U.S. patent application number 13/806424 was filed with the patent office on 2013-04-25 for chiller control apparatus.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. The applicant listed for this patent is Minoru Matsuo, Satoshi Nikaido, Kenji Ueda. Invention is credited to Minoru Matsuo, Satoshi Nikaido, Kenji Ueda.
Application Number | 20130098084 13/806424 |
Document ID | / |
Family ID | 45559413 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098084 |
Kind Code |
A1 |
Matsuo; Minoru ; et
al. |
April 25, 2013 |
CHILLER CONTROL APPARATUS
Abstract
A chiller control apparatus increases or decreases chillers in
order to efficiently operate an entire chiller system. When the
number of chillers increases, an insufficient load value
calculation unit calculates an insufficient amount of a load for a
required load. Then, using a COP obtained according to an operating
environment of the chiller, a chiller-to-be-operated selection unit
selects, from among stopped chillers, a chiller having the highest
COP when operated with an insufficient amount of a load, as the
chiller to be subjected to stage increase. Further, when the number
of chillers decreases, an operation pattern extraction unit
extracts operation patterns that are combinations of chillers to be
operated according to the required load. Then, a
chiller-to-be-stopped selection unit obtains a COP of the entire
chiller system for each operation pattern, using the COP obtained
according to the operating environment of the chiller, and selects
a chiller subjected to stage decrease based on the operation
pattern corresponding to the highest COP.
Inventors: |
Matsuo; Minoru; (Tokyo,
JP) ; Ueda; Kenji; (Tokyo, JP) ; Nikaido;
Satoshi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Matsuo; Minoru
Ueda; Kenji
Nikaido; Satoshi |
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP |
|
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
45559413 |
Appl. No.: |
13/806424 |
Filed: |
July 28, 2011 |
PCT Filed: |
July 28, 2011 |
PCT NO: |
PCT/JP2011/067266 |
371 Date: |
December 21, 2012 |
Current U.S.
Class: |
62/129 |
Current CPC
Class: |
F25B 2600/2515 20130101;
F25B 2339/047 20130101; F25B 25/005 20130101; F25B 2400/13
20130101; Y02B 30/741 20130101; F25B 2700/21161 20130101; F25B
49/00 20130101; F25B 2341/0662 20130101; F25B 41/043 20130101; F25B
1/053 20130101; F25B 2700/21171 20130101; F25B 1/10 20130101; F25B
2600/021 20130101; F25B 40/02 20130101; F25B 2400/0411 20130101;
F25B 2600/0251 20130101; F25B 2600/2501 20130101; Y02B 30/70
20130101; F25B 2400/06 20130101 |
Class at
Publication: |
62/129 |
International
Class: |
F25B 49/00 20060101
F25B049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2010 |
JP |
2010-177749 |
Claims
1. A chiller control apparatus for controlling a plurality of
chillers and supplying cold or heat, the chiller control apparatus
comprising: a chiller selection unit configured to select the
chiller to be operated from among the plurality of chillers
according to a required load; and an operation command unit
configured to output an operation signal corresponding to the
required load, to the chiller selected by the chiller selection
unit, wherein the chiller selection unit comprises: a
number-of-chillers change determination unit configured to
determine based on the required load whether to change the number
of currently selected chillers; and a chiller determination unit
configured to determine a chiller whose operation state is to be
changed, based on a relationship between a load of each chiller and
an efficiency index value acquired in advance and on the required
load when the number of chillers is changed based on a result of
determination by the number-of-chillers change determination
unit.
2. The chiller control apparatus according to claim 1, wherein the
chiller determination unit comprises: an insufficient load value
calculation unit configured to obtain an insufficient load value
for each currently operating chiller by subtracting the required
load from an optimal-load-range high value sum that is a sum of
optimal-load-range high values, each of the optimal-load-range high
values being set for each chiller as a threshold value of a load at
a high load side that is an allowed efficiency range, in a case
that the number-of-chillers change determination unit determines to
increase the number of chillers; and a chiller-to-be-operated
selection unit configured to obtain, for each of chillers that are
currently stopped, an efficiency index value when the chiller is
operated with the insufficient load value, based on the
insufficient load value obtained by the insufficient load value
calculation unit and the relationship between the load and the
efficiency index value, and select a chiller indicating the highest
efficiency index value as a chiller to be operated.
3. The chiller control apparatus according to claim 1, wherein the
chiller determination unit comprises: a stage increase operation
pattern extraction unit configured to obtain all chiller operation
patterns of combinations of chillers selected from currently
stopped chillers and currently operating chillers, in a case that
the number-of-chillers change determination unit determines to
change the number of chillers; and a chiller-to-be-operated
selection unit configured to obtain efficiency index values for all
the chiller operation patterns obtained by the stage increase
operation pattern extraction unit and select a chiller
corresponding to the chiller operation pattern making the
efficiency index value highest, as a chiller to be operated.
4. The chiller control apparatus according to claim 2, wherein, in
a case that there are a plurality of selectable chillers, the
chiller-to-be-operated selection unit is configured to acquire an
operation time of the corresponding chiller and selects a chiller
having the shortest operation time.
5. The chiller control apparatus according to claim 1, wherein the
chiller determination unit comprises: a stage decrease operation
pattern extraction unit configured to obtain all chiller operation
patterns of combinations of chillers whose operation is kept by
stopping one chiller of the currently operating chillers in a case
that the number-of-chillers change determination unit determines to
decrease the number of chillers; and a chiller-to-be-stopped
selection unit configured to obtain an entire efficiency index
value for all the chiller operation patterns obtained by the stage
decrease operation pattern extraction unit, and select a chiller
corresponding to the chiller operation pattern making the
efficiency index value highest, as a chiller to be stopped.
6. The chiller control apparatus according to claim 1, wherein the
chiller determination unit comprises: an excess load value
calculation unit configured to obtain an excess load value for each
currently operating chiller by subtracting from the required load,
an optimal-load-range low value sum obtained by summing
optimal-load-range low values, each of the optimal-load-range low
values being set for each chiller as a threshold value of a load at
a low load side that is an allowed efficiency range, in a case that
the number-of-chillers change determination unit determines to
decrease the number of chillers; and a chiller-to-be-stopped
selection unit configured to obtain, for each of currently
operating chillers, an efficiency index value when the chiller is
operated with the excess load value, based on the excess load value
obtained by the excess load value calculation unit and the
relationship between the load and the efficiency index value, and
select a chiller indicating the lowest efficiency index value as a
chiller to be stopped.
7. The chiller control apparatus according to claim 5, wherein in a
case that there are a plurality of selectable chillers, the
chiller-to-be-stopped selection unit is configured to acquire an
operation time of the corresponding chiller and select a chiller
having the longest operation time.
Description
TECHNICAL FIELD
[0001] The present invention relates to a chiller control apparatus
that performs control of chillers in a chiller system including a
plurality of chillers.
[0002] Priority is claimed on Japanese Patent Application No.
2010-177749, filed Aug. 6, 2010, the content of which is
incorporated herein by reference.
BACKGROUND ART
[0003] Generally, chillers have different efficiency (a generated
cold amount with respect to consumed energy) depending on a load.
For this reason, in order to efficiently operate a chiller, it is
necessary to recognize the efficiency of the chiller and control
the chiller so as to operate with an appropriate load.
[0004] In view of this, Patent Document 1 discloses technology for
calculating an optimal operation range (an efficiently operable
range) of a chiller, and technology for determining whether to
change the number of operating chillers based on the calculated
optimal operation range.
