Carbon Dioxide CO2 Levels in the Lab

[EEVblog]

Dave looks at the Carbon Dioxide CO2 levels in the lab, and the effect of the HVAC system.
https://www.uradmonitor.com/products/

[SiliconWizard]

That's something you get aware of when you start using CO2/TVOC sensors. I also have one.

That can be quite shocking. Ventilation is indeed key. Many older buildings are not well ventilated, and that can be a problem in winter (well, in the cold season) when you can't leave windows open. Classrooms or office rooms in such buildings can easily reach CO2 levels of over 1000 ppm, which isn't toxic, but it starts being uncomfortable. Poorly ventilated and overcrowded rooms can even reach levels as high as 3000 ppm. The outside average is around 400 ppm.

VOCs can also be a problem depending on the materials used in the room (from paint to furniture).

[tszaboo]

The outside average is around 400 ppm.

Nono. It's 5-7 percent. That was said by experts on climate change, trying to regulate you from doing something. Must be true. These experts would never be absolutely clueless about these things.

[floobydust]

Fresh (makeup) air is expensive. The energy costs to either heat or cool that incoming air can be significant.
Canadian winter outdoor air -25°C is basic, so that's heating it 50°C worth. Thus HVAC systems controlling the amount of makeup air based on indoor CO2 levels is common. In the USA as well.
Of all things to modulate that damper. Especially in shopping malls, they run them really cheap and just recirculate air, so zombie shoppers walk the mall lol.
The outdoor air filter can get clogged up or damper malfunction as well.

Radon gas is also a big issue here, in residential basements. Maybe uRAD could add that sensor to their lineup.

[golden_labels]

(…) and that can be a problem in winter (well, in the cold season) when you can't leave windows open. (…)

To some people lack of good ventilation is even worse in summer, when everybody turns on AC and seals windows. I’m one of the affected.

I don’t like it, but I can stand high temperature with open windows, but air conditioning is killing me. It feels like in hell the moment humidity and CO₂ levels rise just a little, even if temperature is kept at e.g. 23 °C. Give me 35 °C, an open window, and maybe a room fan.

[brucehoult]

I'd love to have a CO2 meter but I don't want to spend a fortune and I'm afraid of getting crap if I spend too little and don't know enough to know the difference.

At home I'm renting and have not been able to persuade the owners to install a heat pump (they say the wood fire meets the legal requirements), but I like cooling in summer, so I have a Dimplex "4000W" (actually around 1000W electrical consumption) portable air conditioner which actually does the job just fine in this climate.

That's not as efficient as a split unit heat pump because whatever cold air its blowing into the room is exactly matched by hot air its blowing outside through the hose [1], and whatever is blown outside had to be matched by ambient outside air being drawn into the house under doors or down the chimney ... or in my case I leave a window slightly open at the far end of the house, on the south (no sun) side.

BUT ... one benefit of constantly drawing in outside air rather than recirculating the same air all the time is that I probably don't have a problem with CO2 buildup.

It would be good to know for sure.

[1] which is also another inefficiency as the 1.5m or so of hose gets hot and radiates/convects back into the room

[Simmed]

https://sensirion.com/products/catalog/SCD30

yum yum 
looks like 36 yankee bucks on mouser

*looks like they have a newer 2025 product which includes PM2.5 as well
https://sensirion.com/sen6x-air-quality-sensor-platform

[Monkeh]

The outside average is around 400 ppm.

Nono. It's 5-7 percent. That was said by experts on climate change, trying to regulate you from doing something. Must be true. These experts would never be absolutely clueless about these things.

Now this is politics, but as well established I can't leave this sort of bullshit on the table.

The 'experts on climate change' in this hearing are, in order of guessing about CO2:
Marc Williams, Executive Director of the Texas DOT. He's a civil engineer. He's not a scientist, and is not an expert on climate change.
Dwayne Boyd, President for the Midsouth Region of CRH Americas Materials - a construction company. His education includes an internship on a paving crew and a BBA. He is not a scientist, nor an expert on climate change.
Aric Dreher, Assistant General Manager at Cianbro - a construction company. He does have a degree in civil engineering - but again, he's not a scientist, or a climate expert.
Paula Hammond, Senior Vice President at WSP USA - an engineering firm. She also has a degree in civil engineering and is also not a scientist or a climate expert.

Not one of these people is trying to regulate anything. They're executives of organisations which build roads.

