Cooling Towers

Cooling towers

Produced by Bruce Davison. 1

COOLING TOWERS

Introduction

A cooling tower is a device used to

reduce the temperature of water. The

water is then recycled back into the many

processes and industries that use it.

Some industries use the water to control

the temperature (sensible heat), of a

process, like a car radiator. The HVAC

industry uses the water to condense the

refrigerant (latent heat).

In the past most of the processes requiring cooling use piped town water

through the equipment, cooling the equipment, and then drained the water to

the gutter (100% waste).

Because Australia is such a dry continent the water supply authorities

introduced the Water Conservation Act, which forced all the industries to install

cooling towers to recycle the water.

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Terminology Approach, is the difference between the temperature of the water leaving the tower and the Wet Bulb temperature of the air entering the tower. Generally between 4 – 6K. The smaller the approach the more efficient is the tower Range, is the difference between the temperature of the water entering and the water leaving the tower. Generally between 8 – 10K. Drift, is the evaporated water carried out of the tower with the air. The amount of drift must be controlled because the microorganisms can live in the drift and travel to and infect humans. (Legionaries Disease) Drift Eliminators, are to catch and condense the tower water as it is discharged as drift, causing it to fall back into the tower basin as droplets. Bleed Off, is the amount of tower water that is purposely drained away to waste in order to dilute the circulating water with fresh town water. This is needed as only the H2O evaporates leaving behind all the minerals that get into the tower water. The H2O is constantly evaporating to reduce the temperature of the remaining water. Fill, is the component of the tower that causes the circulating water to spread out over a large surface area, which will increase the evaporation rate by offering the water to a greater volume of air. Water Distribution System, is designed to evenly spray the circulating water over the Fill. Make Up Water, is the fresh town water that is constantly being fed into the tower basin via a Ball Valve, to replace the water that is lost to;

Drift (Evaporation) Bleed Off

Louvers, are there to reduce sunlight on the water inside but allow air to be directed onto the fill. They also retain the splash from the droplets falling from the fill. Plume. Under certain atmospheric conditions the drift leaving the tower with condense as it hits the surrounding air. It looks like fog but because it originates from a process it is referred to as Plume. Dissolved Solids. The particles of dirt and minerals that circulate with the water rather than sink to the bottom as mud. Side Filtration. Some of the circulating water is pumped through a filter to remove the dissolved solids. Inhibitor. Is a chemical added to the circulating water to prevent the dissolved solids in the water causing rust and clogging the system’s tubing. Microbial Growth. Or ‘bio-fouling’ is the Algae, Fungi and Bacteria that find the cooling tower environment ideal for their growth. Biocide. A chorine base chemical added to the circulating water to prevent microbial growth. Ultra violet light. Is another method of killing bacteria where the circulating water is passed through clear tubes that are exposed to ultra violet lights. The water must be kept very clean with filters for this method to work (side filtration). Ozone injection. Another means of killing bacteria. Monitoring. Of the circulating water is needed to ensure the chemical additives are at the required concentration. Legionnaire’s Disease. Is caused by the bacteria Legionella Pneumophilia Bacillus, which grows in the cooling tower water and infects humans as they breathe in the aerosols from the tower discharge.

Cooling towers


Construction

Cooling towers


Operation

The Basic Principle of Operation.

Evaporating some of the circulating water, cools the majority of the water in a

cooling tower.

How it Works

The evaporation process only takes place on the surface of a liquid and needs

latent heat of vaporization to happen (2256 kJ/kg). Sensible heat (4.19 kJ/kgK),

is drawn from the body of the water to the surface to supply the energy needed

for the latent heat. It can be seen that for a little evaporation a lot of sensible

heat will be needed therefore the main body of the circulating water is cooled

for very little lost of water.

Warm to hot water from the cooling process is

pumped to the top of the cooling tower and into

the sprays where the water is broken up into

droplets and distributed over the Fill. The water droplet spreads out as it slides down

the Fill creating the surface area necessary for

evaporation.

The evaporation rate of the water is restricted by the amount of moisture

already in the air around it. To maintain evaporation the moistened air must be

replaced with dry air, usually by fans blowing air through the tower, (see types

of towers).

