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Page 1: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

SHE InternationalSingapore Chapter Yearbook 1997

Page 2: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

The American Societyof Mechanical Engineers

Singapore Chapter Yearbook1997

MITA(P) No: 313/07/97

Editor:Dr S H Winoto

Publisher :The American Society ofMechanical EngineersSingapore Chapter39 Carpmael RoadSingapore 429782

Yearbook Committee19W1997

Chairman :Mr Bryan Hobbs

Members :Dr S H WinotoDr Simandiri SimDr V C Venkatesh

Advisor :Dr S H Winoto

Media Representative :Chan Yeow Advertising &Trading Co

Design & Layout:Flexi-Pagination & Design

C O N T E N T S3 Message from ASME President, 1997-98 - Keith B. Thayer

5 Message from ASME President, 1996-97 - Richard Goldstein

7 Message from ASME Section President, 1996-97 - Simandiri Sim

9 Message from The Yearbook Chairman - Bryan Hobbs

11 ASME Singapore Chapter Executive Committee/ Committee Chairmen/ Committee Members

17 Secretary's Report for the Year 1996-97

23 ASME ASIA '97 Planning Meeting

25 Activities of ASME Singapore Chapter

29 Region XIII And ASME ASIA 1997

31 Extraordinary General Meeting - 4 April 1997

3 7 Warping of Foam - Adhesive Bonded Strips Caused By The Additional Use of Mechancial Fasteners

45 Developments In Solar Water Heating

57 Solar Thermal Power Technologies For The Future

67 An Intelligent Plastic Injection Mold Design And Assembly System

75 Bearings: Problems And Prospects

82 Constitution of The American Society of Mechanical Engineers, Singapore Section

0 6 Top 10 Reasons to join ASME

00 Corporate Members

93 Student Members

Page 3: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

DEVELOPMENTS INSOLAR WATER HEATING

Graham L. MorrisonSchool of Mechanical and Manufacturing Engineering

The University of New South WalesSydney, Australia 2052

AbstractSolar water heating system technology is described and thescale of the International solar water heater market issurveyed. New product developments for both direct solarwater heating and solar boosted heat pump water heating areoutlined. Procedures adopted by the International StandardsOrganisation for assessing solar water heater performance andquality are discussed.

1. IntroductionThe world market for solar water heaters expandedsignificantly during the 1990's and as a result there hasbeen a substantial increase in range and quality of productsnow available. Solar water heater production is now amajor industry in China, Australia, Greece, Israel and theUSA. The "self-build" industry has also expandedsignificantly in Europe. The primary exporters of Solarwater heaters are Australia, Greece, Israel and the USA,most other countries only supply domestic demand, solarwater heater technology has recently expanded to include arange of vacuum insulated collectors in both flat plate andtubular form, solar boosted heat pumps and a range ofconcepts to reduce the cost and improve productperformance of pumped circulation systems.

The most common forms of solar water heaters areintegrated solar pre-heaters and thermosyphon systemswith a mantle heat exchanger around a horizontal storagetank. In areas where freezing is not a problem solar waterheaters are based on direct potable water circulationbetween the tank and collector, with protection against theoccasional frost provided by drain valves or an electricheater in the collector. For markets requiring a temperatureregulated hot water supply, auxiliary boosting of solarwater heaters is generally integrated into the solar tank,two tank systems are not commonly used outside ofEurope and North America. The principle types of solarwater heaters are outlined in the following sections.

1.1 Passive systemsThe majority of domestic solar water heaters usethermosyphon circulation of water between the solarcollectors and the storage tank. This requires thestorage tank to be mounted above the collector toproduce thermally driven circulation between thecollector and the tank. The advantage of these systemsis that they do not require an electrical connection andhave very low maintenance. The collector-tankconfigurations used include:

Figure 1. Thermosyphon solar water heater with externallymounted horizontal tank.

Figure 2. Evacuated tube collector with direct connection to tank.

45^

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Rays from the sun

Figure 3. Concentrating collector with heat pipe connection to thetank and water pressure driven tracking.

• Thermosyphon flat plate collectors with directconnection to a horizontal tank or connectionthrough a heat exchanger for freeze protection,Figure 1.

• Thermosyphon evacuated tubular collectors withdirect connection to a horizontal tank, Figure 2.

