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  1. #1

    How long is to long for heat pump temp recovery?

    Hello Folks,

    I've been lurking for a while trying to answer a few questions after purchasing my new heat pump, but I just haven't seen answers to my specific questions. I'll spare you the personal story and get right to the questions.

    Basically i'm trying to determine how low I can setback my thermostat without making my heat pump run FOREVER in recovery mode. I know outdoor temp, home construction etc. determines this but I am assuming that if it takes my heat pump 5 hrs to reach the recovery temp I probably should reconsider my setback temps.

    My variables
    - heat pump with Auxiliary heat
    - programmable T-stat with adaptive intelligence
    - recovery does not utilize auxiliary power (just heat pump compressor)
    - night time temps in 20's and 30's
    - night time set back temp is 65 and wake up temp is 70
    -T-stat is rth7400D (heat pump enabled programmable unit)

    1. At what recovery duration would you say

    A) I am causing unnecessary wear and tear to the heat pump (i.e. give that thing a breather!)
    B) the money saved by setting back the t-stat at night is negated due to a long recovery cycle? (remember just the heat pump, no auxiliary heat)


    2. Is it fair to assme that as long as the setback recovery does not utilize the auxiliary heat that I will save money? (given that the heat pump is able to recover in a reasonable amount of time ....hmmm, what is reasonable by the way?)


    and finally

    3. My T stat reaches recovery temp about 30 - 40 minutes ahead of schedule. Can I get this to be more precise or is this common among programable T-stats?


    Thanks for any responses folks!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,081
    Quote Originally Posted by marcus82 View Post
    Hello Folks,


    1. At what recovery duration would you say

    A) I am causing unnecessary wear and tear to the heat pump (i.e. give that thing a breather!)

    Continuous running doesn't hurt them.

    B) the money saved by setting back the t-stat at night is negated due to a long recovery cycle? (remember just the heat pump, no auxiliary heat)

    As long as strip heaters aren't being used, your saving money.



    2. Is it fair to assme that as long as the setback recovery does not utilize the auxiliary heat that I will save money? (given that the heat pump is able to recover in a reasonable amount of time ....hmmm, what is reasonable by the way?)

    As long as strip heaters aren't being used, your saving money.

    Reasonable time changes by both the outdoor temp and the amount of set back.



    and finally

    3. My T stat reaches recovery temp about 30 - 40 minutes ahead of schedule. Can I get this to be more precise or is this common among programable T-stats?


    Thanks for any responses folks!
    Probably because the heat pump is going into defrost. And the strip heaters are coming on during defrost and raising the temp faster then just the heat pump. And the thermostat can't determine when when the heat pump will defrost. It can only base its start time on previous run cycles during the night/set back period.
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  3. #3
    Join Date
    Aug 2009
    Location
    East TN
    Posts
    129
    We installed a Honeywell programmable T'stat with adaptive recovery when we bought our current home a few years back. Despite giving the stat two weeks to "learn" the house, it never did. The heat would always come on in the wee hours, and we would end up roasting in bed.

    We finally gave up and turned the adaptive feature off. We slept much better after that.

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287

    Hmm Set-back vs savings vs reasonable

    Quote Originally Posted by marcus82 View Post
    I'll spare you the personal story and get right to the questions.

    Basically i'm trying to determine how low I can setback my thermostat without making my heat pump run FOREVER in recovery mode.

    .. it takes my heat pump 5 hrs to reach the recovery temp
    I probably should reconsider my setback temps.

    recovery does not utilize auxiliary power (just heat pump compressor)
    night time temps in 20's and 30's

    (given that the heat pump is able to recover in a reasonable amount of time ....hmmm, what is reasonable by the way?)

    Thanks for any responses folks!
    Reasonable RECOVERY:
    > 35'F one degree recovery per hour
    > 25'F one degree recovery in ~ 2 hours
    < 24'F infinite (spring time: which ever occurs first).

    In other words, do not use set-back below 36'F.
    Or live with the set-back temperature until mid-afternoon.


    5'F Set-back might save ~ 8%.
    What is that - maybe ~ $100 per year?

    You can define REASONABLE.

    Savings > 20%: Set t-stat to 58'F without set back.
    Designer Dan
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  5. #5
    Quote Originally Posted by dan sw fl View Post
    Reasonable RECOVERY:
    > 35'F one degree recovery per hour
    > 25'F one degree recovery in ~ 2 hours
    < 24'F infinite (spring time: which ever occurs first).

    In other words, do not use set-back below 36'F.
    Or live with the set-back temperature until mid-afternoon.


    5'F Set-back might save ~ 8%.
    What is that - maybe ~ $100 per year?

    You can define REASONABLE.

    Savings > 20%: Set t-stat to 58'F without set back.

    thanks for the responses dan and "beenthere". 95% of the answers I have found on the issue of setback and savings have been unquantifiable, but your answers helped a lot. My system is currently outperforming your reasonable times so I think I'm in good shape.

    the information that is available on heat pumps is very vague and its hard for the uneducated consumer to know if and when there is a reason for concern.

  6. #6
    A 2 stage thermostat will have the ability to get your system to temp quicker using supplemental heat. When the thermostat reaches the time it is supposed to bring the house up to temp it will sense the 5 or so degree difference in the room temp and the desired temp and should start your supplemental heat for a short time bringing the temp up quicker until the second stage heat anticipator shuts it off. At which point the heat pump will continue as normal. Its basically making the thermostat think the system has reached its balance point and starting the electric resistance heat or fossil fuel furnace that you have as a supplement to the heat pump.

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