WEBVTT Kind: captions Language: en 00:00:00.000 --> 00:00:02.035 This is a window air conditioner. 00:00:02.535 --> 00:00:04.738 And this is a dehumidifier. 00:00:05.271 --> 00:00:06.909 What's the difference? 00:00:07.140 --> 00:00:09.527 This one's got a bucket. 00:00:09.909 --> 00:00:10.477 Hello. 00:00:10.477 --> 00:00:14.247 You're about to learn a lot about dehumidifiers. 00:00:14.247 --> 00:00:16.616 You're probably looking at this video's length and thinking 00:00:17.050 --> 00:00:20.086 How the heck is there that much to talk about dehumidifiers? 00:00:20.353 --> 00:00:21.688 Well, it's simple. 00:00:21.988 --> 00:00:23.623 I'm a nerd! 00:00:23.623 --> 00:00:31.197 But I'm making this video because these machines have a simple mission with perplexingly confusing side effects. 00:00:31.664 --> 00:00:33.700 Most everyone knows what they do: 00:00:33.700 --> 00:00:37.170 they remove water from the air and decrease humidity. 00:00:37.871 --> 00:00:43.443 But the ramifications of that are, I'd wager, not very well understood. 00:00:44.244 --> 00:00:48.848 I myself didn't realize something pretty profound about these until quite recently, 00:00:48.848 --> 00:00:52.819 so today I'd like to talk about how dehumidifiers work. 00:00:53.453 --> 00:00:55.622 They're actually doing something pretty amazing, 00:00:55.955 --> 00:01:01.594 and when you understand the details, it might cause you to reevaluate where and how best to use them. 00:01:02.562 --> 00:01:06.766 This video is kind of all over the place, so rather than bury the tack too deep, 00:01:07.033 --> 00:01:08.635 I'll get right to the brass ledes. 00:01:09.469 --> 00:01:14.340 The purpose of these machines is not to make you comfortable 00:01:14.340 --> 00:01:16.976 or even to help your air conditioning system. 00:01:17.444 --> 00:01:19.813 They absolutely will not do that. 00:01:20.947 --> 00:01:23.016 This might rub against your intuition. 00:01:23.116 --> 00:01:27.720 We all know from experience that humid air sucks when it's hot outside 00:01:28.021 --> 00:01:32.292 and make air less humid is like... its job. 00:01:33.026 --> 00:01:37.230 But before you run out and grab one of these things thinking it'll help in the next heatwave, 00:01:37.464 --> 00:01:40.700 there's a giant catch you need to be aware of: 00:01:41.301 --> 00:01:48.608 The process of dehumidifying the air generates heat, and it's a lot more heat than you might expect. 00:01:49.175 --> 00:01:52.579 This little machine can put out as much heat as a space heater, 00:01:52.745 --> 00:01:55.482 and larger ones will easily exceed that. 00:01:56.182 --> 00:01:59.519 And you probably don't want to be running a space heater during a heatwave. 00:02:00.120 --> 00:02:03.957 Now where that heat comes from is fascinating, 00:02:03.957 --> 00:02:11.164 and it creates some really interesting implications when you use a dehumidifier alongside an air conditioning system. 00:02:12.065 --> 00:02:15.401 Those implications are really the main point of this video. 00:02:15.802 --> 00:02:20.723 But to fully understand them, we have to get pretty deep into the weeds. 00:02:20.723 --> 00:02:21.474 Which we will. 00:02:21.741 --> 00:02:22.942 Hence the runtime. 00:02:23.042 --> 00:02:24.577 But long story short, 00:02:24.777 --> 00:02:31.985 if you don't have a significant and chronic humidity problem somewhere in your home which requires attention, 00:02:32.886 --> 00:02:35.421 there's really no point to having a dehumidifier. 00:02:35.855 --> 00:02:40.360 It's just going to make a lot of heat, a lot of noise and waste your money. 00:02:41.194 --> 00:02:44.898 So... what qualifies as a humidity problem? 00:02:45.899 --> 00:02:47.467 Well, as a general rule, 00:02:47.600 --> 00:02:56.095 if indoor relative humidity persistently stays above about 65%, (though, you'll find disagreement on the exact number) 00:02:56.442 --> 00:02:57.644 that's bad. 00:02:58.144 --> 00:03:03.049 That can lead to mold and mildew growth which is unpleasant and dangerous. 00:03:03.650 --> 00:03:08.188 In addition to that, high humidity can accelerate corrosion on things that corrode 00:03:08.388 --> 00:03:12.859 and quick and material degradation in materials that degrade 00:03:13.126 --> 00:03:15.094 so it can ruin your belongings. 00:03:15.495 --> 00:03:20.567 And if that's not enough, high moisture environments are more likely to attract certain pests. 00:03:20.900 --> 00:03:25.405 And if the damp gets real bad, it can even cause structural issues. 00:03:26.139 --> 00:03:30.510 So if you live where the air gets mmmmoist, a lot, 00:03:31.277 --> 00:03:32.745 dehumidifiers are common. 00:03:33.346 --> 00:03:37.750 They're practically a staple of Midwestern basements and crawl spaces during the summer months, 00:03:38.051 --> 00:03:41.621 especially when people have problems with stormwater seepage down there. 00:03:42.422 --> 00:03:45.825 Did you catch, though, that I said basements and crawl spaces? 00:03:46.693 --> 00:03:49.229 There's something unique about those areas. 00:03:49.696 --> 00:03:51.864 They're not generally conditioned. 00:03:52.198 --> 00:03:58.204 Or if they are, such as with a finished basement, they're often poorly conditioned compared to the rest of a home. 00:03:59.339 --> 00:04:04.594 The main issue down there is that since those areas are partially underground, 00:04:04.594 --> 00:04:09.882 in the warm months of the year, they're typically cooler than the outside air temperature. 00:04:10.583 --> 00:04:13.753 And that leads to persistently elevated humidity. 00:04:14.854 --> 00:04:18.124 Now, it's important to understand why that is the case. 00:04:18.858 --> 00:04:24.297 When we talk about how much water vapor is in the air, we usually discuss relative humidity. 00:04:25.398 --> 00:04:27.200 Fun fact, though... 00:04:27.200 --> 00:04:32.372 relative humidity doesn't actually tell us how much water vapor is in a given volume of air. 00:04:33.106 --> 00:04:34.307 But that's fine. 00:04:34.641 --> 00:04:36.943 We don't actually need to care about 00:04:37.110 --> 00:04:40.480 how many water molecules are in a cubic meter of air. 00:04:41.414 --> 00:04:44.717 Relative humidity tells us what's usually more important: 00:04:45.385 --> 00:04:49.222 Air's current ability to absorb more moisture. 00:04:50.223 --> 00:04:52.859 It's expressed as a saturation percentage, 00:04:53.159 --> 00:04:58.031 meaning air with 50% relative humidity is 50% saturated, 00:04:58.364 --> 00:05:02.535 and thus it has absorbed half as much water vapor as it theoretically can. 00:05:03.536 --> 00:05:05.338 But there's a wrinkle to this. 00:05:06.239 --> 00:05:11.177 Air's total capacity to absorb moisture depends on its temperature. 00:05:12.178 --> 00:05:16.049 Air can absorb more moisture the warmer it is. 00:05:16.416 --> 00:05:22.422 So if you take a known volume of air with a known saturation percentage and heat it, 00:05:23.056 --> 00:05:25.858 its relative humidity will actually fall. 00:05:26.559 --> 00:05:31.497 It has exactly as much water vapor in there as it did before we warmed it up, 00:05:31.931 --> 00:05:37.870 but the air's increase in temperature unlocked more capacity for it to absorb water vapor, 00:05:38.237 --> 00:05:41.541 which ultimately lowered its relative humidity. 00:05:42.675 --> 00:05:47.714 This is why the indoor air is usually very, very dry in the winter months. 00:05:48.381 --> 00:05:52.719 Elevating the indoor air temperature causes relative humidity to fall. 00:05:53.853 --> 00:05:57.090 But of course, the opposite is also true. 00:05:57.924 --> 00:06:03.563 If you take air and cool it down, it loses its ability to hold on to moisture. 