Does Anyone Monitor Their Home's CO2 Level?

[ano]

There seems to be growing concern that high CO2 levels in your home can be a bad thing. 
 
I recently had the two HVAC units in my home replaced, and as a minor addition, I had the AC people add in an outside air intake to both units. Each goes through an electronic damper, and then feeds into the air intake for each unit.  Presently I can open or close the damper with my HAI.
 
The plan was, since it is often cool here at night, but warm during the day, to suck in this free cooling at night and save some AC costs.  For example, last night it got down to 60, but it is supposed to be 90 today.  The house never dropped below 77 on the side where I don't have the AC on overnight.  If I could drop that 77 to say 70, that would be a big help.
 
So anyway, I just bought a Honeywell CO2 monitor that will also potentially turn on the ventilation if CO2 levels get too high.  It has a relay that can close when CO2 needs to be lowered. 
 
Depending what you read, they say indoor CO2 should be lower than 600 to 800 PPM.  Today mine is reading 585 with just me home.  I put it outside and read about 440, but I only got it yesterday, so need more research. 
 
As it turns out, the fresh air vents are good, but now I think I need to add an in-line fan in each vent.  Presently I need to run my HVAC fan to suck in outside air, but this can be costly, since most of the air it is sucking is not from outside but rather just from the return vents in my house.  The in-line fans should work better and be cheaper to run.
 
So does anyone else monitor their CO2 levels? 

 

[BraveSirRobbin]

I don't presently monitor, but do find this interesting as I was always curious about this as well now that homes are 'sealed up' better with insulation and all.
 
This may sound silly, but have you also considered more green plants inside your home?  (I don't know the effectiveness overall).

 

[ano]

I guess what started this is we had a full utility energy audit before we installed the new HVAC units.  It said we were in good shape, but also that our house was much too "sealed," in fact we has half the air infiltration that was considered normal.
 
This was always confusing to me because they tell you to seal your windows and door gaskets, but I guess they are now sealed too good.  You can't win.  Am I supposed to remove my door seals?  Crazy?
 
As a side note, first, my wife is very sensitive to bad air due to some respiratory problems, and second, although this is rare in AZ, I had my home checked for radon a few years ago, and it was mildly high.  I had a vent installed that sucks air out from the crawlspace.  Levels now are half what they were.
 
So when I was pricing HVAC units and talking to installers, I mentioned this finding of the home being sealed too much.  None of the four really knew much about that, but two said they could install an air exchanger for about an extra $3500.  I researched it, and found out that most people that have these hate them because they waste lots of energy, and I wasn't sure if there was any way for me to "automate" it, so for the time being, I stuck with the simple damper and air inlet.
 
Did I try plants?  I do have some, and nothing against plants. I like them.  Just keeping them alive can be a challenge.
 
I guess I'm really lucky because we have a relatively large house with just the two of us living here. If it was a small apartment with more people, that would be worse. My wife is a teacher and has 30 kids all jammed in a pretty small space.  Do you think the school cares about CO2 or Radon?  What if the low test scores were not from dumb kids but because CO2 levels were too high?  Gets you thinking a bit.  Just Google "high CO2 levels"

 

[garbled]

I am actually very interested in this, but for a different reason.  I keep fish tanks, and some of the equipment runs off bottled CO2.   I've always been terrified of a leak, so never bought any of that stuff.  If I had a sensor however....

 

[ano]

I am actually very interested in this, but for a different reason.  I keep fish tanks, and some of the equipment runs off bottled CO2.   I've always been terrified of a leak, so never bought any of that stuff.  If I had a sensor however....

 
So a million years ago they think outside CO2 levels were about 300PPM. Today, with global warming, its up to about 400PPM.  My sensor read 440 outside.
 
They say good indoor levels are below about 600 or 800.  This sensor could easily help you monitor for a leak.  It has a relay that triggers at 800, 1000, or 1200.  I'm not sure what level would kill you.  It would have to be pretty high.  The sensor is from Honeywell and was about $250.  I can tell you the sensor is VERY responsive.  Just breathing on it from a few feet away can trigger it. 
 
