Ambient heat

[Dusty Ol' Man]

Have any of the greenhouse growers here run ambient heat under the surface of the greenhouse floor? Years ago I saw a setup where a water heater was used as a source and a pump moved the water through tubing imbedded under the gravel. Since I may be moving to a very cold winter climate, I am looking for ideas to make heating as painless and automatic as possible.

[Roberta]

Commercial growers have warm-water pipes under the benches. That gives them pinpoint control. (They can drop the temperature for their Phals for a week or two to trigger spiking) If you were going to use this type of approach, would it perhaps be more efficient to have the warmth closer to the plants? Having never had to deal with a really cold environment I leave it to others to comment from experience.

One thing that I WOULD advise... whatever heating system that you settle on, have a plan for emergencies such as power failures. Like, a portable heater that runs off a propane tank. Your backup doesn't have to maintain an ideal temperature, but it has to keep the temperature high enough for the plants to muddle through, at least.

[estación seca]

An engineer friend did that in his greenhouse, PVC irrigation pipes in a concrete floor. It works very well unless the slab cracks and moves. In gravel this is less an issue.

A friend in St Louis dug down to have a 3 foot/0.9 meter deep layer of pea gravel as her greenhouse floor. Aside from excellent drainage, it absorbs a lot of heat on sunny winter days.

A cycad grower I know arranged his benches in long rows, with the surface closer to the ground than most orchid growers have them. He draped heavy plastic landscape sheeting over the benches, so it hung down to the ground on both sides, and was held down by bricks here and there. He put a high-output heater with powerful fan at one end. This provided bottom heat the entire length of a long series of benches.

[Ray]

There was once an AOS article about someone who had built a large, insulated sump under the structure. Water was pumped to the top of a large, flat, black plastic panel (north wall, perhaps?), trickled down over the surface where it gained solar heating as it returned to the sump.

At night, that same circulation put heat into the structure.

[Dusty Ol' Man]

Thanks for the ideas. I like the low bench with homemade heating duct idea. Using water to transfer heat in northern Michigan could present problems in sub zero temps. 🤔

[SG in CR]

I remember reading an article years ago about a guy, I think it was in Minnesota, who dug up the ground underneath where he wanted to build his greenhouse several feet deep. He insulated the bottom and sides with solid foam sheets and refilled it with big pipes drainage pipes running through it. The idea was to use the ground beneath his greenhouse as a huge heat and humidity buffer by pumping air from the greenhouse through the pipes. In summer the cool ground would absorb some moisture and cool the air. In fall and winter it would warm and humidify the air. Not sure how well it worked but it might be something to consider.

[Maryanne]

Hello Dusty!
Well, I think there are a few more points/variables to ponder. Ask your self
How far north - and to what zone. (I'm in Zone 5 -hot now but winter is bbrrrr)
How large a g'house will you have?
will the g'house be attached to your living house or stand-alone? (so much easier to heat if attached. My tiny g'house fits into the "L" of the very old house and added-on kitchen, so only 2 sides are glass) I can cook and keep an eye on plants at the same time. : -)
How warm do you want to keep it at night? (I let mine drop to the 40sF in the winter, so I choose plants that tolerate those conditions. No fussy phals, but Laelias and Dendrobiums seem happy)
You can have a stand-alone heating system or if attached to the home, you can integrate somehow.
Draw pictures of what you want and figure on paper the different variables.
Check the prices of building supplies and labor in the are to which you are moving : -)
Good luck with your dream g'house.
Best wishes,
Maryanne in Massachusetts

[Ray]

Originally Posted by SG in CR

I remember reading an article years ago about a guy, I think it was in Minnesota, who dug up the ground underneath where he wanted to build his greenhouse several feet deep. He insulated the bottom and sides with solid foam sheets and refilled it with big pipes drainage pipes running through it. The idea was to use the ground beneath his greenhouse as a huge heat and humidity buffer by pumping air from the greenhouse through the pipes. In summer the cool ground would absorb some moisture and cool the air. In fall and winter it would warm and humidify the air. Not sure how well it worked but it might be something to consider.

There was another, similar article about someone who took a different twist:

If I recall correctly, he used 500 feet of 12-inch diameter, unglazed clay sewer pipe, buried some 6 feet underground. One end came up to the surface inside the greenhouse, and the other was in an above-ground shelter away from it. That end had a combination screen and air filter to keep critters out.

Exhaust fans running 24/7 in the greenhouse drew warm, humid air through the pipe in the summer, where it would be cooled and the excess moisture would condense, be absorbed by the unglazed clay and be passed through to the surrounding soil.

In winter, the cold, dry air would pass through the pipe, be warmed and actually pick up moisture from the clay. I don't know that it provided 100% of the heating demand, but it couldn't hurt!

[Dusty Ol' Man]

There are clearly a lot of variables involved. And being a hands on homeowner for the last 30 or so years, I'm aware of the effort involved with constructing additions and such. All these ideas are great food for thought. As far as how far north? How about northern Michigan? Yes I'm going from the extreme heat of the gulf coast to the frozen tundra. I'm just considering my options at this point. I won't be adding any new plants before the move because the few I have will fit indoors wherever we end up. And when this move will happen is still up in the air.
Thanks for the input. And if you happen to think of anything not previously mentioned, I'm all ears.

[Diane56Victor]

If you enter
building cold climate sustainable greenhouse
in YouTube there are plenty of different builds featured. Tney would probably help with different ideas.