6 ms·

I assume just installing CO2 scrubbers would have no benefit though, since the CO2 level is just a proxy for how much the air is recirculating.

Syzygies 6y ago
Exactly. A proxy.
Robotbeat 6y ago
Unless you use high quality HEPA filtration (and/or UV sterilization?) as well.
- nibsfive 6y ago
  Yes that increases air quality but it would not add oxygen back into the air in place of CO2.
  - Robotbeat 6y ago
    I’ve thought a lot about CO2 scrubbing of indoor air. Oxygen concentrators are cheaper than air scrubbing and much easier to do regeneratively. The simplest and cheapest scrubber is to just use sodalime, but that’s disposable and single-use. A regenerative system that heats up the lime (and vents the CO2 elsewhere) is more complicated and expensive and very energy intensive. Other solutions using amines or other chemicals to remove the oxygen can be more efficient, but many of them don’t work efficiently except at higher CO2 concentrations. We are, of course, talking about miniaturizing a Direct Air CO2 capture system, which usually operates at large scale to get efficiency. Replaceable cartridges that are regenerated at a central location may be a better option. But oxygen concentrators are small and cheap and portable and don’t require much energy to operate.
  - gpm 6y ago
    Oxygen depletion doesn't seem to be the issue though, CO2 toxicity does. At 1400ppm CO2, we've turned what, 1000ppm O2 into CO2 (is it 1-1?), or 1% of the atmosphere. Dropping O2 from (Edit: Fixed numbers) 21% to 20%. Or about a 5% reduction in O2 density. Equivalent to approximately 1500 feet of elevation... That's just not that much. (There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them)
    - taxicabjesus 6y ago
      > At 1400ppm CO2, we've turned what, 1000ppm O2 into CO2 (is it 1-1?), or 1% of the atmosphere. 1400ppm is 0.14%. Earth's current atmospheric co2 level is around 400ppm, or 0.04%. While the jump from 0.04% to 0.14% might seem significant (3.5x more co2!), it's not. Submariners survive on 3400 to 11300 ppm co2, or 0.34 to 1.13%: > Submarine crew are reported to be the major source of CO2 on board submarines (Crawl 2003). Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO2 concentration of 3,500 ppm with a range of 0-10,600 ppm, and data collected on 10 nuclear-powered attack submarines indicate an average CO2 concentration of 4,100 ppm with a range of 300-11,300 ppm (Hagar 2003). [0] [0] https://www.nap.edu/read/11170/chapter/5 https://www.nap.edu/read/11170/chapter/5 I'd like to emphasize that the average CO2 concentration for submariners is 4,100 ppm or 0.40%, or ten times Earth's current CO2 level. Oxygen is much more toxic than small amounts of CO2. Pure CO2 will kill you quickly, pure o2 will kill you slowly. > (There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them) I'm interested.
      - gpm 6y ago
        Oops, today really isn't my day for math apparently :(... 1% did seem high. --- > I'm interested. Well I don't have a blog post ready to go yet, but I can point you to some papers now. - This review cites a bunch of papers about health effects in the 1-10k ppm range: https://www.nature.com/articles/s41893-019-0323-1.epdf?referrer_access_token=eE4mU6nzyLJz_7TLn_xNMNRgN0jAjWel9jnR3ZoTv0Nmh56_6v6IG1wyUXiF6sNTHAt-0vDDZqKRyKQg__8_oxrm08uvJsMrDK8PUmvmArkegYALMahVANSDeRSyA8bTgKfjffuaO26tlP3hD6cHFJFm0RG8oSheeD0KC5mI-WlSIvZFjIL2uyZaN9KCm3_Lbdv7vGDkqNLiWzCKvPLh_8frf88zlrpECCEpeNnT6fFdkuk5mdFgJYeS6LPRWtSJ3t0qVO-l-XeqvTlXVLKdJ67nc_EcZbx81TO5U6j_0n-5SVon62qg8lNRw9-x8xkOCiys08VULZjj_p25Brz_0Q%3D%3D&tracking_referrer=www.theguardian.com https://www.nature.com/articles/s41893-019-0323-1.epdf?refer... - Table 3 in this paper references a bunch of papers around 10kppm: https://www.researchgate.net/profile/Susan-Rice-3/publication/228863103_Human_Health_Risk_Assessment_of_CO2_Survivors_of_Acute_High-Level_Exposure_and_Populations_Sensitive_to_Prolonged_Low-Level_Exposure/links/5526bb3b0cf229e6d635bcbf/Human-Health-Risk-Assessment-of-CO2-Survivors-of-Acute-High-Level-Exposure-and-Populations-Sensitive-to-Prolonged-Low-Level-Exposure.pdf https://www.researchgate.net/profile/Susan-Rice-3/publicatio... - These papers show mental effects in the 1-4k ppm range: https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1104789 https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1104789 http://www.aretas.ca/sites/default/files/imce_images/Indoor%20Environment%20in%20Schools%20%E2%80%93%20Pupils%20Health%20%26%20Performance%20in%20Regard%20to%20CO2%20Concentrations.pdf http://www.aretas.ca/sites/default/files/imce_images/Indoor%... - These two are from nasa about the ISS - which brings it's own complications but otherwise also show mental effects in the above range https://web.archive.org/web/20190613133240/https://ston.jsc.nasa.gov/collections/trs/_techrep/TP-2012-217358.pdf https://web.archive.org/web/20190613133240/https://ston.jsc.... https://pubmed.ncbi.nlm.nih.gov/24806559/ https://pubmed.ncbi.nlm.nih.gov/24806559/
