Now stretch it firmly and quickly secure it on your temperature sensitive upper lip. You will feel warmer than before. This is because you add energy to the rubber band, which increases the temperature of the rubber band.
Are you ready for the exciting part? Keep it stretched for a while until it returns to room temperature. Now let the rubber band relax and quickly touch it to your lips again.Snowing colder Than room temperature! Seriously, try it yourself.
So if you had a rubber band big enough, could you use it to cool your house? Wait a minute, you say: In the first stage, when we stretch the rubber band, it heats up, then cools back to its original temperature – in the process, it gets hotter. heated Air. you’re right. But what if we could push the warm air outside? Then you can just keep the cooling phase inside.
Prosperity. You just reinvented air conditioning! Instead of rubber bands, air conditioners use a fluid called refrigerant that circulates from the inside to the outside in a closed loop. This liquid has a low specific heat, so it changes temperature quickly, and has a very low boiling point, turning into a gas at about –15 degrees Fahrenheit.
How about it? The gas is first compressed, causing it to heat up to about 150 degrees. Hot gas circulates through a set of copper coils on the outside, over which a fan blows, so the gas loses thermal energy to the atmosphere. (Copper also has a lower specific heat.)
It is then pumped back inside, where the pressure rapidly decreases, causing it to expand and immediately cool to around 40 degrees. As the now cold fluid circulates through the indoor coil, the fan blows the warm inside air over it, heating the fluid again and cooling the indoor air in the process. As the system circulates, it essentially absorbs heat energy from inside the room and brings it outside.
By the way, this is the exact same process that a refrigerator uses to keep cheese and soda cold. In both cases, the process cools the temperature indoors and warms the temperature outside. Put your hands on the back of the refrigerator and you’ll see what I mean. Just for fun, this guy actually built a refrigerator that ran on rubber bands.
So heat pumps are not new!
You thought this was going to be an article about heat pumps, right? Well, guess what. We keep talking about heat pumps because they operate on the same principle. A heat pump, like an air conditioner, cools your home by circulating refrigerant and changing the pressure to change the temperature, so it takes the heat energy from one place and puts it in a different place.
So back to the big mystery: How do heat pumps raise the temperature of indoor air on cold days without actually producing any heat? It’s simple: just run it in reverse! This time we let the hot compressed refrigerant cool inside the room to increase the indoor air temperature. Then the low-pressure cold gas goes outside to be heated.
Go outside to keep warm? Yes. Even on cold days, there is still heat energy in the air. As long as it’s above absolute zero (and trust me, it is, since that’s about minus 460 degrees Fahrenheit), the air molecules are in motion. And, because we cool the refrigerant to minus 15 degrees (which is colder than winter temperatures in most places), it’s squeezing heat energy out of even the frigid air.
Of course, you don’t get energy for free. Heat pumps rely on electricity to drive compressors and fans. But if you have solar panels on your home, or your area’s electricity comes even in part from non-carbon sources, replacing a gas furnace with a heat pump can make a huge difference in reducing greenhouse gas emissions. In the process, it may lower your utility bills.