Structure Model of Energy Efficiency Indicators and Its Applications

Transcription

1 tuctue Moel of negy fficiency Inicatos an Its Applications Li-Ming Wu Yun-Chang Bo Bai-heng Chen 3 Dept. of lectical ngineeing Ching Yun Univesity Taiwan ROC. Chung Hua Institution fo conomic Reseach Taiwan ROC. 3 Dept. of Inustial ngineeing Chung Yuan Chistian Univesity Taiwan ROC. Abstact Fo puposes of enegy consevation an envionmental potection the govenment of Taiwan has set long-tem soli policies to continuously encouage an assist the inusty in impoving efficiency of enegy utilization. While pactical enegy saving has been successful to a limite extent ue to multiple actions no stong evience of impovement in enegy efficiency was obseve fom the enegy efficiency inicatos (I) system accoing to annual national enegy statistics an suvey. In oe to unestan the ole enegy efficiency plays in the I system a stuctual analysis of I is absolutely inevitable. This pape makes use of function theoy to evelop a stuctue moel fo I at the pocess level of inusty secto. The moel is evelope base on pemises that not only it is able to estimate enegy efficiency fo a system but also it shoul be able to povie a function of inteface that connects I at the national level with I at the inusty level. With the inusty enegy efficiency inicato efine as negy Consumption Pe Unit (CPU) of pouct ove a yea two inepenent vaiables ae fomulate to etemine the value of CPU: fist the utilization inex (UI) of system pouction capacity secon the vaiation inex (VI) of system enegy utilization. The esigne value of UI is unity an the esigne value of VI is zeo. By taking esigne values of these two inices as cente a simple but inclusive stuctue moel of CPU can be establishe though pocesses of mathematical function expansion an linea appoximation. Majo chaacteistic of the moel elies on the sepaation capability of UI facto fom the CPU calculation such that the actual enegy saving contibuting to the impovement of CPU can be evaluate. To make pactical application of the moel an item of ominant pouct pouce by the enegy system shoul be etemine fist. Then fou sets of atum elate to the selecte pouct ae equie to be collecte fom the enegy system: the esigne enegy consumption the esigne pouctivity at full capacity the annual enegy consumptions an the annual pouctivity. To emonstate the application the moel has been applie to two enegy intensive systems that ae selecte fom the steel inusty in Taiwan. Necessay ata ae collecte fom the steel plants. ualitative intepetations on the annual enegy efficiency of the system will follow fom the moel analysis. uantitative amounts of enegy that the system has been save o aitionally use can be given as well. Finally impovement suggestions about enegy management fo enegy system to be moe efficient in the futue can also be extacte fom the moel analysis. D. Li-Ming Wu Associate Pofesso Depatment of lectical ngineeing Ching Yun Univesity 9 Chien-Hsin R. Jung-Li Taiwan 3 R.O.C. TL: ext. 533 FAX: mail: lmwu@cyu.eu.tw

