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Old 01-29-14, 04:54 PM   #431
Fornax
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Quote:
Originally Posted by kostas View Post
Any news about your hrv? Did you get those heat exchangers from recair?
Actually I did order and receive one of those heatexchangers and I did build a new HRV. I have been using it since early october and it is much better than the one I initially build with the aluminium HX-core.
I took a few pictures which I will finaly post here soonish..

In october I collected numbers on temperatures and efficiency but back then the weather was quite warm so the difference in temperature was low giving meaningless numbers. Time for a follow-up indeed :- )

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Old 01-29-14, 05:04 PM   #432
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Great, I'm looking forward to have a look!
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Old 02-06-14, 02:33 PM   #433
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Hi All,

As I told Kostas above I did build a new HRV using a heatexchangercore I
ordered readymade. It's the exact one some commercial brands are using
in their commercial HRV's and the specs look impressive, it wasn't too
expensive either.

I didn't take a lot of pictures and they aren't the best quality I am afraid
but they do tell the story nicely.


Bare cabinet with the core in it, playing with dimensions here.



Here I added a roster in the top left to put a filter on, it's 30x40cm (12"x16").
One of the fans will be internal, like this. I also added the holes to connect
the tubing.



My first HRV didn't have a bypass for when it's hot, I had to remove part of
the plates and block the rest, rather clumsy.
In this one i created a bypass inside the cabinet, this is in the 'open'state.
The two pieces of styrofoam on the fan are used to block it.



Like seen in this picture.



This is the finished product, working.
It is a bit larger than my first one but it is 16" less tall so hanging close to
the ceiling there's still a lot more room underneith.

Then I took some temperature readings inside the cabinet:
Code:
 
FAI   OAO   OAI   FAO    Eff IN  Eff OUT
 T1    T2   T3   T4   
18.3  18.6  22.2  21.8      90%    92%
15.2  15.6  20.2  19.8      92%    92%
16.0  16.4  20.1  19.7      90%    90%
(degrees celcius)
One (luxury) problem I have calculating the efficiency is that the
temperatures are so close to eachother. The middle one is recorded in
the morning when it was freezing a few degrees all night. I get my supply-air
from my crawlspace which acts as a 50m^2 (550SQF) geothermal heating
surface. Also the supply-air is heated a bit while travelling through the tube
in my shed.

With supply-air this warm you could debate wether I even need an HRV... /grin.

After turning off the central heating (20,5C in the evening) at 11PM the next
morning it's still 18,5C in the livingroom and the floor doesn't feel cold (I
added extra insulation underneath it last year and the windows stay closed
now so the bottom half of the livingroom stays warm.) Most of the time we
don't turn up the heat untill after noon.

This plastic HX-core is performing very good, which works fine for me. If your
intake-air is very cold though an HX-core this good creates extra challenges.
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Old 02-06-14, 02:57 PM   #434
kostas
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Good to see some new stuff here
Fornax, I have some doubts about this, though. If you draw the air from the crawl space, you simply recycle it as it comes from your house and not from outside. The fact that it is warm means that you are subtracting air from your home and pushing it back in. I bet you have had no dew inside the case, right?. With no cold air coming from outside there is no reason for condensing the out coming air.... At least that is what those temperatures indicate, inmho.
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Old 02-06-14, 03:42 PM   #435
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Quote:
Originally Posted by kostas View Post
Fornax, I have some doubts about this, though. If you draw the air from the crawl space, you simply recycle it as it comes from your house and not from outside.
My crawlspace is outside the livingspace. The floor is made out of concrete with poured on concrete, finished with glued on PVC flooring. Aside of newly created holes it is completely sealed off, it's outside.

I did create 1 hole, where I draw my air from. This fresh air comes from 4 existing ventilation-holes, and thus it comes from outside.

You are welcome to come and have a look, from Italy it's only a day driving, I'll buy you lunch : -)

Seriously though: The air taken in is fresh, it comes from outside. I can prove that with a fryingpan, some oil and some garlic.

Last edited by Fornax; 02-07-14 at 12:48 AM..
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Old 02-07-14, 03:45 PM   #436
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Ok then, I'll be there by Sunday

How many cfm or m2/h can you push trough that recair exchanger? Was it the 160 model?
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Old 02-08-14, 02:33 AM   #437
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Indeed, it is the RS160 model with a heigth of 300mm as seen on www.recair.nl.
Identical heatexchangers (300mm) are used in commercial HRV's that are rated up to 300m3/h. Those HRV's use stronger fans than I do though.
With my fans I estimate some 60 and 120m3/h (lowest and middle setting).
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Old 02-08-14, 01:25 PM   #438
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Recair makes excellent exchangers. Indeed, I recently saw one of them installed in a custom made ERV and the fans inside were rated 800 m3/h.
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Old 06-09-14, 11:30 PM   #439
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I just got my hands on about 8 cubic feet of coroplast for free through Craigslist. I wonder how big the heat exchanger needs to get before diminishing returns just make it ridiculous? IIRC that Danish paper had one about 3x2x.5 feet and it was 80-something% efficient. I'm not sure I'll get around to doing anything with my coroplast soon but I'll try to come back to this thread whenever I start working on it.
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Old 06-10-14, 07:15 PM   #440
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I've been thinking more about design.

I originally wanted to make a counter-flow HX, for maximum efficiency, but it seems like sealing up the alternating channels at the ends would be really finicky and prone to leaking. A square cross-flow HX seems much easier, but efficiency isn't as good. So what I'm thinking about doing is simply making many small cross-flow HX's and putting them in series. It would get close to counter-flow efficiency, but is simpler to make. The hexagonal ones seem like a pain to make and still just a compromise between counter-flow and cross-flow. The counter-flow HX is just so elegant and simple, I find myself maybe irrationally biased towards it.

It doesn't get that cold here in Portland, so I'm thinking I could just have a thermistor in the outside air inlet and shut down at the freezing point and wait until it warms back up before turning back on. The house leaks more during deep cold anyway, due to the stack effect. The most useful time for the HRV is during temperate times when there is no stack effect. Also, I could use a microcontroller to make the HRV run at higher CFM for a while when coming out of a below-freezing shutdown period. So during the winter it'd run at higher speed when above freezing, and then not at all when below freezing, while during warm times it would just run constantly at a low/moderate speed.

I'm a little concerned about condensate draining. Creating a sloped pan in the bottom of the enclosure seems like it might be tricky, and how do you keep it from leaking air? A trap will only work during times that create enough condensation to keep the trap full. During spring and fall, the trap might dry out, and then what? Air would be leaking out the condensate tube. Maybe it's a small enough leak (though a small long tube with lots of airflow resistance) to not care.


Last edited by mackstann; 06-10-14 at 07:18 PM..
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