U.S. patent application number 13/285859 was filed with the patent office on 2012-05-03 for screw chiller economizer system.
This patent application is currently assigned to Johnson Controls Technology Company. Invention is credited to Douglas Alan Kester, William L. Kopko, Paul Nemit, JR..
Application Number | 20120103005 13/285859 |
Document ID | / |
Family ID | 45995164 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120103005 |
Kind Code |
A1 |
Kopko; William L. ; et
al. |
May 3, 2012 |
SCREW CHILLER ECONOMIZER SYSTEM
Abstract
Screw chillers have economizer systems that include a low
pressure economizer and a high pressure economizer. According to
certain embodiments, the low pressure economizer includes a flash
tank, an expansion device and a flow control valve while the high
pressure economizer includes a heat exchanger and an expansion
device. The screw chillers also include a screw compressor that
compresses refrigerant. The screw compressor includes a low
pressure economizer port designed to receive lower pressure
refrigerant from the flash tank within the low pressure economizer
and a high pressure economizer port designed to receive higher
pressure refrigerant from the heat exchanger within the higher
pressure economizer. The screw compressor is designed to compress
the refrigerant received from the evaporator, the refrigerant
received through the low pressure economizer port, and the
refrigerant received through the high pressure economizer port and
to discharge the refrigerant through a common discharge.
Inventors: |
Kopko; William L.; (Jacobus,
PA) ; Kester; Douglas Alan; (York, PA) ;
Nemit, JR.; Paul; (Waynesboro, PA) |
Assignee: |
Johnson Controls Technology
Company
Holland
MI
|
Family ID: |
45995164 |
Appl. No.: |
13/285859 |
Filed: |
October 31, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61408752 |
Nov 1, 2010 |
|
|
|
Current U.S.
Class: |
62/430 |
Current CPC
Class: |
F25B 2600/2509 20130101;
F25B 1/10 20130101; F25B 2400/13 20130101; F25B 1/047 20130101 |
Class at
Publication: |
62/430 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F25D 11/00 20060101 F25D011/00 |
Claims
1. A refrigeration system, comprising: a condenser configured to
condense refrigerant; a first economizer system comprising a first
expansion device configured to expand a first portion of the
condensed refrigerant and a heat exchanger configured to subcool a
second portion of the condensed refrigerant with the first portion;
a second economizer system comprising a second expansion device
configured to expand the refrigerant and a flash tank configured to
separate the refrigerant into vapor phase refrigerant and liquid
phase refrigerant; an expansion device configured to receive the
refrigerant from the first economizer system or the second
economizer system and to expand the refrigerant; an evaporator
configured to evaporate the expanded refrigerant; and a screw
compressor comprising a suction port configured to receive the
evaporated refrigerant, a first economizer port configured to
receive the first portion of the refrigerant, a second economizer
port configured to receive the vapor phase refrigerant, and a
discharge port, wherein the screw compressor is configured to
compress the evaporated refrigerant, the first portion of the
refrigerant, and the vapor phase refrigerant and to discharge the
compressed refrigerant through the discharge port.
2. The refrigeration system of claim 1, wherein the first
economizer system is disposed upstream from the second economizer
system and downstream of the condenser.
3. The refrigeration system of claim 1, wherein the second
economizer system is disposed upstream from the first economizer
system and downstream of the condenser.
4. The refrigeration system of claim 1, wherein the first
economizer port comprises a lower pressure port relative to the
second economizer port.
5. The refrigeration system of claim 1, wherein the first
economizer port comprises a higher pressure port relative to the
second economizer port.
6. The refrigeration system of claim 1, wherein the condenser
comprises an air cooled condenser.
7. The refrigeration system of claim 1, wherein the first
economizer system comprises a flow control valve configured to
control flow of the first portion of the refrigerant to the first
economizer port.
8. The refrigeration system of claim 1, wherein the second
economizer system comprises a flow control valve configured to
control flow of the vapor phase refrigerant to the second
economizer port.
9. A refrigeration system, comprising: a condenser configured to
condense refrigerant; a high pressure economizer system comprising
a high pressure expansion device configured to expand the condensed
refrigerant and a high pressure flash tank configured to separate
the expanded refrigerant into a high pressure vapor phase
refrigerant and a high pressure liquid phase refrigerant; a low
pressure economizer system comprising a lower pressure expansion
device configured to expand the high pressure liquid refrigerant
and a lower pressure flash tank configured to separate the expanded
refrigerant into lower pressure vapor phase refrigerant and lower
pressure liquid phase refrigerant; a third expansion device
configured to receive and to expand the lower pressure liquid phase
refrigerant; an evaporator configured to evaporate the expanded
refrigerant from the third expansion device; and a screw compressor
comprising a suction port configured to receive the evaporated
refrigerant, a first economizer port configured to receive the high
pressure vapor phase refrigerant, a second economizer port
configured to receive the lower pressure vapor phase refrigerant,
and a discharge port, wherein the screw compressor is configured to
compress the evaporated refrigerant, the high pressure vapor phase
refrigerant, and the lower pressure vapor phase refrigerant and to
discharge the compressed refrigerant through the discharge
port.
