U.S. patent application number 17/602513 was filed with the patent office on 2022-07-14 for very low temperature refrigeration system with fast operation cycle.
The applicant listed for this patent is Edwards Vacuum LLC. Invention is credited to Renqiang Xiong.
Application Number | 20220221197 17/602513 |
Document ID | / |
Family ID | 1000006291996 |
Filed Date | 2022-07-14 |
United States Patent
Application |
20220221197 |
Kind Code |
A1 |
Xiong; Renqiang |
July 14, 2022 |
VERY LOW TEMPERATURE REFRIGERATION SYSTEM WITH FAST OPERATION
CYCLE
Abstract
Methods for shortening the cycle time in each of the defrost,
standby and cool modes of operation of a very low temperature
refrigeration system. These methods can be used alone or in
combination with one or more of each of the other techniques,
including, for example, in a single very low temperature
refrigeration system, to provide a fast total cycle of one, two or
all three of the defrost, standby and cool modes.
Inventors: |
Xiong; Renqiang;
(Chelmsford, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Edwards Vacuum LLC |
Sanborn |
NY |
US |
|
|
Family ID: |
1000006291996 |
Appl. No.: |
17/602513 |
Filed: |
April 9, 2020 |
PCT Filed: |
April 9, 2020 |
PCT NO: |
PCT/IB2020/053398 |
371 Date: |
October 8, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62833563 |
Apr 12, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 9/006 20130101;
F25B 47/022 20130101 |
International
Class: |
F25B 9/00 20060101
F25B009/00; F25B 47/02 20060101 F25B047/02 |
Claims
1. A very low temperature refrigeration system, the system
comprising: a compressor; a plurality of heat exchangers; an
expander; a defrost valve and a controller comprising a processor
and a memory, the controller being configured to: (i) during
startup of the compressor, control said defrost valve in a hot gas
defrost circuit to open to bypass flow of a refrigerant around a
high pressure side of the plurality of heat exchangers and the
expander and to an evaporator inlet from which the refrigerant
flows to an evaporator, thereby accommodating a volume of the
refrigerant in the evaporator to limit an initial increase in
pressure of the refrigerant during the startup of the compressor;
and (ii) to subsequently control the defrost valve to close so that
flow of the refrigerant proceeds through the high pressure side of
the plurality of heat exchangers and the expander to the
evaporator.
2. The very low temperature refrigeration system according to claim
1, wherein the refrigerant comprises a mixture of a plurality of
different refrigerant components, the mixture comprising: argon,
R-14, R-23, R-125 and R-245fa.
3. (canceled)
4. The very low temperature refrigeration system according to claim
1, wherein the controller is configured to subsequently control the
defrost valve to close after at least about 3 seconds from the
startup of the compressor and before at least about 6 seconds from
the startup of the compressor.
5. (canceled)
6. The very low temperature refrigeration system according to claim
1, the controller being configured to control the system to enter a
standby mode upon the subsequently closing of the defrost valve,
the standby mode comprising the controller controlling a cool valve
to close to prevent flow of refrigerant from the high pressure side
of the plurality of heat exchangers to the evaporator, while
permitting flow of refrigerant through the high pressure side of
the plurality of heat exchangers and a low pressure side of the
plurality of heat exchangers.
7. The very low temperature refrigeration system according to claim
1, wherein the hot gas defrost circuit is configured to flow the
refrigerant from a high pressure supply line of the compressor to
the evaporator inlet from which the refrigerant flows to an
evaporator.
8. A method of limiting peak operating pressure during startup of a
very low temperature refrigeration system having a compressor, a
plurality of heat exchangers, an expander and an evaporator, the
method comprising: during startup of the compressor, opening a
defrost valve in a hot gas defrost circuit to bypass flow of a
refrigerant around a high pressure side of the plurality of heat
exchangers and the expander and to an evaporator inlet from which
the refrigerant flows to the evaporator, thereby accommodating a
volume of the refrigerant in the evaporator to limit an initial
increase in pressure of the refrigerant during the startup of the
compressor; and subsequently closing the defrost valve so that flow
of the refrigerant proceeds through the high pressure side of the
plurality of heat exchangers and the expander to the
evaporator.
9. The method according to claim 8, wherein the refrigerant is
charged into the system at a refrigerant pressure that would create
a peak pressure of the refrigerant that would exceed a design
pressure of the very low temperature refrigeration system during
startup of the compressor absent the opening of the defrost valve;
and/or wherein a refrigerant flow volume of the evaporator
comprises greater than about 10 percent of a refrigerant system
volume of the very low temperature refrigeration system; and/or
wherein the refrigerant is charged into the system such that the
system has a balance pressure of between about 230 psig and about
300 psig; and/or wherein, during the bypass flow of the
refrigerant, a temperature of the refrigerant is greater than about
25.degree. C.
10-12. (canceled)
13. A very low temperature refrigeration system, the system
comprising: a compressor; a plurality of heat exchangers; an
expander; a defrost valve and a controller comprising a processor
and a memory, the controller being configured to, in a defrost mode
of operation of the system, (i) control said defrost valve in a hot
gas defrost circuit to open to bypass flow of a refrigerant around
a high pressure side of the plurality of heat exchangers and to an
evaporator inlet from which the refrigerant flows to an evaporator,
to effect warming of the evaporator, and (ii) while controlling the
defrost valve to open, control a cool valve to close so that the
refrigerant does not flow from the high pressure side to the
evaporator; the controller being further configured to, (i) based
on an input control signal, set a value of a stored defrost
completion set point temperature of a return temperature sensor on
a low pressure side of the evaporator; and (ii) during the warming
of the evaporator, upon the return temperature sensor on the low
pressure side of the evaporator reaching the stored defrost
completion set point temperature of the return temperature sensor,
control the defrost valve to close to prevent the refrigerant
flowing to the evaporator.
14. The very low temperature refrigeration system of claim 13,
wherein the stored defrost completion set point temperature of the
return temperature sensor is about 0.degree. C. or lower; and/or
wherein the return temperature sensor comprises a thermocouple on
the low pressure side of the evaporator; and/or said controller
being configured to close the defrost valve in response to
receiving a temperature control signal from the return temperature
sensor that is at least as warm as the stored defrost completion
set point temperature of the return temperature sensor, the
controller comprising a memory for storing a defrost completion set
point temperature.