• Heat pipe energy transfer from parabolic troughconcentrating collectors with the heat pipecondenser inserted directly into the base of ahorizontal water tank, Figure 3.

1.2 Integral tank-collector systemsIntegral systems combine the tank and collector intoone unit, Figures 4, 5. These systems are simple andeffective however, due to high heat loss at night theyonly provide hot water during the day and earlyevening. The products range from simple glazed low-pressure plastic tanks to high quality steel tanksystems with selective surface coatings to minimise

Figure 5. Integral collector-tank solar pre-heater withconcentrating collector

heat loss. These systems make up the major portion ofthe large market in Japan. The main limitation withthis system concept is that it is only a pre-heater andhence must be connected in series with a conventionalwater heater if a 24hr hot water supply is required.

1.3 Pumped circulation systemsPumped circulation solar collector arrays connected toconventional enamelled steel hot water tanks havebeen widely used for domestic solar water heating inNorth America and Europe. The development of this

Figure 4. Integral collector-tank solar pre-heater with flat platecollector.

Figure 6. Pumped circulation system with drain down freezeprotection.

design concept was driven by the need to providefreeze protection in these climates. The market shareof such systems dropped significantly during the1990's due to the lower cost of externally mountedthermosyphon systems. However production ofpumped systems has started to increase in recent years,due to an increasing number of consumers who are notwilling to accept the visual .impact of an external roof-

Page 5: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

mounted tank, even though such systems are cheaper Comparison of markets in different countries is difficultand have better performance. New design concepts for due to the wide range of designs used for different climatespumped systems may result in increased use of this and different demand requirements. In Scandinavia andconfiguration however, it is primarily suited to larger Germany a solar heating system will typically be acommercial systems. combined water heating and space heating system with 10

to 20 m2 collector area. In Japan the number of solar2. MARKET SCALE domestic water heating systems being installed is large

The solar water heater market in many parts of the world however, most installations are simple integral preheatingwas recently surveyed by IT Power for the CEC systems. The market in Israel is large due to a favourableDirectorate General for Energy [1], the IEA CADDET climate and to regulations mandating installation of solarRenewable Energy review [2] in 1 994- 1 995 and the APEC water heaters. The largest market is in China where there isCompendium of renewable energy programs in 1995 [3]. widespread adoption of advanced evacuate tubular solarThe findings of these studies are summarised in table 1. collectors.

Table 1Major solar water heater markets

Country

AustraliaAustriaCanadaChinaCyprusDenmark

FranceGermanyGreeceIsraelJapanKoreaNetherlandsNew ZealandNorwayPortugalSpainSweden

SwitzerlandThailandTaiwanUK

USA

Number ofSDHW systems

in use.

350,000*

12,000*

14,000*

3,800,000*>8660*10,000*10,000*

100*

9,300*

45,000*

1,200,000*

Number ofSDHW systems

produced in1994

30,000*

2,000*

150,000*

3,000*750*20*

2,000*

1,300*>740*

1,821*

Total glazedcollector area

installedm2

1,400,000*400,000+

600,000+

2,400,000+

7,000,000*

200,000"

4,000,000*

Glazed solarcollector areaproduced in

1994m2

140,000*

100,000

500,000*30,000+

8,000°18,000+40,000+170,000+300,000+

50,000+9,000°3,000*200°

13,000+12,000+20,000°

6,000°

7200°70,000**

+ CEC survey [ 1 ] , * CADDET survey [2] , * APEC Compendium [3] ,

** DOE USA [4], estimated, " primarily "self-build" products.

47.

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The largest exporters of solar water heaters are Australia,Greece and the USA. The majority of exports from Greeceare to Cyprus and the near Mediterranean area. France alsoexports a substantial number of systems to its overseasterritories. The majority of US exports are to the Caribbeanarea, Australian companies export approximately 50% ofproduction (mainly thermosyphon systems with externalhorizontal tanks) to most areas of the world that do nothave hard freeze conditions.

