Method for evaluating refrigeration cycle performance

Abstract

The present invention discloses a method for field testing refrigeration cycle equipment to evaluate condenser and evaporator performance.

1 . A method of testing a refrigeration system comprising:
 operate all compressors under full load in cooling mode for the refrigeration circuit to be tested;   allow all compressors to reach at least a quasi-steady operating condition;   measure the refrigeration cycle parameters;   where the refrigeration cycle parameters include at least the condenser entering air dry-bulb temperature and the return air wet-bulb temperature are measured;   where at least one of the liquid line pressure or the suction line pressure is measured;   use one refrigeration cycle parameter to determine a temperature parameter;   calculate at least one performance parameter;   determine at least one target parameter and range;   compare at least one performance parameter to the corresponding target parameter and range;   determine whether the performance parameter falls outside the target parameter and range; and   where if comparison fails then the system is eligible for correction.   
   
   
       2 . The method of  claim 1  where the condenser saturation temperature is determined from the liquid line pressure;
 where the performance parameter is condensing temperature over ambient;   where condensing temperature over ambient is calculated from the condenser saturation temperature and the condenser entering air dry-bulb temperature; and   where the condensing temperature over ambient is compared to a corresponding target parameter.   
   
   
       3 . The method of  claim 2  where
 the target parameter is determined from at least one of a performance model, manufacturer's data or a default value of 25° F.; and   where if the condensing temperature over ambient is over about 12° F. from the target parameter, then the refrigeration circuit is eligible for correction.   
   
   
       4 . The method of  claim 3  where the condenser performance is being evaluated. 
   
   
       5 . The method of  claim 1  further comprising
 measuring suction line refrigerant temperature; and   where the evaporator saturation temperature is determined from suction line pressure.   
   
   
       6 . The method of  claim 5  further comprising
 calculating an actual superheat from the suction line refrigerant temperature and the evaporator saturation temperature;   determining a target evaporator saturation temperature; and   calculating a difference of evaporator saturation temperature (Dtevap) from evaporator saturation temperature and a target evaporator saturation temperature.   
   
   
       7 . The method of  claim 6  further comprising;
 determining a target superheat; and   calculating a difference of superheat (DTsh) from the actual superheat and the target superheat.   
   
   
       8 . The method of  claim 7  where the evaporator system is being evaluated. 
   
   
       9 . The method of  claim 8  further comprising determining whether a TxV metering device or a non-TxV metering device is being tested. 
   
   
       10 . The method of  claim 9  where if the system has a TxV metering device, and the difference of evaporator saturation temperature (DTevap) is less than a predetermined value, such as −8 degrees F., and the difference of superheat (DTsh) is less than a predetermined value, such as 5 degrees F., then the system is eligible for correction. 
   
   
       11 . The method of  claim 9  where an evaporator performance parameter (Epp) is calculated as a function of the parameters DTevap (difference of evaporator saturation temperature) and Dttsh (difference of superheat). 
   
   
       12 . The method of  claim 11  where if the system has a non-TxV metering device, and the evaporator performance parameter (Epp) is less than a predetermined value, such as minus seven degrees Farenheit, then the system is eligible for correction. 
   
   
       13 . A method of evaluating the performance of a condenser in a refrigeration cycle machine, the method comprising the steps of:
 a) operate all compressors under full load in cooling mode for the refrigeration circuit to be tested;   b) allow all compressors to reach at least a quasi-steady operating condition;   c) measure condenser entering air dry-bulb temperature (Toutdoor, db);   d) measure return air wet-bulb temperature (Treturn, wb);   e) measure liquid line refrigerant pressure (Pcondenser) at the condenser outlet (preferred) or discharge line refrigerant pressure (Pdischarge) at the compressor outlet;   f) if measuring the discharge pressure, calculate Pcondenser as Pdischarge minus 15 psi (or OEM specification for condenser pressure drop if available);   g) using the liquid line pressure (Pcondenser), determine the condenser saturation temperature (Tcondenser) from the standard refrigerant saturated pressure/temperature chart;   h) calculate condensing temperature over ambient (Tcoa) as the condenser saturation temperature minus the condenser entering air temperature (Tcoa=Tcondenser−Toutdoor); and   i) determine target value for condensing temperature over ambient (Tcoa) from performance model, manufacturer's data or use a default value of 25° F. If Tcoa is more than a predetermined tolerance greater than the target value, such as 12 degrees F. greater, for any circuit, then the unit is eligible for a condenser correction.   
   
