Abstract:
A noise control method is provided for a cooling system having at least one refrigerant circuit. The refrigerant circuit includes a compressor, a condenser, at least one condenser fan, and an evaporator. Noise control is only performed periodically in response to requirements for reduced operation at predetermined times. The request for reduced noise triggers the commencement of the noise control method. The noise control method involves reducing the operating speed of the compressor, as well as reducing the operating speed of at least one condenser fan, to within a predetermined range of allowable reduced operating speeds. The noise control method temporarily overrides the ability of the cooling system to fully respond to increased cooling or heating demands. When the noise control method is terminated, such as by the end of the stated period of time requiring reduced noise generation, the system is restored to normal operation, and remains fully responsive to cooling and heating demand until commencement of the next period of reduced noise requirements.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/561,435 filed Apr. 12, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to a sound reduction control system and method for a cooling system. More specifically, the present invention relates to a system and method for reducing the sound generated by a compressor driven chiller system having a variable speed drive by selectively and controllably reducing the speed of the compressor, the speed of the condenser fans, or the number of operating condenser fans in the system.  
         [0003]     In chiller, HVAC or refrigeration systems, a refrigerant gas is compressed by a compressor and passed to a condenser where it exchanges heat with another fluid, such as the ambient air forced over condenser coils by one or more condenser fans. From the condenser, the pressurized refrigerant passes through an expansion device and then to an evaporator. An environment to be cooled is cooled by refrigerant passing through the evaporator. The refrigerant returns from the evaporator back to the compressor, and the cycle is repeated.  
         [0004]     Large capacity chiller systems are required to provide adequate cooling of the interiors of large buildings. Such systems typically include one or more compressors, as well as one or more air-cooled condensers having condenser fans for cooling the compressed refrigerant. Compressor speed and condenser fan speed, or number of condenser fans running, are interdependent on one another. When the compressor operates at a higher speed, a higher rate of compressed refrigerant is passed to the condenser. In order to cool the increased flow of compressed refrigerant, a larger rate of heat exchange by the condenser is required. One way to increase condenser heat exchange is to increase airflow across the condenser coils. Accordingly, operation of a higher number of condenser fans, or operation of the fans at a higher speed, will increase airflow around the condenser coils, resulting in higher rate of heat exchange by the condenser.  
         [0005]     Increasingly, it is necessary to reduce the total sound generated by chillers during certain times, particularly for chillers installed near residential areas. Indeed, some localities have laws that require sound levels at property lines to be lower at nighttime than during the day. One known method of reducing the chiller noise is to disable the system during selected hours, thereby preventing the generation of noise by the chiller system. However, disabling the chiller system means that no cooling can be performed by the chiller systems, thus causing the interior building temperatures to rise to uncomfortable levels. Therefore, it would be advantageous for a building owner to be able to reduce the sound level of the chiller system at selected times, while maintaining some cooling capability within the building.  
         [0006]     The sound generated by a typical air-cooled compressor chiller system is predominately created by the compressor and the condenser fans. Therefore, in order to reduce the amount of sound generated by the chiller system, it is desirable that the compressor and the condenser fan(s) be made to operate more quietly. This goal can be accomplished by several known ways. For example, mechanical modifications such as the application of sound-insulating coatings can be made to the compressor, condenser fans, and any housings encasing such components, to reduce operating noise. Alternatively, new compressors and new condenser fans manufactured with sound-absorbing or sound-attenuating features can be installed. However, such modifications or replacements can be expensive as a result of the materials, labor, and downtime costs that are potentially involved. Therefore, what is needed is a cost-effective method for selectively reducing the noise generated by an installed chiller system.  
       SUMMARY OF THE INVENTION  
       [0007]     What is disclosed is a method of providing noise or sound control of a chiller, HVAC or refrigeration system. A chiller system includes a control panel, a compressor, a condenser arrangement, at least one condenser fan, and an evaporator arrangement. Upon receiving a sound control signal at the control panel, the sound control signal initiates a reduced sound control mode of operation. The reduced sound control mode of operation includes the steps of measuring an operating speed of the compressor; controllably reducing the operating speed of the compressor in response to the measured operating speed of the compressor being greater than a maximum operating speed; the maximum operating speed being directly related to the sound control signal; and measuring an operating speed of the compressor; determining an operating parameter of at least one condenser fan; and controllably altering an operating configuration of the at least one condenser fan in response to the determined operating parameter of the at least one condenser fan being greater than a maximum operating parameter; the maximum operating parameter being directly related to the sound control signal.  
