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quintus_horatius t1_j19w0bu wrote

Reply to comment by Bunslow in Why do we use phase change refrigerants? by samskiter

> in other words, how much of a waste is it to heat my place via use of stove/oven rather than the central electrical heating?

Since the rest of the conversation is about heat pumps, do you mean a central heat pump when you say "central electrical heating"?

Resistive electrical heating, as others have stated, is 100% efficient: every joule of electricity is used to produce heat.

A heat pump, however, can move a lot more joules of energy than it consumes. The term is "coefficient of performance" rather than efficiency, but you can think of it the same way. Most heat pumps have a CoP of 3 (or more), which means they're effectively 300% efficient - they move three times more heat than the electricity they consume, or three times more efficient than resistive heating.

OP was wrong, btw. Heat pumps are available with CoPs of 4.0.

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Bunslow t1_j19zc1y wrote

well i dont know what mine is, but i'd always assumed it was a heat pump exactly since it is indeed 2-4x more efficient than simply dumping a whole bunch of power into heat thru a resistor. but it could be resistive heating for all i know.

and if there are indeed heat pumps with 400% heating efficiency (or CoP or whatever we want to call it), then probably 300% is a very achievable number for even "merely" residential purposes, one would assume?

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quintus_horatius t1_j1a6369 wrote

You only have a few options for heat, and only one that can exceed 100% efficiency - a heat pump.

A typical heat pump exceeds 2.5, a good heat pump exceeds 3.0, and a fantastic heat pump approaches 4.0.

The latter generally show up in highly specialized applications like geothermal, where you can tailor your working fluid to a narrow, predictable temperature range.

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Bunslow t1_j1ajqfp wrote

cool, so 2.5-3 is totally achievable for residential/end consumer purposes. is that what residential air conditioners achieve as well?

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seven_tech t1_j1assin wrote

Mine almost does.

It uses a maximum of 1.9kW of electricity to move up to 5.2kW of heat in best circumstances. That's a CoP of 2.74. And it's definitely not as efficient as they get.

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samskiter OP t1_j1co3h0 wrote

There are residential heat pumps with SCOP (seasonal cop) of 5.

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bluesam3 t1_j1b6eed wrote

Yes, 3.0 is a very achievable number for a residential heat pump in a mild-ish climate.

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