Ulllted States Patent [19]
`Sibik
`
`US006085532A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,085,532
`Jul. 11, 2000
`
`[54] CHILLER CAPACITY CONTROL WITH
`
`5,553,997
`
`9/1996 Goshaw et al. .................. .. 62/228.4 X
`
`VARIABLE CHILLEI) WATER FLOW
`
`5,561,599 10/1996 Lu . . . . . . . . . . . . . . . . . . . . . .
`
`. . . .. 364/164
`
`COMPENSATION
`
`_
`-
`-
`-
`[75] Inventor‘ Lee L‘ Slblk’ Onalaska’ WIS‘
`
`[73] Assignee: American Standard Inc., PiscataWay,
`N.J.
`
`21 A l. N .: 09 244 786
`[
`1
`pp
`0
`/
`’
`[22]
`Filed:
`Feb. 5, 1999
`
`5,600,960
`
`2/1997 Schwedler et al. .
`
`62/99
`
`5,632,154
`
`5/1997 Sibik et al. . . . . . . . . .
`
`. . . .. 62/99
`
`5,669,225
`5,946,926
`
`9/1997 Beaverson et al. ..................... .. 62/201
`9/1999 Hartman .................................. .. 62/201
`
`OTHER PUBLICATIONS
`
`“Why Must Chillers Be Constant FloW Devices?”, Jan
`.—Feb. 1980 vol. 9 No. 1 Trane Engineer’s Newsletter.
`’
`’
`’
`’
`“Don’t Ignore Variable FloW”, by James P. Waltz, Jul. 1997,
`Contracting Business.
`
`Int. Cl.7 .................................................... .. F25D 17/00
`[51]
`[52] US. Cl. ............................... .. 62/179; 62/177; 62/180;
`62/201; 62/203; 62/228_4
`[58] Field Of Search ............................ .. 62/177, 179, 180,
`62/181, 185, 201, 228.4, 209, 203, 204
`
`Primary Examiner—Henry Bennett
`Assistant Examiner—Chen-Wen Jiang
`Attorney, Agent, or Firm—William J. Beres; William
`O’Driscoll; Peter D- Ferguson
`[57]
`ABSTRACT
`
`[56]
`
`References Cited
`U S PATENT DOCUMENTS
`'
`'
`1/1973 Porter ...................................... .. 165/62
`3,710,852
`5/1981 RZeChula --
`---- -- 62/141
`4,269,034
`6/1981 APdreS
`62/201 X
`472747264
`472837152 1g1984 B_1t°nd° """ "
`62/210 X
`g’z?ggg
`igl?igesfer
`62/é4
`5’347’821
`9/1994 oltman ct
`Q01
`5:355j691 10/1994 Sullivan et
`62/295
`5,396,782
`3/1995 Ley et al. .... ..
`5,419,146
`5/1995 Sibik et a1. ............................. .. 62/115
`
`"" "
`'
`
`A method of controlling chiller capacity in a chiller system.
`The method comprises the steps of: measuring entering the
`?uid temperature of a ?uid entering a heat exchanger;
`measuring the ?uid temperature of the ?uid leaving the heat
`exchanger; determining a desired leaving ?uid temperature;
`establishing chiller capacity as a function of the difference
`betWeen leaving ?uid temperature and the desired leaving
`?uid temperature; and adjusting the determined chiller
`capacity as a function of the difference betWeen entering
`?uid temperature and the desired leaving ?uid temperature.
`
`14 Claims, 4 Drawing Sheets
`
`64
`
`16
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`44
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`PAGE 1 of 9
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`PETITIONER'S EXHIBIT 1224
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`U.S. Patent
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`Jul. 11,2000
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`Sheet 1 of4
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`6,085,532
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`54
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`82
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`5O 52
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`44~
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`74
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`42 L
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`T
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`k
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`78
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`24
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`FIG.
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`PAGE 2 of 9
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`PETITIONER'S EXHIBIT 1224
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`PAGE 3 of 9
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`PETITIONER'S EXHIBIT 1224
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`U.S. Patent
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`Jul. 11,2000
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`Sheet 3 of4
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`6,085,532
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`86 84
`?zz
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`‘
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`21s
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`Q5
`32
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`2|
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`44
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`FIG. 4
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`I00
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`FIG. 3
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`I02
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`PETITIONER'S EXHIBIT 1224
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`PAGE 5 of 9
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`PETITIONER'S EXHIBIT 1224
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`1
`CHILLER CAPACITY CONTROL WITH
`VARIABLE CHILLED WATER FLOW
`COMPENSATION
`
`BACKGROUND OF THE INVENTION
`
`The present invention is directed to chillers providing a
`chilled ?uid such as Water for use in air conditioning,
`refrigeration and the like. More particularly, the present
`invention is directed to the control of a variable ?oW chilled
`Water system and represents an improvement in chiller
`capacity control.
