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  1. #27
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    Apr 2002
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    11,808
    he was 290 PPM above ambient with the ERV shut off, that is better than anything you logged in your home.

    And lo and behold his RH dropped and the dehu never came on

    what were the CO2 numbers in the Super IAQ house? 200 above ambient maybe?
    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/

  2. #28
    Join Date
    Jun 2008
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    128
    OK, so came home to empty house.. ERV was off for 24 hours. Wife was only home about 6 hours since this morning (50%). CO2 was 230ppm over ambient ~45CFM for 1 person, but since she wasn't here half the time I'm not sure how that calculates out... Probably ends up close to the 30 CFM of infiltration I calculated earlier???

    Turned the ERV back on and let it run for 90 minutes. CO2 only dropped to 210ppm on the main floor (Of course now 2 adults + toddler at home). I'm not sure I can get any accurate numbers in such a short amount of time. Again, I think the large air volume takes a while to equalize. The basement reads 170ppm.

    So in the case of tight homes, or in the case of "low" occupancy, it seems the 4-5 ACH per hour number does not match up well with actual needs based on CO2. I know that CO2 is not the only indicator, but I would think it is a primary reference for required ventilation rates. It would appear I am somewhere in the 1.25-1.5 ACH range with good CO2 levels.

    Something that I'm not sure matters (hopefully not in a house with proper make up air), but we are 100% electric. No combustion in the house at all (would be more CO than CO2 I think anyway...).

  3. #29
    Join Date
    Jun 2008
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    128
    Had 220ppm this morning, ERV 30% all night. Had storms and wind. 3 people in house (2 adults, 9yr old + toddler). Should be 137CFM total exchange, 60 from ERV & 77 from infiltration.

  4. #30
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,065
    Quote Originally Posted by patchesj View Post
    Had 220ppm this morning, ERV 30% all night. Had storms and wind. 3 people in house (2 adults, 9yr old + toddler). Should be 137CFM total exchange, 60 from ERV & 77 from infiltration.
    This is reasonable. An air change in the home without occupants should remove 70% of the residule CO2. Does your meter go to 0 ppm when in outside air? Whatever the meter shows in outside air, is the starting point. Your ach numbers are:
    total volume of inside space / by cfm = minutes to change the air
    or hours to change the air in the home.
    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"

  5. #31
    Join Date
    Jun 2008
    Posts
    128
    I've been zeroing the meter to outside air before each measurement to take the outdoor fluctuations out of the equation. Interior volume is ~54200 cu ft. so roughly 6.5 hours per change.

  6. #32
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    Apr 2002
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    11,808
    if you logged the CO2 decay when it was empty, it is exponential

    after 3 air changes it begins to flattens out , by 4 air changes it is approaching an asymptote, so in your case it would be close to and almost parallel to zero.

    You cannot go by the instantaneous readings, but I think if you zeroed the meter in the morning after everyone was up you would be the closest possible.

    There is a good article on it in the December 2008 ASHRAE Journal

    There is also a link on comparing how accurate the various sensors are, bottom line is you always need to compare it to outside and get the net change, as they are all off and typically by more than what the manufacturer claims. I can dig that one up if you would like.

    My experience is that the sensors accuracy is not linear.

    Something off by 25 PPM outside could be off by 100 PPM inside at higher concentrations
    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. #33
    Join Date
    Apr 2002
    Posts
    11,808
    I have a pretty tight house, no problems with humidty, no shortage of fresh air. I received an ERV to test out, it is the type with a wheel, it sounds of simialr capacity as yours. I advocate intermittent ventialtion so that I can treat the air as I bring it in.

    SO I am running the final test on my home just before I get the ERV going. Right now, I force in 80 CFM of fresh air with an inline fan whenever my compressor runs. I have about 80% of my glass covered with galvanized hurricane panels at the moment so what you will see is the effect of oversized air conditioning in a tight home.



    So you can see the place averged about 77F, 40.5% RH, CO2 897 PPM ( 487 above ambient) and a dew point of 51.2F. I use no dehumidifier.

    I should be able to easily add even more fresh air without breaking 50% RH and I intend on doing this with an ERV. I will try 120 CFM when the system runs, and I also intend to add a CO2 sensor to kick it on, but I have a feeling this will rarely happen in my situation.

    I have a small home, I have a sealed attic and I condition it with about 30 CFM of supply and return air. So if I include the attic in my ACH rate it is about 0.22. If I neglect it, then I was averaging zbout 0.27 ACH.

    Now, you may notice something here, I have put graphs with the same characteristics up in the past, and my critic here always seems to miss the point.

    I usually keep the place on the warmer side up around 78 or 79 and with my very low humidity and some ceiling fans this is usually quite comfortable. But this past April, I had a house full of visitors, so they are not acclimatized to the warmer temperatures so, I set it down a few degrees at night so it was easier for them to sleep and it also gives some more fresh air.

    So since April, I have been keeping this strategy and now with just the two of us it keeps CO2 levels about 200 PPM lower this way.

