U.S. patent application number 11/908619 was filed with the patent office on 2008-08-07 for transcritical refrigeration with pressure addition relief valve.
This patent application is currently assigned to Carrier Commercial Refrigeration, Inc.. Invention is credited to Yu Chen, Hans-Joachim Huff, Tobias H. Sienel, Parmesh Verma.
Application Number | 20080184717 11/908619 |
Document ID | / |
Family ID | 37024111 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080184717 |
Kind Code |
A1 |
Sienel; Tobias H. ; et
al. |
August 7, 2008 |
Transcritical Refrigeration With Pressure Addition Relief Valve
Abstract
A refrigeration system (20) includes a pressure addition relief
valve (62) in parallel with an expansion device (63).
Inventors: |
Sienel; Tobias H.; (East
Hampton, MA) ; Chen; Yu; (East Hartford, CT) ;
Huff; Hans-Joachim; (West Hartford, CT) ; Verma;
Parmesh; (Manchester, CT) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C. (UTC)
900 CHAPEL STREET, SUITE 1201
NEW HAVEN
CT
06510-2802
US
|
Assignee: |
Carrier Commercial Refrigeration,
Inc.
Charlotte
NC
|
Family ID: |
37024111 |
Appl. No.: |
11/908619 |
Filed: |
December 31, 2005 |
PCT Filed: |
December 31, 2005 |
PCT NO: |
PCT/US05/47578 |
371 Date: |
September 14, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60663959 |
Mar 18, 2005 |
|
|
|
Current U.S.
Class: |
62/115 ;
62/527 |
Current CPC
Class: |
F25B 2500/18 20130101;
F25D 31/007 20130101; F25B 41/20 20210101; F25B 2400/0411 20130101;
F25B 2309/061 20130101; F25B 9/008 20130101; F25B 2600/2525
20130101; F25B 41/31 20210101 |
Class at
Publication: |
62/115 ;
62/527 |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 41/00 20060101 F25B041/00 |
Claims
1. A cooler system comprising: a compressor (22) for driving a
refrigerant along a flow path in at least a first mode of system
operation; a first heat exchanger (24) along the flow path
downstream of the compressor in the first mode so as to act as a
gas cooler; a second heat exchanger (28) along the flow path
upstream of the compressor in the first mode so as to act as an
evaporator to cool contents of an interior volume of the system; an
expansion device (63) in the flow path downstream of the first heat
exchanger (24) and upstream of the second heat exchanger (28); and
a pressure addition relief valve (62) in parallel with the
expansion device.
2. The system of claim 1 wherein: the pressure addition relief
valve (62) is a purely mechanical valve.
3. The system of claim 1 wherein: the expansion device (63) is a
purely mechanical device.
4. The system of claim 1 wherein: the pressure addition relief
valve (62) is normally closed and configured to open responsive to
a combined force produced by pressures essentially respectively
immediately downstream of the first heat exchanger and upstream of
the second heat exchanger.
5. The system of claim 4 wherein: a bias force acts opposite the
combined force, the bias force comprising at least one of: a
supplemental spring (94) bias force; a bias force provided by a
system condition sensor (110); and a bias force exerted by ambient
air pressure.
6. The system of claim 1 wherein: the pressure addition relief
valve (62) is integral with the expansion device (63).
7. The system of claim 1 wherein: the expansion device (63)
comprises a fixed orifice (120) in a common body (70) of the
pressure addition relief valve.
8. The system of claim 1 wherein: the expansion device (63)
comprises non-EEV device.
9. The system of claim 1 wherein: the pressure addition relief
valve comprises a sheet metal spring membrane (84) and no other
spring.
10. The system of claim 1 wherein: the pressure addition relief
valve comprises a membrane (84) and a coil biasing spring (94).
11. The system of claim 1 wherein: flowpath portions upstream (76)
and downstream (78) of the expansion device have effective
counterbias areas of the pressure addition relief valve, the lesser
being no less than 10% of the greater.
12. The system of claim 1 being a self-contained externally
electrically powered beverage cooler positioned outdoors.
13. The system of claim 1 wherein: the refrigerant comprises, in
major mass part, CO.sub.2; and the first and second heat exchangers
are refrigerant-air heat exchangers.
