DIY ventilation heat exchanger

[Piwoslaw]

Originally Posted by DerekG

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

• The filters and/or ventilation motors may get wet.
• Excessive moisture may lead to mold.
• Enough water can start to clog some of the passages, both reducing efficiency and increasing risk of mold.
• In certain situations the water may freeze.

[dreamtech]

Greetings! Just found your forum and your thread while googling I also want to build a recuperator. I am thinking of buying 1000x2000x1mm aluminium sheets, cutting them into 200x200 squares and then gluing the squares with silicon, maybe, or putting window sealing D type rubber bands and screwing them together; if silicon, then also some hard material to separate the sheets (silicon is liquid after all). I would like a counterflow, so I am thinking about building two of such cassettes. Al sheets are not a problem-non anodized one costs some 20eur, anodized one some 23eur. Now here are my questions:
1.what should be the gap between the sheets? Corrugated plastic holes you are using are some 5mm, so maybe I should plan the same?
2.what could be the heat power transfer (watts) of one such cassette and what could be the air speed (m/s) for good results?
3.should I build some fins or other things in my gaps inside cassettes to generate some turbulence? Or maybe build some forms (like 5mm high semisphere) from wood and with help of them and hammer bend some depressions into aluminium? Turbulent flow could collect more heat from surface than laminar one, right?
For answering my questions-a bonus idea. I dont want to drill any walls, but I came across an idea-balcony door would open, making some 10cm gap at the side, the gaps at the top and bottom would be covered by "slice of pie" semicircle plastic, the side gap would face some plastic sheets with two holes and holes would be connected to my recuperator (air in, air out). I open balcony 10cm->there isnt a lot of cold air leaking in->the outside air interacts directly with my recuperator. You open door more-then its like simply opening the door

[IamIan]

FYI
Video of my prototype.

Design and build
https---://youtu.be/_kJB9LPhZDs

Performance test results
https---://youtu.be/fCgf1lCK4qQ

I was blocked from directly posting links .. remove the "---" used above to fool the bot.

[ThomSjay]

Originally Posted by IamIan

FYI
Video of my prototype.

Design and build
https---://youtu.be/_kJB9LPhZDs

Performance test results
https---://youtu.be/fCgf1lCK4qQ

I was blocked from directly posting links .. remove the "---" used above to fool the bot.

I thought I'd let you know that you have to make a few more posts before you can share links.

[donspain]

Were in Norway are you based?

[donspain]

Has things changed since 2011? My exhaust air holds normally around 10 degrees C in the winter time, with the preheater working slightly to avoid freezing in the inlet. Expelling this relatively hot air for hours, must represent a loss in energy and money. Am I totally wrong? My inlet temp during winter is set to 18 degrees C, and returned inside air is normally in the area of 21-23 degrees C. The efficiency of my exchanger is very high due to enfalty construction, with heat recovery also from moist in the air. My system will in automatic mode and with the use of modbus sensors and modbus emulated knx and 1 wire sensors, be completely run by itself, with the minimum speed of 3%. Having way to much fresh air in the house when no-one is present, is a waste of energy....

[donspain]

Originally Posted by Ko_deZ

What about smell food smell? Gas leaks? Should the ventilation run at maximum when there is a fire? Temperature? Certainly, a non-humidity recovering system like the window unit mentioned earlier should not be running if the outside temperature is below freezing since there would be a huge buildup of ice in the outgoing path. That would actually have to measure outside humidity as well, as that is an important factor in the efficiency of the HX and would determine the lowest temperature possible.

There are too many factors for this to be a good system. Sure, efficiency will be higher, but how much higher than >90% will you get? If you manage to cut the energy loss in half again, that sounds like a lot, but if your energy loss was just a few watt-hour anyway? Is it worth significantly reducing the experienced indoor climate (smell) because there is only one person in the house?

Also worth considering is that you without a ducted system will have to have one in each room, making the one in the bathroom much more troubled with icing up. Having a normal fan vent in this room would be throwing away a whole lot of energy since the hot and humid air during and after showering contains a whole lot of energy.

If your ceiling height is high, then it is very efficient to pull out energy from the high area and regenerate the heat to other parts of the house.

Not having a close to average temperature in your house will possibly cause moisture problems in your wall. The humidity-block (directly translated from norwegian. We use plastic for this) is inside the wall, thus at a cooler place than the inside air. Humidity has a tendency to even out troughout the house, but relative humidity will be higer in cooler rooms for this reason. If the humidity then also spreads into the walls, as it does, it might hit dew point before meeting the humidity-block in your wall. So a evenly heated house is important in cold climates.

