DIY ventilation heat exchanger - Page 29

kostas · 12-23-12, 09:45 AM

Fornax if I may ask, are you sure about the design of the flows? The counterflow Hxs I've seen have an hexagonal shape and the flow goes from, let's say, the upper left side to the lower right. You have a rectangle and the incoming air goes directly to the opposite side (red arrow)not passing trough the space near the angles (blue areas).
Have a look at the photo:

Piwoslaw · 12-23-12, 02:56 PM

Quote:

Originally Posted by kostas

Fornax if I may ask, are you sure about the design of the flows? The counterflow Hxs I've seen have an hexagonal shape and the flow goes from, let's say, the upper left side to the lower right. You have a rectangle and the incoming air goes directly to the opposite side (red arrow)not passing trough the space near the angles (blue areas).
Have a look at the photo:

The hexagonal shape does pretty much the same, but uses less material. From a DIY POV this increases the amount of triangular scraps that are left over, and is a bit harder to make.

Add some weatherstripping to make baffles. One possibility:

There are probably better ways to it, but you get the idea.
Adding baffles will not only increase the airflow's path length, but (just as important) should make the airflow more turbulent, increasing air-plate heat transfer.

kostas · 12-23-12, 03:28 PM

Yes. But also more turbulent means more resistance, you'll have to use more powerful fans and thus more noise. That's, of course, for equal amounts of air flow.

Fornax · 12-23-12, 03:37 PM

Hi Kostas,

I share your thoughts but I didn't decide what to put in to direct the airflow yet.
I guess a simple 5cm strip would do the trick though, shown in the left drawing.
Perhaps slightly better is the midle drawing, but also more work for 70-ish plates.
Or I could go all fancy with something like in the 3rd drawing. This would force the air to follow a roughly 40% longer pathway, introduce some turbulence (which is good) but increase the resistance (no idea how much).

I'll go for the 1st option, without being a rocketscientist I can state that it'll most likely be good enough to get the job done..

-> At this point while previewing my post I see Piwoslaw's reply. I asume Daox will have a good chuckle to see how much the 3 of us think in the same direction.

As for the counterflow cores that are named hexagonal or diamond shaped, the real counterflow part is quite short. I suspect that is because the comercial builders can stick to a simpler design for the cabinet they place the core in.
There is one example that pops up a few times where the counterflow part stays a constant 246mm and the other size can vary between 200-600mm. So either that is a convenient size for them or 246mm is enough (Or a higher efficiency would introduce new problems, like frost in the OAO).

As you say Piwoslaw, rectangular is easier for me as a DIY'er. I ordered the plates precut from a company. I could only order rectangular plates and the cutting to size was free. I found another company where the cutting would have cost me another 132 euros.

With the more hexagonal shape the direction the airflow enters the HX will be slightly different, but with some baffles that would be solved. My weatherstrips cost 3,70 per 6 meters ($5 for 20') so I am not bothered by using an extra package. I'd appreciate a fairly simple design though since it's still 72 plates.

AC_Hacker · 12-24-12, 01:56 AM

Quote:

Originally Posted by kostas

...more turbulent means more resistance, you'll have to use more powerful fans and thus more noise...

More turbulence also means less boundary layer to resist heat transfer.

-AC

Fornax · 12-28-12, 05:44 PM

Since my last post (23dec2012) I took some rest, spend quality-time with the family and went to work (shifts), today I worked on my project again after waking up at 3PM.

I finished all the aluminium plates and placed them in the cabinet: the HX-core is done.

To-do: electrical wiring, drilling holes in brickwork, blockwork and concrete (my floors/walls/ceilings are not made of wood), arranging the ductwork, and finish the project so it is visually nice to the people who live here.
Also I need to document what I build and give directions on how to maintain the installation.

kostas · 12-29-12, 07:48 AM

Glad to know that your work is going on.
You seem to be quite sure about the results. Would'nt be wiser if you do some heavy testing before breaking down some walls? I have a brick house too, so I can imagine how painful rethinking afterwards can be. My two pennies, of course

As for me, I try to get on with mine stealing every free moment of the day (but you know how it is, it's holidays for all the family, too)...
Today I almost finished with internal insulation and cabling and did some pre assembling of the HXs, should be ready to rock in a couple of days!

Fornax · 12-29-12, 04:37 PM

Kostas, it was just the to-do list, indeed I'll be running some tests before drilling the holes.

