FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“High COP Vapour Absorption Machine”

APPLICANTS:

Name Nationality Address
Voltas Ltd Indian Voltas Ltd , 2nd Pokhran Road , Thane(W) 400601

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:-

FIELD OF INVENTION
[001] The embodiments herein relate to a vapor absorption machines, and more particularly but not exclusively to a vapor absorption machine having high coefficient of performance and a method for achieving high coefficient of performance in vapor absorption machines.

BACKGROUND OF INVENTION
[002] A Vapor Absorption Machine (VAM) is a refrigeration system which primarily works on heat source unlike a conventional refrigeration system which operates on electricity. The VAM accomplishes removal of heat from the medium to be cooled through the evaporation of a refrigerant which is water at a low pressure and the rejection of heat through the condensation of the refrigerant at a higher pressure. Further, VAM employs energy in the form of heat which makes the system economic, since cheap sources of heat are available such as hot water produced from solar heat, low and medium pressure steam waste heat of exhaust gases of diesel generators set and so on.
[003] Conventional vapor absorption machine mainly includes an evaporator, an absorber, a generator and a condenser. Further, the conventional VAM employs water as a refrigerant and lithium bromide (LiBr) as an absorbent. The diluted LiBr solution is delivered to the generator where the solution is heated with the help of available heat source. The heating of the solution causes the refrigerant (water) to vaporize and separate thereby leaving behind the concentrated lithium bromide solution. The concentrated LiBr solution obtained in the generator is sent back to the absorber. Further, the vaporized refrigerant (water) is passed to the condenser section where the water vapors will be condensed back to its liquid state. The condensed water flows down to the evaporator section and forms the refrigerant, wherein the condensed water is sprayed onto the tubes containing the fluid to be cooled. Spraying of condensed water on the tube in vacuum enables absorption of heat from the fluid flowing through the tube thereby lowering its temperature. Evaporated water vapors then passes into the absorber section where it is absorbed in the LiBr solution thereby diluting the LiBr solution sprayed in the absorber section. Further, the diluted LiBr solution travels to the heat exchanger and then to the generator in order to repeat the cycle.
[004] Further, it is observed that the spread of LiBr solution in the absorber section of conventional VAM is about 4.5% - 5% and hence with the increase in number of cycles, the concentration of LiBr solution in generator section may increase. Furthermore, increase in concentration of LiBr solution demands relatively high steam input in generator section, thereby decreasing the coefficient of performance of the vapor absorption machines.
[005] Further, in conventional VAM, the temperature of LiBr solution that is passed to the generator section decreases because of the absorption of refrigerant and the cooling water that flows inside the absorber section. Further, the decrease in temperature of LiBr solution demands relatively high steam input in generator section, thereby decreases the coefficient of performance of the vapor absorption machines.
[006] Further, conventional VAM employs shell and tube type heat exchangers in order to preheat the dilute LiBr solution. However, the heat transfer efficiency of conventional shell and tube type heat exchanger is low and also it requires more space. Further, there is a possibility of corrosion in the conventional heat exchangers which makes the conventional heat exchanger partially inefficient.
[007] Therefore, there is a need for a vapor absorption machine that is capable of achieving high coefficient of performance. Further, there is a need for a method of achieving high coefficient of performance in vapor absorption machines.

OBJECT OF INVENTION
[008] The principal object of this invention is to provide a vapor absorption machine having high coefficient of performance.
[009] Another object of the invention is to provide a method for achieving high coefficient of performance in vapor absorption machines.
[0010] A further object of the invention is to increase the spread of LiBr solution in the absorber section of the vapor absorption machines.
[0011] A further object of the invention is to provide an effective heat exchanger with high heat transfer efficiency and free from corrosion.

