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Posted by D Sherman [72.47.153.24] on Wednesday, February 15, 2012 at 12:56:26 :
In Reply to: electricity can exceed 100% posted by Mike Hernke [63.151.218.18] on Wednesday, February 15, 2012 at 09:31:06 :
The whole thing with a heat pump just like with a water pump -- you want to pump heat "up" as short a distance as possible. Anything you can do to warm up the evaporator helps. From what I've ready, they lose efficiency rapidly below 50 degree. That's why "geothermal" heat pumps using ground heat are best in colder climates. Once you get more than about 6' deep, the ground temperature tends to be constant year-round. Ideally the coils would be placed below the water table, because dry soil doesn't conduct heat very well. The catch, of course is that all of this can get pretty expensive.
What I was trying to do with my numbers, though, was provide a concrete accurate answer to the question of comparing oil to electricity and propane. It's one thing to talk in general terms and quite another to work out the specifics. A heating system is a major expense and it takes many years to recoup the value of paying extra for higher efficiency. It's worth figuring it out pretty accurately, including local conditions, before spending a lot of money.