U.S. patent application number 11/803222 was filed with the patent office on 2007-09-27 for vapor compression system and method for controlling conditions in ambient surroundings.
This patent application is currently assigned to XDX Technology LLC. Invention is credited to David A. Wightman.
Application Number | 20070220911 11/803222 |
Document ID | / |
Family ID | 27358950 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070220911 |
Kind Code |
A1 |
Wightman; David A. |
September 27, 2007 |
Vapor compression system and method for controlling conditions in
ambient surroundings
Abstract
A vapor compression system including an evaporator, a
compressor, and a condenser interconnected in a closed-loop system
and a method of operating such a system. The method includes the
conversion of expanded liquid heat transfer fluid from a liquid
form to a high quality liquid vapor mixture before delivery to the
evaporator. In one embodiment, the heat transfer surface of the
evaporator coil is smaller than that required to obtain an
equivalent evaporator capacity when the expanded liquid heat
transfer fluid is not converted from a liquid form to a high
quality liquid vapor mixture
Inventors: |
Wightman; David A.;
(Arlington Heights, IL) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE/CHICAGO/COOK
PO BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
XDX Technology LLC
Chicago
IL
|
Family ID: |
27358950 |
Appl. No.: |
11/803222 |
Filed: |
May 14, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10948446 |
Sep 23, 2004 |
7225627 |
|
|
11803222 |
May 14, 2007 |
|
|
|
10129339 |
May 2, 2002 |
6951117 |
|
|
PCT/US00/14648 |
May 26, 2000 |
|
|
|
10948446 |
Sep 23, 2004 |
|
|
|
PCT/US00/00663 |
Jan 11, 2000 |
|
|
|
10129339 |
May 2, 2002 |
|
|
|
09431830 |
Nov 2, 1999 |
6185958 |
|
|
10129339 |
May 2, 2002 |
|
|
|
Current U.S.
Class: |
62/222 ; 62/115;
62/216 |
Current CPC
Class: |
F25B 2400/22 20130101;
F25B 2400/0403 20130101; F25B 41/20 20210101; F25B 2500/18
20130101; F25B 2400/075 20130101; F25B 2500/01 20130101; F25B
47/022 20130101; F25B 5/02 20130101 |
Class at
Publication: |
062/222 ;
062/115; 062/216 |
International
Class: |
F25B 41/04 20060101
F25B041/04 |
Claims
1. A method of operating a vapor compression system, comprising:
compressing a heat transfer fluid in a compressor; condensing the
heat transfer fluid in a condenser; expanding the heat transfer
fluid in an expansion device to form an expanded heat transfer
fluid; supplying the expanded heat transfer fluid to a first
evaporative line of an evaporator, wherein the evaporator comprises
the first evaporative line and an evaporator coil and wherein the
expansion device is in fluid communication with the evaporator coil
via the first evaporative line; converting a portion of a liquid
form of the expanded liquid heat transfer fluid to a high quality
liquid vapor mixture within the first evaporative line; supplying
the high quality liquid vapor mixture to the evaporator coil,
converting a portion of a liquid form of the high quality liquid
vapor mixture to a vapor form within the evaporator coil; and
returning the heat transfer fluid to the compressor by a suction
line.
2. The method of claim 1, wherein the heat transfer fluid is
received by the evaporator coil as a saturated vapor.
3. The method of claim 1, wherein the heat transfer fluid is
received by the evaporator coil in a turbulent state.
4. The method of claim 1, wherein the expansion device forms part
of a multifunctional valve.
5. The method of claim 4, wherein the multifunctional valve is
adjacent to the evaporator.
6. The method of claim 4, wherein the evaporator further comprises
a portion of the multifunctional valve.
7. The method of claim 1, wherein the expansion device forms part
of a recovery valve.
8. The method of claim 1, wherein a temperature sensor is mounted
to the suction line and is operatively connected to the expansion
device.
9. The method of claim 8, wherein the heat transfer fluid undergoes
expansion at the expansion device at a rate determined by a
temperature of the suction line at the temperature sensor.
10. The method of claim 1, wherein the heat transfer fluid expanded
within the expansion device is not passed through a distributor
before delivery to the evaporator coil.
11. The method of claim 1, wherein, at a fixed cooling load, the
heat transfer fluid within the expansion device and the heat
transfer fluid within the evaporator are at a temperature within 20
deg F.
12. The method of claim 6, wherein, at a fixed cooling load, the
heat transfer fluid within the multifunctional valve and the heat
transfer fluid within the evaporator are at a temperature within 20
deg F.
13. A method of operating a vapor compression system, comprising:
compressing a heat transfer fluid in a compressor; condensing the
heat transfer fluid in a condenser; expanding the heat transfer
fluid in an expansion device to form an expanded heat transfer
fluid; supplying the expanded heat transfer fluid to an evaporator
comprising an evaporator coil having a heat transfer surface;
converting a portion of a liquid form of the expanded heat transfer
fluid to a high quality liquid vapor mixture prior to delivery to
the evaporator coil; converting a portion of a liquid form of the
high quality liquid vapor mixture to a vapor form within the
evaporator coil; and returning the heat transfer fluid to the
compressor by a suction line.
14. The method of claim 13 wherein, at a fixed cooling load, the
heat transfer surface of the evaporator coil is smaller than that
required to obtain an equivalent evaporator capacity when the
portion of the liquid form of the expanded heat transfer fluid is
not converted from the liquid form to the high quality liquid vapor
mixture prior to delivery to the evaporator coil.
15. The method of claim 13 wherein, at a fixed cooling load, the
conversion of the portion of the liquid heat transfer fluid from a
liquid form to a high quality liquid vapor mixture prior to
delivery to the evaporator coil results in a decreased variation in
refrigerated air temperature when compared to a method in which the
portion of the liquid form of the expanded heat transfer fluid is
not converted from the liquid form to the high quality liquid vapor
mixture prior to delivery to the evaporator coil.
16. The method of claim 13 wherein, at a fixed cooling load, less
power is required to power the compressor than is required when the
portion of the liquid form of the expanded heat transfer fluid is
not converted from the liquid form to the high quality liquid vapor
mixture prior to delivery to the evaporator coil.
17. The method of claim 13, wherein, at a fixed cooling load, the
heat transfer fluid within the expansion device and the heat
transfer fluid within the evaporator are at a temperature within 20
deg F.
18. The method of claim 13, wherein the expansion device forms part
of a multifunctional valve.
19. The method of claim 18, wherein the multifunctional valve is
adjacent to the evaporator.
20. The method of claim 18, wherein the evaporator further
comprises a portion of the multifunctional valve.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 10/948,446, filed Sep. 23, 2004, which is a
continuation-in-part of U.S. patent application Ser. No.
10/129,339, filed May 2, 2002, which is a National Stage of
PCT/US00/14648, filed May 26, 2000. PCT/US00/14648 is a
continuation-in-part of P.C.T. application PCT/US00/00663, filed
Jan. 11, 2000, which was published in English and designated the
United States and a continuation-in-part of U.S. patent application
Ser. No. 09/431,830, filed Nov. 2, 1999, now U.S. Pat. No.
6,185,958. The contents of these prior applications are
incorporated by reference.
BACKGROUND
[0002] In a closed-loop vapor compression cycle, the heat transfer
fluid changes state from a vapor to a liquid in the condenser,
giving off heat, and changes state from a liquid to a vapor in the
evaporator, absorbing heat during vaporization. A typical
vapor-compression system includes a compressor for pumping a heat
transfer fluid, such as a freon, to a condenser, where heat is
given off as the vapor condenses into a liquid. The liquid flows
through a liquid line to a thermostatic expansion valve, where the
heat transfer fluid undergoes a volumetric expansion. The heat
transfer fluid exiting the thermostatic expansion valve is a low
quality liquid vapor mixture. As used herein, the term "low quality
liquid vapor mixture" refers to a low pressure heat transfer fluid
in a liquid state with a small presence of flash gas that cools off
the remaining heat transfer fluid, as the heat transfer fluid
continues on in a sub-cooled state. The expanded heat transfer
fluid then flows into an evaporator, where the liquid refrigerant
is vaporized at a low pressure absorbing heat while it undergoes a
change of state from a liquid to a vapor. The heat transfer fluid,
now in the vapor state, flows through a suction line back to the
compressor. Sometimes, the heat transfer fluid exits the evaporator
not in a vapor state, but rather in a superheated vapor state.
[0003] In one aspect, the efficiency of the vapor-compression cycle
depends upon the ability of the vapor compression system to
maintain the heat transfer fluid as a high pressure liquid upon
exiting the condenser. The cooled, high-pressure liquid must remain
in the liquid state over the long refrigerant lines extending
between the condenser and the thermostatic expansion valve. The
proper operation of the thermostatic expansion valve depends upon a
certain volume of liquid heat transfer fluid passing through the
valve. As the high-pressure liquid passes through an orifice in the
thermostatic expansion valve, the fluid undergoes a pressure drop
as the fluid expands through the valve. At the lower pressure, the
fluid cools an additional amount as a small amount of flash gas
forms and cools of the bulk of the heat transfer fluid that is in
liquid form. As used herein, the term "flash gas" is used to
describe the pressure drop in an expansion device, such as a
thermostatic expansion valve, when some of the liquid passing
through the valve is changed quickly to a gas and cools the
remaining heat transfer fluid that is in liquid form to the
corresponding temperature.
[0004] This low quality liquid vapor mixture passes into the
initial portion of cooling coils within the evaporator. As the
fluid progresses through the coils, it initially absorbs a small
amount of heat while it warms and approaches the point where it
becomes a high quality liquid vapor mixture. As used herein, the
term "high quality liquid vapor mixture" refers to a heat transfer
fluid that resides in both a liquid state and a vapor state with
matched enthalpy, indicating the pressure and temperature of the
heat transfer fluid are in correlation with each other. A high
quality liquid vapor mixture is able to absorb heat very
efficiently since it is in a change of state condition. The heat
transfer fluid then absorbs heat from the ambient surroundings and
begins to boil. The boiling process within the evaporator coils
produces a saturated vapor within the coils that continues to
absorb heat from the ambient surroundings. Once the fluid is
completely boiled-off, it exits through the final stages of the
cooling coil as a cold vapor. Once the fluid is completely
converted to a cold vapor, it absorbs very little heat. During the
final stages of the cooling coil, the heat transfer fluid enters a
superheated vapor state and becomes a superheated vapor. As defined
herein, the heat transfer fluid becomes a "superheated vapor" when
minimal heat is added to the heat transfer fluid while in the vapor
state, thus raising the temperature of the heat transfer fluid
above the point at which it entered the vapor state while still
maintaining a similar pressure. The superheated vapor is then
returned through a suction line to the compressor, where the
vapor-compression cycle continues.
[0005] For high-efficiency operation, the heat transfer fluid
should change state from a liquid to a vapor in a large portion of
the cooling coils within the evaporator. As the heat transfer fluid
changes state from a liquid to a vapor, it absorbs a great deal of
energy as the molecules change from a liquid to a gas absorbing a
latent heat of vaporization. In contrast, relatively little heat is
absorbed while the fluid is in the liquid state or while the fluid
is in the vapor state. Thus, optimum cooling efficiency depends on
precise control of the heat transfer fluid by the thermostatic
expansion valve to insure that the fluid undergoes a change of
state in as large of cooling coil length as possible. When the heat
transfer fluid enters the evaporator in a cooled liquid state and
exits the evaporator in a vapor state or a superheated vapor state,
the cooling efficiency of the evaporator is lowered since a
substantial portion of the evaporator contains fluid that is in a
state which absorbs very little heat. For optimal cooling
efficiency, a substantial portion, or an entire portion, of the
evaporator should contain fluid that is in both a liquid state and
a vapor state. To insure optimal cooling efficiency, the heat
transfer fluid entering and exiting from the evaporator should be a
high quality liquid vapor mixture.
[0006] The thermostatic expansion valve plays an important role and
regulating the flow of heat transfer fluid through the closed-loop
system. Before any cooling effect can be produced in the
evaporator, the heat transfer fluid has to be cooled from the
high-temperature liquid exiting the condenser to a range suitable
of an evaporating temperature by a drop in pressure. The flow of
low pressure liquid to the evaporator is metered by the
thermostatic expansion valve in an attempt to maintain maximum
cooling efficiency in the evaporator. Typically, once operation has
stabilized, a mechanical thermostatic expansion valve regulates the
flow of heat transfer fluid by monitoring the temperature of the
heat transfer fluid in the suction line near the outlet of the
evaporator. The heat transfer fluid upon exiting the thermostatic
expansion valve is in the form of a low pressure liquid having a
small amount of flash gas. The presence of flash gas provides a
cooling affect upon the balance of the heat transfer fluid in its
liquid state, thus creating a low quality liquid vapor mixture. A
temperature sensor is attached to the suction line to measure the
amount of superheating experienced by the heat transfer fluid as it
exits from the evaporator. Superheat is the amount of heat added to
the vapor, after the heat transfer fluid has completely boiled-off
and liquid no longer remains in the suction line. Since very little
heat is absorbed by the superheated vapor, the thermostatic
expansion valve meters the flow of heat transfer fluid to minimize
the amount of superheated vapor formed in the evaporator.
