Refrigeration system employing multiple economizer circuits

BACKGROUND OF THE INVENTION

The present invention relates generally to a refrigeration system employing multiple economizer circuits to increase capacity and efficiency of the refrigeration system.

System capacity can be increased by increasing the subcooling of the refrigerant leaving the condenser. In a standard (non-economized) refrigeration system, the amount of subcooling typically ranges from 0 to 15° F. An economizer can be employed to additionally subcool the liquid refrigerant exiting the condenser, increasing the capacity and efficiency of the refrigeration system.

In an economized system, the refrigerant is split into two flow paths after leaving the condenser. The first flow path is expanded to a low pressure by an expansion valve prior to passing into the economizer heat exchanger. The second flow path flows directly into the economizer heat exchanger and is cooled by the refrigerant in the first flow path. The refrigerant from the first path then flows along an economizer return path and is injected through economizer ports into the compressor. The vapor refrigerant in the second path is then expanded by a main expansion valve. By employing an economizer, both system capacity and efficiency is increased.

It would be beneficial to employ multiple economizer circuits to further increase the capacity of the refrigeration system. The benefits of employing multiple economizer circuits are especially pronounced for a refrigeration system operating with a high discharge to suction pressure ratio. Multiple economizers have not been employed in prior refrigeration systems as the refrigerant flow from each of the economizers mixes at the point of injection. For example, prior screw compressors include a pair of rotors. As only two rotors are employed, the rotational angle of the compression process is not large enough to prevent vapor communication among the suction port, the low pressure economizer port, the high pressure economizer port, and the discharge port.

SUMMARY OF THE INVENTION

The multiple stage economizer refrigeration system of the present invention includes a compressor, a condenser, a high pressure economizer circuit, a low pressure economizer circuit, expansion valves, and an evaporator. After the refrigerant exits the condenser, the refrigerant splits into two flow paths. The first path of refrigerant is expanded to a lower pressure in an expansion valve prior to flowing into the high pressure economizer heat exchanger. Refrigerant from the main path flows through the high pressure economizer heat exchanger and is cooled by the refrigerant in the first path. The refrigerant in the first path is returned to the compressor through the high pressure economizer port.

After being cooled in the high pressure economizer, the refrigerant from the main path again splits into two flow paths. Refrigerant in the second path is expanded to a low pressure in an expansion valve prior to flowing into the low pressure economizer heat exchanger. Refrigerant from the main path passes through the low pressure economizer heat exchanger and is cooled by the refrigerant in the second path. The refrigerant from the second path is returned to the compressor through the low pressure economizer port. Thus, additional subcooling of the main flow of the refrigerant is accomplished by subcooling in two stages. For even greater subcooling benefits, more than to stages can be implemented.

After being cooled in the low pressure economizer heat exchanger, the refrigerant is expanded in the main expansion valve, heated in the evaporator, and enters the compressor at the suction port. After compression, the refrigerant is discharged through the discharge port.

The multiple economizer refrigeration system can be employed in a screw compressor or a scroll compressor. The screw compressor includes a male rotor including a plurality of helical threads and a pair of opposing female rotors each including a plurality of helical threads. The helical threads of the male rotor engage the helical threads of the female rotors to create two sets of compression chambers. One set of compression chambers communicates with refrigerant from the high pressure economizer, and the other set of compression chambers communicates with refrigerant from the low pressure economizer.

Alternately, a scroll compressor is employed in the multiple economizer refrigeration system. Vapor refrigerant from the low pressure economizer is injected into the scroll compressor through a pair of low pressure injections ports. The low pressure ports are located such that vapor injection initiates shortly after the suction port is covered and the compression chambers are sealed from suction. Vapor refrigerant from the high pressure economizer is injected into the scroll compressor through a high pressure injection port. The high pressure injection port is located proximate to the discharge port. Refrigerant injection through the high pressure injection port and the low pressure injection ports occurs into separate scroll compressor pockets.

