dyqik wrote: ↑
Fri Feb 11, 2022 11:46 pm
Thanks to a local town Facebook group argument, I have found out that it's at least twice as efficient to run a natural gas or oil generator at home to power a cold climate heat pump as to run a gas or oil furnace or boiler for heat.
And that's in central Massachusetts.
You can get gas boilers (US=furnace) that are 90% efficient. We call them condensing boilers here. It is in fact illegal to install any other kind of gas boiler in a house these days in Britain. Maybe your 50% gain is relative to a less efficient kind of gas boiler?
The heat pump will typically give you 3 times as much heat as pump power that you put into it. And if your heat pump is a ground source heat pump, no reason you shouldn't get that efficiency even in mid-winter in Massachusetts. Bit more difficult with an air-source heat pump when its -15C. But maybe it is cold enough only sufficiently occasionally that on average you still get something like 2.5 across the winter. But let's assume it is ground source and you are getting 3 from it.
So, to be double the efficiency of a 90% efficient boiler, you need 180% output from gas put in. So 1.8/3 = 60%. So you will need your gas-powered pump to be at least 60% efficient to achieve that. I think that's not unreasonable to be able to achieve that, but it sounds a stretch at the 20kW level that we are talking about for domestic heat pumps.
Never heard of such a product existing here. But I find this 2016 BEIS paper on gas-driven heat pumps
. (BEIS is the UK dept of Business, Energy and Industrial Strategy.) It suggests that there are near market products available, and their running costs are 60-80% of the cost of a gas boiler. Not quite as good as the double you mention, which makes me suspect that your comparator was not the 90% efficient condensing boiler. When your objective is zero carbon, a 20%-40% saving just isn't good enough, so doubtless it went on the virtual scrap heap, like a lot of other useful efficiency gains that aren't good enough when your aim is zero. Unfortunately now that our aim is zero carbon in Britain, a lot of sensible things to do aren't being pursued any more, in case they prove the wrong thing to do in 5-10 years time, as we all wait for those fully developed reasonably priced zero-carbon technologies to be put in front of us very shortly, without which we'll never get there.