| New Clothes Dryer Could Save Billions |
| Written by Hank Green | |
| Friday, 15 February 2008 | |
|
The device, really, is fairly simple. Instead of using a traditional air-in-contact-with-heating-coils heater, it uses an oil as the heat-transfer medium. The oil is then used to heat the air that gets blown into the drying drum. The heat transfer between the oil and the air is nearly two times more efficient than the air simply being blow across ultra hot heating coils. The device is so much more efficient that it can be plugged into a regular 110 V plug (instead of 220s now required by dryers.) Considering how simple this is, it's a marvel (or perhaps a travesty) that GE or Whirlpool didn't think of it first. Additionally, the heating unit only ever reaches about 150 F, since the heat-transfer is so much more efficient. Traditional dryers have to heat their elements up to 1000 F in order to reach optimal efficiency, resulting in about 15,000 household fires each year. The device can be installed by a technician in 30 minutes at a total cost of around $300, which would be recouped in less then four years. A quick calculation based on the number of households with electric dryers (around 80 million) and the average amount spent on electricity for drying clothes a year ($85 per household) shows that this device could indeed save several billion dollars per year just in America. Already Brown is in talks with a major European manufacturer to integrate the device into new units, and he's raised several million dollars in angel funding. He's also talking to the EPA about getting his dryers Energy Star rated. Up until now, dryers have been so inefficient that not a single one on the market has been awarded with the Energy Star label. While it would have been easy to call his dryers the most efficient on Earth. Brown always qualifies the statement with "aside from the sun." And that's a touch of modesty that, to me anyway, is very welcome. Via CNet Clean Tech Comments
(42)
how about forced air heating?
written by xrmb , February 15, 2008
Couldn't we do the same for these inefficient forced air heaters we use? I know that I'm blowing cold air over glowing metal strings for a few hours every day... costing me big time and not keeping me warm.
retro fit
written by jeff , February 15, 2008
I've seen a liquid-to-air heat exchanger (essentially like the heater core in a car) made to work with the air handler of an existing forced air system. It was used with a solar thermal system and an on demand gas or electric backup heater.
I can't find a link to the particular product but see the last paragraph of this link for information: http://www.eere.energy.gov/con...opic=12500 See also Solar Water Heating by Bob Ramlow starting on pg 108. I found a preview on Google Books.
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written by EV , February 15, 2008 The oil needs less energy to heat, and, once heated, holds onto the heat better. That oil is then used to heat the air that gets blown into the drying drum. Something seems to be wrong with this explanation. Maybe it's just the many years of engineering I've had, but heat is heat. This should be no more energy efficient than a regular heating coil from what I know about how they work.
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written by Space , February 15, 2008
why does this thing keep telling me "your comment is too short" when it's longer than others?
nonsense
written by Space , February 15, 2008
This looks like a scam to me.
"The oil needs less energy to heat" - less energy than what? Than not using oil? That cannot be true. " holds onto the heat better." - If it holds onto the heat better, then it must be harder to heat up in the first place, so no gain overall. This makes no sense.
Hmm???
written by Lou Grinzo , February 15, 2008
I'm with the others here questioning this invention, or at least the explanation. You expend energy to heat the air directly or to heat the oil which then heats the air. How can one possibly be better than the other? Ultimately the heat energy winds up in the ambient air, and if the only energy input is the original heating element, then where does the extra energy come from?
The only other explanation I can see is that the oil gizmo reduces a lot of heat loss in the original design, meaning much more of the heat winds up where you want it, not as waste.
cool?
written by brian goldner , February 15, 2008
so, this is totally an ecogeek solution to drying clothes...but isn't there a zero-electricity alternative?
Seriously, hanging your clothes to dry in the wind is fairly quick (esp in hot or windy areas) and makes your clothes smell great. Seriously, I've been to supermarkets and seen ppl buy fabric softener that makes your clothes smell "wind fresh." Just get a rope and some clothespins!!