00:06:04.230 --> 00:06:08.127 And that means the same volume of air, when chilled - 00:06:08.127 --> 00:06:15.875 even though we haven't added any water vapor - becomes more saturated and thus its relative humidity goes up. 00:06:17.043 --> 00:06:22.682 What this means for a house or structure is that when there's any air exchange at all 00:06:22.682 --> 00:06:28.287 between the cool basement or crawl space and the outside air (or even just the rest of the house), 00:06:28.788 --> 00:06:33.426 relative humidity will be persistently higher in those cooler spaces. 00:06:34.160 --> 00:06:38.257 That means it's harder for liquid water to evaporate down there, 00:06:38.257 --> 00:06:42.335 which in turn means wet stuff dries out more slowly. 00:06:43.136 --> 00:06:44.537 And that's the problem. 00:06:45.271 --> 00:06:52.093 If humidity levels are elevated enough stuff will dry out so slowly that you risk damage to whatever's down there, 00:06:52.093 --> 00:06:53.713 or even your home itself. 00:06:54.614 --> 00:06:56.616 So what do you do in that situation? 00:06:57.683 --> 00:06:58.951 You conditioned the air. 00:06:59.585 --> 00:07:05.224 Dehumidifiers technically are a form of air conditioning, but they don't provide cooling. 00:07:05.625 --> 00:07:11.931 They simply extract moisture from the air and collect it in a bucket, or send it down a hose to a drain. 00:07:12.799 --> 00:07:15.768 That makes them less energy intensive than cooling. 00:07:16.035 --> 00:07:21.574 And for a space that's already kind of cool but a little too damp, they make perfect sense. 00:07:22.341 --> 00:07:25.709 Simply pick a humidity percentage you'd like it to maintain, 00:07:25.709 --> 00:07:30.714 and it will switch on when the air's too humid, begin extracting water from the air 00:07:30.714 --> 00:07:34.220 and then switch back off once humidity is back in range. 00:07:34.921 --> 00:07:38.491 Now, I don't have a basement or crawl space at home, 00:07:38.491 --> 00:07:40.426 but I do have a garage. 00:07:40.693 --> 00:07:43.618 And that space is not conditioned at all - 00:07:43.618 --> 00:07:48.968 which isn't necessarily a problem and genuinely isn't in the winter months. 00:07:49.735 --> 00:07:55.475 But I live in the Midwest, and in the summer months it can get quite humid outside. 00:07:56.442 --> 00:08:01.781 I store a good deal of stuff in my garage which I don't want to be damaged from that humidity, 00:08:01.781 --> 00:08:04.884 and that's why I have this little dehumidifier. 00:08:05.485 --> 00:08:09.121 It keeps the air in the garage from exceeding 50% humidity, 00:08:09.255 --> 00:08:12.325 and thus keeps all the stuff out there nice and dry. 00:08:12.792 --> 00:08:19.365 Even when I come home in the rain and park a very wet car in the same space with all that stuff. 00:08:20.199 --> 00:08:27.440 As the car drips water onto the floor and starts to dry out, the air in the garage starts to get very wet. 00:08:27.840 --> 00:08:33.846 But, the dehumidifier always notices "it's getting a little bit damp in here" and switches on. 00:08:34.514 --> 00:08:37.149 And that is the point of a dehumidifier. 00:08:37.383 --> 00:08:40.853 It keeps the air dry to protect your stuff. 00:08:41.454 --> 00:08:42.655 That's what it's for. 00:08:43.523 --> 00:08:47.426 Though it does have the side benefit of helping the car dry off a lot faster. 00:08:47.827 --> 00:08:49.028 That's pretty neat. 00:08:49.428 --> 00:08:53.232 Before we explore how they work, I want to give two pieces of advice. 00:08:53.966 --> 00:08:57.570 First, if you are in actual need of a dehumidifier, 00:08:57.870 --> 00:09:07.013 for it to be any good at all it needs to cost more than $100 and it needs to be a fairly heavy and cumbersome machine. 00:09:07.980 --> 00:09:12.785 This little one, which is the smallest capacity you can get from a mainstream brand, 00:09:13.152 --> 00:09:16.789 came with casters because it weighs about 30 pounds. 00:09:17.757 --> 00:09:22.728 I'll show you what's making it so heavy shortly, but please know and share with your friends 00:09:22.728 --> 00:09:27.633 that cheap machines that you can easily pick up are useless junk. 00:09:28.734 --> 00:09:32.104 This thing from Amazon, as far as I'm concerned, 00:09:33.272 --> 00:09:36.909 is a piece of e-waste which should not exist. 00:09:37.476 --> 00:09:41.447 This has no business calling itself a dehumidifier, 00:09:41.747 --> 00:09:47.386 as it can't even counteract the added moisture from your average human breathing. 00:09:48.654 --> 00:09:57.063 There are a lot of purported "dehumidifiers" just like this for sale these days which simply do not, in fact, do that. 00:09:57.396 --> 00:10:00.600 And they're starting to show up in mainstream hardware stores, too. 00:10:01.734 --> 00:10:07.340 In the US, dehumidifiers are rated in pints of moisture removal per day. 00:10:07.535 --> 00:10:09.016 I know. 00:10:09.016 --> 00:10:14.911 And this unit, which I will remind you is the smallest capacity you can get from a mainstream brand, 00:10:14.911 --> 00:10:17.283 is rated at 22 pints per day. 00:10:17.984 --> 00:10:25.191 Yet Home Depot will gladly sell you this 3.2 pint unit from Magic Chef for 63 bucks, 00:10:25.458 --> 00:10:29.862 and Menards will sell you this one pint machine for 70 bucks. 00:10:30.363 --> 00:10:31.464 So will Lowe's. 00:10:32.598 --> 00:10:36.369 Don't waste your time with anything like that and put it back on the shelf. 00:10:37.269 --> 00:10:41.474 And if you'd rather not waste your time emptying the bucket from a real dehumidifier 00:10:41.474 --> 00:10:44.844 but you also don't have access to a drain where you need to put it 00:10:45.544 --> 00:10:50.249 before you resign yourself to the bucket brigade, look into getting one of these. 00:10:51.550 --> 00:10:53.653 This is called a condensate pump. 00:10:54.253 --> 00:11:00.793 It's a tiny, self-contained sump pump which you can drain a dehumidifier into using an abridged garden hose. 00:11:01.327 --> 00:11:04.664 And once the dehumidifier fills the sump with extracted water, 00:11:05.031 --> 00:11:07.800 a float switch is tripped and the pump will turn on. 00:11:08.501 --> 00:11:10.236 Then it pumps that water... 00:11:10.870 --> 00:11:12.505 somewhere else. 00:11:13.439 --> 00:11:16.456 You can easily hook vinyl tubing up to these things, 00:11:16.456 --> 00:11:23.449 and if you've got a reasonable way to run that tubing to another room with a sink or drain, or even through an outside wall, 00:11:24.216 --> 00:11:26.052 it will make your life a lot easier. 00:11:26.852 --> 00:11:30.656 Some dehumidifiers are now being sold with built in pumps, 00:11:30.656 --> 00:11:34.126 but in my experience they don't work that well. 00:11:34.760 --> 00:11:39.065 I bought one some years ago and its pump broke after less than a year. 00:11:39.432 --> 00:11:41.701 So I ended up having to get one of these for it anyway. 00:11:42.601 --> 00:11:47.406 These dedicated pumps are much more robust, though they can still fail. 00:11:47.540 --> 00:11:50.976 So if you're using one where an overflowing pump would cause a mess, 00:11:51.477 --> 00:11:54.246 you should periodically check on it to confirm it's working. 00:11:55.114 --> 00:12:00.019 But with that out of the way, why is this such a heavy and cumbersome machine? 00:12:01.053 --> 00:12:02.855 We should probably take a look inside. 00:12:03.189 --> 00:12:08.794 And through the magic of having a broken one, I could tear this bigger fella apart with reckless abandon. 00:12:09.028 --> 00:12:11.030 And what we find inside is... 00:12:12.098 --> 00:12:13.365 an air conditioner. 00:12:14.300 --> 00:12:19.618 These are all the same parts we find in a small window air conditioner like this. 00:12:19.651 --> 00:12:22.708 In the dehumidifier, they're simply rearranged. 00:12:23.476 --> 00:12:24.677 Here's the compressor. 00:12:24.677 --> 00:12:27.980 Here's a blower fan to move air through the evaporator coil. 00:12:28.314 --> 00:12:30.049 Here's the evaporator coil itself. 