Hackaday Prize Entry: Dave Thomas’ Desert Dryer

It seemed utter madness — people living in hot desert climates paying to heat air. At least it seemed that way to [David Thomas] before he modified his tumble dryer to take advantage of Arizona’s arid environment.

Hanging the wash out to dry is a time-honored solution, and should be a no-brainer in the desert. But hanging the wash takes a lot of human effort, your laundry comes back stiff, and if there’s a risk of dust storms ruining your laundry, we can see why people run the dryer indoors. But there’s no reason to waste further energy heating up your air-conditioned interior air when hot air is plentiful just a few meters away.

[David]’s modification includes removing the gas heating components of the dryer and adding an in-line filter. He explains it all in a series of videos, which at least for his model, leave no screw unturned. It’s not an expensive modification either, consisting mostly of rigid dryer hose and copious amounts of aluminum duct tape. He mentions the small fire that resulted from failing to remove the gas igniter, so consider yourself warned. The intake filter and box were originally intended for a house air-conditioning system, and required only minimal modifications.

This is a great build, being both cheap and easy to implement as well as being environmentally friendly without requiring a drastic change to [David]’s lifestyle. It makes us wish we had a similar endless supply of hot air.

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33 thoughts on “Hackaday Prize Entry: Dave Thomas’ Desert Dryer

  1. Very Apollo 13 of him.
    I have been thinking of adding a solid state relay and a humidity sensor system to shut down my dryer when the clothing is dry summer or winter.
    In summer if the blow-air is piped into the house it will humidify the air but in the evaporation it will drop the temp, so a tradeoff.

      1. Most “automatic” dryers are controlled by a simple thermal switch (160F in the US) that starts a timer as the cooling effect of the ever-drier clothes diminishes and the exhaust air temperature rises.

        It would be a simple matter to monitor the cooling effect (dare I use the “A” word here?) and switch the dryer based on a similar temperature-differential effect. This type of control is common in industrial drying operations of many types but would be fairly inexpensive to do. The only real challenge would be that the drum air supply temperature would not be constant as it is in heated dryers, but would vary with ambient conditions.

        Bonus points for using humidity sensors and encoding psychrometric tables/interpolation into the algorithm.

      2. Humidity sensors in clothes dryers aren’t very common. They tend to have issues with getting clogged with lint. There are two other methods for auto dry that tend to dominate. The oldest method is to run a timer in parallel with the exhaust thermostat; when the thermostat is open the timer runs. The other, newer, method is to measure the conductance of the fabric using either parallel bars inside the drying chamber or with the drum itself.

  2. sorry, this hack is too american to not comment – if you want to save even more money use clothes line in the first place. or you can use old fridge enclosure to make desert air dryer without heating the house. you can also dry foods with desert air so you can save some space in fridge/freezer.

    1. I have a line, and I still use it. But when in a hurry, or to fluff up the hard laundry from the line, it’s nice to have a dryer. It may sound all very American, but this can be used anywhere where the dew point is low. It may actually be effective/efficient in other environments when compared to a regular dryer, I just have no way to test. This is just an option between line drying and paying to heating up air.

    1. In Ontario they want us to get rid of gas all together and use nothing but electricity.
      They are saying they are losing money with electricity and we are not using anoff of it, and it is good for the environment. They funny thing is our new hydro plants that they want to make because we have to much hydro will run gas…??????
      They say It will make our hydro bill 6x more then gas to heat our homes. But we will be greener? but we will not be able to eat of buy anything because 60% of our income will be going to hydro. But we will be Greener.

        1. @ Protolamer, I only found a couple of spelling, mistakes nothing that distorted the meaning. I’d feel the same if I was being pressured into heating my house with electricity instead of gas.

  3. This hack could be applied anywhere there is a summer, or an attic, without major modifications to the dryer. The thermostat in a dryer is designed to click on at 120 degrees and back off around 150. Usually the dryer is inside a home that has air conditioning. The dryer has vent holes to allow the room air in to be heated. If you were to seal the vent holes on the dryer, and pipe in air from the attic or outside the gas or electric heating elements would have to work less to dry the clothes. There is often a punchout hole already on the dryers case for another vent pipe.

    The “humidity” sensors in the dryer are not measuring the humidity of the air but rather the wetness of the clothes. They are just 2 strips of metal that the clothes bump against and when the clothes are still wet the metal conducts allowing the timer to advance. Also easy to hack.