`A chiller is a device providing a chilled ?uid. For many
`years it Was considered necessary that chillers be constant
`?oW devices. Articles such as “Why Must Chillers be
`Constant FloW Devices?”, the Trane Engineering
`NeWsletter, Volume 9, Number 1, January—February 1980
`cite reliable heat transfer from a temperature control and
`instability in the control system as reasons supporting the
`premise that chillers must be constant ?oW devices.
`In recent years this has changed and variable ?oW chilled
`Water systems have begun to be implemented. An article
`“Don’t Ignore Variable FloW” by James P. WaltZ Was pub
`lished in the July 1997 issue of Contracting Business (pages
`133—144) discussing basic variable ?oW chilled Water sys
`tems. On the ?nal page of the article, the author recogniZes
`the ongoing problems in controlling variable ?oW chilled
`Water systems. Problems are cited regarding minimum ?oW
`control, incorrect speed control, and insufficient cooling or
`?oW capacity.
`Many of these problems result from a chiller system
`Which cannot compensate for simultaneous changes in the
`capacity of one or more chillers and in the ?oW rate of the
`chilled Water being provided to the air handlers.
`
`SUMMARY OF THE INVENTION
`
`It is an object, feature and advantage of the present
`invention to solve the problems of the prior art systems.
`It is an object, feature and advantage of the present
`invention to provide a variable ?oW chilled Water system
`With controls that compensate for changes in chiller capacity
`and chilled Water ?oW rate simultaneously.
`It is an object, feature and advantage of the present
`invention to provide a controlled method for a chiller
`capacity control Which automatically adjusts chiller capacity
`control to reject disturbances caused by variable ?oWs in
`chilled Water While maintaining control stability at loW
`Water ?oW rates
`It is a further object, feature and advantage of the present
`invention to accomplish this While adjusting chiller capacity
`to compensate for changes in the load.
`It is an object, feature and advantage of the present
`invention to predict load changes and adjust the chiller
`capacity before the leaving Water temperature of the chiller
`is affected by load changes and to adjust the chiller capacity
`before the leaving Water temperature of the chiller is
`affected.
`It is an object, feature and advantage of the present
`invention to improve chiller e?iciency as Water ?oW rates
`are reduced.
`The present invention provides a method of controlling
`chiller capacity in a chiller system. The method comprises
`the steps of: measuring entering the ?uid temperature of a
`?uid entering a heat exchanger; measuring the ?uid tem
`perature of the ?uid leaving the heat exchanger; determining
`a desired leaving ?uid temperature; establishing chiller
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`capacity as a function of the difference betWeen leaving ?uid
`temperature and the desired leaving ?uid temperature; and
`adjusting the determined chiller capacity as a function of the
`difference betWeen entering ?uid temperature and the
`desired leaving ?uid temperature.
`The present invention also provides a chiller system
`including a chilled ?uid loop Where the temperature of the
`?uid is controlled by varying the capacity of a chiller. The
`system comprises a variable capacity chiller including an
`evaporator; a chilled ?uid loop in heat transfer relation With
`the evaporator; a sensor measuring the leaving ?uid tem
`perature of the evaporator; and a sensor measuring the
`entering ?uid temperature of the evaporator. The chiller
`system also comprises a mechanism for providing a desired
`leaving ?uid temperature; a pump controlling the rate of
`?uid ?oW in the ?uid loop; and a controller operably
`controlling the chiller capacity in response to changes in the
`variable ?oW rate of the pump. The controller is connected
`to the setpoint mechanism and the entering and leaving ?uid
`temperature sensors. The controller includes a feedback loop
`controlling chiller capacity in response to leaving ?uid
`temperature and a feed forWard loop controlling chiller
`capacity in response to entering ?uid temperature.
