1 00:00:00,160 --> 00:00:03,236 This slowly rotating disc of... stuff 2 00:00:03,236 --> 00:00:07,055 may not look like anything but a slowly rotating disc of stuff. 3 00:00:07,055 --> 00:00:11,246 But would you believe it's actually part of a dehumidifier? 4 00:00:11,673 --> 00:00:14,010 Well, probably. You saw the title. 5 00:00:14,010 --> 00:00:19,346 Not long ago, I made a video about what I'd call ordinary dehumidifiers. 6 00:00:19,346 --> 00:00:22,671 You can check it out through that card if you like, but long story short: 7 00:00:22,671 --> 00:00:28,714 most dehumidifiers work by making something cold and blowing air past the cold thing 8 00:00:28,714 --> 00:00:35,214 so the air drops below the dew point temperature, which forces the water in the air to condense on the cold surface. 9 00:00:35,214 --> 00:00:39,615 And the most efficient way to make something cold is to use the refrigeration  cycle, 10 00:00:39,615 --> 00:00:47,861 So dehumidifiers, at least good ones, are really just air conditioners with the parts rearranged and with different controls. 11 00:00:47,861 --> 00:00:49,584 Don't be confused by that, though- 12 00:00:49,584 --> 00:00:54,261 they do not cool the air. In fact, they make it hotter as they extract moisture 13 00:00:54,261 --> 00:00:56,802 because of how latent heat works. 14 00:00:56,802 --> 00:01:00,149 The other video explains all that in much too much detail. 15 00:01:00,149 --> 00:01:04,282 But it turns out you don't have to use the refrigeration cycle. 16 00:01:04,282 --> 00:01:08,148 This is a totally different kind of dehumidifier. 17 00:01:08,148 --> 00:01:10,403 It's nowhere near as bulky and heavy. 18 00:01:10,403 --> 00:01:15,112 It's a lot quieter, and it doesn't have anything inside of it that gets cold. 19 00:01:15,112 --> 00:01:18,079 In fact, part of it gets very hot. 20 00:01:18,079 --> 00:01:26,803 And somewhat strangely, while it does rely on the condensation of water on a cold-ish surface to collect it in this bucket, 21 00:01:26,880 --> 00:01:30,942 it doesn't have to do anything at all to get water out of the air. 22 00:01:30,942 --> 00:01:33,403 That happens naturally. 23 00:01:33,403 --> 00:01:38,444 This is called a rotary desiccant dehumidifier, and they are quite fascinating. 24 00:01:38,444 --> 00:01:43,789 But they're also really, really uncommon here in the US. 25 00:01:43,789 --> 00:01:48,855 I had to resort to this "Aeocky" thing from Amazon just to tinker with one. 26 00:01:48,855 --> 00:01:50,980 And having run some tests with it, 27 00:01:50,980 --> 00:01:54,067 I think I'm pretty sure I know why they're not common here. 28 00:01:54,067 --> 00:01:57,034 Uh, first though, let me explain how it works. 29 00:01:57,034 --> 00:02:02,501 If the word desiccant rings a bell, that's a substance which is hygroscopic. 30 00:02:02,501 --> 00:02:07,322 It likes moisture so much that it'll just absorb it right out of the air. 31 00:02:07,322 --> 00:02:11,829 Though it might adsorb it, but I am not getting into that distinction. 32 00:02:11,829 --> 00:02:13,194 Ask a scientist. 33 00:02:13,194 --> 00:02:18,417 Silica gel is a common desiccant and  you've probably run across that in those little pouches which, 34 00:02:18,417 --> 00:02:21,969 through the misuse of quotation  marks, appear to be daring you to eat it 35 00:02:21,969 --> 00:02:24,951 despite the fact that you genuinely should not. 36 00:02:24,951 --> 00:02:29,931 Uh anyway, there are also desiccant products sold specifically for dehumidification purposes. 37 00:02:29,931 --> 00:02:35,594 Damprid is a product which contains various salts which are very hygroscopic. 38 00:02:35,594 --> 00:02:38,682 Those work well for small spaces  like closets, 39 00:02:38,682 --> 00:02:43,933 but the trouble with that approach is that most desiccants are single-use items. 40 00:02:43,933 --> 00:02:48,096 Once they've absorbed moisture, they're used up and stop working. 41 00:02:48,096 --> 00:02:51,083 Except, not always. 42 00:02:51,083 --> 00:02:53,608 Silica gel has a trick up its sleeve. 43 00:02:53,608 --> 00:02:57,873 It'll adsorb moisture from the air just fine, but if you get it hot enough 44 00:02:57,873 --> 00:03:01,493 it'll actually release the moisture it's adsorbed. 45 00:03:01,493 --> 00:03:03,732 That means it's a reversible process, 46 00:03:03,732 --> 00:03:10,857 and some clever person figured out a way to exploit that and make a functional dehumidifier using silica gel. 47 00:03:10,857 --> 00:03:12,912 That's what's going on inside of here. 48 00:03:12,912 --> 00:03:18,711 And through the magic of buying two of them, I have a pre-made one right here so I can show you. 49 00:03:19,728 --> 00:03:20,726 Now, 50 00:03:20,800 --> 00:03:24,738 you may notice there's a bit of a wiring situation going on. 51 00:03:24,738 --> 00:03:27,890 This was to run an experiment which turned out to be a dud. 52 00:03:27,890 --> 00:03:31,577 I'm not going to get into it here, but I will tell the story on Connextras. 