15-16. (canceled)
17. A method of reducing time spent in a defrost mode of operation
of a very low temperature refrigeration system, the method
comprising: in a defrost mode of operation of the system, (i)
opening a defrost valve in a hot gas defrost circuit to bypass flow
of a refrigerant around a high pressure side of a plurality of heat
exchangers and to an evaporator inlet from which the refrigerant
flows to an evaporator, to effect warming of the evaporator, and
(ii) while opening the defrost valve, closing a cool valve so that
the refrigerant does not flow from the high pressure side to the
evaporator; based on an input control signal, setting a value of a
stored defrost completion set point temperature of a return
temperature sensor on a low pressure side of the evaporator; and
during the warming of the evaporator, upon the return temperature
sensor on the low pressure side of the evaporator reaching the
stored defrost completion set point temperature of the return
temperature sensor, closing the defrost valve to prevent the
refrigerant flowing to the evaporator.
18. A very low temperature refrigeration system, the system
comprising: a compressor; a plurality of heat exchangers; an
expander; a temperature sensor; a plurality of valves; and a
controller comprising a processor and a memory, the controller
being configured to, based on an input control signal, set a value
of a stored bypass control set point temperature of a return
temperature sensor on a low pressure side of an evaporator; the
controller being further configured to, upon a return temperature
sensor on a low pressure side of the evaporator warming to be at or
above the stored bypass control set point temperature of the return
temperature sensor, (i) control a return valve to close to prevent
refrigerant flow through a low pressure side of the plurality of
heat exchangers, and (ii) control a bypass valve to open to bypass
flow of the refrigerant around the low pressure side of the
plurality of heat exchangers and to a suction line that enters a
low pressure side of the compressor; and the system being
configured to warm the bypassed flow of the refrigerant in the
suction line before it enters the low pressure side of the
compressor, wherein at least one of the plurality of heat
exchangers is configured to exchange heat between the suction line
and a high pressure side of the plurality of heat exchangers to
warm the bypassed flow of the refrigerant in the suction line; or
wherein the refrigeration system comprises a heater for warming the
bypassed flow of the refrigerant in the suction line.
19-20. (canceled)
21. The very low temperature refrigeration system of claim 18,
wherein the stored bypass control set point temperature of the
return temperature sensor is less than a rated input flow
temperature of the compressor, wherein the stored bypass control
set point temperature of the return temperature sensor is between
about -40.degree. C. and about -70.degree. C.
22. (canceled)
23. A method of reducing recovery time after defrost of a very low
temperature refrigeration system, the method comprising: based on
an input control signal, setting a value of a stored bypass control
set point temperature of a return temperature sensor on a low
pressure side of the evaporator; upon a return temperature sensor
on a low pressure side of the evaporator warming to be at or above
the stored bypass control set point temperature of the return
temperature sensor, (i) closing a return valve to prevent
refrigerant flow through a low pressure side of a plurality of heat
exchangers, and (ii) opening a bypass valve to bypass flow of the
refrigerant around the low pressure side of the plurality of heat
exchangers and to a suction line that enters a low pressure side of
a compressor; and warming the bypassed flow of the refrigerant in
the suction line before it enters the low pressure side of a
compressor.)
24. A very low temperature refrigeration system, the system
comprising: a compressor; a plurality of heat exchangers; an
expander; a flow metering device and a cool valve with which the
flow metering device is in a series flow connection to an inlet of
an evaporator; and a controller comprising a processor and a
memory, the controller being configured to, upon a discharge
pressure of a compressor of the system being at least as high as a
stored set point of a maximum discharge pressure during the cooling
mode of operation, control an unload valve to open to permit
refrigerant flow to bypass around the flow metering device and to
the cool valve, until the discharge pressure reduces to be less
than the stored set point of the maximum discharge pressure,
wherein said controller is further configured to: during startup of
the compressor to (i) control a defrost valve in a hot gas defrost
circuit to open to bypass flow of a refrigerant around a high
pressure side of the plurality of heat exchangers and the expander
and to an evaporator inlet from which the refrigerant flows to an
evaporator, thereby accommodating a volume of the refrigerant in
the evaporator to limit an initial increase in pressure of the
refrigerant during the startup of the compressor; (ii) to
subsequently control the defrost valve to close so that flow of the
refrigerant proceeds through the high pressure side of the
plurality of heat exchangers and the expander to the evaporator;
and during defrost to (i) control a defrost valve in a hot gas
defrost circuit to open to bypass flow of a refrigerant around a
high pressure side of the plurality of heat exchangers and to an
evaporator inlet from which the refrigerant flows to an evaporator,
to effect warming of the evaporator, and (ii) while controlling the
defrost valve to open, control a cool valve to close so that the
refrigerant does not flow from the high pressure side to the
evaporator; the controller being further configured to, (i) based
on an input control signal, set a value of a stored defrost
completion set point temperature of a return temperature sensor on
a low pressure side of the evaporator; and (ii) during the warming
of the evaporator, upon the return temperature sensor on the low
pressure side of the evaporator reaching the stored defrost
completion set point temperature of the return temperature sensor,
control the defrost valve to close to prevent the refrigerant
flowing to the evaporator; and following defrost upon a return
temperature sensor on a low pressure side of the evaporator warming
to be at or above the stored bypass control set point temperature
of the return temperature sensor, (i) control a return valve to
close to prevent refrigerant flow through a low pressure side of
the plurality of heat exchangers, and (ii) control a bypass valve
to open to bypass flow of the refrigerant around the low pressure
side of the plurality of heat exchangers and to a suction line that
enters a low pressure side of the compressor; and the system being
configured to warm the bypassed flow of the refrigerant in the
suction line before it enters the low pressure side of the
compressor.