`The present invention further provides a method of con
`trolling chiller capacity and chilled Water ?oW rate in the
`chiller system. The method comprises the steps of: deter
`mining a leaving Water temperature of chiller Water leaving
`an evaporator; determining an entering Water temperature of
`chilled Water entering the evaporator; controlling the speed
`of a variable ?oW pump as a function of the leaving Water
`temperature; controlling the capacity of a chiller system,
`operably connected to the evaporator and providing a heat
`sink, as a function of the entering Water temperature and as
`a function of the leaving Water temperature.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a diagram of an air conditioning system includ
`ing a chiller and a cooling toWer in accordance With the
`present invention.
`FIG. 2 is a diagram of an air conditioning system shoWing
`the parallel piping arrangements for multiple cooling toWers
`and multiple chillers in accordance With FIG. 1.
`FIG. 3 is a diagram of an alternative pump arrangement
`to the arrangements of FIGS. 1 and 2.
`FIG. 4 is a diagram of an absorption refrigeration system
`suitable for use With the present invention.
`FIG. 5 is a control diagram shoWing the present invention.
`
`DETAILED DESCRIPTION OF THE DRAWING
`
`FIG. 1 shoWs an air conditioning system 10 Which
`includes an air side loop 12, a ?rst Water transport loop 14,
`a refrigeration loop 16, and a second Water transport loop 18.
`As indicated, the loops 14 and 18 use Water as a transport
`?uid since Water is safe, fairly e?icient and non-?ammable.
`Other transport ?uids are commercially available, and a
`person of ordinary skill in the art Will recogniZe that the
`transport ?uids need not be the same in each loop 14, 18.
`Representative air conditioning systems 10 are sold by
`The Trane Company. These systems include centrifugal
`chiller compressor systems and related equipment sold by
`The Trane Company under the trademark CenTraVac and
`include Trane Models CVHE, CVHF and CVHG.
`Additionally, The Trane Company sells helirotor chiller
`compressor systems under the trademark Series R including
`Models RTHA and RTHB. Scroll chiller compressor sys
`
`PAGE 6 of 9
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`PETITIONER'S EXHIBIT 1224
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`6,085,532
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`tems are sold by The Trane Company under the trademark
`3D including Model CGWD. Arepresentative chiller system
`is described in US. Pat. No. 5,600,960 to SchWedler et al.
`Which is commonly assigned and hereby incorporated by
`reference. Representative helirotor systems are described in
`US. Pat. No. 5,347,821 to Oltman et al. and US. Pat. No.
`5,201,648 to LakoWske, both of Which are assigned to the
`assignee of the present invention and incorporated by ref
`erence herein. Additionally, chiller systems can use non
`mechanical refrigeration compressors such as one or tWo
`stage absorption machines to chill the Water used by the ?rst
`Water loop 14. Such systems are sold by The Trane Company
`under the trademarks Thermachill, HoriZon, and Cold
`Generator, or under the Model Numbers ABSC or ABTE. A
`representative absorption apparatus is described in US. Pat.
`No. 3,710,852 to Porter, this patent being assigned to the
`assignee of the present invention and incorporated by ref
`erence herein. The Trane Company also sells suitable air
`handlers under the trademarks Climate Changer and Modu
`lar Climate Changer. An exemplary air handler is described
`in US. Pat. No. 5,396,782 to Ley et al., this patent being
`assigned to the assignee of the present invention and incor
`porated by reference herein.
`In the air side loop 12, a load such as a space 20 to be air
`conditioned is cooled by an air handler 22. The air handler
`22 can also be used for heating but is described in terms of
`a single application, cooling, for ease of explanation. The air
`handler 22 uses the ?uid transported by the ?rst Water loop
`14 to transfer heat energy from air being circulated from the
`space 20 by means of a fan 26 and ductWork 28 to a heat
`exchange coil 24 in the air handler 22.
`The transport ?uid in the ?rst Water loop 14 is circulated
`by a pump 30 betWeen the air handler 22 and the evaporator
`32 of the refrigeration system 16. The pump 30 is capable of
`varying the How rate in the loop 14 and is preferably a
`variable speed pump such as those made by the Buffalo
`Pump Company, but could alternatively be replaced With a
`multistage pump. After leaving the pump 30, the evaporator
`32 conditions the transport ?uid to a predetermined tem
`perature such as 44° F. so that the ?uid can be reused and
`transported by piping 34 to any one of various air handlers
`22 (See FIG. 2). The energy extracted from the transport
`?uid by the evaporator 32 is transported by refrigeration
`conduit 36 to a compressor 38 Which loWers the condensa
`tion point of the refrigerant so that the refrigerant can be
`condensed by a condenser 40 effectively transferring energy
`to the second Water loop 18. A metering device 42 such as
`an expansion valve or an ori?ce maintains the pressure
`differential betWeen the evaporator 32 and the condenser 40.
