Ground as a heat sink?

AJ Drew

AJ Drew

I think we all know that the ground will hold and release heat.  Often times people will plant seeds, water, and cover the patch with black plastic to keep the ground warm over the night time.  Lets us plant even before the first frost.

I wonder how it works when you are trying to keep an area heated above lets say 70 degrees.  If you use artificial methods to heat, not just the son and compost, how much does the soil work against you to suck the heat out of the area you are trying to heat?

Mini Green House 1 - Heated, floor is the earth.
Mini Green House 2 - Raised wood floor.

Which do you think would take more heat to maintain the same temperature?
 
Local conditions need to be considered. Here, it often gets and stays below freezing for most of the winter, often with a "lovely" layer of snow on top of the ground. Where you're at is typically warmer than it is here, and it likely does not get as much snow (we get lake-effect snow, which blows.) I would want to experiment, if at all possible, to see which works best - the outcome of this experiment would inform you for years to come, so would be a worthwhile investment, if you can afford it. Let's say you do two mini green houses - one on a raised wood floor and one directly on the earth. Which ever one turns out to work the best, you could then convert later.
 
Random thoughts without putting too much effort into it: Likely we can take a clue from our houses. Double-pane windows, for example, offer more of a buffer against the outside temperature than single-pane windows do. Similarly, our houses really have two layers, with insulation in between. This would lead me to believe your raised floor greenhouse would take the least heat, whether you left the space between the floor empty or filled it with some kind of insulation. Also, with the bare ground as floor, likely you'd be fighting too much radiative cooling from the surrounding cold ground. But again, your local conditions are a factor for both greenhouse versions.
 
Air temperature fluctuations is the reason for greenhouses in the first place. Think about it. The air temperature changes much quicker than ground temerature. Therefore a raised wood floor would work against you as far as regulating temperatures inside your greenhouse. If you really want to harness geothermal regulation, dig your greenhouse footprint down into the earth a foot or two.
 
Scoville DeVille said:
Air temperature fluctuations is the reason for greenhouses in the first place. Think about it. The air temperature changes much quicker than ground temerature. Therefore a raised wood floor would work against you as far as regulating temperatures inside your greenhouse. If you really want to harness geothermal regulation, dig your greenhouse footprint down into the earth a foot or two.
Click to expand...

I'm thinking Scovie is on to something.

+1
 
     Yup. You don't want to insulate your greenhouse from the soil, you want to insulate it along with the soil. Same principal as throwing straw or other mulch on root veggies to get them to over winter in the garden. 
 
Have read much about pit houses / semi underground green houses.  Often they claim a major heating benefit from the natural heat in the earth.  Thing is, I have also read much about underground homes.  Often they claim a major cooling benefit from being a heat sink. 

It is about to be February and today was mid 60s.  It just seems like with some heat on certain nights, a person could grow year round in Kentucky.  So my mind is scheming n dreaming.
 
The earth will be an equalizer .
Like a cave , when its very hot it will be cooler underground , when it is suddenly very cold it will be warmer underground.
But , water and damp earth has a huge thermal capacity and will suck up any heat you throw at it.
So if you are throwing heat/dollars into your greenhouse, insulate.
 
There's a reason our water line is 6 feet under ground. So it won't freeze. Heating a greenhouse geothermally, and cooling a home are not quite the same thing. If the ambient outdoor temperature is 95°, your house will stay cooler because the earth around / on top of your home is what's called, thermal mass, while your greenhouse will cook at those higher temperatures. Matter (earth) and gasses (air) change temperatures at vastly different rates.

I have a friend here in North Central WA that has a dug out house (like one big daylight basement with 2 feet of earh on top of it), and she has a 30 year old tomato plant that is about 25 feet long growing like ivy across her windows. Her house stays temerate year round, easy to heat in the winter and easy to cool in the summer. So, there you have it.


Don't get me started on 'Wind Chill'. lol
 
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