Sunday, October 22, 2006

Ground Source Heat Grump

In today's Observer, Lucy Siegel repeats the old chesnut about Ground Source Heat Pumps producing 3-4 units of energy for every unit that is put in.

What she doesn't say is it takes 1 unit of electricity to get 3 units of heat. To get 1 unit of electricity you need to burn 3 units of gas in a power station. A modern condenser boiler is 90% efficient, so you'd get 2.7 units of heat if you just burnt the gas directly. On top of this I've been told that GSHPs struggle in practice to deliver 2.5 units of heat (1 of which is waste heat from the electricity running the pump's motor). Then the gas boiler wins.

"Ah, but you could use renewable energy!" say the Heat Pump acolytes. Yes, but who has too much renewable electricity? You'd be much better off using that electricity to power IT, lights and all the other stuff that can't run on lower forms of energy.

I've got a willing student doing an engineering project to look at the whole energy balance of Heat Pumps. I've challenged him to prove to me that they are a good idea. I'll keep you posted on how he gets on.


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