`The heat of condensation in the condenser 40 is trans
`ferred to the second Water loop 18 Where that heat is
`transported by conduit 44 and a Water pump 46 to at least
`one cooling toWer 50. Suitable cooling toWers are sold by
`Marley Cooling ToWer Company under the identi?ers Series
`10, Series 15 and Sigma 160. The cooling toWer 50 includes
`heat exchange surfaces 52 to transfer heat from the second
`Water loop 18 to ambient air, and includes condenser fans 54
`Which move ambient air over the heat exchange surfaces 52.
`A cooling toWer controller 60 controls the speed and
`staging of the cooling toWer condenser fans so as to maintain
`a near optimal cooling toWer condenser Water temperature as
`monitored by a sensor 62 and reported to the controller 60
`by a connecting line 64. The sensor 62 can be located in the
`conduit 44 or in a sump or basin of the cooling toWer 50.
`Similarly, a chiller controller 70 determines Whether a chiller
`is on and controls the chiller operation by a connecting line
`72 to the compressor 38 and by a connecting line 74 to the
`
`55
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`60
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`65
`
`4
`expansion valve 42. A suitable chiller controller is sold by
`The Trane Company under the trademark UCPII. Other
`suitable chiller controllers are described in US. Pat. No.
`5,355,691 to Sullivan et al. and US. Pat. No. 5,419,146 to
`Sibik et al., these patents being assigned to the assignee of
`the present invention and incorporated by reference herein.
`Although described herein as a single device, the controller
`70 can be implemented as a number of discrete devices, such
`as microprocessors, Working together.
`Sensors 76 and 78 are provided to monitor the leaving
`Water temperature and the entering Water temperature of the
`evaporator 32 respectively. Electrical lines 79 are provided
`to connect those sensors 76 and 78 to the controller 70. The
`difference (Delta T) betWeen the leaving Water temperature
`as measured by the sensor 76 and the entering Water tem
`perature as measured by the sensor 78 provides a measure of
`the actual load on any given chiller, particularly When the
`How rate in the ?rst Water loop, as measured by a sensor 81
`measuring the pressure drop across the evaporator, is also
`knoWn. Thus actual load is a function of Delta T (AT) and
`the How rate.
`Although there are a number of Ways to accomplish the
`controls, applicant prefers the use of a system controller 90
`overseeing and managing the individual controllers 60, 70 of
`each equipment group 50, 16. Such a controller 90 is sold by
`The Trane Company under the trademark Tracer. As shoWn
`in FIG. 2, each cooling toWer 50 has an individual controller
`60, and each chiller 16 has an individual controller 70. The
`system controller 90 is operably connected to each cooling
`toWer controller 60 and to each chiller controller 70 so as to
`integrate their operation. The system controller 90 is also
`operably connected to the pump(s) 46 and controls the
`variable ?oW rate of the pump(s) 46. Additionally, the
`system controller 90 can be arranged to receive the input
`signals from the condenser Water temperature sensor 62, the
`Wet bulb temperature sensor 80, the How rate sensor 82 and
`the steam rate sensor 86 and process and forWard the input
`signals to the controllers 60,70. For this reason, the system
`controller 90 includes a conventional microprocessor for
`undertaking the calculations described With respect to FIG.
`4 and for forWarding the cooling toWer setpoint to the
`cooling toWer controllers 60 and for forWarding other infor
`mation to the controller 60, 70 such as the inputs from the
`sensors.
`With reference to FIG. 2, the terms chiller, cooling toWer
`and air handler are used both in the singular and plural sense
`throughout this document. For example, FIG. 2 shoWs a
`plurality of chillers 16 piped in parallel (shoWn) or in series
`(not shoWn) to provide the cooling Water to the ?rst Water
`loop 14 by means of its conduit 34. The Water is provided to
`a plurality of air handlers 22 also piped in parallel. Similarly,
`the cooling toWers 50 are piped in parallel in the second
`Water loop 18 and connected in parallel With the condensers
`40 of the various chillers. Thus the chiller controllers 70 and
`the cooling Water toWer controllers 50 can turn on chillers 16
`as needed to meet the air handler load by maintaining a
`particular temperature in the ?rst Water loop 14. Similarly,
`the cooling toWer controllers 60 can turn on cooling toWers
`50, stage fans 54, or vary the fan speed of the fans 54 in
`those cooling toWers 50 to maintain a particular Water
`temperature in the second Water loop 18.