- SEJeff 6y ago
  You can use ozone generators instead of UV. There is actually a really good residential one that is self cleaning my own HVAC guy recommended. He recommended I buy it myself on amazon and linked me to a youtube to install it: https://www.iwaveair.com/products/iwave-r https://www.iwaveair.com/products/iwave-r He said that his company would install it, but they'd overcharge and it is easy for anyone to install themselves. He had one in his house and told me all about it like a sales pitch. I installed one not because of the coronavirus, but because it helps with particulates in the air such as pollen and dander, which absolutely wreck me. I've only had it for a year, but it does seem to be noticeably better allergy-wise.
  - petre 6y ago
    UVC also generates ozone as a byproduct but it's toxic and it damages the lungs. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners#harmful-ozone https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-... Do read the warning from the EPA.
  - myself248 6y ago
    That one specifically says it ionizes without creating ozone. That's a good thing, because there is no safe/acceptable level of ozone in indoor air: https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-... Ionizing can be a great way to remove fine particulate from the air, but it works best when there are charged surfaces for the charged particles to plate-out on. Simply ionizing them in the ductwork means the particles stick to whatever's handy, which may be the ducts, may be the furniture, may be your lungs. Which is to say, this product uses a lot of the right vocabulary, to describe precisely the wrong engineering.
amluto 6y ago
I have never heard of a building with a CO2 scrubber. Submarines and spacecraft, perhaps.
tjmc 6y ago
HVAC engineer here. Correct - and the reason that ventilation is currently limited in buildings is to reduce energy loss. Exhausting warm air in winter or cool air in summer is enormously resource intensive for a building. Depending on the building configuration, you can reclaim some but not all of that energy by using heat exchangers, where the exhaust and supply air streams exchange heat without mixing but then you impose an energy penalty via increased pressure on the ventilation fans in mild conditions when the heat exchange is of less benefit. So all the standards and codes are designed around reducing unnecessary ventilation and frankly, there's been very little consideration of the health implications until COVID hit.
- edejong 6y ago
  If you would be building a new house and willing to spend double the usual on HVAC, what would your focus be on?
  - tjmc 6y ago
    The perhaps non-intuitive answer is - everything that reduces the need for HVAC. I'd be looking at things like passive solar design so windows are shaded in summer but let sunlight in for heat in winter. Very good insulation and building sealing. Double glazing (possibly triple if you're in a very cold climate). Thermal mass in the right places for temperature stablity. On the HVAC side, you want a system with a high CoP and I'd probably be looking at some form of energy recovery on the ventilation side.
    - eecc 6y ago
      Yup, very much so: https://www.treehugger.com/praise-dumb-box-4853131 https://www.treehugger.com/praise-dumb-box-4853131 I live in a relatively new building in NL, where many of these configurations are applied and on its own it won’t go lower than 21C in winter and 25C in summer. Thick walls, thick anhydrous cement floor layer for insulation (although I think it’s also meant to give the option to implement floor heating), _external_ blinds on the South side. I simply can’t justify a smart thermostat/radiator valve build, despite my inside nerd constantly whispering I should. Only downside is the heat exchanger air recirculator: it dries the air terribly in winter. You need a humidifier to avoid getting parched skin and mucosa.

