Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 2 9
- MET~OD AND APPARATUS FOR RECOVERING AND PURIFYING REFRIGERANT
~ 1 1
:
A wide variety of mechanical refrigeration systems are currently
in use in a wide variety of applications. These applications
include domestic refrigeration, coDercial refrigeration, air
conditioning, dehumidifying, food freezing, cooling and
manufacturing processes, and numerous other applications. The
vast majority of mechanical refrigeration systems operate
according to similar, well known principals, employing a
closed-loop fluid circuit through which a refrigerant flows. A
number of saturated fluorocarbon ~ompounds and azeotropes are
commonly used as refrigera~ts in refrigeration systems.
Representative of these .refrigerants are R-12, R-22, R-500 and
R-502.
Those familiar with mechanical refrigeration systems will
recognize that such systems periodically require service. Such
service may include removal, of, and replacement or repair of, a
component of the system. Further during normal system operation
the refrigerant can become contaminated by foreign matter within
the refrigeration circuit, or by excess moisture in the system.
The presence of excess moisture can cause ice formation in the
expansion valves and capillary tubes, corrosion of metal, copper
plating and chemical damage to insulation in hermetic
compressors. Acid can be present due to motor burn out which
causes overheating of the refrigerant. Such burn outs can be
temporary or localized in nature as in the case of a friction
producing chip which produces a local hot spot which overheats
the refrigerant. The main acid of concern is HCL but other acids
and contaminants can be produced as the decomposition products of
oil, insulation, varnish, gaskets and adhesives. Such
contamination may lead to component failure or it may be
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desirable to change the refrigerant to improve the operating
efficiency of the system.
When servicing a refrigeration system it has been the practice
for the refrigerant to be vented into the atmosphere, before the
apparatus is serviced and repaired. The circuit is then
evacuated by a vacuum pump, which vents additional refrigerant to
the atmosphere, and recharged with new refrigerant. This
procedure has now become unacceptable for environmental reasons,
specifically, it is believed that the release of such
fluorocarbons depletes the concentration of ozone in the
atmosphere. This depletion of the ozone layer is believed to
adversely impact the environment and human health. Further, the
cost of refrigerant is now becoming an important factor with
respect to service cost, and such a waste of refrigerant, which
could be recovered, purified and reused, is no longer acceptable.
To avoid release of fluorocarbons into the atmosphere, devices
have been provided that are designed to recover the refrigerant
from refrigsration systems. The devices often include means for
processing the refrigerants so recovered so that the refrigerant
may be reused. Representative examples of such devices are shown
in the following United States Patents: 4,441,330 "Refrigerant
Recovery And Recharging System" to Lower et al: 4,476,688
"Refrigerant Recovery And Purification System" to Goddard:
4,766,733 "Refrigerant Reclamation And Charging Unit" to Scuderi;
4,809,520 "Refrigerant Recovery And Purification System" to Manæ
et al; 4,862,699 "Method And Apparatus For Recovering, Purifying
and Separating Refrigerant From Its Lubricant" to Lounis;
4,903,499 "Refrigerant Recovery System" to Merritt: and 4,942,741
"Refrigerant Recovery Device" to Hancock et al.
When most suc:h systems are operating, a recovery compressor is
used to withdraw the refrigerant from the unit being serviced.
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As the pressure in the service unit is drawn down, the pressure
differential across the recovery compressor increases because the
pressure on the suction side of the compressor becomes
increasingly lower while the pressure on the discharge side of
the compressor stays constant. High compressor pressure
differentials can be destructive to compressor internal
components because of the unacceptably high internal compressor
temperatures which accompany them and the increased stresses on
compressor bearing surfaces. Limitations on the pressure
differentials or pressure ratio across the recovery compressors
are thus necessary, such limitations, in turn can limit the
percentage of the total charge of refrigerant contained within
the unit being serviced that may be successfully recovered.
When using such recovery systems in servicing larger
refrigeration systems it is particularly advantageous to have the
capability of withdrawing refrigerant from the system in the
liquid form and delivering it directly to a storage cylinder.
The recovery of the refrigerant in liquid form, because of its
much greater density, is obviously far quicker than recovery in
the vapor state.
Another feature considered desirable in such recovery systems is
to have a refrigerant quality test system incorporated in the
recovery systems itself.
According to the invention protection of the recovery compressor
is achieved by providing an apparatus and method for recovering
compressible refrigerant from a refrigeration system and
delivering the recovered refrigerant to a refrigeration storage
means. The recovery method includes the steps of withdrawing
refrigerant from a refrigeration system being serviced and
compressing the withdrawn refrigerant in a compressor to form a
high pressure gaseous refrigerant. The high pressure gaseous
2 ~ J~ 9
refrigerant is delivered to a condenser where it is condensed to
form liquid refrigerant. The liquid refrigerant from the
condenser is delivered to the refrigerant storage means. Means
are provided for determining the pressure ratio across the
recovery system compressor and monitoring the determined pressure
ratio. When the monitored pressure ratio exceeds a predetermined
value above which the compressor may be adversely affected the
system is caused to stop the withdrawal of refrigerant from the
refrigeration system being serviced.
.
At that point, the system begins to withdraw stored refrigerant
from the storage means. The re~rigerant withdrawn from the
storage means is then compressed in the same compressor which was
used to compress refrigerant withdrawn from the refrigeration
system. This refrigerant is then condensed to form liquid
refrigerant which is then passed through a suitable expansion
device and delivered back to the storage means to thereby cool
the storage means and the refrigerant contained therein. This
cooling cycle is performed for a period of time until the
temperature of the storage means falls to a predetermined value.
At that point the system resumes withdrawal of refrigerant from
the refrigeration system being serviced. When the suction
pressure of the recovery system compressor falls below a
predetermined value the recovery operation is terminated.
