DIY ventilation heat exchanger

[AC_Hacker]

I came across this very interesting unit last year and had forgotten the URL. I bumbled into it again and decided to post the info before it sinks beneath the waves again. It is amongst the most interesting designs I have come across.

This is an Enthalpy Wheel ERV with a claimed maximum efficiency of 96%, (real efficiency is likely in the 80% range). This is pretty good, because cross-flow HRVs have a real efficiency close to 60%.

From looking at the documents below, it would not be a casual undertaking to DIY an enthalpy wheel HRV.

Here's a Link to the User Manual.

Here's a link to the Installation Manual.

Link to Dealer Brochure

Here's a link to the company.

They seem to run about $1600 bucks, with one currently on ebay at $1,270 OBO.

Regards,

-AC_Hacker

[mrd]

AC_Hacker, I haven't seen you mention static pressure. You'll need to determine the static pressure your fan(s) will be presented, then cross reference that value to the fan specs to determine if the fan will meet your airflow needs.

Aside from any ducting, the core itself will cause a pressure drop. Unlike the ducting, there isn't any way to estimate this pressure drop without taking measurements. If you currently have a fan with known specs, you could set it up and take airflow or pressure measurements to establish an estimate. Otherwise, you could try finding static pressure drop ratings for commercial ERVs and use that as a base estimate.

[Piwoslaw]

The good thing about a cheap homemade core is that you can always add another one parallel to the first, doubling the heat exchange surface area and halving the pressure drop. And the addition requires less space than the original box since it doesn't need it's own fans, filters, etc.

[AC_Hacker]

Originally Posted by mrd

AC_Hacker, I haven't seen you mention static pressure. You'll need to determine the static pressure your fan(s) will be presented, then cross reference that value to the fan specs to determine if the fan will meet your airflow needs...

mrd,

Good thinking.

A friend loaned me a couple of fans (each different) to use for testing. He also loaned me an air velocity measuring transducer & meter. I'm planning to take the coward's way out and make a mock-up out of cardboard and duct tape and test the core at various thicknesses, so as to get some idea what the loss curves would look like.

I also have some samples of 3 inch pipe, and I thought if I measured the pressure drop over three or more lengths, I could get close to a velocity-loss-per-foot factor.

I'm thinking this will give me enough information to size my fans (and core) correctly.

Xringer's idea of making a small window-sized unit is also interesting to me. The up side is that the ducting issue pretty much goes away. The down side is that the HRV has to be optimized to a smaller envelope, and there are sealing issues, which aren't insurmountable, and also one side of the ERV would be exposed to outside air temp.

Pictures & data to come soon...

-AC_Hacker

Interesting. In 1988, I designed a homemade HRV. I used aluminum flashing as the heat exchange medium, and I use plastic lumber to space the plates apart. (Or at least it was the only form of plastic lumber I could find in 1988.)
You can get my “recipe” for the HRV at a website, which also has links to related energy conservation data for houses: The links and narratives are on the top half of the web page. The actual PDF and Word documents are on the bottom half of the web page, which have the HRV diagrams and text.

This forum would not let me post the actual link.
So, if you go to google, and use these search words: homemade hrv Meinert
You should be able to access the google groups webpage with this information. (When I used these search words, the link was about 6 entries down on the displayed page)

The HRV which I made recovered about 70% of the heat from the exhaust air, which made the incoming air a fairly pleasant temperature, even in the dead of winter.

[Piwoslaw]

Hello, welcome to EcoRenovator

That's a nice set-up you made.

In constructing the basic core of the 14-inch-wide exchanger, the
assembly time was about 30 hours and the cost of material was $220,
plus the fan costs.

And pretty cheap for alu and that efficiency.

[AC_Hacker]

dlmeinert,

[NOTE: I finally bit the bullet and joined the Yahoo Group and the PDFs are working, please ignore message below. -AC_Hacker]

[* NOTE #2: I just got the book PDF in, and what a wonderful resource you have shared with us! It would be good to resolve the complicated link-to-group-and-join-etc problem, this info is just too valuable.]

I got this forum to post the link (see below).
However, the links seem to contain invalid PDF files, all the same size.

I am very interested in seeing your PDFs.

You could email me here and we can figure something out.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Originally Posted by dlmeinert

This forum would not let me post the actual link.

Homemade HRV, Jan 2004

1st half of Energy Conservation in Housing (PDF)
(* unable to get valid PDF to download *)

2nd half of Energy Conservation in Housing (PDF)
(* unable to get valid PDF to download *)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

-AC_Hacker

[KiwiMark]

Hi AC Hacker, mrd, Piwoslaw et.al.

Have been reading your exploits with much interest and thought I'd weigh in with my limited knowledge.

I too have been making and experimental HRV using plastic corrugated board (coroplast). Unfortunately, the only board I have lying around the house is 5mm thick so not as fine as a commercial heat exchanger.

The heatex core is approx 10" x 10" x 16" (at a guess... converting from millimeters in my head), layered alternately, and held together with masking tape. Good enough for a prototype.

I made the HRV cabinet out of coroplast as well though it still needs a layer of insulation. Internal cabinet height is size of heatex core across end diagonally and width is 16". The heatex core is placed in the cabinet diamond shape ie. corners towards the top, bottom and ends of cabinet. As the length of the cabinet is longer than height a divider is used to separate the core flows at each end.

The condensate drain is placed in the bottom of the cabinet on the exhaust (to outside) side. This is run off to outside guttering or drain.

Only problem I've had so far is fans. The 4" 12v PC power supply fans don't have enough force to drive air 20+ feet along ducts. Centrifugal fans are recommended for this and I don't have any in the parts bin.

Having worked for a company manufacturing HRVs (with Swedish HeatEx cores) my only regret was I didn't buy one when I had the chance... burnt bridges!

I wait with baited breathe to see how you overcome these issues.

With regards ASHRAE, you really only need to calculate the volume of your home (h x w x d all areas to be vented) and divide by 2 for a modern well-insulated home or divide by 3 for an older air-leaky home. This will give you the cfh (cu. feet per hour) required to exhaust and replace... divide by 60 for cfm. Air should be allowed to flow between rooms by open doors or door vents.

Sorry to waffle on... maybe pictures to follow.

Thanks for reading.
Mark

The Google Groups site has the Word and PDF documents that allow access without sign-in. The Yahoo and Multiply sites add photos and videos, but have some sign-in requirements. That's all I have come up with for websites I can use for free.

Dave Meinert

In the last page of the PDF document for Energy Conservation in Housing (page 161 pdf page, or 153 as I numbered them), I discuss the fan type dilemma, and what I used when I needed to replace a fan. I obtained a Tjernlund duct booster, but had to modify the fan wheel so it could handle the air flow. 120 Volt AC fan.
In the above messages, AC Hacker was able to make a link to my multiply site. (click his link “the actual link” on his message.) On that Multiply site, there is a links option, “Links about insulation data” The third link has my google groups site, and the PDF copies can be accessed on the bottom half of the web page.

Dave Meinert