14. The system of claim 1 wherein: the refrigerant consists
essentially of CO.sub.2; and the first (24) and second (28) heat
exchangers are refrigerant-air heat exchangers each having an
associated fan (30; 32), an air flow across the first heat
exchanger being an external to external flow and an airflow across
the second heat exchanger being a recirculating internal flow.
15. The system of claim 1 in combination with said contents which
include: a plurality of beverage containers in a 0.3-4.0 liter size
range.
16. The system of claim 15 being selected from the group consisting
of: a cash-operated vending machine; a transparent door front,
closed back, display case; and a top access cooler chest.
17. A transcritical CO.sub.2 refrigeration system comprising: a
compressor (22) for driving a refrigerant along a flow path in at
least a first mode of system operation; a first heat exchanger (24)
along the flow path downstream of the compressor in the first mode
so as to act as a gas cooler; a second heat exchanger (28) along
the flow path upstream of the compressor in the first mode so as to
act as an evaporator; an expansion device (63) in the flow path
downstream of the first heat exchanger (24) and upstream of the
second heat exchanger (28); and a pressure addition relief valve
(62) in parallel with the expansion device.
18. A method for operating a transcritical CO.sub.2 refrigeration
system comprising: compressing and driving a refrigerant along a
flow path in at least a first mode of system operation; cooling the
compressed refrigerant along the flow path downstream of the
compressing; expanding the cooled refrigerant; and heating the
expanded refrigerant; wherein: the expanding comprises a
mechanically automated varying of an effective flow restriction
based upon an additive combination of forces from pressures
respectively upstream and downstream of the restriction.
19. A method for remanufacturing a transcritical CO.sub.2
refrigeration system or reengineering a configuration thereof
wherein a baseline configuration comprises: a compressor (22) for
driving a refrigerant along a flow path in at least a first mode of
system operation; a first heat exchanger (24) along the flow path
downstream of the compressor in the first mode so as to act as a
gas cooler; a second heat exchanger (28) along the flow path
upstream of the compressor in the first mode so as to act as an
evaporator; and an expansion device (26) in the flow path
downstream of the first heat exchanger (24) and upstream of the
second heat exchanger (28), the method comprising at least one of:
adding a pressure addition relief valve (62) in parallel with the
expansion device (26); and replacing the expansion device (26) with
a pressure addition relief valve (62) and a structurally different
expansion device (63).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Benefit is claimed of U.S. Patent Application 60/663,959,
entitled TRANSCRITICAL REFRIGERATION WITH PRESSURE ADDITION RELIEF
VALVE, and filed Mar. 18, 2005. Copending International Application
docket 05-258-WO, entitled HIGH SIDE PRESSURE REGULATION FOR
TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filed on even date
herewith, discloses prior art and inventive cooler systems. The
present application discloses possible modifications to such
systems The disclosures of said two applications are incorporated
by reference herein as if set forth at length.
BACKGROUND OF THE INVENTION
[0002] The invention relates to refrigeration. More particularly,
the invention relates to transcritical refrigeration systems such
as CO.sub.2 beverage coolers.
[0003] Transcritical vapor compression systems have an extra degree
of control freedom when compared to subcritical vapor compression
systems. In subcritical systems, pressure in the high and low
pressure components of the system are largely controlled by the
heat exchanger fluid temperatures. If the system is an air-to-air
system, the evaporator pressure is a strong function of the air
temperature entering the evaporator, and the condenser pressure is
a strong function of the air temperature entering the condenser.
This is because these temperatures are closely correlated with the
saturation pressures in the heat exchangers. In a transcritical
system, the high pressure side of the system does not have any
saturation properties, and thus pressure is independent from
temperature. It is well known that the choice of the high side
pressure has a very strong effect on the performance of the system,
and that there is an optimal pressure which provides maximum energy
efficiency. This optimal pressure will change as the operating
conditions of the unit change. Control of the high side pressure
can be achieved in many different ways, but for systems which have
fixed speed and volume compressors, the strongest influence is
through the expansion device.
[0004] FIG. 1 schematically shows transcritical vapor compression
system 20 utilizing CO.sub.2 as working fluid. The system comprises
a compressor 22, a gas cooler 24, an expansion device 26, and an
evaporator 28. The exemplary gas cooler and evaporator may each
take the form of a refrigerant-to-air heat exchanger. Airflows
across one or both of these heat exchangers may be forced. For
example, one or more fans 30 and 32 may drive respective airflows
34 and 36 across the two heat exchangers. A refrigerant flow path
40 includes a suction line extending from an outlet of the
evaporator 28 to an inlet 42 of the compressor 22. A discharge line
extends from an outlet 44 of the compressor to an inlet of the gas
cooler. Additional lines connect the gas cooler outlet to expansion
device inlet and expansion device outlet to evaporator inlet.
