U.S. patent application number 10/954499 was filed with the patent office on 2006-03-30 for cooling systems.
Invention is credited to Michal K. Grabon.
Application Number | 20060064997 10/954499 |
Document ID | / |
Family ID | 36097475 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060064997 |
Kind Code |
A1 |
Grabon; Michal K. |
March 30, 2006 |
Cooling systems
Abstract
An apparatus has a compressor having suction and discharge
ports. One or more conduits form a main flowpath from the discharge
port through a condenser, a heat exchanger first leg, a first
expansion device, and an evaporator to return to the suction port.
The conduits also form a bypass flowpath bypassing the heat
exchanger first leg, the first expansion device, and the evaporator
but passing through a second leg of the heat exchanger in heat
exchange relation with the first leg.
Inventors: |
Grabon; Michal K.;
(Bressolles, FR) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510
US
|
Family ID: |
36097475 |
Appl. No.: |
10/954499 |
Filed: |
September 29, 2004 |
Current U.S.
Class: |
62/197 ; 62/113;
62/210; 62/513 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 41/00 20130101 |
Class at
Publication: |
062/197 ;
062/113; 062/513; 062/210 |
International
Class: |
F25B 41/00 20060101
F25B041/00; F25B 49/00 20060101 F25B049/00; F25B 13/00 20060101
F25B013/00 |
Claims
1. An apparatus comprising: a compressor having suction and
discharge ports; a condenser; a first expansion device; a second
expansion device; an evaporator; a heat exchanger having first and
second portions in heat exchange relation with each other; and one
or more conduits forming: a main flowpath from the discharge port
through the condenser, the heat exchanger first portion, the first
expansion device, and the evaporator and returning to the suction
port; and a bypass flowpath bypassing the heat exchanger first
portion, the first expansion device, and the evaporator, but
passing through the second expansion device and the heat exchanger
second portion.
2. The apparatus of claim 1 wherein: the evaporator lacks a
distributor.
3. The apparatus of claim 1 wherein: the second expansion device is
a TXV having a bulb essentially in heat exchange relation with a
suction port condition.
4. The apparatus of claim 1 wherein: the second expansion device is
an EXV.
5. The apparatus of claim 4 further comprising: a controller
coupled to the EXV and programmed to control the EXV responsive to
indicated superheat.
6. The apparatus of claim 1 wherein: the heat exchanger first
portion is downstream of the condenser and upstream of the
evaporator along the main flowpath; and the heat exchanger second
portion is downstream of the condenser along the bypass
flowpath.
7. The apparatus of claim 6 wherein: the heat exchanger first
portion is upstream of the first expansion device along the main
flowpath.
8. The apparatus of claim 1 wherein: the evaporator is a
refrigerant-to-air heat exchanger.
9. The apparatus of claim 1 wherein: in at least a bypass mode, a
bypass flow along the bypass flowpath enters the heat exchanger
second portion in a two-phase gas/liquid condition and exits the
heat exchanger second portion in a single-phase superheated gas
condition; and in the bypass mode, a main flow along the main
flowpath remains essentially a single-phase liquid in said heat
exchanger second portion.
10. The apparatus of claim 1 wherein: the compressor is selected
from the group consisting of screw compressors and scroll
compressors.
11. A method for operating the apparatus of claim 1 comprising:
detecting at least one operational parameter; and responsive to the
detecting, operating at least the second expansion device so as to
maintain essentially single-phase liquid refrigerant entering the
evaporator along the main flowpath.
12. The method of claim 11 wherein: the at least one operational
parameter includes at least one of: saturated suction temperature;
and actual suction temperature.
13. A method for operating a cooling system comprising: causing a
main flow of refrigerant through an evaporator; and precooling the
main flow upstream of the evaporator so as to so as to maintain
said main flow essentially as a liquid entering the evaporator.
14. The method of claim 13 wherein: the precooling comprises
controlling a bypass flow in heat exchange relation with the main
flow.
15. The method of claim 13 further comprising: determining whether,
absent the precooling, the main flow would enter the evaporator
essentially as a two-phase flow.
16. The method of claim 15 wherein: the determining includes
determining that a superheat of refrigerant exiting the evaporator
exceeds a threshold.
