DIY ventilation heat exchanger

[kostas]

Piwoslaw I had already done some tests with the two versions earlier this autumn.
As I noticed there is no big difference by the two materials, the only one is that the aluminum core reaches it's working temperature faster.
But I can certainly say that the construction is way too harder than the coroplast, so I would definitely recommend the later.

[kostas]

Today I made the first of the two blowers. I used a new universal 135W motor for kitchen extractor fan. For the housing I copied the design of an old Rover 200 heating blower and I cut the sides out of plywood, then covered with aluminum tape. A piece of aluminum sheet covered the sides giving the final shape.
Tested it and it works great!

[Piwoslaw]

Kostas, in those pics I see shiny foil and some foam. Are those for thermal insulation? Or is the foam to reduce vibrations and noise?

[kostas]

I used some strings of foam just to fill a slight gap between the motor and the case.
Lack of design I must admit!

[Fornax]

I like your craftmanship Kostas, the aluminium is skillfully bend in shape.
Looking at the background in your pictures I get the impression you have a workshop with nice tools, which makes any job easier, I am not so lucky : -)

Did you cheat a little and continue with coroplast when you ran out of aluminium while building the HX-cores?

-----

Today I found the time to go to our DIY-store and get me some of the things I needed. This includes the wood (particleboard actualy) I need to house the heatexchanger core, and have it cut by them (which is free of charge, and straight).

Where in the US people often use OBS which is made of large chips here in the Netherlands we use particleboard with much finer woodchips, but not as fine as in MDF. The material is finished with a waterproof plastic, but the corners and bare cuts are vulnerable to moist, a point of attention.

Everything does fit snugly, and I sealed of every connection with an acrylic goop that is water- and weatherproof. Since the fans I'll be using are handy standalone machines that easily connect I kept the design of the housing for the HX very minimal. In the last picture you can see the enclosing with 2 HX-plates in it for an impression, I still need to saw the holes to connect the tubing.

Next comes the job to build the HX-core. It will be build from about 70 aluminum plates. Sealing will be made of selfadhesive PVC weatherstrips (4x9mm), these are compressable but do seal well. Since they are compressable I need to keep the individual plates separate by glueing a 3.5mm nut at the top and bottom centre.
It's not hard work but cutting 90m (300 feet) of weatherstrip to size and stick it in place will keep me busy for a while, but I guess it's not worse than glueing the same amount of coroplast strips in place.

I did have another minor setback. I planned to drill a hole in the floor of our shed and connect to the crawlspace under our livingroom. Our shed has no crawlspace, under the concrete slab is 60cm (2') of sand with no access. That means I'll have to reroute the ducting, which will make it longer than planned.

Anyway, the casing of the HX-cores is almost ready. The second fan that was missing from my order arrived quite fast. Most of the materials I need I have in the house so hopefully construction will go fast.

Perhaps I should tell you more about my home, in another thread. It's not a special house but it's obviously different than US, polish, italian, canadian and brittish houses.

[kostas]

Originally Posted by Fornax

I like your craftmanship Kostas, the aluminium is skillfully bend in shape.
Looking at the background in your pictures I get the impression you have a workshop with nice tools, which makes any job easier, I am not so lucky : -)

Did you cheat a little and continue with coroplast when you ran out of aluminium while building the HX-cores?

Thanks, indeed having the right tools makes the work much easier. I grew up in my father's workshop, he was a carpenter, and since I was a kid I used to collect power tools. I don't have much room in my garage, but I managed to make it a good working place by the years.


And -yes you guessed it, I finished all the aluminum sheets!!

If I can give you some advice, be careful with the PVC stripes. If they are sqiuzable that means that some of them could collapse by the overall weight .
In my case some stripes of coroplast eventually got smashed by the weight of 60 sheets over them...

[Fornax]

I finished the cabinet that will house the HX-core.
Well, almost finished: I need to caulk the tubes where they pass through the holes and apply a few layers of varnish to the 2 bare faces of particlewood. But the constructing is done.

Kostas, you are right about the PVC weatherstrips being compressable, they are flexible foam.
When my order of aluminium sheets arrived I realized I was facing a designflaw. The package weighted 20.0kg (44 pounds).
So I went looking for some noncompressable spacers to guarantee an even spacing of the plates. I went for 2 nuts per plate, center top and bottom, put in place with thin doublesided tape. I thought a drop of glue was not a good thing since it's not guaranteed to be the same thickness along all the 70-ish plates.
Today I discovered the approximately 120cm of strip (4 feet) I'll be using per plate is more sturdy than I thought, it might be a problem to even get the plates close enough to eachother. I'll put the nuts in anyway, should the strip give in over time.

On the left side are OAI at the top and FAI at the bottom. Both the fans will be at the right side for FAO at the top and OAO at the bottom. The fan in the picture is just fitted into the hole in the cabinet and stays put. I'll secure it with some screws and caulk the connecting duct so it's airtight.

[kostas]

Okey, I see that we were working together today!

You are doing a fine job, can't wait to see it finished. You've got a good feline companion, too!!
Is this a dual-hx housing? I see there is plenty of space inside.
I'd suggest you to use some aluminum foil to cover the inside of the box in order to create a useful UV barrier and save some more energy.
Beware of the water that will drip down the exchangers, as you said that kind of fiber board is not very keen of it. You could use a plastic collector underneath and drill a small hole for an evacuation plastic tube.

I tried to fix the first motor housing in place and drilled the exit hole. Was a bit tricky to calculate the optimal position, but i think I got it right.
This time I used some urethane foam sheets on the back side and neoprene tape for the vibrations

[AC_Hacker]

I just wanted to say to both of you how great it is to see the progress of your two HRVs.

I just can't get over how miraculous it is to be able to easily communicate this kind of information and these kind of efforts to such distant parts of the world.

Very fortunate to be living in this age.

Best,

-AC

[Fornax]

Originally Posted by kostas

Is this a dual-hx housing? I see there is plenty of space inside.

No, it's for a counterflow core with plates of 25x50cm (10"x20") and the core will be 30cm (12") thick consisting of up to 72 plates. The cabinet isn't that large, 90x30x30cm (3'x1'x1') on the outside.

I just removed the protective foil from the plates which resulted in an impressive stack of foil, which compressed well. (Plastic waste is collected separately and for free over here.)

In the 3rd thumbnail you see how the weatherstripping will go for the 2 different airstreams. The 4th shows how they will go into the cabinet. The remaining exposed aluminium will be roughly 23x48cm resulting in 0.11m per side per plate resulting in almost 16m2 for the entire exchanger (~170sqf).