A cooling tower takes the heat transfer law ‘the greater the exposed surface area, the greater will be the rate of heat transfer

Cooling towers


Types of Towers

Two basic types; Natural Draft Mechanical Draft Natural Draft Towers, rely on

the heat of the water to generate

the air movement inside the

tower.

They are only used for very large

capacity systems such as

Electricity Generation Plants,

where they are called

Hyperbolic Towers. Cooling towers are not part of the refrigeration system, as no refrigerant flows

through them.

Cooling towers


Mechanical Draft, are fitted with fans to improve the airflow through the tower

which increases the evaporation rate of the water which increases the capacity

of the tower. Mechanical Draft Towers are used just about everywhere

including the HVAC industry.

Generally a centrifugal fan is used to force the air into a tower, and tube axial

(propeller) fans are used to induce the air out the tower.

Mechanical towers are classified by the way the air flows through the water.

(remember, the water always falls).

• Induced draft cross flow

• Induced draft counter flow

• Forced draft cross flow

• Forced draft counter flow

Induced draft counter flow Forced draft cross flow

Cooling towers


Evaporative Condensers. An evaporative condenser (EC), is

considered to be part of the

refrigeration system as it directly

condensers the refrigerant.

An EC doesn’t have fill it uses the

refrigerant piping to break up the

water drop as they spread around

the piping absorbing Latent Heat

directly from the refrigerant.

.

Evaporative Condenser and Chillers Circuit

Capacity control for evaporative condensers is limited to varying the volume of air flowing in to the fan.

Cooling towers


Water Circuits Open Water Circuit. These systems have the water that is doing the condensing or cooling being

passed through the air to reject the heat, e.g. a cooling tower is an Open Water

Circuit system.

Closed Water Circuits, (like a car radiator) The condensing water in this situation is

contained within a closed loop circuit (i.e.

the water being circulated between the

evaporative cooler and the shell and tube

condenser never comes in contact with

the outside atmosphere). The water is

pumped through a device like an

evaporative condenser although the

water in the tubes only gives up

sensible heat from the circulating

water. The cooled circulating water is

then fed to the remote water-cooled

condensers, (generally the shell and tube

type). This arrangement is common in

situations where a large number of

individual condensing units are used (e.g.

supermarkets).

Closed water circuits operate with a

high Td because the heat energy is

passed from the refrigerant to the closed

circuit water (in the shell and tube

condenser) and then from the closed

circuit water to the water in the

evaporative cooler, then to the air.

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CAPACITY CONTROL In order to maintain the required condensing

or process temperature against the changing

ambient WB temperature and varying load,

cooling towers need some form of capacity

control. The capacity of the tower depends

on the wet bulb temperature of the air

entering the cooling tower.

1. The simplest form of control is Fan

Cycling. It is inexpensive, but the fan should

not be cycled too often as it can lead to

motor burnout. This system is used on

single and multi fan units, and units that do

not require critical temperature control.

2. The next step is to have multi speed fan motors with cycling control combinations.

This method offers reduced operational costs and broader capacity control. Useful on

single fan towers. Both of the methods described above are used on tube axial fan

units.

Centrifugal fans normally use the following.

3. Modulating dampers are placed in the inlet of the centrifugal fan housing.

As the water temperature reduces the dampers are moved towards a closed

position. If they close fully the modulating motor will trip a limit switch isolating

the fan motor. This method offers the best regulation if the fan type capacity control

is used.

4. If the ambient remains above freezing

a modulating valve can be used to re-

circulate the water back to the

condenser bypassing the cooling tower.

This method of capacity control is also

used when multiple condensers are

connected to the one cooling tower.

The lower the WB temperature the greater the capacity

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CALCULATING THE CAPACITY Three factors need to be known: The mass flow rate of the water flowing through the tower (kg/sec) The specify heat capacity of the water (kJ/kg.K) The change in temperature of the water (RANGE of the Tower).

Where:

Q = Quantity of energy in kJ/sec ( or kW) M = Mass Flow Rate kg/sec (or L/s) c = Specific heat in kJ/kg.K (c of water = 4.19 kJ/kg.K) Δť = Change in Temperature (K) THUS: Q = M c Δť

EXAMPLE 1 A Cooling Tower has 6.7 litres (6.7kg/sec), of water passing through it per second. The water is entering the tower at 34o C and leaving the tower at 28 o C. Calculate the capacity.

