Note: Descriptions are shown in the official language in which they were submitted.
SS';~'8
Thc present invcn~ion relates to cascade cooling
systems capable of continuous operation despite the failure
of certain components therein. The system also prolongs
the life and improves the reliability of compressors used
therein by operating them intermittently.
In the prior art relating to low -temperature
continuously operated three stage cascade cooling apparatus
numerous applications can be found in storage freezers,
environmental test chambers, metal treating baths, etc.,
where each cooling stage is comprised of a single refriger-
ating motor compressor. In most cases at the medium and
low temperature stage cooling level, the motor compressor
operation is for a short period of time. Continuous
operation for periods of months and years has not been
completely satisfactory with single motor compressors
particularly when operated in high ambient environment and
with fluorinated refrigerants as the cooling medium. It has
been difficult to provide long term effective motor
compressor lubrication because fluorinated refrigerants
tend to displace and wash the oil film from reciprocating
motor compressor components. This is due to low oil
solubility and the difficulty in keeping the oil in the
motor compressor. A further handicap to overcome in a
conventional designed three stage low temperature cascade
cooling apparatus operated with single motor compressors
for each stage is the necessary periodic termination of
the coo]ing apparatus in order to limit friction increase
in the motor compressor reciprocating components. Increased
friction will lead to motor compressor seizure and electric
winding burn out. A further handicap to overcome is that
during failure of a single motor compressor in a three
stage cascade cooling apparatus arrangement, the process
of refrigerating the storage enclosure stops and rapid
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temperature risc occurs. Unless a hack up C02 or LN2
liquid injection cooling system is provided, the storage
enclosure contents have to be transferred to a standby
enclosure immediately to prevent their spoilage.
The present invention provides cascade cooling
apparatus in which at least one stage uses a dual motor
compressor arrangement controlled by a simple system.
In one arrangment a First or High temperature staae is
provided with a single motor compressor and a cooling
medium which is compatible with lubricating oils and has
been used for many years in domestic and commercial storage
freezers. The First or ~igh temperature stage singie
motor compressor is arranged to continuously operate in
order to produce cooling for the Second or Medium stage
dual motor compressor arrangement. The cooling medium
of the Second or Medium stage by heat exchange is liquified
to enter the throttling device connected to the storage
enclosure evaporator coil of the Second or Medium stage to
produce cooling. From here the refrigerating superheated
gases return to the suction side of the Second or Medium
stage cascade cooling arrangement. The dual motor
compressors are electrically connected to a temperature
responsive switch which is further connected to a magnetic
switching relay. These connections alternately energize
one motor-compressor and deenergize the second motor-
compressor. An interval timer electrically connected to
the magnetic coil of the switching relay effects the
switching process of the dual motor compressor Second or
Medium stage arrangement.
In a more complex embodiment of my invention I
provide each stage of a three stage cascade cooling
apparatus with a dual motor compressor cooling arrangement
and with a simple control system. The latter includes an
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interval t:imer ~or the purpose of switching electromechanical
relays, to which each dual motor compressor cooling stage
is clectrically connected in such a manner that only one
motor compressor of each cooling stage can be energized at
any one time while the second motor compressor must remain
deenergized. The period of timing for the interval timer
is set in accordance with the requirement to maintain a
safe low temperature level for the storage enclosure
contents, and also to insure each dual motor compressor
cooling stage will oeprate at its maximum efficiency by
preventing excessive temperature increase to motor compressor
electric windings during high ambient temperature, or
during heavy loading of the storage enclosure by contents
to be frozen or by too frequent opening of the storage
enclosure door. A further important feature of the interval
timer is to limit the enclosure temperature rise to an
acceptable temperature level during failure of one motor
compressor, when the entire cooling process stops for one
timing interval. Durinq the next timing interval the
defective motor compressor is deenergized and the next
operative motor compressor energized to provide cooling
and restart the three stage cascade cooling process, thus
lowering the enclosure temperature to the previous level.
During the next successive timing intervals when the
defective motor compressor will again inhibit the cooling
process, the temperature enclosure warm up will be limited
to a safe level by the timing interval length. The motor
compressor failed condition can therefore be tolerated for
days and weeks before remedial action need be taken to
replace the defective motor compressor. Durina this time
a safe and low temperature level in the storage enclosure
will be maintained thereby protecting its contents from
spoilage.
