Yes, over 90% with 20º C Δt

I watched all the videos and that was an hour of my life well spent!

You impress me with how thought through the design is with all the controlls of the various valves and airpathways and the amount of electronic controlls and sensors in the HRV you built. And on top of that the efford you put in filming -every- stage of building it, from multiple angles. I approve :)

Thanks, Fornax. It was a promise I made to the whole community of tinkerers out there, I hope it helps! :thumbup:

Wow that's very impressive Kostas, those valves are exactly what I was worrying about, I will take some time to figure out everything you did.

I have a question about the heat exchangers, here people are talking about 20dT efficiency. To qualify for the subsidy my heat exchanger needs to be at least 90% efficient, it is not said at what thermal difference that efficiency should hold, but the commercial ones all list a single efficiency as conforming to the EPN (Energy Performance Directive) norm.

Does anyone have an idea how this norm might be established? It seems all commercial exchangers perform well in excess of 90% (some even 95%) even though 20dT is not very common at all (in The Netherlands I think the average would be closer to 10dT).

Tinco, as you can see here the calculation is on a 21° dT basis.
Maybe you should consult the ASHRAE requirements for more details.

:thumbup:Glad to help!

First time poster, so hope I am asking this question in the best thread. If not, your advice on the most appropriate thread is appreciated.

I am currently building a HRV/ERV, but with a twist, in that it will be used to cool a small computer room in my home i.e. the external 'cooler' air will lower the temperature of the heat exchanger, which in turn will lower the temperature of the internal air.

I've noticed some of you building your own ERV/HRV units have been lining the enclosure with what looks like an adhesive product with a silver (aluminium) looking backing. I assume this is being used as a noise deadener/insulation or condensation protection.

I have also noted some of you using a silver tape to join everything together, and I suspect to water/air proof some sections of the ERV/HRV.

Is one of you able to give me advice on the lining and tape products you have used?

Thanks, Mark

Hi Kostas, awesome videos. What was the silver adhesive tape you were using in the video?

Thanks mate! ;)
It is aluminium tape, used for insulating heat pipes and stuff like that. You can find it the hardware shop.

i like you

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.

I have 200 qm of air volume and my HVAC is set to 120 qm/h of fresh air ventilation.
The needed amount depends on the gap between the current and the comfort RH level (45% @20°C). Maybe two trasducers are insufficient. I'll do some more extensive tests in the next days.

You could also slow ventilators down to keep more moisture in. I have read that here code recommends 1 airchange/hour (i would use that in boost mode), but more practical is 0.5 or even 0.3 airchanges/hour (one airchange in 3 hours)
Slow down ventilators and/or double your ultrasonic disks.

Just registered here. This thread is awesome and the best DIY discussion on the internet I found so far.

I'm currently building a HRV unit myself. Will be installed in a 112m² house.
Dual-Cross-Flow-HX cores that I got from eBay (Heatex). One Aluminium core, one Cellulose (Paper?) core in series.

Controlling fans and reading temp and humidity with an ESP8266 NodeMCU.
Can control that from my home automation and send values to thingspeak for visualisation and logging. Using some MosFETs now as power transistors didn't work out. They needed too much current to drive and got warm.

Main purpose of the system is to get good air in the sleeping rooms, and pump out wet or stinky air from bathrooms.

Using DHT22 sensors that I balanced yesterday to show similar values.
MosFETS are IRFZ44N that seem to work with 3.3V Gate Voltage.

Fans are Scythe Ultra Kaze: 133CFM, 3000RPM, 45,90dBA, 80 Pa, 12V, 0.6A.
Using them in a Push-Pull Setup per Channel to have more Pressure. Had the impression that Airflow dropped too much with only one fan per channel. Those are more or less the most powerfull 12cm fans I could find (before started too investigate on non-PC/industrial fans).
Will try out how much airflow I can get from those or if I have to replace them with something with more static pressure.

Currently finishing cabling before I will start drilling holes in the ceiling for 2 test vents.

Hey guys, here's the post in my blog for the diy ultrasonic humidificator I've made for my heat exchanger: https://diyvmc.wordpress.com/2018/03/30/umidificazione/
It is in Italian but you can use google to translate.
I've also made a small video to show how it works. It is still work in progress but I thought it worthed sharing.
https://www.youtube.com/watch?v=VcxYxdM52To

Pics or it didn't happen. Cabling done for now. A bit adventurous, but works.
Need to order ducts and vents.

