U.S. patent application number 13/199489 was filed with the patent office on 2012-03-08 for refrigeration apparatus.
Invention is credited to Ran Luo, Kenneth W. Owen.
Application Number | 20120055185 13/199489 |
Document ID | / |
Family ID | 45769642 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120055185 |
Kind Code |
A1 |
Luo; Ran ; et al. |
March 8, 2012 |
Refrigeration apparatus
Abstract
An extra low temperature refrigeration system consisting of a
two-stage compressor that has an electronic controller. The
electronic controller controls an electric expansion valve in the
evaporator, which modulates the true superheat. There is also an
electric pressure control valve in the condenser, which modulates
the head pressure in cool mode, and the suction pressure in defrost
mode. The defrost cycle uses a reversing valve. The liquid
refrigerant for the inter-stage sub-cooling circuit is constantly
provided by a sub-condenser separated from a conventional one
condenser system. Therefore, the system provides constant cooling
for the compressor motor windings as the compressor runs. There is
a one-way pathway from the main condenser circuit to the
sub-condenser circuit. This pathway will call for more refrigerant
from the main circuit to the sub-cooling circuit as demanded. The
inter-stage sub-cooling circuit uses an electric expansion valve
true superheat control for its sub-cooler.
Inventors: |
Luo; Ran; (New Albany,
MS) ; Owen; Kenneth W.; (New Albany, MS) |
Family ID: |
45769642 |
Appl. No.: |
13/199489 |
Filed: |
August 31, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61402657 |
Sep 2, 2010 |
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Current U.S.
Class: |
62/222 |
Current CPC
Class: |
F25B 6/02 20130101; F25B
1/10 20130101; F25B 2400/13 20130101; F25B 49/027 20130101; F25B
40/02 20130101; F25B 47/025 20130101 |
Class at
Publication: |
62/222 |
International
Class: |
F25B 41/04 20060101
F25B041/04 |
Claims
1. A refrigeration system for cooling a space, said system having a
refrigeration mode and having a defrost mode, said system
comprising: a two-stage compressor to compress a refrigerant; a
two-circuit condenser connected to said two-stage compressor, said
condenser comprising a sub-condenser circuit and a main condenser
circuit; an evaporator connected to said main condenser circuit of
said two-circuit condenser, said evaporator absorbs heat from the
space that is to be cooled during refrigeration mode; a sub-cooling
heat exchanger having a first connection between said sub-condenser
circuit of said two-circuit condenser and said two-stage compressor
and a second connection that is between said main condenser and
said evaporator; a first electric expansion valve connected between
said sub-condenser circuit of said two-circuit condenser and said
sub-cooling heat exchanger; a second electric expansion valve
connected between said sub-cooling heat exchanger and said
evaporator; a third electric expansion valve connected between main
condenser circuit of said two-circuit condenser; said third
electric expansion valve also controls head pressure of said main
condenser circuit of said two-circuit condenser during
refrigeration mode; means for electronic controlling said system
wherein said controller means controls said first electric
expansion valve to modulate the true superheat of said sub-cooling
heat exchanger and wherein said controller means controls said
second electric expansion valve to modulate the true superheat of
said evaporator when said system is in the refrigeration mode and
wherein said controller means controls said third electric
expansion valve to modulate the suction pressure of said main
condenser circuit of said two-circuit condenser when said system is
in the defrost mode and modulates the head pressure when said
system is in the refrigeration mode.
2. The system of claim 1 further comprising: a differential oil
pressure switch associated with said controller means such that
said defrost mode is initiated when oil level is low.
3. The system of claim 1 further comprising: a drain pan beneath
said evaporator; a drain pan loop associated with said evaporator,
wherein a portion of said refrigerant enters said loop to melt the
ice or frost and the major portion of said refrigerant enters said
evaporator to melt the ice or frost when said system is in the
defrost mode.
4. The system of claim 1 further comprising a refrigerant reservoir
interposed between said sub-cooling heat exchanger and said main
condenser in the connection connecting said sub-cooling heat
exchanger and said main condenser.
5. The system of claim 1 further comprising an oil separator
connected between said two-stage compressor and said two-circuit
condenser such that refrigerant oil is separated by said oil
separator and discharged back to a crankcase in said two-stage
compressor.
Description
[0001] This application claims benefit under Title 35 U.S.C 119(e)
of U.S. Provisional Application Ser. No. 61/402,657 filed Sep. 1,
2010.
FIELD OF THE INVENTION
[0002] This invention relates generally to space cooling systems,
in particular to a low temperature refrigeration apparatus for
providing space cooling with significant energy and cost
savings.
