U.S. patent application number 15/283809 was filed with the patent office on 2017-10-12 for refrigeration system with fluid defrost.
The applicant listed for this patent is Hussmann Corporation. Invention is credited to Tobey D. Fowler, Sean M. Hanlon, Paul R. Laurentius.
Application Number | 20170292770 15/283809 |
Document ID | / |
Family ID | 59998015 |
Filed Date | 2017-10-12 |
United States Patent
Application |
20170292770 |
Kind Code |
A1 |
Fowler; Tobey D. ; et
al. |
October 12, 2017 |
REFRIGERATION SYSTEM WITH FLUID DEFROST
Abstract
A refrigeration system having a refrigerant circuit including a
condenser, a flow control device, an evaporator, and a compressor
connected in series. The compressor is configured to circulate a
cooling fluid through the refrigerant circuit. The refrigerant
circuit has an inlet line fluidly connecting the condenser to the
evaporator and a suction line fluidly connecting the evaporator to
the compressor. A heater is positioned to heat the cooling fluid
during a defrost mode, and a pressure control is coupled to the
refrigerant circuit downstream of the evaporator. In the defrost
mode, the pressure control apparatus is configured to increase
system pressure during the defrost mode to maintain flow of
refrigerant into the evaporator and to control flow of cooling
fluid to the compressor.
Inventors: |
Fowler; Tobey D.; (St.
Charles, MO) ; Hanlon; Sean M.; (O'Fallon, MO)
; Laurentius; Paul R.; (Saint Charles, MO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hussmann Corporation |
Bridgeton |
MO |
US |
|
|
Family ID: |
59998015 |
Appl. No.: |
15/283809 |
Filed: |
October 3, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15093346 |
Apr 7, 2016 |
|
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15283809 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 2600/2513 20130101;
F25B 2700/21175 20130101; F25B 2500/07 20130101; F25D 21/004
20130101; F25B 2600/2515 20130101; F25D 21/08 20130101; F25B 41/043
20130101; A47F 3/0443 20130101; A47F 3/0469 20130101; A47F 3/0478
20130101; F25B 2341/0681 20130101; F25B 49/02 20130101; F25D
2400/02 20130101; A47F 3/0447 20130101 |
International
Class: |
F25D 21/08 20060101
F25D021/08; A47F 3/04 20060101 A47F003/04; F25D 21/00 20060101
F25D021/00 |
Claims
1. A refrigeration system comprising: a refrigerant circuit
including a condenser, a flow control device, an evaporator, and a
compressor connected in series, the compressor configured to
circulate a cooling fluid through the refrigerant circuit, and the
refrigerant circuit having an inlet line fluidly connecting the
condenser to the evaporator and a suction line fluidly connecting
the evaporator to the compressor; a heater positioned to heat the
cooling fluid during a defrost mode; and pressure control apparatus
coupled to the refrigerant circuit downstream of the evaporator,
wherein, in the defrost mode, the pressure control apparatus is
configured to increase system pressure during the defrost mode to
maintain flow of refrigerant into the evaporator and to control
flow of cooling fluid to the compressor.
2. The refrigeration system of claim 1, wherein the heater is
positioned downstream of the flow control device.
3. The refrigeration system of claim 1, wherein the pressure
control apparatus includes a solenoid valve or a pressure
regulator.
4. The refrigeration system of claim 1, wherein the pressure
control apparatus includes a first pressure regulator coupled to
the suction line, the refrigerant circuit further including a
bypass line that bypasses the first pressure regulator and that has
a second pressure regulator, and wherein the first pressure
regulator has a first pressure setpoint and the second pressure
regulator has a second pressure setpoint that is higher than the
first pressure setpoint.
5. The refrigeration system of claim 4, wherein the first pressure
regulator includes an evaporator pressure regulator valve and the
second pressure regulator includes a solenoid valve.
6. The refrigeration system of claim 1, wherein the heater includes
a first heater, the refrigeration system further comprising a
second heater in communication with the flow control device,
wherein the second heater is configured to control the flow control
apparatus to selectively permit or restrict flow of cooling fluid
to the evaporator during the defrost mode.
7. The refrigeration system of claim 1, further comprising a sensor
coupled to the evaporator and configured to detect a temperature of
the evaporator, and a controller in communication with the heater
to activate the heater in response to buildup of frost on the
evaporator, wherein the controller is configured to terminate the
defrost mode by deactivating the heater in response to the sensor
detecting a cooling fluid temperature at or above a predetermined
temperature threshold.
8. The refrigeration system of claim 7, wherein the temperature of
the evaporator detected by the sensor includes a temperature of the
cooling fluid in or exiting the evaporator.
9. The refrigeration system of claim 7, wherein the controller is
further in communication with the pressure control apparatus to
regulate a position of the pressure control apparatus between an
open position and a closed position.
10. The refrigeration system of claim 1, wherein the refrigeration
circuit further includes a recirculation line fluidly connected
between the suction line and the inlet line, wherein the
recirculation line is configured to recirculate cooling fluid
exiting the evaporator to the inlet line upstream of the
heater.