Accordingly, the thermostatic expansion valve determines the amount
of low-pressure liquid flowing into the evaporator by monitoring
the degree of superheating of the vapor exiting from the
evaporator.
[0007] In addition to the need to regulate the flow of heat
transfer fluid through the closed-loop system, the optimum
operating efficiency of the vapor compression system depends upon
periodic defrost of the evaporator. Periodic defrosting of the
evaporator is needed to remove icing that develops on the
evaporator coils during operation. As ice or frost develops over
the evaporator, it impedes the passage of air over the evaporator
coils reducing the heat transfer efficiency. In a commercial
system, such as a refrigerated display cabinet, the build up of
frost can reduce the rate of air flow to such an extent that an air
curtain cannot form in the display cabinet. In commercial systems,
such as food chillers, and the like, it is often necessary to
defrost the evaporator every few hours. Various defrosting methods
exist, such as off-cycle methods, where the refrigeration cycle is
stopped and the evaporator is defrosted by air at ambient
temperatures. Additionally, electrical defrost off-cycle methods
are used, where electrical heating elements are provided around the
evaporator and electrical current is passed through the heating
coils to melt the frost.
[0008] In addition to off-cycle defrost systems, vapor compression
systems have been developed that rely on the relatively high
temperature of the heat transfer fluid exiting the compressor to
defrost the evaporator. In these techniques, the high-temperature
vapor is routed directly from the compressor to the evaporator. In
one technique, the flow of high temperature vapor is dumped into
the suction line and the vapor compression system is essentially
operated in reverse. In other techniques, the high-temperature
vapor is pumped into a dedicated line that leads directly from the
compressor to the evaporator for the sole purpose of conveying
high-temperature vapor to periodically defrost the evaporator.
Additionally, other complex methods have been developed that rely
on numerous devices within the vapor compression system, such as
bypass valves, bypass lines, heat exchangers, and the like.
[0009] In an attempt to obtain better operating efficiency from
conventional vapor-compression systems, the refrigeration industry
is developing systems of growing complexity. Sophisticated
computer-controlled thermostatic expansion valves have been
developed in an attempt to obtain better control of the heat
transfer fluid through the evaporator. Additionally, complex valves
and piping systems have been developed to more rapidly defrost the
evaporator in order to maintain high heat transfer rates. While
these systems have achieved varying levels of success, the vapor
compression system cost rises dramatically as the complexity of the
vapor compression system increases. Accordingly, a need exists for
an efficient vapor compression system that can be installed at low
cost and operated at high efficiency.
BRIEF SUMMARY
[0010] According to a first aspect of the present invention, a
vapor compression system is provided that maintains high operating
efficiency by feeding a saturated vapor into the inlet of an
evaporator. As used herein, the term "saturated vapor" refers to a
heat transfer fluid that resides in both a liquid state and a vapor
state with matched enthalpy, indicating the pressure and
temperature of the heat transfer fluid are in correlation with each
other. Saturated vapor is a high quality liquid vapor mixture. By
feeding saturated vapor to the evaporator, heat transfer fluid in
both a liquid and a vapor state enters the evaporator coils. Thus,
the heat transfer fluid is delivered to the evaporator in a
physical state in which maximum heat can be absorbed by the fluid.
In addition to high efficiency operation of the evaporator, in one
preferred embodiment of the invention, the vapor compression system
provides a simple means of defrosting the evaporator. A
multifunctional valve is employed that contains separate
passageways feeding into a common chamber. In operation, the
multifunctional valve can transfer either a saturated vapor, for
cooling, or a high temperature vapor, for defrosting, to the
evaporator.
[0011] In one form, the vapor compression system includes an
evaporator for evaporating a heat transfer fluid, a compressor for
compressing the heat transfer fluid to a relatively high
temperature and pressure, and a condenser for condensing the heat
transfer fluid. A saturated vapor line is coupled from an expansion
valve to the evaporator. In one aspect of the invention, the
diameter and the length of the saturated vapor line is sufficient
to insure substantial conversion of the heat transfer fluid into a
saturated vapor prior to delivery of the fluid to the evaporator.
In one preferred embodiment of the invention, a heat source is
applied to the heat transfer fluid in the saturated vapor line
sufficient to vaporize a portion of the heat transfer fluid before
the heat transfer fluid enters the evaporator. In one aspect of the
invention, a heat source is applied to the heat transfer fluid
after the heat transfer fluid passes through the expansion valve
and before the heat transfer fluid enters the evaporator. The heat
source converts the heat transfer fluid from a low quality liquid
vapor mixture to a high quality liquid vapor mixture, or a
saturated vapor. Typically, at least about 5% of the heat transfer
fluid is vaporized before entering the evaporator.
[0012] In one embodiment of the invention, the expansion valve
resides within a multifunctional valve that includes a first inlet
for receiving the heat transfer fluid in the liquid state, and a
second inlet for receiving the heat transfer fluid in the vapor
state. The multifunctional valve further includes passageways
coupling the first and second inlets to a common chamber. Gate
valves positioned within the passageways enable the flow of heat
transfer fluid to be independently interrupted in each passageway.
The ability to independently control the flow of saturated vapor
and high temperature vapor through the vapor compression system
produces high operating efficiency by both increased heat transfer
rates at the evaporator and by rapid defrosting of the evaporator.
The increased operating efficiency enables the vapor compression
system to be charged with relatively small amounts of heat transfer
fluid, yet the vapor compression system can handle relatively large
thermal loads.
[0013] In yet another embodiment, heat transfer fluid enters the
common chamber of the multifunctional valve as a liquid vapor
mixture and generally follows a flow direction. By controlling the
flow rate of the heat transfer fluid and the shape of the common
chamber, its is possible to separate a substantial amount of the
liquid vapor mixture into liquid and vapor so that heat transfer
fluid exists the common chamber through an outlet as liquid and
vapor, wherein a substantial amount of the liquid is separate and
apart from a substantial amount of the vapor.
[0014] In one embodiment, the vapor compression system includes a
compressor, a condenser, an evaporator, an XDX valve, and an
expansion valve. In accordance with this embodiment, the flow of
heat transfer fluid from the condenser to the evaporator can be
switched to go through either the XDX valve or the expansion valve.
Preferably, the vapor compression system includes a sensor that
measures the conditions of ambient surroundings, that is, the area
or space in which the conditions such as temperature and humidity
are controlled or altered by vapor compression system. Upon
determining the conditions of the ambient surroundings, the sensor
then decides whether to direct the flow of heat transfer fluid to
either the XDX valve or the expansion valve.
[0015] Another aspect of the invention provides a method of
operating a vapor compression system, comprising: compressing a
heat transfer fluid in a compressor; condensing the heat transfer
fluid in a condenser; expanding the heat transfer fluid in an
expansion device to form an expanded heat transfer fluid and
supplying the expanded heat transfer fluid to an evaporator feed
line, at least one of the expansion device, a diameter of the
evaporator feed line, and a length of the evaporator feed line
converting a significant amount of a liquid form of the expanded
liquid heat transfer fluid to a high quality liquid vapor mixture;
supplying the high quality liquid vapor mixture to an evaporator
coil having a heat transfer surface, converting a portion of a
liquid form of the high quality liquid vapor mixture to a vapor
form within the evaporator coil; and returning the heat transfer
fluid to the compressor.
[0016] In one embodiment of this aspect, at a fixed cooling load,
the heat transfer surface of the evaporator coil is smaller than
that required to obtain an equivalent evaporator capacity when the
significant amount of the liquid heat transfer fluid is not
converted from a liquid form to a high quality liquid vapor
mixture.
[0017] In another embodiment of this aspect, at a fixed cooling
load, the conversion of the significant amount of the liquid
refrigerant from a liquid form to a high quality liquid vapor
mixture allows for at least an equivalent evaporator capacity to be
achieved using an decreased heat transfer fluid load when compared
to the heat transfer fluid load required when the significant
amount of the liquid heat transfer fluid is not converted from a
liquid form to a high quality liquid vapor mixture.
[0018] In another embodiment of this aspect, operating at a fixed
cooling load, the conversion of the significant amount of the
liquid heat transfer fluid from a liquid form to a high quality
liquid vapor mixture allows for at least an equivalent evaporator
capacity to that achieved when the significant amount of the liquid
heat transfer fluid is not converted from a liquid form to a high
quality liquid vapor mixture and wherein a distributor is present
between the evaporator feed line and the evaporator coil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic drawing of a vapor-compression system
arranged in accordance with one embodiment of the invention;
[0020] FIG. 2 is a side view, in partial cross-section, of a first
side of a multifunctional valve in accordance with one embodiment
of the invention;
[0021] FIG. 3 is a side view, in partial cross-section, of a second
side of the multifunctional valve illustrated in FIG. 2;
[0022] FIG. 4 is an exploded view of a multifunctional valve in
accordance with one embodiment of the invention;
[0023] FIG. 5 is a schematic view of a vapor-compression system in
accordance with another embodiment of the invention;
[0024] FIG. 6 is an exploded view of the multifunctional valve in
accordance with another embodiment of the invention;
[0025] FIG. 7 is a schematic view of a vapor-compression system in
accordance with yet another embodiment of the invention;
[0026] FIG. 8 is an enlarged cross-sectional view of a portion of
the vapor compression system illustrated in FIG. 7;
[0027] FIG. 9 is a schematic view, in partial cross-section, of a
recovery valve in accordance with one embodiment of this
invention;
[0028] FIG. 10 is a schematic view, in partial cross-section, of a
recovery valve in accordance with yet another embodiment of this
invention;
[0029] FIG. 11 is a plan view, partially in section, of a valve
body for a multifunctional valve in accordance with a further
embodiment of the present invention;
[0030] FIG. 12 is a side elevational view of the valve body for the
multifunctional valve shown in FIG. 11;
[0031] FIG. 13 is an exploded view, partially in section, of the
multifunctional valve shown in FIGS. 11 and 12;
[0032] FIG. 14 is an enlarged view of a portion of the
multifunctional valve shown in FIG. 12;
[0033] FIG. 15 is a plan view, partially in section, of a valve
body for a multifunctional valve in accordance with a further
embodiment of the present invention;
[0034] FIG. 16. is a schematic drawing of a vapor-compression
system arranged in accordance with another embodiment of the
invention;
[0035] FIG. 17 is a cross sectional view of a valve body for a
multifunctional valve in accordance with a further embodiment of
the present invention;
[0036] FIG. 18 is a cross sectional view of a valve body for a
multifunctional valve in accordance with a further embodiment of
the present invention;
[0037] FIG. 19 is a cross sectional view of a valve body for a
multifunctional valve in accordance with a further embodiment of
the present invention;
[0038] FIG. 20 is a schematic drawing of a vapor-compression system
arranged in accordance with another embodiment of the
invention;
[0039] FIG. 21 is a side view of a fast-action capillary tube in
accordance with a further embodiment of the present invention;
and
[0040] FIG. 22 is an enlarged cross-sectional view of a portion of
the vapor compression in accordance with another embodiment of the
invention.
[0041] FIG. 23 is a schematic drawing illustrating three manifold
configurations: (a) an up-feed manifold; (b) a down-feed manifold;
and (c) a side-feed manifold.
[0042] FIG. 24 is a schematic drawing illustrating the delivery of
expanded heat transfer fluid from an expansion device to a
multi-circuit evaporator coil via a distributor nozzle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] An embodiment of a vapor-compression system 10 arranged in
accordance with one embodiment of the invention is illustrated in
FIG. 1. Vapor compression system 10 includes a compressor 12, a
condenser 14, an evaporator 16, and a multifunctional valve 18.
Compressor 12 is coupled to condenser 14 by a discharge line 20.
Multifunctional valve 18 is coupled to condenser 14 by a liquid
line coupled to a first inlet 24 of multifunctional valve 18.
Additionally, multifunctional valve 18 is coupled to discharge line
20 at a second inlet 26. A saturated vapor line 28 couples
multifunctional valve 18 to evaporator 16, and a suction line 30
couples the outlet of evaporator 16 to the inlet of compressor 12.
A temperature sensor 32 is mounted to suction line 30 and is
operably connected to multifunctional valve 18. In accordance with
the invention, compressor 12, condenser 14, multifunctional valve
18 and temperature sensor 32 are located within a control unit 34.
Correspondingly, evaporator 16 is located within a refrigeration
case 36. In one preferred embodiment of the invention, compressor
12, condenser 14, multifunctional valve 18, temperature sensor 32
and evaporator 16 are all located within a refrigeration case 36.
