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two 2.5 ton heat pumps for one 5 ton heat pump

Has any one used two separate heat pumps in place of one large heat pump. A contractor suggested i use two 2.5 tons in place of 5 ton. The 2.5 ton will come on for a little heat or ac if needed and a 2nd stage thermostat will call for the second heat pump to fire if the heat or ac is not increasing fast enough. Does this save money and has anyone have experience with this? Thanks  

Comments

  • Spence
    Spence Member Posts: 316
    2 HPs

    This is a horrible idea, an application nightmare, and a frivolous waste of money and resources. Twinning normally works the other way; one OD unit on two furnaces and one large evaporator.



    We need to get your load squared away before looking at more equipment options, especially those that lead you farther and farther away from the comfort and economy for which you're looking.
  • oakland
    oakland Member Posts: 23
    3 ton compressor with a 5 ton evap coil

    What kind of conditions would we get with a 3 ton compressor attached to a 5 ton inside evap coil? Then if needed a 2 ton compressor would come on making it a 5 ton compressor with a 5 ton evap coil? Thanks
  • alotlikeearl
    alotlikeearl Member Posts: 68
    2-Stage

    Why not use a 2-stage heat pump with variable speed indoor unit?  First stage is usually 60% of capacity.  Works well depending on climate and load.

                 Jerry
  • oakland
    oakland Member Posts: 23
    Do not have a variable speed blower

    I don't have a variable speed blower and the contractor was trying to optimize the system, so the full 5 or 4 tons does not have to come on all the time.
  • John Mills_5
    John Mills_5 Member Posts: 935
    What are you replacing?

    You are replacing something  but not the blower? 
  • oakland
    oakland Member Posts: 23
    how would they be combined with non variable speed motor.

    I am replacing the 5 ton AC with a 5 ton heat pump and the contractor suggested a 3 and 2 ton or 2-2.5 tons instead of the 5 tons. He said the 3 ton would do most of the work and when needed the 2 ton back-up would come on. I don't have a variable speed blower so i don't know how this would work. Also, I don't know how the two heat pumps would be spliced together? Lastly, when the heat pump could not keep up with the heat the oil furnace would kick on. This complicated, but this contractor indicated he done But I am not so sure this before this would work.
  • Techman
    Techman Member Posts: 2,144
    BAD BAD

    Don't do it. If 1st stage HP (2.5 t) comes on , the CFM of one unit will be going into a duct sized for 5t. It CAN be done, but foolish if done. Let the GC put his name down as being the one responsible for this setup. I had a customer who insisted on having a Walk-in refrig put in on a flat ,but not level slab of concrete. He paid dearly for the repair of  HIS WANT , I got paid dearly for his want also. 1st stage HP ,2nd stage oil/gas
  • oakland
    oakland Member Posts: 23
    thanks to all for your help

    thanks
  • don_9
    don_9 Member Posts: 395
    It can be done

    You would have to use a twining kit that will bring both fans on.You will also have to live with the mix air that would be coming thru the off unit.So when only one unit is running your delta t will be lower then what it would be with both units running.

    We have done it in the pass.Got a church we twin two furnaces together and two five ton ac for two stage heat n cool operation.They are  around 14 years old now and still going strong.

    The trick here is to always maintain max cfms.The mixed air is not going to hurt in the least bit in milder weather.