6 ms·

The Ashrae Ventilation Recommendations Are Too Low

52 points by NavinF 3y ago

sporf 3y ago
Not sure where the author is getting their ventilation rates. ASHRAE 62.2* says "4.1.1 Total Ventilation Rate. The total required ventilation rate (Qtot) shall be as specified in Table 4-la (I-P) or 4-1b (SI) or alternatively calculated using Equation 4-la (I-P) or 4-1b (SI). Qtot = 0.03 Afloor + 7.5(Nbr + 1)" (in I-P) Where Afloor is the floor area and Nbr is the number of bedroom. A 2000 square foot 3 bedroom house would be 90cfm or ~45L/s. * indirect link https://www.ashrae.org/technical-resources/standards-and-guidelines/read-only-versions-of-ashrae-standards https://www.ashrae.org/technical-resources/standards-and-gui... direct link but blocked: https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ONLY_STANDARDS/STD_62.2_2022 https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ONLY_STANDARDS/ST...
Enginerrrd 3y ago
The article assumes buildings are air sealed. Which... they typically are not, even without considering things like operable windows. Real world C02 levels will be lower than calculated at that ventilation rate. As we chase down ever more efficiency gains with insulation and modern materials, you end up with buildings that are substantially more air-sealed. That said, I've long thought, even pre-COVID, that prescribed ventilation rates ARE too low for my preference. One of the problems though is you end up conflicting with energy requirements. You have to heat, cool, and sometimes humidify/dehumidify any outside air to match the inside conditions. If outside air makes up a significant fraction, the energy use can be enormous.
- PeterisP 3y ago
  > If outside air makes up a significant fraction, the energy use can be enormous. I don't work on HVAC, but don't even simple passive mechanical heat exchangers cut out most of the heat difference from ventilation of outside air?
  - Enginerrrd 3y ago
    Yes! But outside of urban areas, like in my area for example, that level of sophistication is relatively uncommon.
- quickthrowman 3y ago
  > If outside air makes up a significant fraction, the energy use can be enormous. This is what ERVs are for, conditioning incoming air from outdoors with the exhaust air. Enthalpy wheels are the most effective. https://en.m.wikipedia.org/wiki/Energy_recovery_ventilation https://en.m.wikipedia.org/wiki/Energy_recovery_ventilation > The article assumes buildings are air sealed. Which... they typically are not New buildings typically have a sealed building envelope/vapor barrier (excluding doors, obviously) and the HVAC system is balanced to account for pressure differentials. Commercial buildings typically don’t have operable windows, either.
  - Enginerrrd 3y ago
    This is a very urban centric view. Not everywhere is so modernized and sophisticated.
    - TeMPOraL 3y ago
      Per-capita, in most of the world approximately everywhere is urban - non-urban dwelling is a rounding error.
onetimeuse92304 3y ago
When I bought a good CO2 monitor I have discovered how difficult it is to keep CO2 levels down in an apartment that does not have two permanently open windows on two sides of the building. For example, the most surprising thing I have discovered is that just keeping the window open IS NOT ENOUGH. In my location, it is common for the outside temperature to be lower than room temperature at night but higher than room temperature during the day. There obviously is some time in the morning / evening where the temperature inside and outside is exactly the same. At this time, the air stops flowing in and out of the apartment, even if you have the windows wide open. The CO2 starts accumulating at a very high rate pretty much as if the windows were closed. I was very surprised by the graph showing large spikes up to 1500ppm in the morning while I was asleep. I was suspecting it is causing me to feel poorly in the morning and I started to feel much better when I started to sleep in a room with also the door open so that the air can freely flow through entire apartment.
- throwaway290 3y ago
  Is it year round? Can I ask where? What's the humidity on average?
  - onetimeuse92304 3y ago
    Central Europe. Humidity varies widely depending on weather and temperature, typically ranging from about 40% during the day and 80-90% in the morning on a nice day. Higher on a rainy day.
    - throwaway290 3y ago
      Sounds like nearly perfect climate! Perhaps you can fit an extractor fan somewhere strategic:) That should rule out morning lack of airflow
      - onetimeuse92304 3y ago
        My plan is to have a heat exchanger to help with this, which will also improve the situation much more on very hot and very cold days when I can't keep windows wide open.
bob1029 3y ago
> I do not know the reasoning that was used to calculate these guidelines. It is quite possible they were focused on factors other than CO2, such as maintaining comfortable moisture levels I feel like humidity (or lack thereof) is what most are struggling with when it comes to comfortable air. A non-trivial % of my energy use goes towards dehumidification. I have to run a central unit 24/7 if I want to keep RH below 55% during summer months. You can immediately tell how long the HVAC system has been running when you walk into a building in this area. Some mornings you walk in and it feels like a mild sauna, even if the outside temps are mild. The problem is that in most systems the dehumidification is linked directly to the cooling. If you decouple these concerns, you can much more easily achieve comfort. Variable speed heat pumps are another way to approach this issue.
frankus 3y ago
As a sanity check I looked at it from the standpoint of a 2400-calorie diet of 100% carbs (glucose) and it works out to around 32 grams per hour of CO2, which agrees with a figure of around 1000 liters per minute to dilute it down to 400 ppm over ambient.
AnotherGoodName 3y ago
Back when CO2 was ~300ppm in the atmosphere I used to sleep with windows closed. These days now that it's well up over 400ppm I'm putting fans in front of windows. It makes sense since a doubling (from being indoors) of 300ppm isn't pushing the noticeable 800ppm range whereas a doubling of 420ppm is. These recommendations probably worked in the 80s in my experience.
