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Simple measures can oten improve theenergy eciency o chilled water andcooled water systems signicantly.

Two recommended measures are:

Maximising the growth and successo plastics-based technology in NewZealand in an economically, socially andenvironmentally responsible manner.

Water Cooling...

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ENERGY EFFICIENT

Savings o up to 25% o cooling

water costs can be easily achieved.Cooling water is typically produced by the use of cooling towers,often in conjunction with chiller units. In rare instances coolbore water is used directly from the ground to save water andenergy costs.Chiller units are used i you need to reduce waterto temperatures below the capabilities o a cooling tower, or toprovide stable temperatures. Typically a chiller will use 30 kWho electricity or every 100kW o cooling capacity. Some plasticsprocessing sites can require up to 200 kW o cooling capacity.

Reliable and consistent coolingwater is essential or the efcient

manuacture o plastics. Energy is

needed to reduce water temperature

to the required level using cooling or

chilling plant, oten consuming up to

10% o the total energy used in a plastics

manuacturing site. This energy use can

oten be reduced with some simple measures.

03

Reduce1 Cooling Loads Optimise Chilled &2 Cooled Water Systems

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1 Reducing Cooling Loads

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Optimise the temperature setpoint

Identiy the optimum temperature setpoint or the chilled waterused in your plant.

New Zealand plastics plants are requently ound to havethe temperature o the chilled water set unnecessarily low.Temperature setpoints or plastics processing are typically inthe 3-5C range. Particular production lines may requirewater temperatures lower than this, so wherever possiblethese should be isolated rom the rest o the cooling system.

As a rule o thumb every C you can raise the chilled water

temperature by reduces the energy used by about 3%.

Eliminating or reducing cooling loads will reduce running costs and improve eciency.The rst logical step is to supply cooling only where it is needed.

Other ways o reducing cooling loads include:

Increase the watertemperature setpoint

Correctly design yourwater distribution system

Use ree coolingwherever possible

Raising chilled water setpoint saves injectionmoulder $2,487 in energy costs

A Waikato injection moulder had been running their chilled water at an unusually low 11C. The companyincreased the temperature setpoint to 15C with no adverse eects on processing.

With zero costs to implement, this initiative saves the company $2,487 in energy costs every year.

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Maximising the growth and successo plastics-based technology in NewZealand in an economically, socially andenvironmentally responsible manner.

Correctly design your waterdistribution system

Correct sizing and design o chilled and cooled water pipes in the setup o a manuacturing plant can have

signicant implications or energy use. Designing pipes too small or with too many joints or bends will increasethe rictional losses.

Analysing the chilled water pipework or a new Auckland injection moulding site revealed the extent o potentialenergy losses rom incorrect pipe sizing. The chart and table below show that energy losses decrease as pipesize increases. For this site, the optimal pipe size was calculated at between 90 and 0mm diameter. Usingsmaller pipe would result in greater energy losses, and using larger pipe would give diminished savings andincreased pipe costs.

50 70 90 110 130 150 170

$300.00

$250.00

$200.00

$150.00

$100.00

$50.00

$

Energy

Loss

NominalPipeDiameter(mm)

Nominal PipeDiameter

(mm)

PressureLoss

(m head)

PowerLoss(W)

Power LossAnnual

Cost

OverallWeight(kg/m)

MaxVelocity

(m/s)

50 38.56 545.33 $5,095.85 .94 4.684

75 6.89 387. $,30.8 4.37 3.344

90 9.05 80. $,96.56 6.8 .56

0 3.98 563.8 $56.66 9.36 .788

5 .33 330.4 $308.4 .0 .4

60 0.77 08.8 $0.90 9.79 0.864

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Use ree cooling wherever possible

In some cases it is possible to do away with the chilled water system and onlyuse cooled water rom a standard cooling tower. By utilising the wet-bulb ambienttemperatures you can achieve ree cooling.

Using a chiller with a new or retrotted ree cooling circuit can show large reductionsin operating costs due to shorter chiller running times, lower maintenance costs,and extended chiller lie.

Condenser

Evaporator

Chiller

ChilledWaterToPlantChilled

Water

From

Plant

CoolingWaterToPlant

CoolingWaterFromPlant

ChilledWater

Reservoir

Replacing chilled water system with a cooling towersaves Auckland frm $6,338 every yearChilled water at an Auckland plastics factory was supplied by 4 separate ring main systems using 4 pumps.

