DIY ventilation heat exchanger

[Istrian]

Hello,

I just register on this forum but I am reading for the last couple on months and found very interesting subjects and ideas. First of all I would like to thank you for all the post as they have helped me take some decisions. For one of those decisions I am writing this post.

I have decided to make a ventilation system for my house with heat recovery. For the heat recovery unit I have already decided what to do based on your experiments/models/posts. Now I would like to know your opinion on two aspects:

1. Every room will have supply and extraction. I would like to add individual pipes for each room that will connect together in my attic in some kind of plenum and then to pass through the heat exchange. For all the system I will have CO2 and humidity sensors in order to increase or decrease fan speed.

2. Total ventilated volume. Accordingly to Romania standards I should have for my entire house 700mc/h. But there are different ventilation values depending the designation of the room. Is there going to be a problem if I will ventilate, let's say, from bedroom 50mc/h (required by standards 40mc/h) and from bathroom 20mc/h (required by standard 30mc/h)?. Hard to find my words, but what I would like to say that total ventilated volume will be as required even if it will not be as per standard from each room.

[natethebrown]

Originally Posted by Istrian

Hello,

I just register on this forum but I am reading for the last couple on months and found very interesting subjects and ideas. First of all I would like to thank you for all the post as they have helped me take some decisions. For one of those decisions I am writing this post.

I have decided to make a ventilation system for my house with heat recovery. For the heat recovery unit I have already decided what to do based on your experiments/models/posts. Now I would like to know your opinion on two aspects:

1. Every room will have supply and extraction. I would like to add individual pipes for each room that will connect together in my attic in some kind of plenum and then to pass through the heat exchange. For all the system I will have CO2 and humidity sensors in order to increase or decrease fan speed.

2. Total ventilated volume. Accordingly to Romania standards I should have for my entire house 700mc/h. But there are different ventilation values depending the designation of the room. Is there going to be a problem if I will ventilate, let's say, from bedroom 50mc/h (required by standards 40mc/h) and from bathroom 20mc/h (required by standard 30mc/h)?. Hard to find my words, but what I would like to say that total ventilated volume will be as required even if it will not be as per standard from each room.

Welcome to the forum! I don't have much knowledge about this topic, so I won't say anything about that. I will say you have a beautiful country and I really enjoyed the short time I was there.

[LarryBertsc]

I see of Heat Recovery Ventilators usually use a cross-flow cell, with the air paths crossing at a 90 degree angle. They usually have an efficiency of about 60% to 70%. I have seen write-ups of experiments done on cells that had a 180 degree cross-flow and the efficiency was increased to some degree (maybe 5% to 8%). Sorry, but I didn't book mark the studies.

[tinco]

Hi people,

I was thinking about the idea of reversing the flow through the heat exchanger every N minutes, to regulate the moisture content of the air. It's an appealing idea, but I could not come up with a design that does not require at least 4 actuators. 2 for switching the air supply/exhaust on one side, 2 for switching them on the other sides and a pretty clunky maze of canals. The actuators are pretty costly, especially when you buy them in a store instead of on ebay. Am I missing some clever design idea that requires less actuators?

Has anyone ever built this idea, is it applied in commercial HRV units?

[JRMichler]

Google rotating heat exchanger. Rotating heat exchangers have very high efficiency and no actuators or dampers.

I don't know if frost in cold temperatures (-35 deg C) would be a problem, especially if it is designed for high efficiency.

Be a great project to build one...

[AC_Hacker]

Originally Posted by tinco

Hi people,

I was thinking about the idea of reversing the flow through the heat exchanger every N minutes, to regulate the moisture content of the air. It's an appealing idea, but I could not come up with a design that does not require at least 4 actuators. 2 for switching the air supply/exhaust on one side, 2 for switching them on the other sides and a pretty clunky maze of canals. The actuators are pretty costly, especially when you buy them in a store instead of on ebay. Am I missing some clever design idea that requires less actuators?

Has anyone ever built this idea, is it applied in commercial HRV units?

I have seen HRVs that have reversible DC fans.

The reversing work is done with electronics.

In these HRVs the core has enough thermal mass, that:

1. a 'charge' of indoor air is blown out, thus warming the core,
2. there is some dwell time for the core to absorb the heat from the charge
3. a 'charge' of outdoor air is drawn into the core, to be warmed
4. there is some dwell time for the core to release heat
5. REPEAT

If you are able to work with a micropressor like Arduino (or similar), the timing and duration can be finely optimized, depending on the thermal mass of the core, etc.

The Arduino can be also programmed to continuously vary the fan speeds, and ramp-up or ramp-down rate, to maximize efficiency.

Best,

-AC_Hacker

[csz]

Hello, this is my first time writing on this forum. I just spent all this night reading this tread from begining, and seeing how much work you all have put into it.

I want to build a HRV core for 1200m3/h ventilation system, from aluminium sheets 0.3 mm thick.

I saw that mainly coroplast (Is coroplast = celular polycarbonate panel ?) was used in similar proiects, but in my opinion there are too many layers between the two air streams that need to change heat)

You can see attached my initial design option, but with that I still felt that there is too much material between the two air streams.
There should be one thin wall.

I want to build some kind of a roller setup that can make the "bumps" in the sheets, to act like spacers and turbulence generators.
The flow will be 180 degree counterflow.

I mostly know how to build it, I know how I can seal up the edges, my main problem is I don't know how to size it for 1200 m3/h, to have max. possible efficiency, and lowest possible pressure drop.

My current thought is to size it for maintaining the fi315 inlet/outlet pipe's interior cross section area, thru the core, but don't know how long should be the section, where the two streams will flow in paralel(oposit directions).

This is why I want to ask Kostas to share the design (and size) of this new "homemade countercurrent 600mm heat exchanger" that he mentioned in th below quote.

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!

I welcome every opinion on this matter.

[kostas]

Hi guys, what goes around comes around, so here I am with the latest news: I finally finished my diy HRV system!To be honest I completed and installed it last February but only now I managed to make the video tutorial, as promised.
It is in Italian, as well as my blog, but I added some english subtitles so everyone can understand. I hope you enjoy!

https://youtu.be/phIWQD5LAcA

Btw, here's my blog if you want to see every part of the process, for I've made a video for every custom component: https://diyvmc.wordpress.com/

[Fordguy64]

That is beautiful

[Zwerius]

Looks good.
Did you do any temperature measurements in/out and in/out?
So what's the efficiency?