BRIEF DESCRIPTION OF FIGURES
[0012] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:;
[0013] FIG. 1 shows a line diagram that depicts a vapor absorption machine according to an embodiment of the present invention;
[0014] FIG. 2 depicts a perspective view of a tube sheet pattern according to an embodiment of the present invention;
[0015] FIG. 3 is a flow chart that depicts the process of reducing the concentration of absorbent that flows into the high temperature generator of a vapor absorption machine according to an embodiment of the present invention;
[0016] FIG. 4 is a flow chart that depicts the flow of absorbent through the heat exchangers according to an embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION
[0017] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0018] The embodiments herein achieve a lower temperature working fluid in vapor absorption machine thereby developing a vapor absorption machine that can be operated under low temperature and a method to generate low temperature working fluid as described herein below. Referring now to the drawings, and more particularly to FIGS. 1 through 4, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0019] Throughout the specification, the word dilute solution and weak solution have been used interchangeably. The dilute solution and weak solution refers to a mixture that has a relatively high refrigerant content and low absorbent content. Further, throughout the specification, the word concentrated solution and strong solution have been used interchangeably. The concentrated solution or strong solution refers to a mixture that has a relatively high absorbent content and low refrigerant content. The refrigerant refers to the solution that is used to absorb heat from the working fluid. Furthermore, throughout the specification, the word Lithium Bromide solution and absorbent have been used interchangeably. The Lithium bromide solution and absorbent refers to the medium that is used to absorb refrigerant vapors. Further, throughout the specification, the word communication refers to all of the liquid communication, vapor communication and gaseous communication.
[0020] FIG. 1 shows a line diagram depicting a vapor absorption machine 100 according to an embodiment of the present invention. The vapor absorption machine 100 includes a chiller module 102, a high temperature generator 104, a low temperature generator 106, a condenser 108, a low temperature heat exchanger 110, a high temperature heat exchanger 112, an auxiliary heat exchanger 114, a drain cooler 116, a solution circulation pump 118, a solution spray pump 120, a refrigerant pump 122 and a heat transfer pipe 124. Further, the vapor absorption machine 100 includes water as a refrigerant and lithium bromide solution as an absorbent. However, it is also within the scope of the invention that other forms of refrigerant and absorbent may be used without otherwise deterring the intended function of refrigerant and absorbent as can be deduced from the description.
[0021] The chiller module 102 includes an evaporator section 126, an absorber section 128 and a mist eliminator 131. The mist eliminator 131 may be provided in fluid communication between the evaporator section 126 and absorber section 128. In one embodiment, the mist eliminator 131 may be provided with a tube sheet pattern 129, wherein the tube sheet pattern 129 enables the flow of refrigerant vapor from evaporator section 126 to the absorber section 128. Further, the evaporator section 126 includes a first stage evaporator 130, a second stage evaporator 132, refrigerant spray trees 134 and 136 and an evaporator sump 138. The refrigerant spray trees 134 and 136 are configured to provide a smooth falling film flow of the refrigerant. Further, in one embodiment, the refrigerant spray trees 134 and 136 are provided with holes of 2mm diameter. In one embodiment, the first stage evaporator 130 and the second stage evaporator 132 are provided as an integral element. Further, the refrigerant spray trees 134 and 136 are provided in the first stage evaporator 130 and the second stage evaporator 132 respectively such that the refrigerant spray trees 134 and 136 are configured to spray down a refrigerant in first stage evaporator 130 and second stage evaporator 132 respectively. In one embodiment, spray trees 134 and 136 may be provided at top of the first stage evaporator 130 and the second stage evaporator 132 respectively. However, it is also within the scope of the invention that the spray trees 134 and 136 may be provided at different position inside the first stage evaporator 130 and the second stage evaporator 132 respectively without otherwise deterring the intended function of the spray trees 134 and 136 as can be deduced from this description. Further, the first stage evaporator 130 and second stage evaporator 132 may be provided in series such that it enables the heat transfer pipe 124 to extend between the first stage evaporator 130 and second stage evaporator 132. In one embodiment, the second stage evaporator 130 is provided at the top of the first stage evaporator 132.