25. (canceled)
26. A method of reducing a cool down time of a very low temperature
refrigeration system, the method comprising: during a cooling mode
of operation of the system, flowing refrigerant through a high
pressure side of a plurality of heat exchangers, through a flow
metering device and a cool valve with which the flow metering
device is in a series flow connection to an inlet of an evaporator,
through the evaporator and through a low pressure side of the
plurality of heat exchangers; and upon a discharge pressure of a
compressor of the system being at least as high as a stored set
point of a maximum discharge pressure during the cooling mode of
operation, opening an unload valve that permits refrigerant flow to
bypass around the flow metering device and to the cool valve, until
the discharge pressure reduces to be less than the stored set point
of the maximum discharge pressure wherein an inlet of the
evaporator or an outlet of the evaporator is at a temperature of
less than about -110.degree. C., and/or wherein the stored set
point of the maximum discharge pressure is less than an activation
pressure of a buffer solenoid valve of the system.
27-28. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Section 371 National Stage Application
of International Application No. PCT/IB2020/053398, filed Apr. 9,
2020, and published as WO 2020/208573 A1 on Oct. 15, 2020, the
content of which is hereby incorporated by reference in its
entirety and which claims priority of U.S. Provisional Application
No. 62/833,563, filed on Apr. 12, 2019. The entire teachings of the
above application are incorporated herein by reference.
BACKGROUND
[0002] Very low temperature refrigeration systems are used for a
variety of different purposes, including removing water vapor and
creating high vacuum environments for the coating industry. Such
systems typically operate in three different modes: standby mode,
in which the unit is recovering or is in readiness; cool mode, in
which the system is cooling to serve the process or application
need; and defrost mode, in which the system is regenerating the
cryocoil. For a typical batch coating process, the system runs in
cycles of these three modes. However, different applications have
different constraints on how much time can be spent in each mode.
Some applications require short time in the defrost mode, and can
tolerate a long time in the standby mode after the defrost mode
completes. Some applications require a fast cool down to a target
supply temperature (for example, -110.degree. C. or -120.degree.
C.), so that the coating process can start earlier. Some
applications require a fast total cycle of defrost/standby/cool,
which can put demands on shortening all three operating modes.
[0003] The discussion above is merely provided for general
background information and is not intended to be used as an aid in
determining the scope of the claimed subject matter. The claimed
subject matter is not limited to implementations that solve any or
all disadvantages noted in the background.
SUMMARY
[0004] Methods for shortening the cycle time in each of the
defrost, standby and cool modes of operation of a very low
temperature refrigeration system are taught herein. These methods
can be used alone or in combination with one or more of each of the
other techniques, including, for example, in a single very low
temperature refrigeration system, to provide a fast total cycle of
one, two or all three of the defrost, standby and cool modes.
[0005] A method of limiting peak operating pressure during startup
of a very low temperature refrigeration system having a compressor,
a plurality of heat exchangers, an expander and an evaporator
comprises, during startup of the compressor, opening a defrost
valve in a hot gas defrost circuit to bypass flow of a refrigerant
around a high pressure side of the plurality of heat exchangers and
the expander and to an evaporator inlet from which the refrigerant
flows to the evaporator, thereby accommodating a volume of the
refrigerant in the evaporator, to limit an initial increase in
pressure of the refrigerant during the startup of the compressor.
Subsequently the defrost valve is closed so that flow of the
refrigerant proceeds through the high pressure side of the
plurality of heat exchangers and the expander to the
evaporator.
[0006] The refrigerant may be charged into the system at a
refrigerant pressure that would create a peak pressure of the
refrigerant that would exceed a design pressure of the very low
temperature refrigeration system during startup of the compressor
absent the opening of the defrost valve. The refrigerant flow
volume of the evaporator may be greater than about 10 percent of a
refrigerant system volume of the very low temperature refrigeration
system. The refrigerant may comprise a mixture of a plurality of
different refrigerant components. The mixture may comprise argon,
R-14, R-23, R-125 and R-245fa. The refrigerant may be charged into
the system such that the system has a balance pressure of between
about 230 psig and about 300 psig. Subsequently closing the defrost
valve may be performed after at least about 3 seconds from the
startup of the compressor; and may be performed before at least
about 6 seconds from the startup of the compressor. The method may
comprise entering a standby mode of the system upon the
subsequently closing the defrost valve, the standby mode comprising
closing a cool valve to prevent flow of refrigerant from the high
pressure side of the plurality of heat exchangers to the
evaporator, while permitting flow of refrigerant through the high
pressure side of the plurality of heat exchangers and a low
pressure side of the plurality of heat exchangers. During the
bypass flow of the refrigerant, a temperature of the refrigerant
may be greater than about 25.degree. C. The hot gas defrost circuit
may bypass the refrigerant from a high pressure supply line of the
compressor to the evaporator inlet from which the refrigerant flows
to an evaporator.
[0007] A method of reducing time spent in a defrost mode of
operation of a very low temperature refrigeration system comprises,
in a defrost mode of operation of the system, (i) opening a defrost
valve in a hot gas defrost circuit to bypass flow of a refrigerant
around a high pressure side of a plurality of heat exchangers and
to an evaporator inlet from which the refrigerant flows to an
evaporator, to effect warming of the evaporator, and (ii) while
opening the defrost valve, closing a cool valve so that the
refrigerant does not flow from the high pressure side to the
evaporator. Based on an input control signal, a value of a stored
defrost completion set point temperature of a return temperature
sensor on a low pressure side of the evaporator is set. During the
warming of the evaporator, upon the return temperature sensor on
the low pressure side of the evaporator reaching the stored defrost
completion set point temperature of the return temperature sensor,
the defrost valve is closed to prevent the refrigerant flowing to
the evaporator.
[0008] The stored defrost completion set point temperature of the
return temperature sensor may be about 0.degree. C. or lower,
depending on the application. The return temperature sensor may
comprise a thermocouple on the low pressure side of the evaporator.
The method may comprise closing the defrost valve when a controller
receives a temperature control signal from the return temperature
sensor that is at least as warm as the stored defrost completion
set point temperature of the return temperature sensor, the stored
defrost completion set point temperature being stored in a memory
of the controller.
