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  1. #27
    Join Date
    Jul 2008
    Location
    Rochester NY
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    4,702
    Quote Originally Posted by ga-hvac-tech View Post
    It would appear the BIG advantage is if the system (equipment and ducts) is in the attic.
    Well, that might be called the "no-brainer" situation.

    Sometimes it's not the quantifiable benefits but the unquantifiable quality of life ones. I think really the big advantage is hard to know until you've lived in a foamed house. Not many people who have would go back if they had a choice.

    That said, I do like cellulose. But I sell redefine in some circumstances where there is no hvac in the attic. If you have to count on a level of quality in attic air sealing which is not likely to be achieved by regular human beings than redefine is simply the safe approach.

    I prefer to avoid recommending work that has a high likelihood of poor or mediocre results. I ask myself is the attic in question particularly likely to be a failure addressed other way?
    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. #28
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,776
    Quote Originally Posted by ChaseAir View Post
    The homes we have done were so tight they really needed a dehumidifier to remove moisture. An 85 degree day was simply not enough to cause the units to run with the stat set at 78. Gross oversizing?

    Well even 2 stage units are "grossly oversized" on a light load day with a homeowner who doesn't have thermostat set as low as the "design conditions" were determined in the load calc.

    Not to mention that big oak tree on the west side of the house that reduces the load by 3/4 ton in some circumstances. Needless to add, the load calc is a great tool, but it does not answer all things.
    A home that needs 17,500 BTU sensible cooling capacity at 95 outside and 70 inside would have a sensible load of 10,769 at 85 outdoor and 70 inside, and a sensible load of 7,368 sensible at 85 outside and 78 inside temp.

    Thermostats that require a 2 degree temp rise to bring on the A/c will tend to keep the A/C off too long in a well insulated tight house. And ERV's that are bringing in too much fresh air will cause the humidity to rise.

    If there is an oak tree shading the house enough to knock off 3/4 of cooling load, then the tree should be allowed for in the load calc.
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  3. #29
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,941
    Quote Originally Posted by rickboggs View Post
    2668 sq ft home
    R38 Ceiling
    R13 Walls
    Total 22506
    Sensible 18025
    Latent 4479

    R25 Foam Encapsulated
    R13 Walls
    Total 20720
    Sensible 17494
    Latent 3226

    Add duct in the attic

    R38 Ceiling
    Total 33307
    Sensible 26707
    Latent 6600

    R25 Foam Encapsulated
    Total 26620
    Sensible 21476
    Latent 5144
    Thanks Rick. How many inches of foam did you use to get R-25, and did you account for the conductive heat gain through the rafters that were not covered in foam? I can't see getting an R25 out of 3 inches of foam and the rafters are left exposed.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  4. #30
    Join Date
    Jul 2006
    Posts
    1,091
    Quote Originally Posted by tipsrfine View Post
    Thanks Rick. How many inches of foam did you use to get R-25, and did you account for the conductive heat gain through the rafters that were not covered in foam? I can't see getting an R25 out of 3 inches of foam and the rafters are left exposed.
    5 1/2" of foam. I think, am not sure, that Manual J assumes 15%..... or is it 10%..... for roof construction.

  5. #31
    Join Date
    Jul 2006
    Posts
    1,091
    Quote Originally Posted by beenthere View Post
    A home that needs 17,500 BTU sensible cooling capacity at 95 outside and 70 inside would have a sensible load of 10,769 at 85 outdoor and 70 inside, and a sensible load of 7,368 sensible at 85 outside and 78 inside temp.

    Thermostats that require a 2 degree temp rise to bring on the A/c will tend to keep the A/C off too long in a well insulated tight house. And ERV's that are bringing in too much fresh air will cause the humidity to rise.

    If there is an oak tree shading the house enough to knock off 3/4 of cooling load, then the tree should be allowed for in the load calc.
    All the above is true true true. Beenthere, man do I have some stories. We've been working with a contractor on some problem foam houses.... data loggers are your friend.

  6. #32
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,776
    You could tell us some of them.
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  7. #33
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,702
    Quote Originally Posted by beenthere View Post
    Thermostats that require a 2 degree temp rise to bring on the A/c will tend to keep the A/C off too long in a well insulated tight house. And ERV's that are bringing in too much fresh air will cause the humidity to rise.
    I wish I counted all the lightbulb moments you've provided me. Gonna parse through the meaning of that statement. I think it really supports smaller is better.

    We are not likely to get situations where the equipment can always run continuously. When weather conditions make your equipment oversized it is likely you may be uncomfortable either at the beginning or end of a cycle. You will be faced with adjusting the thermostat temp rise (what's the correct term, anticipator?) to a shorter (dead-band?) swing. But this will beat up your equipment.

    Wider dead band means longer off times and higher likelihood of being hot and sweaty one movement, then cold and clammy the next.

    Needs some polishing. But this explanation can lay off responsibility for discomfort onto the homeowner if you offer 2 stage equipment and they don't bite.

