FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A CHILLER SYSTEM AND A METHOD FOR CONTROLLING OPERATION OF A CHILLER SYSTEM;
BLUE STAR LIMITED A COMPANY
INCORPORATED UNDER THE
COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVAN) CHOWK, JAMSHETJl TATA ROAD, MUMBAI - 400 020, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION PARTICULARLY , DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF INVENTION
This invention relates to a chiller system. Particularly, the present invention relates to a chiller control system for controlling the operation of a chiller system in order to reduce oil carryover in the chiller system and a method for controlling chiller system to reduce oil carryover.
BACKGROUND AND PRIOR ART
Typically, a chiller system comprises a compressor to compress gaseous refrigerant, a condenser in which compressed gas from the compressor liquefies, an evaporator in which the liquid refrigerant evaporates prior to returning to the compressor and chilled the chilling liquid, and an adjustably controllable expansion valve connected in the liquid refrigerant supply line from the condenser to the evaporator. Such chilling system also usually comprises control means or system to adjust/modulate the expansion valve so as to control liquid refrigerant level in the evaporator for cooling efficiency while preventing possibly damaging flow of liquid refrigerant to the compressor. In order to improve the efficiency of operation of the refrigeration system, several different types of control systems have been developed.
In order to help maintain proper operation of the evaporator and the compressors, the refrigerant before leaving the evaporator must be fully converted into a gaseous

state. If the refrigerant is not fully converted into a gaseous state, but remains at least partially liquefied status, this liquid refrigerant while discharging from the compressor, causes oil carryover and this may result in severe damage to the compressor. Generally, the expansion valve operation is based on the liquid refrigerant level in the flooded type evaporator. The refrigerant level inside the evaporator is controlled by opening and closing of the expansion valve with the help of the level sensor. More specifically, under normal running condition, the liquid level controller maintains a pool of liquid in the bottom of the evaporator. A liquid level sensor measures the level of refrigerant in evaporator and affects the rate of refrigerant flow into the evaporator by controlling the opening and closing of the expansion valve. During this modulation, sometimes due to delay in response time or due to operating conditions beyond the design of controller causes flooding of the evaporator or entering of the liquid refrigerant in the compressor which results in carryover of oil in the compressor. If the refrigerant leaving the evaporator does not vaporize completely, oil from the compressor starts to move from oil separator of compressor and gets accumulated in the evaporator shell side. That promotes foaming and more liquid carryover, increasing the liquid refrigerant concentration in oil separator (inbuilt in compressor, or condenser or external in system) there by reducing the separator effectiveness. Reduction in oil separator efficiency, increase the concentration of refrigerant in oil which is in turn further increases the amount of oil in evaporator and ultimately reduced the refrigerant system efficiency and later reduce the supply of oil to compressor. This will reduce the life of compressor parts in certain condition.

Therefore, there is need of a chiller system which will solve at least one of the above discussed problems.
SUMMARY OF THE INVENTION
Accordingly, the present invention in first aspect provides a chiller system, comprising a compressor to compress gaseous refrigerant, a condenser supplied with compressed gas from the compressor to liquefy the compressed gas, an evaporator for chilling liquid, said evaporator having inlet port for receiving liquid refrigerant and outlet port for supplying vaporized refrigerant to the compressor, an expansion device connected between the condenser and the evaporator, said expansion device having an electronic expansion valve and an orifice adapted parallelly defining total flow across the expansion device, and a control means to adjust the expansion valve and ON/OFF the orifice based on discharge superheat of the refrigerant at compressor or refrigerant level in the evaporator. According to the present invention the controller being responsive to a decrease in the superheat of the refrigerant effect closes the orifice first before modulation of the electronic expansion valve in order to reduce superheat conditions to said predetermined value of superheat.
In second aspect, the present invention provides a method for controlling operation of a chiller system having an evaporator, a compressor, a condenser, an expansion device arranged in series, wherein said expansion device comprises an electronic expansion valve and an orifice adapted parallelly between the condenser and the evaporator of the refrigeration system. The said method comprises the steps of monitoring discharge superheat of compressed refrigerant, adjusting both the

expansion valve and the orifice to maintain predetermined level of refrigerant in evaporator, closing the orifice first before modulating the electronic expansion valve when the discharge superheat of refrigerant falls below a predetermined set point to raise the superheat above the said set point.
In third aspect, the present invention provides a controller system for a chiller system having a compressor, a condenser, an evaporator device, and an electronic expansion valve, said controller system comprising an orifice adapted parallelly to the expansion valve of the chiller system between the condenser and evaporator; means for measuring suction temperature and discharge temperature of the refrigerant at inlet and outlet of the compressor; means for measuring suction pressure and discharge pressure of said refrigerant at inlet and outlet of the compressor; means for calculating and monitoring discharge superheat continuously for adjusting the electronic expansion valve and ON/OFF the orifice and means for measuring liquid level in the evaporator for interrupting. The control system closes the orifice first before modulating of the electronic expansion valve based on superheat condition at the compressor or refrigerant level in the evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, aspects and other advantages of the present invention will become better understood when the following description is read with reference to the accompanying drawings, wherein:
Figure 1 shows a schematic flow diagram of a chiller system according to the present invention;

