3 11 cooling water v11d final

8/6/2019 3 11 Cooling Water v11d FINAL

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3.11 Water-cooling System

3.11 - 1

3.11 Water-cooling system and corrosion

3.11.1 Design philosophy

Thermal waste is removed by de-ionized water and forced air flow. Figure 3.11.1 depicts the

thermal propagation. The chilled water undergoes a secondary heat exchange. All thermal waste

eventually purge into the air via the cooling towers. In the accelerator facility, the cooling-water

system, including de-ionized water, chilled water, cooling-tower water and hot water are supplied in

closed-loop systems. The return water must flow into heat exchangers and water treatment systems,

before being pumped bach into heat load devices. The total system consists of high stable quality

and stable cooling devices and air conditioners.

Fig. 3.11.1.1 Diagram to show thermal propagation

In the accelerator field, water is the main cooling medium. De-ionized water is the primary

heat-exchange refrigerant, providing a stable cooling capacity. The cooling-water system is divided

into four subsystems, such as de-ionized water of Cu piping system for magnets and power devices,de-ionized water of Al piping system for vacuum chambers, de-ionized water for the RF stations,

de-ionized water for booster devices and beam line optical instruments. The separate water

subsystems can prevent corrosion induced by voltage difference and each has its own working

pressure, flow rate and temperature controls during operation. The Cu, Al, RF, and booster

de-ionized water is regulated at pressure of 7.5±0.1 kg/cm2 and a temperature of 25±0.1 to

satisfy the requirements of the TPS accelerators. Some diagnostic facilities including XBPMs and I0

monitors have a stricter criterion for temperature control, which is targeted within 25±0.01.

In Fig. 3.11.1.2 and 3.11.2.1, the green line represents the de-ionized water loop in the water

processing system. The return water from the heat-loaded device flows first into a separator, which

separates air from water. The air is purged via an expansion tank and about 5 % of return water flows into the loop for de-ionization water treatment. Finally, the water is pumped forward to all

heat-loaded devices. Between heat-loaded devices and pumps, two heat exchangers are required:

one exchanges heat with chilled water (7.0) to extract thermal waste, shown as a blue line, and

another exchanges heat with hot water (50) to stabilize the supply water temperature, shown as a

red line. The whole process forms a closed-loop water cooling system. If there is water leakage, the

level sensor can trigger a process to add water from a RO reservoir. The electric heater and buffer

tank are employed to minimize the variation in temperature if the high precision temperature control,

e.g. of ±0.01, is needed.

De-ionized Water

Air Conditioning

Chilled WaterCooling-Tower

Water Facility



NSRRC - TPS Design Handbook - June 2008

3.11- 2

Fig. 3.11.1.2 System for de-ionized water

The chilled water, hot water and cooling-tower water are the second and the third

heat-exchange processes. Chilled water at 7.0±0.2, hot water at 32±0.5 and cooling tower

water at 32±0.5 are required to ensure the stability of the temperature of the water.

3.11.2 Facility and Piping Design

The cooling-water system has numerous components and piping that are distributed over the

location of heat-loaded devices and air conditioners, as shown in Fig. 3.11.2.1. The central water

facility is located in a utility building with isolation to diminish effects of vibration or high-power

electric noise caused by compressors, fans, pumps and other equipments. The utility building has a

trench in which effective anti-vibration piping links the tunnel and the experimental area located on

the storage ring. Each lattice cell has two underground trenches providing stable de-ionized water.

Fig. 3.11.2.1 A 3-D layout of the cooling water system extracting the thermal waste




3.11 - 3

Fig. 3.11.2.2 Piping and trench design near the storage ring

The water system includes some primary facilities, such as pumps, inverters, heat exchangers,

chillers, cooling towers and boilers, which are described below.

3.11.2.1 Pump

Pumps of three types – centrifugal, rotary and reciprocating – are available. According to a

pump curve, we can adopt an adequate flow and suction (??) head to meet our requirements. Theaccurate calculation of NPSH (Net Positive Suction Head) to prevent cavitation damage and an

effective anti-vibration-support design must be noted.

3.11.2.2 Inverter

As the flow throughout the subsystem is variable, the inverter is introduced to shift the pump

characteristic curve, as shown in Fig. 3.11.2.3. The pump can provide stable pressure within ±0.1

kg/cm2 and enough flow for all subsystems. Using two synchronous inverters, that provide the

possibility to perform pump exchange or maintenance without affecting the operation. Dual

inverters also extend the lifespan with a low loading. The electric circuit of the inverter typically

generates electric harmonics and therefore an isolation transformer and filters must be installed toreduce the harmonics interference to other devices.




