LIFE CYCLE GREEN COST ASSESSMENT METHOD FOR GREEN BUILDING DESIGN. Lijing Gu1, Daojin Gu1, Borong Lin1, Mingxing Huang2, Jiazi Gai3, Yingxin Zhu1

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1 LIFE CYCLE GREEN COST ASSESSMENT METHOD FOR GREEN BUILDING DESIGN Ljng Gu1, Daojn Gu1, Borong Ln1, Mngxng Huang2, Jaz Ga3, Yngxn Zhu1 1Department of Buldng Scence, Tsnghua Unversty, Bejng , Chna 2School of Archtecture, Tsnghua Unversty, Bejng , Chna 3School of Desgn and Envronment, 4 Archtecture Drve, Natonal Unversty of Sngapore, , Sngapore ABSTRACT Lfe cycle green cost assessment (LCGCA) method, whch can evaluate buldng envronmental load and economc performance throughout ts lfe cycle comprehensvely, s propounded n ths paper n order to gude green buldng desgn. In LCGCA, envronmental load (EL) cost s proposed based on concept of envronmental tax and counted nto general buldng ntal cost and operatng cost, and then green payback tme (GPT) could be worked out. Wth ths method, an offce buldng n Bejng s studed. The operatng energy consumpton, lfe cycle EL, lfe cycle cost (LCC) and GPT of dfferent envelope schemes have been compared. The results ndcate GPT s obvously shorter than the general payback tme when EL cost s consdered. Especally, the exteror shadng scheme changes to be economcally feasble through GPT evaluaton. Ths assessment method s more sutable to gude green buldng desgn practce because envronmental performance and economcal performance are consdered together. KEYWORDS Green buldng desgn, Envronmental load, Green payback tme, Lfe cycle cost analyss BACKGROUND Green buldngs have got rapd development around the world n recent 10 years. Then how to evaluate green performance and determne green level of buldngs becomes one of the research emphases. In Chna, green buldng desgn s stll at begnnng stage. Recently, domestc scholars begn to pay attenton to buldng envronmental mpact and use lfe cycle assessment (LCA) method to quantfy t n order to get evaluaton ndex of green buldng. Moreover, some scholars try to use ths method to gude buldng coolng and heatng resources selecton and envelope desgn (L 2005, Ln 2004, Gu 2007), but researches lke these are just a few part. However, when real projects n practce are desgned, the research concluson wll not be consdered, because economc performance s most mportant n market and better envronmental performance sometmes leads to hgher ntal constructon cost. To promote energy savng and envronment protecton n practce, natonal polcy s needed. In some foregn countes, envronmental tax has been s mposed to lead some ndustry to control and reduce polluton. Chnese government also has ssued notfcaton of begnnng to study envronmental tax mposton (Anon.) not long before. Although most envronmental tax ams at energy producton and use now, buldngs wll be nvolved n the future for ts hgh energy and resources consumpton. Then a comprehensve assessment method that can evaluate both envronmental and economc performance of buldng s urgently needed. But there s no correspondng study n Chna yet. Some results of foregn study (Gluch and Baumann 2004) may not be used drectly because of dfferent status of Chna. Therefore, lfe cycle green cost assessment (LCGCA) method s propounded n ths paper as an attempt to solve ths problem. LCGCA METHOD LCGCA nvolves two ndexes: buldng envronmental load (EL) and buldng green cost (GC). EL (unt: pont and pt for short) can be calculated wth LCA method by Buldng Envronmental Load Evaluaton System (BELES) developed by Department of Buldng Scence n Tsnghua Unversty (Gu 2006). GC can be calculated accordng to lfe cycle cost analyss (LCCA) method. GC s dfferent from the general cost whch manly ncludes ntal cost (IC) and operatng cost (OC). It also ncludes envronmental load cost (ELC) whch s the economc value of EL. The prce of unt EL can be determned accordng to CO 2 prce. Influenced by Clean Development Mechansm of Kyoto protocol, nternatonal carbon trade s very actve at present, the general prce of CO 2 s about 80RMB/t (trade n Chna) (Anon A). BELES analyss result shows EL of CO 2 s 0.463pt/t, so prce of unt EL s 173 RMB/pt. Then ELC of buldng constructon phase plus general IC comes to be green ntal cost (GIC), and ELC of operaton phase plus general OC comes to be green operatng cost (GOC). Wth above calculaton and redefnton, buldng envronmental performance and economc performance are connected together. Fnally the ntegrated evaluaton ndex of LCGCA, green payback tme (GPT), can be calculated wth equatons (1)-(6). ELC = EL V pt (1) GIC = ELCc + IC (2)

