Claims:We Claim :
1. A refrigeration system of a chiller, comprising:
a flooded evaporator filled with a refrigerant fluid;
a level control system connected to the flooded evaporator, the level control system having:
a probe;
first and second stoppers mounted at first and second predefined heights on the probe; and
a movable float mounted between the first and second stoppers on the probe such that height of the float varies according to level of the refrigerant fluid in the flooded evaporator;
first and second contact switches connected to the level control system such that the first contact switch is closed when the movable float touches the first stopper and the second contact switch is closed when the movable float touches the second stopper;
an electronic expansion valve configured to control rate of flow of the refrigerant fluid in the flooded evaporator; and
a controller connected to the electronic expansion valve and the first and second contact switches, the controller configured to control operation of the electronic expansion valve to maintain a predefined level of the refrigerant fluid in the flooded evaporator based on the open or closed state of the first and second contact switches.

2. The refrigeration system as claimed in claim 1, wherein the first stopper is mounted at a high height and is indicative of a high level of the refrigerant fluid in the flooded evaporator, and wherein closing of the first contact switch indicates that the refrigerant level in the flooded evaporator is at the high level.

3. The refrigeration system as claimed in claim 2, wherein the second stopper is mounted at a low height and is indicative of a low level of the refrigerant fluid in the flooded evaporator, and wherein the closing of the second contact switch indicates that the refrigerant level in the flooded evaporator is at the low level.

4. The refrigeration system as claimed in claim 3, wherein the controller closes the electronic expansion valve when the first contact switch is closed and the controller opens the electronic expansion valve when the second contact switch is closed.

5. A method of controlling level of a refrigerant fluid in a flooded evaporator of a refrigeration system, said refrigeration system having an electronic expansion valve, first and second control switches, and a float switch, the method comprising:
determining the level of the refrigerant fluid in the flooded evaporator based on position of the float switch;
closing the first contact switch when the float switch reaches a first predefined height, said first predefined height indicative of a high level of the refrigerant fluid in the flooded evaporator;
closing the second contact switch when the float switch reaches a second predefined height; said second predefined height indicative of a low level of the refrigerant fluid in the flooded evaporator;
closing the electronic expansion valve when the first contact switch is closed, thereby decreasing the flow of the refrigerant fluid into the flooded evaporator; and
opening the electronic expansion valve when the second contact switch is closed, thereby increasing the flow of the refrigerant fluid into the flooded evaporator.
Dated this 17th day of November, 2016
FOR BLUE STAR LIMITED
By their Agent

(GIRISH VIJAYANAND SHETH) (IN/PA 1022)
KRISHNA & SAURASTRI ASSOCIATES LLP
, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

REFRIGERATION SYSTEM OF A CHILLER;


BLUE STAR LIMITED, A COMPANY INCORPORATED UNDER COMPANIES ACT 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANI CHOWK, JAMSHETJI TATA ROAD, MUMBAI-400020, MAHARASTRA, INDIA;

THE FOLLOWING SPECIFICATION PARICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

FIELD OF THE INVENTION
The present invention relates generally to refrigeration systems and particularly to a flooded evaporator refrigeration system for chillers.
BACKGROUND ART OF THE INVENTION
Refrigeration cycle utilized in typical Heating, Ventilation, and Air Conditioning (“HVAC”) systems is well-known. Specific components of a refrigeration system may differ based on performance specifications and system requirements. A refrigerant fluid is pumped through the refrigeration system to achieve heat transfer. Since the refrigeration system is a closed system, the same refrigerant fluid is reused to achieve more heat transfer in multiple refrigeration cycles. The refrigerant fluid is at different physical states (such as liquid and vapor), at different temperatures (such as hot or cool), and at different pressures (such as compressed or expanded) in different components of the refrigeration system.
A refrigeration system (100) for chillers, as shown in Figure 1, generally includes a condenser (102), a cooler (104), a compressor (106), an oil separator (108), and an electronic expansion valve (110). The electronic expansion valve (110) functions as a metering device and controls flow of the refrigerant fluid in the cooler (104). The refrigerant fluid is a low-pressure and low-temperature liquid when it enters the cooler (104). As the refrigerant fluid passes through the cooler/evaporator (104), it absorbs heat within the cooler (104) and turns into low-pressure and low-temperature vapor. This low-pressure and low-temperature vapor enters the compressor (106) through a suction line. In the compressor (106), the refrigerant fluid is compressed to form high-temperature and high-pressure vapor. This high-temperature and high-pressure vapor is passed through oil separator (108) which separates residual oil from the refrigerant fluid therein if the compressors are oil based compressors. Subsequently, the refrigerant fluid which is in form of high-temperature and high-pressure vapor enters the condenser (102) through a discharge line. At the condenser (102), the refrigerant fluid is condensed to form high-pressure and high-temperature liquid. This high-pressure and high-temperature liquid is fed to the electronic expansion valve (110). The electronic expansion valve (110) turns the refrigerant fluid into low-pressure and low-temperature liquid. Further, the electronic expansion valve (110) controls the rate of flow of the refrigerant fluid in to the cooler (104). Similarly, a subsequent refrigeration cycle starts when the refrigerant fluid which is in the form of low-pressure and low-temperature liquid enters the cooler (104) through the electronic expansion valve (110).
Typically, the most common form of cooler (104) used in water cooled chiller is a flooded evaporator wherein water flows through the tube and refrigerant is in the shell of the shell and tube heat exchanger. Presently, the refrigeration systems of water cooled chillers utilizing flooded evaporator measure discharge super heat and operate the electronic expansion valve based on the measured discharge super heat. However, this may lead to unstable operation and as there is no dead zone, high electronic expansion valve cycling may lead to reduction in life of the electronic expansion valve. Further, leak of refrigerant from the refrigeration system may lead to frequent tripping of the refrigeration system on low suction pressure. Moreover, when compressor is started, the discharge superheat is very unstable which causes frequent opening and closing of the electronic expansion valve which may lead to nuisance tripping of the refrigeration system on low suction pressure.
Therefore, there is a need of a low cost refrigeration control system that provides precise control and optimum performance of the refrigeration cycle, ensures a stable operation of the electronic expansion valve, and eliminates abnormal tripping of the refrigeration system on low suction pressure.

