I just had this idea after reading conserve clothes dryer heat. Instead of venting all the heat from the dryer outside, how about using a heat exchanger to collect some of the heat and put it back into the dryer? This would dramatically reduce the amount of energy wasted. The advantage of this idea over the idea above is that the system could be completely built into the dryer itself, requiring no modification to the house.

The hot air from the dryer would blow through one side of the heat exchanging unit. The intake to the dryer would simply draw air through the other side of the heat exchanger. It doesn't have to be a super-efficient exchanger, any increase in efficiency will be an improvement over a traditional dryer. The exchanger should be designed to be easy to open and clean so you can remove the lint buildup.

As the hot moist air is cooled in the exchanger, some of the moisture in it will condense back into water. This will have to be removed. Fortunately, dryers are usually placed right next to a washer that already requires a drain. So the dryer could simply use a small pump to pump the condensed water up to and out the washer drain.

Instead of building it directly inside the dryer, it might be good to make it a separate unit that sits behind or beside the dryer. It could be designed as an optional item that the consumer could pass on if he/she doesn't have enough space for it. This would also enable the manufacturer to make one exchanger fit different dryers or, conversely, make different exchangers to fit one dryer. That way, the consumer could select a set up to fit their needs.

What do you think of this idea or comment?
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