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  1. #14
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,649
    Quote Originally Posted by energy_rater_La View Post
    for your size house the target leakage in cfm would
    be close to sq ft. more than this is still leaky
    ...and everything else he said.

    Without seeing the house I'd have to say the equipment sounds BIG.

    The point of COMPREHENSIVE assessment is to do a current and an IMPROVED load calc (missed by some HVAC contractors just getting into weatherization, they don't yet believe what a little air sealing will do, and they'd rather err on the side of too big because "Clammy" isn't an unpaid phone call they have to listen to, "Not cooling from 140 to 63 in 10 minutes" is).

    If I take you HERE we can put in 40mbtu/1.5 ton:

    I had a nice retired couple, wanted a quiet furnace for their 17 year old 1700 sf double wide. So I found the smallest MH rated furnace and set about playing with Infiltration until I saw where I needed to take the home so that furnace would work.

    Took the home from 3000 cfm50 to just over 2000. Target for the calc was 2200. 1.5 ton heat pump, which we lock out at 40f because supply temps start to become uncomfortable. NBD as they are on Natural Gas (or I would have put in 2 ton)

    Comments: the house is much more comfortable, much more even temperatures throughout (replaced 84mbtu/2.5 ton), and energy bill? Down about 35%. (She sends me pictures of her meter - it's in my blog as Ken & Karen.)

    Aggressive downsizing does mean you can't set the thermostat back when temperatures get to extremes. But who really wants to do that anyway?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  2. #15
    Join Date
    Apr 2007
    Location
    Saint Augustine, Florida, United States
    Posts
    1,149
    You are on the right track, but get someone else out there, sounds like a big co. partnered with the 'free' city plan. There are other contractors out there that will take more time and an honest interest in the job.

  3. #16
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    2,998
    "All of my ducts are in the conditioned space of the house."

    that is great. wish more houses/designers/architects would
    do this. it puts us a step ahead of the game.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  4. #17
    Join Date
    Jun 2011
    Location
    SW Ohio
    Posts
    224
    Thanks for the info guys. I would love to go to a 2.5Ton two stage AC eventually but I think they only come in whole sizes (2,3 ect).

    I need to work on sealing up those spots but the biggest area (basement) is going to have to wait. I need to remodel our bathroom to put in a bathtub so we can bath our 5 month old, she's growing fast!

    Yeah, the audit cost me $50 through the city program but it deffinetly seems like they are more concerned with selling products.

    Now I just need to keep my current system going for another year or two to get time to seal up this house.

  5. #18
    Join Date
    Nov 2010
    Location
    Montreal, Quebec.
    Posts
    71
    I think there is something wrong with your ACH number. The link provided by freeagent shows that a house with ACH below 5 is considered tight. I had my energy audit done and the tech said she never tested a house as tight as mine and my ACH at 50Pa is 1.63. My house has R40 in walls and ceiling with a continuous undisturbed vapor barrier, it was mitucuously built for low energy consumption.

  6. #19
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by Norm01 View Post
    I think there is something wrong with your ACH number. The link provided by freeagent shows that a house with ACH below 5 is considered tight. I had my energy audit done and the tech said she never tested a house as tight as mine and my ACH at 50Pa is 1.63. My house has R40 in walls and ceiling with a continuous undisturbed vapor barrier, it was mitucuously built for low energy consumption.
    My own house was tested at 5.3 ACH50 and it is not an energy hog. 3317 CFM at 50 pascals. Fairly well sealed but not exceptional. The blower door report also told me "estimated annual average air change rate" was 0.32 (0.40 winter, 0.24 summer). As someone else suggested, it looks like a couple of numbers may have been swapped. There are a lot of technical numbers which take awhile to learn.

    Hope this helps -- Pstu

  7. #20
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
    Posts
    207
    Quote Originally Posted by Norm01 View Post
    I think there is something wrong with your ACH number. The link provided by freeagent shows that a house with ACH below 5 is considered tight. I had my energy audit done and the tech said she never tested a house as tight as mine and my ACH at 50Pa is 1.63. My house has R40 in walls and ceiling with a continuous undisturbed vapor barrier, it was mitucuously built for low energy consumption.
    My house was 8.42 which is high. Target figure auditor gave us was 7.24 (figures based on 50Pa vac). I am hoping to do a lot better than that because we have found a number of large leaks.

    The OP said his figures were at -50Pa (ACH50), but that was probably a mistake - the figures had probably been converted to natural (ACHn)?

    I would be interested in some of the Pros confirming what the <1.0 ACH numbers mean. There appears to be different numbers used for cooling and heating.

  8. #21
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by Freeagent View Post
    My house was 8.42 which is high. Target figure auditor gave us was 7.24 (figures based on 50Pa vac). I am hoping to do a lot better than that because we have found a number of large leaks.

    The OP said his figures were at -50Pa (ACH50), but that was probably a mistake - the figures had probably been converted to natural (ACHn)?

    I would be interested in some of the Pros confirming what the <1.0 ACH numbers mean. There appears to be different numbers used for cooling and heating.
    We still may not be communicating properly. Your number of 8.4 ACH50 is only about 50% higher than mine, it is an entirely plausible number. I have heard that a crude way to estimate natural ACH is to divide the above number by 50 -- anyone at all please confirm or correct me here.

    I would expect your natural ACH number to be something less than 1. One reason for different summer and winter numbers, I understand to be the "stack effect" whereby warm air stratifies higher in the building and escapes a little faster because of that. In summer the stratification tends to be lower. Almost surely the stack effect will be stronger in multi story houses. There is an article from a 2010 issue of Fine Homebuilding magazine which explains the stack effect -- search for it. I have a PDF copy but they are adamant I should not distribute that.

    Someone here linked a fine article by Joseph Lstiburek where he observed it is not too hard to build a house where the ACH50 number tests down in the 2-3 range. He says it is truly difficult to build one where the ACH50 number is below 1.0 -- possible but really hard. These are extreme examples built to the Canadian R2000 or the German Passivehaus (sp?) standard.

    For many tight houses it is necessary for human health to add a ventilation system to meet ASHRAE ventilation standards, which will be in the ballpark of 0.35 ACH for many houses.

    Hope this helps -- Pstu

  9. #22
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
    Posts
    207
    Quote Originally Posted by pstu View Post
    We still may not be communicating properly. Your number of 8.4 ACH50 is only about 50% higher than mine, it is an entirely plausible number. I have heard that a crude way to estimate natural ACH is to divide the above number by 50 -- anyone at all please confirm or correct me here.
    Found this post on another forum. It seems that the number to divide by varies from area to area. For example, 17 in Minnesota and 50 in Florida. I would guess we in Canada would be similar to Minnesota, so my natural infiltration might be 8.42/17=0.495. If we halve the leakage area (230sq.in) by sealing leaks and other openings like the fireplace, our natural infiltration could be ~0.25?

  10. #23
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    More expert info

    Thanks for sharing that, it is far more accurate than my memory was.

    I think your arithmetic is right, you could get down to approximately that natural ACH if you could halve your leakage area. Lstiburek endorses the attached checklist for places to seal against leakage.

    Hope this helps -- Pstu
    Attached Images Attached Images

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