According to another feature of the invention a refrigerant
recovery system is operated to withdraw compressible refrigerant
from a refrigeration system by first drawing liquid refrigerant
from the system being serviced through a suitable conduit and
delivering the withdrawn refrigerant to a refrigerant storage
means. In the refrigerant storage means at least a portion of
the refrigerant so withdrawn exits in gaseous form. A portion of
this gaseous refrigerant is withdrawn from the storage means and
compressed to form a high pressure gaseous refrigerant. The high
pressure gaseous refrigerant is then condensed to form a high
pressure liquid refrigerant. The high pressure liquid
refrigerant is passed through an expansion device where the
refrigerant under goes a pressure drop and is at least partially
flashed to a vapor. The liquid vapor mixture is then delivered
to the storage means where it evaporates and absorbs heat from
the refrigerant within the storage means thereby cooling the
storage means and lowering the pressure therein, thereby
increasing the withdrawal of liquid refrigerant from the
refrigeration system through the conduit.
According to one control system, the rate of liquid level change
in the storage means is monitored. When that rate reaches a
value which indicates that liquid is no longer being withdrawn,
the system shifts automatically to the vapor recovery mode of
operation.
According to another control system means are provided for
sensing a system control parameter which has a detectable change
in value which occurs at a time which may be correlated with the
time at which the state of the refrigerant being withdrawn from
the refrigeration system changes from a liquid to vapor. A
signal indicating that the detectable change has occurred causes
the system to shift from a liquid recovery mode to a vapor
recovery mode.
Purity of the recovered refrigerant may be determined by use of a
method and apparatus for sampling the purity of the refrigerant
flowing through a refrigeration system. The refrigeration system
includes a compressor having an inlet port which has an inlet
conduit associated therewith and defining in part the low
pressure side of the refrigeration system. The compressor
further has an outlet port for having an out conduit associated
therewith which defines in part the high pressure side of the
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refrigeration system. A refrigerant sampling chamber is
operatively connected in parallel in fluid flow communication
with the compressor. The compressor is then operated to
establish the flow of refrigerant through the system and a
quantity of refrigerant is withdrawn from the high pressure side
of the system. The withdrawn quantity of refrigerant is then
passed through the sampling chamber and thence returned to the
low pressure side of the system.
Figure 1 is a diagrammatical representation of a refrigeration
recovery and purifying system embodying the principles of the
present invention;
Figure 2 is a flow chart of an exemplary program for controlling
the elements of the present invention in a vapor recovery cycle;
Figure 3 is a flow chart of an exemplary program for controlling
the elements of the present invention in a recycle mode of
operation; and
Figure 4A is a flow chart of a program for controlling the system
in a liquid recovery mode of operation using rate of liquid
recovery as a control parameter;
Figure 4B is a continuation of the flow chart of Figure 4A
showing a program for controlling the system in a vapor recovery
mode of operation;
Figure 5 is a graphical showing of quantity of refrigerant
recovered versus time in the liquid recovery mode of operation;
Figure 6A is a flow chart of a program for controlling the system
in a liquid recovery mode of operation using a control parameter
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which may be correlated to the change of state of refrigerant
being withdrawn;
Figure 6B is a continuation of the flow chart of Figure 6A
showing a program for controlling the system in a vapor recovery
mode of operation;
Figure 7 is a graphical showing of storage cylinder temperature
versus time in the liquid recovery mode of operation;
Figure 8 is a graphical showing of pressure leaving the
compressor versus time in the liquid recovery mode of operation:
Figure 9 is a graphical showing of pressure entering the
compressor versus time in the liquid mode of operation;
Figure lo is a chart showing the operation of the various
components of the system during different modes of operation.
An apparatus for recovering and purifying the refrigerant
contained in a refrigeration system is generally shown at
reference numeral 10 in Figure 1. The refrigeration system to be
evacuated is generally indicated at 12 and may be virtually any
mechanical refrigeration system.
As shown the interface or tap between the recovery and
purification system 10 and the system being serviced 12 is a
standard gauge and service manifold 14. The manifold 14 is
connected to the refrigeration system to be serviced in a
standard manner with one line 16 connected to the low pressure
side of the system 12 and another line 18 connected to the high
pressure side of the system. A high pressure refrigerant line 20
is interconnected between the service connection 22 of the
2 ~
service manifold and a T connection 11 for coupling the line 20
to the recovery system 10.
Located in the interconnecting line 20 is a filter-dryer 13 which
is mounted external of the recovery system. This device as will
be seen, is normally installed in the line 20 only when the
system is to be operated first in the liquid recovery mode of
operation.
The recovery system 10 includes two sections, as shown in Figure
1 the components and controls of the recovery system are
contained within a self contained compact housing (not shown)
schematically represented by the dotted line 24. A refrigerant
storage section of the system is contained within the confines of
the dotted lines 26. The details of each of these sections and
their interconnection and interaction with one another will now
be described in detail.
As will be appreciated as the description of the operation of the
system continues there are two refrigerant paths extending from
the T-connection 11 at the end of interconnecting line 20. The
first path, i.e. the liquid path, extends to the left of the T-11
to an electrically actuatable solenoid valve SV7. This valve
will selectively allow refrigerant to pass therethrough when
actuated to its open position or will prevent the flow of
refrigerant therethrough when electrically actuated to its closed
position. Additional electrically actuatable solenoid valves
contained in the system operate in the same conventional manner.
From SV7 a liquid refrigerant line 15 extends to the refrigerant
storage section of the system 26 where it communicates through a
valve 90 with a refrigerant storage cylinder 86. In the liquid
recovery mode of operation of the system liquid refrigerant
passes through the line 15 directly from the refrigeration system
12 to the storage cylinder 86.
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21~3~,").3
When the system is operated in the vapor recovery mode gaseousrefrigerant flowing through the interconnecting line 20 flows
through the T-ll and to the right to electrically actuatable
solenoid valve SV3. From SV3 refrigerant passes through a
conduit 28 through a check valve 98 to a second electrically
actuatable solenoid valve SV2. From SV2 an appropriate conduit
30 conducts the refrigerant to the inlet of a combination
accumulator/oil trap 32 having a drain valve 34. Refrigerant gas
is then drawn from the oil trap through conduit 36 to an acid
purification filter-dryer 38 where impurities such as acid,
moisture, foreign particles and the like are removed before the
gases are passed via conduit 40 to the suction port 42 of the
compressor 44. A suction line accumulator 46 is disposed in the
conduit 42 to assure that no liquid refrigerant passes to the
suction port 42 of the compressor. The compressor 44 is
preferably of the rotary type, which are readily commercially
available from a number of compressor manufacturers but may be of
any type such as reciprocating, scroll or screw.
