Piwoslaw,
Quote:
Originally Posted by Piwoslaw
Back to GSHP, I remembered another rule I came across somewhere: For every square meter of area of the building you want to heat there should be 4 meters of underground piping. Also, laying the pipes about 1.5 meters below the surface is supposed to be slightly better than deep drilling, under the assumption that that area of ground gets a lot of sun. 1.5 meters is about how deep the sun's heat penetrates, but is also the the freezing depth. Of course, the difference isn't that big, but if you have a sunny southern slope next to the house, it'd be sin to start drilling instead of digging.
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I'm curious about the rule which says: 4 meters of pipe for every square meter of building.
Obviously this ignores the heat loss characteristics of the building, it also ignores whether the system uses heated forced air or radiant floors, and if radiant floors, whether the piping is embedded in concrete (feed temp = 90 F), is embeded in non-concrete material on top of the floor (feed temp = 100 F), or is fastened below the floor (feed temp = 120 F). It also seems to ignore whether the ground-source piping is in boreholes or is in trenches, and if in trenches, how is it arrayed? As slinkeys? as parallel pipes? So many things to consider...
Where I live, the rule of thumb (which ignores all the above factors, too...) is for every 1000 square feet (93 square meters), you'll need 12,000 BTU/hr (3517 watts), which requires about 200 feet (60.96 meters) of borehole, or about 80 feet (24 meters) of trench, with about 320 feet (98 meters) of pipe in the trench. I may have errors in my conversions, but this is quite a bit different from the rule of thumb you are suggesting. I do realize that I live in a mild climate and that it gets pretty cold in Poland...
Regards,
-AC_Hacker
P.S: There are some new posts about polyethylene welding and also proceedure for testing a borehole for thermal transfer rate over at this link:
The Homemade Heat Pump Manifesto - Page 2 - EcoRenovator