6.7kg/sx4.19kJ/kg Kx6K 6.7x4.19x6 168.438 kJ/s or (kW)

APPROACH The APPROACH is the difference of the WATER LEAVING the tower and the WB

TEMPERATURE of the AIR ENTERING the tower.

With a WB temp of 22 'C,

Approach = Water temp leaving - WB temp of air entering = 28°C-22°C = 6K

RANGE The RANGE is the difference between the temperature of the WATER ENTERING the tower and the WATER LEAVING the tower. Range = 34°C - 28°C = 6 K

Cooling towers


Water used over the operational time of the tower

Water will be lost because of the evaporation of water and a percentage of water will be bled off to reduce TDS.

Evaporation requires Latent Heat, LH = 2256 kJ/kg this is a constant.

Our example system has a capacity to remove 168.438 kJ/s of heat so if we divide the capacity by the latent heat the answer will be the amount of water evaporated to carry away the heat from the system.

Water = Q ÷LH 168.438kJ/sec ÷2256 kJ/kg = 0.075kg/sec. The amount of water bled off to waste is proportional to the amount of water evaporated, which is proportional to the Range of the tower and the flow rate.

Therefore our example system has a towers range of 6K, which equals 0.41% bleed off.

Convert % to decimal (0.41 / 100) that equates to 0.0041

Bleed off rate = Flow rate (kg /sec) x % of bleed off (as a decimal).

6.7kg/sec x 0.0041 = 0.0275kg/sec. If our example tower operates for 12 hours (12 x 3600 sees) each day then the volume of water used will be; Operation time (in seconds) x Evaporation Rate + Bleed off rate (kg/sec) Water used =12 hours x 3600 secs x (0.075 kg/sec + 0.0275kg/sec = 4426.7 litres

OTHER FACTORS (affecting the Tower Capacity)

The amount of surface area the water evaporates off and length of exposure time; The velocity of the air passing through the cooling tower (too fast results in excessive 'drift'); The direction of airflow in relation to the water flow.

The lowest temperature to which the water can be cooled is the W.B. temperature of the air entering, in which the water vapour in the leaving air will be saturated, (any heat removed will cause the water to change back to a liquid).

Cooling Range K % of Bleed Off. 3.5 0.15 4.0 0.22 5.5 0.33 6.0 0.41 8.5 0.55 11.0 0.75 15.0 1.00

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Review questions.

1. What type of heat is removed by the cooling tower water for the purpose of the HVAC industry? ………………………………………………………………………………………….

2. Why did Australia introduce cooling towers?

………………………………………………………………………………………….

3. What is Bleed Off?

…………………………………………………………………………………………..

4. Why can Dissolved Solids become a problem?

………………………………………………………………………………………….. …………………………………………………………………………………………..

5. List the two types of Biocides? ……………………………………………………………………………………………

……………………………………………………………………………………………

6. How do humans catch Legionnaires Disease? ……………………………………………………………………………………………

……………………………………………………………………………………………

7. How is cooling of the water achieved in a cooling tower?

……………………………………………………………………………………………

8. Why is the greater surface area heat transfer law applied to cooling towers? ……………………………………………………………………………………………

……………………………………………………………………………………………

9. What will restrict the amount of heat transfer within a cooling tower? …………………………………………………………………………………………..

…………………………………………………………………………………………..

10. List the two basic types of cooling towers? ………………………………………………………………………………………….

………………………………………………………………………………………….

11. Where are hyperbolic towers used?

…………………………………………………………………………………………

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12. List the four types of fan draft towers?

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…………………………………………………………………………… …………………………………………………………………………… ……………………………………………………………………………

13. What two types of fans are used on cooling towers?

………………………………………………………………………….. …………………………………………………………………………..

14. Is an evaporative condenser part of the refrigeration system?

……………………………………………………………………………

15. Do evaporative condensers have fill?

…………………………………………………………………………..

16. List the two types of water circuits?

…………………………………………………………………………… ……………………………………………………………………………

17. What is the difference between them?

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18. Why is capacity control necessary on cooling towers?

………………………………………………………………………………. ……………………………………………………………………………….

19. List the types of capacity control devices used on cooling towers?

………………………………………………………………………………. ………………………………………………………………………………… ……………………………………………………………………………….

