I was thinking of using something like a hair-dryer or a weak heat gun
on the warm air input 'port' and a cool air fan on the 'heat-pick-up' port.

Maybe let the warmed-up air blow out on a strip of copper,
so the temperature can be easily measured with the IR Pistola.?.

I'll have to check my stock of 4mm coroplas and see if there is enough
available to make a small X-block exchanger.
~
Yeah, I have some left-over sheets of white, blue and yellow,
and two larger un-cut sheets of yellow, if it comes to that..

Yeah, it looks like I could use it all and make an 8x8x8 core.. :rolleyes:

Wow, I was just looking at the specs for the Airiva units and they are using a 12x12 core that's 11.25" tall..
http://www.suncourt.com/Images/HE150SS-1106.jpg
It's 74 12x12 (4mm thick) sheets..

Maybe a little DIY 8x8x8 core could be used in a practical application after
testing is complete.. (If it has good heat transfer)..

How about use a pair of car radiators and a pump to circulate a water/coolant mixture through it?

Aren't you the guy that built a data logger? This would be a perfect application for it.


And, I think that a thermistor just hanging in the air stream would be great. Thermistors are pretty quick to respond and most of them have a midrange close to the temperatures you're working with.

You're going to have to do some research to be able to calculate efficiency, but with a data logger and thermistor, you could at least rank various test configurations. That would be pretty useful in itself.

I'm trying to build a hydronic floor that doesn't weigh a ton (literally), and I tried testing several different materials using a data logger and a ranking scheme, and I really learned a lot. I'm still not ready to build, but I know what NOT to build.

-AC_Hacker

I have the hardware, but not the software.. And I'm getting too old to program.. :(

I do have a couple of probe type thermometers that should work,
and if the core seems like it can handle the job,
I could build a fan case and give the core a practical use test.
Even a little 8" core might be enough to provide a bit of fresh air to the basement..
Too bad I don't have more coroplas, I could build the box from it..

Spare time is the problem these days. Right now, it's in short supply..
The Honey-Do list never seems to shorten..

Yeah, hardening of the brain, I guess...

If your data logger will output a comma-separated or tab-separated or space-separated text file, you could pick it up in Excel and use Excel's graphing capabilities.

Don't know if you know Excel, but it's far easier than traditional programming.

That's what I did with mine. Worked good enough for my purposes.

-AC_Hacker

Calculating Air Changes Per Hour...
 

As long as active minds & hands are involved with DIY HRV/ERV, I thought it would be a good idea to post some links regarding HVAC industry approved levels of room air replacement. They boil it down to Air Changes per Hour (AKA: ACH). This takes into consideration the Cubic Feet Per Minute, and also the volume of the room.

Here's a link to a page that clearly explains how to do the claculation.


And here is a link to a PDF that has the industry-approved air change rates, and also the formulas used to calculate the air change rate. (* download & save *).

Interesting to note that the Passive House standard is different and lower, and has a per-person standard or a per-area standard.

Early Passive Houses were able to hit the stringent heat-retention targets that were saught, but people complained that the Passive Houses were "stuffy". After rentless Germanic testing the following ventilating level was determined:

• Passive House per-person = 15 CFM per person.
• Passive House per-area = 15 CFM per 377 square feet floor area.

This works out to 0.3 ACH for a house. This works out to 1/20 to 1/67 of the recommended ASHRE standards. Interesting, huh?

I know that the Americans pretty much invented the science of air conditioning and ventilating, but the Germans should not be lightly dismissed.

Anyway I read an interview with one of the most prominent European Passive House spokesmen, and the question was raised as to whether or not a HRV would really pay for itself, and he essentially said that you should begin your design with Heat Recovery Ventilating.

I'm sold.

-AC_Hacker

First, do no harm..
 

My wife is printing out pages on the Laser printer. Since it's about 2 feet from me,
I'm getting Ye Olde Laser Air right now.. Stinky! :eek:

So, right now, I'm thinking almost any amount of fresh air, is going to be better than none at all..

If I can build something that brings in some fresh air, without too much loss
of indoor heat (or cool air), it would be an improvement.

