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Old 06-19-10, 10:14 AM   #31
AC_Hacker
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Default We may have reached 'lift-off'...

Regarding whether to use HRV (sensible heat recovery only) or ERV (sensible + latent heat recovery) I came across the above graphic that spells it out...

Quote:
Originally Posted by Xringer View Post
I saw some HRV units on Ebay in the $450 range. Looked up the maker and found this HRV Airiva Heat Recovery Ventilator.
Interesting that it uses a Polypropylene core...


They show the core in the video, it looks to be the same kind of material that political yard signs are made of, cut into 10 to 12 inch squares, and glued together with the air channels in an 'alternating' orientation.


Since building the core seems to be the biggest snag in making a DIY HRV, we may have reached 'lift-off'.

DaoX,
A 90% or greater HRV is very difficult to achieve, the only one I have seen is an 'enthalpy wheel' design.

http://www.drirotors.com/pdf/article..._ac_wheels.pdf

http://platinum.ts.odu.edu/Apps/FAAU...enFileResource

This ERV?s For You - Feature Articles - Extra Edition - Air Conditioning, Heating & Refrigeration NEWS

Quote:
Enthalpy wheels and permeable (or enthalpic) plates recover temperature and humidity. Enthalpy wheels are the most popular and effective technology for commercial applications, particularly where outdoor air is a source of humidity and indoor humidity must be controlled.

In an enthalpy wheel, as the heat exchanger rotates from one airstream to the other, it transfers water molecules from the wetter to the drier side. In summer, the cool, dry surfaces of the heat exchanger strip heat and moisture from the entering outside air. In winter, those same, now relatively warm and moist surfaces heat and humidify the ventilation air.

In an enthalpic plate, water molecules are allowed to move through a membrane to transfer to the opposing airstream. Sharing some of the characteristics of enthalpy wheels, they generally are less efficient at transferring humidity and are more widely used in residential applications where outside air is a smaller percentage of the load.
Also, I came across a Ventilating Industry Test Proceedure used for certifying ERVs. May supply some interesting ideas for makers:

http://web.archive.org/web/200708201...on+30sep05.pdf

...and here's a Certified Product Directory, with efficiency ratings of various tested HRVs:

http://www.hvi.org/assets/pdfs/CPD/H...01June2010.pdf


-AC_Hacker

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Last edited by AC_Hacker; 06-19-10 at 11:43 AM.. Reason: Clarifying PIX...
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Old 06-20-10, 02:03 AM   #32
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Coroplas sheets? Coroplast Is there enough heat transfer??
It's plastic.. Or is it some special heat-conductive coroplas?
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Old 06-21-10, 01:17 AM   #33
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Quote:
Originally Posted by Xringer View Post
Coroplas sheets? Coroplast Is there enough heat transfer??
It's plastic.. Or is it some special heat-conductive coroplas?
I guess that more research and/or some experimenting would be in order here.

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Old 06-21-10, 11:21 AM   #34
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I guess it must have some thermal conductivity, since people have made solar collectors and PV coolers out of it.. Since it's hard to glue water connections on the ends, it's more trouble than it's worth.. But for air? That sure looks easy..

I'll try some DIYer testing.

It's not a great conductor, but it works. I held some Blue coroplas in the sun for about 45 seconds.
It got up to 126 F on top, and the bottom side zoomed right up to 113 F.
It's about 86 is the shade outside and my cedar deck is about 140!

It cools off very quickly in the shade, so it's got some good heat transfer characteristics..

My test strip was about 2"x15" with the holes running the long 15" path.
I'll bet it would conduct heat (top to bottom) better if I sealed the end holes
off with tape. Trapping the hot air (140?) inside.

Last edited by Xringer; 06-21-10 at 11:41 AM..
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Old 06-22-10, 04:34 AM   #35
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I put those coroplast core pics up in the heat exchanger thread on the local builders' forum and they said that it can be done, but in order to extract a useful amount of heat it would have to be very big. Instead of glueing sheets of perpendicular coroplast it would be better to have them go in one direction with spacers in between, then there is only one layer of plastic for the heat to go through, and it could be made into a countercurrent set-up (one direction inside the coroplast sheets, the other between them). But it would still have to be big.

IMO the ribs in the metal core help transfer heat by increasing area, but this probably doesn't work for plastic. It will however increase the strength, so there won't be a problem if the two air streams are at different pressures.

If only they made "corocopper" at a similar price...

EDIT: Someone proposed stacking a few sheet of coroplast parallel-wise and somehow plumbing it so that intake air and exhaust air go in different directions in every other tunnel. Then the ribs also transfer heat and get a much larger (at least 2x) area. Getting it hooked up would be terribly tedious, but it may be worth a try.

I've got some scrap coroplast, but it's 5mm thick. To maximize surface area I'd need the 3mm, or even 2mm, variety. That's going to be hard to work with. Then find some heat sink glue that will stick to plastic?

Last edited by Piwoslaw; 06-22-10 at 06:36 AM..
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Old 06-22-10, 07:32 AM   #36
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I've used Coloplas sheets to make RC model airplanes and I've read there is a coating
on the surface that makes if very-very difficult to glue to.. (Or even paint).

SPA3D pictures by Xringer - Photobucket

I've never even tried to glue anything to it. It's slick stuff..
There is a process called 'flashing', where you lightly pass a propane torch over
the surface to burn away the coating, without (maybe) burning the plastic..
IIRC, that was a bit difficult for me.
RC Airplane/Coroplast - Wikibooks, collection of open-content textbooks

When I have painted Coroplas, I used paint made just for plastic, PVC etc.
Krylon Fusion, supposedly bonds to the molecules of plastic surface being painted.
But it didn't stick to Coroplas very well. I could easily remove it using a fingernail..

Easy stuff to cut, but, not very easy to glue.. For making an exchanger 'X' stack,
I would try a very small shot of spray glue between sheet layers. Just a mist of Duro All-Purpose Spray Adhesive.
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Old 06-22-10, 09:19 AM   #37
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I don't know about polystyrene and polycarbonate, but I remember someone telling me that polypropylene doesn't react with anything, so it's almost impossible to paint or glue.

Here's some info from EcoModder:
Coroplast Kammback: joining or bending?

Now that I think about it, the sheets do not need to be firmly glued. They can be bound together, maybe also pressed, so only a layer of thermal paste is needed.
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Old 06-23-10, 03:00 AM   #38
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Default corocopper

Quote:
Originally Posted by Piwoslaw View Post
If only they made "corocopper" at a similar price...
On the company website. it does say that the physical properties of the material can be modified prior to the extrusion process, implying that the company is interested in working with customers in that manner,

I sent an email to the company inquiring about thermal enhancing additives, but haven't heard back yet.

I will post if & when I hear something.

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Old 06-23-10, 08:47 AM   #39
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I wonder how well a very small coro-core would work, as a test bed?
Maybe 6" x 6" ??
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Old 06-23-10, 02:14 PM   #40
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Quote:
Originally Posted by Xringer View Post
I wonder how well a very small coro-core would work, as a test bed?
Maybe 6" x 6" ??
I think this would be the perfect place to start...

-AC_Hacker

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