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A clefinite timing period is set for the interval
timer switching operation. This period rnust limit to a
safe level the motor compressors electric winding
temperature increase of each stage and also mus-t keep to
a minimum the friction increase of the mo-tor compressors
reciprocating components. One result of this design is
that the motor compressors operate at their maximum
cooling efficiency. Also and most important, the enclosure
temperature rise is limited to a safe level during failure
of one operative motor compressor. During failure, the
interval timer switches off the defective side motor
compressor arrangement and simultaneously switches on the
inoperative parallel-connected motor compressor arrangement
to provide cooling which will rapidly lower the enclosure
temperature to the previous temperature level. This
temperature will be maintained for a time period dependent
on the interval timer timing. Since the duration of the
timer period is related to the enclosure temperature rise,
to ambient temperature in which the storage enclosure is
located and also to the maximum allowable storage enclosure
warm up permitted, failure in a motor compressor can be
tolerated for an extended time. During this time,
corrective action can be taken to repair the failed motor
compressor. A safe temperature level for the enclosure
contents will be maintained without requiring immediate
attention.
The invention relates to a cascade cooling system
for an enclosure, the cooling system having a first stage
and a second stage, at least the second stage consisting
of a pair of motor driven compressors with their coolant
flow paths connected in parallel, timing means connected
to control the energization of the motor driven compressors
of the second stage whereby they are alternately energized
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for predetermined periods of time, the capacity of one
of the motor driven compressors being sufficient to
maintain the enclosure below a safe temperature level
when energized for the predetermined periods of time.
In its method aspect, the invention relates to a
method of maintaining a safe low temperature level in an
enclosure having a two stage cooling system, comprising
providing at least the second stage with a pair of motor
driven compressors and alternately energizing the
compressors for predetermined time periods, the capacity
of each compressor operating alone being sufficient to
maintain the enclosure below the safe temperature level
when energized for the predetermined time periods.
The full object and advantages of my invention
will appear from the detailed description in the appended
specifications. The novel features of the invention will
be particularly pointed out in the claims.
In the drawings:
Fig. 1 is a schematic diagram of an electrical
control system forming the present invention.
Fig. 2 is a schematic of a three stage dual motor
compressor cascade cooling system to which the invention
is applied.
Fig. 3 is a schematic diagram of an electrical
control system applied to the Medium Temperature Fail
Safe Two Stage Cascade Cooling Apparatus forming part of
the present invention.
Fig. 4 is a schematic of a Two Stage dual motor
compressor second stage and single motor compressor first
stage cooling arrangement to which the invention is applied.
Referring now to figures 3 and 4 of the drawings,
one embodiment of the invention will be explained in
detail.
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I~'IG~
Indicat-ed hy reference numeral 4 is refrigerant
motor compressor of the first cooling staye. The high
pressure side of motor compressor 4 is connected to
conduit 9A. Conduit 9A is further connected to air cooled
condenser 10 which is provided with finned surface 11.
Conduit 12 which is the extension of air cooled condenser
10 is connected to a capillary tube restrictor 13 which
is connected to the inlet end of cascade condenser heat
exchanger tube 14 of the first stage with its outlet
connected to low pressure suction conduit 15 to enter
motor compressor 4.
Indicated by reference numeral 5 and 6 are
refrigerant motor compressors of the second cooling stage.
The high pressure side of motor compressor 5 is connected
by conduit 17 and the high pressure side of motor
compressor 6 is connected by conduit 17A. Conduit 17
and 17A are further connected in parallel at which point
they enter the inlet heat exchanger tube 18 of the second
stage. The outlet of heat exchanger tube 18 is connected
to conduit 19 which is further connected to capillary tube
restrictor 27 which is connected to the inlet of the
storage enclosure cooling coil evaporator 28 which connects
to suction conduit 29. Conduit 29 connects into parallel
low pressure conduit 23 to enter motor compressor 5 and
suction conduit 23A to enter motor compressor 6.