CITATION LIST
Patent Document
[0005] [Patent Document 1] Japanese Patent Application Laid-Open
Publication No. 2009-204262
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0006] However, Patent Document 1 does not disclose a method of
optimizing efficiency of an entire chiller system. Accordingly,
with the technology disclosed in Patent Document 1, operation
conditions of individual chillers can be evaluated for
optimization, but optimal control of the entire chiller system
cannot be immediately performed.
[0007] Regarding a chiller system including chillers having
different characteristics, such as a chiller system including
multiple types of chillers, the efficiency of the entire chiller
system differs depending on operating chillers. For this reason, it
is necessary to appropriately select a chiller to be operated
depending on conditions. For example, regarding a variable-speed
chiller (a chiller with a compressor that can be variable-speed
controlled), a load enabling efficient operation differs depending
on a cooling water temperature, thereby requiring flexible judgment
depending on the cooling water temperature.
[0008] The present invention has been made in view of the
circumstances described above. An object of the present invention
is to provide a chiller control apparatus capable of appropriately
selecting a chiller to be subjected to stage increase or stage
decrease depending on conditions in order to efficiently operate an
entire chiller system.
Means for Solving the Problems
[0009] The present invention has been made to solve the above
problems. A chiller control apparatus according to one aspect of
the present invention is a chiller control apparatus for
controlling a plurality of chillers and supplying cold or heat, the
chiller control apparatus including: a chiller selection unit
configured to select the chiller to be operated from among the
plurality of chillers according to a required load; and an
operation command unit configured to output an operation signal
corresponding to the required load, to the chiller selected by the
chiller selection unit. The chiller selection unit includes: a
number-of-chillers change determination unit configured to
determine based on the required load whether to change the number
of currently selected chillers; and a chiller determination unit
configured to determine a chiller whose operation state is to be
changed, based on a relationship between a load of each chiller and
an efficiency index value acquired in advance and on the required
load when the number of chillers is changed based on a
determination result of the number-of-chillers change determination
unit.
[0010] Further, regarding the chiller control apparatus, the
chiller determination unit may include an insufficient load value
calculation unit configured to obtain an insufficient load value
for each currently operating chiller by subtracting the required
load from an optimal-load-range high value sum that is a sum of
optimal-load-range high values, each of the optimal-load-range high
values being set for each chiller as a threshold value of a load at
a high load side that is an allowed efficiency range, in a case
that the number-of-chillers change determination unit determines to
increase the number of chillers; and a chiller-to-be-operated
selection unit configured to obtain, for each of chillers that are
currently stopped, an efficiency index value when the chiller is
operated with the insufficient load value, based on the
insufficient load value obtained by the insufficient load value
calculation unit and the relationship between the load and the
efficiency index value, and select a chiller indicating the highest
efficiency index value as a chiller to be operated.
[0011] Further, regarding the chiller control apparatus, the
chiller determination unit may include a stage increase operation
pattern extraction unit configured to obtain all chiller operation
patterns of combinations of chillers selected from currently
stopped chillers and currently operating chillers, in a case that
the number-of-chillers change determination unit determines to
increase the number of chillers; and a chiller-to-be-operated
selection unit configured to obtain efficiency index values for all
the chiller operation patterns obtained by the stage increase
operation pattern extraction unit and select a chiller
corresponding to the chiller operation pattern making the
efficiency index value highest, as a chiller to be operated.
[0012] Further, regarding the chiller control apparatus, in a case
that there are a plurality of selectable chillers, the
chiller-to-be-operated selection unit may be configured to acquire
an operation time of the corresponding chiller and select a chiller
having the shortest operation time.
[0013] Further, regarding the chiller control apparatus, the
chiller determination unit may include: a stage decrease operation
pattern extraction unit configured to obtain all chiller operation
patterns of combinations of chillers whose operation is kept by
stopping one chiller of the currently operating chillers, in a case
that the number-of-chillers change determination unit determines to
decrease the number of chillers; and a chiller-to-be-stopped
selection unit configured to obtain an entire efficiency index
value for all the chiller operation patterns obtained by the stage
decrease operation pattern extraction unit, and select a chiller
corresponding to the chiller operation pattern making the
efficiency index value highest, as a chiller to be stopped.
[0014] Further, regarding the chiller control apparatus, the
chiller determination unit may include an excess load value
calculation unit configured to obtain an excess load value for each
currently operating chiller by subtracting from the required load,
an optimal-load-range low value sum obtained by summing
optimal-load-range low values, each of the optimal-load-range low
values being set for each chiller as a threshold value of a load at
a low load side that is an allowed efficiency range, in a case that
the number-of-chillers change determination unit determines to
decrease the number of chillers; and a chiller-to-be-stopped
selection unit configured to obtain, for each of currently
operating chillers, an efficiency index value when the chiller is
operated with the excess load value, based on the excess load value
obtained by the excess load value calculation unit and the
relationship between the load and the efficiency index value, and
select a chiller indicating the lowest efficiency index value as a
chiller to be stopped.
[0015] Further, regarding the chiller control apparatus, when there
are a plurality of selectable chillers, the chiller-to-be-stopped
selection unit may be configured to acquire an operation time of
the corresponding chiller and select the chiller having the longest
operation time.
Effects of the Invention
[0016] According to the present invention, the chiller control
apparatus can appropriately select a chiller to be subjected to
stage increase or stage decrease depending on conditions in order
to efficiently operate the entire chiller system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a configuration diagram illustrating a schematic
configuration of a chiller system 1 according to an embodiment of
the present invention.
[0018] FIG. 2 is a configuration diagram illustrating a schematic
configuration of a chiller 21-1 according to the embodiment.
[0019] FIG. 3 is a configuration diagram illustrating a schematic
configuration of a chiller control apparatus 100 according to the
embodiment.
[0020] FIG. 4 is a flowchart illustrating a procedure of a process
for the chiller control apparatus 100 to select a chiller whose
operation state is to be changed according to the embodiment.
[0021] FIG. 5 is a configuration diagram illustrating a schematic
configuration of the chiller control apparatus 100 including an
excess load value calculation unit 132 according to the
embodiment.
[0022] FIG. 6 is a flowchart illustrating a procedure of a process
for the chiller control apparatus 100 to determine whether a
required flow amount is satisfied, in addition to whether a
required load is satisfied according to the embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] Hereinafter, embodiments of the present invention will be
described with reference to drawings. Hereinafter, a case in which
a chiller system 1 supplies cold is explained. The present
invention may be applied similarly to a case in which the chiller
system 1 supplies heat.
[0024] FIG. 1 is a configuration diagram illustrating a schematic
configuration of the chiller system 1 according to an embodiment of
the present invention. In FIG. 1, the chiller system 1 includes: n
chillers 21-1 to 21-n (n is a positive integer); chilled water
pumps 31-1 to 31-n; a bypass valve 41; and a chiller control
apparatus 100. Further, the chiller system 1 is connected to an
external load 51.
[0025] The chillers 21-1 to 21-n cool chilled water and supply the
chilled water to the external load 51. Accordingly, the external
load 51 is cooled by the chilled water from the chiller 21.
[0026] The chilled water pumps 31-1 to 31-n send the chilled water
to the respective chillers. The bypass valve 41 bypasses the
chilled water from the chillers 21-1 to 21-n. The chiller control
apparatus 100 controls each unit. Particularly, the chiller control
apparatus 100 determines a timing to switch the number of operating
chillers among the chillers 21-1 to 21-n, determines a chiller
whose operation is to be switched, and thereby controls the number
of chillers 21-1 to 21-n.
[0027] FIG. 2 is a configuration diagram illustrating a schematic
configuration of the chiller 21-1. In FIG. 2, the chiller 21-1
includes: a centrifugal compressor 211; a condenser 212; a
sub-cooler 213; a high-pressure expansion valve 214; a low-pressure
expansion valve 215; an evaporator 216; an intermediate cooler 217;
an inverter 221; a hot-gas bypass valve 225; a cooling water heat
exchanger tube 231; a chilled water heat exchanger tube 232; a
hot-gas bypass tube 233; and a control unit 234. The centrifugal
compressor 211 includes an electric motor 222 and an inlet guide
vane (IGV) 224.
[0028] The chiller 21-1 cools a refrigerant in a 2-stage
compression, 2-stage expansion sub-cooling cycle and cools the
chilled water using the cooled refrigerant.
[0029] The centrifugal compressor 211 is a 2-stage compressor and
compresses a gas refrigerant. The condenser 212 condenses and
liquefies a high-temperature, high-pressure gas refrigerant
compressed by the centrifugal compressor 211. The sub-cooler 213 is
provided downstream of a refrigerant flow of the condenser 212, and
subcools a liquid refrigerant condensed by the condenser 212. The
cooling water heat exchanger tube 231 is inserted into the
condenser 212 and the sub-cooler 213, and cools the refrigerant
using the cooling water flowing inside the tube. The cooling water
flowing inside the cooling water heat exchanger tube 231 cools the
refrigerant. In a cooling tower, the condensing heat is discharged
to the outside and flows inside the cooling water heat exchanger
tube 231 again.
[0030] The high-pressure expansion valve 214 and the low-pressure
expansion valve 215 expand the liquid refrigerant from the
sub-cooler 213. The intermediate cooler 217 cools the liquid
refrigerant expanded by the high-pressure expansion valve 214. The
evaporator 216 evaporates the liquid refrigerant expanded by the
low-pressure expansion valve 215. The chilled water heat exchanger
tube 232 is inserted into the evaporator 216. The chilled water
flowing inside the chilled water heat exchanger tube 232 is cooled
by absorbing vaporization heat when the refrigerant is
evaporated.
[0031] Thus, the chiller 21-1 cools the chilled water and supplies
the chilled water to the external load 51.
[0032] Further, when the chiller 21-1 is a chiller in which a
compressor is capable of being variable speed controlled, load
control of the chiller 21-1 is performed by control of the number
of revolutions of the centrifugal compressor 211 and control of
capacity using the inlet guide vane 224 and the hot-gas bypass tube
233.
[0033] The electric motor 222 drives the centrifugal compressor
211. The inverter 221 controls the number of revolutions of the
centrifugal compressor 211 by controlling the number of revolutions
of the electric motor 222.
[0034] The inlet guide vane 224 is provided in a refrigerant inlet
of the centrifugal compressor 211 and controls a suction
refrigerant flow amount to perform the capacity control of the
chiller 21-1.
[0035] The hot-gas bypass tube 233 is provided between a gas phase
portion of the condenser 212 and a gas phase portion of the
evaporator 216 to bypass the refrigerant gas. The hot-gas bypass
valve 225 controls a flow amount of the refrigerant flowing inside
the hot-gas bypass tube 233. The hot-gas bypass valve 225 adjusts
the hot gas bypass flow amount to thereby perform more detailed
capacity control than the capacity control by the inlet guide vane
224.
[0036] Further, when the chiller is a chiller with a fixed-speed
controlled compressor, the load control is performed by the
capacity control by the inlet guide vane 224 and the hot-gas bypass
tube 233.
[0037] The control unit 234 controls each unit. In particular, the
control unit 234 operates the stopped chiller 21-1 or stops the
operating chiller 21-1 based on a control signal input from the
chiller control apparatus 100 (FIG. 1). (Hereinafter, to operate a
stopped chiller or to stop an operating chiller is referred to as
"to change an operation state"). Further, the control unit 234
controls the inverter 221, the inlet guide vane 224, and the
hot-gas bypass valve 225 based on the control signal input from the
chiller control apparatus 100 to perform load control of the
chiller 21-1. Further, the control unit 234 obtains
optimal-load-related information, which will be described
below.
[0038] By the load control performed by the control unit 234, the
chiller 21-1 supplies the chilled water at a rated temperature
(e.g., 7.degree. C.) to the external load 51.
[0039] Further, a cooling water flow amount is measured by a
flowmeter F2, a cooling water outlet temperature is measured by a
temperature sensor Tcout, and a cooling water inlet temperature is
measured by a temperature sensor Tcin. Further, the chilled water
flow amount is measured by the flowmeter F1, a chilled water outlet
temperature is measured by the temperature sensor Tout, and a
chilled water inlet temperature is measured by a temperature sensor
Tin. These measured values are used when the control unit 234
controls each unit, and are used for the control unit 234 to obtain
the optimal-load-related information, which will be described
below.
[0040] Further, configurations of the chillers 21-2 to 21-n are
similar to that described with reference to FIG. 2.
[0041] FIG. 3 is a configuration diagram illustrating a schematic
configuration of the chiller control apparatus 100. In FIG. 3, the
chiller control apparatus 100 includes: a data acquisition unit
111; a required load determination unit 112; a required load
calculation unit 113; a stage increase determination unit 121; an
insufficient load value calculation unit 122; a
chiller-to-be-operated selection unit 123; a stage decrease
determination unit 131; a chiller-to-be-stopped selection unit 133;
an operation command unit 141; and an operation pattern extraction
unit (a stage decrease operation pattern extraction unit) 151.
[0042] The data acquisition unit 111 transmits and receives to and
from the chillers 21-1 to 21-n, information such as supply and
return water temperature, a main tube flow amount, an optimal load
range of the chiller, or efficiency of the chiller when operated in
the optimal load range.
[0043] The required load calculation unit 113 calculates a required
load indicating a cold amount or a heat amount to be generated by
the chiller system 1, based on the supply and return water
temperature and the main tube flow amount acquired by the data
acquisition unit 111.
[0044] The required load determination unit 112 compares a sum of
optimal loads with the required load for operating chillers to
determine whether to perform a process at the time of stage
increase (when the number of operating chillers is increased) or a
process at the time of stage decrease (when the number of operating
chillers is decreased).
[0045] When the required load determination unit 112 determines to
perform the process at the time of stage increase, the stage
increase determination unit 121 determines whether to actually
perform stage increase.
[0046] The insufficient load value calculation unit 122 calculates
an insufficient load value indicating an insufficient amount of a
load when each operating chiller is operated with an optimal
load.
[0047] The chiller-to-be-operated selection unit 123 selects the
chiller to be started up by the chiller system 1 in order to
satisfy the required load and efficiently operate the chillers,
based on the insufficient load value calculated by the insufficient
load value calculation unit 122 and the optimal-load-related
information of each stopped chiller.
[0048] When the required load determination unit 112 determines to
perform the process at the time of the stage decrease, the stage
decrease determination unit 131 determines whether to actually
perform the stage decrease.
[0049] The operation pattern extraction unit 151 extracts a
possible combination of chillers to be operated in such a manner
that the required load is satisfied (hereinafter, information
indicating a combination of chillers to be operated is referred to
as "a chiller operation pattern"). The chiller-to-be-stopped
selection unit 133 selects chillers to be stopped by the chiller
system 1 in order to satisfy the required load and efficiently
operate chillers, based on the chiller operation pattern extracted
by the operation pattern extraction unit 151 and the
optimal-load-related information of each operating chiller.
[0050] The operation command unit 141 transmits a control signal
for operating the chiller to be started up, transmits a control
signal for stopping the chiller to be stopped, and transmits to the
operating chiller, a control signal as a flow amount command for
changing load sharing.
[0051] Further, the required load determination unit 112, the stage
increase determination unit 121, and the stage decrease
determination unit 131 constitute a number-of-chillers change
determination unit, which determines based on the required load
whether to change the number of currently selected chillers.
[0052] In other words, as will be described below, first, the
required load determination unit 112 determines based on the
required load whether to perform the process at the time of stage
increase or the process at the time of the stage decrease. If the
required load determination unit 112 determines to perform the
process at the time of stage increase, the stage increase
determination unit 121 determines whether to actually perform the
stage increase.
[0053] On the other hand, if the required load determination unit
112 determines to perform the process at the time of the stage
decrease, the stage decrease determination unit 131 determines
whether to actually perform the stage decrease.
[0054] Further, the insufficient load value calculation unit 122,
the chiller-to-be-operated selection unit 123, the operation
pattern extraction unit 151, and the chiller-to-be-stopped
selection unit 133 constitute a chiller determination unit, which
determines a chiller whose operation state is to be changed, based
on a relationship between a load and an efficiency index value (a
COP, which will be described below) of each chiller and on the
required load, when the number of chillers is changed based on the
determination result of the number-of-chillers change determination
unit.
[0055] In other words, as will be described below, when the stage
increase determination unit 121 determines to perform the stage
increase, the insufficient load value calculation unit 122
calculates the insufficient amount of the load, and the
chiller-to-be-operated selection unit 123 determines a chiller
suitable for operation with the insufficient amount of a load,
based on the relationship between the load and the COP of each
chiller.
[0056] On the other hand, when the stage decrease determination
unit 131 determines to perform the stage decrease, the operation
pattern extraction unit 151 extracts the chiller operation pattern
according to the required load, and the chiller-to-be-stopped
selection unit 133 determines a chiller to be stopped based on the
chiller operation pattern achieving high efficiency of the entire
chiller system 1 among the extracted chiller operation
patterns.
[0057] Further, the number-of-chillers change determination unit
and the chiller determination unit constitute a chiller selection
unit, which selects a chiller to be operated from among a plurality
of chillers in response to the load request. In other words, based
on the result of the determination by the number-of-chillers change
determination unit, the chiller determination unit selects a
chiller to be subjected to stage increase or a chiller to be
subjected to stage decrease, and thereby selects the chiller to be
operated from among the chillers 21-1 to 21-n (FIG. 1).
[0058] Next, an operation of the chiller control apparatus 100 is
described with reference to FIG. 4.
[0059] FIG. 4 is a flowchart illustrating a procedure of a process
for the chiller control apparatus 100 to select a chiller whose
operation state is to be changed. In FIG. 4, first, the data
acquisition unit 111 transmits information, such as a cooling water
inlet temperature or a cooling water flow amount for each stopped
chiller.
[0060] Further, when all the chillers are stopped, a reachable
cooling water inlet temperature is calculated based on an ambient
wet-bulb temperature. Further, the cooling water flow amount is
assumed to be a rated flow amount (step S101).
[0061] Then, each of the chillers 21-1 to 21-n calculates an
optimal-load-range high value, an optimal-load-range low value, an
optimal-load-range optimal value, an optimal-load-range high value
COP, an optimal-load-range low value COP, and an optimal-load-range
optimal value COP, and transmits those calculated values to the
data acquisition unit 111.
[0062] Here, a COP (Coefficient Of Performance) is an efficiency
index value indicating efficiency of the chiller, and is calculated
by dividing a load of the chiller (refrigeration capability) by
consumption energy. Generally, chillers have different COPs
depending on operating environments of the chillers, such as the
cooling water inlet temperature or the cooling water flow amount,
and loads required for the chillers.
[0063] For this reason, each of the chillers 21-1 to 21-n in an
actual apparatus stores a table in which an operating environment,
each value of the load, and the COP for each value are associated
with one another, which are generated based on the COPs previously
measured under various operating environments and loads.
Alternatively, each of the chillers 21-1 to 21-n previously stores
in the table, an equation for deriving the COP according to
mechanical properties from the cooling water condition and each
value of the load.
[0064] Further, a COP based on consumption energy of the chiller
may be used as the COP. Alternatively, a COP based on consumption
energy including consumption energy of an auxiliary device, such as
a chilled water pump, a cooling water pump or a cooling tower fan,
may be used as the COP.
[0065] Further, the optimal load range refers to a range of a load
in which the chiller can be operated with high efficiency, such as
a load range in which the COP of the chiller is equal to or more
than a predetermined value. Each of the chillers 21-1 to 21-n can
obtain the optimal load range using the above-described table or by
applying the cooling water condition and each value of the load to
the above-described equation.
[0066] Further, the optimal-load-range high value refers to a
maximum load value in the optimal load range. The
optimal-load-range high value is a threshold value set as a target
so that a load of the chiller does not exceed this value. Further,
the optimal-load-range low value refers to a minimum load value in
the optimal load range. The optimal-load-range low value is a
threshold value set as a target so that a load of the chiller does
not go below this value. Further, the optimal-load-range optimal
value refers to a load value in the optimal range at which the COP
is maximized.
[0067] Further, the optimal-load-range high value COP refers to a
COP when the chiller is operated with the optimal-load-range high
value. The optimal-load-range low value COP refers to a COP when
the chiller is operated with the optimal-load-range low value. The
optimal-load-range optimal value COP refers to a COP when the
chiller is operated with the optimal-load-range optimal value.
[0068] Hereinafter, the optimal-load-range high value, the
optimal-load-range low value, the optimal-load-range optimal value,
the optimal-load-range high value COP, the optimal-load-range low
value COP, and the optimal-load-range optimal value COP are
referred to as "optimal-load-related information."
[0069] The operating chiller acquires information such as a cooling
water inlet temperature or a cooling water flow amount, as data for
control of the chiller, and calculates the optimal-load-related
information based on the information. Meanwhile, the stopped
chiller cannot measure the cooling water inlet temperature, the
cooling water flow amount, or the like, since auxiliary devices are
stopped. For this reason, the stopped chiller calculates the
optimal-load-related information based on the information such as
the cooling water inlet temperature or the cooling water flow
amount transmitted from the data acquisition unit 111.
[0070] Further, the data acquisition unit 111, rather than the
control unit of each chiller, may calculate the
optimal-load-related information. Accordingly, the amount of
communication from the chiller to the chiller control apparatus 100
can be reduced. Meanwhile, when the control unit of each chiller
calculates the optimal-load-range high value or the like, the
control unit can calculate the optimal-load-range high value or the
like according to the actual control, thus reducing the calculation
amount of the chiller control apparatus 100. Further, when the
control unit of each chiller calculates the optimal-load-related
information, the chiller control apparatus 100 need not store a
characteristic parameter of each chiller. Accordingly, when a
chiller is exchanged, it is unnecessary to perform adjustment on
the chiller control apparatus 100 (step S102).
[0071] Next, the required load calculation unit 113 calculates a
required load Qr (a value required as a sum of loads of the
chillers) and outputs the required load to the required load
determination unit 112. The required load calculation unit 113
multiplies a temperature difference between the main tube feedback
water temperature and the main tube sent water temperature by the
main tube flow amount to thereby calculate a cold amount or heat
amount to be generated by the chillers 21-1 to 21-n as a required
load. Further, when all the chillers are stopped, a value
previously set as an initial required load is set to be the
required load.
[0072] Then, the required load determination unit 112 determines
whether a sum Qopt of the optimal-load-range optimal values Qopt of
the respective operating chillers acquired by the data acquisition
unit 111 is less than the required load Qr calculated by the
required load calculation unit 113 (step S103). If it is determined
that the optimal-load-range optimal value sum is less than the
required load (step S103: YES), whether to perform the stage
increase is determined as the process at the time of the stage
increase in steps S111 to S122, and the chiller to be subjected to
stage increase is further selected when it is determined to perform
the stage increase.
[0073] Specifically, the stage increase determination unit 121
determines whether to perform stage increase, based on whether the
required load calculated by the required load calculation unit 113
is equal to or more than the stage increase switching point. Here,
the stage increase switching point is a load value set for each
number of operating chillers. The stage increase determination unit
121 uses, as the stage increase switching point, a load value set
as a stage increase switching point in association with the number
of currently operating chillers (step S111). When the required load
is less than the stage increase switching point, the stage increase
determination unit 121 determines not to change the number of
operating chillers (step S111: NO), and ends the process of FIG.
4.
[0074] On the other hand, if the required load is determined to be
equal to or more than the stage increase switching point, the stage
increase determination unit 121 determines to perform stage
increase of chillers (step S111: YES), and the insufficient load
value calculation unit 122 calculates an insufficient load value
.DELTA.Qs based on Equation (1).
.DELTA.Qs=Qu-.SIGMA.Qopt Equation (1)
[0075] Here, Qu denotes the stage increase switching point, Qopt
denotes the optimal-load-range optimal value, and .SIGMA.Qopt
denotes a sum of optimal-load-range optimal values of all operating
chillers (step S121).
[0076] Next, the chiller-to-be-operated selection unit 123 obtains
a COP of each stopped chiller when the chillers are operated with
an insufficient load value .DELTA.Qs. For example, the
chiller-to-be-operated selection unit 123 transmits the
insufficient load value .DELTA.Qs to each stopped chiller, requests
a corresponding COP and acquires the COP.
[0077] Alternatively, the chiller-to-be-operated selection unit 123
may obtain an approximate equation of a relationship between the
load and the COP based on three points of the optimal-load-range
high value and the optimal-load-range high value COP, the
optimal-load-range optimal value and the optimal-load-range optimal
value COP, and the optimal-load-range low value and the
optimal-load-range low value COP, and obtains a COP corresponding
to the insufficient load value .DELTA.Qs based on the equation. For
example, the chiller-to-be-operated selection unit 123 obtains a
quadratic curve passing through the three points where the load is
indicated by an X axis and the COP is indicated by a Y axis, and
obtains a COP corresponding to the insufficient load value
.DELTA.Qs on the quadratic curve.
[0078] Then, the chiller-to-be-operated selection unit 123 selects
a chiller having the highest COP as the chiller to be subjected to
stage increase, i.e., a chiller to be operated. The operation
command unit 141 transmits a control signal for operating a chiller
to the selected chiller. Further, the operation command unit 141
transmits a control signal as a flow amount command for changing
load sharing, to operating chillers including a chiller that newly
starts its operation. For example, the operation command unit 141
proportionally distributes the required load calculated by the
required load calculation unit 113 according to the number of
operating chillers, and transmits a control signal to each chiller
so that the operation is performed with a load resulting from the
proportional distribution. As the proportional distribution of the
load, for example, division of the load at a ratio according to the
optimal-load-range optimal value of each chiller may be
considered.
[0079] Further, if the optimal-load-range high value is less than
the insufficient load value (Qmax<.DELTA.Qs), the
chiller-to-be-operated selection unit 123 compares, for the
chiller, the optimal-load-range high value COP max, instead of the
COP when operated with the insufficient load value .DELTA.Qs, with
the COP of the other chiller. In other words, the
chiller-to-be-operated selection unit 123 compares the COP when the
chiller is operated with the maximum load in the optimal load range
with the COP of the other chiller. Alternatively, when the
insufficient load value .DELTA.Qt is proportionally distributed to
and shared among a plurality of stopped chillers and the operation
can be performed within the optimal load range, a value obtained by
weighted averaging of the COPs of the chillers according to the
proportionally distributed and shared load may be compared with the
COP of the other chiller.
[0080] Further, if the optimal-load-range low value is greater than
the insufficient load value (Qmin>.DELTA.Qs), the
chiller-to-be-operated selection unit 123 compares, for the
chiller, the optimal-load-range low value COPmin, instead of the
COP when operated with the insufficient load value .DELTA.Qs, with
the COP of the other chiller. In other words, the
chiller-to-be-operated selection unit 123 compares the COP when the
chiller is operated with the minimum load in the optimal load range
with the COP of the other chiller.
[0081] Further, when there are a plurality of chillers having the
same COP value, the chiller-to-be-operated selection unit 123
selects a chiller having the shortest accumulated operation time,
as a chiller to be subjected to stage increase. For example, each
of the chillers 21-1 to 21-n measures an accumulated operation time
of the chiller and transmits the accumulated operation time to the
chiller control apparatus 100 at any time. If there are a plurality
of chillers having the same COP value, the chiller selection unit
123 selects a chiller having the shortest accumulated operation
time based on the accumulated operation times transmitted from the
respective chillers. Accordingly, it is possible to suppress a
discrepancy between the accumulated operation times of the
chillers.
[0082] Further, the chiller-to-be-operated selection unit 123 may
not only select a chiller having the highest COP, but also
determine operation priorities of the stopped chillers in order of
higher COPs. If the chiller system 1 starts up the chillers one by
one, the chiller-to-be-operated selection unit 123 may select one
chiller to be started up, as described above. Meanwhile, the
chiller-to-be-operated selection unit 123 determines operation
priorities of the plurality of chillers, making it possible for the
chiller system 1 to start up other chillers when the selected
chiller cannot be started up, for example, due to failure of the
chiller (step S122).
[0083] Then, the chiller control apparatus 100 ends the process of
FIG. 4.
[0084] Meanwhile, if it is determined in step S103 that a sum Qopt
of the optimal-load-range optimal values Qopt of the operating
chillers is equal to or more than the required load (step S103:
NO), whether to perform the stage decrease is determined in steps
S131 to S152 as the process at the time of the stage decrease, and
a chiller to be subjected to stage decrease is selected if it is
determined to perform the stage decrease. Further, in steps S161 to
S181, if the number of operating chillers is 1, it is determined
whether to switch the chiller to another chiller.
[0085] Specifically, the stage decrease determination unit 131
determines whether to perform the stage decrease, based on whether
the required load calculated by the required load calculation unit
113 is equal to or less than the stage decrease switching point.
Here, if the chillers have the same capacities, the stage decrease
switching point is a load value set for each number of operating
chillers. If capacities of the chillers are different, the stage
decrease switching point is a load value set by the combination.
The stage decrease determination unit 131 uses, as the stage
decrease switching point, a load value set as a stage decrease
switching point in association with the number of currently
operating chillers (step S131). If the required load is determined
to be more than the stage decrease switching point, the stage
decrease determination unit 131 determines not to change the number
of operating chillers (step S131: NO) and ends the process of FIG.
4.
[0086] On the other hand, if the required load is determined to be
equal to or less than the stage decrease switching point, the stage
decrease determination unit 131 determines to perform the stage
decrease of the chiller (step S131: YES), and the stage decrease
determination unit 131 also determines whether the number of
operating chillers is 2 or more (step S141). If the number of
operating chillers is determined to be 2 or more (step S141: YES),
the operation pattern extraction unit 151 selects one chiller from
among the operating chillers, and extracts patterns of combinations
of all the other operating chillers, as the chiller operation
pattern. The operation pattern extraction unit 151 extracts the
chiller operation patterns for all the operating chillers (step
S151).
[0087] Then, the chiller-to-be-stopped selection unit 133 obtains
the COP of the entire chiller system 1 for all the chiller
operation patterns extracted by the operation pattern extraction
unit 151. For example, the chiller-to-be-stopped selection unit 133
obtains the COP of each chiller when the chiller is operated
according to a chiller operation pattern and the required load is
proportionally distributed and shared, and obtains a value as the
COP of the entire chiller system 1 by weighted averaging of the
COPs of the chillers according to the proportionally distributed
and shared load.
[0088] Then, the chiller-to-be-stopped selection unit 133 selects
the chiller operation pattern making the COP of the entire chiller
system 1 maximum, and selects a chiller to be subjected to stage
decrease according to the selected chiller operation pattern. The
operation command unit 141 transmits to the selected chiller, a
control signal for stopping the chiller. Further, the operation
command unit 141 transmits to the other operating chillers, a
control signal as a flow amount command for changing load sharing.
For example, the operation command unit 141 proportionally
distributes the required load calculated by the required load
calculation unit 113 according to the number of operating chillers,
and transmits a control signal to each chiller so that operation is
performed with a load resulting from the proportional
distribution.
[0089] Further, the operation pattern extraction unit 151 may
extract, as the chiller operation pattern, a combination of other
operating chillers remaining after a plurality of chillers are
selected from among the operating chillers. Accordingly, when the
operation cannot be performed within the optimal load range only by
subjecting one chiller to stage decrease, it is possible to obtain
a high COP of the entire chiller system 1 by subjecting a plurality
of chillers to stage decrease.
[0090] Meanwhile, according to the method in which the operation
pattern extraction unit 151 selects only one chiller from among the
operating chillers and extracts the chiller operation pattern, it
is possible to extract only the chiller operation pattern highly
likely to be optimal and to reduce the calculation amount. In other
words, under a premise that the required load is not suddenly
changed, it is possible to cope with the required load only by
subjecting one chiller to stage increase. Therefore, only the
chiller operation pattern that subjects one chiller to stage
increase is extracted to select the chiller, thereby enabling a
reduction in a calculation amount while coping with the required
load (step S152).
[0091] Then, the chiller control apparatus 100 ends the process of
FIG. 4.
[0092] On the other hand, if it is determined in step S141 that the
number of chillers to be operated is 1 (step S141: NO), the
chiller-to-be-stopped selection unit 133 determines whether an
optimal-load-range low value of the operating chiller is greater
than the required load (Qmin>Qr) (step S161). If the
optimal-load-range low value of the operating chiller is determined
to be greater than the required load (step S161: YES), the
chiller-to-be-stopped selection unit 133 determines whether the
chillers that are stopped include a chiller whose COP when operated
with the required load is higher than that of the operating chiller
(step S171). If it is determined that the chillers that are stopped
include a chiller whose COP when operated with the required load is
higher than that of the operating chiller (step S171: YES), a
chiller having the highest COP when operated with the required load
is selected as a chiller to be switched (step S181).
[0093] Then, the chiller control apparatus 100 ends the process of
FIG. 4.
[0094] On the other hand, if it is determined in step S161 that an
optimal-load-range low value of the operating chiller is equal to
or less than the required load (step S161: NO), and if it is
determined in step S141 that the stopped chillers include no
chiller whose COP when operated with the required load is higher
than that of the operating chiller (step S171: NO), the chiller
control apparatus 100 ends the process of FIG. 4 without performing
switching of the chiller.
[0095] Further, the chiller system 1 may not perform the process
described in steps S161 to S181. In other words, the operation of
the operating chiller may be continued without switching chillers
irrespective of whether the optimal-load-range low value of the
operating chiller is greater than the required load. Accordingly,
the operation switching frequency of the chillers can be reduced.
Further, the process of steps S161 to S181 need not be performed,
and therefore the calculation amount can be reduced. Meanwhile,
when the process described in steps S161 to S181 is performed,
operation may be performed with a higher COP.
[0096] Further, the method in which the chiller-to-be-operated
selection unit 123 selects a chiller to be subjected to stage
increase is not limited to the method described in step S122.
[0097] For example, the operation pattern extraction unit (the
stage increase operation pattern extraction unit) 151 may extract
the chiller operation patterns according to the required load, and
the chiller-to-be-operated selection unit 123 may select the
chiller to be subjected to stage increase based on the chiller
operation pattern achieving the optimal COP among the extracted
chiller operation patterns.
[0098] Specifically, the operation pattern extraction unit 151
selects one chiller from among the stopped chillers, and combines
the selected chiller with the operating chillers to extract a
chiller operation pattern. The operation pattern extraction unit
151 extracts the chiller operation pattern for all the stopped
chillers.
[0099] Also, the chiller-to-be-operated selection unit 123 obtains
the COP of the entire chiller system 1 for all chiller operation
patterns extracted by the operation pattern extraction unit 151.
The COP of the entire chiller system 1 is calculated by, for
example, weighted averaging of the COPs of the chillers according
to a proportionally distributed and shared load when the required
load is proportionally distributed to and shared among the chillers
involved in the chiller operation pattern, as described in step
S152.
[0100] Then, the chiller-to-be-operated selection unit 123 selects
the chiller operation pattern making the COP of the entire chiller
system 1 maximum, and selects the chiller to be subjected to stage
increase according to the selected chiller operation pattern.
[0101] Thus, the chiller-to-be-operated selection unit 123 selects
the chiller to be subjected to stage increase according to the
chiller operation pattern, and thereby the COP is calculated based
on a load actually shared by each chiller after the stage increase.
Accordingly, the COP can be calculated more accurately and the
chiller to be subjected to stage increase can be selected more
appropriately.
[0102] Meanwhile, according to the method described in step S122, a
COP for each stopped chiller may be calculated, and it is
unnecessary to calculate the COP of the entire chiller system 1 by
performing the extraction of the chiller operation pattern and the
weighted average with the COP of the already operating chiller.
Accordingly, a calculation amount decreases and chiller selection
is performed more rapidly.
[0103] Further, the operation pattern extraction unit 151 may
extract chiller operation patterns of combinations of a plurality
of stopped chillers and operating chillers. Accordingly, when the
operation cannot be performed within the optimal load range only by
subjecting one chiller to stage increase, it is possible to obtain
a high COP of the entire chiller system 1 by subjecting a plurality
of chillers to stage increase.
[0104] Meanwhile, according to the above-described method in which
the operation pattern extraction unit 151 selects only one chiller
from among the stopped chillers and extracts the chiller operation
pattern, only a chiller operation pattern highly likely to be
optimal is extracted so that a calculation amount can be reduced.
In other words, under the premise that the required load is not
suddenly changed, the required load can be coped with by subjecting
one chiller to stage increase. Therefore, only the chiller
operation pattern that subjects one chiller to stage increase is
extracted to select the chiller, it is possible to reduce the
calculation amount while coping with the required load.
[0105] Further, the method in which the chiller-to-be-stopped
selection unit 133 selects a chiller to be subjected to stage
decrease is not limited to the method described in step S152.
[0106] For example, the chiller control apparatus 100 may include
an excess load value calculation unit 132, as shown in FIG. 5.
[0107] In this case, in step S151 of FIG. 4, the excess load value
calculation unit 132 calculates an excess load value .DELTA.Qt
based on Equation (2).
.DELTA.Qt=.SIGMA.Qopt-Qd Equation (2)
[0108] Here, Qd denotes a stage decrease switching point. Further,
Qopt denotes the optimal-load-range optimal value, and Qopt denotes
a sum of optimal-load-range optimal values Qopt for all the
operating chillers.
[0109] Next, in step S152, the chiller-to-be-stopped selection unit
133 obtains, for each operating chiller, a COP when the chiller is
operated with the excess load value .DELTA.Qt.
[0110] Then, the chiller-to-be-stopped selection unit 133 selects
the chiller having the lowest COP as a chiller to be subjected to
stage decrease, i.e., a chiller to be stopped. The chiller having
the lowest COP is stopped, thereby enabling an increase in the COP
of the entire chiller system 1. The operation command unit 141
transmits to the selected chiller, a control signal for stopping
the chiller. Further, the operation command unit 141 transmits to
the other operating chillers, a control signal as a flow amount
command for changing load sharing.
[0111] Further, when the optimal-load-range low value is greater
than the excess load value (Qmin>.DELTA.Qt), the
chiller-to-be-stopped selection unit 133 compares, for the chiller,
an optimal-load-range low value COPmin, instead of the COP when the
chiller is operated with the excess load value .DELTA.Qt, with the
COP of the other chiller. In other words, the chiller-to-be-stopped
selection unit 133 compares a COP reduction amount when the chiller
operated with the minimum load in the optimal load range is stopped
with the COP reduction amount of the other chiller.
[0112] Further, when the optimal-load-range high value is less than
the excess load value (Qmax<.DELTA.Qt), the
chiller-to-be-stopped selection unit 133 compares, for the chiller,
the optimal-load-range high value COPmax, instead of the COP when
the chiller is operated with the excess load value .DELTA.Qt, with
the COP of the other chiller. In other words, the
chiller-to-be-stopped selection unit 133 compares a COP reduction
amount when the chiller operating with the maximum load in the
optimal load range is stopped, with the COP reduction amount of the
other chiller. Alternatively, when an excess load value .DELTA.Qt
is proportionally distributed to and shared among a plurality of
operating chillers and the chillers can be operated in the optimal
load range, a value obtained by weighted averaging of the COPs of
the chillers according to the proportionally distributed and shared
load may be compared with the COPs of the other chillers.
[0113] Further, when there are a plurality of chillers having the
same COP value, the chiller-to-be-stopped selection unit 133
selects a chiller having the longest accumulated operation time as
the chiller to be stopped. Accordingly, it is possible to suppress
a discrepancy between the accumulated operation times of the
chillers.
[0114] Further, the chiller-to-be-stopped selection unit 133 may
determine stop priorities for the operating chillers in order of
higher COPs, as in the case in which the chiller to be started up
is selected.
[0115] Thus, the chiller-to-be-stopped selection unit 133 selects
the chiller to be subjected to stage decrease based on the excess
load value, and thus the COP for each operating chiller may be
calculated. It is unnecessary to extract the chiller operation
pattern and to calculate the COP of the entire chiller system 1
based on a weighted average of the COPs of the other operating
chillers. In this respect, a calculation amount decreases, and the
chiller selection can be performed more rapidly.
[0116] Meanwhile, according to the method described in step S152,
the COP is calculated based on a load actually shared by each
chiller after the stage decrease, thereby enabling more accurate
calculation of the COP and more adequate selection of the chiller
to be subjected to stage decrease.
[0117] Further, in FIG. 5, the insufficient load value calculation
unit 122, the chiller-to-be-operated selection unit 123, the excess
load value calculation unit 132, and the chiller-to-be-stopped
selection unit 133 constitute a chiller determination unit.
[0118] Alternatively, the chiller control apparatus 100 may not
include the required load determination unit 112, the stage
increase determination unit 121 may always determine whether to
perform the stage increase, and the stage decrease determination
unit 131 may always determine whether to perform the stage
decrease. Accordingly, it is possible to simplify a configuration
of the device.
[0119] Alternatively, the chiller-to-be-operated selection unit 123
may always select a chiller at the time of stage increase. In other
words, since a chiller is selected before the determination by the
stage increase determination unit 121, the stage increase can be
rapidly performed when the stage increase determination unit 121
determines to perform the stage increase. The same applies to the
chiller-to-be-stopped selection unit 133.
[0120] Further, when the required flow amount is set, it may be
determined whether the required flow amount is satisfied, in
addition to whether the required load is satisfied.
[0121] FIG. 6 is a flowchart illustrating a procedure of a process
for the chiller control apparatus 100 to determine whether a
required flow amount is satisfied, in addition to whether the
required load is satisfied.
[0122] Steps S201 to S203 shown in FIG. 6 are similar to steps S101
to S103 shown in FIG. 4, step S222 is similar to step S122 shown in
FIG. 4, step S251 is similar to step S141 shown in FIG. 4, and
steps S271 to S291 are similar to steps S161 to S181 shown in FIG.
4.
[0123] If it is determined in step S203 of FIG. 6 that the
optimal-load-range optimal value sum .SIGMA.Qopt of the operating
chillers is equal to or more than the required load Qr (step S203:
NO), the required load determination unit 112 also determines
whether the optimal-flow-amount-range optimal value sum .SIGMA.Fop
of the operating chillers is less than the required flow amount Fr.
In this case, the optimal flow amount Fopt for each operating
chiller is obtained using Equation (3), and a sum of the optimal
flow amounts Fopt for the operating chillers is calculated and used
as the optimal-flow-amount-range optimal value sum .SIGMA.Fopt.
Fopt=Qopt/Cp.times..rho..times.(Tr.sub.--i-Ts.sub.--i) Equation
(3)
[0124] Here, Tr_i denotes a chilled water return temperature of the
chiller i (i is a positive integer such that 1.ltoreq.i.ltoreq.n)
and Ts_n denotes a chilled water supply temperature of the chiller
i. Further, Cp denotes a specific heat [kJ/(kg.degree. C.)] of the
chilled water and .rho. denotes a density [kg/m.sup.3] of the
chilled water (step S231).
[0125] Also, if the optimal-flow-amount-range optimal value sum
.SIGMA.Fopt is determined to be less than the required flow amount
Fr (step S231: YES), whether to perform the stage increase is
determined in steps S211 to 222 as the process at the time of stage
increase is to be performed is determined, and the chiller to be
subjected to stage increase is selected when it is determined to
perform the stage increase. On the other hand, if the
optimal-flow-amount-range optimal value sum .SIGMA.Fopt is
determined to be equal to or more than the required flow amount Fr
(step S231: NO), whether to perform the stage decrease is
determined in steps S241 to S262 as the process at the time of the
stage decrease, and the chiller to be subjected to stage decrease
is selected when it is determined to perform the stage decrease.
Further, in steps S271 to S291, when the number of operating
chillers is 1, whether to switch the one chiller to other chillers
is determined.
[0126] In step S211, the stage increase determination unit 121
determines based on the required load whether the stage increase is
necessary based on the required flow amount, in addition to whether
the stage increase is necessary, which has been described in step
S111 of FIG. 4. Specifically, the stage increase determination unit
121 determines whether the required load is equal to or more than
the stage increase switching point, and determines whether the
required flow amount is equal to or more than the stage increase
switching flow amount. Here, the stage increase switching flow
amount is a flow amount value set for each number of operating
chillers. The stage increase determination unit 121 uses, as the
stage increase switching flow amount, a flow amount value set as a
stage increase switching flow amount in association with the number
of currently operating chillers (step S211). If the required load
is determined to be less than the stage increase switching point
and if the required flow amount is determined to be less than the
stage increase switching flow amount, the stage increase
determination unit 121 determines not to change the number of
operating chillers (step S211: NO), and ends the process of FIG.
6.
[0127] On the other hand, if the required load is determined to be
equal to or more than the stage increase switching point or if the
required flow amount is determined to be equal to or more than the
stage increase switching flow amount, the stage increase
determination unit 121 determines to perform stage increase of the
chillers (step S211: YES), and the process proceeds to step
S221.
[0128] In step S221, the stage increase switching point Qu is
calculated based on Equation (4) instead of using the stage
increase switching point Qu used in step S121 of FIG. 4.
Qu=Fu.times.(Tr-Ts).times.Cp.times..rho. Equation (4)
[0129] Here, Fu denotes the stage increase switching flow amount
[m.sup.3/h], Tr denotes a chilled water return temperature
[.degree. C.], Ts denotes a chilled water supply temperature
[.degree. C.], Cp denotes a specific heat [kJ/(kg.degree. C.)] of
the chilled water, and .rho. denotes density [kg/m.sup.3] of the
chilled water.
[0130] Then, the required load determination unit 112 calculates
the insufficient load value .DELTA.Qs based on Equation (1),
similarly to step S121 of FIG. 4.
[0131] Further, in step S241, the stage decrease determination unit
131 not only determines based on the required load whether the
stage decrease is necessary, as described in step S131 of FIG. 4,
but also determines based on the required flow amount whether the
stage decrease is necessary. Specifically, the stage decrease
determination unit 131 determines whether the required load is
equal to or less than the stage decrease switching point and
determines whether the required flow amount is equal to or less
than the stage decrease switching flow amount. Here, the stage
decrease switching flow amount is a flow amount value set for each
number of operating chillers. The stage decrease determination unit
131 uses, as the stage decrease switching flow amount, a flow
amount value set as a stage decrease switching flow amount in
association with the number of currently operating chillers (step
S241). If the required load is determined to be equal to or more
than the stage decrease switching point and if the required flow
amount is determined to be equal to or more than the stage decrease
switching flow amount, the stage decrease determination unit 131
determines not to change the number of operating chillers (step
S241: NO) and ends the process of FIG. 6.
[0132] On the other hand, if the required load is determined to be
equal to or less than the stage decrease switching point or if the
required flow amount is determined to be equal to or less than the
stage decrease switching flow amount, the stage decrease
determination unit 131 determines not to perform stage decrease of
the chillers (step S241: YES), and the process proceeds to step
S251.
[0133] In step S261, the stage decrease switching point Qd is
calculated based on Equation (5) instead of using the stage
decrease switching point Qd used in step S151 of FIG. 4.
Qd=Fd.times.(Tr-Ts).times.Cp.times..rho. Equation (5)
[0134] Here, Fd denotes the stage decrease switching flow amount
[m.sup.3/h], Tr denotes a chilled water return temperature
[.degree. C.], Ts denotes a chilled water supply temperature
[.degree. C.], Cp denotes specific heat [kJ/(kg.degree. C.)] of the
chilled water, and p denotes density [kg/m.sup.3] of the chilled
water.
[0135] Also, the required load determination unit 112 calculates an
excess load value .DELTA.Qt based on Equation (2), as in step S151
of FIG. 4.
[0136] In step S262, the chiller-to-be-stopped selection unit 133
obtains, for each operating chiller, a COP when the chiller is
operated with the excess load value .DELTA.Qt, in a similar manner
to that described above.
[0137] Then, the chiller-to-be-stopped selection unit 133 selects
the chiller having the lowest COP as a chiller to be subjected to
stage decrease, i.e., a chiller to be stopped. The chiller having
the lowest COP is stopped, thereby enabling an increase in the COP
of the entire chiller system 1. The operation command unit 141
transmits a control signal as a stop command to the selected
chiller. Further, the operation command unit 141 transmits to the
other operating chillers, a control signal as a flow amount command
for changing load sharing. For example, the operation command unit
141 proportionally distributes the required load calculated by the
required load calculation unit 113 according to the number of
operating chillers, and transmits a control signal to each chiller
so that the chiller is operated with a load resulting from the
proportional distribution.
[0138] Thus, the required load determination unit 112 determines
whether the required flow amount is satisfied with the operating
chillers, in addition to whether the required load is satisfied
with the operating chillers. Thereby, it is possible to cope with
the case in which the required flow amount in addition to the
required load are set, and it is possible to select the chiller to
be subjected to stage increase or stage decrease in such a manner
that the COP of the chiller system 1 increases.
[0139] As described above, the chiller control apparatus 100
obtains the COP depending on environment of the chillers and
selects based on the obtained COP, a chiller whose operation state
is to be changed. Thereby, it is possible to appropriately select a
chiller to be subjected to stage increase or stage decrease
depending on a situation, in order to efficiently operate the
entire chiller system stage.
[0140] Further, an operator of the chiller system 1 can operate the
chiller system 1 while keeping the optimal operation range even
when the operator does not know the characteristics of the chillers
in detail.
[0141] Further, a program for realizing all or part of functions of
the chiller control apparatus 100 may be recorded in a
computer-readable recording medium, and a computer system may read
and execute the program recorded in this recording medium to
perform the process of each unit. Further, the "computer system"
cited herein includes an OS and hardware such as peripheral
devices.
[0142] Further, the "computer system" also includes a
homepage-providing environment (or a display environment) if a WWW
system is used.
[0143] Further, the "computer-readable recording medium" refers to
a portable medium such as a flexible disk, a magnetic optical disc,
a ROM, and a CD-ROM, or a storage device such as a hard disk
embedded in the computer system. The "computer-readable recording
medium" also includes a recording medium that dynamically holds a
program for a short time, like a communication line in a case in
which the program is transmitted via a network such as the Internet
or a communication line such as a telephone line, or a recording
medium that holds a program for a certain time, like a volatile
memory in the computer system including a server and a client in
the above case. Further, the program may be a program for realizing
part of the above-described functions or may be a program capable
of realizing the above-described functions in combination with a
program already recorded in the computer system.
[0144] While the embodiments of the present invention have been
described above with reference to the drawings, a specific
configuration is not limited to the embodiments, and various
variations made without departing from the scope of the present
invention fall within the present invention.
INDUSTRIAL APPLICABILITY
[0145] The present invention is suitable for use in a chiller
control apparatus that controls chillers in a chiller system
including a plurality of chillers.
DESCRIPTION OF REFERENCE NUMERALS
[0146] 100: chiller control apparatus [0147] 111: data acquisition
unit [0148] 112: required load determination unit [0149] 113:
required load calculation unit [0150] 121: stage increase
determination unit [0151] 122: insufficient load value calculation
unit [0152] 123: chiller-to-be-operated selection unit [0153] 131:
stage decrease determination unit [0154] 132: excess load value
calculation unit [0155] 133: chiller-to-be-stopped selection unit
[0156] 141: operation command unit [0157] 151: operation pattern
extraction unit
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