00:12:30.382 --> 00:12:35.454 And then sitting right behind the evaporator is the condenser coil. 00:12:36.388 --> 00:12:38.724 That's... hmm. 00:12:39.759 --> 00:12:44.096 If you know anything about air conditioners, this arrangement will seem more than a little strange. 00:12:44.463 --> 00:12:47.800 But it actually makes sense given what the purpose of this device is. 00:12:48.434 --> 00:12:49.835 It's not an air conditioner. 00:12:50.336 --> 00:12:51.537 It's a dehumidifier. 00:12:52.338 --> 00:12:53.539 But wait. 00:12:53.939 --> 00:12:56.475 Don't air conditioners also dehumidify? 00:12:57.676 --> 00:12:59.245 Why, yes they do. 00:12:59.478 --> 00:13:02.214 And that's why this is weird and complicated 00:13:02.681 --> 00:13:04.216 This dehumidifier 00:13:04.650 --> 00:13:07.586 literally is an air conditioner. 00:13:07.920 --> 00:13:11.423 But it's controlled by a humidity that rather than a thermostat. 00:13:11.724 --> 00:13:18.864 And it has provisions to collect the condensate that an air conditioner typically sends down a drain or simply lets drip outside. 00:13:19.799 --> 00:13:24.770 Other than the different controls and the float switch that will shut it down when the bucket is full, 00:13:25.538 --> 00:13:30.409 this is the same machine that cools air, except it doesn't cool the air. 00:13:30.976 --> 00:13:34.814 In fact, it makes the air very hot when it's running in a humid environment. 00:13:36.048 --> 00:13:38.384 I suppose I should demonstrate that.... [snaps fingers] 00:13:38.384 --> 00:13:41.520 I know! I'll set up a wireless hose! 00:13:42.354 --> 00:13:45.558 I put this dehumidifier in an enclosed bathroom, 00:13:45.558 --> 00:13:50.696 and then put one of my temperature data loggers on top of it in the airstream of its exhaust. 00:13:51.430 --> 00:13:54.900 Then I switched it on and let it run nonstop for an hour. 00:13:55.968 --> 00:14:02.274 When operating, this small unit only consumes about 300W of power, which is not very much. 00:14:02.908 --> 00:14:05.578 If we were releasing that into the room as heat, 00:14:06.111 --> 00:14:10.249 it would raise the air temperature a little bit, but not a whole lot. 00:14:10.883 --> 00:14:12.084 And that's what we see - 00:14:12.685 --> 00:14:16.689 over an hour of adding 300W of heat to the room, 00:14:16.689 --> 00:14:24.396 the exhaust temperature slowly rose and by the end it had reached about 90°F, roughly 32 Celsius. 00:14:25.097 --> 00:14:29.370 But then I switched on the arch nemesis of a dehumidifier: 00:14:29.370 --> 00:14:30.669 a humidifier. 00:14:30.936 --> 00:14:33.249 And in fact, two of them. 00:14:33.249 --> 00:14:38.077 Working together in that little bathroom they dramatically increased humidity levels. 00:14:38.244 --> 00:14:42.448 But the dehumidifier worked diligently to undo that, 00:14:42.448 --> 00:14:46.318 which you can see as this fairly steady drip of water coming out of the hose. 00:14:47.586 --> 00:14:53.845 But notice what happened to the dehumidifier's exhaust temperature once the battle began: 00:14:53.845 --> 00:14:55.861 it climbed significantly. 00:14:56.528 --> 00:15:00.266 In just 15 minutes, it was above 100°F. 00:15:00.532 --> 00:15:05.271 And by the end of the hour, it was tickling 105 (about 40 Celsius). 00:15:06.372 --> 00:15:09.475 That might not seem like a huge increase in temperature, 00:15:09.808 --> 00:15:13.879 but these machines move a ton of air through them. 00:15:14.246 --> 00:15:17.950 So it's actually quite a lot of heat energy being expelled. 00:15:18.684 --> 00:15:23.789 And that's despite only using about 300W the entire time. 00:15:24.857 --> 00:15:28.594 How and why is there so much extra heat all of a sudden? 00:15:29.561 --> 00:15:31.530 Well, it's because of two things: 00:15:31.997 --> 00:15:35.929 Latent heat and latent heat. 00:15:37.136 --> 00:15:43.609 To help explain this, I want to set the dehumidifier aside for a moment and go over how an air conditioner works. 00:15:44.076 --> 00:15:48.013 And I promise, this isn't just another chance for me to explain the refrigeration cycle. 00:15:48.380 --> 00:15:52.017 It's actually very important to understanding the whole picture here. 00:15:52.751 --> 00:15:57.456 But if you're not a newcomer to this channel and already know the basics of heat pumps 00:15:57.456 --> 00:15:59.858 and what coefficient of performance means, 00:16:00.359 --> 00:16:02.161 then you can go ahead and skip to 00:16:03.329 --> 00:16:04.530 if you'd like. 00:16:05.130 --> 00:16:12.237 So an air conditioner is a machine which is exploiting the physical properties of a chemical known as a refrigerant 00:16:12.237 --> 00:16:16.208 in order to move heat energy from one location to another. 00:16:16.909 --> 00:16:22.715 And when you do that, the location which is getting energy removed from it becomes cooler. 00:16:23.682 --> 00:16:30.689 We can do this because refrigerants have very useful relationships between their boiling points and their pressure. 00:16:31.690 --> 00:16:38.364 The refrigerant inside this air conditioner, difluoromethane or R32 is normally a gas. 00:16:38.464 --> 00:16:43.902 And at atmospheric pressure its boiling point is about -35°F. 00:16:44.603 --> 00:16:50.642 In other words, you'd need to get it that cold in order for the gas to transition to a liquid. 00:16:51.477 --> 00:16:54.546 But we've trapped some of this gas, 00:16:54.580 --> 00:16:58.417 in fact, 7.58oz, or 215g of it 00:16:58.417 --> 00:17:01.286 inside a big loop of piping. 00:17:01.920 --> 00:17:05.024 And that allows us to do some very interesting things. 00:17:05.924 --> 00:17:09.762 When this machine is operating, a mechanical compressor 00:17:09.762 --> 00:17:11.521 (that's this fella here) 00:17:11.521 --> 00:17:16.568 squeezes our gaseous refrigerant and forces it into this maze of piping. 00:17:17.436 --> 00:17:19.338 This is what's called a heat exchanger. 00:17:19.738 --> 00:17:27.813 All of those fins attached to the copper pipe looping back and forth help to quickly transfer heat energy from those pipes to the air. 00:17:28.180 --> 00:17:35.639 And a fan helps speed up that process even further by moving lots and lots of air through these fins. 00:17:35.639 --> 00:17:40.321 [compressor starts buzzing] We need to do this because once the refrigerant exits the compressor, 00:17:40.321 --> 00:17:45.297 it's under very high pressure - typically above 300 PSI. 00:17:46.365 --> 00:17:50.736 All that pressure is squeezing the refrigerant molecules together, 00:17:50.969 --> 00:17:56.041 which has the effect of dramatically elevating the refrigerant's boiling point to temperature. 00:17:56.942 --> 00:18:04.283 In fact, under these sorts of pressures, the refrigerant boiling point becomes higher than outdoor air temperature. 00:18:04.550 --> 00:18:07.219 Typically by about 20°F. 00:18:08.487 --> 00:18:11.790 This ultimately means that after it leaves the compressor, 00:18:11.857 --> 00:18:14.660 the refrigerant cannot remain a gas. 00:18:14.960 --> 00:18:20.332 The pressure in these pipes is too high and the ambient air temperature is too cold, 00:18:20.799 --> 00:18:26.004 so the refrigerant inside begins condensing into a liquid. 00:18:26.939 --> 00:18:30.042 That's why we call this heat exchanger the condenser. 00:18:30.742 --> 00:18:32.911 And as the refrigerant condenses, 00:18:33.078 --> 00:18:36.915 it releases lots and lots of heat. 00:18:38.050 --> 00:18:39.799 Why? 00:18:39.799 --> 00:18:40.719 Hold that thought. 00:18:41.487 --> 00:18:45.958 Once sufficiently cooled down by all the air being forced through the condenser, 00:18:46.492 --> 00:18:53.932 liquid refrigerant begins to stack up at the end of the condensers piping thanks to a restriction known as a metering device. 00:18:54.800 --> 00:19:01.773 That's there to limit flow and maintain a pressure imbalance between the two sides of the refrigeration circuit. 00:19:02.708 --> 00:19:09.756 After the liquid refrigerant passes through the metering device, it moves into a second heat exchanger. 