SUMMARY OF THE INVENTION
The objective of the present invention is to provide a refrigeration system with a flooded evaporator.
In an embodiment of the present invention, the present invention provides a refrigeration system for a chiller comprising a flooded evaporator, a level control system, first and second contact switches, an electronic expansion valve, and a controller. The flooded evaporator is filled with a refrigerant fluid. The level control system is connected to the flooded evaporator. The level control system includes a probe, first and second stoppers, and a movable float. The first and second stoppers are mounted at first and second predefined heights on the probe. The movable float is mounted between the first and second stoppers on the probe such that height of the float varies according to level of the refrigerant fluid in the flooded evaporator. The first and second contact switches are connected to the level control system such that the first contact switch is closed when the movable float touches the first stopper and the second contact switch is closed when the movable float touches the second stopper. The electronic expansion valve is configured to control rate of flow of the refrigerant fluid in the flooded evaporator to maintain a predefined level of the refrigerant fluid in the flooded evaporator based on the open or closed state of the first and second contact switches.
In another embodiment of the present invention, a method of controlling level of a refrigerant fluid in a flooded evaporator of a refrigeration system is provided. The refrigeration system has an electronic expansion valve, first and second control switches, and a float switch. The method includes determining the level of the refrigerant fluid in the flooded evaporator based on position of the float switch. The method further includes closing the first contact switch when the float switch reaches a first predefined height and closing the second contact switch when the float switch reaches a second predefined height. The first predefined height is indicative of a high level of the refrigerant fluid in the flooded evaporator and the second predefined height is indicative of a low level of the refrigerant fluid in the flooded evaporator. The method further includes opening the electronic expansion valve when the second contact switch is closed. This increases the flow of the refrigerant fluid into the flooded evaporator. Further, the electronic expansion valve is closed when the first contact switch is closed. This decreases the flow of the refrigerant fluid into the flooded evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments:
Figure 1 shows a conventional refrigeration system;
Figure 2 shows a level control system in accordance with an embodiment of the present invention;
Figure 3 shows a controller in accordance with an embodiment of the present invention;
Figure 4 shows operation of the level control system in accordance with an embodiment of the present invention; and
Figure 5 shows a method of controlling level of a refrigerant fluid in a flooded evaporator of a refrigeration system in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the invention selected for illustration in the drawings, and are not intended to define or limit the scope of the invention.
References in the specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, characteristics, or function, described in connection with the embodiment, is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
In general, the present invention provides a refrigeration system.
Referring Figure 2 shows a level control system (200) for a refrigeration system of the choiller in accordance with an embodiment of the present invention. The level control system (200) includes a probe (202), first and second stoppers (204a and 204b), a movable float (206), and control switches (208).
The level control system (200) is connected to a flooded evaporator (not shown) in a refrigeration system (not shown) of the chiller (not shown). The flooded evaporator is filled with a refrigerant fluid. Height of the movable float (206) on the probe (202) varies according to the change in level of the refrigerant fluid in the flooded evaporator. Specifically, the movable float (206) is at the same level as the level of the refrigeration fluid in the flooded evaporator.
The first stopper (204a) is mounted on the probe (202) at a first predefined height. The first predefined height is indicative of a high level of the refrigerant fluid in the flooded evaporator.
The second stopper (204b) is mounted on the probe (202) at a second predefined height. The second predefined height is indicative of a low level of the refrigerant fluid in the flooded evaporator.
The movable float (206) freely moves between the first and second stoppers (204a and 204b).
The control switches (208) include two contact switches C1 and C2. The contact switch C1 closes when the movable float (206) reaches the second stopper (204b). This indicates that the level of the refrigerant fluid in the flooded evaporator has reached the low level. The contact switch C2 closes when the movable float (206) reaches the first stopper (204a). This indicates that the level of the refrigerant fluid in the flooded evaporator has reached the high level.
The status of the control switches C1 and C2 is as shown below:-
Level of refrigerant fluid in the flooded evaporator C1 C2
Equal to or less than the low level Close Open
Between the low level and the high level Open Open
Equal to or higher than the high level Open Close

