We have a heat pump for heating. How is it that it’s cheaper to use it than just turn the oven on to warm the house? Also when the heat pump is off it still circulates air.
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A heat pump takes heat from the outside air and pumps it inside. This means that you spend less energy on producing heat than the amount of heat energy you’re adding to the inside. Even if it’s cold outside, there’s still heat in that air you can pull out to bring inside. Also any waste heat created in this process is still useful.
Let’s assume our power comes from natural gas. Natural gas power plants are about 50% efficient at turning gas into electricity.
If we use a space heater to heat our home (which is by definition 100% efficient) we are still only getting 50% energy efficiency from that initial gas.
If we use gas to heat our home directly, that’s about 80% efficient. Better than a space heater.
If we use electricity to run a heat pump. We don’t measure the efficiency of a heat pump, but rather the coefficient of performance (CoP) which has a minimum of 1. That is because if it gets down to 1, it’s exactly the same.as a space heater. It’s pulling in no heat from the outside and turning the electricity only into heat. In most conditions, the CoP is about 5, so the heat pump is providing 5x the heat as it consumes in electricity. So with out 50% efficient power generation, we are getting 250% the heating in our homes as the natural gas had in initial energy.
Even with a CoP of 2, you are still matching the efficiency of a space heater.
You can calculate it based on the conditions CoP = Th/Th – Tc where Th is the temperature of the hot side and Tc is the temperature of the cold side, both measured in Kelvin
This doesn’t break conservation of energy because we are simply stealing heat from the air outside.
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