Wow. I’m impressed and grateful.

I had installed the same higher than OEM level Bosch cabin air filter at your data indicates as well worthwhile. So good to see confirmation in numbers.
I have not really given much thought to the CO2 increase when running recirculate. so thanks for the heads up on that . Levels of 2000 are starting to slightly impair cognitive function.

One thing I did that you might want to experiment with:
I have sprinkled the upper surface of the air filter with granules of activated carbon.
they are capable of removing many volatile chemicals, including even some carbon monoxide from the air. I haven’t done any measurements and can’t say how often the granules would need to be changed to be of significant effect.
I put them in because here in my area of the West Coast each of the last five summers they have been significant number of days from forest fires, where the external air quality has been. Very smoky, in some cases right up to the EPA classification of "extremely unhealthy"and briefly up to "hazardous."
Needless to say, under those conditions, I’m running on recirculate.

 

I'm skeptical that a sprinkling of activated carbon granules would do anything to clean the air. Proper carbon air filters have powdered carbon embedded in a fibrous matrix, or a thick bed of granules. The air needs to be forced through paths that maximize the contact with the carbon. With just a sprinkling of granules, there wouldn't be that much surface area and the air would tend to flow around the granules. Regardless, I don't have the means to test carbon filters.

Wildfire smoke contains a lot of things, but the particles are the main health threat.

 

"Sprinkling" may have been misleading. It's a robust amount. filling most of the pleats. I'm sure it absorbs SOME nonparticulate contaminants. Some is better than none.
Could you not attempt to replicate what I have done (I'd be willing to mail you the activated carbon) and test out of curiosity? Just a thought.

 

Thank You for the write up. The HVAC on this car is the most confusing I have ever used.

 

Excellent write up, @balazer!

Could you go into a little depth about your test equipment and mockup/jig used for external testing?

 

Balazer, thanks for putting this information together - measurements, interpretation, and summary. I never thought about CO2 levels being affected by the recirc mode, and your "Air Delivery Mode Table" helps make sense of all the permutations of climate controls that might affect when the A/C might automatically come on.

After driving my Bolt about one and a half years now, I have observed that the HVAC system does not always respect how I have set the climate controls. This is true even in "fully manual" mode - that is, when I individually turn the heat and A/C ON or OFF, select 1, 2, or 3 air vent locations, set the fan speed, and set the "Auto Defog" to OFF. Despite my efforts to control the climate settings manually, my Bolt knows better than me, and occasionally turns the A/C or cabin heater ON even when I want them OFF. I know this from looking at various OBD2 data; the indicator lights on the climate control screen (or climate control buttons) do not always "tell the truth," as you mentioned (two examples) in your write-up.

I think if the Bolt had only an automatic setting for climate controls, I would quit complaining and just accept it. It is the over-riding of manually-set controls that I don't like. In my opinion (feel free to disagree, I am no expert) the behavior of the HVAC system really does not need to be this complex, and certainly not in manual mode. The behavior is opaque to the user and the complexity will make problems difficult to reproduce and diagnose. My Subaru (not an EV) doesn't try to do any of this, it is intuitive and simple, and fogging is not a problem.

 

...when I individually turn the heat and A/C ON or OFF, select 1, 2, or 3 air vent locations, set the fan speed, and set the "Auto Defog" to OFF. Despite my efforts to control the climate settings manually, my Bolt knows better than me, and occasionally turns the A/C or cabin heater ON even when I want them OFF...

For the cabin A/C, it's the same compressor as used for cooling the battery. It's possible you were seeing some battery cooling behavior. The Bolt would then have to turn on the heat to maintain the cabin temperature.

It's sort of efficient in one way (one less cooling system), sort of inefficient in another (have to run cooling and heating for the cabin when the battery needs cooling, even if the cabin doesn't). It was probably a calculated risk that if the battery needs to be cooled, the cabin HVAC system is probably running anyway.

 

• To keep the CO2 concentration below 1000 ppm, turn off recirculation and set the fan speed to the same number as the number of occupants. High CO2 levels can impair decision making.

That's an arbitrary threshold. High CO2 levels cause increased respiration. Our sense of the need to breath isn't triggered by diminishing oxygen, but instead the concentration of CO2. Exhaled air is 38,000 ppm CO2. For humans, the difference between 1,000 and 2,000 ppm air is fairly unimportant. Going from air that is 1,000 ppm to 2,000 ppm CO2 would imperceptibly increase respiration rate.

The way to measure "decision making" with regards to oxygen deprivation is with a SpO2 meter. 95%, and you're fine. These meters are 8 bucks online.

 

For humans, the difference between 1,000 and 2,000 ppm air is fairly unimportant.