3.11- 4

20

40

60

80

100

120

20 40 60 80 100 120 140 160

%Flow

% P

r e s s

u r e

12

3

CharacteristicCurveofPump

LoadCurve

Fig. 3.11.2.3 Characteristic curve of a pump operating with an inverter

3.11.2.3 Heat exchanger

The heat exchanger is made from thin metal with a rough and uneven surface. Each metal

surface separating cool and hot water channels enables the heat of the water to be exchanged. The

thickness of the plate varies with the material used, such as stainless steel, titanium, copper and

nickel of thickness about 0.6~1 mm. The plates are commonly made with a wave shape to enhance

thermal conduction and structural stress.

The heat-exchanger plate of de-ionized water is made from stainless steel. In addition to flow

capacity, the pressure drop of the plates within 0.5 kg/cm2

is important to decrease load of the pumpand to reduce operating cost. The inner piping in the heat exchange, also should prevent blocking

from associated particles or rust.

3.11.2.4 Chiller

Chillers are core components of a water-cooling system. A chiller has a compressor to control

the refrigerant with adequate pressure and to exchange the thermal waste into the cooling-tower

water. The temperature of chilled water is specified to be 7.0±0.2. The chiller should be

interlocked with pumps, valves and cooling towers to perform optimal operation. Because of

high-power consumption, the chiller with an inverter should also be considered in order to achieve

the goal of energy savings. Besides, the selected refrigerant must meet the regulation of

environmental protection.

3.11.2.5 Cooling tower

Cooling towers use the convection of air to exchange the thermal waste from the water in the

chiller condenser. There are three types of cooling tower designs using – natural flow, jet flow and

forced flow. Due to poor performance, the natural-flow and jet-flow cooling tower are no longer

used. The forced-flow cooling towers perform satisfactorily and meet our temperature requirement

of 32±0.5. The wet bulb temperature and the approach of cooling towers must be considered

carefully and a perfect design can perform variable-speed fan control. Also a cooling tower mayinduce vibration and must therefore have a good support design with anti-vibration devices.




3.11 - 5

3.11.2.6 Boiler

Hot water is required to ensure that the moisture content in air conditioners is small and that

the temperature of the cooling-water system can be precisely controlled. A boiler with a

silicon-controlled rectifier (SCR) is introduced to ensure the stability of the temperature within

50±0.3. The SCR has two mechanisms – zero-voltage control and phase-voltage control – that

rectify the voltage and current to balance the thermal load output. A heat pump serving as a primaryheater is employed for energy saving, because of its high Coefficient Of Performance (COP).

3.11.3 Evaluating capacity and saving energy

3.11.3.1 Evaluating capacity

Adequate cooling capacity and water flow should be evaluated carefully. These evaluations

involve the temperature stabilization and energy-saving issues. For instance, a parallel-piping loop

replaces a serial loop to maintain smaller temperature variations between inlet and outlet water. A

smaller increment of temperature corresponds to a greater flow capacity. The constraints invariation of temperature also affect total thermal load. Table 3.11.3.1 presents the requirements of

temperature and flow capacity.

Table 3.11.3.1 Requirements of the cooling-water system

Temperature Pressure Capacity

Cu De-ionized Water 25±0.1 7.5±0.1 kg/cm2 1600 GPM

AL De-ionized Water 25±0.1 7.5±0.1 kg/cm2 380 GPM

RF De-ionized Water 25±0.1 7.5±0.1 kg/cm2 1200 GPM

Booster De-ionized Water 25±0.1 7.5±0.1 kg/cm2 700 GPM

Cooling Tower Water 32±0.5 3.0±0.2 kg/cm2 9000 RT

Chilled Water 7.0±0.2 3.5±0.2 kg/cm2 7000 RT

Hot Water 50±0.3 2.5±0.2 kg/cm2 1600 kW

3.11.3.2 Saving energy

In an accelerator facility, most power is consumed by the air-conditioning and cooling-water

systems. Chillers with a satisfactory Energy-Efficient Ratio (EER) and Coefficient Of Performance

(COP) must be chosen carefully to save the long-term operation cost. Additionally, the chiller is an

important subsystem for secondary heat exchange, which supplies chilled water to the air

conditioner and de-ionized water. Figure 3.11.3.1 plots the relationship between the chiller

efficiency and the load. Control logic is also employed to evaluate an optimal operating condition

above 50 % thermal load and to yield acceptable efficiency. The alternative is to use inverters,

which apply adaptive control logic to decrease the rotor speed so as to minimize power

consumption, as shown in Figure 3.11.3.1. The starting mechanism is improved and sonic noise is

also suppressed.