  4. Line-drying clothing doesn’t result in stiff clothes. Using too much detergent results in stiff clothes, and many people use way, way too much detergent. So much so that if you put your clothes back into the washer after a cycle with no detergent, you’ll probably see suds! If your water has a lot of mineral content, then add some vinegar into the softener dispenser, if it’s working properly (ie not opening until a rinse cycle.)

    Hack your laundry, people! Get a cheapo scale or a plastic syringe, and start dialing back the amount of detergent you use to see what still gets your clothes clean. And for god sakes, stop coating your clothing in a fat-perfume sludge (aka softener.)You also don’t generally need water hotter than what your detergent needs for the enzymes to work properly, which is usually around room temperature.

    All over the world people have indoor and outdoor drying racks and drying “cabinets” (some of which are heated a bit, others just contain a fan or two.) Ski resorts have drying rooms, equipped with a fan and dehumidifiers.

    Ikea sells a very sturdy ~$10-15 metal drying rack that can dry a boatload of clothes in one go (and you can speed it up a bit by placing a box fan near it if you’re in a rush.) You can buy retractable wall-mount line units that hook to an opposite wall and provide 5-6 lines to hang clothes from. Paracord and some hooks works, too, though it might be too slippery; good laundry line is intentionally a bit rough to keep clothes from sliding off.

    The concept of a machine that beats the hell out of your clothing while heating it to scorching temperatures is very much an American one and insanely wasteful, both from an energy standpoint and a clothing wear-and-tear standpoint. In the winter or otherwise dry locations, hung clothes dry surprisingly fast, and you can speed it up quite a bit just by running a box fan (or if you have a room with a ceiling fan, turning that on to a low setting.) Having a front-load washer helps, as they are much better at extracting water in the final spin.

    1. Btw, I dilute my soap by a third and towels still come out hard because all of the fibers are aligned. This is something that is in-between heating up and tumble drying and line drying. It also works for people who might not be able to line dry. On my project page I include a good recipe for fabric softener. Combined with homeade fabric softener the clothes come out feeling like brand new every time.

  5. I’ve often wanted to have a related capability for the fridge in winter (I live in Michigan). It seems silly to me that I’ve try to keep my house in the high 60s – low 70s, and then inside that house I have a box that is attempting to keep things inside it in the 30-40 range when the outside temperature is 15 degrees. It would be great to have a hybrid fridge that makes use of the cooler outdoor temperatures for about 3 months.

    I guess on the plus side, the waste heat from the fridge compressor cycle is helping heat the house…

    1. There are a lot of dumb people around. Two years ago, winter storm in Ontario knocked power out for days, in parts of Toronto as well. People went ballistic claiming that their food in refrigerators has been spoiled, and demanded cash for food from the government. City government gave in. The solution was obvious, but TV stations didn’t mention it: put your food in a plastic box outside, where it was comfortably bellow zero Celsius.

    2. My in-laws keep their deep freeze in the Garage, which is not heated in the winter. Saves a lot of energy in the Wisconsin winters. We also have a large family, and through the Christmas season it’s not uncommon to just setup a spare folding table in the garage to place leftovers.

      If you were feeling super hacky, you could always tap into the coolant line on the fridge and setup an external condensor, just like the AC unit. Have some valves to automatically switch to the external one based on the outside tempurature. That way in the summer that excess heat isn’t putting more load on your AC.

      1. It seems that a couple of well placed and insulated ducts could be designed into these units to couple to the outside. Freezing air in winter and excess heat in summer both controlled by the fridge.

        1. The problem with ducting outside air into a food refrigerator is that the fridge is designed, unlike an air conditioner, to keep the cool air humidified so the food doesn’t dry out. Outside cold air is going to tend to be way too dry if you’re circulating it.

          You don’t have this problem with the plastic boxes outside because first it’s not as big a deal for freezers and second you’re not circulating the air in the plastic box.

          1. I would like to plumb my fridge to outside too but there are some complications. If you mount it in a room that is below fridge temperature, e.g. freezing, the fridge cannot heat and so items will freeze instead of cool, also modern fridges are CFC free and like certain temperatures to operate, so they expect to be in a room at room temperature. This being said it should be possible to connect it to outside colder areas, even just the piping on the rear. A simple air tight box, with vents to outside might reduce costs.

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