U.S. patent number 3,744,264 [Application Number 05/238,811] was granted by the patent office on 1973-07-10 for refrigeration apparatus and method of operating for powered and non-powered cooling modes.
This patent grant is currently assigned to The Trane Company. Invention is credited to Chester D. Ware.
United States Patent |
3,744,264 |
Ware |
July 10, 1973 |
REFRIGERATION APPARATUS AND METHOD OF OPERATING FOR POWERED AND
NON-POWERED COOLING MODES
Abstract
This specification discloses the method and apparatus for
operating a refrigeration system in both powered and nonpowered
(free cooling) modes of operation including the method and
apparatus for rapidly converting from one mode to the other.
Inventors: |
Ware; Chester D. (La Crosse,
WI) |
Assignee: |
The Trane Company (La Crosse,
WI)
|
Family
ID: |
22899412 |
Appl.
No.: |
05/238,811 |
Filed: |
March 28, 1972 |
Current U.S.
Class: |
62/115; 62/119;
62/174; 62/149; 62/498 |
Current CPC
Class: |
F25B
25/00 (20130101); F24F 5/001 (20130101); Y02B
30/542 (20130101); F25B 2400/0401 (20130101); Y02B
30/54 (20130101) |
Current International
Class: |
F24F
5/00 (20060101); F25B 25/00 (20060101); F25b
001/00 () |
Field of
Search: |
;62/115,119,149,174,498 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: O'Dea; William F.
Assistant Examiner: Ferguson; Peter D.
Claims
I claim:
1. A method of operating a refrigeration system including a
compressor, a condenser, and a shell-and-tube type evaporator
arranged respectively in a closed refrigerant circuit and having a
liquid refrigerant storage chamber comprising the steps of:
A. operating said refrigeration system on a free cooling mode
by,
1. bypassing refrigerant vapor from said evaporator around said
compressor to said condenser without operating said compressor,
2. returning refrigerant thereby condensed from said condenser to
said evaporator for re-evaporation in said evaporator, and
3. retaining an additional quantity of liquid refrigerant in said
evaporator sufficient to immerse substantially all the tubes in
said evaporator;
B. passing from the free cooling mode of operation to the powered
mode of operation by,
1. energizing said compressor,
2. passing compressed refrigerant vapor through said compressor to
said condenser, and
3. removing from said closed refrigerant circuit a quantity of
condensed refrigerant equal to said additional quantity by passing
substantially said quantity of condensed refrigerant into said
storage chamber to thereby reduce the equivalent quiescent level of
refrigerant in said evaporator substantially below the upper tubes
of said evaporator to a substantially reduced level during
operation of said compressor;
C. continuing to operate said system by,
1. continuing energization of said compressor, and
2. continuing to withhold from said closed refrigerant circuit in
said storage chamber during continued energization of said
compressor substantially said additional quantity of
refrigerant.
2. The method as defined by claim 1 wherein the step B3 includes
the step of passing said quantity of condensed refrigerant out of
said closed refrigerant circuit by applying thereto a differential
in pressure within said refrigerant circuit generated by said
compressor.
3. The method as defined by claim 2 for operating a refrigeration
system having an economizer wherein said quantity of condensed
refrigerant is forced from said refrigerant circuit at
substantially condenser pressure and simultaneously vented to a
portion of said refrigerant circuit at substantially economizer
pressure.
4. The method as defined by claim 2 wherein said quantity of
condensed refrigerant is forced from said refrigerant circuit at
substantially condenser pressure and simultaneously vented to a
portion of said refrigerant circuit at substantially evaporator
pressure.
5. The method as defined by claim 2 for operating a refrigeration
system having an economizer wherein said quantity of condensed
refrigerant is forced from said refrigerant circuit at
substantially econimizer pressure and simultaneously vented to a
portion of said refrigerant circuit at substantially evaporator
pressure.
6. A method of operating a refrigeration system including a
compressor, a condenser, and a shell-and-tube type evaporator
arranged respectively in a closed refrigerant circuit and a storage
chamber outside said closed refrigerant circuit for storing above
the tubes of said evaporator during operation of said compressor an
additional quantity of liquid refrigerant sufficient to immerse
substantially all of the tubes in said evaporator when said system
is operated on a free cooling mode without operation of said
compressor comprising the steps of:
A. preparing said system for operation on a free cooling mode
by:
1. venting vapor from said refrigerant circuit to said storage
chamber,
2. passing by force of gravity the additional liquid refrigerant
from said storage chamber into said evaporator to immerse
substantially all of the tubes therein, and
3. providing said refrigeration system with a vapor bypass from
said evaporator around said compressor to said condenser;
B. subsequently operating said refrigeration system on a free
cooling mode by,
1. bypassing refrigerant vapor from said evaporator around said
compressor to said condenser without operating said compressor,
2. returning refrigerant thereby condensed from said condenser to
said evaporator for re-evaporation in said evaporator, and
3. retaining the additional quantity of refrigerant in said
evaporator sufficient to immerse substantially all of the tubes in
said evaporator.