00:19:09.756 --> 00:19:16.588 And thanks to the suction created by the intake of the compressor inside here the pressure is relatively low, 00:19:16.922 --> 00:19:19.124 perhaps 120 PSI. 00:19:20.225 --> 00:19:29.360 That causes the refrigerant's boiling point to plummet, landing somewhere around 40°F (about 5 Celsius). 00:19:29.601 --> 00:19:32.671 That's much colder than room temperatures. 00:19:32.871 --> 00:19:37.093 So once the refrigerant makes its way into here, 00:19:37.093 --> 00:19:43.549 the air in a room is actually hot enough to cause it to boil off and become a vapor again. 00:19:44.650 --> 00:19:49.354 Since the refrigerant vaporizes in this heat exchanger, we call it the evaporator. 00:19:49.955 --> 00:19:56.528 And when the liquid refrigerant starts boiling inside of these pipes, it gets very, very cold. 00:19:57.462 --> 00:19:58.664 Why is that? 00:19:59.097 --> 00:20:02.034 Well, key to understanding the refrigeration cycle 00:20:02.167 --> 00:20:08.507 is that the refrigerant cannot boil away until it absorbs its latent heat of vaporization. 00:20:09.308 --> 00:20:15.113 That's the heat energy a substance must absorb to change phases from a liquid to a gas. 00:20:16.315 --> 00:20:19.484 Now, latent heat is very strange. 00:20:20.085 --> 00:20:24.389 Unlike sensible heat, which we experience as temperature, 00:20:24.389 --> 00:20:28.627 we can't feel latent heat or even detect it with a thermometer. 00:20:29.528 --> 00:20:32.598 For instance, when boiling water on a stove, 00:20:32.598 --> 00:20:36.356 if you're measuring the temperature of the liquid water with a thermometer, 00:20:36.356 --> 00:20:40.672 you will see it slowly and continuously rise as the water absorbs heat. 00:20:41.006 --> 00:20:42.241 And that's what you would expect. 00:20:42.908 --> 00:20:47.872 But then it will get stuck at its boiling point temperature. 00:20:47.872 --> 00:20:49.815 Which is kind of weird, right? 00:20:50.415 --> 00:20:53.986 I mean, boiling water is very hot to us fragile humans, 00:20:54.186 --> 00:20:59.791 but compared to the temperature of a flame or a glowing heating element, it's quite cold. 00:21:00.158 --> 00:21:03.462 And so it's still going to absorb lots of heat energy from a stove. 00:21:04.329 --> 00:21:07.866 Yet despite the fact that it's absorbing lots of heat, 00:21:08.233 --> 00:21:10.302 it's not getting any hotter. 00:21:10.736 --> 00:21:12.771 The temperature is just stuck. 00:21:14.039 --> 00:21:17.342 Now, the reason is that once it's at its boiling point, 00:21:17.576 --> 00:21:21.813 the only heat energy the water can absorb is latent heat. 00:21:22.481 --> 00:21:25.917 And rather than increase the temperature of the liquid water, 00:21:26.385 --> 00:21:32.391 that heat energy is transforming the liquid water into its gaseous form: water vapor. 00:21:33.358 --> 00:21:36.862 We can observe this as violent bubbling at the bottom of the pot. 00:21:37.362 --> 00:21:39.598 But the thermometer doesn't show us this. 00:21:40.032 --> 00:21:44.803 All it sees is the fact that the water is at its boiling point temperature. 00:21:45.370 --> 00:21:51.710 Now, very importantly, all the latent heat energy which turned the water into a vapor 00:21:51.710 --> 00:21:54.513 is now stored in that water vapor. 00:21:54.946 --> 00:21:56.181 It didn't disappear. 00:21:56.915 --> 00:22:01.553 That heat energy is what's keeping the water at a higher state of matter. 00:22:02.321 --> 00:22:05.023 So let's bring this back to the air conditioner. 00:22:05.023 --> 00:22:07.759 When the liquid refrigerant enters the evaporator, 00:22:08.193 --> 00:22:14.266 the pressure inside is so low that its boiling point falls below ambient air temperature, 00:22:14.266 --> 00:22:16.768 meaning the refrigerant cannot remain a liquid. 00:22:17.602 --> 00:22:22.174 But to actually vaporize it has to absorb latent heat energy. 00:22:23.342 --> 00:22:25.811 It first gets this energy from itself. 00:22:26.211 --> 00:22:29.181 This is why it immediately becomes so cold. 00:22:29.848 --> 00:22:32.851 It will use its excess heat energy to begin boiling, 00:22:32.951 --> 00:22:38.357 which causes its sensible temperature to fall until it's at its new boiling point temperature. 00:22:38.423 --> 00:22:42.294 And like the water on a stove, it gets stuck there. 00:22:43.028 --> 00:22:48.066 But the refrigerant needs much, much more heat energy to completely vaporize. 00:22:48.834 --> 00:22:52.137 That's why the evaporator is also a heat exchanger. 00:22:52.738 --> 00:22:57.909 We need all these fins to help transfer heat energy from the air in the room 00:22:57.909 --> 00:23:01.847 into the cold refrigerant boiling inside the pipes. 00:23:02.748 --> 00:23:09.554 And when heat is transferred from the air into a colder substance, the air itself gets colder. 00:23:10.655 --> 00:23:13.492 Once the refrigerant has completely boiled away, 00:23:13.492 --> 00:23:18.196 the now gaseous refrigerant contains lots more energy than it did moments ago. 00:23:18.764 --> 00:23:25.370 It's still holding on to its latent heat energy that it just took from the room's air to become a gas. 00:23:26.371 --> 00:23:28.455 And, here's the amazing thing, 00:23:28.455 --> 00:23:31.777 simply by taking another spin through the compressor, 00:23:31.777 --> 00:23:35.280 we can force the refrigerant to get rid of that heat energy. 00:23:36.314 --> 00:23:40.790 Once re pressurized by the compressor and sent back to the condenser, 00:23:40.790 --> 00:23:48.293 the refrigerant's under high pressure again, and its boiling point is back up in the well above ambient air temperature range. 00:23:49.194 --> 00:23:55.233 Since it's once again not possible for it to remain a gas, it will spontaneously condense. 00:23:55.801 --> 00:24:01.440 And as it does that, it releases the latent heat energy it just absorbed. 00:24:02.174 --> 00:24:04.142 Which means it gets hot. 00:24:04.709 --> 00:24:13.552 at a pressure of 350 PSI the refrigerant's condensing temperature will be about 105°F or 40 Celsius. 00:24:13.885 --> 00:24:17.222 So it's gonna be that hot once it starts to condense. 00:24:17.789 --> 00:24:23.428 And to allow it to keep condensing, we need to help it get that heat out as quickly as possible. 00:24:23.628 --> 00:24:25.530 Hence, all the fans and the fan. 00:24:26.531 --> 00:24:29.201 And of course, once it's condensed, 00:24:29.201 --> 00:24:32.737 it ends up back at the evaporator and the whole process repeats. 00:24:33.338 --> 00:24:35.907 The refrigerant is simply traveling in a loop, 00:24:36.141 --> 00:24:40.412 and the process runs continuously so long as the compressor is operating. 00:24:41.213 --> 00:24:43.281 Now I want you to notice two things. 00:24:43.715 --> 00:24:48.453 One, the condenser has the same basic structure as the evaporator. 00:24:49.321 --> 00:24:57.896 This is because it will be releasing just as much heat from the condensing refrigerant as the evaporator absorbs when the refrigerant boils. 00:24:58.864 --> 00:25:05.070 And two, notice that the condenser is in a very different location from the evaporator. 00:25:06.171 --> 00:25:09.338 This is the basic principle behind a heat pump. 00:25:10.108 --> 00:25:12.143 Air conditioners are heat pumps, 00:25:12.143 --> 00:25:19.701 and they use the refrigerant as a working fluid to capture heat energy from indoors and move it outside, 00:25:19.701 --> 00:25:22.454 which results in the indoor air getting colder. 00:25:23.522 --> 00:25:30.295 When installed in a window, this machine's heat absorbing evaporator coil ends up inside the home, 00:25:30.629 --> 00:25:34.332 and the heat rejecting condenser coil ends up outside. 00:25:34.766 --> 00:25:40.438 So it pumps heat from inside to outside, which cools the indoor air. 00:25:41.239 --> 00:25:43.508 This is also how your refrigerator works, by the way. 00:25:43.775 --> 00:25:47.612 Though it's just got to get heat from inside the box to outside the box. 00:25:48.246 --> 00:25:51.516 And the hot new thing is for heat pumps to be reversible. 