[0009] A method of reducing recovery time after defrost of a very
low temperature refrigeration system comprises, based on an input
control signal, setting a value of a stored bypass control set
point temperature of a return temperature sensor on a low pressure
side of the evaporator. Upon a return temperature sensor on a low
pressure side of the evaporator warming to be at or above the
stored bypass control set point temperature of the return
temperature sensor, the method comprises (i) closing a return valve
to prevent refrigerant flow through a low pressure side of a
plurality of heat exchangers, and (ii) opening a bypass valve to
bypass flow of the refrigerant around the low pressure side of the
plurality of heat exchangers and to a suction line that enters a
low pressure side of a compressor; and warming the bypassed flow of
the refrigerant in the suction line before it enters the low
pressure side of a compressor.
[0010] Warming the bypassed flow of the refrigerant in the suction
line may comprise warming the bypassed flow using a heat exchanger
that exchanges heat between the suction line and a high pressure
side of the plurality of heat exchangers. Warming the bypassed flow
of the refrigerant in the suction line may comprise using a heater
to heat the suction line. The stored bypass control set point
temperature of the return temperature sensor may be less than the
compressor's rated input flow temperature, for example, less than
about -40.degree. C. For example, the stored bypass control set
point temperature of the return temperature sensor may be between
about -40.degree. C. and about -70.degree. C.
[0011] A method of reducing a cool down time of a very low
temperature refrigeration system comprises, during a cooling mode
of operation of the system, flowing refrigerant through a high
pressure side of a plurality of heat exchangers, through a flow
metering device and a cool valve with which the flow metering
device is in a series flow connection to an inlet of an evaporator,
through the evaporator and through a low pressure side of the
plurality of heat exchangers. Upon a discharge pressure of a
compressor of the system being at least as high as a stored set
point of a maximum discharge pressure during the cooling mode of
operation, an unload valve is opened that permits refrigerant flow
to bypass around the flow metering device and to the cool valve,
until the discharge pressure reduces to be less than the stored set
point of the maximum discharge pressure.
[0012] An inlet of the evaporator or an outlet of the evaporator
may be at a temperature of less than about -110.degree. C. The
stored set point of the maximum discharge pressure may be less than
an activation pressure of a buffer solenoid valve of the
system.
[0013] A very low temperature refrigeration system comprises a
compressor, a plurality of heat exchangers, an expander, and a
controller comprising a processor and a memory. The controller is
configured to, (i) during startup of the compressor, control a
defrost valve in a hot gas defrost circuit to open to bypass flow
of a refrigerant around a high pressure side of the plurality of
heat exchangers and the expander and to an evaporator inlet from
which the refrigerant flows to an evaporator, thereby accommodating
a volume of the refrigerant in the evaporator to limit an initial
increase in pressure of the refrigerant during the startup of the
compressor; and (ii) to subsequently control the defrost valve to
close so that flow of the refrigerant proceeds through the high
pressure side of the plurality of heat exchangers and the expander
to the evaporator.
[0014] Another very low temperature refrigeration system comprises
a compressor, a plurality of heat exchangers, an expander; and a
controller comprising a processor and a memory. The controller is
configured to, in a defrost mode of operation of the system, (i)
control a defrost valve in a hot gas defrost circuit to open to
bypass flow of a refrigerant around a high pressure side of the
plurality of heat exchangers and to an evaporator inlet from which
the refrigerant flows to an evaporator, to effect warming of the
evaporator, and (ii) while controlling the defrost valve to open,
control a cool valve to close so that the refrigerant does not flow
from the high pressure side to the evaporator. The controller is
further configured to, (i) based on an input control signal, set a
value of a stored defrost completion set point temperature of a
return temperature sensor on a low pressure side of the evaporator;
and (ii) during the warming of the evaporator, upon the return
temperature sensor on the low pressure side of the evaporator
reaching the stored defrost completion set point temperature of the
return temperature sensor, control the defrost valve to close to
prevent the refrigerant flowing to the evaporator.
[0015] Another very low temperature system comprises a compressor,
a plurality of heat exchangers, an expander, and a controller
comprising a processor and a memory. The controller is configured
to, based on an input control signal, set a value of a stored
bypass control set point temperature of a return temperature sensor
on a low pressure side of an evaporator. The controller is further
configured to, upon a return temperature sensor on a low pressure
side of the evaporator warming to be at or above the stored bypass
control set point temperature of the return temperature sensor, (i)
control a return valve to close to prevent refrigerant flow through
a low pressure side of the plurality of heat exchangers, and (ii)
control a bypass valve to open to bypass flow of the refrigerant
around the low pressure side of the plurality of heat exchangers
and to a suction line that enters a low pressure side of the
compressor. The system is configured to warm the bypassed flow of
the refrigerant in the suction line before it enters the low
pressure side of the compressor.
[0016] The system may comprise a heat exchanger that exchanges heat
between the suction line and a high pressure side of the plurality
of heat exchangers. The system may comprise a heater to heat the
suction line.
[0017] Another very low temperature refrigeration system comprises
a compressor, a plurality of heat exchangers, an expander, a flow
metering device and a cool valve with which the flow metering
device is in a series flow connection to an inlet of an evaporator,
and a controller comprising a processor and a memory. The
controller is configured to, upon a discharge pressure of a
compressor of the system being at least as high as a stored set
point of a maximum discharge pressure during the cooling mode of
operation, control an unload valve to open to permits refrigerant
flow to bypass around the flow metering device and to the cool
valve, until the discharge pressure reduces to be less than the
stored set point of the maximum discharge pressure.
[0018] Systems may be configured to implement any or all of the
methods taught herein.
[0019] The summary is provided to introduce a selection of concepts
in a simplified form that are further described in the detailed
description. This summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing will be apparent from the following more
particular description of example embodiments, as illustrated in
the accompanying drawings in which like reference characters refer
to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead being placed upon
illustrating embodiments.
[0021] FIG. 1 is a schematic diagram of a very low temperature
refrigeration system.
[0022] FIG. 2 is a graph showing defrost time for a system with
increased flow through capillary tubes.
[0023] FIG. 3 is a graph of test data showing the reduction of
defrost time with an increased refrigerant charge, using a
technique of limiting the peak operating pressure during
startup.
