Greenhouse Heating Options

[Dutch]

Hi FourOaks,
Its' basically an inner plastic shell. I use a 3mil 20' x 24' piece of plastic I buy at Menard's for a little under 20 bucks. I only use it for a couple months. I think it takes 3 or 4 months for the stuff to start to deteriorate. The framework that supports it is common 1/2 pcv pipe. The pvc pipe framework I leave up and reuse every year.
The greenhouse is in the back on a hill next to the garden. I'm going back up there to do some more transplanting in a couple of minutes. I just came down to the house to make my bladder gladder. I'll take some more picture when I go back up there and explain a little better in a post this evening.
Dutch

[Dutch]

The canopy creates an air gap between the outer wall which is exposed to the outside elements (temp, moisture, etc.) and the inner canopy wall which is exposed to inside elements (temp, moisture, etc.). In my case it also reduces the volume of upper area I needed to heat. If you had a tunnel, it would be a tunnel with closed ends in a tunnel.
My canopy or one piece sub-ceiling with walls is supported by 1” balls mounted on the outer wall. The round balls help to minimize tearing the inner plastic. The first year I made it, I had to run nylon rope across to keep the bows bowed. After a year of being bowed they now retain their shape.
My greenhouse is doubled layered with a 1” air gap between the layers, but the top has gable ends that open for cooling. I felt that the upper ceiling area was a waste to heat and making a sub-ceiling, the canopy, would reduce the area I needed to heat and solve my air leak problems on the gable ends too. It has done both.

The south wall of the canopy only extends down a foot or so because the door is there and the wall is already double layered. There is a plastic roll down door on the outside that I roll down at night as a storm door. The north wall which is the back wall and the side walls of the canopy extend to the floor. The ceiling and walls are all one piece of plastic draped over a pvc frame.
SouthWall2.JPG
Dutch

[PhilaGardener]

Nicely installed!

[Cole_Robbie]

I am starting to learn that the real point of the double-inflated poly layer that is a common covering is not the increase in r-value nearly as much as it is that you don't drop 5 to 7 degrees below the outside temperature due to atmospheric radiation cooling. On a cold night this week, my single-layer poly structure felt like a refrigerator inside. I could feel the temperature difference on my skin when I stood outside and reached in.

[FourOaks]

Dutch... I see what you mean now. Thanks for the pics and description.

Originally Posted by Cole_Robbie

I am starting to learn that the real point of the double-inflated poly layer that is a common covering is not the increase in r-value nearly as much as it is that you don't drop 5 to 7 degrees below the outside temperature due to atmospheric radiation cooling. On a cold night this week, my single-layer poly structure felt like a refrigerator inside. I could feel the temperature difference on my skin when I stood outside and reached in.

Interesting premise.

[biscuitridge]

Double poly doesn't prevent it from being colder inside,mine always is colder and I have inflated double poly.

[Cole_Robbie]

Originally Posted by biscuitridge

Double poly doesn't prevent it from being colder inside,mine always is colder and I have inflated double poly.

Interesting. Have you measured it? Cornell research found a 5-7 degree difference, but I think they only tested a single-layer structure. I would be curious to know if a double layer is the same.

The amount of energy required to heat my greenhouse the 7 degrees that it drops below the outside is huge. It is mind-boggling to think that a big heater would accomplish the same thing as just leaving the doors open.

[biscuitridge]

Usually around 3 to 4 degrees cooler.

[FourOaks]

Hey Cole.. hows Mother Nature treating yall up there? Last night I left my sides rolled up.

Im sure Mother Nature will come back swinging to punish me.

[Cole_Robbie]

It finally got warm, but it is supposed to frost again in a few days. I'm pretty much giving up on my plant-selling season altogether. Between a cold month of almost no sun and a lot of freeze damage, I don't have anything to take to market for at least a couple more weeks. Weather-wise, this has been the worst spring for growing plants that I can remember, some of my fellow vendors who have been in the business 30+ years say the same thing.

If I were to do this all over again, I would build a fortress of a greenhouse with an insulated north wall and end walls, and insulated shutters I can close at night and turn on the heat. Trying to keep a plastic tent warm at night is just ridiculous.

[FourOaks]

Cole.. I really hate that for you. Its been tough for all of us this year, thats for sure.


So are you still in the produce business for this year?

[Cole_Robbie]

Thanks. I am trying to transition to being a cut flower grower instead of a tomato grower. My garden has persistent disease issues that have taken out my plants earlier each year for the past few years. I can still sell a few container flowers and plants through the summer as well. My family still has the market membership; I'll just let them grow the actual produce. My cousin just built two high tunnels and wants to be a grower now, too.

Growing actual food has been far from profitable for me, unfortunately. I think all of our prices are set by international competition, whether we realize it or not. Live plants are harder to ship internationally, which is why the prices are higher, as compared to food, and thus more profitable to grow.