7. The method of operating a refrigeration system as defined in
claim 6 further including the steps of:
A. passing from the free cooling mode of operation to the powered
mode of operation by,
1. energizing said compressor,
2. passing compressed refrigerant vapor through said compressor to
said condenser, and
3. removing from said closed refrigerant circuit a quantity of
condensed refrigerant equal to said additional quantity by passing
substantially said quantity of condensed refrigerant into said
storage chamber to thereby reduce the equivalent quiescent level of
refrigerant in said evaporator substantially below the upper tubes
of said evaporator to a substantially reduced level during
operation of said compressor;
B. continuing to operate said system by,
1. continuing energization of said compressor, and
2. continuing to withhold from said closed refrigerant circuit in
said storage chamber during continued energization of said
compressor substantially said additional quantity of
refrigerant.
8. Refrigerant apparatus comprising a shell-and-tube type
refrigerant evaporator; a refrigerant compressor and a refrigerant
condenser serially connected in a closed refrigerant circuit; said
refrigerant compressor having a suction inlet connected to the
shell side of said evaporator and a discharge outlet connected to
said condenser; said circuit including first conduit means for
conveying liquid refrigerant from said condenser to said evaporator
during operation of said compressor; and means for controlling the
flow of liquid refrigerant in said first conduit means; second
conduit means extending from the shell of said evaporator to said
condenser bypassing said compressor for conveying refrigerant vapor
from said evaporator to said condenser; a shutoff valve disposed in
said second conduit means; a storage chamber outside said closed
refrigerant circuit disposed to store liquid refrigerant above the
uppermost tubes of said evaporator; a third conduit means
connecting said storage chamber and said evaporator for conveying
liquid refrigerant from said storage chamber to said evaporator in
preparation for operation of said refrigeration apparatus without
operation of said compressor; and means for holding liquid
refrigerant in said storage chamber during operation of said
compressor.
9. The apparatus as defined by claim 8 including fourth conduit
means for conveying liquid refrigerant from said condenser to said
storage chamber.
10. The apparatus as defined by claim 9 including a refrigerant
vapor vent passageway extending from the upper portion of said
storage chamber to that portion of said circuit at substantially
evaporator pressure.
11. The apparatus as defined by claim 9 wherein said first conduit
means includes an economizer chamber and further including a vapor
vent passageway extending from the upper portion of said storage
chamber to that portion of said circuit at substantially economizer
chamber pressure.
12. The apparatus as defined by claim 8 wherein said first conduit
means includes an economizer chamber and further including a fourth
conduit means for conveying liquid refrigerant from a portion of
said circuit at substantially economizer chamber pressure to said
storage chamber.
13. The apparatus as defined by claim 12 including a refrigerant
vapor vent passageway extending from the upper portion of said
storage chamber to that portion of said circuit at substantially
evaporator pressure.
Description
BACKGROUND OF THE INVENTION
During certain seasons when the cooling load is relatively small
such as less than 40 percent peak load and if the heat sink is
sufficiently cool, it is possible to operate compressor type
refrigeration systems, such as for cooling a building, without
energizing the compressor. Refrigerant vapor is simply conveyed
without compression to a condenser which is maintained at a lower
temperature than the evaporator. The condensed refrigerant flows
back to the evaporator to again be re-evaporated by the heat from
the building conveyed thereto such as by the building chilled water
system. The mode of operation is conducted without operation of the
compressor, hence its name "free cooling."
In order that the free cooling mode can be operated with a high
degree of capacity, it has been found necessary to provide a bypass
around the compressor to permit vapor from the evaporator to pass
without much restriction to the condenser and to provide a bypass
around liquid flow control devices to permit free flow of liquid
from the condenser to the evaporator. Further it has been found
necessary to provide special means of more fully wetting the tubes
in the evaporator with refrigerant to increase the evaporator
capacity. This is so because refrigeration systems are ordinarily
charged with a minimum of refrigerant sufficient only to wet all of
the evaporator tubes during full load conditions. Because of the
violent boiling of the refrigerant under these conditions and the
presence of flash gas entering the evaporator, the equivalent
quiescent refrigerant level is ordinarily maintained substantially
below the top of the tube bundle in the evaporator. For purposes of
this disclosure "equivalent quiescent level" is intended to mean
the level of refrigerant in the evaporator if suddenly all boiling
were to cease without any further ingress or egress of refrigerant
to or from the evaporator.