`In FIG. 2, a separate variable speed Water pump 98 for
`each air handler 22 replaces the single variable speed Water
`pump 30 of FIG. 1. Referencing FIG. 3, the pump 30 is
`represented by several pumps 100, 102 in parallel circuited
`arrangement. This alloWs more discrete control by having
`several pumps With narroWer operating ranges as opposed to
`the single larger pump shoWn in FIG. 1.
`
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`6,085,532
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`5
`FIG. 1 is shown as a mechanical refrigeration system. As
`shown in FIG. 4, an absorber 202, generator 204, pump 206
`and recuperative heat exchanger 208 replace the compressor
`38 in an absorption refrigeration system. Like mechanical
`refrigeration, the cycle “begins” When high-pressure liquid
`refrigerant from the condenser 40 passes through a metering
`device 42 into the loWer-pressure evaporator 32, and collects
`in the evaporator pan or sump 210. The “?ashing” that
`occurs at the entrance 212 to the evaporator cools the
`remaining liquid refrigerant Which is then sprayed over a
`coil 216 using a spray tree 218. Similarly, the transfer of heat
`from the comparatively Warm system Water 34 to the noW
`cool refrigerant causes the refrigerant to evaporate, and the
`resulting refrigerant vapor migrates to a loWer-pressure
`absorber 202. There, the refrigerant is “soaked up” by an
`absorbent lithium-bromide solution. This process not only
`creates a loW-pressure area that draWs a continuous How of
`refrigerant vapor from the evaporator 32 to the absorber 202,
`but also causes the vapor to condense as the vapor releases
`the heat of vaporiZation picked up in the evaporator 32 to
`cooling Water in the conduit 44. This heat—along With the
`heat of dilution produced as the refrigerant condensate
`mixes With the absorbent—is transferred to the cooling
`Water in the conduit 44 and released in the cooling toWer 50.
`Assimilating refrigerant dilutes the lithium-bromide solu
`tion and reduces its affinity for refrigerant vapor. To sustain
`the refrigeration cycle, the solution must be reconcentrated.
`This is accomplished by constantly pumping dilute solution
`from the absorber 202 through the pump 206 to the generator
`204, Where the addition of heat from a heat source 214 such
`as steam boils the refrigerant from the absorbent. Once the
`refrigerant is removed, the reconcentrated lithium-bromide
`solution returns to the absorber, ready to resume the absorp
`tion process. The refrigerant vapor “liberated” in the gen
`erator 204 migrates to the condenser 40. In the condenser 40,
`the refrigerant returns to its liquid state as the cooling Water
`in the conduit 44 picks up the heat of vaporiZation carried by
`the vapor and transfers it to the cooling toWer 50. The liquid
`refrigerant’s return to the metering device 42 marks the
`cycle’s completion. Further details of absorption systems
`can be derived from the previously referenced US. Pat. No.
`3,710,852 to Porter.
`The operation of the present invention is discussed With
`regard to FIG. 5. FIG. 5 is a control diagram 300 of the
`present invention. A person of ordinary skill in the art Will
`recogniZe that the control diagram can be implemented in
`hardWare, softWare, or ?rmWare, and is preferably imple
`mented Within the controller 70.
`The controller 70 uses a combination of feed forWard and
`feedback control to control chiller capacity. The controller
`70 includes a conventional PID controller 320 Which is part
`of a feedback control system 322. The controller 70 also
`includes a feed forWard control system 324 Which operates
`in parallel With the feedback control system 322. Avariable
`?oW section 325 is common both to the feedback control
`system 322 and to the feed forWard control system 324. The
`controller 70 varies the chiller cooling capacity in response
`to the system error. Preferably, the chiller cooling capacity
`is controlled as a function of the leaving Water temperature,
`but the chiller cooling capacity may also be controlled as a
`function of the entering Water temperature or as a function
`of the difference betWeen the entering Water temperature and
`the desired leaving Water temperature (AT). The preferable
`control mechanism is to compare the leaving Water tem
`perature With a desired temperature conventionally entered
`by a user in the form of a setpoint, and to control the chiller
`capacity to minimiZe that error.