11. The refrigeration system of claim 1, wherein the heater is
positioned in and coupled to the evaporator.
12. The refrigeration system of claim 1, wherein the heater is
positioned directly below the evaporator.
13. A refrigeration system comprising: a refrigerant circuit
including a condenser, a flow control device, an evaporator, and a
compressor connected in series, the compressor configured to
circulate a refrigerant through the refrigerant circuit, and the
refrigerant circuit having an inlet line fluidly connecting the
condenser to the evaporator and a suction line fluidly connecting
the evaporator to the compressor; a refrigeration mode in which
refrigerant is directed through the evaporator in a first direction
via the inlet line; a defrost mode in which refrigerant is directed
through the evaporator in the first direction via the inlet line; a
first heater coupled to the inlet line and configured to heat the
refrigerant during the defrost mode; and a pressure control
apparatus coupled to the refrigerant circuit downstream of the
evaporator and configured to increase system pressure to maintain
flow of refrigerant into the evaporator during the defrost
mode.
14. The refrigeration system of claim 13, wherein the heater is
positioned downstream of the flow control device.
15. The refrigeration system of claim 11, wherein the pressure
control apparatus includes a solenoid valve or a pressure
regulator.
16. The refrigeration system of claim 11, wherein the pressure
control apparatus includes a first pressure regulator coupled to
the suction line, the refrigerant circuit further including a
bypass line that bypasses the first pressure regulator and that has
a second pressure regulator, and wherein the first pressure
regulator has a first pressure setpoint and the second pressure
regulator has a second pressure setpoint that is higher than the
first pressure setpoint.
17. The refrigeration system of claim 14, wherein the first
pressure regulator includes an evaporator pressure regulator valve
and the second pressure regulator includes a solenoid valve.
18. The refrigeration system of claim 11, wherein the heater
includes a first heater, the refrigeration system further
comprising a second heater in communication with the flow control
device, wherein the second heater is configured to control the flow
control apparatus to permit flow of cooling fluid to the evaporator
during the defrost mode.
19. The refrigeration system of claim 11, further comprising a
sensor coupled to the evaporator and configured to detect a
temperature of the evaporator, and a controller in communication
with the heater to activate the heater in response to buildup of
frost on the evaporator, wherein the controller is configured to
terminate the defrost mode by deactivating the heater in response
to the sensor detecting a cooling fluid temperature at or above a
predetermined temperature threshold.
20. The refrigeration system of claim 17, wherein the controller is
further in communication with the pressure control apparatus to
regulate a position of the pressure control apparatus between an
open position and a closed position.
21. The refrigeration system of claim 11, wherein the refrigeration
circuit further includes a recirculation line fluidly connected
between the suction line and the inlet line, wherein the
recirculation line is configured to recirculate cooling fluid
exiting the evaporator to the inlet line upstream of the
heater.
22. A method of defrosting a refrigeration system having a
refrigeration mode and a defrost mode, the method comprising:
circulating refrigerant in the refrigeration mode through a
condenser, a flow control device, an evaporator, and a compressor
of the refrigeration system; circulating refrigerant in the defrost
mode through the evaporator in the same direction as the
refrigeration mode; heating the refrigerant in the defrost mode;
and increasing system pressure in the defrost mode to maintain flow
of refrigerant into the evaporator during the defrost mode.
23. The method of claim 22, further comprising deactivating the
defrost mode based on a temperature of refrigerant exiting the
evaporator meeting or exceeding a temperature threshold.
24. The method of claim 22, further comprising heating the
refrigerant upstream of the evaporator.
25. The method of claim 22, further comprising heating the
refrigerant within the evaporator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and is a
continuation-in-part of U.S. patent application Ser. No.
15/093,346, filed Apr. 7, 2016, the entire contents of which are
incorporated by reference herein.
BACKGROUND
[0002] The present invention relates to refrigeration systems and,
more particularly, to fluid defrost of heat exchangers in
refrigeration systems.
[0003] Refrigeration systems are well known and widely used in
supermarkets, warehouses, and elsewhere to refrigerate product that
is supported in a refrigerated space. Conventional refrigeration
systems include a heat exchanger or evaporator, a compressor, and a
condenser. The evaporator provides heat transfer between a
refrigerant flowing within the evaporator and a fluid (e.g., water,
air, etc.) passing over or through the evaporator. The evaporator
transfers heat from the fluid to the refrigerant to cool the fluid.
The refrigerant absorbs the heat from the fluid and evaporates in a
refrigeration mode, during which the compressor mechanically
compresses the evaporated refrigerant from the evaporator and feeds
the superheated refrigerant to the condenser, which cools the
refrigerant. From the condenser, the cooled refrigerant is
typically fed through an expansion valve to reduce the temperature
and pressure of the refrigerant, and then the refrigerant is
directed through the evaporator.