Anemometer gives me something like 160 m³/h. But it's a bit hard to measure...

Working on Barometers right now. Want to measure pressure inside, outside, in and out.

Update:

Ventilation unit now moved to one of the attics (there are 2 seperated ones) and first 100mm vent is ducted to the unit, Pumping fresh air to the sleeping room.

Suction duct is currently ending in another attic and pulling warm air out of there in case sun warms the roof (usually it is 3 to 5° Warmer there compared to outside temp).

So currently the unit if more like a regenerative energy harvester and not runnig in heat regeneration mode :-) This will change this weekend when the first suction vent will be installed (ran out of flex-pipes).

Fan currently set to 30% duty cycle. This results in 9.2W Power consuption.
Below 18% they do not start to turn. Will programm the controller to set anything below 10% to 0 and 10 to 20% to 20%.

Also have the feeling that at 20% duty cycle the air flow and pressure is so low, that convetion is stronger than the fan causing there to be pretty much no flow in the ducting. Will messure flow on 0% and 20% to see if there is a difference messurable. At least readings from the temp/humidity sensors look "strange".

Some trouble with the DHT22 sensors and the ESP8266. In case where the fans are set to duty cylces other than 0% or 100% I sometimes get no results from the sensors. Might be problem with cable lenth and noise added by the motors. Might also be the library I used. Seems to be a bit buggy and the Internet proposed some bug fixes to be applied. Will give that a try and see if I get better results from the sensors. Another EPS8266 is already flashed with bugfixed version of the library I use.

Increased fan duty cycle from 20% to 30% an hour ago.

Some numbers to get a feeling on what the unit is doing right now:

Outside temp: 19°C (Fresh air comes from here)
Attic Temp: 26°C (This is where suction side is pulling air from right now)
Fresh air temp 20.4 (might be a bit warmer as outside as pulling air from inside an open roof).
Inlet air: 23°C (So Air going to the house is warmed by 3°C compared to outside).
Exit Air: 20.6°C (Cooled down from 26°C most likely).

I think there can be gained more if there is more airflow. Will increase to 50% now. But looking at the graphs it looks like inlet air still rises (so does attic temp and fresh air).

with 50% duty cycle the inlet temp went up to 25°C with 26° attic temp while outside temp was 20°C. Not too bad.

Had 2 vents installed for some time (currenlty I'm at three).
One pushing fresh air to thge bed room, one pulling bad air (smoke) from my office. Roughly 70 m³/h at full speed of the fans in and out.

Added a vent pulling from a small toillet room.
Also added filters to the vents to keep the ducts clean.

Total air pulled is reduced now to around 50 m³/h. I think the filters cost a lot. Will change the way they are done. Currently they are flat of the size of the vent. Think I'll have to change them to a cone shaped filter to have more surface and allow for more air flow.

Also will continue to add more vents.

Update: Changed first filter to a cone shaped one and I'm back to 60 m³/h

diy hrv help needed.
 

so i have read this whole thread. great info in it but it leaves me with questions. i have a tiny house. 24 long x 8 wide x 10 high. it is built by me and was done so it is super tight. it about to get cold hear and i needed a way to get fresh air in while not losing a lot of heat. commercial units are to expensive, and i'm a handy person. i got a nice size of coroplast to use as my hx core. they are 12 x 12. considering using pc high static fans to fun the unit.

based on this formula:
room CFM:

Step One – Use the above Air Changes per Hour Table to identify the required air changes needed for the use of the room. Let’s say it’s a conference room requiring 10 air changes per hour.

Step Two - Calculate the volume of the room (L’xW’xH’).

Step Three - Multiply the volume of the room by the required room air changes.

Step Four Divide the answer by 60 minutes per Hour to find the required room CFM

i get 192 cfm. that seems aweful high.
another one i found said i needed 12 cfm. so i'm kinda stuck on how big to size my unit. i feel 12x12x8 hx core would be way to big. I havent ordered any materials to start this yet. Figured i better get more info on sizes i should be going with. i plan to put the unit in a storage area i have over my bathroom. looking to use 4" intake and exhaust ports. and possibly arduino to control my fan speeds. Any help is appreciated. I see this post is kinda old, so i hope i get a reply or may have to move to new thread. thanks all

p.s i also am a vapor, so the is a fair amount of moisture in my air, but that isnt to big of an issue, as i plan to have a way to dain the hx in some way. just thought i should add that in case it changes any thing.

