This is a working Energy Recovery Ventilator, tested for basic functions in range of ways. I have not been able to test the unit quantitatively to determine the exact efficiency that it gets in a range of temperature conditions, however testing of the core thermal regenerator/thermal wheel module was performed, during the development process, and it indicated greater than 80 percent sensible efficiency at a temperature differential of only 10 degrees C. (21 degrees inside, 11 degrees outside.) Efficiency goes up with greater temperature differential, so this is really good.

Flow rate is adjustable from about 7 CFM to 22 CFM. It makes more noise at higher levels. It makes about 48 dBa at full power, and bout 24 dBa noise at low power (0.5 sone). These specs are taken from the specs of the fans, which are the only component that makes noise. The stepper drive is silent, using TMC2209 drivers.

The carbon saved per year, per dollar of capital investment is literally ten times higher for this unit than it is for a photovoltaic array. The money saved on energy per dollar of capital cost is more than twice as high, if you heat with natural gas, and 4 times as good if you heat with electricity. The carbon payback period (embodied carbon divided by yearly carbon savings) is literally more than sixty times better, that is 1/60th as much as it is for a PV array which saves the same amount of carbon dioxide emissions per year.

Whether you want to save money or you want to save the environment, this unit at this price is a better bet than a PV array, in my climate at my energy prices.

This unit has a bit of a limitation regarding the amount of torque the stepper motor can provide, and I am a bit concerned that the regenerator may stop turning if dirt gets in the seal or something. That doesn't damage the unit, it is not harmful that way, it would just stop recovering heat until the jam was cleared. It's a bit of a gamble, but for someone who pays a lot for heating it could easily pay for itself in a season or two/improve your air quality quickly, so it may be a winning one.

To determine if this is true for you with your energy prices, insolation, weather conditions etc., you can use the spreadsheets available at openERV.org. Here is a link to the financial and carbon emission sheet: https://docs.google.com/spreadsheets/d/116Zo_kcxLSTzkiw5lbofJJ0vPNLvXxe8Esu2196i8oA/edit#gid=0

It features a fully 3d printed regenerator core, printed with a 0.2 mm nozzle, it took more than 6 days of printing time to produce from 1.6 kilograms of plastic. It was produced in segments that were stacked upon each other to form the final unit.

As with other units of this type, which do not contain desiccant, such as the luno e2 or ego, latent heat efficiency does not come into play until the dew point of the air inside the home is higher than the outdoor air. Using hourly weather data to determine how often this happens and how much energy would be recovered, in a spreadsheet(which can be downloaded off the website), it appears to be about 42% net seasonal latent heat recovery efficiency, which is not too shabby.

This also applies in reverse. The result is that it doesn't block very much water vapor from entering a home in air conditioning situations, however it may in extreme conditions. It still blocks sensible heat, however, which is still helpful. So it can help you get fresh air while staying cool in summer.

It may be possible to improve latent heat efficiency by simply sprinkling some silica desiccant gel powder into the regenerator. Those dessicant packets should work fine, and could be ground with a coffee grinder to a suitably fine powder. However this is something I would have to try and test to determine the efficacy of, some other day. This would give relatively good efficiency even in an air conditioning scenario, keeping a lot of water vapor out of the home. About as good as any unit on the market possibly can.

Note that as far as I can tell, there are no single room units that contain desiccant, so this would be better than any other unit you can get. However this would be a hobby project, I cannot promise that it would give much actual return on investment, it would be interesting and I might undertake such a project myself in the future.

The core is a so called thermal wheel, but it currently has no desiccant in it.

This unit actually has probably a substantially higher efficiency than any commercially sold single room Energy Recovery ventilator. You have to understand that the efficiency figures quoted by manufacturers are highly unreliable, there is no agency forcing them to tell the truth, and the testing conditions do not reflect real world conditions, mostly due to unbalanced flow issues (caused by wind, primarily, for these types of units, for ducted units the length of the ducts is also a major factor). The standard testing procedures assume no wind, which is unrealistic and allows manufacturers to use fans that are cheap and quiet and move air with little energy consumption, but the efficiency of the unit drops to near zero when the wind blows enough to overwhelm the fans.

This unit uses high pressure centrifugal fans (static pressure of 25 mm of H2O, compared with only 2mm for a typical quiet axial fan), and secondly the system monitors the efficiency of the thermal wheel and adjusts the fan speeds to optimize it in real time, regardless of the cause of the suboptimality.

This is also important in buildings where the chimney effect is causing a pressure that tends to force air out of the unit! Such effects are common and substantial, especially in a high rise.

Why did you make it?

I made it as part of the development process to develop the OpenERV. Unfortunately it all cost me an enormous amount of time and money, and I would like to sell this unit to help support that effort.

I am choosing to use a different method of meeting my own ventilation needs this winter, by constructing a gigantic recouperator, because my house smells terrible and needs a vast amount of ventilation, more than 200 CFM, so this unit is not for me, otherwise I would just keep and use it.

What makes it special?

It is a unique prototype. However, it works and should work for many years, giving a true return on investment even from a strictly financial standpoint. I have priced it so that the return on investment is similar to or better than a photovoltaic panel in Ontario. There are spreadsheets available on the OpenERV site which help you to determine the exact payoff period financially, and in terms of saved carbon emissions, for your area and at the prices you pay for energy.

This is a rare, and I believe possibly historically significant, first example of a truly utilitarian, hard nosed, real value proposition on a basic, fundamental issue, through open source hardware and 3d printing, where the ultimate performance and financial and carbon emission return on investment is very favorable. And yet it is produced in a low capital manner by and for the people.

In other words, everything fundamental is aligned, for once, and on a bread and butter issue - energy, financial, comfort, housing.

It is also reprogrammable and highly hackable, you can reprogram the Raspberry Pi Pico to your liking, the USB micro port is accessible, and the electronics include a diode which allows you to connect to it while everything is powered on. The electronics are relatively simple, but I should add the caveat that they are pretty messy. They are soldered for reliability, but there are a lot of long wires and things may be hard to parse if you look at it visually. Ultimately, it is simple, though, there is a "silent stepper driver" module, a TMC2209, a voltage regulator, and 2 mosfet switch modules to control fan speed, and two 10k thermistors to monitor the temperature differential on either side of the thermal wheel.

Note that although I see no reason this unit should not last for many years of reliable operation, I cannot offer any warranty. It is much cheaper than a commercially available unit of the same airflow capability, and has higher efficiency. This is probably best suited to someone that needs a quick solution for a damp basement, or greenhouse or something.