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Test of cabin air quality

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Old 08-10-14, 06:28 AM   #1
gappell
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Angry Test of cabin air quality

I have a 2014 Lexus ES350 UL model and have been concerned about the cabin air quality. The air intake control has a recirculate, auto and outside air setting. The micro dust and pollen filter sets the intake to the recirculation mode for 3 minutes then restores the previous setting. In the auto mode the car will stay in the recirculate mode if the AC is on and the outside air is warmer than the preset inside air temperature. In this mode the cabin still gets 15% outside air.

The effect of the recirculate mode on cabin air quality is a buildup of carbon dioxide (CO2) in the cabin. The carbon dioxide in the cabin is a function of the number of occupants as humans consume oxygen from the air and expel carbon dioxide. Good indoor air quality is considered below 1000 ppm of carbon dioxide. Outside air is about 400 ppm and indoor air usually varies between 600 and 800 ppm depending on number of occupants and fresh air exchange.

I conducted a test of the cabin air quality with a CO2 meter and found that with 2 occupants the CO2 levels exceeded 3000 ppm in the recirculate mode. Forcing the control to outside air quickly dropped the level to below 600 ppm. The effect of high CO2 levels is a feeling of drowsiness.

Lexus tries to maximize fuel economy by using the recirculate mode to minimize the AC operation at the sacrifice of air quality. I would caution readers of this forum to pay attention to the air intake control setting especially when on a long trip.
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Old 08-10-14, 08:27 AM   #2
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About a year ago, there was a fairly long thread on this board in which people were complaining about a musty smell inside the cabins of their ES vehicles, and there were similar threads on other Lexus owner forums.

I have no doubt that the cause of that musty smell (and, perhaps, other air quality issues) is the decision by Lexus to have the climate control system default to recirculate air whenever the outside temperature is about 75 degrees or higher, and I also don't believe that it is just a coincidence that the bulk of those who were complaining about the musty smell were people who lived in areas where summer temperatures tended to be consistently high and where, thus, the climate control systems were running constantly with recirculated air. When I have suggested to some people that they need to get into the habit of manually switching the climate control system to the fresh air setting, they have reported that doing so has eliminated the air quality issues.

While it is the case that Lexus made the (misguided) decision to have the climate control system default to the recirculate setting when the outside temperature is warmer in order (marginally) to improve fuel economy, I suspect that having the system default to recirculate actually results in hurting fuel economy. On a hot day when the vehicle has been parked in the sun, cabin air temperatures can rise to 120 degrees or higher. When the cabin temperature is 120 degrees or higher, the last thing that you want to be doing is to be recirculating that 120 degree air. Even if the outside temperature is 90 or 100 degrees, the outside air is still significantly cooler than the 120 degree air in the cabin. Thus, if fresh air was being brought into the cabin, the air conditioner compressor would be working less hard, and it would be cooling the cabin faster than if the air was being recirculated, which would actually result in better fuel economy.

On other vehicles that I've owned, including a couple of other Lexus vehicles, the climate control system defaulted to the recirculate setting only if the outside temperature was around 95 degrees or higher, and, on those other vehicles, if you manually switched the system to bring in fresh air, the system would remain in the fresh air mode until/unless you manually switched the system back to recirculate or to auto. Unfortunately, with the ES, even if you do manually switch to the fresh air setting, every time the vehicle is shut down and, then, restarted, the system goes back to the default recirculate setting, and you need to remember, with each restart, to manually switch to the fresh air setting.

It seems like it should be simple for Lexus to do a software modification that would stop the system from defaulting to recirculate whenever the outside temperature is around 75 or warmer. At a minimum, it should also be simple for Lexus to make a software change that allowed the user to manually put the system into fresh air mode and have the system remain in that fresh air mode until or unless the user changes that setting. Absent Lexus making such a software modification, the only solution seems to be to get into the habit of manually switching the system to the fresh air mode with each restart of the vehicle.

Last edited by lesz; 08-10-14 at 12:26 PM..
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Old 08-10-14, 05:52 PM   #3
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gappell - can you provide some details on how your CO2 test was conducted - test location (city or rural), vehicle speed, fan speed, meter make/model, etc?
Having done some CO2 monitoring in work spaces, I am surprised to see such a high reading in a vehicle.
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Old 08-11-14, 07:42 AM   #4
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In regards to the musty smell in cabins, this is more likely due to clogged air conditioner drains. The cabin relative humidity with the AC on is about 37%, mold and mildew requires humidities greater than 50%. If the drain is clogged the water accumulates and is re-evaporated into the car growing mold in the ducts and AC coils.

The CO2 meter is an Autopilot and is used for plant growth. It has an accuracy of 70 ppm or +- 5% of reading with a range of 0 to 3000 ppm. I have an inverter in the car to provide 120 volt operation of the meter. It also provides relative humidity and temperature.

