How do heat pumps work and why are the energy efficient?
Edit: the question is sufficiently answered. Thanks guys!
In: 50
Complicated answer, look up for rankine cycle. 5 years old answer, it brings the heat from the environment and mix with the heat it produces itself, so it brings more heat energy than the electric energy it consumes
Imagine two half filled buckets of water, and a sponge.
You want to move water from one bucket to the other.
So you put the sponge in bucket A, and let it spread out as much as possible (like it’s at low pressure). It will soak up a bunch of water.
Then you move it to bucket B and squeeeeeeze it out (put it under high pressure). You have just used pressure to transfer a liquid from one place to another.
In a heat pump, the “water” is latent heat. The “sponge” is a liquid called refrigerant or coolant. It gets passed between two tanks in a circular pattern. One tank puts it under low pressure, which forces it to evaporate into a gas. To be in a gas state, it HAS to absorb heat from its surroundings, making them cold.
Then this gas with heat in it gets pumped to the other side, which is under high pressure. The pressure squeezes the gas back into a liquid, and thus it gives up its heat and makes that area hot. Then it continues on its journey back to the low pressure tank to absorb more heat.
There are other devices at play to make this efficient, but that is the fundamental idea. You use pressure to change the temperature, using gas laws.
I read this question as meat pumps and I wanted to know how meat pumps work as well.
You know how, on a hot day, the air conditioner component that sits outside blows hot air out of it, even though your house is cooler than the outdoors? That’s a heat pump.
You know how a freezer works? It’s the exact same but backwards. You put the cold bit where you don’t care about it getting colder and the warm bit where you want to be warmer.
Eli10, it has a gas that can condense and boil at a very cold temperature.
When something condenses it lets a little extra energy off as heat.
And when it boils it absorbs that much energy from around it making it seem colder then it was as a liquid.
A lot of organic and chlorinated gasses do this, and some alcohols.
It’s the same reason boiling water won’t get above 100°c or 212f unless it’s got impurities.
The evaporating steam absorbs all heat above that boiling temperature.
Tldr, it’s a fridge inside out.
This is super high level, so there are more details to explain why, but i’ll skip those to make it easier to understand
gases get hot when you compress them. gases get cold when they expand. let’s say the different from compressed to uncompressed is 60 degrees for our silly high level example
air in your house is 70. the refrigerant is compressed, and it gains 60 degrees, so it’s now 130 degrees. it goes through a radiator, like the one on the front of your car. (also the same as liquid coolers in a computer) this is the loud box outside your house that blows hot air out of the top
now after the radiator, let’s say we get the temperature down from 130 to 90. now it goes j to the condenser. it lets the gas expand. remember the 60 degree difference between compressed and expanded? well now that we expanded the gas, it drops 60 degrees. now it’s 30 degrees. the condenser is basically like a radiator, but for cold. the air that blows through this is where the cold air comes from in your air conditioner. i completely pulled numbers out of my butt for the purpose of explaining this very simply
heat pump does the same thing. it just reverses the process. AC is just a heat pump. pumps heat from inside the house to outside. heat pump mode for heating is just reversed direction of AC.
let’s say outside is 30 degrees, so below freezing. sounds crazy to pump heat from outside to inside, right? but let’s look at the numbers. outside, the refrigerant starts at 30 degrees. it then gets compressed. it gains 60 degrees. now it’s 90 degrees. it goes through the radiator and a fan blows air through it and it heats the air (which pulls heat out of the refrigerant). this is the hot air you feel when your heat pump is heating your house. let’s say it drops 40 degrees after the radiator so it’s 50 now
it then goes back outside, is expanded, and that causes the 60 degree change, so it’s -10 degrees now. heat goes from hot to cold. despite outside being colder than freezing, the 30 degree air is much warmer than the -10 degree refrigerant, so it absorbs the heat. just repeat this cycle and that’s how heat pump works. it’s just air conditioning, but reversed to pump the heat in the other direction. heat pump capable systems just have a valve system that allows for this reversal.
now a big downside to heat pump: the temperature differences are limited by physics. for this reason, it it’s too cold outside; it won’t be able to get too hot. the heat from most heat pump systems on a really cold sub-freezing days won’t give you super hot air. it will usually feel slightly warm. that’s the only major problem. otherwise they’re very efficient
Probably not ELI5 grade explanation, but the guy from Technology Connections on YouTube made a pretty informative video on how heat pumps work: https://youtu.be/7J52mDjZzto
Think lf heat as how much energy there is in one place. Even if it’s cold outside there is still energy in the air, only less than inside. So the idea is to take some of that less dense energy, make it more energy dense than inside air(by increasing the pressure) and letting the now more energy dense air increase the temperature inside. If the energy spent to increase the pressure leads to more heat being produced than just burning gas, the efficiency can be said to be over 100%.
Non ELI-5:
There are fundamental physical problems with creating an efficient heat pump if the difference in temperature is too high (look up Carnot Heat Pump), therefore in cold climates(mostly scandinavia afaik) what is called a geothermal heat pump is often used. Instead of using outside air a hole is drilled into the ground. Once you get into bedrock/deep enough the temperature doesn’t fluctuate much (often assumed 10c/50f) so the temperature difference is qyite small and they retain high efficiencies regardless of outside temperatures. Also fun fact, a refrigerator/freezer is essentially a heat pump run in reverse.
Heat pumps work just like an air conditioner or refrigerator. They move heat from one place to another. It’s typically much more efficient to move heat around, rather than create it.
They work like an airconditioner in reverse. They pump the refrigerant around and evaporate it when it gets to the outside of the house and condense it when it gets to the inside of the house. This is more efficient than electric heaters because you can pump more than 1W of heat into your house by using 1W of electricity to run the pump, a normal heat just converts that 1W of electricity directly to 1W of heat
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