I have never owned a Greenhouse and have a limited amount of knowledge about their day to day, season to season operation. From what I have read it is not real hard to maintain a growing temperature during the winter months in the growing zone 8. It does appear that it is much harder to maintain a good growing temperature during the hottest summer months if the Greenhouse receives full sun all day long.

Years ago I had a friend / neighbor that had a 8 x 12 Greenhouse but during the summer months it was completely shaded from around noon until dark and if I recall correctly, he did not have an overheating problem. I do remember that he did grow several vegetables in pots through out the summer and quite a few flowers.

This leads me to my two questions: 1) is this an accurate assessment of the problem?, and 2) would an overhead removable “slide on a wire canopy” possible solve the problem?

Thank you for any help and information,
Thomas

@Thomas75, I don't know why your post does not show you are a new ATP member, but regardless,

I have owned greenhouses for almost four decades, from a really grand 15'x32' one, a 3' skirt built of brick, marine aluminum framing, and glass (two hurricanes finally took that one away). I now have two, 10x12', BIY ones. I have these two with 60% and 75% shade cloth (one gets more afternoon sun), multiple fans, and vents and doors wide open. About the only thing I can use those greenhouse for in the summer is to grow succulents, root plumeria, and start seeds. It is not unusual for those greenhouses to get110-120F when the ambient temperature is 90F. We are often in the mid to upper 90's and two summers ago, we had a string of two weeks with temperatures above 100F. The only way I could lower that temperature would be to install swamp coolers or AC, or have full afternoon shading via dense trees.

Hi drdawg

Thanks for the information, do you think that a correctly built and installed awning / canopy of a proper size would be sufficient to cool down a Greenhouse for summer use? The biggest advantage to me, would be that the canopy would be placed a couple of feet higher than the top of the Greenhouse thus allowing for cooling airflow between the two. Then during the fall and winter the cover could be either moved back out of the way or completely removed. The search that I have done so far shows that most of these covers are designed to be removed easily for cleaning and storage.

By the way, you sure have a lot of nice looking plants

Thank you again,

Thank you, Thomas.

The reason I stated that a stand of trees, affording almost full shade during the heat of the day, would allow a greenhouse to remain cool, or at least at/near the ambient temperature, is because that's what I see with one of mine. A canopy or awning, mimicking the tree-shading, should do the same thing. I would think that it would have to completely shield the entire greenhouse from the sun for it to be efficient.

Whatever you end up doing, please keep us informed. Almost everyone faces the problem with super-heated greenhouses, particularly those of us who have the sun high in the sky during the spring and summer. Perhaps those in the northern tier of states and Canada don't have quite the problems with heat that we do down here.

I am attaching a drawing of my idea which should be easier to vision.

The Black Outline is of course the Greenhouse which will be 8-ft by 12-ft.

The Blue Outline would be the needed frame work to support the “Wire Slide Canopy”. This I would fabricate out of aluminum tube and TIG weld together. The “Slide Wire” would be stainless steel.

The Red Outline would be the special sun blocking / waterproof fabric and all the hardware would be either brass or stainless. The holes in the Canopy serve two purposes, 1) they allow wind to go through to resist strong gust and 2) they also would allow water to drain through to prevent build up.

The Canopy itself can be pulled back to a “folded’ position to allow sun on to the Greenhouse or it can be easily removed for cleaning and storage during the winter. The Canopy would be 14-ft by 18-ft allowing a full 3-ft overhang of the Greenhouse all around.

Open to any and all helpful suggestions.

Thomas
click on the photo to enlarge

drdawg said:Thank you, Thomas.

The reason I stated that a stand of trees, affording almost full shade during the heat of the day, would allow a greenhouse to remain cool, or at least at/near the ambient temperature, is because that's what I see with one of mine. A canopy or awning, mimicking the tree-shading, should do the same thing. I would think that it would have to completely shield the entire greenhouse from the sun for it to be efficient.

Whatever you end up doing, please keep us informed. Almost everyone faces the problem with super-heated greenhouses, particularly those of us who have the sun high in the sky during the spring and summer. Perhaps those in the northern tier of states and Canada don't have quite the problems with heat that we do down here.

Thank you drdawg. After I get the Greenhouse built, I will take photos of this Canopy System as it is being constructed and post the progress here. I do appreciate all the help.

Thomas

Search some of the old posts here. I can't remember his name but he is from FL and built the most artistic sun shade I have seen? I loved it. I will try to find it for you.

ShadyGreenThumb said:Search some of the old posts here. I can't remember his name but he is from FL and built the most artistic sun shade I have seen? I loved it. I will try to find it for you.

Hi Cheryl,

Sure would appreciate it if you find that post.

Thomas

Found it! About the middle of the first page in the Greenhouse forum is the Harbor Freight Greenhouse Thread. On page 7 of that thread, twoards the bottom is a post with pictures. I think there are more photos after that in different posts as we all commented on the cool sun shade he built.
The thread "Harbor Freight Greenhouse projects" in Greenhouses forum

Towards the middle from DavidDeLand who is no longer here.

