Patent Application
20090217679
Cooling systems are used in a variety of applications such as refrigeration systems and air-conditioning systems. Many cooling systems are energy inefficient.
Refrigeration Cooling system 22 comprises an arrangement of compressors, condensers, evaporators, and pumps, etc configured to withdraw heat directly or indirectly from a cooled environment and to transmit the withdrawn heat to a remote environment and or atmosphere outside. In the example illustrated, refrigeration cooling system 22 comprises a two-stage cooling system including circulation system 28, holding tank 30, intermediate temperature evaporators 32, intermediate stage gas suction tank 34, low temperature in evaporators 38, low stage gas suction tank 40, low stage compressors 42, high stage compressors 44 and condenser/s 46. Circulation system 28 delivers or directs refrigerant between holding tank 30, intermediate temperature evaporators 32, intermediate stage gas suction tank 34, low temperature evaporators 38, low stage gas suction tank 40, low stage compressors 42, high stage compressors 44 and condenser 46. Circulation system 28 includes piping system 50, expansion valves 52, 53 and level maintenance valve 54. Piping system 50 comprises headers, and piping, plenums and the like configured to direct the flow of refrigerant, whether in gaseous or liquid form. Piping system 50, along with the other components of refrigeration cooling system 22, form a closed circuit refrigerant cooling system in which refrigerant is contained as it is repeatedly compressed, condensed and expanded or evaporated to transfer or conduct heat from one or more cooling areas (in communication with evaporators 32, 38), where heat is absorbed, to condensers 46, where heat is discharged.
Expansion valve 52 (schematically illustrated) comprises one or more expansion valves along conduit 50 between holding tank 30 and intermediate temperature evaporators 32. Expansion valve 52, when actuated or opened, permits liquid refrigerant to expand and flow across intermediate temperature evaporators 32. Likewise, expansion valve 53 (schematically illustrated) comprises one or more expansion valves along conduit 50 between holding tank 30 and low temperature evaporators 38 and/or between intermediate stage gas suction tank 34 and low temperature evaporators 38. Expansion valve 53, when actuated or opened, permits liquid refrigerant to expand and flow across low temperature evaporators 38.
Holding tank 30 comprises one or more tanks configured to store and contain liquid refrigerant. Holding tank 30 is supplied with liquid refrigerant after the refrigerant gas has been compressed and condensed. One example of a refrigerant includes ammonia gas. In other embodiments, other refrigerants may be utilized.
Intermediate temperature evaporators 32 comprise one or more coils, conduits or other structures configured to contain and direct the flow of liquid and refrigerant while facilitating the absorption of heat from the processes to be cooled ing or from the surrounding volume of in such a room to be cooled. Intermediate temperature evaporators 32 receive expanded refrigerant after it is passed across expansion valve 52. In one embodiment, air from the room or other region to be cooled may be directed across the evaporators 32 using a fan. In other embodiments, evaporators 32 may be provided as part of other cooling arrangements.
Intermediate stage gas suction tank 34 comprises a tank or other container configured to collect and store and contain refrigerant from evaporators 32. Most of such refrigerant collected from evaporators 32 may be in gaseous form. Such gaseous refrigerant is contained in tank 34 until taken up by compressors 44. In the example illustrated, tank 34 also receives the gas refrigerant from the low stage gas compressors 42. Tank 34 further contains and supplies liquid refrigerant to low temperature evaporators 38. As noted above, level maintenance valve 54 maintains a predetermined level or amount of liquid refrigerant within tank 34 for supply to low temperature evaporators 38.
Low temperature evaporators 38 comprise one or more coils, conduits or other structures configured to contain and direct the of refrigerant while facilitating the absorption of heat from the processes to be cooled or from the surrounding volume in such a room to be cooled by the ing. Low temperature evaporators 38 receive expanded refrigerant after it is passed across expansion valve 53. In one embodiment, air from the room or other region to be cooled may be directed across the evaporators 38 using a fan. In other embodiments, evaporators 38 may be provided as part of other cooling arrangements.