         [0008]     Also disclosed is a method of providing sound control in a chiller, HVAC or refrigeration system. The chiller system includes a compressor, a condenser arrangement, at least one condenser fan, and an evaporator arrangement. The method includes the steps of determining whether a sound control signal is received by the control panel; assigning a maximum operating speed for a motor powering the compressor responsive to said sound control signal; assigning a maximum operating parameter for the at least one condenser fan responsive to the sound control signal; determining whether the compressor and the at least one condenser fan are within a corresponding permissible range, wherein the corresponding permissible range has an upper limit of the corresponding maximum operating speed and maximum operating parameter; adjusting at least one of a) the speed of the compressor motor or b) the operating parameter of the at least one condenser fan, responsive to the determination that the compressor and the at least one condenser fan are outside the corresponding permissible range; wherein the step of adjusting the speed operates to reduce the noise generated by the chiller system.  
         [0009]     The present invention is also directed to a chiller system. The chiller system includes a control panel, a compressor, a condenser arrangement, at least one condenser fan, and an evaporator arrangement. Also provided is means for receiving a sound control signal at the control panel, the sound control signal being configured to initiate a reduced sound control mode of operation. There is also provide means for measuring an operating speed of the compressor; and means for controllably reducing the operating speed of the compressor in response to the measured operating speed of the compressor being greater than a maximum operating speed. The maximum operating speed is directly related to the sound control signal. Also, means is provide for measuring an operating parameter of at least one condenser fan; and a means for controllably altering the operating configuration of the at least one condenser fan responsive to the sound control signal.  
         [0010]     One embodiment of the present invention is directed to a method for reducing the sound level of a chiller system by selectively and periodically limiting the maximum operating speed of the compressor, maximum operating speed of at least one condenser fan, and/or of the number of fans to be operated.  
         [0011]     Another embodiment of the present invention is directed to a chiller system having a control panel with a control algorithm for limiting the maximum operating speed of the compressor, and varying the speed of at least one condenser fan or adjusting the total number of operating condenser fans.  
         [0012]     One advantage of the present invention is that the sound generated by an installed chiller system can be selectively reduced without requiring mechanical modifications to system components.  
         [0013]     Another advantage of the present invention is that comfort cooling in the interior space is not completely sacrificed when the system is required to comply with periodic reduction of sound requirements, such as during nighttime operation.  
         [0014]     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  illustrates schematically an embodiment of a heating, ventilation and air conditioning system for use with the present invention.  
         [0016]      FIG. 2  illustrates a flow chart detailing one embodiment of the noise control methods of the present invention.  
         [0017]      FIGS. 3-4  illustrate the effect of an input signal on the maximum frequency of a compressor and condenser fan in one embodiment of the present invention. 
     
    
       [0018]     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The present invention therefore provides systems and methods for selectively controlling the speed of the compressor and the condenser fans of a chiller system to reduce sound generated by the system at selected times. The selective operation of the condenser fans can include any combination of disabling one or more fans, operating less than all fans, operating one or more fans at lower fixed speed, operating one or more fans at a lower variable speed. It is noted that the control of fan speed, as it is describe below, also includes switching some or all of the condenser fans on or off.  
         [0020]      FIG. 1  illustrates generally a chiller, HVAC or refrigeration system  100  that can be used with the present invention. An AC power source  102  supplies a variable speed drive (VSD)  104 , which powers one or more motors  106 . Each motor  106  is used to drive a corresponding compressor  108  that feeds high-pressure and high-temperature refrigerant gas to a condenser  110 . The compressor  108  is preferably a screw compressor or centrifugal compressor, however the compressor can be any suitable type of compressor including reciprocating compressors, scroll compressors, or rotary compressors. The output capacity of the compressor  108  can be based on the operating speed of the compressor  108 , which operating speed is dependent on the output speed of the motor  106  driven by the VSD  104 . The system  100  can include many other features that are not shown in  FIG. 1 , and those features have been purposely omitted to simplify the drawings for ease of illustration.  