I like your ideas, Thomas. The canopy looks roomy enough to shield the greenhouse's top and sides, which is important. If you have room, you might want to consider at least a 10x12' greenhouse. My two are that size. I wish I had built 12x16' or 12x20' ones. No matter what size, you'll wish it was larger.

Hey again Cheryl,

Thank you for this link

It appears his canopy is a fixed design and not able to "fold up" but very close to what I had in mind. He has the tree for protection on half of his greenhouse so he only needs the canopy on one side.

Thank you again for this help,
Thomas

drdawg said:I like your ideas, Thomas. The canopy looks roomy enough to shield the greenhouse's top and sides, which is important. If you have room, you might want to consider at least a 10x12' greenhouse. My two are that size. I wish I had built 12x16' or 12x20' ones. No matter what size, you'll wish it was larger.

Hey Ken,

You know everybody is telling me the same thing...build it bigger and I most likely will do that.

I was thinking that on the north (back end) of the greenhouse where my support legs will be for the canopy, I can span that with some wire fencing and turn that into a trellis for vegies. That will help keep some of that a little bit cooler. In fact, I could also do that along each side on the support post.

Really do appreciate all the great advice and help,
Thomas

I have attached a new drawing showing the relative position of the Sun for four (4) of the summer months in relationship to the Canopy over the Greenhouse. This will show where the Sun will shine directly onto the Greenhouse at 11:58 AM for the months of May, June, July and August. Beyond August the Sun is rising lower ever month and is beginning to “cool” and will have less effect on over-heating the Greenhouse. Even as Early as September the Canopy could be folded back exposing all of the Greenhouse.


NOTE: these figures are calculated for Deep East Texas and will vary according to your Latitude and Longitude. Also note that the Greenhouse is positioned in a true North and South centerline.

I know this is hard to read due to the scale so I color coded each month and here is the key:
May is Dark Blue and the Sun’s angle is 71.71 degrees from North.
June is Red and the Sun’s angle is 78.34 degrees from North, a bit higher than May.
July is Cyan and the Sun’s angle is 73.86 degrees from North and has started a decline.
August is Green and the Sun’s angle is 65.31 degrees from North and a significant decline from the peak in June.

Due to the off-axis rotation of -23.5 degrees of the earth, the Sun’s rays will have to penetrate more of the Earth’s atmosphere as we head into Fall and thus the “cooling” we will experience.

Only a small frontal portion of the Greenhouse will receive direct sun during this four month period and those months are, May and August.

I am open to any and all suggestions that can improve on this concept and I appreciate the interest and help already received.

By golly Watson, I think this just might work!

Click on the photo to enlarge

Thomas, how far are your from Nederland, or if you are really "deep", how far from Galveston?

drdawg said:Thomas, how far are your from Nederland, or if you are really "deep", how far from Galveston?

Hi Ken,

I am north of Nederland up here on Sam Rayburn Lake which is about 100 miles and about 30 miles west of the Texas / Louisiana border.

lat 31 degrees north by Long 94 degrees west.

Deep, deep East Texas

Thomas

Not quite as "deep" as I thought then. I was born in Beaumont (Daddy was a welder for a shipyard there and then went away to war) and lived in Nederland and then in Houston during my youth. I moved to Mississippi just before starting high school and other than a four-year stint at Loyola School of Dentistry, 1966-1970, have lived in Mississippi ever since.

drdawg said:Not quite as "deep" as I thought then. I was born in Beaumont (Daddy was a welder for a shipyard there and then went away to war) and lived in Nederland and then in Houston during my youth. I moved to Mississippi just before starting high school and other than a four-year stint at Loyola School of Dentistry, 1966-1970, have lived in Mississippi ever since.

Hey again Ken,

Wow small world, I was born in Beaumont and went to South Park High school, lived in Nederanld for several years and kept my airplane out at ole BPT ( Jeff-County Airport ), my daddy was a Leaderman at the ship yard during the war. We could be first cousins.....or sump-en.

Have a great day,

It is a small world, Thomas. Are you a "war-baby" (WWII)?

drdawg said:It is a small world, Thomas. Are you a "war-baby" (WWII)?

Born 1941 and still alive???

Hi Thomas -- what are you planning to grow inside the greenhouse during the summer? and... why? Also, you mentioned growing veggies on the north end of the GH because they would be cooler there; do you mean on the outside of the GH? Because if so, they're going to be pretty much shaded and most veggies need full sun. Inside the GH, especially in the summer, the heat is not the only problem -- things can dry out really fast, necessitating a LOT of watering. Are you maybe thinking about an automatic watering system?

Even way north where I am, my GH -- which is 8x16 and has 6 roof vents and a 4-foot-wide door on one end -- becomes too hot for most things to grow happily during the summer; and the temperature in the winter, with everything closed up, often goes over 100F on a sunny day with an outside temp close to zero. Just to give you an idea of how much they can heat up.