[0004] Some evaporators operate at evaporating refrigerant
temperatures that are near or lower than the freezing point of
water (i.e., 32 degrees Fahrenheit). Over time, water vapor from
the fluid freezes on the evaporator (e.g., on the coils) and
generates frost. Accumulation of frost decreases the efficiency of
heat transfer between the evaporator and the fluid passing over the
evaporator, which causes the temperature of the refrigerated space
to increase above a desired level. Maintaining the correct
temperature of the refrigerated space is important to maintain the
quality of the stored product. To do this, evaporators must be
regularly defrosted to reestablish efficiency and proper operation.
Many existing refrigeration systems use electric heaters that are
placed underneath the evaporator to defrost the evaporator using
convection heat. Other existing systems re-route hot gaseous
refrigerant from the compressor directly to the evaporator so that
heat from the hot refrigerant melts the frost on the evaporator
(i.e. reverse hot gas defrost).
SUMMARY
[0005] In one aspect, the present invention provides a
refrigeration system having a refrigerant circuit including a
condenser, a flow control device, an evaporator, and a compressor
connected in series. The compressor is configured to circulate a
cooling fluid through the refrigerant circuit. The refrigerant
circuit has an inlet line fluidly connecting the condenser to the
evaporator and a suction line fluidly connecting the evaporator to
the compressor. A heater is positioned to heat the cooling fluid
during a defrost mode, and a pressure control is coupled to the
refrigerant circuit downstream of the evaporator. In the defrost
mode, the pressure control apparatus is configured to increase
system pressure during the defrost mode to maintain flow of
refrigerant into the evaporator and to control flow of cooling
fluid to the compressor.
[0006] In another aspect, the present invention provides a
refrigeration system having a refrigerant circuit including a
condenser, a flow control device, an evaporator, and a compressor
connected in series. The compressor is configured to circulate a
refrigerant through the refrigerant circuit. The refrigerant
circuit has an inlet line fluidly connecting the condenser to the
evaporator and a suction line fluidly connecting the evaporator to
the compressor. A refrigeration mode directs the refrigerant
through the evaporator in a first direction via the inlet line. A
defrost mode directs refrigerant though the evaporator in the first
direction via the inlet line. A first heater is coupled to the
inlet line and configured to heat the refrigerant during the
defrost mode. A pressure control apparatus is coupled to the
refrigerant circuit downstream of the evaporator and configured to
increase system pressure to maintain flow of refrigerant into the
evaporator during the defrost mode.
[0007] In another aspect, the present invention provides a method
of defrosting a refrigeration system having a refrigeration mode
and a defrost mode. The method includes circulating refrigerant in
the refrigeration mode through a condenser, a flow control device,
an evaporator, and a compressor of the refrigeration system. The
method also includes circulating refrigerant in the defrost mode
through the evaporator in the same direction as the refrigeration
mode. The method also includes heating the refrigerant in the
defrost mode and increasing the system pressure in the defrost mode
to maintain flow of refrigerant into the evaporator during the
defrost mode.
[0008] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross-section of a refrigerated merchandiser
including a product display area and an evaporator that is disposed
in a refrigerant circuit of a refrigeration system embodying the
present invention.
[0010] FIG. 2a is a schematic view of an exemplary refrigeration
system that is in a refrigeration mode and that includes a
refrigerant circuit with the evaporator, pressure control
apparatus, a compressor, a condenser, and a flow control device
fluidly arranged in series with each other, the refrigeration
system also including a heater that is disposed upstream of the
evaporator.
[0011] FIG. 2b is a schematic view of the refrigeration system of
FIG. 2a in a defrost mode including a heater that is disposed
upstream of the evaporator and a pressure control apparatus.
[0012] FIG. 3 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes
the first heater disposed upstream of the evaporator, a second
heater disposed downstream of the evaporator, and a first and
second pressure regulator.
[0013] FIG. 4 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
first heater disposed upstream of the evaporator, a second heater
disposed downstream of the evaporator, and a solenoid valve.
[0014] FIG. 5 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
first heater disposed upstream of the evaporator, a second heater
disposed downstream of the evaporator, and an electronic pressure
regulator.
[0015] FIG. 6 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
heater that is disposed upstream of the evaporator, the flow
control device including an electronic expansion valve, and first
and second pressure regulators.
[0016] FIG. 7 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
heater that is disposed upstream of the evaporator, the flow
control device including the electronic expansion valve, and the
pressure control apparatus including a solenoid.
[0017] FIG. 8 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes
the heater that is disposed upstream of the evaporator, the flow
control device including the electronic expansion valve, and the
pressure control apparatus including an electronic pressure
regulator.
[0018] FIG. 9A is a schematic view of another exemplary
refrigeration system that is in a refrigeration mode and that
includes a refrigerant circuit similar to the circuit illustrated
in FIG. 2a and including a recirculation line.
[0019] FIG. 9B is a schematic view of the refrigeration system of
FIG. 9A in a defrost mode that is in a first state.
[0020] FIG. 9C is a schematic view of the refrigeration system of
FIG. 9A in the defrost mode that is in a second state.
[0021] FIG. 10 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
heater disposed within the evaporator and includes a refrigerant
circuit similar to the circuit illustrated in FIG. 2b.