[0022] Similarly, the absorber section 128 includes a first stage absorber 140, a second stage absorber 142, absorbent spray trees 144 and 146 and an absorber sump 148. In one embodiment, the first stage absorber 140 and the second stage absorber 142 are provided as an integral element. Further, the absorbent spray trees 144 and 146 are provided in the first stage absorber 140 and the second stage absorber 142 respectively such that the absorbent spray trees 144 and 146 are configured to spray down an absorbent in first stage absorber 140 and second stage absorber 142 respectively. In one embodiment, the absorbent spray trees 144 and 146 may be provided at top of the first stage absorber 140 and the second stage absorber 142 respectively. . The absorbent spray trees 144 and 146 are configured to provide a smooth falling film flow of the refrigerant. Further, in one embodiment, the absorbent spray trees 144 and 146 are provided with holes of 2mm diameter. However, it is also within the scope of the invention that the absorbent spray trees 144 and 146 may be provided at different position inside the first stage absorber 140 and the second stage absorber 142 respectively without otherwise deterring the intended function of the absorbent spray trees 144 and 146 as can be deduced from this description. Further, the first stage absorber 140 and second stage absorber 142 may be provided in series such that it enables a bundle of tubes 150 to extend between the first stage absorber 140 and second stage absorber 142. In one embodiment, the second stage absorber 140 is provided at the top of first stage absorber 142. Further, the bundle of tubes 150 may carry a cooling water to reject heat from the absorber section 128.
[0023] Further, the evaporator sump 138 may be provided in communication with the evaporator spray trees 134 and 136 through the refrigerant pump 122. However, it is also within the scope of the invention that the communication between evaporator sump 138 and evaporator spray trees 134 and 136 may be established by means of other actuating means without otherwise deterring the intended function of the communication as can be deduced from this description. Similarly, the absorber sump 148 may be provided in communication with the high temperature generator 104 and low temperature generator 106 through the solution circulation pump 118. However, it is also within the scope of the invention that the communication between the absorber sump 148 and high temperature generator 104 and low temperature generator 106 may be provided by using other actuating means without otherwise deterring the intended function of the communication as can be deduced from this description. Further, in one embodiment, the low temperature heat exchanger 110 may be provided such that the low temperature heat exchanger 110 is configured to establish communication between the absorber sump 148 and the generators, wherein the generators may include the high temperature generator 104 and low temperature generator 106. Further, the low temperature heat exchanger 110 is configured to establish communication between the high temperature generator 104 plus low temperature generator 106 and absorbent spray trees 144 and 146.
[0024] Further, the high temperature heat exchanger 112 may be configured to establish communication between the high temperature generator 104 and the low temperature heat exchanger 110. Further, the auxiliary heat exchanger 114 may be configured to establish communication between the low temperature generator 106 and the condenser 108. Furthermore, the auxiliary heat exchanger 114 may be configured to establish communication between the absorber sump 148 and the low temperature generator 106 The drain cooler 116 may be configured to establish communication with the absorbent sump 148 and the high temperature generator 104. In one embodiment, the drain cooler 116 may not be present in the system. In one embodiment, the low temperature heat exchanger 110, the high temperature heat exchanger 112 and the auxiliary heat exchanger 114 is a nickel brazed plate type heat exchanger. The condenser 108 may be provided with the bundle of tubes 150 that carries cooling water. Further, the condenser 108 may be provided in communication with the evaporator section 126.
[0025] FIG. 2 depicts a perspective view of a tube sheet pattern 129 according to an embodiment of the present invention. In one embodiment, the tube sheet pattern 129 is made up of steel. However, it is also with in the scope of invention that the tube sheet pattern may be made of some other materials without otherwise deterring the intended function of the tube sheet pattern 129 as can be deduced from this description. The tube sheet pattern 129 includes an absorber flow module 202 and an evaporator flow module 204. The absorber flow module 202 may be provided in the absorber section 128 of the chiller module 102 and the evaporator flow module 204 may be provided in the evaporator section 126. A plurality of holes 206 may be reamed in the absorber flow module 202 of the tube sheet pattern 129 such that the pitch distance between the adjacent holes is in the increasing order. As referred in the fig. 2, the pitch distance d2 between the adjacent holes h2 and h3 is greater than the pitch distance d1 between the adjacent holes h2 and h1. Further, the evaporator flow module 204 is provided with a plurality of holes 208 such that the pitch distance between the adjacent holes is in the decreasing order. As referred in the fig. 2, the pitch distance d3 between the adjacent holes h5 and h6 is lesser than the pitch distance d4 between the adjacent holes h5 and h4. In one embodiment, the number of holes 206 that are reamed in the absorber flow module 202 is greater than the number of holes 208 that are reamed in the evaporator flow module 204 thereby providing least resistance to the flow of refrigerant vapor from the evaporator section 126 to the absorber section 128. Further, the absorber flow module 202 and the evaporator flow module 204 are connected to each other such that the holes 206 and 208 in absorber flow module 202 and the evaporator flow module 204 provides an aerodynamic flow pattern. Further, in one embodiment the position of holes in the absorber flow module 202 and the evaporator flow module 204 enables the refrigerant vapor from the first stage evaporator 130 to flow in a curved path into the first stage absorber 140.