2 I. Intouction In Taiwan ue to the shotage of fossil fuel esouces moe than 97% of enegy eman must ely on impots fom foeign counties. With a high oppotunity cost of enegy consumption the GNP expenitue pe capita use fo puchasing enegy fom othe counties is as high as U$333.5 anke as the 3 place in a coss county compaison next to outh Koea an Japan. To secue an stabilize omestic enegy supply an to euce negative impacts on envionment an ecology fom buning chemical fuels sustainable evelopment is always a majo concen in making national enegy policies. In tems of stategies leaing to sustainable evelopment seveal impotant measues ha been taken in Taiwan which have inclue impovement of enegy efficiency pomotion of enewable enegy utilization an incease in investment on enegy technology eseach an evelopment ationalization an eajustment of enegy system infastuctue ivesification of enegy categoy selection etc. In oe to cope with the pact of Kyoto Potocol since the en of 997 Taiwan Govenment ha calle fo the fist National negy Confeence in the sping of 998. The main pupose of the confeence was to iscuss the issue of geenhouse gas emission with espect to situations of enegy economics an envionment on a national basis. Although thee has been no nee fo Taiwan to atify the Potocol aggessive conclusions on stategies to euce geenhouse gas emission nonetheless was the esult of the confeence. specially a national pogam calle Pomotion Pogam of Complete negy Consevation an fficiency nhancement was initialize. Fom this pogam a cluste of action plans aiming at the impovement of enegy efficiency an mitigation of geenhouse gas emission was popose fom the inusty secto the tanspotation secto the commecial an esiential secto an the electical powe secto etc. The govenment gante all the poposals. Thus afte yeas of joint effots fom pivate entepises an the govenment the annual nationwie enegy auiting system ha eveale infomation showing a geat eal of save enegy fom vaious elate pogams. Fo example in the inusty secto enegy is save fom moto opeation with taitional moto contol eplace by vaiable fequency invete contol; heating an ying system is opeate with highe enegy efficiency when waste heat is ecovee; in the commecial an esiential secto lighting enegy is consume less when fluoescent lamp is opeate with magnetic ballast eplace by high fequency electonic ballast etc.. Despite the fact that a measuable amount of enegy ha been save by implementing enegy consevation pogams infomation fom the annual nationwie enegy statistics an suvey eveals that howeve thee is no significant evience to suppot the claim that such enegy saving exist. pecifically when national enegy pouctivity (GNP pe lite of oil equivalent) o enegy intensity (Lite of oil equivalent pe olla of GNP) is use as the enegy efficiency inicato (I) fo efficiency evaluation thee is no sign inicating the influence of save enegy on the vaiation of I. In othe wos it is not easy to see the ole these enegy consevation pogams play in the I system even though ata collecte at the inusty level inicates the effectiveness of enegy saving. To unestan whee the enegy saving goes an what the ole the enegy efficiency plays in the efficiency evaluation system it is absolutely necessay to make a eepe analysis on the stuctue of I system. Fig. shows the I system [] that ha been use to evaluate Taiwan s oveall enegy efficiency. Fom the pyami stuctue of the system the inicatos consist of fou iffeent levels. The apex level is the national enegy balances fom which the national enegy pouctivity an enegy intensity ae geneate. The seconay level is the sectoal enegy intensity which is futhe compose of vaious sub-sectoal enegy intensities. The enegy uses an equipments take up the thi level which facilitate the attibutes of enegy utilization an quality. The bottom level is the pocess efficiency whee iffeence mae by enegy efficiency impovements an enegy consevation measues takes place. While the Is at the fist an secon levels ae pimaily etemine by economical factos the Is at the thi an fouth levels ae basically

3 etemine by physical factos. With the enegy pouctivity o enegy intensity as I at the top levels the enegy consumption pe unit (CPU) of pouct is moe suitably use as efficiency inicato at the bottom level [] Fig. is a wiely accepte system that has been use to evaluate national an inustial enegy efficiency in many evelope counties [34]. ince events of enegy savings mainly occu at the bottom level of the inicato system it is hope that the CPU vaiation fom inustial pocess will eflect the iffeence mae by actions of enegy efficiency impovements. If the amounts of enegy savings fom the CPU vaiation can be ientifie then it is hope that thee is a way that can be fomulate so that it will pass the enegy iffeence infomation fom the bottom to the top level. If things happen as esie then it is possible to evaluate the ole that the enegy saving plays in the national I system. Unfotunately exteme ifficulties exist when such kin of wok is intene. Fig. Pyami stuctue of enegy efficiency inicato system Fist of all the vaiation of CPU at the pocess level is in geneal a esult fom many factos. xcept enegy efficiency impovement othe factos influencing the vaiation of I inclue () pocess equipments () opeation metho (3) enegy categoy (4) feeing mateial (5) system management (6) enegy saving activity an (7) utilization of pouction capacity etc. Basically all these factos ae inepenent of each othe an can be categoize as inteio factos an exteio factos. The fist 6 factos liste above ae of inteio facto because they ae iectly enegy-matte elate an can be contolle by the pocess itself. The 7 th facto is of exteio facto since it is not iectly enegy-matte elate an to a lage extent it elies on pouct maket vaiation which is almost completely out of the pocess contol with a small extent attibute to the pocess annual maintenance. In oe to etemine the CPU vaiation fom a single facto fo example the enegy saving activity it is necessay to keep the est of the factos constant (unvaie) which in pactice is impossible. This is the fist ifficulty encountee when the ole analysis of enegy saving in the I system is consiee. The secon ifficulty aises when the poblem of passing enegy saving message fom the bottom level to the top level is consiee. ince it is equie to aess all the enegy savings fom pocesses in the entie county an the total numbe of pocess is so huge it is not possible to finish the job without a systematic collection of enegy saving ata fom all the pocesses on an annual an national basis. Futhemoe when the infomation egaing enegy savings moves upwa to uppe levels the same ifficulty as in the bottom level will be encountee in each level because thee ae factos othe than the enegy saving facto affecting the I vaiation. Fo

