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  1. #14
    Join Date
    Jun 2008
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    128
    Quote Originally Posted by Carnak View Post
    sounds like you have quite an abundance of fresh air

    perhaps shut the ERV off as an experiment to see how high the CO2 goes. If it does not start getting upwards to 700 above ambient, could mean a lot of air on its own moves through your home naturally, OR your meter reads way low.
    Shut off ERV at 6:30p. 190ppm over ambient
    8:30p 230ppm over
    6:30a 290ppm over.

    2 adults + 1 toddler in the house during that time. Will check again later today to try and get a 24 hour look. Also noted that the RH dropped from 48% at 6:30p to 43% at 8:30p. Was back at 48% this morning, but the dehumidification cycle had not run. Usually we hover around 47-48% and require dehum in the early morning hours to stay <50%.

    Looking at Carnak's and http://www.illinoisashrae.org calculations, 10080/(Indoor CO2-Outdoor [my meter zero'd to ambient])=CFM per person

    My conditioned space is 53,600 cu ft. I'm assuming it will take a while for things to equalize with only 1 or 2 people occupying the house?

    My average inside with ERV running 30% was 170. So about 60CFM per person? 120CFM total, and 63 CFM should be from the ERV (210cfm * 30%). That would leave 60CFM of leakage, or .065 ACH naturally? Is that possible for a new house, closed cell foam insulation, warm day, low wind???

    Without the ERV running that should be about 30 CFM per person and put me at 310 or so over ambient? Just a little shy of where I measured it after 12 hours. This makes me think my infiltration is a bit higher, and the ERV is running a little less than published spec.

    Thanks.

  2. #15
    Join Date
    Apr 2002
    Posts
    11,808
    0.065 is possible , but would need a ceiling vapour barrier or a sealed attic and it sounds like you are guessing on what the ERV does

    Infiltration will go up and down with wind other factors, if you run exhausts like a dryer, bathroom fans, range hood.

    Interesting as it seems the home breathes enough for the few of you in there and when the extra ventilation was stopped, the need to dehumidify stopped. The effect would have been more pronounced if you did not use an ERV
    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/

  3. #16
    Join Date
    Jun 2008
    Posts
    128
    I don't have access to a flow hood at the moment, so I can't confirm the "installed" performance of the ERV. I can only go by the manufacturer specs.

    Part of the house has a sealed roof deck, with spray closed cell. The basement is 2700 sq ft * 9ft, 80% of the walls are concrete with the "daylight" walls 2x6 and spray closed cell. The band joist areas were all filled well with spray foam, so the "volume" of the basement is very well sealed in relation to the impact it has on an ACH number when it is included. It is a conditioned space, so must be figured in the calculations right? I still find the calculated ACH low to believe. Need to find someone with a blower door around here to get solid numbers.

  4. #17
    Join Date
    Apr 2002
    Posts
    11,808
    A lot of times there will be either flow collars installed or pressure taps built right into the unit to measure HRV/ERV air flow for balancing purposes. You would need a manometer

    R2000 houses in Canada are meticuolusly well sealed and in the dead of winter (when houses are most prone to infiltration) carrying a natural air change rate of 0.07 per hour in furnace sizing calculations is conservative.

    I have a well sealed home including the attic and I believe I am down around 0.05 ACH in a cooling environment and it does pretty good even against strong wind.
    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/

  5. #18
    Join Date
    Jun 2008
    Posts
    128
    The unit is a Nordyne ERV-210 (Venmar). I haven't noticed pressure taps on it, but I'll check again. I have a manometer, so I'll see what I can come up with.

    Thanks

  6. #19
    Join Date
    Apr 2002
    Posts
    11,808
    there may be some ports right in the door
    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/

  7. #20
    Join Date
    Jun 2008
    Posts
    128
    The door is completely smooth, no ports. Installation manual references flow collars for balancing.