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written by EV , February 15, 2008
Brian, that's great and all. But what about those of us who live where it gets cold (well below freezing), have rainy seasons or don't have a yard? Not all of us live in Southern California.
Just use low heat setting!
written by kballs , February 15, 2008
This sounds like it's just not being heated as much and is giving less heat to the clothes... meaning it's working like the low heat setting (which COULD run on a 110v outlet if you rewired the machine). Then the clothes come out as dry as the regular dryer... which means they are either being OVER-DRIED in the regular dryer, or the modified dryer is being run longer. Modern high-efficiency dryers use a humidstat to measure when the clothes are actually dry (saving you from wasting energy on over-drying).
X BTUs of heat is X BTUs of heat. Using oil as a transfer medium isn't going to gain you anything. However using a lower heat setting WILL, because moving air is more efficient at drying on it's own than hot air... you only heat the air because then it will hold more moisture (by lowering the vapor pressure), thus improving the drying performance, but lowering overall energy efficiency. High-efficiency washer dryer combos work best together because the washer spins the clothes at high RPM (spinning out most of the water), and the dryer uses the moisture sensor to stop when the clothes are dry.
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written by rob , February 15, 2008
I would imagine that the system is more efficient, because it "evens" out the heat delivery, rather like using an oil filled radiator, compared to a fan heater.
Whereby the oil filled radiator takes longer to warm a room, but once it is up to temperature, uses a lot less electric than a fan heater, to maintain the temparture.
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written by RhapsodyInGlue , February 15, 2008
Being an electrical engineer, I'd suspect that kball may have landed on the only plausible explanation if there indeed is any difference with this device.
With any electric device, energy lost to inefficiency means energy lost to heat. So heaters that are simply electric resistance strips are inherently 100% efficient. Granted the dryer may leak heat into the room, but anyone that has a dryer knows that no where near half of the heat is lost into the room compared to what goes out the exhaust vent. Oil or no oil, a certain number of KWh is going to generate the same amount of heat, and that heat can only go one of two places, into the dryer drum or into the room. I'll have to give the low heat setting a try. I suppose I can get a quick estimate of the energy use just by checking the outside meter before and after drying if I turn almost everything else off inside. I feel bad for anyone that pays $300 dollars for something that simply permanently sets their dryer on low. I suspect that this Mr. Brown is probably many things... modest is not popping into my mind at the moment. BTW... if you want a volunteer technical editor let me know. I always hate to see people preying on the good will of those seeking to be environmentally conscious. At least a story like this good be posted with a word of caution that it doesn't pass the technical sniff test.
Heat Transfer
written by dave , February 15, 2008
Oils and greases are frequently used as heat transfer mediums because they transfer heat more efficiently than air. One example would be the white silicone heat sink grease, with which I'm sure most of you are familiar. It's purpose is to fill in any small air gaps between a hot semiconductor and a heat sink thereby improving heat transfer to the 'sink. Another example would be the big "pole pig" power transformers, many of which are filled with oil to improve heat transfer from the transformer itself to the outer metal case. I think this may be the same principle used in a different way.
The Great American Corporation
written by GDAEman , February 16, 2008
Lumbering, wealth consolidating behemouths, like General Electric (owner of MSBMC) can't make this "discovery"? It says something about American's misplaced beliefs in the corporate form of business. Corporate charters are a scam.
Greenwash
written by cmu , February 16, 2008
I'm so sick of seeing this "green" hogwash all over the web; I could not find a single instance where the OP had done any due diligence, it was always respouting the company PR.
To dave: maybe true, but then the oil would have to be in contact with the clothes, which I'm sure you would not want. Eventually the heat is transferred via air to the clothes, so it's the same as if the unit were not there. Thanks kball and rhapsody for clear explanations. Now if only there was a way to counter the misinformation on a thousand sites...it does, however, beg the question as to how they claim the *drying time* is reduced as well.
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written by RhapsodyInGlue , February 16, 2008
Dave...
