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  1. #1
    Join Date
    Jun 2009
    Location
    Spicewood, Tx
    Posts
    35

    Two stage HP switching?

    What determines when a two stage heat pump switches from 1st stage to 2nd stage? Somewhere I heard that after 10 min. it will switch to 2nd stage if the system hasn't satisfied the set point, but that makes little sense if best efficiency and dehumidification requires longer run times. Does the tstat make a difference? I'm using a White Rogers 90 Series Touchscreen on my current single stage heat pump so it will support dual stage units, but the manual doesn't provide much info.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    The thermostat determines when to switch.
    Must be a multistage thermostat, if you get a 2 stage heat pump.
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  3. #3
    Join Date
    Jun 2009
    Location
    Spicewood, Tx
    Posts
    35

    More detail

    Quote Originally Posted by beenthere View Post
    The thermostat determines when to switch.
    Must be a multistage thermostat, if you get a 2 stage heat pump.
    As I indicated, my tstat is a multistage unit. But what data is used to determine the switch over? Purely run time or rate of temperature drop or something else? The tstat manual has configurations for single stage and dual stage, but that is all it says, nothing to indicate the criteria it uses for switch over.

  4. #4
    Join Date
    Dec 2007
    Location
    chicago
    Posts
    249
    I would check w/r website

  5. #5
    Join Date
    Dec 2003
    Location
    Kenilworth New Jersey
    Posts
    230
    What determines when a two stage heat pump switches from 1st stage to 2nd stage? Somewhere I heard that after 10 min. it will switch to 2nd stage if the system hasn't satisfied the set point,


    You probably read this in the heat pump manual,under: Usage with a single stage thermostat. My 2 stage furnace would control staging this way if I did not use a 2 stage stat.

  6. #6
    Join Date
    Jun 2009
    Location
    Spicewood, Tx
    Posts
    35

    No luck

    Quote Originally Posted by ccut View Post
    I would check w/r website
    Already tried that, no more info than the setup manual. It does show both fast cycle and slow cycle options, fast is 1.2 F and slow is 1.7 F. But I assume that just means how much the temp must change for the tstat to cycle the system off and/or on. But still, nothing about how it determines that 1st stage is not sufficient and that 2nd stage is needed.

    So, I figured someone here would know the answer. Anyone know how ANY tstat manages this switch over?

  7. #7
    Join Date
    Dec 2003
    Location
    Kenilworth New Jersey
    Posts
    230
    Proprietary algorithms within the stats software.

  8. #8
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,217
    You've pretty much got the idea of how it works.
    Each t-stat manufacturer has their own way of doing it & some are adjustable but basically
    they use a number above the set point & a time the set point is not reached. Some actually calculate whether or not the temp has changed enough in a certain amount of time before allowing the 2nd stage to come on. Some White Rogers have an adjustable setting in the configuration mode that will let you bypass the time limit if the set point is x amount above the actual temperature. If you look real close at the setup & configuration in your manual you might find something about 2nd stage.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    By temp drop.

    How much varies with the brand.
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  10. #10
    Join Date
    Jul 2009
    Posts
    23
    any way to tell when the 2nd stage comes on from inside the house?

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    Some thermostats will show it. Others won't.

    I think WR stats show it on the screen.
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  12. #12
    Join Date
    Jul 2009
    Posts
    23
    I have the trane version of the IAQ and it doesn't show...or should it?

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    Nope, it doesn't tell you.
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