In another preferred embodiment of the invention, the vapor
compression system comprises control unit 34 and refrigeration case
36, wherein compressor 12 and condenser 14 are located within the
control unit 34, and wherein evaporator 16, multifunctional valve
18, and temperature sensor 32 are located within refrigeration case
36.
[0044] The vapor compression system of the present invention can
utilize essentially any commercially available heat transfer fluid
including refrigerants such as, for example, chlorofluorocarbons
such as R-12 which is a dicholordifluoromethane, R-22 which is a
monochlorodifluoromethane, R-500 which is an azeotropic refrigerant
consisting of R-12 and R-152a, R-503 which is an azeotropic
refrigerant consisting of R-23 and R-13, and R-502 which is an
azeotropic refrigerant consisting of R-22 and R-115. The vapor
compression system of the present invention can also utilize
refrigerants such as, but not limited to refrigerants R-13, R-113,
141b, 123a, 123, R-114, and R-11. Additionally, the vapor
compression system of the present invention can utilize
refrigerants such as, for example, hydrochlorofluorocarbons such as
141b, 123a, 123, and 124, hydrofluorocarbons such as R-134a, 134,
152, 143a, 125, 32, 23, and azeotropic HFCs such as AZ-20 and AZ-50
(which is commonly known as R-507). Blended refrigerants such as
MP-39, HP-80, FC-14, R-717, and HP-62 (commonly known as R-404a),
may also be used as refrigerants in the vapor compression system of
the present invention. Accordingly, it should be appreciated that
the particular refrigerant or combination of refrigerants utilized
in the present invention is not deemed to be critical to the
operation of the present invention since this invention is expected
to operate with a greater system efficiency with virtually all
refrigerants than is achievable by any previously known vapor
compression system utilizing the same refrigerant.
[0045] In operation, compressor 12 compresses the heat transfer
fluid, to a relatively high pressure and temperature. The
temperature and pressure to which the heat transfer fluid is
compressed by compressor 12 will depend upon the particular size of
vapor compression system 10 and the cooling load requirements of
the vapor compression system. Compressor 12 pumps the heat transfer
fluid into discharge line 20 and into condenser 14. As will be
described in more detail below, during cooling operations, second
inlet 26 is closed and the entire output of compressor 12 is pumped
through condenser 14.
[0046] In condenser 14, a medium such as air, water, or a secondary
refrigerant is blown past coils within condenser 14 causing the
pressurized heat transfer fluid to change to the liquid state. The
temperature of the heat transfer fluid drops about 10 to 40.degree.
F. (5.6 to 22.2.degree. C.), depending on the particular heat
transfer fluid, or glycol, or the like, as the latent heat within
the fluid is expelled during the condensation process. Condenser 14
discharges the liquefied heat transfer fluid to liquid line 22. As
shown in FIG. 1, liquid line 22 immediately discharges into
multifunctional valve 18. Because liquid line 22 is relatively
short, the pressurized liquid carried by liquid line 22 does not
substantially increase in temperature as it passes from condenser
14 to multifunctional valve 18. By configuring vapor compression
system 10 to have a short liquid line 22, vapor compression system
10 advantageously delivers substantial amounts of heat transfer
fluid to multifunctional valve 18 at a low temperature and high
pressure. Since the heat transfer fluid does not travel a great
distance once it is converted to a high-pressure liquid, little
heat absorbing capability is lost by the inadvertent warming of the
liquid before it enters multifunctional valve 18, or by a loss in
liquid pressure. While in the above embodiments of the invention,
the vapor compression system uses a relatively short liquid line
22, it is possible to implement the advantages of the present
invention in a vapor compression system using a relatively long
liquid line 22, as will be described below. The heat transfer fluid
discharged by condenser 14 enters multifunctional valve 18 at first
inlet 24 and undergoes a volumetric expansion at a rate determined
by the temperature of suction line 30 at temperature sensor 32.
Multifunctional valve 18 discharges the heat transfer fluid as a
saturated vapor into saturated vapor line 28. Temperature sensor 32
relays temperature information through a control line 33 to
multifunctional valve 18.
[0047] Those skilled in the art will recognize that vapor
compression system 10 can be used in a wide variety of applications
for controlling the temperature of an enclosure, such as a
refrigeration case in which perishable food items are stored. For
example, where vapor compression system 10 is employed to control
the temperature of a refrigeration case having a cooling load of
about 12000 Btu/hr (84 g cal/s), compressor 12 discharges about 3
to 5 lbs/min (1.36 to 2.27 kg/min) of R-12 at a temperature of
about 110.degree. F. (43.3.degree. C.) to about 120.degree. F.
(48.9.degree. C.) and a pressure of about 150 lbs/in.sup.2 (1.03 E5
N/m.sup.2) to about 180 lbs/in..sup.2 (1.25 E5 N/m.sup.2)
[0048] In accordance with one preferred embodiment of the
invention, saturated vapor line 28 is sized in such a way that the
low pressure fluid discharged into saturated vapor line 28
substantially converts to a saturated vapor as it travels through
saturated vapor line 28. In one embodiment, saturated vapor line 28
is sized to handle about 2500 ft/min (76 m/min) to 3700 ft/min
(1128 m/min) of a heat transfer fluid, such as R-12, and the like,
and has a diameter of about 0.5 to 1.0 inches (1.27 to 2.54 cm),
and a length of about 90 to 100 feet (27 to 30.5 m). As described
in more detail below, multifunctional valve 18 includes a common
chamber immediately before the outlet. The heat transfer fluid
undergoes an additional volumetric expansion as it enters the
common chamber. The additional volumetric expansion of the heat
transfer fluid in the common chamber of multifunctional valve 18 is
equivalent to an effective increase in the line size of saturated
vapor line 28 by about 225%.
[0049] Those skilled in the art will further recognize that the
positioning of a valve for volumetrically expanding of the heat
transfer fluid in close proximity to the condenser, and the
relatively great length of the fluid line between the point of
volumetric expansion and the evaporator, differs considerably from
systems of the prior art. In a typical prior art system, an
expansion valve is positioned immediately adjacent to the inlet of
the evaporator, and if a temperature sensing device is used, the
device is mounted in close proximity to the outlet of the
evaporator. As previously described, such system can suffer from
poor efficiency because substantial amounts of the evaporator carry
a liquid rather than a saturated vapor. Fluctuations in high side
pressure, liquid temperature, heat load or other conditions can
adversely effect the evaporator's efficiency.
[0050] In contrast to the prior art, the inventive vapor
compression system described herein positions a saturated vapor
line between the point of volumetric expansion and the inlet of the
evaporator, such that portions of the heat transfer fluid are
converted to a saturated vapor before the heat transfer fluid
enters the evaporator. By charging evaporator 16 with a saturated
vapor, the cooling efficiency is greatly increased. By increasing
the cooling efficiency of an evaporator, such as evaporator 16,
numerous benefits are realized by the vapor compression system. For
example, less heat transfer fluid is needed to control the air
temperature of refrigeration case 36 at a desired level.
Additionally, less electricity is needed to power compressor 12
resulting in lower operating cost. Further, compressor 12 can be
sized smaller than a prior art system operating to handle a similar
cooling load. Moreover, in one preferred embodiment of the
invention, the vapor compression system avoids placing numerous
components in proximity to the evaporator. By restricting the
placement of components within refrigeration case 36 to a minimal
number, the thermal loading of refrigeration case 36 is
minimized.
[0051] While in the above embodiments of the invention,
multifunctional valve 18 is positioned in close proximity to
condenser 14, thus creating a relatively short liquid line 22 and a
relatively long saturated vapor line 28, it is possible to
implement the advantages of the present invention even if
multifunctional valve 18 is positioned immediately adjacent to the
inlet of the evaporator 16, thus creating a relatively long liquid
line 22 and a relatively short saturated vapor line 28. For
example, in one preferred embodiment of the invention,
multifunctional valve 18 is positioned immediately adjacent to the
inlet of the evaporator 16, thus creating a relatively long liquid
line 22 and a relatively short saturated vapor line 28, as
illustrated in FIG. 7. In order to insure that the heat transfer
fluid entering evaporator 16 is a saturated vapor, a heat source 25
is applied to saturated vapor line 28, as illustrated in FIGS. 7-8.
Temperature sensor 32 is mounted to suction line 30 and operatively
connected to multifunctional valve 18, wherein heat source 25 is of
sufficient intensity so as to vaporize a portion of the heat
transfer fluid before the heat transfer fluid enters evaporator 16.
The heat transfer fluid entering evaporator 16 is converted to a
saturated vapor wherein a portion of the heat transfer fluids
exists in a liquid state 29, and another portion of the heat
transfer fluid exists in a vapor state 31, as illustrated in FIG.
8.
[0052] Preferably heat source 25 used to vaporize a portion of the
heat transfer fluid comprises heat transferred to the ambient
surroundings from condenser 14, however, heat source 25 can
comprise any external or internal source of heat known to one of
ordinary skill in the art, such as, for example, heat transferred
to the ambient surroundings from the discharge line 20, heat
transferred to the ambient surroundings from a compressor, heat
generated by a compressor, heat generated from an electrical heat
source, heat generated using combustible materials, heat generated
using solar energy, or any other source of heat. Heat source 25 can
also comprise an active heat source, that is, any heat source that
is intentionally applied to a part of vapor compression system 10,
such as saturated vapor line 28. An active heat source includes but
is not limited to a source of heat such as heat generated from an
electrical heat source, heat generated using combustible materials,
heat generated using solar energy, or any other source of heat
which is intentionally and actively applied to any part of vapor
compression system 10. A heat source that comprises heat which
accidentally leaks into any part of vapor compression system 10 or
heat which is unintentionally or unknowingly absorbed into any part
of vapor compression system 10, either due to poor insulation or
other reasons, is not an active heat source.
[0053] In one preferred embodiment of the invention, temperature
sensor 32 monitors the heat transfer fluid exiting evaporator 16 in
order to insure that a portion of the heat transfer fluid is in a
liquid state 29 upon exiting evaporator 16, as illustrated in FIG.
8. In one preferred embodiment of the invention, at least about 5%
of the of the heat transfer fluid is vaporized before the heat
transfer fluid enters the evaporator, and at least about 1% of the
heat transfer fluid is in a liquid state upon exiting the
evaporator. By insuring that a portion of the heat transfer fluid
is in liquid state 29 and vapor state 31 upon entering and exiting
the evaporator, the vapor compression system of the present
invention allows evaporator 16 to operate with maximum efficiency.
In one preferred embodiment of the invention, the heat transfer
fluid is in at least about a 1% superheated state upon exiting
evaporator 16. In one preferred embodiment of the invention, the
heat transfer fluid is between about a 1% liquid state and about a
1% superheated vapor state upon exiting evaporator 16.
[0054] While the above embodiments rely on heat source 25 or the
dimensions and length of saturated vapor line 28 to insure that the
heat transfer fluid enters the evaporator 16 as a saturated vapor,
any means known to one of ordinary skill in the art which can
convert the heat transfer fluid to a saturated vapor upon entering
evaporator 16 can be used. Additionally, while the above
embodiments use temperature sensor 32 to monitor the state of the
heat transfer fluid exiting the evaporator, any metering device
known to one of ordinary skill in the art which can determine the
state of the heat transfer fluid upon exiting the evaporator can be
used, such as a pressure sensor, or a sensor which measures the
density of the fluid. Additionally, while in the above embodiments,
the metering device monitors the state of the heat transfer fluid
exiting evaporator 16, the metering device can also be placed at
any point in or around evaporator 16 to monitor the state of the
heat transfer fluid at any point in or around evaporator 16.
[0055] Shown in FIG. 2 is a side view, in partial cross-section, of
one embodiment of multifunctional valve 18. Heat transfer fluid
enters first inlet 24 and traverses a first passageway 38 to a
common chamber 40. An expansion valve 42 is positioned in first
passageway 38 near first inlet 24. Expansion valve 42 meters the
flow of the heat transfer fluid through first passageway 38 by
means of a diaphragm (not shown) enclosed within an upper valve
housing 44. Expansion valve 42 can be any metering unit known to
one of ordinary skill in the art that can be used to meter the flow
of heat transfer fluid, such as a thermostatic expansion valve, a
capillary tube, or a pressure control. In one preferred embodiment,
expansion valve 42 is a fast-action capillary tube 500, as
illustrated in FIG. 21. Fast-action capillary tube 500 includes an
inlet 505, an outlet 510, an expansion line 515, and a gating valve
520. Heat transfer fluid enters fast-action capillary tube 500 at
inlet 505 and passes through expansion line 515. Expansion line 515
is sized with a length and diameter such that heat transfer fluid
is allowed to expand within expansion line 515. In one preferred
embodiment, heat transfer fluid enter expansion line 515 as a
liquid and expansion line 515 is sized such that heat transfer
fluid expands from a liquid to a low quality liquid vapor mixture.