[floobydust]

Graph source NOAA CO2 atmospheric trends

Sensiron CO2 sensor flyer
Three different technologies used : IR, Photoacoustic NDIR and thermal conductivity. They have some new CO2 sensors coming.
In the past I have just bought their eval boards.

[brucehoult]

https://sensirion.com/products/catalog/SCD30

yum yum 
looks like 36 yankee bucks on mouser

±30 ppm on a 400 ppm measurement doesn't sound like high accuracy to me!

Is that the randomness on repeated measurements, or manufacturing variation between units and any given unit will give significantly more stable readings?

[Simmed]

https://sensirion.com/products/catalog/SCD30

yum yum 
looks like 36 yankee bucks on mouser

±30 ppm on a 400 ppm measurement doesn't sound like high accuracy to me!

Is that the randomness on repeated measurements, or manufacturing variation between units and any given unit will give significantly more stable readings?

just my guess
on another model STC31-C
the ADC is 16bit and resolution is 30.5ppm
that could explain why
they probably used the same architecture (or ADC ?)
so just need more samples i guess ? (or use a dozen sensors ?)
 

[brucehoult]

For ventilation of stuffy rooms a method called Stoßlüften (shock airing), traditionally used in Germany is excellent. Two or three times a day you literally change the air in your space by opening all the windows wide to allow a strong draught to clear the stale air, it's generally only necessary to do it a few minutes at a go,

I do this from time to time, but for sure not every day.

My main kitchen / dining / living / office room is around 7m x 7m x 2.4m ~= 120 m^3. So the air in it weighs around 120 kg and the water content at 25 C and 50% RH is 1.2 kg. The mass of the walls / floor / ceiling / furniture is far greater, so exchanging with air at, say 10 C and 100% RH (which is also right around 10g/m^3 of water) takes surprisingly little time for the air temperature to equalise with the room contents, and even the humidity is the same as before.

it also helps prevent damp and mold growth in wet or cold conditions.

That's what I have a dehumidifier for.

[floobydust]

We all live in a yellow submarine, yellow submarine...

[TimFox]

From the NOAA website:

"Based on the annual analysis from NOAA’s Global Monitoring Lab, global average atmospheric carbon dioxide was 422.8 parts per million (“ppm,” for short) in 2024, a new record high.
The increase during 2024 was 3.75 ppm—the largest one-year increase on record.
At Mauna Loa Observatory in Hawaii (graph above), where the modern carbon dioxide record began in 1958, the annual average carbon dioxide in 2024 was 424.61 ppm, also a new record."

I keep tabs on my indoor level with an Extech meter:  normally reads roughly 450 ppm, but can go to 600-700 ppm when cooking on a gas range in the next room.

[ejeffrey]

https://sensirion.com/products/catalog/SCD30

yum yum 
looks like 36 yankee bucks on mouser

±30 ppm on a 400 ppm measurement doesn't sound like high accuracy to me!

Is that the randomness on repeated measurements, or manufacturing variation between units and any given unit will give significantly more stable readings?

7.5% isn't super accurate but indoor CO2 within a room unless you have a lot of air mixing.  When I have used these I wouldn't really worry about a 30 ppm error. 

Another issue is that I think all the cheap sensors also have significant base line drift on the time scale of several weeks so they implement auto-zeroing based on the assumed outdoor background level.  This can give an error if the room you have it in is never unoccupied or has very poor ventilation.

[SiliconWizard]

For just indoors air quality purposes, accuracy doesn't matter at all. There's a wide margin before CO2 levels become annoying and even more so before they become toxic. You don't care about 30 ppm, you don't even care about +/-100 ppm.

[Smokey]

For another dose of questionable "science" I give you FortNine and Motorcycle Helmet CO2:

Code: [Select]

https://www.youtube.com/watch?v=x_ej8sehs8k

[thm_w]

I keep tabs on my indoor level with an Extech meter:  normally reads roughly 450 ppm, but can go to 600-700 ppm when cooking on a gas range in the next room.

The NO2, CO, and methane from the gas stove are much more of a concern than the CO2 itself. Though the CO2 might be a good proxy for how well you are ventilating.

https://news.stanford.edu/stories/2024/05/people-with-gas-and-propane-stoves-breathe-more-unhealthy-nitrogen-dioxide

[TimFox]

I set up that meter as a proxy for ventilation measurements.  I quickly learned about the importance of the exhaust fan on the kitchen range, along with the kitchen window.