Syzygies 3y ago
People used to die of Cholera in London because they were drinking sewer water. There were so many deaths that they were motivated to fix this. We still breathe sewer air. There weren't enough pandemic deaths to motivate us to fix this. Proper ventilation gets CO2 levels down below 500ppm, at which point all respiratory illness transmission rates approach zero. CO2 is a proxy for how well our exhales are clearing the room before other people inhale. What makes fixing this expensive is that one doesn't want to trade energy use for clean air. Modern heat exchange technologies require more space than old building support without modification. There has been much written about this. Here is one article: https://www.theatlantic.com/health/archive/2021/09/coronavirus-pandemic-ventilation-rethinking-air/620000/ https://www.theatlantic.com/health/archive/2021/09/coronavir...
- J_Shelby_J 3y ago
  No one wants to hear that the solution is to move to somewhere they can keep the windows open year long. The most intellectually productive places in the modern world are good climates. This is one potential reason.
  - AlotOfReading 3y ago
    I don't normally associate places like the Pearl river delta and Iceland (most writers per capita) with clean air and great weather respectively. What's the point of comparison here, Mars?
    - tomjakubowski 3y ago
      Iceland's climate is quite temperate. It doesn't get hot in the summer and the winters are mild. Someone who's lived there could say if they are able to keep windows open most of the year. I would bet yes.
      - AlotOfReading 3y ago
        My family lives there. It's considered mild relative to the Arctic, one of the harshest environments on earth, but it's not compared to most places people actually live. Hurricane force winds and blizzards are extremely common during the winter months. You can open the windows in spring and summer if you're willing to deal with the bugs (which don't include mosquitos, thankfully), but you'll mainly be outside already trying to get your annual supply of vitamin D. Storms are fairly common most months, like everywhere else in the North Atlantic.
terminous 3y ago
I'm going to trust the recommendations of a professional association with dozens of named authors written after an extensive public notice-and-comment period, rather than what seems like a bespoke equation from some pseudonymous blogger with no expertise in the field, cobbled together in 15 minutes with coefficients that appears to just be the first figures found on Google.
- J_Shelby_J 3y ago
  TBH, the research into the effects of CO2 on cognition are limited. If your goal is to err on the side of safety, you ought to consider that a regulatory body tends to only consider data that exists. Given that little data exists for this, they likely did not consider cognition in their recommendations. Additionally, this is pre-covid. It's very clear now that most buildings do not cycle air enough to mitigate transmission of disease. This was less of a consideration when these recommendations were made.
tikkun 3y ago
Side note: if you can, check your thermostat and see if you can set your thermostat’s “fan mode” to on, instead of auto, for all the schedule settings that apply while you’re in the house. Ecobee allows this (comfort settings -> select presets that apply while you’re in the house -> change heat mode fan and cool mode fan to on). It’s the most effective way I’ve found for lowering CO2 for rooms that don’t have windows or when opening a window is impractical.
- LUmBULtERA 3y ago
  In my area it is very humid the the summer months. If I leave the fan to “on” without the AC on it ends up also increasing indoor humidity quite a bit. We have a single stage AC unit… ideally a variable speed unit could just run longer at a lower speed, allowing more ventilation and humidity reduction.
- quercusa 3y ago
  If you have the option, a "circ" or timed mode (e.g., 10 minutes/hour) is better than "on" when using air conditioning, as the fan will blow condensed water back off the coil, raising the humidity you just paid to reduce.
  - schiffern 3y ago
    On the other hand, if you don't evaporate water off the coil then it stays wet all the time and grows mold quickly. This is very bad for indoor air quality. For this reason I intentionally run the fan after a dehumidification cycle. Yes a small amount of humidity goes back in the air, but it's a small price to pay for non-toxic air! You should probably have your AC unit professionally cleaned and inspected.
    - quercusa 3y ago
      The water doesn't need to evaporate off the coil; the coils are designed for it to drip off to the drain pan and out to a hose or condensate pump.
BXLE_1-1-BitIs1 3y ago
Ashrae is there to give management cover for poorly=cheaply ventilated buildings. Some decades ago I worked in a Bell Canada data center which had Ashrae minimum air quality. I found another job. Employer owned buildings are vulnerable to ventilation penny pinching. Employee productivity does not enter the equation. Schools are also problematic, especially with more bodies/ft². With Covid, some parents equipped their kids with CO2 monitors. Some cash strapped boards tried to ban them. Commercial landlords with multiple tenants are less inclined to cheap out on ventilation if they want to retain tenants.
panax 3y ago
If only there was a way to do direct air carbon capture for the home and office with high CO2 concentrations to lower them economically https://arstechnica.com/science/2020/10/start-up-wants-to-do-carbon-capture-on-stale-indoor-air-turn-it-into-fuel/ https://arstechnica.com/science/2020/10/start-up-wants-to-do... I wonder how this compares to the cost of properly ventilating in an non ideal climate for ventilation. My guess is that it is way more expensive
- deleted 3y ago
  [deleted]
- ActionPlankton 3y ago
  Played with these ideas a little: https://news.ycombinator.com/item?id=24530731 https://news.ycombinator.com/item?id=24530731