FIGURE 3 -
Figure 3 schematically shows the electricalconnection of the first stage motor compressor 4, the
second staye motor compressor 5 and 6, magnetic switching
relays 34, high pressure limit switch 100, magnetic
starter 33 and interval timer 35 which control the operation
of said two stage cascade cooling apparatus.
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~1] of these instrumentalities are, or may be of
standard construction. The uniqueness of the invention
resides in the dual motor compressor cooling arrangement
and in the means by which controlling operation is performed.
Under normal operating conditions (with the parts
in position shown in figure 3), current is flowing from
mains supply 92 through conductor 37 to terminal 97 through
switchblade 98, terminal 99 of high pressure limit switch
100 to terminal 56 of motor compressor 6 and through
extension conductor 37C to terminal 55 of motor compressor
5 of the second cooling stage. Current flowing in
conductor 37 further enters terminal 44 of motor compressor
4 of the first cooling stage. Current flowing in conductor
36 from mains supply 92 enters terminal 86 of interval
timer 35 with extension conductor 36A to enter terminal 61
through normally closed switchblade 76 to terminal 62 of
magnetic switching relay 34 with extension conductor 62A
to enter terminal 63 through closed switchblade 64 to
terminal 65 of magnetic starter 33 with extension conductor
51A to terminal 52 of motor compressor 6 of the second
cooling stage which is in operative state.
Current in conductor 36 further flows to terminal
40 of motor compressor 4 of the first cooling stage which
is in operative state. Further current from terminal 86
enters magnetic coil of timing motor 91 of interval timer
35 and into conductor 37 which rotates armature 90 with
pivoted arm 89 and switchblade 87 which is in open position
between terminals 86 and 88. Assuming now the storage
enclosure tempera-ture level is reached~ a thermostatic
controller (not shown) connected to terminal 85 and 84
of magnetic coil 83 releases armature 82 connected to
switchblade 73 and 64, thus braking contacts 74, 72 and 63,
65 of magnetic starter 33. This disconnects operative motor
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compressor G of the sccond cooling stagc for a differential
temperaturc level rise dcpendcnt on the thermostatic
contro]ler function. Motor compressor ~ of the first
cooling stage is thus in continuous operative state
producing cooling for the cascade condenser heat exchanger
of the second stage. In this way immediate liquid
refrigerant is made available for the second stage cooling
process when motor compressor 6 is again energi~ed and
contacts 63, 65 are closed by switchblade 64. Contact 74
and 72 are closed by switchblade 73 of magnetic starter 33
by a thermostatic controller (not shown), which energizes
magnetic coil 83 and actuates armature 82 to perform said
contact closure.
Assuming now a change to a second operative
condition after interval timer 35 switches into the next
timing interval, switchblade 87 closes to contact 88 to
allow current to flow to terminal 80 through magnetic
coil 79, then to terminal 81 of switching relay 34. This
pulls armature 78 with switchblade 76 from contact 62 to
contact 75 to disconnect motor compressor 6 and connect
motor compressor 5. Current will then flow through
extension conductor 74A to contact 74, switchblade 73,
contact 72 of magnetic starter 33, through conductor 53A
to terminal 54. This energi~es motor compressor 5 of
the second cooling stage.
Assume now a third operative condition when motor
compressor 5 fails through electrical or mechanical defects.
In this situation the second cooling stage becomes
inoperative and therefore no heat exchange is produced
for heat exchanger tube 18 of the second cooling stage.
Thus pressure will rise in conduit 17 and 17A of high
pressure side motor compressor 5, 6 and high pressure
limit switch 100. Switchblade 98 will then move from
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contact 97 to interrupt current f~ow from contact 99
through ext:ension conductor 37C to terminal 55 of motor
compressor 5. The cooling process of the second cooling
stage is thereby stopped and a temperature rise will
occur in the storage enclosure for one interval timing
period. During the next interval timing period, magnetie
eoil 79 is deenergized. This moves armature 78 with
switchblade 76 to contact 62. In this way, eurrent flow
is interrupted in extension conductor 74A to terminal 54
of failed motor compressor 5 which will be deenergized.