00:25:51.917 --> 00:25:58.290 That way they can also absorb energy from outside air and bring it inside to produce heating. 00:25:59.057 --> 00:26:03.428 It's actually not new at all, but we've gotten much better at making them work in cold climates. 00:26:04.296 --> 00:26:07.566 But anyway, there's one last thing to know about heat pumps. 00:26:08.333 --> 00:26:13.038 The actual work this device is doing is mechanical in nature. 00:26:13.772 --> 00:26:16.908 It's using an electric motor inside this enclosure 00:26:16.975 --> 00:26:20.845 to spin a mechanical compressor which compresses a gas. 00:26:21.313 --> 00:26:22.781 And that's all it's doing. 00:26:23.548 --> 00:26:30.322 The whole "refrigerant turns into a liquid and back" part happens naturally as a result of heat transfer. 00:26:31.156 --> 00:26:35.694 It's absorbing and releasing its latent heat energy all on its own. 00:26:36.261 --> 00:26:39.898 The machine is simply creating the conditions for that to happen. 00:26:40.000 --> 00:26:43.568 And it uses heat exchangers and fans to speed it up. 00:26:44.569 --> 00:26:50.642 Because the refrigerant condenses and vaporizes separately to the act of compressing it, 00:26:50.642 --> 00:26:58.583 the refrigeration circuit is actually capable of moving more heat energy than is required to run the compressor. 00:26:59.684 --> 00:27:02.253 We call this the coefficient of performance. 00:27:02.587 --> 00:27:08.693 And when you get, say, three times as much heat moving capacity as you do input power, 00:27:09.094 --> 00:27:11.694 that's a COP of 3. 00:27:12.030 --> 00:27:13.999 Now, in an air conditioner like this, 00:27:14.332 --> 00:27:20.205 that would mean that for every watt of input power, you get three watts of cooling power. 00:27:21.006 --> 00:27:23.341 That's precisely how this little window unit, 00:27:23.341 --> 00:27:29.014 which is rated for 5000 BTUs per hour, (equivalent to roughly 1.5kW) 00:27:29.014 --> 00:27:31.850 only draws about 500W from the wall. 00:27:32.684 --> 00:27:37.155 The motors in the compressor and fan assembly consume that much power, 00:27:37.155 --> 00:27:42.193 but the refrigeration circuit is producing three times as much cooling power. 00:27:43.061 --> 00:27:49.434 And that is precisely why the dehumidifier has all the same parts as this air conditioner. 00:27:50.001 --> 00:27:55.106 You're getting extra heat moving capacity because the refrigeration cycle is awesome. 00:27:55.769 --> 00:27:57.275 Except.... 00:27:57.909 --> 00:27:59.110 well, wait a minute. 00:27:59.411 --> 00:28:05.417 Yes, this machine has all the parts of a heat pump, but it isn't pumping heat anywhere at all. 00:28:06.051 --> 00:28:13.158 The condenser, which in an air conditioner has to go outside so it can actually get heat energy out of the building to cool it down... 00:28:14.059 --> 00:28:16.494 is, uh, here. 00:28:17.295 --> 00:28:22.834 It's sitting literally right behind the evaporator and in the same airstream. 00:28:23.468 --> 00:28:31.309 Which means that immediately after air is drawn through the evaporator and chilled by the refrigerant, absorbing latent heat energy, 00:28:32.711 --> 00:28:38.083 the air gets heated right back up on its way out by the refrigerant releasing latent heat energy. 00:28:39.050 --> 00:28:40.251 What's the deal? 00:28:41.386 --> 00:28:46.591 Well, we don't actually care at all about moving heat in this case, 00:28:46.858 --> 00:28:51.463 we just want to make a cold surface for water in the air to condense on. 00:28:52.163 --> 00:28:55.066 That's one way we can get water vapor out of the air. 00:28:55.366 --> 00:28:58.570 And the reason that works goes back to relative humidity. 00:28:59.337 --> 00:29:03.208 Remember that air can only hold on to so much water vapor, 00:29:03.575 --> 00:29:08.046 and the cooler the air is, the less water vapor it can absorb. 00:29:09.047 --> 00:29:17.922 This means that if you're able to cool it below the temperature at which air would become fully saturated and at 100% humidity 00:29:17.922 --> 00:29:21.282 (which, by the way, is a temperature we call the dew point), 00:29:21.726 --> 00:29:30.000 well, then suddenly the air's gonna have too much water in it, and the excess moisture will precipitate out of the air and onto cold surfaces. 00:29:30.401 --> 00:29:34.873 That temperature is called the dew point because that's why dew happens. 00:29:35.206 --> 00:29:39.043 You could say it's the, uh, dew process. 00:29:39.844 --> 00:29:42.447 Hey, side note, that was an awful pun, 00:29:42.447 --> 00:29:46.706 but did you know that due process (d. u. e. due process) 00:29:46.706 --> 00:29:52.624 is really just a fancy way of saying everyone is innocent until proven guilty? 00:29:53.558 --> 00:29:57.395 Last I checked, that's a core belief that all Americans share. 00:29:58.029 --> 00:30:05.069 If for some reason you no longer feel that everyone deserves the presumption of innocence until they are proven guilty, 00:30:06.104 --> 00:30:09.340 I think you might be having some un-American thoughts at the moment. 00:30:09.808 --> 00:30:11.209 Might want to get that checked out. 00:30:11.890 --> 00:30:15.046 Anyway, that's enough reinforcement of societal norms for today. 00:30:15.814 --> 00:30:20.285 You've experienced water condensing on cold things many times before. 00:30:20.885 --> 00:30:23.555 Cold drinks sweat in the summer months 00:30:23.755 --> 00:30:29.861 because the air right next to the cold surface of a can or glass becomes cooled below the dew point, 00:30:29.861 --> 00:30:31.863 so dew forms. 00:30:32.463 --> 00:30:35.733 That water used to be water vapor in the air, 00:30:36.100 --> 00:30:39.370 but the cold surface of the can caused it to condense. 00:30:40.205 --> 00:30:47.645 A dehumidifier is simply a machine with a very large, cold surface that we force air through 00:30:47.645 --> 00:30:51.583 so that we can cause the same effect at a much larger scale. 00:30:51.783 --> 00:30:57.922 So large that we can decrease the humidity in an enclosed space, or even an entire house. 00:30:58.857 --> 00:31:03.127 Now, as we know, the dehumidifier doesn't cool the air in a room, 00:31:03.361 --> 00:31:07.031 but it is still using a refrigeration circuit to do its job. 00:31:08.066 --> 00:31:12.003 I don't know precisely what coefficient of performance this machine runs at, 00:31:12.337 --> 00:31:17.008 but for the sake of the video, I'm going to assume it operates with a COP of 4. 00:31:17.976 --> 00:31:22.259 That means since this machine draws about 300W when it's running, 00:31:22.259 --> 00:31:27.118 it produces 1200 watts of cooling power in the evaporator right here. 00:31:28.286 --> 00:31:35.526 But of course, that also means it's producing 1200 watts of heating power in the condenser right in front of it. 00:31:35.994 --> 00:31:38.496 Those numbers are always going to match. 00:31:39.364 --> 00:31:44.802 Which would imply that since the condenser and evaporator are in the same airstream, 00:31:45.103 --> 00:31:49.340 their combined heating and cooling power will always cancel each other out. 00:31:50.541 --> 00:31:52.677 BUT THAT'S NOT WHAT HAPPENS. 00:31:53.278 --> 00:31:57.615 See, refrigerants aren't the only substances with a latent heat of vaporization. 00:31:58.316 --> 00:32:02.320 All substances have that, including water. 00:32:03.321 --> 00:32:07.959 Just as liquid water needs to absorb latent heat energy in order to vaporize, 00:32:08.559 --> 00:32:13.698 water vapor needs to release that latent heat energy to condense into a liquid. 