20. Explain why a modulating valve is needed on multiple condenser systems?

……………………………………………………………………………………. …………………………………………………………………………………….. ……………………………………………………………………………………..

Cooling towers


Legionnaires’ Disease

Legionnaires Disease is a form of pneumonia that can be fatal. It is caused by the

common bacteria Legionella Pneumophila Bacillus.

It is possible for anyone to catch the disease, provided the bacteria can get to the

deep parts of the lungs where the disease can grow, but certain groups within the

community are more prone to the illness that are others.

The groups most at risk generally include people with one or more of the following

characteristics:

• Age over 50 years of age;

• Are male;

• Have a history of smoking;

• Have a history of heavy alcohol intake;

• Have a medical condition or are undergoing a treatment that impairs the body’s

natural defence mechanisms.

Legionella is found in moist environments such as Lakes, Rivers, Creeks, Mud and

other water sources at temperatures ranging from approximately 5oC to 55oC.

However no cases of Legionnaires’ Disease has been proven to have been caused by

Legionella present in the natural environment.

All of the Legionnaires Disease outbreaks have been attributed to man made

environments.

The optimum conditions for the multiplication of Legionella Bacteria has been shown

to be between 35oC and 37oC with an acid balance between pH 6.5 and pH 6.9.

COOLING TOWERS and, EVAPORATIVE CONDENSERS provide this environment.

The primary concern with the cooling tower is its ability to spread the Legionella over a

vast area due to the Drift (aerosols) carrying the bacteria from the tower. The aerosols

are small enough to get into the lungs.

Cooling towers


Operational and Servicing Checks of Cooling Towers

Before working on any cooling towers you must be aware and familiar with the following

Legislation The NSW Public Health Act 1991, Part 4, and the Regulation 2000 covers cooling

towers and lays out the laws controlling the maintenance and cleaning of cooling

towers, in the Public Health Act, a cooling tower is referred to as a Regulated System.

Other states may have their own statuary requirements.

Standards

AS/NZS3666 parts 1,2,3.

Part 1 covers installation of Air Handling and Water Systems.

Part 2, covers Operation and Maintenance.

Part 3, covers control of Legionella through constant monitoring of water quality.

In New South Wales the AS/NZS 3666 has been incorporated into the Public Health

Act, so anything in AS/NZS 3666 is enforceable by the act.

Hand Book 32 (HB32), explains the Australian Standard 3666 and helps to show

how some procedures are to be done. The New Zealand standard uses another

publication.

Code of Practice. By the NSW Health Department. Explains what the Health Department wants done to control microbial growth.

On page 29 of the code of Practice it states that only competent persons be

employed to carry out work on regulated systems. To be classed as competent, a

person needs to have completed some form of recognized training. Therefore it is

recommended that any person that is required to work on a cooling tower complete a

Health Department approved course,

As part of the licensing agreement with the NSW Department of Fair Trading, the refrigeration trade course

must contain an element of microbial control and the Public Health Act part 4, and the Regulations

Cooling towers


Class Exercise.

Aim. To be able to use AS/NZS 3666 parts 1, 2, 3, the Public Health Act and Regulations.

Purpose. Because of the requirement of the Department of Fair Trading licensing, and because the standards are incorporated into the NSW Public Health Act you must be able to reference information from them.

Task. Use the Australian standards, Acts and Regulation to locate the answers for the following questions. Record where you found the answers.

a. What is the purpose of the Public Health Act part 4 or any other state equivalent Act.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

b. In order to comply with AS/NZS 3666.2 what manuals must be with the regulated system?

…………………………………………………………………………………………………………………………………………………………………………

c. What is the required interval between cooling tower cleans?

…………………………………………………………………………………………………………………………………………………………………………

d. Can a cooling tower that does not have a working disinfection process installed be turned on?

…………………………………………………………………………………………………………………………………………………………………………

e. From the NSW PH.act Regulation 2000, list the two maintenance precautions?

…………………………………………………………………………………………………………………………………………………………………………

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f. Use AS/NZS 3666.2 to list the personal protective equipment needed to clean a cooling tower?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

g. According to AS/NZS 3666.2 what must be done to an evaporative cooler every three months?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

h. How often should a water sample be taken? Refer to AS/NZS 3666.3

…………………………………………………………………………………………………………………………………………………………………………

i. How long should the results from water sample be kept?

