Abstract:
A method of determining thermal performance of a condenser and a condensing unit within a cooling system includes selecting the condenser and the condensing unit from a condensing unit database. A compressor is selected from a compressor database based on at least one of capacity, electrical characteristics and refrigerant flowing through the cooling system. Simulation points for the cooling system are determined and condensing unit characteristics and compressor characteristics are processed based on user-specified simulation points to provide thermal performance data for the condenser or condensing unit.

Description:
FIELD OF THE INVENTION 
     The present invention relates to condensers, and more particularly to simulating performance of a condensing unit of an air-conditioning or refrigeration system. 
     BACKGROUND OF THE INVENTION 
     Traditional cooling systems, such as refrigeration and air-conditioning systems, include a compressor, a condensing unit, an expansion valve and an evaporator. The compressor compresses gaseous refrigerant exiting the evaporator and discharges the high pressure refrigerant to the condensing unit. The condensing unit operates as a heat exchanger enabling heat transfer from the gaseous refrigerant to a heat sink (e.g. air or water). The refrigerant condenses within the condensing unit and a state change occurs from gas to liquid. The liquid refrigerant exits the condensing unit and flows to the evaporator through the expansion valve. The evaporator also operates as a heat exchanger enabling heat transfer from the atmosphere surrounding the evaporator to the liquid refrigerant. As the heat transfer occurs, the temperature of the refrigerant increases until a state change occurs from liquid to gas. The gas refrigerant is drawn into the suction side of the compressor and the cooling cycle continues. 
     The condensing unit can be one of an air-cooled condensing unit (ACU) or a water-cooled condensing unit (WCU). An ACU typically includes a fin-tube refrigerant-to-air heat exchanger, an air flow device such as a fan motor and fan blade and associated controls (not shown). In the case of an ACU, air provides the heat sink enabling heat transfer from the condensing unit. A WCU typically includes a refrigerant-to-water heat exchanger and associated controls (not shown). In the case of a WCU, water provides the heat sink enabling heat transfer from the condensing unit. 
     In order to competently design a new cooling system or maintain an existing cooling system, the potential performance of the individual components within the system need be estimated. Traditionally, system condensers are selected based on the refrigerant type and ratings provided by the manufacturer. However, these ratings are determined under fixed conditions and not actual system operational conditions. Therefore, although the rating of a condenser may suggest that it is proper for the particular cooling system, the actual performance of that condenser within the cooling system may be far less than optimal. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of determining thermal performance of a condensing unit within a cooling system. The method includes selecting the condensing unit from a condensing unit database and selecting a compressor from a compressor database based on a refrigerant flowing through the cooling system. Simulation points are determined and condensing unit characteristics and compressor characteristics are processed based on the simulation points to provide thermal performance data for the condensing unit. 
     In one feature, selecting the condensing unit from a condensing unit database further includes selecting a condenser, selecting a fan motor and selecting a fan blade. 
     In another feature, selecting the condensing unit is achieved by inputting part numbers of condensing unit components that are cross-referenced with the database. 
     In still another feature, determining the simulation points includes selecting an application type for an evaporator of the cooling system. The application type includes one of a low temperature range, a medium temperature range, an extended medium temperature range and a high temperature range. 
     In yet another feature, the method further includes outputting the thermal performance data in one of a graphical format, a spreadsheet format and a tabulated format. The thermal performance data includes condensing unit capacity across each of the simulation points for a given ambient temperature at which the condensing unit operates. 