00:32:14.699 --> 00:32:17.535 This always happens whenever water condenses, 00:32:17.769 --> 00:32:23.574 but it can be incredibly difficult for us to notice because it's latent heat and we can't feel it. 00:32:24.342 --> 00:32:29.614 For instance, when you grab a cold beverage from the fridge and condensation starts to form on its sides, 00:32:30.114 --> 00:32:33.985 that condensation doesn't feel hot because it isn't. 00:32:34.319 --> 00:32:39.824 Those water droplets will have a sensible temperature pretty close to the dew point temperature. 00:32:40.191 --> 00:32:45.530 But the water will impart its latent heat into the can as it condenses, 00:32:45.797 --> 00:32:52.370 causing the contents inside to warm up much more quickly than if the air was perfectly dry. 00:32:53.304 --> 00:33:00.945 And that heating effect won't stop until the surface of the can is above the air's dew point temperature. 00:33:01.245 --> 00:33:04.515 All right, and where does the dehumidifier fit into all this? 00:33:05.350 --> 00:33:09.387 Well, its whole job is to get water vapor out of the air, 00:33:09.554 --> 00:33:14.125 which it does by forcing it to condense onto the cold surface of the evaporator. 00:33:14.525 --> 00:33:19.063 And that means it's going to have to deal with the latent heat of water vapor. 00:33:20.098 --> 00:33:21.866 And how exactly does it deal with it? 00:33:22.700 --> 00:33:27.505 By converting it into sensible heat which we can feel. 00:33:28.339 --> 00:33:32.577 That's why the exhaust got so hot after I switched on the humidifiers. 00:33:33.945 --> 00:33:38.416 Now, I don't think the reason that happens is very easy to intuit, 00:33:38.616 --> 00:33:44.122 but it's pretty dang fascinating and is the key to this whole video, so I'm going to do my best to explain it. 00:33:45.289 --> 00:33:48.459 If the air in a room has no moisture in it at all, 00:33:48.760 --> 00:33:52.497 then when it goes through this dehumidifier, nothing would really happen. 00:33:53.197 --> 00:33:59.675 The air would be chilled by the 1,200 watts of... cold the evaporator is sucking out of it, 00:33:59.675 --> 00:34:05.476 but then it would be heated right back up by the 1,200 watts of heat being released by the condenser. 00:34:06.277 --> 00:34:08.774 Since the two coils are right next to each other, 00:34:08.774 --> 00:34:14.519 the air coming out of the machine should be essentially the same temperature it was when it entered, 00:34:14.786 --> 00:34:17.855 plus 300W of heat from the motor windings. 00:34:18.823 --> 00:34:22.460 When humid air is drawn through the cold evaporator, though, 00:34:23.127 --> 00:34:24.729 weird stuff happens. 00:34:25.463 --> 00:34:30.101 Its cold surfaces will cause the air passing through it to fall below the dew point, 00:34:30.468 --> 00:34:36.674 and that forces water vapor in the air to begin condensing into water on the surfaces of the evaporator. 00:34:37.642 --> 00:34:43.614 And when that happens, as it always does, the water releases its latent heat energy 00:34:43.881 --> 00:34:46.017 which the refrigerant absorbs. 00:34:46.751 --> 00:34:49.120 But it's latent heat. 00:34:49.654 --> 00:34:53.691 It's heat we cannot feel and thermometers cannot register, 00:34:54.025 --> 00:34:56.394 which causes a very strange effect. 00:34:57.428 --> 00:35:03.234 No matter what's going on, the evaporator can only absorb 1200 watts of heat total. 00:35:03.868 --> 00:35:08.673 So if it's absorbing water's latent heat as it condenses, 00:35:09.474 --> 00:35:14.745 then it's actually losing the ability to cool the air that passes through. 00:35:15.780 --> 00:35:21.853 For example, if it's absorbing, say, 800W of latent heat from water condensing on it, 00:35:22.520 --> 00:35:31.329 then two thirds of the evaporator's cooling capacity is going towards a process which does not lower the air temperature. 00:35:32.263 --> 00:35:34.999 However, there's a fact we cannot get around. 00:35:35.566 --> 00:35:39.370 The evaporator still absorbed 1,200 watts of heat. 00:35:40.171 --> 00:35:47.712 We couldn't feel 800W of it because it was latent heat, but it was still heat that was absorbed by the refrigerant. 00:35:48.679 --> 00:35:55.653 With 1,200 watts going into the evaporator, 1,200 watts has to come out of the condenser. 00:35:56.053 --> 00:36:00.691 And it does - the condenser releases all the heat the evaporator absorbs. 00:36:00.892 --> 00:36:05.830 Latent or not, it doesn't care, and the total is always 1,200 watts. 00:36:06.597 --> 00:36:11.435 But with the 800W of cooling not happening because of condensing water, 00:36:11.936 --> 00:36:17.141 we experience a surplus 800W of sensible heat coming out of the condenser. 00:36:17.875 --> 00:36:24.315 All of the latent heat the evaporator absorbed becomes sensible heat when the condenser rejects it. 00:36:24.949 --> 00:36:28.152 Add that to the 300W of heat coming from the motor windings, 00:36:28.486 --> 00:36:33.024 and now there's 1,100 watts of sensible heat coming from this little machine. 00:36:33.858 --> 00:36:37.228 That's why the air leaving the dehumidifier is hot. 00:36:37.762 --> 00:36:44.702 This machine is converting the latent heat from condensing water vapor into sensible heat we can actually feel. 00:36:45.770 --> 00:36:48.372 And it just plops that heat right into the room. 00:36:49.240 --> 00:36:52.783 I find this incredibly fascinating because I'm a heat pump nerd, 00:36:52.783 --> 00:36:58.849 and this is one of the most visceral ways I've found to experience a machine generating much more heat 00:36:58.849 --> 00:37:00.318 than it apparently should. 00:37:01.219 --> 00:37:08.593 It seems impossible for a device which only draws 300W from the wall to produce air as hot as this does. 00:37:09.360 --> 00:37:12.964 But that's precisely what happens thanks to the power of a heat pump. 00:37:14.298 --> 00:37:17.468 But this isn't just trivia that's fun to play around with. 00:37:17.702 --> 00:37:24.375 It's actually a very important concept to understand because of how it relates to comfort and cooling. 00:37:25.376 --> 00:37:30.081 Most people agree that when the weather is warm, drier air is more comfortable. 00:37:30.681 --> 00:37:34.619 But while these machines can and will certainly dry out the air, 00:37:35.186 --> 00:37:40.791 the basic reality here is they're going to release a lot of heat to do that. 00:37:41.425 --> 00:37:44.195 Less when the air is already fairly dry. 00:37:44.428 --> 00:37:49.867 But even at 50% relative humidity, these things can produce a surprising amount of heat. 00:37:50.935 --> 00:37:55.706 Since they're usually controlled by a humidistat it won't produce that heat constantly, 00:37:55.706 --> 00:37:58.042 just when it needs to run to lower humidity. 00:37:58.876 --> 00:38:01.379 But it might as well be a space heater when it's running, 00:38:01.846 --> 00:38:05.616 so don't expect them to make you comfortable because they don't. 00:38:05.783 --> 00:38:07.151 That's not their job. 00:38:07.585 --> 00:38:13.724 They make otherwise humid environments safe for things which can be affected by moisture damage, 00:38:14.058 --> 00:38:15.760 and that's the extent of their role. 00:38:16.694 --> 00:38:19.879 If you're wondering how I can say that with such confidence, 00:38:19.879 --> 00:38:26.437 well, now it's time to imagine what would happen if you use a dehumidifier when you also have air conditioning. 00:38:27.471 --> 00:38:31.876 An air conditioner also has a cold evaporator absorbing energy from the air, 00:38:32.076 --> 00:38:37.882 so it also has to deal with the latent heat load from water vapor in the air condensing on it. 00:38:38.983 --> 00:38:40.951 But unlike the dehumidifier, 00:38:41.085 --> 00:38:48.726 an air conditioner can move that heat outside as it deals with it, which means for our intents and purposes it's gone. 00:38:49.794 --> 00:38:56.500 But the air conditioner still faces the same problem in that it can only move so much heat. 00:38:56.934 --> 00:39:02.840 And for every watt of its cooling capacity it spends condensing water out of the air, 00:39:02.840 --> 00:39:06.344 a watt of sensible cooling power is lost. 00:39:07.211 --> 00:39:10.147 This means when the air is extremely humid, 00:39:10.147 --> 00:39:16.854 an air conditioner is mainly just producing a lot of water and seems to struggle to cool the air temperature. 