………………………………………………………………………………………………………………………………………………………………………..

j. List the requirements for the location of air intakes according to AS/NZS 3666.1?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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Safety Personal Safety. Clothing should conform to Australian Standards AS/NZS 3666, part 2, which incorporates other standards, AS 1715 and AS 1716. AS 1715 specification of respirators and AS 1716, the wearing of the respirators and masks. The gloves and waterproof coveralls are used to protect your skin from the biocides in the circulating water.

Wear gloves, waterproof shoes and water resistance coveralls and a half face respirator with P2 grade twin filter Public safety. Always restrict public access when cleaning, and ensure that the cleaning spray is contained within the operational area.

Full Face Cartridge Respirator

The safety and responsibilities can not be stressed enough when microbial infection is involved

Only used to take water sample

Cooling Towers

Complied by Bruce Davison. 19

Taking a Water Sample. Safety. If the sample has to be taken from an operational tower, then all the

appropriate safety clothing should be worn. Make sure the gloves are long

enough so that none of the circulating water will come into contact with the

skin.

Equipment.

• A sterile 250ml re-sealable container, containing Sodium Thiosulphate to

neutalize the chlorine. Usually supplied by the analysing company.

• A means of keeping the sample between 2 and 6oC, while transporting it

for analysing.

• A means of recording sample location and time of sample taking.

Procedure.

• Only open the container once it is in the water to be sampled.

• Do not open it and leave it sitting, as other contamination can enter giving

false readings.

• Take the sample from circulating water, not some place where the water is

still.

• Place the container in an insulated transport vessel.

• Do not leave in direct sunlight.

• Record the sample taken for Authorities records.

Water Analysis. Only use a National Analytical Test Authority (NATA) accredited laboratory to

analyze a sample. The laboratory must notify you if they find a sample that

has a high legionella count.

The results of the test must be recorded and stored safely for seven years.

Cooling Towers


Water Sample Collection Practical. Aim: To be able to collect a water sample from an operating

cooling tower in accordance with AS/NZS 3666 part 3, while meeting the OH&S requirements.

Task.

1. Read AS/NZS 3666 part 3 section 2 ( risk assessment)

2. Read AS/NZS 3666 part 3 section 2 (technique for sample collection).

3. Complete the risk assessment and hand it in to the teacher

for approval.

4. Complete the water sample collection while the teacher is present.

Review.

Complete the worksheet on water sample collection from the package or hand out.

Cooling Towers


Decontamination

If a tower has a high Legionella reading confirmed by the analysing

laboratory, then the system will have to be shut down and decontaminated.

Recommended procedure;

1. Circulate a dispersant throughout the system.

2. Drain and refill.

3. Dose with Sodium hypochlorite to maintain a free chlorine residual of 25 to

50 mg/l at a pH of 7 to 7.6 for 30 minutes.


5. Dose with Sodium Hypochlorite to maintain a Chlorine residual of 5 mg/l at

a pH of 7 to 7.6 for 12 hours.

6. Drain the system and clean cooling tower wetted surfaces.

7. Dose with Sodium Hypochlorite to maintain a free Chlorine residual of

5mg/l at a pH of 7 to 7.6 for one hour.


9. Start full water treatment and put system back into service.

10. Wait at least 72 hours before taking another water sample.

Draining of the system should be to the sewer or in accordance with Local

Authority or other relevant authority. Some authorities require the water to be

pumped into a container for disposal.

Safety with Chemicals

The chemicals used to clean and disinfect a cooling tower are harmful and

extreme care must be observed when using them. There must be Material

Safety Data Sheets for all the chemicals where they are stored and used.

Cooling Towers


Cleaning Cooling Towers & Evaporative Condensers The most effective way of avoiding all the problems encountered with a

cooling tower is a regular and thorough manual washout every six months.

(see AS/NZS 3666 Part 2) The process is particularly important before a

tower is commissioned or restarted after a shutdown period of one week or

more. Wash out is compulsory under the Public Health Act, which carry heavy

fines if it is not done.

Before cleaning a tower the operator must check the service and

maintenance records to see if there has been any changes made to the

system or if anything needs to be done before shut down.