Actually I connected the fans with the 3-settingsswitch today (test setup) and played with them a bit, one at a time. They are actually working.
On the slowest setting it is fairly silent, that is the bare fan with nothing connected to it, speeds 2 & 3 are louder and loud. (1 = 75m3/hr, 2=150, 3=230) I noticed no fibration, even at high speed, these are quality fans.
Then I mounted the fan to the cabinet, pulling air through the HX. This was much quieter. In the final install there will also be sounddampening plus the apparatus will be on the other side of the wall. (Speed-1 will be the normal usage and that will be almost unaudible, speed-3 will not be used normally.)

After that I put the fan near where the fresh air inlet in the livingroom will be and my wife became enthousiastic: she clearly felt moving air. (Unconnected fan moves more air and the final installed apparatus should bring the air into the room in a more difuse manner, so a less windy experience by then.)

Then I started to make room in the shed, as it is full of stuff and I need access to every corner of it to install the ductwork. After that we went to the store to get the final ductwork I need to connect everything. By then it was dinnertime already and after that I finished the electrical connections. Tomorrow I'll run some tests and start making the holes for the final installation, at last.

kostas · 12-29-12, 05:03 PM

Excellent! I am curious to see the performance of the hx, the climate is perfect now, you have several degrees of difference between in and outside the house.
And, btw, having the wife's approval is definitely helpful

mini23 · 12-30-12, 02:44 PM

Excelent work, you guys are doing.
I was looking to purchase a heat recovery system to install over the Christmas period, but work commitments took up to much of my time, so didnt find the time to research.
I'm glad I never ordered a ready made unit, you guys have really inspired me to have a go at making my own.
Will be going the correx sheet route. I have found a company selling 8' x 4' x 4mm boards for £9 each, so shall order some up in the new year.

I would have had to purchase a reasonably priced unit, with efficiency of around 70% claimed.

Xpelair claim 92% for theirs, but thats around £1300!

Hope you gather some results soon

12-23-12, 09:45 AM	#281
kostas Helper EcoRenovator Join Date: Dec 2012 Location: Venice, Italy Posts: 89 Thanks: 15 Thanked 41 Times in 19 Posts	Fornax if I may ask, are you sure about the design of the flows? The counterflow Hxs I've seen have an hexagonal shape and the flow goes from, let's say, the upper left side to the lower right. You have a rectangle and the incoming air goes directly to the opposite side (red arrow)not passing trough the space near the angles (blue areas). Have a look at the photo: Attached Thumbnails

12-23-12, 03:37 PM	#284
Fornax Helper EcoRenovator Join Date: Oct 2012 Location: Beuningen (Gld), the Netherlands Posts: 64 Thanks: 4 Thanked 19 Times in 16 Posts	Hi Kostas, I share your thoughts but I didn't decide what to put in to direct the airflow yet. I guess a simple 5cm strip would do the trick though, shown in the left drawing. Perhaps slightly better is the midle drawing, but also more work for 70-ish plates. Or I could go all fancy with something like in the 3rd drawing. This would force the air to follow a roughly 40% longer pathway, introduce some turbulence (which is good) but increase the resistance (no idea how much). I'll go for the 1st option, without being a rocketscientist I can state that it'll most likely be good enough to get the job done.. -> At this point while previewing my post I see Piwoslaw's reply. I asume Daox will have a good chuckle to see how much the 3 of us think in the same direction. As for the counterflow cores that are named hexagonal or diamond shaped, the real counterflow part is quite short. I suspect that is because the comercial builders can stick to a simpler design for the cabinet they place the core in. There is one example that pops up a few times where the counterflow part stays a constant 246mm and the other size can vary between 200-600mm. So either that is a convenient size for them or 246mm is enough (Or a higher efficiency would introduce new problems, like frost in the OAO). As you say Piwoslaw, rectangular is easier for me as a DIY'er. I ordered the plates precut from a company. I could only order rectangular plates and the cutting to size was free. I found another company where the cutting would have cost me another 132 euros. With the more hexagonal shape the direction the airflow enters the HX will be slightly different, but with some baffles that would be solved. My weatherstrips cost 3,70 per 6 meters ($5 for 20') so I am not bothered by using an extra package. I'd appreciate a fairly simple design though since it's still 72 plates. Attached Thumbnails