53 00:03:31,577 --> 00:03:38,080 The Cliffsnotes version is that if you spot what might be a design flaw in this thing's operational logic... 54 00:03:38,080 --> 00:03:39,166 no you didn't. 55 00:03:39,166 --> 00:03:42,212 This is more or less an optimal design. 56 00:03:42,212 --> 00:03:48,939 What we find inside is a slowly rotating wheel made of silica gel with a tight corrugated structure. 57 00:03:48,939 --> 00:03:54,226 Quick side note, my brain doesn't like that this is called gel. 58 00:03:54,226 --> 00:03:59,265 To me, that implies soft and squishy and this stuff is very hard. 59 00:03:59,265 --> 00:04:03,191 But the technical meaning of gel  has to do with chemical structures and polymer science, 60 00:04:03,191 --> 00:04:04,626 and I don't make the rules. 61 00:04:04,626 --> 00:04:07,979 Anyway, the corrugated structure gives it a large surface area, 62 00:04:08,209 --> 00:04:14,878 and a fan not unlike one you'd find in a PC case, gently pulls air through the desiccant wheel. 63 00:04:14,878 --> 00:04:16,898 But not all of it. 64 00:04:16,898 --> 00:04:22,004 One section, roughly a fifth of the wheel's area, is covered both front and back 65 00:04:22,004 --> 00:04:25,288 so it's not in the airstream of the large  fan. 66 00:04:25,288 --> 00:04:30,653 Instead, that section of the wheel has a completely separate airflow situation going on. 67 00:04:30,653 --> 00:04:33,119 Notice this small blower. 68 00:04:33,119 --> 00:04:40,639 It takes air in through this hole, then sends it via a duct to a metal box sitting right behind the desicant wheel. 69 00:04:40,639 --> 00:04:42,792 That box contains a heating element. 70 00:04:42,792 --> 00:04:45,605 You can actually see it glowing when operating. 71 00:04:45,605 --> 00:04:51,665 And that heats the air coming from the blower before it's sent through that small section of the desiccant wheel. 72 00:04:51,760 --> 00:04:57,898 The now hot air is able to regenerate the desiccantand release the moisture it's holding on to. 73 00:04:57,898 --> 00:05:04,266 I can actually feel when I put my hand in front of the hole that the air coming out is very damp. 74 00:05:04,266 --> 00:05:08,837 It's like the air in a bathroom after taking a long hot shower. 75 00:05:08,837 --> 00:05:10,525 But that's not really helpful. 76 00:05:10,525 --> 00:05:15,717 We're trying to remove that water from the air, not just heat it up and move it around. 77 00:05:15,717 --> 00:05:20,068 And that's why this machine also has this heat exchanger. 78 00:05:20,068 --> 00:05:25,332 This simple plastic... thing is constructed much like a radiator. 79 00:05:25,332 --> 00:05:28,812 The bottom side of it has a wall separating it into two halves. 80 00:05:28,812 --> 00:05:32,964 So these two holes become an intake and an exhaust. 81 00:05:32,964 --> 00:05:39,261 Air pushed through this hole will travel up all these tubes which are definitely not just plastic drinking straws. 82 00:05:39,261 --> 00:05:46,081 And then when it reaches the top, it ends up coming back down these tubes before exiting the second hole. 83 00:05:46,081 --> 00:05:50,088 This bundle of straws may be simple, but when it's installed in the unit 84 00:05:50,088 --> 00:05:56,580 we find that its intake and exhaust holes line up with the intake and exhaust of the small blower. 85 00:05:56,580 --> 00:06:04,687 That means the blower is actually just repeatedly moving air through this thing and that small section of the  desiccant wheel in a loop. 86 00:06:04,687 --> 00:06:10,025 Before long, because of the heating element, that loop of air gets very  hot and very damp 87 00:06:10,025 --> 00:06:13,033 from all the moisture it's releasing from the desiccant wheel. 88 00:06:13,033 --> 00:06:21,635 In fact, it's so damp that the air inside of it is practically fully saturated with water and at nearly 100% humidity. 89 00:06:21,635 --> 00:06:27,001 That means if the air inside these tubes is cooled even just a little bit, 90 00:06:27,001 --> 00:06:31,565 it's gonna fall below the due point and moisture will condense out of it. 91 00:06:31,565 --> 00:06:38,293 And wouldn't you know it, when assembled, the straws are in the same air path as the rest of the desiccant wheel. 92 00:06:38,293 --> 00:06:42,627 So, the large PC fan ends up cooling them with ambient air. 93 00:06:42,627 --> 00:06:46,331 You can actually see them right here in this assembled machine. 94 00:06:46,331 --> 00:06:52,295 The slightly chilly walls of these straws will quickly build up condensation on their insides. 95 00:06:52,295 --> 00:06:58,308 And once enough builds up, it falls down into the bottom cavity and comes out these two holes. 96 00:06:58,308 --> 00:07:02,288 Then that water is directed into the little collection bucket. 97 00:07:02,288 --> 00:07:04,510 This is a really clever idea. 98 00:07:04,510 --> 00:07:09,299 The desiccant naturally grabs moisture from the air regardless of temperature, 99 00:07:09,299 --> 00:07:14,263 which is a huge advantage compared to a conventional dehumidifier. 