[teekert]

I so need this, and I so need it to function with Home Assistant. I would love to ventilate based on values of my Aranet 4 (a bluetooth CO2 sensor). Also, would be nice if it coordinates with multiple units, ie what this brand does: [0]

EDIT: It does, if you click on "learn more", you'll learn more: "The OpenERV TW4 modules are made to always work in pairs. One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect!

Currently I have two holes in my wall for ventilation, when it is windy it's too much (feel the wind blowing inside), when some people visit and there is no wind, boom, >3000 ppm CO2 in 20 minutes.

I just really hope it is very quiet, although it says ~37 dBa (which is quite a lot imho), I replaced my bathroom ventilator recently, it produces 25 db! [1]). The previous one [2] produced 52 dB (cheapest around), that was pretty annoying, you'd hear it in the bedrooms above the room it was used in. Maybe 37 dB it isn't so bad, especially since you can wind it down and mostly need it when it's busy/noisy (many people) anyway.

Btw, don't buy a CO2 sensor, pretty soon you're a ventilation nerd, or as my wife would call it, a ventilation curmudgeon.

[0] https://blaubergventilatoren.de/en/series/vento-expert-a50-1...

[1] https://www.filterfabriek.nl/ventilatoren/badkamerventilator...

[2] https://www.hornbach.nl/p/rotheigner-toilet-badkamerventilat...

[Y_Y]

> One always sucks air while the other blows air, synchronized over WiFi. This should be done, or hot air would be pushed out from the building through the walls during the ingress phase, causing heat loss." ...Perfect!

Absolutely.

> A room is not heated by increasing its internal energy but by decreasing its entropy due to the fact that during heating, the volume and pressure remain constant and air is expelled.

https://pubs.aip.org/aapt/ajp/article-abstract/79/1/74/10418...

The point about balancing airflow is crucial, but I think underappreciated by non-professionals. Thermodynamics is highly non-intuitive in places, and the enclosed climate-controlled spaces we love to inhabit are certainly included in that.

Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.

[teekert]

Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.

Oh man I had this discussion with my wife yesterday, we have a small electric heater in a room where a pipe burst and I still need to fix that (no heating means instant fungus problems). It keeps its fan rotating always, that way it determines the input temp for its thermostat more accurately. But wife insists it is sometimes blowing cold air and thus very very bad... I explain what a thermostat is (bimetals and all) and that she experiences "coldness" because a layer of warm air is blown from her skin, it's not blowing cold air... she doesn't follow... I even measure the energy usage and the thing only uses 20 W or so when just blowing, not heating. Even when just blowing it's moving cold moist air from the walls so overall good. It's difficult dealing with her like this.

I'll pay someone to tell me how to deal with someone like this and maintain a positive atmosphere. The thing is, I also do it for things that really are probably not worth discussing... I should pick my battles better, is there ever a good time for some mansplaining? Or should I say... Nerdsplaining?

[sneak]

The problem as it stands now is that she is experiencing something (“it is blowing cold air”) and your claims (“no it’s not”) run counter to that direct experience.

Place and leave a thermometer in front of it and give her the information that you are using to make your own claims.

You went through a process to learn that moving air feels colder than still air at the same temperature. It seems that perhaps she has not. Surfacing the ground truth of the air temperature may help the situation.

[teekert]

Full of enthusiasm I did this whole thing as they did in Veratasium [0]. Didn't impress anybody in my family. Although my son is getting there I think... Maybe I'm just too bad and lengthy at nerdsplaining.

Actually, I didn't put an ice cube on the metal, that is the trick. of course.

[0] https://www.youtube.com/watch?v=vqDbMEdLiCs

[vanderZwan]

> Don't get me started on the idea that you can cool a closed room by running a fan or opening a fridge.

On that note, I'm curious if hybrid heating/cooling solutions will ever take off. Other than this OpenERV product I mean, which I guess technically counts!

Low Tech Magazine mentioned some experiments in their article on compressed air energy storage (CAES). Instead of trying to make that form of energy storage an adiabatic process, the idea is to use the heat produced/required in the compression/decompression steps in the household to improve the energy efficiency (e.g. use heat produced during compression to heat water; do the decompression in a space that should be cold anyway like a basement used for food storage).

[0] https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie...

[pzduniak]

Check out Komfovent units if you want a ready solution. My setup is Komfovent HRV (over MODBUS TCP), NIBE heatpump (over MODBUS UDP + esphome-nibe), Vaillant gas boiler (over eBUS-WiFi) + a bunch of AirGradients scattered around the house. Nothing has access to the internet, everything is glued together with HA. Works surprisingly well :)

[salomonk_mur]

37dba is practically nothing. Like a very soft whisper from a couple meters away. Remember the scale is logarithmic, 37 is almost 2 orders of magnitude below 52.

[open_erv2]

Thank you, this is correct. Using my class 2 sound meter, if I stand in my house in nowhereland cornwall with power shut off to the whole house, it's 38 dBa. 37 dBa is audible in that environment but nearly inaudible in a normal environment where your computer cooling fan is making 45 dBa at 1 meter, etc. 42 dBa is pretty quiet too, my furnace makes 43 dBa at 1 meter from the duct when it turns on. And that 42 dBa is a full 60 cfm, full blast. That's more than twice the airflow of competing units like the blauberg vento. You don't turn it up that high when you are sleeping.

[teekert]

Ok, so that 25 dB fan is a lie then because it can very easily be heard over other noise.

[open_erv2]

You have to look closely at the actual test protocol, which they rarely share. And in reality noise is hard to measure and hard to understand. There is also SPL and SWL, which are not the same. The marketing department has no clue and convert back and forth with approximations, adding or losing decibels, and nobody ever checks or really knows or, usually, cares. We need third party reviewers with actual sound meters or the numbers mfrs give us are practically useless. This is why I am prioritizing selling beta units to people who can actually test the units.

[gcormier]

Why not just buy an ERV? It's available, comparable in costs, and in 5-10 years, there will still be parts, unlike this project where the author hasn't actually shared the most crucial component, the exchanger.