The balance of flows among the pipelines is important. Pumps with inverters and accurate

balance valves can serve the purpose of optimizing the water flow. Furthermore, piping withisolation from air can prevent thermal conduction, especially in chilled water at 7 and hot water

at 50.




3.11- 6

Fig. 3.11.3.1 Relationship between chiller loading and efficiency [kW in figure]

3.11.4 Requirements of the control system and stability

3.11.4.1 Control system

The cooling-water system with a set of hybrid Supervisory Control and Data Acquisition

(SCADA) systems includes extensive control logic. For example, pumps with inverters can be

controlled using programmable logical controls (PLC); boilers are controlled via SCR driving;

chillers have their own control panels and system sensors including pressure, flow, temperature, pH

and conductivity are monitored via a Direct Digital Controller (DDC) or a Distributed Control

System (DCS). These highly complicated hybrid-control systems ensure precise control andoptimization. No single SCADA can manage the entire system. Finally, overall utility system will

be integrated with the Experimental-Physics and Industrial-Control System (EPICS) of the

accelerator.

To achieve a purpose of integration, the overall control device must provide an open database

connectivity or protocol. Such a device may be RS232, RS485 and GPIB hardware or DDE, OPC,

Modbus, BACNet, PSP, TXT and ODBC software. Figure 3.11.4.1 shows the data flow that is

finally integrated into the EPIC system. Furthermore, the optical-fiber network and database are

installed to provide real-time data archiving. The trend-logger and data-analysis software as shown

in Figure 3.11.4.2 are also developed to view, to compare, to analyze and to diagnose relations

between devices at any time and anywhere.




3.11 - 7

Fig. 3.11.4.1 Data flow of the control system

Fig. 3.11.4.2 Data analysis and user interface of archive viewer

3.11.4.2 Stability requirements

Thermal effects must be minimized to meet the requirements of high precision in the

accelerator field. Table 3.11.1 presents the requirement of temperature stability for all subsystems.




3.11- 8

The design guidelines of cooling water control are as follows.

• The de-ionized water system must include two heat exchangers for heating and cooling to

avoid valve-closing problems and to support a mechanism for finely tuning the

temperature within ±0.1 .

• The nonlinear flow rate of heat exchanger and valves limit the control precision.

Introducing a mixing buffer tank and periodic variation of temperature control via aheater enabling temperature variation better than ±0.1 requirement is the long-term

target in precision measurement system.

• The differences between the flows in the heat-loaded devices are likely to cause a

problem of piping balance. Using a traditional bypass valve to balance the water flow still

leaves a problem of unstable flow. Introducing an inverter can minimize all deficiency

and stabilize the pressure control within ±0.1 kg/cm2.

• Each valve for flow balance must be examined frequently and optimized appropriately,

whenever the heat-loaded device is installed or removed.

• The shut-off status and the nonlinear flow of the control valve must be considered. As

commercial large size control valves are normally not obtainable, using two control

valves of smaller size with the same flow as a single large valve helps to optimize control.

3.11.5 Suppressing and preventing corrosion

As the cooling water circulates in the closed-loop water system year after year, acidic and

alkaline ions might produce corrosion and deposition inside the piping; water treatment is thus

important. Types of impurities in water include suspension, electrolyte, particles, microorganisms,

organic substances and gases, which can be removed by individual physical or chemical methods,

presented in Table 3.11.5.1.

For example, a leakage of electric power from the dipole magnet may damage some devicesvia the cooling water and the water resistivity needs therefore to be controlled carefully. In the

accelerator facility, the water is de-ionized. About 5 % of return water flows into the

water-treatment system, which comprises 5-μm filters, resin basins, 1-μm filters, 0.1-μm filters,

membranes for dissolved oxygen and ultraviolet lamps. The added water is processed with a

Reverse Osmotic (RO) system. The total system requirement must have a resistivity over 10

MΩ-cm and dissolved oxygen less than 10 ppb as shown in Fig 3.11.5.1.




3.11 - 9

Table 3.11.5.1 Foreign particles and removal techniques

Suspension Electrolyte Particles Micro-

OrganismsOrganic

compounds Gas

Flocculation and

precipitation filtering device

Sand Filter

Active Carbon Filter

Ion-Exchange Device

Carbon Dioxide Removal

Tower

Vacuum Degassing Tower

Reverse Osmotic Device

Ultra-filtration Device

Micro filter

Ultraviolet Sterilizer

Dissolved-oxygen

Membrane

Fig. 3.11.5.1 A 3-D layout of water treatment system

3 11 cooling water v11d final

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