         [0021]     The refrigerant vapor delivered to the condenser  110  enters into a heat exchange relationship with a fluid, preferably air. To assist in the passage of the air around the heat exchanger coils of condenser  110 , at least one fan  112  can be used to force or draw air over the coils of the condenser  110 . More preferably, a bank of multiple condenser fans  112  can be used. Each condenser fan  112  can be single speed, multiple fixed speed, or variable speed in nature, depending upon the type of fan and drive mechanism. In each embodiment, the condenser  110  is cooled by at least one condenser fan  112 .  
         [0022]     The condensed liquid refrigerant from condenser  110  flows through an expansion device to an evaporator  114 . The evaporator  114  can include connections for a supply line and a return line of a cooling load. A secondary liquid, which is preferably water, but can be any other suitable secondary liquid, e.g. ethylene, calcium chloride brine or sodium chloride brine, travels into the evaporator  114  via return line and exits the evaporator  114  via supply line. The liquid refrigerant in the evaporator  114  enters into a heat exchange relationship with the secondary liquid to chill the temperature of the secondary liquid. The refrigerant liquid in the evaporator  114  undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the secondary liquid. The vapor refrigerant in the evaporator  114  then returns to the compressor  108  via a suction pipe  116  to complete the cycle. It is to be understood that any suitable configuration of condenser  110  and evaporator  114  can be used in the system  100 , provided that the appropriate phase change of the refrigerant in the condenser  110  and evaporator  114  is obtained.  
         [0023]     A control panel  118  is provided to control operation of the VSD  104  to monitor and control operation of the motor  106 , thus controlling the operating speed of the compressor  108 . The control panel  118  further permits monitoring and control of the operation of each condenser fan  112 . The control panel  118  also allows interdependent and selective operation and control of the VSD  104  and motor  106 , as well as the condenser fans  112 . With respect to the selective operation of each condenser fan  112 , the control panel  118  can selectively disable each fan  112 , and can preferably adjust the operating speed of each fan  112  if the fan  112  is capable of multiple operating speeds. Fans  112  may be variable speed fans linked to a common VSD (not shown) dedicated to controlling the speed of condenser fans to allow nearly infinite adjustment of fan speed using the control panel  118 . Alternatively, where fixed speed fans are used in a bank of multiple condenser fans  112 , the fans  112  are configured so that less than all fans can be selectively operated at any given time. As another alternative, condenser fans  112  may also be commonly linked to VSD  104  along with motor  106 ; as yet another alternative, fans  112  may be multiple fixed speed fans, typically two-speed, configured to operate in various combinations of high-speed, low-speed and off.  
         [0024]     In an alternative embodiment, the system can alternatively include two or more compressors incorporated in corresponding refrigerant circuits, and it is to be understood that the system can have one refrigerant circuit, two refrigerant circuits, or more than two refrigerant circuits for providing the desired system load and can have more than one compressor for each refrigerant circuit. Such an alternative system can further include a condenser arrangement wherein a single condenser is partitioned or otherwise configured to allow operation of two separate refrigerant circuits within a single condenser housing so that the refrigerant output by each compressor is not mixed with output from other compressors. Similarly, the system  100  can include an evaporator arrangement wherein a single evaporator housing is provided to serve two or more separate refrigeration circuits. For example, the condenser housing and evaporator housing can maintain the separate refrigerant circuits either through a partition or other dividing means with the evaporator housing, or by providing separate coil arrangements. In yet another embodiment of the present invention, the refrigerant output by two or more compressors can be combined into a single refrigerant circuit to travel through the components of the system before being separated to reenter the compressors.  
         [0025]     Preferably, the control panel  118  includes a microprocessor or controller to provide control signals to the VSD  104  to control the operation of the VSD  104 . More preferably, the control panel  118  can control the output power of the VSD  104  to control the speed of the motor  106 , and the compressor  108 , to satisfy the sound requirements of the operating environment of the system during periods requiring reduced noise operation. Most preferably, the control panel  118  can control the VSD  104  to operate the motor  106  within a predetermined range of speed during periods requiring reduced noise operation, which has the effect of lowering the condenser discharge pressure. The reduced discharge pressure causes some or all condenser fans  112  to shut down due to the reduced cooling demand. If variable speed type condenser fans  112  are employed, one or more VSDs may be provided. Reducing the compressor speed in this instance causes the condenser fans  112  to operate at reduced speed, rather than shutting down a portion of the fans in the system.  