Low stage gas suction tank 40 comprises a tank or other container configured to collect and to act as a buffer tank to dynamically store and contain refrigerant from evaporators 38 until such evaporated refrigerant is taken up by low stage compressors 42. In the example illustrated, tank 40 includes a suction mechanism for drawing evaporated refrigerant from evaporators 38 and directing the refrigerant to compressors 42.
Low stage compressors 42 comprise one or more compressors configured to receive gaseous refrigerant and to compress the gaseous refrigerant to higher pressure. Compressed refrigerant is discharged from low stage compressors to intermediate gas suction tank 34. In one embodiment, low stage compressors 42 may comprise reciprocating, rotary screw, centrifugal, scroll or vane type compressors. Each compressor is specified load capacity and a specified maximum discharge pressure. The discharge pressures of compressors 42 are adjustable within some range up to the specified maximum discharge pressure. In another embodiment, one or more of the compressors 42 have a fixed discharge pressure. In one embodiment, compresses 42 have controllable slide valves for adjusting an inlet volume of such compressors. Prime movers for such compressors 42 may be driven by electricity, fossil or other fuels, or steam, for example. Compressors 42 may comprise any combination of types, makes or models of compressors.
High stage compressors 44 are similar to low stage compressors 42 but are configured to compress gaseous refrigerant to a greater pressure level. High stage compressors 44 gaseous refrigerant from intermediate stage gas suction tank 34 and discharge compressed gaseous refrigerant to condenser/s 46. Like compressors 42, compressors 44 may comprise reciprocating, rotary screw, centrifugal, scroll or vane type compressors each compressor is specified by load (TR or Volume rate) capacity and a specified maximum discharge pressure. The discharge pressures of compressors 44 are adjustable within some range up to the specified maximum discharge pressure. In another embodiment, one or more of the compressors 44 have a fixed discharge pressure. Prime movers for such compressors 44 may be driven by electricity, fossil or other fuels, or steam, for example. Compressors 44 may comprise any combination of types, makes or models of compressors.
Condensers 46 comprise one more devices configured to receive compressed refrigerant gas and to extract heat from such refrigerant. In one embodiment, condenser 46 comprises one or more in parallel condenser coils through which the compressed refrigerant flows and from which heat is extracted. In one embodiment, condenser 46 may extract heat using one or more fans. In one embodiment, condenser 46 may comprise an evaporative condenser in which water showered upon the coils, wherein the water vaporizes and mixes with the ambient air. In this case, the latent heat of vaporization of the water is supplied by the hot refrigerant inside the condenser tubes. Air force on the outside of the evaporative condensers carries evaporated water vapor from the condenser surface to the ambient air. In another embodiment, condenser 46 may comprise a direct heat transfer condenser. In one embodiment, heat extraction may be performed by directing water across such coils, wherein the water is heated while extracting heat from the gas refrigerant surrounding the outside of the tubes. For example, in one embodiment, condenser 46 may include one or more water cooling towers. In other embodiments, other mechanism for devices may be utilized to extract heat from the refrigerant (cool and condense the compressed refrigerant). The condensed refrigerant is directed to the holding tank 30 via conduit 50, ready to absorb heat once expanded across one or more of expansion valve 52, 53 and directed across evaporators 32, 38.
Control system 24 comprises a system or arrangement of sensors and one or more controllers that are configured to monitor cooling demands and various parameters of refrigerant cooling system 22 and the environment of cooling system 22. In particular, control system 24 is configured to receive and store various analog (pressures, temperatures, flows etc. and digital signals (compressor on/off etc.) and manually in put data (such as compressor parameters, temperature set points etc. Control system 24 is programmed to compute dynamically the total enthalpy of circulating liquid refrigerant of the cooling system and a rate of change of the enthalpy of the evaporated refrigerant gas contained in cooling system 22. Based upon such values, control system 24 adjusts the operating parameters of cooling system 22 to reliably satisfy cooling demands while enhancing energy efficiency. In one embodiment, cooling system 24 controls the loading and unloading of compressors 42 and 44 to satisfy cooling demands while enhancing energy efficiency. In other embodiments, cooling systems 24 may control and adjust other operating parameters of cooling system 22 as well.