From the compressor discharye port 48 gaseous refrigerant is
directed through conduit 50 to a conventional float operated oil
separator 52 where oil from the recovery system compressor 44 is
separated from the gaseous refrigerant and directed via float
controlled return line 54 to the conduit 40 communicating with
the suction port of the compxessor. From the outlet of the oil
separator 52 gaseous refrigerant passes via conduit 56 to the
inlet of a heat exchanger/condenser coil 60. An electrically
actuated condenser fan 62 is associated with the coil 60 to
direct the flow of ambient air through the coil as will be
described in connection with the operation of the system.
From the outlet 64 of the condenser coil 60 an appropriate
conduit 66 conducts refrigerant to a T-connection 68. From the T
68 one conduit 70 passes to another electrically actuated
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solenoid valve SV4 while the other branch 72 of the T passes to a
suitable refrigerant expansion device 74. In the illustrated
embodiment the expansion device 74 is a capillary tube and a
strainer 76 is disposed in the refrigerant line 72 upstream from
the capillary tube to remove any particles which might
potentially block the capillary. It should be appreciated that
the expansion device could comprise any of the other numerous
well known refrigerant expansion devices which are widely
commercially available. The conduit 72 containing the expansion
device 74 and the conduit 70 containing the valve SV4 rejoin at a
second T connection 78 downstream from both devices. It will be
appreciated that the solenoid valve SV4 and the expansion device
74 are in a parallel fluid flow relationship. As a result, when
the solenoid valve SV4 is open the flow of refrigerant will be,
because of the high resistance of the expansion device, through
the solenoid valve in a substantially unrestricted manner. On
the other hand, when the valve SV4 is closed, the flow of
refrigerant will be through the high resistance path provided by
the expansion device. Combination devices such as electronically
actuated expansion valves are known which would combine the
functions of the valves SV4 and the capillary tube 74, however,
as configured and described above, the desired function is
obtained at a minimum cost.
From the second T-78 a conduit 80 passes to an appropriate
coupling (not shown) for connection of the system as defined by
the confines of the line 24, via a flexible refrigerant line 82
to the liquid inlet port 84 of the previously referred to
refillable refrigerant storage container 86. The container 86 is
of conventional construction and includes a second port 88
adapted for vapor outlet. The storage cylinder 86 further
includes a liquid level indicator 92. The liquid level
indicator, for example, may comprise a compact continuous liquid
level sensor of the type available from Imo Delaval Inc., Gems
2~3 J$~,9
Sensors Division. Such an indicator is capable of providing an
electrical signal indicative of the level of the refrigerant
contained within the storage cylinder 86.
Refrigerant line 94 interconnects the vapor outlet 88 of the
cylinder 86 with a T connection 96 in the conduit 28 extending
between solenoid valve SV3 and solenoid valve SV2. An additional
electrically actuated solenoid valve SV1 is located in the line
94. A check valve 98 is also positioned in the conduit 28 at a
location downstream of the T-96 which is adapted to allow flow in
the direction from SV3 to SV2 and to prevent flow in the
direction from SV2 to SV3.
With continued reference to Figure 1 a refrigerant gas
contamination detection circuit 100 is included in the system in
a parallel fluid flow arrangement with the compressor 44. The
contamination detection circuit 100 includes an inlet conduit 102
in fluid communication with the conduit 56 extending from the oil
separator 52 to the condenser inlet 58. The inlet conduit 102
has an electrically actuated solenoid valve SV6 disposed there
along and from there passes to the inlet of a sampling tube
holder 104. The outlet of the samplinq tube holder 104 i8
interconnected via conduit 106 with the conduit 40 which
communicates with the suction port 42 of the compressor. An
electrically controlled solenoid valve SV5 is disposed in the
conduit 106.
The solenoid valves SV5 and SV6, when closed, isolate the
sampling tube holder 104 from the system and allow easy
replacement of the sampling tube contained therein. The sampling
tube holder may be of the type described in U. S. Patent
4,389,372 Portable Holder Assembly for Gas Detection Tube.
Further, the refrigerant contaminant testing system is preferably
of the type shown and described in detail in U. S. Patent
20539~9
12
4,923,806 entitled Method and Apparatus For Refrigerant Testing
In A Closed System and assigned to the assignee of the present
invention.
Automatic control of all of the components of the refrigerant
recovery system 10 is carried out by an electronic controller 108
which is formed of a micro-processor having a memory storage
capability and which is micro-programmable to control the
operation of all of the solenoid valves SV1 through SV7 as well
as the compressor motor and the condenser fan motor. Inputs to
the controller 108 include a number of measured or sensed system
control parameters. In the embodiment disclosed these control
parameters include the temperature of the storage cylinder Tstor
which comprises a temperature transducer capable of accurately
providing a signal indicative of the temperature of the
refrigerant in the storage cylinder 86. Ambient temperature is
measured by a temperature transducer positioned at the inlet to
the condenser coil or condenser fan 62 and is referred to as
Tamb. The temperature of the refrigerant flowing through the
compressor discharge line 50 is sensed by a temperature
transducer 110 posi~ioned on the compressor discharge line 50.
Most important in the control scheme of the systems are the
compressor suction pressure designated as P2 and the compressor
discharge pressure designated as P3. As indicated in Fi~ure 1 a
pressure transducer labeled P2 is in fluid flow communication
with the suction line 40 to the compressor while a second
pressure transducer P3 is in fluid communication with the high
pressure refrigerant line 56 passing to the condenser. The
pressure ratio across the compressor 44 is defined as the ratio
P3/P2. An additional input to the controller 108 is the signal
from the liquid level indicator 92.
X'
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13
Looking now at Figure 10 it will be noted that the operating
modes of the system are identified and the condition of the
electrically actuatable components of the system are shown in the
different modes. In the Standby mode the system has been turned
on and all electrically actuatable mechanical systems are
de-energized and ready for operation. In the Service mode, the
electrically actuated solenoid valves SVl through SV4 are all
open thereby equalizing the pressures within the system so that
it may be serviced without fear of encountering high pressure
refrigerant.