These and other features of the present invention will be best understood from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1

illustrates a schematic diagram of a prior art refrigeration system employing a single economizer circuit;

FIG. 2

illustrates a graph relating pressure to enthalpy for the prior art refrigeration system of

FIG. 1

;

FIG. 3

illustrates a schematic diagram of the refrigeration system of the present invention employing dual economizer circuits;

FIG. 4

illustrates a graph relating pressure to enthalpy for the refrigeration system of

FIG. 4

;

FIG. 5

illustrates a cross sectional view of a screw compressor employed in a refrigerant system utilizing dual economizers taken along line

5

—

5

of

FIG. 6

;

FIG. 6

illustrates a top view of the screw compressor of

FIG. 5

;

FIG. 7

illustrates a scroll compressor employed in a refrigerant system utilizing dual economizers when injection of refrigerant begins; and

FIG. 8

illustrates the scroll compressor of

FIG. 7

when injection of the refrigerant from the low pressure economizer is still in progress, and injection of refrigerant from the high pressure economizer is almost complete.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1

illustrates a schematic diagram of a prior art single economizer refrigeration system

20

. The system

20

includes a compressor

22

, a condenser

24

, a main expansion device

26

, an evaporator

28

, and an economizer heat exchanger

30

. Refrigerant circulates though the closed circuit system

20

. After the refrigerant exits the compressor

22

through the discharge port

42

at high pressure and enthalpy, the refrigerant loses heat in the condenser

24

, exiting at lower enthalpy and high pressure. The refrigerant then splits into two flow paths

32

and

34

. Refrigerant in path

34

is expanded to a low pressure in the expansion valve

36

prior to flowing through the economizer heat exchanger

30

. As the refrigerant in the path

32

flows through the economizer heat exchanger

30

, it is cooled by the refrigerant in path

34

. Refrigerant in path

34

from the economizer heat exchanger

30

is returned along the economizer return path

56

to the compressor

22

through the economizer port

38

at a pressure between the suction pressure and the discharge pressure. The refrigerant in line

32

is expanded by the main expansion device

26

and then heated in the evaporator

28

. The refrigerant enters the compressor

22

at the suction port

40

. Downstream, this refrigerant mixes with the refrigerant from the return path

56

. A graph relating enthalpy to pressure for the refrigeration system

20

is illustrated in FIG.

2

. The length of the evaporation line

29

illustrates the cooling capacity of the system

20

.

FIG. 3

illustrates a schematic diagram of the refrigeration system

120

of the present invention employing dual economizer heat exchangers

130

a

and

130

b

. The system

120

includes a compressor

122

, a condenser

124

, a high pressure economizer heat exchanger

130

a

, a low pressure economizer heat exchanger

130

b

, an expansion valve

126

, and an evaporator

128

. After the refrigerant exits the compressor

122

at high pressure and enthalpy through the discharge port

142

, the refrigerant loses heat in the condenser

124

, exiting the condenser

124

at low enthalpy and high pressure. The refrigerant then splits into two flow paths

132

a

and

134

a

. Refrigerant in path

134

a

is expanded to a low pressure by the low pressure expansion valve

136

a

prior to flowing through the economizer heat exchanger

130

a

. As the refrigerant in the path

132

a

flows through the high pressure economizer heat exchanger

130

a

, it is cooled by the refrigerant in path

134

a

. Refrigerant from the economizer heat exchanger

130

a

is returned along the economizer return path

156

a

to the compressor

122

through the high pressure economizer port

138

a

for compression in compression chambers

148

a.

After being cooled in the high pressure economizer heat exchanger

130

a

, the refrigerant in path

132

a

splits into two flow paths

132

b

and

134

b

. Refrigerant in path

134

b

is expanded to a low pressure by the low pressure expansion valve

136

b

prior to flowing through the low pressure economizer heat exchanger

130

b

. As the refrigerant in the path

132

b

flows through the low pressure economizer heat exchanger

130

b

, it is cooled by the refrigerant in path

134

b

. Refrigerant in path

134

b

from the economizer heat exchanger

130

b

is returned along the economizer return path

156

b

to the compressor

122

through the low pressure economizer port

138

b

for compression in compression chambers

148

b.

Refrigerant from path

132

b

is then expanded in the main expansion valve

126

. The main expansion valve

126

, as well as the high pressure and low pressure expansion valves

136

a

and

136

b

, can be electronic EXV (electric expansion vales) or TXV valves. After evaporation in the evaporator

128

, the refrigerant enters the compressor

122

through the suction port

140

. Refrigerant from the paths

134

a

and

134

b

enters the compressor

122

through the high pressure economizer port

138

a

and the low pressure economizer port

138

b

, respectively, and mixes with the refrigerant in the compressor

122

for compression.