Substances with higher thermal conductivity move heat more rapidly... so in that sense might be said to be more efficient. That sense of the word is similar to saying that a subway car traveling at 50mph is getting you to work more efficiently than a subway car at 40mph. But highly conductive liquids are not more efficient in somehow preventing heat from being lost. If we're talking about an element heated through electric resistive heating, X KWh of electricity is going to produce Y Btu (or Joules) of heat. If that element is located in a hyper insulated thermos it will take a very long time for the heat to dissipate into the surroundings. If the element is in a swimming pool it will be a very quick process. However, the amount of heat transfered overall will be the same. Heat sink grease is used because without it the semiconductor still must dissipate the same amount of energy as heat (it can't go anywhere else) and the laws of physics indicate that it will reach a higher temperature in order to achieve the same rate of heat dissipation in an environment with lower thermal conductivity. But higher temperatures are bad for semiconductors, hence the use of heat sinks and grease. Part of my career was designing semiconductors. Potentially a heating element bathed in a high thermal conductivity liquid would exhibit a longer lifetime because it does not reach the same temperatures. But that boils down to a question of whether its life is sufficiently longer to make up for the higher costs. Certainly at $300 it would seem unlikely. Further, the same lifetime increases might be seen simply by setting the dryer on LOW. I do not have central heat in my quaint old house. A very few days a year it gets cold enough that I mind, so I have two electric room heaters. I have a very cheap one for the bathroom that has two electric coils (low and high) and a fan to blow air over them. I have a much bigger thing in my bedroom that looks kind of like a radiator and is filled with oil... it was way more expensive. The advantage of the oil filled heater is that no part of it ever gets hot enough to start a fire or burn someone... however, it in no way saves energy. X KWh into either of these units is going to produce Y Btu of heat. There simply is no place for energy to escape... it doesn't disappear. The oil filled heater might last longer due to the lower temp, but both are still alive after many, many years. As for energy conservation... use a clothes line whenever possible and get a gas dryer if you can... and according to kball use the LOW setting. Save the $300 and put it towards a solar water heater.
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written by RhapsodyInGlue , February 16, 2008
A few more thoughts on dryers... hopefully someone with more expertise might confirm my ideas.
The issue of optimal temperature for drying is probably dependent on the ambient relative humidity. For instance if you're in Florida with 98% relative humidity, running the dryer on air only is probably going to take forever and waste energy just from the motor. If one is in an extremely low relative humidity situation having no extra heat may turn out to be most energy efficient. Companies probably could make dryers save energy if they added another moisture sensor to determine the relative humidity of the incoming air. They could then adjust the heating temperature for optimal efficiency. The companies likely have not yet done this because there would be a drawback for the consumer. It would be much harder to predict how long it would take for the drying to finish. But there probably would be a growing market segment that might pay a bit extra to at least have a selectable mode that would say... take as long as you want but save as much energy as possible. Consider this my public disclosure for patent purposes if no one else has thought of this.
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written by dave , February 16, 2008
RhapsodyInGlue...
Isn't the purpose of the heat sink grease to reduce the thermal resistance of the case to sink junction? We're talking here about a heating element in a container of oil. Basically a french fry cooker. Stick one end of a big heat sink into the oil. Now blow air over the other end of the heat sink and into the clothes drum. The oil, analogous to the heat sink grease, has a lower thermal resistance than air alone. This would allow the heat generated by the heating element to be more easily transferred to the large surface area of the heat exchanger (similar to the semiconductor heat sink) and then to the air being blown into the drum (or out of the computer case). I think this is basically how this dryer works. How much more efficient this ultimately would be than blowing air over a bare element, I don't really know. Hmmmm....I've got some big heat sinks, an old french fry cooker, and a currently non-functioning dryer....I believe I hear the call of power tools.....
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written by RhapsodyInGlue , February 16, 2008
Yes... higher thermal conductivity = lower thermal resistance.
