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Old 02-28-10, 05:12 PM   #7
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Default ERV, HRV, de-humidifier hack...

Originally Posted by Piwoslaw View Post
Any ideas on how to go about making a more or less efficient (60+%) heat exchanger? Pictures/drawings of the insides of different types would be nice, as would a cost vs. efficiency comparison.

Here's a URL for a DIY Heat Recovery Ventilator:

Make - Volume 18

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The photos I see of Heat Recovery Ventilators usually use a cross-flow cell, with the air paths crossing at a 90 degree angle. They usually have an efficiency of about 60% to 70%. I have seen write-ups of experiments done on cells that had a 180 degree cross-flow and the efficiency was increased to some degree (maybe 5% to 8%). Sorry, but I didn't book mark the studies.

There's also a wheel type that claims efficiency up to 90%. Here's an example:

Heat Exchangers Energy Recovery Ventilator Air

Additionally, there's a heat pipe HRV, but I don't see very many Internet references to that type, but here is one:

Computer Environment, Inc. Website

Here's a page with a pretty good overview of the topic: Energy Recovery Ventilator

It looks like the need for and success of a HRV/ERV are based on having a very tight house...

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Regarding the 90 degree cross-flow types, if my understanding is correct, there are Heat Recovery Ventilators (HRV) and then there are Energy Recovery Ventilators (ERV), the difference being that the ERV uses a water permeable membrane to allow outgoing air condensed moisture to be used to re-humidify the incoming air.

I have seen a page that represented various Chinese companies, that listed just the cross-flow cells of various sizes. I tried to locate that URL for this post but was not able to find the page I remembered. But I'm pretty sure that the cells for most, if not all of the ERVs made in the US and probably also Europe are manufactured in China, and put into locally made boxes. I have seen the completed units coming from China:


Here also

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In this photo is the de-humidifier someone left on my front porch, minus the plastic & steel covers.

The way it works is air is drawn through the evaporator coils, where it is chilled and frost forms and then passes through the condenser coils, where the air is warmed back up. There is a sensor on the evaporator coil and when it senses that the evaporator is likely to be full of frost, the compressor stops for a few minutes, the frost melts to water that goes into a bucket.

But the evaporator core and the condenser core are made separately, and are attached by sheet metal screws. With a little bit of luck and some very gentle handling, the cores can be separated, with the refrigeration lines intact. Then incoming air could be made to pass through an air filter and then through the condenser (hot) and into the house, while outgoing air would be made to pass through an air filter and then through the evaporator (cold) and out to the world.

Thus, the hacked de-humidifier would extract heat from the air that is exiting the house, and then return that heat to the air that is entering the house.

This is a hack that is begging to be done!


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Last edited by AC_Hacker; 02-28-10 at 05:18 PM..
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