Preferably, heat transfer fluid expands from a liquid to a high
quality liquid vapor mixture within expansion line 515. Upon
passing through expansion line 515, heat transfer fluid exits
fast-action capillary tube 500 at outlet 510. Gating valve 520 is
coupled to outlet 510 and control the flow of heat transfer fluid
through fast-action capillary tube 500. Preferably, gating valve
520 is a solenoid valve capable of terminating the flow of heat
transfer fluid through a passageway, such as expansion line 515, in
response to an electrical signal. However, gating valve 520 may be
any valve capable of terminating the flow of heat transfer fluid
through a passageway known to one of ordinary skill, such as a
valve that is mechanically activated.
[0056] When a vapor compression system, such as vapor compression
system 10, is in operation, heat transfer fluid is pumped through
fast-action capillary tube 500 from inlet 505 to outlet 510, and
gating valve 520 is opened to allow heat transfer fluid to exit
from fast-action capillary tube 500. When a vapor compression
system has ceased operation, or has been cycled off, gating valve
520 is closed to allow heat transfer fluid to fill up fast-action
capillary tube 500. By allowing fast-action capillary tube 500 to
fill up with heat transfer fluid, fast-action capillary tube 500 is
able to immediately supply a unit, such as an evaporator, with a
rush of heat transfer fluid in a liquid state. By being able to
supply a unit, such as an evaporator, with a rush of heat transfer
fluid in a liquid state, fast-action capillary tube 500 allows a
vapor compression system to cycle on, or begin operation,
rapidly.
[0057] Control line 33 is connected to an input 62 located on upper
valve housing 44. Signals relayed through control line 33 activate
the diaphragm within upper valve housing 44. The diaphragm actuates
a valve assembly 54 (shown in FIG. 4) to control the amount of heat
transfer fluid entering an expansion chamber 52 (shown in FIG. 4)
from first inlet 24. A gating valve 46 is positioned in first
passageway 38 near common chamber 40. In a preferred embodiment of
the invention, gating valve 46 is a solenoid valve capable of
terminating the flow of heat transfer fluid through first
passageway 38 in response to an electrical signal.
[0058] Shown in FIG. 3 is a side view, in partial cross-section, of
a second side of multifunctional valve 18. A second passageway 48
couples second inlet 26 to common chamber 40. A gating valve 50 is
positioned in second passageway 48 near common chamber 40. In a
preferred embodiment of the invention, gating valve 50 is a
solenoid valve capable of terminating the flow of heat transfer
fluid through second passageway 48 upon receiving an electrical
signal. Common chamber 40 discharges the heat transfer fluid from
multifunctional valve 18 through an outlet 41.
[0059] An exploded perspective view of multifunctional valve 18 is
illustrated in FIG. 4. Expansion valve 42 is seen to include
expansion chamber 52 adjacent first inlet 24, valve assembly 54,
and upper valve housing 44. Valve assembly 54 is actuated by a
diaphragm (not shown) contained within the upper valve housing 44.
First and second tubes 56 and 58 are located intermediate to
expansion chamber 52 and a valve body 60. Gating valves 46 and 50
are mounted on valve body 60. In accordance with the invention,
vapor compression system 10 can be operated in a defrost mode by
closing gating valve 46 and opening gating valve 50. In defrost
mode, high temperature heat transfer fluid enters second inlet 26
and traverses second passageway 48 and enters common chamber 40.
The high temperature vapors are discharged through outlet 41 and
traverse saturated vapor line 28 to evaporator 16. The high
temperature vapor has a temperature sufficient to raise the
temperature of evaporator 16 by about 50 to 120.degree. F. (27.8 to
66.7.degree. C.). The temperature rise is sufficient to remove
frost from evaporator 16 and restore the heat transfer rate to
desired operational levels.
[0060] While the above embodiments use a multifunctional valve 18
for expanding the heat transfer fluid before entering evaporator
16, any thermostatic expansion valve or throttling valve, such as
expansion valve 42 or even recovery valve 19, may be used to expand
heat transfer fluid before entering evaporator 16.
[0061] In one preferred embodiment of the invention heat source 25
is applied to the heat transfer fluid after the heat transfer fluid
passes through expansion valve 42 and before the heat transfer
fluid enters the inlet of evaporator 16 to convert the heat
transfer fluid from a low quality liquid vapor mixture to a high
quality liquid vapor mixture, or a saturated vapor. In one
preferred embodiment of the invention, heat source 25 is applied to
a multifunctional valve 18. In another preferred embodiment of the
invention heat source 25 is applied within recovery valve 19, as
illustrated in FIG. 9. Recovery valve 19 comprises a first inlet
124 connected to liquid line 22 and a first outlet 159 connected to
saturated vapor line 28. Heat transfer fluid enters first inlet 124
of recovery valve 19 to a common chamber 140. An expansion valve
142 is positioned near first inlet 124 to expand the heat transfer
fluid entering first inlet 124 from a liquid state to a low quality
liquid vapor mixture. Second inlet 127 is connected to discharge
line 20, and receives high temperature heat transfer fluid exiting
compressor 12. High temperature heat transfer fluid exiting
compressor 12 enters second inlet 127 and traverses second
passageway 123. Second passageway 123 is connected to second inlet
127 and second outlet 130. A portion of second passageway 123 is
located adjacent to common chamber 140.
[0062] As the high temperature heat transfer fluid nears common
chamber 140, heat from the high temperature heat transfer fluid is
transferred from the second passageway 123 to the common chamber
140 in the form of heat source 125. By applying heat from heat
source 125 to the heat transfer fluid in common chamber 140, the
heat transfer fluid in common chamber 140 is converted from a low
quality liquid vapor mixture to a high quality liquid vapor
mixture, or saturated vapor, as the heat transfer fluid flows
through common chamber 140. Additionally, the high temperature heat
transfer fluid in the second passageway 123 is cooled as the high
temperature heat transfer fluid passes near common chamber 140.
Upon traversing second passageway 123, the cooled high temperature
heat transfer fluid exits second outlet 130 and enters condenser
14. Heat transfer fluid in common chamber 140 exits recovery valve
19 at first outlet 159 into saturated vapor line 28 as a high
quality liquid vapor mixture, or saturated vapor.
[0063] While in the above preferred embodiment, heat source 125
comprises heat transferred to the ambient surroundings from a
compressor, heat source 125 may comprise any external or internal
source of heat known to one of ordinary skill in the art, such as,
for example, heat generated from an electrical heat source, heat
generated using combustible materials, heat generated using solar
energy, or any other source of heat. Heat source 125 can also
comprise any heat source 25 and any active heat source, as
previously defined.
[0064] In one preferred embodiment of the invention, recovery valve
19 comprises third passageway 148 and third inlet 126. Third inlet
126 is connected to discharge line 20, and receives high
temperature heat transfer fluid exiting compressor 12. A first
gating valve (not shown) capable of terminating the flow of heat
transfer fluid through common chamber 140 is positioned near the
first inlet 124 of common chamber 140. Third passageway 148
connects third inlet 126 to common chamber 140. A second gating
valve (not shown) is positioned in third passageway 148 near common
chamber 140. In a preferred embodiment of the invention, the second
gating valve is a solenoid valve capable of terminating the flow of
heat transfer fluid through third passageway 148 upon receiving an
electrical signal.
[0065] In accordance with the invention, vapor compression system
10 can be operated in a defrost mode by closing the first gating
valve located near first inlet 124 of common chamber 140 and
opening the second gating valve positioned in third passageway 148
near common chamber 140. In defrost mode, high temperature heat
transfer fluid from compressor 12 enters third inlet 126 and
traverses third passageway 148 and enters common chamber 140. The
high temperature heat transfer fluid is discharged through first
outlet 159 of recovery valve 19 and traverses saturated vapor line
28 to evaporator 16. The high temperature heat transfer fluid has a
temperature sufficient to raise the temperature of evaporator 16 by
about 50 to 120.degree. F. (27.8 to 66.7.degree. C.). The
temperature rise is sufficient to remove frost from evaporator 16
and restore the heat transfer rate to desired operational
levels.
[0066] During the defrost cycle, any pockets of oil trapped in the
vapor compression system will be warmed and carried in the same
direction of flow as the heat transfer fluid. By forcing hot gas
through the vapor compression system in a forward flow direction,
the trapped oil will eventually be returned to the compressor. The
hot gas will travel through the vapor compression system at a
relatively high velocity, giving the gas less time to cool thereby
improving the defrosting efficiency. The forward flow defrost
method of the invention offers numerous advantages to a reverse
flow defrost method. For example, reverse flow defrost systems
employ a small diameter check valve near the inlet of the
evaporator. The check valve restricts the flow of hot gas in the
reverse direction reducing its velocity and hence its defrosting
efficiency. Furthermore, the forward flow defrost method of the
invention avoids pressure build up in the vapor compression system
during the defrost system. Additionally, reverse flow methods tend
to push oil trapped in the vapor compression system back into the
expansion valve. This is not desirable because excess oil in the
expansion valve can cause gumming that restricts the operation of
the expansion valve. Also, with forward defrost, the liquid line
pressure is not reduced in any additional refrigeration circuits
being operated in addition to the defrost circuit.
[0067] It will be apparent to those skilled in the art that a vapor
compression system arranged in accordance with the invention can be
operated with less heat transfer fluid those comparable sized
system of the prior art. By locating the multifunctional valve near
the condenser, rather than near the evaporation, the saturated
vapor line is filled with a relatively low-density vapor, rather
than a relatively high-density liquid. Alternatively, by applying a
heat source to the saturated vapor line, the saturated vapor line
is also filled with a relatively low-density vapor, rather than a
relatively high-density liquid. Additionally, prior art systems
compensate for low temperature ambient operations (e.g. winter
time) by flooding the evaporator in order to reinforce a proper
head pressure at the expansion valve. In one preferred embodiment
of the invention, vapor compression system heat pressure is more
readily maintained in cold weather, since the multifunctional valve
is positioned in close proximity to the condenser.
[0068] The forward flow defrost capability of the invention also
offers numerous operating benefits as a result of improved
defrosting efficiency. For example, by forcing trapped oil back
into the compressor, liquid slugging is avoided, which has the
effect of increasing the useful life of the equipment. Furthermore,
reduced operating cost are realized because less time is required
to defrost the vapor compression system. Since the flow of hot gas
can be quickly terminated, the vapor compression system can be
rapidly returned to normal cooling operation. When frost is removed
from evaporator 16, temperature sensor 32 detects a temperature
increase in the heat transfer fluid in suction line 30. When the
temperature rises to a given set point, gating valve 50 and
multifunctional valve 18 is closed. Once the flow of heat transfer
fluid through first passageway 38 resumes, cold saturated vapor
quickly returns to evaporator 16 to resume refrigeration
operation.
[0069] Those skilled in the art will appreciate that numerous
modifications can be made to enable the vapor compression system of
the invention to address a variety of applications. For example,
vapor compression systems operating in retail food outlets
typically include a number of refrigeration cases that can be
serviced by a common compressor system. Also, in applications
requiring refrigeration operations with high thermal loads,
multiple compressors can be used to increase the cooling capacity
of the vapor compression system.
[0070] A vapor compression system 64 in accordance with another
embodiment of the invention having multiple evaporators and
multiple compressors is illustrated in FIG. 5. In keeping with the
operating efficiency and low-cost advantages of the invention, the
multiple compressors, the condenser, and the multiple
multifunctional valves are contained within a control unit 66.
Saturated vapor lines 68 and 70 feed saturated vapor from control
unit 66 to evaporators 72 and 74, respectively. Evaporator 72 is
located in a first refrigeration case 76, and evaporator 74 is
located in a second refrigeration case 78. First and second
refrigeration cases 76 and 78 can be located adjacent to each
other, or alternatively, at relatively great distance from each
other. The exact location will depend upon the particular
application. For example, in a retail food outlet, refrigeration
cases are typically placed adjacent to each other along an isle
way. Importantly, the vapor compression system of the invention is
adaptable to a wide variety of operating environments. This
advantage is obtained, in part, because the number of components
within each refrigeration case is minimal. In one preferred
embodiment of the invention, by avoiding the requirement of placing
numerous system components in proximity to the evaporator, the
vapor compression system can be used where space is at a minimum.
This is especially advantageous to retail store operations, where
floor space is often limited.