10. The refrigeration system of claim 9, wherein the screw
compressor is configured to draw the vapor phase refrigerant into
the screw compressor based on a pressure difference between a
pressure of the vapor phase refrigerant and a pressure in a
compression area of the screw compressor coupled to the low
pressure economizer port.
11. The refrigeration system of claim 9, wherein the high pressure
economizer system comprises a first flow control valve disposed
downstream of the high pressure flash tank, wherein the first flow
control valve is configured to control flow of the high pressure
vapor phase refrigerant to the first economizer port, wherein the
low pressure economizer system comprises a second flow control
valve disposed downstream of the lower pressure flash tank, and
wherein the second flow control valve is configured to control flow
of the lower pressure vapor phase refrigerant to the second
economizer port.
12. The refrigeration system of claim 11, comprising a controller
operably coupled to the first and second flow control valves and
configured to govern operation of the first control valve to enable
and disable operation of the high pressure economizer system, and
to govern operation of the second control valve to enable and
disable operation of the lower pressure economizer system.
13. The refrigeration system of claim 9, comprising a controller
configured to operate the high pressure expansion device to limit a
level of liquid refrigerant in the high pressure flash tank, and to
operate the low pressure expansion device to limit a level of
liquid refrigerant in the low pressure flash tank.
14. The refrigeration system of claim 9, wherein the condenser
comprises an air cooled multichannel heat exchanger.
15. A refrigeration system, comprising: a condenser configured to
condense refrigerant; a high pressure economizer system comprising
a first expansion device configured to expand a first portion of
the condensed refrigerant and a heat exchanger configured to
subcool a second portion of the condensed refrigerant with the
first portion; a low pressure economizer system comprising a low
pressure expansion device configured to expand the subcooled second
portion and a flash tank configured to separate the expanded second
portion into vapor phase refrigerant and liquid phase refrigerant;
a third expansion device configured to expand the liquid phase
refrigerant; an evaporator configured to evaporate the expanded
refrigerant; and a screw compressor comprising a suction port
configured to receive the expanded refrigerant, a low pressure
economizer port configured to receive the vapor phase refrigerant,
a high pressure economizer port configured to receive the first
portion of the refrigerant, and a discharge port, wherein the screw
compressor is configured to compress the refrigerant received
through the suction port, the low pressure economizer port, and the
high pressure economizer port and to discharge the compressed
refrigerant through the discharge port.
16. The refrigeration system of claim 15, wherein the condensed
refrigerant is separated into the first portion of the condensed
refrigerant and the second portion of the condensed refrigerant
upstream of the heat exchanger.
17. The refrigeration system of claim 15, wherein the first and
second portions of the condensed refrigerant both flow through the
heat exchanger.
18. The refrigeration system of claim 15, wherein the screw
compressor is configured to mix the first portion of the
refrigerant received through the high pressure economizer port with
existing refrigerant in the screw compressor, and wherein the screw
compressor is configured to mix the vapor phase refrigerant
received through the low pressure economizer port with existing
refrigerant in the screw compressor.
19. The refrigeration system of claim 15, wherein the high pressure
economizer system comprises a first flow control valve disposed
upstream of the first expansion device, wherein the flow control
valve is configured to control flow of the first portion of the
condensed refrigerant to the high pressure economizer port, wherein
the low pressure economizer system comprises a second flow control
valve disposed downstream of the flash tank, and wherein the second
flow control valve is configured to control flow of the vapor phase
refrigerant to the low pressure economizer port
20. The refrigeration system of claim 19, comprising a controller
operably coupled to the first and second flow control valves and
configured to govern operation of the first and second flow control
valves based on an ambient air temperature, or a temperature of the
refrigerant, or both.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from and the benefit of
U.S. Provisional Application Ser. No. 61/408,752, entitled "SCREW
CHILLER ECONOMIZER SYSTEM", filed Nov. 1, 2010, which is hereby
incorporated by reference
BACKGROUND
[0002] The invention relates generally to economizer systems for
screw chillers.
[0003] Many applications exist for refrigeration systems including
residential, commercial, and industrial applications. For example,
a commercial refrigeration system may be used to cool an enclosed
space such as a data center, laboratory, supermarket, or freezer.
