Geo Thermal

[DavidJames]

Hello,

 

I live in the country in central Florida. The temperature drops to as low as 24 degrees F, maybe 15 nights during the winter months, and daytime temperatures are generally between 45 and 60.

 

I'd like to build a greenhouse with plastic film that would be good for year round service, without using any electric or gas heating during the mild winters. I was thinking about driving a number of galvanized conduit pipes, with capped ends on the bottom of each pipe to keep them from filling with dirt, into the ground to allow heat to rise from the ground during winter months.

 

I need to know if I'm deluded on this idea or if it's possible to do so. If it's possible, I'm wondering how deep I'd need to drive the pipes and how many I'd need per square foot of garden space. Would I have to dig a hole and take soil temperatures at different levels and compare them as I dig down, in order to get an idea of how deep the pipe would need to go?

 

Thanks, David James

[Externet]

Hi.

You need to find the data for your zone.

This is not for Florida, but will give you a good idea how deep to dig and what temperature shifts occur along the year:

 

http://www.geo4va.vt.edu/A1/time-lag-vs-depth.gif

 

http://dnr.louisiana.gov/assets/TAD/education/ECEP/drafting/h/dr-h60.gif

 

http://www.texas-geology.com/Soil%20Temp%20vs%20depth.jpg

 

U.S. :

 

http://www.earthrivergeo.com/img/geothermal-article/geothermal-subterrainean-temperature-contour-map.jpg

 

http://mb-soft.com/solar/soilmap.gif

 

Florida may have subterranean aquifers, hitting one may alter the expectancy.

At certain depth, the soil is at a stable temperature all year; but during Florida winter, fine-tuning the depth may yield warmer soil at less depths.

 

Hope it helps.

[Enthalpy]

So little deluded that this method is used.

 

Even before half a metre beyond surface, you get a temperature constant all the year, the reason why water pipes are just buried here in tempered Europe to protect them against icing winter.

 

Complete houses get cool air in Summer by this method, and, err, cool air as well in Winter, as the mean temperature is like +15°C here, so a supplement of heating is needed in Winter.

 

Alternately, some people live in caves to benefit from a constant temperature.

 

For your network of pipes, which is compounded with a heat pump in Germany or Switzerland, you need enough soil mass to store heat (and cold) for a season, and pipes close enough to draw that heat (or cold) within a season, but the depth isn't critical if soil is used as a heat accumulator. The pipes can be horizontal (adios for some time, nice garden) or vertical (bore holes instead of digging trenches).

 

The situation would be very different if you wanted to exploit the geothermal temperature gradient for good. This would require hundreds of metres just to get a few degrees more. A few places are exceptions, in Iceland for instance. In the Rhine valley, you'd get an important gradient, like 300°C within 3000m. Hard to exploit for a home.

 

But to keep a greenhouse well over freezing temperature, that's the perfect use. Give your tubes a U-form, or have concentric tubes, to circulate air in them. They'll also provide fresh air in Summer, to your greenhouse or outside as you wish.