Control system 24 generally includes pressure transmitters 60, 62 and 63, temperature transmitters 64, 66, 68, 70, 72, 74 and, flow transmitters 78, 80, 82 and 84, wet bulb temperature transmitter 88, dry bulb temperature transmitter 90, variable frequency drive 92 and controller 94. Pressure transmitters 60, 62 and 63 comprise devices configured to sense pressure of refrigerant. Transmitter 60 is retrofitted on the low stage gas suction tank 40 and senses and detects the pressure of gaseous refrigerant in tank 40. Transmitter 62 is retrofitted on the intermediate stage gas suction tank 34 and senses the pressure of gaseous refrigerant in tank 34. Pressure transmitter 3 is retrofitted or otherwise connected to the inlet side of holding tank 30 and is configured to sense or detect the pressure of condensation of holding tank 30.
Temperature transmitters 64, 66, 68, 70, 72, 74 and comprise devices configured to sense and transmit temperatures of refrigerant. Transmitter 64 is retrofitted on a liquid outlet line of holding tank 30 and senses the temperature of the liquid refrigerant discharged from holding tank 30. Transmitter 66 is retrofitted at an upstream side of expansion valve 53 and senses & transmits the temperature of liquid refrigerant from holding tank 30 and from tank 34 prior to the liquid refrigerant passing through expansion valve 53. Transmitter 68 is retrofitted on low stage gas suction tank 40 and senses the temperature of gaseous refrigerant in tank 40. Transmitter 70 is retrofitted on intermediate stage gas suction tank 34. Transmitter 72 is retrofitted to the water line/s to condenser/46 and senses the temperature of the inlet water being supplied to condenser/s 46. Transmitter 74 is retrofitted to an outlet water line of condenser 46 and senses the temperature of the return or remaining water that has passed through condenser 46. Transmitter 76 is retrofitted to holding tank 30 and senses the condensing temperature of the refrigerant in condenser/s 46 as well as the holding temperature of the refrigerant in tank 30.
Flow transmitters 78, 80, 82 and 84 comprise the sensors configured to detect and transmit the volume/mass flow of the refrigerant liquid and or gas. Flow transmitter 78 is retrofitted or otherwise connected to the refrigerant liquid outlet line of holding tank 30 so as to detect and transmit the total flow of liquid refrigerant from holding tank 30. Flow transmitter 80 is retrofitted or otherwise connected to an upstream or inlet side of expansion valve 53 so as to detect t and transmit the flow of liquid refrigerant through expansion valve 53 prior to expansion of such liquid refrigerant. Flow transmitter 82 is retrofitted and or connected to the water inlet line of condenser 46 and is configured to sense and transmit the flow of water to condenser 46. Flow transmitter 84 is retrofitted or otherwise connected to the water outlet line of condenser 46 and is configured to sense and transmit the flow of water from condenser 46.
Wet bulb temperature transmitter 88 comprises a sensor configured to sense and transmit a wet bulb temperature of ambient air proximate condenser 46. Dry bulb temperature transmitter 90 comprises a sensor configured to measure and transmit a dry bulb temperature of ambient air proximate condenser 46. Transmitters 88 and 90 enable controller 94 to adjust operation of cooling system 22 based upon the ambient conditions such as the temperature, humidity, etc of the air which may affect the ability of heat to be extracted from liquid refrigerant passing through condenser 46.