Generally, refrigeration systems may operate by circulating a
fluid, such as refrigerant, through a closed loop between an
evaporator where the fluid absorbs heat and a condenser where the
fluid releases heat. The fluid flowing within the closed loop is
generally formulated to undergo phase changes within the normal
operating temperatures and pressures of the system so that
considerable quantities of heat can be exchanged by virtue of the
latent heat of vaporization of the fluid.
[0004] Some refrigeration and air conditioning systems rely on
chillers to reduce the temperature of a process fluid, typically
water. In such applications, the chilled water may be passed
through downstream equipment, such as air handlers, to cool other
fluids, such as air in a building. In typical chillers, the process
fluid is cooled by an evaporator that absorbs heat from the process
fluid by evaporating refrigerant. The refrigerant is then
compressed by a compressor and transferred to a condenser. In the
condenser, the refrigerant is cooled, typically by airflow, and
recondenses into a liquid. Air cooled condensers typically comprise
a condenser coil and a fan that induces airflow over the coil. In
some conventional designs, an economizer is utilized in the chiller
design to improve performance. For example, a flash tank economizer
may be employed to at least partially evaporate a portion of the
condensed refrigerant. The vapor phase refrigerant may be extracted
from the flash tank and redirected to the compressor, while the
liquid phase refrigerant from the flash tank is directed to the
evaporator, closing the refrigeration loop. Although a flash tank
economizer may improve performance, at extremely high ambient
temperatures, additional performance enhancements may be
desired.
SUMMARY
[0005] The present invention relates to a refrigeration system that
includes a condenser configured to condense refrigerant, a first
economizer system, a second economizer system, an expansion device
configured to receive the refrigerant from the first economizer
system or the second economizer system and to expand the
refrigerant, an evaporator configured to evaporate the expanded
refrigerant, and a screw compressor. The first economizer system
includes a first expansion device configured to expand a first
portion of the condensed refrigerant and a heat exchanger
configured to subcool a second portion of the condensed refrigerant
with the first portion. The second economizer system includes a
second expansion device configured to expand the refrigerant and a
flash tank configured to separate the refrigerant into vapor phase
refrigerant and liquid phase refrigerant. The screw compressor
includes a suction port configured to receive the evaporated
refrigerant, a first economizer port configured to receive the
first portion of the refrigerant, a second economizer port
configured to receive the vapor phase refrigerant, and a discharge
port. The screw compressor is configured to compress the evaporated
refrigerant, the first portion of the refrigerant and the vapor
phase refrigerant and to discharge the compressed refrigerant
through the discharge port.
[0006] The present invention also relates to a refrigeration system
that includes a condenser configured to condense refrigerant, a
high pressure economizer system, and a lower pressure economizer
system. The high pressure economizer system includes a high
pressure expansion device configured to expand the condensed
refrigerant and a high pressure flash tank configured to separate
the expanded refrigerant into a high pressure vapor phase
refrigerant and a high pressure liquid phase refrigerant. The low
pressure economizer system includes a low pressure expansion device
configured to expand the high pressure liquid refrigerant and a
lower pressure flash tank configured to separate the expanded
refrigerant into lower pressure vapor phase refrigerant and lower
pressure liquid phase refrigerant. The refrigeration system further
includes a third expansion device configured to receive and to
expand the lower pressure liquid phase refrigerant, an evaporator
configured to evaporate the expanded refrigerant from the third
expansion device, and a screw compressor. The screw compressor
includes a suction port configured to receive the evaporated
refrigerant, a first economizer port configured to receive the high
pressure vapor phase refrigerant, a second economizer port
configured to receive the lower pressure vapor phase refrigerant,
and a discharge port. The screw compressor is configured to
compress the evaporated refrigerant, the high pressure vapor phase
refrigerant, and the lower pressure vapor phase refrigerant and to
discharge the compressed refrigerant through the discharge
port.
[0007] The present invention further relates to a refrigeration
system that includes a condenser configured to condense
refrigerant, a high pressure economizer system, and a low pressure
economizer system. The high pressure economizer system includes a
first expansion device configured to expand a first portion of the
condensed refrigerant and a heat exchanger configured to subcool a
second portion of the condensed refrigerant with the first portion.
The low pressure economizer system includes a low pressure
expansion device configured to expand the subcooled second portion
and a flash tank configured to separate the expanded second portion
into vapor phase refrigerant and liquid phase refrigerant. The
refrigeration system further includes a third expansion device
configured to expand the liquid phase refrigerant, an evaporator
configured to evaporate the expanded refrigerant, and a screw
compressor. The screw compressor includes a suction port configured
to receive the expanded refrigerant, a low pressure economizer port
configured to receive the vapor phase refrigerant, a high pressure
economizer port configured to receive the first portion of the
refrigerant, and a discharge port. The screw compressor is
configured to compress the refrigerant received through the suction
port, the low pressure economizer port, and the high pressure
economizer port and to discharge the compressed refrigerant through
the discharge port.