[0024] FIG. 4 is a graph showing improved recovery time of a very
low temperature refrigeration system using different return valve
set points.
[0025] FIG. 5 is a simplified schematic block diagram of a
controller.
DETAILED DESCRIPTION
[0026] A description of example embodiments follows.
[0027] Methods for shortening the cycle time in each of the
defrost, standby and cool modes of operation of a very low
temperature refrigeration system are taught herein. As used herein,
"very low temperature" means the temperature range from 90 K to 203
K. The methods can be used alone or in combination with one or more
of each of the other techniques, including, for example, in a
single very low temperature refrigeration system, to provide a fast
total cycle of one, two or all three of the defrost, standby and
cool modes.
[0028] FIG. 1 is a schematic diagram of a very low temperature
refrigeration system. The system can, for example, be an
auto-cascade refrigeration system 100. Such systems use a mixture
of two or more refrigerants in which the difference between the
normal boiling points from the warmest boiling component to the
coldest boiling component is at least 50 K or 100 K or 150 K or 200
K. Such systems can include a refrigeration compressor 101, a
condenser 102 or desuperheater heat exchanger for rejecting heat, a
series of two or more heat exchangers 103 (also referred to herein
as a "heat exchanger array" or "refrigeration process"), one or
more expanders 104, such as a throttle or flow metering device 104,
and an evaporator 105 for heat removal from an application process.
In addition, such systems can include phase separators 106, 107
which are positioned on the discharge side between heat exchangers
and remove liquid phase refrigerant for use in an internal recycle
loop. Such systems can have the ability to operate in different
operating modes, including cool mode in which the evaporator 105 is
cooled, defrost mode in which hot gas from the compressor 101 is
supplied to the evaporator 105, and standby mode in which neither
cold refrigerant nor hot refrigerant is delivered to the evaporator
105. Flow through various flow loops within the system can be
controlled via a series of capillary tubes 108, 109, 110 and 111
which restrict flow and allow for expansion and thus cooling of
refrigerant, and/or via on/off solenoid valves, such as cool
solenoid valve 112, bypass solenoid valve 113, return solenoid
valve 114, buffer solenoid valve 116, defrost solenoid valve 123,
and unload solenoid valve 130. In the embodiment shown in FIG. 1,
capillary tubes 108, 109, 110 and 111 are not associated with any
solenoid valves, while capillary tube 104 is in parallel with
unload solenoid valve 130 and in series with cool solenoid valve
112. Other arrangements of capillary tubes and solenoid valves can
be used. The capillary tubes and/or the solenoid valves can be
replaced with a proportional valve such as a thermal expansion
valve, or a pressure actuated or stepper motor actuated valve. Such
systems can also contain an expansion tank 115 which is used to
manage high evaporation and expansion of the liquefied refrigerants
once the system is turned off and warmed to room temperature.
Further, such systems with expansion tanks 115 can also have a
buffer solenoid valve 116 which allows high pressure gas to be
directed to the expansion tank 115. Such a buffer solenoid valve
116 allows the amount of refrigerant gas in circulation to be
reduced, which in turn reduces compressor discharge and suction
pressures. For example, any of the methods can be used that are
disclosed in U.S. Pat. No. 6,574,978 B2 of Flynn et al., the entire
disclosure of which is hereby incorporated herein by reference.
Systems as described in this patent enable additional operating
modes such as controlled cool down and warm up processes, and
extended operation in a hot gas flow mode, or bakeout mode, in
which a portion of the hot gas exiting the compressor is
continuously circulated from the compressor to the evaporator coil
and then back to the compressor, while another portion of the
refrigerant exiting the compressor continuously flows through the
condenser and then the heat exchanger array and then returns to the
compressor.
[0029] The buffer solenoid valve 116 is a connection between the
discharge (or high pressure) side of the unit and one or more
expansion tanks 115. When a high pressure condition exists the
controller opens this buffer solenoid valve 116 and allows a
portion of the refrigerant to be stored in the expansion tanks 115,
thereby reducing the discharge pressure. This can prevent an
excessive discharge pressure fault condition.
[0030] A hot gas defrost system 121 of the very low temperature
system can be used to achieve warming of the evaporator 105. The
hot gas defrost system 121 includes a defrost hand shut-off valve
122 and a defrost solenoid valve 123, and directs hot gas from a
high pressure supply line 192 of the compressor 101 to the
evaporator inlet 124 of the evaporator feed line which sequentially
flows through the feed line, the evaporator 105 (also known as
cryocoil or cryosurface), the return line 125 and then through the
low pressure side of the heat exchanger array 103. There is an oil
separator 138 in the high pressure supply line 192 downstream of
compressor 101 for separating oil from the flow and returning it to
the compressor 101.
[0031] The possibility of freezeout of refrigerant that is
discharged from the compressor, or another warmer point in the
system, and that is being directed to a colder point in the system,
can be addressed. Such refrigerant that is being discharged from
the compressor may have a higher risk of freezeout because it has
not yet passed through the phase separators in the system, and
therefore has a different composition than later in the
refrigeration process, and thus may have a warmer freezing point
and be more likely to freezeout when directed to a colder point in
the system. To prevent such freezeout, a freezeout prevention
circuit or temperature control circuit can be used, which uses a
controlled bypass flow to warm the lowest temperature refrigerant
in the system, to warm the stack sufficiently that the refrigerant
discharged from the compressor (or another warmer point) does not
freezeout when redirected to a colder point in the system. For
example, any of the freezeout prevention circuits or temperature
control circuits can be used that are disclosed in U.S. Pat. No.
7,478,540 B2 of Flynn et al., the entire disclosure of which is
hereby incorporated herein by reference. In the example in FIG. 1,
a freezeout prevention valve 131 directs refrigerant that is
exiting phase separator 107 to the low pressure inlet 117 of the
subcooler 118, which is positioned closer to the evaporator than
the next-coldest heat exchanger 119 in the heat exchanger array
103.