Also the tower should be inspected for any possible faults that may affect the

cleaning process.

During the cleaning process the public must be kept out of the operational

area, and the sprays must be confined to the operational area.

The tower must be fully dismantled and the interior and components scrubbed

with a high pressure water cleaner

Local councils have been given the job of monitoring the installation

maintenance and cleaning of cooling towers, as set out in the Public Health

Act 1991.

They are required by the Public Health Act 1991, to set up a register of all the

“regulated systems” (cooling towers),in their area and to routinely go and

check that the systems complies with the Act.

The council officer has the right under the Act to inspect any Regulated

System and view all associated maintenance records, when ever the council

thinks it is necessary.

The council will also require written notification of any changes that are made

to a Regulated System.

Any maintenance must be recorded (Public Health Act

1991), giving the details of the work and the record must

be signed by the person doing the work and the owner

or owner appointed representative.

Local Councils have an obligation to the public to conduct inspections and to police accurate records of maintenance, cleaning and microbial control.

Cooling Towers


Practical. Cleaning a Cooling Tower Aim: to learn the skills necessary to clean a cooling tower.

Task: Clean a cooling tower as required by AS/NZS3666 and the Public

Health Act.

Equipment:

a. Safety clothing as required by AS/NZS3666.

b. Cooling tower.

c. Operation manual.

d. Cleaning equipment.

Procedure:

a. Complete a Risk Assessment for the task.

b. Wear all required PPE.

c. Follow operation manual and shut down the tower.

d. Dismantle tower.

e. High pressure clean all internal components as instructed.

f. Reassemble tower.

g. Fill the tower with water to the required depth.

h. Follow the operations manual and start the tower.

i. Check operation.

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Maintenance Expensive breakdowns, Legionella, inefficiencies and increased running costs

can mostly be attributed to poor maintenance.

Preventative maintenance should provide the owner/user with the following;

• Early detection of problems that may lead to a breakdown.

• Maintain the systems efficiency.

• Determine that the system is complete and operating correctly.

• Remove the need to do corrective repairs.

• Maintain Bacteria to safe levels.

The maintenance management should contain the following;

Inspection reports, each individual system, regardless if they are side by

side and the same brand, need to have an inspection report developed for it.

Maintenance and Operating Manuals, need to be clear and comprehensive,

there should be no doubt as what needs to be done.

The object of the manuals is to apply AS 3666, to the system and to ensure

that the maximum performance and operating life are gained with effective

use of labour.

All manuals should have the following generic information;

1. Define the system that the manual applies to.

2. List the function and performance of the system.

3. Provide normal operating instructions.

4. Detail shut down and corrective procedures.

5. Provide details of any repairs, modifications or breakdowns.

Records and log book, of any work on the system must be kept on-site, and

copies should be given to the owner/user.

Water treatment information should include a Material Safety Data Sheet for

all chemicals stored on-site. There also should be an authorisation to use the

chemicals for the type of system on-site.

All maintenance and maintenance records are to be completed to the AS

3666 minimum standard. Failure to comply with these Standards can result in

Supreme Court action under the Public Health Act 1991.

It is imperative that service personnel, owners and users of cooling towers are

committed to ongoing preventative maintenance

Cooling Towers


Operational Check List.

Cooling Tower Casing. • rattles and vibrations. • water and air leaks while in operation. • amount of drift discharge. • signs of rusting. • condition of louvres and screens. • paint or coating for damage.

Cooling Tower Internal Components. • fill for alignment, seal, distortion, damage, slime, algae and

poor water coverage. • sprays or decks for operation and uniformity of distribution

over the fill. • drift eliminators for location, damage, seal, scale, algae, slime

or blockage. • Ball float operation.

Fan. • noise, vibration and free running. • where fitted, the fan drive for adjustment and alignment. • guards and screens for rust and fixing. • motor full load amps. • condition of impeller, housing scroll, shaft, bearings and

supports. Pump and Pipe work.

• leaks. • corrosion. • vibration. • Drains are clear. • pumps smooth running. • pump's gland. • motor amps.

Chemical Dosing System, (normally a separator contractor). • Pumps operation. • Chemical levels and types, safety data sheets. • Bleed off rate.

