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Piston

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Why charge wet bulb and dry bulb when system use piston metering device ? And why txv doesn’t charge by wet bulb and dry bulb ?

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  • ChrisJ
    ChrisJ Member Posts: 15,784
    edited May 2022
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    As far as I know with a fixed orifice device like a piston you charge by superheat.

    With a txv you charge by subcooling because the txv controls superheat, so you can't really charge by it.   Personally I watch superheat as well with a txv and adjust the txv if possible to get both superheat and subcooling where they need to be .

    Subcooling is really just showing you how much reserve liquid refrigerant you have backed up in the condenser.  



    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    mattmia2
  • pedmec
    pedmec Member Posts: 988
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    because with fixed metering device a greater portion of the refrigerant is used to remove the latent heat plus the sensible heat. so on a humid day your superheat will increase due to the higher latent heat load on the evaporator coil.
    with a txv it will just open up to maintain the proper superheat due to the increased load.
  • johnjohn89
    johnjohn89 Member Posts: 100
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    ChrisJ said:
    As far as I know with a fixed orifice device like a piston you charge by superheat.

    With a txv you charge by subcooling because the txv controls superheat, so you can't really charge by it.   Personally I watch superheat as well with a txv and adjust the txv if possible to get both superheat and subcooling where they need to be .

    Subcooling is really just showing you how much reserve liquid refrigerant you have backed up in the condenser.  

    Ture thanks


  • johnjohn89
    johnjohn89 Member Posts: 100
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    pedmec said:
    because with fixed metering device a greater portion of the refrigerant is used to remove the latent heat plus the sensible heat. so on a humid day your superheat will increase due to the higher latent heat load on the evaporator coil. with a txv it will just open up to maintain the proper superheat due to the increased load.
    Great answer thank u so much