Claims:
1. A method of operating a flooded-type chiller without pressure transducers, the method comprising the steps of:
storing, by a controller, a pre-defined suction pressure values range and a pre-defined discharge pressure values range in a memory, after start of a compressor;
sensing and determining, by the controller in communication with a plurality of sensors, a plurality of first and a second group of parameter values, said plurality of sensors positioned in the flooded-type chiller;
calculating, by a controller, a plurality of third group of parameter values using the measured values of the plurality first group of parameters;
determining, by the controller, a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values;
comparing, by the controller, said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range; and
controlling and maintaining, by the controller, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.

2. The method as claimed in claim 1, further comprising a step of calculating, by the controller, a plurality of fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values.

3. The method as claimed in claim 2, wherein based on calculated fourth group of parameters values an oil carryover condition or an entry of liquid refrigerant in said compressor is determined by the controller.

4. The method as claimed in any of the preceding claims 1-3, wherein the step of controlling and maintaining, said flooded-type chiller within predefined pressure values range includes invoking, by said controller, said control signal for loading/unloading of said flooded-type chiller and / or for opening/closing an electronic expansion valve of said flooded-type chiller, when determined virtual suction and virtual discharge pressure values are above / below said stored pre-defined pressure values range and pre-defined discharge pressure values range.

5. A method as claimed in claim 1, further comprising a step of monitoring, the controller, operation of the flooded-type chiller at a pre-defined interval.

6. The method as claimed in any of the preceding claims 1-5, wherein the pre-defined suction pressure values are in the range of 20 PSIG to 60 PSIG (pounds per square in gauge).

7. The method as claimed in any of the preceding claims 1-6, wherein the pre-defined discharge and oil pressures values are in the range of 70 PSIG to 270 PSIG (pounds per square in gauge).

8. The method as claimed in any of the preceding claims 1-7, wherein plurality of said first group of parameters values include a leaving water temperature value, a first liquid refrigerant temperature value and a current value.

9. The method as claimed in any of the preceding claims 1-8, wherein plurality of said second group of parameter values include a second liquid refrigerant temperature value and a current value.

10. The method as claimed in any of the preceding claims 1-9, wherein said current values range is about 20 Amps to 500 amps, leaving water temperature values range is about 39 F (Fahrenheit) to 85 F, first liquid refrigerant temperature values range is about 70 F to 120 F and second liquid refrigerant temperature values range is about 20 F to 70 F.

11. The method as claimed in any of the preceding claims 1-10, wherein said third group of parameter values include a saturated liquid pressure value and a current correction value.

12. The method as claimed in any of the preceding claims 1-11, wherein said fourth group of parameter values include suction and discharge superheat values.

13. A system for operating a flooded-type chiller without pressure transducers, said system comprising:
a memory configured to store a pre-defined suction pressure values range and a pre-defined discharge pressure values range, after start of a compressor;
a plurality of sensors, positioned in the flooded-type chiller, configured for sensing a plurality of first and a second group of parameter values; and
a controller in communication with plurality of sensors and said memory, controller configured to:
receive the measured values of the plurality first group of parameters,
calculate a plurality of third group of parameter values based the measured values of the plurality first group of parameters,
determine a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values,
look-up said stored pre-defined pressure values range and pre-defined discharge pressure values range from the memory,
compare said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range,
control and maintain, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.

14. The system as claimed in claim 13, wherein said controller is further configured to:
calculate a plurality of fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values for determining an oil carryover condition or an entry of liquid refrigerant in said compressor.

15. The system as claimed in any of the preceding claims 13-14, wherein said controller is in communication with at least one processor for processing a fuzzy logic that controls operation of said flooded-type chiller.
, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)

&

THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

METHOD OF OPERATING FLOODED-TYPE CHILLER AND SYSTEM THEREOF

BLUE STAR LIMITED A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANI CHOWK, JAMSHETJI TATA ROAD, MUMBAI – 400 020, MAHARASHTRA, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
TECHNICAL FIELD OF THE INVENTION
[001] The present invention relates to a method and a system for operating a flooded-type chiller.