Current is then allowed to flow through extension conduit
51A to terminal 52 energizing motor compressor 6 to
provide immediate eooling for heat exehanger tube 18.
Pressure in eonduit 17A, 17 and high pressure limit switeh
100 is thus lowered to move switehblade 98 from open
position to eontaet 97. Current can now flow from
eontaet 99 to terminal 56, thus energizing motor eompressor
6 of the second eooling stage. Immediate eooling is then
produeed for the storage enelosure. Temperature will be
lowered to its present eontrolled temperature level until
the next interval timing period arrives.
During following interval timing periods, failed
motor eompressor 5 of the seeond eooling stage will be
energized whenever magnetie eoil 79 is aetivated. Aetiva-
tion pulls armature 78 with switehblade 76 to eontaet 75.
Current is thus allowed to flow to terminal 54 but no
eooling is produeed for the heat exehanger tube 18 of the
seeond eooling stage. This will again raise pressure in
eonduit 17 and 17A of the high pressure side of motor
eompressor 5, 6 and high pressure limit switeh 100.
Switehblade 98 will then have to move from contact 97 to
interrupt current flow to motor compressor 5, thereby
stopping the cooling process of the second cooling stage
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and therefore again causing temperature rise in the storage
enclosure for one interval timing period. While temperature
rise in the st:orage enclosure is limited by the interval
timer timing length, motor compressor failed condition can
be tolerated for periods of days and weeks during which
time corrective action to rep]ace the defective motor
compressor can be taken without spoilage of storage
enclosure contents, This feature is not available with
standard design single motor compressor two stage cascade
cooling apparatus.
A highly important advantage of the invention is
in the provision of a dual motor compressor arrangement
for the second stage cascade cooling apparatus. The
apparatus can operate continuously under unfavourable
environmental condition. The interval timer switches one
motor compressor on to produce maximum cooling efficiency
and the second motor compressor is off, During the off
times, internal heat is completely dissipated and original
oil lubricating efficiency is restored. Loss of lubricating
efficiency has been a handicap in the past where it has
been customary to use single motor compressors leading to a
high failure rate.
An embodiment of the invention using a three stage
cascade cooling apparatus will now be described in
conjunction with Figures 1 and 2.
FIGURE 2 -
Indicated by reference numeral 3 and 4 arerefrigerant motor compressors of the first cooling stage.
The high pressure side of motor compressor 3 is connected
by conduit 9 and the high pressure side of motor compressor
4 is connected by conduit 9A. Conduit 9 and 9A are further
connected in parallel at which point they enter the inlet
of air cooled condenser 10 which is provided with finned
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surface 1l. Conduit ~2 which is the extension of air
cooled condenser 10 is connected to a capillary tube
restrictor 13 which is connected to the inlet end of
cascade condenser heat exchanger tube 14 of the first
stage with its outlet connected to conduit 15, which
connects into parallel-connected low pressure suction
conduit 16 to enter motor compressor 3 and suction conduit
16A to enter motor compressor 4.
Indicated by reference numeral 5 and 6 are
refrigerant motor compressors of the second cooling stage.
The high pressure side of motor compressor 5 is connected
by conduit 17 and the high pressure side of motor
compressor 6 is connected by conduit 17A. Conduit 17 and
17A are further connected in parallel at which point they
enter the inlet heat exchanger tube 18 of the second stage.
The outlet of heat exchanger tube 18 is connected to
conduit 19 which is further connected to capillary tube
restrictor 20 which is connected to the inlet of cascade
condenser heat exchanger t~be 21 of the second stage with
its outlet connected to conduit 22 which connects into
parallel low pressure suction conduit 23 to enter motor
compressor 5 and suction conduit 23A to enter motor
compressor 6.
Indicated by reference numeral 7 and 8 are
refrigerant motor compressors of the third cooling stage.
The high pressure side of motor compressor 7 is connected
by conduit 24 and the high pressure side of motor compressor
8 is connected by conduit 24A. Conduit 24 and 24A are
further connected in parallel at which point thev enter
the inlet heat exchanqer tube 25 of the third stage.