The recovery and purification system 10 is capable of operating
in both liquid recovery and vapor recovery modes. It should be
appreciated that a vapor recovery cycle may begin under two
different sets of circumstances: 1) in the case of a system
containing more than five pounds of refrigerant the vapor
recovery cycle will follow a previously performed liquid recovery
cycle; and 2) in the case of a refrigeration system containing
less than five pounds of refrigerant the vapor recover cycle
represents the initiation of the recovery sequence.
.
Further it should be appreciated that the shift from liquid
recovery to vapor recovery may be initiated by several different
control schemes.
To facilitate a complete understanding of the system in its
various modes of operation the system will be described first in
the Vapor Recovery and Cylinder Cool modes in connection with
Figures 1,2,3 and 10. Following that a combination Liquid-Vapor
cycle with liquid level control will be described in connection
with Figures 1,4A & B, 5 and 10. Last, a combination
Liquid-Vapor cycle with control by a parameter which may be
correlated to the change of state of the refrigerant being
14
withdrawn will be described in connection with Figures 1, 6A & B,
and 7-10.
The Recover and Cylinder Cool modes will now be described in
detail in connection with the flow chart of Figure 2. The
Recover mode is the mode in which the device 10 has been coupled
to an air conditioning system 12 for removal of refrigerant
therefrom. Looking now to Figure 2 it will be noted that the
first step performed by the controller 108 when the Recover cycle
is selected is to compare the compressor discharge pressure P3 to
the compressor inlet pressure P2. If the pressure differential
(P3-P2) is greater than 30 psi the controller 108 will open
valves SVl-SV4 in order to equalize the pressures within the
system. When the difference between P3 and P2 falls to less than
10 psi the system will then go to the Recover mode of operation.
; If the initial comparison of P3 and P2 shows a difference of less
than or equal to 30 psi the system will go directly to the
Recover mode. The reason for this comparison is that the
compressor may readily start up when the pressure differential is
less than or equal to 30 psi, whereas, when the pressure
differential is greater than 30 psi, compressor start up is
difficult and dictates a reduction in the pressure difference
thereacross.
Upon initiation of the Recover mode the controller 108 will open
valves SV2, SV3 and SV4, valve SVl will remain closed. Valves
SV5 and SV6 as noted in Figure 4 operate together as a single
output from the micro-processor (controller) and the only time
these valves are opened is when t~e contaminant testing process
is being carried out. These valves will not be discussed further
in connection with the other modes of operation of the system.
The compressor 44 and the condenser fan 62 are also actuated upon
initiation of the Recover mode.
2~5~ 3
Looking now at operation of the system in the Recover mode, and
referring to Figure 1, with valve SV3 open refrigerant from the
system being serviced 12 is forced by the pressure of the
refrigerant in the system, and by the suction created by
operation of the compressor 44, through conduit 20, through
valve SV3, check valve 98, valve SV2 and conduit 30 to the
accumulator/oil trap 32. Within the accumulator/oil trap the oil
contained in the refrigerant being removed from the system being
serviced falls to the bottom of the trap along with any liquid
refrigerant withdrawn from the system. Gaseous refrigerant is
drawn from the accumulator/oil trap 32 through the filter dryer
38 where moisture, acid and any particulate matter is removed
therefrom, and, from there passes via conduit 40, through the
suction accumulator 46 to the compressor 44.
The compressor 44 compresses the low pressure gaseous refrigerant
entering the compressor into a high pressure gaseous refrigerant
which is delivered via conduit 50 to the oil separator 52. The
oil separated from the high pressure gaseous refrigerant in the
separator 52 is the oil from the recovery compressor 44 and this
oil is returned via conduit 54 to the suction line 40 of the
compressor to assure lubrication of the compressor. From the oil
separator 52 the high pressure gaseous refrigerant passes via
conduit 56 to the condenser coil 60 where the hot compressed gas
condenses to a liquid. Liquified refrigerant leaves the
condensing coil 60 via conduit 66 and passes through the T68
through the open solenoid valve SV4, and passes via the liquid
lines 80 and 82, to the refrigerant storage cylinder 86 through
liquid inlet port 84.
While refrigerant recovery is going on the controller 108 is
receiving signals from the pressure transducers P3 and P2,
calculating the pressure ratio P3/P2, and, comparing the
calculated ratio to a predetermined value. Compressor suction
2~ ~, '2~
16
pressure P2 is also being looked at alone and being compared to a
predetermined Recovery Termination Suction Pressure. As shown in
Figure 2, the predetermined Recovery Termination Suction Pressure
is 4 psia, and if P2 falls below this value the Recover mode is
terminated and the controller 108 initiates the refrigerant
quality test cycle, identified as Totaltest. This cycle will be
described below following a complete description of the other
modes of operation. Totaltest is a registered Trademark of
Carrier Corporation for ~Testers For Contaminants in A
Refrigerant".
The selection of the predetermined recovery termination suction
pressure of 4 psia results from recovery system operation wherein
it has been shown that a compressor suction pressure, P2, of 4
psia or less results in recovery of 98 to 99% of the refrigerant
from the system being serviced. Achieving this pressure during
the first Recover mode cycle is unusual, however, it is
achievable. As an example, P2 may be drawn down to the 4 psia
termination value in low ambient temperature conditions where the
condensing coil temperature (which is ambient air cooled) is low
enough to allow P3 to remain low enough for P2 to reach 4 psia
before the pressure ratio limit is reached.
Returning now to compressor pressure ratio, as indicated in
Figure 2, in the illustrated embodiment, when the pressure ratio
exceeds or is equal to 16 the microprocessor in the controller
108 performs what is referred to as the Recovery Cycle Test. If
the Recovery Cycle just performed is the first Recovery Cycle
performed and the compressor suction pressure P2 is greater than
or equal to 10 psia the system will shift to what is known as a
Cylinder Cool mode of operation. If the Recovery Cycle just
performed is a second or subsequent recovery cycle and the
compressor suction pressure P2 is less than 10 psia the
controller will consider the refrigerant Recovery as completed
,
: ' ~, , -
~, ' :' , ' ' ''.