52 points by NavinF 3y ago

Not sure where the author is getting their ventilation rates. ASHRAE 62.2* says "4.1.1 Total Ventilation Rate. The total required ventilation rate (Qtot) shall be as specified in Table 4-la (I-P) or 4-1b (SI) or alternatively calculated using Equation 4-la (I-P) or 4-1b (SI). Qtot = 0.03 Afloor + 7.5(Nbr + 1)" (in I-P) Where Afloor is the floor area and Nbr is the number of bedroom. A 2000 square foot 3 bedroom house would be 90cfm or ~45L/s. * indirect link https://www.ashrae.org/technical-resources/standards-and-guidelines/read-only-versions-of-ashrae-standards https://www.ashrae.org/technical-resources/standards-and-gui... direct link but blocked: https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ONLY_STANDARDS/STD_62.2_2022 https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ONLY_STANDARDS/ST...

Enginerrrd 3y ago

The article assumes buildings are air sealed. Which... they typically are not, even without considering things like operable windows. Real world C02 levels will be lower than calculated at that ventilation rate. As we chase down ever more efficiency gains with insulation and modern materials, you end up with buildings that are substantially more air-sealed. That said, I've long thought, even pre-COVID, that prescribed ventilation rates ARE too low for my preference. One of the problems though is you end up conflicting with energy requirements. You have to heat, cool, and sometimes humidify/dehumidify any outside air to match the inside conditions. If outside air makes up a significant fraction, the energy use can be enormous.