BACKGROUND OF THE INVENTION
[0003] A typical space cooling system includes at least one
evaporator system contained within the space that is to be cooled,
a condenser system that is located outside of the cooled space, and
a compressor positioned between the condenser system outlet and the
evaporator system inlet and, finally, an expansion valve which
completes the loop joining together the condenser system outlet and
the evaporator system inlet. A refrigerant is circulated within the
loop, which cools the space as follows. The refrigerant is
compressed by the compressor, which raises the temperature and
pressure of the refrigerant. The hot pressurized refrigerant gas
then flows through the condenser system, which serves as heat
exchanger to allow the refrigerant to dissipate the heat of
pressurization. The refrigerant condenses into a liquid and then
flows through the expansion valve, where the liquid refrigerant
moves from a high-pressure zone into a low-pressure zone, thus
expanding and evaporating. In evaporating, the refrigerant becomes
cold where it then passes into coils of the evaporator, thus
absorbing heat from inside the space that is to be cooled and the
cycle then repeats until the space reaches the desired
temperature.
[0004] In addition to these major components, additional components
are also included. A fan assists the heat transfer from the cooled
space to the coils of the evaporator system and another fan is used
to assist the heat transfer from the coils of the condenser to the
outside environment. A negative pressure differential is present on
the evaporator outlet when the device is operating in a
refrigeration mode thereby suctioning the gas refrigerant to the
compressor. Further, thermistor sensors are placed at the inlet and
outlet of the evaporator system for measuring the level of
superheat across the evaporator. A sensor located on the outlet
side of the compressor measures the discharge temperature of
compressor. The ambient temperature of the space to be cooled is
measured by still another sensor. Finally, the need to defrost the
evaporator from any ice build-up due to the cooling process is
determined by another sensor that is associated with the evaporator
so that defrosting procedures can be monitored.
[0005] However, there is not found in the prior art an extra low
temperature refrigeration system that combines the features of dual
valve control, dual circuit condenser design, superheat control on
the sub-cooler circuit, a liquid receiver to store extra
refrigerant charge, an oil-pressure initiated defrost, parallel hot
gas drain pan loop design on the evaporator to defrost the drain
pan, and a compressor superheat control that will provide
performance and protection features and lower head pressure to
achieve high reliability and substantial operating cost
savings.
SUMMARY OF THE INVENTION
[0006] It is an aspect of the invention to provide a refrigeration
apparatus that has a dual valve control.
[0007] Another aspect of the invention is to provide a
refrigeration apparatus that has a two-stage compressor.
[0008] It is still another aspect of the invention to provide a
refrigeration apparatus that uses a dual circuit condenser
design.
[0009] Another aspect of the invention is to provide a
refrigeration apparatus that uses an electric expansion valve for
true superheat control for the sub-cooler.
[0010] It is an aspect of the invention to provide a refrigeration
apparatus that features a bi-flow liquid receiver and surge
protector.
[0011] Another aspect of the invention is to provide a
refrigeration apparatus that has an oil pressure initiated
defrost.
[0012] Another aspect of the invention is to provide a
refrigeration apparatus that has compressor superheat control.
[0013] Finally, it is an aspect of the invention to provide a
refrigeration apparatus that utilizes parallel hot gas drain pan
loop design on the evaporator.
[0014] The invention is an extra low temperature refrigeration
system consisting of a two-stage compressor that has an electronic
controller. The electronic controller controls an electric
expansion valve in the evaporator, which modulates the true
superheat. There is also an electric pressure control valve in the
condenser, which modulates the head pressure in cool mode, and the
suction pressure in defrost mode. The defrost cycle uses a
reversing valve. The liquid refrigerant for the inter-stage
sub-cooling circuit is constantly provided by a sub-condenser
separated from the conventional one condenser system. Therefore,
the system provides constant cooling for the compressor motor
windings as the compressor runs. There is a one-way pathway from
the main condenser circuit to the sub-condenser circuit. This
pathway will call for more refrigerant from the main circuit to the
sub-cooling circuit as demanded. The inter-stage sub-cooling
circuit uses an electric expansion valve true superheat control for
its sub-cooler. This accurate cooling of superheat improves the
life span the compressor and maximizes the main liquid sub-cooling.
The reverse cycle defrost method, which is disclosed in U.S. Pat.
No. 7,073,344, permits the defrosting the evaporator system in less
time required for conventional defrost methods. The reverse flow
during defrost also brings the lubrication oil back to the
compressor. This cooling system also eliminates the need for a
mechanical head pressure control valve and many check valves
typically seen in conventional systems. The lower head pressure
operation allows energy savings during low ambient conditions.
Also, the system uses a liquid reservoir to store extra refrigerant
charge. The liquid reservoir acts as a liquid receiver for cooling
mode and a refrigerant surge protection tank for defrosting mode.