2'J~ 7,~
17
and will initiate the refrigerant contaminant test cycle
(Totaltest).
The latter conditions, i.e. second or subsequent recover cycle,
and P2 less than 10 psia, are conditions that are found to exist
at high ambient temperatures. For example, such conditions may
exist when recovering R-22 from an air conditioning system at an
ambient temperature of 105~F and above. Under such conditions it
has been found that attempts to reduce the compressor suction
pressure P2 to values less than 10 psia are counterproductive in
that a substantial length of operating time would be necessary in
order to obtain a very small additional drop in suction pressure.
Further~ it has been found, at these conditions, that shifting to
the Cylinder Cool mode, which will be described below, also would
not substantially increase the amount of refrigerant that would
ultimately be withdrawn from the system and accordingly
termination of the Recover mode and initiation of the refrigerant
contaminant test cycle is indicated.
`,
Assuming that the Recovery Cycle Test has indicated that either:
it is the first recovery cycle, or, the compressor suction
pressure P2 is greater than or equal to 10 psia, the controller
108 will initiate the Cylinder Cool mode of operation.
In the Cylinder Cool mode, as indicated in Figure 10, the
solenoid valves SVl and SV2 are energized and thereby in the open
condition. Solenoid valves SV3 and SV4 are closed, and, the
compressor motor and condenser fan motor continue to be
energized. The Cylinder Cool mode of operation essentially
converts the system to a closed cycle refrigeration system
wherein the refrigerant storage cylinder 86 functions as a
flooded evaporator. By closing solenoid valve SV3 the
refrigerant recovery and purification system 10 is isolated from
the refrigeration system 12 being serviced. The opening of
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18
solenoid valve SVl establishes a fluid path between the vapor
outlet 88 of the storage cylinder 86 and the conduit 28 which is
in communication with the low pressure side of the compressor 44.
The closing of solenoid valve SV4 routes the refrigerant passing
from the condenser 60 through the refrigerant expansion device
74.
With the control solenoids set as described above, in the
Cylinder Cooling mode of operation the compressor 44 compresses
low pressure gaseous refrigerant entering the compressor and
delivers a high pressure gaseous refrigerant via conduit 50 to
the oil separator 52. From the oil separator 52 the high
pressure gaseous refrigerant passes via conduit 56 to the
condenser coil 60 where the hot compressed gas condenses to a
liquidr Liquified refrigerant leaves the condensing coil 60 via
conduit 66 and passes through the T-connection 68 through the
strainer 76 and, via conduit 72, to the refrigerant expansion
device 74. The thus condensed refrigerant, at a high pressure,
flows through the expansion device 74 where the refrigerant
undergoes a pressure drop, and is at least partially, flashed to
a vapor. The liquid-vapor mixture then flows via conduits 78 and
82 to the refrigerant storage cylinder 86 where it evaporates and
absorbs heat from the refrigerant within the cylinder 86 thereby
cooling the refrigerant.
.
Low pressure refrigerant vapor then passes from the storage
cylinder 86, via vapor outlet port 88, through conduit 94 and
solenoid valve SVl to the T connection 96. From there it passes
through the check valve 98, solenoid valve SV2, oil separator/
accumulator 32, filter dryer 38 and conduit 40 to return to the
compressor 44, to complete the circuit.
As the Cylinder Cool mode of operation continues, the cylinder
temperature, as measured by the temperature transducer Tstor,
2~3~ ~
19
continues to drop as the refrigerant is continuously circulated
through the closed refrigeration circuit. Also during this time
the refrigerant is passed through the refrigeration purifying
components, i.e. the oil separator 32 and the filter dryer 38, a
plurality of times to thereby further purify the refrigerant.
.,
Referring again to Figure 2, the Cylinder Cool mode of operation
will terminate when any one of thres conditions occur; 1) the
cylinder temperature, as measured by Tstor falls to a level 70F
below ambient temperature (Tamb), or, 2) when the Cylinder
Cooling mode of operation has gone on for a duration of 15
minutes, or, 3) when the cylinder temperature Tstor falls to O~F.
Regardless of which of the three conditions has triggered the
termination of the Cylinder Cool mode the result is substantially
the same, i.e., the temperature (Tstor) of the refrigerant stored
in the cylinder 86 is now well below ambient temperature. As a
result, the pressure within the cylinder, corresponding to the
lowered temperature is substantially lower than any other point
in the system.
When any one of the Cylinder Cool mode termination events occur,
the controller 108 will shift the system to a second Recover mode
of operation. In the second Recover mode the solenoid valves,
and compressor and condenser motors are energized as described
above in connection with the first Recover mode. Because of the
low temperature Tstor that has been created in the refrigerant
storage cylinder, however, the capability of the system to
withdraw refrigerant from the unit being serviced, without
subjecting the recovery compressor to high pressure differentials
is dramatically increased.
An understanding of this phenomenon will be appreciated with
reference to Figure 1. It will be described by picking up a
Recover cycle at the point where refrigerant withdrawn from the
2 ~ ~ 3 v~ 3
system being serviced is discharged from the compressor 44 and is
passing, via conduit 56, to the condenser 60. At this point the
pressure within the system, extending from the compressor
discharge port 48 through to and including the storage cylinder
86, is dictated by temperature and pressure conditions within the
storage cylinder 86. As a result the storage cylinder 86 now
effectively serves as a condenser with the recovered refrigerant
passing as a super- heated vapor through the condenser coil,
through the solenoid valve sV4 and the conduits 80 and 82 to the
storage cylinder 86 where it is condensed to liquid form.
It is the dramatically lower compressor discharge pressure P3
experienced during a second or subsequent Recover mode (i.e. any
Recover mode following a Cylinder Cool mode) that allows the
recovery compressor 44 to draw the system being serviced 12 to a
pressure lower than heretofore obtainable while still maintaining
a permissible pressure ratio across the recovery compressor.