[0032] The refrigeration system can include a series of internal
return paths 108, 109, 110 from the high pressure side of the
system to the low pressure side in addition to the return path via
the evaporator 105. Typically, the internal return paths 108, 109,
110 are throttle devices. Example throttle devices are capillary
tubes and thermal expansion valves. In other scenarios, turbo
expanders or other means to reduce the pressure of the refrigerant
are used. In a typical defrost warming process the internal
throttle devices 108, 109, 110 are allowed to have flow. In other
scenarios their flow rate is stopped or controlled. In one example,
capillary tubes can be used for the internal throttle devices 108,
109, 110 with no upstream valves. As a result, these throttle
devices continue to permit flow during the defrost warming
process.
[0033] In addition, in the embodiment of FIG. 1, there is also a
low pressure side bypass circuit, which includes a bypass solenoid
valve 113. This bypasses refrigerant around the low pressure side
of the heat exchanger array 103 when the temperature of refrigerant
returning from the evaporator 105 is at or above a stored
temperature that can be set based on an input control signal. Such
a temperature of returning refrigerant can be measured at the
location indicated by Tc in FIG. 1, at the low pressure side of the
evaporator 105, and can be detected by a temperature sensor, such
as, for example, a thermocouple in that location. A sensed
temperature signal from the thermocouple can, for example, be
provided to a controller, which can compare the sensed temperature
signal with the stored temperature based on the input control
signal. When the sensed return temperature is at or above the
stored temperature based on the input control signal, a return
solenoid valve 114 can be shut off by the controller, while the
bypass solenoid valve 113 is opened. This permits refrigerant to be
bypassed around the low pressure side of the array of heat
exchangers 103, in order to prevent overloading the heat exchanger
array 103 with returning refrigerant that is too warm.
[0034] The system of the embodiment of FIG. 1 also includes a
suction line heat exchanger 132, the operation of which will be
described further, below. It is connected with its high pressure
side in series fluid connection with the outlet 120 of the
condenser 102, and with its low pressure side in series fluid
connection with the low pressure side of the heat exchanger array
103.
[0035] The system of FIG. 1 also includes a control module or
controller 180, which is described further, below, with reference
to FIG. 5.
[0036] In one embodiment, a defrost mode of operation of the system
100 is made faster by increasing the flow through capillary tubes
in the system, such as 108, 109, 110 and 104, by using larger
diameter and/or shorter length capillary tubes than would otherwise
be used, and keeping approximately the same flow ratio for any two
of the capillary tubes. For example, an existing set of capillary
tubes can be duplicated and connected in parallel. This decreases
the system's flow resistance, and increases the maximum suction
pressure from a range of about 40-50 psig to a range of about 50-70
psig during the defrost mode of operation. FIG. 2 is a graph
showing defrost time for a system with increase flow through
capillary tubes, here, by having duplicated capillary tubes.
Defrost time was reduced by more than 15%, although with the
tradeoff of reducing cooling capacity somewhat. In an alternative
embodiment, capillary tubes such as 108, 109, 110 and 104 can be
adjustable flow metering devices (such as proportional valves or
stepper motor expansion valves) instead of capillary tubes, and
flow increase can be achieved by adjusting the valve opening.
[0037] In another embodiment, a method is provided of limiting the
peak operating pressure during startup of the very low temperature
system. One method of increasing the speed of defrost of the system
is to increase the quantity of refrigerant charged to the system.
However, with more charge mass, the system will have a higher
balance pressure (for example, between about 230 and about 300
psig), and the compressor may have difficulty starting because the
peak pressure will exceed the design pressure limit, which results
in the system shutting off automatically. In order to avoid this, a
method is used that limits the peak operating pressure during
startup. In this method, the system is started in defrost mode, so
that the defrost refrigerant line and evaporator 105 can be used as
an additional volume to expand the gas and reduce the peak pressure
during startup. This peak pressure during startup typically lasts
between about 3 seconds and about 5 seconds. Once the system
overcomes the peak pressure, the system can switch back to the
standby mode of operation. FIG. 3 is a graph of test data showing
the reduction of defrost time with an increased refrigerant charge,
using such a technique of limiting the peak operating pressure
during startup. Here, the defrost time was reduced by more than
20%. When the increased refrigerant charge is used, a freezeout
prevention circuit (as described above) can be used to prevent
freezeout.
[0038] As used herein the "balance pressure" means a pressure
achieved when the high pressure and low pressure of the system are
equal, or approximately equal, for example when the stack is warmed
such that the average heat exchanger array temperature is at least
as warm as a temperature from the group consisting of -5.degree.
C., 0.degree. C., 5.degree. C., 10.degree. C., 15.degree. C.,
20.degree. C., 25.degree. C., 30.degree. C., 35.degree. C.,
40.degree. C.; or for example when the heat exchanger array is
warmed such that the range of temperatures in the stack is from at
least -5.degree. C. up to 40.degree. C., or is a smaller range
within the range of -5.degree. C. to 40.degree. C.
[0039] With reference to FIG. 1, by way of illustration, in one
embodiment, a method of limiting peak operating pressure during
startup of a very low temperature refrigeration system 100
comprises, during startup of a compressor 101, opening a defrost
valve 123 in a hot gas defrost circuit 121 to bypass flow of a
refrigerant around a refrigerant circuit of a high pressure side of
a plurality of heat exchangers 103 and to an evaporator inlet 124
from which the refrigerant flows to an evaporator 105, thereby
accommodating a volume of the refrigerant in the evaporator 105, to
limit an initial increase in pressure of the refrigerant during the
startup of the compressor 101. Subsequently the defrost valve 123
is closed so that flow of the refrigerant proceeds through the
refrigerant circuit of the high pressure side of the plurality of
heat exchangers 103. The refrigerant can be charged into the system
100 at a refrigerant pressure that would cause peak pressure to
exceed a design pressure of the very low temperature refrigeration
system during startup of the compressor absent the opening of the
defrost valve; for example, the refrigerant can be charged to reach
a pressure of about 230 to about 300 psig, which would normally
create peak pressures higher than the system's design pressure
during startup. The refrigerant flow volume of the evaporator 105
can, for example, be greater than about 10 percent of a refrigerant
system volume of the entire very low temperature refrigeration
system 100, or even greater than about 15 percent. The volume
increase will depend on the size of the evaporator 105 in the
system. The refrigerant can be a mixture of a plurality of
different refrigerant components, and can, for example, consist of
argon, R-14, R-23, R-125 and R-245fa.
