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  1. #27
    What does the code say on what temp you have to plan a HVAC unit for. I can tell you that I took temps in every vent in the house. I am loosing 4 degree's from the return air duct to the return air plenum. Most of the vents that are away from the plenum are loosing any where from 6-7 degree's. It is coming out at 62-66 degree's at some vents. The air in the plenum after it leave's the evaporator coil is 59.9 degree's.
    ===========================

    6-7 degrees? That seems like a lot!
    If you were getting a 20 degree temp drop across the Evaporator, a 6 degree temp drop from evaporator to the register would mean you're losing 30% of your cooling capacity to that register. No wonder you're not able to get the temp down. You need to find out if your ductwork is insulated and if the joints were sealed.

  2. #28
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Exclamation CLEAR as in CRSYTAL CLEAR !

    Originally posted by docholiday
    I cant imagine he had a house built in Houston with single pane clear glass.
    Sounds like __THE STANDARD__ for Tract housing developments. YES, even in FL And TX.

    Will builders EVER Learn? _NO_

    Use of CLEAR Windows in the south should be a Felony.
    That's WHY Uncle Sam is here to kick some butt.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #29
    Join Date
    Jun 2005
    Posts
    37
    double pain glass. More than likely not of high quality. I am going to try to get the building materials used in the construction of the house from the builder.

    Tommorro when I get home from working at the fire station I am going to calculate the actual square feet in the house by measuring. I am also going to calculate the square feet of windows on each side of the house.

    I will post the results here.

    What does the code say about what temperature you want to design for?

    In some places is it ok to design for 78 degree's on a 95 degree day?

    Does the code talk about humidity?

    If I want to get an independent load calculation done what type of person with what certification's and back ground do I want?

    Are there certain types of inspector's that deal with this kind of stuff?

  4. #30
    Join Date
    Jun 2005
    Posts
    37
    Here is everything from my measurements I took today.

    House is 1500 square feet.
    House faces West
    Square footage of windows (double pain not that thick)
    ---------------------------
    North 47.78 sqf
    West 21.385 sqf
    East 56.38 sqf
    south 47.11 sqf
    ----------
    Total 172.65 sqf

    1.)Front door 20 feet square with 4.5 square feet of lead
    glass
    2.)door entering into garage 18 square feet
    3.)Door to backyard 20 square feet w/ 5.10 square feet of
    double pain glass

    Ceiling height in house is 8' in bedroom 2,3, utility, bath#2

    Rest of house has 9' ceilings

    Attic gets to 134 degree's on a 95 degree day

    So is 2.5 tons big enough? Should I get them to upgrade the unit? Should I get them to do something about the cooling loss in the vents?

    Thanks.


  5. #31
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295

    Exclamation NO RE-Sizing for ACTUAL Layout IF__

    Originally posted by smp7015
    Here is everything from my measurements I took today.

    House is 1500 square feet.
    West 21. sqf .. East 56. sqf
    Total 173. sqf

    Attic gets to 134 degree's on a 95 degree day

    So is 2.5 tons big enough?
    Should I get them to upgrade the unit? _" NO "
    Should I get them to do something about the cooling loss in the vents? _"reply: DEFINITELY"
    1.......Glass___8,739 BTUh
    2......Ceiling__4,736
    3........Walls__1,705
    4.........Duct__4,643
    5.Infiltration__1,651
    6.Internal Gains2,280
    7.......People__1,286
    8.......TOTAL__25,039_BTUh

    2.5 Ton should provide 30,000 BTU Total
    _____ * 0.73=_~21,900__BTUh SENSIBLE.

    13% less actual capacity than MY calculated
    should only make the unit run ~15% longer
    when ALL seven Design Loads are Concurrent loads.

    NO one home or No Internal Gains from Kitchen or other:
    Subtract loads 6 & 7 above..3,566 BTUh
    21,473 BTUh sensible

    The 2.5 ton unit should run nearly continously from 1 PM to 7 PM. However, 7 PM to Mid-night it is should run ~50+% of the time, and maybe 35% from mid-night to 10AM.

    It appears that the duct load due to leakage or other REAL Cause may be >10,000 BTUh at-this-time.