Thus when first attempts were made to operate ordinary
refrigeration systems in a free cooling mode, it was found that the
evaporator capacity was excessively low due to the lack of
refrigerant liquid on the middle and upper rows of tubes.
Several schemes to remedy this problem have been suggested. One
scheme that utilizes a refrigerant liquid pump to spray refrigerant
liquid over the evaporator tubes is described in U.S. Pat. No.
2,718,766.
Another scheme adds refrigerant from the free cooling mode to
immerse all of the tubes of the evaporator and is illustrated in
U.S. Pat. No. 3,191,396. In this latter patent a special chamber is
provided for storing the additional refrigerant. This chamber is
located below the upper most tubes of the evaporator and is filled
with refrigerant liquid from the evaporator by venting the special
chamber with the evaporator until substantially a common level is
reached in the evaporator and special chamber. Only after this
level is reached are the chamber liquid line and vent valves closed
and the compressor allowed to start for a powered mode of
operation. Thus considerable time may be consumed to pass from a
free cooling mode to a powered mode of operation.
Likewise considerable time may be consumed to prepare the system
for free cooling. A small heater is provided in the special chamber
to heat the refrigerant. Only after the refrigerant has reached a
certain pressure would refrigerant be forced to higher levels in
the evaporator.
SUMMARY OF THE INVENTION
This invention is distinct from the aforementioned prior art as it
does not utilize the time consuming means of pressurizing the
refrigerant to obtain transfer of the added refrigerant to the
evaporator. Furthermore means are provided for resuming normal
operation of the compressor immediately upon switching from a free
cooling mode of operation to the powered mode of operation.
The first of these distinctive features is accomplished by allowing
a predetermined additional liquid refrigerant to flow by gravity to
the evaporator without the necessity of pressurizing any liquid
refrigerant.
The second mentioned of these distinctive features is accomplished
by utilizing the compressor under power to transfer refrigerant
from the evaporator to an area where it may be retained out of the
evaporator zone.
This invention thus provides a method of operating a refrigeration
system which may be converted from a free cooling mode to a powered
mode of operation and vice versa without undue delay between the
modes of operation.
More specifically this invention provides a method of operating a
refrigeration system including a compressor, a condenser, and a
shell-and-tube type evaporator arranged respectively in a closed
refrigerant circuit and a storage chamber outside said closed
refrigerant circuit for storing above the tubes of said evaporator
during operation of said compressor an additional quantity of
liquid refrigerant sufficient to immerse substantially all of the
tubes in said evaporator when said system is operated on a free
cooling mode without operation of said compressor comprising the
steps of: preparing said system for operation on a free cooling
mode by: venting vapor from said refrigerant circuit to said
storage chamber, passing by force of gravity the additional liquid
refrigerant from said storage chamber into said evaporator to
immerse substantially all of the tubes therein, and providing said
refrigeration system with a vapor bypass from said evaporator
around said compressor to said condenser; subsequently operating
said refrigeration system on a free cooling mode by, bypassing
refrigerant vapor from said evaporator around said compressor to
said condenser without operating said compressor, returning
refrigerant thereby condensed from said condenser to said
evaporator for re-evaporation in said evaporator, and retaining the
additional quantity of refrigerant in said evaporator sufficient to
immerse substantially all of the tubes in said evaporator; passing
from the free cooling mode of operation to the powered mode of
operation by, energizing said compressor, passing compressed
refrigerant vapor through said compressor to said condenser, and
removing from said closed refrigerant circuit a quantity of
condensed refrigerant equal to said additional quantity by passing
substantially said quantity of condensed refrigerant into said
storage chamber to thereby reduce the equivalent quiescent level of
refrigerant in said evaporator substantially below the upper tubes
of said evaporator to a substantially reduced level during
operation of said compressor; continuing to operate said system by,
continuing energization of said compressor, continuing to withhold
from said closed refrigerant circuit in said storage chamber during
continued energization of said compressor substantially said
additional quantity of refrigerant. Further, this invention
provides refrigerant apparatus comprising a shell-and-tube type
refrigerant evaporator; a refrigerant compressor and a refrigerant
condenser serially connected in a closed refrigerant circuit; said
refrigerant compressor having a suction inlet connected to the
shell side of said evaporator and a discharge outlet connected to
said condenser; said circuit including first conduit means for
conveying liquid refrigerant from said condenser to said evaporator
during operation of said compressor; and means for controlling the
flow of liquid refrigerant in said conduit means; second conduit
means extending from the shell of said evaporator to said condenser
bypassing said compressor for conveying refrigerant vapor from said
evaporator to said condenser; a shut off valve disposed in said
conduit means; a storage chamber disposed to store liquid
refrigerant above the uppermost tubes of said evaporator; a second
conduit means connecting said storage chamber and said evaporator
for conveying liquid refrigerant from said storage chamber to said
evaporator in preparation for operation of said refrigeration
apparatus without operation of said compressor; and a shut off
valve disposed in said second conduit means for holding liquid
refrigerant in said storage chamber during operation of said
compressor.