2 GOC = ELCo + OC (3) ( GIC-GIC ) = ( OC- OC ) P + ( ELC ELC ) P 0 0 G o o0 EL namely: Δ GIC = ΔOC PG + ΔELCo P (4) EL 1+ e 1+ e N 1 ( ( ) G + e PG = )/(1 ) (5) e 1+ e N 1 ( ( ) G + e P EL EL )/(1 EL EL = ) (6) Where EL s buldng EL per unt floor area (pt/m 2 ), V pt s prce of unt EL (RMB/pt); ELC c s ELC of constructon phase per unt floor area (RMB/m 2 ) (all the other cost parameters n ths paper refers to the cost of per unt area, no statement s made n the followng text except specal condton), ELC o s ELC of operaton phase (RMB/m 2 ); IC s general IC (RMB/m 2 ), OC s general annual OC (RMB/yr/ m 2 ),GIC s GIC (RMB/m 2 ), GOC s annual GOC (RMB/yr/m 2 ), subscrpt 0 refers to GIC and annual GOC of base case; N G s GPT (yr); P G s dscount coeffcent of total OC n N G years, t s a functon of energy prce growth rate e and bank rate ; P EL s dscount coeffcent of total ELC n N G years, t s a functon of CO 2 prce growth rate e EL and bank rate. The dfference value s used to calculate N G, so there s no need to consder the same part of each scheme, only comparson of dfferent part s enough to get results. The calculaton workload can be smplfed. The results of case study n ths paper are all carred out wth comparson of only dfferent part of schemes. Green buldng desgn can be optmzed through comparson of GPT of each desgn scheme. If GIC>GIC 0 and GOC>GOC 0, t means the scheme not only ncreases GIC but also ncreases GOC, t s less green than the base case and should not be chosen; If GIC<GIC 0 and GOC<GOC 0, t means the scheme not only decreases GIC but also decreases GOC, t s more green and economc than the base scheme. There s no payback tme for above two condtons n theory. If GIC>GIC 0 and GOC<GOC 0, N G may be worked out, the greater t s, the longer the GPT s. When N G s n an acceptable range, the scheme s greener than the base case and economcally feasble n lfe cycle. CASE STUDY Investgaton data show that energy consumpton per unt floor area of commercal buldngs s much more than that of resdental buldngs, besdes, facade desgns of commercal buldngs are always complcated than that of resdental buldngs. Therefore, an offce buldng n Bejng s taken as a study case n ths paper. Several schemes of envelope desgn and energy savng strategy of t are analyzed. Energy consumpton, lfe cycle envronmental load (LCEL), lfe cycle cost (LCC) and GPT are compared respectvely. In addton, the dfference between GPT and general payback tme (PT) are analyzed too. The buldng has 30 floors wth total area 49445m 2, and the frst four floors are desgned as annex. HVAC system of t s fan-col unt plus fresh ar system, centrfugal water chllers for coolng n summer and gas-fred boler for heatng n wnter. The orgnal envelope scheme s all-glass curtan wall and s taken as base case. All the schemes are descrbed n table 1. Table1 Lst of desgn schemes DESIGN SCHEME case1 all-glass curtan wall, base case case2 ARWW * 0.65 & alumnum curtan wall case3 ARWW 0.45 & aerated concrete block glass curtan wall wth louver and ventlaton case4 adjustable double-skn facade for south facade glass curtan wall wth fxed exteror louver case5 (500mm wde) for south facade, 4 layers for floor 1 and 4, 3 layers for the other floors *ARWW s the area rato of wndow over wall Buldng operatng energy consumpton analyss 1. Buldng load smulaton Buldng load s hourly smulated by an energy smulaton software DeST (Desgner s Smulaton Toolkts) (Yan etc. 2004), whch s also developed by Department of Buldng Scence n Tsnghua Unversty. Accordng to the local desgn standard of publc buldngs (Mnstry of Constructon P.R.Chna 2005), dfferent wndow thermal performance s requred for dfferent buldng ARWW scheme. Double skn facade and exteror louver shadng schemes are desgned for energy effcency and better comfort based on the orgnal scheme. Envelope thermal parameters of each scheme are shown n Table 2, and smulaton results of buldng load are shown n Table 3. Table2 Envelope performance of each scheme K* of K of WINDOW WALL ROOF K SC* case case case case s * 1.4/w * 1.33 s0.11/w0.47 case hourly dfferent *K s heat transfer coeffcent, W/(m 2 K), SC s shadng coeffcent of glass, s stands for summer, w for wnter Table3 Results of buldng load smulaton MAX MAX TOTAL TOTAL HEATING HEATING HEATING COOLING LOAD LOAD LOAD LOAD (W/m 2 ) (W/m 2 ) (kwh) (kwh) case case case case case

3 2. Operatng energy consumpton Dfferent envelope scheme has dfferent coolng and heatng load, as well as dfferent operatng electrcty and gas consumpton. Buldng load affect not only energy consumpton of coolng or heatng unts, but also electrcty consumpton of supply system (ncludng pumps, fans etc.). A concept of TCOP (total coeffcent of performance) s proposed to descrbe the total energy effcency of coolng system. TCOP s the rato of total coolng load n summer over total electrcty consumpton of coolng system. TCOP s qute dffcult to be calculated precsely, t s greatly depend on the type of dstrbuton system and equpment specalty. As for ths buldng, t s estmated to be 2.5 accordng to energy consumpton measurement and nvestgaton to many offce buldngs n Bejng by our department. Because heatng load of ths buldng s much less than coolng load and the dfference of heatng pump electrcty consumpton among schemes s small, so t s not counted n the total electrcty consumpton of HVAC system. Then annual operatng electrcty and gas consumpton can be worked out wth equaton (7)-(8). Where TCOP s TCOP of coolng system; CON e s annual operatng electrcty consumpton per unt floor area (kwh/yr/m 2 ); CON g s annual operatng gas consumpton per unt floor area (m 3 /yr/m 2 ); η boler s gas-fred boler effcency, s assumed to be 0.89 accordng to the local standard; r s heat value of natural gas, 8500kcal/m 3 ; Q c and Q h s the total coolng load n summer and heatng load n wnter respectvely (kwh/m 2 ). The results are shown n Fg.1 and Fg.2. Q c CONe = TCOP Qh CONg = η r electrcty consumpton (kwh/a/m 2 ) gas consumpton (m 3 /a/m 2 ) boler (7) (8) 30.6 case1 case2 case3 case4 case5 Fg.1 Operatng electrcty consumpton case1 case2 case3 case4 case5 Fg.2 Operatng gas consumpton It shows the smaller the ARWW (case2, case3) s, the less the electrcty consumpton s and the more gas consumpton s. Energy consumpton of double skn facade scheme (case4) s less than that of base case both n summer and n wnter. Electrcty consumpton of exteror shadng scheme (case5) s less than that of base case, but gas consumpton s a lttle bgger snce the fxed louver decrease solar heat gan n wnter and makes heatng load hgher. Case3 has the least electrcty consumpton for ts smallest ARWW, and case4 has the least gas consumpton for ts largest ARWW and hgher SC of glass. LCEL analyss Each scheme s dfferent only n exteror envelope desgn, so only EL of exteror walls and wndows are consdered when calculatng buldng constructon EL. There are many knds of materals n envelop, but consumpton of some knds are just a lttle, so only consumpton of man materals are counted for comparson. Besdes, some buldng materals have shorter lfe-span than buldng, so they need to be replaced durng buldng use lfe. Buldng lfespan s assumed to be 50 years, and curtan walls, double skn facade, exteror louver are assumed to be 40 years (IBEC 2004). Operatng EL manly comes from energy use of coolng and heatng system. Accordng to buldng materals consumpton and buldng