100 00:07:14,263 --> 00:07:21,067 Since those work by cooling, in colder ambient conditions they can freeze up, which limits their effectiveness — 101 00:07:21,067 --> 00:07:24,999 a potentially huge issue if you live where it's cold and damp, 102 00:07:24,999 --> 00:07:29,953 as this freezing up can start to happen at fairly normal room temperatures. 103 00:07:29,953 --> 00:07:34,261 In contrast, this thing doesn't care what the air temperature is. 104 00:07:34,261 --> 00:07:39,965 It does need to be above freezing, of course, as otherwise the water it collects will turn to ice. 105 00:07:39,965 --> 00:07:41,433 But if the air's got water in it, 106 00:07:41,520 --> 00:07:47,385 the silica gel will simply yoink it right out as it passes through the honeycomb structure. 107 00:07:47,385 --> 00:07:51,217 And since you can reverse that process simply by heating it up, 108 00:07:51,217 --> 00:07:57,805 a slowly rotating wheel of the substance can create an infinitely repeatable moisture charge discharge cycle 109 00:07:57,805 --> 00:08:00,000 with just a few moving parts. 110 00:08:00,560 --> 00:08:05,507 You could say this machine has more moving parts than a conventional dehumidifier 111 00:08:05,507 --> 00:08:11,350 since it has two fans plus the synchronous motor to rotate the  wheel and the gears inside of there. 112 00:08:11,350 --> 00:08:16,225 But all of those parts are a lot simpler than a refrigeration compressor. 113 00:08:16,225 --> 00:08:21,684 And this approach doesn't require any environmentally harmful refrigerant, which is a nice bonus. 114 00:08:22,504 --> 00:08:23,365 Although. 115 00:08:23,365 --> 00:08:26,584 We've made a lot of progress making better refrigerants 116 00:08:26,584 --> 00:08:31,304 and I kind of wish we'd stopped paying so much attention to that as a boogeyman 117 00:08:31,304 --> 00:08:37,207 because it's not only a solvable problem  but actually has been solved in many applications. 118 00:08:37,207 --> 00:08:42,277 Every article I read about some new alternative to refrigeration generally ignores that progress 119 00:08:42,277 --> 00:08:44,384 and it annoys me very muchly. 120 00:08:44,384 --> 00:08:52,144 On that note, what a perfect segue to the, uh not exactly small caveat of this approach. 121 00:08:52,144 --> 00:08:55,768 That heating element is pretty power hungry. 122 00:08:55,768 --> 00:09:00,903 While the motors in here are small and only consume about a dozen watts of power, 123 00:09:00,903 --> 00:09:05,248 the heating element needs roughly 300 watts. 124 00:09:05,248 --> 00:09:12,224 That puts it at an extremely similar power consumption to this conventional vapor compression machine. 125 00:09:12,224 --> 00:09:16,259 Which is somewhat surprising considering how much smaller and lighter this is. 126 00:09:16,259 --> 00:09:23,172 But it's also convenient because it means we can simply run these things in the same conditions for the same amount of time 127 00:09:23,172 --> 00:09:28,127 to judge how much more or  less energy efficient they might be compared to each other. 128 00:09:28,127 --> 00:09:33,854 And if this footage looks familiar,  that's because I did all this testing last year. 129 00:09:33,854 --> 00:09:41,278 I set up two very large humidifiers in this small bathroom to keep the humidity as high as reasonably possible. 130 00:09:41,278 --> 00:09:45,281 Together, they got the room to around 80% relative humidity. 131 00:09:45,281 --> 00:09:47,696 Mm mm moist. 132 00:09:47,696 --> 00:09:54,643 The first test I ran last year was with the rotary desiccant machine because this was the one I was most curious about. 133 00:09:54,643 --> 00:09:58,074 I've used plenty of these  conventional dehumidifiers in my life, 134 00:09:58,074 --> 00:09:59,924 but never one of these. 135 00:09:59,924 --> 00:10:06,461 After two hours of running in that miserable room, it had consumed 600 watt-hours of energy. 136 00:10:06,461 --> 00:10:12,577 And at the end of two hours, it was clear that the dehumidifier was losing the battle with the humidifiers 137 00:10:12,577 --> 00:10:17,725 as the room remained at about 80%  humidity the whole time. 138 00:10:17,725 --> 00:10:20,723 But how much moisture did this thing get out? 139 00:10:22,003 --> 00:10:24,080 N- not, not a whole lot. 140 00:10:24,080 --> 00:10:31,476 I poured the water from its collection bucket into this container on a tared scale and it read 188 grams. 141 00:10:31,476 --> 00:10:33,868 After I spilled a little of it... 142 00:10:33,868 --> 00:10:39,062 I tried to get as much as I could back into the container and got it up to 191 g. 143 00:10:39,062 --> 00:10:42,179 But let's just go ahead and call that 195 just to be fair. 144 00:10:43,360 --> 00:10:47,346 That doesn't seem like very much, but to calculate liters per kilowatt-hour, 145 00:10:47,440 --> 00:10:51,348 first I needed to convert the 195 grams of water into ounces. 