DIY ventilation heat exchanger

[poorwill]

I have sealed our house to about 2 air exchanges per hours at 50 Pa. I fear some of the bedrooms are even tighter with their doors shut. Making a heat recovery ventilator may be the solution or just blowing a little fresh air in each of the bedrooms may be enough. Where I live, the Connecticut coast, a recuperator would achieve very little in the spring-summer-fall. Running the fresh fan at night and not during the day may be enough. In the middle of the winter, the stale air inlet could be from the ceiling above the wood stove as well as the bathrooms.

I have looked at the difference between aluminum verses plastic as an exchanger material. The efficiency seems dominated by the film coefficient and not the material conductivity. Plastic may be weaken by ice but I have not confirmed this. Plastic (coroplast) appears cheaper than aluminum flashing. Icing could be controlled by timing the fans and/or a bypass valve on the fresh air side.

The first step is to make an fresh air distribution manifold to the bedrooms. The bathrooms are already plumbed through a single Fantech FR100 to the outside. I purchased another Fantech FR100 for the fresh air side. I will connect this fan to a filter -- check valve -- outside. I will instrument and control this with Auduino. I hope then the final steps will become obvious.

I will try to post updates. Please advise at any point along the journey.

[poorwill]

I realized after the previous post that most of my questions were already answered in this thread. Many thanks to all the contributors.

[poorwill]

I got Platform IO to work with my Arduino Mega card. It is much better than the Arduino IDE. I ordered an ESP32-DevKitC-32E development board. The micro USB cords and wireless breadboards cost $20. The esp32 controller was only $10.

I may be able to use a Raspberry Pi as the data recording and presentation station. Esp cards can talk and control each other. Some have a battery and storage built into them. Truly amazing stuff for the price. I found out the Dallas DS 18B20 (digital temperature output) can be multiplexed into one channel.

I need to build the mechanical stuff also which could take some time in the hot attic. A few more post and maybe I will be able to show pictures...

[Robl]

We have a commercial mvhr which gives good efficiency of 90%. It’s got plastic sheets as the counterflow heat exchanger, as they're more efficient than metal. The fans are dc speed controlled. When the out going external air drops below 5C, the incoming fan starts to slow down rather than match the outgoing one, lowering efficiency, to protect the heat exchanger.
Control is from timers built in, but we leave it on auto - it came with an RH sensor, and I added a CO2 sensor, which works very well.
Originally i plumbed the condensation line straight out of the house - but this froze, and the unit indoors flooded, leaking water from loft through the ceiling. So i added an overflow bucket… which filled up and leaked(inevitable)…. Now its plumbed internally, it Tees into the drain of our bath.

For a while i considered adding a timer controlled duct restrictor/valve/damper, on the basis that flow is needed to bedrooms at night, but not during the day. I just never got round to it.

[Robl]

Continuing describing the system we have, in case it's helpful:
It's a Vent Axia Sentinel Kinetic Plus BH unit, which was the biggest I could fit through the loft hatch. Bigger meaning it runs slower and quieter!
I installed it myself, and the ducting is generally 6 inch diameter, the long loft run is even 10inch. Bigger means slower airflow - keeping it below 4m/s is crucial to keeping airflow non turbulent and quiet. The main unit is in our loft, and so are most of the ducts - I used "safe" metal ducting which fits together nicely, and is less likely to cut you. Then it connects to vents that are upstairs, or travels downwards in rectangular plastic pipes (still with the same cross sectional area as the 6" pipes) that are easy to hide in the back of the built in cupboards that our house has. Between the unit and the metal ducts, I used 6" "Tecsonic" insulated ducting, which is supposed to attenuate fan noise, and it allows an easier fit to the unit.
We have fresh air coming into 2 bedrooms and the lounge, leaving from kitchen and bathroom. Not that many places, but I find it works ok, as we have big gaps under doors. I had (lent it out ages ago, didn't come back) a CO2 monitor with a display, and tried it in various places - my conclusion was 1 person in a bedroom with an open door didn't necessarily need a vent, 2 did for sure. We have ~2.5ACH at 50Pa.
To commission the unit, I used a cone over each vent, noting the airspeed (unit at 50%). When I added up the air-outs, they equalled the air-ins, so I didn't bother adjusting the vent axia unit. The vents themselves screw in and out - so you could reduce the airflow - I haven't though, I'm sure this would reduce efficiency. The air mixes in the house, I don't see the purpose in precisely matching some ideal flow rate in each room when what you actually need varies depending on occupancy anyway.
I think we've had it around 8 years. I change the filters every 3 or 4 months when it nags me - remove the old filters, take off the old material (save the clips) so I'm left with the original wire former. Then cut out a new piece of filter from a massive roll of G4 filter I got years ago. The filter clips onto the wire using "Supaclips", and there - avoided spending £20 on new filters again!
I considered diy-ing the heat exchanger itself - they are expensive for what you get. Diy-ing the install gives big savings I'm sure though.

[vonronge]

I'm just going to leave this here. (I am not the seller, nor do I profit in any way.)

This is not a filter, it is a full replacement ERV core.

aliexpress.com/item/1005001685483437.html