How a Heat Pump Works | This Old House

[Music] richard for years you have told us with a heat pump that you're installing a lot of these days that it has the ability to find heat even on the coldest of days that's right that's a hard thing to get your head around in order to understand that we're going to start with a basic understanding of air conditioning okay so this is a little markup of how every air conditioning system around the planet works it works on the most important principle to me in thermodynamics which is heat always goes to cold no matter what so imagine this is the inside unit the inside the part that's inside your building has a fan going across it this is the coil yeah right now it's filled with refrigerant if i can get that really cold the air the heat that is in the air on a hot summer day passes by this coil and the pipes inside this are really cold the heat has no choice but to be absorbed into the refrigerator make something cold put it here heat comes to it right and simply put now that heat that's now trapped inside that refrigerant moves through the piping through a compressor to outside and now this coil is hotter now and now what happens the same law happens if this is really hot inside the fringe of piping now and even though the air outside is warm but or slightly warm it's still going to be this is heat it's going to go to the cooler air so it's 90 degrees outside that's right so long as this is more than 90 degrees let's call it 120. that's right it now thinks the 90 is cold it has no choice so it's going to go to that heat goes to cold so now that dumps out now this gets a little bit cooler coming back and now we just have to make that refrigerant really cold cold cold again okay so cold here attracts the heat hot here dumps the heat that's right this is the part that doesn't make any sense how can you have something that is both colder than the warm inside air but then hotter than the hot outside air the same thing is both things well if i can compress a refrigerant it has no choice but to get hot okay now any gas will get hotter if you compress it this is a perfect example here this is a little sample unit now this is just filled with air and you can see there's a little piece of cotton right here whoa whoa air so not even refrigerant just it's a gas so air works the same way what will happen is we'll compress that air and get it so hot we'll get to the flash point that'll light it up i don't believe this watch this i don't believe this okay you just lift that on fire all right it wasn't for nano second but it was it helps you understand that if we compress a gas and it's it's directly proportional to the change in pressure too it'll get hotter as i compress it more so that's what this is doing that's right okay and this is one speed now so this is so that little bit of gas that picked up heat from inside you make it super hot now i could get up to 150 out here it can get really hot right but now i dump the heat to outside now how do i get it cold again well just like when we compress a gas it gets hot if we release a gas and get it to a lower pressure just the opposite it'll get cold so that every single air conditioning system has a valve like this called an expansion valve so here is the high pressure refrigerant right here hot right and now it goes to a little tiny needle valve so the best way to understand that so this is a can of compressed air but it's actually in a liquid state inside the can because it's so compressed right and this needle right here is very similar to the expansion valve so you can see right here i have a digital thermometer 82 degrees okay so now oh look at a drop wow we've already lost 20 degrees and that's just air that's just there holy that is a oh yeah it's like a block of ice so with this type of refrigerant we could get as low as minus 37 degrees okay and so that's what's going on where the same process that expansion valve when it releases it lets it go into larger space and just drops that and makes that coil really really cold we pick up the heat inside the building move the heat through the compressor dump it to outside the cycle repeats it just continues billions and billions of times every hour of the day worldwide in every basic air conditioning system that's sort of how i make a hot day comfortable right how do i make a really cold day come we want to just reverse everything that we got here right here we've got a cold coil here and hot outside we want it just to be the opposite we want it to be cold and we want to be really cold so just like you said even if it's hot outside so long as this is hotter the heat's going to move correct now you're saying that so long as if it's cold outside as long as this is colder the heat will move again if that refrigerant got down to -37 and there was zero degree air around it there's 37 degrees of temperature would go to coal to go into that cold refrigerant okay so you pick up heat the compressor pumps it up gets it hotter that coil is now hotter the cold air that's in the room crosses the what goes across that coil that's hotter the coal goes into the building now what do you got to do you got to go back through a different expansion valve because now we got to get that outside coil again cold so valve is there just pointed in the different different valve but it has to go in the opposite direction all right so you could have two separate systems a heating system moving this way and a cooling system going this way the way that we use the same equipment to do both functions is an ingenious device called a reversing valve now this sits right here and the compressor always puts out the hottest refrigerant so if i look here it normally come right here and it goes right to an air conditioning wheel goes right to the outside coral remember we want it to be hotter outside now if i switch the thermostat and i say let's now go to heating of the building here's the hot refrigerant going right inside the building it's just a simple little gate absolutely just moving back and forth between air conditioning and heating man it doesn't look like magic that's right but it it's just brilliant it's just absolutely brilliant this technology is pretty basic you know and what the complaint was with heat pumps you get down to 30 35 degrees outside and you often have electric strip heat or backup heat right and it really was the nature of this level of technology the compressor was just on at 100 miles an hour and then off and these fans were on and they were off and that expansion valve just opened and closed and so what happens is it would gather a little bit heat and then it would rest and it would wouldn't be able to keep up it was every time it rested would leave the house right so all the modern systems the inverter style heat pumps what happens is it has let's take the compressor for example this compressor now instead of being on at full blast this thing has 150 different speeds so it's constantly changing the pressure of the refrigerant which means it's changing the temperature so if i didn't want really really hot and i wanted say half degrees could i get 87 absolutely precisely that absolutely wow right so now that's on the heating side we change the compressor speed and spin okay the expansion valve remember the expansion valve that just was a simple open closed device this thing is a modern expansion valve and this thing will open and close at 400 different positions in 3 8 of an inch of travel so now you're matching the perfect amount of pressure for the heating side on the cooling side you're just changing it just right so if i didn't want 30 degrees really cold i wanted say 47 and a half degrees i could get just that absolutely and then also these fans now the fans are all ecm fans which means they're going to spin in concert with the expansion valve and the compressor so all the fans will also change their speed ecm is what electronic electronically commutated motor right so here if you look here the regular fan is was always on right but this would be like adding a dimmer to it so now as you need less it would just change it okay so an ecm motor gives you that control variable speed right here's our reversing valve we talked about remember here's the expansion valve right here here's the compressor and then two lines right here that are gonna either send heat into the building or send heat out of the building and wherever that heat is it's gonna go to cold you have demystified a very complicated subject thank you if there's no show fifth or sixth law of thermodynamics we'd name it after you nobody could spell it thanks for watching this whole house has got a video for just about every home improvement project so be sure to check out the others and if you like what you see click on the subscribe button make sure that you get our newest videos right in your feed

Channel: This Old House

Views: 1,223,076

Keywords: This Old House, Ask This Old House, DIY, Home Improvement, DIY Ideas, Renovation, Renovation Ideas, How To Fix, How To Install, How To Build, How to, this old house pbs, this old house how to, how a heat pump works, heating pump, heat pump, this old house plumbing, plumbing, plumbing videos, richard trethewey, richard trethewey this old house, how to video

Id: -vU9x3dFMrU

Length: 8min 37sec (517 seconds)

Published: Sat Oct 05 2019