146 00:10:51,348 --> 00:10:53,814 And I got 6.87 oz. 147 00:10:53,814 --> 00:10:58,513 And since this is water, that's the same as 6.87 fluid ounces. 148 00:10:58,513 --> 00:11:02,763 Now, as I'm sure you know, there are 128 fluid ounces in a US gallon. 149 00:11:02,763 --> 00:11:06,510 So, that's 0.05367 gallons. 150 00:11:06,510 --> 00:11:09,516 And of course, there are 3.8 L in a US gallon. 151 00:11:09,516 --> 00:11:13,513 So, I multiplied that by 3.8 and got 0.2L, 152 00:11:13,513 --> 00:11:16,138 though I think some rounding may have happened. 153 00:11:16,138 --> 00:11:25,169 Anyway, with 0.2L produced using 600 watt-hours of energy, that works out to 1/3 of a liter per kilowatt-hour. 154 00:11:25,169 --> 00:11:29,531 Remember that number, 0.33L per  kilowatt-hour. 155 00:11:29,531 --> 00:11:32,858 Then I moved on to the conventional dehumidifier. 156 00:11:32,858 --> 00:11:35,622 With this guy set up in the same testing environment, 157 00:11:35,622 --> 00:11:40,115 at first it used a little less electricity than the rotary desiccant model. 158 00:11:40,115 --> 00:11:46,601 When first powered on, it was only consuming 265 watts, and this was on its highest fan setting. 159 00:11:46,601 --> 00:11:49,262 Power draw does vary though as refrigerant moves 160 00:11:49,360 --> 00:11:51,434 throughout the system and pressures change, 161 00:11:51,434 --> 00:11:53,235 so that did climb up a bit. 162 00:11:53,235 --> 00:11:57,573 Shortly into the test, it had increased to 345 watts. 163 00:11:57,573 --> 00:12:04,909 Also noteworthy, this fella was actually able to overcome the humidifiers and drop the ambient humidity. 164 00:12:04,909 --> 00:12:10,649 Running non-stop, the room stabilized at about 60% relative humidity. 165 00:12:10,649 --> 00:12:14,358 If that sounds like this machine was removing a lot more moisture, 166 00:12:14,358 --> 00:12:16,510 that's because of how it was. 167 00:12:16,510 --> 00:12:22,119 At the end, it had consumed 680 watt-hours, just a hair more than the desiccant unit. 168 00:12:22,119 --> 00:12:25,337 Yet, it nearly overtopped the water container. 169 00:12:25,337 --> 00:12:30,193 It produced over a liter of water, in fact, 1.2 L. 170 00:12:30,193 --> 00:12:33,956 After correcting for the difference  in weight between these two glass containers, 171 00:12:33,956 --> 00:12:38,560 the precise total was 1,207 grams of water. 172 00:12:38,560 --> 00:12:46,389 Which means this machine under these conditions will remove 1.775 L of water per kilowatt-hour, 173 00:12:46,389 --> 00:12:51,429 which is over five times as efficient as the rotary desiccant unit. 174 00:12:51,429 --> 00:12:53,568 But you know what's worse? 175 00:12:53,568 --> 00:12:57,063 Well, I also tested this piece of garbage. 176 00:12:57,063 --> 00:13:04,288 This is a "dehumidifier" which uses a Peltier element to create a cold surface via thermoelectric electric cooling 177 00:13:04,288 --> 00:13:10,030 and has a piddly little fan to blow a bit of air across that cold surface. 178 00:13:10,030 --> 00:13:14,125 Now thermoelectric cooling is just not an efficient technology 179 00:13:14,125 --> 00:13:22,236 and I'm pretty confident that the only reason these exist is to have the cheapest search result on [insert website] for "dehumidifier" 180 00:13:22,236 --> 00:13:26,146 and they're mostly just exploiting people who don't know any better. 181 00:13:26,146 --> 00:13:32,053 Want to know how much water this thing produced in that same incredibly damp testing environment after 2 hours? 182 00:13:32,053 --> 00:13:34,047 22g. 183 00:13:34,047 --> 00:13:36,517 Twenty-two grams. 184 00:13:36,517 --> 00:13:39,710 And how much energy did it spend producing that? 185 00:13:39,710 --> 00:13:41,625 70 watt-hours. 186 00:13:41,625 --> 00:13:45,124 Its only saving grace is that it uses just 35 watts of power. 187 00:13:45,124 --> 00:13:51,447 But its efficiency still works out to a paltry 0.31 L per kilowatt-hour. 188 00:13:51,447 --> 00:13:56,264 That is 1/5th as efficient as the vapor compression machine. 189 00:13:56,264 --> 00:13:57,578 Uh-oh. 190 00:13:57,578 --> 00:14:04,933 If this piece of junk is 1/5th as efficient as the machine which is five times as efficient as this machine... 191 00:14:04,933 --> 00:14:08,751 that means these two machines are equally efficient. 192 00:14:08,751 --> 00:14:17,166 It's not quite exactly the same, but 0.31 versus 0.33 L per kilowatt-hour is awfully darn close. 193 00:14:17,166 --> 00:14:22,431 And both of them are much much less than 1.775. 194 00:14:22,431 --> 00:14:24,139 Oh boy. 195 00:14:24,139 --> 00:14:31,010 So, uh, are rotary desicant dehumidifiers just as inefficient as Peltier dehumidifiers? 