[0005] The major difference between transcritical and conventional
operation is that heat rejection in the gas cooler is in the
supercritical region because the critical temperature for CO.sub.2
is 87.8.degree. F. Consequently, pressure is not solely dependent
on temperature and this opens additional control and optimization
issues for system operation.
[0006] For a fixed gas cooler discharge temperature, as the high
side pressure is increased, the exit enthalpy of the refrigerant
decreases, yielding a higher differential enthalpy through the gas
cooler. The capacity of the gas cooler is a function of the mass
flowrate of refrigerant and the enthalpy difference across the gas
cooler. For a beverage cooler, the evaporator may be essentially at
the cooler interior temperature. It is typically desired to
maintain this temperature in a very narrow range regardless of
external condition. For example, it may be desired to maintain the
interior very close to 37.degree. F. This temperature essentially
fixes the steady state compressor suction pressure.
[0007] For a fixed compressor suction pressure, as the high side
pressure increases, the amount of energy used by the compressor
increases, and the volumetric efficiency of the compressor
decreases. When the volumetric efficiency of the compressor
decreases, the flowrate through the system decreases. The balance
of these two counteracting effects is typically an increase in gas
cooler capacity as the high side pressure is increased. However,
above a certain pressure the amount of capacity increase becomes
very small. Because the expansion device is usually isenthalpic,
the evaporator capacity will also typically increase as the high
side pressure increases.
[0008] The energy efficiency of a vapor compression system, the
Coefficient of Performance (COP), is usually expressed as a ratio
of the system capacity to the energy consumed. Because an increase
in pressure typically produces both a higher capacity and a higher
energy consumption, the balance between the two will dictate the
overall COP. Therefore, there is typically an optimal pressure
which yields the highest possible performance.
[0009] An electronic expansion valve is usually used as the device
26 to control the high side pressure to optimize the COP of the
CO.sub.2 vapor compression system. An electronic expansion valve
typically comprises a stepper motor attached to a needle valve to
vary the effective valve opening or flow capacity to a large number
of possible positions (typically over one hundred). This provides
good control of the high side pressure over a large range of
operating conditions. The opening of the valve is electronically
controlled by a controller 50 to match the actual high side
pressure to the desired set point. The controller 50 is coupled to
a sensor 52 for measuring the high side pressure.
[0010] 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
[0011] FIG. 1 is a schematic of a prior art CO.sub.2 bottle
cooler.
[0012] FIG. 2 is a schematic of a modified CO.sub.2 bottle
cooler.
[0013] FIG. 3 is a sectional view of a pressure addition relief
valve of the cooler of FIG. 2 in a closed condition.
[0014] FIG. 4 is a sectional view of a pressure addition relief
valve of the cooler of FIG. 2 in an open condition.
[0015] FIG. 5 is a graph of discharge pressure against ambient
temperature for three different expansion methods.
[0016] FIG. 6 is a graph of coefficient of performance against
ambient temperature for said three different expansion methods.
[0017] FIG. 7 is a graph of capacity against ambient temperature
for said three different expansion methods.
[0018] FIG. 8 is a graph of discharge pressure against evaporating
temperature during pulldown for said three different expansion
methods and an inventive method.
[0019] FIG. 9 is a graph of coefficient of performance against
evaporating temperature during pulldown for said three different
expansion methods and said inventive method.
[0020] FIG. 10 is a graph of capacity against evaporating
temperature during pulldown for said three different expansion
methods and said inventive method.
[0021] FIG. 11 is a side schematic view of a display case bottle
cooler including a refrigeration and air management cassette.
[0022] FIG. 12 is a view of a refrigeration and air management
cassette.
[0023] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0024] A pressure addition relief valve (PARV) may be used in
combination with a primary expansion device. FIG. 2 shows a system
60 formed as a modification of the prior art system 20. In the
example, the PARV 62 and expansion device 63 are coupled in
parallel between a high pressure (upstream) portion 64 of the
refrigerant flow path from the gas cooler and a low pressure
(downstream) portion 66 to the evaporator. A combination of the
pressures at the opposite sides of the PARV 62 acts to open the
PARV to permit flow therethrough. The PARV and expansion device may
be combined in a combination valve 68.