[0022] FIG. 11 is a schematic view of another exemplary
refrigeration system that is in a defrost mode and that includes a
heater disposed below the evaporator and includes a refrigerant
circuit similar to the circuit illustrated in FIG. 2b.
[0023] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways.
DETAILED DESCRIPTION
[0024] FIG. 1 illustrates a refrigerated merchandiser 10 that may
be located in a supermarket or a convenience store (not shown) for
presenting fresh food, beverages, and other food product to
consumers. The merchandiser 10 includes a case 15 that has a base
20, a rear wall 25, a canopy 30, and an opening 35 allowing access
to the food product. The area partially enclosed by the base 20,
the rear wall 25, and the canopy 30 defines a product display area
40 for supporting the food product in the case 15. For example,
food product can be displayed on racks or shelves 43 extending
forward from the rear wall 25, and is accessible by consumers
through the opening 35 adjacent the front of the case 15. Although
the merchandiser 10 is illustrated as an open-front merchandiser,
the merchandiser can include doors.
[0025] With reference to FIGS. 1 and 2a, the exemplary refrigerated
merchandiser 10 has a portion of a refrigeration system 45 that is
in communication with the case 15 to provide a refrigerated airflow
to the product display area 40. The refrigeration system 45
illustrated in FIG. 2a is a generic, exemplary system and includes
a refrigerant circuit 47 that has a condenser 50, a flow control
device 55, an evaporator 60, and a compressor 65 connected in
series. The refrigerant circuit 47 has an inlet line 85 that
fluidly connects the condenser 50 to the evaporator 60, and a
suction line 90 that fluidly connects the evaporator 60 to the
compressor 65. The flow control device 55 is disposed in the inlet
line 85 and controls refrigerant flow to the evaporator 60 (and
thus, the superheat at the evaporator outlet). The refrigerant
circuit 47 also has a heater 75 (e.g., a ceramic heater, an
induction heater, etc.) that is coupled to the inlet line 85
(illustrated downstream of the flow control device 55) upstream of
the evaporator 60, and pressure control apparatus 80 that is
disposed in the suction line 90. Referring back to FIG. 1, the
evaporator 60 is disposed in an air passageway 70 of the
merchandiser 10 to condition air that is directed through the air
passageway 70.
[0026] The refrigeration system 45 has a refrigeration mode during
which the evaporator 60 conditions an airflow (e.g., the air
flowing through passageway 70 in the merchandiser 10) based on heat
transfer between the refrigerant in the evaporator 60 and the air
passing over the evaporator 60. The refrigeration system also has a
defrost mode during which frost buildup on the evaporator 60 is
reduced or removed.
[0027] Although the invention is described with reference to its
application in the refrigerated merchandiser 10, it will be
appreciated that the refrigeration system 45 and method for
defrosting the refrigeration system 45 described in detail below
will have other applications.
[0028] FIG. 2a illustrates a schematic view of the refrigeration
system 45 in the refrigeration mode. In the refrigeration mode, the
compressor 65 is configured to circulate high pressure gaseous
cooling fluid or refrigerant (described as "refrigerant" for
purposes of description) to the condenser 50. The condenser 50
rejects heat from the compressed hot gas, causing the refrigerant
to condense into high pressure liquid. The condensed refrigerant is
directed through the inlet line 85 as a liquid to the flow control
device 55, which expands the refrigerant into a low pressure (e.g.,
saturated) vapor refrigerant. The saturated refrigerant is
evaporated as it passes through the evaporator 60 as a result of
absorbing heat from air passing over the evaporator 60. The
absorption of heat by the refrigerant allows the temperature of the
airflow to decrease as it passes over the evaporator 60. The heated
or gaseous refrigerant then exits the evaporator 60 and is directed
back to the compressor 65 through the suction line 90 for
re-processing through the refrigeration system 45. In the exemplary
merchandiser 10, the cooled or refrigerated airflow exiting the
evaporator 60 via heat exchange with the liquid refrigerant is
directed through the remainder of the air passageway 70 and is
introduced into the product display area 40 where the airflow will
remove heat from and maintain the food product at desired
conditions.
[0029] As shown in FIGS. 2a and 2b, the refrigeration system 45
also includes a sensor 95 (e.g., a defrost termination sensor),
that is coupled to the evaporator 60, and a controller 100 that is
communication (wired or wirelessly) with the sensor 95 and other
electric or electronically-controlled devices (e.g., the flow
control device 55, the compressor 65, the heater 75, the pressure
control apparatus 80, etc.). The sensor 95 is coupled to the
evaporator 60 to detect the temperature of refrigerant exiting the
evaporator 60. It will be appreciated that the sensor 95 can be
coupled to the suction line 90 just downstream of the evaporator 60
and accomplish the same task. The controller 100 is programmed to
receive a signal from the sensor 95 that is indicative of the
evaporator-refrigerant temperature, and to control various devices
based on the signal. The controller 100 also can control other
components of the system 45 based on or independent of the
signal.
