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Old 06-26-10, 07:30 AM   #51
mrd
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Commercial codes are more stringent, and it's easy to see why with ventilation standards. Commercial settings will see many more people in a given area, and the rate may be increased to reduce the incidence of airborne infections spreading.

I believe most of the US residential code now falls under IRC (International Residential Code) and the most recent version requires 0.35ACH or 15CFM per occupant. It also requires 100CFM intermittent or 25CFM continuous from kitchens and 50CFM intermittent/20CFM continuous from bathrooms.

ASHRAE 62.2 is residential ventilation industry standard, and I believe the latest version stipulates 7.5CFM/occupant + 1CFM/100sqft (Environmental Energy Technologies Division News)

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Old 06-28-10, 07:05 PM   #52
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Default 1 Cubic Foot Polypropylene DIY HRV Core...

(NOTE: My original post said 'polyethylene', my error. I should have said 'polypropylene' and have corrected this post.)

Today, I picked up my black plastic sign-board material.


I explained to them that I was going to stack the 12" square pieces and that I wanted to end up with with a 1 foot cubed stack. Since the material is 4mm thick, it turned out that I required about 72 pieces, which worked out to about two and a third 4' x 8' pieces to make one heat exchanger.

I was a bit off on the prices in my previous post, but the Corex charge for black was $15.25 per 4 x 8 sheet, and the cutting charge was $15, so the overall cost to me was $45.50. They had a bit of scrap laying about, so they didn't charge for it.

Since I'm trying to build a $700 Energy Recovery Ventilator for far less, $45.50 cost for the core seems reasonable, but I do think it could be done for less.

When I was stacking the 12" square sheets (alternating the orientation of each layer) , I noticed that most of the sheets had a slight 'cup' to each sheet, so I pit them all 'cup-side' down. My resulting pile had less 'spring' than my original, randomly oriented pile, so that should mean that the sheets are in closer contact.


I have done some searching for polypropylene cement, and it doesn't seem to exist. So, it looks like some kind of pressure arrangement will be the way to go. If anyone has any other ideas, I'm all ears. I suspect that even with fiters, periodic cleaning of the core will be required.


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Old 06-28-10, 09:22 PM   #53
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Hopefully pressure alone will be enough to maintain isolation of the two air streams. If not, 3M spray adhesive #72 says it bonds polypropylene. Not sure if it would be safe for household air, once adhered. The MSDS shows hazards, but I don't know if that's only while in aerosol form, or what.
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Old 06-29-10, 07:20 AM   #54
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I guess I'd try to use some material that has a decent heat transfer rating.
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Old 06-29-10, 08:43 AM   #55
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As I said above, "I would try a very small shot of spray glue between sheet layers.
Just a mist of Duro All-Purpose Spray Adhesive."
@Local hardware stores.
In the directions, they say to spray 'one surface', so you can re-posistion.
If you spray Both surfaces, it's an Instant bond. Faster than super glue!


Anyways, the idea being, use very-very little adhesive. One molecule thick if possible..
That should give you the best possible coro-to-coro contact.

I've put off cutting my coroplas, since I've been so dang busy with car-recall, medical, dental, basement repairs, & FiOs problems..

Now, I just might wait to see how your DIY OFC (One Foot Cube) works out,
before I start hacking my little 8" Cube..
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Old 06-29-10, 01:15 PM   #56
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Default 8 inch cube

Quote:
Originally Posted by Xringer View Post
Now, I just might wait to see how your DIY OFC (One Foot Cube) works out, before I start hacking my little 8" Cube..
I've been pouring over more literature, looking at cross-flow Heat Recovery Ventilators and their reported efficiencies. Here are some HRV's that use almost identical design concepts and are almost identical in size.


NOTE:
The Panasonic is different because it is a design meant for one modest room, and is designed to fit between ceiling joist spaces. This is of special interest to me because I have limited the amount of my house that I heat and cool.
(info here)
I think the brand-to-brand efficiencies should be cautiously compared because there are so many ways to 'enhance' test results, with the lower numbers shown probably being closer to reality.

But the variations within a brand are probably a reliable indicator. In that light I find it interesting that the lower the CFM, the higher the efficiency.

My house is pretty small to begin with, and I'm not heating/cooling the whole thing, so my heating/cooling bills have been laughably small. But, eco-minded tightwad such as I am, I'm constantly trying to beat it down even smaller.

So most of the HRV's on the chart above are meant to be used with a house of 1600 feet and above (up to 3500 sq ft) , which is how the American market usually lives. But my conditioned space is only about 600 sq ft, so with the exception of the Panasonic, even on the lowest setting, the HRV's are changing out air at twice the optimum rate for my house-space... I wouldn't even be able turn it down... only off.

I looked at the scale drawing of the Panasonic, in particular the core, and did a graphic divide across the length dimension and came up with the size of the core being 5.5 inches square. Pretty darn small. But the efficiency is pretty darn average...

Using the criteria supplied by mrd in a previous post,

Quote:
ASHRAE 62.2 is residential ventilation industry standard, and I believe the latest version stipulates 7.5CFM/occupant + 1CFM/100sqft
My house is small (600 sq ft) and single occupancy, so:

7.5CFM + 6CFM = 13.5CFM = minimum ventilation.

So I'm thinking that the core I am copying is really appropriate for a much bigger house (4x to 10x bigger), but if I am very careful in the selection of my fans and achieve a CFM of 15CFM minimum, my efficiency should be pretty favorable.

So Xringer depending on your conditioned house volume, your little 8 inch cube may not be so little after all...

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Old 06-29-10, 02:42 PM   #57
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Default What??

Am I reading that right? The Airiva cores are the best? Better than Aluminum?
How the heck can plastic be better than aluminum??

My off-hand guess on for the Panasonic cube was 4.5"x4.5"xn"..

So, maybe I should see if I find enough coro to make a box too..
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Old 06-29-10, 02:59 PM   #58
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Quote:
Originally Posted by Xringer View Post
Am I reading that right? The Airiva cores are the best?
Ariva cores might be the best, then again their test results might be the most 'enhanced'. You really can't compare unless one lab did all the testing under identical conditions and also did the reporting, treating all data by the same criteria.

Don't be fooled by numbers.

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Old 06-29-10, 07:21 PM   #59
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Did that chart come from the Airiva website?

Yeah, maybe I better wait until you have done some testing..
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Old 06-29-10, 08:41 PM   #60
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Default HVR Links of Interest...

HVR links of interest:

Here's one from UK that is a cointer-flow and claims 80% efficiency. 80 percent seems to be a suspiciously round number to me. Not much detail pictured, but I'd guess it to be a cross-flow that has been flattened out like a squashed "X" and called a cross-flow.
http://www.fahrenergy.co.uk/FAHR_Installation.pdf

Here's a paper that is done by the University of South Dakota. Note the efficiency numbers there. They aren't trying to sell anything.
http://www.ag.ndsu.edu/pubs/ageng/structu/ae1393.pdf

Here's a FAQ done by the University of Minnesota.
Common Questions about Heat and Energy Recovery Ventilators

Here's a Guy named Marsen who installed one (Airiva) in his workshop in Maine. Well documented. Curiously, he never comments on the quality of the air after the installation.
Guy Marsden - Installing a heat recovery ventilation system in my workshop

Here's a paper that focuses on using the ERV in primarily hot humid climates.
http://www.advancedenergy.org/buildi...lation/erv.pdf

-AC_Hacker


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