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kostas 03-23-18 08:21 AM

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% @20C). Maybe two trasducers are insufficient. I'll do some more extensive tests in the next days.

meelis11 03-23-18 08:27 AM


Originally Posted by kostas (Post 58863)
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% @20C). 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.

LF-X 04-04-18 04:38 AM

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 112m 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.

kostas 04-04-18 06:48 AM

Hey guys, here's the post in my blog for the diy ultrasonic humidificator I've made for my heat exchanger:
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.

LF-X 04-04-18 05:34 PM

4 Attachment(s)
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 m/h. But it's a bit hard to measure...

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

LF-X 05-04-18 06:31 AM


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.

LF-X 05-04-18 07:42 AM

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: 19C (Fresh air comes from here)
Attic Temp: 26C (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: 23C (So Air going to the house is warmed by 3C compared to outside).
Exit Air: 20.6C (Cooled down from 26C 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).

LF-X 05-04-18 04:59 PM

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

LF-X 06-03-18 04:21 PM

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 m/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 m/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 m/h

scion19801 10-15-18 03:13 PM

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.

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