Sure, 1000 ppm is an arbitrary CO2 threshold. But the differences aren't negligible. Here's one study showing that on several types of decision making tasks, going from 1000 ppm to 2500 ppm drops performance by more than a quartile. In other words, you get stupider when you're breathing high CO2 air. Even at 1000 ppm, performance is measurably worse than at 600 ppm.

A study of pilots taking flight exams in a simulator found that going from 2500 ppm air to 1500 ppm air made the odds of passing a flight maneuver go up by 52%.

And there are lots of other studies showing similar cognitive impairment in high CO2 air. It's unclear how any of this translates to driving, but there's definitely something going on with CO2 and the brain. It's not just increased respiration, and it's not from any lack of oxygen in the air.

 

The indoor air oxygen concentration was controlled in those studies. Only the CO2 level was varied. I can't say if they controlled for the time since eating, but in both studies they randomized the orders of exposures.

I'm not sure why you think measuring blood oxygen saturation should be important in a study intended to measure the effects of CO2 on cognitive performance.

 

I'm not sure why you think measuring blood oxygen saturation should be important in a study intended to measure the effects of CO2 on cognitive performance.

Where is the evidence that CO2 concentration alone predicts cognitive function? Human metabolism requires oxygen, and CO2 is the waste product. There is very solid evidence that cognitive function and blood oxygen concentration are correlated. There's a reason why an $8 (medicine pays more) SpO2 meter is among the basic diagnostic equipment used in the medical profession.

It's irresponsible to publish a paper based on 24 participants, and it's furthermore irresponsible to not measure the cheapest and easiest variable. It's lazy to control for a single variable and ignore everything else. That's a study put together by a regular group of middle-school students. I'd be ashamed to have my name mentioned as even remotely participating in such a "study".

 

Fram makes the active charcoal car filter. I have one in my other vehicle.

 

@LoneR, I have two kinds of PM2.5 detectors: one based on a Plantower PMS5003, and the Unitrend A25M, which is based on the Plantower PMS7003. Both can detect particles in the 0.3-3 μm range, and report PM2.5 particle mass concentrations in whole numbers of μg/m^3. The first detector also reports particle number concentrations for several ranges of particle sizes. The devices are laser particle counters. They count the individual particles that pass through the measurement chamber and measure their sizes, and then estimate the particle mass concentration from the known densities of standard particles of different sizes. Incidentally, the PM2.5 μg/m^3 readings from these devices are directly comparable to the raw PM2.5 values of outdoor sensors on the Purpleair map. Purpleair uses Plantower sensors.

To test a filter outside of the car, first I wait for someone to make some toast, which sends PM2.5 levels to 40 or 50 μg/m^3. I put the filter in front of a box fan and put the detector in front of the filter, right against it at its center. This placement ensures that I am only measuring air that passed throught the filter. I take the particle mass or number concentration at the output side of the filter divided by the concentration at the input side of the filter, which is the fraction of particles that made it through. One minus that is the filtration efficiency. So for example if I'm reading 40 μg/m^3 at the input side and 4 μg/m^3 at the output side, it's a filtration efficiency of 90%. When the output numbers get really low the precision is limited. I get more precision using the particle counts, which are much higher. For example with the Bosch filter I got a particle count of 2576 at the input side and 38 at the output side, from which I calculated an efficiency of 98.5% for that size of particle.

 

That sounds like a decent and inexpensive DIY measuring setup, for external testing. What are you using for your velocity and volume measurements?

 

I measured air velocity with a Unitrend UT363 handheld anemometer. I didn't measure volumetric airflow directly, but it should be proportional to air velocity. I measured CO2 with an Autopilot APCEMDL.

 

@balazer One would assume your career may have involved IAQ and/or HVAC/R technician. However, if you're like me, you may have collected many test instruments over the years.

 

That certainly applies to other skill-sets, too.

I've got an oscilloscope, a (nice) solder-station, tone generator, battery chargers and testers, and various hand tools and meters.

I call myself a "recovering EE". (Once an EE, always an EE.)

"Now, where'd that x10 probe get to?"

 

@GregBrew That's funny. I had those exact same pieces of equipment 35 years ago when I was a car audio "engineer". My work was in a few 'Car Wars', back in the day.

 

Poor ventilation has been associated with headaches, sleepiness, and difficulty in thinking clearly. ...

High CO2 levels have been associated with impaired decision making in some studies, even when ventilation was otherwise sufficient. I'm not aware of any tests on driving performance and CO2 concentrations, but one study showed that pilots were more likely to fail a flight exam in a high CO2 environment....

Recirculation mode uses 100% inside air and 0% outside air. ....

I love the methods you used to create this report!

I had always read that 'Recirc' legally had to have ~10% outside air to avoid this situation and Carbon Monoxide build up if there is an exhaust system leak.
Maybe that is old Legacy Gasser policy....