I conducted several tests during drives with the longest being 45 minutes. The AC was on auto with cabin temperature set to 75 degrees. I travelled on both rural and high speed roads. The outside temperature was greater than 85 degrees with a high humidity; I live in south Florida. When on the recirculate mode the meter would gradually go between 2000 and 3000 ppm. On several occasions it would exceed full scale and show “Hi” indicating greater than 3000 ppm. I was amazed at how fast it would drop in the outside mode. I do not know the response time of the meter.

I could run some more tests to see the effects of fan speeds, etc. I did not conduct specific test but just brought the meter along as I was curious about the CO2. I have been annoyed that Lexus would design a car that defaults to a recirculate mode. This is our fifth Lexus and I do not remember previous models having this problem.
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Old 08-11-14, 08:39 AM   #5
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Can a lawsuit vs. Toyota/Lexus be far behind from someone who falls asleep at the wheel and has an accident?
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Old 08-11-14, 09:12 AM   #6
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Perhaps tests using the same instrument and conditions in other makes/models is in order before anyone condemns Lexus. I for one wonder how many bad fumes come in when not in recirculate mode. I have personally driven 14 hours in Lexus vehicles on Auto and have not been drowsy. :-)
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Old 08-11-14, 09:24 AM   #7
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Quote:
Originally Posted by jollick View Post
Perhaps tests using the same instrument and conditions in other makes/models is in order before anyone condemns Lexus. I for one wonder how many bad fumes come in when not in recirculate mode. I have personally driven 14 hours in Lexus vehicles on Auto and have not been drowsy. :-)
Same here. I usually keep the HVAC on Auto and driven many miles and long days with no drowsiness issues.

I was being facetious with the lawsuit comment.
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Old 08-11-14, 01:09 PM   #8
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I have not had a problem with musty odors or bad air quality in ether of my cars and here in Houston the temperatures are extreme in the summer. Around 95-100 or more for at least 2 months in the summer and 80% or higher humidity. I do occasionally set the filter mode on but only once a month or so. At times I wonder if it is better to have a bit more human CO2 in the car rather than all the other odors you get on a busy freeway.
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Old 08-11-14, 02:31 PM   #9
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gappell - Thanks for the additional CO2 test info. This peaked my interest in this subject, so a Google search brought up this link on recent SAE research regarding contaminants and vehicle cabin recirculation rates. http://www.engr.ucr.edu/~heejung/pub...13-CO2-exp.pdf
I found it quite educational in that under certain conditions, the study data parallels your test results. Even tho this research was done with Hyundai, Lexus/Toyota most likely have done similar work related to air recirculation and fuel economy.

One factor they found was that vehicle speed has a major impact on the CO2 level. Driving above 40mph significantly decreased the CO2 level by increasing the cabin air leakage rate.

For those who do not want to read the entire article, here is their conclusion.
"Passengers currently can choose either full air-recirculation
or outside air for ventilation. This study suggests fractional
air recirculation can keep the benefits of full recirculation
(reduction of particle pollutant concentrations in cabin and
reduction in AC power consumption), while suppressing side
effects (increase of cabin CO2 and H2O level)."
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Old 08-11-14, 04:26 PM   #10
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I wonder if this is affected by the exhaust gas sensor sensitivity setting?
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Old 08-11-14, 05:48 PM   #11
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Living in South Florida, I normally keep cars on "recirculate" anyway... just adding some fresh air on the nice days, or if it begins to feel stuffy. But after reading this thread the other day, I decided to put it on "fresh" this morning on the way to work. Big mistake. The road was pretty crowded. Almost immediately after poking the button to let in the outside air, I got a very strong scent of exhaust.

I do know that these cars take in some fresh air all the time, even in recirculate mode.. I think I read somewhere a figure of 10 percent, but I don't know where I read that, so it could be more or less..

From my perspective, any extra little bit of CO2 that might stay in the cabin from passenger breathing, is much less bad than the extra large amounts of both CO2 and CO (and various foul-smelling gasses) that come in from the other vehicles on the highway.
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Old 08-16-14, 05:36 PM   #12
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Thanks for that link, I found the article fascinating and informative. I just returned from a 90 mile trip to Miami and again took the CO2 meter for more testing. As mentioned in the article, a steady speed of 75 mph on I95 kept the CO2 levels at 2300 ppm in the recirculate mode with 2 passengers. Fan and AC were in auto mode. The high speed does tend to force more air into the cabin, perhaps more than the 15%. The cabin air quality is a function of many factors. As stated by others, make a personal choice but be aware of what is happening to the stuff you are breathing.
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Old 08-16-14, 05:41 PM   #13
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One more thing in regards to cabin humidity. It was noted during my drive in recirculate mode that cabin humidity dropped to 23%. That is pretty dry air! ( Outside air temperature in the 90's and cabin temp set to 75)
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Old 08-16-14, 07:02 PM   #14
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You are correct about the dry air. 23% RH at 75F cabin temp means your AC evap coil is making 35F saturated air based on the old psych chart. The large amount of condensation coming from the AC is another sign of a good working cooling system.
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Old 08-16-14, 07:02 PM
 
 
 
 
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