DRAWINGS
[0008] FIG. 1 depicts an embodiment of a commercial heating
ventilating, air conditioning and refrigeration (HVAC&R) system
that employs a screw chiller with an economizer system in
accordance with aspects of the present techniques.
[0009] FIG. 2 is a diagrammatical view of an embodiment of a screw
chiller economizer system in accordance with aspects of the present
techniques.
[0010] FIG. 3 is a diagrammatical view of another embodiment of a
screw chiller economizer system in accordance with aspects of the
present techniques.
[0011] FIG. 4 is a diagrammatical view of another embodiment of a
screw chiller economizer system in accordance with aspects of the
present techniques.
DETAILED DESCRIPTION
[0012] The present disclosure is directed to screw chillers with
economizer systems that include a low pressure economizer and a
high pressure economizer. According to certain embodiments, the low
pressure economizer includes a flash tank, an expansion device and
a flow control valve, while the high pressure economizer includes a
heat exchanger and an expansion device. In certain embodiments, the
high pressure economizer also may include a flow control valve. The
screw chillers also include a screw compressor that compresses
refrigerant received from an evaporator. The screw compressor
includes a low pressure economizer port designed to receive lower
pressure refrigerant from the low pressure economizer and a high
pressure economizer port designed to receive higher pressure
refrigerant from the high pressure economizer. The screw compressor
is designed to compress the refrigerant received from the
evaporator, the refrigerant received through the low pressure
economizer port, and the refrigerant received through the high
pressure economizer port and to discharge the compressed
refrigerant through a common discharge port. The injection of the
lower pressure refrigerant and the higher pressure refrigerant into
the screw chiller through the economizer ports may be designed to
reduce the mass flow rate of refrigerant through the lower pressure
regions of the screw compressor, which in turn may reduce the load
on the compressor, thereby providing increased system capacity.
Further, the economizers may be designed to provide additional
subcooling of the refrigerant, which in turn may increase the
system efficiency. According to certain embodiments, the screw
chillers disclosed herein may be particularly well suited to
environments with high ambient temperatures.
[0013] FIG. 1 depicts an exemplary application for a refrigeration
system. Such systems, in general, may be applied in a range of
settings, both within the heating, ventilating, air conditioning,
and refrigeration (HVAC&R) field and outside of that field. The
refrigeration systems may provide cooling to data centers,
electrical devices, freezers, coolers, or other environments
through vapor-compression refrigeration, absorption refrigeration,
or thermoelectric cooling. In presently contemplated applications,
however, refrigeration systems may be used in residential,
commercial, light industrial, industrial, and in any other
application for heating or cooling a volume or enclosure, such as a
residence, building, structure, and so forth. Moreover, the
refrigeration systems may be used in industrial applications, where
appropriate, for basic refrigeration and heating of various
fluids.
[0014] FIG. 1 illustrates an exemplary application, in this case an
HVAC&R system for building environmental management, that may
employ heat exchangers. A building 10 is cooled by a system that
includes a chiller 12 and a boiler 14. As shown, chiller 12 is
disposed on the roof of building 10 and boiler 14 is located in the
basement; however, the chiller and boiler may be located in other
equipment rooms or areas next to the building. Chiller 12 is an air
cooled or water cooled device that implements a refrigeration cycle
to cool water. Chiller 12 is housed within a single structure that
includes a refrigeration circuit, a free cooling system, and
associated equipment such as pumps, valves, and piping. For
example, chiller 12 may be single package rooftop unit. Boiler 14
is a closed vessel in which water is heated. The water from chiller
12 and boiler 14 is circulated through building 10 by water
conduits 16. Water conduits 16 are routed to air handlers 18,
located on individual floors and within sections of building
10.
[0015] Air handlers 18 are coupled to ductwork 20 that is adapted
to distribute air between the air handlers and may receive air from
an outside intake (not shown). Air handlers 18 include heat
exchangers that circulate cold water from chiller 12 and hot water
from boiler 14 to provide heated or cooled air. Fans, within air
handlers 18, draw air through the heat exchangers and direct the
conditioned air to environments within building 10, such as rooms,
apartments, or offices, to maintain the environments at a
designated temperature. A control device, shown here as including a
thermostat 22, may be used to designate the temperature of the
conditioned air. Control device 22 also may be used to control the
flow of air through and from air handlers 18. Other devices may, of
course, be included in the system, such as control valves that
regulate the flow of water and pressure and/or temperature
transducers or switches that sense the temperatures and pressures
of the water, the air, and so forth. Moreover, control devices may
include computer systems that are integrated with or separate from
other building control or monitoring systems, and even systems that
are remote from the building.
