Can You Conserve Home Heat & Recycle Dryer Heat Using An Air-to-Air Heat Exchanger?

Review of Air-to-Air Heat Exchanger
by 00orange00 (3,868 pts ) , published Jan 23, 2009
2

Why isn't every clothes dryer hooked up to an Air-to-Air Heat Exchanger? This would conserve a lot of the clothes drying heat that is ordinarily lost to the great outdoors. Why is this not available?

Suncourt's Airiva Heat Exchanger

Suncourt's Airiva heat exchanger model, # HE150, "is not designed to connect to a clothes dryer in any way, shape or form," states a company official who contacted Bright Hub.

A heat exchanger or ventilator, such as the model listed here, is designed to "exchange heat between house ambient air and fresh outside air. Connecting it to the clothes dryer is dangerous advise."

Is There Fool Proof Heat Recovery from a Clothes Dryer using an Air-to-Air Heat Exchanger?Rating Average

For those who are very serious about turning their ordinary clothes dryer into a 'green clothes dryer' this idea is for a clothes dryer vent/heat reclaimer that will work in any house, new or old. If someone were to invent such a product, it would actually involve taking an off the shelf Air-to-Air Heat exchanger and installing it as an add-on to your dryer exhaust vent. When your dryer is operating, an Air-to-Air Heat Exchanger would return most of the heat from your dryer back indoors yet still sending the moisture outdoors.

If you were to install a product that could operate in this way on the exhaust of your electric dryer you will be saving more than half of the dryer heat that you would otherwise give up to the great out doors. At the same time, you will be completely preventing the negative pressure that a dryer usually causes as air tries to make its way back into the home that the clothes dryer has blown the air out of (at a less visible, but very significant energy saving).

You would have to be a do-it-yourselfer (or a local handiman with some low voltage controls experience) to install a product such as this that could actually work with your clothes dryer exhaust. With the proper know-how, it would be possible to accomplish this in the course of an afternoon.

The mechanism works by blowing the exhast air through one side of a heat exchanger (similar in principal to the heat exchanger in a furnace for instance) while at the same time drawing fresh air from out of doors into the house through the other side of the heat exchanger. This means the moist exhaust air gives up its heat to the cold dry incoming air which is replacing it. As a result the exhaust air leaves in a cooled state, and the replacement air enters in a warmed state. Consequently, a lot less heat from the dryer is lost to the out of doors while all dryer induced draughts are eliminated.

An Air-to-Air Heat Exchanger would need to come with a filter which you would want to check frequently, and change often. This is very important. If an Air-to-Air heat exchanger became plugged with lint and air flow was reduced as a result the drier would pose a serious fire hazard. Ideally this would never happen with proper maintenance. You would need to check an air-to-air heat exchanger each time you used the drier, just as you do with the drier lint collecter already. But, as a safeguard, you could add a sail switch to the exhaust air duct that leads from an air-to-air heat exchanger to the outdoors. Sail switches are commonly used in HVAC applications and serve as safety switches. They cut the power off from the whole system (the dryer in this case) if the air flow becomes to low for proper operation of the system under consideration.

An Air-to-Air heat exchanger would need to have a removable heat exchanger module. This is commonly how these mechanisms are made since in any application from time to time you would need to remove the heat exchanger and wash it out.

This home-made green clothes dryer option is not for the faint of heart. For example, the Suncourt HE 150 Air-to-Air Heat exchanger costs $550.00. At first I recomended this particular model as the correct Air-to-Air heat exchanger for the job. However, the Suncourt is not designed to work with temperatures as high as those that are generated by a clothes dryer. A more industrial version would be needed, one that could handle the type of air temperatures that a dryer can put out.

At approximately $500.00, if this device were designed for this usage, it would pay for itself very nicely overtime, though, at today's prices it would take a few years. In the mean time, however, you would have given the environment a big lift, not to mention that you would also have made your house that much more comfortable during the winter months. An industrial version of an Air-to-Air heat exchanger is likely to be much more expensive.

Probably, right now, there is an inventer out there, somewhere, busy putting a dryer together that already has an Air-to-Air heat exchanger built right into the machine.

Comments

Nov 16, 2009 1:11 PM
Ken Huck
Dryer efficiency & recovering dryer heat
Hi 00orange00,

That is a great question. I just started thinking about that yesterday while I was building a superinsulated home designed to reduce its energy use by 70%.

For more info see news section at http://www.susten.com

The energy efficient home owner above is emphasizing line drying but the best I can do (Sorry Greggr) is run my dryer at off peak times. There are a number of reasons why we keep our dryer outside. A big one being that clothes are laden with poly vinyl chloride PVC / Plastisol inks particles of which will produce very dangerous dixions and furans if they get to hot.

Based on a rudimentary analysis I agree with Robert F. I believe that purpose built heat exchanger that condensed out the moisture when combined with high spin speed washer could reduce dryer energy consumption by at least 50%.

I have heard that heat pump dryers are availale in europe and they would certainly pump the heat out of the exhaust stream.

I share the concerns of the Suncourt people and would recommend caution if using thermoformed plastic heat exchangers.

Ken Huck
"Make the Earth Sing" with
Ecosavvy Energy
828-350-7529


Nov 10, 2009 2:56 AM
Steve
Dehumidifier
Why can't you just run a dehumidifier in the same space (heated basement for eg) you are venting the moist, hot air?
Oct 8, 2009 6:03 PM
Robert Fairchild
clothes dryer heat exchange
Build your own simple counterflow heat exhanger: Use rigid 4" aluminum duct for the dryer vent. Surround with 6" aluminum duct or galvanized stovepipe with 1" spacers (1" bolts through the outer pipe for example) and several inches short at the dryer end. Cut a 4" hole through a 6" elbow and attach near outside exhaust end. [this is the tricky part, cutting a hole for a cylinder (duct) in a curving cylinder (elbow)] Attach 6" fan to the open end of the elbow. Blow air down the 6" pipe from the exhaust end toward the dryer when the dryer is running. You'll at least reclaim some of the heat. You might need to make provision to collect any resulting condensation. (As evaporation is a cooling process, condensation is a heating process, the more condensation the more heat you've recaptured).


fan
heat / ---\/--- /
[ /\ ---------------------------/ \/ /
[-----------------------------------------------------------
dryer ->dryer vent -> exit-->
[-----------------------------------------------------------
[ \/ -------------------------------------/
heat

Bob
Jun 23, 2009 2:40 PM
Greggr
Clothes Dryer Heat Exchange
Simple physics makes recovering heat from a dryer vent more complicated that it seems at first. Dryer exhaust contains moisture and lint as well as heat. If heat is removed from the exhaust the ability of the air to retain the same amount of moisture is also lost. Think of sweat on the inside of the dryer vent or inside the heat exchanger just as the outside of a cold pipe sweats on a hot humid day. Now add lint, washing detergents, and residual dirt. This is a potential fire hazard with a hot dryer exhaust. There were heat recovery devices sold in the 1970's for dryers and most of them were removed from the market for this reason.

For the same reason venting a dryer into a home isn't a good idea. Imagine the clothes moisture now condensing inside the walls and ceiling of a home viola! MOLD.

A better solution might be to experiment with using a larger air volume and less heat to dry clothes but this will create negative pressure when it is exhausted outside.

Then there's the Amish solution. Hang your clothes outside to dry year 'round and be patient. As long as there's no rain or snow they will slowly freeze dry even in the dead of winter. Just requires some vigilance and patience.
 
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