DIY ventilation heat exchanger

[AC_Hacker]

Originally Posted by kostas

Btw guys, here's a sneak peak of the 2.0 diy hrv unit I'm currently working on.
Featuring two centrifugal EC brushless fans, 650m3/h each, post heating radiator, homemade countercurrent 600mm heat exchanger, freecooling bypass damper and fresh air exclusion damper, all of them driven by 5V step motors. And of course the arduino Mega.
Stay tuned!

Awesome information!

You must post more.

-AC_Hacker

[imgreen]

Looks like a simple design!

[tinco]

Before I start building my exchanger I want to run some numbers by you folks. The house I'm doing this for is ~60m2. The Dutch government says we should ventilate at 0.9dm3/s so that comes out at ~180m3/hour. My GF is really sensitive to stuffy atmospheres, do you think the 0.9dm3/s is good enough?

For the recuperation unit I'd go with the 300mm high Recair RS160, for a ~90% efficiency at 160 euro.

For the fan I found these (ventilatieshop.com) Soler Palau TD 160 at 100 euro rated for 180m3/h. I guess that calculation does not take into account the air has to be pushed through the recuperator. Should I go for the slightly stronger model that's rated to do 240m3/h for 180 euro? It seems the stronger model is also more power efficient. Does it make sense to think of it that way or do the fans always put through the same amount of air, and just take more power to push through the recuperator (and any network of airducts)? Would it perhaps be smarter to for example have two of the weaker ones in series or parallel?

On the Dutch ebay/craigslist (marktplaats) I also found a (canfan.nl/cfrk100l.html) Can Fan 100L RK which is plenty powerful but it seems it takes 66W which seems like a lot, it also doesn't say much about noise, apart that they claim the design reduces noise.

I haven't read much here about fan power efficiency, it seems like it's really important since they're basically always on in a balance ventilation system and they can differ as much as 25-66W.

[Fornax]

Hoi Tinco,

Just a short reply for now, I'll go in more detail later.

Originally Posted by tinco

Before I start building my exchanger I want to run some numbers by you folks.

---8<--- snip

I haven't read much here about fan power efficiency, it seems like it's really important since they're basically always on in a balance ventilation system and they can differ as much as 25-66W.

The fan you picked can do 180 m^3/h indeed, if it has to overcome no presuredifference at all. With a difference of 60Pa (Which is not even much after the heatexchanger and a dustfilter only 50m^3/h remains, while using 30W per fan (times 2 fans equals about 120 euro a year here in the Netherlands).

I build an HRV about 2 years ago with fans that perform similar to the ones you picked and I am in the process of replacing them.

[tinco]

Thanks Fornax! I tried to reproduce your numbers, but then I realised I can just look at the product sheet. It says that at ~60Pa the airflow drops to 50m3/h. That's pretty straightforward. Could I say that if I put two in parallel the pressure drop halves to 30Pa, giving me 2*130m3/h = 260m3/h or does it not work like that?

Now with the power of datasheets, the Can Fan one looks much more attractive. The RK 125LS has a flow of ~180m3/h when Pa = ~60 on its lowest setting. I see I could pick one up for just 70 euro's in my own city. And it operates at 43W at that setting, so that's significantly lower than 60W.

Unfortunately it doesn't list any sound measurements, though with a 30% better power efficiency I'd be surprised if it made more noise.

Looking forward to your more detailed response

[Snowman]

Great thread, glad you have all participated and I thank you. What a great year to be looking at a project like this when coroplast is such an abundant upcycle resource.

My home is circa 1950's and 1400 sq.ft, located in New Hampshire USA. As such I have "need" for summer A/C for a few weeks (3-4) and a month on either side where I would like some stretch of the A/C dehumidification, especially of the overnight air to keep the house cool but dry and comfortable. Then the spring and fall allow open windows and doors all day and night. But the winter is 3+ months of being shut in where some fresh air is needed. I want to build an HRV for both the summer A/C and dehumidification seasons as well as heating season to optimize fresh air with heat exchange. Bonus for cooking, bathroom and laundry extraction and filtered fresh air even during times of reduced "need" and bypassing the HX cores with increased venting and fans.

My conceptual design after reading this thread is a thin quad core cross flow design using coroplast to ease construction and optimize efficiency as a pseudo counterflow HX. I also think it would be easily cleanable and minimize freezing due to the long condensing path, enabling more water extraction prior to icing. I'm planning 12"x12" cells stacked 6-8" thick with the "spacing" design; balancing the "open" and "restricted" airflow paths to equalize flow restriction across the core(s) and put the "open" paths in the condensing area to promote draining.

Phase 1: Build cores and housing with 2" foil lined rigid foam and plumb insulated lines for supply and return to the interior and exterior.
Phase 2: Upgrade fan controls with T/RH feedback and web interface for control of PWM.

Further upgrades or options to consider:
1. Automate HX core bypass for extraction and filter modes.
2. Evaporative misting in exhaust stream for intake cooling assistance.
3. Integration of thermal mass or zeolite.

I'm having fun and will update as progress is made.

[tinco]

Hey Fornax, I'm working on designing the ventilation canals in my house. I am thinking of having the fresh air go in to the right side of the living room, the bedrooms and the attic guest room, and then the stale air drawn from the kitchen, the bathroom and the top of the attic.

What I am wondering is when I'm splitting fresh air channels, should I match the "impedances" of the channels, so the amount of fresh air for each room is balanced, or does that not really matter?

For example because the living room is the size of the two bedrooms combined, I guess it could do with 2 channels, or perhaps one larger one, to match the 2 channels in the bedrooms? And since it's also further from the fresh air source (which would be in the top of the attic) would I use a larger channel to it? I may be overthinking things.

Did you work out your fan situation yet? What do you think of the Can Fan RK 125? I wonder if push/pull would be better than just push.

[Piwoslaw]

Originally Posted by tinco

What I am wondering is when I'm splitting fresh air channels, should I match the "impedances" of the channels, so the amount of fresh air for each room is balanced, or does that not really matter?

For example because the living room is the size of the two bedrooms combined, I guess it could do with 2 channels, or perhaps one larger one, to match the 2 channels in the bedrooms? And since it's also further from the fresh air source (which would be in the top of the attic) would I use a larger channel to it? I may be overthinking things.

One large diameter channel will give you less noise (and less resistance) than two individual channels. If you can afford (either price- or space-wise) a larger diameter, then go for it! You can later tweak the airflow with an anemostat.

[kose2ik]

However, when I use the material for Polycarbonate
sheets 2100*6000* 4mm (300mm*300mm sheets 35pcs x 3 cubes )?
(proplastik.ee/wp-content/uploads/2015/07/Makroloni-erinevad-variandid.pdf
, proplastik.ee/wp-content/uploads/2015/07/Makrolon_2_4mm.pdf )
Heat transfer efficiencies % ?
If inside +22*C and outside -10 (or -20*C) (then I have one/three blocked (ice)cubes?
Need inside coming cool/fresh air "tube-iside-tube" wildsnow.com/17884/how-to-build-air-cross-flow-heat-exchanger-budget/ )?
Like this i66.tinypic.com/r0w2gp.png

[AC_Hacker]

Originally Posted by kose2ik

(HTTP://www.wildsnow.com/17884/how-to...hanger-budget/)

Really like the "WildSnow" HRV.

Just brilliant!

-AC_Hacker