[0016] FIG. 2 schematically depicts an embodiment of chiller 12,
which incorporates an economizer system. As noted above with
respect to FIG. 1, chiller 12 is housed within a single structure
and may be located outside of a building or environment, for
example on a rooftop. Chiller 12 includes a cooling fluid loop 24
that circulates a cooling fluid, such as chilled water, an ethylene
glycol-water solution, brine, or the like, to a cooling load, such
as a building, piece of equipment, or environment. For example,
cooling fluid loop 24 may circulate the cooling fluid to water
conduits 16 shown in FIG. 1. In certain embodiments, the cooling
fluid may circulate within the cooling fluid loop 24 to a cooling
load, such as a research laboratory, computer room, office
building, hospital, molding and extrusion plant, food processing
plant, industrial facility, machine, or any other environments or
devices in need of cooling.
[0017] Chiller 12 includes an evaporator 26 that transfers heat
from the cooling fluid loop 24 to refrigerant flowing within a
closed refrigerant loop 28. The refrigerant may be any fluid that
absorbs and extracts heat. For example, the refrigerant may be a
hydrofluorocarbon (HFC) based R-410A, R-407C, or R-134a, or it may
be carbon dioxide (R-744) or ammonia (R-717). As the refrigerant
flows through evaporator 26, the refrigerant absorbs heat from the
cooling fluid flowing within evaporator 26 to cool the cooling
fluid before the cooling fluid returns to the cooling load.
[0018] The heated refrigerant from evaporator 26 is circulated
through refrigerant loop 28 to cool the refrigerant before
returning the refrigerant to evaporator 26 where the refrigerant
may again absorb heat from the cooling fluid. In particular, the
heated refrigerant from evaporator 26 flows to a compressor 30 as a
low pressure and temperature vapor. The refrigerant from evaporator
26 enters compressor 30 through a suction port 31. Compressor 30
reduces the volume available for the refrigerant vapor,
consequently, increasing the pressure and temperature of the vapor
refrigerant. According to certain embodiments, compressor 30 may be
a screw compressor, such as a tri-rotor screw compressor.
Compressor 30 is driven by a motor 32 that receives power from a
variable speed drive (VSD) or from a direct AC or DC power source.
According to certain embodiments, motor 32 receives fixed line
voltage and frequency from an AC power source. Further, in certain
applications, motor 32 may be driven by a variable voltage or
frequency drive. The motor may be a switched reluctance (SR) motor,
an induction motor, an electronically commutated permanent magnet
motor (ECM), or any other suitable motor type.
[0019] Compressor 30 includes two economizer ports 34 and 36 that
also direct refrigerant into compressor 30. Economizer port 34
receives lower pressure refrigerant from a low pressure economizer
system 38, and economizer port 36 receives higher pressure
refrigerant from a high pressure economizer system 40. Each of the
economizer ports 34 and 36 direct refrigerant into a different
pressure area within compressor 30. For example, economizer port 36
may direct refrigerant into a higher pressure area than economizer
port 34, and economizer port 34 may direct refrigerant into a
higher pressure area than suction inlet 31. Further, the pressure
of the refrigerant entering through each economizer port 34 and 36
is higher than the pressure of the refrigerant within the
compression area coupled to each economizer port 34 or 36.
Accordingly, relatively higher pressure refrigerant enters
compressor 30 through economizer ports 34 and 36 to mix with
existing refrigerant of a relatively lower pressure.
[0020] In certain embodiments, the pressure difference may be
designed to draw refrigerant into compressor 30 through economizer
ports 34 and 36. For example, the refrigerant entering compressor
30 through economizer port 34 may be at a pressure higher than the
pressure of the refrigerant within the compression chamber coupled
to economizer port 34. Accordingly, the higher pressure refrigerant
entering through economizer port 34 may be drawn into the
compressor 30, where the refrigerant may mix with the existing
refrigerant and expand within the constant volume of compressor 30,
thereby further increasing the pressure within compressor 30. In a
similar example, the refrigerant entering compressor 30 through
economizer port 36 may be at a higher pressure than the pressure of
the refrigerant within the compression area coupled to economizer
port 36. The pressure difference may draw the higher pressure
refrigerant into compressor 30, where the higher pressure
refrigerant may mix with the existing refrigerant and expand to
further increase the pressure within compressor 30. As the
refrigerant from suction inlet 31 and from economizer ports 34 and
36 flows through compressor 30, the refrigerant is compressed. The
compressed refrigerant from suction inlet 31 and from economizer
ports 34 and 36 is discharged through a common discharge port 37
that directs the compressed refrigerant to a condenser 42.