BACKGROUND OF THE INVENTION
[002] Chillers are used to chill water in an evaporator. Chillers are majorly classified into two types namely air-cooled chillers and water-cooled chillers. In air-cooled chiller, chiller water may pass through air handling units which conditions the air for use in a building, mall etc. In a water-cooled chiller, temperature of water is controlled by heat exchange with refrigerant. Water-cooled chillers may further be classified into flooded type or direct expansion type chillers.
[003] Referring Figure 1 shows the refrigerant circuit of a conventional flooded water-cooled chiller (100). Flooded type chillers are the chillers in which evaporator (140) is a shell and tube heat exchanger (130) wherein refrigerant is on the shell side of the evaporator and water/fluid to be cooled is on the tube side of the evaporator. The refrigerant circulates throughout the chiller system by means of a refrigerant loop. In a flooded type chiller system, a compressor (110) compresses a low-pressure refrigerant gas into a high-pressure refrigerant vapour. An oil separator (120) receives the high-pressure refrigerant vapour where oil gets separated and high-pressure refrigerant vapour is again returned to the compressor through solenoid valve SV2. A condenser (130) receives the high-pressure refrigerant vapour where it is converted into high pressure refrigerant liquid by heat exchange with water. The high-pressure refrigerant liquid refrigerant from the condenser passes through an expansion device (150), thereby lowering the pressure of the refrigerant liquid before reaching an evaporator. Low pressure refrigerant liquid enters an evaporator (140) where heat exchange with water causes it to become a low-pressure refrigerant vapour. The evaporator vaporizes the liquid refrigerant in shell and returns to a suction inlet of the compressor to repeat the process. Separated oil is returned back to the compressor through the oil return line.
[004] It is desired to calculate suction and discharge superheats in the chiller system using suction and discharge pressures thereby identifying if there is a condition of liquid refrigerant entering the compressor, or if an oil carryover condition has occurred.
[005] Conventionally, in order to safeguard chiller from suction or discharge pressures above threshold ranges, there is provided a ON/OFF pressure switch that directly shuts down the compressor, without giving any opportunity to the controller to carry out further actions. Therefore, in such systems, the values of suction, discharge, oil pressures and superheat values remain unknown and there are no means to identify any oil carryover condition.
[006] Nowadays, chiller systems are configured with pressure transducers that determine above said parameters. However, employment of such pressure transducers increases the cost of the chiller systems and serviceability of such systems is also a limitation.
[007] Therefore, there is a need to overcome one or more abovementioned drawbacks.

