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  1. #1
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Checking fresh air changes with CO2 meter

    A simple CO2 meter for less than a couple hundred is a excellent device for determining the actual fresh air changes in any occupied structure. The amount of CO2 per person is known volume. Using the number of occupants in a space multiplied by the volume of CO2 per person divided by the cfm of fresh air equals the cfm per occupant.
    Attached is a graph of interal ^F temp, %RH, and CO2 ppm. 800 ppm CO2 equals 30 cfm per person fresh air in a house with 2-6 occupants during last week, 7-20-09. A CO2 level of 1,500 ppm CO2 equals 10 cfm per person. Healthy homes should have an air change in 3-5 hours when occupied. Ideally they should not exceed 1,000 ppm for extended periods. This is a handy tool for an modern a/c contractor to estimate the real fresh air infiltration/ventilation rate of home. This technology could put the V back in H_AC. Also the CO2 meter will indicate excessive air leak caused by duct leaks and wind which helps determining wether the a/c is functioning properly. High indoor humidity with extremely low CO2 levels indicates excessive outside infiltration/duct leakage. Normal CO2 levels indicates adequate fresh air and attention to the a/c set-up (air flow/refrigerant charge/etc.) Regards TB
    Last edited by teddy bear; 07-22-2009 at 10:39 PM.
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  2. #2
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    964
    Where's the graph?
    Bill

  3. #3
    Join Date
    Apr 2002
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    11,808
    it does put the V back into HVAC

    as far as a spot reading to work out a rate goes you are better off showing up first thing in the morning if you are not logging what happens.

    Just takes time for the meter to warm up -- high RH and low CO2 and it is an instant excessive outside air problem, you then just have to solve where it comes from.

    Been doing this for a couple years now, nice to see others repeat the point
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  4. #4
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by wptski View Post
    Where's the graph?
    Table? The meter values are with 450 outside. +increase is with the meter increase above outside. All of these values are dependent on good mixing of fresh air with house air and the meter in the center of the home.
    Is this what you are looking for?
    Regards TB
    Here is a table of the values:
    CO2 ppm Fresh air
    meter +increase CFM per person

    450 0 outside
    500 50 212.0
    550 100 106.0
    600 150 70.7
    650 200 53.0
    700 250 42.4
    750 300 35.3
    800 350 30.3
    850 400 26.5
    900 450 23.6
    950 500 21.2
    1000 550 19.3
    1050 600 17.7
    1100 650 16.3
    1150 700 15.1
    1200 750 14.1
    1250 800 13.3
    1300 850 12.5
    1350 900 11.8
    1400 950 11.2
    1450 1000 10.6
    1500 1050 10.1
    1550 1100 9.6
    1600 1150 9.2
    1650 1200 8.8
    1700 1250 8.5
    1750 1300 8.2
    1800 1350 7.9
    1850 1400 7.6
    1900 1450 7.3
    1950 1500 7.1
    2000 1550 6.8
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    May 2006
    Location
    Warren, MI
    Posts
    964
    Quote Originally Posted by teddy bear View Post
    Table? The meter values are with 450 outside. +increase is with the meter increase above outside. All of these values are dependent on good mixing of fresh air with house air and the meter in the center of the home.
    Is this what you are looking for?
    Regards TB
    Here is a table of the values:
    CO2 ppm Fresh air
    meter +increase CFM per person

    450 0 outside
    500 50 212.0
    550 100 106.0
    600 150 70.7
    650 200 53.0
    700 250 42.4
    750 300 35.3
    800 350 30.3
    850 400 26.5
    900 450 23.6
    950 500 21.2
    1000 550 19.3
    1050 600 17.7
    1100 650 16.3
    1150 700 15.1
    1200 750 14.1
    1250 800 13.3
    1300 850 12.5
    1350 900 11.8
    1400 950 11.2
    1450 1000 10.6
    1500 1050 10.1
    1550 1100 9.6
    1600 1150 9.2
    1650 1200 8.8
    1700 1250 8.5
    1750 1300 8.2
    1800 1350 7.9
    1850 1400 7.6
    1900 1450 7.3
    1950 1500 7.1
    2000 1550 6.8
    Yes, Thanks!
    Bill

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,637
    We had wet high dew points and low dew points this week. Three short cooling cycles removing 8 lbs. of moisture and 200 lbs. of moisture removed for the week removed by the 65 pint /day Ultra-Aire. We maintained 60 cfm of fresh make-up air for 14 hours each day. The humidity on the mainfloor was <50%RH. Stable CO2 levels during late evening/early morning hours indication effective 50-65 cfm of fresh air when occupied by two adults. House very nice. Check the graph.
    Regards TB
    Attached Images Attached Images
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #7
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    dumb question, what is considered to be normal CO2 levels? cause and effect for too low and too high of CO2?
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  8. #8
    Join Date
    Apr 2002
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    11,808
    Following ASHRAE 62.1 can result in CO2 levels upwards to 2000 PPM inside depending on the building occupancy.

