some of those experiences, and will be looking for substantive input from y’all (as we say here in Alabama). Not to sound anti-social, but please, only advice and opinions. No feel-good attaboys.

The green house, 7 x 14 ft, with a slanted roof that goes from about 6.5 ft to 8 is covered in clear vinyl plastic, with a clear corrugated plastic roof. The vinyl offers some drawbacks and some interesting advantages. One day, in the middle of winter, it was 35 degrees outside and 91 in the greenhouse. That was before the electric venting fan was installed on the North side (wrong end) with a passive louvered vent on the south side. Great 12’ fan. Quite, and moves 932 cfm.

She has two electric feeds, one 240, one 120 volt. We ordered a 240v electric heater which works fine. I looked into covering the whole thing in polycarbonate panels, and while it would be a great project, and I’d love to oversee it, I stopped, once the price tag on the supplies alone, reached $1,800. I’d rather focus on getting her money’s worth out of what she already has.

The vinyl used is just a little thicker than the thickest plastic drop cloth, a falling branch, can tear through it with no trouble. In fact it already has happened, and I repaired it with vinyl tape.

To deal with the direct sunlight, I ordered and installed a 7 x 14 aluminet 50% shade cloth for the roof, and a 7 x 11 aluminet 50% shade cloth, that I installed on the west side. Amazing product. Between, these, and the vent, it cools things down pretty nicely.

So now, for the first two subjects
1) I have received samples of 20 gauge and 30 gauge vinyl. The former cost $5.90 a yard, the latter $9.90, and I’d need about 18 yards. Both seem almost bullet proof.
a. Which would you recommend?
b. The old vinyl was stapled on from the outside, and half inch strips nailed over it. Should we pry off the strips, and replace it with new, or should we staple the new to the strips, creating a ½ gap, and then install strips over that?

2) For when the outside temps start reaching the 100s, the most common option is a swamp cooler. This is a 100 sq ft greenhouse. Found one for $298 (there are cheaper ones) that will cool 600 sq ft. it’s advantage is that you can hook it up to a water supply so that you do not have to fill it every day. For just $100 I could buy a 5000 or 6000 BTU window air conditioner. We have plenty of moisture in our Alabama air, and the floor is several inches of crushed rock, which can be watered daily. Which would you choose, swamp cooler or air conditioner, and why?

[harpspiel]

The efficiency of swamp coolers decreases as humidity rises. This means that no matter how much air a swamp cooler can move, at some point it will not be able to drop the temperature any further. Here is an approximate chart:



I doubt a swamp cooler is going to provide adequate cooling for your situation, given the high RH of outside air in Alabama, so I would recommend a window A/C. If that seems to be drying the air inside the greenhouse out too much, I'm sure you could rig something where it blows through a wet pad, similar to a swamp cooler setup, which might actually help drop the temperature a little further.

[kg5]

So you can not work with a roll up wall?

We are putting together a hot & shade house combination. In the sub tropics with filtered sunlight for a min of 10hrs per Summer day.

The hot house opens onto a shade house and a roll up wall installed in the joining area. But the hot house part is 8f to 10f high x 22f long x 13f wide so it has a reasonable air space. The cloth is white & is 50% shade.

I see the wall as rolled up approx in 2nd week of Spring , Summer and untill the last 2 weeks of Autumn.

Just helped with a sealed up hothouse for carnivorous plant and pushed that it is going too get too hot with just a small window. And yep she has burn problems even with the door open and it is 3rd week of Autumn. It is a very small hothouse so it has only a very small amount of air space which by memory seems to be the most important thing in our climate.

Our humidity is very high for most of the time the wall would be rolled up. Most times with the wall rolled up we have a steady outside temp of 90f.

[Ray]

Concerning the covering, assuming both thicknesses are UV stabilized, I believe I'd go for the thicker one, if for no other reason than it being stronger and will likely last longer before needing to be replaced.

As you DO get cold in winter, I'd seriously recommend that you consider a double layer covering to save on the cost of heating. A thick sheet over the thin one would work, providing you leave a dead air space between them.

If you're only doing a single sheet, strip to the frame and reinstall from scratch.

