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  1. #1
    Join Date
    Mar 2010
    Posts
    10

    Trane defrost on demand

    I recently had a new Trane XL15i heat pump (4TWX5036) with variable speed air handler installed replacing an older Bryant system. The system seems to be a big improvement over what I had … at least when the temperature is above 40 deg outside. My question is about how the defrost on demand should work … and how best to verify it is working. The overnight setting is 60 deg and the daytime setting is 68 deg. I usually adjust the set point around 5 am … and when the outside air temp is below 40 deg … the unit frosts up quickly … and the heat output goes way down … taking an hour to raise the inside temp 1 deg. Heavy frost is a solid blanket of frost/ice on the coil fins from top to bottom of the inlet vents. It is clear that very little airflow is reaching the coils at this level of frost. After an hour or more … I usually lower the set point … and wait for the outside air temp to increase when the sun comes up … which is obviously not a solution. The installation contractor has come out and tested the defrost board and the coil temperature sensor … and both checked out and they feel everything is ok. I want to be able to provide better input for the contractor … so they can correct this problem. It is difficult for them to be here at 5 am … to witness the level of frost. If I could monitor the actual coil outlet temp … and outside ambient temp … and if I knew the logic used to activate the defrost … then I could provide the contractor with the information they would need to troubleshoot the issue.

  2. #2
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
    Posts
    6,957
    Be careful, setting back that far on a closely sized heat pump and you may not be able to recover without Aux. Ht.
    If they can't catch it frosted maybe you can shoot a digital or two to show them.

  3. #3
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,138
    jfinet

    I totally agree with Stamas. That setback is too extreme-I recommend no more than three degrees if you are determined to use a setback. Try that and see if your icing issues go away.

    As you know, the main purpose of "electronic demand defrost" is to eliminate unnecessary and nuisance defrost calls from timed based defrost systems.

    what is your location? I would note the time,outside temperature, humidity conditions when you see icing conditions. take some pictures.

    I have an XLi heat pump setup in a duel fuel system-changeover from HP to gas furnace is 30 degrees. I have never seen ice/frost buildup on my condenser and when system had PM last fall, I purposely had defrost function dblchecked.

    If this condition continues, then I would get dealer back out and check defrost cycle from top to bottom. You might get disagreement from others but I would say what you describe is not normal for an XL15i heat pump.

    IMO
    Good Luck!

  4. #4
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,360
    Quote Originally Posted by jfinet View Post
    if I knew the logic used to activate the defrost …
    The Trane Demand Defrost Controls operate in an adaptive process to optimize the heat pump performance.

    The Demand Defrost Controls will adapt to the heat pump it is installed on and learn it’s optimum defrost conditions and store them in memory.

    The Demand Defrost Control will adjust the time between defrost cycles to match the weather conditions.

    The initiate value is not a constant, but instead, a value that the defrost control has learned and will provide a fast thorough defrost at a given out door temperature.

    The control is continuously varying the initiate value slightly to learn the best value.
    Instead of learning the tricks of the trade, learn the trade.

  5. #5
    Join Date
    Mar 2010
    Posts
    10
    I am in Southern Oregon ... I have collected temp data for the installer ... such as the following:
    6:20 am 28 deg outside 61 inside change setpoint to 68 deg
    6:40 am 28 outside 61 inside heavy frost on coils ... no aux heat ... foggy with lots of moisture in the air
    6:50 am 28 outside 61 inside heavy frost ... no aux heat ... tubing to inside air handler warm to touch ... frosted top to bottom
    7 am 28 outside 61 inside very little heat coming through inside ducts
    7:15 same
    7:25 28 outside 62 inside ... no defrost cycle ... no aux heat ... sun coming up
    7:28 shut down HP manually and wait for outside temp to warm up

    I like the idea of taking digital pictures ... and I will start doing that ... I have never seen this system go into defrost mode ... and one more detail ... the installation contractor has locked out the aux heat at 30 deg ... to optimize the energy savings in this area ... I have not seen the aux heat ever come on either

  6. #6
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,138
    jfinet

    foggy conditions at the right outside temp are notorious for causing frosting/icing issues. you need to add humidity to your list of documentation. if you are seeing frost buildup at the condenser without a defrost call/cycle, then something is not correct.

    IMO

  7. #7
    Join Date
    Mar 2010
    Posts
    10
    Ok ... this information is helpful ... my unit has obviously not been educated yet ... slow learning curve ... anyway ... if for some reason ... the primary inputs for this learning curve ... ambient temp and coil temp ... are for some reason not providing the right information ... then the system will never learn to kick on the defrost ... so this is what I am trying to understand ... maybe the coil sensor is not in the right location ... or not in contact with the coil surface (the installer said it was reading ok) ... or maybe the unit has to run for two hours with fully frosted coils to get that first learning point ... I would love to be able to read both of these temperatures from the control console ... and record them during my data collection exercises

  8. #8
    Join Date
    Mar 2010
    Posts
    10
    On all the days I have collected data ... the Honeywell aux outside air temp reading includes humidity ... and it has always been 80% +-4 deg ... so moisture in the air for sure ... I am not sure how accurate this humidity reading is though

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,699
    Leave it run. instead of turning it off and waiting ofr it to warm up outside. It will go into defrost.

    Your aux heat may be locked out at too low of a temp for it to recover weather it is frosted up or not.

    Having your indoor temp so low can cause it to frost up quicker, and heavier.

    As a test. Leave your stat set to 68 over night. And see if it maintains 68 when its 28 or 30° outside.
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  10. #10
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
    Posts
    6,957
    And don't do what 1 of my customers did Sunday morning the his XLi-tried to defrost it with a hammer and a screwdriver. 1.5 years into the 10year extended warranty.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,699
    Quote Originally Posted by Stamas View Post
    And don't do what 1 of my customers did Sunday morning the his XLi-tried to defrost it with a hammer and a screwdriver. 1.5 years into the 10year extended warranty.
    LOL... hammer and screw driver damage isn't covered by extended warranty.
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  12. #12
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by jfinet View Post
    The overnight setting is 60 deg and the daytime setting is 68 deg
    seems as if you may be wasting gobbs of energy trying to recover all that heat at one time

    try using 62 degrees as a setback temp, then set a program for 4:00am for a 3 degree rise which will bring it to 65

    then set a program for 5:00 am for another 3 degree rise which will bring you to 68 degrees with much less energy sucking auxillary heat

    you can add another recovery period as well and/or modify my suggestion of multiple recovery sessions



    .

  13. #13
    Join Date
    Feb 2010
    Location
    Front Royal Va
    Posts
    82
    try setting your aux heat lock out higher set the stat at one temp and leave it (set it and foget it ) for winter use your set backs for cooling , I have found it much more comfortable and economical to use that method .

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