Other aspects and advantages will be apparent as the specification
proceeds to describe the invention in detail with reference to the
drawings in which like reference characters are used to designate
like elements through wherein:
FIG. 1 is a semi-schematic of a refrigeration machine constructed
and adapted to perform the method of operating a refrigeration
system in accordance with the methods of this invention,
FIG. 2 is a simplified schematic electric diagram for the machine
shown in FIG. 1, and
FIG. 3 is a modification of the schematic of FIG. 2 whereby the
operating modes may be made completely automatic.
FIG. 4 is a modification of the refrigeration machine shown in FIG.
1.
FIG. 5 is another modification of the refrigeration machine shown
in FIG. 1.
Now with reference to the refrigeration machine shown in FIG. 1 it
will be seen that the refrigeration system 10 includes a
refrigerant evaporator 12, a refrigerant compressor 14, and a
refrigerant condenser 16. The evaporator 12 is of the flooded
shell-and-tube type having a bundle of horizontal tubes 18 through
the interior of which water warmed by a load, such as a building,
is conducted via inlet and outlet header connections 20 and 22
respectively to boil refrigerant within the evaporator shell. The
refrigerant vapor is conducted to the compressor 14 via an inlet
conduit 24. The compressor 14 shown is intended to designate a two
stage compressor although aspects of the instant invention are
equally applicable to single stage compressor refrigeration
systems. The inlets of one or both stages are provided with inlet
vanes for controllably throttling the flow of refrigerant to the
compressor. It is common practice to control such inlet vanes in
response to the temperature of water leaving the evaporator for the
building such as near outlet 22. As the water temperature rises,
the vanes are opened to thereby load the compressor. Such inlet
vanes 26 have been placed in the inlet conduit 24 for purposes of
illustration, it being understood that such vanes are generally
located with the confines of the compressor shell per se. The
compressor input shaft is connected to a drive motor which may be
an electric motor, steam turbine or other form of prime mover 28.
If electric, motor 28 could also be confined within the compressor
shell to thereby make the compressor hermetic.
The vapor discharged from the compressor is conducted via
compressor outlet conduit 30 to the condenser 16 which may be also
of the shell-and-tube type wherein cooling water such as from a
cooling tower is passed through the tubes via cooling water inlet
and outlet header connections 32 and 34 respectively.
Refrigerant condensed at the outer surface of the tubes flows
during the powered mode of operation from the condenser shell
downwardly through a stand pipe 36 through a first flow control
device 38 which may take the form of a fixed orifice flow control
valve, such as 38 described in U.S. Pat. No. 3,260,067 assigned to
the assignee of this invention, or the form of a more conventional
variable orifice float valve. The refrigerant then passes from the
valve 38 through a conduit 40 to an economizer flash chamber 42.
The flash gas from the economizer 42 is conducted via conduit 44 to
inlet of the second stage of compressor 14 for recompression. The
liquid refrigerant from the economizer is conducted to a second
stand pipe 46 which leads to a second flow control device 48, which
may be similar to flow control device 38, from whence the
refrigerant is conducted via conduit 50 to be distributed into the
evaporator shell. The operation and advantages of an economizer are
well known and for the sake of brevity will not be further
discussed here.
For purposes of carrying out the preferred embodiment of the
instant invention, a chamber 52 is located above evaporator 12.
Chamber 52 is used as a means for storing a predetermined
additional amount of liquid refrigerant and thus preventing this
additional quantity of refrigerant from returning to the evaporator
when the system is operated in the powered mode. A conduit 56
connects the bottom of stand pipe 36 to the bottom of chamber 52.