SUMMARY OF THE INVENTION
[008] Accordingly, an aspect of the present invention discloses a method of operating a flooded-type chiller without pressure transducers, the method comprising the steps of storing, by a controller, a pre-defined suction pressure values range and a pre-defined discharge pressure values range in a memory, after start of a compressor; sensing and determining, by the controller in communication with a plurality of sensors, a plurality of first and a second group of parameter values, said plurality of sensors positioned in the flooded-type chiller; calculating, by a controller, a plurality of third group of parameter values using the measured values of the plurality first group of parameters; determining, by the controller, a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values; comparing, by the controller, said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range; and controlling and maintaining, by the controller, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[009] According to an embodiment, the method further comprises a step of calculating, by the controller, a plurality of fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values.
[0010] According to the embodiment, based on calculated fourth group of parameters values an oil carryover condition or an entry of liquid refrigerant in said compressor is determined by the controller.
[0011] According to the embodiment, the step of controlling and maintaining, said flooded-type chiller within predefined pressure values range includes invoking, by said controller, said control signal for loading/unloading of said flooded-type chiller and / or for opening/closing an electronic expansion valve of said flooded-type chiller, when determined virtual suction and virtual discharge pressure values are above / below said stored pre-defined pressure values range and pre-defined discharge pressure values range.
[0012] According to the embodiment, the method further comprises a step of monitoring, the controller, operation of the flooded-type chiller at a pre-defined interval.
[0013] According to the embodiment, the pre-defined suction pressure values are in the range of 20 PSIG to 60 PSIG (pounds per square in gauge).
[0014] According to the embodiment, the pre-defined discharge and oil pressures values are in the range of 70 PSIG to 270 PSIG (pounds per square in gauge).
[0015] According to the embodiment, the plurality of said first group of parameters values include a leaving water temperature value, a first liquid refrigerant temperature value and a current value.
[0016] According to the embodiment, the plurality of said second group of parameter values include a second liquid refrigerant temperature value and a current value.
[0017] According to the embodiment, said current values range is about 20 Amps to 500 amps, leaving water temperature values range is about 39 F (Fahrenheit) to 85 F, first liquid refrigerant temperature values range is about 70 F to 120 F and second liquid refrigerant temperature values range is about 20 F to 70 F.
[0018] According to the embodiment, the third group of parameter values include a saturated liquid pressure value and a current correction value.
[0019] According to the embodiment, the fourth group of parameter values include suction and discharge superheat values.
[0020] According to another aspect, the present invention discloses a system for operating a flooded-type chiller without pressure transducers, said system comprising a memory configured to store a pre-defined suction pressure values range and a pre-defined discharge pressure values range, after start of a compressor; a plurality of sensors, positioned in the flooded-type chiller, configured for sensing a plurality of first and a second group of parameter values; and a controller in communication with plurality of sensors and said memory, controller configured to: receive the measured values of the plurality first group of parameters; calculate a plurality of third group of parameter values based the measured values of the plurality first group of parameters, determine a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values, look-up said stored pre-defined pressure values range and pre-defined discharge pressure values range from the memory, compare said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range, control and maintain, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[0021] According to the embodiment, the controller is further configured to: calculate a plurality of fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values for determining an oil carryover condition or an entry of liquid refrigerant in said compressor.
[0022] According to the embodiment, the controller is in communication with at least one processor for processing a fuzzy logic that controls operation of said flooded-type chiller.

BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 shows a system diagram of the refrigerant circuit of a standard flooded water-cooled chiller, according to conventional prior art;
Figure 2 shows the controller of the chiller for determining virtual suction pressure value, according to an embodiment of the present invention;
Figure 3 shows the controller of the chiller for determining virtual discharge pressure, according to the embodiment of the present invention;
Figure 4 shows a flow chart of a method operating a flooded-type chiller without pressure transducers, according to another aspect of the present invention;
Figure 5 illustrates a graph representing a comparison between actual and virtual suction pressure, according to the embodiment of the present invention; and
Figure 6 illustrates a graph representing a comparison between actual and virtual discharge pressure, according to the embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE INVENTION
[0023] In general, the present invention provides a method operating a flooded-type chiller without pressure transducers, the flooded-type chiller having at least one compressor, a condenser, an expansion valve EXV, and an evaporator. According to an aspect, a memory is configured to store a pre-defined suction pressure values range and a pre-defined discharge pressure values range, after start of a compressor; a plurality of sensors are positioned in the flooded-type chiller, configured for sensing a plurality of first and a second group of parameter values; and a controller in communication with plurality of sensors and said memory is configured to: receive the measured values of the plurality first group of parameters; calculate a plurality of third group of parameter values based the measured values of the plurality first group of parameters, determine a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values, look-up said stored pre-defined pressure values range and pre-defined discharge pressure values range from the memory, compare said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range, control and maintain, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[0024] According to the present invention, the flow of refrigerant (liquid or gas) through the expansion valve is dependent upon the pressures in the condenser and the evaporator and on the geometry and positioning of the valve. Ideally, the valve is positioned such that the resistance to fluid flow in the expansion device matches that required to optimize the flow to the evaporator. Further, the refrigerant circuit may include one or more processor and a plurality of sensors which are positioned at various components in the circuit. The processor and the sensors are operatively coupled to retrieve various parameter information for processing.
[0025] According to the present invention, the first group of parameter values include but not limited to a leaving water temperature value, a second liquid refrigerant temperature value and a current value. The leaving water temperature value is the water temperature value measured at the outlet of the evaporator, the second liquid refrigerant temperature value is the refrigerant temperature value measured after the expansion device and before the evaporator, and the current value is the input current value to the compressor measured with the help of a current transformer.
[0026] According to the present invention, the second group of parameter values include but not limited to a first liquid refrigerant temperature value and a current value. The first liquid refrigerant temperature value is the refrigerant temperature value measured after the condenser and before the expansion device.
[0027] According to the embodiment, the range of first and second parameter is provided as follows:
Parameter Range
Amps 20 Amps to 500 Amps
LWT 39 F to 85 F
Liqd Tmp 1 70 F to 120 F
Liqd Tmp 2 20 F to 70 F
[0028] According to the present invention, the third group of parameter values include but not limited to a saturated liquid pressure value and a current correction value. Saturated liquid pressure is obtained by standard refrigeration charts. It is saturated pressure value corresponding to the second liquid temperature value.
[0029] The current correction value is determined by the equation:
AMPS Corr=C1*AMPS/LWT
Where,
C1- A constant value dependent of the Capacity (in TR) of the chiller system in the range of 1-3;
AMPS - The running Current (in Amps);
LWT - Water Temperature value measured at the outlet of the evaporator.
[0030] According to the aspect of the present invention, the controller determines a virtual suction and discharge pressure value as a control signal based on said third and second group of parameter values. The controller, then compares determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range in the memory. Based on determined virtual suction and discharge pressure values the controller controls and maintains the flooded-type chiller within pre-defined pressure values range and pre-defined discharge pressure values range.
[0031] The virtual suction pressure (Vr SP) is determined based on third group of parameter values and is given by the following equation:
VrSP =Sat LP - AMPS Corr
The virtual discharge pressure value (Vr DP) is determined based on second group of parameter values and is given by the following equation:
Vr DP =AMPS/C2+Liq Tmp1/C3
Where,
C2 - Constant value dependent of the Capacity (in TR) of the chiller system in the range of 2 to 4;
C3 – Constant – 1.2;
AMPS - The running Current (in Amps); and
LIQ TMP1 – First liquid refrigerant temperature at input of the expansion valve.
[0032] According to the embodiment, the controller calculates a fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values. The fourth group of parameter values include but not limited to suction and discharge superheat values which enables to determine an oil carryover condition or an entry of liquid refrigerant in a compressor.
[0033] According to the embodiment, the refrigerant in the chiller includes but not limited to R134a.
[0034] According to the embodiment, the pre-defined suction pressure values are in the range of 20 PSIG to 60 PSIG (pounds per square in gauge).
[0035] According to the embodiment, the pre-defined discharge and oil pressures values are in the range of 70 PSIG to 270 PSIG (pounds per square in gauge).
[0036] According to another aspect, the present invention discloses, a system for operating a flooded-type chiller without pressure transducers, said system comprising a memory configured to store a pre-defined suction pressure values range and a pre-defined discharge pressure values range, after start of a compressor; a plurality of sensors, positioned in the flooded-type chiller, configured for sensing a plurality of first and a second group of parameter values; and a controller in communication with plurality of sensors and said memory, controller configured to: receive the measured values of the plurality first group of parameters; calculate a plurality of third group of parameter values based the measured values of the plurality first group of parameters, determine a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values, look-up said stored pre-defined pressure values range and pre-defined discharge pressure values range from the memory, compare said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range, control and maintain, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[0037] According to the embodiment, controller is further configured to calculate a plurality of fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values for determining an oil carryover condition or an entry of liquid refrigerant in said compressor.