  8. #21
    Join Date
    Apr 2002
    Posts
    11,808
    blower door math breaks down on a truely tight home. I know a guy who keeps procrastinating doing a paper on the subject.
    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. #22
    Join Date
    Jun 2008
    Posts
    128
    Quote Originally Posted by Carnak View Post
    blower door math breaks down on a truely tight home. I know a guy who keeps procrastinating doing a paper on the subject.
    So would you just stick with CO2 monitoring to determine ventilation requirements? Unfortunately, humans are such a variable...

  10. #23
    Join Date
    Apr 2002
    Posts
    11,808
    Blower door tests find out how much you leak under a significant pressure differential. It helps you find the leaks to seal. But the math breaks down for tight houses with respect to how to use a big pressure differential to estimate how much a home naturally breathes.

    I have been watching how CO2 decays in my own home with all systems shut off while we are at work, and using this to work out my infiltration air change rate. It suggests a low number.

    Now going back to blower door math, the air volume to depressurize my home following their math would be of a similar order of magnitude as to what my clothes dryer exhausts.

    Interestingly enough, my ears never pop like I am going up in altitude when my wife dries laundry and they should be.

    So this tells me that a blower door test is going to predict a higher air change rate than I have been documenting.
    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. #24
    Join Date
    Apr 2002
    Posts
    11,808
    CO2 montiroing is used in commercial and public buildings to control the volume of ventilation air.

    van EE, used to sell a residential CO2 sensor to kick their HRV units on high speed ventilation on a rise in CO2. Usually I found, that in winter in Canada, kicking the HRV on high speed on a rise in RH worked fine.

    People exhale both water vapour and CO2. In winter you tend to need more air to keep your windows clear of condensation. Most of the water vapour comes from people breathing. So the system responding to a rise in RH in winter was indirectly responding to a rise in CO2
    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/

  12. #25
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,439
    Quote Originally Posted by patchesj View Post
    Shut off ERV at 6:30p. 190ppm over ambient
    8:30p 230ppm over
    6:30a 290ppm over.

    2 adults + 1 toddler in the house during that time. Will check again later today to try and get a 24 hour look. Also noted that the RH dropped from 48% at 6:30p to 43% at 8:30p. Was back at 48% this morning, but the dehumidification cycle had not run. Usually we hover around 47-48% and require dehum in the early morning hours to stay <50%.

    Looking at Carnak's and http://www.illinoisashrae.org calculations, 10080/(Indoor CO2-Outdoor [my meter zero'd to ambient])=CFM per person

    My conditioned space is 53,600 cu ft. I'm assuming it will take a while for things to equalize with only 1 or 2 people occupying the house?

    My average inside with ERV running 30% was 170. So about 60CFM per person? 120CFM total, and 63 CFM should be from the ERV (210cfm * 30%). That would leave 60CFM of leakage, or .065 ACH naturally? Is that possible for a new house, closed cell foam insulation, warm day, low wind???

    Without the ERV running that should be about 30 CFM per person and put me at 310 or so over ambient? Just a little shy of where I measured it after 12 hours. This makes me think my infiltration is a bit higher, and the ERV is running a little less than published spec.

    Thanks.
    An air change in 5 hours would be a total of 178 cfm per min of combined ERV and infiltration/exfiltration air. This would be my minimal recommendation for hours of occupancy. Converting total in a CO2 meter reading would be 72 cfm per person with 2.5 occupants. This would be an average of +225 ppm CO2 above the outside.

    Stack effect and wind can decline to near nothing in the summer. During cold weather the stack effect is constantly high plus the wind. The CO2 meter will give a better summer number than the Blower Door test.
    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"

  13. #26
    Join Date
    Apr 2002
    Posts
    11,808
    with your meter zeroed to the outside you will be a little more accurate, espcially when you have the high air rates.

    If it was 450 PPM outside and 600 PPM inside you would be 10080/(600-450)=67 CFM per

    If it was 400 outside and 600 inside you would be 10080/(600-400) = 50 CFM.

    Big difference
    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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