[0025] The exemplary valve 68 (FIG. 3) has a body 70 with an inlet
port 72 receiving the conduit portion 64 and an outlet 74 receiving
the conduit portion 66. The inlet port 72 and outlet port 74
respectively communicate with a high pressure volume 76 and a low
pressure volume 78, both within the body. The exemplary body 70
includes a main portion 80 and a cover 82 secured thereto. The
exemplary cover seals and secures the periphery of a membrane 84 to
the main portion 80. The exemplary membrane is a disk of sheet
spring steel.
[0026] The membrane has a front face/surface 86 normally
engaged/sealed to a seat surface 88 of the body main portion 80.
The volumes 76 and 78 have respective ports 90 and 92 in the
surface 88. The ports 90 and 92 are normally blocked by engagement
with membrane front face 86. The engagement may be assisted by a
biasing spring 94 if the particular membrane is not sufficiently
self sprung (e.g., a film rather than a metal sheet spring). An
exemplary biasing spring 94 is a coil compression spring having a
first end 96 engaging the backside/face 98 and a second end 100
engaging an underside 102 of the cover 82. A membrane backside
volume (backspace) 104 is formed containing the spring. A port 106
in the cover may expose the backside volume 104 to a reference
pressure. The reference pressure may be ambient air pressure, may
be a vacuum or other sealed fixed pressure (in which case, the port
106 might be omitted), or a pressure dependent upon a system
condition (e.g., connected via a conduit 108 to a TXV-type bulb 110
located elsewhere in the system to provide a variable pressure
force). This backside pressure serves to maintain the membrane in
its closed condition.
[0027] The pressures in the high and low pressure volumes 76 and 78
act on the membrane with forces based upon the relative areas of
their ports 90 and 92 and in view of mechanical advantage factors
such as port positioning. These pressures act counter to the
pressure of the backside volume 104. If the relative balance of
the
[0028] If the effect of combined high pressure and low pressure
forces exceed the effect of backside pressure and spring force on
the backside of the membrane, then the membrane will flex outward
to an open condition (FIG. 4), allowing a flow 112 from the port 90
and back into the port 92 (and thus through the valve 68). If the
combined effects of the high pressure and low pressure forces do
not exceed those of the forces on the backside of the membrane,
then the membrane will remain closed, allowing little to no flow.
In this way, the membrane and associated components act as a PARV
to regulate the additive pressure force to a controlled level.
[0029] The PARV is used in combination with a primary expansion
device to provide a better mechanism for controlling the high
pressure. The primary expansion device can be a simple orifice as
discussed further below, or can be another type of expansion
device, such as a capillary tube, TXV, EXV, or other valve. For
example, a TXV type valve can be used with the bulb sensing the
temperature of the exit of the gas cooler or condenser in one
embodiment. In another, a dual bulb TXV can be used to sense the
air temperature and gas cooler or condenser discharge
difference.
[0030] In the FIGS. 3&4 example, an orifice 120 passing a flow
122 provides the principal function of the fixed expansion device
portion of the combined valve. For purposes of discussion, the term
PARV may be used to identify both the pure PARV and the combined
valve.
[0031] An exemplary system design may reflect specific design
external (ambient) and internal temperatures. An exemplary design
ambient temperature is 90.degree. F. (32.degree. C.). An exemplary
design pulldown temperature is 16.degree. F. (-9.degree. C.).
[0032] A theoretical optimal control is that which yields the
highest possible COP.
[0033] FIG. 5 shows a plot 400 of discharge pressure against
ambient temperature for the optimal control strategy. A plot 402
represents a fixed orifice dimensioned to provide the same pressure
at the design ambient pressure. For lower ambient temperatures, the
fixed orifice will produce higher than optimum discharge pressure.
For higher ambient temperatures, the fixed orifice will produce
lower than optimum discharge pressure. A plot 404 represents a
fixed pressure situation which involves even greater departures
from optimum.
