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  1. #1

    Heat of Rejection Calculation

    I am looking for a formula to calculate heat of rejection of a refrigerator. Is it as simple as the inverse of the the amount of work done in Btu/Hr?

  2. #2
    Join Date
    Nov 2008
    Posts
    1,673

    Does this work?

    total heat of rejection for a system with
    the following performance characteristics would be
    calculated like this:

    Compressor Performance

    110F condensing temperature
    10F evaporating temperature
    75F incoming water temperature
    Refrigerant R–22
    Evaporating Watts = 6500
    Evaporating Load:
    40,200 Btu
    watts x 3.4 = Heat of Compression
    Heat of Compression + Evaporating Load =
    Total Heat of Rejection
    6500 watts x 3.4 = 22,100 Btu
    Heat of Compression = 22,100 Btu
    Evaporating Load = 40,200Btu
    Total Heat of Rejection = 62,300 Btu

    Total Heat of Rejection (THR) is the heat absorbed
    at the evaporator plus the heat picked up in the
    suction line plus the heat added to the refrigerant in
    the compressor.

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,436
    A good calc for a suction cooled compressor. An heat from the compressor radiated to the air should be subtracted. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #4
    Join Date
    Jun 2005
    Location
    Las Vegas NV
    Posts
    1,152
    crane,

    THR = compressor capacity @ a given SST X the HOR factor.

    Open this attachment and scroll down to page two for more information.
    Attached Images Attached Images

  5. #5
    Join Date
    Feb 2009
    Posts
    11
    I agreee with the above if the refrigeration system operated 24 hours a day. Since a properly designed system operates 16 hours a day or less the operation factor needs to be considered.

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,364
    Quote Originally Posted by HeatMover View Post
    I agreee with the above if the refrigeration system operated 24 hours a day. Since a properly designed system operates 16 hours a day or less the operation factor needs to be considered.
    I think you may be confusing "selecting a condensing unit" and "selecting a condenser".

    While it's true box loads are based upon a Btu/24 hour load calculation where the system's daily operating times are then factored in to arrive at the Btu/hr requirement, the Btu/hr requirement for the condenser is only related to the heat rejected by the system at design conditions.

    So...at design...the total heat of rejection (THR) is the sum of the compressor capacity plus the motor power input expressed in Btu/hr.

    The energy in equals the energy out.

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