4 example at the sectoal level the stuctual facto an the maket facto will play citical oles in the calculation of I. To make sue that the enegy savings ata oiginate fom the bottom level is accounte fo without istotion uing the passing pocess pesents a seious challenge. A popula appoach use in many eseaches [5678] analyzing the stuctue of I is the ecomposition metho. In this metho the inicato is isaggegate into a goup of component factos though the mathematical chain ule. ach of the component factos is analyze inepenently an the esult is multiplexe back via the same chain ule to e-obtain the inicato. While this metho is useful at the top levels of the I system ifficulty aises at the pocess level whee enegy efficiency impovement takes place. The ifficulty lies in how accuately the enegy efficiency can be quantifie. The motivation of the pape is to evelop a stuctue moel fo I at the pocess level of inusty secto. Instea of using taitional ecomposition appoaches at the national an sectoal levels this pape makes use of function theoy to evelop a stuctue moel fo inicato at the bottom level fom which actual enegy savings o enegy oveuse can be allocate. The metho an the poceue use to evelop the stuctue moel incluing both qualitative an quantitative analysis ae escibe in ection II. To emonstate the application the moel is applie to two enegy intensive systems in Taiwan s steel inusty. Results fom moel implementations ae etaile in ection III. Finally the conclusion an iscussion on futue woks ae given in ection IV. II. Reseach Metho A. Moel Development As mentione in the intouction thee ae at least 7 factos affecting the value of CPU in a typical inustial pocess. If CPU is viewe as a mathematical function then it coul be a function of 7 inepenent vaiables. Togethe these vaiables contibute to etemining the CPU values. The CPU can be teate as a function of time eithe an the function values can be compute simply by iviing the pocess enegy consumption by the pocess pouctivity at iffeent time points. While it is easy to etemine the vaiation of CPU with espect to time it is extemely ifficult to etemine the vaiation of CPU with espect to each of the 7 inepenent vaiables. The ifficulty lies in the fact that CPU function is highly nonlinea in stuctue an lacks function expession in 7 vaiables not to mention how to quantify these factos into vaiables. To simplify the poblem it has been notice that among the 7 vaiables mentione befoe the fist 6 of them ae closely enegy elate (the inteio factos) while the last one is not (the exteio facto). If all of these inteio factos ae lumpe togethe as a single vaiable of enegy then the CPU function of 7 vaiables can be euce to be a function of two vaiables which makes the enegy efficiency analysis possible. Mathematically the two vaiables can be efine as follows: () vaiable efine by the utilization inex of pocess pouction capacity expesse in symbol an () vaiable efine by the vaiation inex of pocess enegy utilization expesse in. If symbol f is use to epesent CPU then f can be expesse as f f ( ) () whee an Designe annual pouctivity of the pocess

5 Real annual pouctivity of the pocess Designe annual enegy consumption of the pocess Real annual enegy consumption of the pocess Accoing to efinitions liste above when is occuing the pocess is having highe pouctivity than esigne value ( ). When < is occuing the pocess is having smalle pouctivity than esigne. When is the case the pocess is consuming less enegy than esigne ( ). When < is taking place the pocess is consuming moe enegy than esigne. It is also woth noting that paametes an ae two constants that wee esigne at the beginning when the pocess was initially constucte. Thei values may be change when the pocess is moifie fo bette pefomance but uing peios between changes the two paametes ae constants an shoul be file by system manage as impotant engineeing ata. The values of an ae time-vaying which in tun make vaiables an also time-vaying. With CPU fomulate as a two vaiable function it is possible to analyze the vaiation of CPU with espect to each of the two vaiables i.e. if elationships between vaiation of CPU an vaiations of an can be constucte then a stuctue moel can be establishe an the pocess enegy efficiency analysis becomes possible. To constuct such a stuctue moel theoy of function expansion is applie as follows. If esign values an ae chosen as two baseline ata an the CPU function is assume to be continuously iffeentiable with espect to vaiables an is high oe iffeentiable then the function can be expane as a Taylo seies aoun the cente an : () f ( ) f ( ) ( ) + f f f f 3 3 ( ) + ( )( ) + O ( ) f whee 3 3 O ( ) ummation of tems with oe highe than. Defining f ( ) f ( ) an neglecting all the nonlinea tems q.() can be linealy appoximate as f f (3)

