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  1. #27
    Join Date
    Aug 2003
    Posts
    626
    The reason I brought up the duct issue is that manual j7 has minimum 25% over capacity built in for the problems of duct leakage and extra infiltration caused by duct leakage.

  2. #28
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,321
    For all you guys prognosticating in regards to what will and won't work in Houston remember this. There is a new law in Texas that requires that you warranty the system for two years and it must maintain a maximum of 78* in the center of the room.
    I don't doubt that there are some homes that can be built that 3.5-tons can and will cool 5200 Sq. Ft. but not the one described by Panama. The house described by Slice is an example of such a house; it however is exactly what Bill described a cave.

    Uktra you have post your assertion about homes and HVAC systems here for the past year or so and do not provide any clue as to your background. I suspect that you work for a builder and have a background in Architecture or an ME. That is all well and good but I go to houses every day that have nice quality load calcs by builders and systems are inadequate. As Dash states many don't work because they are inadequately installed and poorly charged and or maintained. However many even after addressing ductwork and return issues adjusting charge to spec they still end up being undersized by as much as 2-tons granted most are more like 1-ton undersized.

    Theory is great but I deal in comfort and satisfying my customers.

  3. #29
    Join Date
    Jun 2003
    Location
    Jacksonville, FL.
    Posts
    4,313

    I'm with Mrbillpro....

    There's doing things all on computer & then there's the real world. Mrbillpro & I live in the real world so we've both come to the conclusion that there is no way in a million years that 3 1/2 tons will cool a 5200sq.ft. home. Then, of course, you would have to zone it....

  4. #30
    Join Date
    Feb 2002
    Location
    Houston Tx
    Posts
    344
    mrbillpro: MY post was stating as well as that house is insulated, at 3200 sq ft that it required 3.5 tons So I agree that a 5000 sq ft dream home 3.5 tons will never have a chance.......

  5. #31
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    By the way, do you guys all belong to the Flat Earth Society?

  6. #32
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,944
    No, but I do belong to the "Realistic Society"
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  7. #33
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,321
    No we exist in the REAL WORLD!!

  8. #34
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,944
    Originally posted by Panama
    By the way, do you guys all belong to the Flat Earth Society?
    He lives in Colorado and is trying to convince us were out of touch,boy they must grow some good erb up in them there mountains.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  9. #35
    Join Date
    Aug 2003
    Posts
    626
    Classical--You and I have had this go around before. Yes I am an ME that has also studied building science. I am also a licensed contractor. I do not work for a builder, I work for people who want a better built home than most of what is being built today. I help design both the thermal envelope as well as the HVAC system. I have been in hot attics and dirty crawl spaces, so I live in the real world. In the real world (even in Houston) homes exsist that work at manual j numbers and work better than 95% of all other homes. The homes also guarrantee comfort and heating and cooling costs. I also live in a climate very much like Houston and have designed and help build homes that work in that type of climate without the 2-3 ton oversizing that I normally run into. To say a normal, run of the mill code home of 5200 sq. ft. can be cooled properly in your climate by 3.5 tons is not a reality. But for someone to say Panamas 5200 sq. ft home cannot be cooled by 3.5 tons is also not a reality.

    [Edited by uktra on 06-29-2005 at 09:37 PM]

  10. #36
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,944
    Originally posted by uktra
    I also live in a climate very much like Houston and have designed and help build homes that work in that type of climate without the 2-3 ton oversizing that I normally run into.

    If the homes you run into you say are oversized are we comparing apples to apples? in good old Texan that would mean that they would have to be close to the same home type your designing or it would not be a fair statement to say there oversized, that would be just an opinion.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  11. #37
    Join Date
    Aug 2003
    Posts
    626
    well you can call it opinion if you want, but I run into a lot of folks that have short cycle times and high humidity.

  12. #38
    Join Date
    Apr 2002
    Posts
    11,808
    The latent load seems too low for Houston.

    I don't use manual j but when they say 47 grains for 50% does that mean that the ambient air holds 47 grains more than the room air?

    If so that would imply that Houston has a design ambient of 112 grains, I would guess it would be more like 130 or higher.

    All I have is worst case humidity data for Houston and it ranges from 137 to 147 grains.

    I would guess the latent load would be more than double what was calculated considering 0.3 air changes, plus six occupants and mama simmering some chili.
    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
    Mar 2001
    Posts
    288


    3.5 tons on 5200 square feet. I'd say run the Manual J one more time. Might be a good idea to take into consideration internal load...lights...computers, TV sets, people, pets, refrigerators and the like. Going to be interesting on a 4th of July party with 25 people over too.

    Double check your stuff. I'd want at least 2 systems with that square footage if it were MY home. I'm just a homeowner and not an HVAC pro, but I would consider slightly oversizing 2 stage cooling.


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