Why you would select it as conference room if it is your house? I home you dont need more than one air change per hour - and that is boostmode. Normal everyday mode is 0.5-0.3 airchanges per hour.

lol. opps. i never even caught the conference room reference. i just copied and pasted the formula that i used from another site. i'm pretty sure based on the formula with using 1 air change per hour it still comes out as the 192...actually i think i used 5. basically my floor plan is all open with a loft, and a small 4'x8' bathroom. but the bathroom door is left open 90% of the time.

doing the same formula again with 1 air change it comes out as 32cfm?????

Looking at using 2 Corsair Air Series SP120 High Performance Edition 120mm High Static Pressure Twin Pack Fan (CO-9050008-WW). the move about 62 cfm, but i could use a potientiometer to slow them down and also to balance out the draw so they would be fairly balanced. ala this thru a coroplast core. just not sure how big a core i would need to make.

Since I have a full sheet I'm going to try and make my hx core 8x8x11w. And the casing is gonna be 15 tall x 11w x 18L. Going to also use 2" foam to insulate. Got my 2 sp120 corsair fans. So hopefully this will go together fairly easily. Which side does condensation usually build up on? The out going air or incoming? That way I know where to put my drain.

will be interesting to see how much air flow you get after filters and the heat exchanger. The fans you have provide 30 Pa max. That is not much.
Note that the air flow mentioned on the product page is measured at zero static pressure. Air flow will drop the more pressure the fans fave to overcome. Might be to weak. My fans provide 80 Pa and I use two in a push-pull config giving me 160 Pa. That resulted in a 25% Airflow going to the ventilation compared to what the fans would be able to provide.
Alos PC fans do not like humidity and the temperature range they have to operate in a ventilation system. My started to fail after 6 months. Rattling sound the make....
Exchanging them now against Delta Fans with 120 Pa and comparable air flow (a bit less - but should end up same or more resulting air flow).

Im only trying to do a 250 sq ft tiny house. Now that cold weather is here, im finding air drafts that i didnt know i had. I took extreme caution during my build process to make sure i was sealed up as tight as possible. If the fans last the winter ill be happy. Just mainly need the fresh air so i can run my main heater which is a propane unit. Didnt want to waste by cracking a window and running my bathroom exhaust fan and wasting heat that way. So figured a small hrv would work better than just wasting

Mini counter-flow HRV - too small?
 

Hello! First time poster, long time lurker (on this thread anyway).

I'm toying with making a counter-flow HRV as a hobby project for a finished backyard office/studio/workshop (~1050 cu. ft.). How does one go about sizing the core itself?

Pictures show a Sketchup model of an 6"x6"x32" counter-flow core made out of 4mm coroplast, which would use just about exactly one sheet (including strips). I'm not sure if that is too small to be effective for this size space. If I was doing the math right, maybe 80-90 CFM for this space?

ISO View:
https://ecorenovator.org/forum/attac...1&d=1548280107

Segment View. The center support strips are probably unnecessary for this 6x6 design... it started out as 10x10.
https://ecorenovator.org/forum/attac...1&d=1548280107

Sketchup 2016 model in attachments.

My experience is that about 35 CFM is normally enough for a house with two or three people in it. The house is fairly tight at 0.85 ACH50. We run the HRV at a higher speed for a couple days when the weather first gets cold to control condensation on the windows.

Don't forget freeze protection. In cold weather, moisture in the outgoing air will freeze inside the heat exchanger and plug it off. My (purchased) HRV has a frost removal cycle that turns off the makeup air blower, and switches the exhaust air blower to high for one or two minutes every half hour or so when the outside air temperature is below about 20 deg F.

the outgoing interior air has the humidity. It meets the incoming cold air and condenses. Not sure how you are going to deal with this in your coroplast

outgoing air should be little-bit "downhill", so water does not get trapped in heat exchanger core. After that you need drain-hose with water-lock (just make round loop with zip-tie)

What's the worst thing that can happen if some water gets trapped in there?