GenericUsername2056 t1_j19r3cj wrote on December 22, 2022 at 6:35 PM

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

It's 100% efficient, that is all electricity is converted into heat, eventually. So a 1 kW oven running at maximum capacity will consume some 1 kW of electricity to produce the same amount of heat. So it generates heat from electricity. A heat pump on the other hand merely 'pumps heat' using electricity. This means at certain operating conditions (this is dependent on e.g. the outside and inside temperatures) it will use 1 kW of electricity to move 3 kW of heat from the cold outside into your warm home. This gives it a Coefficient Of Performance (COP) of 3 kW/1 kW = 3 at those operating conditions.

Bunslow t1_j19z1mz wrote on December 22, 2022 at 7:27 PM

right, but do residential heat pumps actually reach 300%, or do they only actually reach 250% or 200% or whatever and 300% is only possible with industrial heat pumps?

SufferingIdiots t1_j1a1nrq wrote on December 22, 2022 at 7:44 PM

This be will dependent on the temperature differential, the refrigerant and your specific equipment.

>At 8°C, the coefficient of performance (COP) of air-source heat pumps typically ranges from between 2.0 and 5.4. This means that, for units with a COP of 5, 5 kilowatt hours (kWh) of heat are transferred for every kWh of electricity supplied to the heat pump. As the outdoor air temperature drops, COPs are lower, as the heat pump must work across a greater temperature difference between the indoor and outdoor space. At –8°C, COPs can range from 1.1 to 3.7

Bunslow t1_j1ajws0 wrote on December 22, 2022 at 9:45 PM

hmm, so if it's -10C or -20C outside, and inside i want it at the usual 21 or 22C, then my cop might drop as low as 2? for residential purposes

bluesam3 t1_j1b6s2k wrote on December 23, 2022 at 12:31 AM

It will vary between models and setups, but yes, that seems like a reasonable number to expect, broadly speaking.

Bunslow t1_j1bfjlc wrote on December 23, 2022 at 1:39 AM

wonderful, good to know, thanks

bluesam3 t1_j1b6pb7 wrote on December 23, 2022 at 12:30 AM

It's very climate-dependent - the colder the outside is, the less efficient air-source heat pumps tend to be (partly due to inherent reasons, and partly due to having to do work to defrost the outside unit) - if you're somewhere with relatively mild winters, COPs above 3.0 are very achievable with domestic units. If you live somewhere with extremely cold winters, it's much less achievable.