Water for the whole system was chilled to 14C by an 11kW chiller.

Only one chilled water loop required water to be at 14C. Using the chilled water in other parts of the plantwas also causing production issues due to condensation.

Installing a cooling tower to cool the water in three of the loops cost approximately $13,000 and saves $6,338in energy every year. This initiative will pay for itself in about 2 years.

ExampleofaChillerInstallationwithCoolingTowerBypass

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Maximising the growth and successo plastics-based technology in NewZealand in an economically, socially andenvironmentally responsible manner.

2 Optimise Chilled and CooledWater Systems

Minimising the load allows a betterassessment o the system design andparticularly how it responds to partloads. Ater you have minimised theloads or your cooling water system youshould look to optimise the system youhave in place.

Use the most suitable rerigerant andoptimise the system or high part-loadand winter eciency. This is particularlyimportant when additional chillers havebeen added to the system.

Tuning cooling water pump(VSD) delivers instant paybackAn audit o a plastics site with a variable speed drive (VSD) uniton their cooling water pump ound signifcant pump speedoscillation due to a high PID gain setting. Reducing the gainsetting on the VSD unit reduced the power consumed by thepump rom 15.8kW to 13.5kW.

With zero costs to implement, this initiative is saving thecompany $1,792 every year.

Use VSD on pumps and ansI your cooling tower has no way ocontrolling the operation o the an on

the tower then valuable energy is beingwasted as the an will run continuallywhenever the plant is operating. Thismeans that even during winter, whenthe water is much cooler than required,the cooling tower ans will be runningunnecessarily and wasting energy.

Cooling tower ans should be controlledusing either a temperature switch that turnsthe an on or o depending on the coolingtower water temperature, or a temperaturetransducer and variable speed drive (VSD)

that controls the ans speed.

Installing a VSD on cooling toweran saves plastics frm $2,436 inenergy every yearAn Auckland frm has a MST MSX-250 cooling tower on site.The cooling tower an has no control on its an and the an uses32,537kWh o energy every year.

By installing a 7.5kW VSD at a cost o $5,000 they will save22,455kWh o this energy. This will save $2,436 every year and payor itsel within 2 years.

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Best PracticeEnergyProgramme

PlasticsNewZealandisanationaltradeorganisationrepresentingover200membercompanies.

ItisestimatedthattheNewZealandplasticsindustryconsumesmorethan1.7petajoulesofenergy

perannum.

ThePlasticsNZBestPracticeenergyProgrammehelpsplasticcompaniestominimisetheirenergyfootprintthroughenergyauditsandpracticalactions.

Maximising the growth and successo plastics-based technology in NewZealand in an economically, socially andenvironmentally responsible manner.

www.plastics.org.nz

Plastics New Zealand Incorporated

PO Box 76 378

Manukau City

New Zealand

Phone: +64-9-6-3773

Fax: +64-9-6-3850

Email: ino@plastics.org.nz

Maintain the System

Cooling systems oten operate at low eciency due to a lack o routinemaintenance.

Service chillers regularly and keep records o plant conditions.

Clean evaporators, air blast coolers and heat exchanger suraces regularly.

Check fow/return temperatures and system fow rates to veriy these arecorrect and optimised.

Set all systems components to turn o automatically when not in use.

VSDs installed on cooling tower ans can produce signicant energysavings. The relationship between energy consumption o a an and itsspeed is cubic. I the an speed is reduced to 50%, the energy used isreduced to 0.53 = 0.5 or .5% o the nominal energy consumption.For example, i you have a 7.5kW an motor and you are able to reducethe motors speed by 0% it will consume 3.84kW, and i you can reducethe speed by 50% the motor will be using just 0.94kW.

Additional benefts rom installing VSDs are:

less variation in the cooling water temperature

a reduction in noise rom the cooling tower, and

less stopping and starting, thereore less wear and tear on the an motor

Cooling water solutions vary according to the needs and setup o anindividual plant. Cooling water solutions should ideally be developedas part o an overall site energy eciency project. We recommendthat companies undertake a detailed, Level energy audit under thePlastics New Zealand Best Practice Energy Programme. ContactPlastics New Zealand to nd out more.