         [0026]     In a preferred embodiment, the control panel  118  executes a control algorithm(s) or software to control operation of the system  100 , and to determine and implement an operating configuration for the VSD  104  to operate the compressor  108 . The control algorithm or software of the control panel also determines, implements, and controls the speed of each condenser fan  112  in order to satisfy the sound requirements of the operating environment, while still providing some condenser cooling. In one embodiment, the control algorithm(s) can be computer programs or software stored in the non-volatile memory of the control panel  118  and can include a series of instructions executable by the microprocessor of the control panel  118 . While it is preferred that the control algorithm be embodied in a computer program(s) and executed by the microprocessor, it is to be understood that the control algorithm may be implemented and executed using digital and/or analog hardware by those skilled in the art. If hardware is used to execute the control algorithm, the corresponding configuration of the control panel  118  can be changed to incorporate the necessary components and to remove any components that may no longer be required.  
         [0027]     The reduced noise control process can be initiated in response to user input, or can be initiated automatically, such as by a preprogrammed instruction from a system primary control program. The reduced noise control process can be a stand-alone process or program, or it can be incorporated into a larger control process or program, such as a capacity control program for the chiller system. For example, the control process can be used to generate an industry standard 4-20 mA or 0-10V signal as a noise control signal to be sent to the VSD  104  to reduce the maximum allowed compressor  108  speed, as well as to limit the maximum operational speed of each condenser fan  112 . Alternately, the noise control signal can also be generated from a user interface such as a keypad on the control panel  118 , or the noise control signal can be automatically generated such as by a microprocessor control of the control panel  118 . The noise reduction control process prevents the VSD  104  from providing power at a frequency higher than the maximum value specified by the noise control signal. The noise control signal may also limit the maximum speed of at least one condenser fan  112  or the maximum number of condenser fans  112  that can operate. By limiting the maximum frequency or speed of the VSD  104 , compressor  108  and optionally, fan  112 , the system  100  is prevented from exceeding a given sound level during particular periods of operation. The sound reduction is due in part to the compressor  108  being quieter when operating at a lower speed within a predetermined speed range. The sound reduction is further due to quieter operation of condenser fan  112  as a result of lower fan speed. In alternative embodiments having multiple condenser fans  112 , the control panel  118  reduces total fan noise in noise control mode by selectively operating less than all fans  112 , or by operating all fans  112  at low speeds within a predetermined range of fan speeds permitted by the noise control signal.  
         [0028]     In another embodiment, the control panel  118  can also allow the discharge pressure in the condenser  110  to rise during periods when a low system sound level is desired to be maintained. This is achieved by raising the pressure settings for some or all of the condenser fan(s)  112  to allow the pressure in the condenser  110  to rise during periods when a low system sound level is desired to be maintained. Increasing the pressure in the condenser will result in less cooling need in the condenser  110 , thereby allowing operation of condenser fans  112  at lower speed, and/or operation of fewer fans  112  within a multiplicity of provided condenser fans  112 . The pressure setting is adjusted electronically by the control algorithm, by changing the discharge pressure setpoint stored in the control panel. Raising of the discharge pressure setpoint reduces the need for cooling in the condenser as the condenser is allowed to run hotter and at a higher pressure.  
         [0029]     A control program or algorithm executed by a microprocessor or control panel  118  is used to determine the speed of the compressor  108 , as well as to control other system parameters such as the operational status and speed of any condenser fans  112 . The control program can receive a variety of inputs, such as temperature, pressure and/or flow measurements, to be used in making the determination of when to reduce the speed of the compressor  104  and condenser fans  112 . It is to be understood that the particular control program and control criteria for reducing compressor speed and condenser fan speed can be selected based on the particular performance requirements of the system  100 .  
         [0030]     In addition, the system  100  can include one or more sensors for detecting and measuring operating parameters of the system  100 . The signals from the sensors can be provided to a microprocessor or control panel  118  that controls the operation of the system  100 . Sensors can include pressure sensors, temperature sensors, flow sensors, or any other suitable type of sensor for evaluating the performance of the system  100 .  