6 f whee Vaiation of CPU ue to incement of only f an Vaiation of CPU ue to incement of only. Futhemoe fom iffeential opeation the two patial tems in q.(3) can be expesse as f an f Afte binging in an making tems eaangement q.(3) becomes (4) q.(4) is the stuctue moel fo I at the pocess level of inusty secto. Accoing to q.(4) seveal impotant obsevations can be mae: (a) If conitions an ae substitute into the moel q.(4) becomes (5) which is exactly the esie CPU expession fo pocess at the esigne conitions. (b) The CPU consists of two tems. The fist tem contains vaiable only which means this tem epens on equipment utilization only an is not enegy elate. The secon tem contains an which means this tem epens on both enegy utilization an equipment utilization an theefoe is enegy elate. (c) With a given the smalle the value the lage the value of CPU. This behavio is consistent with eal situation fequently seen in the inusty. The invese popotionality between an CPU is also acceptable fom physical an engineeing point of view. () The value of CPU is mainly etemine by the fist tem on the ight sie of q.(4) since is small in magnitue an appeas only in the secon tem. (e) q.(4) is a linea appoximation moel that equies fou sets of ata to finish the CPU calculation: an. B. Moel Application

7 () Compae with esigne value the values of CPU may have thee cases : (). < an (3) ualitative Analysis: () Fo case the pocess is in aveage consuming moe enegy than esigne in poucing pouct. This is a situation not esie in the sense that the pocess may be consiee opeating inefficiently. Howeve one shoul not jump to the conclusion that the pocess is opeating with a absolutely be enegy efficiency because a smalle value of ( <) coul make the magnitue of the fist tem on the ight sie of q.(4) gowing lage an this tem is in geneal not enegy elate. If the value of the secon tem on the ight sie of q.(4) goes positive ( <) which makes its summation with the fist tem even lage then one can say that the pocess is opeating in a moe of not goo enegy efficiency. On the othe han if the value of the secon tem goes negative ( ) which contibutes to lowe the value of CPU then the pocess shoul be consiee in a moe of insufficient enegy efficiency only. Fo the case of an < the enegy efficiency conition is insufficient as well base on the simila analysis poceue. Thee is enegy ovetakes fom all the thee cases but two of them is not as not goo as the thi one. () Fo case < the pocess is in aveage consuming less enegy than esigne in poucing pouct. This is a esie situation in the sense that the pocess may be consiee opeating efficiently. Howeve one shoul not make the conclusion immeiately that the pocess is opeating with absolutely goo enegy efficiency because a lage value of ( ) coul make the magnitue of the fist tem on the ight sie of q.(4) eucing smalle an this tem is in geneal not enegy elate. If the secon tem on the ight sie of q.(4) goes negative ( ) which contibutes to futhe lowe the value of CPU then the pocess can be fimly consiee opeating in a moe of goo enegy efficiency. On the othe han if the secon tem on the ight sie of q.(4) goes positive ( <) which contibutes to incease the value of CPU then the pocess shoul be consiee opeating in a moe of sufficient enegy efficiency only. Fo the case of < an the enegy efficiency conition is sufficient as well base on the simila analysis poceue. Thee is enegy save fom all the thee cases but two of them ae not as goo as the thi one. (3) Fo case the pocess is consuming in aveage the same enegy as esigne in poucing pouct. Vaiables an ae elate each othe in this case an the CPU epens on one vaiable only. The total enegy consume fo poucing poucts is amounte to be ( ) an the vaiation inex of enegy utilization expesse as in this case is:

8 ----- (6) Binging q.(6) back to q.(4) the CPU becomes a function of single vaiable: ) ( (7) If is eplace by in q.(7) q.(5) is etieve as expecte: #. Note that q.(7) is an exact equality athe than an appoximation. q.(6) suggests the fact that as long as vaiables an satisfy the linea elationship the pocess will be opeating with enegy efficiency the same as the pocess initially esigne. The CPU value will be kept constant in this case no matte what the value is. Two inequalities can be obtaine fom obseving q. (7): < <. when when (8) Gaphical Analysis: Accoing to the efinitions efine in the moel evelopment possible values of an lie in the anges of < < an < <. Fom physical point of view the maximum enegy efficiency of a pocess occus at the conitions of infinite pouctivity an zeo enegy consumption i.e. at the limits of an. Using q.(4) these conitions pouce CPU value as follows: lim lim (9)

