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  1. #27
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,347
    Here is what i see sometimes in new construction.
    1. Man. j. for house used but it is generic, house orientation not the same. A lot of east west glass and duct not sized for it will eat your lunch.
    2. Shoddy construction for energy savings.
    3. ductwork fell down.

    Seriously, it will be a combination of problems but they will probably throw on a 4 ton.

  2. #28
    Join Date
    Nov 2006
    Location
    Oregon
    Posts
    853
    Quote Originally Posted by captube View Post
    Seriously, it will be a combination of problems but they will probably throw on a 4 ton.
    Yes, and the 4T could possibly short cycle and fail to remove the humidity. It's all a balancing act!! Manual J and a good contractor can pick the sweet spot.

    Is there high humidity in OK?

  3. #29
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,347
    Yes on the humidity. N.E. Ok..)
    I agree on the moisture removal, i was guessing on the out come on the problem. Although it's been done more than once.

  4. #30
    Join Date
    Jul 2009
    Posts
    4
    sounds to me you have a air flow problem,not a ac problem....

  5. #31
    Join Date
    Jul 2009
    Posts
    4

    Thumbs up

    sounds to me you have a air flow problem did you do a static test ? is there enough ra?

  6. #32
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,451
    A lot Techs don't have anything to check static pressures, airflow velocity & CFM. They also don't know how to do a duct layout using manual D.

    The airflow determines the amount of sensible & latent heat of condensation the evaporator coil can absorb for transferring to the condenser.

    Airflow determines how much BTUH the E-Coil can absorb, therefore correct airflow is crucial to the nominal performance of the system.

    First & foremost, get all the test instruments you need to optimize the airflow.
    Click udarrell for more info on ductwork & airflow...
    - Darrell

  7. #33
    Join Date
    Jul 2009
    Posts
    12
    Yes the humidity seems pretty insane here if ya never been to Oklahoma just wait until ya have it's crazy all year around I just got home at 2 and the ac was still running she ginnally shut off after a 12 hour jog to stay at 74 degrees

  8. #34
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,451

    Simple Way to Ball-Park Operating BTHU

    For anyone, to Ball-Park Operating BTUH, you need the diameter size of each duct & a way to check the velocity from each run. A low cost anemometer to check the velocity in FPM will work. (If you want a more precise BTUH; There are also some great uses for a thermometer & a low cost humidity gage.)

    Check & record the temp rise off the outdoor condenser against OD ambient.

    Check & record the temp drop of the supply outlets, record indoor relative humidity. Record Dry bulb & Wet bulb of both the Supply Air & Return Air along with CFM airflow & I’ll tell you the BTUH it is delivering.


    Let's say you have a 1.5-Ton 18,000-BTUH Rated A/C. All the 5 ducts are 6" dia., & they all average 688-FPM velocity. You need the sq.ft. of the duct; 6X6= 36 *X's .7854= 28.2744/ by 144= 0.19635sq.ft. area *X's 688-FPM = 135-CFM *X's 30= 4,050 *X's 5= 20,250-BTUH.

    A 1.5-Ton Goodman Data with 2-Ton indoor E-Coil; 95-F outdoors; at 75-F IDB, a high humidity 71-F IWB; at 600-CFM delivers 20,500-BTUH. NOT close to nominal BTUH Rating, Call a Tech; call one anyway they need to be busy, ha!

    Just remove one diffuser & check the velocity in FPM, it’ll be close enough for Govt., work, . There are also other options...
    =========================================------------------
    The easiest way is to use Hart & Cooley Engineering Data (P-16, deflection A).
    A 10x4 adjustable fin register at 700-fpm delivers140-CFM; Pres. Loss is .031”; with a 13-ft throw.

    You don’t have to do this procedure below.
    Depends on how close you want your ballpark figure to be, Ha.

    Compare ratio of register sq.ft., open area to duct sq.ft. area.
    Measure only the area where the blades are to get sq.ins., divide by 144 to get the net free area sq.ft., (or get mfg'ers data) area of the grille *X's FPM velocity = CFM *X's 30 = BTUH. - Darrell
    Last edited by udarrell; 07-03-2009 at 10:52 AM. Reason: For anyone...