So, if what you say is true, the Bolt can be a dangerous, deadly vehicle if the driver sets the Climate Controls a certain way.
Is this ever mentioned in the Owner's Manual?

So how long would an unsuspecting owner have, before falling asleep or unconsciousness begins, if they are driving a long time with the Climate settings on Recirc?
What if 4 people are in the car at a DCFC stop for an hour with Recirc on? Maybe taking a nap. Will they wake up dead?

I drive with Recirc on anytime I have the heat working, but if it's really cold and fogging begins and I'll switch to outside air to clear the windows, then back to Recirc.
Now I have to start monitoring my 'alertness'? What's a simple on the road test for that?


How can GM sell a car that you could die in if you select certain Climate Settings?

 

It takes very high levels of CO2 before confusion or unconsciousness sets in: 50,000 - 100,000 ppm. Those levels won't be reached in the Bolt even with a car full of people and recirculation turned on or the climate system turned off. The car is leaky and some fresh air will enter.

I didn't test how high CO2 could get with 4 people in the car, but with 2 people, it never exceeded 2300 pm and stabilized around 2200 ppm. Extrapolation suggests levels could reach 4000 or 5000 ppm with more people in the car. Those levels are not inherently dangerous. At worst, occupants might experience mild effects, and not necessarily due to the CO2: headache, a sense of sleepiness, increased response times, and impaired decision making. You're not going to become unconscious and run off the road due to lack of ventilation. But you might be slightly less alert or make driving mistakes.

Using recirculation for short periods shouldn't be a problem, for example to heat up the car more quickly or to avoid an area of poor air quality or odors. But I recommend driving with recirculation turned off most of the time. If air quality is a concern, the cabin air filter can be upgraded. If energy usage is a concern, running a low fan speed saves climate system power while still delivering some fresh air.

 

It takes very high levels of CO2 before confusion or unconsciousness sets in: 50,000 - 100,000 ppm. Those levels won't be reached in the Bolt even with a car full of people and recirculation turned on or the climate system turned off. The car is leaky and some fresh air will enter.

I didn't test how high CO2 could get with 4 people in the car, but with 2 people, it never exceeded 2300 pm and stabilized around 2200 ppm. Extrapolation suggests levels could reach 4000 or 5000 ppm with more people in the car. Those levels are not inherently dangerous. At worst, occupants might experience mild effects, and not necessarily due to the CO2: headache, a sense of sleepiness, increased response times, and impaired decision making. You're not going to become unconscious and run off the road due to lack of ventilation. But you might be slightly less alert or make driving mistakes.

Using recirculation for short periods shouldn't be a problem, for example to heat up the car more quickly or to avoid an area of poor air quality or odors. But I recommend driving with recirculation turned off most of the time. If air quality is a concern, the cabin air filter can be upgraded. If energy usage is a concern, running a low fan speed saves climate system power while still delivering some fresh air.

passing the cow farms, would you rather breath CO2 or methane? Tough choices!

 

Reviving the thread to ask about the Bosch 6091C filter. I've got a 2023 Bolt EV, a new case of asthma, and a residence in metro Atlanta, where pollen flows in rivers. I'd love to be able to put a HEPA filter in the car, but the Bosch site says the 6091Cwon't fit the 2023 Bolt, nor do they indicate any filters available for this car. There's a YT video of a guy cutting down a filter to fit an older model Bolt, which probably messes up the filter's usability, so not doing that. Can anyone confirm whether this filter actually fits a 2023 Bolt EV? TIA.

 

@GA Bolt, all Bolt EVs and EUVs take the same cabin air filter regardless of the model year. The Bosch 6091C should fit.

 

OK, thanks, I'll take the chance.

 

Fantastic write-up, OP. Glad I stumbled across it.

I currently use the Bosch you tested, but am curious about the MicroGard HEPA 4062HP with the activated carbon. Lots of reviews about reduced air flow – I wonder how it'd compare to the Bosch. May pick one up to test.

 

Interesting approach! How often do you re-apply the carbon?

 

I honestly don't really have a schedule. On the car cabin filter (and BTW I do the same thing on our Subaru's cabin filter) I only have put new carbon on when putting in a new filter.
On the HVAC filter IIRR about halfway through the life of the filter I have vacummed the dust off and replaced the carbon. It's dirt cheap stuff compared to the cost of the filters.
But I really have no method to assess when its chemical absorbing ability has expired or been over saturated. And even if there's some data on that out there it would depend greatly on how much crap was in the air and what volume of air had run past it.

On gotch'ya for anyone thinking of doing this on their HVAC filter (or for that matter any filter) the orientation of the filter has to be horizontal (not vertical in the was as in some homes) so gravity holds the granules in the folds.