    Now teddy will like to say how an air conditioning system recovering from a temperature set back runs for a while and gives good mositure removal. This is of course very true and you can see the RH in a tropical home dropping down under 40% RH. WHat you will also see, is the tropical home getting purged with fresh air.

    During this recovery period, if you count the total vloume with an attic, during the recovery period there was 0.6 air changes happening and this is precise, so many known, measured CFM vs so many minutes, this is not a CO2 estimate. Again if you were to neglect the attic it is more like 0.75ACH.

    Now during the week, every day, the temperature is set back and this very same effect happens. The system does not run at all during the day, and then runs bringing down the temperature, humidity, and CO2 as it recovers.

    Anyways, I will keep this test on for a few days for a good baseline of a home with oversized AC, then later I can compare it to an ERV.

    I am actually looking forward to some higher RH, as I find my throat is very dried out every morning when it starts dipping down below 40%.

    I should of ran the test when my filters were dirtier, it tends to hold under 40% without a dehu.

    I have cermaic tile flooring throughout, my walls are concrete. I do have pressure treated joists holding up my ceiling, but they are not being cooked by a superheated attic and I do not get the VOCs aka 'the smell of hot wood'

    I do not think I am being poisoned with VOCs, no bed bugs, no dust mite allergies.

    I do not need to ventilate just for the sake of running a dehumidifier, and I truly believe that the saying in my signature is a universal truth
    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/

  8. #34
    Join Date
    Jun 2008
    Posts
    128
    Are you going to run the ERV in place of your inline fan or in addition?

  9. #35
    Join Date
    Apr 2002
    Posts
    11,808
    It is going to replace two bathroom fans and the inline fresh air fan

    My wife is under the weather and at home today, I expect the CO2 levels to indicate more like 40 CFM a person when I get home if not higher

    I think with the ERV I will be up close to 40 CFM per person average with both of us in there. It is capable of moving some air, however the fresh air intake is limited in size of the inlet hood and the duct. Not easy to change in my situation, was why I had to go to an inline fan in the first place in my home. Air handler fan power was insufficient unless I ran it 24/7 and that foolishly re-evaporated mositure and elevated RH.

    Most of the condensate on my coil was from the fresh air so the constant fan was acting like a pure humidifier
    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/

  10. #36
    Join Date
    Jun 2008
    Posts
    128
    So you are going to pull from the bathrooms and push the fresh air back to the main return duct? I was a bit leary of pulling air from the bathrooms with the ERV. My logic was that it was better to isolate and exhaust the bathroom humidity than to have some of that moisture transfer across the ERV membrane and re-enter the intake air. I guess it depends on if the outside air has more moisture than your bathroom air. For an HRV, I think the bathroom exhaust hookup would make more sense. Or am I off?

  11. #37
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    Apr 2002
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    11,808
    Well, I would say that the relatively short periods of time that you are showering there is the possibility that some of the moisture gets re-cycled, I may get a brief RH spike but it will rapidly dissappear as my set up has an automatic affinity for 40% RH.

    There is a lot of moisture in the outside air, from June through end of November here the out door dewpoint will be in the range of 77 to 82F. Sometimes it gets even higher, some times it gets a little lower than that range, but usually involves a sudden shift in prevailing winds or an intense sudden thunderstorm
    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. #38
    Join Date
    Apr 2002
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    11,808
    In Canada, you can have multiple bathrooms, a kitchen area, a laundry area hooked up to an HRV.

    So say a typical HRV that moves 180 CFM in a perfect world at 0.4". Assuming there are 6 exhausts that is 30 CFM per.

    Sometimes, such as after a night out where there are cheap deals on 'buckets of corona' and all you can eat burrittos, you may wish to for quicker removal of odours than what 30 CFM does so for that reason I would always go with bathroom fans.

    Presently I have two bathrooms, so I will have two exhausts. I should get at least 120 CFM if not a little more out of this unit so I will be 60 CFm or more from each bathroom. The exhaust duct work is not restrictive, the problem is the fresh air.

    Now do I think it is necessary to use ERVs or HRVs to draw from the bathrooms , no, I believe you could have a central exhaust, and just use bathroom fans. Am I worried about mositure re-cycle in my own home, no-- I do not sell products that compete with the ERVs. I am in a shower 5 minutes tops , my wife takes longer shower.

    But is say 15 minutes a day of showering going to make a difference, the answer is no.

    Would there be a difference if this was a locker room for a fitness centre, the answer is yes
    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. #39
    Join Date
    Apr 2002
    Posts
    11,808
    Right now I have no ERV, I have very humid outside air, more humid than the vast majority of posters in here, going to my cooling coil right now. It can take more moisture, I can obviously add a lot more fresh air given my homes present affinity for low humidity.

    The house cannot take stupidly pumping in untreated fresh air around the clock. That is why I advocate ventialting at high rates intermittently and conditioning it first.

    The reason it works is I do not have to worry about infiltration.
    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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