PeterisP 3y ago
> If outside air makes up a significant fraction, the energy use can be enormous. I don't work on HVAC, but don't even simple passive mechanical heat exchangers cut out most of the heat difference from ventilation of outside air?
- Enginerrrd 3y ago
  Yes! But outside of urban areas, like in my area for example, that level of sophistication is relatively uncommon.
quickthrowman 3y ago
> If outside air makes up a significant fraction, the energy use can be enormous. This is what ERVs are for, conditioning incoming air from outdoors with the exhaust air. Enthalpy wheels are the most effective. https://en.m.wikipedia.org/wiki/Energy_recovery_ventilation https://en.m.wikipedia.org/wiki/Energy_recovery_ventilation > The article assumes buildings are air sealed. Which... they typically are not New buildings typically have a sealed building envelope/vapor barrier (excluding doors, obviously) and the HVAC system is balanced to account for pressure differentials. Commercial buildings typically don’t have operable windows, either.
- Enginerrrd 3y ago
  This is a very urban centric view. Not everywhere is so modernized and sophisticated.
  - TeMPOraL 3y ago
    Per-capita, in most of the world approximately everywhere is urban - non-urban dwelling is a rounding error.

onetimeuse92304 3y ago

When I bought a good CO2 monitor I have discovered how difficult it is to keep CO2 levels down in an apartment that does not have two permanently open windows on two sides of the building. For example, the most surprising thing I have discovered is that just keeping the window open IS NOT ENOUGH. In my location, it is common for the outside temperature to be lower than room temperature at night but higher than room temperature during the day. There obviously is some time in the morning / evening where the temperature inside and outside is exactly the same. At this time, the air stops flowing in and out of the apartment, even if you have the windows wide open. The CO2 starts accumulating at a very high rate pretty much as if the windows were closed. I was very surprised by the graph showing large spikes up to 1500ppm in the morning while I was asleep. I was suspecting it is causing me to feel poorly in the morning and I started to feel much better when I started to sleep in a room with also the door open so that the air can freely flow through entire apartment.

throwaway290 3y ago
Is it year round? Can I ask where? What's the humidity on average?
- onetimeuse92304 3y ago
  Central Europe. Humidity varies widely depending on weather and temperature, typically ranging from about 40% during the day and 80-90% in the morning on a nice day. Higher on a rainy day.
  - throwaway290 3y ago
    Sounds like nearly perfect climate! Perhaps you can fit an extractor fan somewhere strategic:) That should rule out morning lack of airflow
    - onetimeuse92304 3y ago
      My plan is to have a heat exchanger to help with this, which will also improve the situation much more on very hot and very cold days when I can't keep windows wide open.

bob1029 3y ago

> I do not know the reasoning that was used to calculate these guidelines. It is quite possible they were focused on factors other than CO2, such as maintaining comfortable moisture levels I feel like humidity (or lack thereof) is what most are struggling with when it comes to comfortable air. A non-trivial % of my energy use goes towards dehumidification. I have to run a central unit 24/7 if I want to keep RH below 55% during summer months. You can immediately tell how long the HVAC system has been running when you walk into a building in this area. Some mornings you walk in and it feels like a mild sauna, even if the outside temps are mild. The problem is that in most systems the dehumidification is linked directly to the cooling. If you decouple these concerns, you can much more easily achieve comfort. Variable speed heat pumps are another way to approach this issue.

frankus 3y ago

As a sanity check I looked at it from the standpoint of a 2400-calorie diet of 100% carbs (glucose) and it works out to around 32 grams per hour of CO2, which agrees with a figure of around 1000 liters per minute to dilute it down to 400 ppm over ambient.

AnotherGoodName 3y ago

Back when CO2 was ~300ppm in the atmosphere I used to sleep with windows closed. These days now that it's well up over 400ppm I'm putting fans in front of windows. It makes sense since a doubling (from being indoors) of 300ppm isn't pushing the noticeable 800ppm range whereas a doubling of 420ppm is. These recommendations probably worked in the 80s in my experience.

Syzygies 3y ago

People used to die of Cholera in London because they were drinking sewer water. There were so many deaths that they were motivated to fix this. We still breathe sewer air. There weren't enough pandemic deaths to motivate us to fix this. Proper ventilation gets CO2 levels down below 500ppm, at which point all respiratory illness transmission rates approach zero. CO2 is a proxy for how well our exhales are clearing the room before other people inhale. What makes fixing this expensive is that one doesn't want to trade energy use for clean air. Modern heat exchange technologies require more space than old building support without modification. There has been much written about this. Here is one article: https://www.theatlantic.com/health/archive/2021/09/coronavirus-pandemic-ventilation-rethinking-air/620000/ https://www.theatlantic.com/health/archive/2021/09/coronavir...