~he outlet of heat exchanqer tube 25 is connected to-
conduit 26 which is further connected to capillary tube
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restKictor 27 which is connected to the inlet of the
storage enclosure coo]ing coil evaporator 28 which connects
to suction conduit 29. Conduit 29 connects into parallel
low pressure conduit 30 to enter motor compressor 7 and
suction 30A to enter motor compressor 8.
FIGU~E 1 -
Figure 1 schematically shows the electrical
connection of the first stage motor compressor 3 and 4,
the second stage motor compressor 5 and 6, the third
stage motor compressor 7 and 8, magnetic switehing relays
31, 32, 34, high pressure limited switeh 100 and 96,
magnetie starter 33 and interval timer 35 which control
the operation of said three stage caseade eooling apparatus.
All of these instrumentalities are, or may be of
standard construction. The uniqueness of the invention
resides in the dual motor compressor eooling arrangement
and in the means by whieh eontrolling operation is performed.
Under normal operating eonditions (with the parts
in position shown in figure 1), current is flowing from
mains supply 92 through conduetor 37 to terminal 93 of
high pressure limit switeh 96, through switehblade 94 in
elosed position to terminal 95 and to terminal 68 of motor
eompressor 8 and through extension eonduetor 37B to terminal
69 of Motor eompressor 7 of the third eooling stage.
Current flowing on eondueto-r 37 further enter terminal 97
through switchblade 98, terminal 99 of high pressure limit
switeh 100 to terminal 56 of motor eompressor 6 and through
extension conductor 37C to terminal 55 of motor compressor
5 of the second eooling stage. Current flowing in
conductor 37 further enters terminal 44 of motor compressor
4 and through extension conductor 37D to terminal 43-of
motor compressor 3 of the first cooling stage. Current
flowing in conductor 36 from mains supply 92 en-ters terminal
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86 of i.nterval timer 35 with extension conductor 36A to
enter termi.nal 61 through normal.ly closed switchblade 76
to terminal 62 of magnetic switching relay 34 wi.th extension
conductor 62A to enter terminal 63 through closed switch-
blade 64 to tern.inal 65 of magnetic starter 33 with extension
conductor 66 to terminal 67 of motor compressor 8 of the
third cooling stage which is in operative state.
Current in conductor 36 further flows to terminal
50 through closed switchblade 56 to terminal 51 of magnetic
switching relay 32 with extension conductor 51A to terminal
52 of motor compressor 6 of the second cooling stage which
is in operative state. Current in conductor 36 further
flows to terminal 38 through close switchblade 45 to
terminal 39 of magnetic switching relay 31 with extension
conductor 39A to enter terminal 40 of motor compressor 4
of the first cooling stage which is in operative state.
Further current from terminal 86 enters magnetic coil of
timlng motor 91 of interval timer 35 and into conductor 37
which rotates armature 90 with pivoted arm 89 and switch-
blade 87 which is in open position between terminals 86and 88. Assuming now the storage enclosure temperature
level is reached, a thermostatic controller (not shown)
connected to terminal 85 and 84 of magnetic coil 83
releases armature 82 connected to switchblade 73 and 64,
thus braking contacts 74, 72 and 63, 65 of magnetic
starter 33. This disconnects operative motor compressor
8 of the third cooling stage for a differential temperature
level rise dependent on the thermostatic controller function.
Motor compressor 6 of the second cooling stage and motor
compressor 4 of the first cooling stage are thus in
continuous operative state producing cooling for the
cascade condenser heat exchanger of the second and third
stages. In this way immediate liquid refrigerant is made
.
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available for t}le third stage cooling process when motor
compressor 8 is again energized and contacts 63 ~ 65 are
closed by switchb],ade 64~ Contacts 74 and 72 are closed
by switchblade 73 of magnetic starter 33 by a thermostatic
controller (not shown), which energizes maqnetic coil 83
and actuates armature 82 to perform said contact closure.