[0071] In operation, multiple compressors 80 feed heat transfer
fluid into an output manifold 82 that is connected to a discharge
line 84. Discharge line 84 feeds a condenser 86 and has a first
branch line 88 feeding a first multifunctional valve 90 and a
second branch line 92 feeding a second multifunctional valve 94. A
bifurcated liquid line 96 feeds heat transfer fluid from condenser
86 to first and second multifunctional valves 90 and 94. Saturated
vapor line 68 couples first multifunctional valve 90 with
evaporator 72, and saturated vapor line 70 couples second
multifunctional valve 94 with evaporator 74. A bifurcated suction
line 98 couples evaporators 72 and 74 to a collector manifold 100
feeding multiple compressors 80. A temperature sensor 102 is
located on a first segment 104 of bifurcated suction line 98 and
relays signals to first multifunctional valve 90. A temperature
sensor 106 is located on a second segment 108 of bifurcated suction
line 98 and relays signals to second multifunctional valve 94. In
one preferred embodiment of the invention, a heat source, such as
heat source 25, can be applied to saturated vapor lines 68 and 70
to insure that the heat transfer fluid enters evaporators 72 and 74
as a saturated vapor.
[0072] Those skilled in the art will appreciate that numerous
modifications and variations of vapor compression system 64 can be
made to address different refrigeration applications. For example,
more than two evaporators can be added to the vapor compression
system in accordance with the general method illustrated in FIG. 5.
Additionally, more condensers and more compressors can also be
included in the vapor compression system to further increase the
cooling capability.
[0073] A multifunctional valve 110 arranged in accordance with
another embodiment of the invention is illustrated in FIG. 6. In
similarity with the previous multifunctional valve embodiment, the
heat transfer fluid exiting the condenser in the liquid state
enters a first inlet 122 and expands in expansion chamber 152. The
flow of heat transfer fluid is metered by valve assembly 154. In
the present embodiment, a solenoid valve 112 has an armature 114
extending into a common seating area 116. In refrigeration mode,
armature 114 extends to the bottom of common seating area 116 and
cold refrigerant flows through a passageway 118 to a common chamber
140, then to an outlet 120. In defrost mode, hot vapor enters
second inlet 126 and travels through common seating area 116 to
common chamber 140, then to outlet 120. Multifunctional valve 110
includes a reduced number of components, because the design is such
as to allow a single gating valve to control the flow of hot vapor
and cold vapor through the multifunctional valve 110.
[0074] In yet another embodiment of the invention, the flow of
liquefied heat transfer fluid from the liquid line through the
multifunctional valve can be controlled by a check valve positioned
in the first passageway to gate the flow of the liquefied heat
transfer fluid into the saturated vapor line. The flow of heat
transfer fluid through the vapor compression system is controlled
by a pressure valve located in the suction line in proximity to the
inlet of the compressor. Accordingly, the various functions of a
multifunctional valve of the invention can be performed by separate
components positioned at different locations within the vapor
compression system. All such variations and modifications are
contemplated by the present invention.
[0075] Those skilled in the art will recognize that the vapor
compression system and method described herein can be implemented
in a variety of configurations. For example, the compressor,
condenser, multifunctional valve, and the evaporator can all be
housed in a single unit and placed in a walk-in cooler. In this
application, the condenser protrudes through the wall of the
walk-in cooler and ambient air outside the cooler is used to
condense the heat transfer fluid.
[0076] In another application, the vapor compression system and
method of the invention can be configured for air-conditioning a
home or business. In this application, a defrost cycle is
unnecessary since icing of the evaporator is usually not a
problem.
[0077] In yet another application, the vapor compression system and
method of the invention can be used to chill water. In this
application, the evaporator is immersed in water to be chilled.
Alternatively, water can be pumped through tubes that are meshed
with the evaporator coils.
[0078] In a further application, the vapor compression system and
method of the invention can be cascaded together with another
system for achieving extremely low refrigeration temperatures. For
example, two systems using different heat transfer fluids can be
coupled together such that the evaporator of a first system
provides a low temperature ambient. A condenser of the second
system is placed in the low temperature ambient and is used to
condense the heat transfer fluid in the second system.
[0079] Another embodiment of a multifunctional valve 225 is shown
in FIGS. 11-14 and is generally designated by the reference numeral
225. This embodiment is functionally similar to that described in
FIGS. 2-4 and FIG. 6 which was generally designated by the
reference numeral 18. As shown, this embodiment includes a main
body or housing 226 which preferably is constructed as a single
one-piece structure having a pair of threaded bosses 227, 228 that
receive a pair of gating valves and collar assemblies, one of which
being shown in FIG. 13 and designated by the reference numeral 229.
This assembly includes a threaded collar 230, gasket 231 and
solenoid-actuated gating valve receiving member 232 having a
central bore 233, that receives a reciprocally movable valve pin
234 that includes a spring 235 and needle valve element 236 which
is received with a bore 237 of a valve seat member 238 having a
resilient seal 239 that is sized to be sealingly received in well
240 of the housing 226. A valve seat member 241 is snuggly received
in a recess 242 of valve seat member 238. Valve seat member 241
includes a bore 243 that cooperates with needle valve element 236
to regulate the flow of heat transfer fluid therethrough.
[0080] A first inlet 244 (corresponding to first inlet 24 in the
previously described embodiment) receives liquid feed heat transfer
fluid from expansion valve 42, and a second inlet 245
(corresponding to second inlet 26 of the previously described
embodiment) receives hot gas from the compressor 12 during a
defrost cycle. In one preferred embodiment multifunctional valve
225 comprises first inlet 244, outlet 248, common chamber 246, and
expansion valve 42, as illustrated in FIG. F. In one preferred
embodiment, expansion valve 42 is connected with first inlet 244.
The valve body 226 includes a common chamber 246 (corresponding to
common chamber 40 in the previously described embodiment).
Expansion valve 42 receives heat transfer fluid from the condenser
14 which then passes through inlet 244 into a semicircular well 247
which, when gating valve 229 is open, then passes into common
chamber 246 and exits from the multifunctional valve 225 through
outlet 248 (corresponding to outlet 41 in the previously described
embodiment).
[0081] A best shown in FIG. 11 the valve body 226 includes a first
passageway 249 (corresponding to first passageway 38 of the
previously described embodiment) which communicates first inlet 244
with common chamber 246. In like fashion, a second passageway 250
(corresponding to second passageway 48 of the previously described
embodiment) communicates second inlet 245 with common chamber
246.
[0082] Insofar as operation of multifunctional valve 225 is
concerned, reference is made to the previously described embodiment
since the components thereof function in the same way during the
refrigeration and defrost cycles. In one preferred embodiment, the
heat transfer fluid exits the condenser 14 in the liquid state
passes through expansion valve 42. As the heat transfer fluid
passes through expansion valve 42, the heat transfer fluid changes
from a liquid to a liquid vapor mixture, wherein the heat transfer
fluid is in both a liquid state and a vapor state. The heat
transfer fluid enters the first inlet 244 as a liquid vapor mixture
and expands in common chamber 246.
[0083] In one preferred embodiment, the heat transfer fluid expands
in a direction away from the general flow of the heat transfer
fluid. As the heat transfer fluid expands in common chamber 246,
the liquid separates from the vapor in the heat transfer fluid. The
heat transfer fluid then exits common chamber 246. Preferably, the
heat transfer fluid exits common chamber 246 as a liquid and a
vapor, wherein a substantial amount of the liquid is separate and
apart from a substantial amount of the vapor. The heat transfer
fluid then passes through outlet 248 and travels through saturated
vapor line 28 to evaporator 16. In one preferred embodiment, the
heat transfer fluid then passes through outlet 248 and enters
evaporator 16 at first evaporative line 328, as described in more
detail below. Preferably, the heat transfer fluid travels from
outlet 248 to the inlet of evaporator 16 as a liquid and a vapor,
wherein a substantial amount of the liquid is separate and apart
from a substantial amount of the vapor.
[0084] In one preferred embodiment, a pair of gating valves 229 can
be used to control the flow of heat transfer fluid or hot vapor
into common chamber 246. In refrigeration mode, a first gating
valve 229 is opened to allow heat transfer fluid to flow through
first inlet 244 and into common chamber 246, and then to outlet
248. In defrost mode, a second gating valve 229 is opened to allow
hot vapor to flow through second inlet 245 and into common chamber
246, and then to outlet 248. While in the above embodiments,
multifunctional valve 225 has been described as having multiple
gating valves 229, multifunctional valve 225 can be designed with
only one gating valve. Additionally, multifunctional valve 225 has
been described as having a second inlet 245 for allowing hot vapor
to flow through during defrost mode, multifunctional valve 225 can
be designed with only first inlet 244.
[0085] In one preferred embodiment, multifunctional valve 225
comprises bleed line 251, as illustrated in FIG. 15. Bleed line 251
is connected with common chamber 246 and allows heat transfer fluid
that is in common chamber 246 to travel to saturated vapor line 28
or first evaporative line 328. In one preferred embodiment, bleed
line 251 allows the liquid that has separated from the liquid vapor
mixture entering common chamber 246 to travel to saturated vapor
line 28 or first evaporative line 328. Preferably, bleed line 251
is connected to bottom surface 252 of common chamber 246, wherein
bottom surface 252 is the surface of common chamber 246 located
nearest the ground.
[0086] In one preferred embodiment, multifunctional valve 225 is
dimensioned as specified below in Table A and as illustrated in
FIGS. 11-14. The length of common chamber 246 will be defined as
the distance from outlet 248 to back wall 253. The length of common
chamber 246 is represented by the letter G, as illustrated in FIG.
11. Common chamber 246 has a first portion adjacent to a second
portion, wherein the first portion begins at outlet 248 and the
second portion ends at back wall 253, as illustrated in FIG. 11.
First inlet 244 and outlet 248 are both connected with the first
portion. The heat transfer fluid enters common chamber 246 through
first inlet 244 and within the first portion of the common chamber
246. In one preferred embodiment, the first portion has a length
equal to no more than about 75% of the length of common chamber
246. More preferably, the first portion has a length equal to no
more than about 35% of the length of common chamber 246.
TABLE-US-00001 TABLE A DIMENSIONS OF MULTIFUNCTIONAL VALVE Inches
(all Millimeters dimensions not specified (all dimensions not
specified Dimensions are to be +/-0.015) are to be +/-0.381) A
2.500 63.5 B 2.125 53.975 C 1.718 43.637 D1 (diameter) 0.812 20.625
D2 (diameter) 0.609 15.469 D3 (diameter) 1.688 42.875 D4 (diameter)
1.312 (+/-0.002) 33.325 (+/-0.051) D5 (diameter) 0.531 13.487 E
0.406 10.312 F 1.062 26.975 G 4.500 114.3 H 5.000 127 I 0.781
19.837 J 2.500 63.5 K 1.250 31.75 L 0.466 11.836 M 0.812 (+/-0.005)
20.6248 (+/-0.127) R1 (radius) 0.125 3.175
[0087] In one preferred embodiment, the heat transfer fluid enters
common chamber 246 through first inlet 244 as a low quality liquid
vapor mixture 270. Liquid vapor mixture 270 is in both a liquid
state and a vapor state, wherein the liquid is suspended within the
vapor. As used herein, the heat transfer fluid that is in a liquid
state will be referred to as liquid 280 and the heat transfer fluid
that is in a vapor state will be referred to as vapor 285. As the
heat transfer fluid passes from the inlet 244 of common chamber 246
to the outlet 248 of common chamber 246, a portion of liquid 280
coalesces. As used herein, the term "coalesces" means to unite or
to fuse together. Therefore, when the phrase "a portion of liquid
280 coalesces" is used, it is meant that a portion of liquid 280
becomes united with or fused together with another portion of
liquid 280. As the heat transfer fluid enters common chamber 246,
liquid 280 is arranged with liquid vapor mixture 270 as liquid
droplets suspended in vapor 280. After the heat transfer fluid
enters common chamber 246 as a liquid vapor mixture 270, the slower
moving liquid 280 begins to coalesce and settle at bottom surface
252 of common chamber 246 while the faster moving vapor 285 is
forced through outlet 248, as illustrated in FIGS. 17-19. By
allowing liquid 280 to coalesce and separate from vapor 285, heat
is released from the liquid vapor mixture 270 allowing liquid 280
to cool off. The cooling off of liquid 280 decreases the enthalpy
of liquid vapor mixture 270, converting the heat transfer fluid in
common chamber 246 from a low quality liquid vapor mixture to a
high quality liquid vapor mixture, or a saturated vapor.
[0088] In one preferred embodiment, as heat transfer fluid travels
through common chamber 246, a portion of liquid 280 within liquid
vapor mixture 270 coalesces into larger droplets which exit through
outlet 248 along with vapor 285. In one preferred embodiment, the
larger droplets of liquid 280 coalesces into a stream of liquid
280, wherein the stream of liquid 280 exits through outlet 248
along with a stream of vapor 285, as illustrated in FIGS. 17-19.
Preferably, at least 10% of liquid 280 coalesces into larger
droplets of liquid 280 or a stream of liquid 280. More preferably,
at least 35% of liquid 280 coalesces into larger droplets of liquid
280 or a stream of liquid 280.