[0026] Further, in one embodiment the position of holes in the absorber flow module 202 and the evaporator flow module 204 enables the refrigerant vapor from the second stage evaporator 132 to flow in a curved path into the second stage absorber 142.
[0027] FIG. 3 is a flow chart that depicts the process of reducing the concentration of absorbent that flows into the high temperature generator 104 and the low temperature generator 106 of a vapor absorption machine according to an embodiment of the present invention. The absorbent with first concentration level flows in to the absorber section 128 of the chiller module 102. In one embodiment, the first concentration level of the absorbent is 64.5% to 65%. The absorbent of first concentration level is sprayed in to the first stage absorber 140 through the absorbent spray tree 144 thereby enables the first stage spray (step 304). The first stage spray enables the absorbent to absorb the refrigerant vapor that flows into the first stage absorber 140 from the first stage evaporator 130. Further, the flow of refrigerant vapor from the from the first stage evaporator 130 into the first stage absorber 140 may be by means of the tube sheet pattern 129. In one embodiment, holes in tube sheet pattern 129 may be provided in aerodynamic profile such that the tube sheet pattern 129 enables least resistance to the flow of refrigerant vapors. Further, the absorption of the refrigerant vapor by the absorbent condenses the refrigerant vapors and releases heat. The heat released from the condensation of refrigerant vapors and their absorption by the absorbent may be removed through the cooling water that is circulated through the bundle of tubes 150 provided within the first stage absorber 140. Further, the absorbent of first concentration may be sprayed into the second stage absorber 142 through the absorbent spray tree 146 thereby enables the second stage spray (step 306). The second stage spray enables the absorbent to absorb the refrigerant vapor that flows into the second stage absorber 142 from the second stage evaporator 132. Further, the flow of refrigerant vapor from the from the second stage evaporator 132 into the second stage absorber 142 may be by means of the tube sheet pattern 129. In one embodiment, holes in tube sheet pattern 129 may be provided in aerodynamic profile such that the tube sheet pattern 129 enables least resistance to the flow of refrigerant vapors. Further, the absorption of the refrigerant vapor by the absorbent condenses the refrigerant vapors and releases heat. The heat released from the condensation of refrigerant vapors and their absorption by the absorbent may be removed through the cooling water that is circulated through the bundle of tubes 150 provided within the second stage absorber 142. The absorption of refrigerant vapor that flows into the second stage absorber 142 from the second stage evaporator 132 reduces the concentration of the absorbent to the second concentration level (step 308). In one embodiment, the second concentration of the absorbent is 58% - 58.5%. Further, the absorbent with the second concentration level may be passed onto the high temperature generator 104 and the low temperature generator 106 through the solution circulation pump 118 (step 310).
[0028] Further, the bundle of tubes 152 with a high temperature energy source are immersed in a second concentrated absorbent solution provided in high temperature generator 104. In one embodiment, the high temperature energy source is steam or hot water. However, it is also within the scope of the invention that the different source of heat energy may be used in the bundle of tubes 150 without otherwise deterring the intended function of the high temperature energy source as can be deduced from this description. The absorbent with second concentration level absorbs heat from the high temperature energy source thereby enables the refrigerant present in the second concentrated absorbent to vaporize and separate from the absorbent solution. Further, the vaporization of refrigerant provides the absorbent solution with third concentration level (step 312), wherein the third concentration level may be relatively higher than the second concentration level. In one embodiment, the third concentration level of the absorbent is approximately equal to the first concentration level. Further, the absorbent solution with third concentration level may be passed on to the absorber section 128 through the solution spray pump 120.
[0029] Further, the refrigerant vapor generator in the high temperature generator 104 may be passed onto the low temperature generator 106 thereby the refrigerant vapor drives the low temperature generator 106. The absorbent with second concentration level provided in the low temperature generator 106 absorbs heat from the refrigerant vapor thereby enables the refrigerant present in the second concentrated absorbent to vaporize and separate from the absorbent solution. Further, the vaporization of refrigerant may provide the absorbent solution with fourth concentration level, wherein the fourth concentration level may be relatively higher than the second concentration level (step 314). In one embodiment, the fourth concentration level of the absorbent is approximately equal to the third concentration level of the absorbent. Further, the absorbent solution with fourth concentration level may be passed on to the absorber section 128 through the solution spray pump 120. Furthermore, the refrigerant vapors generated in the low temperature generator 106 may be passed onto the condenser 108. The cooling water that may flow through the bundle of tubes 150 provides the heat transfer from the refrigerant vapor to the cooling water. The heat transfer enables the refrigerant to condense. Further, the condensed refrigerant may be passed on to the evaporator section 126. In one embodiment, the low temperature generator 106 and the condenser 108 may be provided in a single shell.
