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Determining the coefficient of performance of a refrigeration system

  • US 4,768,346 A
  • Filed: 08/26/1987
  • Issued: 09/06/1988
  • Est. Priority Date: 08/26/1987
  • Status: Expired due to Term
First Claim
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1. A method for reducing the coefficient of performance to a design value from measured temperature conditions of a vapor compression type refrigeration system of the type having series arranged compressor, condenser and evaporator units and an electric motor for driving said compressor unit, said system further having a condenser water supply line and evaporator chilled water supply and return lines, said method comprising the steps of:

  • storing a value (CWF) for the chilled water flow through said condenser;

    sensing the condenser water supply temperature (Tcon),sensing the evaporator water supply and return temperatures (Tchw,in and Tchw,out),sensing the power input (φ

    ) to said motor;

    calculating the cooling load (Qc)* from the expression Qc =CWF*(Tchw,in -Tchw,out);

    storing the manufacturers'"'"' performance data for said system comprising the condenser supply water design (Tcon,D) and the evaporator return water design temperature (Tchw,D);

    storing a value (α

    temp) which is the ratio of the required change in condenser temperature to a unit change in chilled water temperature to maintain the same rated chiller capacity;

    calculating the equivalent temperature (Tr) which compensates for variation from the given design temperatures from the expression
    
    
    space="preserve" listing-type="equation">T.sub.r =(T.sub.con -T.sub.con,D)/α

    .sub.temp -(T.sub.chw -T.sub.chw,D),storing experimentally determined coefficients b1, b2, and b3 for the quadratic expression
    
    
    space="preserve" listing-type="equation">β

    cap=b.sub.1 +b.sub.2 *T.sub.r +b.sub.3 *(T.sub.r).sup.2wherein β

    cap is the ratio of the available capacity (CAP) at the actual chilled water and condenser water conditions to the design capacity (CAPD);

    calculating said β

    cap and said CAP;

    calculating the part-load ratio Γ

    load from the expression Γ

    load =Qc /CAP, storing experimentally determined coefficients a1, a2 and a3 for the quadratic expression
    
    
    space="preserve" listing-type="equation">δ

    .sub.pow =a.sub.1 +a.sub.2 *Γ

    .sub.load +a.sub.3 *(Γ

    .sub.load).sup.2wherein δ

    pow is a fraction of full-load power, calculating the full-load power (PFL) from the expression PFL=φ



    pow ; and

    calculating said COPA from the expression COPA=CAP/PFL.

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