[0030] FIG. 2b illustrates a schematic view of the refrigeration
system 45 in the defrost mode. The sensor 95 can be used to detect
buildup of frost on the evaporator 60 based on the temperature of
the refrigerant exiting the evaporator 60, although frost buildup
can be detected in other ways. In some constructions, the
controller 100 automatically initiates the defrost mode at preset
time periods (e.g., every two hours) or preset times (e.g., 2
a.M.).
[0031] In the defrost mode, the controller 100 activates the heater
75, which begins heating the refrigerant flowing to the evaporator
60. The flow control device 55 regulates (e.g., maintains,
increases, or decreases) the flow of refrigerant to the evaporator
60 during the defrost mode, and ensures that refrigerant continues
to flow to the evaporator 60 in the defrost mode. The pressure
control apparatus 80 is configured to increase system pressure
during the defrost mode to maintain flow of refrigerant into the
evaporator 60 and to control flow of refrigerant to the compressor
65. As illustrated in FIG. 2b, refrigerant continues to flow to the
compressor 65 during the defrost mode. In general, the pressure
control apparatus 80 increases the amount of refrigerant mass in
the evaporator 60 while controlling backfeeding of liquid
refrigerant to the compressor 65. The constant flow of the heated
refrigerant during the defrost mode increases the temperature of
the evaporator 60 and melts frost on the exterior of the evaporator
60.
[0032] The defrost mode is deactivated by the controller 100 in
response to the sensor 95 detecting a refrigerant temperature at or
above a predetermined temperature threshold, and the refrigeration
system 45 returns to the refrigeration mode. The heater 75 is
turned off at this transition between modes, and the controller 100
can control the pressure control apparatus 80 to regulate how much
refrigerant flows to the compressor 65.
[0033] FIG. 3 illustrates a schematic view of an exemplary
refrigeration system 145 in the defrost mode. The refrigeration
system 145 incorporates the components of the refrigeration system
45, and these components are labeled with the same reference
numerals. The flow control device 55 includes a mechanical thermal
expansion valve 130 and a second heater 125 that is in
communication with the suction line 90 to control the opening
amount of the thermal expansion valve 130 based on the temperature
of refrigerant at or adjacent the evaporator outlet. More
specifically, the second heater 125 controls the dry bulb
temperature and can be controlled to heat the thermal expansion
valve 130 to feed refrigerant (or maintain refrigerant flow) to the
evaporator during the defrost mode.
[0034] The pressure control apparatus 80 for the refrigeration
system 145 includes a first pressure regulator 105 that is disposed
in the suction line 90, and a solenoid valve 120 and a second
pressure regulator 115 that are disposed in a bypass line 110 that
bypasses the first pressure regulator 105. The first pressure
regulator 105 (e.g., an evaporator pressure regulator valve) has a
first pressure setpoint (e.g., 30 psi) and the second pressure
regulator 115 (e.g., an evaporator pressure regulator valve) has a
second pressure setpoint (e.g., 78 psi, 130 psi) that is higher
than the first pressure setpoint.
[0035] The solenoid valve 120 controls the flow of refrigerant in
the bypass line 110 and to the second pressure regulator 115. The
solenoid valve 120 is closed during the refrigeration mode (not
shown) for the refrigeration system 145. During the defrost mode,
the solenoid valve 120 is open and the first and second pressure
regulators 105, 115 restrict or prevent flow of refrigerant to the
compressor 65 to build pressure in the system 145 and maximize the
amount of refrigerant in the evaporator 60. When the system
pressure exceeds the first pressure setpoint, refrigerant begins to
flow to the compressor 65 through the first pressure regulator 105
and the suction line 90. Between the first pressure setpoint and
the second pressure setpoint, refrigerant does not flow through the
bypass line 110 to the compressor 65. Refrigerant only flows
through the bypass line 110 when the system pressure exceeds the
second pressure setpoint. The defrost mode is terminated when the
sensor 95 detects an evaporator temperature that exceeds the
predetermined threshold.
[0036] FIG. 4 illustrates a schematic view of an exemplary
refrigeration system 245 in the defrost mode. The refrigeration
system 245 incorporates the components of the refrigeration system
45. The flow control device 55 includes a mechanical thermal
expansion valve 230 and a second heater 225 that is in
communication with the suction line 90 a second heater 225 that is
in communication with the suction line 90 to control the opening
amount of the thermal expansion valve 130 based on the temperature
of refrigerant at or adjacent the evaporator outlet. More
specifically, the second heater 225 controls the dry bulb
temperature and can be controlled to heat the thermal expansion
valve 230 to feed refrigerant (or maintain refrigerant flow) to the
evaporator during the defrost mode. The pressure control apparatus
80 for the refrigeration system 245 includes a solenoid valve 235
that is disposed in the suction line 90. The solenoid valve 235 is
in communication with the controller 100 so that the controller 100
can open and close the solenoid valve 235.
[0037] The solenoid valve 235 controls the flow of refrigerant in
the suction line 90 by permitting or inhibiting refrigerant flow.