The economizer ports

138

a

and

138

b

communicate with the compression chambers

148

a

and

148

b

, respectively, which are each at a pressure which varies during the compression cycle of the compressor

122

. To prevent high pressure to low pressure leak of refrigerant from line

156

a

to

156

b

, the refrigerant from the economizer heat exchangers

130

a

and

130

b

which flows in the compression chambers

148

a

and

148

b

must remain separate at the point of injection in the compressor

122

.

Multiple steps of compressor

122

unloading are also possible with the system

120

of the present invention. In one step, both of the economizer heat exchangers

130

a

and

130

b

are engaged. Alternatively, in additional steps, either of the economizer heat exchangers

130

a

and

130

b

can be disengaged by shutting off the expansions valves

136

a

and

136

b

, respectively. Both of the economizer heat exchangers

130

a

and

130

b

can be disengaged for non-economized operation by shutting off both of the expansion valves

136

a

and

136

b.

To regulate capacity of the system

120

, two additional solenoid valves

144

a

and

144

b

may be employed. A first solenoid valve

144

a

regulates the flow of refrigerant between the high pressure economizer port

138

a

and the low pressure economizer port

138

b

. A second solenoid valve

144

b

regulates the flow of refrigerant between the low pressure economizer port

138

b

and the compressor suction port

140

.

The solenoid valves

144

a

and

144

b

can be opened or closed depending on system

120

requirements to achieve steps of compressor

122

or system

120

unloading. By opening the solenoid valves

144

a

and

144

, the refrigerant flow from both the high pressure and the low pressure economizer ports

138

a

and

138

b

can be by-passed into the suction port

140

to reduce cooling. Alternately, by opening the solenoid valve

144

a

and closing the solenoid valve

144

b

, the refrigerant flow from the high pressure economizer port

138

a

can be by-passed into the economizer port

138

b

. Alternately, by closing the solenoid valve

144

a

and opening the solenoid valve

144

b

, the refrigerant flow from the low pressure economizer port

138

b

can be bypassed into suction line

166

.

By controlling the expansion valves

136

a

and

136

b

and solenoid valves

144

a

and

144

b

, the operation of the compressor

122

and system

120

can be adjusted to meet the cooling demands and achieve optimum capacity and efficiency. A worker of ordinary skill in the art would know how to control these valves depending on the system

120

requirements.

FIG. 4

illustrates a graph relating enthalpy to pressure for the refrigeration system

120

of

FIG. 3

employing dual economizer heat exchangers

130

a

and

130

b

. As shown, the evaporation line

129

of the refrigerant system

120

is longer than the evaporation line

29

of the refrigeration system

20

employing one economizer

30

(illustrated in FIG.

2

). This indicates that the refrigeration system

120

employing dual economizers

130

a

and

130

b

has a greater cooling capacity than the refrigeration system

20

employing a single economizer

30

.

FIG. 5

illustrates a cross-sectional view of a tri-rotor screw compressor

222

employed in the dual economizer system

120

of the present invention. The screw compressor

222

includes a housing

244

having a central portion

246

c

and a pair of opposing portions

246

a

and

246

b

. The central portion

246

c

houses a male rotor

248

c

including a plurality of helical threads

250

c

. The opposing portions

246

a

and

246

b

each house a female rotor

248

a

and

248

b

, each including a plurality of helical threads

250

a

and

250

b

, respectively. The helical threads

250

c

of the male rotor

248

c

engage the helical threads

250

b

of the female rotors

248

a

and

248

b

, respectively, to create high pressure compression chambers

252

a

and low pressure compression chambers

252

b

, respectively. Refrigerant from the high pressure economizer

130

a

enters the compressor

222

through the high pressure economizer port

238

a

and is compressed in the high pressure compression chambers

252

a

. Refrigerant from the low pressure economizer

130

b

enters the compressor

222

through the low pressure economizer port

238

b

and is compressed in the low pressure compression chambers

252

b

. As the refrigerant from the economizer heat exchangers

130

a

and

130

b

is injected into the compressor

222

through separate economizer ports

238

a

and

238

b

, respectively, the refrigerant from the economizers

130

a

and

130

b

remains separate at the point of injection into the compressor

222

.

