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Old 01-03-12, 11:15 AM   #181
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Quote:
Originally Posted by Student 07 View Post
How big is the coroplast that he is using for his heat exchanger? It seems logical that more surface area in a heat exchanger will increase efficiency; however, I think all those turns are causing the problems.
I think the coroplast for his HX attempt was about 3' x 1'. The idea was very clever, but the resistance to flow was too high.

Quote:
Originally Posted by Student 07 View Post
The vertical pipe heat exchanger is great. It seems very similar in principal to an evacuated tube solar collector.
He is having trouble getting a significant amount of heat into and out of his heat pipe HX. The fins he put on were not doing the job.

Quote:
Originally Posted by Student 07 View Post
I found this heat exchanger, which is kind of different, so I thought I would post it for discussion.
One name that is given to units like this is "active HRV". I have seen units similar to this being marketed in Europe (where the cost of energy is 2X what ours is, and the effort being put into energy efficient designs is also 2X). These units are sometimes referred to as 'combi units'.


Here's a link to specifications on one unit that is an HRV, Water heater, solar assisted, and apparently a home heater, too (assuming uber insulation).

I really like the Thermal Air concept.

-AC_Hacker

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Old 01-03-12, 12:20 PM   #182
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Hi,
I just got off the phone with a representative of Thermal Air. The company is in Florida. The HRVs are manufactured in Canada. They are kind of spendy at $2,800.

One thing he pointed out which I kind of liked was that since it has two fans it is possible to adjust the speed of each independantly. Since most homes aren't 100% air tight and have a little leakage, some people turn down the exhaust speed and turn up the incoming fresh air speed a little.

This provides a little positive pressure to overcome any leaks in the house envelope. I wouldn't want to set these too far out of balance, because it would only waste energy; however, IMHO it is better to have a little positive pressure instead of a negative pressure, which would only suck in unconditioned air.

Another reason I like these is that a standard HRV is about 80% efficient; where as, the thermal air has a COP of 3.9 and an EER of 7.1. I know it would still use more energy than a standard HRV, but a standard HRV will blow cool fresh air into the house during winter. The heat pump HRV will blow warm fresh air in the winter, and cool fresh air in the summer. The heat it blows into the house would "lighten the load" for your primary heating system. The simplicity of this design makes it a good candidate for a hack.

AC: that Combi 185 is great. Although it is a much more complcated system it is much better. Using a Heat exchanger with the heat pump allows the heat pump to work less: that in itself makes it a better option than the Thermal Air. But, it also produces ~80 gl of hot water per day by working as an ASHP. I am sure they have it balanced out to where it doesn't take more heat out of the house than what it is supplying to the house, at least in the winter, in the summer this would work great.

I really wish our country would get with the program, great products are being made, but not in our country and we can't even import them. The Combi 185 uses 220V since it is made for the German market. It would be possible to use a transformer to step up our 110v to 220v; however, the transformer would provide 220v @60hz (in the states) and the machine is designed for 220v @50hz.

It is a very interesting time to be following these new inventions. And I am sure it is only a matter of time before they show up on our shores.
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Old 01-03-12, 12:56 PM   #183
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With a pressurized house, you are pushing warm/moist air out your leaky path. There is a possibility of moisture build up and mold growth. Balancing them as much as possible would probably be better.
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Old 01-04-12, 09:51 PM   #184
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"This provides a little positive pressure to overcome any leaks in the house envelope. I wouldn't want to set these too far out of balance, because it would only waste energy; however, IMHO it is better to have a little positive pressure instead of a negative pressure, which would only suck in unconditioned air."

If the pressure isn't balanced, you want negative pressure in the winter and positive pressure in the summer. This is because the dew point inside the house is more likely to condense inside leaky areas going outside during the winter. In the summer the dew point on a hot day is usually above the temperature that is inside so a positive pressure is a good idea in this case.
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Old 01-05-12, 12:50 AM   #185
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These are all really good comments.

A small dehumidifier has all of the components to make one of these things...

Except that you'd want more efficient fans.

This would be a really interesting hack, and pretty easy, too.

There's just one thing about these units, they supply a VERY LARGE amount of air. I looked at the Combi, thinking that it would fit so nicely into a cozy, compact, space-efficient European house, then I calculated how much space it could actually ventilate, and saw that it could supply the ventilation needs for a 3500 sq. ft. house... and that's with a (quite small) 350 watt compressor, too. To be clear, that was on high speed, but that's a lot of air...