It will be appreciated that in a second Recover mode, the
pressure ratio P3/P2 could exceed the predetermined value (which
in the example given is 16) and, depending upon the other system
conditions, as outlined in the flow chart of Figure 2, will
result in an additional Cylinder Cool mode of operation or
termination.
"
With continued reference to Figure 2, the system will then
operate as described until conditions exist which result in the
controller 108 switching to the refrigerant contaminant test
(Totaltest) mode of operation. Prior to initiation of a Recover
cycle an operator should make sure that a sampling tube has been
placed in the sampling tube holder 104. Upon initiation of the
Totaltest mode of operation, solenoid valves SY1, SV2, SV4 and
SV5/SV6 are all energized to an open position. The solenoid
valve SV3 is not energized and is therefore closed. With the
2 ~
flow control valves in the condition described the flow of
refrigerant through the recovery system is similar to that
described above in connection with the Cylinder Cooling mode
except that the solenoid valve SV4 is open and therefore the
refrigerant does not pass through the expansion device 74. With
the refrigerant flowing through the circuit in this manner, and
with the solenoid valves SV5 and SV6 open, the pressure
differential existing between the high and low pressure side of
the system induces a flow of refrigerant through conduit 102
solenoid valve sV6, the sampling tube holder 104 (and the tube
contained therein), solenoid valve SV5 and conduit 106 to thereby
return the refrigerant being tested to the suction side of the
compressor 44.
A suitable orifice is provided in conduit 102, or in the sampling
tube holder 104, to provide the necessary pressure drop to assure
that the flow of refrigerant through the testing tube held in the
sampling tube holder 104 is at a rate that will assure that the
testing tube will receive the proper flow of refrigerant
therethrough during the Totaltest run time in order to assure a
reliable test of the quality of the refrigerant passing
therethrough. With reference to Figure 2 will be noted that the
~un time of the refrigerant quality test is indicated as X
minutes. The normal run time for a commercially available
Totaltest system is about ten minutes and the controller may be
programmed to run the test for that length of time or different
time for different refrigerants. The quality test however may be
terminated sooner if the refrigerant being tested contains a
large amount of acid and the indicator in the test tube changes
color in less than the programmed run tims. If this occurs, the
refrigerant quality test may be terminated, and, an additional
refrigerant purification cycle initiated.
2-J~ ~Y~,9
The additional purification cycle is identified as the Recycle
mode and a flow chart showing the system operating logic is shown
in Figure 3. With reference to Figure 4 it will be noted that
the condition of the electrically actuable components is the same
in Recycle as it is for the Cylinder Cool mode except that the
solenoid valve SV4 is open so that the refrigerant does not flow
through the expansion device 74 but flows through the open
solenoid valve SV4. This increases the volume flow of
refrigerant through the system during the Recycle mode. The
function of this mode is strictly to further purify the
refrigerant by multiple passes through the oil trap 32 and the
filter dryer 38.
:~
With reference to Figure 3 the length of time in which the system
is run in the Recycle mode is determined by the operator as a
number of minutes "X" which varies as a function of refrigerant
type and quality and ambient air temperature. The type of
refrigerant is known, the ambient temperature may be measured,
and the quality is determined by the operator upon the evaluation
of the test tube used in the refrigerant quality test cycle.
With continued referenced to Figure 3, upon the end of the
selected recycle time the system, if so selected by the operator,
will run another refrigerant quality test, and, if the results of
this test so indicate another recycle period may initiated
following the procedure set forth above.
. .
The object of the system and control scheme described above is to
remove as much refrigerant as possible from a system being
serviced, under any given ambient conditions, or ~ystem
conditions, while, at all times monitoring system control
parameters which will assure that the compressor of the Recovery
system is not subjected to adverse operating conditions. As
described above, the system control parameter is the pressure
ratio P3/P2, across the recovery compressor 44. In the example
: .
2 ~ 2 9
` 23
given above a value of P3/P2 of 16 was used as the pressure ratio
above which the compressor could be adversely affected. It
should be appreciated that for different compressors the value of
;~this parameter could be different.
:
The ultimate goal in the control of this system is to limit
compressor operation to predetermined limits to assure long and
reliable compressor life. As pointed out above, in the
Background of the Invention. the internal compressor temperature
is considered by compressor experts to be the controlling factor
in preventing internal compressor damage during operation. In
the presently disclosed preferred embodiment the pressure ratio
has been found to be an extremely reliable effective control
parameter which may be related to the internal compressor
temperature and has thus been selected as the preferred control
parameter in the above described preferred embodiment. Pressure
differential, (i.e. P3-P2) could also be effectively used to
control the system.
It should be appreciated however, that other system control
parameters such as the compressor discharge temperature as
measured by the temperature transducer 110 in the compressor
;discharge line 50, or the compressor suction pressure P2 could
also be used to control the operation of the system, to limit the
system to operation only at conditions at which the compressor is
not adversely effected.
With respect to temperature, it is generally agreed that an
internal compressor temperature at which the lubricating oil
begins to break down is about 325F. Above this temperature
adverse compressor operation and damage may be expected. In the
present system the controller 108 has been programmed such that,
should the compressor discharge temperature, monitored by the
~ u ~ 9
24
temperature transducer 110 exceed a maximum of 225F regardless
of pressure ratio conditions, the system will be shut off.
It is further contemplated that, if the compressor discharge
temperature, as measured at the transducer 110 were used as the
primary system control parameter that a temperature in the
neighborhood of 200F would be used to switch the recovery system
from a Recover mode to a Cylinder Cooling mode of operation in
order to assure that the compressor would not be adversely
affected during operation of the system.
According to another embodiment of the invention, as mentioned
above, the system control parameter being sensed for compressor
protection could be the compressor suction pressure P2. In this
case the microprocessor of the controller 108 would be programmed
with compressor suction pressures P2 which would be considered
indicative of adverse compressor operation, for a range of
ambient air temperatures and for the different refrigerants which
may be processed by the system. A~ an example, when processing
refrigerant R-22 at an ambient air temperature of 90F a suction
pressure P2 in the range of 13 psia to 15 psia would be
programmed to change the system from a Recover mode t~y~inder
Cooling mode of operation.