I think poor indoor air is a bigger problem then most people want to acknowledge.  Just Google "sick building syndrome"

 

[apostolakisl]

CO2 levels wouldn't concern me.  The deal with co2 is that it affects the ph of your blood.  You can actually tolerate very high co2 levels if you work it up gradually.  Your body has a very good ability to buffer the pH changes from reasonable co2 levels in very short order.  Consider what happens when you exercise, co2 levels in your blood go way up.  People with emphysema have extremely high levels of co2 in their blood (not because its in the air but because their lungs can't expel it).
 
The much more concerning thing is the off-gassing from the other stuff in your house, like carpets, fabrics, plastics, glues, and many other things.  Also radon if you have that in your soil.
 
I own one of those thermal capturing air exchange devices in my house.  I don't think it is any where near worth what it costs.  Just bring fresh air into your intake plenum using dampers that open and close according to time of day.  In the summer, open at night, in the winter, open during the day.  
 
You don't want to just un-seal your house, because then the air intake is not controlled and is not filtered first.  It also hits your living space without first being warmed or cooled to proper temp causing drafts.  Of course if you don't have any allergies, don't mind dusting, and are OK with drafts, then take off your weather stripping. :huh:
 
I would say that measuring co2 in your house would be more of an indicator of your overall air exchange rate and thus may have value.  You certainly can't try to measure every air contaminant so using co2 as an indicator of overall air quality might be valuable.

 

[ano]

I own one of those thermal capturing air exchange devices in my house.  I don't think it is any where near worth what it costs.  Just bring fresh air into your intake plenum using dampers that open and close according to time of day.  In the summer, open at night, in the winter, open during the day. 

So what prompted you to get an air exchanger?  They are required in all new homes in Minnesota.
 
I agree that I think the dampers and fan is enough.  As I said, I initially added it more to save energy than for air exchange, but the energy audit got me thinking more of ventilation. 
 
Don't confuse CO2 in the blood with CO2 in your house and CO2 outside.  They are all a bit different, but certainly related.  I haven't read that high CO2 in the air leads to high CO2 in your blood, etc. It is more complex than has been studied.  What they HAVE studied is high CO2 levels in the air you take in CAN have negative health effects.  Still they have had ventilation requirements in commercial buildings for 40 years.  In the home, no much is looked at.
 
Here is a good link I found on the acceptable levels:
http://www.engineeringtoolbox.com/co2-comfort-level-d_1024.html

 

[Bugman]

If you sit around worrying about abbient CO2 levels and your health (other than global warming of course), then you've got way too much time on your hands.
 
We are talking 300-400 ppm ambient atmospheric levels here and when you exhale you emit around 4% with every breath. As a biologist I must say ambient CO2 is nothing to be concerned about from a health standpoint. Now CO is another matter, and that I WOULD consider to monitor.
 
Bugman

 

[apostolakisl]

So what prompted you to get an air exchanger?  They are required in all new homes in Minnesota.
 
I agree that I think the dampers and fan is enough.  As I said, I initially added it more to save energy than for air exchange, but the energy audit got me thinking more of ventilation. 
 
Don't confuse CO2 in the blood with CO2 in your house and CO2 outside.  They are all a bit different, but certainly related.  I haven't read that high CO2 in the air leads to high CO2 in your blood, etc. It is more complex than has been studied.  What they HAVE studied is high CO2 levels in the air you take in CAN have negative health effects.  Still they have had ventilation requirements in commercial buildings for 40 years.  In the home, no much is looked at.
 
Here is a good link I found on the acceptable levels:
http://www.engineeringtoolbox.com/co2-comfort-level-d_1024.html

 
 
Why did I buy it?  Good question.  I didn't do the math and realize that there is no way you will save $3k in energy costs.  I just built a new office, all sealed up with foam, and here I am just sucking in air, no exchanger.  I learned!
 
The only problem with CO2 in the air is CO2 in the blood.  Your lungs expel CO2 based on the partial pressure in your blood as compared to the partial pressure in the air.  So if the air levels go up, then the blood levels have to go up in order for the rate of exhalation to stay the same (which it more or less must do since you keep making co2 at the same rate).
 