This would mean that at thermal equilibrium, where the amount of heat energy leaving the heating element is equal to the electric energy put in, the heating element would remain cooler if surrounded by a material of higher thermal conductivity. But the bottom line is that if you have 500 watts going into a heating element within seconds it will reach thermal equilibrium where 500 watts is transmitted to the environment around it. If you want to play around with this, try finding one of those old heating elements that you dropped in a coffee cup to heat water. If you put it in water it's probably cool enough that you could reach in and touch it while its heating the water... until of course the water gets too hot. Pull it out of the water with it plugged in and it would get way too hot to touch almost immediately. However, it gets hot enough so that even with the higher thermal resistance of air it is still transmitting the same amount of heat into the air as it did into the water. Just check the wattage on the label and that's the amount of electric energy in and is also the amount of transmitted heat energy. Energy in must equal energy out. Though your heart will thank you if you decommission your french fry cooker in the name of science.
Thermal Equilibrium?
written by dave , February 18, 2008
Isn't the purpose of this device to get heat out of the element and into the air being blown into the dryer as quickly as possible? Maybe the heatsink analogy isn't the best.
Using only a 120V 20A 2400W heating element, how would you heat up the air? You could obviously just blow air directly over the element, but is that the best way to heat the air? Can that heat be transferred to the air more quickly?
Umm.....well I think it has something to
written by Joseph , February 18, 2008
So with the coils, you have a very small surface area contacting the passing area so there is poor heat transfer. With the oil transfering heat to larger fins, you the increase the contact surface as the air passes over the fins.
Don't ask me where the momentary BTU in the coils goes if its not picked up by the passing air, but its a fact that the smaller surface area of the coil means less efficient heat transfer. The increase in thermal transfer from fin to air VS coil to air means you would have to use less heat to produce the same BTU at the target, ie the clothes. Pretty simple stuff. No engineering degree here.
CPU Heatsink Analogy Update:
written by Joseph , February 18, 2008
Forgot to say that the idea with the CPU heat sink is to transfer the heat to an object with a larger surface area to increase the ability to transfer heat away from the chip (DUH!) So the oil helps to transfer the heat to the heat sink more efficiently, because air is not a great conductor of heat.
One more thing....
written by Joseph , February 18, 2008
After thinking about it a second, the heat from a traditional coil that doesn't can transfered to air particles is probably release as radiant energy across a broad spectrum of radiation.
The elements in a dryer actually glow red. This is all so simple, I really don't see whats so hard about this.
Easy enough, but could be cheaper?
written by Peter , February 18, 2008
$300 for the conversion? What if this was produced on a massive scale? Would the price be cut in half?
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written by Terra Verde , February 18, 2008
This could easily be a stupid point, as I know little about the subject, but honestly the first thing that comes to mind for me is either you would need to change out/refill the oil from time to time, or there would be a safety issue with the possibility of heating oil to it's flammable point? So it's either unnecessarily wasting a resource or a safety issue. Is there anything to these assumptions?
Insulation
written by Craig , February 18, 2008
Why not just insulate the living hell out of the dryer? Then just regulate the temperature with the heating element? How about recycling the dryer exhaust, that way your not heating the outside by piping out. Keep it simple.
the recycling exhaust
written by eric , February 18, 2008
sounds like a good idea to me, but then i've no degree in anything either. It sounds to me as though the efficiency of using oil comes from maintaining temperature. The oil loses heat much less rapidly than air. The coil wouldn't need to be on as much to maintain high temperatures of oil as it would with the heated air.
I may be getting something wrong here, but it sounds like only by setting the dryer on low, in conjunction with the oil system, can one get the results claimed. From my POV, the oil by itself helps, but not nearly as much as claimed.