[0030] FIG. 4 is a flow chart that depicts the flow of absorbent through the heat exchangers according to an embodiment of the present invention. In one embodiment, the absorbent solution with second concentration level from the absorbent sump 148 flows (step 402) through the solution circulation pump 118. The solution circulation pump 118 divides the flow of absorbent. In one embodiment, the flow of absorbent from the outlet of solution circulation pump 118 is divided into four. Further, the solution circulation pump 118 feeds the second concentrated absorbent separately into low temperature heat exchanger 110, auxiliary heat exchanger 114, high temperature heat exchanger 112 and drain cooler 116 (step 404). Further, the low temperature heat exchanger 110 enables the flow of hot absorbent having a third concentration from the high temperature generator 104 and hot absorbent having a fourth concentration from the low temperature generator 106 to the absorber section 128. Further, in the low temperature heat exchanger 110 heat transfers from the absorbent with third concentration and the absorbent with fourth concentration to the absorbent with second concentration, thereby enabling preheating of the absorbent with second concentration (step 408). Furthermore, flow of preheated absorbent with second concentration from the low temperature heat exchanger 110 is divided into two and the absorbent with second concentration flows separately into the low temperature generator 106 and high temperature heat exchanger 112, respectively (step 414). In one embodiment, the solution spray pump 120 is configured to establish communication between the high temperature generator 104, low temperature generator 106 and the low temperature heat exchanger 110.
[0031] Further, the high temperature heat exchanger 112 enables the flow of hot absorbent with third concentration from the high temperature generator 104 to the low temperature heat exchanger 110. Further, in the high temperature heat exchanger 112 heat transfers from the hot absorbent with third concentration to the mixture of absorbent with second concentration from the absorber sump 148 and preheated absorbent with second concentration from the low temperature heat exchanger, thereby enables preheating of the mixture of absorbent with second concentration from the absorber sump 148 and preheated absorbent with second concentration from the low temperature heat exchanger (step 410). Furthermore, the preheated mixture of second concentrated absorbent from the absorber sump 148 and preheated absorbent with second concentration from the low temperature heat exchanger flows into the high temperature generator 104 (step 416).
[0032] Further, the drain cooler 116 preheats the absorbent with second concentration from the absorbent sump 148 by utilizing the high temperature energy source from the outlet of the bundle of tubes 152 (step 412). Further, the preheated absorbent with second concentration from drain cooler flows into the high temperature generator 104 (step 418). Further, the auxiliary heat exchanger 114 preheats the absorbent with second concentration from the absorber sump 148 by utilizing the hot refrigerant vapors from the low temperature generator 106 (step 406). Further, the preheated absorbent with second concentration from the auxiliary heat exchanger 114 flows into the low temperature generator 106 (step 420). Further, the preheated second concentrated absorbent that flows into the high temperature generator 104 reduces the consumption of high temperature energy source, thereby increases the Coefficient of performance of the vapor absorption machine 100. In one embodiment, the Coefficient of performance of the vapor absorption machine 100 is 1.5. Furthermore, the hot refrigerant vapors are passed onto the condenser 108, where the refrigerant vapor may be condensed.
[0033] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims
We Claim:
1. A vapor absorption machine for achieving high coefficient of performance, said machine comprising:
a chiller module having a first stage evaporator with a first stage evaporator spray tree, a second stage evaporator with a second stage evaporator spray tree, a first stage absorber with a first stage absorber spray tree, a second stage absorber with a second stage absorber spray tree, a tube sheet pattern, an evaporator sump and an absorber sump;
a high temperature generator;
a low temperature generator;
a solution circulation pump in a fluid communication with said absorber sump,
a solution pump configured to be in a fluid communication with said first stage spray tree, said second stage spray tree, said high temperature generator and said low temperature generator;
a heat transfer pipe configured to allow a working fluid to flow into the second stage evaporator and subsequently into the first stage evaporator; and
a bundle of tubes configured to allow a flow of cooling water into the second stage absorber and the first stage absorber, wherein
said solution circulation pump configured to allow passage of an absorbent to each of said high temperature generator and said low temperature generator;
each of said first stage evaporator spray tree and said second stage evaporator spray tree are configured to provide a smooth falling film flow of a refrigerant into said first stage evaporator and said second stage evaporator respectively; and
each of said first stage absorber spray tree and said second stage absorber spray tree are configured to provide a smooth falling film flow of an absorbent into said first stage absorber and said second stage absorber respectively.

