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  1. #1
    Join Date
    Mar 2006
    Posts
    115
    I just ordered 2 x Honeywell C7089U1006 outdoor temp sensors for my trane 803 (visionpro 8321). I always know what the outdoor temperature is as I have plenty of outdoor sensors (in the attic and around the outside of the house). What got me going about these was the ability to lock out the heat strips above a given outdoor temp - arkansas winters being usually mild - (albeit the given cold day). I saw this as a potential energy saver as I could prevent the heat strips from kicking on unless really necessary. How low can I expect the heat pumps (XR13's) to function properly without hurting anything? what setpoints would you recommend for this?

  2. #2
    Probably an absolute limit is about 35F, but as outside temperature drops efficiency goes down. Whether or not the system has a compressor heater will prevent damage at low ambients. Compressor heaters can be retrofit options. I'm speaking in general terms, not specific for your HP. Where you measure temperature is also important, so you don't want to be close to the limit if your sensor in no way represents the temperature around the condenser.
    e.g. don't put the sensor under a rock or in the front yard in the sun when your heat pump is in tha back yard and in the shade.

  3. #3
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    6,356
    What youre looking for is the Balance Point . This temperature is unique to your particular area and equipment selection. It should only be determined by the installing contractor.

    You should not use the same t-stat wiring harness used for the equipment with the sensor. They should be run with a separate cable.

  4. #4
    Balance point - The temperature in which the HP can keep up with the losses in the house.

  5. #5
    Join Date
    Mar 2006
    Posts
    115

    Hmm

    pecmsg: why do i need to use another cable if I have an extra pair in the one already connected? I do have an extra cable pulled but I also think I have 18/8 thermostat cable with 2 spares...I cannot think of a reason...

    I'll make the balance point 38F then. for mild arkansas weather should work nicely.

    whats the deal with the compressor heater???? dont know if I have one, but the compressor does have a thick sound insulation blanket around it. When it is that cold wont the heatpump run constantly thus keeping the compressor warm?

  6. #6
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    6,356
    Most sensors need a separate cable due to E M F produced by low voltage & high voltage wiring.

  7. #7
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,909
    Experiment a little bit to see what the balance/lockout point should be.

    Start at 38F and reduce the limit until the system can no longer keep up. You want to run the heat strips at little as possible; they cost a hell of a lot to operate.

    [Edited by amd on 08-24-2006 at 07:28 PM]

  8. #8
    Join Date
    Mar 2006
    Posts
    115
    makes sense AMD - i will start from 38F for balance point. What about compressor lockout point? - 25F????

    pecmsg - the temperature sensor measures the temperature outside by changing the resistance (ohms) in the sensor wires - i dont think EMF can really be of any consequence here with the ohms can it?. Also there is no high voltage nearby anyway is there?? How much EMF does a 24V line really produce??? I could be wrong of course...

  9. #9
    Join Date
    Mar 2003
    Location
    cincinnati, ohio
    Posts
    36
    I agree with tundra, it does say to run a separate cable for the sensor in the manual for the stat, and for the sensor. But I have installed it several times with extra wires over 3 years and I am yet to have a problem.

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