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Old 10-30-14, 06:52 PM   #1
jray3
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Default Clothes dryer to heat pump energy recovery

Greetings from an EcoModder, new to EcoRenovator.

I'm trying to make some lemonade of the fact that my clothes dryer vent exhausts right onto my outdoor heat pump compressor and coil. Luckily, this is a heating-dominated climate. Idea is to create a 'winter mode' such that the dryer only runs when the compressor is running, and to do so simply by supplying the voltage to pull in the dryer's main contactor from the HVAC compressor relay. This would cause the dryer to turn on and off in sync with the heat pump. I'd also include a switch to return to stock configuration as a summer mode/manual override for faster drying when necessary. A seasonal hood that directs more dryer exhaust into the compressor coils would also be used (made of heavy vinyl or corroplast).
If I'm good, that same hood could be repositioned to keep exhaust away from the coils during summer.

Upside is energy savings, potentially better net effect than the new closed-loop heat pump clothes dryers that sell for $1500-1800..
Downsides could include coil icing due to all that humidity, as well as lint buildup on the coil (which I already have to clean off regularly).

Anybody tried something similar? I've already reviewed the thread discussing homebuilt heat exchangers, and plan to add venting and weatherstripping to the laundry room doors to pull dryer process air from the cool dry garage rather than the warm and humid house.

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Old 10-30-14, 07:32 PM   #2
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Just hang the clothes in a closet and run a dehumidifier in the closet.
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Old 10-30-14, 08:08 PM   #3
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Quote:
Originally Posted by NiHaoMike View Post
Just hang the clothes in a closet and run a dehumidifier in the closet.
As in a dehumidifier that uses a cold plate to condense humidity and then heats up the exiting air? I don't see how that would accomplish anything other than create a musty closet that dries clothes much more slowly for a greater expenditure of energy. After the hanging clothes have pulled a lot of heat out of the air through evaporation, then we would put energy into chilling the air to condense the humidity, and then warm it up again. That's more overall energy than to heat it once and then recover much of it with a heat pump... The dehumidifier would use at least twice the energy. It's just that a lot of it would be hidden as added load on the HVAC.

The cold plate approach works in new ventless dryers because it is part a closed loop. In an open loop like a closet, (even a closed closet) efficiency would suffer.

During heating season, my house is ventilated only by the dryer and bathroom/kitchen exhaust fans on manual control, but CO2 rarely rises above 800 ppm.
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Old 10-30-14, 09:15 PM   #4
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The most efficient dryers on the market are in fact just dehumidifiers. They easily use less than half the energy of a regular dryer. What you're thinking of doing is just a roundabout way to make a rather inefficient dehumidifier.
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Old 10-31-14, 07:21 PM   #5
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It seems to me that the OP has not done enough research on the subject at hand.

Normal, forced-air dryers are second in line in home energy consumption. Average running load is 4KW or higher. Not only that, but they rob conditioned air and add to the heating and cooling load of the house. In contrast, the new ventless dryers typically average under 1500 Watts, and help heat and dry out the house when running. Roasting your clothes is not a highly efficient way of drying them, but it is faster.

The "heat sink" heat pump boosting has been tried before. It is, in fact, a Rube Goldberg machine in the making. No matter how you slice the pie, the heat pump will never be able to keep up with the dryer. As outdoor temperatures plummet, more and more heat blows by the outdoor hx before it has a chance to shed the energy. The heat pump cannot cope with a mixed flow of warm and cold air, and not enough dryer heat gets reclaimed.

I dare you to prove me wrong. Take lots of pics.
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Old 01-17-15, 01:21 PM   #6
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A dehumidifier is the way to go , after the cloths are 100% dry you can toss them into the dryer and fluff them up again , making your cloths and towels soft and wrinkle free.

I am going to try it this winter , the dryer draws air from your warm house and expels it outside at about 50cfm , which will empty a 10x10 rooms warm air every 16 minutes , most drying takes say 45 minutes , which means you have vented the rooms air 2.8 times in that duration. Which causes cold outside air to be drawn into the house.

A dehumidifier will convert ALL of its energy into heat in the long run so you get to heat your house instead of vent its heat outside.

Or if you do not fancy the noisy dehumidifier
It might be a good idea to have a cold air intake to the dryers base , where I imagine it draws its air from.
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Old 01-18-15, 03:13 AM   #7
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Why not just use a heat exchanger to capture the outgoing heat, I think that would be far superior to dumping waste heat onto your coils.

Personally I would definitely go for the dehumidifier and maybe even construct a dryer cabinet. The heatpump dryers I've seen here take about 1.5 kwh to dry 8 kg of laundry, but cost €800-€1200; while a simple dryer cabinet takes 2 kwh to do the same load. They're very popular here in the more northern part of Europe since you can dry anything in them, the downsides are the size and duration it takes for drying.

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