Syzygies 6y ago

Exactly. A proxy.

Robotbeat 6y ago

Unless you use high quality HEPA filtration (and/or UV sterilization?) as well.

nibsfive 6y ago
Yes that increases air quality but it would not add oxygen back into the air in place of CO2.
- Robotbeat 6y ago
  I’ve thought a lot about CO2 scrubbing of indoor air. Oxygen concentrators are cheaper than air scrubbing and much easier to do regeneratively. The simplest and cheapest scrubber is to just use sodalime, but that’s disposable and single-use. A regenerative system that heats up the lime (and vents the CO2 elsewhere) is more complicated and expensive and very energy intensive. Other solutions using amines or other chemicals to remove the oxygen can be more efficient, but many of them don’t work efficiently except at higher CO2 concentrations. We are, of course, talking about miniaturizing a Direct Air CO2 capture system, which usually operates at large scale to get efficiency. Replaceable cartridges that are regenerated at a central location may be a better option. But oxygen concentrators are small and cheap and portable and don’t require much energy to operate.
- gpm 6y ago
  Oxygen depletion doesn't seem to be the issue though, CO2 toxicity does. At 1400ppm CO2, we've turned what, 1000ppm O2 into CO2 (is it 1-1?), or 1% of the atmosphere. Dropping O2 from (Edit: Fixed numbers) 21% to 20%. Or about a 5% reduction in O2 density. Equivalent to approximately 1500 feet of elevation... That's just not that much. (There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them)
  - taxicabjesus 6y ago
    > At 1400ppm CO2, we've turned what, 1000ppm O2 into CO2 (is it 1-1?), or 1% of the atmosphere. 1400ppm is 0.14%. Earth's current atmospheric co2 level is around 400ppm, or 0.04%. While the jump from 0.04% to 0.14% might seem significant (3.5x more co2!), it's not. Submariners survive on 3400 to 11300 ppm co2, or 0.34 to 1.13%: > Submarine crew are reported to be the major source of CO2 on board submarines (Crawl 2003). Data collected on nine nuclear-powered ballistic missile submarines indicate an average CO2 concentration of 3,500 ppm with a range of 0-10,600 ppm, and data collected on 10 nuclear-powered attack submarines indicate an average CO2 concentration of 4,100 ppm with a range of 300-11,300 ppm (Hagar 2003). [0] [0] https://www.nap.edu/read/11170/chapter/5 https://www.nap.edu/read/11170/chapter/5 I'd like to emphasize that the average CO2 concentration for submariners is 4,100 ppm or 0.40%, or ten times Earth's current CO2 level. Oxygen is much more toxic than small amounts of CO2. Pure CO2 will kill you quickly, pure o2 will kill you slowly. > (There's also a long list of papers showing issues with CO2 toxicity at low levels of CO2... I keep intending to write a blog post summarizing them) I'm interested.
    - gpm 6y ago
      Oops, today really isn't my day for math apparently :(... 1% did seem high. --- > I'm interested. Well I don't have a blog post ready to go yet, but I can point you to some papers now. - This review cites a bunch of papers about health effects in the 1-10k ppm range: https://www.nature.com/articles/s41893-019-0323-1.epdf?referrer_access_token=eE4mU6nzyLJz_7TLn_xNMNRgN0jAjWel9jnR3ZoTv0Nmh56_6v6IG1wyUXiF6sNTHAt-0vDDZqKRyKQg__8_oxrm08uvJsMrDK8PUmvmArkegYALMahVANSDeRSyA8bTgKfjffuaO26tlP3hD6cHFJFm0RG8oSheeD0KC5mI-WlSIvZFjIL2uyZaN9KCm3_Lbdv7vGDkqNLiWzCKvPLh_8frf88zlrpECCEpeNnT6fFdkuk5mdFgJYeS6LPRWtSJ3t0qVO-l-XeqvTlXVLKdJ67nc_EcZbx81TO5U6j_0n-5SVon62qg8lNRw9-x8xkOCiys08VULZjj_p25Brz_0Q%3D%3D&tracking_referrer=www.theguardian.com https://www.nature.com/articles/s41893-019-0323-1.epdf?refer... - Table 3 in this paper references a bunch of papers around 10kppm: https://www.researchgate.net/profile/Susan-Rice-3/publication/228863103_Human_Health_Risk_Assessment_of_CO2_Survivors_of_Acute_High-Level_Exposure_and_Populations_Sensitive_to_Prolonged_Low-Level_Exposure/links/5526bb3b0cf229e6d635bcbf/Human-Health-Risk-Assessment-of-CO2-Survivors-of-Acute-High-Level-Exposure-and-Populations-Sensitive-to-Prolonged-Low-Level-Exposure.pdf https://www.researchgate.net/profile/Susan-Rice-3/publicatio... - These papers show mental effects in the 1-4k ppm range: https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1104789 https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1104789 http://www.aretas.ca/sites/default/files/imce_images/Indoor%20Environment%20in%20Schools%20%E2%80%93%20Pupils%20Health%20%26%20Performance%20in%20Regard%20to%20CO2%20Concentrations.pdf http://www.aretas.ca/sites/default/files/imce_images/Indoor%... - These two are from nasa about the ISS - which brings it's own complications but otherwise also show mental effects in the above range https://web.archive.org/web/20190613133240/https://ston.jsc.nasa.gov/collections/trs/_techrep/TP-2012-217358.pdf https://web.archive.org/web/20190613133240/https://ston.jsc.... https://pubmed.ncbi.nlm.nih.gov/24806559/ https://pubmed.ncbi.nlm.nih.gov/24806559/
SEJeff 6y ago
You can use ozone generators instead of UV. There is actually a really good residential one that is self cleaning my own HVAC guy recommended. He recommended I buy it myself on amazon and linked me to a youtube to install it: https://www.iwaveair.com/products/iwave-r https://www.iwaveair.com/products/iwave-r He said that his company would install it, but they'd overcharge and it is easy for anyone to install themselves. He had one in his house and told me all about it like a sales pitch. I installed one not because of the coronavirus, but because it helps with particulates in the air such as pollen and dander, which absolutely wreck me. I've only had it for a year, but it does seem to be noticeably better allergy-wise.
- petre 6y ago
  UVC also generates ozone as a byproduct but it's toxic and it damages the lungs. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners#harmful-ozone https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-... Do read the warning from the EPA.
- myself248 6y ago
  That one specifically says it ionizes without creating ozone. That's a good thing, because there is no safe/acceptable level of ozone in indoor air: https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-... Ionizing can be a great way to remove fine particulate from the air, but it works best when there are charged surfaces for the charged particles to plate-out on. Simply ionizing them in the ductwork means the particles stick to whatever's handy, which may be the ducts, may be the furniture, may be your lungs. Which is to say, this product uses a lot of the right vocabulary, to describe precisely the wrong engineering.

