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  1. #1
    Join Date
    Sep 2011
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    Nj and Delaware
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    75

    Different ACH50 Numbers and Duct Leakage Numbers

    I have been reviewing the numbers the builder gave me for the Energy Star certification report and comparing to a recent test that was done on my home as part of a sales call to sell me a new system.

    The house is 2 stories with a heated 2900 SqFt and a volume of almost 25,000 CuFt. It is located near zip 19975 in Southern Delaware. There are no trees around the house and the neighboring houses are 30- 50' away.

    The original test was done by a Energy Star rating company in Maryland on the completed house in July of 2010 and showed a result of 1350 CFM. This calculates to 3.24 ACH @50pa

    The second test was done on October of this year, by a local HVAC company, and showed the leakage to be 1715CFM which would indicate 4.2 ACH @50pa

    Is it normal to see such a change in the ACH50 numbers after 2 1/2 years? We have not made any modifications to the structure since it was built.

    Based on these numbers and location, what would the natural ACH work out to?

    What is a "good" number range for a house that is not to leaky to be inefficient or too tight that it needs mechanical ventilation?

    The duct leakage as per the Energy Star certification was 124CFM@25pa. Is this a good number?

  2. #2
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    Hey MODS,
    Would this thread be better suited for the Indoor Air Quality forum? Not seeing much activity here.

    Tim

  3. #3
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    Is it normal to see such a change in the ACH50 numbers after 2 1/2 years?

    it isn't unusual, weatherstrippings age and have less seal.
    flue for fireplace may be open?
    it isn't a big change, and your numbers are good.
    could be difference in equipment calibrations.

    duct leakage should be 5% for energy star, but 10% is the norm for
    a well seald duct system. if you are building new construction it is
    easy to get the 5%, retrofitting..10%.

    depending upon the size of your system.. 20 cfm per ton.

    company should use ASHRAE ventilation standard 62.2
    to determing fresh air requirements. usually bleow .25
    ach requires fresh air, some states use .35 like La. but
    it seems to vary from state to state.

    were whole house numbers 1350 & 1715 and duct leakage
    125 cfm 25? we test ducts at 59 pascals rather than 25.
    just a state thing.

    can you attach the reports?
    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  4. #4
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    Whole house test was done at 50pa and duct was done at 25pa.
    System is a 3.5T Split.
    No fireplace flue, just a glass door vented propane fireplace so that should not have caused the difference in the two readings.

    Based on duct CFM numbers, what is the duct leakage %? Is it calculated from house volume?

    And what would the natural ACH work out to? Someone said just divide ACH50 / 20 to get the result.

    What would be considered "too" tight for a 4 person occupancy?

    Sorry for all the questions, just trying to get a feeling for these things.

  5. #5
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    5% leakage of 3.5 ton system would be 70 cfm
    duct leakage calc is different from whole house sq ft & volume

    I'd think that weatherstripping has deteriorated & different
    equipment used for testing would account for difference
    is whole house numbers.

    I use sq ft of house & blower door reading, my shortcut to determining
    if house is in need of fresh air intake. blower door reading & sq ft should
    be about the same. teddkidd adds in another factor for his cold climate.
    somewhere there is a formula that you use to calculate achn.
    I've found it to be very close to my shortcut. so I don't do the
    formula, in my almost 14 years in the rating business I find it
    to hold true.

    no such thing as too tight. build tight ventilate right.
    whole house dehumidifiers can be set up to add air to
    house. Teddy Bear would have info as to what you'd
    require for your home. the man knows his stuff.
    rather than putting hrv unit..dehumidifier is much
    better.
    wouldn't be much more than hrv (heat recovery unit)
    and it serves more than one purpose.

    don't worry about asking questions. thats why we
    are here.

    can you attach the reports from testing?

    I'll drop teddy bear a pm and ask him to contribute
    his input as my experience is hot humid climates.

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

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,266
    Quote Originally Posted by pendetim View Post
    I have been reviewing the numbers the builder gave me for the Energy Star certification report and comparing to a recent test that was done on my home as part of a sales call to sell me a new system.

    The house is 2 stories with a heated 2900 SqFt and a volume of almost 25,000 CuFt. It is located near zip 19975 in Southern Delaware. There are no trees around the house and the neighboring houses are 30- 50' away.