196 00:14:32,618 --> 00:14:34,495 Well... 197 00:14:34,495 --> 00:14:41,552 First I would be remiss if I didn't mention that this technology isn't unique to standalone dehumidifiers like this. 198 00:14:41,552 --> 00:14:44,801 It has a lot of applications in commercial spaces, 199 00:14:44,880 --> 00:14:50,930 especially where humidity must be kept in  control even when the air has to be quite cool. 200 00:14:50,930 --> 00:14:56,725 You'll also find similar rotating wheels of  silica gel in some energy recovery ventilators. 201 00:14:56,725 --> 00:15:00,613 Those are devices which allow for the exchange of indoor and outdoor air 202 00:15:00,613 --> 00:15:05,075 without changing the temperature or humidity of the indoor air very much. 203 00:15:05,075 --> 00:15:09,995 It's not always a rotating wheel, sometimes it's more like a cube surrounded by careful ducting, 204 00:15:09,995 --> 00:15:13,989 but they're starting to become common in residential settings, which is great. 205 00:15:13,989 --> 00:15:18,391 But the rest of this video is only going to address devices like these: 206 00:15:18,391 --> 00:15:25,471 standalone boxes you put in a room and plug into the wall which extract moisture from the air and collect it. 207 00:15:25,471 --> 00:15:31,436 Also, I don't want to suggest that this machine is representative of the technology writ large. 208 00:15:31,436 --> 00:15:34,871 For a start, this model is very cost cut. 209 00:15:34,871 --> 00:15:37,337 It can only be on or off. 210 00:15:37,337 --> 00:15:43,394 It doesn't have a humidistat - it only has two fan speeds and a sleep timer. 211 00:15:43,394 --> 00:15:46,084 That doesn't scream peak performance. 212 00:15:46,084 --> 00:15:51,293 Plus, my test conditions weren't exactly this technology's bread and butter. 213 00:15:51,293 --> 00:15:53,723 It was pretty warm in the room when I ran the test, 214 00:15:53,723 --> 00:16:00,960 which might have limited the ability of the plastic straw radiator  thing to cool the air inside below the dew point. 215 00:16:01,520 --> 00:16:05,286 So perhaps it would work better in cooler temperatures. 216 00:16:05,286 --> 00:16:09,675 Well, I've let this thing run for 2 hours in a whole bunch of different conditions 217 00:16:09,675 --> 00:16:16,089 and the amount of moisture it extracts from the air is weirdly consistent no matter what. 218 00:16:16,089 --> 00:16:18,687 I first tried my air conditioned office. 219 00:16:18,687 --> 00:16:26,246 The relative humidity during that test was only about 40%  and the air temperature was 72 Fahrenheit, 22 C. 220 00:16:26,246 --> 00:16:30,622 It still managed to pull out 160 grams of water in 2 hours, 221 00:16:30,622 --> 00:16:35,493 which is over 80% of what it did in the damp AF bathroom. 222 00:16:35,493 --> 00:16:38,866 Later, I did a test at home  with ambient humidity much higher, 223 00:16:38,866 --> 00:16:46,840 about 60% and roughly the same temperature, and it still extracted 186 g of water - not much more. 224 00:16:46,840 --> 00:16:54,927 Then I did it again in the morning with the temperature  down to 66° F, that's about 19° C, and the humidity at 50% 225 00:16:54,927 --> 00:16:58,713 and it extracted 169 grams of water. 226 00:16:58,713 --> 00:17:04,077 Kind of seems like no matter what it's going to pull out something like 80 to 90 grams of water per hour. 227 00:17:04,077 --> 00:17:09,152 So its efficiency is apparently not that affected by ambient conditions. 228 00:17:09,152 --> 00:17:13,035 Now, granted, I never tried this over the winter. 229 00:17:13,035 --> 00:17:17,194 I should have, but I forgot because of the fact that I live in the Midwest 230 00:17:17,194 --> 00:17:22,923 and DEhumidifying is the last thing on anybody's mind from October to March. 231 00:17:22,923 --> 00:17:29,377 But the weirdly consistent results I was getting were backed up by a little internet sleuthing. 232 00:17:29,377 --> 00:17:31,766 And speaking of internet sleuthing, 233 00:17:31,766 --> 00:17:38,707 if you watched the first video, you'll remember that I said cold but damp just isn't much of a thing here. 234 00:17:38,707 --> 00:17:43,121 And to clarify by "here" I mean most of the United States. 235 00:17:43,121 --> 00:17:47,410 Those are the conditions where a rotary desiccant machine is the most useful. 236 00:17:47,410 --> 00:17:51,532 So long as the air temperature is above freezing, this will keep working. 237 00:17:51,532 --> 00:17:54,971 And so they're fairly common in other climates. 238 00:17:54,971 --> 00:17:57,662 Like for instance, the United Kingdom. 239 00:17:57,662 --> 00:18:04,420 So I spun up Amazon.co.uk in the hopes I could see what the efficiency of other models is like. 240 00:18:04,420 --> 00:18:07,098 Luckily, it gave me this nice comparison chart. 241 00:18:07,098 --> 00:18:12,028 And, well, none of this looks much better. 242 00:18:12,028 --> 00:18:15,329 Granted, I have not done my own testing on any of these, 243 00:18:15,329 --> 00:18:21,217 and I don't know whether these numbers are the result of government testing or manufacturer testing. 