[0021] The compressed refrigerant enters condenser 42 as a high
pressure and temperature vapor. According to certain embodiments,
condenser 42 may be a fin and tube heat exchanger, brazed aluminum
multichannel heat exchanger, or other suitable heat exchanger. A
fan 44, which is driven by a motor 46, draws air across condenser
42 to cool the refrigerant flowing within condenser 42. According
to certain embodiments, the refrigerant vapor may condense to a
liquid as the refrigerant flow through condenser 42. The liquid
refrigerant then flows through economizer systems 38 and 40, where
the refrigerant may be subcooled.
[0022] After flowing through economizer systems 38 and 40, the
liquid refrigerant flows through an expansion device 48 where the
refrigerant expands to become a low pressure and temperature
liquid. Typically, expansion device 48 will be a thermal expansion
valve (TXV); however, according to other exemplary embodiments, the
expansion device may be an electronic expansion valve, a fixed
orifice, or the like. According to certain embodiments, after the
refrigerant exits the expansion device, some vapor refrigerant may
be present in addition to the liquid refrigerant. From expansion
device 48, the refrigerant flows through evaporator 26 where the
refrigerant may again absorb heat from the cooling fluid flowing
within cooling fluid loop 24.
[0023] Economizer systems 38 and 40 may be designed to provide
additional subcooling of the refrigerant entering evaporator 26,
which, in turn may increase the efficiency of chiller 12.
Economizer systems 38 and 40 also may be designed to direct a
portion of the refrigerant back to compressor 30, bypassing
evaporator 26, which may reduce the mass flow rate of refrigerant
in the lower pressure regions of compressor 30, thereby reducing
the load on compressor 30.
[0024] High pressure economizer system 40 includes a heat exchanger
50, an optional flow control valve 52, and an expansion device 54.
According to certain embodiments, heat exchanger 50 may be a brazed
plate heat exchanger; however, in other embodiments, any suitable
type of heat exchanger may be employed. High pressure economizer
system 40 receives the condensed refrigerant from condenser 42 and
separates the refrigerant into a first portion that directly enters
heat exchanger 50 and a second portion that flows through optional
flow control valve 52 and expansion device 54 prior to entering
heat exchanger 50. As the second portion of the refrigerant flows
though expansion device 54, the refrigerant is expanded, thereby
reducing the pressure and temperature of the refrigerant. According
to certain embodiments, expansion device 54 may be a thermal
expansion valve (TXV), an electronic expansion valve, or a fixed
orifice, among others. In certain embodiments, an optional flow
control valve 52 may be disposed upstream of expansion device 54 to
control the flow of refrigerant within high pressure economizer
system 40. Flow control valve 52 may be a solenoid valve, ball
valve, gate valve, rotor valve, or the like, controlled by
electromechanical actuators, pneumatic actuators, hydraulic
actuators, or other suitable controls. In other embodiments, for
example, where expansion device 54 is an electronic expansion
valve, flow control valve 52 may be omitted and expansion device 54
may be used to control the flow of refrigerant through economizer
system 40.
[0025] From expansion device 54, the second portion of refrigerant
flows through heat exchanger 50 where the lower pressure second
portion of refrigerant absorbs heat from the first portion of
refrigerant that directly enters heat exchanger 50 from condenser
42. As the second portion of the refrigerant is heated within heat
exchanger 50, the second portion of refrigerant may evaporate to
produce vapor refrigerant that is directed to compressor 30 through
economizer port 36. As noted above, the refrigerant entering
compressor 30 through economizer port 36 may have a higher pressure
than the existing refrigerant within compressor 30. The higher
pressure may draw the refrigerant into compressor 30 and also may
further increase the pressure of the refrigerant within compressor
30.
[0026] As the first portion of refrigerant flows through heat
exchanger 50, the first portion of refrigerant transfer heats to
the second portion of refrigerant flowing through heat exchanger
50. Accordingly, the first portion of refrigerant flowing through
heat exchanger 50 may be subcooled by the second portion of
refrigerant that has passed through expansion device 54. According
to certain embodiments, heat exchanger 50 approximates a
counter-flow configuration to maximize heat transfer. The subcooled
refrigerant exiting heat exchanger 50 is then directed to the lower
pressure economizer system 38, where the refrigerant may undergo
further subcooling. In other embodiments, the second portion of
refrigerant that is directed through expansion device 54 may be
drawn from a point downstream of heat exchanger 50. For example,
the first portion of refrigerant may flow through heat exchanger
50. The second portion of refrigerant may then be drawn from the
first portion of refrigerant that has exited heat exchanger 50. The
second portion of refrigerant may then be directed through
expansion device 54 and heat exchanger 50. According to certain
embodiments, the additional subcooling may improve operation of the
expansion device 54.
