This week's Economist has a review of a Dutch company that uses much the same technology to heat its office. The tarmac of the road in front of the building is threaded with pipes, and Summer's hot water is pumped into the aquifer and later recovered. This is a specifically West Netherlands solution, in that the soil is sand, and the aquifers shallow, slow moving and omnipresent.
The volumes and masses involved are fairly titanic and this is not something for amateurs. A tonne of water, cooling by 20C, will release 20 megajoules. If this cools over 12 hours, that is the equivalent of about 460 watts. To replace a 1kW heater, one would need a bit over two tonnes of well-insulated water reservoir, somehow coupled to the heat in the glass house. That can be done with a heat pump during the 12 day lit hours. However, this will cost some energy, typically a fair fraction of the 1kW that one expects to see back in the night. The net gain might be something like 4-6 kWh, which is not to be sneered at, but would plainly take some time to pay back the large capital cost. (Equally, one might heat with relatively cheap fuels, whereas a heat pump will usually employ electricity. ) Note that a typical small glasshouse uses a 3 kW heater, requiring anything up to five tonnes of water to replace it, or roughly the volume of the glasshouse itself. That is easy to achieve if you are sitting on a sand pile with a static lake under your feet. It is not so easy where this is not so. It may be cost effective when you are operating on a vast scale - as is the tomato factory that is illustrated on Viateur's web link - but it may be a degree daunting to non-industrial orchid growers. I suspect that many readers are more interested in a day-night leveling system than a winter-summer one. ______________________________ Oliver Sparrow +44 (0)1628 823187 www.chforum.org _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