     In still another feature, the method further includes scaling the thermal performance data based on compressor frequency. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a schematic illustration of a generic cooling system incorporating a condensing unit; 
     FIG. 2 is a flowchart detailing the condensing unit performance simulator according to the present invention; 
     FIG. 3 is a screen-shot illustrating software-based input of air-cooled condensing unit (ACU) information; 
     FIG. 4 is a screen-shot illustrating a compressor selection screen; 
     FIG. 5 is a screen-shot illustrating a condenser selection screen; 
     FIG. 6 is a screen-shot illustrating a condenser geometry and temperature characteristic screen; 
     FIG. 7 is a screen-shot illustrating an ACU settings screen; 
     FIG. 8 is a screen-shot illustrating a simulation point selection screen; 
     FIG. 9 is a screen-shot illustrating ACU thermal performance output in spreadsheet format; 
     FIG. 10 is a screen-shot illustrating ACU thermal performance output in graphical format; 
     FIG. 11 is a screen-shot illustrating ACU thermal performance output in tabulated format including design envelope flags; 
     FIG. 12 is a screen-shot illustrating ACU thermal performance output in tabulated format including operating envelope flags; 
     FIG. 13 is a screen-shot illustrating an input screen for water-cooled condensing unit (WCU) information; 
     FIG. 14 is a screen-shot illustrating a WCU settings screen; 
     FIG. 15 is a screen-shot illustrating a simulation point selection screen; 
     FIG. 16 is a screen-shot illustrating a WCU output summary screen; 
     FIG. 17 is a screen-shot illustrating WCU thermal performance output in tabulated format; 
     FIG. 18 is a screen-shot illustrating a condenser output summary screen; 
     FIG. 19 is a screen-shot illustrating condenser thermal performance output in tabulated format; 
     FIG. 20 is a screen-shot illustrating rated compressor capacity; 
     FIG. 21 is a screen-shot illustrating rated compressor power; 
     FIG. 22 is a screen-shot illustrating re-rated compressor capacity; 
     FIG. 23 is a screen-shot illustrating re-rated compressor power; and 
     FIG. 24 is a screen-shot illustrating compressor current. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     The performance simulator of the present invention enables rapid simulation of steady-state thermal performance of either air- or water-cooled condensing units. The condensing unit is a sub-system of a cooling system such as a refrigeration or air-conditioning system. The condensing unit rejects evaporator heat and compressor energy. Insight into the thermal performance of the condensing unit enables matching of an appropriate condensing unit with a particular cooling system. In other words, the ability to simulate the thermal performance of a particular condensing unit for a given cooling system enables a designer to select an appropriate condensing unit for that cooling system. 
     Referring now to FIG. 1, a generic cooling system  10  includes a compressor  12 , a condensing unit  14 , an expansion valve  16  and an evaporator  18 . The compressor  12  is controlled by a controller  20  and compresses gaseous refrigerant exiting the evaporator  18 . The compressor  12  discharges the high pressure refrigerant to the condensing unit  14 . The condensing unit  14  operates as a heat exchanger enabling heat transfer (Q 1 ) from the gaseous refrigerant to a heat sink (e.g. air or water). The refrigerant condenses within the condensing unit  14  and a state change occurs from gas to liquid. The liquid refrigerant exits the condensing unit  14  and flows to the evaporator  18  through the expansion valve  16 . The evaporator  18  also operates as a heat exchanger enabling heat transfer (Q 2 ) from the atmosphere surrounding the evaporator  18  to the liquid refrigerant. As the heat transfer occurs, the temperature of the refrigerant increases until a state change occurs from liquid to gas. The gas refrigerant is drawn into the suction side of the compressor  12  and the cooling cycle continues. 
     The condensing unit  14  can be one of an air-cooled condensing unit (ACU) or a water-cooled condensing unit (WCU). An ACU typically includes a fin-tube refrigerant-to-air heat exchanger, an air flow device such as a fan motor and fan blade and associated controls (not shown). A WCU typically includes a refrigerant-to-water heat exchanger and associated controls (not shown). 
     The performance simulator includes a series of sub-routines to determine the thermal performance of the condensing unit  14 . The sub-routines include a routine to model the thermodynamic property of refrigerants, a curve-fitting routine to fit discrete data values of condenser and compressor performance and a numerical routine to determine convergence of condenser and compressor data. In the case of an ACU, the performance simulator further implements an air-cooled condenser modeling routine and air flow rate look-up tables. In the case of a WCU, the performance simulator further implements a routine to determine the water-side pressure drop. The performance simulator accesses compressor and condenser databases that include compressor coefficients, compressor shell loss factors, ACU and WCU geometries, fan blades, fan motor data, condensing unit physical attributes and tested air flow rates. 
     The performance simulator is preferably provided as a software package that enables easy entry of pertinent data, as well as automatic access to various databases containing pertinent component information. As a software package, the performance simulator quickly and seamlessly determines the thermal performance of the condensing unit  14  and provides comprehensive performance information in the form of graphs and tables. The performance simulator summarizes the thermal simulation results in a final report. 