9 q.(9) efines the lowest bounay fo CPU. Any combination of an within thei espective omain will geneate CPU value not smalle than. It is also ealize fom obseving q.(8) that fo numbe pais ( ) with element values lie in a limite ange q.(4) will bing about CPUs with the same featues. If possible omain of ( ) ae examine in a ectangula cooinate system with vaiable as the abscissa an vaiable as the oinate six iffeent egions can be categoize as illustate in Fig.. Fig. is an efficiency iagam since each egion in the iagam can be chaacteize by almost iffeent pefomance in enegy efficiency theefoe the iagam is calle the ( ) efficiency iagam theeafte. The staight line on the iagam having slop - an passing though the oigin is the line of the equation. Any point on the line will have CPU value equals. ince is use as the cente point fo Taylo eies xpansion as iscusse in the last paagaph the line of equation in the ( ) efficiency iagam theefoe can be utilize as the cente line fo CPU stuctue compaison. The staight line an cooinate axes in the ( ) efficiency iagam fom the bounaies between egions. Fo egions locate to the ight of the staight line the CPU is smalle than esigne value. Fo egions locate to the left of the staight line the CPU is lage than esigne value. To chaacteize the CPU in each of the egions table I lists six assigne egion numbes an coesponing enegy efficiency evaluations. Reasons fo the evaluations will be explaine in the next paagaph. It is notewothy that fo points close to the staight line in the ( ) iagam absolute values of CPU ae not fa fom the esigne value. Howeve thei meanings with espect to the pocess enegy efficiency ae quite iffeent. On the othe han fo egion locate at the upight aea ( ) in the fist quaant the pocess has the best conitions on enegy efficiency while fo egion locate at the own left aea ( << ) in the thi quaant the pocess has the most insufficient conitions on enegy efficiency. (II) (III) (IV) (V) (I) (VI) < Fig. ( ) fficiency Diagam fo I valuations Table I. Regional negy fficiency valuations

10 uantitative Analysis Region < < < < < < negy fficiency valuation Goo * CPU < ufficient < < < *Compae with pocess esigne values. Insufficient Not Goo Insufficient ufficient Compae with esigne CPU q.(4) can be use to estimate the amounts of enegy that is actually save o oveuse in a pocess ove a yea (o any fixe peio of time). The enegy savings o the enegy ovetakes fom a pocess is meant to be the pat of enegy that is cause iectly by iffeent enegy utilization conitions with the effect of enegy efficiency impovements inclue but exclusive of the effect of equipment utilization. While the CPU value is mainly etemine by the fist tem on the ight sie of q.(4) the pocess enegy vaiation elies entiely on the secon tem. With the fist tem epens on only the secon tem epens on both an. ince is the only vaiable that eflects the vaiation in enegy the value compute fom the secon tem theefoe stans fo the amounts of enegy vaiation that is cause by both the enegy utilization conitions an the equipment utilization conitions. The effect eive fom the equipment utilization conitions howeve can be cancelle out of the secon tem if the same effect fom the esigne CPU is subtacte i.e. afte compaing with esigne CPU the enegy savings o ovetakes exclusively ue to vaiation of enegy utilization can be calculate as follows: < ( + ) + + O( ) + + O( ) + + O( ) negy savings o ovetakes O( ) () whee + an q.(7) ha been use an O( ) epesents the summation of high oe tems. To analyze the enegy vaiation iffeent cases coesponing to six egions in the ( ) iagam ae ientifie. The enegy savings o ovetakes the enegy euctions o incements the enegy efficiency evaluations an the gaph of enegy levels in each egion ae escibe. Fo pupose of convenience the enegy savings (ovetakes) an enegy euctions (incements) ae all expesse in positive numbes.