17. A system comprising: a compressor; a condenser; a discharge
line, coupling the compressor to the condenser to carry at least a
main flow of refrigerant from the compressor to the condenser; an
expansion device; an evaporator; a suction line, coupling the
evaporator to the compressor to carry refrigerant from the
condenser to the compressor and comprising a first and second
parallel segments; and means for precooling refrigerant entering
the expansion device so as to maintain said main flow essentially
as a liquid while flowing along a flowpath length at least from the
expansion device to the evaporator.
18. The system of claim 17 wherein: the evaporator lacks a
distributor.
19. The system of claim 17 wherein: within the evaporator, the main
flow transitions to a two-phase liquid/gas flow and then to a
one-phase superheated gas flow.
20. The system of claim 17 wherein: the bypass flow represents
10%-35%, by weight, of a total refrigerant flow through the
compressor.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to cooling systems. More particularly,
the invention relates to the control of refrigerant phase in
evaporators of air conditioning and refrigeration systems.
[0002] Many engineering considerations attend the design and
operation of closed air conditioning and refrigeration systems.
Among these are a variety of efficiency and other considerations
attendant to evaporator operation. Proper evaporator operation is
important for obtaining efficient and reliable system operation.
Considerations include the handling of refrigerant and the
management of heat transfer. Among problems that must be managed is
excessive icing as this may interfere with heat transfer.
Accordingly, much effort has gone into evaporator design and
engineering.
[0003] A particular area of emphasis has been the engineering of
distributor systems. A distributor receives two-phase refrigerant
from the expansion device and provides balanced delivery of liquid
and gas refrigerant phases among the various coils of an evaporator
so as to prevent uneven performance. Various types of distributors
have been developed. These include capillary-type distributors and
impingement/turbulence distributors. Exemplary distributors are
shown in U.S. Pat. Nos. 2,148,414, 2,461,876, 3,795,259, 4,543,802,
5,832,744, and 5,842351, EP 0160542, and JP 5-322378 and
10-185363.
[0004] Nevertheless there remains room for further improvement in
the art.
SUMMARY OF THE INVENTION
[0005] One aspect of the invention involves an apparatus including
a compressor having suction and discharge ports, a condenser, first
and second expansion devices, an evaporator, and a heat exchanger
having first and second portions in heat exchange relation with
each other. One or more conduits form a main flowpath and a bypass
flowpath. The main flowpath runs from the discharge port through
the condenser, the heat exchanger first portion, the first
expansion device, and the evaporator, and returns to the suction
port. The bypass flowpath bypasses the heat exchanger first
portion, the first expansion device, and the evaporator, but passes
through the second expansion device and the heat exchanger second
portion.
[0006] In various implementations, the evaporator may lack a
distributor. The second expansion device may be a TXV having a bulb
essentially in heat exchange relation with a suction port
condition. The second expansion device may be an EXV. A controller
may be coupled to the EXV and programmed to control the EXV
responsive to indicated superheat. The heat exchanger first portion
may be downstream of the condenser and upstream of the evaporator
along the main flowpath. The heat exchanger second portion may be
downstream of the condenser along the bypass flowpath. The heat
exchanger first portion may be upstream of the first expansion
device along the main flowpath. The evaporator may be a
refrigerant-to-air heat exchanger. In at least a bypass mode, a
bypass flow along the bypass flowpath may enter the heat exchanger
second portion in a two-phase gas/liquid condition and exit the
heat exchanger second portion in a single-phase superheated gas
condition. In the bypass mode, a main flow along the main flowpath
may remain essentially a single-phase liquid in said heat exchanger
second portion. The compressor may be selected from the group
consisting of screw compressors and scroll compressors.
[0007] Another aspect of the invention involves a method for
operating such an apparatus. At least one operational parameter is
detected. Responsive to the detection, at least the second
expansion device is operated so as to maintain essentially
single-phase liquid refrigerant entering the evaporator along the
main flowpath. The at least one operational parameter may include
at least one of saturated suction temperature and actual suction
temperature.
[0008] Another aspect of the invention involves a method for
operating a cooling system. A main flow of refrigerant is caused to
pass through an evaporator. The main flow is precooled upstream of
the evaporator so as to maintain the main flow essentially as a
liquid entering the evaporator. The precooling may comprise
controlling a bypass flow in heat exchange relation with the main
flow. The method may further comprise determining whether, absent
the precooling, the main flow would enter the evaporator
essentially as a two-phase flow.
