I have traced the air with a smoke generator, there is a youtube video of me doing this on my youtube channel. There is not significant re-inhalation (short circuiting) of the air. The reason for the window mount is that a lot of people rent or otherwise cannot punch holes in their walls. However the reason the window mount is nearly the same as the TW4 (through wall) type, is that I cannot invest the time and money to re-design a whole new machine for a window. The primary value is in the TW4, but a lot of people wanted window mount ones so I helped some people out by deving a quick window adapter and then they helped me out by testing some of the components/the fundamentals of the system in the real world. Unfortunately the window mount units nobody is willing to really pay the cost of manufacture for, so they have to use grade B parts etc. and they have to serve the purpose of testing the TW4 or they aren't worth making.
That is half correct. The TW4 units operate in synchronized pairs. When one is exhausting (egressing), the other is ingressing (bringing air in). This always happens. They even have quite nice pressure sensors that precisely regulate the pressure the fans exert, controlling flow precisely and preventing the house from becoming pressurized at any time, which as you say would imply heat loss.
My price is for a pair, remember, not one. And those pioneer things don't work very well, poor flow and efficiency unfortunately. They claim high efficiency but it's only at the lowest flow rates and not the average for the cycle, only at the beginning of the cycle. There is one company that keeps emailing me trying to sell me units wholesale, I keep telling them to send me actual test data and then I might buy some (for testing), and they never do.
The MPLA (not pla) does not absorb the water vapor, but it condenses on the plastic and then evaporates. There is also the option of sorbent, which grabs the water vapor and then releases it with each cycle, before condensation occurs, getting higher efficiency.
The material in the whispercomfort is IIRC a fiberglass paper. It can only transfer liquid water, not solid water, and not vapor, effectively. The water condenses, whets the paper, then evaporates out the other side. It's a reasonable approach but does not work well in very low temperatures, and also the condensation process implies certain limits to efficiency, same as a non sorbent coated regenerative heat exchanger. The water doesn't start to condense until 100% RH, so it is 100% when it leaves the exchanger, while the air coming in is lower than that, usually. Thus water is lost.
Very interesting! Do you have a method of adding sorbent to a 3d print?
I wonder if it'd be worth having three TW4 modules with sorbent on only one of them. That way you can control humidity better by choosing 2 of the 3 to use at a time. Eg after a long shower you might wanna discard water vapor for an hour
What's the significance of the model numbers 4 and 12?
Yeah that would probably work, it's just a matter of cost. A lot of people balk at $700 CAD, the eventual price is supposed to be $1300 for a pair, you do that and you are looking at a lot of $ for the flow and energy recovered.
The numbers are the number of versions before it stabilized, so 12 tries for the window mount, 4 for the through wall. It took a while.
The step files are also there, which is the best common denominator for CAD files. Again, it's open source for the purpose of maintenance and repair, not cloning, and frankly earlier on I did make it more community oriented and nobody ever contributed even a little bit, so I just gave up on that idea.
The most likely scenario for longer term is that people may submit minor patches or suggestions, which I roll into the hardware or firmware. In reality, hardware is not like software. You can't make changes easily. Some wizards may take it upon themselves to spruce up the firmware with fancy features and release something, which anyone is free to do. There would then be multiple compatible versions of the firmware, one which I curate for reliability with minimal features, and others which others can provide. Same as for 3d printer firmware.
The firmware is Micropython, which is extremely easy to understand and modify.
There is the tw4, which is made to be put in a wall, and there is the WM12, which goes in the window. The main focus is the TW4. There are instructions in the manual for making an ERV core. It is not trivial.
I understand that the addition of desiccant material is the core aspect of what makes this an ERV. I don't actually see any clear explanation of how the desiccant material is added to the printed part. While the creator (open_erv2) mentions that sorbent/desiccant can be used to handle moisture ("If you have sorbent, it gets grabbed out of the air before it can condense"), they don't specify how it's incorporated into the design.
Is it added mid-print? After printing? Is it difficult to add?
I invented a process using some environmentally friendly solvents, grinding the sorbent and so on. It is not diy friendly unfortunately so there is little point in sharing the recipe.
The latest and greatest heat exchanger is produced directly with python script generated gcode specific to the printer I use and cannot be practically produced diy, unfortunately. However the old model can be, and the STL is included for that, in the source repository. To do this, simply use Cura, load th STL in, put it in the center of the build plate, and set it to do “lines” infill with about 2.5 mm on center (between centers of the lines) spacing and 0.45 mm width, no top layer and no bottom layer (set them to zero). Check the preview and it should show you a structure which is much like grid infill, parallel channels which are square in cross section, with the outer wall. Tape can be applied over the nubs on the side to fit in an oversized pipe, or they can be sanded if the pipe is too small. You could also use grid infill, but the roads tend to have problems where they intersect. When the nozzle goes over one road, it wipes the plastic off, and not enough is deposited on the lee side. I don’t know how to solve this in Cura without using lines infill. If you could make it so the nozzle went in alternate directions each layer that would probably solve it well enough.
You can add a filter to the TW4, there is an adapter/kit. It's a hepa filter from a car cabin filter system design. You rarely need both anti pollen and also ERV, so you would take the heat exchanger out and just use the filter and fan. As for dust, I recommend a good pc fan filter based appliance, not putting the filter in the flow path of the ERV.
It condenses on the heat exchanger, then it evaporates when the airflow reverses direction. That's if you don't have sorbent. If you have sorbent, it gets grabbed out of the air before it can condense.
It's better compared to a blauberg vento or lunos e2. That product probably gets poor efficiency, I have not checked the technical sheet but if they say 80% that means at the minimal flow levels, which are only 10 cfm or something. The TW4 gets >85% sensible and comparable latent efficiency, at 60 cfm. It also has twice the maximal flow of that device. It's got many other features as well, and is more durable. Ultimately, it's about return on investment. You have to make a spreadsheet and see which one is best, given the actual tested values for efficiency flow, maintenance cost, etc. If that's not possible, it's a shot in the dark.