[0040] The refrigerant can be charged into the system such that the
system has a balance pressure of between about 230 psig and about
300 psig. Subsequently closing the defrost valve 123 can be
performed after at least about 3 seconds from the startup of the
compressor 101; and can be performed before at least about 6
seconds from the startup of the compressor. The method can comprise
entering a standby mode of the system upon the subsequently closing
the defrost valve 123. The standby mode comprises closing the cool
valve 112 that permits flow of refrigerant from the refrigerant
circuit of the high pressure side of the plurality of heat
exchangers 103 to the evaporator 105, while permitting flow of
refrigerant through the high pressure side of the plurality of heat
exchangers and a low pressure side of the plurality of heat
exchangers. During the bypass flow of the refrigerant, a
temperature of the refrigerant can, for example, be greater than
about 25.degree. C. The hot gas defrost circuit can, for example,
bypass the refrigerant from a high pressure supply line 192 of the
compressor 101 to the evaporator inlet 124 from which the
refrigerant flows to the evaporator 105.
[0041] A defrost completion set point can be set to 0.degree. C. or
lower, which differs from a conventional fixed setting of
20.degree. C. This provides not only a fast defrost, but also a
fast recovery, because less heat is absorbed in the refrigerant
supply line and the application cryocoil. In applications where the
chamber containing the cryocoil is evacuated during defrost, the
chamber pressure can stay below the triple point of water. If so,
the ice on the cryocoil may sublime to vapor directly at a lower
temperature, hence negating the need for a higher defrost
temperature setting.
[0042] By way of illustration, with reference to FIG. 1, an
embodiment of a method of reducing time spent in a defrost mode of
operation of a very low temperature refrigeration system 100
comprises, in a defrost mode of operation of the system, (i)
opening a defrost valve 123 in a hot gas defrost circuit 121 to
bypass flow of a refrigerant around a refrigerant circuit of a high
pressure side of a plurality of heat exchangers 103 and to the
evaporator inlet 124 from which the refrigerant flows to an
evaporator 105, to effect warming of the evaporator 105, and (ii)
while opening the defrost valve 123, closing a cool valve 112 so
that the refrigerant does not flow from the refrigerant circuit of
the high pressure side to the evaporator 105. A value of a stored
defrost completion set point temperature of a return temperature
sensor 133 on a low pressure side of the evaporator 105 is set
based on an input control signal. During the warming of the
evaporator 105, upon the return temperature sensor 133 on the low
pressure side of the evaporator 105 reaching the stored defrost
completion set point temperature of the return temperature sensor
133, the defrost valve 123 is closed to prevent the refrigerant
flowing to the evaporator 105. The stored defrost completion set
point temperature of the return temperature sensor 133 can be about
0.degree. C. or lower. The return temperature sensor 133 can be,
for example, a thermocouple on the low pressure side of the
evaporator 105. The method can include closing the defrost valve
123 when a controller receives a temperature control signal from
the return temperature sensor 133 that is at least as warm as the
stored defrost completion set point temperature of the return
temperature sensor 133, the stored defrost completion set point
temperature being stored in a memory of the controller.
[0043] A return solenoid valve 114 is used to control flow through
a return side of the heat exchanger array 103. There is a return
hand shut off valve 136 in the return side line to the heat
exchanger array 103 and a bypass hand shut off valve 137 in the low
pressure bypass line. The return valve 114 and low pressure bypass
valve 113 are controlled by a control scheme that is based on the
temperature Tc in the return location. Only one of the valves 114
and 113 is activated, depending on how the temperature Tc compares
with the set point temperature stored in the controller. For
example, when the temperature Tc is at or higher than the set point
temperature, the bypass valve 113 is opened and the return valve
114 is closed, so that flow is bypassed through the low pressure
bypass around the low pressure side of the heat exchanger array
103; but when the temperature Tc is lower than the set point
temperature, then the return valve 114 is opened and the bypass
valve 113 is closed, so that flow proceeds through the low pressure
side of the heat exchanger array 103. In addition, the set point
range of the control temperature for the return valve 114 and
bypass valve 113 can be set lower than a previous conventional
limit of -40.degree. C., which was previously used because it
represents the lower operating limit of compressor 101. FIG. 4 is a
graph showing improved recovery time of a very low temperature
refrigeration system using different return valve set points. To be
able to set the return valve set point lower than -40.degree. C., a
suction line heat exchanger 132 is added between the discharge
(high pressure) and suction (low pressure) refrigerant lines in the
heat exchanger array 103. The suction line heat exchanger 132 uses
refrigerant at the liquid line temperature (for example, between
about 14.degree. C. and about 40.degree. C.) to warm up the suction
temperature to protect the compressor, so that the setpoint can be
set lower than -40.degree. C. At the same time, it lowers the
liquid line temperature and helps the system to recover to be
colder in the standby mode of operation. It also improves the
overall system efficiency due to the use of internal heat transfer.
In another embodiment, the function of the suction line heat
exchanger 132 can be performed using, or supplemented with, a
heater, such as an electrical resistance heater. Using a heater
such as an electrical resistance heater can, for example, permit
enhanced control of the temperature of flow to the compressor.
[0044] By way of illustration, with reference to FIG. 1, an
embodiment of a method of reducing recovery time after defrost of a
very low temperature refrigeration system 100 comprises, upon a
return temperature sensor 133 on a low pressure side of the
evaporator 105 warming to be at or above a stored bypass control
set point temperature of the return temperature sensor 133, (i)
closing a return valve 114 to prevent refrigerant flow through a
refrigerant circuit on a low pressure side of a plurality of heat
exchangers 103, and (ii) opening a bypass valve 113 to bypass flow
of the refrigerant around the refrigerant circuit on the low
pressure side of the plurality of heat exchangers 103 and to a
suction line 134 that enters a low pressure side of a compressor
101; and warming the bypassed flow of the refrigerant in the
suction line 134 before it enters the low pressure side of the
compressor 101. The bypassed flow of the refrigerant in the suction
line 134 can be warmed using a heat exchanger 132 that exchanges
heat between the suction line 134 and a refrigerant circuit on a
high pressure side of the plurality of heat exchangers.