[0009] Another aspect of the invention involves a system comprising
a compressor, a condenser, an expansion device, and an evaporator,
a discharge line couples the compressor to the condenser to carry
at least a main flow of refrigerant from the compressor to the
condenser. A suction line couples the evaporator to the compressor
to carry refrigerant from the condenser to the compressor. The
system includes means for precooling refrigerant entering the
expansion device so as to maintain the main flow essentially as a
liquid while flowing along a flowpath length at least from the
expansion device to the evaporator.
[0010] In various implementations, the evaporator may lack a
distributor. Within the evaporator, the main flow may transition to
a two-phase liquid/gas flow and then to a one-phase superheated gas
flow. The bypass flow may represent 10%-35%, by weight, of a total
refrigerant flow through the compressor.
[0011] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic representation of a refrigeration or
air conditioning system employing the present invention.
[0013] FIG. 2 is a phase diagram for a prior art system.
[0014] FIG. 3 is a phase diagram for the system of FIG. 1.
[0015] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0016] FIG. 1, shows an exemplary closed refrigeration or air
conditioning system 10. The system 10 has a hermetic compressor 12,
from which a compressor discharge conduit or line 14 extends
downstream to a condenser 16. An intermediate line 18 extends
downstream from the condenser 16 to an expansion device 20 and an
evaporator 22. A suction line 24 extends downstream from the
evaporator 22 to the compressor 12 to complete the main
circuit/flowpath 26.
[0017] To form a bypass circuit/flowpath 28, a bypass line 30
branches off from the intermediate line 18 and contains an
auxiliary expansion device 32 and connects with the suction line
24. A heat exchanger 34 is located such that the bypass line 30,
downstream of the expansion device 32, and the line 18, upstream of
the main expansion device 20, are in heat exchange
relationship.
[0018] The exemplary evaporator 22 is a cross-flow
refrigerant-to-air heat exchanger having a number of parallel
refrigerant coils 36 extending from inlet ends at a liquid
collector or manifold 38 to outlet ends at a suction collector or
manifold 40. A fan 42 drives an airflow 44 across the coils 36 so
that the refrigerant passing through the coils may draw heat from
the airflow.
[0019] Exemplary expansion devices 20 and 32 are electronic
expansion valves (EEVs) and are illustrated as coupled to a
monitoring/control system 44 (e.g., a microprocessor-based
controller) for receiving control inputs via control lines 45 and
46, respectively. The exemplary control system 44 may receive
inputs such as zone inputs from one or more sensors 47, system
condition inputs from one or more sensors (e.g., suction
temperature sensor 50 and suction pressure sensor 52), and external
control inputs from one or more input devices (e.g., thermostats
60).
[0020] Alternatively to the EEVs, any of a variety of expansion
devices may be used (e.g., a thermal expansion valve (TXV) 32
having a remote bulb 70, a fixed orifice device, or a capillary
tube device).
[0021] A basic prior art system would lack the bypass flowpath 28
and heat exchanger 34. FIG. 2 shows pressure 100 and enthalpy 102
for the refrigerant flow in such a basic system (or the present
system with no bypass flow). A boundary 104 separates a two-phase
gas/liquid mixture domain 106 from a single phase sub-cooled liquid
domain 108 and a single phase superheated gas domain 110. Suction
conditions are shown as point or condition 120 at enthalpy 122 and
pressure 124. These conditions are essentially present in the
flowpath downstream from the suction manifold 40 to the compressor
suction port. The refrigerant is compressed (plot compression
segment 125) in the compressor 12 to a compressed point 126 with
increased enthalpy 128 and increased pressure 130. During the
compression 125, the refrigerant may typically remain in the
superheated gas domain 110 or may transition thereto from the
two-phase domain 106. The refrigerant is condensed (condensing
segment 131) in the condenser 16 to a condensed point 132 with
reduced enthalpy 134 but at the same pressure as the
compressed/discharge condition. During the condensing 131, the
refrigerant state may transition from the superheated gas domain
110 to the two-phase domain 106 and even into the sub-cooled liquid
domain 108. The refrigerant is expanded (expansion segment 135) in
the expansion device 34 to an expanded point 136 with decreased
pressure 138. During the expansion 135, enthalpy may remain
essentially constant at 134. The refrigerant may reenter or remain
in the two-phase domain 106 during the expansion 135. This expanded
two-phase refrigerant must enter the evaporator. The refrigerant is
evaporated (evaporation segment 139) in the evaporator to return to
the suction point 120 with substantially increased enthalpy and
slightly decreased pressure relative to the expanded point 136.