Figure 2 shows a schematic view of an expansion device according to the present invention; and
Figure 3 shows a flow chart of method of operation of the chiller system according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring Figures 1 and 2 show a preferred embodiment of a chiller system (100) according to the present invention. The chiller system (100) comprises a compressor (120), a condenser (110), an evaporator device (130), and an electronic expansion valve (142), arranged in series and a controller (160) for controlling operation of the chiller system (100). The expansion device (140) according to the present invention comprises an electronic expansion valve (142) and an orifice (144) adapted parallelly connecting the condenser (110) and an inlet port of the evaporator (130). The electronic expansion valve (142) and the orifice (144) define total flow across the expansion device and. According to preferable embodiment of the invention, the ratio of flow through the orifice (144) and the electronic expansion valve (142) generally depends upon the capacity of the chiller system. Advantageously, the ratio of the flow between the orifice (144) and the electronic expansion valve (142) can be varied between 10:90 and 20:80. According to the preferred embodiment of the invention the preferable ratio is 15:85. The orifice (144) is operated by solenoid valve between ON and OFF position. The evaporator (130) shown in the Figure 1 is a shell and tube type evaporator with flooded type of system. Generally, the refrigerant in on shell side and water is on tube side in evaporator in flooded type system. A line connects the evaporator (130)

flooded type as shown Figure 1 to the compressor (120) is called as suction line passing vaporized refrigerant from the evaporator to the compressor (120) where the vapour is then compressed and discharged to condenser,(110) via a line called as discharge line with a valve (not shown) and non-return valve (not shown) too. According to the preferred embodiment, the controller (160) controls the system (100) based on the discharge superheat of the refrigerant and/or refrigerant level in the evaporator. Accordingly, suction temperature sensor (ST), discharge temperature sensor (DT), pressure transducer (SP) to measure suction pressure and pressure transducer (DP) to measure discharge pressure are provided at inlet and outlet of the compressor (120) for providing suction and discharge temperatures and pressures to the controller (160). The saturated suction and discharge temperature (ST, DT) is calculated by the controller (160) based on pressure and temperature chart of the refrigerant used. Accordingly, the controller calculates the discharge superheat from the difference between the discharge temperature (ST) and saturated discharge temperature (DT). According to the present invention, temperature sensors (T1, T2) are also provided to measure temperatures of chilling liquid at the inlet and outlet of the evaporator (130) and provide to the controller (160) to control the chiller system (100). Temperature sensors (T3, T4) are also provided to measure the inlet and outlet temperature of refrigerant in the condenser (110) and provide to the controller (160) to control the chiller system (100).
The refrigerant compressed in the compressor (120) is cooled in the condenser (110) which then enters in the electronic expansion valve (142) & orifice (144) at a high-pressure. The refrigerant flow is restricted by the orifice (144) and the

electronic expansion valve (142). As the refrigerant passes through the orifice (144) and the electronic expansion valve (142), refrigerant pressure changes from a high-pressure liquid to a low-pressure liquid.
As shown in Figure 1, the inlet and outlet for electronic expansion valve (142) & orifice (144) are connected in parallel in circuit.
According to the present invention the controller monitors the discharge superheat in real time to control the chiller system. In normal operation, the orifice (144) and the electronic expansion valve (142) operate to maintain the refrigerant level to the predetermined set level. Referring to Figure 3 along with Figure 1, when the discharge superheat starts decreasing and goes below the predetermined set point, the controller monitors the condition for predetermined time period preferably one minute. If the discharge superheat goes above the set point within the predetermined time period, the system works normal along with electronic expansion valve (142) and orifice (144) works as per feedback from level sensor. If discharge superheat decreases and goes below the predetermined set point more than the predetermined time period, according to the present invention the controller (160) closes the orifice (144) immediately lowering the chillers capacity till for a predetermined time period. If discharge superheat increases higher than the set point or minimum possible unloading of the unit compressor (120), the controller opens the orifice (144).
If even after closing the orifice (144), the discharge superheat lowers than the set point or fails to raise the superheat above the set point, the controller starts modulating the expansion valve till the expansion valve reaches to its minimum position or discharge superheat start increases more than the set point.