12-29-12, 07:48 AM	#287
kostas Helper EcoRenovator Join Date: Dec 2012 Location: Venice, Italy Posts: 89 Thanks: 15 Thanked 41 Times in 19 Posts	Glad to know that your work is going on. You seem to be quite sure about the results. Would'nt be wiser if you do some heavy testing before breaking down some walls? I have a brick house too, so I can imagine how painful rethinking afterwards can be. My two pennies, of course As for me, I try to get on with mine stealing every free moment of the day (but you know how it is, it's holidays for all the family, too)... Today I almost finished with internal insulation and cabling and did some pre assembling of the HXs, should be ready to rock in a couple of days! Attached Thumbnails

12-23-12, 03:28 PM	#283
kostas Helper EcoRenovator Join Date: Dec 2012 Location: Venice, Italy Posts: 89 Thanks: 15 Thanked 41 Times in 19 Posts	Yes. But also more turbulent means more resistance, you'll have to use more powerful fans and thus more noise. That's, of course, for equal amounts of air flow.

12-28-12, 05:44 PM	#286
Fornax Helper EcoRenovator Join Date: Oct 2012 Location: Beuningen (Gld), the Netherlands Posts: 64 Thanks: 4 Thanked 19 Times in 16 Posts	Since my last post (23dec2012) I took some rest, spend quality-time with the family and went to work (shifts), today I worked on my project again after waking up at 3PM. I finished all the aluminium plates and placed them in the cabinet: the HX-core is done. To-do: electrical wiring, drilling holes in brickwork, blockwork and concrete (my floors/walls/ceilings are not made of wood), arranging the ductwork, and finish the project so it is visually nice to the people who live here. Also I need to document what I build and give directions on how to maintain the installation.

12-29-12, 04:37 PM	#288
Fornax Helper EcoRenovator Join Date: Oct 2012 Location: Beuningen (Gld), the Netherlands Posts: 64 Thanks: 4 Thanked 19 Times in 16 Posts	Kostas, it was just the to-do list, indeed I'll be running some tests before drilling the holes. Actually I connected the fans with the 3-settingsswitch today (test setup) and played with them a bit, one at a time. They are actually working. On the slowest setting it is fairly silent, that is the bare fan with nothing connected to it, speeds 2 & 3 are louder and loud. (1 = 75m3/hr, 2=150, 3=230) I noticed no fibration, even at high speed, these are quality fans. Then I mounted the fan to the cabinet, pulling air through the HX. This was much quieter. In the final install there will also be sounddampening plus the apparatus will be on the other side of the wall. (Speed-1 will be the normal usage and that will be almost unaudible, speed-3 will not be used normally.) After that I put the fan near where the fresh air inlet in the livingroom will be and my wife became enthousiastic: she clearly felt moving air. (Unconnected fan moves more air and the final installed apparatus should bring the air into the room in a more difuse manner, so a less windy experience by then.) Then I started to make room in the shed, as it is full of stuff and I need access to every corner of it to install the ductwork. After that we went to the store to get the final ductwork I need to connect everything. By then it was dinnertime already and after that I finished the electrical connections. Tomorrow I'll run some tests and start making the holes for the final installation, at last.

12-29-12, 05:03 PM	#289
kostas Helper EcoRenovator Join Date: Dec 2012 Location: Venice, Italy Posts: 89 Thanks: 15 Thanked 41 Times in 19 Posts	Excellent! I am curious to see the performance of the hx, the climate is perfect now, you have several degrees of difference between in and outside the house. And, btw, having the wife's approval is definitely helpful

12-30-12, 02:44 PM	#290
mini23 Lurking Renovator Join Date: Dec 2012 Location: Pembrokeshire UK Posts: 4 Thanks: 0 Thanked 0 Times in 0 Posts	Excelent work, you guys are doing. I was looking to purchase a heat recovery system to install over the Christmas period, but work commitments took up to much of my time, so didnt find the time to research. I'm glad I never ordered a ready made unit, you guys have really inspired me to have a go at making my own. Will be going the correx sheet route. I have found a company selling 8' x 4' x 4mm boards for £9 each, so shall order some up in the new year. I would have had to purchase a reasonably priced unit, with efficiency of around 70% claimed. Xpelair claim 92% for theirs, but thats around £1300! Hope you gather some results soon