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`The feedback control system 322 and the feed forWard
`control system 324 each make independent control deter
`minations. The control determinations of the feedback con
`trol system 322 and the feed forWard control system 324 are
`then combined in a comparitor 326 and used in a chiller
`capacity control portion 330 of the controller 70 to deter
`mine chiller capacity.
`In the control diagram 300, a line 302 represents the
`evaporator Water temperature including the entering Water
`temperature at 304 as measured by the sensor 78 and the
`leaving Water temperature at 306 as measured by the sensor
`76. Aleaving Water temperature setpoint is entered by a line
`308. At step 310, the evaporator entering Water temperature
`from line 304 is compared to the leaving Water temperature
`setpoint from line 308 to determine a desired AT.
`In the feedback control system 322, the evaporator leav
`ing Water temperature is returned on line 332 and compared
`by a comparitor 334 With the leaving Water temperature
`setpoint from line 308 to determine an error. The resultant
`error is forWarded on line 336 to the feedback controller 322.
`At a feedback gain adjuster 338, the variable ?oW control
`section 325 is used to improve the feedback control 322.
`Since a large reduction in chilled Water How can cause
`control instabilities in the feedback loop, the gain must be
`adjusted to compensate.
`For example, typical chilled Water How is 2.4 gallons per
`minute for every ton of designed chiller capacity. This
`corresponds to a temperature difference in chilled Water
`entering and leaving Water temperatures of 10° F. At nomi
`nal Water ?oW rates, a 1° error in leaving Water temperature
`is 10% of chiller capacity. If How is reduced to 1.2 gallons
`per minute per ton, or in half, then a 1° error in leaving Water
`temperature should only be 5% of chiller capacity. If the
`feedback gains are not adjusted, the effective gains can be
`doubled and, as How is further decreased, the effective gain
`Will continue to increase and can cause instability in the
`feedback controller.
`For further example, using data obtained in the test of a
`500 ton chiller tuned to operate at a nominal Water ?oW rate
`of 2.4 gallons per minute per ton, the How is reduced to 0.6
`gallons per minute per ton. The feedback gain essentially
`increased by a factor of 4 times nominal. In the feedback
`gain adjuster 338, a feedback correction in chiller capacity
`Q6 is calculated. Q6 is determined by the folloWing formula.
`
`Where
`Q6 equals the feedback correction in chiller capacity in
`percent;
`e equals the error in chiller capacity as determined by the
`chilled Water supply temperature minus the chilled
`Water setpoint; and
`dV equals the chilled Water How in gallons per minute per
`ton.
`The feedback correction Q6 is then forWarded by line 340
`to the PID controller 320, recogniZing that any single input,
`single output controller or equivalent could be used in place
`of the PID controller. The PID controller 320 calculates a
`desired chiller capacity and forWards it by line 342 as an
`output.
`At the same time this is going on, the feed forWard
`controller 324 is making major changes in chiller capacity to
`cancel out measured load disturbances. The feed forWard
`
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`6,085,532
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`control 324 changes chiller capacity to match measured
`changes in the load applied to the chilled Water loop 14. The
`feed forWard controller 324 calculates a desired chiller
`capacity QC using the following formula.
`
`dV
`QC : — -Desired AT- 100%
`24
`
`Where
`Qc equals the desired chiller capacity in percent;
`desired AT equals the chilled Water return temperature
`minus the chilled Water setpoint in degrees Fahrenheit;
`and
`dV equals the chilled Water ?oW in gallons per minute per
`ton.
`In the formulas for calculating Q6, and QC, measured ?oW
`is divided by the chiller’s design capacity to obtain dV in
`gallons per minute per ton to make the application of the
`comparable ?oW easier. This makes the application of the
`variable ?oW calculation identical for every chiller siZe. In
`a variable ?oW chilled Water system, dV is not constant. The
`feed forWard control cancels out both load disturbances and
`?oW rate disturbances.