The system uses an oil differential pressure switch as a digital
input to the main controller to initiate defrost for proper oil
return when the oil pressure falls below a permitted pressure
level. Further, the system uses a temperature-sensing probe mounted
at the compressor suction copper tubing to measure the compressor
true superheat. The compressor true superheat is controlled by
varying the evaporator electric expansion valve opening in order to
protect the compressor from overloading and liquid refrigerant
flood-back. The evaporator uses compressor-discharged vapor to
defrost the drain pan. The drain pan piping is paralleled to the
refrigerating circuit piping which is not seen in previous reverse
cycle defrost systems. This reduces pressure drop of reverse flow
and offers a fast and clean defrost throughout the evaporator
coil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic of the most basic embodiment of the
invention operating during a refrigeration cycle.
[0016] FIG. 2 is a schematic of the embodiment shown in FIG. 1
operating during a defrost cycle.
DETAILED DESCRIPTION OF THE INVENTION
Refrigeration Mode:
[0017] As shown in FIG. 1, invention utilizes two-stage
reciprocating compressor 10. Refrigerant (not shown) is compressed
by compressor 10. The temperature and pressure of the refrigerant
is raised. The hot pressurized refrigerant gas then flows through
the oil separator 42. The refrigerant oil is then separated by 42
and discharged back to the compressor 10 crankcase. Oil return
solenoid valve 44 is powered with the synchronization of the
compressor 10. When compressor 10 is in operation, solenoid valve
44 is open allowing oil to flow through.
[0018] The refrigerant after oil separator 42 is diverted into two
directions. The first direction goes to the main circuit condenser
38 through the four way reversing valve 40. The second direction is
to the sub-circuit condenser 36.
[0019] The majority of the high-pressure refrigerant goes to main
condenser 38 and is condensed into a liquid state. Electric
pressure control valve 32 is used to modulate the pressure of the
refrigerant inside the main condenser 38. The liquid refrigerant
then enters liquid receiver/surge protector 28. Sub-cooling heat
exchanger 24 is used to cool the refrigerant from upstream while
the pressure maintains constant. The liquid refrigerant of cold and
high-pressure state flows through bi-flow filter/drier 22 and is
metered into an evaporator 14 inside freezer box by electric
expansion valve 20. The liquid refrigerant expands and now is in
low-pressure state in evaporator 14. The refrigerant absorbs heat
from ambient around the evaporator and changes to vapor state. The
amount of the refrigerant is modulated by electric expansion valve
20 such that when it leaves the evaporator all refrigerant becomes
in the vapor state. The vapor refrigerant goes though four way
reversing valve 40 and suction accumulator 12 and then returns to
compressor 10 via suction port S.
[0020] The amount of refrigerant required for the sub-cooling
circuit is determined by the inter-stage sub-cooling capacity of
the two-stage compressor 10 and the required cooling temperature.
This refrigerant enters sub-condenser 36 and is condensed into a
liquid state. The liquid refrigerant flows through filter/drier 30
and is metered into an evaporator of sub-cooling heat exchanger 24
by electric expansion valve 26. After evaporating into a vapor
state, the refrigerant returns to the inter-stage of compressor 10.
The mixture of the refrigerant from the low stage discharge and the
sub-cooling is also used to cool the compressor motor windings.
Check valve 34 is used to allow some refrigerant to flow from the
main circuit to the sub-cooling circuit when more refrigerant is
needed for sub-cooling.
Defrosting Mode:
[0021] As shown in FIG. 2, during defrosting mode, four way
reversing valve 40 is switched to the defrosting position as
illustrated. The high temperature and pressure refrigerant in the
vapor state discharged from compressor 10 enters evaporator 14 on
the opposite side of the refrigerating mode after it flows through
four-way reversing valve 40. A portion of this refrigerant enters
drain pan heater loop 16 and melts the ice or frost residing on the
drain pan. The major portion of the refrigerant enters the
evaporator coil circuit and melts the ice or frost residing within
the evaporator coil. The refrigerant in drain pan heater loop 16
flows through check valve 18 and meets the refrigerant from the
evaporator 14. Electric expansion valve 20 is completely open
allowing refrigerant to free flow back to the compressor. After
defrosting, the refrigerant flows through bi-flow filter/drier 22
and sub-cooling heat exchanger 24 and back to liquid receiver/surge
protector 28. Electric pressure control valve 32 then meters the
amount of refrigerant going through main condenser 38. Main
condenser in the defrosting mode is then an evaporator absorbing
heat from the outside environment.
[0022] The refrigerant in the sub-condenser circuit provides
constant cooling to the compressor motor windings as it does during
refrigerating mode.
[0023] Although the present invention has been described with
reference to certain preferred embodiments thereof, other versions
are readily apparent to those of ordinary skill in the preferred
embodiments contained herein.
* * * * *