[0027] Low pressure economizer system 38 includes a flash tank 56,
an expansion device 58, and a flow control valve 60. Within low
pressure economizer system 38, the refrigerant flows through an
expansion device 58 where the refrigerant is expanded to reduce the
pressure and temperature of the refrigerant. According to certain
embodiments, expansion device 58 may be a thermal expansion valve,
electronic expansion valve, fixed orifice, or the like. Further, in
certain embodiments, a controller 62 may operate expansion device
58 to limit the level of liquid refrigerant in flash tank 56. The
refrigerant from expansion device 58 then enters flash tank 56
where the vapor and liquid phases within the refrigerant may be
separated. The vapor phase refrigerant exits flash tank 56 through
an upper portion of flash tank 56 and flows through a flow control
valve 60, which may control the flow of refrigerant through low
pressure economizer system 38. Flow control valve 60 may be a
solenoid valve, ball valve, gate valve, rotor valve, or the like,
controlled by electromechanical actuators, pneumatic actuators,
hydraulic actuators, or other suitable controls. From flow control
valve 60, the vapor phase refrigerant is directed to compressor 30
through economizer port 34. As noted above, the refrigerant
entering compressor 30 through economizer port 34 may have a higher
pressure than the pressure of the existing refrigerant in the
compression area coupled to economizer port 34. The relatively
higher pressure may draw the refrigerant into compressor 30 and
also may further increase the pressure of the refrigerant within
compressor 30.
[0028] Within flash tank 56, the liquid phase refrigerant may
separate from the vapor phase refrigerant and collect within a
lower portion of flash tank 56. From flash tank 56, the liquid
phase refrigerant is directed through expansion device 48 and
returned to evaporator 26, where the liquid phase refrigerant may
absorb heat from the cooling fluid flowing through cooling fluid
loop 24.
[0029] Operation of economizer systems 38 and 40 may be controlled
by one or more controllers 62, which may receive information from
input devices 64 and 66. For example, input device 64 may be a
temperature sensor that measures the ambient air temperature, and
input device 66 may be a temperature sensor that measures a
temperature of the fluid within cooling fluid loop 24. However, in
other embodiments, control of economizer systems 38 and 40 may be
based on other input devices, such as a level sensor, pressure
sensors, and/or pressure and temperature transducers in
communication with controller 62.
[0030] Controller 62 may adjust operation of the economizer systems
38 and 40 based on input from input devices 62 and 64. Controller
62 is coupled to flow control valve 52 within high pressure
economizer system 40 and to flow control valve 60 within low
pressure economizer system 38. Controller 62 may open and close
flow control valves 52 and 60 to enable and disable operation of
one or both economizer system 38 and 40 based on control signals
received from input devices 64 and 66. For example, controller 62
may enable both economizer systems 38 and 40 when ambient
temperatures are high and/or when the temperature within the
cooling fluid loop 24 is high. If the ambient temperature and/or
the cooling fluid temperature decrease, controller 62 may close one
or both valves 52 and 60 to bypass one or both of the economizer
system 38 and 40. For example, when flow control valve 52 is
closed, all of the refrigerant from condenser 42 may flow directly
to heat exchanger 50 and no refrigerant may enter compressor 30
through economizer port 36. In another example, when flow control
valve 60 is closed, all of the refrigerant exiting heat exchanger
50 may flow through flash tank 56 to expansion device 48, and no
refrigerant may enter compressor 30 through economizer port 34. In
certain embodiments, controller 62 may adjust valves 52 and 60
between open and closed positions. Further, in certain embodiments,
controller 62 may adjust the amount that valves 52 and 60 are open
to regulate the amount of flow to compressor 30 through economizer
ports 34 and 36.
[0031] Controller 62 may execute hardware or software control
algorithms to regulate operation of chiller 12. According to
exemplary embodiments, controller 62 may include an analog to
digital (A/D) converter, a microprocessor, a non-volatile memory,
and an interface board. Controller 62 also includes, or is
associated with, input/output circuitry for receiving sensed
signals from input devices 64 and 66, and interface circuitry for
outputting control signals for valves 52 and 60 and motors 32 and
46. Other devices may, of course, be included in the system, such
as additional pressure and/or temperature transducers or switches
that sense temperatures and pressures of the refrigerant, the heat
exchangers, the compressor, the flash tank, the inlet and outlet
air, and so forth. Further, other values and/or set points based on
a variety of factors, such as system capacity, cooling load, and
the like may be used to determine when to operate economizer
systems 38 and 40. Moreover, according to certain embodiments,
controller 62 also may be coupled to motor 46 of condenser 42 and
to motor 32 of compressor 30. In these embodiments, controller 62
also may govern operation of condenser 42 and compressor 30 based
on input received from input devices 62 and 64.
