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2 stage heat pump

We are installing a boiler on a new hydro air job,has a 2 stage heat pump already installed.Was going to make the boiler the second stage. Any issue with running the heat pump and boiler simultaneously?

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  • Empire_2
    Empire_2 Member Posts: 2,343
    Not at all.

    Second stage can be anything you like.  Differential will control boiler only when calling for stg. #2.  2* to 3*  Diff will work, and short cycling should not be a problem. 

    Mike T.
  • Techman
    Techman Member Posts: 2,144
    edited May 2012
    2nd stage

    Hi Robert,the H.W. coil would have to be in the supply trunk so that  the cool return air in the return trunk can enter the H.P. indoor coil (condensor coil). Some  A.C. mfrg's don't want the H.W. coil in the return trunk anyway due to over heating &  stressing the blower motor .The H.P. vs. the boiler/hot water coil Coefficientcy Of Performence (COP) should be concidered. The colder it gets the worse the H.P. COP gets.

    Mike T. all the best to you and yours!
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,280

    Thanks! HW coil is in supply. Is there a chart that shows COP vs outdoor air temp?
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  • Techman
    Techman Member Posts: 2,144
    COP Chart

    I'm not sure about a chart,as compared to doing a formula figure out thing. Energy in thing vs. BTU produced thing.Professor? A little mathmatical help here ,please!Our friend Robert needs it! I could use a little refresher also.
  • EddieG
    EddieG Member Posts: 150
    I would....

    What kind of t-stat are you using Bob? You could do it multiple ways. I wouldn't have the HWC come on with a second stage call. You don't want the HWC to come on and satisfy the call right away. You want to give the HP time to try and satisfy the call. I would set it up as a 3rd stage along with an outdoor temperature control to hold the HWC off until it gets below a certian outdoor temperature. You can call me if you want to discuss.
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