Variable frequency drive 92 comprises a device associated with controller 94 that is configured to receive signals or data from the sensors or transmitters to a control system 24 and, based upon optimization algorithms and analysis performed by one or both of drive 92 or controller 94, is further configured to transmit control signals that would selectively increase or decrease the volume of the refrigerant gas being compressed prior to condensation and accordingly load and or unload a selected one of compressors 42, 44 operating at a partial load (a trim compressor) at a variable frequency. In other embodiments, drive 92 may be incorporated into or as part of controller 94. In still other embodiments, where the one or more trim compressors are variably controlled by adjusting controllable slide valves, drive 92 may be omitted.
Controller 94 comprises a processing unit configured to receive input or data from transmitters 64-90 as well as inputs from the human operators, and to generate control signals based upon such data directing the operation of compressors 42, 44 and condenser 46. For purposes of this application, the term “processing unit” shall mean a presently developed or future developed processing unit that executes sequences of instructions. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. For example, controller 94 may be embodied as part of one or more application-specific integrated circuits (ASICs). Unless otherwise specifically noted, the controller is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit.
As shown by
As shown in
As shown by block 303, based upon the determined the instant thermal content or load (enthalpy), a dynamic rate of change of thermal load (rate of change of enthalpy), a response time and the immediate future thermal load (enthalpy), controller 94 selects a combination of compressors for the particular stage that together, have a total capacity, that will closely approximate, but generally not exceed, the immediate future thermal load. Such compressors (base compressors) are operated at full load. Controller 94 will also select one of the remaining compressors for the particular stage as a partially loaded or trim compressor. Only one compressor serves as a partially loaded compressor for each stage at any moment in time. The partial loading of the selected compressor may be enabled either by drive 92 or compressor's own volumetric control or a combination of both.
As indicated by blocks 304 and 305 in
As shown by blocks 304, 306 and 307 in
As shown by block 303, controller 94 may further adjust the operational parameters of condenser 46 which may permit controller 94 to further adjust the operation of the compressors to enhance energy efficiency. Likewise, controller 94 may adjust the inlet volume or discharge pressure of one or more the compressors to adjust to the condensing pressure in condenser 46, which again is determined dynamically from the measured ambient wet bulb and dry bulb temperatures through transmitters 88 & 90. In addition, controller 94, in some embodiments, may adjust the operational parameters of condenser 46, such as by adjusting the number of fans or fan speed of condenser 46 which may allow controller 94 to also adjust the particular discharge pressure or inlet volume of one or more of the selected base & trim compressors. By increasing the ability of condenser 46 to extract heat, such as by increasing the number of fans or increasing their speed, the discharge pressure of all the selected compressors may be lowered when the ambient conditions permit so while still satisfying the cooling load demands. In one embodiment, controller 94 controls the variable parameters of condenser 46 as well as the inlet volume or discharge pressure of one or more of the selected trim compressors for enhanced energy efficiency. In particular, based upon a known energy consumption of such fans and the known or determined differences in the amount of energy consumed by the compressor to operate at a different discharge pressures or set pressures, controller 94 may optimize the parameters of each. In other words, controller 94 may select a particular combination of condenser fans at selected speeds and may select a discharge pressure appointed for the compressor to optimize or at least enhance energy efficiency.
In addition to adjusting the inlet volume and or discharge pressure of one or more selected compressors based upon the controllable variables or parameters of condenser 46, controller 94 may also adjust the inlet volume or discharge pressure of the one or more (transient only) selected trim compressor based upon environmental conditions which also impact the ability of condenser 46 to extract heat and condense the gaseous refrigerant. For example, in situations where cooling system 22 is in a location having a seasonal climate, the ability of condenser 46 to extract heat from the refrigerant may greatly vary depending upon ambient outside temperature and humidity. Based upon the detected outside temperature and humidity from transmitters 88, 90, controller 94 adjusts the inlet volume or discharge pressure of the one or more selected trim compressors for enhanced energy efficiency. For example, in response to a more humid and/or warmer condensing environment, controller 94 may increase the discharge pressure of the selected compressors for a given cooling load. Alternatively, in response to a more dry and/or cooler condensing environment, controller 94 may lower the discharge pressure of one of more selected compressors for the same given heat load.