When the CO2 dissolves in your blood, it forms a weak acid.  Your body buffers that with bicarbonate.  The amount of bicarbonate can be controlled by your kidneys, so mostly your body can maintain the same pH at various levels of CO2.  But rapid and extreme changes can overwhelm the system.  Like Apollo 13.

 

[ano]

If you sit around worrying about abbient CO2 levels and your health (other than global warming of course), then you've got way too much time on your hands.
 
We are talking 300-400 ppm ambient atmospheric levels here and when you exhale you emit around 4% with every breath. As a biologist I must say ambient CO2 is nothing to be concerned about from a health standpoint. Now CO is another matter, and that I WOULD consider to monitor.
 
Bugman

 
Its not so much that CO2 is the problem, its all the other odors and chemicals that go along with it.  The CO2 is just an indicator of the ventilation that your home is receiving.  When CO2 levels are high, its an indication of poor ventilation.  High CO2 levels are not a health risk themselves, but they can make it feel stuffy.

 

[ano]

Why did I buy it?  Good question.  I didn't do the math and realize that there is no way you will save $3k in energy costs.  I just built a new office, all sealed up with foam, and here I am just sucking in air, no exchanger.  I learned!

The part about these things that bugs me is they say they are 90% etc. efficient, and that may be true from their side, but I don't see it like that.  If its 70 degrees inside and 110 outside (a cool summer day in Phoenix) then AT BEST my air going out is warmed to 90 degrees and the air coming in is cooled to 90 degrees.  And that would be perfect conditions, so I still have to cool this 90 degree air to 70 degrees.  They would call that 100% efficiency. 

 

[mghan]

The part about these things that bugs me is they say they are 90% etc. efficient, and that may be true from their side, but I don't see it like that.  If its 70 degrees inside and 110 outside (a cool summer day in Phoenix) then AT BEST my air going out is warmed to 90 degrees and the air coming in is cooled to 90 degrees.  And that would be perfect conditions, so I still have to cool this 90 degree air to 70 degrees.  They would call that 100% efficiency. 

 
At first glance you might think so, but actually the air returned to your interior would be cooled to 74 degrees (given your scenario).  This is because the air flows in opposite directions across the heat exchanger surface.  If it flowed in the same direction (a very poor design) then, yes, the return fresh air would be 90 degrees.  The efficiency is just a matter of air flow and heat exchanger surface area – lower air flow or larger surface area yields a higher efficiency rating.
 
Mike

 

[johnlaroux]

I  have CO2 sensors in my house so I know when to exchange the air.   I just tapped into my 18" return air flex duct and ran an 18" flex duct to outside with a 20" x 40" filter rack to filter outside air.  I put an 18" motorized damper in the outside air duct and an 18" motorized damper between my inside return filter rack and the duct tee that runs to the outside.  The outside air damper is NC  and the damper that closes off the return air from indoors is a NO and I just energize a relay to power the damper motors that have a spring return when the power to the dampers  is removed.  This gives me 100% outside air exchange which will exchange all the air in the house in about 10 to 15 minutes.   This is just a hobby. no real concerns for health.  Also works good to get rid of odors in the house from cooking. 
 
I also track the indoor enthalpy vs. the outdoor enthalpy  so as not to introduce energy to the indoor air that will need to be removed by the ac unit.
 
Here are a couple of graphs of the CO2 and Enthalpy.
 

[sharedmedia=gallery:images:557]
 
[sharedmedia=gallery:images:556]
 

 

[potts.mike]

From an engineer I'm training but not in practice, how do you track enthalpy?

 

[johnlaroux]

I just calculate it using temperature and humidity  using this equation.
 
    Loc = 273.16 /  ((Temp - 32) / 1.8 + 273.16)
    Loc = 10.79586 * (1.0 - Loc) - 2.1836 * Log(Loc) + 2.2196
    Loc = 29.9 * (1.0 / exp(2.3026 * Loc))
    Loc =  humidity * Loc / 100
    Loc = .622 * Loc / (29.9 - Loc)
    Enthalpy  = 0.24 * Temp + Loc * (1061.2 +0 .45 * Temp)
 
 
I forgot to mention this equation calulates enthalpy as BTU's per pound of air.