I agree that the air conditioner will be more effective than the swamp cooler, although I have seen them be effective in Houston, which is definitely more humid that Birmingham. However, you should also consider energy costs. A fan uses a lot less juice than does an A/C unit.

I would also recommend Aluminet shade cloth. There is no plant that requires full, mid-day Birmingham sunlight intensity, and all of those rays entering the structure really heat things up. Gothic Arch Greenhouses in Mobile will make one to spec, and at the best prices around.

[jmmehler]

Thanks for the input. I figure I owe youse guys some pictures. Will try to get some this weekend and post them.

Some additional information. At the south end of the greenhouse are two 100+ ft trees, that right now have no leaves. That is why I opted for only 50% shade cloth, as I'm not sure how much shade there will be in the summer.

While I love the effectiveness of the venting fan, I think I am leaning towards the window air conditioner, and will have to rig up something to keep the cooled air from being blown out the passive vent on the other side. It may be as simple as hanging a piece of vinyl over it, so that it gets pressed against the vent when the air conditioner is blowing air in. The vents for the fan, get pushed open when the fan activates, so turning off the venting fan, or raising the temp on its thermostat, may solve that problem.

[jmmehler]

Current plan is to leave the very thin vinyl that is installed, with 1 x 2 and 1 x 4 strips, and to install a 20 or 30 gauge vinyl onto the strips so that we will have about a 1 inch gap between the two layers. We will also opt for an window air conditioner instead of a swamp cooler.

1st picture is the western wall at 4:30 PM, with 50% aluminet blocking out the harsh sunlight.
2nd picture is the southeastern exposure facing one of two 100 ft trees on the south end. You can also see the 50% aluminet on the roof.
3rd is the southwestern exposure with the passive inlet vent
4th is the northern exposure with the 12 inch thermostatically controlled exhaust fan, and an air king 9012 for circulation. Window air conditioner to be installed behind the air king fan.

[kg5]

Very nice to see your images.

It looks like we are using the same size timber as yourself.

It is strange trying to get the idea of weather conditions in the US but I am slowly learning. It sounds like our weather conditions are more favorable than for yourself.

All The Very Best. Keep the great work happening. You are a big encouragement to us here. Thank You! kg5

[jmmehler]

So we found a company that sells vinyl. They sent us samples of the 20 and 30 gauge clear, UV protected. Apparently this stuff is used for windows in boats. We selected the 30 gauge, which seems 'bullet proof'.

Found a product called Screen Tight. Home Depot sells it, but for our selection, we had to special order it and have it delivered. The product consists of a base strip which has spline grooves, and a base strip cover which comes in white, grey, and brown. It is meant for screen material, but we gave it a try with vinyl.

The results were spectacular. Now we need to see how long the vinyl lasts. replacement is very easy. Just pull out the spline, and spline in a new piece.

Just in case, we hung the aluminet shade cloth on the inside, while we were installing the vinyl. It is now back on the outside.

We also removed the shade cloth from the roof, as the surrounding trees are now providing enough shade.

[Ray]

John, I see a really serious problem:

There aren't enough plants in there!!!!

[jmmehler]

Oh but Ray, you are so wrong. This greenhouse was commissioned by a recent widow, who is looking for a new outlet in life.

I'm playing catch up, and trying to slow her down. Her fellow church ladies are just piling her under in noid phals, I've given her about 8 no-id cats, et-al, which are now outside.

She wants to get into vandas now and is starting to look. The greenhouse is not really tall enough but we are already trying to figure out where to put the vandas.

She is ready to buy a humidifier but I've finally convinced her that the humidity is fine (93 percent every morning)

Not sure how we are going to use the air conditioner and venting fan together, once we get into our Alabama summer.

She also had the carpenter in-bed wire mesh on the bottom of the bench frames for expansion.

As stated in the initial post, the fellow who built it, knows nothing about greenhouses. I came along after it was built and have tried to improve upon it.

Total cost, is now pushing that of a kit. By next summer, if she is going at this pace, I'll probably be posting pictures of a total tear down and replacement with a bigger greenhouse.