Is There Fool Proof Heat Recovery from a Clothes Dryer using an Air-to-Air Heat Exchanger?
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 industrial strength 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 handyman 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.
An air-air heat exchange mechanism works by blowing the exhaust 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 through the heat exchanger surfaces 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 droughts in the house 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 but safety switches would need to be added just in case lent built up anywhere in the air flow pathway. You would need to check the filter of the air-to-air heat exchanger each time you used the drier, just as you do with the drier lint collector already. But, as a safeguard, you would want to 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 heat exchange application, you would from time to time, 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 recommended 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.
If you managed to find an appropriate air-to-air heat exchanger for $500.00 , one which was 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 than just $500.00 dollars.
Probably, right now, there is an inventor out there, somewhere, busy putting a dryer together that already has an Air-to-Air heat exchanger built right into the machine.