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written by RhapsodyInGlue , February 18, 2008
Joseph... yes some energy is converted to light, but really very little. An incandescent light bulb is basically the same thing, electricity through a wire. It presumably has been optimized to produce as much light as possible and yet according to wikipedia it seems they convert somewhere between 95-98% percent of the electricity they use into heat. I would thus assume a dryer element probably at most converts 2% of the electricity into light... likely less than 1%. Glowing resistors are simply very bad at generating light. Not to mention if the dryer element is enclosed then the light gets absorbed by something and converted into... heat.
Craig... The exhaust from the dryer is at near 100% relative humidity... it can hold no more moisture. One would have to run it through some sort of desiccant to dry it, which could be done but then there is the problem of drying or replacing the desiccant. Another option would be a heat exchange system where the hot moisture saturated exhaust preheats new dry air before it enters the dryer. That might actually turn out to be economical with rising energy prices. Very efficient air-to-air heat exchangers are being used in home ventilation systems these days. Dave... If you have 120VAC across an element with a certain electrical resistance such that 20A flows, this means that 2400W is converted into heat in the element (setting aside the very small percent given off as light). All of this heat has to be transmitted to the surroundings because it can't indefinitely build up. Just as a higher voltage across a resistor will force more current to flow, so too a higher temperature difference across a thermal resistor will cause more heat to flow. So for a heating element surrounded by something with a high thermal resistance (air), when energy flows in at a rate of 2400W, at first 2400W of heat will not flow into the air. The remainder of the heat will build up in the element raising it's temperature. This will continue, but as the element gets hotter it forces heat to flow more quickly across the thermal resistance. Eventually it will reach a temperature at which the full 2400W is being dissipated across the thermal resistance and thus it will stop heating further. With a dryer element this "eventually" is probably only a matter of seconds. If the element is surrounded by oil it will not heat up as much before 2400W of heat is flowing into the oil. In neither case is heat energy being lost, and the rate of heat flow ends up being the same.
Quick Backtrack
written by RhapsodyInGlue , February 18, 2008
Joseph... my comment above in response to what you said is obviously a bit off the mark... I guess it's getting late. The 2-5% figure for bulbs is obviously for "visible" light. Probably much more than that is in the IR part of the spectrum. Though for dryers as with light bulbs that IR gets absorbed by whatever is surrounding the bulb and converted into heat.
Not an engineer
written by champ , February 20, 2008
If air vs liquid doesn't matter, why are our cars liquid cooled, and not air cooled (for those of you without a classic VW beetle). The answer to that question would probably be the same answer to why a liquid heat exchanger works better too.
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written by G , February 21, 2008
Smells like snake oil to me. Mentions NASA and MIT, but doesn't cite a single reputable lab study. No real technical description of how such a wonder would work, just enough pseudo-scientific babble to confuse the easily mislead.
Years ago I worked for a disreputable investment banking house that underwrote a lot of these crackpot inventions. They'd find a carnival-barker type that could stir up some press, produce some nice looking marketing info, and then sell shares to the public. Lots of hype, not much in the way of any real products that ever got produced. They'd pump and dump the stock from region to region, and leave the last ones in holding the bag when the company slowly folded up their almost-nonexistent operations. Anyway... Liquid cooling in a car lets the same amount of heat move away faster that air cooling. In a car, moving heat faster is better for the motor, since heat in the air a mile behind you is not making metal parts expand in your expensive motor. The same amount of energy goes into making the same amount of heat - the heat just gets moved away from the expensive stuff faster. Same deal with heat sinks in electronics. Same energy=same amount of heat. Idea is just to move it from point "A" to point "B" faster so's not to cook the expensive bits. In a dryer, all of the heat (except the part that is lost into the body of the dryer) is transferred to the air, and the air all gets pushed out into the the dryer drum, and then to the outside world, carrying moisture with it. We don't need to move the heat any faster - we want to move it in a nice controlled fashion that doesn't turn the clothes quickly into crispy bits