During the refrigeration mode (not shown) for refrigeration system
245, the solenoid valve 235 is open. During the defrost mode, the
solenoid valve 235 is closed and builds pressure in the system 245
to maximize the amount of refrigerant in the evaporator 60. If the
pressure of refrigerant in the system 245 exceeds a safety pressure
setpoint (e.g., 130 psi), the controller 100 opens the solenoid
valve 235 and refrigerant begins to flow to the compressor 65
through the suction line 90. The defrost mode is terminated when
the sensor 95 detects an evaporator temperature that exceeds the
predetermined threshold.
[0038] FIG. 5 illustrates a schematic view of an exemplary
refrigeration system 345 in the defrost mode. The refrigeration
system 345 incorporates the components of the refrigeration system
45. The flow control device 55 includes a mechanical thermal
expansion valve 330 and a second heater 325 that is in
communication with the suction line 90 to control the opening
amount of the thermal expansion valve 330 based on the temperature
of refrigerant at or adjacent the evaporator outlet. More
specifically, the second heater 325 controls the dry bulb
temperature and can be controlled to heat the thermal expansion
valve 130 to feed refrigerant (or maintain refrigerant flow) to the
evaporator during the defrost mode. The pressure control apparatus
80 for the refrigeration system 345 includes an electronic pressure
regulator 340 (e.g., an electronic evaporator pressure regulator
valve) that is disposed in the suction line 90. The electronic
pressure regulator 340 is in communication with the controller
100.
[0039] The electronic pressure regulator 340 controls the flow of
refrigerant in the suction line 90. During the refrigeration mode
(not shown) for refrigeration system 345, the electronic pressure
regulator 340 is open. During the defrost mode, the electronic
pressure regulator 340 is controlled to build pressure in the
system 345 to maximize the amount of refrigerant in the evaporator
60. When a predetermined pressure setpoint or threshold (e.g., 30
psi, 78 psi, 130 psi, etc.) is exceeded, the electronic pressure
regulator 340 at least partially opens and releases refrigerant to
the compressor 65 through the suction line 90 to relieve pressure
in the system 345. The defrost mode is terminated when the sensor
95 detects an evaporator temperature that exceeds the predetermined
threshold.
[0040] FIG. 6 illustrates a schematic view of an exemplary
refrigeration system 445 in the defrost mode. The refrigeration
system 445 incorporates the components of the refrigeration system
45. The flow control device 55 includes an electronic expansion
valve 460 that is in communication with the controller 100 that
determines the opening amount of the electronic expansion valve 460
based on the temperature of the refrigerant at or adjacent the
evaporator outlet. The pressure control apparatus 80 for the
refrigeration system 445 includes a first pressure regulator 405
that is disposed in the suction line 90, and a solenoid valve 420
and a second pressure regulator 415 that are disposed in a bypass
line 410 that bypasses the first pressure regulator 105. The first
pressure regulator 405 (e.g., an evaporator pressure regulator
valve) has a first pressure setpoint (e.g., 30 psi, 78 psi) and the
second pressure regulator 415 (e.g., an evaporator pressure
regulator valve) has a second pressure setpoint (e.g., 78 psi, 130
psi) that is higher than the first pressure setpoint. The pressure
setpoints can be determined in part based on the type of
refrigerant flowing through the system, or set at a pressure that
is significantly higher than phase-change pressure to ensure that
defrost is complete.
[0041] The solenoid valve 420 controls the flow of refrigerant in
the bypass line 410 and to the second pressure regulator 415.
During the refrigeration mode (not shown) for the refrigeration
system 445, the solenoid valve 420 is closed. During the defrost
mode, the solenoid valve 420 is open and the first and second
pressure regulators 405, 415 build pressure in the system 445 to
maximize the amount of refrigerant in the evaporator 60. When the
system pressure exceeds the first pressure setpoint, refrigerant
begins to flow to the compressor 65 through the first pressure
regulator 405 and the suction line 90. Between the first pressure
setpoint and the second pressure setpoint, refrigerant does not
flow through the bypass line 410 to the compressor 65 due to the
higher pressure setpoint of the second pressure regulator 415.
Refrigerant only flows through the bypass line 410 when the system
pressure exceeds the second pressure setpoint. The defrost mode is
terminated when the sensor 95 detects an evaporator temperature
that exceeds the predetermined threshold.
[0042] FIG. 7 illustrates a schematic view of an exemplary
refrigeration system 545 in the defrost mode. The refrigeration
system 545 incorporates the components of the refrigeration system
45. The flow control device 55 includes an electronic expansion
valve 560 in communication with the controller 100 that determines
the opening amount of the electronic expansion valve 560 based on
the temperature of the refrigerant at or adjacent the evaporator
outlet. The pressure control apparatus 80 for the refrigeration
system 545 includes a solenoid valve 535 that is disposed in the
suction line 90. The solenoid valve 535 is in communication with
controller 100.
[0043] The solenoid valve 535 controls the flow of refrigerant in
the suction line 90. During the refrigeration mode (not shown) for
the refrigeration system 545, the solenoid valve 535 is open.
During the defrost mode, the solenoid valve 535 is closed and
builds pressure in the system 545 to maximize the amount of
refrigerant in the evaporator 60. If the pressure of refrigerant in
the system 545 exceeds a safety pressure setpoint (e.g., 130 psi),
the controller 100 opens the solenoid valve 535 and refrigerant
begins to flow to the compressor 65 through the suction line 90.