[0032] FIG. 3 depicts another embodiment of chiller 12 that
incorporates high pressure economizer system 40 and low pressure
economizer system 38. The embodiment shown in FIG. 3 is generally
similar to the embodiment described above with respect to FIG. 2.
However, rather than including a heat exchanger as shown in FIG. 2,
the high pressure economizer system 40 shown in FIG. 3 includes a
flash tank 68, an expansion device 70, and a flow control valve 72.
According to certain embodiments, expansion device 70 may be a
thermal expansion valve, electronic expansion valve, fixed orifice,
or the like.
[0033] Condensed refrigerant from condenser 42 enters high pressure
economizer system 40 and flows through expansion device 70 where
the refrigerant is expanded to reduce the pressure and temperature
of the refrigerant. The refrigerant then enters flash tank 68,
where the liquid and vapor phases separate. The vapor phase
refrigerant exits flash tank 68 and flows through control valve 72
to enter compressor 30 through economizer port 36. The liquid phase
refrigerant collects within a lower portion of flash tank 68 and is
directed to low pressure economizer system 38.
[0034] FIG. 4 depicts an embodiment of chiller 12 that includes a
heat exchanger within high pressure economizer system 40 and a
flash tank within low pressure economizer system 38. The embodiment
of chiller 12 shown in FIG. 4 is generally similar to the
embodiment of chiller 12 shown in FIG. 3; however, the positions of
the flash tank and the heat exchanger are interchanged.
[0035] As shown in FIG. 4, condensed refrigerant from condenser 42
enters high pressure economizer system 40 and flows through
expansion device 70, where the refrigerant is expanded. The
refrigerant then enters a flash tank 68 where the vapor and liquid
phase refrigerant separates. The vapor phase refrigerant flows
through a flow control valve 72 to enter compressor 30 through
economizer port 36, while the liquid phase refrigerant flows from
flash tank 68 to low pressure economizer system 38.
[0036] Within low pressure economizer system 38, the liquid phase
refrigerant from flash tank 68 is separated into a first portion
that flows directly to a heat exchanger 74 and a second portion
that flows through an optional flow control valve 76 and an
expansion device 78 prior to entering heat exchanger 74. According
to certain embodiments, heat exchanger 74 may be a brazed plate
heat exchanger; however, in other embodiments, any suitable type of
heat exchanger may be employed. Expansion device 78 may be a
thermal expansion valve (TXV), an electronic expansion valve, or a
fixed orifice, among others. Flow control valve 76 may be a
solenoid valve, ball valve, gate valve, rotor valve, or the like,
controlled by electromechanical actuators, pneumatic actuators,
hydraulic actuators, or other suitable controls. In other
embodiments, for example, where expansion device 78 is an
electronic expansion valve, flow control valve 76 may be omitted
and expansion device 78 may be used to control the flow of
refrigerant through economizer system 38.
[0037] As the second portion of refrigerant is expanded within
expansion device 78, the pressure and temperature of the
refrigerant may be reduced. Accordingly, within heat exchanger 74,
the expanded second portion of refrigerant may absorb heat from the
first portion of refrigerant that flows directly from flash tank 68
to heat exchanger 74. As the second portion of the refrigerant is
heated within heat exchanger 50, the second portion of refrigerant
may evaporate to produce vapor refrigerant that is directed to
compressor 30 through economizer port 34. The first portion of
refrigerant may be subcooled within heat exchanger 74 as the first
portion of refrigerant transfers heat to the second portion of
refrigerant. The subcooled refrigerant may then be directed through
expansion device 48 to evaporator 26.
[0038] While only certain features and embodiments of the invention
have been illustrated and described, many modifications and changes
may occur to those skilled in the art (e.g., variations in sizes,
dimensions, structures, shapes and proportions of the various
elements, values of parameters (e.g., temperatures, pressures,
etc.), mounting arrangements, use of materials, orientations, etc.)
without materially departing from the novel teachings and
advantages of the subject matter recited in the claims. It is,
therefore, to be understood that the appended claims are intended
to cover all such modifications and changes as fall within the true
spirit of the invention. Furthermore, in an effort to provide a
concise description of the exemplary embodiments, all features of
an actual implementation may not have been described (i.e., those
unrelated to the presently contemplated best mode of carrying out
the invention, or those unrelated to enabling the claimed
invention). It should be appreciated that in the development of any
such actual implementation, as in any engineering or design
project, numerous implementation specific decisions may be made.
Such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure, without undue experimentation.
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