Alternatively, a heater can be used to heat the suction line. The
stored bypass control set point temperature of the return
temperature sensor 133 can be less than about -40.degree. C. For
example, the stored bypass control set point temperature of the
return temperature sensor 133 can be between about -40.degree. C.
and about -50.degree. C., between about -50.degree. and about
-60.degree. C., or between about -60.degree. about -70.degree.
C.
[0045] A cool down time of a very low temperature system can be
reduced. Typically, a coating application requires a certain target
temperature, such as from about -110.degree. C. to about
-120.degree. C. at the evaporator in (124) or evaporator out, based
on the maximum water vapor pressure permissible. The time required
to achieve this target process temperature is an important factor
in the throughput of the coating process. During cool down, it is
often observed that the buffer solenoid valve 116 is triggered due
to high discharge pressure. When this valve opens, some of the high
pressure gas is diverted to an expansion tank 115, and this flow
diversion, however temporary, can result in a delay in the cool
down time, due to a decrease in refrigerant flow to the cryocoil.
In order to reduce the cool down time, activation of the buffer
solenoid valve 116 is reduced or eliminated by removing the
occurrence of high pressure faults during cooling. An unloader
solenoid valve 130 is placed in parallel with flow metering device
104 in the cooling path to the evaporator 105. There is also a cool
hand shutoff valve 135 and a cool solenoid valve 112 in the cooling
path to the evaporator 105. During cool down, when the discharge
pressure exceeds a setpoint, for example 415 psig, this unloader
solenoid valve 130 will open so as to allow refrigerant to bypass
the flow meter device 104 for a few seconds. This allows the system
pressure to be reduced below the limit, without diverting any flow
away from the application cryocoil.
[0046] By way of illustration, with reference to FIG. 1, an
embodiment of a method of reducing a cool down time of a very low
temperature refrigeration system 100 comprises, during a cooling
mode of operation of the system, flowing refrigerant through a high
pressure side of a plurality of heat exchangers 103, through a flow
metering device 104, a cool hand shutoff valve 135 and a cool valve
112 with which the flow metering device 104 is in a series flow
connection, to an inlet of an evaporator 105, through the
evaporator 105 and through a low pressure side of the plurality of
heat exchangers 103. Upon a discharge pressure of a compressor 101
of the system being at least as high as a stored set point of a
maximum discharge pressure during the cooling mode of operation, an
unload valve 130 is opened that permits refrigerant flow to bypass
around the flow metering device 104 and to the cool valve 112,
until the discharge pressure reduces to be less than the stored set
point of the maximum discharge pressure. An inlet 124 of the
evaporator 105 or an outlet (at 133) of the evaporator 105 can be
at a temperature of less than about -110.degree. C. The stored set
point of the maximum discharge pressure can be less than an
activation pressure of a buffer solenoid valve 116 of the
system.
[0047] One or more sensors, such as 133, can be used to provide
sensed temperature signals that can be provided to a controller, to
be compared with one or more stored temperature setpoints, which
can be stored in the memory of the controller. The sensors can, for
example, be thermocouples brazed onto one or more locations (such
as 133) in the system. For example, the discharge inlet to or
discharge outlet from one or more heat exchangers, or the suction
inlet to or suction outlet from one or more heat exchangers, can be
used as locations for temperature sensors. Also, temperatures at
any of the solenoid valves can be used, or inlets or outlets to
solenoid valves. In one example, a temperature Tc at the low
pressure side of the evaporator, and at the inlet of the return
solenoid valve 114, at 133, is sensed. In another example, other
temperature sensors can be used in place of, or in addition to,
thermocouples, such as silicon diodes or other similar devices.
[0048] Various techniques set forth herein are implemented using a
controller, and can include computer implemented components.
[0049] FIG. 5 is a simplified schematic block diagram of a
controller that can be used, for example, as the controller 180 of
FIG. 1. Control techniques discussed herein can be implemented
using hardware, such as a controller 580 that includes one or more
processors 581, which can for example include one or more
Application Specific Integrated Circuits (ASICs) 582, 583;
application software running on one or more processors 581 of the
controller 580; sensor lines 584, 585 delivering electronic signals
from sensors that are coupled to systems set forth herein (such as
sensor lines from temperature sensor 133 and any pressure sensors)
to the controller 580; and actuator lines 586-588 delivering
electronic signals to actuated components within systems set forth
herein (such as actuator lines delivering electronic signals to
actuated valves or other controlled components). The controller 580
can also include user input module 589, which can include
components (such as a keyboard, touch pad, and associated
electronics in connection with the processor 581 and memory 590) to
receive user input to provide set point temperatures, such as
control signals that set the stored defrost completion set point
temperature, the stored bypass control set point temperature or the
stored set point of the maximum discharge pressure. The controller
580 can also include a memory 590 to store such set point
temperatures, and to implement procedures under control of computer
hardware and software. It will be appreciated that other control
hardware may be used, including control hardware that is at least
in part pneumatic.
[0050] Portions of the above-described methods and systems can be
implemented using one or more computer systems, for example to
permit automated implementation of control techniques for
refrigeration systems and related components discussed herein. For
example, techniques can be implemented using hardware, software or
a combination thereof. When implemented in software, the software
code can be executed on any suitable processor or collection of
processors, whether provided in a single computer or distributed
among multiple computers.
[0051] The teachings of all patents, published applications and
references cited herein are incorporated by reference in their
entirety.
[0052] While example embodiments have been particularly shown and
described, it will be understood by those skilled in the art that
various changes in form and details may be made therein without
departing from the scope of the embodiments encompassed by the
appended claims.
[0053] Although elements have been shown or described as separate
embodiments above, portions of each embodiment may be combined with
all or part of other embodiments described above.
[0054] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are described as example forms of implementing the
claims.
* * * * *