    Industry wide the perceived indoor limit is 1000

    out doors it will be somewhere 400 to 500 ppm. the outdoor level will fluctuate with time of day, which way the wind blows, whether or not it is raining. Time of day is tied into traffic levels

    if you come across a home with low CO2 under say 600 PPM all the time it means a lot of air moves through the building either it leaks bad or too much ventilation. In a lot of places the low CO2 will tie into high RH. The humidity problem is beacuse there is too much outside air.

    Too high of a level depends, but generally if you are no more than 700 ppm higher than outdoors you most likely have enough fresh air moving through so under 1100 to 1200 (depending where you are) is not bad. California says you have to be within 600 PPM of outdoor levels so would be 1000 to 1100.

    People exhale CO2, so the CO2 level is used to indicate how much fresh air you are getting. OSHA says no more than 8 hours exposure at 5000 ppm, guys on submarines breathe 10000 ppm. So even at these high sounding levels the CO2 will not hurt you.

    It merely indicates how much fresh air you are getting and it is not to ensure you have enough oxygen, it is to make sure there is enough air to purge bioeffluents so that a place does not start smelling like a monkey den.

    buildings made out of lots of synthetic materials that off gas and poison hypochondriacs will need even more ventilation and hence lower CO2 levels.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #9
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    Jun 2003
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    Quote Originally Posted by beachtech View Post
    dumb question, what is considered to be normal CO2 levels? cause and effect for too low and too high of CO2?
    In public spaces like a class room, small space with high occupancy, CO2 levels are a concern for oxygen and odors. Most suggest 1,000 ppm as ideal. 20 teenagers in 1,000 sqft. room with 10' ceiling would need 20 cfm per person or about 400 cfm. This is 2 air changes in a hour.
    In a home, I use CO2 levels to provide documentation on the amount of effective fresh air ventilation we really providing to the living space to purge indoor pollutants. Most experts suggest an air change in 4-5 hours as adequate to purge indoor pollutants, mostly Volitile Organic Compounds.
    My posted data is from 32,000 ft^3 volume home. During calm summer weather, the natural infiltration declines to as low as 10-25 cfm. The home is typically unoccupied 12 hours per day. By measuring the CO2 levels with known number of occupants in the home, I can estimate the actual fresh air change rates.

    Calculating an air change in 5 hours would be 106 cfm of fresh air. During the coldest, windy weather, this has about 100 cfm of fresh air from natural infiltration. I can verify this with a 650-700 ppm CO2 level during steady state winter conditions. In the home with good air ciriculation, an increase of 200-250 ppm above outside CO2 levels, suggest 50 cfm of fresh air per occupant in the home. 2 occupants X 50 cfm/ = 100 cfm of natural fresh air infiltration. During calm, warm weather with the minimal natural infiltration, I have documented a 1,500-2,000 ppm CO2 levels with 2 adults in the home. This suggest a total of 25 cfm of natural fresh air infiltration. 25 cfm is an air change in 21 hours, certainly not enough to purge indoor pollutants from a typical home.
    During the last year, I added a ventilating dehumidifier to provide 60 cfm of make-up fresh air ventilation to home 14 hours per day during typical occupancy. The location of the CO2 monitor verses the occupants causes variable readings. I operate the VS fan on the air handler "on" slow mode to mix the fresh air into the home. Being next to the meter raises the reading while being in the bedroom for 6-8 hours allows readings to stabilize. In summary, monitoring CO2 levels documents the real effective air change rate in the home with during real conditions, occupants, and actual mechanicals. Thank you for your interest.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  10. #10
    Join Date
    Apr 2002
    Posts
    11,808
    If those are the levels you need teddy, you better go back to selling HRVs and ERVs.

    160 CFM model would be ideal for your own home
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Because of the complexity of this subject for all of us, I am attaching a chart showing the different levels of ventilation for various sized homes and various air infiltration/ventilation rates and the effect on CO2 levels. Also I am showing the various CO2 levels with various numbers of occupants to maintain an air change in 5 hours. These numbers are based on outside air having 450 PPM CO2 levels. These charts make the point need more fresh air in small homes with many occupants. Also that large homes only a couple of occupants need more fresh air to purge indoor pollutants than than required to maintain <1,000 PPM CO2 levels. Raise the questions needed to understand the points. Regards TB
    Attached Images Attached Images
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Apr 2002
    Posts
    11,808
    Assuming your spread sheet is right, 2 people and 1150 PPM in a 1000 square foot house is getting the air changes to purge, so if you are generally under the 1150 then you have to be doing okay?



    This one broke 1000 when the wife was too close to the meter. But is comparable to two people in 1000 sq feet getting a steady "41.4" CFM, note ambient CO2 was noticed to be on the low side then

    Low dewpoints, no dehumidifer, oversized air conditioning

    Don't feel so bad, I actually told someone to buy a UA-65 today
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  13. #13
    Join Date
    Apr 2002
    Posts
    11,808
    And what you never acknowledge teddy is there is a lot of attic duct work in your green glass market that unintentionally induces a large amount of fresh air into a home when the wind is a dead calm.

    These are the people posting that get the answer that "they are getting high RH because their AC is oversized" or their "blower speed is too fast" and quite often a dehumidifier is used as a band aid fix to the problem.

    No shortage of air moving through the home and the CO2 meter would point this out right away.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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