of carbon. If we transferred the heat to oil first, it still has to move from the oil into the air, since a forced hot air dryer dries with... forced hot air. If you want to dry a load of clothes in 45 minutes, you need to heat X volume of air to Y temperature, and maintain that temperature within certain tolerances for about 45 minutes. Too hot and you toast the clothes to a nice golden tone. Too cool and drying takes longer. Dryers are designed to dry clothes as quickly as reasonable possible without the undesirable charring (good for steak, bad for your underpants). To make heat directly from electricity, there's a simple formula: 1 kWh=3413 BTU. That number doesn't change if you use the resistive element to heat the air directly, or if you bathe the element in hot oil and then blow air over that, or if you bathe the element in hot mashed potatoes and blow the air over that (well, I suppose the potatoes would dry out and eventually burn, and that would release some additional heat. Maybe that's the secret - the oil burns!) Moving the heat off of the dryer's heating element (or firebox in a gas dryer) faster doesn't help, since our goal is to heat a specific mass of air, and it is always going to take the same amount of energy to heat a given volume of air to a given temperature and to maintain that temperature over time (assuming humidity, air pressure, and incoming air temperature are all relatively constant). One way to use electricity to efficiently heat an enclosed area is to use it to power a heat pump. In a heat pump, heat isn't directly converted from electricity, instead, electricity is used to move heat from one place to another. The amount of heat depends on the temperature differential between the two areas. This is especially efficient when a lot of heat (relative to the air being heated) is available, say waste heat from an air conditioner condenser. Still won't reduce drying time, though. Anyway, I'd like to see results of a controlled energy consumption test from a reputable lab. (Energy cost per volume of water extracted). I bet we won't...
All have missed the point, except Eric
written by Bob Smith , February 21, 2008
Thermostats inside of oil filled (or resistance) heaters regulate when coils are on(electricity being used). The oil filled heaters have the coils on substantially less(once optimum temp is achieved) than a resistance heater. I have both resistance and oil filled heaters in my house(both 1500w on high), and I have a "Power Miser" device(monitors power consumption). So I tried this experiment today, and once the oil filled got up to operating temp...it used about HALF of the power of the radiant heater!
No Degree or complex formula needed. All it does is turn on the heating element less(because the oil retains the heat longer), there by reducing consumption of energy.
yes, a degree is needed, apparently
written by Space , February 21, 2008
clearly some people haven't studied enough physics to realize that if something "retains the heat longer", then it will be just harder to heat up in the first place, and no energy will be saved.
The fact that oil "retains heat longer" makes no difference whatsoever. The amount of energy consumed is EQUAL to the amount of heat given to the air (that actually dries clothes), regardless of how much intermediate things retain heat or how fast they transmit it. It is actually a bad thing to retain heat, because it means it will take longer to warm up, and it will stay warm after use, when not needed.
Y'know what WOULD be good idea ?
written by David Keech , February 28, 2008
It occurred to me while reading this that there are two simple add-ons to a dryer that could make a significant difference to the amount of energy it uses.
1. Auto cut-off. Monitor the exhaust port for humidity and when the humidity drops (because the clothes are now dry) switch the heating off and skip to the cool-down phase. Now you don't need to guess how long to set the dryer for; just switch it on and forget about it. 2. Recycling of waste heat. Obviously the exhaust air is too humid to help drying clothes but it still has plenty of heat. Even something as simple as running the exhaust air past the intake before venting it would help. I suspect that would only help the efficiency in the order of a single-digit* percentage but with some refinements I suspect they could hit double-digits*. It would also produce water as the water-laden air cooled down which would mean that the dryer would now need a water outlet. * These numbers are the result of me eye-balling the temperature differences of incoming and outgoing air and their period of contact along with a vaguely remembered transfer rate of heat energy. Hence they are even less reliable than a back-of-a-napkin calculation.
Person
written by SherryD , March 14, 2008
What would cause the heating element of a newer dryer to catch a load of clothes on fire? Lint has become a four-letter word to me. I continually cleaned the lint filter, vacuumed out the vent hose and kept the unit clean.
Thanks for any help.