Cooling Towers


Sample of a maintenance report of a Water Cooling System. Date of Service. Type of service Maintenance................ Water sample.............. Name of Owner or User............................................................................................... Address of Premises.................................................................................................... Location of Tower......................................................................................................... Tower: Site Number....................................................................................................... Type.................................................................................................................. Make and Model............................................................................................... Treatment Type.............................................................................................................. Brand and chemicals used............................................................................................. Water Sample; Total Plate Count.................................................................................... Legionella report required yes. no. Report forwarded to Local Authority yes no Physical Condition of tower.......................................................................................... Cleanliness of Tower.................................................................................................... Nature of any work preformed ..................................................................................... ....................................................................................................................................... ....................................................................................................................................... Date of next maintenance ............................................................................................ Nature of any repairs to be made during the next maintenance ....................................... ....................................................................................................................................... ....................................................................................................................................... Signature of service person ……………………………………………………………….. Signature of Owner/user .............................................................................................. To Be Completed by the Local Authority (if required Report checked by .................................................................................................. Signature ................................................................................................................. Date ......................................................................................................................... Any action to be taken: No Yes, .........................................................................................................................

..................................................................................................................................

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Shut Down. This process should be followed if the tower is to be off line for a while.

• Drain the system to prevent stagnant water, or circulate the

chemicals if the water is to be left in the system.

• Repair any rust or damaged paint.

• Clean the tower.

• Co-ordinate a condenser clean for this time period.

Emergency Shut Off. A procedures manual should be written for each individual C.T. and site, but

generally;

1. Notify the owner and users of the cooling tower.

2. Shut off condensers and all other equipment supplied by the

Cooling Tower.

3. Stop the fan.

4. Stop the pump.

Cooling Towers


Review Questions

1. List four groupings of components that need to be checked during a service?

2. List three items that need to be checked on the Dosing system?

3. List the four steps for an emergency shut down?

4. How long must the results from a water sample be kept?

5. What must be done to the sump water from a cooling tower during cleaning?

6. Why are towers cleaned?

7. How often are they cleaned?

8. List the two pre-cautions that must be followed during a tower clean?

Cooling Towers


9. Where does Legionnaires disease manifests? (C of P)

10. Why are cooling towers such a concern regarding Legionnaire disease?

11. Beside Legionnaire disease what other things are harmful in cooling towers?

12. What are the optimum conditions for the growth of Legionella?

13. What is the purpose of preventative maintenance?

14. Why are new cooling tower installations washed out before use?

15. What must be added to the circulating water after the clean?

Cooling Towers


Assignment.

Aim. To gain an understanding of the pipe work and components of an operational cooling tower.

Task. Draw a schematic diagram of the twin cooling towers installation at TAFE NSW Sydney Institute.

Procedure. • Locate and record all the components attached to the systems pipe

work. • Draw a sketch of the pipe work and component placement. • Convert your sketch to a schematic using the correct symbols or

labelling the component on the drawing. • Hand in the drawing for marking.

Cooling tower Pipe work

Cooling Towers


OH&S HAZARD IDENTIFICATION AND RISK ASSESSMENT OF WORKING PROCEDURES IN TAFE Examples of Potential hazards may include but are not limited to:

Electrical Mechanical Pressure Chemical Gravity / Noise Gas Welding Radiation Biomechanical Biological • Contact with live wires or terminals causing

- Shock - Flash to eyes - Burns - Falls • Discharge of capacitor causing

- Shock - Flash to eyes - Burns - Falls

• Caught by operating machinery • Struck by moving machinery or objects • Caught by movement of mechanical parts • Crushed by objects moving or falling • Entrapment • Excessive vibration

Injury from releases of stored energy in - Refrigerants - Nitrogen - Oxy – Acetylene.

- Propane. - Ammonia.