load, EL of constructon, replacement and operaton can be worked out wth BELES. Then buldng LCEL of each scheme can be calculated. The results are shown n Table 4 and Fg.3. Table 4 Buldng lfe cycle envronmental load * EL c * EL r * EL o LCEL (pt/m 2 ) (pt/m 2 ) (pt/yr/m 2 ) (pt/m 2 ) case case case case case *The subscrpt c stands for constructon phase, r for replacement and o for annual operaton. lfe cycle EL (pt/m 2 ) constructon EL operatng EL replacement EL case1 case2 case3 case4 case5 Fg.3 Buldng lfe cycle envronmental load It s found that, constructon and replacement EL of case4 s hghest, operatng EL of base case s hghest,

4 and ELs of all phases of case3 are lowest. Although constructon EL of case2, case4 and case5 are hgher than that of base case, LCEL of them are all lower than that of base case. Ths means the ncreased constructon and replacement EL of optmzed strategy can be balanced out by the decreased operatng EL, and the total lfe cycle envronmental performance of these optmzed schemes are better than that of base case. LCC analyss LCC of buldng contans many knds of cost, such as IC, OC, mantenance and replacement cost and so on. In ths case, IC, OC and replacement cost (RC) are consdered. Cost for mantenance s not ncluded because the type and amount of mantenance s dffcult to estmate. Besdes, there s just a lttle dfference between the max heatng and coolng load of each scheme, so the cost dfference of coolng and heatng source equpment s very small (the largest equpment cost dfference s 3.3RMB/m 2 ) and can be gnored. Snce there s only dfference of exteror envelope among cases, IC calculaton only ncludes ths part. The total area of buldng facade s 19991m 2. The total length of alumnum louvers of case5 s 4729m. Accordng to current cost analyss from curtan wall company, the cost of concealed-frame double-layer glass curtan wall s RMB/m 2 ; the cost of alumnum curtan wall of case2 s RMB/m 2 ; the cost of aerated concrete block of case3 s 39.5 RMB/m 2 ; the cost of double skn facade of case4 s 2500 RMB/m 2 ; the cost of alumnum louvers of case5 s 600 RMB/m. Then IC and RC can be worked out. OC manly s energy use cost. Electrcty cost for coolng s calculated hourly accordng to tme-dfferentated electrcty prce n Bejng (Anon B), and natural gas cost for heatng s calculated accordng to gas prce 1.9 RMB/m 3 n Bejng. LCC results of each scheme can be fgured out wth equaton (9)-(11), where LCC s the LCC of buldng (RMB/m 2 ); N r s the lfe-span of curtan wall and louver (yr), whch s assumed to be 40 n ths paper as stated before; RC s the RC of buldng materals (RMB/m 2 ); e m s the growth rate of buldng materals prce, s assumed to be 3% accordng to statstc data (Anon C); P l s dscount coeffcent of total OC n buldng 50-year lfespan, t s a functon of energy prce growth rate e and bank rate. e s assumed to be 5% accordng to the growth tend of electrcty and gas prce n Bejng n recent years, and s assumed to be 6.12% accordng to the general bank rate n Chna n 2006 (Anon D). Then general payback tme (PT) can be calculated wth equatons (12)-(13), where N s PT of scheme (yr); P s dscount coeffcent of total OC n N years. All the results are shown n table em N LCC = IC + RC ( ) r + OC P (9) l e 1+ e 1+ e Pl = ( ( ) )/(1 ) (10) ( IC-IC ) = ( OC- OC ) P (11) e 1+ e N 1+ e P = ( ( ) )/(1 ) (12) Table 5 Lfe cycle cost analyss IC RC OC LCC PT (RMB/m 2 ) (RMB/m 2 ) (RMB/yr/m 2 ) (RMB/m 2 ) (yr) case / case / case / case case It shows that, both IC and OC of case2 are lower than that of base case, so does that of case3. Therefore there s no PT for these two cases n theory. LCC of these two cases are lower than that of base case. they have better economc performance. Case4 and case5 pay much n constructon phase to get lower OC. But the PTs of them are all longer than 50-year buldng lfe-span and LCC of them are hgher than that of base case, so n terms of economc performance wth general meanng they are worse than the base case. GPT