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calculate cooling load from volts & amps for A/C & Refrigeration

Unless you can't read the model number, I like to use the model number to get the nominal tonnage or btu rating.

From my experiance, the rooftops have the actual btu rating incorperated into the model number. The 5 ton and under "residential" units have the tonnage incorperated into the model number. Wait!!!! I think I have that backwards!!! Anyway as with everything in life there are exceptions!

Another good way to find out the btu rating is the model number of the compressors. Also, look at the TXV, if it has one.

On the heating side, measure the orfices is about the only way I know.

Of course with electric heat, the amps and volts will work.

Don in MO


  • Jim De Tata
    Jim De Tata Member Posts: 3
    calculate cooling load from volts & amps for A/C & Refrigeration

    Is there a mathematical method of calculating cooling loads or the tonnage of roof top air conditioning units and refrigeration loads from the volts and RLA on the nameplates? If not, can I calculate the nominal tons from the lbs. of refrigerant that is listed on the nameplate? Would I need to assume some temperatures for the evaporator and the condenser?
  • don_185
    don_185 Member Posts: 312

    The reason I say no is because, with cooling its not only removing sensible heat.Its also removing latent heat.

    So that what we call total heat.A ac unit removed both.

    You would need to know cfm,drybuld temps,wetbulb and enthalpy.

    Here the formula for total heat.

    BTUH=4.5 x cfm x enthalphy difference.

    For me,with the lack of schooling coming up I find the math and psychrometric chart to be so much easier nailing down
    cacacity issue.Its also a great help when dealing with air and peoples comfort.

    Pressure enthalpy charts is another way to get where you want to go.For me,I'm still in the learning process with
    pressure enthalphy comment.
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