In the particular example illustrated, cooling system 22 includes two stages: a low temperature evaporator stage and an intermediate temperature evaporator stage. For the low temperature evaporator stage, controller 94 determines the instant thermal content or load (enthalpy), a dynamic rate of change of thermal load (rate of change of enthalpy), a response time and the immediate future thermal load (enthalpy) for the low stage. The enthalpy of the refrigerant gas is determined using the temperature and pressure of the refrigerant gas from transmitters 60 and 68 in conjunction with the input or determined volume containing the gas. In the example illustrated, gas refrigerant is contained in tank 40, portions of conduit 50 from tank 40 to compressors 42.
The enthalpy of the liquid refrigerant is determined using the flow lbs/min, and temperature of refrigerant (from flow transmitters 7880 and temperature transmitters 64, 66. The total enthalpy is the sum of the enthalpy of the gas refrigerant and the liquid refrigerant. In some embodiments, the total enthalpy may be estimated using just the enthalpy of the liquid refrigerant since the enthalpy of the gas refrigerant may comprise a small percentage of the total enthalpy.
To determine the enthalpy for the low temperature stage, controller 94 utilizes data from transmitters 66, 80, 60 and 68. To determine the rate of change of enthalpy for the low temperature stage, controller 94 utilizes data from transmitters 60 and 68.
To determine the enthalpy for the intermediate temperature stage, controller 94 utilizes data from transmitters 64, 78, 62, 70 as well as the determined volume of refrigerant gas in tank 34 (based upon a sensed level of liquid refrigerant and tank 34 and the known volume of tank 34 and open piping or conduit extending from tank 34). The enthalpy of the refrigerant gas is determined using the temperature and pressure of the refrigerant gas from transmitters 62 and 70 in conjunction with the input or determined volume containing the gas, portions of conduit from compressors 42 to tank 34, portions of conduit 50 from compressors 44 to condenser 46 and portions of tank 34 not occupied by liquid refrigerant. Since the volume of liquid refrigerant in tank 34 is measured and transmitted to controller 94, controller 94 may determine the instant volume of gas in tank 34. To determine the rate of change of enthalpy for the intermediate temperature stage, controller 94 utilizes data from transmitters 60 and 68 as well as the determined volume of refrigerant gas in tank 34 based upon a sensed level of liquid refrigerant and tank 34 and the known volume of tank 34 and open piping or conduit extending from tank 34. To determine the immediate future load or enthalpy for the intermediate temperature stage, controller 94 utilizes the determined current enthalpy and the rate of change of enthalpy. To determine a response time (the time at which the inlet gas volume to the running compressors is to be increased or decreased while still meeting the cooling demands at the low temperature stage or cooled area), controller 94 utilizes the current enthalpy for the intermediate temperature stage, the immediate future enthalpy the intermediate temperature stage, the capacities of the compressors 44 and the response times of the various available compressors 44.
In one embodiment, controller 94 validates the determined heat load or enthalpy against the amount of heat being extracted by condenser 46. The amount of heat extracted by condensers 46 may be determined from the information from transmitters 72 and 82 and transmitters 74, 84. The amount of the extracted may approximate the enthalpy. In other embodiments, this validation may be omitted.
In the example illustrated, controller 34 is configured to operate in either a set pressure mode or a floating pressure mode, as selected by an operator. In the set pressure mode, a minimum pressure is maintained in tank 34 to facilitate defrosting or other requirements. In the floating pressure mode, controller adjustably controls the pressure in tank 34 for energy savings. For example, it has been found that energy savings is achievable by maintaining the pressure with tank in proportion to the condensing pressure and the pressure of low stage gas suction tank 40. In one embodiment, the pressure in tank 40 is maintained so as to be equal to the square root of the product of the condensing pressure and the low stage gas suction tank pressure. Since the condensing pressure and the low stage gas suction tank pressure may vary, so will the controlled pressure of tank 34.