According to the present invention, if the discharge superheat fails to increase more than the set point within the time duration specified in the controller even after closing and orifice (144) and the expansion valve reaches to its minimum position, the chiller system (100) trips.
According to the present invention, a level sensor (not shown) is also mounted on the evaporator (130). The level sensor passes the analogue signal to the controller (160) by measuring the refrigerant level present in the evaporator. The controller compares this measured level with predetermined set level and if the level is above the set level, it trips the chiller system (100).
The controller of the present invention can be used to upgrade the controller of the present chiller system by minor modifications in the system such as providing an orifice operated by solenoid valve and means to measure temperatures and pressures at compressor and level measuring means at the evaporator. The present invention helps to reduce the liquid refrigerant level fast by cycling of orifice as compared to modulation of expansion valve. The present invention protects the chiller system from flooding of evaporator due to malfunctioning of the expansion valve, overcharge by limiting the tripping of high refrigerant level. The present invention also help to reduce the de-rating of the compressor parts caused due to poor lubrication caused due to liquid flood back. The present invention will help to operate the refrigeration system as lower capacity than required to reduce the oil carry over.
The forgoing description of the invention has been described for purpose of clarity and understanding. In practicing the invention, the set point of discharge superheat and predetermined time period can be set depending upon the

requirement and the capacity of the chiller. Further, chiller circuit may comprise of other well known parts such as valves, receiver between condenser and evaporator, driers between condenser and evaporator which are not discussed herein above as they are well known and a person skilled in the art can easily understand, and hence It is not intended to limit the invention to the precise from disclosed. Furthers, means for measuring pressures and temperatures are very well known and hence not require to describe in detail. Various modifications may be possible within the scope and equivalence of the appended claims:

WE CLAIM:
1. A chiller system, comprising:
a compressor to compress gaseous refrigerant;
a condenser supplied with compressed gas from the compressor to liquefy the
compressed gas;
an evaporator for chilling liquid, said evaporator having inlet port for receiving
liquid refrigerant and outlet port for supplying vaporized refrigerant to the
compressor;
an expansion device connected between condense and the evaporator, said
expansion device having an electronic expansion value and an orifice adapted
parallelly defining total flow across the expansion device; and
a control means to adjust the expansion valve and ON/OFF the orifice based on
discharge superheat of the refrigerant at compressor or refrigerant level in the
evaporator.
2. The refrigeration system as claimed in claim 1, wherein ratio of flow through the orifice and electronic expansion valve depends upon capacity of the chiller system.
3. The refrigeration system as claimed in claim 1, wherein ratio of flow through the orifice and electronic expansion valve is between 10:90 and 20:80 and preferably the ratio is 15:85.

4. The refrigeration system as claimed in claim 1, wherein the evaporator is flooded type shell and tube evaporator.
5. The refrigeration system as claimed in claim 1 wherein the controller comprises:
a. means for measuring suction temperature and discharge temperature of the
refrigerant at inlet and outlet of the compressor;
b. means for measuring suction pressure and discharge pressure of said
refrigerant at inlet and outlet of the compressor;
c. means for calculating and monitoring discharge superheat continuously for
adjusting the electronic expansion valve and ON/OFF the orifice and
d. means for measuring liquid level in the evaporator for interrupting.
6. The system as claimed in one of the claim 1 or 5 wherein the controller being responsive closes the orifice first before modulation of the electronic expansion valve in order to gain superheat conditions to said predetermined value of superheat.
7. A method for controlling operation of a chiller system having an evaporator, a compressor, a condenser, an expansion device arranged in series, wherein said expansion device comprises an electronic expansion valve and an orifice adapted parallelly between condenser and evaporator of the refrigeration system, said method comprising steps of:
monitoring discharge superheat of compressed refrigerant;

adjusting both the expansion valve and the orifice to maintain predetermined level of refrigerant in evaporator;
closing the orifice first before modulating of the electronic expansion valve when the discharge superheat of refrigerant falls below a predetermined set point to raise the superheat above the said set point.
8. The method as claimed in claim 7 further comprises a step of modulating expansion valve step by step to increase to raise the superheat above the said set point if the superheat is below the said predetermined set point even after the closing of the orifice.
9. The method as claimed in claim 8 further comprises a step of interrupting operation of the refrigeration system if the superheat is still lower than the predetermined set point even after closing the orifice and expansion valve.
10. The method as claimed in the claim 7 wherein the step of monitoring discharge superheat of compressed refrigerant includes step of:
a. measuring suction temperature and discharge temperature of the refrigerant
at inlet and outlet of the compressor;
b. measuring suction pressure and discharge pressure of said refrigerant at
inlet and outlet of the compressor; and
c. calculating and monitoring discharge superheat continuously for adjusting
the electronic expansion valve and ON/OFF the orifice.

11. A controller system for a chiller system having a compressor, a condenser, an evaporator device, and an electronic expansion valve, said controller system comprising:
an orifice adapted parallelly to the expansion valve of the chiller system between the condenser and evaporator;
means for measuring suction temperature and discharge temperature of the refrigerant at inlet and outlet of the compressor;
means for measuring suction pressure and discharge pressure of said refrigerant at inlet and outlet of the compressor;
means for calculating and monitoring discharge superheat continuously for adjusting the electronic expansion valve and ON/OFF the orifice and means for measuring liquid level in the evaporator for interrupting; wherein the control system closes the orifice first before modulating of the electronic expansion valve based on superheat condition at the compressor or refrigerant level in the evaporator.