    The original test was done by a Energy Star rating company in Maryland on the completed house in July of 2010 and showed a result of 1350 CFM. This calculates to 3.24 ACH @50pa

    The second test was done on October of this year, by a local HVAC company, and showed the leakage to be 1715CFM which would indicate 4.2 ACH @50pa

    Is it normal to see such a change in the ACH50 numbers after 2 1/2 years? We have not made any modifications to the structure since it was built.

    Based on these numbers and location, what would the natural ACH work out to?

    What is a "good" number range for a house that is not to leaky to be inefficient or too tight that it needs mechanical ventilation?

    The duct leakage as per the Energy Star certification was 124CFM@25pa. Is this a good number?
    Typically you divide by 19-20 to get your natural air leakage with average wind, 7.5 mph, and average winter stack effect. With your home size, this would be an air change in 4-5 hours. This is ok during cold windy weather. Keep in mind that as the winds calm and the outside/inside temperature difference decreases, the natural air change decreases. On a calm, 70^F day, your natural ventilation air change rate is near zero. Most suggest that the minimum ventilation rate is an air change in 4-5 hours. You need 70-80 cfm of fresh air ventilation during calm winds and occupied. You live in a green grass climate that has outdoor dew points that are +60^F most of the spring/summer/fall. The moisture from the fresh air and the occupants amounts to upto 5-6 lbs. of moisture per hour. On a hot day, a properly setup a/c will maintain <50%RH. During rainy, cold weather, a good whole house dehumidifier will maintain <50%RH when the a/c has low/no cooling load.
    Units like the Ultra-Aire whole house dehumidifier with the fresh air ventilation option will provide the desired amount of filtered fresh air and blind it into your home. Also the system will maintain <50%RH without any cooling. These units connect to your a/c and are high efficiency. Go Ultra-Aire.com and comeback with questions if interest in fresh, filtered, dry air when needed. Search my past posts for more info.
    This makes your healthy and very comfortable.
    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"

  7. #7
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,702
    2900 sf, 1300 is awesome, 1700 quite good. Both require mechanical ventilation, BAS is probably 2300 ish? So ever 1700 is below 70%.

    Propane fireplace? Typically those installations S U C K. So that could well explain the big jump. Even if installer knew better, eh, whatsa lil leak, NMEB.

    3.5 ton sounds big for your low leakage.

    Duct leakage not great. Temp imbalance? Aeroseal.

    How's cooling? Short cycling? Humidity problems?

    Tb can help you solve humidity and fresh air req. lot cheaper n cancer.
    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.

  8. #8
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    Funny you mention about the 3.5 T being oversize! How does a 80kBTUH single stage propane furnace sound in the same house? In all fairness, there are 2 systems in the house. One 3.5T was for the downstairs 2000ft^2 and a 1.5T HP + strips for the 900ft^2 upstairs

    When the home was built, we complained about the Rh in the summer. On the hottest day, the Rh never went below 55% and the A/C cycled on a less than 25% duty cycle, this is with an OAT of 102* at 4PM. Furnace was the same way: it would run less than 20% of the time when the OAT was 15*, one of the coldest we see.

    The builder's response : "That is a good thing , you don't want to work these things to hard". I asked for a copy of their Manual J and saw where the load they calculated, would have fit very nicely in a 3T AC, however the Calculation was riddled with false assumptions that padded the numbers.
    For instance: they assumed the ACH50 value to be almost 2X the actual. Also the house has an insulated, "conditioned" crawl space with 1 3x4 supply vent and no return. The load they calculated on the crawl was ~10kBTUH cooling and ~15kBTUH heating,(how do you get 15kBTUH through a 3x4 vent balanced at 100cfm?) then they also made an allowance for heat loss through the main floor into the crawl for ~8kBTUH. Also the supply ducts run through the crawl and they had their heat loss added to the load. My observation was that when the system ran, with the vent closed in the crawl, the conditions warmed up and approached the upstairs. I assume this was from the duct losses and leakage. So I was being "charged" for conditioning the crawl, heat transfer between 2 conditioned areas and heat loss of the ducting in a conditioned space. Assumptions on insulation values were also inaccurate. The list went on and on.

    Long story short, I did my own Manual J and the heat loss came in at 30kBTUH and gain came in at 24kBTUH, which surprisingly was almost what I verified from the builder's installed equipment runtimes I observed.

    Had a few discussions with builder, he would not admit any fault so recently had a 2 stage 3T Amana 18 SEER heatpump and strip heat installed for downstairs.

    The heating so far has been as expected: no more "jet blast" when there is a call for heat, and my wife does not miss the too hot, too cold feelings we saw last year.