Hydrogen fired dryer?
written by TMax , March 19, 2008
I think this oil-based exchanger has merit, but only if one takes it to the next step.
How hard would it be to fire the dryer with hydrogen?
...
written by Chris , March 26, 2008
Mr. Brown's device may perform better because of a better desired air temperature and volume flow rate combination. Perhaps with conventional dryers, the inlet air is overheated relative to the operating flow rate... that the higher temperature achieved(or greater capacity to absorb moisture) of the drying air is not fully utilized based on the heat and mass transfer occuring within the drum.
In addition, radiation should contribute a significant heat loss since it is a function of T^4. It is a question of where it is absorbed and how it is radiated back out. If there is one thing I learned from Thermodynamics... it's that if you can meet a heating demand with lower temperatures, your system will have a higher overall efficiency in reality by doing so. Yes, energy in is energy out... but unfortunately, in the real world your losses to the environment or other pesty sinks worsen as the temperature difference widens.... and naturally avoiding a complex mode of heat transfer like Radiation in this case is definitely favorable as well. Joseph, good call on the radiant losses. RhapsodyInGlue, I await your comments.
Swindle
written by boxthinker2000 , April 07, 2008
Some people are just determined to be swindled. Radiant "losses" (??) nothing to do with anything. Where are your supposed radiant "losses" lost to? To the air flow?
Science: the proof is in the pudding
written by Peter , April 21, 2008
Sorry folks but I couldn't leave this thread and not comment on what's been said here. The whole thing is ridiculous.
Firstly, an electrical engineering degree (which I hold) is not a degree in thermodynamics no matter how many ic heatsinks we install. Trust me, I do better against those folks with my management degree. The problem with electronics today is that so many of us work in the quantum part of physics, not thermodynamics, so we forget all those real-world aspects that lead to major heat losses within a system. Yes we all learned conservation of energy back in 10th grade but that really didn't make us experts in the field, did it? Chris seems to be the smart guy here. He's identified that the inefficiencies in any resistive heating system come from incidental loss. As everyone here agrees, that's the only possibility and the inventor doesn't seem to be claiming anything different. Along what Chris said, if you increase the efficiency of the heat path you want and decrease the efficiency of heat paths you don't want (by decreasing the thermal gradient) you get a much better system. Furthermore, lets all please just take a look at our toaster ovens before laughing off radiant energy. Notice there are top and bottom coils? Ever wonder why? From an efficiency standpoint, we obviously only need bottom coils. However, if you want to brown your food evenly, since so much of the heat comes from radiant energy, you need to have coils on top. Thus, a lot of energy from those very hot coils may be going straight to the housing around the coils rather than the air passing through, and then we're relying on the unit's insulation to try to get that energy over to the clothes. Lastly, remember that science is grounded in experimentation so for all we might debate, if you take two identical dryers and measure the power used to get dry clothes (yes, modern dryers have humidity sensors so they know to stop) with and without this modification, you've got a very valid test -- professional labs be damned -- and the science needs to explain the result, not vice-versa. Talk all you want about repeating it 100 times, etc., but you've got a valid energy claim. Does it take longer to dry the clothes? No -- it really can't. As everyone has pointed out, energy is energy. If the thermostat wants the clothes at a particular temperature, perhaps this system will make it swing below that temp a little more gradually and keep heating a little longer than the thermostat expects making the average temperature a tad higher, but overall it'll be very close in temperature to whatever the thermostat was originally trying to establish. Sounds like a swell invention to me. Beats a clothspin, especially if it's raining.
Okay, but...
written by Amy , May 09, 2008
What happened to the good old fashioned method of hanging your clothing up on a rack or a clothes line, and letting them air dry? People did that for hundreds of years, so it obviously works. What changed since then?....Oh yeah, people became impatient with having to wait.
Mr.
written by TomTrottier , June 13, 2008
I think the only way that could save energy is to have a heat exchanger on the exit path of the damp air to heat up the dry incoming air.
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