I haven't written the idea of it off, not yet... I did see a tiny cube refrigerator today at Goodwill that had a 125 watt compressor, for $25. Now that's more my size... and I have a couple of very small HXs left over from my first GSHP project...

Oh the temptation!

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Old 01-05-12, 12:10 PM   #186
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A few days ago, I went over to Mike's (AKA: Mad scientist Guy) to do some testing on the coroplast squares I bought a while back.


Here's a photo of the test setup:


You can see the heater blowing into the air input of the centrifugal fan at "A".

I put some heavy stuff on top of the coroplast to make sure that it was in good contact.

We ran quite a few tests, here is some of the non-conclusive data we recorded:

Ambient temperature of testing lab (AKA: Mike's garage) = 53F

Heated airflow was from A to A'

Recovered airflow was from B to B'

No heat:
  • A = 56.2F
  • A' = 56.0F
  • B = 52.3F
  • B' = 54.5F

After several minutes of heat (Heater drew 1092 watts):
  • A = 101.4F
  • A' = 83.8F
  • B = 54.7F
  • B' = 77.5F

Increased Fan (B, B') voltage to 12V
  • A = 102.2F
  • A' = 80F
  • B = 55.8F
  • B' = 75.9F

Reduced fan (B, B') voltage to 7.68v
  • A = 144F
  • A' = 86F
  • B = 55.9F
  • B' = 78.4F

THOUGHTS:
  • It does work, but the results are not stunning.
  • It works better than no HRV.
  • The low numbers were most likely affected adversely because the core was in ambient (low temperature) environment.
  • It really make me want to see how a counter-flow coroplast HX would work.
  • We need to capture data that would give us an efficiency measurement.

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Old 01-05-12, 12:38 PM   #187
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Default Mike Does Weld Test on Coroplast...

Mike came across this patent on making coroplast HRV cores. and shortly after, Mike sent me his initial results of trying to weld coroplast (polyethylene)...


Quote:
Looks like you can weld coroplast just fine.
I used a soldering iron with the temperature dialed down.
Joints are plenty strong.
With a small backing plate to mash against, they'll probably be sufficiently pretty and not so disruptive
to air flow.
I was gonna make a tweezer-like heater, but doesn't look necessary.


Got the coroplast all cut. Thought I'd wait till I can open the door tomorrow
and not gas myself with plastic fumes.

Another thought...
What if I built two HRV's with only one fan each.
One fan blows out, the other blows in.
Put 'em in different rooms.
Set the blows out fan to 90% speed.
Dynamically adjust the fan speed on the other one to
make the net internal pressure zero.

Think that gets you about twice the air flow for the same
fan energy...depends on a tight house...and ventilation in two
rooms...and easier construction.

I think I know how to do the differential pressure measurement.

mike
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Old 01-05-12, 02:34 PM   #188
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Nice numbers, AC and Mike

Over at the Polish builders forum someone posted this:




Apparently, it is a PP coroplast HX, produced by Canadian Greentek, which claims its efficiency matches that of other (metal) crossflow heat exchangers.
From the images above it appears that the HX is not made of squares of coroplast rotated 90, but instead the squares have spacers between them. This has two advantages: lower pumping losses (on one side) and single walls (instead of double) between airflow streams. Could you guys try a test with spacers?
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Old 01-05-12, 08:19 PM   #189
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Default Fantastic Coloroplastic

Mike has been at it again:

Quote:
OK, here's what I got...








Results
Stale hot air in 98.6F
Stale hot air out 67.8F
Fresh cold air in 66.2F
Fresh cold air out 79.0

Air flow on the order of 200 linear feet/minute >> 20CFM
Rough estimate cause flow varies all over the map depending on the position in the output stream.
Pressure in the coroplast tube was about 0.05inches of water.

There are leaks and thermocouple position issues.
But it looks promising enough to finish it.


deltaT inside/outside = 15.4F
deltaT outgoing air/incoming air = 5.8F.
Those are pretty good numbers. But the delta is small and the measurement uncertainty
is a big part of that.

After my nap, I think I'll move the second fan inside, fix the leaks, weld it together and tilt it downward
so water can run out.

Are we having fun yet?
mike
Attached Thumbnails
hrv-hillbilly-01-jpg   hrv-hillbilly-02-jpg   hrv-hillbilly-03-jpg   hrv-hillbilly-04-jpg   hrv-hillbilly-05-jpg  

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Old 01-05-12, 10:40 PM   #190
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The 'stale air' temp drop improved to 30 deg F., but the 'incoming air' DeltaT got worse. Why would that be? Previous to that the DeltaT was approx. 20 degF on both. Go figure.

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