11 () Region I: negy savings: negy euctions: negy fficiency valuation: Goo () Region II: < negy savings: negy euction: negy fficiency valuation: ufficient (3) Region III: < < negy ovetakes: negy incements: negy fficiency valuation: Insufficient Designe CPU negy avings CPU Fig.3 negy levels fo egion I negy saving CPU Designe CPU Fig.4 negy levels fo egion II

12 (4) Region IV: < < < negy Ovetakes: negy Incements: negy fficiency valuation: Not Goo (5) Region V: < < negy Ovetakes: negy Incements: negy fficiency valuation: Insufficient negy ovetakes CPU Designe CPU Fig.5 negy levels fo egion III CPU Designe CPU Fig.6 negy levels fo egion IV negy Ovetakes

13 negy Ovetakes CPU Designe CPU Fig.7 negy Levels fo Region V (6) Region VI: < negy avings: negy Reuctions: negy fficiency valuation: ufficient negy avings Fig.8 negy Levels fo Region VI Designe CPU CPU III. Case tuies To make pactical applications of the I moel evelope in the pevious sections two steel plants selecte fom Taiwan s steel inusty ae tagete fo enegy efficiency evaluation. The steel inusty is one of the most enegy intensive inusties that consume the lagest amounts of enegy in the inusty secto of Taiwan. The govenment an the steel inusty itself both have spent a lot of effots woking on the issue of enegy efficiency enhancement fo the puposes of enegy saving an envionmental potection. Base on iffeent feeing mateials an pouction technologies thee ae two kins of steel plants in the inusty. One of them uses the pocess of blast funace to pouce steel slabs blooms pig ions an uses olling mills to pouce vaious finishe steel poucts such as col olle coil hot olle ban wie o etc. the othe one uses the pocess of electic ac funace to pouce cue steels an uses olling mills to pouce finishe poucts like Re-bas H-beams an plates. Thee ae ozens of electic ac funace plants an only one blast funace plant in Taiwan fo the time being. Fo completeness an

14 emonstation puposes two plants fom each of the two kins of steel plants ae selecte fo the veification of the I stuctue moel. To pocee the fist step is to etemine a ominant item of pouct out of vaious poucts pouce by the pocess o enegy system of the steel plants. ince in geneal moe than one pouct ae pouce in a pocess at iffeent time the ominant pouct shoul be selecte with espect to the weighting factos of maximum pouctivity the maximum woth o the maximum enegy consumption of the pocess an the pouct shoul be fully epesentative of the pocess as well. In the cases being stuie the ominant pouct selecte fom the blast funace plant is the steel billet which inclues steel slabs blooms an pig ions an the ominant pouct selecte fom the electic ac funace plant is the Re-bas. The secon step to implement the moel is to collect fou sets of atum elate to the selecte pouct fom each of the chosen steel plants: the esigne annual enegy consumption the esigne annual pouctivity at full capacity the annual enegy consumptions an the annual pouctivity. Although is the annual pouctivity associate with the ominant pouct can be selecte to be the annual enegy consumptions e an easily collecte fom the fom all of the poucts pouce by th plants. With ata plant the esigne ata an ae little hae to obtain because these ata ae in geneal not equie in the egula enegy auiting poceues an wee not available when they wee fistly equie. In the case whee is available an is not pope metho shoul be applie to help appoximating the values. () Blast Funace Plant The selecte blast funace steel plant is initially establishe in 979 with only one set of blast funace in the pocess. Thee moe sets with iffeent capacities ae ae into the pocess in an 997 espectively in oe to incease the plant s pouction capacity. The esigne annual pouctivity of the plant change values wheneve new funace joine the system. The esigne enegy consumptions s howeve wee not available at the moment when the ata wee equeste fo this ese ach ue to uncetainty. To appoximate these impotant ata the linea egessive appoach ha been applie to etemine the values of. Table II lists the collecte input ata an necessay quantities that ae eive fom using an the compute fo the plant. The enegy savings (o ovetakes) an the enegy euctions (o incements) compute fom the moel implementation fo each unit of pouct ae also liste in the same table. The ( ) efficiency iagam fo the blast funace steel plant is plotte in Fig.. Accoing to the lists in Table II the majo outputs fom the I moel implementation ae expesse in tems of eithe enegy savings (-) o ovetakes (+). The minus sign (-) associate with the enegy savings is use to inicate that the pocess enegy has been consume less than esigne fo each unit of pouct pouce an the save enegy is iectly cause by the enegy-elate activities in the pocess. Thus the amounts of enegy saving evaluate by the moel is the enegy actually save fom these activities. The moe the enegy save the bette the pocess in enegy efficiency. The elative magnitue of enegy savings fom iffeent yeas stans fo elative conitions on pocess enegy efficiency at iffeent time. The positive sign (+) associate with the enegy ovetakes is use to inicate that the pocess enegy has been consume moe than esigne fo each unit of pouct pouce an the oveuse enegy is iectly ue to the enegy-elate activities in the pocess. The moe the enegy oveuse the wose the pocess in tem of enegy efficiency.

