like topic :))

That's nice. I would advice you to go with the professional consultation for better advise.

AWESOME!!!
I am making the twin core (or dual core) system myself, borrowing lots of ideas from here! Thank God I came across this thread as I was also thinking of other ways which have all been addressed here and the fact that the simplest method - SOLID PP as kostas calls it - is actually the most efficient, has made my day as I had already set out to do it this way :)
THANKS to you all, I will post updates with photos as I progress with my contraption ;)

This thread is one of the most interesting threads I've ever read. I just had to join even if to just thank you Kostas for your epic build. That video is amazing! The craftsmanship is remarkable!

Thanks Rebuilder, hope my effort helps everyone out there ;)

Hi,
This topic is awesome! I just registered because this topic so I can answer here.

I have read all this topic planned to make DIY HRV already 1.5years ago, I have bought motors and RECAIR heat exchanger core (160 model, 300mm thick) and now I started to make box for it. I live in Estonia and it is cold country, february was mostly -10...-15 degrees celsius, peak was -25C at some nights.

Few questions to people who have done it already:
1) how you have resolved defrost - what strategy are you using? What options are available?
2) Is it best to put both motors in warm side (stale air out, prewarmed fresh air in)
3) Kostas - You made air humidifier, do you still use it? Please give more details about it - does it help, are there any issues?

Meelis

Hi Meelis,

glad we inspired your project! ;)
You should avoid of course frosting. You have few options for this, either you stop the ventilation when exhausting air riches limit temperature, that is around 2-3 °C, or you reverse the flows so to heat up the frozen side of the exchanger. Alternatively you should preheat the incoming external air so to avoid freezing.
Both motors have to be at the warm side. In my case one motor pushes the air whilst the other pulls it.
As for the humidifier, I'm still working on it. It sure helps, as RH drops down to 25% when really cold outside, so humidification becomes mandatory. It is, though, a bit complicated to integrate it to the exchanger and the pipes, you have to be very careful not to have water drops around and water remains as the could form harmful mold.
Here's a couple of photos of the finished version. It is a completely stand-alone machine with it's own arduino board.
I'll post some data as soon as I can.

How many mL/h that humidifier produces and do you get white dust layer around your house? I have read that could happen when you have hard water. Is it fundamentally similar than commercial ultrasonic humidifiers? Why you decided DIY solution - was that just cheaper solution (and you like DIY) or do you have some features that are unique?

About defrost - probably easiest is to turn off ventilator that pulls fresh air in when outgoing air is below 0 degrees celsius (or 2-4C, don't know best numbers, must experiment). When outgoing air temperature rises above 5C then turn ventilator on again. Some commercial HRVs use similar algorithm. I also have seen units where one ventilator is on cold side, they are not always in warm side, but it seems best to put them on warm side if design allows that.

The steam production is approximately 300ml/h. It is too early to tell for the white dust problem, I also read about it in the web. We'll se next winter.
I did it myself spending roughly €50, whereas commercial products cost 7-10 times more!
The function is almost identical, the major difference is the steam production, which for those models is at least 500ml /h. And, of course, they have 2 years warranty :D
Anyway, at least for the time being, I'm not very satisfied with the results. I'm using it 24h/day for the last three days but the RH is stucked to 28% :(
I'll dig deeper and let you guys know.

How big is room what you try to humidify (commercial 300-350ml units are for 40-50m2 room max)? Maybe it is too small, you could add one extra humidifier disk.