The Ashrae Ventilation Recommendations Are Too Low | Hacker News Reader

The Ashrae Ventilation Recommendations Are Too Low

cerereanscratchpad.blogspot.com

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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/coronavir...

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.

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?

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.

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.

The solution can be implemented in any climate, whether in the middle of the Sahara or Antarctica, without crazy energy usage either.

It's just that the energy recovery equipment is expensive, bulky and needs to be maintained.

> It's just that the energy recovery equipment is expensive, bulky and needs to be maintained.

ERVs can be had for US$ 500:

* https://www.amazon.com/Panasonic-FV-04VE1-WhisperComfort-Ven...

* https://www.youtube.com/watch?v=-3CRGhu8C5I

You can get some pretty small units as well:

* https://www.youtube.com/watch?v=V-wCCJHIZAo&t=10m35s

* https://www.youtube.com/watch?v=LGB83pSLMiI

Yes for a small room, but a whole house system typically needs a lot more then one small ceiling mounted unit.

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.

Is it year round? Can I ask where? What's the humidity on average?

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.

Sounds like nearly perfect climate! Perhaps you can fit an extractor fan somewhere strategic:) That should rule out morning lack of airflow

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.

Don't know what a heat exchanger is. Where I am currently extractor fans seem to be part of building code and now I can't imagine living without one

Heat exchanger blows outside air in and inside air out. Both air streams are flowing through the box in opposite directions, without mixing, so that outgoing air heats up and gets cooled by incoming air (assuming outside is colder than inside). These devices can be extremely efficient as they can recover something like 80-90% of energy.

In my case I am not necessarily looking to save up more energy, I am interested in being able to ventilate the apartment better without breaking the bank on energy.

Cool device.

But if your nights are slightly colder and days slightly hotter and humidity is so low then why be so complicated? You don't need heating, don't need AC... unlike tropics with constant +30 and 90% humidity or snowy places where it's -30 in winter, seems like you can just ventilate

See this cool chart btw: https://drajmarsh.bitbucket.io/psychro-chart2d.html (pick your place, select comfort overlay -> Givoni and it will show what you need to be in comfort zone in a given month based on temperatures and humidity)

Because we have winters? Like -20C? And then just opening the window to keep the apartment well ventilated is no longer very practical when you ask for a latte but get frappe if you don't drink it immediately...

Oh, I thought the weather you described was year round... Yeah heat exchanger sounds really cool. From Wikipedia, are they those big industrial things for houses? or can you fit a flat with it, like a window unit or something?

I don't live in an apartment but I have a basement and I experience the same thing. My CO2 levels constantly hover around 500ppm. Opening windows will clear out CO2 if it gets to critical levels but has diminishing returns at the 500ppm level. I suspect this is because CO2 is a heavy gas that often sits near the floor. My next experiment is to install a small fan near the floor and run it 24/7 to see if I can "pump out" the CO2 while the split units I have are running.

Ambient levels outside are 420ppm or so. If you're around 500, you're doing very well and I doubt there's much point in trying to do better.

Technically, any level of CO2 causes detriment. Even our ambient level is higher than some decades ago and apparently it is possible to measure the effect on us (mostly related to nervous system).

Personally, I can't discern any difference below 600 any way I tried to measure it.

I carry my Aranet4 with me and in some apartments of my friends and family it is normal for CO2 to not go below 2000ppm in winter. So you are doing pretty well.

I think this is incorrect. You may be thinking about PM2.5 levels of which there are no safe level, any amount is harmful. Similar for CO. But a certain non-zero amount of CO2 is actually required.

> it is normal for CO2 to not go below 2000ppm in winter.

How many IQ points lost does that count for I wonder.

That makes sense; they do peak at 1000ppm if someone sleeps down there, which my detector records as not good, which is why it's caught my eye.

Your CO2 sensor is likely inaccurate.

a) Good ones are expensive, and the consumer grade ones are valuable mostly for trends rather than precise readings.

b) They do occasionally require re-calibration. Meaning, leave it outside for 24 hours. The ones I have experience with expect an occasional return to atmospheric baseline, but if that never happens naturally - which never does in my apartment - they tend to drift.

c) Your basement might have amazing circulation. I have an air pump (it's a big radon fan) pumping in fresh air to my apartment any time CO2 rises about 700ppm, and the exhaust fan pulling air out as well. In theory, my circulation is quite good. However, even with all that the CO2 is quite high (700-1000ppm) while we're home.

You should consider an energy recovery ventilator. It blows in fresh outside air but it uses exhausted inside air to bring it up to the temperature of your home.

And this will work in a the apartment that OP is living in? Because that sounds like it might involve some invasive installation. If it's just a box one can plug in, maybe a vent hose, that would be great.

I’ve seen them in a form factor that resembles a short, shallow window air conditioner that you just close your window on top of and optionally lock into place with screws.

Some ERVs come in the shape of a cylinder, about 10cm x 30cm for use in apartments. Yes, installation requires cutting a hole in the wall, but it is doable.

I'm surprised that there are no portable ERVs similar to portable AC units that just vent out a window. I have a small ERV in my shed/office that uses a single outdoor and indoor vent for combined intake/exhaust. (ie minimal ducting)

Most require a hole in the wall. This company makes window units: http://www.purifresh.com/index.html

Yep. You are right. This is my main problem here -- not only the inside installation is extremely invasive. But the local laws basically prevent me from being able to make the large holes in the wall needed to pass the massive amounts of air.

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-gui...

direct link but blocked: https://ashrae.iwrapper.com/ASHRAE_PREVIEW_ONLY_STANDARDS/ST...

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.

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.

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.

> 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?

Yes! But outside of urban areas, like in my area for example, that level of sophistication is relatively uncommon.

> 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

> 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.

This is a very urban centric view. Not everywhere is so modernized and sophisticated.

Per-capita, in most of the world approximately everywhere is urban - non-urban dwelling is a rounding error.

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.

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.

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.

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.

Some water drips off, yes. Some water remains clinging to the coil and contributes to mold growth, especially if it's allowed to remain for long periods of time.

After all, if there were no residual clinging water then the fan couldn't "blow condensed water back off the coil", which was your original concern. ;-)

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.

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.

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.

> 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.

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.

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...

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

Played with these ideas a little:

https://news.ycombinator.com/item?id=24530731

Reply on news.ycombinator.com