     Referring now to FIG. 2, a flowchart provides a general outline of the performance simulator. FIGS. 3 through 19 provide software screen-shots illustrating particular steps of the performance simulator. Initially in step  100 , the performance simulator determines whether ACU, WCU or condenser simulation is desired based on a user input. If ACU simulation is desired, the performance simulator continues in step  102 . If WCU simulation is desired, the performance simulator continues in step  104 . If air-cooled condenser simulation alone is desired, the performance simulator continues in step  106 . 
     In step  102 , a designer inputs pertinent information for the ACU. As shown in FIG. 3, this information includes the refrigerant type, the compressor, the condenser, the fan motor and fan blade. The compressor is selected from a compressor database based upon the refrigerant type, capacity requirements, and operating characteristics (volts, phase, frequency). As shown in FIG. 4, the compressor database provides the compressor options. The appropriate compressor is automatically selected by the performance simulator based on the selected ACU components. A brief summary of the pertinent compressor characteristics is provided. The condenser, fan motor and fan blade details can be selected by particular part numbers from the database. As shown in FIG. 5, the designer inputs the particular part numbers for the components. The performance simulator automatically inputs geometry and temperature characteristics (see FIG. 6) based on the particular condenser, fan motor and fan blade part numbers. The geometry and temperature information is stored in a database accessible by the performance simulator. There is also an option to include multiple condensers, fan motors and fan blades by adjusting the quantity of each. The performance simulator also provides scaling of the compressor and condenser performance. This option enables a designer to match the simulator results with laboratory measured data. 
     In step  108 , the ACU settings are provided (see FIG.  7 ). The settings include rating conditions, ambient temperatures, compressor shell loss factors, compressor frequency, compressor envelope check, check of engineering design standards and compressor type. Generally, the settings are default settings based on the ACU components. Other settings may be specified by the designer, such as ambient air temperatures. In step  110 , the simulation points are provided. The simulation points indicate the evaporator temperatures at which the ACU performance will be simulated (see FIG.  8 ). An application type is input by the user and the simulation points are automatically set based thereon, The condensing unit application types include high temperature, extended medium temperature, medium temperature and low temperature evaporators. These application types include predetermined simulation points, which can be altered by the user. A “special” application type is also provided and enables the designer to manually change the simulation points. 
     After inputting the compressor and condenser information and simulation points, the performance simulator processes the information in step  112  to provide ACU thermal performance data. More particularly, the performance simulator models the ACU and the refrigerant using the condenser modeling sub-routine and refrigerant modeling sub-routine, respectively. The performance simulator further implements the curve-fitting routine, the numerical convergence routine and air flow rate look-up tables to determine the thermal performance of the ACU at the given simulation points. 
     In step  114 , the thermal performance data is provided in either a spreadsheet format (see FIG.  9 ), graphical format (see FIG. 10) or a tabulated format (see FIG.  11 ). Regardless of the format chosen, the thermal performance data is provided based on user-specified ambient temperature (e.g. 90, 100, 110, 120° F.). For a given ambient temperature the unit capacity, unit power, unit energy efficiency ratio (EER) and condenser temperature are provide for each simulation point (see FIGS.  9  and  11 ). The difference between the condenser temperature and ambient is also provided, in addition to refrigeration side pressure drop and air side pressure drop. For 90° F. ambient, data points can be flagged to indicate those that exceed preferred engineering design standards but that are still within the compressor&#39;s operating envelope. Any data that falls outside of the compressor&#39;s operating envelope is shown with a strike through (see FIG. 12) and will not be included in the final report. 
     The performance simulator also enables scaling of the data based on compressor operating frequency. More particularly, an operator can scale ACU&#39;s 50 Hz performance data to 60 Hz and vice-versa. Using the software-based performance simulator, scaling is achieved in the spreadsheet format by clicking on a scaling icon. The requisite data entries are automatically entered by the performance simulator and can be manually altered by the operator. The performance simulator then updates the thermal performance data based on the scaling information. 