15 Yea The iffeences between the CPU an its esigne value is expesse in tems of eithe the enegy euctions (-) o the enegy incements (+). The minus sign (-) associate with the enegy euctions means that the CPU is smalle than the esigne value. The positive sign (+) associate with the enegy incement implies that the CPU is lage than the esigne value. These iffeences ae esulte fom integating both the enegy-elate activities an pocess equipment utilization. Table II Blast Funace teel Plant: Inputs an Outputs fom the I tuctue moel Moel Inputs Moel Outputs (Ton) (O) (O/Ton) (O/Ton) (O/Ton) negy negy Incements(+) Ovetakes(+) o o Reuctions(-) avings(-)

16 In accoance with th e moel outputs liste in Table II an illustate in Fig. the geneal pefomance of the blast funace steel plant in enegy efficiency can be escibe as follows:. The numbe of yeas that enegy savings (-) occue takes 76% out of the plant s lifetime epesenting that most of the time the blast funace steel plant was opeate une conitions of sufficient enegy efficiency. The ( ) efficiency iagam shown in Fig. also shows that most of the plant points ae locate in egions (II) an (VI).. The absolute magnitue of enegy savings (-) is iffeen t fom an usually smalle than that of enegy euctions (-) in each yea. But cases with a lage enegy savings (-) o occu as in the yea of 99 an 996 which means that in these paticula yeas the plant was opeate in status of goo enegy efficiency. 3. The statement: the lage the value (pouctivity) the moe the enegy save is not necessaily tue as can be seen fom the ata of yea 993 an 995 although it is geneally a vali statement. 4. The appeaance of enegy euctions (-) oes not guaantee the existence of enegy savings (-) as inicate by the yea of 993 which means that the plant was opeate une the conition of not goo enegy efficiency. 5. The enegy ovetakes (+) appeae at yeas when new sets of blast funace wee installe into the pouction line which means that the new facilities usually cost moe enegy in thei fist yea opeation. But expeience accumulate by the plant may mitigate the poblem as can be seen fom the yea of 997 when plant opeation patten appeas 6. iffeently. The enegy ovetakes (+) also occue at yeas of an 995 but thei magnitues ae smalle than those yeas when new funaces wee ae into the system. 7. The enegy savings (-) has appeae continuously ove the last 8 yeas along with the inceasing of pouctivity. Howeve the ate of inceasing of the enegy saving (-) is not as api as that of the pouctivity an even a phenomenon of satuation in enegy efficiency enhancement has been obseve. Fig. ( ) fficiency Diagam of the Blast Funace teel Plant

17 () lectic Ac Funac e teel Plant The electic ac funace steel plant selecte as a case stuy was foune in 988. Dominant pouct of the plant is the high stength Re-bas fo builing constuctions. The ata collectable fom the plant inclue an stating fom the yea of 997 to 3. The ata is not available at the moment when it is equeste fo this eseach ue to uncetainty. To obtain this impotant ata linea egessive appoach ha been applie once again as in the case of blast funace steel plant to appoximate the value. Table III lists the collecte ata an eive quantities that ae necessay in the I moel implementation. The moel s outputs incluing the ene gy savings (-) the enegy ovetakes (+) the enegy euctions (-) an the enegy incements (+) ae also liste in the same table. The ( ) efficiency iagam of the electic ac funace steel plant is illustate in Fig.3. The geneal pefomance of the electic ac funace steel plant in enegy efficiency in accoance with Table III an Fig.3 can be escibe as follows:. The numbe of yeas that the plant ha enegy ovetakes (+) occue takes 7% out of the last 7 yeas epesenting that most of the time the plant was not opeate with sufficient enegy efficiency. The ( ) efficiency iagam shown in Fig.3 also shows that most of the plant points lie in the egion (III) an (IV).. The magnitue of enegy ovetakes (+) is always lage than that of enegy incements (+) in most of the yeas which confims that the plant in these yeas was not opeate with sufficient enegy efficiency. 3. The statement: the lage the value (pouctivity) the bette the enegy efficiency is almost tue in this paticula electic ac funace steel plant. 4. The enegy savings (-) stat to appea in the last yeas along with incease of pouctivity. Howeve the incease ate of enegy saving (-) is not as api as that of pouctivity. 5. The enegy efficiency of the selecte electic ac funace plant is sensitive to the vaiation of pouctivity. Table III. lectic Ac Funace teel Plant: Inputs an Outputs fom the I tuctue moel Moel Inputs Moel Outputs negy negy Incements(+) Ovetakes(+) Yea O o Reuctions(-) avings(-) (Ton) (O) (O/Ton) (O/Ton) (O/Ton)

