How a coefficient of performance greater than 1 is possible?


How is it that a machine (like a heat pump) can consume 1kw of power and produce an amount greater than that of heat? What am I misunderstanding?

In: 320


It’s because what’s being measured in this case is how much energy you spend in order to move a given amount of energy. Because heat pumps aren’t generating energy in he same way a heater does, they just move it. Hence the name “pump”

Like a big oil tanker truck might spend 100 gallons of gas to transport 10,000 gallons of gas (I have no idea if these numbers are accurate, just an example) you could say it then has a coefficient of performance of 100. It didn’t turn 100 gallons of gas into 10,000 gallons of gas. It just moved it where you want them.

It’s the same thing with heat pumps. You spend one 1 unit of energy to move more than 1 unit of energy then you have a COP of over 1.

>How is it that a machine (like a heat pump) can consume 1kw of power and produce an amount greater than that of heat?

Because it doesn’t “produce” the heat

Heat pumps pump heat, they don’t make it

They’re air conditioners and you can set the hot side to be inside the room. Just like an AC or a fridge, refrigerant runs around through the coils and when in heatmode it goes outside the house, gets expanded so it transitions from a liquid to a cold gas, absorbs some heat from the outside air, gets squished from a gas into a much hotter liquid, then gives off its heat to the air inside the house

The power consumed is running the compressor which is pushing the refrigerant around, but the heat coming into the house is being stolen from the air outside and moved inside and that’s not related to the power consumed by the compressor.

Heat pumps work like they sound. They pump heat around. It’s not a cheat of the laws of thermodynamics. They use energy to transfer heat from one area to another. And the coefficient of performance is “how much heat is moved” over “how much energy was put in the system in order to do so”.

So let’s use a fridge as an example. As made-up round numbers, we’ll say it uses 200W, and has a coefficient of 2. So it uses 200W to remove 400W of heat from the inside of the refrigerator. What isn’t explicitly stated is that 600W of heat is ejected out of the back of the refrigerator (the 400 that came from the interior, and the 200 that came from running the heat pump).

Coefficient of performance does not measure heat *produced*. It measures the heat which is added to the hot end.

In a regular heater this is just heat generated from throwing away energy. In a heat pump, there *is* that heat, but *also* heat *moved* by the pump.