244 00:18:21,217 --> 00:18:26,304 But assuming their best quoted moisture extraction occurs on their highest power setting, 245 00:18:26,304 --> 00:18:30,104 then these six models can manage 0.54, 246 00:18:30,104 --> 00:18:32,134 0.54 again, 247 00:18:32,134 --> 00:18:34,002 0.535... 248 00:18:34,002 --> 00:18:36,574 which rounds to 0.54 again, 249 00:18:36,574 --> 00:18:38,064 0.66, 250 00:18:38,064 --> 00:18:39,234 0.61, 251 00:18:39,234 --> 00:18:42,910 and 0.62 62 L per kilowatt-hour, respectively. 252 00:18:43,963 --> 00:18:46,518 That's just not that great. 253 00:18:46,518 --> 00:18:50,474 The best of these is twice as efficient as the one I've tested, 254 00:18:50,474 --> 00:18:55,406 but that's still only one third as efficient as a vapor compression machine. 255 00:18:55,406 --> 00:19:00,465 But I wanted to see how big boy commercial versions of this technology might fare. 256 00:19:00,465 --> 00:19:05,861 So I found this brochure from Technofrigo Tuscany, and it has charts! 257 00:19:05,861 --> 00:19:10,314 They back up the notion that the moisture removal of these things is oddly consistent, 258 00:19:10,314 --> 00:19:12,226 at least above room temperature. 259 00:19:12,226 --> 00:19:15,759 It seems to plateau right at about 20 degrees C. 260 00:19:15,759 --> 00:19:22,658 And the first model listed,  the AD3000, can remove 23 kg of water per hour. 261 00:19:22,658 --> 00:19:26,195 That's quite a lot, but so is its power input. 262 00:19:26,195 --> 00:19:29,403 32.3 kilowatts! 263 00:19:29,403 --> 00:19:31,818 That's like 10 British kettles! 264 00:19:31,818 --> 00:19:37,158 And it means its efficiency is only 0.71 L per kilowatt-hour, 265 00:19:37,158 --> 00:19:46,635 which is still significantly worse than the 1.771 L per kilowatt hour I observed in my test of the vapor compression dehumidifier. 266 00:19:46,635 --> 00:19:52,344 Frankly, I'm surprised this thing doesn't quote some average moisture removal per energy unit but... 267 00:19:52,344 --> 00:19:58,426 then again, the moisture it can pull out of the air varies a lot, especially once the temperature starts to fall, 268 00:19:58,426 --> 00:20:03,206 so I can understand that being  a practically impossible metric to give. 269 00:20:03,206 --> 00:20:09,772 And I should also note that the conditions for the vapor compression machine were fairly close to ideal during my testing 270 00:20:09,772 --> 00:20:13,123 and its efficiency is by no means consistent. 271 00:20:13,123 --> 00:20:19,228 So, the same general [?] factor applies to giving it an efficiency metric. 272 00:20:19,228 --> 00:20:22,092 So, seems pretty bad, right? 273 00:20:22,092 --> 00:20:25,758 Well, here's where things get a little complicated. 274 00:20:25,758 --> 00:20:31,273 First, setting efficiency aside, the rotary desiccant machine does have several advantages. 275 00:20:31,273 --> 00:20:33,117 For one, noise. 276 00:20:33,117 --> 00:20:34,682 Here's how loud it gets. 277 00:20:35,109 --> 00:20:41,198 [slowly building soft whooshing sound] 278 00:20:42,463 --> 00:20:44,877 And here's the one with the heat pump in it. 279 00:20:45,271 --> 00:20:48,751 [compressor growls to life and a loud fan starts] 280 00:20:49,112 --> 00:20:50,929 Yeah, these are pretty noisy. 281 00:20:50,929 --> 00:20:53,961 There's a compressor in there and a blower, which is quite loud. 282 00:20:53,961 --> 00:20:58,030 But in fairness, that's mainly because these move a lot of air. 283 00:20:58,030 --> 00:21:01,949 The little fan in here is hardly doing a thing in comparison. 284 00:21:01,949 --> 00:21:05,269 But in its lower power mode, it's even quieter, 285 00:21:05,360 --> 00:21:09,417 though its power level and effectiveness are  cut roughly in half. 286 00:21:09,417 --> 00:21:13,959 This thing is also much less resource-intensive to manufacture. 287 00:21:13,959 --> 00:21:21,038 It doesn't have nearly as much copper, steel, and aluminum in there as this thing, and is mostly just a plastic box. 288 00:21:21,038 --> 00:21:24,263 And while it has more components to put inside the box, 289 00:21:24,263 --> 00:21:26,457 a lot of them are commodity parts 290 00:21:26,457 --> 00:21:32,952 and none of them require brazing pipes together or pulling a refrigeration loop into a vacuum or charging it with refrigerant. 291 00:21:32,952 --> 00:21:36,819 And unless there's some dark secret to silica gel I don't know about, 292 00:21:36,819 --> 00:21:42,390 this thing doesn't appear to be any more environmentally costly than your average gadget. 293 00:21:42,390 --> 00:21:45,304 But more importantly to the efficiency conversation, 294 00:21:45,304 --> 00:21:49,527 because these things regenerate the silica gel using a heating element, 295 00:21:49,527 --> 00:21:53,608 they add heat to whatever space they're put in. 296 00:21:53,608 --> 00:21:57,063 Now, you'll recall from the last video that so does this thing, 297 00:21:57,063 --> 00:22:02,932 but most of the heat it generates is coming from the water condensing on the evaporator. 