2.1 Impact on UtilityThe adoption of solar water heating is not wide spreadhowever these renewable energy products make asignificant contribution to the energy supply systemsin countries such as Australia, China, Greece, Israeland the USA. The magnitude of the energy supplyfrom 100,000 m2 of flat plate domestic water heatercollector area is of the order of 50 MW during themiddle of the day (assuming 1000 W/m2 and 50%collector efficiency). Thus the peak power capacity ofsolar water heaters in a number of countries alreadyexceeds 1000 MW. The wide scale adoption of solarwater heaters can have benefits for electricity supplyutilities as solar water heaters displace a significantpart of the expensive peak electricity demandgenerated by domestic water heating [5].

2.2 Financing and EconomicsIn countries with large coal or gas based electricitygrids solar water heating is not generally costcompetitive. The current low price of coal and gasmakes competition very difficult however, whenexternal factors such as environment benefits, areincluded the economics of solar waters are veryfavourable. As countries accept the new greenhousegas emission targets the low cost of pollutionreduction through the expansion of a local solar waterheater industry can substantially change the economicvalue of these products.

However consumers are discouraged from purchasingsolar water heaters due to the high initial cost, eventhough the life cycle return of the investment may bevery good provided the consumer remains in thedwelling for more than six years. When utilities arerequired to meet lower pollution targets the benefit ofpollution reduction through solar water heating can bea profitable way for the industry to maintain businessvolume while implementing energy conservation andpollution reduction. A number of utilities havedetermined that there is a better return from investingcapital to promote solar water heating then investing innew low pollution and costly generating equipment.

3. NEW CONCEPTSA wide range of concepts for solar water heating have beenproposed in the literature, some of the designs that have

reached prototype status or recent commercial availabilityare outlined below.

3.1 Pumped circulation systemsInnovative pumped circulation system designs, basedon the low flow concepts, have recently beendeveloped that achieve reductions of capital cost andimproved performance, a significant contribution tothis development was an International Energy Agencyprogram to develop and test new systemconfigurations. The eight countries participating in theIEA program each developed a system configurationthat was considered the "Dream System" for theirmarket, accounting for local climate and technology.Some of the "Dream Systems" were successfullycommercialised before the IEA report [6] waspublished. The concepts incorporated in the "DreamSystems" include

Low flow rate circulation of the working fluid in thecollector loop resulting in lower capital cost, lowerparasitic energy use and improved performance due toincreases thermal stratification in the storage tank.

silcontubecollector to tank

flexible insulation

•sensor wire.con tube

tank to collector

'flexible insulation

Figure 7. Cross section of flexible integrated collector-tankinterconnection for pumped circulation.

• Integration of supply and return working fluid linesand the collector temperature sensor lead in oneflexible bundled connector between the tank and thecollector as shown in Figure 7. This greatly simplifiesinstallation.

• Efficient natural circulation heat exchangers toremove the need for two pumps in pumped circulationfreeze protected systems.

• Evacuated tube collector systems

The low collector flow rate concept adopted has beendemonstrated to be an important design principle that givesscope for system cost reductions at the same time as thesystem performance is improved. A low flow rate system

48.

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incorporating the integrated collector/tank connectionsystem developed as part of the IEA program inSwitzerland is shown in Figure 8.

t/ Solarcollector

E(fjyjfin)

-line 1

Mantle heatexchanger

Controllerl ,\ *\

;~— r^r*i/^>v "̂-1 (5_/

1

ip

cold

Figure 8. Swiss "Dream system " developed during the IEA program

The features of this system are reduced installation costsdue to improved tank design and reduced installation costsachieved by the use of the flexible "life-line" between thecollector and the tank. The single run low flow rate "life-line" connector replaces two hard pipes and the controllersensor wire used in standard pumped circulation systemdesigns. The low flow rate design enhances performanceas a result of improved thermal stratification in the storagetank and reduced parasitic energy use. The system shownin Figure 8 uses a vertical tank with a manifold heatexchanger around the bottom of the tank. This tankconfiguration has been adopted by a number of Europeanmanufacturers.

Another outcome of the IEA program was thecommercialisation of a cheap and compact heat exchanger,designed for low collector flow rate (pumped) in onestream and thermosyphon flow between the other side ofthe heat exchanger and the tank. This heat exchanger isbased on a small diameter spiral tube construction and isnow manufactured in Germany and Canada.

A combination of low flow rate collector circulation with acompact heat exchanger fitted to a low cost standard waterheater tank has been developed in Canada. This system hasthe benefit of easy installation and low shipping cost as thesolar components can be fitted to any locally available hotwater tank.