The outstanding refrigerant recovery capability of a system
according to the present invention is reflected in the following
example. The recovery apparatus was connected to a refrigeration
system having a system charge of 4.5 pounds of refrigerant R-12
at an ambient temperature of 70~ F. Such a system is typical of
an automobile air conditioning system.
Upon initiation of recovery the system performed a first Recover
cycle for 8.67 minutes before the systen reached the limiting
pressure ratio P2/P3 of 16. At that point 3.73 pounds had been
2t3.~?~3~3
recovered from the system. This represents 82.9% of the systems
total charge. Typical prior art systems would stop at this
point, leaving .77 pounds, or more than 17% of the charge in the
system. This .77 pounds would eventually be released to the
atmosphere.
.
At this point, the system shifted to the Cylinder Cool mode of
operation. The Cylinder Cool cycle ran for 15 minutes, bringing
the cylinder temperature (Tstor) down to 10F. At this point a
second Recover cycle was initiated by the system controller. The
second Recover cycle ran for 3.8 minutes at which time Recover
was terminated when the suction pressure P2 fell to 4.0 psia.
At this point, the total system run time had been 27.5 minutes
and a total of 4.42 pounds of refrigerant had been recovered from
the system. This represents 98.2% of the total charge of 4.5
pounds, leaving only .08 pounds in the system.
Following completion of recovery and purification, the storage
cylinder 86 contains clean refrigerant which may be returned to
the refrigeration system. With reference to Figure 10, the
Recharge mode, when selected, results in simultaneous opening of
valves SVl and SV3 to establish a direct refrigerant path from
the storage cylinder 86 to the refrigeration system 12. All
other valves and the compressor and condenser are de-energized in
this mode. The amount of refrigerant to be delivered to the
system is selected by the operator, and, the controller 108, with
input from the liquid level sensor 92 will assure accurate
recharge of the selected quantity of refrigerant to the system.
The liquid recovery mode will now be described in detail in
connection with the flow chart of figure 4A. It should be
appreciated that the liquid recovery mode is designed to be used
in larger systems for example systems having a refrigerant charge
2 ~ ;} ~ ~ ;J ~
26
of greater than 5 pounds of refrigerant. In systems where less
than 5 pounds of refrigerant are contained in the system the
liquid recover mode of operation may be omitted and the operator
may go directly to the previously described vapor recovery mode
which will be subsequently described.
At this point it is assumed that a system containing greater than
5 pounds of refrigerant is being serviced and that the device 10
has been coupled to the system 12 for removal of refrigerant
therefrom. With preference now to Figure 4A and Figure 10 it
will be seen that upon initiation of the Liquid Recover mode the
controller 108 will open valves SVl, SV2 and SV7. The valves
SV3, SV4, SV5 and SV6 will remain closed. Valves SV5 and SV6 as
noted in Figure 10 operate together as a single output from the
microprocessor (controller 108) and the only time these valves
are open is when the contaminant testing process is being carried
out. These valves will not be discussed further in connection
with other modes of operation of the system. The motors of the
compressor 44 and the condenser fan 62 are also energized upon
initiating the liquid recover mode.
Looking now at operation of the system in the liquid recover
mode, and referring to Figure 1. With valve SV3 closed and valve
SV7 open refrigerant from the system being serviced 12 is forced
by the pressure of the refrigerant in the system through conduit
20, through the T-ll, through valve SV7 and via liquid
refrigerant line 15 to the valve 90 on the refrigerant storage
cylinder 86 and directly into refrigerant storage cylinder.
Upon entering the storage cylinder 86 at ambient conditions, a
portion of the liquid refrigerant will exist in gaseous form. At
this time because, the solenoid valve SY1 is open, a fluid path
is directly established between the vapor outlet 88 of the
storage cylinder 86 and the conduit 94 which is in communication
.; -.
;~ 2 ~
with the low pressure side of the compressor 44. With the
solenoid valve SV4 closed refrigerant passing from the condensers
60 will pass through the refrigerant expansion device 74.
Accordingly with the control solenoids set as described above,
during liquid recovery, the compressor 44 acts to withdraw low
pressure gaseous refrigerant directly from the storage cylinder
86. This refrigerant passes via conduit 94 and T-96. through the
check valve 98, valve SV2 and conduit 30 to the oil separator 32.
From the oil separator it passes via conduit 36 to the filter
drier 38, and thence via conduit 40 and accumulator 46 to the
compressor 44 delivers high pressure gaseous refrigerant via
conduit 50 to the oil separator 52. From the oil separator 52 the
high pressure gaseous refrigerant passes via conduit 56 to the
condenser coil 60 where the hot compressed gas condenses to a
liquid.
."
Liquified refrigerant leaves the condensing coil 60, via conduit
66 and passes through the T-connection 68 through the strainer 76
and, via conduit 72 to the refrigerant expansion device 74. The
thus condensed refrigerant, at a high pressure, flows through the
expansion device 74 where the refrigerant undergoes a pressure
drop, and is at least partially flashed to a vapor. The
liquid-vapor mixture then flows via conduit 78 and 82 back to the
refrigerant storage cylinder 86 where it evaporates and absorbs
heat from the refrigerant within the cylinder 86 thereby lowering
the pressure and temperature within the storage cylinder 86. As
a result of the lowered temperature and pressure within the
storage cylinder 86 the pressure differential between the
refrigeration system being serviced 12, which is at ambient
temperature, and the storage tanX 86 is substantially increased
and as a result the flow of liquid refrigerant through the liquid
refrigerant line 15 to the storage cylinder is substantially
increased.
. .
2 ~ 7 9
28
It will be appreciated, that during this mode of operation
refrigerant will continue to recirculate through the cooling and
purifying circuit described above.
With reference to Figure 4A it will be seen that the liquid
recovery mode is run according to the illustrated embodiment, for
two minutes at which time the system is shifted to the Cylinder
Cool cycle. With reference to Figure 7, the only difference
between the operation of the system in the Cylinder Cool cycle
and the liquid recovery cycle iB that the solenoid valve SV7 is
closed and the system operates in a closed circuit, as described
with no connection to the system being serviced. As the Cylinder
Cool mode of operation continues the cylinder temperature
continues to drop as the refrigerant i8 continuously circulated
through the closed refrigeration circuit. Also during this time
the refrigerant is passed through the refrigeration purifying
components, i.e. the oil separator 32 and the filter dryer 38, a
plurality of times to thereby further purify the refrigerant.