The defrost mode is terminated when the sensor 95 detects an
evaporator temperature that exceeds the predetermined
threshold.
[0044] FIG. 8 illustrates a schematic view of an exemplary
refrigeration system 645 in the defrost mode. The refrigeration
system 645 incorporates the components of the refrigeration system
45. The flow control device 55 includes an electronic expansion
valve 660 in communication with the controller 100 that determines
the opening amount of the electronic expansion valve 660 based on
the temperature of the refrigerant at or adjacent the evaporator
outlet. The pressure control apparatus 80 for the refrigeration
system 645 includes an electronic pressure regulator 640 (e.g., an
electronic evaporator pressure regulator valve) that is disposed in
the suction line 90. The electronic pressure regulator 640 is in
communication with the controller 100.
[0045] The electronic pressure regulator 640 controls the flow of
refrigerant in the suction line 90. During the refrigeration mode
(not shown) for refrigeration system 645, the electronic pressure
regulator 640 is open. During the defrost mode, the electronic
pressure regulator 640 is controlled by the controller 100 to build
pressure in the system 645 to maximize the amount of refrigerant in
the evaporator 60. The electronic pressure regulator 640 releases
refrigerant through the suction line 90 to the compressor 65 to
relieve pressure in the system 645 based on the pressure setpoint
of the pressure regulator 640. The defrost mode is terminated when
the sensor 95 detects an evaporator temperature that exceeds the
predetermined threshold.
[0046] FIG. 9A illustrates a schematic view of an exemplary
refrigeration system 745 in the refrigeration mode. The
refrigeration system 745 incorporates the components of the
refrigeration system 45. The refrigerant circuit further includes a
recirculation line 750 that is fluidly connected between the
suction line 90 and the inlet line 85, and a solenoid valve 755
that is disposed in the recirculation line 750. During the
refrigeration mode for the refrigeration system 745, the solenoid
valve 755 is closed, and refrigerant circulates through the circuit
747 consistent with what has been described with regard to FIG.
2a.
[0047] FIGS. 9B and 9C illustrate a schematic view of the
refrigeration system 745 of FIG. 9A in the defrost mode. During the
defrost mode, the solenoid valve 755 is opened (via the controller
100) and refrigerant recirculates through the recirculation line
750 from the suction line 90 (upstream of the pressure control
apparatus 80) to the inlet line 85 upstream of the heater 75. As
illustrated in FIG. 9B, the pressure of the refrigerant exiting the
evaporator 60 is below the pressure setpoint of the pressure
control apparatus 80. As a result, refrigerant pressure in the
system increases (i.e. no refrigerant flows to the compressor in
this initial cycle of the defrost mode) and the heated refrigerant
that is directed into the evaporator 60 is only recirculated to the
inlet line 85 upstream of the heater 75, where the refrigerant is
again heated and directed through the evaporator 60 for further
defrost of the evaporator 60.
[0048] As illustrated in FIG. 9C, the refrigerant pressure in the
system 745 may exceed the pressure setpoint of the pressure control
apparatus 80 during the defrost mode. When this happens, some
refrigerant exiting the evaporator 60 recirculates from the
evaporator outlet to the inlet line 85 upstream of the heater 75,
and some refrigerant flows through the pressure control apparatus
80 to the compressor 65 via the suction line 90 to relieve system
pressure.
[0049] FIGS. 10 and 11 illustrate schematic views of other
exemplary refrigeration systems in the defrost mode. The
refrigeration system 845 shown in FIG. 10 is similar to the
refrigeration system 45 of FIG. 2b, except that the system 845 has
a refrigeration circuit 847 with a heater 875 that is disposed or
positioned in the evaporator 60 (e.g., coupled to the coil or fins
or both). The refrigeration system 945 shown in FIG. 11 is similar
to the refrigeration system 45 of FIG. 2b, except that the system
945 has a refrigeration circuit 947 with a heater 975 that is part
of and disposed or positioned below the evaporator 60. The systems
845, 945 can include any of the various flow control devices 55
(e.g., mechanical thermal expansion valve, electronic expansion
valve, etc.) and any of the various pressure control apparatus 80
(e.g., evaporator pressure regulator valve, electronic evaporator
pressure regulator valve, etc.) that have been described with
regard to FIGS. 2-9C.
[0050] In general, the pressure control apparatus 80 described with
regard to FIGS. 1-11 increase system pressure during the defrost
mode to maintain flow of refrigerant into the evaporator 60 and to
control flow of refrigerant to the compressor 65. The pressure
setpoint(s) for the pressure control apparatus 80 can be set at a
pressure that is significantly higher than phase-change pressure to
ensure that defrost is complete, or the setpoint(s) can be
determined in part based on the type of refrigerant flowing through
the system. For exemplary refrigeration systems that have a
setpoint pressure or release pressure (i.e. the pressure at which
the pressure control apparatus 80 begins to permit refrigerant flow
to the compressor 65) that is only slightly higher than the phase
change pressure for a given refrigerant or coolant (e.g., to a
value that is within 15 percent or within 1-10 psi of the phase
change pressure for a given refrigerant) minimizes heat buildup in
the evaporator during defrost, which in turn minimizes the amount
of excess heat that would need to be rejected to the ambient
environment by the condenser 50 upon startup of the refrigeration
mode.