3.2 Single tank gas boosted systemsFor markets that require 24-hour availability ofregulated temperature hot water it is necessary to havean auxiliary heating system. In North America solarwater heaters are primarily used as pre-heaters toconventional gas or electric water heaters. In mostother markets electric auxiliary heating is incorporatedinto the primary solar system storage tank. Recently anumber of integrated single tank gas boosted solarwater heaters have been developed. These systemsintegrate a low cost thermosyphon solar water heaterwith a high efficiency gas booster in one integratedpackage. Such water heating systems have the lowestpollution rating possible, as a result of thecombination of a zero pollution natural circulationsolar pre-heater and a high efficiency gas burner withpiezoelectric ignition. Although these systems aremore expensive than electrically boosted systems theyare ideally suited to off-grid applications wherebottled gas or liquid fuels are the only alternative forwater heating.

3.3 Solar boosted heat pumpsThe heat pump water heater concept has beenextended to incorporate solar boosting of the heatpump evaporator performance. Solar boosted heatpumps are now manufactured in a number ofcountries. The original system concept proposed byCharters [7] was for a system with direct evaporationof the heat pump working fluid in the solar collector.This was a significant simplification over earlierdesigns based on a solar pre-heater in series with aheat pump. To minimise system costs and parasiticenergy requirements this system incorporates the heatpump condenser directly in the water storage tank. Theintegration of the condenser into the tank eliminatedthe parasitic energy of the pump used to transport heat

Evaporator platest

• it>

JC

1 1

• 3< 'j

. ~___^~// Expansion valve -^

W

Accumulator

Hot water "

Condenser coil

Insulation "

-JC]i*\j

f^7/****^

'

-zr*.;aonn*~»-^

1

"̂**~— — ̂ _..yp.

-•̂

==

HI

Figure 9. Solar boosted heat pump water heater.

Page 8: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

from the heat pump condenser to the water storagetank in more conventional solar heat pumpconfigurations. The solution for an effectivecondenser was to use an external wrap-around heatexchanger covering the bottom two thirds of the tankas shown in Figure 9. The disadvantage of this systemis that the condenser heat transfer is limited by freeconvection over the tank wall however, this penaltycan be minimised by using a large heat transfer area inthe tank. Systems incorporating the wrap-aroundcondenser on the outside of the storage tank are nowmanufactured in Australia, New Zealand and Korea.

Air flow flow

Solarradiation

Air flpw Ij

Hot out

Cylindericalevaporator panel

Wrap-aroundcondenser

Cold in

Condensertubing

Evaporatorpanel

Air channel

Figure 10. Compact "solar boosted" heat pump water heater.

Although this system has achieved significantacceptance it has the disadvantage that the heat pumprefrigeration circuit must be evacuated and charged atthe installation site.

A compact heat pump system has also been developedto reduce installation costs due to the need for on-siterefrigeration component installation. This systemincorporates an evaporator mounted round the outsideof the water tank with natural convection aircirculation over the evaporator as shown in Figure 10.

This system can be installed outdoors in order to gainsolar boosting however, a significant part of itsoperation may be in the conventional air to water heatpump mode [8]. This system is being extensively usedin commercial plant rooms where there is a highambient temperature due to heat generated by other

equipment. It can also be installed near or inside airconditioner exhaust outlets to benefit from the warmhumid exhaust air passing over the evaporator. Theadvantage of this system over a conventional air towater heat pump is that it does not have the significantparasitic energy of a conventional fan coil unit. Thepackaged system also has the advantage that all thecomponents are assembled in the factory and theinstallation is simpler than a conventional electricwater heater since the unit does not require a highcurrent electrical connection, as the compressor motorpower is typically only 500 W.

3.4 Evacuated tubular absorbersExtensive development of evacuated tubular solarcollectors in Australia and China has led to thedevelopment of a range of selective surfaces for use inall-glass evacuated tubes. The Australian designedtubes are manufactured under licence in Japan andhave been adopted in China where they are nowproduced in very large quantities for wet tubedomestic water heaters. The wet tube concept in whichwater is in contact with the glass tube can only be usedfor low-pressure water heating systems, as the tubescannot withstand more than a few metres waterpressure. Systems incorporating pressure tubinginside the evacuated tubes have been developed inAustralia and are manufactured in Japan.