In the particular example illustrated, refrigeration cooling system 22 includes two stages: a low temperature evaporator stage and an intermediate temperature evaporator stage. For the low temperature evaporator stage, controller 94 determines the instant thermal content or load (enthalpy), a dynamic rate of change of thermal load (rate of change of enthalpy), a response time and the immediate future thermal load (enthalpy) for the low stage. The enthalpy of the refrigerant gas is determined using the temperature and pressure of the refrigerant gas from transmitters 60 and 68 in conjunction with the input or determined volume containing the gas. In the example illustrated, gas refrigerant is contained in tank 40, portions of conduit 50 from tank 40 to compressors 42.
The enthalpy of the liquid refrigerant is determined using the flow (lbs/min) and temperature of refrigerant (from flow transmitters 78 and 80 and temperature transmitters 64, and 66. The total enthalpy is the sum of the enthalpy of the gas refrigerant and the liquid refrigerant. In some embodiments, the total enthalpy may be estimated using just the enthalpy of the liquid refrigerant since the enthalpy of the gas refrigerant may comprise a small percentage of the total enthalpy.
To determine the enthalpy for the low temperature stage, controller 94 utilizes data from transmitters 66, 80, 60 and 68. To determine the rate of change of enthalpy for the low temperature stage, controller 94 utilizes data from transmitters 60 and 68.
To determine the enthalpy for the intermediate temperature stage, controller 94 utilizes data from transmitters 64, 78, 62, 70 as well as the determined volume of refrigerant gas in tank 34 (based upon a sensed level of liquid refrigerant and tank 34 and the known volume of tank 34 and open piping or conduit extending from tank 34). The enthalpy of the refrigerant gas is determined using the temperature and pressure of the refrigerant gas from transmitters 62 and 70 in conjunction with the input or determined volume containing the gas, portions of conduit from compressors 42 to tank 34, portions of conduit 50 from compressors 44 to condenser 46 and portions of tank 34 not occupied by liquid refrigerant. Since the volume of liquid refrigerant in tank 34 is measured and transmitted to controller 94, controller 94 may determine the instant volume of gas in tank 34. To determine the rate of change of enthalpy for the intermediate temperature stage, controller 94 utilizes data from transmitters 60 and 68 as well as the determined volume of refrigerant gas in tank 34 based upon a sensed level of liquid refrigerant and tank 34 and the known volume of tank 34 and open piping or conduit extending from tank 34. To determine the immediate future load or enthalpy for the intermediate temperature stage, controller 94 utilizes the determined current enthalpy and the rate of change of enthalpy. To determine a response time (the time at which the inlet gas volume to the running compressors is to be increased or decreased while still the meeting the cooling demands at the low temperature stage or cooled area), controller 94 utilizes the current enthalpy for the intermediate temperature stage, the immediate future enthalpy the intermediate temperature stage, the capacities of the compressors 44 and the response times of the various available compressors 44.
In one embodiment, controller 94 validates the determined heat load or enthalpy against the amount of heat being extracted by condenser 46. The amount of heat extracted by condensers 46 may be determined from the information from transmitters 72 and 82 and transmitters 74, 84. The amount of the extracted may approximate the enthalpy. In other embodiments, this validation may be omitted.
Overall, controller 94 performs one or more of the following functions. First, controller 94 selects optimal combinations of base, full load compressors and a single trim compressor at each stage and also determines an optimal start time for loading of each of the selected compressors based upon a predicted or forecasted future cooling load which is determined based upon an existing enthalpy for the particular stage and the rate of change of enthalpy for the particular stage.