If we were talking a very minor improvement, then forget it.
But, if it were a noticeable improvement.?. Might be fun to build.. :)

The standard for house ventilation systems is:

• Fresh air goes into "clean" rooms (bedroom, livingroom),
• Used air gets sucked out of "dirty" rooms (bathroom, kitchen).

Since the "dirty" rooms are getting their air from the rest of the house, in many circumstances those rooms don't even need their own heating/cooling.
As for air flow, I believe the minimum is 0.5 house volumes per hour, the maximum is either 2 or 4 house volumes per hour (don't remember). When replacing more than 2 (or 4) house volumes per hour the heating/cooling/recovery system may not be able to keep up, leading to noticeable drafts and energy loss. Also, the ducts should be sized to keep air speed below 5 m/s to keep noise down.

Coroplast clone...
 

I called a sign-supply shop and ordered some Coroplast, or more correctly the same product made under another name.

There was a difference in price with regard to color...

White was about $13 per 4 ft x 8 ft sheet.

Black was about $17 per 4 ft x 8 ft sheet.

I went with black even though it was a bit more expensive, because I think that carbon is probably the pigment used and is likely to improve thermal transfer.

I bought 2 4x8 sheets. Since I don't have a van or truck, I had them cut into 12" x 12" squares (slightly less because they use a saw and kerf allowances were needed).

There was a small charge for cutting.

I still have the problem of if and how to join the pieces...

-AC_Hacker

Difference in ACH figures...
 

Comparing your figures with ASHRE figures helps explain why the US uses 2 times as much energy per person, compared to Europe!

-AC_Hacker

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)

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.


Best Regards,

-AC_Hacker

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.

I guess I'd try to use some material that has a decent heat transfer rating.

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.. :eek:

Now, I just might wait to see how your DIY OFC (One Foot Cube) works out,
before I start hacking my little 8" Cube..

8 inch 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,

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...

-AC_Hacker

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".. :o

So, maybe I should see if I find enough coro to make a box too.. :)

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.

-AC_Hacker

Did that chart come from the Airiva website?

Yeah, maybe I better wait until you have done some testing.. ;)

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

Duct Sizing (making it quiet)...
 

I'm working out the details of the design now.

From reading product literature, it looks like condensation will be an issue. There seem to be various schemes involving sensors and circuitry and "drying cycles", but for now I'm going to plunge ahead and ignore condensation to see just how big a problem it really is.

Since my realization that I have greatly over-sized my core, I have decided to go with a dual-core design. I'll divide the core stack in two, the cores being in series, with the air passing from one core to the next. This will double the distance over which heat exchange will take place, and should approximate a counter-flow heat exchanger.


So the next design issue will be duct sizing... I recall that Piwoslaw posted this:

There is a wonderful little program called CurveExpert, that is true shareware and does a great job of curve fitting and formula generation.

I tried inputting value tables from HVAC sites, in order to generate an automated formula for you, my reader. Unfortunately my first attempt failed so I found some online calculating pages that will calculate duct sizes from CFM.

Here one for metric

Here's one for US measurements

And here is a table just to double check your results.


The issue here is that if the air in the duct flows too quickly, it goes into turbulent mode and can make a lot of noise. A friend of mine re-did the ductwork in his house and neglected this issue. Silence really is golden.

The ventilation rate I previously calculated was about 15CFM, at least that's what I rounded it up to.

Using the online calculator for US measurements, and using the value of 15 CFM, and using PVC as my duct material, I get a diameter of 2.85 inch ID.


So anything bigger than 2.85 inch will be nice and quiet. Three inch looks to be a winner so long as I keep my runs short. Four inches will just cost me more money and it will require more insulation to be efficient.

Bigger isn't always better.


Regards,

-AC_Hacker

PS: Next is fans

ignore condensation??
 

I've been thinking about how to install a unit, so the core is sitting with
the (filtered) outdoor-air-input (carrying the moist air) at the best angle.

I would want the (moist) air coming into the top of the core, so it will
have gravity (and air pressure) helping push the water droplets down and out of the core.
(Into a drain pan with a hose on the bottom).

