Intuitively cold winter air is cold, but that’s just our perspective. From a physics perspective any air that exists anywhere on this planet at any time has still got huge amounts of heat stored in it (it’s literally hundreds of degrees above absolute zero, the most blisteringly cold arctic air still represents a huge reservoir of physical heat energy even when it’s cold enough to kill us). A heat pump doesn’t care about how heat feels to humans, it uses physics: specifically evaporation and condensation of refrigerants to extract heat from the cold winter air outside (making that air even colder while the refrigerant absorbs heat from it) and move it indoors (making it warmer when the refrigerant releases the heat).
To use a water level analogy, the heat pump moves its heat out of an absolutely massive heat reservoir (the planet’s atmosphere) that at any point might be slightly lower or higher than the level you actually want, and deposits the results of its pumping into a tiny reservoir (your indoor air) that it is responsible for controlling the heat level of. In both cases there is lots and lots of water (in the analogy, heat) available to pump around and the contents of your little tank makes no real significant difference either way, depending on how much water you need in that tank you can easily pump it in either direction you want, within reason, but eventually if the water levels start to get too different, you start running into practical problems with pressure and the amount of power you need to pump the water level up that high to overcome the height difference, and can also run into problems with inlets being uncovered if the water level drops too low. In the analogy this represents the range of temperatures and pressures where the refrigerant can still change between a gas or a liquid, which is determined by the design of the system and the refrigerant used.
Air conditioners do the same thing (in fact essentially ARE the same thing) as heat pumps, it just makes more sense to us intuitively because we’re familiar with how they work, and are unfamiliar with the idea of this principle being reversed. Imagine if you put the hot-air blasting outdoor part of an air conditioner inside, and put the cold part that normally lives inside your house, outside. Now turn it on, and it starts working as a heater, and it’s making the outdoors colder for no reason, and we call this “wasteful” but when you actually need heat it’s actually not wasteful. So we add a reversing valve so you can make either end the hot side or the cold side, as needed, and you’ve got a heat pump. They sometimes select different refrigerants that are more efficient across the desired temperature ranges and they will have some different sizing considerations and mechanical needs to operate optimally, but fundamentally they’re the same kind of machine, just with a slight rearrangement of the plumbing.
Flip your refrigerator inside out. That is exactly what is happening.
You need to understand the difference between “heat” and “temperature”.
When you squeeze a gas inside a perfectly insulated container, no heat is transferred, but the temperature increases. If you allow the gas to expand again, it will return exactly to the temperature it started at. Again, no heat has transferred into or out of the gas, due to our (hypothetical) perfect insulation. The temperature has changed, but no heat has moved.
In reality, we aren’t using a perfect insulator. When we compress the gas, the temperature of the gas rises. Heat starts flowing from the compressed gas to the container, and into the air. The gas is still compressed after the heat has left, but its temperature falls to ambient. This all happens inside the house.
The cooled, compressed gas is now piped outside. It is expanded. Because it doesn’t have the same amount of heat that it started with, the temperature plummets. It gets extremely cold, far colder than the outside atmosphere. Heat from the atmosphere flows into the cold gas. The cold, decompressed gas then goes to a compressor, and the cycle repeats.
A bicycle pump or other type of air pump warms up when the air is compressed.
A spray can or propane cylinder cools off when the gas inside it is released.
Plug the two together in a loop, put some coils on either side so that heat (or lack thereof) can be easily exchanged with the space, and you have a heat pump.
A heat pump doesn’t generate heat, it just moves it using the physics of pressure and state changes of a fluid (refrigerant). Moving heat in this manner uses less electrical energy than would be used generating heat from that electricity.
Heat pumps are very common. Refrigerators would be the most ubiquitous (heat pumped from inside to outside), but there are AC units, of course, and also clothes dryers and water heaters that are available.
Basically it doesn’t produce heat by converting energy into heat, rather, it uses energy to move heat from one place to another. Hence the name heat pump - it literally just pumps heat around. The place where it gets the heat in this case is the outside. While it’s usually colder than inside at the times when you’d want to use a heat pump for heating, it’s still way more than absolute zero - the freezing point of water is 273 Kelvin, after all. This means there’s always some amount of heat that you can ‘steal’ from the outside and pump indoors.
You may infer that this means that the heat pump is going to be pumping colder air outside, and you’d be correct in that inference. What’s even more interesting is the realization that you can harness that property by running the heat pump ‘in reverse’ to cool a space - which is exactly what an air conditioner does. It’s merely a heat pump that pumps the heat out of a space.
How does it even work, I can’t understand it at all.