[0089] Common chamber 246 is divided into a first portion 290 and a
second portion 295. First portion 290 includes first inlet 244 and
outlet 248. By including first inlet 244 and outlet 248, first
portion is also the portion of common chamber 246 upon which heat
transfer fluid must flow through upon entering common chamber 246,
and therefore the portion of common chamber 246 wherein flow
direction 265 generally resides. Flow direction 265 is the general
direction the heat transfer fluid flows as the heat transfer fluid
travels from first inlet 244 to second inlet 248, as illustrated by
arrows in FIGS. 17-19. Second portion 295 is located in common
chamber 246 and allows for a portion of the heat transfer fluid to
coalesce. Preferably, second portion 295 is located away from flow
direction 265, as illustrated in FIGS. 17-19. By locating second
portion 295 away from flow direction 265, the slower moving liquid
280 is allowed to accumulate in and coalesce in second portion 295
and the faster moving vapor 285 is able to become separated from
liquid 280, as illustrated in FIGS. 17-19. Preferably, the heat
transfer fluid exists common chamber 246 through outlet 248 as a
high quality liquid vapor mixture, wherein liquid 280 has coalesced
and is substantially separate and apart from vapor 285, as
illustrated in FIGS. 17-19. Upon exiting common chamber 246 at
outlet 248, the heat transfer fluid then passes through saturated
vapor line 28 to evaporator 16.
[0090] In one preferred embodiment, the flow of heat transfer fluid
is in a turbulent state upon entering first inlet 244, so that a
portion of vapor 285 gets trapped in second portion 295, creating
eddy 275 in common chamber 246, and more preferably in second
portion 295 of common chamber 246. Eddy 275 is a current of heat
transfer fluid that flows in a generally circular direction, as
illustrated in FIGS. 17-19. Eddy 275 helps liquid 280 to coalesce.
In one preferred embodiment, the heat transfer fluid enters first
inlet 244 in a turbulent state and creates at least one vortex 276
in common chamber 246, and more preferably in second portion 295 of
common chamber 246. Vortex 276, as defined herein, is a mass of
heat transfer fluid having a whirling or circular motion that forms
a cavity or vacuum in the center of the circle and that draws
toward this cavity or vacuum bodies subject to this action. For
example, when a vortex 276 is formed within common chamber 246, a
cavity or vacuum forms in the center of vortex 276 that tends to
draw vapor 285 away from liquid vapor mixture 270. In this way,
liquid 280 can be separated from vapor 285 in liquid vapor mixture
270.
[0091] Common chamber 246 can comprise any one of a variety of
geometrical configurations which allow a portion of liquid 280 to
coalesce within common chamber 246 and separate from liquid 280. In
one preferred embodiment, first inlet 244 is a distance N1 away
from outlet 248 and a distance N2 from back wall 253, wherein the
sum of N1 and N2 equals the length of common chamber 246, as
illustrated in FIG. 17. Preferably, N1 is anywhere from about 5% to
about 75% the length of common chamber 246. In one preferred
embodiment, common chamber 246 includes reservoir 305 located along
bottom surface 252 of common chamber 246, as illustrated in FIG.
17. Reservoir 305 traps a portion of heat transfer fluid within
common chamber 246, which causes liquid 280 to coalesce.
[0092] In one preferred embodiment, inlet 244 is adjacent with back
wall 253 and bottom surface 252 is located a distance N3 from
outlet 248 and a distance N4 from inlet 244, as illustrated in
FIGS. 18-19. N3 is anywhere from about 25% to about 95% the length
of N4. In this configuration, second portion 295 is able to trap a
portion of heat transfer fluid within common chamber 246, which
causes liquid 280 to coalesce. In one preferred embodiment, common
chamber 246 includes notch 300 between first inlet 244 and outlet
248, as illustrated in FIG. 19. Notch 300 reduces the amount of
heat transfer fluid that can exit common chamber 246 through outlet
248. By reducing the amount of heat transfer fluid that can exits
common chamber 246, notch 300 encourages the faster moving vapor
285 to separate from the slower moving liquid 280, which causes
liquid 280 to coalesce. Preferably, notch 300 has a height N5 and
outlet 248 has a diameter N6, wherein N5 is anywhere from about 15%
to about 95% of N6. The embodiments of common chamber 246 discussed
above, and as illustrated in FIGS. 17-19, are merely illustrative
of the invention and are not meant to limit the scope in any way
whatsoever.
[0093] In one preferred embodiment, the flow rate upon which heat
transfer fluid is forced through first inlet 244 is increased to
facilitate the separation of liquid 280 from vapor 285 in liquid
vapor mixture 270, which causes liquid 280 to coalesce. For
example, in a vapor compression system having a compressor of size
X, a condenser of size Y, an evaporator of size Z, and first inlet
244 having a diameter of D, if the flow rate is increased from A to
B, liquid 280 will more readily separate from vapor 285 and
coalesce. Preferably, the flow rate of heat transfer fluid is
increased so that the heat transfer fluid entering common chamber
226 is in a turbulent flow. More preferably, the flow rate of heat
transfer fluid is increased so that the heat transfer fluid
entering common chamber 246 is at such a rate that Eddy 275 forms
within common chamber 246, as illustrated in FIGS. 17-19. In one
preferred embodiment, the heat transfer fluid passes through
expansion valve 42 and then enters the inlet of evaporator 16, as
illustrated in FIG. 16. In this embodiment, evaporator 16 comprises
first evaporative line 328, evaporator coil 21, and second
evaporative line 330. First evaporative line 328 is positioned
between outlet 248 and evaporator coil 21, as illustrated in FIG.
16. Second evaporative line 330 is positioned between evaporative
coil 21 and temperature sensor 32. Evaporator coil 21 is any
conventional coil that absorbs heat. Multifunctional valve 225 is
preferably connected with and adjacent evaporator 16. In one
preferred embodiment, evaporator 16 comprises a portion of
multifunctional valve 225, such as first inlet 244, outlet 248, and
common chamber 246, as illustrated in FIG. 16. Preferably,
expansion valve 42 is positioned adjacent evaporator 16. Heat
transfer fluid exits expansion valve 42 and then directly enters
evaporator 16 at inlet 244. As the heat transfer fluid exits
expansion valve 42 and enters evaporator 16 at inlet 244, the
temperature of the heat transfer fluid is at an evaporative
temperature, that is the heat transfer fluid begins to absorb heat
upon passing through expansion valve 42.
[0094] Upon passing through inlet 244, common chamber 246, and
outlet 248, the heat transfer fluid enters first evaporative line
328. Preferably, first evaporative line 328 is insulated. Heat
transfer fluid then exits first evaporative line 328 and enters
evaporative coil 21. Upon exiting evaporative coil 21, heat
transfer fluid enters second evaporative line 330. Heat transfer
fluid exists in second evaporative line 330 and evaporator 16 at
temperature sensor 32.
[0095] Preferably, every element within evaporator 16, such as
saturated vapor line 28, multifunctional valve 225, and evaporator
coil 21, absorbs heat. In one preferred embodiment, as the heat
transfer fluid passes through expansion valve 42, the heat transfer
fluid is at a temperature within 20.degree. F. of the temperature
of the heat transfer fluid within the evaporator coil 21. In
another preferred embodiment, the temperature of the heat transfer
fluid in any element within evaporator 16, such as saturated vapor
line 28, multifunctional valve 225, and evaporator coil 21, is
within 20.degree. F. of the temperature of the heat transfer fluid
in any other element within evaporator 16. While the above
embodiments were described in reference to multifunctional valve
225, any multifunctional valve described herein, can be used as
well.
[0096] In one preferred embodiment, vapor compression system 410
includes a compressor 412, a condenser 414, an evaporator 416, an
XDX valve 418, and a metering unit 449, as illustrated in FIG. 20.
XDX valve 418 is any device known to one of ordinary skill in the
art that can be used to meter the flow of heat transfer fluid an
that can convert the heat transfer fluid into a saturated vapor
upon entering evaporator 16, as described in the above embodiments.
Examples of XDX valve 418 are multifunctional valves 18, 90, 94,
110 and 225, recovery valve 19, any metering unit coupled to a
relatively short liquid line and a relatively long saturated vapor
line sufficient in length and diameter to vaporize a portion of the
heat transfer fluid before the heat transfer fluid enters the
evaporator, as described herein, and any metering unit in which a
heat source is applied to the heat transfer fluid in the saturated
vapor line sufficient to vaporize a portion of the heat transfer
fluid before the heat transfer fluid enters the evaporator, as
described herein. Metering unit 449 can be any device known to one
of ordinary skill in the art that can be used to meter the flow of
heat transfer fluid, such as a thermostatic expansion valve, a
capillary tube, a fast-action capillary tube 500, or a pressure
control.
[0097] Compressor 412 is coupled to condenser 414 by a discharge
line 420. XDX valve 418 includes first inlet 461, second inlet 462
and outlet 463. Metering unit 449 includes inlet 464 and outlet
465. First inlet 461 of XDX valve 418 and inlet 464 of metering
unit 449 are coupled to condenser 414 by a bifurcated liquid line
422.
[0098] A saturated vapor line 428 couples outlet 463 of XDX valve
418 to inlet 455 of evaporator 416, and a suction line 430 couples
the outlet of evaporator 416 to the inlet of compressor 412. A
refrigerant line 456 couples outlet 465 of metering unit 449 to
inlet 455 of evaporator 416. A temperature sensor 432 is mounted to
suction line 430 and is operably connected to XDX valve 418 and
metering unit 449. Temperature sensor 432 relays temperature
information through a control line 433 to XDX valve 418 and through
a second control line 434 to metering unit 449.
[0099] In accordance with one preferred embodiment, the flow of
heat transfer fluid from condenser 414 to evaporator 416 can be
directed to go through either XDX valve 418 or metering unit 449.
Preferably, the flow of heat transfer fluid from condenser 414 to
evaporator 416 can be directed to go through either XDX valve 418
or metering unit 449 based on the conditions of the ambient
surroundings 470. Ambient surroundings 470 is the area or space in
which the conditions, such as temperature and humidity, are
controlled or altered by vapor compression system 410. For example,
if vapor compression system 410 was an air conditioning unit, then
ambient surroundings 470 would be defined by the area within a
building or house being cooled by the air conditioning unit.
Moreover, if vapor compression system 410 was a refrigeration unit,
for example, then ambient surroundings 470 would be the area within
a freezer or a refrigerator being cooled by the refrigeration
unit.
[0100] In one preferred embodiment, a sensor 460 is located in
ambient surroundings 470 and measures the conditions of ambient
surroundings 470. Sensor 460 is any metering device known to one of
ordinary skill in the art that can measure the conditions of
ambient surroundings 470, such as a pressure sensor, a temperature
sensor, or a sensor that measures the density of the fluid. Sensor
460 relays information through a control line 481 to metering unit
449 and through a second control line 483 to XDX valve 418. In this
way, sensor 460 is able to direct the heat transfer fluid to run
either through XDX valve 418 or metering unit 449 based upon the
conditions of ambient surroundings 470.
[0101] In one preferred embodiment, sensor 460 is located in
ambient surroundings 470 and measures the humidity of ambient
surroundings 470. A desired humidity level is programmed into
sensor 460. Upon determining the humidity of ambient surroundings
470, sensor 460 then decides whether to direct the flow of heat
transfer fluid to either XDX valve 41.8 or metering unit 449 based
upon the desired humidity level programmed into sensor 460. If the
desired humidity level is less than the actual humidity of the
ambient surroundings 470, sensor 460 directs the flow of heat
transfer fluid to flow through metering unit 449 by closing first
inlet 461, and by opening inlet 464. By directing the heat transfer
fluid to flow through metering unit 449, vapor compression system
410 operates in what will be referred to as a conventional
refrigeration cycle. When vapor compression system 410 operates in
a conventional refrigeration cycle, the amount of humidity in the
ambient surroundings 470 is decreased. If the desired humidity
level is greater than the actual humidity of the ambient
surroundings 470, sensor 460 directs the flow of heat transfer
fluid to flow through XDX valve 418 by opening first inlet 461, and
by closing inlet 464. By directing the heat transfer fluid to flow
through XDX valve 418, vapor compression system 410 operates in
what will be referred to as an XDX cycle. When vapor compression
system 410 operates in an XDX cycle, the amount of humidity in the
ambient surroundings 470 increases.
[0102] In one preferred embodiment, gating valves 471 and 474 are
located at first inlet 461 and inlet 464, respectively, as
illustrated in FIG. 20. Preferably, gating valves 471 and 474 are
solenoid valves capable of terminating the flow of heat transfer
fluid through a passageway, such as liquid line 422, in response to
an electrical signal. However, gating valves may be any valve
capable of terminating the flow of heat transfer fluid through a
passageway known to one of ordinary skill, such as a valve that is
mechanically activated. Gating valves 471 and 474 can be used to
open or close first inlet 461 and inlet 464 at any time either
mechanically or in response to an electrical signal.