Thus during the powered mode of operation, some liquid passing in
stand pipe 36 will also pass through conduit 56 into chamber 52. So
that the chamber 52 may be substantially filled with refrigerant
liquid, it is provided with a vapor vent 58 which extends between
the upper portion of chamber 52 via restriction or orifice 60 to
conduit 40. When chamber 52 is filled with refrigerant liquid,
orifice 60 operates to limit the flow of liquid through chamber 52.
Flow control device 38 is sized to compensate for the flow through
orifice 60.
The elevation of chamber 52 above the evaporator is limited only by
the pressure differential between its liquid supply and return
vent. It will also be evident that the chamber 52 may be vented to
evaporator pressure through a vent 58a and orifice 60a shown in
FIGS. 4 and 5 in which case the liquid supply may be either from
the condenser as shown in FIG. 4 or from the economizer zone as
shown in FIG. 5 by line 56a. It is thus the pressure differential
within the system when operated on the power mode that causes
chamber 52 to be filled with liquid refrigerant.
For purposes of carrying out the free cooling mode of operation in
accordance with the methods of this invention, the bottom of stand
pipe 36 is connected via an automatically powered normally closed
shutoff valve 62 and conduit 57 to conduit 50. Furthermore there is
provided a compressor valve bypass conduit 66 extending between
upper portions of the shells of condenser 16 and evaporator 12
adjacent ends thereof remote from the heretofore mentioned conduits
24 and 30. Conduit 66 is also provided with an automatically
powered normally closed shutoff valve 64.
The method of operating the above described refrigeration system
may best be understood by referring further to the schematic
diagram of FIG. 2. For purposes of this description let it be
assumed that the system had previously been operating with power
and that chamber 52 accordingly is substantially full of liquid
refrigerant and that the quiescent level of liquid refrigerant in
the evaporator is correspondingly reduced by the predetermined
quantity of refrigerant retained in chamber 52. Further let it be
assumed that conditions are such that the free cooling mode of
operation is preferred, i.e. the load is less than about 40% of
full load and that the temperature of cooling water entering
condenser 16 at 32 is sufficiently below the desired temperature
for the water leaving evaporator 12 at outlet 22.
The system is set into the free cooling mode of operation simply by
moving switch 68 into the solid line position to complete a circuit
from line 1 to line 2 including switch 68, the actuator of valve 62
and the actuator of valve 64 whereby valves 62 and 64 are powered
to the fully open positions. A second circuit is also completed
which includes switch 68, normally closed contact 69, and actuator
control 72 for inlet vanes 26.
The opening of valve 62 in FIGS. 1 and 4 permits substantially all
the liquid refrigerant retained in chamber 52 to be immediately
dumped into the evaporator 12 thereby raising the liquid
refrigerant therein to a high level 78 to immerse substantially all
the tubes of the evaporator. If sufficient time has lapsed from the
end of the power mode, the liquid refrigerant will have already
drained to the evaporator via conduit 56a in FIG. 5 and conduit 40,
economizer 42 in FIGS. 1 and 4, stand pipe 46, orifice 48 and
conduit 50. The opening of valve 64 permits refrigerant vapor to
ass freely from evaporator 12 to condenser 16 whereupon it is
condensed and returned via stand pipe 36, valve 62, conduit 57, and
conduit 50 to evaporator 12. A secondary path for passage of
refrigerant vapor from condenser 12 to evaporator 16 also is
provided by conduit 24, compressor 14 and conduit 30. It should be
reiterated that during this mode of operation compressor 14 is not
operated, however the compressor does not block the free flow of
refrigerant therethrough. Upon the aforementioned energization of
actuator 72, vanes 26 are actuated from a preset minimum opening to
the fully open position.
Should the load exceed the capacity of the system as operated on
the free cooling mode, switch 68 may be instantaneously placed in
the dot-dash line position of FIG. 2 whereby valves 62, 64 are
immediately closed and vanes 26 returned to a minimum opening
position. Furthermore a first circuit is immediately energized
including switch 68, and contactor coil 80 whereupon contacts 82
are immediately closed to energize a second circuit including
switch 68, contacts 82 and compressor motor 28. A third circuit is
established including switch 68, rheostat 84, contacts 85, and vane
actuator 72 whereby vanes 26 are immediately moved to a second
preselected minimum position at which excessive quantities of
liquid refrigerant will not be drawn into the compressor inlet
despite the high level of refrigerant in the evaporator. This
minimum may be manually adjusted at rheostat 84. A fourth circuit
is also established including switch 68 and coil 86 of snap-acting
time delay relay 88.