analyss As stated above, ELC s ncluded n GC. Accordng to the EL results, ELC of constructon and operaton phase of each scheme can be calculated, and then GIC and GOC can be worked out, consequently GPT, N G, can be calculated wth equaton (4)-(6). Consderng the uncertanty of CO 2 prce growth rate e EL, t s assumed to be 0 n calculaton. The results are shown n Table 6. Table 6 Green payback tme analyss ELC C GIC ELC O GOC GPT (RMB/m 2 ) (RMB/m 2 (RMB (RMB ) /yr/m 2 ) /yr/m 2 ) (yr) case / case / case / case case It s found that, GIC and annual GOC of both case2 and case3 are lower than that of base case, so there s no PT for these two cases n theory, they are better schemes than base case n comprehensve performance of envronment and economy. GPTs of case4 and case5 are obvously shorter than PTs of them when ELC s counted n. GPT of case5 turns to be 24 years, whch means the exteror shadng scheme s better than base case n comprehensve performance of envronment and economy. GPT of case4 turns to be 48 years, however, t s longer than the lfe-span of curtan wall and louvers, so the double skn facade scheme s stll economcally unfeasble. Ths s because the double skn façade technque s very expensve under the current stuaton of Chna

5 CONCLUSION To evaluate envronmental and economc performance of green buldng desgn comprehensvely, a new assessment method, LCGCA, s proposed n ths paper, whch takes ELC nto account and use GPT as an ntegrated evaluaton ndex. Based on the new method, a real offce buldng n Bejng s studed. Several dfferent schemes of envelope desgn have been compared from aspects of buldng operatng energy consumpton, LCEL, LCC and GPT. And dfferent results can be obtaned from dfferent evaluaton aspect. 1. Operatng energy consumpton: all the optonal schemes (case2-5) have less operatng energy consumpton than ntal scheme (base case). 2. LCEL: both constructon and operaton EL of case3 are lower than that of base case. Although constructon EL of case2, case4 and case5 are hgher than that of base case, LCEL of them are all lower. So all the optonal schemes perform better n lfe cycle envronmental mpact than base case does. 3. LCC: case2 and case3 have lower LCC than base case, but case4 and case5 have hgher. There s not PT for case2 and case3 n theory. PTs of case4 and case5 are longer than buldng lfe-span. So as general economy analyss s concerned, both double skn facade scheme and fxed exteror shadng scheme are economcally worse than base case. 4. LCGCA: GPTs of case4 and case5 are obvously shorter than PTs of them. GPT of case5 s 24 years, whch ndcates the fxed exteror shadng scheme s better than base case n comprehensve performance of envronment and economy. GPT of case4 s 48 years, however, s stll longer than lfespan of curtan wall and louvers, whch ndcates double skn facade scheme s stll economcally worse than base case. As for case2 and case3, both GIC and GOC of them are lower than that of base case, there are no GPTs for them, they are better than base case n comprehensve performance of envronment and economy. It can be concluded, comparson results may be dfferent from that of general economy analyss when ELC s consdered. Snce energy and polluton problem become more and more serous and envronmental tax mposton s upcomng, envronmental and economc performance of green buldng desgn should be evaluated comprehensvely. Therefore LCGCA, whch can meets ths need, s worth beng recommended to be the evaluaton and gude tool for green buldng desgn n Chna. What need to be explaned s the conclusons n ths paper are obtaned from ths specal case, they may not sutable for other cases, and so specal case needs specal analyss. But LCGCA s a unversal method. Besdes constructon EL and ELC only nclude the exteror envelope part, whch s only a small part of the total constructon system. So the value n ths paper s not the total EL and ELC of the whole constructon system. Consequently LCEL and LCC value n ths paper s not the real