    Yes I can relate to the propane fireplace leaking. I felt a draft coming from the lower louver. When I took the grill off, there was a 2x3" oval hole the flex gas line was routed through. When installed a small piece of aluminum tape was put there in an attempt to seal that space. However that had pealed off the area and was allowing outside air in. This is hole now stuffed with insulation.

    My next step is to find someone to test& seal ductung and balance the system now that we have equipment properly sized. Balance is not too bad however: The family room where I have the thermostat is 70* and the master bedroom, furthest from the AHU is 68.5*. This is OK for winter, but probably will not work for summer if the swing is +1.5* above family room.

  9. #9
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,702
    Quote Originally Posted by pendetim View Post
    The builder's response : "That is a good thing , you don't want to work these things to hard". I asked for a copy of their Manual J and saw where the load they calculated, would have fit very nicely in a 3T AC, however the Calculation was riddled with false assumptions that padded the numbers.

    For instance: they assumed the ACH50 value to be almost 2X the actual. Also the house has an insulated, "conditioned" crawl space with 1 3x4 supply vent and no return. The load they calculated on the crawl was ~10kBTUH cooling and ~15kBTUH heating,(how do you get 15kBTUH through a 3x4 vent balanced at 100cfm?)

    then they also made an allowance for heat loss through the main floor into the crawl for ~8kBTUH. Also the supply ducts run through the crawl and they had their heat loss added to the load. My observation was that when the system ran, with the vent closed in the crawl, the conditions warmed up and approached the upstairs. I assume this was from the duct losses and leakage. So I was being "charged" for conditioning the crawl, heat transfer between 2 conditioned areas and heat loss of the ducting in a conditioned space. Assumptions on insulation values were also inaccurate. The list went on and on.

    Long story short, I did my own Manual J and the heat loss came in at 30kBTUH and gain came in at 24kBTUH, which surprisingly was almost what I verified from the builder's installed equipment runtimes I observed.

    Had a few discussions with builder, he would not admit any fault so recently had a 2 stage 3T Amana 18 SEER heatpump and strip heat installed for downstairs.

    The heating so far has been as expected: no more "jet blast" when there is a call for heat, and my wife does not miss the too hot, too cold feelings we saw last year.

    Yes I can relate to the propane fireplace leaking. I felt a draft coming from the lower louver. When I took the grill off, there was a 2x3" oval hole the flex gas line was routed through. When installed a small piece of aluminum tape was put there in an attempt to seal that space. However that had pealed off the area and was allowing outside air in. This is hole now stuffed with insulation.

    My next step is to find someone to test& seal ductung and balance the system now that we have equipment properly sized. Balance is not too bad however: The family room where I have the thermostat is 70* and the master bedroom, furthest from the AHU is 68.5*. This is OK for winter, but probably will not work for summer if the swing is +1.5* above family room.
    Poignant example of catastrophic EnergyStar design failure. The builder is harming people left and right. You've paid for 3 systems instead of one, that sucks!

    I think MD has programs with rich subsidy for aeroseal.
    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.

  10. #10
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    I would like to participate in an Aeroseal program with a generous subsidy, unfortunately I am in Delaware. There are no currently funded programs in this state I am aware of, all ran out of money last year.

    I hope someone comes along and tells me I am wrong and can point me to a program. (:>)

  11. #11
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,702
    No recourse against the builder?
    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.

  12. #12
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    Yes. (That is all I can really say for a bunch of reasons.)

  13. #13
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    it isn't clear if the duct leakage is for both units or just the 3.5 ton system.

    leakage is above 5% mandated by energy star.

    return leakage contributes to high RH
    short run cycles of oversized equipment lessens dehumidification of systems.

    I'd address duct & return leakage.

    I'm not a big fan of aeroseal as it has limits as to what it can seal.
    large leakage sites leak more air and are beyond what aeroseal can achieve
    in sealing.
    if ductwork is acessable, a bucket of mastic & a roll of hardcast mastic tape
    can seal every size hole, not just small ones.
    mastic is much more affordable than the large price of aeroseal.

    of course independent verification of duct sealing is always a good idea.
    good to know what you had in leakage before & after. also gives you a
    chance to catch what you missed.

    not to start the whole debate again..its been done..kind of..there was another
    thread at the same time about duct leakage that ran parallel to this
    previous aeroseal thread.
    http://hvac-talk.com/vbb/showthread....amp%3B+mirrors
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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