How do heat pumps work?


Now pull it very hard and quickly hold it on your upper lip, which is sensitive to temperature. You will feel that it is warmer than before. This is because you are adding energy to the rubber band, which increases its temperature.

Are you ready for the amazing part? Keep it spread for a while until it comes back to room temperature. Now release the rubber band loosely and quickly attach it to your lips again. it's snow Cold Higher than room temperature! Seriously, try it yourself.

So if you had a big rubber band, could you use it to cool your house? Wait a minute, you'll say: In the first step, when we pulled the rubber band, it got hot, and then it cooled back down to its original temperature – and in doing so, it Hot Air. You are right. But what if we could get that hot air out? Then you can just put the cooling stage inside.

Boom. You have just invented the air conditioner! Instead of rubber bands, ACs contain a fluid called refrigerant that circulates in a closed loop from inside to outside. This liquid has a low specific heat – so it changes temperature rapidly – ​​and has a very low boiling point, turning into a gas at something like -15 degrees Fahrenheit.

What kind of work is this? The gas is first compressed, heating it to approximately 150 degrees. The hot gas circulates around a set of copper coils outside, over which a fan runs, so the gas loses thermal energy to the atmosphere. (The specific heat of copper is also low.)

It is then pumped back inside, where the pressure is immediately reduced, causing it to expand and instantly cool to about 40 degrees. As the now cooled fluid circulates through the indoor coils, a fan blows the hot air inside over it, reheating the fluid and cooling the indoor air in the process. As the system circulates, it basically picks up the thermal energy inside the house and moves it outside.

By the way, this is the exact same process your fridge uses to keep your cheese and soda cold. In both cases, this process causes some part of the inside to become cold and some part of the outside to become hot. Put your hand behind the fridge and you'll see what I mean. Just for the sake of show, here's a guy who actually built a refrigerator that runs on rubber bands.

So heat pumps are not new!

You thought this would be an article about heat pumps, right? Well, guess what – we've been talking about heat pumps this whole time, because they operate on similar principles. A heat pump cools your home like an air conditioner: by circulating a refrigerant and varying the pressure to change its temperature, so it takes thermal energy from one place and puts it in a different place. Is.

So back to the big mystery: How can a heat pump raise the temperature of indoor air on a cold day without actually producing any heat? Simple: just run it in reverse! This time we allowed the hot compressed refrigerant to cool inside the house to increase the indoor air temperature. The low-pressure, cold gas then moves out to be heated.

Get hot outside? Yes. Even on a cold day, the air still contains thermal energy. As long as it's above absolute zero (which, believe me, it is, because it's about -460 degrees Fahrenheit), air molecules are in motion. And since we are cooling the refrigerant to, say, -15 degrees, which is below winter temperatures in most places, it will also take thermal energy out of the cold air.

Of course, you can't get energy for free. Heat pumps rely on electricity to run the compressor and fan. But if you have solar panels on your home, or if electricity in your area comes partly from non-carbon sources, replacing a gas furnace with a heat pump can make a big difference in reducing greenhouse gas emissions. And it'll probably lower your utility bills in the process.