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  1. #1

    Heat Pump - to lockout or not to lockout

    Been lurking here for over a decade, fascinating board.

    So for my first question here:

    Live it Montreal, winters go down to -25F for a few days. I have an 11 year old contractor grade 3.5T Ruud 11 SEER heat pump (performed flawlessly all these years except for leaking reset valve that was fixed this year) with resistance heat backup, and a Honeywell Prestige touch-color thermostat with outdoor stat (love that thing!). 3000SFT house.

    I have set the stat aux lockout to 24F outdoor, and heat-pump heats house fine enough with no expensive resistance AUX down to that.

    However the heat-pump lockout on the thermostat can only be set to 4F outdoor at the lowest, or never lockout beyond that. At 4F my heat pump can still produce a delta T of 12F. Wish Honeywell allowed a lower setting!!!

    Have read conflicting info:
    1) Dont bother running heat pump below freezing (I think this mainly pertains to fuel backup, not for expensive resistance backup).
    2) Dont bother running heat pump below 0F, as it will only produce negligible heat and cold drafts.
    3) Never turn off heat-pump, since COP is always greater than 1 (then there are theories of defrost cycle killing efficiency, and beating your heat pump to death running it indefinitely)

    Original installer just said to switch it to emergency heat on the coldest days, if I want to do the equipment a favour.

    What do you all say? Set it to lockout at 4F, or let her run forever?
    (I dont mind "cold blow" too much, want to save electricity if I can, and don't want to have to get a new compressor any time soon!)

  2. #2
    Join Date
    May 2008
    Location
    Missouri
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    3,504
    I'd set lock out at 4 degrees as the COP will be close to 1 to 1 at that temperature. It's probably be close to 1.5 to 1.7 at 17 degrees so once you hit zero it'll not produce enough heat to justify leaving on. Now if the mid-day temps rise enought to justify, it'll come back on.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    34,086
    One thing would be nice to know is if that beast has demand defrost or a timer. With demand, at 4 when there is little moisture in the air, the thing probably won't defrost more than once or twice a day. But a timer will go in to cool mode for 5 to 10 minutes an hour or 90 minutes, whatever the timer is set to. That usually more than wastes any savings from keeping the pump on. My house, it goes off around 10 or so.

  4. #4
    Thanks for the responses so far, looks like it is leaning toward lockout at 4.

    I was under the impression it was a timer defrost since it is over 10yrs old builder grade.

    But checking the specs online for my RUUD UPKA-043JAZ, I found:
    COP= 3 at 47F DB / 43F WB DOE High Temp
    COP= 2.2 at 17F DB / 15F WB DOE Low Temp

    SEER=10, HSPF Region IV= 7.35, HSPF Region V= 6.65
    "Demand Defrost Controls (featured on odd numbered models.)"

    So I guess I have demand defrost after all! (I do hear the reverse swooshing a few times a day)

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,913
    Lock out at -10 would be good. but if 4 is the lowest, set it for that.
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  6. #6
    Join Date
    Dec 2012
    Location
    Fairborn, OH 45324
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    2
    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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    Last edited by jpsmith1cm; 01-11-2013 at 05:32 AM. Reason: non AOP member

  7. #7
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    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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  8. #8
    Join Date
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    AND here I thought < 20'F was a fairly aggressive lockout plan.
    . ______ .
    I guess it all depends on amount of moisture in the locale (i.e. close proximity to lake that hasn't frozen over early in season)
    However, at the same time, NOT Much moisture at those temps.
    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

  9. #9
    Join Date
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    Quote Originally Posted by dan sw fl View Post
    AND here I thought < 20'F was a fairly aggressive lockout plan.
    . ______ .
    I guess it all depends on amount of moisture in the locale (i.e. close proximity to lake that hasn't frozen over early in season)
    However, at the same time, NOT Much moisture at those temps.
    It's called C-O-L-D. Often associated with more than 2 or 3 seasons. I know it's a foreign concept down there. No need to explain hot and humid, we get plenty of that too.


    Do you heat pumps even need a defrost mode or do you just do that manually once or twice a year like a deep freeze?

  10. #10
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    Quote Originally Posted by motoguy128 View Post
    It's called C-O-L-D. Often associated with more than 2 or 3 seasons. I know it's a foreign concept down there. No need to explain hot and humid, we get plenty of that too.


    Do you heat pumps even need a defrost mode or do you just do that manually once or twice a year like a deep freeze?
    ROFL.
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  11. #11
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by motoguy128 View Post
    It's called C-O-L-D. Often associated with more than 2 or 3 seasons. I know it's a foreign concept down there. No need to explain hot and humid, we get plenty of that too.


    Do you heat pumps even need a defrost mode or do you just do that manually once or twice a year like a deep freeze?
    d'frost is what happens to one's breathe
    I know cold = lack of Heat ... Billings MT 10'F

    Billings Heating and Cooling
    ________ ___ ___ ___ Jan _Feb _Mar _Apr _ May _ Jun Jul Aug _Sep _Oct _Nov Dec Annual
    Heating Degree Days 1308 1008 915 582 _316 _119 _12.0 42.0 242 498 897 1225 7164
    Cooling Degree Days 0.0 __0.0 __0.0 __0.0 _6.0 113 244 219 65.0 _5.0 _0.0 _0.0 652
    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

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by motoguy128 View Post
    It's called C-O-L-D. Often associated with more than 2 or 3 seasons. I know it's a foreign concept down there. No need to explain hot and humid, we get plenty of that too.


    Do you heat pumps even need a defrost mode or do you just do that manually once or twice a year like a deep freeze?
    When I'm in FL, I Don't Use Heat except a few times a decade. Need A/C now.
    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

  13. #13
    Join Date
    Dec 2012
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    62
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    Last edited by beenthere; 01-11-2013 at 04:51 PM. Reason: Non Pro * Member

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