Assuming now a change to a second operative
condition after interval timer 35 switches into the next
timing interval, switchblade 87 closes to contact 88 to
allow current to flow to terminal 80 through magnetic
coil 79 ~ then to terminal 81 of switching relay 34 ~ This
pulls armature 78 with switchblade 76 from contact 62 to
contact 75 to disconnect motor compressor 8 and connect
motor compressor 7~ Current will then flow through extension
conductor 74A to contact 74 ~ switchblade 73 / contact 72
of magnetic starter 33 ~ through conductor 71 to terminal 70
This energizes motor compressor 7 of the third cooling stage~
Further, current in conductor 36B enters terminal 60 of
magnetic coil 58 ~ terminal 59 and conductor 37Ao This
energizes magnetic switching relay 32 pulling armature 57
with switchblade 56 from contact 51 to contact 53~ This
current is allowed to flow through conductor 53A to
terminal 54 to energize motor compressor 5 and disconnect
motor compressor 6 of the second cooling stage. Further,
current in conductor 36B enters terminal 48 of magnetic
coil 47 / terminal 49 and conductor 37A to energize magnetic
switching relay 31 pulling armature 46 with switchblade 45
from contact 39 to contact 41 to allow current flow through
conductor 4lA~ This energizes motor compressor 3 and
30 disconnect motor compressor 4 of the first cooling stage.
Assume now a third operative condition when motor
compressor 5 fails through electrical or mechanical defects.
In this situation the second cooling stage becomes
mg~ 14 ~
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inoperative and therefore no heat exchange is produced
for heat exchan~er tube 25 of the third cooling stage.
Thus pressure will rise in conduit 24 and 24A of high
pressure side motor compressor 7, 8 and high pressure
limit switch 96. Switchblade 94 will then move from
contact 93 to interrupt current flow from contact 95
through extension conductor 37B to terminal 69 of motor
compressor 7. The cooling process of the third cooling
stage is thereby stopped and a temperature rise will occur
in the storage enclosure for one interval timing period.
During the next interval timing period, magnetic coil 58
is deenergized. This moves armature 57 with switchblade
56 to contact 51. In this way, current flow is interrupted
in extension conductor 53A to terminal 54 of failed motor
compressor 5 which will be deenergized. Current is then
allowed to flow through extension conduit 51A to terminal
52 energizing motor compressor 6 to provide immediate
cooling for heat exchanger tube 25. Pressure in conduit
24A, 24 and high pressure limit switch 96 is thus lowered
to move switchblade 94 from open position to contact 93.
Current can now flow from contact 95 to terminal 68, thus
energizing motor compressor 8 of the third cooling stage.
Immediate cooling is then produced for the storage
enclosure. Temperature will be lowered to its present
controlled temperature level until the next interval
timing period arrives.
During following interval timing periods, failed
motor compressor 5 of the second cooling stage will be
energized whenever magnetic coil 58 is activatedO Activation
pulls armature 57 with switchblade 56 to contact 53. Current
is thus allowed to flow to -terminal 54 but no cooling is
produced for the heat exchanger tube 25 of the third cooling
stage. This will again raise pressure in conduit 24 and
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2~A of the high prcssure side of motor compressor 7, 8
and higll pressllre limit switch 96. Switchblade 9~ will
then havc to move from contiact 93 to interrupt current
flow to motor compressor 7, thereby stopping the cooling
process of the third cooling stage and therefore again
causing temperature rise in the storage enclosure for
one interval timing period. While temperature rise in
the storage enclosure is limited by the interval timer
timing length, motor compressor failed condition can be
tolerated for periods of days and weeks during which time
corrective action to replace the defective motor compressor
can be taken without spoilage of storage enclosure contents.
This feature is not available with standard design single
motor compressor three stage cascade cooling apparatus.
A highly important advantage of the invention is
in the provision of a dual motor compressor arrangement
for each stage of a three stage cascade cooling apparatus.
The apparatus can operate continuously under unfavorable
environmental condition. The interval timer switches one
motor compressor on to produce maximum cooling efficiency
and the second motor compressor is off. During the off
times, internal heat is completely dissipated and original
oil lubricating efficiency is restored. Loss of lubricating
efficiency has been a handicap in the past where it has
been customary to use single motor compressors. Consequently
a high rate of failure was evident for the purpose set forth.
As the invention is subject to minor changes that
are within the skill of ordinary mechanics, the invention
is not limited to the extent of the disclosure, but is
only limited to the extent of the appended claim.
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