[0034] FIG. 6 shows a plot 410 of coefficient of performance
against ambient temperature for the optimal control strategy. A
plot 412 represents the fixed orifice and a plot 414 represents the
constant pressure situation. FIG. 7 shows a plot 420 of capacity
against ambient temperature for the optimal control strategy. A
plot 422 represents the fixed orifice and a plot 424 represents the
constant pressure situation. From FIGS. 5-7 it is seen that that
the fixed orifice provides a small difference in pressure relative
to the optimal control. This difference causes a relatively modest
reduction in efficiency (COP) and an even smaller reduction in
capacity. The low cost of the fixed orifice device may outweigh
these modest performance reductions. However, there are other
considerations.
[0035] FIG. 8 shows a plot 430 of discharge pressure against
evaporating temperature during pulldown for the optimal control
strategy. A plot 432 represents the fixed orifice and a plot 434
represents the constant pressure situation. From the plot 432, it
can be seen that pulldown conditions cause the fixed orifice to
produce much higher discharge pressures than the optimal control.
At higher evaporator temperatures, the resulting high pressures
might damage the system. Thus, the problem with using only a simple
fixed orifice is that the high (discharge) pressure will exceed a
practical design pressure for the system hardware when the low
pressure is much higher, such as during a pulldown condition (e.g.,
when the system is turned on with a high temperature in the volume
to be refrigerated and a high ambient temperature). The PARV may
function to avoid such high discharge pressures. A plot 436
represents the orifice and PARV combination and is shown departing
from the plot 432 at/above a temperature of an exemplary
7.5.degree. C. to cap the discharge pressure at an exemplary 12000
kPa selected based upon hardware strength. The PARV will not allow
the pressure to exceed a certain value during pulldown, thus
preventing damage to the system, and allowing the use of a simple
pressure control device such as the fixed orifice device. The
effect of the parv strategy on the regulation of the high pressure
is a mechanism which acts very close to the optimal pressure
control, but which does not over pressurize during periods of
excessive refrigerant flow.
[0036] FIG. 9 shows a plot 440 of coefficient of performance
against evaporating temperature during pulldown for the optimal
control strategy. A plot 442 represents the fixed orifice, a plot
444 represents the constant pressure situation, and a plot 446
represents the orifice plus PARV combination. FIG. 10 shows a plot
450 of capacity against ambient temperature for the optimal control
strategy. A plot 452 represents the fixed orifice, a plot 454
represents the constant pressure situation, and a plot 456
represents the orifice plus PARV combination. Plots 446 and 456
show that efficiency (COP) is not dramatically affected, while
capacity is actually gained by the use of the PARV relative to a
controlled expansion device regulating to the optimum pressure. The
effect of this is that the pulldown time will be reduced and
therefore the overall energy consumption of the device will be
reduced as well.
[0037] A particular area for implementation of the PARV is in
bottle coolers, including those which may be positioned outdoors or
must have the capability to be outdoors (presenting large
variations in ambient temperature). FIG. 11 shows an exemplary
cooler 200 having a removable cassette 202 containing the
refrigerant and air handling systems. The exemplary cassette 202 is
mounted in a compartment of a base 204 of a housing. The housing
has an interior volume 206 between left and right side walls, a
rear wall/duct 216, a top wall/duct 218, a front door 220, and the
base compartment. The interior contains a vertical array of shelves
222 holding beverage containers 224.
[0038] The exemplary cassette 202 draws the air flow 34 through a
front grille in the base 224 and discharges the air flow 34 from a
rear of the base. The cassette may be extractable through the base
front by removing or opening the grille. The exemplary cassette
drives the air flow 36 on a recirculating flow path through the
interior 206 via the rear duct 210 and top duct 218.
[0039] FIG. 12 shows further details of an exemplary cassette 202.
The heat exchanger 28 is positioned in a well 240 defined by an
insulated wall 242. The heat exchanger 28 is shown positioned
mostly in an upper rear quadrant of the cassette and oriented to
pass the air flow 36 generally rearwardly, with an upturn after
exiting the heat exchanger so as to discharge from a rear portion o
the cassette upper end. a drain 250 may extend through a bottom of
the wall 242 to pass water condensed from the flow 36 to a drain
pan 252. A water accumulation 254 is shown in the pan 252. The pan
252 is along an air duct 256 passing the flow 34 downstream of the
heat exchanger 24. Exposure of the accumulation 254 to the heated
air in the flow 34 may encourage evaporation.
[0040] 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
remanufacturing of an existing system or reengineering of an
existing system configuration, details of the existing
configuration may influence details of the implementation.
Accordingly, other embodiments are within the scope of the
following claims.
* * * * *