J_Shelby_J 3y ago
No one wants to hear that the solution is to move to somewhere they can keep the windows open year long. The most intellectually productive places in the modern world are good climates. This is one potential reason.
- AlotOfReading 3y ago
  I don't normally associate places like the Pearl river delta and Iceland (most writers per capita) with clean air and great weather respectively. What's the point of comparison here, Mars?
  - tomjakubowski 3y ago
    Iceland's climate is quite temperate. It doesn't get hot in the summer and the winters are mild. Someone who's lived there could say if they are able to keep windows open most of the year. I would bet yes.
    - AlotOfReading 3y ago
      My family lives there. It's considered mild relative to the Arctic, one of the harshest environments on earth, but it's not compared to most places people actually live. Hurricane force winds and blizzards are extremely common during the winter months. You can open the windows in spring and summer if you're willing to deal with the bugs (which don't include mosquitos, thankfully), but you'll mainly be outside already trying to get your annual supply of vitamin D. Storms are fairly common most months, like everywhere else in the North Atlantic.

terminous 3y ago

I'm going to trust the recommendations of a professional association with dozens of named authors written after an extensive public notice-and-comment period, rather than what seems like a bespoke equation from some pseudonymous blogger with no expertise in the field, cobbled together in 15 minutes with coefficients that appears to just be the first figures found on Google.

J_Shelby_J 3y ago
TBH, the research into the effects of CO2 on cognition are limited. If your goal is to err on the side of safety, you ought to consider that a regulatory body tends to only consider data that exists. Given that little data exists for this, they likely did not consider cognition in their recommendations. Additionally, this is pre-covid. It's very clear now that most buildings do not cycle air enough to mitigate transmission of disease. This was less of a consideration when these recommendations were made.

tikkun 3y ago

Side note: if you can, check your thermostat and see if you can set your thermostat’s “fan mode” to on, instead of auto, for all the schedule settings that apply while you’re in the house. Ecobee allows this (comfort settings -> select presets that apply while you’re in the house -> change heat mode fan and cool mode fan to on). It’s the most effective way I’ve found for lowering CO2 for rooms that don’t have windows or when opening a window is impractical.

LUmBULtERA 3y ago
In my area it is very humid the the summer months. If I leave the fan to “on” without the AC on it ends up also increasing indoor humidity quite a bit. We have a single stage AC unit… ideally a variable speed unit could just run longer at a lower speed, allowing more ventilation and humidity reduction.
quercusa 3y ago
If you have the option, a "circ" or timed mode (e.g., 10 minutes/hour) is better than "on" when using air conditioning, as the fan will blow condensed water back off the coil, raising the humidity you just paid to reduce.
- schiffern 3y ago
  On the other hand, if you don't evaporate water off the coil then it stays wet all the time and grows mold quickly. This is very bad for indoor air quality. For this reason I intentionally run the fan after a dehumidification cycle. Yes a small amount of humidity goes back in the air, but it's a small price to pay for non-toxic air! You should probably have your AC unit professionally cleaned and inspected.
  - quercusa 3y ago
    The water doesn't need to evaporate off the coil; the coils are designed for it to drip off to the drain pan and out to a hose or condensate pump.

BXLE_1-1-BitIs1 3y ago

Ashrae is there to give management cover for poorly=cheaply ventilated buildings. Some decades ago I worked in a Bell Canada data center which had Ashrae minimum air quality. I found another job. Employer owned buildings are vulnerable to ventilation penny pinching. Employee productivity does not enter the equation. Schools are also problematic, especially with more bodies/ft². With Covid, some parents equipped their kids with CO2 monitors. Some cash strapped boards tried to ban them. Commercial landlords with multiple tenants are less inclined to cheap out on ventilation if they want to retain tenants.

panax 3y ago

If only there was a way to do direct air carbon capture for the home and office with high CO2 concentrations to lower them economically https://arstechnica.com/science/2020/10/start-up-wants-to-do-carbon-capture-on-stale-indoor-air-turn-it-into-fuel/ https://arstechnica.com/science/2020/10/start-up-wants-to-do... I wonder how this compares to the cost of properly ventilating in an non ideal climate for ventilation. My guess is that it is way more expensive

deleted 3y ago
[deleted]
ActionPlankton 3y ago
Played with these ideas a little: https://news.ycombinator.com/item?id=24530731 https://news.ycombinator.com/item?id=24530731