00:39:17.788 --> 00:39:20.180 When that's happening, you might think 00:39:20.180 --> 00:39:22.159 "well, then add a dehumidifier! 00:39:22.526 --> 00:39:27.531 Give it the job of dealing with that water vapor so the air conditioner doesn't have to." 00:39:28.766 --> 00:39:30.234 But have you spotted the problem? 00:39:31.168 --> 00:39:37.241 While the dehumidifier will absolutely reduce the latent heat load that the air conditioner must deal with, 00:39:37.775 --> 00:39:40.845 it won't actually reduce the total heat load. 00:39:41.679 --> 00:39:48.686 It simply turns the water's latent heat into sensible heat, which the air conditioner will still have to deal with. 00:39:49.754 --> 00:39:55.059 What I'm saying here is that using a dehumidifier in a space that's already air conditioned 00:39:55.493 --> 00:39:56.961 generally doesn't help. 00:39:57.661 --> 00:40:05.002 If you are cooling the air anyway, the air conditioner will generally remove enough moisture to keep everything safely dry. 00:40:05.903 --> 00:40:11.041 There are situations where adding a dehumidifier to your HVAC strategy can make sense. 00:40:11.442 --> 00:40:15.413 For instance, in the shoulder seasons it might be getting too damp inside 00:40:15.413 --> 00:40:18.015 when it's not warm enough to run the air conditioner. 00:40:18.749 --> 00:40:22.119 And sometimes it can be legitimately necessary. 00:40:22.887 --> 00:40:28.692 If your air conditioner wasn't sized correctly, it might not be handling the moisture on its own. 00:40:29.493 --> 00:40:33.022 This whole can of worms (the latent heat load of water vapor) 00:40:33.022 --> 00:40:37.835 is precisely why sizing an air conditioner correctly is so important. 00:40:38.636 --> 00:40:44.141 It needs to run fairly long cycles for it to actually extract water from the air, 00:40:44.542 --> 00:40:49.980 and an oversized air conditioner can produce too much sensible cooling too quickly, 00:40:50.247 --> 00:40:54.652 which causes it to run short cycles which don't effectively dehumidify. 00:40:55.486 --> 00:41:02.026 Although modern variable-capacity systems are much more flexible and they are improving the situation greatly. 00:41:02.960 --> 00:41:05.529 Still, even with an optimal air conditioner, 00:41:05.830 --> 00:41:10.968 if you have bad enough moisture ingress issues from poor air sealing or seepage, 00:41:11.535 --> 00:41:13.537 a dehumidifier can still be necessary. 00:41:14.405 --> 00:41:19.637 But in an ideal world, assuming you have air conditioning and you regularly use it, 00:41:19.637 --> 00:41:26.183 you shouldn't really need a dehumidifier at all except in unconditioned or poorly conditioned spaces 00:41:26.350 --> 00:41:29.119 like basements, crawl spaces, garages, etc. 00:41:30.154 --> 00:41:32.323 But there is one last wrinkle: 00:41:33.123 --> 00:41:36.694 an air conditioner can only get the air so dry. 00:41:37.495 --> 00:41:41.866 Because air's dew point temperature falls as humidity does, 00:41:41.866 --> 00:41:45.736 before long, an air conditioner reaches humidity equilibrium. 00:41:46.437 --> 00:41:53.177 At 72°F and 50% relative humidity, the dew point is about 52°F. 00:41:53.844 --> 00:42:00.351 And the evaporator coil in a properly functioning air conditioning system doesn't get much colder than that. 00:42:00.885 --> 00:42:03.220 So at ordinary room temperatures, 00:42:03.220 --> 00:42:07.625 an ordinary air conditioner can't drop humidity much below 50%. 00:42:08.759 --> 00:42:11.595 If you truly need or want it lower than that, 00:42:12.029 --> 00:42:17.501 a dehumidifier can get you a little bit lower and most allow you to run them nonstop if you wish. 00:42:18.369 --> 00:42:23.140 Just keep in mind it'll be working hard to do that consuming energy of its own, 00:42:23.541 --> 00:42:26.644 and it will produce more heat for your air conditioner to deal with. 00:42:27.327 --> 00:42:28.746 But can they save money? 00:42:29.780 --> 00:42:33.384 Well, that's a big, fat, "it depends." 00:42:33.984 --> 00:42:39.757 I mean, it's a concrete Yes if you have damp problems and a dehumidifier saves your stuff from damage. 00:42:40.391 --> 00:42:42.426 But when it comes to energy costs, 00:42:43.114 --> 00:42:45.462 ehhhhh.... that's not easy to determine. 00:42:46.363 --> 00:42:51.735 Assuming a dehumidifier can remove more moisture per kilowatt-hour than your air conditioner can, 00:42:52.403 --> 00:42:56.740 then so long as your air conditioner can keep up with the extra heat it's producing, 00:42:56.941 --> 00:43:00.744 that might lower your energy costs a bit. 00:43:01.712 --> 00:43:03.614 But to be honest, I wouldn't expect it to. 00:43:04.415 --> 00:43:08.986 These things are great at what they do, but they aren't exactly energy misers 00:43:09.286 --> 00:43:14.825 and full blown air conditioning systems (at least recent ones) are really energy efficient. 00:43:15.526 --> 00:43:18.696 High-end systems with variable speed blowers and compressors 00:43:18.696 --> 00:43:25.235 can even alter the ratio between latent and sensible heat loading by tinkering with airflow and refrigerant pressures. 00:43:25.903 --> 00:43:31.342 Slowing air down can get the evaporator colder which will remove more moisture. 00:43:31.675 --> 00:43:34.845 And with the right sensors, you can make sure the coil doesn't ice up. 00:43:35.746 --> 00:43:38.115 But even with basic air conditioning, 00:43:38.382 --> 00:43:44.221 if it's keeping your home dry on its own, there's really not much a dehumidifier is going to do for you. 00:43:44.488 --> 00:43:47.224 It's just gonna make noise for no good reason. 00:43:48.025 --> 00:43:54.000 The only situation where I personally think of a dehumidifier as a potential cost saving thing 00:43:54.000 --> 00:43:58.435 is when you're away from home and not using air conditioning at all, 00:43:58.602 --> 00:44:02.206 but you still want to ensure indoor humidity doesn't get too high. 00:44:03.173 --> 00:44:09.246 If you don't care about the temperature, well then you should be happy to let a dehumidifier run its little heart away. 00:44:09.380 --> 00:44:13.550 That's definitely going to be more cost effective than cooling the place when nobody's home, 00:44:13.751 --> 00:44:18.989 and a warmer indoor temperature compared to outside air tends to reduce humidity issues anyway. 00:44:20.157 --> 00:44:25.429 But unless you travel a lot or like you've got a vacation home somewhere, 00:44:25.663 --> 00:44:31.502 I would be very surprised if you'd actually get your money's worth out of the purchase of a dehumidifier. 00:44:32.503 --> 00:44:37.007 Also, to make a single dehumidifier effective for an entire house, 00:44:37.007 --> 00:44:42.146 you'd probably need to use your HVAC system's fan setting to move air around, 00:44:42.146 --> 00:44:45.416 and you'd be surprised how much power those blower motors use. 00:44:45.849 --> 00:44:48.018 It's usually a couple hundred watts at least. 00:44:48.819 --> 00:44:55.092 Alright, so now it's time to close this video out, which I'll do by acknowledging the flaw of dehumidifiers like this. 00:44:56.126 --> 00:44:59.363 These don't work very well in colder temperatures. 00:44:59.830 --> 00:45:04.935 And the temperature doesn't even need to be that cold for them to stop working so well, or indeed at all. 00:45:06.003 --> 00:45:10.574 These things are built to a cost and use very simple refrigeration circuits. 00:45:10.941 --> 00:45:12.676 They're either running or they're not. 00:45:13.377 --> 00:45:21.218 And this means that the operating pressures in the evaporator and condenser are going to depend mostly on the ambient air temperature. 