Overheating of solar water heaters in summer is aproblem in many parts of the world particularly withpressurised water tanks attached to evacuated tubularsolar collectors, due to their high efficiency attemperatures above 100°C. Introduction of a hightemperature switch in the heat loss from evacuatedtubes by the use of temperature dependent gasdesorption materials has been investigated however,these devices have not gained commercial acceptance.

An unusual evacuated tube system using air in thetubes rather than water was developed to overcome thetwo extreme problems of overheating in summer andfreezing in winter.

This system uses a fan to circulate air through thetubes and a concentric heat exchanger around ahorizontal tank. Using air as the working fluidovercomes freezing problems in the collector and thefan controller can be used to avoid tank overheating.The tube outlet is mounted above the tank so thatthermosyphoning is restricted between the collectorand the tank when the fan is off. The tubes can operatesafely under stagnation conditions in the non-concentrating configuration that was adopted for thissystem as shown in Figure 11. Commercialisation ofthis system has not proceeded due to the high cost ofevacuated tubes manufactured under licence in Japan,

Page 9: SHE Internationalusers.tpg.com.au/t_design/papers/ASME-Singapore1997.pdf · through a heat exchanger for freeze protection, Figure 1. • Thermosyphon evacuated tubular collectors

Figure 11. Evacuated tube solar water heater with air as theworking fluid.

however, with low cost tubes now available fromChina this system and other evacuated tubeconfigurations may be commercialised in the nearfuture.

3.5 Seasonally biased collectorsFor locations outside the tropics a major operationalproblem with domestic solar water heaters is overheating in summer and insufficient capacity in winter.The summer over temperature problem is often due tothe practice of mounting collectors flush with lowinclination roofs to minimise the installation cost. Theover temperature problem can be easily overcome byusing a dump valve to control the tank temperaturehowever, consumers think water discharge is anindication of system failure and water supplyauthorities often do not allow water dumping as anoperational feature. Manufacturers go to considerabletrouble to incorporate over temperature controlwithout excessive water dumping which requiresconsiderable ingenuity in thermosyphon systemsdesign.

An alternative approach to over temperature controland improved winter performance is to use a collectordesign that can be mounted on a standard 20° to 25°roof pitch and yet give a winter biased performance.Such a collector was originally developed for a solarcooking system and then adapted to solar waterheating [9]. The collector employs a series of lowprofile reflectors that give a winter bias to the systemperformance, Figure 12. These collectors have beenused on a number of demonstration projects andelements of this technology are being adopted forcommercial production.

3.6 Low cost tanksThe high cost of specially designed tanks for solar

Figure 12. Evacuated tube solar water heater with seasonallybiased concentrating collector.

water heating systems is one of the major barriers tothe development of cost effective systems [10]. In thestandard thermosyphon design the weight of the tankis also a significant contributor to high installationcosts, as the tank is mounted on top of the roof. A newlow weight tank has been developed in Australia forsolar water heaters. This system is based on a plasticbag welded to rigid plastic end flanges with thepressure load taken by a thin steel cylinder that clipsonto the plastic end flanges. This tank has low weight,

* excellent corrosion resistance and needs relatively lowcapital investment for production.

4. TEST PROCEDURESA wide variety of solar domestic hot water systems aremarketed throughout the world. Hence there is a need forstandardised test methods to evaluate, predict, andcompare the performance of competing systems.International trade in solar water heaters could be greatlyfacilitated if the performance evaluation and certificationprocedures were the same in all countries. However ageneralised performance model, which is applicable to allsystems, has not yet been developed and it has not beenpossible to obtain an international consensus for one testmethod, and one standard set of test conditions for allcountries. Work is continuing internationally on thedevelopment of universal system test procedures throughthe International Standards Organisation (ISO), TechnicalCommittee ISO/TC 180, Solar Energy, Subcommittee SC4, Systems - Thermal Performance, Reliability andDurability. Until such methods are available simplemeasurement and data correlation methods have beenpromulgated by ISO while the more general proceduresare being finalised.

