7 ms·

Not being snarky, but a window is one of the best options. Air conditioners can often be your worst option, as the air is recirculated more aggressively. We use

Not being snarky, but a window is one of the best options. Air conditioners can often be your worst option, as the air is recirculated more aggressively. We use a window fan that has multiple settings: circulate, ingress, egress. I find that no matter what setting you use, air is recirculated significantly well. On hot days, the fan is set on egress. This seems to do a really great job of removing excess CO2 while not bringing that much hot air into the house. We have a window fan running in the kitchen for the bulk of the year. We also find that simply cracking the windows in the winter makes a large and measurable difference in CO2, but not with heat.

gandalfgreybeer 2y ago
> a window is one of the best options. Add a fan and it's hard to find something more optimal and cheap for this problem.
- ratg13 2y ago
  Also, don’t put the fan directly in the window, but a leave a small gap between the fan and the window to take advantage of Bernoulli’s principle
  - everdrive 2y ago
    Do you have a good visual of what would be best here? I've been making sure my fan is as tightly sealed around the window as possible, but it'd be interesting to learn if there's a better solution.
    - ratg13 2y ago
      This teacher helps visualize this concept pretty well https://www.reddit.com/r/Damnthatsinteresting/comments/ul8mth/physics_teacher_shows_the_bernoullis_principle/ https://www.reddit.com/r/Damnthatsinteresting/comments/ul8mt...
  - user32489318 2y ago
    Yes! This video covers window and fans in more detail : https://m.youtube.com/watch?v=1L2ef1CP-yw https://m.youtube.com/watch?v=1L2ef1CP-yw
nequo 2y ago
> We also find that simply cracking the windows in the winter makes a large and measurable difference in CO2, but not with heat. Have you maybe done measurements of what difference between the inside and outside temperature is enough to reduce CO2 without a fan?
- guerrilla 2y ago
  This is a good question. Last fall I did some experimenting just trying to get the humidity out of my bathroom without a fan and it requires huge temperature differentials to do it in any reasonable amount of time. I bet CO2 is similar. A slight breeze fixes everything though.
- everdrive 2y ago
  I have. We live in the northeastern US, so our winters get quite cold. Our house is VERY well insulated, so I imagine you'll get different results depending on your situation. We have a CO2 meter, as well as a radon meter. Both work as analogues for air circulation. In the winter, you can measure temperature loss by measuring how often the heat comes on. And of course you can measure CO2 / radon just by looking at the gauges. What we've found is that in the winter putting two windows open a crack makes a very significant different in CO2 and radon builup. CO2 without the cracked windows will be around 1200 or more, while with cracked windows can be as low as 600-800. Not perfect, but like I said, a major improvement. I don't have a precise way to measure if the heat comes off more often, but my experience is that it does not.
- tzs 2y ago
  Temperature isn't going to be much of a factor at the temperatures and temperature differences humans encounter in their homes. The dominant factor in CO₂ exchange is the difference in CO₂ concentrations. Imagine a completely closed room surrounded by open atmosphere with the room air having twice the number of CO₂ molecules per m^3 as the open atmosphere. The room air and the outside air are at the same temperature. Now imagine opening a small vent in the room, and consider what happens to the air close to the vent. Molecules near the vent and moving toward it have a chance of crossing to the other side. At the vent we have a constant flow of molecules from inside to outside and a constant flow of molecules from outside to inside. What counts as "near" depends on the mean free path, which is proportional to temperature. With the temperatures the same the mean free path will be about the same. Since there are twice as many CO₂ molecules near the vent on the inside, twice as many CO₂ molecules will be flowing out of the room as are flowing in. A temperature difference would increase this, by increasing the mean free path on the hot side which increases what counts as "near" on that side. But what matters is what the temperature is above absolute 0. For a room at 40℃ (104℉) and an outside at 0℃ (32℉) that's only about a 15% temperature difference.
therobots927 2y ago
Also if you live in an area with low humidity look into getting a swamp cooler. It won’t make the air as cold as AC but I personally prefer it
- slau 2y ago
  Swamp coolers can get really nasty and smelly due to being the perfect breeding ground for spores and other nasties.
  - therobots927 2y ago
    I wasn’t aware of that. I haven’t had any issues and the swamp cooler at my place is old. It’s very dry here, but I guess if you were to not run the cooler for a while the water may sit and you could see stuff start to grow in it. If the water is running 20 hours a day I’d be skeptical that anything would settle there but I could be wrong. As soon as we stop using it for the season I drain the water out of the reservoir.
  - DougN7 2y ago
    I wonder what would cause that. It seems intuitive that it would happen, but like the other commenter I don’t recall any bad smells when we used on growing up. But it was also a very dry climate, so maybe that is the solution?
  - paulmd 2y ago
    same as humidifiers and they make bacteriostatic additives that help control this (although eventually it does need to be cleaned regardless).
    - therobots927 2y ago
      Thanks, I’ll look into additives
  - hagbard_c 2y ago
    I suspect a UV lamp over the evaporator would solve this problem. It would not need to be lit continuously, just at a regular interval short enough to quash any fledgeling fungal or bacterial growth. There may be swamp coolers which have such a sterilising function integrated, otherwise it'd be a useful hack with market potential.