     In step  104 , pertinent information for the WCU is input. As shown in FIG. 13, this information includes the refrigerant type, the compressor, the condenser/receiver, inlet and outlet water temperatures. The designer selects a desired WCU model number from a pop-up menu. The performance simulator automatically fills-in the remaining information based on the selected WCU model number. The compressor is selected from a compressor database based upon the refrigerant type. The compressor database provides the compressor options for the compressor types automatically selected by the performance simulator based on the WCU model number. A brief summary of the pertinent compressor characteristics is provided. 
     In step  116 , the WCU settings are provided (see FIG.  14 ). The settings include rating conditions, condensing temperatures, compressor shell loss factors, compressor frequency, compressor envelope check and design check. The rating conditions include return gas temperature, compressor suction temperatures, condenser sub-cooling temperature and condensing water temperatures. Generally, the settings are default settings based on the WCU components. In step  118 , the simulation points are provided. The simulation points indicate the evaporator temperatures at which the WCU performance will be simulated (see FIG.  15 ). An application type is input by the user and the simulation points are automatically set based thereon. The application types include high temperature, extended medium temperature, medium temperature and low temperature evaporators. A “special” application type is also provided and enables the designer to manually change the simulation points. 
     After inputting the compressor and condenser information and simulation points, the performance simulator processes the information in step  120  to provide WCU thermal performance data. More particularly, the performance simulator models the compressor performance using the refrigerant modeling sub-routine and determines the water-side pressure drop using the corresponding sub-routine. The performance simulator further implements the curve-fitting routine, the numerical convergence routine to determine the thermal performance of the WCU at the given simulation points. As similarly described above, the thermal performance data is provided in step  114  in either a spreadsheet format, graphical format or a tabulated format (see FIGS.  16  and  17 ). 
     In step  106 , the air-cooled condenser, fan motor and fan blade can be selected by particular part numbers or selected from a menu. As similarly shown in FIG. 5, the designer inputs the particular part numbers for the components. The performance simulator automatically inputs geometry and temperature characteristics based on the particular condenser, fan motor and fan blade selected. The geometry and temperature information is stored in the condenser database accessible by the performance simulator. There is also an option to include multiple condensers, fan motors and fan blades by adjusting the quantity of each. The performance simulator also provides scaling of the condenser performance. This option enables a designer to match the simulator results with laboratory measured data. 
     After inputting the condenser information, the performance simulator processes the information in step  122  to provide condenser thermal performance data. The performance simulator processes the information as described above with regard to the ACU. As similarly described above, the thermal performance data can be provided in step  114  in either a spreadsheet format, graphical format or a tabulated format. The thermal performance data is provided based on user-specified ambient temperature (e.g. 90, 100, 110, 120° F.). For a given ambient temperature the condenser capacity, refrigeration flow, the refrigeration side pressure drop and air-side pressure drop are provide for a range of condensing temperatures (see FIGS.  18  and  19 ). 
     In step  124 , the performance simulator assembles and prints a final report summarizing the performance results. Also included is a sign-off sheet that summarizes pertinent information such as the identification of the simulation requester, the date of simulation request, the file names under which the performance results are stored, the application type and the like. 
     Referring now to FIGS. 20 through 24, the performance simulator provides detailed compressor information including compressor capacity (see FIG.  20 ), compressor power (see FIG. 21) and current (see FIG. 24) based on evaporator and condenser temperatures. The compressor capacity and power can be scaled based on displacement, the EER or both. Additionally, the compressors operating envelope can be extended. The scaling and envelope extension options enable “what if” design analysis. The compressor capacity and performance can also be re-rated to reflect performance at actual conditions (see FIGS.  22  and  23 ). Actual conditions are often different than those at which the compressor is rated. Re-rating is achieved based on the thermodynamic properties of the particular refrigerant. 
     The software-based performance simulator further includes a directory management routine for managing and organizing performance data files. The directory management routine enables an operator to specify directories in which files are to be stored and reorganize the files and directories as desired. 
     The performance simulator of the present invention enables quick steady-state thermal performance simulation of ACU&#39;s, WCU&#39;s and stand-alone condensers. The thermal performance data is used to evaluate system requirements such that an appropriate ACU, WCU or condenser can be selected to either replace a unit within a current cooling system or in the design of a new cooling system. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.