The five thermal performance test procedures selected fordevelopment as international standards and the stage ofdevelopment of each procedure are described below:

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4.1 Indoor test methodsThe test method defined in ISO 9459-1 [11] definesprocedures for indoor testing of solar water heatersunder specified benchmark conditions. Theprocedures are based on testing with a solar irradiancesimulator or non-irradiated thermal simulation.

Specification of solar simulator requirements includesduplication of air mass 1 .5 spectrum defined inISO9845-1 , with a total irradiance of 952 W/m2 and aspatial irradiance uniformity of ± 10% in the collectoraperture plane and variation of average irradianceduring a test less than ± 2%. A test sequence isrepeated each day until the daily system solar energycontribution for solar-only and solar-preheat systemsor the daily system supplemental energy required forsolar-plus-supplementary systems, is within 3% of thevalue on the previous test day. The entire test sequenceusually takes 3-5 days and is a rather expensiveprocedure due to the complex equipment required.

4.2 Outdoor test for solar only systemsThis test ISO 9459-2 [12] evaluates the daily energygain in solar pre-heat systems. The system is chargedto a required temperature at the start of the day andthen left to operate during the day without any loadsapplied. At the end of the day the contents of the tankare drawn off and the useful accumulated energyevaluated.

The useful energy collected in the tank is correlatedwith the daily radiation level and a temperaturedifference factor (Ta-T().

where

T" =T =Ha,b,c =

b(T-T

useful delivered energytank temperature at start of dayambient temperaturedaily total irradiationcorrelation coefficients

The daily energy gain is determined for at least fourdays, with a range of daily irradiation from 8 to 25 MJ/day, with approximately the same value of (Ta-TL) eachday. The tests are repeated for a range of Tu-Tt. values.

A calculation procedure is used to evaluate the effectsof night-time heat loss and energy carry over from dayto day, on the long-term system performance. Thelong-term system performance is determined by a dayby day calculation procedure accounting for climaticconditions, load volume and energy carry over fromday to day. The Commission of EuropeanCommunities, Ispra Research Centre, developed thisprocedure [13].

4.3 Outdoor test for solar plus auxiliary systemsThis procedure ISO 9459-3 [14] uses a model of solarwater heater performance to correlate data collectedwhile the system is operating under typical load cycleconditions. The parameters monitored are dailythermal energy delivery (load), bulk mean deliverytemperature, auxiliary energy use, daily irradiation onthe collectors and ambient temperature. Monitoring islimited to input/output factors so the system can betreated as a "black box." The correlation model is thenused to compute the annual performance for the testsite or for other locations, and for a range of loads. Thecorrelation model given by equation (2) has beenfound to correlate outdoor test data and solar simulatordata, for both passive and active SDHW systems [15].

/= (a + b(To-TJ/L)H/L + c(To-TJ/L

whererrLa,b,c =

delivery temperatureambient temperatureload energycorrelation coefficients

In this procedure the effect of internal energy changein the tank is minimised by averaging the performanceover 5 to 15 number of days, so that the change of tankenergy is small compared to the total load energy forthe period.

4.4 Computer simulationThis method ISO 9459-4 [16] combines test resultsfrom individual components with computersimulation models for the balance of system. Forexample, test data are used to determine performancecorrelations for the collector and heat exchanger andcomputer simulation models are used to provideperformance equations for the store, pump, controller,etc. The result is a computer simulation program thatthas great flexibility, which can be used to predictsystem performance under a wide range of solarmeteorological conditions, loads, load profiles, andoperating set points.

The USA Solar Rating & Certification Corporation[17] and the Australian Standards Association [18],use this technique to determine ratings of solardomestic water heating systems. Thermalperformance ratings are determined usingmathematical models and empirical correlations inconjunction with the computer simulation programTRNSYS [19].

4.5 Outdoor system test and parameter identificationThis procedure ISO 9459-5 [20] is based on anumerical model of the solar water heater andparameter identification software [21]. The

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parameters in the numerical model are determined bycomparison of measured and predicted performanceresults. This method has the advantage over directsimulation methods in that the performance predictionis based directly on system measurements and notcomponent measurements or performance models.The prediction will therefore reflect any differencesbetween actual system operation and the systemoperation deduced from design information and directsimulation models. Performance data for the waterheater are collected at one to two minute intervals,with more frequent monitoring during load draw-offperiods. An identification process is then used tocompute the system parameters that produce theclosest match between the simulation modelpredictions and the observed performance. Measuredinputs and outputs are entered into the identificationprocedure as a function of time, rather than as dailyaverages used in the correlation methods. Thus loadpattern effects are accounted for in the parameteridentification process. The process is based onmatching the simulation model prediction with shorttime step experimental data, and is referred to as theDynamic Test Method. Typically fifteen to twentydays of monitoring are required.