Intuitively cold winter air is cold, but that’s just our perspective. From a physics perspective any air that exists anywhere on this planet at any time has still got huge amounts of heat stored in it (it’s literally hundreds of degrees above absolute zero, the most blisteringly cold arctic air still represents a huge reservoir of physical heat energy even when it’s cold enough to kill us). A heat pump doesn’t care about how heat feels to humans, it uses physics: specifically evaporation and condensation of refrigerants to extract heat from the cold winter air outside (making that air even colder while the refrigerant absorbs heat from it) and move it indoors (making it warmer when the refrigerant releases the heat).
To use a water level analogy, the heat pump moves its heat out of an absolutely massive heat reservoir (the planet’s atmosphere) that at any point might be slightly lower or higher than the level you actually want, and deposits the results of its pumping into a tiny reservoir (your indoor air) that it is responsible for controlling the heat level of. In both cases there is lots and lots of water (in the analogy, heat) available to pump around and the contents of your little tank makes no real significant difference either way, depending on how much water you need in that tank you can easily pump it in either direction you want, within reason, but eventually if the water levels start to get too different, you start running into practical problems with pressure and the amount of power you need to pump the water level up that high to overcome the height difference, and can also run into problems with inlets being uncovered if the water level drops too low. In the analogy this represents the range of temperatures and pressures where the refrigerant can still change between a gas or a liquid, which is determined by the design of the system and the refrigerant used.
Air conditioners do the same thing (in fact essentially ARE the same thing) as heat pumps, it just makes more sense to us intuitively because we’re familiar with how they work, and are unfamiliar with the idea of this principle being reversed. Imagine if you put the hot-air blasting outdoor part of an air conditioner inside, and put the cold part that normally lives inside your house, outside. Now turn it on, and it starts working as a heater, and it’s making the outdoors colder for no reason, and we call this “wasteful” but when you actually need heat it’s actually not wasteful. So we add a reversing valve so you can make either end the hot side or the cold side, as needed, and you’ve got a heat pump. They sometimes select different refrigerants that are more efficient across the desired temperature ranges and they will have some different sizing considerations and mechanical needs to operate optimally, but fundamentally they’re the same kind of machine, just with a slight rearrangement of the plumbing.
Flip your refrigerator inside out. That is exactly what is happening.
You need to understand the difference between “heat” and “temperature”.
When you squeeze a gas inside a perfectly insulated container, no heat is transferred, but the temperature increases. If you allow the gas to expand again, it will return exactly to the temperature it started at. Again, no heat has transferred into or out of the gas, due to our (hypothetical) perfect insulation. The temperature has changed, but no heat has moved.
In reality, we aren’t using a perfect insulator. When we compress the gas, the temperature of the gas rises. Heat starts flowing from the compressed gas to the container, and into the air. The gas is still compressed after the heat has left, but its temperature falls to ambient. This all happens inside the house.
The cooled, compressed gas is now piped outside. It is expanded. Because it doesn’t have the same amount of heat that it started with, the temperature plummets. It gets extremely cold, far colder than the outside atmosphere. Heat from the atmosphere flows into the cold gas. The cold, decompressed gas then goes to a compressor, and the cycle repeats.
A bicycle pump or other type of air pump warms up when the air is compressed.
A spray can or propane cylinder cools off when the gas inside it is released.
Plug the two together in a loop, put some coils on either side so that heat (or lack thereof) can be easily exchanged with the space, and you have a heat pump.
A heat pump doesn’t generate heat, it just moves it using the physics of pressure and state changes of a fluid (refrigerant). Moving heat in this manner uses less electrical energy than would be used generating heat from that electricity.
Heat pumps are very common. Refrigerators would be the most ubiquitous (heat pumped from inside to outside), but there are AC units, of course, and also clothes dryers and water heaters that are available.
Basically it doesn’t produce heat by converting energy into heat, rather, it uses energy to move heat from one place to another. Hence the name heat pump - it literally just pumps heat around. The place where it gets the heat in this case is the outside. While it’s usually colder than inside at the times when you’d want to use a heat pump for heating, it’s still way more than absolute zero - the freezing point of water is 273 Kelvin, after all. This means there’s always some amount of heat that you can ‘steal’ from the outside and pump indoors.
You may infer that this means that the heat pump is going to be pumping colder air outside, and you’d be correct in that inference. What’s even more interesting is the realization that you can harness that property by running the heat pump ‘in reverse’ to cool a space - which is exactly what an air conditioner does. It’s merely a heat pump that pumps the heat out of a space.
Here’s a Technology Connections video explaining the concept even better than I could: https://www.youtube.com/watch?v=7J52mDjZzto