The longer water is allowed to sit in those passages, the more likely
that water is going to collect airborne dust particles, pollen & etc.

Once a water droplet filled with particles evaporates, the residue
left from the contaminates can build up and be difficult to remove..

The dew point temperature have been so high these last few weeks,
anything that is cold is instantly wet when left out..

~~
Instead of making more holes in my house, I've been thinking of building
my unit like a window AC. (Custom sized for my windows).
So, it could be installed easily and easily pulled out to be tweaked or cleaned.
The drain hose would just water the flowers below the window..

I like the idea, but how am I going to get that good drain angle with a window rig?? Humm...

I've read that centrifugal or crossflow fans are most efficient for household ventilation. Also, they should be DC powered:

• AC powered fans "hum" at the grid's frequency and may cause the whole installation to vibrate,
• AC fans can cause electromechanical interference,
• DC can be easily tied into an RE or back-up power installation.

When HRV is not an afterthought (a real game changer)
 

I came across information about a Passivhaus (AKA: Passive House) that was built in Illinois.

• Here is a link to an HTML site.
• Here is a downloadable PDF.

The house uses an HRV that is almost the size of a furnace, but uses only a tiny fraction of the energy (NOTE: there is an integrated 1 kWatt resistance heater for severe occasions).


This is the first time I have seen the kind of serious HRV that a Passivhaus would utilize. This really alters the definition of HRV... Now all the others seem like toys.

In this particular project, the Westaflex WAC 250 HRV utilizes a 100 foot ling, 8 inch diameter buried earth tube. The WAC 250 unit has sensors and dampers and can switch the incoming air between earth tube air or straight outside air as the situation demands (wow!).

This PDF has the picture shown below


It looks like there is a real-deal counterflow heat exchanger at the heart of it all (or could it be a dual-crossflow?).

I think I finally understand why someone would build a house around a HRV, especially if it was one of these.


Regards,

-AC_Hacker

Wow, that is sweet lol. Thanks for posting that info. I've seen that house before and love it. I didn't know of the monster HRV in it though.

Fans...
 

Yes, quite right.

At this point, since my application is so undemanding, I'm considering a pair of 3 inch fans.


But I'm also looking into cross flow fans (AKA: tangential flow).


I also investigated Pulse Width Modulated fans...


...but the energy used by the above fans is so small that energy savings would be very small.


Regards,

-AC_Hacker

Windows.air.exchange
 

Since I'm thinking small (and no new holes in the walls), I looked around and found this.
Amazon.com: Bionaire BAP336-U EverFresh Air Exchange System: Kitchen & Dining

I'm not sure how this works, and the from factor is 'out there',
but it shows that my idea of a DIY window mounted unit, wasn't very original.

But that's not going to stop me from trying to figure out how to make one.. :)

"Fresh Air" Mini-Split
 

I noticed that the latest Mini Splits are featuring "Fresh Air".

Search for the "Fresh Air" term, download the appropriate PDF, you might be able to do a "Fresh Air" hack on yours.

-AC_Hacker

No way my wife is going to let me touch that Sanyo! She loves that thing!

Plus, there is no venting as you well know.. Only an Ion generator (whatever that does).

Your dual core diagram above has given me a clue about core mounting
(in a window unit) that will allow the core to drain..

German Counterflow Heat Exchanger...
 

A design that is different from the cross-flow types.


Klingenburg GmbH - Energy Recovery - Counterflow plate heat exchanger

Appears to be very similar to the core used in the Westaflex mentioned earlier.

Don't overlook this link, it has lots of interesting literature.

Here's a grab from one of the the documents above.


The company appears to be in the business of selling high efficiency counterflow cores.

Regards,

-Jim

Enthalpy Wheel ERV
 

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

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.

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.

The Coward's Way Out...
 

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.

Hello, welcome to EcoRenovator:)

That's a nice set-up you made.
And pretty cheap for alu and that efficiency.

Links to the informatione PDFs
 

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.

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

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

Watching and learning...
 

Hi AC Hacker, mrd, Piwoslaw et.al. :thumbup:

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

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 :rolleyes:

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