    I think many hvac guys sell to homeowner budget and that this is a huge mistake. Consult, recommend the best, then let the homeowner de-select features. Then when their comfort problem is due to a feature they de-selected, it's on them not you.
    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. #34
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,776
    On foamed homes. 2 stage should probably be the only thing offered, and be sized as close to the load as possible. And thermostats that don have to let the temp drop 2 degrees to bring on the A/C should probably be the only thermostat choice. Or the home will end up with high humidity from the ERV that will probably be set too high most of the time.
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  9. #35
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,271
    Quote Originally Posted by beenthere View Post
    On foamed homes. 2 stage should probably be the only thing offered, and be sized as close to the load as possible. And thermostats that don have to let the temp drop 2 degrees to bring on the A/C should probably be the only thermostat choice. Or the home will end up with high humidity from the ERV that will probably be set too high most of the time.
    Add in the point that a cooling coil accumulates moisture for the first 15-30 minutes of the cooling cycle before moisture goes down the drain. During the off cycle the moistue on the coil/pan evaporates back to the home.
    The occupants and fresh infiltrating/ventilating air contribute the moisture.
    During evenings and cool wet days with low/no cooling loads, an undersized a/c or 2 stage a/c will not maintain <50%RH. Reheat or a dehumidifier are solutions to proper fresh air ventilating and occupants moisture to maintain <50%RH. An adequately sized for peak loads a/c and 2-4 lbs, per dehumidifier make a good simple combination for a healthy and comfortable 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"

  10. #36
    Join Date
    May 2009
    Posts
    264
    Quote Originally Posted by beenthere View Post
    A home that needs 17,500 BTU sensible cooling capacity at 95 outside and 70 inside would have a sensible load of 10,769 at 85 outdoor and 70 inside, and a sensible load of 7,368 sensible at 85 outside and 78 inside temp.

    Thermostats that require a 2 degree temp rise to bring on the A/c will tend to keep the A/C off too long in a well insulated tight house. And ERV's that are bringing in too much fresh air will cause the humidity to rise.

    If there is an oak tree shading the house enough to knock off 3/4 of cooling load, then the tree should be allowed for in the load calc.
    Trees frequently lower the load on a building substantially. An example being when they shade a large area of eastern fenestration. If you include them as a factor, what do you do when the neighbor cuts it down?

    The one home we did was designed with no direct sunlight on the east and West fenestration by the use of overhangs and Bahamas shutters. The home was foamed to r-30 all the way around (off grade). As a result we were able to install a three ton on 4400 sq ft. The other guys bid was to install TEN tons. The three ton is a two stage and still does not run enough on typical days to dehumidify adequately so we used a dehumidifier.

  11. #37
    Join Date
    May 2009
    Posts
    264
    Quote Originally Posted by teddy bear View Post
    Add in the point that a cooling coil accumulates moisture for the first 15-30 minutes of the cooling cycle before moisture goes down the drain. During the off cycle the moistue on the coil/pan evaporates back to the home.
    The occupants and fresh infiltrating/ventilating air contribute the moisture.
    During evenings and cool wet days with low/no cooling loads, an undersized a/c or 2 stage a/c will not maintain <50%RH. Reheat or a dehumidifier are solutions to proper fresh air ventilating and occupants moisture to maintain <50%RH. An adequately sized for peak loads a/c and 2-4 lbs, per dehumidifier make a good simple combination for a healthy and comfortable home.
    Regards TB
    You don't like dehumidifiers do you TB?

    Hard to believe they used to live in unconditioned homes here in Florida with 90% RH.ow The Waudoni tribe in Ecuador lives in humidity constantly and their only health issues are falling out of trees. I know someone whose family has lived with them for generations.

  12. #38
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,941
    Quote Originally Posted by ChaseAir View Post
    You don't like dehumidifiers do you TB?

    Hard to believe they used to live in unconditioned homes here in Florida with 90% RH.ow The Waudoni tribe in Ecuador lives in humidity constantly and their only health issues are falling out of trees. I know someone whose family has lived with them for generations.
    That's a discussion worthy of having. Comfort levels vary in different parts of the world & apparently at different parts in time in the same location. This is partly/mainly why ASHRAE adapted the "adaptive comfort standard".
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  13. #39
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,776
    Quote Originally Posted by ChaseAir View Post
    Trees frequently lower the load on a building substantially. An example being when they shade a large area of eastern fenestration. If you include them as a factor, what do you do when the neighbor cuts it down?

    The one home we did was designed with no direct sunlight on the east and West fenestration by the use of overhangs and Bahamas shutters. The home was foamed to r-30 all the way around (off grade). As a result we were able to install a three ton on 4400 sq ft. The other guys bid was to install TEN tons. The three ton is a two stage and still does not run enough on typical days to dehumidify adequately so we used a dehumidifier.
    Does it ever have to run continuous on design days?


    If the neighbor cuts the tree down, plant another.
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