High Tunnel Gets Colder Than Outside

[Cole_Robbie]

great pics in that link

[whoose]

Quite the site. Kind of whish my GH was not already built.

[Cole_Robbie]

It was supposed to be 38 and cloudy tonight. Now it says 35 and partly cloudy. I walked outside, and I see stars everywhere, no clouds. That means high 20's in my plastic greenhouse. I'm going to go cover everything up and turn my heaters on before I go to bed.

[Cole_Robbie]

Well, that was fun, greenhousing at 2 am. I'm actually at 2 degrees above the outside temperature right now. All the water I have in there is helping a lot. I have about 1,000 gallons or so. The open troughs are steaming like they are on fire. There is a thick layer of condensation on the greenhouse plastic, which I can only presume helps to add to the plastic's r-value. I think the water is the cure for the radiative cooling effect, either from its mass, or from the humidity it creates.

[BigVanVader]

Which makes me think a few bucket heaters might work well. I'm not sure how much power they use but I would think if you got 1000 gallons too 100 degrees it would likely stay warm all night?

[Cole_Robbie]

Bucket heaters won't get water that hot, as far as I understand. They are meant to keep water from freezing. It would take a residential or commercial hot water heater, and a large enough insulated tank to store the water. It's not a bad idea...just expensive.

[Worth1]

Just drill down into the geothermal about 1600 feet and you will have 140 F temps to circulate water.


Worth

[Cole_Robbie]

It's my last night of near-freezing temps, hopefully. I covered everything up for what will hopefully be the last time. I also sprayed down the greenhouse gravel floor with water to help make the humidity higher.

[nancyruhl]

Just lost lots of seedlings and larger plants when the heaters tripped off during the night in my "greentents". It was 32 and clear outside. My plants were in the basement and really needed the sunlight so I moved them out. Mistake. Weird thing was that there was no clear pattern to the plants that froze. Guess there is some truth to the different hardiness in the different varieties.

Looking for a new home with a south facing hill where I can build a earth sheltered greenhouse with a bubble filled roof. This has been an eye opening thread.

[Cole_Robbie]

d'oh. Electric heaters can be unreliable. I had the same thing happen to me two years ago. I'm using my favorite of my cheap electric heaters now. A lot of them have safety switches to make them shut off if they get too hot in a small space. I had one that would run at night, then shut off when the sun hit it in the morning.

I hope it's not too bad. Anything that is still standing will recover. I froze my seedlings down to the stem, then they grew back.

[nancyruhl]

Good to know because a few had no backups and no more seeds. Most were for a project I do to support my roof garden. I couldn't wait to see if they would regrow as folks are expecting decent looking plants by Mother's Day.

[BlackBear]

I had an idea for my place in that the thermal mass (H20) is held in food grade barrels /Tubs ( at least 200 gallons to be worth while for a small situation)

50-60 gallons/barrel and that they would be able to "enhanced " with in dwelling

submersible fish tank heaters...... that could be adjusted to what you wanted

70 F.....or 60 F (if economize at end of season etc.) and only kick in when

needed at beginning and end of extended growing season. The enhanced warmed thermal mass water is also the source of thermal enhanced plant water (non hydroponic system).

If I really got it together I guess I could enhance the nutes in solution as well with the thermal enhanced water . ( I am sure some of you have a recirculating system to recycle thermal mass water with nutes etc. )

When the submersible heaters keep the tanks a certain temp . of course
they radiate and keep the inside greenhouse area air temp above freezing .

If you wanted to get all hard edged about it you could get a 12 volt system with an inverter as a safety back up ...I guess ....but also if you had an actual commercial operation you might also have a back up generator (rent) to supply electricity at the "sticky" part of the year if need be.... and preserve your hard won tomato venture . I have heard of some people with propane emergency systems (with proper venting) ...any time the weather gets close ...they apply some insurance heat
to tide the greenhouse over ......I have even seen the old woodstove with a

Big boiler system to enhance the Greenhouse at certain times of the season.

I guess however you do it ...you want the space above freezing Low by at least 6 degrees or more ... margin of safety to extend the season and utilize the high temps still available in the day .

[Cole_Robbie]

The best idea I had for wood heat for my greenhouse, which I didn't have the money for, was to run pex tubing through the gravel floor and use a wood stove to heat the water that ran through it. There's a product I looked at that is a hollow metal element to install in a wood stove so that it will heat the water inside. It is possible to circulate water without an electric pump if the stove is slightly below the system, like an old-fashioned boiler.

The best solar idea I saw is called active solar. Instead of water-filled tubing through the gravel floor, air ducts pull air down into the rock to heat it during the day. At night, the fans reverse, and pull air back up out of the warm rock.

[BlackBear]

Originally Posted by Cole_Robbie

The best idea I had for wood heat for my greenhouse, which I didn't have the money for, was to run pex tubing through the gravel floor and use a wood stove to heat the water that ran through it. There's a product I looked at that is a hollow metal element to install in a wood stove so that it will heat the water inside. It is possible to circulate water without an electric pump if the stove is slightly below the system, like an old-fashioned boiler.

The best solar idea I saw is called active solar. Instead of water-filled tubing through the gravel floor, air ducts pull air down into the rock to heat it during the day. At night, the fans reverse, and pull air back up out of the warm rock.

geese what a great idea....Pex ! I have bundles of pex (Blue, Red, White) but I actually use it for "non plumbing " purposes ...LOL


I see the problem is justifying the next "upgrade" step to the full system green house from ..the unheated solar only etc.....

Most can get stuck at the point of only using temp "auxiliary heat sources" to tide them over the sticky times of the extended season.

I have a solar fountain pump in my place I am trialing as development ...it is a cheap one that only is useful at about 1 ft or less but it does move water at the hottest/brightest sun part of the day ......one could make a step system with 4 pumps to get 4 ft of lift etc.(reread your Bernoulli ..LOL) I believe all these are readily convertable to 12vdc

with 12vdc one could have marine battery back up power for circulation as well

I guess a Big green house would take a lot of these cheap pumps ...but it could be done ........

Wouldn't it be nice to have a solar circulation pump with a woodstove optional thermal upgrader in the line ....LOL

[Tracydr]

Originally Posted by Cole_Robbie

Bucket heaters won't get water that hot, as far as I understand. They are meant to keep water from freezing. It would take a residential or commercial hot water heater, and a large enough insulated tank to store the water. It's not a bad idea...just expensive.

They make bucket heaters for the barn to get water really hot for washing,etc in winter. That may be what he's thinking of.