         [0031]     The operation of the system  100  in the reduced noise control mode is controlled by a control panel  118 . The control panel  118  can receive input signals from a microprocessor, or alternatively from a user interface, indicating a demand for reduced noise. The control panel  118  then processes these input signals using the control method of the present invention and generates the appropriate control signals to the components of the system  100 , including the VSD  104 , compressor  108 , and condenser fans  112  to obtain the desired reductions in operating speed to reduce noise generated by the components, and thus reducing the total noise generated by the system  100 .  
         [0032]     In the preferred embodiment of the reduced noise control mode, the control panel  110  and noise control algorithm only overrides the normal capacity control features of the system when those capacity controls attempt to operate the compressor or the condenser fans above the limits imposed by the noise control algorithm. Simply put, in the noise control mode, cooling demand is still monitored, and capacity control features can respond to operate the compressors and condenser fans, but the noise control mode places an upper limit on system capacity. Cooling demand is independent of the chiller and is a function of the building or process being cooled. The noise control process of the present invention sets a maximum frequency for each compressor  108 , as well as a maximum speed or number of condenser fans  112  to be operated. Those frequency or speed limits are imposed on the capacity control algorithms, including the compressor and the condenser fan control algorithms. If those capacity control algorithms do not call for the controlled component to be operated above the provided limits, the noise control algorithm does not interfere with normal operation. However, if the system algorithms call for operating the components above the provided limits, they are overridden by the noise control algorithm.  
         [0033]      FIG. 2  illustrates a flow chart detailing one embodiment of the reduced noise control process of the present invention for the exemplary system  100  shown in  FIG. 1 . The process begins with a determination of whether a reduced noise control signal has been received in step  202 . The reduced noise control signal is either generated automatically such as by a microprocessor controller, timer, or user interface linked to the control panel  118 . The noise control signal can be preset or variable, and is based upon the noise profile and properties of the particular system  100 . Preferably, the noise control signal is variable so as to allow for selective reduction of total noise generated by the system and corresponding cooling effect in the reduced noise mode. More preferably, the noise control signal is variable and is automatically initiated at predetermined times and for predetermined periods. The relationship between system noise and the speed of the compressor  108  and condenser fan  112  will vary depending upon the type and number of compressors  108  and fans  112  incorporated into the system  100 . For example,  FIGS. 3-4  illustrate an exemplary relationship between the maximum VSD frequency for a standard 4-20 mA input and a standard 0-10V input on a compressor  108  having a 200 Hz maximum running frequency. For each chiller system  100 , a similar relationship can be derived between sound level and operating frequency of the compressor  108  and condenser fans  112  to determine the effect of operating at given frequencies on the sound level generated by the chiller system  100 .  
         [0034]     If a reduced noise control signal is not received in step  202 , the system  100  operates in normal mode based upon heating and cooling demand and other system control inputs. However, if a reduced noise control signal is received, the system enters noise control mode, and the process continues to step  204 . In step  204 , the control panel  118  processes the noise control input signal to assign a corresponding maximum operating speed or frequency to the compressor  108 , as well as to assign a corresponding maximum speed or frequency for the condenser fan  112  or the maximum number of fans to operate. Preferably, this variable noise control signal is generated via a straight line but can be based on any function, equation, or lookup table. When the minimum sound control signal is received in step  202 , the compressor maximum speed is allowed to reach an upper speed limit, which may correspond to the maximum speed of the compressor. The minimum sound control signal generally provides the least amount of sound reduction. When the maximum sound reduction signal is received in step  202 , the compressor maximum speed is reduced down to its minimum speed. All other sound reduction signal inputs in step  202  fall on the straight line connecting the two points, as in  FIGS. 3 and 4 .  
         [0035]     In one aspect of the system, the level of the noise control signal may be determined over the range of operating frequencies. The maximum motor operating frequency is a characteristic of the make and model of the various compressor or fan motor(s). The minimum motor operating frequency for the motor(s) is normally approximately 50 Hz. After determining the span of the frequency range associated with the analog signal, the sound levels along the range may be plotted by measuring the sound level at each operating frequency. Preferably the operating frequency may be referenced as a percentage of the maximum speed of the motor or motors by a control algorithm. A table may be constructed from the plotted sound measurements of the actual decibel level of a specified operating frequency, or for the corresponding percentage of maximum speed.  