[0051] The release pressure for the apparatus 80 is
refrigerant-specific due to each refrigerant having a different
phase change pressure at 32 degrees Fahrenheit (the melting point
of water that has frozen on the evaporator). For example,
refrigerant R404 has a phase change pressure of approximately 72
psi that corresponds to 32 degrees Fahrenheit, so setting the phase
change pressure of the apparatus 80 to approximately 78 psi will
maximize defrost (i.e. completely, or nearly completely eliminate
frost on the evaporator 60) and minimize excess heat in the
refrigeration system.
[0052] With reference to FIGS. 10 and 11, the pressure control
regulator 80 in each system 845, 945 controls the system pressure
of the refrigerant during the defrost mode to maintain flow of the
refrigerant into the evaporator 60 while minimizing or eliminating
flow of liquid refrigerant to the compressor. When the regulator 80
has a release pressure that is within 15 percent of the phase
change pressure, additional pressure regulators are generally
unnecessary. Also, the location and position of the heater 875, 975
in the systems 845, 945 permits more specific or targeted heating
in the evaporator 60 based on the frost/defrost profile for the
evaporator 60. For example, each heater 875, 975 can include a
cal-rod heater or another heater that is suitable for defrosting
the evaporator 60 (e.g., a heater designed to generate more or less
heat at specific sections of the heater, such as more heat on the
ends of the heater to produce a parabolic frost profile, etc.). In
the system 845, the heater 875 is attached to the coils and/or the
fins of the evaporator 60 (e.g., inserted into a tube channel of
the evaporator 60 as shown and described, for example, in U.S.
patent application Ser. No. 14/599,919, filed Jan. 19, 2015, now
U.S. Patent Publication No. 2016/0209125, which is herein
incorporated by reference in its entirety).
[0053] In the exemplary systems described with regard to FIGS.
2-11, the evaporator 60 can be defrosted by placing a heater
upstream of the evaporator 60 or by coupling the heater to the
evaporator 60 (e.g., in or below the evaporator) without having to
reverse the flow of refrigerant within the system. That is, the
systems illustrated and described relative to the Figures do not
require the complex refrigerant piping of conventional reverse
hot-gas defrost system that pipes heated refrigerant from the
compressor 65 to the evaporator 60. In addition, the heater
directly heats the refrigerant, which reduces the amount of time
needed to start and end defrost of the evaporator 60 compared to
existing systems. The flow control device and the pressure control
apparatus keep the evaporator 60 sufficiently hot to facilitate
defrost by controlling the pressure of the system while also
keeping active refrigerant circulation within the circuit. That is,
the refrigeration systems illustrated in FIGS. 2-11 increase the
system pressure to trap the refrigerant at pressure thresholds of
the pressure control apparatus 80 above the release pressure, which
maintains refrigerant flow into the evaporator 60 while at least
initially preventing flow of refrigerant to the compressor 65. Upon
restart of the refrigeration mode, any excess heat in the
refrigerant is rejected to the ambient environment by the condenser
50.
[0054] In the defrost mode of the systems 845, 945, the controller
100 activates the heater 875, 975 which begins heating the
refrigerant within the evaporator 60. The heater 875, 975 defrosts
the coils of the evaporator 60 mostly through convection and
radiation and with conduction occurring in some locations of the
evaporator 60 based on the location of the heater 875, 975 within
the evaporator 60. The flow control device 55 regulates the flow of
refrigerant to the evaporator 60 during the defrost mode and
ensures that refrigerant continues to flow to the evaporator 60 in
the defrost mode. The pressure regulator 80 controls the system
pressure during defrost mode to maintain flow to the evaporator 60
and to control flow to the flow of refrigerant to the compressor
65. The defrost mode in the refrigeration system 845 is deactivated
by the controller 100 in response to a signal from the sensor 95.
The sensor 95 can coupled to the evaporator 60 or to the suction
line 90 to detect the buildup of frost on the evaporator 60 based
on the temperature of refrigerant exiting the evaporator 60. In
some constructions, the controller 100 can automatically initiate
the defrost mode at preset time periods (e.g., every two hours) or
preset times (e.g., 2 A.M., 10 A.M., 3 P.M., 10 P.M.). The defrost
mode is then deactivated by the controller 100 in response to the
sensor 95 detecting a refrigerant temperature at or above a
predetermined temperature threshold, and the refrigeration system
845, 945 returns to the refrigeration mode. The heater 875, 975 is
turned off at the transition between defrost and refrigeration
modes, and the controller 100 can control the pressure control
apparatus 80 to regulate how much refrigerant flows to the
compressor 65 during defrost.
[0055] Various features and advantages of the invention are set
forth in the following claims.
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