After evaporation, the refrigerant splits into two streams. As shown in

FIG. 6

, one stream enters the suction port

254

a

for compression in the compression chambers

252

a

with the refrigerant from the high pressure economizer

130

a

, and the other stream enters suction port

254

b

for compression in the compression chambers

252

b

with refrigerant from the low pressure economizer

130

b

. After compression, the refrigerant in the compression chambers

252

a

and

252

b

is discharged through the discharge ports

242

a

and

242

b

, respectively, for condensation. As shown, the low pressure economizer port

238

b

is positioned closer to the suction ports

254

a

and

254

b

, and the high pressure economizer port

238

a

is positioned closer to the discharge ports

254

a

and

254

b.

As the compression chambers

252

a

and

252

b

are separate and are on opposing sides of the housing

244

, there is no communication between the refrigerant from the high pressure economizer

230

a

and the refrigerant from the low pressure economizer

230

a

. By optimizing the position and size of economizer ports

238

a

and

238

b

, vapor communication between the compression chambers

252

a

and

252

b

, the suction ports

240

a

and

240

b

, and the discharge ports

242

a

and

242

b

is prevented, allowing for control of the pressure in each economizer

130

a

and

130

b.

FIG. 7

illustrates a scroll compressor

322

employed in the refrigeration system

120

employing dual economizer heat exchangers

130

a

and

130

b

. The scroll compressor

322

includes a non-orbiting scroll

344

, an orbiting scroll

346

, and a plurality of compression chambers

348

a

and

348

b

defined therebetween.

As the refrigerant from the economizer heat exchangers

130

a

and

130

b

is injected into the compressor

322

through separate economizer ports

338

a

and

338

b

, respectively, and as long as solenoid valve

144

a

remains closed, the refrigerant in lines

156

a

and

156

b

, respectively, remains separate, and there is no communication between compression chambers

348

a

and

348

b.

Vapor refrigerant from the low pressure economizer heat exchanger

130

b

is injected into a pair of compression chambers

348

b

of the scroll compressor

322

through a pair of low pressure injections ports

338

b

. Vapor refrigerant from the high pressure economizer heat exchanger

130

a

is injected into the compression chambers

348

a

of the scroll compressor

322

through a high pressure injection port

338

a

. The high pressure injection port

338

a

is located proximate to the discharge port

342

. The injection ports

338

a

and

338

b

typically extend through the body of the fixed scrolls

344

and into the compression chambers

348

a

and

348

b

, respectively.

FIG. 7

illustrates the position of scroll compressor

322

when injection of refrigerant from the dual economizer heat exchangers

130

a

and

130

b

begins. The injection ports

338

a

and

338

b

have just opened to allow the vapor refrigerant from each economizer heat exchanger

130

a

and

130

b

to enter the compression chambers

348

a

and

348

b

, respectively.

FIG. 8

illustrates the position of the scroll compressor

322

when refrigerant injection from the low pressure economizer

130

b

into the compression chambers

348

b

is still in progress and refrigerant injection from the high pressure economizer

130

a

into the compression chamber

348

a

is almost complete. At this stage, the high pressure injection port

338

a

is separated from the discharge port

342

as the high pressure injection port

338

a

is still covered by the orbiting scroll

346

prior to the initiation of the discharge process through a discharge valve that may cover the discharge port.

The scroll compressor

322

can alternatively include additional injection ports and compression chambers to allow for three ore more economizer heat exchangers. If three economizers are to be employed, the scroll compressor

322

will preferably have more than 2.5 turns.

There are several benefits to the refrigerant system

120

of the present invention. For one, a higher operating efficiency is possible employing multiple economizer heat exchangers

130

a

and

130

b

. Additionally, an increase in refrigeration capacity is possible. Compressor reliability is also improved due to a decrease in the discharge temperature. Control of system capacity is also increased by alternating the engagement of economizer circuits, as well as initiating bypass operation between the economizer circuits or between any of the economizer circuits and suction line.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.