         [0036]     In this way, the system operator may select the level of the noise control signal to be applied when the system is in noise control mode, by reference to a table or graph representation of the noise versus frequency profile. If a desired noise level is known by the operator, the associated operating frequency may be selected, for setting the noise control signal level. Such a table may optionally be stored on a memory storage device accessible by the control panel, and a user input device may be provided either at the control panel or at a remote terminal, for entering a desired parameter, for example, the desired maximum decibel level or the maximum operating frequency. The control panel may then establish a level for the noise control signal by referencing the value of the input parameter in the table.  
         [0037]     In the preferred embodiment, the control panel  118  processing includes relaying the processed noise control signal to a common VSD  104  configured to permit interdependent control of the speed of the motor  106 , and thus the speed of the compressor  108 . The condenser fan  112  may be controlled by a separate VSD, or a plurality of condenser fans  112  may be provided having any combination of either fixed speed fans, variable speed fans, or both so as to permit adjustable control of airflow across the condenser  110  by controlling the number and speed of operating fans  112 . If more than one variable speed condenser fan is used, two or more fans  112  may be controlled by a common VSD, or each condenser fan may be controlled by a separate VSD.  
         [0038]     The process continues to step  206  to determine whether the current rate of speed of the compressor  108  and the speed or number of the condenser fans  112  are within a predetermined range permitted by the reduced noise control signal received in step  202 . If the compressor  108  and condenser fan  112  of the system  100  are operating within the operational speed range permitted by the reduced noise control signal received in step  202 , no adjustments are made to the speed of the compressor  108  and condenser fans  112 , and the system operates in the “normal” mode. If the compressor or any fans are operating above the permitted maximum speed, the process continues to step  208 , where the control panel adjusts the speed of the compressor  108  and/or fans  112 , to a speed that is equal to or less than the maximum speed permitted by the noise control signal. In a preferred embodiment, in step  208 , the control panel  110  continues to monitor system pressures and temperatures, such as discharge pressure and leaving chilled liquid temperature, and can adjust the speed of the compressor  108  as well as the speed of any condenser fan  112  within the operating range at or below the maximum speeds allowed by the control input signal in order to control the system  100 . By maintaining stable operation of the compressor  108  in the reduced noise mode, the system  100  maintains some cooling while operating in the reduced noise mode. In another embodiment of the reduced noise mode, in step  208 , the system  100  can permit the condenser fan  112  to initially operate at speeds in excess of the maximum operating speed permitted by the noise control signal until such time as the system temperature and pressures have stabilized for the lower operating speed of the compressor  108 .  
         [0039]     The process next returns to step  202  to determine if a reduced noise control signal remains present. If the noise control signal remains present, the above-described process is repeated. If the noise control signal is not detected, the system returns to normal operating mode where it can respond to heating and cooling demands.  
         [0040]     The control panel  118  determines whether there is a noise control signal present at least once during every control program loop. The various types of noise control signal include remote signal, programmed value, or other types as discussed above. If the noise control signal changes state, by increasing, decreasing or going away, the control algorithm makes a corresponding adjustment to the maximum speed of the compressor  108 . Preferable, a timer is associated with the remote system to restrict the number of adjustments that can be made to the chiller system by the remote system in a predetermined time period. For example, the timer may prevent the remote system from changing the noise control signal more often than the timer cycle, which cycle may vary from 5 minutes to 60 minutes. The timer cycle could be more or less than that range, if suitable for the design parameters of the particular chiller system. The timer prevents the chiller system from becoming unstable due to more frequent changes of the noise control signal and the system parameters affected by the noise control signal.  
         [0041]     In another embodiment of the present invention, the user of system  100  can view the control panel  118 , such as by viewing a connected user interface (not shown) to determine the particular system operating mode. For example, if an LED provided on the control panel  118  or user interface is flashing, then the system  100  can be in noise control mode despite any demand for cooling or heating. However, if the LED on the control panel  118  or user interface is not flashing, the system  100  can be in normal operating mode to respond to any demand for cooling or heating. It is to be understood that the display method on the control panel  118  or user interface can be modified for the particular requirements or needs of the user.  
         [0042]     As noted above, in the typical chiller system, the refrigerant vapor delivered to the condenser  110  enters into a heat exchange relationship with a fluid, preferably air. For purposes of the present invention, if heat exchange is effected by a fluid other than air, e.g., a liquid, then the system would not use fans, and noise control is be accomplished solely by regulating the frequency of the compressor motor and, thus, the speed of the compressor.  
         [0043]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.