Second, controller 94 adjusts operational parameters of condenser 46 based upon existing ambient conditions (temperature and humidity) in combination with a predicted or forecasted future cooling load which is determined based upon an existing enthalpy for the particular stage and the rate of change of enthalpy to conserve energy.
Third, controller 94 controls the condensing rate such as by controlling the number of condensers online or such as by controlling fan speed of the condensers so as to maintain minimum pressure requirements for defrosting or for circulation of refrigerant. For example, controller 94 may decrease the condensing rate (lower fan speed or reduce the number of condensers online) to ensure that the minimum pressure of gaseous refrigerant is maintained.
Fourth, controller 94 further adjusts or controls interstage pressure of refrigerant within tank 34. Such adjustment is based upon the condensing pressure at condenser 46 and the low stage pressure at tank 40. In particular, the adjustment is based upon the square root of the product of the condensing pressure at condenser 46 and the low stage pressure at tank 40.
The following is an example comparing performance of refrigeration cooling system 22 riot under control of control system 24 with the performance of refrigeration cooling system 22 under the control of control system 24. In the particular example described, refrigeration cooling system 22 is in the meat processing & packing industry facility. The particular facility requires Minus 40 F (−40 F) for the process area. It requires Plus 17 F (17 F) for the packing and ware house area.
Almost all of the industrial and or commercial refrigeration and air conditioning systems are controlled for maintaining one or more of the following physical conditions:
The control parameters described above are all based on temperature bands. For e.g. if the temperature goes up beyond the temperature band the control if any will start compressing more refrigerant gas, condense and circulate for evaporation to reduce the temperature. Similarly, when the temperature falls below the band, it will reduce the amount of gas compressed, condensed, and circulated for evaporation.
The refrigerant liquid and vapor will be at equilibrium at the saturation temperature. There is only one saturation temperature corresponding to a particular pressure. Therefore if you control the pressure you can control the temperature. Therefore, most users of refrigeration systems, in a bigger scale, control the pressure to control the temperatures.
The trending (ups and downs) of temperature does not follow a predictable pattern in a continuous process industry especially when the process conditions vary dramatically. The unpredictability is even more severe in a refrigeration system which is influenced by ambient temperature and relative humidity.
Therefore, maximum number of compressing, condensing and circulation equipment is run to satisfy the temperature set points all the time irrespective of the actual refrigeration thermal load. For e.g. in the system described in Table 2.1, compressors of total capacity of 3,915 Tons are run to a refrigeration thermal load of 1,617 Tons. The capacity utilization is only 41%. However the electric power consumption is 2,660 kW OR 65% of the running compressors' full load motor power of 4,095 kW. There is an efficiency reduction of 36% because of the partial loading.
The present invention relates to the control of refrigeration fluids during the stages of compression, condensation, distribution to optimize energy efficiency performance of the compressors, cooling fans, distribution pumps etc. of the refrigerant fluids and the carrier of cooling or heating energy like water or air, pumping or blowing systems for the cooling mediums of the refrigerants, and all the above energy performance obtainable without affecting the associated process integrity.
The optimum energy efficiency of these stages is achieved simply by including the thermal load and the ambient conditions as additional control parameters to the process temperatures.
P2=Square Root of P1(Low stage suction pressure)*P3 (Condensing Pressure),
where,
P1=Low stage suction pressure in PSIA, P2=Inter stage pressure in PSIA, and P3=condensing pressure in PSIA.
The ambient wet and dry bulb temperatures will be measured constantly. From the temperatures and using psychometric charts and formulas the condensing pressure will be computed by the controller 94 as described in chapter 4-Control Strategy of Control System 24 and chapter 5-CONTROL ALGORITHM and
Although the present disclosure has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.
The present application is related to co-pending U.S. patent application Ser. No. 11/086,527 filed on Mar. 22, 2005 by Sridharan Raghavachari and entitled MULTIPLE COMPRESSOR CONTROL SYSTEM, the full disclosure of which is hereby incorporated by reference.