[0103] In one preferred embodiment, sensor 460 decides whether to
direct the flow of heat transfer fluid to either XDX valve 418 or
metering unit 449 based upon the temperature of the ambient
surroundings 470. A desired temperature level for the ambient
surroundings 470 must first be programmed into sensor 460. Sensor
460 directs the flow of heat transfer fluid to flow through
metering unit 449 by closing first inlet 461 and by opening inlet
464. By directing the heat transfer fluid to flow through metering
unit 449, vapor compression system 410 operates in what will be
referred to as a conventional refrigeration cycle. When vapor
compression system 410 operates in a conventional refrigeration
cycle, the load capacity of vapor compression system 410 is
decreased. If the desired temperature level cannot be reached after
a predetermined time interval, then sensor 460 directs the flow of
heat transfer fluid to flow through XDX valve 418 by opening first
inlet 461 and by closing inlet 464. By directing the heat transfer
fluid to flow through XDX valve 418, vapor compression system 410
operates in what will be referred to as an XDX cycle. When vapor
compression system 410 operates in an XDX cycle, the load capacity
of vapor compression system 410 is increased.
[0104] Varying the load capacity of vapor compression system 410
allows vapor compression system 410 to be more accurately sized for
cooling ambient surroundings 470. For example, if ambient
surroundings 470 needs to be cooled in a range which varies from an
average amount of .degree. C. to a maximum amount of .degree. C.,
vapor compression system 410 must be sized to cool ambient
surroundings 470 by at least the maximum amount of .degree. C. so
that vapor compression system 410 can achieve the desired
temperature level even when the difference between the temperature
level of the ambient surroundings 470 and the desired temperature
level is the maximum amount of .degree. C. However, this means that
vapor compression system 410 must be sized larger than required,
since more often than not vapor compression system 410 need only
cool ambient surroundings by the average amount of .degree. C.
However, by varying the load capacity of vapor compression system
410, as described above, vapor compression system 410 can be sized
so that it cools ambient surroundings by the average amount of
.degree. C. when operating vapor compression system 410 in a
conventional refrigeration cycle, and up to the maximum amount of
.degree. C. when operating vapor compression system 410 in an XDX
cycle.
[0105] While the above use of sensor 460 to direct the flow of heat
transfer fluid to either XDX valve 418 or metering unit 449 has
been described as being in response to the humidity level or the
temperature level of the ambient surroundings, sensor 460 may
direct the flow of heat transfer fluid to either XDX valve 418 or
metering unit 449 in response to any variable or condition.
Moreover, while the above use of vapor compression system 410 has
required a sensor 460 to direct the flow of heat transfer fluid to
either XDX valve 418 or metering unit 449, the flow may be manually
directed to either XDX valve 418 or metering unit 449, or directed
to either XDX valve 418 or metering unit 449 in any one of a number
of ways known to one of ordinary skill in the art, for any one of a
number of reasons.
[0106] In one preferred embodiment, discharge line 420 is coupled
to both second inlet 462 of XDX valve 418 and condenser 414, to
facilitate the defrosting of evaporator 416. Preferably, discharge
line 420 is bifurcated so as to allow discharge line 420 to be
simultaneously coupled to both second inlet 462 of XDX valve 418
and condenser 414, as illustrated in FIG. 20. Gating valve 472 is
located at second inlet 462 so as to control the flow of heat
transfer fluid from compressor 412 to second inlet 462. In order to
defrost the coils of evaporator 416, gating valves 472 is opened,
and gating valves 471 and 474 are closed to allow heat transfer
fluid from compressor 412 to enter evaporator 416 and defrost
evaporator 416.
[0107] In one preferred embodiment, vapor compression system 10
includes a turbulent line 600 before the inlet of evaporator 16, as
illustrated in FIG. 22. Turbulent line 600 includes an inlet 634,
an outlet 635, and a passageway 630 connecting inlet 634 to outlet
635. Turbulent line 600 also includes dimples 605 located on the
interior surface 615 of passageway 630 of turbulent line 600.
Dimples 605 convert the flow of heat transfer fluid from a laminar
flow to a turbulent flow. By converting heat transfer fluid to a
turbulent flow before heat transfer fluid enters evaporator 16, the
efficiency of evaporator 16 is increased. Dimples 605 may either be
ridges 610 which project inwards towards the flow 625 of the heat
transfer fluid or bumps 620 which project outwards and away from
the flow 625 of heat transfer fluid, as illustrated in FIG. 22.
[0108] Preferably, turbulent line 600 is position between the
metering unit, such as multifunctional valve 18, 90, 94, 110 or
225, recovery valve 19, XDX valve 418, or any conventional metering
unit used to meter the flow of heat transfer fluid upon entering
evaporator. The placement, size, and spacing of ridges 610 to
create a turbulent flow depends on the diameter and length of
turbulent line 600 along with the flow rate of the heat transfer
fluid and the type of heat transfer fluid being used, all which are
factors that can be determined by one of ordinary skill in the art.
In one preferred embodiment, the line connecting the metering unit
to the inlet of evaporator 16, referred to herein as either the
saturated vapor line or the refrigerant line, includes turbulent
line 600. Preferably, a portion of saturated vapor line or
refrigerant line includes turbulent line 600.
[0109] As known by one of ordinary skill in the art, every element
of vapor compression system 10 described above, such as evaporator
16, liquid line 22, and suction line 30, can be scaled and sized to
meet a variety of load requirements. In addition, the refrigerant
charge of the heat transfer fluid in vapor compression system 10,
may be equal to or greater than the refrigerant charge of a
conventional system.
[0110] Another embodiment of the present invention provides a high
operating efficiency vapor compression system including an
evaporator having more than one circuit. When operated according to
the method of the present invention, such a system dispenses with
the need for a distributor to partition the heat transfer fluid to
the multiple circuits of the evaporator without the accompanying
large loss in evaporator capacity typically seen when a
conventional system is operated without a distributor.
[0111] In many applications, it is preferred to distribute heat
transfer fluid from the expansion device into the circuits of a
multi-circuit evaporator coil. In such applications, it is
important to distribute the heat transfer fluid equally to each
circuit of the evaporator coil. If this is not done, one or more
circuits of the evaporator can become starved of heat transfer
fluid. In such a situation, the evaporator capacity is reduced.
[0112] In conventional systems having a multi-circuit evaporator,
if a simple manifold divider is used to partition the heat transfer
fluid flow into the multiple evaporator circuits, the circuits of
the evaporator coil tend not receive equal amounts of heat transfer
fluid. Such a situation is illustrated in FIG. 23. This figure
shows three manifold configurations: an up-feed manifold (23(a)), a
down-feed manifold (23(b)) and a side-feed manifold (23(c)).
[0113] The up-feed manifold receives heat transfer fluid at an
input situated below multiple outputs. The down-feed manifold
receives heat transfer fluid at an input situated above multiple
outputs. The side-feed manifold receives heat transfer fluid at an
input situated above some of the outputs but below other outputs.
In each configuration, heat transfer fluid flows along the path of
least resistance from the manifold input to the manifold output. As
illustrated in FIG. 23, those outputs closest to the input, or
lower than the input, tend to receive a greater portion of the heat
transfer fluid than do the other outputs.
[0114] Many conventional systems include a "distributor" in an
attempt to evenly distribute heat transfer fluid from an expansion
device to the coils of a multi-coil evaporator. Typically, a
distributor includes a nozzle positioned to focus heat transfer
fluid flow evenly into a dispersion cone. Output passages are
spaced evenly around the cone to receive the heat transfer
fluid.
[0115] As illustrated in FIG. 24, expanded heat transfer fluid is
delivered from an expansion device (801) to the distributor nozzle
(802). Upon passing though the nozzle, the velocity of the heat
transfer fluid is increased. The heat transfer fluid enters the
distributor dispersion cone (803), where it is distributed between
multiple distributor outputs (804). The distributor outputs (804)
are positioned so that each distributor output receives an equal
quantity of heat transfer fluid. Each distributor output delivers
heat transfer fluid to one circuit of an evaporator coil (805).
Although the inclusion of a distributor tends to equalize the flow
of heat transfer fluid to the coils of a multi-circuit evaporator,
and hence maintain the evaporator efficiency, the cost of the
distributor invariably increases the cost of the vapor compression
system.
[0116] In the method of the invention, the expanded heat transfer
fluid is converted to a high quality liquid vapor mixture before
delivery to the evaporator. Example III shows the results of a test
performed using such a method and also using the conventional
method of operation, i.e. where the expanded heat transfer fluid is
not converted to a high quality liquid vapor mixture before
delivery to the evaporator. Despite the absence of a distributor,
conversion of the expanded heat transfer fluid to a high quality
liquid vapor mixture before delivery to the evaporator allowed the
evaporator capacity to be maintained. This was the case even with a
reduction in the heat transfer surface of the evaporator.
[0117] In another embodiment of the invention, the increased
efficiency obtained when a vapor compression system is operated
according to the method of the present invention allows for a
reduction in the heat transfer fluid load used in the system.
[0118] In another embodiment of the invention, the "heat transfer
surface" of the evaporator coil is smaller than the heat transfer
surface of an evaporator coil, manufactured from the same material,
required to obtain an equivalent evaporator capacity when a
significant amount of the liquid heat transfer fluid is not
converted from a liquid form to a high quality liquid vapor
mixture. For example, for an evaporator coil manufactured from a
material such as copper, having a given diameter and wall
thickness, the length of the evaporator coil may be reduced if the
vapor compression system is operated according to the method of the
present invention. For the purposes of the present invention, the
"heat transfer surface" is the area of the evaporator coil in
contact with the heat transfer fluid.
[0119] Evaporator capacity and mass flow rate are the principal
measures of performance of refrigerant evaporators. Evaporator
capacity is defined as the work done in terms of heat transfer
fluid vaporized per hour. The Mass Flow Rate is the mass of heat
transfer fluid that moves through the evaporator coil to be
vaporized. Evaporator capacity commonly takes into consideration
the amount of heat transfer fluid flow, the amount of heat removed,
and the heat transfer rate. The expansion device size, the amount
of heat transfer fluid in the system and the compressor capacity
are each often used to commercially identify the mass flow
rate.
[0120] Evaporator capacity is viewed as: Q=U*A*(.DELTA.T(log
mean)), where
[0121] The evaporator capacity, Q, through the heating surface of
an-evaporator is the product of three factors;
[0122] A (m.sup.2)-the heat transfer surface,
[0123] U(Wm.sup.-2K.sup.-1)-the overall heat transfer coefficient,
and
[0124] .DELTA.T (log mean)-the overall temperature driving
force(log mean).
[0125] The temperature driving force is a function of the
refrigerant properties, the amount of refrigerant, and the amount
of heat absorbed. The Overall Heat Transfer Coefficient is a
function of the design of the evaporator. Factors affecting the
Overall Heat Transfer Coefficient (U) include: [0126] the frost or
condensing coefficient on the outside of the evaporator coil (ho),
[0127] the thermal resistance of the evaporator coil (R), [0128]
the liquid film heat transfer coefficient on the inside of the
evaporator coil (hi), [0129] the thermal resistance of oil deposits
on the inside of the evaporator coil, [0130] the thermal resistance
of dirt on the outside of the evaporator coil, and [0131]
miscellaneous other factors, such as the amount of moisture in the
air.
[0132] Without further elaboration it is believed that one skilled
in the art can, using the preceding description, utilize the
invention to its fullest extent. The following examples are merely
illustrative of the invention and are not meant to limit the scope
in any way whatsoever.
EXAMPLE I
[0133] A 5-ft (1.52 m) Tyler Chest Freezer was equipped with a
multifunctional valve in a refrigeration circuit, and a standard
expansion valve was plumbed into a bypass line so that the
refrigeration circuit could be operated as a conventional vapor
compression system and as an XDX refrigeration system arranged in
accordance with the invention. The refrigeration circuit described
above was equipped with a saturated vapor line having an outside
tube diameter of about 0.375 inches (0.953 cm) and an effective
tube length of about 10 ft (3.048 m). The refrigeration circuit was
powered by a Copeland hermetic compressor having a capacity of
about 1/3 ton (338 kg) of refrigeration. A sensing bulb was
attached to the suction line about 18 inches from the compressor.
The circuit was charged with about 28 oz. (792 g) of R-12
refrigerant available from The DuPont Company. The refrigeration
circuit was also equipped with a bypass line extending from the
compressor discharge line to the saturated vapor line for
forward-flow defrosting (See FIG. 1). All refrigerated ambient air
temperature measurements were made using a "CPS Date Logger" by CPS
temperature sensor located in the center of the refrigeration case,
about 4 inches (10 cm) above the floor.
XDX System--Medium Temperature Operation
[0134] The nominal operating temperature of the evaporator was
20.degree. F. (-6.7.degree. C.) and the nominal operating
temperature of the condenser was 120.degree. F. (48.9.degree. C.).