Table 1: Status of the control switches C1 and C2
In an example, the height of the probe (202) corresponding to the level of the refrigerant fluid in the flooded evaporator at which the refrigeration system performs optimally is taken as a reference level. The heights at which the first and second stoppers (204a and 204b) are mounted are calculated as follows:
Height of first stopper (204a) = reference level + X % of full length of the probe (202);
Height of second stopper (204a) = reference level - X % of full length of the probe (202);
Referring Figure 3 shows a controller (310) in accordance with an embodiment of the present invention. The controller (310) is connected to the control switches (208). As shown in the Figure 3, a 5V DC supply is provided to common terminal (C) of the control switches (208).
When the movable float (206) touches the second stopper (204b), contact M1 is turned ON. When the movable float (206) touches the first stopper (204a), contact M2 is turned ON.
Based on the status of the contacts M1 and M2, the controller (310) controls the operation of the electronic expansion valve.
During startup of the refrigeration system, the electronic expansion valve opens at a predefined level for a predefined time interval. After the predefined time interval, the electronic expansion valve is operated by the controller (310) to maintain the level of the refrigerant fluid in the flooded evaporator within a predefined range.
Accordingly, the controller (310) opens the electronic expansion valve when the contact M1 is ON and the controller (310) closes the electronic expansion valve when the contact M2 is ON. As a result, the electronic expansion valve increases the flow of the refrigerant fluid into the flooded evaporator when the level of the refrigerant fluid is at or below the low level and the electronic expansion valve decreases the flow of the refrigerant fluid into the flooded evaporator when the level of the refrigerant fluid is at or above the high level. When both M1 and M2 are OFF, the controller (310) operates the electronic expansion valve at a constant and stable rate. This maintains the level of the refrigerant fluid in the flooded evaporator within the predefined range, thereby ensuring stable and optimum operation of the refrigeration system and increasing the efficiency of the refrigeration system.
The operation of the electronic expansion valve, as controlled by the controller (310), is summarized as follows:

Level of refrigerant fluid in the flooded evaporator M1 M2 State of electronic expansion valve
Equal to or less than the low level ON OFF Open
Between the low level and the high level OFF OFF Hold
Equal to or higher than the high level OFF ON Close
Table 2: Status of the electronic expansion valve
Referring Figure 4 shows operation of the level control system (200) in accordance with an embodiment of the present invention.
Accordingly, the height of the second stopper (204b) corresponds to the low level of the refrigerant fluid in the flooded evaporator and the height of the first stopper (204a) corresponds to the high level of the refrigerant fluid in the flooded evaporator.
When the movable float (206) touches the first stopper (204a), the electronic expansion valve closes and when the movable float (206) touches the second stopper (204b), the electronic expansion valve opens. When the movable float (206) is between the first and second stoppers (204a and 204b), the expansions valve operates at a constant rate. Thus, the refrigeration system operates at a stable state when the movable float (206) is between the first and second stoppers (204a and 204b).
Additionally, when the discharge superheat of the refrigeration system reduces below a predefined temperature, the controller (310) closes the electronic expansion valve till the contact M1 turns ON, i.e. till the level of the refrigerant fluid in the flooded evaporator reaches the low level. If the discharge superheat is still below the predefined temperature, the controller (310) sets an alarm and the refrigeration system trips. This enables the refrigeration system to operate in low ambient conditions.
When the suction pressure of the refrigeration system reduces and reaches to a predefined low set-point, the controller (310) opens the electronic expansion valve till the contact M2 turns ON till the suction pressure becomes greater than the predefined low set-point. This enables the refrigeration system to operate when water flow reduces or refrigerant gas leaks in the refrigeration system.
Advantageously, the refrigeration system of the present invention reduces cost and increases efficiency of refrigeration. Further, the operation of the electronic expansion valve by the controller (310) stabilizes the refrigeration system.
Referring Figure 5 shows a method of controlling level of a refrigerant fluid in a flooded evaporator of a refrigeration system in accordance with an embodiment of the present invention.
At step 502, the controller (310) determines the level of the refrigerant fluid in the flooded evaporator based on the position of the movable float (206).
At step 504, the contact C1 closes when the movable float (206) touches the second stopper (204b).
At step 506, the contact C2 closes when the movable float (206) touches the first stopper (204a).
At step 508, the controller (310) closes the electronic expansion valve when the contact C2 closes.
At step 510, the controller (310) opens the electronic expansion valve when the contact C1 closes.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Further, it will be apparent to one of the ordinary skill in the art that many modifications, improvements and sub-combinations of the various embodiments, adaptations and variations can be made to the invention without departing from the scope thereof as claimed in the following claims: