SG191930A1

SG191930A1 - Heat source system, control method therfor, and program therefor

Info

Publication number: SG191930A1
Application number: SG2013053228A
Authority: SG
Inventors: Yuji Miyajima; Hiroshige Kikuchi; Takanari Mizushima; Noboru Oshima; Koji Suzuki
Original assignee: Hitachi Ltd
Priority date: 2011-01-11
Filing date: 2012-01-10
Publication date: 2013-08-30
Also published as: JP2012145263A; WO2012096265A1; CN103314266A

Abstract

Provided is a heat source system for which the system COPis improved without reducing an operating efficiency of the cold source; also provided are a control method therefor and a program therefor. This heat source system (N1) is one for which pumps (P, P3) which transmit a heating medium to a cold source (R) that cools the heating medium and/or to a heat exchangerthat exchanges heat between the cooled heating medium and a load (1), the cold source (R), and a heat exchanger for the load (1), are connected by pipes (rl, r2) through which the heating medium flows. The heat source system has : load heat amount measurement units (3, 4) that measure an amount of heat which the heatingmedium exchanges with the load (1); a cold water return temperature measurement unit (4) that measures the temperature of the heating medium (R) that exchanges heat with the load (1) and returns to the cold source; and a first control unit (2) that lowers a temperature set value of the heating medium atan outlet of the cold source (R) when the temperature of the heating medium falls below the temperature set value thereof and a difference with the temperature set value of the heating medium at the outlet of the cold source (R) becomes less than a predetermined value.

Description

{ DESCRIPTION} {Title of Invention!

HEAT SOURCE SYSTEM, CONTROL METHOD THEREFOR, AND PROGRAM

THEREFOR

{Technical Field) [ 0001} ‘The present invention relates to a heat source system of facilities requiring cooling such as buildings, factories, data centers, and local heating and cooling, and more particularly to a heat source system which performs energy saving, a control method therefor, and a program therefor. { Background Art} {0002}

The heat source system is conventionally a facility for circulating celd water, which is produced by a chiller, in a room or an apparatus on a load side and cooling the room or the apparatus on the load side by exchanging heat with air on the load side. The chiller is controlled in a capacity corresponding to the load size according to an increase or decrease of the lecad. Further, the number of the chiller is increased or decreased so as to supply a capacity corresponaing to the load in some cases. The cold water is circulated by a pump between the load side and the chiller. { 0003}

There are following Patent Documents 1, 2 as prior art documents related to the present invention. Patent Document 1 describes that if an operational round~trip temperature difference, which is a round-trip temperature difference of a heat medium during operation, 1s less than a set round-trip temperature difference, which is a round-trip temperature difference of the medium at the time of design, the heat medium flow rate is shifted fo an excess flow rate. Patent Document 2 describes an operation control method for a cold source machine capable of improving a system COP (Coefficient Of

Performance) under consideration of auxiliary machines such as cold water pumps, cooling water pumps, and cooling towers. { Citation List} { Patent Literatures} {0004} { Patent Document 1}

Japanese Patent No. 3854586 { Patent Document 2}

Japanese Patent Application Publication No. 2008-134013 {Summary of Invention} { Technical Problem} { 0005}

The heat source system is designed with a flow rate condition and a temperature cf cold water corresponding to a iy maximum load expected at the time of design, however, a temperature of returning water from the load is low in many cases in actual operations, with respect to the round-trip temperature difference used to design the load of the cold water.

FIG. 18 is a diagram showing a relationship between the CCP and a cooling amount (%) in a centrifugal chiller. In an operation state in which the round-trip temperature difference for the load of cold water is small, the COP of the chiller decreases and the flow rate reguired for cooling the load increases, and hereby the required pump power increases in some cases as shown in FIG. 18. {0006}

Further, there is a problem that the cooling amount of the load in the designed flow rate decreases and the designed maximum amount of heat processing cannot be performed. For example, when cone chiller and one constant flow rate pump are provided, if the flow rate of the pump is increased before the cooling capacity of the chiller becomes 100 % when the temperature difference is small, two chillers and two pumps are required to be operated instead of cone chiller and one pump.

Therefore, the system COP ¢f the heat scurce system decreases. {000M

In view of the actual circumstances described above, the object of the present invention ls fo provide a heat source system which improves a system COP without decreasing an operating efficiency of a cold source, and also a control method therefor and a program therefor. { Sclution to Problem) {0008}

A heat source system accerding to ciaims 1, Z, 5 is one for which pumps that send a heat medium to at least one of a cold scurce for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold source, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, and has the following characteristics. {0009

The heat source system according to claim 1 includes a load heat amount measurement unit that measures an amcunt of heat which the heat medium exchanges with the load, a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the load and returns to the cold source, and a first control unit that lowers a temperature set value of the heat medium at an outlet of the cold source, 1f a temperature of the heat medium falls below a temperature set value thereof and a difference between the temperature of the heat medium and the temperature set value of the heat medium at the outlet of the cold source becomes less than a predetermined set value. { 0010}

The heat source system according to claim 2 includes a load heat amount measurement unit that measures an amount of heat which the heat medium exchanges with the load, a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the lead and returns to the cold scurce, and a second control unit that changes a temperature set value of the heat medium at an outlet of the cold source to be lower than a predetermined temperature set value at the time of a maximum load. {0011}

The heat source system according to claim 5 includes a ioad heat amount measurement unit that measures an amount of heat which the heat medium exchanges with the load, a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the 1cad and returns to the cold source, a heat medium flow rate measurement unit

That measures a flow rate of the heat medium which exchanges heat with the load, and a third control unit that raises a temperature set value of the heat medium which is cooled by the cold source 1f the flow rate of the heat medium is in a set range of temperature raising determination flow rate, and on the other hand, lowers the temperature set value of the heat medium which is cocled by the cold source if the flow rate of the heat medium is in a set range of temperature lowering determination flow rate and the temperature of the heat medium is lower than a predetermined temperature lowering determination temperature. {0012}

Contrel methods according to claims 11, 12, 15 for heat source systems are control methods for heat source systems according to claims 1, 2, 5, respectively. {0C13}

A program according to claim 19 for the heat source system ig a program for performing on a computer the control method according to any one of claims 11, 12, 13 for the heat source system. { Advantageous Effects of Invention} {0014}

According to the present invention, it is possible to provide a heat source system which prevents the system COP from decreasing without reducing the operating efficiency of the cold source, and aisc a control method therefor, and a program therefor. { Brief Description of Drawings} {0015}

FIG. 11s ablockdiagramof a heat source system according to a first embodiment of the present invention.

FIG. 2A is a diagram showing an operation example of two chillers as cold sources when a cold water cutlet temperature is 7 °C.

FIG. 2B is a diagram showing an operation example of one chiller as a cold source when the cold water outlet temperature is 5.5 °C.

FIG. 3 is a diagram showing a graph of a relationship between a coefficient of performance (COP) ratio (%) and a cooling load factor (%) per chiller when the cold water cutlet temperatures are 5.5 °C and 7 °C.

FIG. 4 is a diagram showing a control flow of a control method for the heat source system according to the first embodiment.

FIG. 5 is a block diagram showing a heat source system according to a second embodiment of the present invention.

FIG. & is a diagram showing a control flow of a control method for the heat source system according to the second embodiment.

FIG. 7 is a diagram showing power of cold water pumps, power of chillers as cold scurces, and total power consumption, against cold water feed temperature (temperature at the outlets of cold sources).

FIG. 8 is a block diagram showing a heat source system according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a control flow of a control method for the heat source system according to the third embodiment.

FIG. 10 is a block diagram showing a heat source system according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a contrecl fiow of a control method for the heat socurce system according to the fourth embodiment.

FIG. 12 is a diagram showing a COP against a cooling amount {%} at each cold water feed temperature (temperature at an outlet of a chiller as a cold source).

FIG. 13 is a diagram showing power of cold water pumps, power of chillers as cold sources, and total power consumption, against cold water feed temperature (temperature of cold water going out of the ccld sources) when cold sources of a constant flow rate are controlled in the number thereof.

FIG. 14 is a diagram showing a relationship between power and a flow rate when each pump controiled in the number thereof is controlled by a constant flow rate control or a variable flow rate control (inverter control}.

FIG. 15 is a block diagram showing a heat source system according to a fifth embodiment of the present invention.

FIG. 16A is a diagram showing a total head against a flow rate of device characteristics of a pump.

FIG. 16B is a diagram showing power of a pump against the flow rate.

FIG. 16C is a diagram showing a pipe resistance against the fiow rate.

FIG. 17 is a block diagram showing a heat source system according tc a sixth embodiment of the present invention.

FIG. 18 is a diagram showing a relationship between the

COP and a cooling amount (%) in a centrifugal chiller. { Description of Embodiments} {0016}

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Heat source systems N (N1 to NS} according to the embodiments of the present invention are heat source systems for cooling facilities such as buildings, factories, data centers, and local heating and cooling. {001% <<First Embodiment>>

FIG. 1 is a block diagram of a heat source system N1 according te a first embodiment of the present invention. The heat source system NI according to the first embodiment includes one or more cold sources R (RL, R2, ~--) which cool water as a heat medium and provide the cold water of desired temperature, and loads 1 (1a, 1b, ===} {alr in cooling target facilities) el which are heat exchanged in heat exchangers (nct shown) with the cold water sent from the cold sources R. {0018}

The heat source system Nl includes cold water pumps P (PI,

P2, ———) which circulate water as a heat medium to each of cold sources R provided on the primary side, pumps P3 (P3a, P3b, ——-) which send the coid water produced by the cold sources R to each of the loads 1 (la, lb, ---) provided on the secondary side, a water tank 5 having a low temperature side tank 5A in which the cold water produced by the cold sources R 1s stored and a high temperature side tank 5B in which water heated by heat exchanging with the lcads 1 is stored, and a computing unit 2 which controls the heat source system NIL. {0019}

The cold water pumps P and the pumps P3 perform rated operations, respectively. The computingunit 2 is a controller such as a PLC (Programmable Logic Controller). Control of the heat source system N1 is performed by executing a program stored in a memory of the controller. 200 {0020}

The cold water ccoled by the cold sources R (R1, RZ} is sent to and stored in the low temperature side tank 5A via cold water liines rl, rZ2 by the cold water pumps P (Pl, P2), respectively. The coldwater stored in the low temperature side tank 5A is sent to each of the leads 1 (la, lb, ---) by the pumps

P3 (P3a, P3b, ——-) on the secondary side. The cold water which has been heated by heat exchanging with the loads 1 (la, 1b, -——-) 1s sent to and stored in the high temperature side tank 5B of the water tank 5 by the pumps P3 on the secondary side. { 0021}

The cold water in the high temperature side tank 5B is sent by the cold water pumps P (Pl, P2) on the primary side to the cold sources R (R1, RZ) to be cooled again, and sent to and stored in the low temperature side tank 3A of the water tank 5. The heat source system Nl includes a flow rate sensor 3 and a temperature sensor 4 as sensors for measuring physical guantities thereof. The flow rate sensor 3 measures a flow rate of the cold water which exchanges heat with the loads 1 {la,

I5 1b, ---) in the heat exchangers (not shown) and returns to the cold sources R, and the temperature sensor 4 measures a temperature (cold water return temperature) of the returning cold water. The flow rate sensor 3 and the temperature sensor 4 are adapted to respectively measure the flow rate and temperature (cold water return temperature) of the cold water which is sent from the cold scurces R (Rl, RZ) and heated by heat exchanging with the loads 1. {0022}

The cold source R 1s a cold water production heat source system composed of chillers such as a centrifugal chiller and an absorption chiller, and direct-contact cooling towers or closed-circuit cooling towers. The cold sources RR (R1, RZ} are, for example, chillers which are capable of controlling the temperature (cold water outlet temperature} of the cold water cecled by the cold scurces R to be constant, and are capable of changing a set value of the cold water cutlet temperature {outward temperature) of the cold sources R. The cold sources

R are capable of setting the cold water outlet temperature lower than the temperature set value of the cold water to be supplied to the loads 1. {0023

Controls of the pumps 3 (F3a, P3b, -~-} on the secondary side may be flow rate controls such as an optimized flow rate i5 control and a constant pressure control of the cold water. As described above, the heat source system Nl is configured with, for example, a plurality of chillers as the heat sources R, and the cold water is sent at a constant flow rate by the cold water pumps P on the primary side and pumps P3 on the secondary side, which perform the rated operations. {0024

FIGS. 2A and ZB are diagrams showing opsraifion siate examples when cold water temperature of chillers Rt as cold sources R 1s lowered, wherein FIG. ZA shows an cperaticn example of two chillers Rt as cold sources R when a cold water outlet temperature is 7 °C, and FIG. 2B shows an operation sxample of one chiller Rt as a cold scurce R when the cold water cutlet temperature is 5.5 °C. FIG. 3 shows a graph of a relationship between a coefficient of performance (COP) ratic (%) and a cooling lead factor (%) per chiller Rt when the cold water cutlet temperatures of the chillers RT as The celd sources R are 5.5 °C and 7 °C. : { 0025)

In FIG. 2A, a cold water inlet temperature which is a temperature of the cold water entering each of chillers Rtl,

Rt2 as cold sources Rl, R2 is 8.5 °C, and the cold water outlet temperature thereof is 7 °C (see FIG. 3). When the cold water cf a designed flow rate flows with 1.5 °C temperature differences between the cold water inlet temperature and the cold water outlet temperature, the two chillers are operated with the load factor 30 % of each of chillers Rtl, Rt2 as the cold sources R1 and the total load factor 60 % of the cold source

RI. In FIG. 2B, the chiller RZ is not operated, and the cold water outlet temperature of the chiller Rtl as the cold scurce

R1 is 5.5 °C, and the cold water inlet temperature thereof is 8.5 °C. This means that the Temperature differences between the cold water inlet temperature and the ccld water outiet temperature cf the chiller Rt: is 3 °C, and one chiller Rtl as the cold source R1 with 60 % lcad factor is capable of processing the loads (see FIG. 3). The cold source Rl may be the chiller

Rtl and the cold source RZ may be the chiller RtZ2. {002¢} 100 % load facter in FIG. 3 shows an example of 5 °C temperature differences between the c¢old water inlet temperature and the cold water cutlet temperature cf each of the chillers Rtl, Rt? with rated flow rates. In FIGS. 1 and 2, although the cooling towers and cooling water pumps sending the cooling water from the cooling towers are not illustrated, they are cperated in conjunction with each of chillers Rt1, Rt2 as the cold scurces R. In FIG. 3, by lowering the cold water outlet temperature of the cold sources R, the number of the cold sources R in operation is reduced. In other words, operations of the chillers Rtl, RtZ turn to be an operation of only the chiller Rtl, and thereby the COP ratio is improved. Further, the number of pumps in operation is reduced, and powers of the cold water pump P, the cooling water pump sending the cooling water from the cooling tower, and the chiller Rtl as the cold source R per unit load, are reduced compared with a case of two chillers. The centrifugal chiller may be an inverter centrifugal chiller, and the COP of the inverter centrifugal chiller is higher than that of a constant rate centrifugal chiller. In a heat source of heat pump type targeting a heating load, when a temperature of returning hot water is higher than a designed value, by raising a hot water cutlet temperature and by raising a load factor of the heat source of heat pump type, the COP of the heat source operation is improved and a system

COP of a heat source system is improved, and thereby power consumption is reduced. {0027} <Control method for heat source system Nl»

Next, a control method for the heat source system N1 will be described with reference to FIG. 4 which shows a control flow therecf. The control of the heat source system N1 shown in FIG. 4 is performed by the computing unit 2 at a predetermined time interval, for example, at any time interval such as 5 minutes interval, 1 hcur interval by measuring time using a timer.

First, in Step 5100, a flow rate (cold water flow rate) and a temperature (cold water return temperature) of the cold water returning to the cold sources R after heat exchanging with the loads 1 (la, 1b, ---) are measured respectively by the flow rate sensor 3 and the Temperature senscr 4 in FIG. 1. In addition, a temperature (cold water outward temperature) of the cold water on an outward path to the loads 1 from the cold sources R 1s chbtained from a temperature control of the cold water in the cold sources R. {0028}

An amount of heat exchanged with the loads 1 is calculated from the flow rate of the cold water measured by the flow rate sensor 3 and a temperature difference between the temperature of the cold water on the outward paths of the cold sources R and the temperature of the cold water measured by the temperature sensor 4 on a return path after heat exchanging with the loads 1. The temperature of the cold water on the outward raths of the cold sources R may be measured by providing a temperature sensor in the low temperature side tank 5A of the water tank 5 or in a pipe leading to the loads 1 on the secondary side, or may be obtained from a cooling control of the cold sources R. { 0029}

Next, in Step 5101, 1t is determined whether or not the flow rate of the cold water measured by the flow rate sensor 3 is smaller than a minimum flow rate of the cold water pump

P plus B (margin amount). If the flow rate of the cold water is smaller than the minimum flow rate of the cold water pump

P plus B (margin amount) (“Yes” in Step 5101), the control flow goes to Step S102, and it is determined whether or not the flow rate of the cold water measured by the flow rate sensor 3 is equal to or larger than the minimum flow rate of the cold water rump P. { 0030}

Tf the flow rate of the cold water measured by the flow rate sensor 3 is equal to or larger than the minimum flow rate of the cold water pump P (“Yes” in Step £102), the control flow goes to Step 5105, and a current set value of the temperature of the cold water on the cutward paths of the cold sources R is maintained. Cn the other hand, if the flow rate of the cold water measured by the flow rate sensor 3 is smaller than the minimum flow rate of the cold water pump P ("No” in Step S102), the control flow goes to Step S106, and a temperature set value of the cold water on the outward paths of the cold sources R is raised by a predetermined value, for example, 0.5 °C, 1 °C.

A temperature width to be raised can be set appropriately to any value in each heat source system. The temperature width to be raised is, for example, 0.5 °C and changed periodically.

IS {0031}

In Step 31C1, if the fiow rate of the cold water is not smaller than the minimum flow rate of the cold water pump P plus

B (margin amount), i.e., the flow rate of the ccld water is equal to or larger than the minimum flow rate of the cold water pump

P plus B (margin amcunt) (“No” in Step 8101), the control flow goes to Step S103, and it 1s determined whether or not the temperature of the cold water returning to the cold sources R after heat exchanging with the loads 1 {la, 1b, ---) is lower than a temperature lowering determination remperature.

{0032}

The temperature lowering determination temperature is, for example, less than the designed value at the time of the maximum load. For example, the temperature lowering determination temperature is 8 °C when the cold water outward temperature is 6 °C and the cold water return temperature is 11 ec. Here, the temperature lowering determination temperature 1s a temperature of the cold water and is set to have a width such as 8 °C * o °C. Although the temperature lowering determination temperature can be 8 °C without a width, it is desirable to have a width such as 8 °C + o °C because the control of the heat source system is more stable and practical when the temperature lowering determination temperature has the width. Note that the temperature lowering determination temperature can be set arbitrarily for each of the heat source systems to be applied. {0033}

If the cold water return temperature ls determined not to be lower than the temperature lowering determination

Temperature (“No” in 3tep S103), it is determined whether or not the temperature (cold water return temperature) of the cold water retuning to the cold sources R after heat exchanging with the lcads 1 (la, 1b, —---) is ecual to the temperature lowering determination temperature (Step $104). Tf the temperature

{cold water return temperature) of the cold water retuning after heat exchanging with the loads 1 (la, 1b, --=}) is determined to be equal to the temperature lowering determination temperature (“Yes” in Step 3104), the control flow goes to Step

S105, and the current set value of the temperature of the cold water on the cutward paths of the cold sources R is maintained. {0034}

On the cther hand; in Step 5104, if the temperature (cold water return temperature) of the cold water retuning to the cold sources R after heat exchanging with the loads 1 (la, lb, —---) is determined to be different from the temperature lowering determination temperature, i.e., higher than the temperature lowering determination temperature (“No” in Step S104}, the control flow goes to Step 5106, and the temperature set value of the cecld water on the outward paths of the cold sources R is raised by the predetermined value. { 0035;

In Step 5103, 1f the cold water return temperature is determined to be lower than the temperature lowering determination temperature (“Yes” in Step S103), it is determined whether or not the temperature set value of the cold water on the cutward paths of the cold sources R (Rl, RZ) is a specific minimum value of the temperature set value determined by devices of the cold sources R (Step S107). If the temperature get value of the cold water on the outward paths of the cold sources R (R1, R2) is determined to be the specific minimum value of the temperature set value determined by the devices of the cold sources R ("Yes” in Step S107), the control flow goes to

Step 8105, and the current set value of the temperature of the cold water on the outward paths of the cold sources R 1s maintained {Step $5105). {0036}

Cn the other hand, in Step 3107, if the temperature set [0 walue of the cold water on the cutward paths of the cold sources

R (Rl, RZ} is determined not to be the specific minimum value of the temperature set value determined by the devices of the cold sources R (“"No” in Step 5107), the temperature set value of the cold water on the outward paths of the ccld sources R is raised by a predetermined value, for example, 0.5 °C, 1 °C.

The temperature width to be raised is, for example, 0.5 °C and changed periodically (Step S108). At this time, the temperature set values of the cold water on the cutlets (outward paths) of the cold sources R are changed in some cases to be lower than a predetermined temperature set value at the time of the maximum load. Hereinabove, a flow of the control method for the heat source system V1 shown in FIG. 4 has been explained. {0037

According te the control method for the heat source system

Nl, at the time of low load, even if the cold water temperature 1s lowered when the cold water on the secondary side is the minimum flow rate and a minimum operation number (for example, one} of the cold heat sources R is enough for cooling loads, the flow rate of the cold water does not decrease, and thereby the power of the cold water pumps P, and the pumps P3 cannot be reduced. Therefore, at the time of low load, the cold water temperature of the cold sources R 1s not lowered, but the temperature when the cold water is the minimum flow rate is maintained. Thus, it is possible to prevent the decrease of the coefficient of performance {COP) caused by lowering the cold water outlet temperature of the chillers Rt as the cold sources

R. {0038}

Characteristics of the heat source system Nl according to the first embodiment are as follows. 1f the coldwater return temperature (the temperature, which 1s measured by the temperature sensor 4, of the cold water returning to the cold resources R after heat exchanging with the loads 1) on the secondary side is low, the cold water feed temperature (the outlet temperature of the cold water cooled by the cold sources

R) is lowered so as to increase a temperature difference between the cold water return temperature and the cold water feed temperature. By increasing the temperature difference, a heat amount per unit flow rate is increased and an efficiency of the system is increased, and thereby it 18 possible to reduce waste of the power of the ccld water pumps P on the primary side and the power of the pumps P3 on the secondary side. Incidentally, the cold water feed temperature is the same as the cold water outward temperature or substantially the same. {0039}

For the chillers Rtl, Rt2 as the celd sources R whose efficiency is lowered in general when the cold water temperature is lowered, it is possible to prevent the temperature difference from reducing by lowering the temperature of the cold water, and to prevent the decrease of the COP of the chillers Rtl, Rt2 as the cold sources R caused by the increase of the number of the chillers in operation, thereby increasing the overall system efficiency. { 0040; <<Second Embodiment>>

FIG. 5 1s a block diagram showing a heat source system

NZ according to a second embodiment of the present invention.

The heat source system N2 according to the second embodiment includes one or more cold sources R (Rl, RZ, ~---) which cool water as a heat medium and provide the cold water of desired temperature, and loads 1 {la, 1b, ~--) which are heat exchangsd in heat exchangers (not shown) with the cold water sent from the cold sources R. In FIG. 5, bypass routes between feed headers and return headers are omitted. The heat source system

NZ includes cold water pumps P (Pl, P2, ~~~) which are inverter controllied and circulate the cold water to each of cold sources

R, and a computing unit Z which controls the heat source system

NZ (cold sources R, cold water pumps P, and the like). { 0041;

The computing unit 2 is a controller such as a PLC (Programmable Logic Controller). Control of the heat source system N2 is performed by executing a program stored in a memory of the controller. The cold water produced by the cold sources

R (Rl, RZ, ---) 1s sent by the cold water pump P (Pl, PZ, ~~~) to the loads 1 (la, 1b, -—--} from the cold sources R (R1, RZ, ~--} via the cold water lines (rl, r2, =-~-}, respectively. {0042}

The heat source system NZ includes a flow rate sensor 3 and a temperature sensor 4 as sensors for measuring physical quantities thereof. The flow rate sensor 3 measures a flow rate of the cold water which exchanges heat with the loads 1 (la, ib, ===} in the heat exchangers (not shown) and returns tc the cold sources R, and the temperature sensor 4 measures a temperature (cold water return temperature) of the returning cold water. Thus, the heat source system NZ is capable of measuring the flow rate and temperature (cold water return temperature) of the cold water, which is sent from the cold sources R (Rl, RZ, ---) and heated by heat exchanging with the ioads 1 in the heat exchangers (not shown), respectively by the flow rate sensor 3 and the temperature sensor 4. {0043}

The cold source R is a cold water production heat source system composed of chillers such as a centrifugal chiller and an absorption chiller, and direct-contact cooling towers or closed-circuit cooling towers. The cold sources R (R1, R2) are, for example, chillers which are capable of controlling the cold water feed temperature (cold water cutlet temperature of the cold water cooled by the cold sources R) to be constant, and are capable of changing a set value of the cold water feed temperature of the cold sources R. The cold water outlet temperature (cold water temperature at the outlets of the sold resources R) of the chillers as the cold resources R can be sei lower than the temperature set value designed for the cold water to be supplied to the loads 1. Controls of the cold water pumps

Pmay be flow rate controls such as an optimized flow rate control and a constant pressure control of the cold water. { D044} <Control method for heat source system NZ>

Next, a control method for the heat source system N2 will be described with reference to FIG. ¢ which shows a control flow thereof. The contrel of the heat source system N2 shown in FIG. 6 1s performed by the computing unit 2 at a predetermined time interval, for example, at any time interval such as 5 minutes interval by measuring time using a timer. {0045}

First, in Step S201 in FIG. €6, a flow rate (cold water flow rate} and temperature (cold water return temperature) of the cold water returning to the cold sources R after heat exchanging with the loads 1 (la, 1b, ---) are measured respectively by the flow rate sensor 3 and the temperature sensor 4. In addition, a temperature (cold water outward temperature) of the cold water on an outward path to the loads 1 from the cold sources R is obtained from a temperature control of the cold water in the cold sources R, or measured by a temperature sensor provided on a pipe of the outward path to the loads 1. An amcunt of heat exchanged with the loads 1 is calculated from the flow rate of the cold water and a temperature difference between the temperature of the cold water on the outward paths of the cold scurces R and the temperature (cold water return temperature) of the cold water measured by the temperature sensor 4 on a return path after heat exchanging with the leads 1. {0046}

FIG. 7 is a diagram showing power of cold water pumps P,

D5 power of chillers as cold sources R, and total power consumption against cold water feed temperature (cold water temperature at the outlets of the cold scurces RR). As shown in FIG. 7, the overall power consumption increases when the cutlet temperature of the cold sources R is high (the flow rate of the cold water pump P is large because the amount of heat exchange is small) and when the outlet temperature of the cold sources R is low {the flow rate of the cold water pump P is small because the amount of heat exchange 1s large}. {0047}

In Step S202 in FIG. 6, it is determined by using a range of temperature raising determination flow rate whether or not the flow rate of the cold water which exchanges heat with the lecads 1 is too small. Then, in Step S203, it is determined by using a range of temperature lowering determination flow rate whether or not the flcw rate of the cold water which exchanges heat with the loads 1 is too large. If the flow rate 1s too small, the efficiency of the cold scurcegs R decreases and thereby the system COP decreases. On the other hand, if the flow rate is too large, the efficiency of the pumps P decreases and thereby the system COP decreases. Therefore, in each case, the temperature set value of the cold water on the outward paths of the coid sources R is reset, so that the flow rates of the pumps P are optimized.

{0048}

In Step S202, it is determined whether or not the flow rate, detected by the flow rate sensor 3, of the cold water which exchanges heat with the lcads 1 (la, 1k, ---) is in the predetermined range of temperature raising determination flow rate (range of flow vate which is too small). In Step S202, if it is determined that the flow rate of the cold water which exchanges neat with the loads 1 is in the predetermined range of temperature raising determination flow rate (range of flow rate which is too small) (“"Yes” in Step 5202), it is determined whether or not a current temperature set value of the cold water on the outward paths of the cold sources R is a maximum value of the temperature set value determined by the devices of the cold sources R (Step 5204). {004%

If it is determined that the current temperature set value of the cold water on the outward paths of the cold sources R is the maximum value of the temperature set value of the cold sources R ("Yes” in Step 3204), the current temperature set wvalue of the cold water on the cutward paths of the cold sources

R is maintained (Step 5203). On the other hand, if it is determined that the current temperature set value of the cold water on the outward paths of the cold sources R is not the maximum value of the temperature set value of the cold sources

R (“No” in Step 5204), the current temperature set value of the cold water on the outward paths of the cold sources R 1s raised by a2 predetermined value, for example, a temperature width such as 0.5 °C and 1 °C. A temperature width to be raised can be set appropriately to any value in each heat source system. The femperature width to be raised is, for example, 0.5 °C and changed periodically (Step 3206). {0050}

On the other hand, in Step 202, if it is determined that the flow rate of the cold water which exchanges heat with the loads 1 is not in the predetermined range of temperature raising determination flow rate (range of flow rate which is too small) ("No” In Step 5202), it is determined whether or not the flow rate of the cold water which exchanges heat with the leads 1 [5 is in the predetermined range of temperature lowering determination flow rate (range of flow rate which is too large) in Step S203. If it is determined that the flow rate of the cold water which exchanges heat with the loads 1 is not in the predetermined range of temperature lowering determination flow rate (range of flow rate which is too large) (“WNo” in Step S203), the control flow goes to Step 5205, and the current temperature set value cf the cold water on the cutward paths of the cold sources R 1s maintained. { 0051}

On the other hand, 1f it is determined that the flow rate cf the cold water which exchanges heat with the loads 1 is in the predetermined range of temperature lowering determinaticn flow rate (range of flow rate which is too large) (“Yes” in Step 5203), the contrel flow goes to Step 3207, and it is determined whether or not a temperature of the flow returning from the loads 1 is lower than a predetermined temperature lowering determination ‘temperature. The temperature lowering determination temperature is, for example, less than the designed value at the time of the maximum load. For example, the temperature lowering determination temperature is 8 °C when the cold water outward temperature is €& °C and the cold water return temperature is 11 °C. Here, since the cold water flows in pipes, the temperature lowering determination temperature is set to have a width such as 8 °C £ 0.5 °C. Although the temperature lowering determination temperature can be 8 °C without a width, it is desirable to have a width such as 8 °C t 0.5 °C because the control of the heat scurce system is more stable and practical when the temperature lowering determination temperature has the width. Note that the temperature lowering determination temperature can be set arbitrarily for each of the heat source systems. { 0052}

In Step 5207, if it is determined that the temperature

{cold water return temperature) of the flow returning from the loads 1 is not lower than the predetermined temperature lowering determination temperature ("No” in Step 3207}, the control flow goes to Step 5208, and it is determined whether or not the temperature of the flow returning from the loads 1 is equal to the predetermined temperature lowering determination temperature. In Step S208, if it is determined that the temperature of the flow returning from the loads 1 is equal to the predetermined temperature lowering determination temperature {“Wes” in Step 5208), the control flow goes to Step 5205, and the current temperature set value of the cold water on the outward paths of the cold sources R is maintained. {0053

On the other hand, in Step 5208, if it is determined that the temperature of the flow returning from the loads 1 is not equal to the predetermined temperature lowaring determination temperature, l.e., higher than the predetermined temperature lowering determination temperature (“No” in Step $208), the control flow goes to Step 5206, and the current temperatures set value of the cold water on the outward paths of the cold sources

R is raised by a predetermined value, for example, a Lemperature width such as 0.5 °C and 1 °C. In Step 5207, if it is determined that the temperature of the flow returning from the loads 1 is lower than the predetermined temperature lowering determination temperature (“Yes” in Step 5207), the control flow goes to Step 5209, and it is determined whether or not the temperature set value of the cold water on the cutward paths of the cold sources R (Rl, RZ) is a specific minimum value of the temperature set value determined by the devices of the cold sources R {Step 3209}. { 0054}

In Step 209, if it is determined that the temperature set value of the cold water on the cutward paths of the cold sources i000 R (Rl, RZ) is the minimum value of the temperature set value of the cold sources R (“Yes” in Step 3209), the control flow goes to Step 3205, and the current temperature set value of the cold water on the outward paths of the cold sources R is maintained. On the other hand, in Step 209, if it is determined

I5 that the temperature set value of the cold water on the outward paths of the ccld sources R (Rl, RZ) is not the minimum value of the temperature set value of the cold sources R (“No” in Step

S209), the control flow goes to Step 8210, and the current temperature set value cf the cold water on the outward paths of the cold sources R is lowered by a temperature width such as 0.2 °C and 1 °C. The temperature width to be lowered is, for example, 0.5 °C and changed periodically (Step 5210). At this time, the temperature set values of the cold water on the outlets {outward paths) of the cold sources R are changed in some cases to be lower than a predetermined temperature set value at the time of the maximum load. Hereinabove, a flow of the control method for the heat source system NZ shown in FIG. 6 has been explained. {0055}

The heat source system NZ according to the second embodiment uses chillers capable of setting the cold water temperature of the chillers as the cold sources R to be lower than an initial Temperature self value, so that the cold water outlet temperature of the chillers as the cold sources R can be lowered by utilizing measured values of the cold water flow rate and the cold water return temperature. For example, it is possible to lower the cold water outlet temperature of the cold sources R so that the cold water pumps P operate at rated

I5 flows, thereby reducing the number of the cold water pumps P in cperation. Therefore, it is possible to reduce the cold water flow rate while the cold sources R are operated in high efficiency, thereby improving the COP of the heat source system

NZ. {0056} <<Third Embodiment>>

FIG. 8 is a block diagram showing a heat source system

N3 according to a third embodiment of the present invention.

The heat scurce system N3 according to the third embodiment includes any number of cold sources R (Ra, Rb, —---} connected in series instead of in parallel in the heat source system N2 according to The second embodiment. Since the heat source system N3 includes the cold scurces R (Ra, Rb, —---) connected in series, there 1s one cold water line rl, and one inverter-controlled pump P1 are used. When the cold sources

R are two, there are a high temperature side cold source Ra and a low temperature side cold scurce Rb. {0057}

This means that the heat source system N3 is a heat source system including two chillers connected in series as the cold sources R. One is a high temperature side chiller (Ra) which cools the loads, for example, from 16 °C to 11 °C at the time of the maximum lcad, and the other is a low temperature side chiller (Rb) which cools the loads, for example, from 11 °C to & °C at the time of the maximum load. In FIG. 8, two cold sources

R (Ra, Rb} connected in series are illustrated, but any number of the ccld sources R can be connected in series. The chiller as a high temperature side cold source Ra and the chiller as a low temperature side cold source Rb can be set at temperatures lower than temperature set values at the time of the maximum load. Since the other configurations of the heat source system

N3 are the same as the heat source system NZ according to the second embodiment, detailed description thereof will be omitted. { 0058} <Control method for heat source system N3>

Next, a control method for the heat source system N3 will be described with reference to FIG. 9 which shows a control flow thereof. The control of the heat source system N3 shown in FIG. 9 is performed by the computing unit 2 at a predetermined time interval, for example, at any time interval such as 5 minutes interval and 1 hour interval by measuring time using a timer. {0059}

The cold water outlet temperatures cf the chillers as the high temperature side and low temperature side cold sources Ra,

Eb can be lowered respectively from the temperature set values, according to the measured value of the cold water flow rate measured by the flow rate sensor 3 and the cold water return temperature measured by the temperature sensor 4. First, in

Step S301 in FIG. 9, a flow rate (cold water flow rate) and a temperature (cold water return temperature) cof the cold water returning to The cold sources R after heat exchanging with the toads 1 (1a, 1b, ——-) in heat exchangers (not shown) are measured respectively by the flow rate senscr 3 and the temperature sensor 4 shown in FIG. 8. A temperature of the cold water on an outward path to the loads 1 {la, 1b, ---) is obtained from a temperature control of the cold water cooled in the high temperature side and low temperature side cold sources Ra, Rb, or measured by a temperature sensor (not shown) provided on the outward path to the lecads 1 (la, 1b, ---). { D060}

An amount of heat exchanged with the loads 1 is calculated from a temperature difference between the temperature of the cold water on the outward path of the cold source Rb and the cold water temperature measured by the temperature sensor 4 on a return path. Next, in Step S302, it is determined by using [0 a range of temperature raising determination flow rate whether or not the flow rate of the cold water which flows for exchanging heat with the loads 1 is too small. Then, in Step S303, it is determined by using a range of temperature lowering determination flow rate whather or not the flow rate of the cold water which flows for exchanging heat with the loads 1 is too large. {0Ge1}

If the flow rate of the cold water which exchanges heat with the loads 1 in heat exchangers {not shown) is too small, the efficiency of the cold sources R (Ra, Rb) decreases and thereby the system COP of the heat source system N3 decreases.

On the other hand, if the flow rate is too large, the efficiency of the pump Pl decreases and thereby the system COP of the heat source system N3 decreases. Therefore, in each case, the temperature set values of the cold water on the outward paths of the cold sources Ra, Rb are reset, so that the flow rate of the pump Pl is optimized. {0062}

Firet, in Step S302, it is determined whether or not the flow rate, detected by the flow rate senscr 3, of the cold water which exchanges heat with the lcads 1 is in the predetermined range of temperature raising determination flow rate {range of flowrate which is too small). In Step 3302, if it is determined that the flow rate of the cold water which exchanges heat with the loads 1 in the heat exchangers (not shown) is in the predetermined range of temperature raising determination flow rate {range of flowrate which is tee small) (“Yes” in Step 3302), it is determined whether or not a current temperature set value i5 of the cold water on the outward path of the high temperature side and low temperature side cold sources Ra, Rb is a maximum value of the temperature set value determined by the devices of each of the cold sources RE (Ra, Rb) (Step S304). {0663}

If it is determined that the current temperature set value of the cold water on the outward path of the high temperature side and low temperature side cold sources Ra, Rb is the maximum value of the temperature set value determined by the devices of each of the cold sources R (Ra, Rb) (“Yes” in Step $304),

the current temperature set values of the cold water on each outward path of the high temperature side and low temperature side cold sources Ra, Rb are maintained (Step S305). On the other hand, if it is determined that the current temperature set value of the cold water on the outward path of the high temparature side and low temperature side cold scurces Ra, Rb 1s not the maximum vaiue of the temperature set value determined by the devices of sach of the high temperature side and low

Lemperature side cold sources Ra, Rb (“Neo” in Step S304), the current temperature set values of the cold water on the outward path ¢f the high temperature side and low temperature side cold sources Ra, Rb are raised by a predetermined value, for example, a temperature width such as 0.2 °C and 1 °C (Step S306}. A temperature width to be raised can be set appropriately to any walue in each heat source system. The temperature width to be raised is, for example, 0.5% °C and changed periodically. {0064}

On the other hand, in Step 302, if it is determined that the flow rate of the cold water which exchanges heat with the loads 1 (la, 1b, =-=--) is not in the predetermined range of temperature raising determination flow rate (range of flow rate which is too smail) (“No” in Step $302), it is determined whether or not the flow rate of the cold water which exchanges heat with the loads 1 is in the predetermined range of temperature _37-

lowering determination flow rate (range of flow rate which is too large). { 0065}

Tn Step $303, if it is determined that the flow rate of the cold water which exchanges heat with the loads 1 is not in the predetermined range of temperature lowering determination flow rate (range of flow rate which is too large) (“No” in Step 3303), the control flow goes to 3tep 3305, and the current temperature set values of the cold water on each outward path of the high temperature side and low temperature side cold sources Ra, Rb are maintained. {0066}

Cn the other hand, in Step 5303, if it is determined that the flow rate, detected by the flow rate sensor 3, of the cold water which exchanges heat with the loads 1 is in the predetermined range of temperature lowering determination flow rate (range of flowrate which is too large) {(“Yes” in Step 8303), the control flow goes to Step 5307, and it 1s determined whether or not a temperature of the cold water returning after heat exchanging with the loads 1 is lower than a predetermined temperature lowering determination temperature {Step S307). {0067}

The temperature lowering determination temperature is less than the designed value at the time of the maximum load,

for example, 12 °C (8 °C) when the cold water cutward temperature of the low temperature side cold source Rb is 5 °C (6 °C) and the cold water return temperature of the high temperature side cold source Ra is 15 °C. Here, since the cold water flows in pipes, the temperature lowering determination temperature is set to have a width such as 12 °C + 0.5 °C. Although the temperature lowering determination temperature can be 12 °C (8 °CYy without a width, it is desirable to have a width such as 12 °C £ 0.5 °C because the control of the heat scurce system is more stable and practical when the temperature lowering determination temperature has the width. Note that the temperature lowering determination temperature can be set arpitrariiy for each of the heat source systems. {0068}

In Step S307, if it is determined that the temperaturs of the cold water returning after heat exchanging with the loads 1 is not lower than the predetermined temperature lowering determination temperature ("No” in Step S307), the control flow goes to Step S308, and it is determined whether or not the temperature (cold water return temperature} of the cold water returning after heat exchanging with the loads 1 is equal to the predetermined temperature lowering determination temperature. In Step S308, if it is determined that the temperature of the flow returning from the lcads 1 (la, lb, ~~~)

is equal to the predetermined temperature lowering determination temperature {(“Yes” in Step $308), the control flow goes to Step 8305, and the current temperature sei values of the cold water on the outward paths of the high temperature side and low temperature side cold sources Ra, Rb are maintained. { 0069}

On the other hand, in Step 3308, if it is determined that the temperature of the flow returning after heat exchanging with the lcads 1 is not equal to the predetermined temperature lowering determination temperature (“No” in Step S308), the control flow goes to Step 2306, and the current temperature set values of the cold water on each outward path of the high temperature side and low temperature side cold sources Ra, Rb are raised by a predetermined value, for example, a temperature width such as 0.5 °C and 1 °C. In Step $307, if it is determined that the temperature of the flow returning after heat exchanging with the leads 1 (la, 1b, ---) is lower than the predetermined temperature lowering determination temperature (“Yes” in Step 8307), the control flow goes to Step S308, and it is determined whether or nct the temperature set value of the cold water on the outward path of the high temperature side and low temperature side cold sources Ra, Rb is a specific minimum value of the temperature set value determined by the devices of the high temperature side and low temperature side cold sources Ra,

Rb (Step S309). { 00708}

In Step 308, if it is determined that the Cemperature set walue of the cold water on the outward path of the high temperature side and low temperature side cold scurces Ra, Rb is the specific minimum value of the temperature set value determined by the devices of the high temperature side and low temperature side cold sources Ra, Rb (“"Yes” in Step 3309), the control flow goes to Step 5305, and the current temperature set values of the cold water on the outward paths cf the high temperature side and low temperature side cold sources Ra, Rb are maintained. {0071}

On the other hand, in Step 309, if it is determined that the temperature set value of the cold water on the outward path of the high temperature side and low temperature side cold sources Ra, Rb is not the specific minimum value of the temperature set value determined by the devices of the high temperature side and low temperature side cold sources Ra, Rb ("No” in Step S309), the control flow goss to Step 5310, and the current temperature set values of the cold water on the outward paths of the high temperature side and low temperature side cold sources Ra, Rb are lowered by a temperature width such wtf]

as 0.5 °C and 1 °C {Step 5310). The temperature width to be lowered is, for example, 0.5 °C and changed periodically. At this time, the temperature set values of the cold water on the outlets (outward paths) of the high temperature side and low temperature side cold sources Ra, Rb are changed in some cases to be lower than predetermined temperature set values at the time of the maximum lcad. Hereinabove, a flow of the control method for the heat source system N3 shown in FIG. 9 has been explained. {0072}

According to the heat source system N3, even when the heat sources R (Ra, Rb, -—-) are connected in series, by controlling the cold water cutlet temperature of the cold sources R to be low, it is possible tec reduce the cold water flow rate while the cold sources R are operated in high efficiency, thereby improving the COP of the heat scurce system N3. { 0073} <<Fourth Embodiment>>

FIG. 10 is a blcck diagram showing a heat source system

N44 according to a fourth embodiment of the present invention.

In the heat source system N4 according to the fourth embodiment, a known unit control (see 13% Edition, Air-Conditicning and

Sanitary Engineering Handbook, by The Society of Heating,

Air-Conditioning and Sanitary Engineers of Japan, pp. 632 to

635) cf two or more cold sources R (Rl, RZ, ---)} by the computing unit Z is added to the heat scurce system NZ according to the second embodiment. { 0074}

For increasing cor decreasing stages of two or more cold gources R (Rl, RZ, ---}, the temperatures of the cold water going cut of and returning to the cold sources R are measured so that the computing unit 2 can calculate the number of the stages by using the cold water flow rate and an amount of the loads. In [0 other words, the temperature of the cold water going out of the cold sources R is obtained from the control of the cold scurces

R or the temperature sensor 14, while the temperature of the cold water returning to the cold sources R after heat exchanging with the loads 1 (la, lb, ---) is measured by the temperature

I5 sensor 4. In addition, the flow rate of the cold water which exchanges heat with the loads 1 in heat exchangers (not shown) is measured by the flow rate senscr 3. Then, an amount of heat consumed in heat exchanging with the loads 1 is calculated by the computing unit 2 from a temperature difference between temperatures of the cold water going out of and returning to the cold sources R, and the flow rate of the cold water exchanging heat with the loads 1. { 6075}

An operation start/stop of the chillers as the cold resources R (Rl, RZ, —---} 1s performed by the unit contrecl by the computing unit 2, and includes performing an operation start/stop of the cold pumps P (Pl, P2, —---) and the chillers as the cold rescurces R. The ccld pumps ?P (Pl, PZ, =---) may be operated by a constant flow rate control or a variable flow rate control by a pressure control. Since the other configurations of the heat source system N4 is the same as the heat source system NZ according to the second embodiment, detailed description thereof will be omitted. {0G76} <Control method for heat source system N4>»

Next, a control method for the heat source system N4 will be described with reference to FIG. 11 which shows a control flow thereof. The control of the heat source system N4 shown in FIG. 11 is performed by the computing unit 2 at any predetermined time interval by measuring time using a timer.

In the heat source system N4, cold water outlet temperatures of the cold sources R (Rl, RZ, =---} are changed based on the cold water flow rate and the cold water return tempsrature {temperature of the cold water returning to the cold scurces

RY. {0077}

First, in Step S400 in FIG. 11, the cold sources R as heat source machines are assumed to output maximum powers at the set

{designed) flow rate and the set (designed) temperatures (cold water inlet temperature, cold water outlet temperature), and the unit control for increasing or decreasing the number of the cold scurces R is performed based on the values of the flow rates and the temperatures. The number of the cold sources R is contrclled based on upper and lower limit values of the cold water Flow rate and a cooling amount. Since Steps S401 to 5410 in FIG. 11 showing the control method for the heat source system

N4 are the same as Steps 3201 to 3210 in FIG. 6 showing the control method for the heat source system N2, detailed description thereof will be omitted. {0078}

Conventionally, when a temperature difference between the cold water inlet temperature and the cold water cutlet temperature of the colds sources Ris smell (when the cold water feed temperature (temperature of the cold water going out of the cold sources R) is low), as shown in FIG. 7, the ccoling amount decreases and the efficiency of the cold sources R falls, and thereby the cold water flow rate 1s increased to increase the number of the cold sources R. By increasing the number of the cold sources R {R1L, RZ, -—--}, the cold water flow rate is increased, and thereby the power of the cold pumps per heat amount is increassd. { 0079}

In contrast, according to the heat source system N4, as shown in FIG. 11, since the cold water outward temperature (cold water feed temperature) is controlled to be lowered so as to increase a temperature difference between the cold water inlet temperature and the cold water outlet temperature of the colds sources R, a cooling amount is increased to increase a cooling load per flow rate, and thereby it is possible to operate the cold sources Rin a range of high efficiency {see FIG. 12). FIG. 12 is a diagram showing a COP against 2 cooling amount (%) at each cold water outlet femperature (cold water feed temperature) of chillers as cold sources. Therefore, it is possible to prevent increasing the number of the cold sources k (Rl, RZ, ---), thereby reducing total power consumption for the heat scurce system N4 as shown in FIGS. 7 and 13. {0080}

FIG. 13 is a diagram showing the power of the cold water pumps P, the power of the chillers as the cold sources R, and the total power consumption, against the cold water feed temperature (temperature of the cold water going out of the cold sources R) when the cold sources BR (Rl, R2, ---) of a constant flow rate are controlled in the number thereof. Further, by controlling the number of the cold sources R, it is possible to operate the cold sources R having the number and the flow rates more precisely appropriate to the loads 1.

{oesll

FIG. 14 is a diagram showing a relationship between the power and the flow rate when each cold water pump P of the unit control is controlled by a constant flow rate control or a wvariable flowrate control (inverter control). As shown in FIG. 14, although the power of fhe cold pumps increases stepwise along a solid line indicating one, two, and three pumps when the constant flow rate control is performed for each cold pump

P of the unit control, it is possible to reduce the power of the pumps corresponding to hatched portions by performing the variable flow rate control (inverter control} for each pump P, thereby performing energy savings. {0082} <<Fifth Embodiment>>

FIG. 15 is a block diagram showing a heat source system

N5 according to a fifth embodiment of the present invention.

The heat source system NS according to the £ifth embodiment is a facility which is capable of switching by a computing unit 52 cold water productions by cold sources R (Rl, R2, ---), and has a cold water tank. The heat source system Nb includes the cold sources R (Rl, RZ) and cooling towers Ry as the devices for producing the cold water which cools loads 51 (51a, 5ib, ---), and performs the cold water production by the cold sources

R.

{ 0083}

The heat source system NS includes on the primary side cold water pumps Pla, P5lb of rated operations which flow the water returning from the loads 51 to each of the cold sources

RL, RZ, and cooling water pumps F5Za, P5Z2b of rated operations which flow the cooling water cooled by the cooling towers Ry to each of the cold sources R1, RZ via a cooling water line tl.

The heat source system NS further includes awater tank 55 having a low temperature side tank 553A in which cold water cooled by the cold sources R is stored, and a high temperature side tank 55B in which the cold water heated by heat exchanging with the loads 51 is stored. {0084}

The cold water sent to the cold sources R (R1, RZ) are sent to the low temperature side tank 55A of the water tank 55 respectively via the cold water lines rl, rZ2. On the loads 51 side of the secondary side, pumps P53 (53a, 53b, —---) in rated operation for sending the cold water which is cooled by the cold sources R and stored in the low temperature side tank 55A of the water tank 35% to each of the loads 51 (51a, 51lb, ---) are provided. Note that pressure control of feed headers on the secondary side ls omitted. For example, the cold water may be returned to the water tank so that discharge pressures of the pumps are constant.

{ 0085}

The heat source system Nb Includes as sensors a temperature sensor 54 which measures the temperature of the water returning to the cold scurces R on the primary side after heat exchanging with the loads 51 (51a, 51k, ---) in heat exchangers {not shown), and a flow rate sensor 53 which measures the flow rate of the water returning to the cold sources R. The heat source system Nb further includes the computing unit 52 such as a controller, as a control unit for controlling the heat source system NS. { 0086}

The computing unit 52 outputs control signals to the devices such as the cold scurces R while detection information is inputted therein from the flow rate sensor 53, the temperature sensor 54, and the like. The computing unit 52 controls the number of The cold sources R and the cooling towers

Ry. Although it is not necessary to control the number of the cold scurces R and The cooling towers Ry, it 1s desirable to contrel the number because the efficiency of the heat source system N5 becomes high. Switchingoperation of the cold sources

R by the computing unit 52 is instructed by calculating an optimized state of the operation so that energy consumption 1s minimized based on the conditions such as the loads 51. {oocg7}

The calculation of the energy consumption is performed by setting pipe resistances and device characteristics of cold water pumps P51, cooling water pumps PLZ, the pumps P53, the cold sources R, and the like, and using a simulator capable of calculating powers of the cold scurces R, the cold water pumps

P51, the cooling water pumps P52, the pumps P53, and the like, from operation conditions thereof. For example, the device characteristics of the cold water pumps P51, the cocling water pumps P52, and the pumps P53 are mentioned as a flow rate Q - a total head (see FIG. 164A) and the flow rate Q - a pump power {see FIG. 16B). FIG. 16C shows a relationship between a pipe registance and the flow rate QQ. {0088}

The device characteristics of the chillers as the cold

I5 sources R is mentioned as the characteristics indicating how much 1s the power at a temperature difference between the inlet temperature and the cutlet temperature, and a cooling amount (see FIG. 12). The heat source system Nb uses, in each operation state, the temperature {cold water outward temperature) of the cold water which is cooled by the cold sources R and stored in the low temperature side tank 550A of the water tank 55, the cold water flow rate measured by the fiow rate sensor 53, and the temperature (cold walter return temperature) cf the cold water measured by The temperature sensor 54. Incidentally, the outward temperature of the cold water stored in the low temperature side tank 55A is obtained by a cooling contrcl of the cold sources R, or measured by an cutward temperature sensor (not shown} which measures the temperature of the cold water on the outward path provided on the loads 51 side or the temperature of the cold water stored in the low temperature side tank 55A of the water tank 55. {0089}

When the temperature difference between the temperature {cold water outward temperature) of the cold water sent To the loads 51 and the temperature {(ccld water return temperature) of the cold water measured by the temperature sensor 54 is small and the flow rate of the cold water is large, the temperature set values of cold water outlets of a system including the cold sources R are lowered. At this time, the temperature set values of the cold water on the cutlets {outward paths) of the system including the cold sources R are changed in some cases to be lower than a predetermined temperature set value at the time of the maximum load. On the other hand, when the temperature difference between the temperature {cold water outward temperature) of the cold water sent to the leads 51 and the cold water return temperature is close to the designed value (set vaiue) and the fiow rate of the cold water is small, the state is controlled to be maintained. Incidentally, by performing a cooling load prediction by a known load prediction means, a control to reduce the number of the cooling towers Ry and the cold sources R in operation may be incorporated without performing a control of reducing the number of the cooling towers and the cold sources in operation with a margin for hunting prevention. { 0020}

As described above, since the temperature of the cold water outlet of the cold sources R may be measured by the temperature sensor provided on the cold water feed pipe lines or obtained from the contrcl of the cold sources R, the temperature can be obtained even if there is no temperature output from the cold sources R. {0091}

I5 <<«<Sixth Embodiment>>

FIG. 17 is 2 block diagram showing a heat source system

N¢ according to a sixth embodiment of the present invention.

The heal source system N6 according to the sixth embodiment is a facility which enables cold water production by chillers Rt (Rti, Rt2). The heat source system N6 includes the chillers

Rt as the devices for producing the cold water which cools loads 6l (¢la, &lb, ---), and performs the cold water production by the chillers Rt. {0092}

The heat source system N6 includes cold water pumps Péla,

P6lb which flow water returning after heat exchanging with the loads 61 respectively to the chillers Rtl, Rt2, and cooling water pumps P6Za, PoZb which flow cooling water cooled by cooling towers Ry respectively to the chillers Rtl, RtZ via a cooling water line t1. { 0093}

The cold water pumps P6la, P6lb and the cooling water pumps

PoZa, Pe2h are inverter controlled and different from the rated operation of the heat source system NS according to the fifth embodiment. In addition, unlike the heat source system Nb according to the fifth embodiment, the heat source system N6 does not include a tank. { 0094}

On the loads 61 side, inverter~controlled pumps P63 {Pé3a, 63b, —--~) for sending the cold water cooled by the chillers Rt (Rtl RtZ, ---) to each of the loads 61 (6la, 6lb, ---) are provided. The heat source system N6 includes, as sensors, an outward temperature sensor 64a for measuring the temperature of the cold water cooled by the chillers Rt and sent to the leads 61 side via the cold water lines rl, r2, a return temperature sensor 64b for measuring the temperature of the water returning to the chillers Rt after heat exchanging with the loads 61 (61a, 61lb, =-=-—) in heat exchangers (not shown), a flow rate sensor

63 for measuring the flow rate of the cold water returning to the chillers Et, an outside alr temperature sensor 44c for measuring a temperature of an cutside air, and a humidity sensor 65 for measuring a humidity of the outside air. {0095

The heat source system N& further includes a computing unit 62 such as a controller, as a control unit for controlling the heat source system N6. The computing unit 62 outputs control signals to the chillers Rt, the cooling towers Ry, cold water pumps P61, cooling water pumps P62, pumps P63, and the like, while detection information is inputted therein from the outward temperature sensor 64a, the return temperature senscr 64b, the flow rate sensor 93, the outside air temperature sensor 64c, the humidity sensor 65, and the like.

Is {0096

The computing unit 62 in the heat source system N6 controls the number of the cold chillers Rt and the cocling Towers Ry.

Although 1t is not necessary to control the number of the chillers Rt and the cooling towers Ry, it is desirable to control the number because the system COP of the heat source system Né becomes high. Switching operation of the cold sources R by the computing unit 62 is instructed by calculating an optimized state of the operation so that energy consumption is minimized based on the conditions such as the outside alr and the loads

{0097} :

The calculation of the energy consumption 1s performed by setting pipe resistances and device characteristics of the cold water pumps P61, the cooling water pumps P62, the pumps

P63, the chillers Rt, the cooling towers Ry, and the like, and using a simulator capable of calculating powers of the chillers

Rt, the cooling towers Ry, the cold water pumps P61, the cooling water pumps P62, the pumps P63, and cooling tower fans, from operation conditions thereof. For example, the device characteristics of the cold water pumps P61, the cooling water pumps P02, and the pumps P63 are mentioned as a flow rate Q - a total head (see FIG. 167A) and the flow rate § — a pump power (see

FIG. 16B). The device characteristics of the chillers Rt is mentioned as the characteristics indicating how much is the power at a temperature difference between the inlet temperature and the outlet temperature, and a cooling amount {see FIG. 12).

The device characteristics of the cooling towers Ry 1s mentioned as the characteristics of the flow rate - the cooling amount - the power. {0098}

The heat source system Nb uses, in each operation state, the cold water outward temperature which is measured by the outward temperature sensor 64a, the cold water flow rate measured by the flow rate sensor 63, and the cold water return temperature measured by the temperature sensor 64b. When the temperature difference between the cold water outward temperature measured by the cutward temperature sensor 64a and the cold water return temperature measured by the return temperature sensor 64b is small and the flow rate of the cold water is large, the temperature set values of cold water outlets of a system including the chillers Rt and the cooling towers

Ry are lowered. At this time, the temperature set values of the cold water on the outlets (outward paths) of the system including the chillers Rt and the cooling towers Ry are changed in scme cases to be lower than a predetermined temperature sat value at the time of the maximum load. On the other hand, when the temperature difference between the temperature (cold water outward temperature) of the cold water sent to the loads 61 and the cold water return temperature is close to the designed value {set value) and the flow rate of the cold water is small, the state 1s controlled to be maintained. {0099

Incidentally, by performing a cooling load prediction by a known load prediction means, a control to reduce the number of the chillers Rt and the cooling towers Ry may be incorporated on the basis of the prediction results without performing a control of reducing the number of the chillers Rt and the cooling “56m towers Ry in cperation with a margin for hunting prevention.

The temperature of the cold water outlet of the chillers Rt may be measured by the outward temperature sensor 64a provided on the cold water feed pipe lines as shown in FIG. 17 cr obtained from the temperature control of the chillers Rt on the water feed side, and the temperature can be obtained even if there is no temperature cutput cf the chillers Rt. The chillers Rt may be inverter-controlled centrifugal chillers, and it is possible to perform energy savings of partial loads by the inverter control. {0100}

According to the first to sixth embodiments, when the return temperature of the cold water flowing at a set flow rate after heat exchanging with the loads is lower than a cold water return temperature set at design time, the outward temperature of the cold water going to the loads is lowered to enlarge the temperature difference on the loads side, and thereby a pump power per heat amount is lowered to save energy. { 0101}

The loads side 1s composed of heat exchangers in which the temperature difference between the inlet temperature and the outlet temperature is enlarged when the inlet temperatures of the cold water in cooling coils and the like used for general plate heat exchangers and air conditioners is lowered. By performing an automatic control of the temperature set values of the cold water from the cold sources according to the outputs from the computing unit, it is possible to save energy by changing the temperature of the cold water in response to the wvarlation of the loads. When the outward temperature of the cold water sent to the loads from the cold sources is constant and the flow rate of one cold source is not enough, even in a case where the number of the chillers as the cold sources must be increased, by lowering the outward temperature of the cold water sent to the loads from the cold sources, it is possible to reduce the flow rate of the cold water for the loads, thereby extending a load range where it is not necessary to increase the number of the cold sources. {0102}

As shown in FIG. 3, the COP of the centrifugal chiller is small at the time of low loads, for example, 30 % load factor per chiller. Therefore, by operating one chiller at 60 % load factor, it is possible to operate the chiller with the COP higher than that in a case where two chillers are operated at 30 % load factor per chiller, thereby eliminating a waste of transport powers of the pumps. Although a pipe resistance is increased when the flow rate of the cold water is increased, it 13 possible to operate the chillers in high efficiency by reducing the flow rate by lowering the cutlet temperature cf the cold sources,

and by increasing the load factor per chiller as a cold source.

