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Office buildings should run like spaceships (2017) (wsj.com)
22 points by jdkee 11 days ago | hide | past | web | favorite | 13 comments

>The solution, he says, is an HVAC system that dynamically responds to both carbon-dioxide levels and levels of airborne particulate matter, pumping in fresh air while filtering out pollutants. It’s remarkably similar to the kind of air-circulation systems that NASA uses—on spaceships.

Ah yes. The NASA spaceships that pump in fresh air from outside the spaceship.

More seriously, I just bought the parts for a homebrew HRV, ( https://en.wikipedia.org/wiki/Energy_recovery_ventilation ) in the hopes of improving the CO2 concentration in my apartment, which is as bad as you'd expect: https://bbot.org/co2/

Nice CO2 graph. What did you use for the sensor & logging system? I bought an off-the-shelf CO2 monitor to tell me when I should open a window, but I can't extract the sensor readings from it. Any recommendations on good sensors compatible with standard home measurement systems? I have a Sense Hat for my RPi that logs temp & humidity and would like to add CO2 to it if possible.

It's a SCD30 talking to a flask.py script that logs the data with sqlite. Graph is done with plotly.js. All hacked together quickly, none of it working terribly well. Never tried to hook it into a home automation system.

The SCD30 carrier board I used was one of the Seeedstudio grove units: https://www.digikey.com/products/en?mpart=101020634&v=1597 Seeed says it's a 3.3/5V compatible unit, so you could even use it with your Pi if you buy a Grove base hat to add to your stack. I'm using it at 5V, so I don't have any direct experience with that configuration, though.

In my experience the SCD30 autocalibration is worthless, so put it outside and manually set it to a plausible number. I used https://www.pmel.noaa.gov/co2/story/Space+Needle as a reference. I think the Grove library ran it at a 2 second poll rate by default, which results in a substantial amount of sensor self-heating. (It draws 75mA while reading co2, since it's a spectrometer) This gives you a tradeoff between accuracy and data staleness, I just run mine at 20s and point a fan at it. If you build it into an air handling unit, which is its intended application, that's not a problem.

> It's a SCD30 talking to a flask.py script that logs the data with sqlite. Graph is done with plotly.


> 2. How do I install this? Um... are you stupid or something? Just attackclone the grit repo pushmerge, then rubygem the lymphnode js shawarma module – and presto!

Here I am with twenty years of a programmer career, more than 15 years of that with open source (just to illustrate I am not unfamiliar with hacking) and ... uh ... I open the balcony door from time to time and air the bedroom before going to sleep. I am too old for y'all.

I mean, I hadn't used flask since 2014, and had never used sqlite, plotly or an esp8266 (as a wifi transceiver) before. The project was intended as a learning exercise for playing around with those tools. Someone who just wants a CO2 sensor would buy https://www.amazon.com/dp/B0784TZFRW/ , which isn't much more expensive than my pile of components and has way more functionality; and someone who was interested in the messing with technology aspect would want to figure it out for themselves. There's maybe 200 lines of code total, in the entire project. Someone who wasn't as determined to wander into blind alleys as I was could do it in a weekend.

All I see in the Wikipedia page is something about a heat exchanger (it looked weird, I only skimmed it but it sounds like snake oil to me.) CO2 concentration would be a chemical thing. On space ships I know they used to use alkali metal peroxides (specifically lithium peroxide because lithium is light.) These decompose into oxygen and an alkali hydroxide which further absorbs CO2 (forming an alkali carbonate.)

Sorry, to be clear, the point of a recuperator is to exchange indoor air with outdoor air, reducing indoor CO2 without losing as much heat as opening a window. There's no chemical reaction taking place at all, it's just a heat exchanger.

Ah! Everything makes sense now. I guess I skimmed too aggressively.

You can buy an ERV commercially off-the-shelf for under $500. Is the homebrew recuperator cheaper and/or better somehow?

[0] - https://en.wikipedia.org/wiki/Energy_recovery_ventilation

Oh no, no better than something like the Panasonic FV-04VE1, and probably substantially worse if I billed my own time spent on a toy project at normal consulting rates. Just for fun. Heck, for $400 I could just leave a window cracked and run the heater slightly more, and still come out ahead.

so I notice that the co2, humidity, and temperature are all strongly correlated. I'm assuming that's because you are running AC during the day, which increases the circulation of fresh air.

I'm curious about the sharp dropoff just after 00:00 though, any idea what causes that?

It's a small apartment. The heat, co2 and water vapor are all from me, breathing or cooking. Sudden spikes are from opening doors. No AC or heating in the last 24 hours, all the temp changes are entirely from sunlight or appliance waste heat.

Article: https://outline.com/9P3z32

Also here's a description of the "spaceship HVAC" on NASA's tech transfer site, I wonder how expensive it would be for an office building: https://technology.nasa.gov/patent/LEW-TOPS-93

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