298 00:22:02,932 --> 00:22:08,448 In a similar way, the water which is adsorbed into the silica gel will also release latent heat energy. 299 00:22:08,448 --> 00:22:13,697 But if this thing pulls 100 grams of water out of the air per hour, 300 00:22:13,697 --> 00:22:16,833 which is more than I've ever observed it to do, 301 00:22:16,833 --> 00:22:22,651 that would only result in 73 watts of heat output, which is small potatoes. 302 00:22:22,651 --> 00:22:27,927 But the wrinkle here is that in the conditions where this machine is most helpful, 303 00:22:27,927 --> 00:22:29,893 cold and damp, 304 00:22:29,893 --> 00:22:32,846 those 300 watts of heat from the heating element 305 00:22:32,846 --> 00:22:38,320 are also going to lower ambient humidity  simply through heating the air in the room. 306 00:22:38,901 --> 00:22:42,494 For the sake of argument, let's say we've got this running in a bedroom 307 00:22:42,494 --> 00:22:46,655 with a floor area of 200 square feet and 8ft ceilings. 308 00:22:46,655 --> 00:22:52,140 That's 1,600 cubic feet of air volume or about 45 cubic meters. 309 00:22:52,140 --> 00:23:02,309 If that volume of air is at room temperature and 60% relative humidity, then there's about 460 g of water in that room's air. 310 00:23:02,309 --> 00:23:06,949 Now, if this is able to remove 80 grams of water from the air in an hour, 311 00:23:06,949 --> 00:23:11,786 then through moisture removal, it will drop relative humidity to about 50%. 312 00:23:12,738 --> 00:23:20,239 But if the air temperature in that room goes up by just 2° C thanks to the 300 watts of heat it's putting out, 313 00:23:20,239 --> 00:23:27,690 then even without removing any moisture, relative humidity would still fall to 53%. 314 00:23:27,690 --> 00:23:33,590 So the effect of the desiccant wheel is only marginally greater than simply heating the air. 315 00:23:33,590 --> 00:23:40,937 But wait, we're not just heating the air or just using the desiccant - we're doing both at the same time so... 316 00:23:40,937 --> 00:23:43,359 that's still good, right? 317 00:23:43,359 --> 00:23:48,564 Yes. So long as you actually need the  heat. 318 00:23:48,564 --> 00:23:51,555 That's the big caveat of these machines. 319 00:23:51,555 --> 00:23:56,217 The regeneration of the desiccant requires a substantial amount of heat energy 320 00:23:56,217 --> 00:24:03,056 which makes them very inefficient from a liters per kilowatt-hour of input power perspective. 321 00:24:03,056 --> 00:24:10,191 But if the extra heat they put out is actually useful, as it often is in the cooler climates these are usually sold in, 322 00:24:10,191 --> 00:24:12,527 then that's not much of a concern. 323 00:24:12,527 --> 00:24:16,796 It is resistive heat, which is typically the most expensive kind of heating, 324 00:24:16,796 --> 00:24:23,144 and that makes a holistic cost evaluation practically impossible when your primary source of heating is less expensive, 325 00:24:23,144 --> 00:24:24,588 which I hope it is. 326 00:24:24,588 --> 00:24:26,938 But it's not wasted energy. 327 00:24:26,938 --> 00:24:32,596 And it also contributes to lowering ambient humidity - which is its job. 328 00:24:32,596 --> 00:24:39,516 And honestly, that's why I find this application of the technology somewhat frustrating. 329 00:24:39,516 --> 00:24:43,328 The desiccant wheel is definitely effective at removing moisture, 330 00:24:43,328 --> 00:24:51,718 but since the heating it does to make that process happen also lowers ambient humidity by virtue of increasing the air temperature, 331 00:24:51,718 --> 00:24:56,253 it's hard to determine how much work the desiccant is actually doing. 332 00:24:56,253 --> 00:25:00,592 And this is especially hard to tease out because each room you might put this in 333 00:25:00,592 --> 00:25:05,356 will have a different rate of moisture ingress and a different amount of insulation - 334 00:25:05,356 --> 00:25:11,566 both of which affect how much each  of the two mechanisms will actually lower the ambient humidity. 335 00:25:11,566 --> 00:25:15,741 But there is clarity in when these make sense to use. 336 00:25:15,741 --> 00:25:19,528 If you're in a climate where it's chilly enough that you need to heat  your home, 337 00:25:19,528 --> 00:25:25,356 but it's so humid that you still have excess moisture issues, this is perfect. 338 00:25:25,356 --> 00:25:32,251 The extra heat it produces is still useful both because it's heat and because it will also lower humidity, 339 00:25:32,251 --> 00:25:37,953 but because it also extracts moisture, it lowers humidity even further. 340 00:25:37,953 --> 00:25:46,233 And if you have a space which is too humid, but also too cold for one of these vapor compression machines to work well due to icing, 341 00:25:46,233 --> 00:25:48,393 these are the perfect option. 342 00:25:48,480 --> 00:25:50,715 They're kind of the only option really. 343 00:25:50,715 --> 00:25:55,958 But if you're not looking for extra heat output when you need a dehumidifier, 344 00:25:55,958 --> 00:25:58,345 these are simply a terrible option. 