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When I have wet clothes coming out of the washing machine, I can either tumble-dry them in an electric clothes-dryer, or I can hang them to dry. But I can only hang them in a basement. The basement has poor air circulation and gets kinda cool and humid in the summer. So there is a dehumidifier in the basement, set to cycle on when the humidity gets above 65%. When wet clothes are hanging in the basement, of course the dehumidifier tends to run longer and more frequently.

So there is an electricity usage tradeoff - either the dryer uses a lot of electricity if I tumble-dry, or the dehumidifier uses extra electricity if I hang-dry. Which is likely to be more energy-efficient overall?

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  • $\begingroup$ Doesn't the tumble-dryer have a "cold" setting that will just blow air through? $\endgroup$ – Blackbody Blacklight Jul 6 '15 at 15:41
  • $\begingroup$ The dehumidifier concept is very questionable in general. It's basically an after the fact fix for a very poor house design with insufficient ventilation. Get a contractor to put ventilation into the home. If you want to reduce your energy use hang dry outside whenever you can, replace the dryer with a gas heated model or get solar. As to your question: get an appliance power meter and measure the total energy consumption. $\endgroup$ – CuriousOne Jul 6 '15 at 17:08
  • $\begingroup$ @CuriousOne I have a dehumidifier because the humidity outside is around 75%-85% so adding ventilation would increase the humidity in the house not decrease it. It also makes drying clothes outside ineffective, as they can sit for days and still be damp. $\endgroup$ – Rick Jul 8 '15 at 14:46
  • $\begingroup$ Indeed, when it is hot outside, a well-ventilated basement has higher RH than the outdoors: When the outside air enters the basement, the walls (heat-sunk to the soil) cool the air. $\endgroup$ – Steve Byrnes Jul 8 '15 at 18:36
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    $\begingroup$ I see. Drying clothing is possible without active heating or cooling near 100% humidity, but you have to create a strong air flow. I have frequently done this in Singapore with a 100W fan and drying times are quite reasonable, but you have to create a bit of a wind tunnel for this to work. In any case I would go back to original suggestion and do a measurement. No amount of theory can replace that, really. $\endgroup$ – CuriousOne Jul 8 '15 at 18:57
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The dehumidifier is probably more efficient.

When the wet clothes are drying, there is a latent heat of evaporation that will cool down the basement as the water evaporates. You then have to run the dehumidifier to cause this water to condense again - in the process you will heat the room (as you expel the excess heat). In principle, no heat leaves the building.

If you run the dryer, you expel a lot of hot moist air to the outside world.

Just considering those two closed systems, the dehumidifier should be the better option. Whether it actually is for you depends on other factors: how much running the dehumidifier heat the basement, and where does that heat end up going?

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  • $\begingroup$ The basement is inside a giant heat sink: the ground. Unless the surrounding soil is warm, or the basement is very small, it will probably absorb more the heat than the clothes. $\endgroup$ – Blackbody Blacklight Jul 6 '15 at 15:38
  • $\begingroup$ @BlackbodyBlacklight - that's possible, but it depends on the insulation of the basement. I think that blowing warm air into the atmosphere is a more visible "there goes the heat" thing, but obviously there is a large surface area between basement and surrounding soil. But I have no data... $\endgroup$ – Floris Jul 6 '15 at 15:41
  • $\begingroup$ @BlackbodyBlacklight while the ground is a good temporary heat sink, dirt is a decent insulator when considering a few feet of it. As a result, in the long term (over the course of several months), if you're heating the basement the ground will cease being a nice heat sink and will act like an insulator. (the electrical analogy would be a huge capacitor in series with a moderate resistor, with a very very high valued resistor in parallel. At first you can dump current into it with no problem, but eventually the capacitor charges) $\endgroup$ – Rick Jul 8 '15 at 14:55
  • $\begingroup$ @Rick In my experience, basements tend to be cold. There are a lot of kinds of dirt, but it would take a real citation to convince me that any is a good insulator. If dry, maybe, but dry dirt is sand or dust, not dirt. "Heating the basement" sounds like an expensive sort of experiment. $\endgroup$ – Blackbody Blacklight Jul 8 '15 at 14:58
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    $\begingroup$ @Floris Nice! Found a reference. Looks like I never heard of that because the higher price meant they weren't popular until recently. That paper mostly refers to prototype and European models. Another paper in the same proceedings mentions a much lower efficiency gain compared to a hot-air model… but most agree that the heat pump costs twice as much. $\endgroup$ – Blackbody Blacklight Jul 9 '15 at 3:57

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