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Community and Q&A

Heat Recovery from Dryer Exhaust

vap0rtranz | Posted in Green Products and Materials on

Are there _no_ heat recovery products on market to recover the energy blown out of dryer vents?

I found 2 prototypes online from the mid 2010s.  One looks similar to standard heat exchangers, like HRV/ERVs.

One on Build It Solar (a DIY site I like:)
https://builditsolar.com/Experimental/DryerHX/DryerHXTest1.htm
An another random one:
http://www.alkeng.com/AL/dryer

The 1st link has more data, including an estimated 32% energy recovery.

I find it odd that we talk about heat pump dryers, drain water heat recovery, etc. but still have no product on the market to take the humidity out of dryer exhaust so we can actually re-use the hot air in wintertime: either to pre-heat air intake back to the clothes dryer, or to help heat a conditioned space.  No?  O.O

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Replies

  1. Expert Member
    Zephyr7 | | #1

    Both of those designs are likely to get clogged up with lint and be very difficult to clean. Clever idea, but lots of downsides in actual use. A dryer likely doesn’t run often enough to be as big of a contributor to energy loss as something that runs nearly continuously like an HRV either. I suspect those are the reasons you don’t see devices like this out there as commercial products.

    Bill

    1. vap0rtranz | | #2

      Bill,

      Both prototypes needed filters. I mean, if we were to only use that rational, no space heating/cooling system should use forced air. Maybe the Europeans are smarter than American after-all :)

      Also, if we base the problem on infrequent use, I'd argue that hot water heaters are infrequently used appliances. Example: 2 people, 5min showers daily, makes a hot water heater useful for barely more than ONE hour per week. My example excludes hot dishwashing, hot clothes washing, etc. but I think others have made the point that traditional hot water tanks waste of lot of time (at set temp for hot water) not being directly used. Now we have lots of options on the market: heat pump heaters, tankless ones, spot hot water heaters, waste water heat recovery, -- the point is several products on the market to get at reducing the wastefulness of an appliance that isn't always in use. So clothes dryers are also infrequently used appliances, yet we have few options here.

      Justin

  2. Trevor Lambert | | #3

    I think if condensing and heat pump dryers weren't around, this idea might get some traction. The non-venting dryers are far more effective at saving energy than the 32% heat recovery you're talking about with these exhaust exchangers. Not only do they use less energy while running, they don't bring in unconditioned air (effective 100% energy recovery vs 32% that the proposed vent heat recovery would recover). I think a good analogy would be if compact fluorescent bulbs were invented after household LED lights.

    I agree that dryers are significant enough energy users to take into consideration. A typical household will run the dryer anywhere from 3-7 times a week, at least in the winter. That's 1.5-5 hours a week at 4-6kW, plus 21,000-100,000 cubic feet of unconditioned air to heat for a conventional dryer. Not to mention the 24/7 air leakage and thermal bridge to the outside that is presented by the exhaust pipe.

  3. Rich Cowen | | #4

    It is not impossible to design and mass produce an electric dryer where the exhaust direction can be shifted from outside to inside when there is a low humidity level in the home. It makes a lot of sense and in a cold climate when a home humidity level in winter is below 30% (or in a desert climate like in las vegas in summer) you would get a big benefit from this. The exhaust exchanger sounds complicated to clean out... could you just send filtered exhaust directly into the house. A "try to keep exhaust indoors" mode could be set up to slow down the dryer cycle time and send air in based on the home humidity level. It would be optional and it might change dry time from 50 minutes to 1:45 or whatever, but it is a lower energy mode that would take better advantage of the dry air within the home and use the same electricity to run the cycle.

    Not an easy hack but it is totally within the capabilities of manufacturers to build this into their product.

    1. C L | | #5

      This would be a perfect solution for the SE US
      - in the winter when it is cold indoor humidity tends to be lower than 40%, so an increase would be useful.
      - in the summer when it is hot and humid and you want to get rid of indoor humidity, you would run the thing in heat pump mode where it would essentially become a dehumidifier.

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