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  1. #1
    Join Date
    Jun 2006
    Posts
    40

    variable speed heat pump, variable speed air handler, or both

    Hi all. I just received an estimate that included a 13-Seer Lennox, 2-ton heat pump with a 13-Seer Lennox, 2-ton variable speed air handler (plus a 2.5 ton of each for a total 2,600 sq. ft. house in Connecticut; I already have a boiler with radiant heat). My 1st question is: doesn't the heat pump need to be variable speed too (and not just the air handler)?

    My next questions regard where the estimate includes "two new 2 stage heat/1 stage cool thermostats (non-programmable)". Why is cooling only 1-stage? I like what I've heard about the variable cooling for comfort and dehumidication (more importantly) purposes and will a 1 stage cooling thermostat do this?

    Finally, to pull off the duel fuel in an automated fashion, over the phone the contractor had said it would be easy to have 1 thermostat (or in this case 2 with the two zones) manage both the heat pumps(s) and the boiler for heating purposes, but this brief written description of the thermotsat seems suspect to me....any advice on this one so I don;t have to constantly watch when the 2 systems are turning on and when based on one being set 3 degrees or so higher than the other?

    Thanks!

  2. #2
    Join Date
    Mar 2007
    Location
    Phoenix, AZ
    Posts
    574
    I don't know the answer to your questions, but I do know that what you're trying to refer to is a two-stage heat pump, as opposed to a variable speed heat pump. A two stage heat pump should be paired with a variable speed air handler.

  3. #3
    Join Date
    Apr 2007
    Location
    Tulsa OK
    Posts
    12
    Unless I am missing something, your contractor is telling you the truth. There is such a thing as 2 stage cooling (2 compressors). Ask your contractor to explain the difference between variable speed blower, and multi-stage heat/cool. Units can be 'twinned' to cycle on and off at the same time determined by the thermostat.

  4. #4
    Join Date
    Mar 2007
    Location
    Phoenix, AZ
    Posts
    574
    Quote Originally Posted by Rick Robins View Post
    There is such a thing as 2 stage cooling (2 compressors).
    2 reciprocating compressors, or one unloading scroll compressor can provide 2-stage cooling.

    As an aside...
    There *IS* such a thing as truly variable compressors, but this is newly emerging technology - VERY expensive, very cool, and extremely efficient. It inverts the power to DC and drives a rotary compressor at continuously variable speeds, depending on the heat load. There have been mini-split systems around for several years with this technology ("DC inversion" it's called), but standard residential split systems are just now coming on the market. Click here for an example...

  5. #5
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by Rick Robins View Post
    Unless I am missing something, your contractor is telling you the truth. There is such a thing as 2 stage cooling (2 compressors). Ask your contractor to explain the difference between variable speed blower, and multi-stage heat/cool. Units can be 'twinned' to cycle on and off at the same time determined by the thermostat.
    you dont twin the airhandlers when they are controlling seperate zones!



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