• Fire or Explosion from

- Build up of flammable gases

- Ignition of existing flammable products

• Contaminants/Toxins causing

- Suffocation - Burns - Poisoning from products

• Falls from or into vessels • Falls from structures • Impact injuries from falling objects • Engulfment by product

Sound levels >85dBA causing hearing damage from - Operating machinery • Using equipment

• Injury due to - burns

-high temperature - naked flames - releases from stored pressure vessels. - fire hazard. - risk of explosions - lack of ventilation. -

• Extremes of temperature • Burns • UV from welding flashes • UV from exposure to sun • X-Ray exposure • Eye damage from laser

• Strains and sprains lifting objects • Strains and sprains moving objects • Slips and trips from

- Spillage/slippery surfaces

- Uneven/unstable surfaces

- Poor lighting • Crush injury

• Disease or illness from fungal spores eg. Legionnaires • Disease from blood products eg. Hepatitis, brucellosis

Determine the Risk Ranking 1-2 = High (Immediate action required) 3-5 = Medium Risk 6 = Low

2. How likely is it to be that bad – what is the probability of It happening 1. How severely could it hurt someone

Or How Ill could it make

someone?

VERY LIKELY Could happen at

any time

LIKELEY Could happen

occasionally

UNLIKELEY Could happen very

rarely

VERY UNLIKELEY Probably never will

happen KILL OR PERMANENTLY ABLED

1 1 2 3 LONG TERM ILLNESS OR RIOUS INJURY

1 2 3 4 LOST TIME INJURY 2 3 4 5 FIRST AID 3 4 5 6

Design Design out or modify Eliminate Remove or substitute Adopt a safer process Can it be done any other way Enclose or isolate Use guards, close off Ventilation Provide adequate ventilation

Provide PPE Appropriate PPE for the task training in how to use

Safe work procedures Correct work procedures Job rotation Relieve stress/boredom Training Know the dangers. How to do work

rectly

Cooling Towers


OHS Risk Assessment and Control (Educational) – By activity) College: Sydney Institute/Ultimo Section/ Refrigeration Topic: Cooling Towers.

Activity Potential Hazards Risk

Rating Control Measures Responsibility

Implementation Date

Revised Risk

Rating

Student’s Name: _______________________ Position: __________________ Signature: _________________

Cooling Towers


Answers to review questions. Section1 1. Latent heat. 2. Because of the Water Conservation Act. 3. Controlled draining of the circulating water to reduce TDS. 4. Reduce chemical effectiveness, clog system pipe work. 5. Oxidizing and Non-oxidizing. 6. Breathing in Legionella enriched aerosols. 7. By evaporating some the circulating water. 8. To increase the evaporation rate. 9. High RH% and air flow 10. Natural and Forced draft. 11. Very large industrial process. 12.

a. Induced draft counter flow. b. Induced draft cross flow. c. Forced draft counter flow. d. Forced draft cross flow.

13. Propeller and centrifugal. 14. Yes. 15. No. 16. Open and closed. 17. Closed, the circulating water doesn’t come into contact with the atmosphere, an open does. 18. To compensate for load charges. 19. Fan speed and water by-pass. 20. Individual condenser’s regulating valves will reduce the amount of water flowing in them therefore the cooling tower will need to regulate the volume of water flowing from it to them.

Cooling Towers


Answers to Law Questions.

a. NSW Public Health Act Part 4 clause 43.

b. AS/NZS 3666.2 2.6.1

c. AS/NZS 3666.2 2.5.1

d. AS/NZS 3666.1 4.1.4 also in the Regulation 2000 part 3 clause 9 (2)

e. Regulation 2000 part 4 clause 10.

f. AS/NZS 3666.2 table A1.

g. AS/NZS 3666.2 2.3.4.

h. Refer to AS/NZS 3666.3 foreword and 3.3.1.

i. AS/NZS 3666.3 3.7.

j. AS/NZS 3666.1 2.3.2

Cooling Towers


Section 2. 21.

1. Cooling tower casing. 2. Internal components. 3. Fan. 4. Pump and pipe work. 5. Dosing system.

22. 1. pump 2. chemical levels 3. bleed off rate.

23.

1. Notify the owner. 2. Stop any equipment connected to the cooling tower. 3. Stop the fan. 4. Stop the pump.

24. Seven years. 25. Drained to sewer or contained by trade waste company. 26. It is the LAW. 27. Every six months. 28. Kept the public away and contain the spray from cleaning. 29. In human lungs. 30. They have the ability to spread the disease. 31. Chemicals. 32. 35 to 37oC. 33. Reduce running costs. 34. To remove construction waste. 35. Corrosion inhibitor.

Cooling Towers

Documents

fresh town

wet bulb temperature

public health

free chlorine

water conservation

closed circuit

cooling tower

water sample