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  1. #1
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,245

    Questions Regarding HP Sizing And More

    Hi Guys, I went out to a no heat/heat pump service call yesterday. Found a bad compressor (breaker shutting off, no continuity). I came back today to replace the compressor/run cap/dryer. I pulled a 400 micron vac, weighed the charge in and fired it up only to get a 12* temp rise. I checked the air flow settings and noticed it was set for 4 tons of air for a 3 ton ODU. I set the airflow correctly and was able to get to a 15* rise... This got me going through things with a fine tooth comb. I found that the house had a lot of ductwork (60-70 actual, not equivalent, feet of duct to supply the lower level. 50 actual feet for the upper level. Upper level is 8x20 as far as I can see, lower starts out at 8x20 then goes to 16" round in the crawlspace). There are (9) 4x10x6 supplies, (8) 3x14x6 supplies, and (2) 2 1/4x10 toe kicks. I'm no Einstein but this certainly seems like more duct than 3 tons of air can handle. After setting airflow to 3 tons the flow from the registers was piss-poor. I also noticed all the windows in the house, tons of them. I decided to do a heat loss tonight. Results:

    Heat Loss 45,876
    Heat Gain 38,566
    @ Design Conditions-35* ODT/72* IDT

    Here is some info from the heat pump/coil. I realize I should have checked evap superheat but didn't. Also, there was no True Suction port on the POS heat pump.

    A/H-Trane 4TEE3F49A1000AB
    HP American Standard 4A6H4036B1000AA

    ODT - 52*
    IDT - 62*
    Temp Rise - 15*
    Liquid line temp at coil - 72*
    Suction line temp at coil - 118*
    High side PSI - 216
    Low Side PSI - ?

    The main reason for this drawn out post is to get your feedback on the exact cause of such a low temp rise as well as a possible causes for compressor failure. It sure feels like we are going to replace this 5 year old unit with a 4 ton provided the air handler is adequate, which at a glance I think it is. Also, do you think the stock TXV in this air handler is the correct one for a 3 ton unit? The installing contractor really screwed the pooch on this one but I just wanted to hear your thoughts. I think they sized the HP based on the gain instead of the loss and also paid 0 attention to the duct. Whattaya think?
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,311
    We get a bit colder then your area, and we size for the cooling load/heat gain, not heat loss.

    Did they complain it didn't heat or cool right since its been in?
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  3. #3
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,737
    If you can get to the ductwork, it sounds like a good place to suggest and install zoning.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,299
    Suction tap is on the suction line inside the right panel. Right below where you removed and replaced the built in drier. Or removed and installed biflow on the liquid line . Need to know suction, might have a TXV issue.

    Sounds like a pinch undersized. Is the HO complaining about being warm in the summer?

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,370
    With only a 10 degree split between ODT and IDT you should have deltaT over 15 degrees. Are you sure the A-coil isn't clogged or you aren't pulling return air from unconditioned space?

  6. #6
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,245
    Quote Originally Posted by beenthere View Post
    We get a bit colder then your area, and we size for the cooling load/heat gain, not heat loss.

    Did they complain it didn't heat or cool right since its been in?
    I'm in the pacific northwest near the coast so we don't get warm summers here. I have always sized for loss here, am I doing things incorrectly? The customer has never really used the air conditioning feature. He said maybe two or three times so its hard to get a good idea of how it works in cooling. What kind of bearing does the duct have on the output in this case?
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  7. #7
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,245
    Quote Originally Posted by BaldLoonie View Post
    Suction tap is on the suction line inside the right panel. Right below where you removed and replaced the built in drier. Or removed and installed biflow on the liquid line . Need to know suction, might have a TXV issue.

    Sounds like a pinch undersized. Is the HO complaining about being warm in the summer?
    Geez... So am I supposed to take the damn fan off to hook up to the port? Another genius design by Trane... I suppose the TXV could be an issue. The indoor TXV is more than likely the stock TXV and its a 4 ton air handler, but that wont matter in heating I suppose. I'm at a loss, what do you guys suggest as a next step?
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  8. #8
    Join Date
    Jun 2011
    Location
    Seattle WA
    Posts
    1,245
    Quote Originally Posted by 54regcab View Post
    With only a 10 degree split between ODT and IDT you should have deltaT over 15 degrees. Are you sure the A-coil isn't clogged or you aren't pulling return air from unconditioned space?
    A coil looked fairly clean at a glance but I admit I didn't look at it while thinking about it being clogged, stupid thing not to check. The duct system is actually pretty impressive. Its all rigid duct, fully insulated, and tastefully done. So no unconditioned return air. The customer did say that it never really worked right from the get go and that he called the installing contractor over and he "fixed" it and got it to start blowing warm air. When I came out I saw that the "fix" was to wire AUX to come on in a call for G! That will make it blow warm. So whatever the issue is, the installing contractor knew about it, and Jerry-Rigged it to get out of there.
    America; first we fight for our freedom,
    then we make laws to take it away.

    -Alfred E Newman

  9. #9
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
    Posts
    2,893
    Do you have any subcooling? 118 discharge is low! Maybe your flooded! Most of the tranes that i work on the suction tap is right below the RV. I wouldn't think A/S is any different!

  10. #10
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,370
    I think you are sized OK, it's the improper installation that's the issue. Ductwork is probably fine. Installer didn't know the fix either so thats why he jerryriged the aux heat to come on with G call. Got to get the pressures on both sides for an accurate assesment of what is going on.

  11. #11
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,299
    Right side panel comes off with a couple of screws. Hopefully you changed the drier while you changed the comp so you would have had the right side panel off anyway. With a heating performance issue, would be the outdoor TXV.

  12. #12
    Join Date
    Dec 2011
    Location
    missouri
    Posts
    179
    Won't the jumper from aux to G bring the heat on with a cooling call also??

  13. #13
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,370
    Quote Originally Posted by lynden View Post
    Won't the jumper from aux to G bring the heat on with a cooling call also??
    Probably would, but the customer may not notice if they didn't run the AC much.

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