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Mark Franks (5 Posts)
Mark FranksAs much as I love my Thursday new letter. this one is simply not true.
Henry Gifford does a great job explaining this one http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/ground-source-heat-pumps-don-t-save-energy
Tough OneLet's start with the clear factual error: the earth's core temperature has absolutely nothing to do with the suitability of an area for geo-exchange.
Geo-exchange is not the universal solution many proponents claim; nor is it the scam which opponents sometimes make it out to be. It works best when annual heating and cooling loads are *roughly* balanced (say within a 2:1 range) and when soil moisture is high. Payback over a modern ASHP can take quite awhile depending on the local climate. Ground loop installation costs -- especially on existing sites -- can be prohibitive. Depending on the source of electricity, it can produce less (or more) carbon impact than burning natural gas will.
When correctly applied (sometimes in a hybrid system with GSHP plus a high efficiency boiler) and competently installed and managed it can produce excellent results.
COPWhat is upper limit on COP of ASHP,particularly mini split? I see this being the eventual "winner"
FactsMy point is that their is not a correct fact in the article. The heat pumps run on electricity which is produced in a fossil fuel burning power plant. As Henry points out the net efficiency and carbon footprint doesn't change. A 3 COP from a 30% efficient power source is no different than a 90% efficient boiler. A 3 COP running off PV panels is a different matter.
instead of a loop fieldThis company uses a fence as the loop field. Clever idea.
A GSHP heat pump is really moving solar energy. The energy from the ground to provide heating is from the sun.
I suppose you could make an argument that the coal is also a result of solar energy, from vegetation that grew 400 million years ago :).
A heat pump powered by PV modules would be a nice, but currently expensive, option.