gandalfgreybeer 2y ago

> a window is one of the best options. Add a fan and it's hard to find something more optimal and cheap for this problem.

ratg13 2y ago
Also, don’t put the fan directly in the window, but a leave a small gap between the fan and the window to take advantage of Bernoulli’s principle
- everdrive 2y ago
  Do you have a good visual of what would be best here? I've been making sure my fan is as tightly sealed around the window as possible, but it'd be interesting to learn if there's a better solution.
  - ratg13 2y ago
    This teacher helps visualize this concept pretty well https://www.reddit.com/r/Damnthatsinteresting/comments/ul8mth/physics_teacher_shows_the_bernoullis_principle/ https://www.reddit.com/r/Damnthatsinteresting/comments/ul8mt...
- user32489318 2y ago
  Yes! This video covers window and fans in more detail : https://m.youtube.com/watch?v=1L2ef1CP-yw https://m.youtube.com/watch?v=1L2ef1CP-yw

nequo 2y ago

> We also find that simply cracking the windows in the winter makes a large and measurable difference in CO2, but not with heat. Have you maybe done measurements of what difference between the inside and outside temperature is enough to reduce CO2 without a fan?

guerrilla 2y ago
This is a good question. Last fall I did some experimenting just trying to get the humidity out of my bathroom without a fan and it requires huge temperature differentials to do it in any reasonable amount of time. I bet CO2 is similar. A slight breeze fixes everything though.
everdrive 2y ago
I have. We live in the northeastern US, so our winters get quite cold. Our house is VERY well insulated, so I imagine you'll get different results depending on your situation. We have a CO2 meter, as well as a radon meter. Both work as analogues for air circulation. In the winter, you can measure temperature loss by measuring how often the heat comes on. And of course you can measure CO2 / radon just by looking at the gauges. What we've found is that in the winter putting two windows open a crack makes a very significant different in CO2 and radon builup. CO2 without the cracked windows will be around 1200 or more, while with cracked windows can be as low as 600-800. Not perfect, but like I said, a major improvement. I don't have a precise way to measure if the heat comes off more often, but my experience is that it does not.
tzs 2y ago
Temperature isn't going to be much of a factor at the temperatures and temperature differences humans encounter in their homes. The dominant factor in CO₂ exchange is the difference in CO₂ concentrations. Imagine a completely closed room surrounded by open atmosphere with the room air having twice the number of CO₂ molecules per m^3 as the open atmosphere. The room air and the outside air are at the same temperature. Now imagine opening a small vent in the room, and consider what happens to the air close to the vent. Molecules near the vent and moving toward it have a chance of crossing to the other side. At the vent we have a constant flow of molecules from inside to outside and a constant flow of molecules from outside to inside. What counts as "near" depends on the mean free path, which is proportional to temperature. With the temperatures the same the mean free path will be about the same. Since there are twice as many CO₂ molecules near the vent on the inside, twice as many CO₂ molecules will be flowing out of the room as are flowing in. A temperature difference would increase this, by increasing the mean free path on the hot side which increases what counts as "near" on that side. But what matters is what the temperature is above absolute 0. For a room at 40℃ (104℉) and an outside at 0℃ (32℉) that's only about a 15% temperature difference.

therobots927 2y ago

Also if you live in an area with low humidity look into getting a swamp cooler. It won’t make the air as cold as AC but I personally prefer it

slau 2y ago
Swamp coolers can get really nasty and smelly due to being the perfect breeding ground for spores and other nasties.
- therobots927 2y ago
  I wasn’t aware of that. I haven’t had any issues and the swamp cooler at my place is old. It’s very dry here, but I guess if you were to not run the cooler for a while the water may sit and you could see stuff start to grow in it. If the water is running 20 hours a day I’d be skeptical that anything would settle there but I could be wrong. As soon as we stop using it for the season I drain the water out of the reservoir.
- DougN7 2y ago
  I wonder what would cause that. It seems intuitive that it would happen, but like the other commenter I don’t recall any bad smells when we used on growing up. But it was also a very dry climate, so maybe that is the solution?
- paulmd 2y ago
  same as humidifiers and they make bacteriostatic additives that help control this (although eventually it does need to be cleaned regardless).
  - therobots927 2y ago
    Thanks, I’ll look into additives
- hagbard_c 2y ago
  I suspect a UV lamp over the evaporator would solve this problem. It would not need to be lit continuously, just at a regular interval short enough to quash any fledgeling fungal or bacterial growth. There may be swamp coolers which have such a sterilising function integrated, otherwise it'd be a useful hack with market potential.