2. The machine as claimed in claim 1, wherein the machine further comprises at least one of a low temperature heat exchanger, a high temperature heat exchanger, an auxiliary heat exchanger, and a drain cooler.

3. The machine as claimed in claim 2, wherein each of said low temperature heat exchanger, said high temperature heat exchanger and said auxiliary heat exchanger is a nickel brazed plate type heat exchanger.

4. The machine as claimed in claim 2, wherein
said tube sheet pattern includes a first portion configured to be provided in the first stage absorber and the second stage absorber and a second portion configured to be provided in the first stage evaporator and the second stage evaporator, wherein

said first portion of said tube sheet pattern defines a plurality of holes having a pitch in decreasing order and said second portion of said tube sheet pattern defines a plurality of holes having a pitch in increasing order thereby attenuating resistance to a flow of vapors from said first stage evaporator and said second stage evaporator to said first stage absorber and said second stage absorber respectively.

5. The machine as claimed in claim 1, wherein said chiller module includes a mist eliminator.

6. The machine as claimed in claim 2, wherein a number of holes provided in said first portion of said tube sheet pattern is more than a number of holes provided in said second portion of said tube sheet pattern.

7. A method for achieving high coefficient of performance in a vapor absorption machine, said method comprising:
allowing a passage of an absorbent having first concentration from a low temperature generator and a high temperature generator to a first stage absorber spray tree provided in a first stage absorber and a second stage spray tree provided in a second stage absorber; and
allowing a passage of the absorbent having the first concentration from each of said first stage absorber spray tree and second stage absorber spray tree to attain a second concentration,
wherein said second concentration is lesser than said first concentration.

8. The method as claimed in claim 7, wherein said allowing the passage of the absorbent having the first concentration from each of said first stage absorber spray tree and second stage absorber spray tree to attain the second concentration includes diluting the absorbent having the first concentration with refrigerant vapors from a first and second stage evaporators corresponding to said first and second stage absorbers.

9. The method as claimed in claim 7, wherein the method further comprises
preheating said absorbent having the second concentration;
allowing a passage of said preheated absorbent having the second concentration to said high temperature generator and said low temperature generator;
introducing high temperature energy source in said high temperature generator; and
introducing refrigerant vapors generated in the high temperature generator in said low temperature generator.

10. The method as claimed in claim 9, wherein said allowing a passage of said preheated absorbent having the second concentration to said high temperature generator and said low temperature generator provides high coefficient of performance.

11. The method as claimed in claim 10, wherein said coefficient of performance is 1.5.

12. The method as claimed in claim 7, wherein
said first concentration is in the range of 64.5% to 65%;
said second concentration is in the range of 58% to 58.5%; and
a concentration spread which is a difference between a second low concentration and first high concentration is high.