    ********************************************
    FIX the Air Flow (maintain > 950 CFM), duct leaks, duct insulation. I anticipate that you will be able to achieve at least 21'F < Outside Temeprature.
    95'F - 21'F = 74'F
    ********************************************

    AND
    You should evaluate suing for 13.4% of the Selling Price of your residence because Perry Homes seemed to mis-represent living area as 1733 S.F. and only provided an actual 1500 A/C S.F.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #32
    Join Date
    Nov 2003
    Location
    South Carolina
    Posts
    1,167
    3.5 ton.

  7. #33
    Join Date
    Jun 2005
    Posts
    37
    dan sw fl Thanks for all your help.

    I appreciate it. Being that the actual square footage is 1500 square feet, all my reading on the board, and research I agree with you that 2.5 is ok. Man I feel like an idiot for not measuring square feet to begin with. The builder included the garage in with the to make it 1733 sq feet.

    I truely think that the problem lies with their either not being enough air flow through the system, the attic not being ventillated enough or the combination of the two.

    All in all I will address this to the builder and get them to fix it. I don't think they can justify a vent puting out 71.1 degree's when the return air is taking in 75.6 degree's.

    Another thing I am going to do is take temp readings late at night to see what I am getting from the vents with the attic being cooler.

    Thanks all and I will let everyone know what happens

  8. #34
    Join Date
    Jun 2005
    Posts
    13

    best bet

    take the plans for the house to a local contractor get a quote on a system. if house less then a year old go to builder.

    [Edited by jimtech on 06-26-2005 at 07:10 AM]

  9. #35
    Join Date
    Jan 2005
    Posts
    340
    Originally posted by smp7015
    Going of the appraisal for tax purpose's the total living area is 1840 square feet.
    You need to call the tax assessor's office and get them to correct this. Your taxes may be lower as a result.

  10. #36
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    UNit too small - need at least 3 ton to get 72 / 73 degrees in yur heat & humidity

  11. #37
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Didn't see Manual S ,from ACCA ,mentioned ,and it can make the difference in many cases.


    When indoor design temperature is less than 80F,there is a deduction in sensible capacity,of 835 btu per 1000 cfm ,for each degree below 80.

    So if you want 75,5X835,for a 2.5 ton,1000 cfm system,so dedcut 4175 btus of sensible capacity.

    Good mfrs ,detailed cooling capacity charts have this footnote,mostly ignored by design people.

    My theroery is,that's why a lot of contractors think Man J undersizes ,so they add 1/2 ton.That plus they undersize the ducts and lose more capacity there.

  12. #38
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Likely problem sources

    This house is in Texas, where there are really few standards beyond caveat emptor. So I would think building codes say little of value to this homeowner.

    Airflow is questionable from the get-go, even more so if you accept the easy answer of "more tons". As far as I can tell nothing has been done to establish that 1) the duct system is delivering enough CFM to do the job of cooling, and 2) that it is not leaking big-time into the attic.

    If you have a supply leak 1) that cold air is wasted in the attic, and 2) roughly an equal amount of hot-humid Houston air will be sucked in from the outside, through whatever random openings exist. Very possibly through ceiling cannister lamps, highly heated and moisture laden air from the attic itself. I would expect only the lowest quality of duct sealing, unless a test could show otherwise. This would be a simple, obvious, and relatively easy-to-fix source of the problem. Until you affirm there is not excessive duct leakage, it seems to me a waste of time to pursue more exotic solutions.

    Does this house have radiant barrier on the roof decking? That would be an indicator of how serious Perry is about doing the right thing. From studies I have seen one could expect about 8-12% reduction in cooling load, compared to one without. Are the windows appropriate to this climate, or just the cheapest ones? Being double pane will help but low-E windows designed especially for cooling climates, will help more.

    My home is near Houston and has many of the low quality aspects common in this region's craftsmanship. Built with single pane windows, indifferent duct design, some major leaks after a few years, etc. I would set a bead on craftsmanship issues first.

    One company which can perform an analysis of the AC system's operation is Central City Air. There could be others but it seems in a case like this, you would want to pay for the best to troubleshoot. Possibly too, in the end you could get reimbursed for their charges (don't expect cheap).

    Best of luck to you -- P.Student

  13. #39
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    And Central City Air believes in TXVs.

    smp7015: Does your system have one or not?


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