[0038] According to the embodiment, controller is in communication with at least one processor for processing a fuzzy logic that controls operation of said flooded-type chiller.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Figures discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged environment. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise.
[0039] Referring Figure 2 shows the controller of the chiller (200), according to one embodiment of the present invention. The controller (210) may include but not limited to at least one processor, in communication with a memory and said plurality of sensors positioned at various components of the system. Further, the controller is in communication with an input device to input by a user a pre-defined suction pressure values range and a pre-defined discharge pressure values range. The input values are stored in the memory. The chiller controller (210) may retrieve using plurality of sensors, at least a first group of parameters information values from compressor and evaporator but not limited to a leaving water temperature value (220), a second liquid refrigerant temperature value (230) and a current value (240). The leaving water temperature value is the water temperature measured at the outlet of the evaporator, the second liquid refrigerant temperature value is the refrigerant temperature measured after the expansion device and before the evaporator, and the current value is the input current to the compressor measured with the help of a current transformer.
[0040] Based on the information values obtained from first group of parameters as an input to the chiller controller, the controller is capable of calculating third group of parameter values that include but not limited to a saturated liquid pressure value and current correction value. Saturated liquid pressure value is obtained by standard refrigeration charts. It is saturated pressure value corresponding to the second liquid temperature value.
[0041] According to the aspect of the present invention, the controller determines a virtual suction pressure value as a control signal based on said third group of parameter values, thereby operate to maintain the flooded-type chiller within a pre-defined suction pressure range.
[0042] Referring Figure 3 shows the controller of the chiller (300), according to the embodiment of the present invention. The chiller controller (310) may further retrieve at least a second group of parameter information values corresponding to a first liquid refrigerant temperature value (320) and a current value (330). The first liquid refrigerant temperature value is the refrigerant temperature value measured after the condenser and before the expansion device.
[0043] Based on the information values obtained from second group of parameters as an input to the chiller controller, the controller is capable of calculating a virtual discharge pressure value as a control signal, thereby operate to maintain the flooded-type chiller within a pre-defined suction discharge range.
[0044] According to the aspect of the present invention, the controller looks-up stored pre-defined pressure values range and pre-defined discharge pressure values range from the memory, compares said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range, controls and maintains, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[0045] Referring Figure 4 shows a flow chart of a method (400) operating a flooded-type chiller without pressure transducers, according to another aspect of the present invention. The method comprising the steps of (410) storing, by a controller, a pre-defined suction pressure values range and a pre-defined discharge pressure values range in a memory, after start of a compressor. The method includes the steps of (420) sensing and determining, by the controller in communication with a plurality of sensors, a plurality of first and a second group of parameter values, said plurality of sensors positioned in the flooded-type chiller. The method includes (430) calculating, by a controller, a plurality of third group of parameter values using the measured values of the plurality first group of parameters. (440) The method includes determining, by the controller, a virtual suction and a virtual discharge pressure value as a control signal based on said calculated third and second group of parameter values. (450) The method includes comparing, by the controller, said determined virtual suction and discharge pressure values with said stored pre-defined pressure values range and pre-defined discharge pressure values range. (460). The method includes controlling and maintaining, by the controller, said flooded-type chiller within said stored pre-defined pressure values range and pre-defined discharge pressure values range based on said determined virtual suction and virtual discharge pressure values.
[0046] According to an embodiment, the method further comprises a step of monitoring the operation of the flooded-type chiller at a pre-defined interval.
[0047] In said embodiment, the pre-defined suction pressure is in the range of 20 PSIG to 60 PSIG (Pounds per square in gauge).
[0048] In said embodiment, the pre-defined discharge and oil pressures are in the range of 70 PSIG to 270 PSIG (Pounds per square in gauge).
[0049] Further, according to the aspect of the invention, the method further comprises a step of calculating a fourth group of parameters values based on said determined virtual suction and virtual discharge pressure values.
[0050] In said embodiment, based on calculated fourth group of parameters values an oil carryover condition or an entry of liquid refrigerant in a compressor is determined.
[0051] According to the embodiment, the step of maintaining said flooded-type chiller within predefined pressure ranges includes invoking said control signal for loading/unloading of said flooded-type chiller; and/or for opening/closing an electronic expansion valve of said flooded-type chiller, when determined virtual suction and virtual discharge pressure values are above / below said predefined pressure ranges.
[0052] Even though no pressure transducers are in the chiller of the present invention, suction and discharge pressures are calculated virtually. The chiller of the present invention operates normally and on par in a similar manner like a chiller with pressure transducers installed. The safety and operating controls of the chiller are based on virtual pressures.
[0053] According to the present invention, the cost of the present chiller is less than that of the chiller with pressure transducer and pressure switch and there is no compromise on serviceability as the value of pressures is still available.