   
       14 . The method of  claim 13  where the performance is further evaluated to include the impact of servicing, further comprising the following steps:
 j) save the Pre Test data for each circuit prior to performing condenser correction or performing any other unit service; and   k) after completing condenser correction and any other unit servicing, save Post Test data for each circuit;   l) determine the improvement in Tcoa as the Pre Test Tcoa minus the Post Test Tcoa for each circuit; and   m) determining the capacity weighted average improvement in Tcoa for the unit as follows;
 i) for each circuit calculate the product of the individual circuit Tcoa improvement multiplied by the circuit nominal cooling capacity; 
 ii) sum the circuit values; and 
 iii) divide the sum by the total unit nominal cooling capacity. 
   q) if the capacity weighted average improvement in Tcoa for the unit is greater than or equal to 12° F. then all circuits qualify for the condenser correction incentive. If the capacity weighted average improvement in Tcoa for the unit is less than 12° F., but one or more individual circuits have an improvement in Tcoa greater than or equal to 12° F., the individual circuits qualify for the condenser correction incentive.   
   
   
       15 . A method of evaluating the efficiency of an evaporator in a refrigeration cycle machine, the method comprising the steps of:
 a) operate all compressors under full load in cooling mode for the refrigeration circuit to be tested;   b) allow all compressors to reach at least a quasi-steady operating condition;   c) measure condenser entering air dry-bulb temperature (Toutdoor, db);   d) measure return air wet-bulb temperature (Treturn, wb);   e) measure suction line refrigerant temperature (Tsuction) at compressor suction;   f) measure suction line refrigerant pressure (Pevaporator) at compressor suction;   g) using the suction line pressure (Pevaporator), determine the evaporating (saturation) temperature (Tevaporator) from the standard refrigerant saturated pressure/temperature chart;   h) calculate Actual Superheat as the suction line temperature minus the evaporator saturation temperature. Actual Superheat=Tsuction−Tevaporator;   j) for a Non-TxV metering device, determine the Target Superheat using Table RD-2 of Attachment 1 (SCE program) or Table 1 of HVAC Program Technical Specifications (SDG&E program) or equivalent using the return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db). If the test conditions are outside the range of the table, then the test cannot be used under these conditions;   h) for a TxV metering device, the Target Superheat is 20° F. or the manufacturer's recommended value;   i) using the return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db), determine the target evaporating temperature using (a)  FIG. 3A , Table RD-4a, (b)  FIG. 3B , Table RD-4b, (c) OEM provided equivalent for unit being tested, or (d) alternate method appropriate for unit being tested that considers variation with return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db). If the test conditions are outside the range of  FIG. 3A  (Table RD-4a) and  FIG. 3B  (Table RD-4b), then the test cannot be used under these conditions;   j) calculate the difference (DTevap) between actual evaporating temperature and target evaporating temperature (DTevap=Actual Evaporating Temperature−Target Evaporating Temperature); and   k) calculate the difference (DTsh) between actual superheat and target superheat (DTsh=Actual Superheat−Target Superheat);   l) calculate an evaporator performance parameter (Epp) as a function of the parameters DTevap (difference of evaporator saturation temperature) and DTsh (difference of superheat); and   m) if the system has a TxV metering device, and the difference of evaporator saturation temperature (DTevap) is less than a predetermined value, such as −8 degrees F., and the difference of superheat (DTsh) is less than a predetermined value, such as 5 degrees F., then the system is eligible for correction; or if the system has a non-TxV metering device, and the evaporator performance parameter is less than a predetermined value, such as −7 degrees F., then the system is eligible for correction.   
   
   
       16 . The method of  claim 15  where the performance is further evaluated to include the impact of servicing, the method further comprising the steps:
 n) save Pre test data for each circuit prior to performing evaporator correction or performing any other service on the unit,   o) after completing any unit servicing, save Post test data for each circuit,   p) if the system has a TxV metering device, determine the improvement in evaporator performance as the increase in DTevap from the Pre to the Post test; or if the system has a non-TxV metering device, determine the improvement in evaporator performance as the increase in Epp from the Pre to the Post test;   q) determine the capacity weighted average evaporator improvement for the unit as follows,   for each circuit calculate the product of the individual circuit improvement multiplied by the circuit nominal cooling capacity,   sum the circuit values, and   divide the sum by the total unit nominal cooling capacity.   r) if the system has a TxV metering device, and the capacity weighted average improvement is greater than a predefined threshold, such as 8 degrees F., then all circuits qualify for an evaporator improvement incentive; if the capacity weighted average does not exceed the threshold, then only individual circuits with an improvement exceeding the threshold qualify for the incentive.   s) if the system has a non-TxV metering device, and the capacity weighted average improvement is greater than a predefined threshold, such as 7 degrees F., then all, circuits qualify for an evaporator improvement incentive; if the capacity weighted average does not exceed the threshold, then only individual circuits with an improvement exceeding the threshold qualify for the incentive.