The evaporator handled a cooling load of about 3000 Btu/hr (21 g
cal/s). The multifunctional valve metered refrigerant into the
saturated vapor line at a temperature of about 20.degree. F.
(-6.7.degree. C.). The sensing bulb was set to maintain about
25.degree. F. (13.9.degree. C.) superheating of the vapor flowing
in the suction line. The compressor discharged pressurized
refrigerant into the discharge line at a condensing temperature of
about 120.degree. F. (48.9.degree. C.), and a pressure of about 172
lbs/in.sup.2 (118,560 N/m.sup.2).
XDX System--Low Temperature Operation
[0135] The nominal operating temperature of the evaporator was
-5.degree. F. (-20.5.degree. C.) and the nominal operating
temperature of the condenser was 115.degree. F. (46.1.degree. C.).
The evaporator handled a cooling load of about 3000 Btu/hr (21 g
cal/s). The multifunctional valve metered about 2975 ft/min (907
km/min) of refrigerant into the saturated vapor line at a
temperature of about -5.degree. F. (-20.5.degree. C.). The sensing
bulb was set to maintain about 20.degree. F. (11.1.degree. C.)
superheating of the vapor flowing in the suction line. The
compressor discharged about 2299 ft/min (701 m/min) of pressurized
refrigerant into the discharge line at a condensing temperature of
about 115.degree. F. (46.1.degree. C.), and a pressure of about 161
lbs/in.sup.2 (110,977 N/m.sup.2). The XDX system was operated
substantially the same in low temperature operation as in medium
temperature operation with the exception that the fans in the Tyler
Chest Freezer were delayed for 4 minutes following defrost to
remove heat from the evaporator coil and to allow water drainage
from the coil.
[0136] The XDX refrigeration system was operated for a period of
about 24 hours at medium temperature operation and about 18 hours
at low temperature operation. The temperature of the ambient air
within the Tyler Chest Freezer was measured about every minute
during the 23 hour testing period. The air temperature was measured
continuously during the testing period, while the vapor compression
system was operated in both refrigeration mode and in defrost mode.
During defrost cycles, the refrigeration circuit was operated in
defrost mode until the sensing bulb temperature reached about
50.degree. F. (10.degree. C.). The temperature measurement
statistics appear in Table I below.
[0137] Conventional System--Medium Temperature Operation With
Electric Defrost
[0138] The Tyler Chest Freezer described above was equipped with a
bypass line extending between the compressor discharge line and the
suction line for defrosting. The bypass line was equipped with a
solenoid valve to gate the flow of high temperature refrigerant in
the line. An electric heat element was energized instead of the
solenoid during this test. A standard expansion valve was installed
immediately adjacent to the evaporator inlet and the temperature
sensing bulb was attached to the suction line immediately adjacent
to the evaporator outlet. The sensing bulb was set to maintain
about 6.degree. F. (3.33.degree. C.) superheating of the vapor
flowing in the suction line. Prior to operation, the vapor
compression system was charged with about 48 oz. (1.36 kg) of R-12
refrigerant.
[0139] The conventional vapor compression system was operated for a
period of about 24 hours at medium temperature operation. The
temperature of the ambient air within the Tyler Chest Freezer was
measured about every minute during the 24 hour testing period. The
air temperature was measured continuously during the testing
period, while the vapor compression system was operated in both
refrigeration mode and in reverse-flow defrost mode. During defrost
cycles, the refrigeration circuit was operated in defrost mode
until the sensing bulb temperature reached about 50.degree. F.
(10.degree.C.). The temperature measurement statistics appear in
Table I below.
[0140] Conventional System--Medium Temperature Operation With Air
Defrost
[0141] The Tyler Chest Freezer described above was equipped with a
receiver to provide proper liquid supply to the expansion valve and
a liquid line dryer was installed to allow for additional
refrigerant reserve. The expansion valve and the sensing bulb were
positioned at the same locations as in the reverse-flow defrost
system described above. The sensing bulb was set to maintain about
8.degree. F. (4.4.degree. C.) superheating of the vapor flowing in
the suction line. Prior to operation, the vapor compression system
was charged with about 34 oz. (0.966 kg) of R-12 refrigerant.
[0142] The conventional vapor compression system was operated for a
period of about 241/2 hours at medium temperature operation. The
temperature of the ambient air within the Tyler Chest Freezer was
measured about every minute during the 241/2 hour testing period.
The air temperature was measured continuously during the testing
period, while the vapor compression system was operated in both
refrigeration mode and in air defrost mode. In accordance with
conventional practice, four defrost cycles were programmed with
each lasting for about 36 to 40 minutes. The temperature
measurement statistics appear in Table I below. TABLE-US-00002
TABLE I REFRIGERATION TEMPERATURES (.degree. F./.degree. C.)
XDX.sup.1) XDX.sup.1) Conventional.sup.2) Conventional.sup.2)
Medium Low Electric Air Temperature Temperature Defrost Defrost
Average 38.7/3.7 4.7/-15.2 39.7/4.3 39.6/4.2 Standard 0.8 0.8 4.1
4.5 Deviation Variance 0.7 0.6 16.9 20.4 Range 7.1 7.1 22.9 26.0
.sup.1)one defrost cycle during 23 hour test period .sup.2)three
defrost cycles during 24 hour test period
[0143] As illustrated above, the XDX refrigeration system arranged
in accordance with the invention maintains a desired the
temperature within the chest freezer with less temperature
variation than the conventional systems. The standard deviation,
the variance, and the range of the temperature measurements taken
during the testing period are substantially less than the
conventional systems. This result holds for operation of the XDX
system at both medium and low temperatures.
[0144] During defrost cycles, the temperature rise in the chest
freezer was monitored to determine the maximum temperature within
the freezer. This temperature should be as close to the operating
refrigeration temperature as possible to avoid spoilage of food
products stored in the freezer. The maximum defrost temperature for
the XDX system and for the conventional systems is shown in Table
II below. TABLE-US-00003 TABLE II MAXIMUM DEFROST TEMPERATURE
(.degree. F./.degree. C.) XDX Conventional Conventional Medium
Temperature Electric Defrost Air Defrost 44.4/6.9 55.0/12.8
58.4/14.7
EXAMPLE II
[0145] The Tyler Chest Freezer was configured as described above
and further equipped with electric defrosting circuits. The low
temperature operating test was carried out as described above and
the time needed for the refrigeration unit to return to
refrigeration operating temperature was measured. A separate test
was then carried out using the electric defrosting circuit to
defrost the evaporator. The time needed for the XDX system and an
electric defrost system to complete defrost and to return to the
5.degree. F. (-15.degree. C.) operating set point appears in Table
III below. TABLE-US-00004 TABLE III TIME NEEDED TO RETURN TO
REFRIGERATION TEMPERATURE OF 5.degree. F. (-15.degree. C.)
FOLLOWING Conventional System XDX with Electric Defrost Defrost
Duration (min) 10 36 Recovery Time (min) 24 144
[0146] As shown above, the XDX system using forward-flow defrost
through the multifunctional valve needs less time to completely
defrost the evaporator, and substantially less time to return to
refrigeration temperature.
EXAMPLE III
[0147] A three door reach in freezer was set up in two
configurations and tested to determine the ability of the freezer
to meet defined acceptance criteria under each configuration. The
tests were conducted using a Three-door Reach-In freezer powered by
a Copeland compressor (part number KAKD-011E-CAV) and loaded with
24 ozs of R-404A refrigerant. The compression circuit used a
FSE-1/2-ZP35 expansion valve. In the unmodified configuration, the
system capacity was rated by the manufacturer at 4,280 BTU/hr and
the evaporator capacity at 3,500 BTU/hr.
[0148] In the first (unmodified) configuration, the freezer was
operated as a conventional vapor compression system, i.e. without
the conversion of the heat transfer fluid to a high quality liquid
vapor mixture before delivery to the evaporator. In this
configuration, the evaporator coil consisted of a total of
forty-two (42) passes of 3/8'' copper tubing. The evaporator coil
was fed by a double feed through a distributor.
[0149] In the second (modified) configuration, the freezer was
operated according to the method of the present invention, i.e.
portions of the heat transfer fluid were converted to a high
quality liquid vapor mixture before delivery to the evaporator. In
this configuration, the evaporator coil consisted of a total of
twenty-eight passes of 3/8'' copper tubing. The evaporator coil was
fed directly by a double feed without a distributor.
[0150] The test conditions were those set by Underwriters
Laboratories as per NSF-7, 6.2. The test requires that a freezer
shall be capable of maintaining an air temperature of 0.degree. F.
(-18.degree. C.) or less in all freezer compartment interiors under
defined environmental conditions.
[0151] The testing criteria require that, prior to the start of the
test, the freezer is allowed to establish thermal equilibrium
according to the manufacturer's instructions or cycle on and off at
least two full cycles at an ambient temperature of 73.+-.3.degree.
F. (22.+-.2.degree. C.). The test must be conducted within a test
chamber maintained under the following conditions for the duration
of the test:
[0152] ambient temperature of 100.+-.3.degree. F..degree.
(38.+-.2.degree. C.); and
[0153] no vertical temperature gradient exceeding 1.5.degree. F./ft
(2.5.degree. C./m).
[0154] Air temperatures within the empty freezer compartment must
be monitored using remote sensing devices (thermocouples) accurate
to a .+-.1.degree. F. (0.5.degree. C.). The thermocouples must be
positioned as close as possible to the following locations:
Thermocouple #1: (when facing the front of the unit) 5.+-.0.25 in
(127.+-.6 mm) from the left interior wall, 2+0.25 in (51+6 mm)
above the bottom horizontal plane of the cooling unit, (for units
in which the evaporator is not suspended from the ceiling, the
thermocouple shall be placed 5+0.25 in [127.+-.6 mm] down from the
ceiling) and centered front-to-back;
[0155] Thermocouple #2: centered front-to-back, centered
top-to-bottom, centered left-to-right; and
[0156] Thermocouple #3: (when facing the unit) 5.+-.0.25 in
(127.+-.6 mm) from the right interior wall, 5.+-.0.25 (127.+-.6 mm)
above the internal floor of the unit, and centered
front-to-back.
[0157] Prior to recording the air temperatures, the unit must be
operated for two complete refrigeration cycles at the test chamber
ambient conditions. The temperature at each thermocouple location
must then be recorded at 5-minute intervals over a period of 4
hours.
[0158] The time during which the freezer's compressor(s) is
operating must be monitored over the complete test duration, and
the compressor percentage run time must be calculated for each
compressor using the formula: Compressor percentage run time,
R=d/D.times.100, where: "d" is the elapsed time that the compressor
is operating during a whole number of cycles; and "D" is the total
elapsed time during a whole number of cycles.
[0159] In order to meet the acceptance criteria, the temperature at
each thermocouple location within each freezer compartment must not
exceed 0.degree. F. (-18.degree. C.) during the 4-hour test period,
and the compressor percentage run time must not exceed 80%.
[0160] As shown in Table IV, the conventional system achieved the
acceptance criteria, having a compressor run time percentage of
75%. Table V shows that the XDX (modified) system, i.e. the system
operated so that the heat transfer fluid was converted to a high
quality liquid vapor mixture before delivery to the evaporator,
also achieved the acceptance criteria, even though no distributor
was included to equalize the delivery of heat transfer fluid to the
evaporator and the heat transfer surface is smaller that in the
freezer operated by the conventional (unmodified) method. In
addition, the compressor percentage runtime for the XDX (modified)
system was less than that of the conventional system.
TABLE-US-00005 TABLE IV Conventional (unmodified) System - 42-pass
Evaporator Thermo- Thermo- Thermo- couple 1 couple 2 couple 3 %
Runtime Max. Temp. (.degree. F.) -0.56 -1.12 0.27 Average Temp.
-5.32 -5.77 -6.82 (.degree. F.) Min. temp. (.degree. F.) -9.12
-9.68 -11.34 Compressor 75 Runtime
[0161] TABLE-US-00006 TABLE 5 XDX (modified) System - 28-pass
Evaporator Thermo- Thermo- Thermo- couple 1 couple 2 couple 3 %
Runtime Max. Temp. (.degree. F.) -0.52 -0.97 0.07 Average Temp.
-4.52 -5.07 -5.36 (.degree. F.) Min. temp. (.degree. F.) -8.27
-8.94 -9.78 Compressor 64 Runtime
[0162] Thus, it is apparent that there has been provided, in
accordance with the invention, a vapor compression system that
fully provides the advantages set forth above. Although the
invention has been described and illustrated with reference to
specific illustrative embodiments thereof, it is not intended that
the invention be limited to those illustrative embodiments. Those
skilled in the art will recognize that variations and modifications
can be made without departing from the spirit of the invention. For
example, non-halogenated refrigerants can be used, such as ammonia,
and the like can also be used. It is therefore intended to include
within the invention all such variations and modifications that
fall within the scope of the appended claims and equivalents
thereof.
* * * * *