  9. #35
    Join Date
    Jul 2009
    Posts
    12
    well i am still waiting to hear back from one of the ac guys, he keeps putting me off but today its 90 degrees outside and my ac ran from 3:15pm to 4:44pm without shutting off and my thermostat is just set @ 75. i did another temp reading the return farthest from my unit is sucking air in at 73.6 and the air coming out in the room right next to it is coming at 65.3, so the ac is only cooling it by 8.3 degrees after it goes through the attick!!!!

  10. #36
    Join Date
    Jul 2009
    Posts
    12
    Quote Originally Posted by udarrell View Post
    For anyone, to Ball-Park Operating BTUH, you need the diameter size of each duct & a way to check the velocity from each run. A low cost anemometer to check the velocity in FPM will work. (If you want a more precise BTUH; There are also some great uses for a thermometer & a low cost humidity gage.)

    Check & record the temp rise off the outdoor condenser against OD ambient.

    Check & record the temp drop of the supply outlets, record indoor relative humidity. Record Dry bulb & Wet bulb of both the Supply Air & Return Air along with CFM airflow & I’ll tell you the BTUH it is delivering.


    Let's say you have a 1.5-Ton 18,000-BTUH Rated A/C. All the 5 ducts are 6" dia., & they all average 688-FPM velocity. You need the sq.ft. of the duct; 6X6= 36 *X's .7854= 28.2744/ by 144= 0.19635sq.ft. area *X's 688-FPM = 135-CFM *X's 30= 4,050 *X's 5= 20,250-BTUH.

    A 1.5-Ton Goodman Data with 2-Ton indoor E-Coil; 95-F outdoors; at 75-F IDB, a high humidity 71-F IWB; at 600-CFM delivers 20,500-BTUH. NOT close to nominal BTUH Rating, Call a Tech; call one anyway they need to be busy, ha!

    Just remove one diffuser & check the velocity in FPM, it’ll be close enough for Govt., work, . There are also other options...
    =========================================------------------
    The easiest way is to use Hart & Cooley Engineering Data (P-16, deflection A).
    A 10x4 adjustable fin register at 700-fpm delivers140-CFM; Pres. Loss is .031”; with a 13-ft throw.

    You don’t have to do this procedure below.
    Depends on how close you want your ballpark figure to be, Ha.

    Compare ratio of register sq.ft., open area to duct sq.ft. area.
    Measure only the area where the blades are to get sq.ins., divide by 144 to get the net free area sq.ft., (or get mfg'ers data) area of the grille *X's FPM velocity = CFM *X's 30 = BTUH. - Darrell
    could you explain in a bit more detail on what I need to do??

  11. #37
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,451
    Quote Originally Posted by ZacHolley View Post
    well i am still waiting to hear back from one of the ac guys, he keeps putting me off but today its 90 degrees outside and my ac ran from 3:15pm to 4:44pm without shutting off and my thermostat is just set @ 75. i did another temp reading the return farthest from my unit is sucking air in at 73.6 and the air coming out in the room right next to it is coming at 65.3, so the ac is only cooling it by 8.3 degrees after it goes through the attick!!!!
    The information I gave you in your #36 post, was for knowledgeable Techs. The information I provided, though simple, would probably make most possible DIY'ers roll their eyes & blank out. Everything will probably sound to difficult & involved for DIY'ers.

    An 8.3-F indoor temp-split appears unacceptable, even with a high humidity..
    That tends to point to possible duct system problems; could also be a number of other things, but I have provided enough info, as I get no pay & don't want to be liable for a way-word call from 100's of miles from the equipment.

    A good Tech will know how to troubleshoot the problem that your A/C is experiencing. Nothing is that difficult for someone that knows every aspect of an operating system.

    You could take as many temps as I listed & post them. However, there is nothing close to being there. It would be great to know the CFM & if some runs have low airflow.

    Your Tech(s) can click udarrell then click visit home page & go to that page for a start. They may also roll their eyes & go their way.(?)
    - Darrell

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