345 00:25:58,345 --> 00:26:03,283 The input power of these two machines is roughly the same, just 300 watts. 346 00:26:03,283 --> 00:26:07,182 But this can only do about a fifth as much work. 347 00:26:07,182 --> 00:26:13,570 So if I wanted this rotary desicant machine to actually be as  effective as this small vapor compression machine, 348 00:26:13,570 --> 00:26:18,390 I would need to quintuple its input power to 1,500 watts. 349 00:26:18,390 --> 00:26:25,646 And then it literally would become a space heater which happens to be able to extract some moisture from the air. 350 00:26:25,646 --> 00:26:32,127 And all of that heat will be on top of the heat that's generated in  the desiccant as water adsorption occurs, 351 00:26:32,127 --> 00:26:37,854 which will be similar to the amounts that this thing generates when only using 300 watts. 352 00:26:37,854 --> 00:26:43,048 So yeah, if it's warm when you need to dehumidify, these are terrible. 353 00:26:43,048 --> 00:26:50,753 In conclusion, as nifty and clever as this idea is, it is not fit for purpose in many climates. 354 00:26:50,753 --> 00:26:54,594 Here in the US, it's not fit for purpose practically anywhere, 355 00:26:54,594 --> 00:26:59,083 which might explain why this unit has such poor reviews on Amazon. 356 00:26:59,083 --> 00:27:05,170 For example, here in the Midwest, the outdoor air temperature is so much colder than the indoor temperature throughout the winter 357 00:27:05,170 --> 00:27:08,286 that we simply do not need dehumidifiers. 358 00:27:08,286 --> 00:27:12,441 In fact, we often get out the humidifiers during the heating season. 359 00:27:12,441 --> 00:27:17,943 And by the time indoor humidity starts to climb in the spring to the point of being a problem, 360 00:27:17,943 --> 00:27:21,346 well, we're only a few weeks away from switching on the air conditioning. 361 00:27:21,346 --> 00:27:25,918 And since once that happens the  last thing we want is more heat, 362 00:27:25,918 --> 00:27:32,714 if a dehumidifier is necessary, we always want it to be as efficient and effective as possible. 363 00:27:32,714 --> 00:27:36,861 And the weather's warm enough that the icing probably doesn't matter. 364 00:27:36,861 --> 00:27:40,850 But if you're on one of those islands in the middle of the ocean which is always kind of humid, 365 00:27:40,850 --> 00:27:45,475 and you're far enough north or south of the equator to where it's just a bit nippy outside in the winter 366 00:27:45,475 --> 00:27:51,212 but not so cold that the indoor air is definitely going to be dry from all the heating you need to do... 367 00:27:51,212 --> 00:27:53,509 then these are a great solution! 368 00:27:53,509 --> 00:27:57,857 Although, I will say this one smells a little funny when it's running. 369 00:27:57,857 --> 00:27:59,814 That might just be this one, but I don't know 370 00:27:59,814 --> 00:28:03,710 it does have some very hot parts in there very close to the silica gel wheel 371 00:28:03,710 --> 00:28:08,946 so, I'm inclined to believe it's just the  nature of these things to smell slightly funky. 372 00:28:08,946 --> 00:28:12,243 It's not horrible or anything, but it is noticeable. 373 00:28:12,243 --> 00:28:13,519 Anyway, this is the end. 374 00:28:14,504 --> 00:28:17,036 ♫ adsorbently smooth jazz ♫ 375 00:28:18,000 --> 00:28:21,935 ...at least good ones are really just air  conditioners with the parts rearranged... 376 00:28:21,935 --> 00:28:27,317 and yeah, well, we've already screwed  it up because I completely forgot that 377 00:28:30,400 --> 00:28:32,682 I don't think this should be on the desk yet. 378 00:28:32,682 --> 00:28:34,809 Uh, first though, let me explain how it works. 379 00:28:35,400 --> 00:28:37,457 That was bad. That was just bad. 380 00:28:37,457 --> 00:28:43,210 Once again, I'm doing disassembly work on camera just because that's what I'm doing. 381 00:28:43,210 --> 00:28:46,255 There's something wrong with this paragraph which I didn't notice. 382 00:28:46,255 --> 00:28:50,182 I've used plenty of these conventional dehumidifiers over the years of my life. 383 00:28:51,330 --> 00:28:52,425 Why did I do that? 384 00:28:52,425 --> 00:28:54,573 Those work well for smalls spa sf... 385 00:28:55,196 --> 00:28:56,095 Dammit. 386 00:28:56,095 --> 00:28:58,611 I have a pre-unmade one. 387 00:28:58,611 --> 00:29:01,406 Oh, yeah. I grabbed... I put my finger right on the heat sink. 388 00:29:01,406 --> 00:29:02,468 That hurt. 389 00:29:04,583 --> 00:29:07,679 end of video captions gag 390 00:29:08,434 --> 00:29:11,361 you thought I forgot about this, didn't you? 391 00:29:11,361 --> 00:29:13,797 I mean I did forget to do any testing over the winter. 392 00:29:13,797 --> 00:29:16,202 So I suppose that wouldn't be an outlandish thought. 393 00:29:16,202 --> 00:29:17,534 This isn't much of a gag, though, is it? 394 00:29:17,534 --> 00:29:19,557 Well it was another dry subject.