18 Fig. 3 ( ) fficiency Diagam of the lectic Ac Funace teel Plant IV. Conclusion an Discussion A stuctue moel fo negy fficiency Inicato (I) efine as the negy Consumption Pe Unit (CPU) of pouct at the pocess level of inusty secto has been evelope. Base on the theoy of function expansion an linea appoximation the I moel is establishe with such a stuctue that it is able to istinguish the enegy iffeence between enegy-elate activities an equipment utilization in a pocess. Compae with esigne value the CPU estimate fom the moel can be analyze in both qualitative an quantitative fashions an thus the amounts of enegy savings o ovetakes ue to vaiations of enegy utilization in th e pocess can be calculate. The ( ) efficiency iagam eive fom the moel povies a boa pictue to the oveall unestaning of CPU evelopment in a pocess. To implement the moel enegy systems epesenting two steel plants ae selecte fo case stuies. One of the plants uses a pocess of blast funace to pouce steel billets the othe plant uses a pocess of electic ac funace to pouce Re-Bas. Outcomes fom moel implementation inicate that the blast funace plant is consiee opeating with sufficient enegy efficiency an is stabilize in enegy pefomance ove most of the plant lifetime. The electic ac funace plant with limite plant ata available in the moel is consiee opeating with insufficient enegy efficiency an is lacking of stability in enegy pefomance fo most of its opeating time. It seems that the pouctivity in both plants is a majo facto that affect the occuence of enegy saving o enegy ovetake. The lage the pouctivity is the highe the possibility of enegy saving occus. No fixe ule that egulates the inteepenence between pouctivity an enegy savings (o ovetakes) howeve can be obseve. Possible eason behin this is because thee ae many factos othe than enegy efficiency impovements affecting the vaiation of enegy utilization. When the effect fom movements of enegy efficiency enhancement is oveien by effects fom othe factos amounts of enegy savings ae euce o cases of enegy ovetake esulte. Futue woks on the applications an evelopments of the I moel evelope in this eseach inclue:. To stuy altenatives othe than the linea egessive metho.

19 When paamete is not available fom the pocess the optimal mathematical metho shoul be applie in oe to obtain this impotant ata with the best quality. Fo example the gey peiction appoach may be favoe fo cases with limite ata in size.. To stuy the stuctue of enegy utilization in a pocess Many ingeients ae involve in the enegy utilization of a pocess. If an enegy utilization moel with stuctue sepaable in compositions can be constucte then the enegy savings esulte fom the movements of enegy efficiency impovements can be easily ientifie an quantifie. 3. To pefom stuctual analysis fo the I at the sub-sectoal an sectoal levels. If the enegy savings collecte at the pocess levels can be linke to an iniviualize in the I stuctue at the uppe levels then the vaiation of I is easie to explain an the ole of enegy savings plays in the I system can be ecognize as well. Acknowlegements The authos woul like to acknowlege suppot fom the negy Bueau of the Ministy of conomic Affais Taiwan the Republic of China though thei poject gant to the Chung-Hua Institution fo conomic Reseach. V. Refeence. Intenational negy Agency Inicatos of negy Use an fficiency Pais Woel. Pice L. Matin N. Fala J. haeffe R. negy Intensity in the Ion an teel Inusty: A Compaison of Physical an conomic Inicatos negy Policy 5(7-9) ADM negy fficiency Inicatos: The uopean xpeience ADMM ition Pais Asia Pacific negy Reseach Cente negy fficiency Inicatos Japan. 5. Geening L.A. W.B. Davis L. chippe M. Khushch Compaison of ix Decomposition Methos: Application to Aggegate negy Intensity fo Manufactuing in OCD Counties negy conomics Ang B.W. an F.. Zhang A uvey of Inex Decomposition Analysis in negy an nvionmental tuies negy Ang B.W. an F.L. Liu A New Decomposition Metho: Pefect in Decomposition an Consistent in Aggegation negy Chis J. pafiel The Canaian Decomposition xpeience: Fom to 54 Inusties AC umme tuy On negy fficiency in Inusty Poceeings Vol..