Example 1
[0054] A Chiller is installed with an external suction and discharge pressure transducer to measure an actual pressure. Then, the pressure transducer is disabled, and virtual suction and virtual discharge pressures are tested according to the aspect disclosed in the present invention. A 110 ton of refrigeration chiller with a R314a refrigerant is used in this experiment to measure the virtual suction and virtual discharge pressures. Chillers with the transducer and without the transducer are continuously run for a period of 16 hours.
[0055] Referring figure 5 illustrates a graph representing the comparison between actual suction pressures measured according to the embodiment of the present invention. As seen from the figure 5, Point (A) shows the chiller in standby mode up to Point (B). Point (B) indicates the START of the compressor and point (C) indicates STOP of the compressor. It has been observed that the maximum error value obtained when virtual suction pressure is compared with the actual suction pressure value obtained using sensor during the standby mode is of 5 PSIG. Further, it has been observed that the maximum error value obtained when virtual suction pressure is compared with the actual suction pressure value obtained using sensor during the running mode after START and before STOP of the compressor is of 3.3 PSIG. Thus, the results show that the virtual suction and the actual suction pressure are very close to each other. The difference between both is maximum of 5 PSIG. This 5 PSIG in turn converts to 2.5% error of full scale, which is 200 PSIG in the experiment. Hence, it may be concluded that general accuracy of a pressure transducer used in a Chiller has an accuracy of +2.5% of the full scale. Therefore, the test results show that virtual suction pressure can be used in place of actual suction pressure sensors. This will enable to save costs as well as it will have better control than an Open-Closed type-high pressure /low pressure switch which can only show whether the suction pressure is healthy or unhealthy and cannot show the value of suction pressures.
[0056] Referring figure 6 illustrates a graph representing the comparison between actual discharge pressures measured according to the embodiment of the present invention. As seen from the figure 6, Point (A) shows the chiller in standby mode up to Point (B). Point (B) indicates the START of the compressor and point (C) indicates STOP of the compressor. It has been observed that the maximum error value obtained when virtual discharge pressure is compared with the actual discharge pressure value obtained using sensor during the standby mode is of 4.9 PSIG. Further, it has been observed that the maximum error value obtained when virtual discharge pressure is compared with the actual discharge pressure value obtained using sensor during the running mode after START and before STOP of the compressor is of 5 PSIG. Thus, the results show that the virtual discharge and the actual discharge pressure are very close to each other. The difference between both is maximum of 5 PSIG. This 5 PSIG in turn converts to 2.5% error of full scale, which is 200 PSIG in the experiment. Hence, it may be concluded that general accuracy of a pressure transducer used in a Chiller has an accuracy of +2.5% of the full scale. Therefore, the test results show that virtual discharge pressure can be used in place of actual discharge pressure sensors. This will enable to save costs as well as it will have better control than an Open-Closed type-high pressure /low pressure switch which can only show whether the discharge pressure is healthy or unhealthy and cannot show the value of discharge pressures.
[0057] The present invention has been described in the context of a control logic for operating a flooded-type chiller system, thereby maintaining chiller within a pre-defined suction and a discharge pressure range based on the logic determined virtual suction and virtual discharge pressure values. However, the control logic of the present invention can be used in any type of chiller. To use the control logic in other types of refrigeration systems, some changes may have to be made to the membership functions and the sensor information that is used by the control logic to account for the particular configuration of the system to which the control logic is being applied.
[0058] In the foregoing detailed description of aspects embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of aspects, embodiments of the invention, with each claim standing on its own as a separate embodiment.
[0059] It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” is used as the plain-English equivalent of the respective term “comprising” respectively.
NOMENCLATURE
TR- Ton of Refrigeration
EXV- Electronic Expansion Valve
EXV Mult- EXV Multiplier
AmpCorr - Amps Correction
AMPS-CURRENT
SV: Solenoid Valve
SP: Suction Pressure
Vr SP - Virtual Suction Pressure
DP: Discharge Pressure
Vr DP - Virtual Discharge Pressure
LWT-Leaving Water Temperature
Liq Tmp 1 -First Liquid Refrigerant Temperature
Liq Tmp 2 -Second Liquid Refrigerant Temperature
DSH- Discharge Superheat
SSH- Suction Superheat
F- Fahrenheit