The system is run in the Cylinder Cool cycle for five minutes in
order to assure that the temperature and pressure with$n the
storage cylinder is reduced such that it i~ substantially lowex
than ambient temperature.
At this point, with continued reference to Figure 4A the system
returns to liquid recovery operation. As the second liquid
recovery cycle continues the controller 108 continues to receive
the signal generated by the liguid level sensor 92 which is
indicative of the liquid level within the storage cylinder 86.
The processor receives a succession of these signals and
determines a rate of liquid level increase in the storage
cylinder 86. The processor then generates a signal indicative of
the rate of liquid level increase. The processor is further
programmed to look at the signal indicative of the rate of liquid
2~i3 329
.
29
level increase and determine whether that rate is commensurate
with the withdrawal of liquid refrigerant from the system.
Figure 5 illustrates the decrease in the rate of refrigerant
recovery, and, accordingly, the decrease in the rate of increase
of the liquid level within the cylinder 86 which occurs when the
recovery of refrigerant shifts from a liquid to a vapor state.
The straight line portion of the graph illustrates the linear
increase in the amount of refrigerant recovered as time goes by
when recovery is in the liquid state. At the top of the graph
where the slope changes dramatically the rate of refrigerant
being recovered is in the vapor state. When the microprocessor
senses the dramatic change in the rate that refrigerant is being
recovered the liquid recovery mode of operation is automatically
terminated.
The accuracy of the information which liquid level sensors are
able to provide varies widely. The operation of the Liquid
Recovery system as described above is such that the system will
perform a successful recovery using a level sensor that provides
less accurate readings. In a system using an extremely accurate
level sensor the Liquid Recovery mode of operation described
above, as outlined in Figure 4A, may be performed by omitting the
first Cylinder Cool cycle and the return to Liquid Recovery
cycle.
With reference to Figure 4A it will be seen that at this point
the system shifts to a Cylinder Cool cycle of operation in order
to reduce the temperature and pressure of the storage cylinder 86
prior to the beginning of a vapor recovery cycle. With continued
reference to Figure 4A, this Cylinder Cool mode of operation will
terminate when any one of three conditions occur; 1) the cylinder
temperature, as measured by Tstor falls to a level 70F below
ambient temperature (Tamb), or, 2) when the cylinder cool mode of
'
2 ~ ~ ~3 ~ 3
operation has gone for a duration of 15 minutes, or, 3) when the
cylinder temperature Tstor falls to 0F. Regardless of which of
the three conditions triggers termination of the Cylinder Cool
mode, the result is substantially the same, i.e., the temperature
(Tstor) of the refrigerant stored in the cylinder 86 is well
below ambient temperature. At this point the system will shift
to a vapor recovery mode of operation to complete the withdrawal
of the refrigerant from the system being serviced.
The vapor Recover and Cylinder Cool modes of operation are
illustrated in the flow chart of Figure 4B. The operation of the
system at this time is the same as the previously described Vapor
Recovery and Cylinder Cool cycles and will not be repeated.
Figures 6A and B illustrate the operation of the system in the
liquid recovery mode where the shift from liquid recovery to
vapor recovery is controlled by a parameter which may be
correlated to the change of state of the refrigerant being
withdrawn. Operation of the system is the same as that described
in connection with Figure 4A and B except for the sourGe of the
control signals.
As the second liquid recovery cycle continues, the controller 108
continues to receive signals related to a number of conditions
within the system. Specifically the temperature transducer Tstor
provides a signal indicative of the temperature of the
refrigerant in the storage cylinder 86. The pressure transducer
P2 and P3, provide information with respect to the pressure
entering and leaving, respectively the compressor 44. These
three parameters will collectively be referred to as system
control parameters.
Figures 7, 8 and 9 illustrate the value of the system control
parameters Tstor, P3 and P2 respectively as a function of the
2 g ~ .3 ~ ' 9
length of time the liquid recovery cycle has been run. With
respect to each of these graphical representations it will be
noted that at the seven minute mark each of the parameters
increases, then stabilizes and then begins to drop. The
beginning of the increase of each of the parameters, i.e. the
seven minute point represents the beginning of the second liquid
recovery cycleO The point at which each of theses parameters
begins to drop has been found to be correlatable with the time at
. ~ .
which the state of the refrigerant being withdrawn from the
refrigeration system 12 changes from a liquid state to a vapor
state. The microprocessor of the controller 108 is programmed to
terminate the recovery mode of operation automatically when one
of these selected system control parameters falls a predetermined
amount below its maximum value. As noted in Figure 6A Tstor is
the preferred controlled parameter and in the preferred
embodiment the termination of liquid recovery occurs when Tstor
drops 5F from its maximum value. In the case of the control
parameter being P2 or P3 a drop of 5 psi from the maximum value
has been found to cause the shift from liquid recovery to vapor
recovery to occur at an appropriate time.
~'
With reference to Figure 6A it will be seen that at this point
the system shifts to a Cylinder Cool cycle of operation in order
to reduce the temperature and pressure of the storage cylinder 86
prior to the beginning of a vapor recovery cycle. With continued
reference to Figure 6A, this Cylinder Cool mode of operation will
terminate when any one of three conditions occur; 1) the cylinder
temperature, as measured by Tstor falls tc a level 70-F below
ambient temperature (Tamb), or, 2) when the cylinder cool mode of
operation has gone for a duration of lS minutes, or, 3) when the
cylinder temperature Tstor falls to 0F. Regardless of which of
the three conditions triggers termination of the Cylinder Cool
mode, the result is substantially the same, i.e., the temperature
(Tstor) of the refrigerant stored in the cylinder 86 is well
2 ~
below ambient temperature. At this point the system will shift
to a vapor recovery mode of operation to complete the withdrawal
of the refrigerant from the system being serviced.
:
';