Time delay relay 88 includes contacts 69 and 85 (previously
mentioned) and contacts 90. The relay has two positions; a first
position in which contacts 69 and 85 are closed and contacts 90
open; and a second position in which contacts 69 and 85 are open
and contacts 90 closed. The relay is intended to be snap-acting,
i.e. movement from one position to the other position is
substantially instantaneous. However, the movement from the first
position to the second position is not effected immediately upon
energization of coil 86 as this movement is delayed for a
predetermined time by action of single way dash pot 92. The time
delay selected is the time that it takes to insure that the level
of refrigerant in the evaporator has fallen to that at which no
danger of excessive liquid refrigerant carryover into the
compressor will take place. After this period of time contacts 85
are opened and contacts 90 closed thereby placing the control of
the vanes upon bellows 74 whose sensor bulb 76 is located in outlet
22 to be responsive to the load. It should be appreciated that
coils 80, 86, 62 and 64 are selected to have sufficiently high
impedance whereby they have no substantial effect upon other
parallel circuits.
Now considering the system operation upon moving switch 68 from the
free cooling mode to the powered mode, the following events happen.
Valves 62 and 64 are immediately closed. The compressor is
immediately started. The vanes 26 immediately and temporarily
assume a minimum open position whereby refrigerant gas is withdrawn
from the evaporator, compressed and delivered to the condenser. The
rate is limited to prevent liquid carryover. The condensed
refrigerant passes down stand pipe 36 to chamber 52 (FIGS. 1 and
4). Some of the refrigerant passes through flow control 38 into
flash chamber 42, the gaseous portion being returned to the second
stage of the compressor and the liquid portion being delivered to
the evaporator via flow control 48 for re-evaporation and to
chamber 52 in FIG. 5 via conduit 56a. The pressure at the liquid
supply line for chamber 52 permits chamber 52 to be substantially
filled as the top of the chamber is vented through orifice 60 (60a
in FIG. 4 and 60b in FIG. 5). Because this quantity of refrigerant
retained in chamber 52 is not permitted to return to the evaporator
during the powered mode, the equivalent quiescent refrigerant level
in the evaporator is reduced to a lower level designated at 94.
After sufficient time has lapsed by action of dash-pot 92 to insure
that the lower level has been reached so that no excessive liquid
carryover to the compressor will take place, relay 88 is switched
thereby placing vanes 26 at the control of load sensor 76. If at
any time during the powered mode it is desired to switch to the
free cooling mode, it is only necessary to place switch 68 in the
solid line position and the free cooling mode aforedescribed will
be resumed.
Thus it will be seen that the method of operation permits the
refrigeration system to be switched from the free cooling mode to
the powered mode or vice versa with only a single movement of
switch 68. The reduction of evaporator refrigerant level is
extremely fast as this is done with the assistance of the energized
compressor. The returning of the additional refrigerant to the
evaporator upon switching to the free cooling mode is also
extremely fast as the additional refrigerant is literally dumped
into the evaporator upon opening of valve 62.
Because of this extremely rapid response, it is possible to
completely automate the operative modes simply by automating switch
68. Thus in the modification shown in FIG. 3 switch 68a is an
automatic version of switch 68 and is moved to the power mode
position (dash-dot line) by energization of solenoid actuator 95
and to the free cooling position (solid line) by de-energization of
actuator 95. Solenoid 95 is disposed in series with parallel
switches 96 and 98. Switch 96 is actuated by a bellows and bulb
sensor to close at a predetermined high temperature and is arranged
to sense condenser inlet water temperature as at 32. Switch 98 is
actuated by a bellows and bulb sensor to close at a predetermined
high temperature and is arranged to sense evaporator outlet water
temperature as at 22. Thus if either the condenser temperature is
too high for free cooling as indicated by closure of switch 96 or
the refrigeration load too great for free cooling as indicated by
closure of switch 98, switch 68a will be positioned for the power
mode. Only when the condenser water is sufficiently cool and the
refrigeration load sufficiently light to permit free cooling will
switch 68a be placed in the free cooling position.
It should be appreciated that the controls shown have been greatly
simplified to clearly illustrate the invention. Obviously many
variations can be made both to these controls and the apparatus
without departing from the true spirit of the invention. I
accordingly desire my invention to be limited only by the
claims.
* * * * *