amluto 6y ago

I have never heard of a building with a CO2 scrubber. Submarines and spacecraft, perhaps.

tjmc 6y ago

HVAC engineer here. Correct - and the reason that ventilation is currently limited in buildings is to reduce energy loss. Exhausting warm air in winter or cool air in summer is enormously resource intensive for a building. Depending on the building configuration, you can reclaim some but not all of that energy by using heat exchangers, where the exhaust and supply air streams exchange heat without mixing but then you impose an energy penalty via increased pressure on the ventilation fans in mild conditions when the heat exchange is of less benefit. So all the standards and codes are designed around reducing unnecessary ventilation and frankly, there's been very little consideration of the health implications until COVID hit.

edejong 6y ago
If you would be building a new house and willing to spend double the usual on HVAC, what would your focus be on?
- tjmc 6y ago
  The perhaps non-intuitive answer is - everything that reduces the need for HVAC. I'd be looking at things like passive solar design so windows are shaded in summer but let sunlight in for heat in winter. Very good insulation and building sealing. Double glazing (possibly triple if you're in a very cold climate). Thermal mass in the right places for temperature stablity. On the HVAC side, you want a system with a high CoP and I'd probably be looking at some form of energy recovery on the ventilation side.
  - eecc 6y ago
    Yup, very much so: https://www.treehugger.com/praise-dumb-box-4853131 https://www.treehugger.com/praise-dumb-box-4853131 I live in a relatively new building in NL, where many of these configurations are applied and on its own it won’t go lower than 21C in winter and 25C in summer. Thick walls, thick anhydrous cement floor layer for insulation (although I think it’s also meant to give the option to implement floor heating), _external_ blinds on the South side. I simply can’t justify a smart thermostat/radiator valve build, despite my inside nerd constantly whispering I should. Only downside is the heat exchanger air recirculator: it dries the air terribly in winter. You need a humidifier to avoid getting parched skin and mucosa.