The dynamic parameter identification procedure canbe interpreted as the inverse of dynamic simulation.Conventional simulation models predict the systemoutput on the basis of measured or design values ofparameters for individual components. The dynamicparameter identification procedure computes theparameters from system performance measurementsand then uses these parameters to simulate the annualperformance in the usual simulation process.

4.6 Comparison of test proceduresThe SDWH test procedures being developed asinternational standards range from simple, low costprocedures for assessing solar pre-heaters, to complexprocedures that require extensive equipment andhighly trained staff for assessing complex systemsunder any climatic an load conditions. In terms ofoutcomes, the primary differences between themethods is that the procedures in Part 1 only produce arating for a standard day, while the other Parts predictannual performance for a range of climatic and loadconditions. The results of tests performed under Parts4 & 5 are directly comparable. These two proceduresboth permit performance predictions for a range oflocations and system loads.

The procedure that requires the least investment inequipment and operator skills is Part 2 however, it islimited to solar preheat systems.

In this procedure the system is pre-conditioned at the

start of each day and then left to operate without theneed for data acquisition other than radiation andembient temperature monitoring. Energy monitoringis performed during a single load draw-off at the endof the day. This can be achieved with simpletemperature and flow rate recorders or with an on-linedata acquisition system.

The procedures required for Part 3 closely mirroractual operating conditions of a typical systeminstallation. The main equipment required is acontroller than can apply typical domestic draw offpatterns throughout each day. The main difficulty withthis procedure is that the test is very long, typically sixto ten weeks and an unbroken sequence of steady dailyloads is required over periods of five days or longer.This test is close to the ideal in-situ procedure.However, the results are limited to the particular dailyload draw off pattern used during the tests.

The simulation procedure being developed as Part 4 isthe most flexible. However, it is limited by theavailability of verified numerical models for the typesof systems to be assessed. The problem withsimulation results is that the actual system may not beas good as the ideal design case that the simulationmodel usually represents. An approach to allow forpractical imperfections in a particular product is torequire a comparison between the simulation modelpredictions and observed performance over a periodof a few days. Any difference between the modelresults and the observed performance can be allowedfor by introducing a scaling factor in the simulationresults. The Solar Rating and Certif icationCorporation in the USA [17], have adopted this type ofapproach.

The procedure defined in Part 5 of the standard overcomes the difficulty of obtaining a match between! hesimulation model and the actual system performance.This is achieved by using a parameter identificationprocedure to evaluate the important parameters from aseries of system tests, rather than from componenttests or manufacturers specifications as in the case ofconventional simulation modelling. Part 5 alsorequires a validated simulation model of the systembeing assessed, however, it automatically matches themodel to the observed operation of the particularSDWH system being assessed. A feature of thematching procedure in Part 5 is that stationarymeasuring conditions are not required. This meansthat the experimental effort is minimised as a widevariety of measurement sequences can be used in theparameter identification process.

The ISO development provides measurementprocedures that can be used for applications in

53^

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developing and advanced markets. Due to the widerange of product designs and quality it is essential thatcountries planning to incorporate solar water heatingas a core energy supply element should impl"ement acertification program to guarantee satisfactory productlife for a positive economic and pollution return.

5. CONCLUSIONSThe solar water heater industry has developed into asignificant industry in a number of countries. The peakpower output already exceeds 1000MW during the peaksolar periods in at least four countries and power levelsabove 500MW are achieved in many other countries. Thesignificance of the contribution of solar water heaters toenergy self efficiency, pollution reduction and localmanufacturing capacity should see this industry expandsignificantly in the coming years.

6. REFERENCES

[1] I.T Power Pty Ltd., (1993), "The development ofrenewable energy manufacturing facilities". CECDirectorate General for Energy, contract No 4.104/91-44.

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