00:45:22.086 --> 00:45:28.625 And when the air temperature gets somewhere around 55°F or colder, that's about 13 Celsius, 00:45:28.625 --> 00:45:34.029 the refrigerant pressure in the evaporator might be low enough for the refrigerant boiling point 00:45:34.029 --> 00:45:36.734 to be below the freezing point of water. 00:45:37.468 --> 00:45:42.372 And when that happens, the evaporator will freeze the water that condenses on it. 00:45:43.273 --> 00:45:49.580 And that will eventually plug up the evaporator with ice and then air can't travel through it anymore. 00:45:50.481 --> 00:45:55.185 Now any decent dehumidifier is going to be able to detect that this is happening 00:45:55.352 --> 00:45:59.590 and will shut off the compressor for a long enough period of time for the ice to melt. 00:45:59.990 --> 00:46:03.527 And that will happen pretty quickly since it keeps the blower fan running. 00:46:04.428 --> 00:46:10.334 But those periodic defrosts limit how much it can actually run and thus limit its effectiveness. 00:46:11.235 --> 00:46:16.006 However, this downside may not matter at all depending on your local climate. 00:46:16.707 --> 00:46:21.044 Where I live, you don't have to use a dehumidifier when the weather's cold. 00:46:21.478 --> 00:46:27.017 These things usually only get fired up in April or May and then get turned off around October. 00:46:27.851 --> 00:46:30.988 Cold but damp just isn't much of a thing here. 00:46:31.188 --> 00:46:36.493 We only encounter that in the shoulder seasons, and never for long enough to require intervention. 00:46:37.361 --> 00:46:40.864 And remember, simply heating the air lowers humidity. 00:46:41.431 --> 00:46:44.902 And you don't have to heat it very much to have a dramatic effect. 00:46:45.769 --> 00:46:54.211 When it's 55 degrees outside (13 Celsius), even if it's raining and the outdoor air is fully saturated with water, 00:46:54.211 --> 00:47:01.752 maintaining an indoor temperature of 68 degrees (20 Celsius) will lead to indoor humidity of 63%. 00:47:02.853 --> 00:47:05.122 That's probably a little higher than ideal, 00:47:05.322 --> 00:47:08.592 but it's nowhere near as humid as raining. 00:47:09.693 --> 00:47:13.096 That's why humidity usually isn't a problem in the heating season. 00:47:13.597 --> 00:47:16.033 And here, where it gets real cold in the winter, 00:47:16.400 --> 00:47:22.372 indoor air is so dry that we often want to add moisture, hence the humidifiers. 00:47:22.873 --> 00:47:24.842 The best part of Midwestern weather 00:47:24.875 --> 00:47:27.477 is that humidity is always wrong! 00:47:27.978 --> 00:47:34.918 Anyway, because the icing doesn't really happen when virtually anyone in the US actually needs a dehumidifier, 00:47:35.519 --> 00:47:38.121 this is the only kind that's sold here. 00:47:38.989 --> 00:47:41.658 The refrigeration cycle is just too efficient, 00:47:41.758 --> 00:47:47.564 and our weather patterns mean the icing issue is only a problem for a week or two, if that. 00:47:48.599 --> 00:47:52.736 But as the old saying goes, there's more than one way to dry a flat. 00:47:53.770 --> 00:47:56.406 In a future video, we'll take a look at this: 00:47:56.840 --> 00:47:59.343 a rotary desiccant dehumidifier. 00:48:00.177 --> 00:48:01.979 This is a fascinating little machine 00:48:01.979 --> 00:48:07.451 which doesn't have the cold ambient performance problems a vapor-compression dehumidifier does. 00:48:08.485 --> 00:48:15.659 But it does have several drawbacks, which is probably why I had to wade through tons of Amazon sludge 00:48:15.659 --> 00:48:18.195 just to find this one model for sale. 00:48:19.229 --> 00:48:20.330 That's for later, though. 00:48:20.330 --> 00:48:23.200 And speaking of Amazon sludge, remember this thing? 00:48:23.901 --> 00:48:28.672 Well, this piece of garbage does technically remove moisture from the air, 00:48:28.939 --> 00:48:36.013 and it uses the same "create a cold surface and blow air past it" principle that the real boy dehumidifier does, 00:48:36.713 --> 00:48:39.049 but it's missing a refrigeration circuit 00:48:39.182 --> 00:48:42.920 and uses a Peltier element instead. 00:48:43.787 --> 00:48:45.034 Yeah. Remember those? 00:48:45.034 --> 00:48:49.373 Those things that get put into novelty beverage coolers that don't work? 00:48:49.373 --> 00:48:52.763 Well, they also get put into dehumidifiers which don't work. 00:48:53.730 --> 00:48:57.834 In that same bathroom with ambient humidity over 80%. 00:48:58.402 --> 00:49:04.308 This so-called "dehumidifier" produced this much water in two hours. 00:49:04.775 --> 00:49:06.243 That's 22g. 00:49:07.277 --> 00:49:08.645 Maybe this would be useful 00:49:08.645 --> 00:49:11.748 for like a terrarium or perhaps a small closet, 00:49:11.949 --> 00:49:13.884 but otherwise these things are just silly. 00:49:14.318 --> 00:49:19.820 There is a reason the catch buckets of a proper dehumidifier are so big. 00:49:19.853 --> 00:49:26.363 In the same two hours, this guy removed 1.2 liters of water from the air - 55 times as much! 00:49:26.763 --> 00:49:31.068 And yet it only consumed ten times as much energy as this thing did. 00:49:32.035 --> 00:49:33.737 That's the power of a heat pump. 00:49:33.737 --> 00:49:35.305 Effective and efficient! 00:49:36.139 --> 00:49:42.379 if you noticed in the temperature logger chart I showed earlier that my testing happened back in August of 2024... 00:49:43.113 --> 00:49:49.720 Well, that's because this video had an entirely different scope and concept back then, which I abandoned. 00:49:49.953 --> 00:49:52.556 in no small part because I would have finished it 00:49:52.723 --> 00:49:56.026 right when people would be putting their dehumidifiers away for the winter. 00:49:57.127 --> 00:50:00.597 I wanted to pit these three dehumidifiers against each other 00:50:00.597 --> 00:50:04.735 and was mostly interested in water extracted per kilowatt hour, 00:50:05.268 --> 00:50:08.651 but ultimately that was fluff against the bigger message of 00:50:08.651 --> 00:50:13.110 "latent heat is very confusing and dehumidifiers do not help you stay comfortable." 00:50:14.311 --> 00:50:17.180 But when we look at the rotary desiccant machine, 00:50:17.381 --> 00:50:19.516 we'll definitely bring that topic back up. 00:50:20.450 --> 00:50:21.718 Because, well, 00:50:22.290 --> 00:50:25.589 it's not very efficient, but it is very interesting. 00:50:26.189 --> 00:50:27.609 So stay tuned. 00:50:28.669 --> 00:50:31.182 ♫ condensedly smooth jazz ♫ 00:50:33.930 --> 00:50:35.532 Anyway, that's enough reinforcement of societaul 00:50:36.366 --> 00:50:37.567 Wow, that's a mouthful. 00:50:38.568 --> 00:50:41.538 Anyway, that's enough reinforcement of societal norms for today. 00:50:41.838 --> 00:50:43.807 when we look at the rotary desiccant machine, 00:50:43.974 --> 00:50:45.742 we'll definitely bring that top it back up. 00:50:46.510 --> 00:50:48.011 Well, what happened there? 00:50:48.512 --> 00:50:50.080 so it can ruin your belongings. 00:50:50.547 --> 00:50:52.816 And if that's not enough, yeah, I'm going to restart that. 00:50:53.083 --> 00:50:57.856 relative humidity is 50% saturated and thus has abdorb. 00:50:58.815 --> 00:50:59.450 Blerp. 00:51:00.023 --> 00:51:01.224 It has example. 00:51:01.291 --> 00:51:03.193 Okay, so we got to read this one faster. 00:51:05.195 --> 00:51:07.130 So I screwed up for several reasons. 00:51:07.631 --> 00:51:09.533 worked diligently to undo that 00:51:09.766 --> 00:51:11.968 which you can see as this fairly stready, 00:51:12.369 --> 00:51:13.637 stready dip of water. 00:51:15.939 --> 00:51:16.767 Oh boy. 00:51:20.000 --> 00:51:23.452 OK, so I did the captions in an entirely different way this time and it didn't work as well as I'd hoped. 00:51:23.452 --> 00:51:26.669 But that doesn't mean I'm going to forget the end of video captions gag! 00:51:26.669 --> 00:51:30.463 This is it. It's not a very good one. 00:51:30.943 --> 00:51:33.890 dew process