Transport system of the cold water may be composed of a primary pump system on the cold source side and a secondary pump system cn the load side, and when the temperature difference between the temperature of the outward cold water to the loads on the secondary side and the temperature of the return cold water is large, it is possible to reduce the flow rate of the cold water, thereby reducing the power of the secondary pumps. {0103}

In the present embodiment, since the pipe size does not change, it 1s possible to introduce the heat source system by setting the outward temperature of the cold water sent to the loads lower than a default temperature set value at the time of renewal of a chiller. WNcte that, in the above embodiments,

I5 although water is used as a heat medium as an example, anything other than water may be used as the heat medium. In addition, although each configuration in the first to sixth embodiments has been described individually, 1t may be configured in any combination as appropriate from among configurations of the 200 first to sixth embodiments. { Reference Signs List} {0104} 1, la, 51, 5la, 61, Gla: load 2: cemputing unit (first control unit, second control unit,

third control unit) 3, 53, 63: flowrate sensor {load heat amount measurement unit, flow rate measurement unit) 4, 54: temperature sensor (load heat amount measurement unit, cold water refurn temperature measurement unit) 64a: outward temperature sensor (load heat amount measurement unit) bdb: return temperature senscr (load heat amount measurement unit, cold water return temperature measurement unit)

B: margin amount

Nl, N2, N3, N4, N5, Né6: heat source system

Pp, P1, PZ, P51, P5la, P5lb, P6l, P6la, P6lb: cold water pump (pump)

P3, P3a, P3b, P53, P53a, P53b, P63, Pela, P63k: pump

P52, P52a, P52b, P62, P6Za, P62b: cooling water pump (pump) rl, r2: cold water line {pipe}

R, Rl, RZ: cold source

Ra: high temperature side cold source (unit cold source)

Rb: low temperature side cold source {unit cold source)

Rt, Rti, Rt2: chiller {cold scurce)

Ry: cooling tower (cold scurce) tl: cooling water line (pipe)

Claims

1. A heat source system, wherein pumps that send a heat medium to at least cne of a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold source, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, comprising: a load heat amount measurement unit that measures an amount of heat which the heat medium exchanges with the load; a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the load and returns to the cold source; and a first control unit that lowers a temperature set value of the heat medium at an outlet of the cold source, if a temperature of the heat medium falls below a AR, set value thereof and a difference between the temperature of the heat medium and the temperature set value of the heat medium at the outlet of the c¢cld source becomes less than a predetermined set value.

Z. A heat source system, wherein pumps that send a heat medium to at least one cof a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the ccoled heat medium and a load, the cold source, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, comprising: a load heat amount measurement unit that measures an amount cf heat which the heat medium exchanges with the load; a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the load and returns to the cold source; and a second control unit that changes a temperature set value cf the heat medium at an outlet of the cold scurce to be lower than a predetermined temperature set value at the time of a maximum load.

3. The heat source system as set forth in claim 2, comprising a flow rate measurement unit that measures a flow rate of the heat mediumwhich is heat exchanged with the load, wherein when a flow rate of the heat mediumbecomes a predetermined set flow rate at the time of the maximum lecad, 1f a temperature of the heat medium is lower than the predetermined temperature set value, the second control unit changes the temperature of the heat medium at the outlet of the cold source to be lower than the predetermined temperature set value.

4. The heat source system as set forth in claim 2, comprising a flow rate measurement unit that measures a flow rate of the heat medium which is heat exchanged with the load, wherein the cold source is arranged with a plurality of unit cold sources in series, and the second control unit changes the temperature set value of the heat medium at each outlet of the plurality of unit cold scurces to be lower than the predetermined set value, on the basis of the flcw rate and temperature of the heat medium.

5. A heat source system, wherein pumps that send a heat medium te at least one of a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold source, and the heat exchanger of the lcad, are connected by pipes through which the neat medium flows, comprising: a load heat amount measurement unit that measures an amount of heat which the heat medium exchanges with the load; a cold water return temperature measurement unit that measures a temperature of the heat medium which exchanges heat with the load and returns to the cold source; a heat medium flow rate measurement unit that measures a flow rate of the heat medium which exchanges heat with the load; and a third control unit that raises a temperature set value of the heat medium which is cocled by the cold source if the flow rate of the heat medium is in a set range of temperature raising determination flow rate, and on the other hand, lowers the temperature set value of the heat medium which is cooled by the cold source if the flow rate of the heat medium is in a seb range of temperature lowering determination flow rate and the temperature of the heat medium is lower than a predetermined temperature lowering determination temperature.

6. The heal source system as set forth in claim 5, wherein the third control unit maintains a current temperature set value of the heat medium which is cooled by the cold source, if the flow rate of the heat medium is in the set range of temperature lowering determination flow rate and the temperature of the heat medium is egual to the predetermined temperature lowering determination temperature, and raises the temperature set value of the heat medium which ig cooled by the cold source, if the flow rate of the heat medium is in the set range of temperature lowering determination flow rate and the temperature of the heat medium is higher than the predetermined temperature lowering determination temperature.

7. The heat source system as set forth in claim 5 or 6, wherein the third control unit raises the temperature set values of the heat medium which is cooled by the cold source, if the flow rate of the heat medium is less than a predetermined minimum flow rate, and maintains the current temperature set value of the heat medium which is cocled by the celd source, if the flow rate of the heat medium is equal to or more than the predetermined minimum flow rate and is less than a flow rate of adding a predetermined margin amount to the predetermined minimum flow rate.

8. The heat source system as set forth in any one of claims 1 to &, wherein the cold sources are two or more, and the plurality of cold scurces are controlled in the number thereof. I5

9. The heat source system as set forth in any one of claims 1 to 6, wherein the pumps perform rated operations or inverter control operations.

10. The heat source system as set forth in any one of claims 1 tec 6, wnerein the heat medium is water.

11. A contrel method for a heat source system, wherein pumps that send a heat medium to at least one of a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold source, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, wherein a temperature set value of the heat medium at an outlet of the cold scurce is lowered, if a temperature of the heat medium returning to the cold scurce after heat exchanging with the load falls below a temperature set value thereof and a difference with the temperature set value of the heat medium at the outlet of the cold source becomes less than a predetermined set value.

12. A contrel method for a heat source system, wherein pumps that send a heat medium fo at least one of a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold source, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, wherein a temperature set value of the heat medium at an outlet of the cold source is changed to be lower than a predetermined temperature set value at the time of a maximum load.

13. The control method for the heat source system as set forth in ¢laim 12, wherein when a flow rate of the heat medium which is heat exchanged with the load becomes a predetermined set flow rate at the time of the maximum load, if a temperature of the heat medium is lower than the predetermined temperature set value, the temperature cf the heat medium at the cutlet of the cold source is changed to be lower than the predetermined temperature set value.

14. The control method for the heat source system as set forth in claim 12, wherein the cold source is arranged with a plurality of unit cold sources in series, and the temperature set value of the heat medium at each cutlet of the plurality of unit cold sources is changed to be lower than the predetermined set wvalue, on the basis of the temperature and flow rate of the heat medium which is heat exchanged with the load.

15. A control method for a heat source system, wherein pumps that send a heat medium te at least one of a cold source for cooling the heat medium and a heat exchanger for exchanging heat between the cooled heat medium and a load, the cold scurge, and the heat exchanger of the load, are connected by pipes through which the heat medium flows, wherein if a flow rate of the heat medium which is heat exchanged with the lecad is in a set range of temperature raising determination flow rate, a temperature set value of the heat medium which is cooled by the cold source is raised, and on the other hand, if the flow rate of the heat medium is in a set range of temperature lowering determination flow rate and the temperature of the heat medium is lower than a predetermined temperature lowering determination Temperature, the temperature set value of the heat medium which 1s cooled by the cold source is lowered.

16. The control method for the heat source system as set forth in claim 15, wherein if the flow rate of the heat medium is in the set range of temperature lowering determination flow rate and the temperature of the heat medium is equal to the predetermined temperature lowering determination temperature, a current temperature set value of the heat medium which is cooled by the cold source is maintained, and if the flow rate of the heat medium is in the set range of temperature lowering determination flow rate and the temperature of the heat medium is higher than the predetermined temperature lowering determination temperature, the temperature set value of the heat medium which 1s cooled by the cold source is raised.

17. The control method for the heat source system as set forth in ¢laim 15 or 16, wherein if the flow rate of the heat medium 1s less than a predetermined minimum flow rate, the temperature set value of the heat medium which is cooled by the cold scurce is raised, and if the flow rate of the heat medium is equal to or more than the predetermined minimum flow rate and is less than a flow rate of adding a predetermined margin amount to the predetermined minimum flow rate, the current temperalbure set value of the heat medium which is cooled by the cold source is maintained.

18. The control method for the heat source system as set forth in any one of claims 11 to 16, wherein the cold sources are more than one, and the plurality of cold sources are controlled in the number.

19. A program for performing on a computer the control method for the heat source system as set forth in any one of claims 11 to leé.