value of the whole buldng ether. Although ths wll not affect any of the concluson for exteror envelopes s the only dfferent part between each scheme, we wll try our best to get more detaled data about the buldng and gve total value of the whole buldng n future study. In addton, changng of energy prce growth rate, buldng materal prce or bank rate wll all affect the results of ELC, LCC, PT and GPT and further affect the concluson, so senstvty analyss of these affectng factors may be studed n our future work. NOMENCLATURE Abbrevaton EL envronmental load ELC envronmental load cost GC green cost GIC green ntal cost GOC green operatng cost GPT green payback tme IC ntal cost LCA lfe cycle assessment LCC lfe cycle cost LCCA lfe cycle cost analyss LCEL lfe cycle envronmental load LCGCA lfe cycle green cost assessment OC operatng cost PT general payback tme RC replacement cost TCOP total coeffcent of performance Symbol CON e annual operatng electrcty consumpton per unt floor area (kwh/yr/m 2 ) CON g annual operatng gas consumpton per unt floor area (m 3 /yr/m 2 ) e energy prce growth rate e EL CO 2 prce growth rate e m growth rate of buldng materals prce EL buldng envronmental load per unt floor area (pt/m 2 ) ELC c envronmental load cost of constructon phase per unt floor area (RMB/m 2 ) ELC o envronmental load cost of operaton phase per unt floor area (RMB/m 2 ) GIC green ntal cost per unt floor area (RMB/m 2 ) GIC 0 green ntal cost per unt floor area of base case (RMB/m 2 )

6 GOC annual green operatng cost per unt floor area (RMB/yr/m 2 ) GOC 0 annual green operatng cost per unt floor area of base case (RMB/yr/m 2 ) bank rate IC general ntal cost per unt floor area (RMB/m 2 ) IC 0 general ntal cost per unt floor area of base case (RMB/m 2 ) LCC lfe cycle cost of buldng per unt floor area (RMB/m 2 ) N general payback tme (yr) N G green payback tme (yr) N r lfe-span of curtan wall and louver (yr) OC general annual operatng cost per unt floor area (RMB/yr/ m 2 ) OC 0 general annual operatng cost per unt floor area of base case (RMB/yr/m 2 ) P dscount coeffcent of total operatng cost n N years P EL dscount coeffcent of total envronmental load cost n N G years P G dscount coeffcent of total operatng cost n N G years P l dscount coeffcent of total operatng cost n buldng 50-year lfespan Q c total coolng load n summer per unt floor area (kwh/m 2 ) Q h total heatng load n wnter per unt floor area (kwh/m 2 ) r heat value of natural gas, 8500kcal/m 3 RC replacement cost of buldng materals per unt floor area (RMB/m 2 ) TCOP total coeffcent of performance of coolng system V pt prce of unt EL (RMB/pt) gas-fred boler effcency η boler REFERENCES Anonymty shtml Anonymty A. Anonymty B. Anonymty C. Anonymty D. subjectsnew/dakuanllvnew/ Gluch P, Baumann H The lfe cycle costng (LCC) approach: a conceptual dscusson of ts usefulness for envronmental decson-makng Buldng and Envronment, 2004, 39: Gu DJ Buldng lfe cycle envronmental load evaluaton, Ph.D. Thess, Tsnghua Unversty (Chna). Gu LJ Study on the effect of dfferent envelopes on lfe cycle envronmental load of resdental buldngs, Journal of Harbn Insttute of Technology. 2007, 14(sup.): pp Insttute for Buldng Envronment and Energy Conservaton (IBEC), Comprehensve Assessment System for Buldng Envronmental Effcency (CASBEE) Manual 1: Green Desgn Tool. Bejng: Chna buldng ndustry Press. Mnstry of Constructon P.R.Chna GB Energy savng desgn standard of publc buldngs. Bejng: Chna Standard Press. L R Analyss of energy consumpton and lfe cycle assessment of envronmental mpact of ar condtonng cold and heat source, Master Thess, X an Unversty of Buldng Technology (Chna). Ln MY, Zhang SS, and Chen Y Lfe cycle assessment of envronmental mpact of ar condtonng cold and heat source, Heatng Ventlatng & Ar-condtonng, 2004, Vol. 34 (7) p Yan D, Xe XN, Song FT and Jang Y Buldng envronment desgn smulaton software DeST (1): an overvew of developments and nformaton of buldng smulaton and DeST, HV&AC, 2004, 34(7):