A ducted system also keeps a positive pressure on the incoming air, and a negative on the outgoing as long as you have set it up correctly. Total should be a small negative pressure in the house. This will avoid pushing moist air out trough holes in the humidity-block, avoiding dew and humidity damage. A per-room based system must also have pressure sensors on both indoor and outdoor to make sure it does the same.

This is becoming a whole lot of work, with a whole lot of possible errors and bugs, and all it does is save a tiny bit of energy. Yes, I agree, make it as good as possible, but also consider the amount of time and effort, and investment, compared to the gain. I considered making my own system too, but I decided that it was not worth it.

Example of my house:
93% efficiency, 300m³ per hour, 20C inside 0C outside.
The outgoing air will have a temperature of 0+(20*0.07) = 1.4C. Difference is 1.4K
The specific heat capacity of air is about 0.001297J/cm⁻³k⁻¹.
My energy loss per hour is 1.4K*300000000cm³*0.001297J/cm⁻³k⁻¹ = 544J. That is not very much. 1W for one hour is 1J/s*3600s = 3600J.
If I run my ventilation unit at minimum, I have 150m³, and at max, 600m³. It would still not be a whole lot at max. Actually the fans use more power than that.

I suggest spending time and money insulating and swapping windows instead.

Has things changed since 2011? My exhaust air holds normally around 10 degrees C in the winter time, with the preheater working slightly to avoid freezing in the inlet. Expelling this relatively hot air for hours, must represent a loss in energy and money. Am I totally wrong? My inlet temp during winter is set to 18 degrees C, and returned inside air is normally in the area of 21-23 degrees C. The efficiency of my exchanger is very high due to enfalty construction, with heat recovery also from moist in the air. My system will in automatic mode and with the use of modbus sensors and modbus emulated knx and 1 wire sensors, be completely run by itself, with the minimum speed of 3%. Having way to much fresh air in the house when no-one is present, is a waste of energy....

[CozyCamper]

Hello everyone.

I am currently in the early stages of designing a van conversion (Fiat Ducato) for full time living. One of the problems raised by many people doing this is the excess moisture buildup. Every conversion I saw uses roof mounted windows with fans installed. Some people stated that they are running the fans very frequently even during winter. I really do not like this approach and thought that HRV could be a better solution. Unfortunately I found no one doing this.

My idea is to mount the heat exchanger beneath the floor and have the exhaust and intake below the vehicle. My thinking is that it would potentially result in cooler air in summer and protect the intake from rain ingress and I don't have to make holes in the roof. The total volume of air inside is about 14-16m3. I have 3 distinct spaces I would like to ventilate, the general living space (~8m3), bathroom (~2m3) and a storage space below bed (~4m3). I was thinking about using automotive cabin ventilation fans to move the air - readily available, built for longevity and relatively cheap, especially used ones.

Do you think that this small of a system is viable? There has to be a reason that no one is doing it this way. If I could get 60-80% heat recovery I would be very happy. It sure would beat just pumping out the warm air through the roof windows.

[IamIan]

Originally Posted by CozyCamper

Do you think that this small of a system is viable?

yes

Originally Posted by CozyCamper

There has to be a reason that no one is doing it this way.

I would bet on 3 main reasons.

#1> Follow the leader.
Most people do what they see other people do .. so it becomes a self full-filling loop .. people don't do it because they don't see other people doing it .. because they didn't do it , then other people don't see them doing it .. etc.

#2> DIY
OEM bought HRV is expensive .. it can be a fairly inexpensive not hard to make DIY version .. but most people lean away from DIY , some lean toward it .. but overall the majority of the population lean away from DIY.

#3> Small Space
This is 2 fold:
3a> Small spaces already cost small $ to heat and cool .. so inefficient methods (open windows in winter, etc) don't hit as hard , as they would for much larger spaces .. 50% of a heating bill on $20 is only $10 , but 50% on a heating bill of $2000 is $1000 , even though it's the same 50% either way.

3b> Small Spaces are already tight on space .. and HRV is just one more thing to suck of space .. so even those people who would otherwise do it , might choose to compromise and do without it because of the space limitations.

[paparapa]

Hello everyone. I am in process of gathering information for building my own unit (2 actually). As exchange core & motors/fans are heart of the device, i would like to ask for some recomendations. (I am from EU).

1. Needed air flow is cca 120-150m3/h, in normal operation. Motors have to be moisture resistant of course. Any ideas for fans? @LF-X mentioned Delta fans, which type did you buy?

2. Desire is to also return moisture (enthalpy exchanger), but i don't like the idea to have paper core. I see some comercial product nowadays have enthalpy exchanges that are not made out of paper and are washable. Does anyone know where(if) such exchange cores can be bought? (I noticed Zehnder is selling them as spare parts, but quite expensive).

Thanks for information.