[0022] The presence of the expanded point 136 in the two-phase
domain 106 presents substantial problems. With two-phase
refrigerant entering the evaporator, it becomes difficult to
balance the refrigerant across the evaporator coils. Namely,
otherwise similar coils may see different total amounts of
refrigerant and/or different ratios of the two phases. This can
produce substantially different coil conditions amongst the various
coils. The coils with higher amounts of refrigerant and higher
relative amounts of liquid may overcool so as to produce excessive
frost buildup. Overall efficiency may be reduced. Accordingly, it
is known to use complicated distributor arrangements in place of
the liquid manifold 38 to balance the ratios among the different
coils. Distributors tend to be expensive. Advantageously, under
ambient conditions that would otherwise cause the point 136 to be
in the two-phase domain 106, it would be desirable to shift the
point 136 into the single phase liquid domain 108 eliminating the
need for a distributor. In such a situation, the single-phase
liquid inlet flow to the evaporator could readily be separated into
similar flows for each coil. The coils could be designed/configured
for operating with such an input flow.
[0023] FIG. 3 shows how the bypass flow of the present invention
may be utilized to achieve advantageous refrigerant conditions
entering the evaporator 22. The suction condition/point 220 may be
essentially the same as point 120 of FIG. 2. After compression 225,
the compressed/discharge/point 226 may be similar to the point 126
of FIG. 2. The condensing 231 brings the combined main flow and
bypass flow to a condensed/point 232 which may be similar to point
132.
[0024] From the condensed condition, the bypass flow splits from
the main flow. The bypass flow refrigerant is expanded (segment
233) to reach a point 234 which may be essentially at the suction
pressure 124 and the enthalpy 134. Heat exchange (235 for the
bypass flow and 236 for the main flow) from the main flow to the
bypass flow in the heat exchanger 34 then returns the bypass flow
conditions to point 220 and cools the main flow to a
precooled/point 238 with further reduced main flow enthalpy 240.
The main flow of refrigerant is expanded (segment 241) in the
expansion device 20 to a point 242 with decreased pressure 244
(which may be essentially the same as 138). The main flow of
refrigerant is evaporated (segment 245) in the evaporator 22 to
return the main flow to the initial suction point 220. The heat
exchange from the bypass flow to the main flow tends to shift the
point 242 to a lower enthalpy condition. The required amount of
heat exchange may depend upon ambient conditions.
[0025] A basic operation of the expansion device 32 may be
responsive to sensed superheat of the refrigerant exiting the
evaporator 22. The degree of superheat (actual temperature minus
saturated temperature) may be determined based upon the output of
the temperature sensor 50 for the actual temperature and the
pressure sensor 52 for the saturated temperature (e.g., in view of
known refrigerant properties which may be programmed into the
control system 44). The expansion device 32 may be opened either in
a binary fashion or a progressive fashion in response to the
presence or degree of superheat or superheat parameter (e.g.,
superheat above a threshold). With a TXV as the device 32, control
could be achieved by placing its bulb 70 in heat exchange relation
with the refrigerant at suction conditions. Much more complex
arrangements are also possible.
[0026] The expansion device 32 and/or other components of the
bypass flowpath may be dimensioned in view of main flowpath
components to permit an appropriate balance between bypass and
non-bypass flows. In an exemplary binary configuration (i.e., the
binary flow has only off and on conditions) an exemplary balance
involves having the bypass flow be approximately 30% of the total
flow through the compressor (i.e., 3/7 of the non-bypass flow) by
weight/mass. Broader exemplary figures for binary operation are
25%-33%, and 10%-35%. Progressive or stepwise operation may permit
maximums in such ranges and may, optionally, permit flows smaller
than the lower ends of such ranges.
[0027] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, when implemented as a
modification or a reengineering of an existing system, details of
the existing system may heavily influence details of the
implementation. Although illustrated with regard to a basic system
and with simplified conditions, the principles may be applied to
more complex system configurations, whether existing or
yet-developed. Accordingly, other embodiments are within the scope
of the following claims.
* * * * *