`In FIG. 5, the desired AT is calculated at 310 by a
`comparison of the entering Water temperature provided by
`the line 304 With the leaving Water temperature setpoint
`provided by line 308. This desired AT is forWarded on a line
`346 to the feed forWard controller 324. The variable ?oW
`calculation of QC is made in a block 348 and QC is forWarded
`by a line 350 to a block 352 for a calculation of the
`concentrated chiller capacity. This is output on a line 354
`and combined With the desired chiller capacity determined
`by the feedback controller 320 at comparitor 326. The
`accumulated desired capacity is forWarded on a line 356 to
`the chiller capacity control 330 Which is generally conven
`tional in nature. In the capacity control 330, gain is com
`pensated at step 360 and the compensated signal is for
`Warded by line 362 for a determination of chiller capacity at
`step 364 and the chillers are controlled.
`What has been described is an improvement in chiller
`capacity control. Speci?cally, the present invention
`describes a control method that, given a measurement of
`chilled Water ?oW, Will automatically adjust capacity control
`to reject disturbances caused by variable ?oW chilled Water
`and to maintain control stability at loW Water ?oW rates. The
`variable ?oW control is an adjustment of the feedback
`control loop and a feed forWard control loop. For capacity
`control, the feedback loop is required to achieve Zero steady
`state error While the feed forWard loop alloWs the control to
`reject the disturbance caused by the variable ?oW chilled
`Water. Aperson of ordinary skill in the art Will recogniZe that
`the present invention is applicable to any chiller of ?uids
`particularly including Water but also applicable to all other
`?uids used for air conditioning.
`What is desired to be secured for Letters Patent of the
`United States is set forth in the folloWing claims:
`1. A method of controlling chiller capacity in a chiller
`system comprising the steps of:
`measuring entering the ?uid temperature of a ?uid enter
`ing a heat exchanger;
`measuring the ?uid temperature of the ?uid leaving the
`heat exchanger;
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`8
`determining a desired leaving ?uid temperature;
`establishing chiller capacity as a function of the difference
`betWeen leaving ?uid temperature and the desired
`leaving ?uid temperature; and
`adjusting the determined chiller capacity as a function of
`the difference betWeen entering ?uid temperature and
`the desired leaving ?uid temperature.
`2. The method of claim 1 including the further steps of
`measuring the rate of ?uid ?oW through the heat exchanger
`and scaling the difference betWeen the entering ?uid tem
`perature and the desired leaving ?uid temperature as a
`function of the measured ?uid ?oW.
`3. The method of claim 2 Wherein the ?uid is Water and
`the heat exchanger is an evaporator.
`4. The method of claim 3 Wherein the Water ?oWs in a
`Water loop and including the further step of varying the ?oW
`rate of the Water in the Water loop.
`5. The method of claim 4 including the further step of
`measuring the ?oW rate of Water in the Water loop and
`adjusting a gain associated With a feedback control to
`compensate for changes in the Water loop ?oW rate.
`6. The method of claim 1 Wherein the adjusting step
`predicts load changes and adjusts the chiller capacity before
`the leaving ?uid temperature is affected.
`7. The method of claim 1 including the further step of
`determining a ?oW rate of the ?uid.
`8. The method of claim 7 Wherein the establishing step
`includes the further step of modifying the established chiller
`capacity as a function of the determined ?oW rate.
`9. A method of controlling chiller capacity and chilled
`Water ?oW rate in the chiller system including an evaporator,
`the method comprising the steps of:
`determining a leaving Water temperature of chiller Water
`leaving the evaporator;
`determining an entering Water temperature of chilled
`Water entering the evaporator;
`controlling the speed of a variable ?oW pump as a
`function of the entering Water temperature;
`controlling the capacity of a chiller system, as a function
`of the entering Water temperature and as a function of
`the leaving Water temperature.
`10. The method of claim 9 Wherein the chiller capacity
`controlling step includes using a feed forWard algorithm to
`detect major system disturbances.
`11. The method of claim 10 including using a feedback
`control algorithm in controlling chiller capacity.
`12. The method of claim 11 Wherein the feed forWard
`algorithm adjusts chiller capacity as a function of the ?oW
`pump speed.
`13. The method of claim 12 Wherein the ?oW pump speed
`is determined by a comparison of entering Water temperature
`and desired leaving Water temperature.
`14. The method of claim 13 Wherein the feedback control
`algorithm determines chiller capacity as a function of the
`difference betWeen the leaving Water temperature and the
`desired leaving Water temperature.
`
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`PAGE 9 of 9
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`PETITIONER'S EXHIBIT 1224