A BENCHMARKING STUDY FOR APARTMENT WATER CONSUMPTIONS IN HONG KONG

Transcription

1 Int. Journal for Housng Scence, Vol.3, No. pp. 9-36, 007 Publshed n the Unted States A ENCHMARKING STUDY FOR APARTMENT WATER CONSUMPTIONS IN HONG KONG L. T. Wong, K. W. Mu and L. Y. Law Department of uldng Servces Engneerng, The Hong Kong Poltechnc Unverst, Hong Kong, Chna ASTRACT Fresh water consumpton s one of the prmar consderatons for sustanable water sstem desgns of buldngs. Ths stud proposes a smple statstcal benchmarkng model for some apartments n Hong Kong. The model was tested n a case stud based on an exstng domestc water consumpton surve n whch the average water consumpton dstrbuton of 60 apartments n Hong Kong were selected as the nput parameters of the smulaton model. The dstrbuton was compared wth the Hong Kong global fresh water consumpton patterns to derve the water consumpton benchmarks for apartments n the regon. Ths smple model could be useful for ndcatng the extreme cases of water consumpton and promotng the sustanablt of water consumpton wthout nclusve measurements. Kewords: Resdental buldngs, benchmarkng model, water consumpton, Sustanablt /0/ 9-36, 007 Coprght 007 IAHS

2 30 Wong, Mu and Law Introducton In Hong Kong, over 40% of ts total water consumpton s domestc fresh water consumpton (). The total ranfall n Hong Kong s nsuffcent to meet the local water demands, but water suppl s guaranteed because a total of m 3 fresh water s purchased ever ear from the Guangdong Provnce. Nevertheless, for economc and envronmental protecton ssues, sustanable desgn n water suppl s essental. Domestc water consumpton has been ndcated b the per capta approach (-9). It can be extremel varable due to a range of factors ncludng clmate, culture, econom, ndvdual demands, occupant attrbutes and applance characterstcs. Reported examples of per capta dal domestc water consumpton (excludng WC flushng) were from 65 to 75 L hd d n some European countres and from 05 to 37 L hd d n USA as shown n Fgure, wth some reported n Asan ctes. Drect comparson of these reported fgures from varous ctes would be napproprate due to the reportng method, composton of buldng stocks, cultural dfferences and hence unversal benchmarks across varous ctes mght be defcent n promotng sustanablt of water consumpton. Per capta earl consumpton (m 3 hd r ) Year? UK Netherlands France? German? Sweden? USA? Tawan Tape Sngapore - Toko + Hong Kong Fg. : Reported per capta earl domestc water consumpton excludng WC flushng (-0) As a major concern n water resource management, fresh water consumpton has been dentfed as one of the ke ssues n sustanable buldng desgns (8). Water consumpton benchmarks have been developed for the ndcaton of a sustanable buldng and used as promoton measures for the general publc (3-0). Apart from the occupant load, benchmarkng factors based on the occupanc, floor area, and mx of

3 3 Water Consumptons areas (.e. the ratos of sleepng and lvng areas to the total flat area) have been ncorporated nto the Hong Kong uldng Envronmental Assessment Method (), a voluntar measure amng to enhance the envronmental performance of buldngs n Hong Kong, moderatel. In ths stud, wth varous water consumpton estmates from a surve of 60 apartments n Hong Kong as an example, the Monte Carlo samplng technque was adopted to formulate a smple water consumpton benchmarkng model for apartments n the regon. The average water consumpton dstrbuton obtaned was then compared wth the regonal global fresh water consumpton patterns to derve the water consumpton benchmarks for some local apartments. Consumpton enchmarks For an apartment among apartments of the same tpe, ts water consumpton would be used as an ndcator of sustanablt (3, ). As the per capta annual water consumpton Y was proposed for water consumpton forecastng, t could be used as a normalzng parameter n developng the water consumpton benchmarks (3, 4, 5). Y can be expressed as (m 3 r ), the earl water consumpton, over N p, (n head count or hd), the number of occupants n apartment, Y = () Np, In ths stud, an apartment wth a water consumpton benchmark % ndcates that t s the lowest per capta water consumpton whle the one wth = 00% means t s the hghest. In partcular, the benchmark for the actual per capta annual water consumpton Y (m 3 hd r ) of a sample apartment s determned usng the percentle of the cumulatve frequenc dstrbuton of devatons ε ~ from the expected consumpton Y (m 3 hd r ) for apartments = n. The benchmarks of a sample can be evaluated b a probablt denst functon P wthn certan arbtrar confdence ntervals a and a, where the dstrbuton functon of the benchmarks ~ would be approxmated b a normal dstrbuton usng two unbased estmators, the mean benchmark µ and ts standard devaton s. a P ( a a ) = ( µ, σ ) ; ~ ( σ ) d ε d a ~ ε = ε ~ ε = Y ~ µ () ε ;

4 3 Wong, Mu and Law In a surve stud of water consumpton wth a sample sze n, the mean per capta earl water consumpton µ can be determned from the expected per capta earl water consumpton Y at certan confdence ntervals for a specfc level of sgnfcance a, where s s the standard devaton of the per capta earl water consumpton estmated from the sample standard devatons s (3), σ σ < µ < + ( n ) s ( n ) Y zα Y zα ; < σ < n n χα χ α n n n Y = Y ; = ( Y Y ) = s (3) n = s ; Surve In order to test the applcablt of the proposed model, a prelmnar ntervew surve for the water consumpton patterns was conducted at 60 apartments n Hong Kong (0). The patterns were then used as a template to develop the water consumpton benchmarks. The surve samples were selected based on ther demographc data, geographcal locatons, buldng ages and archtectural desgns. Representatves of each of the responded households partcpated n a face-to-face ntervew n whch procedures smlar to those used n some earler surve studes were appled (4,5). Water blls of the apartments over the past ears were recorded, and so were the tpe, brand name, capact and power consumpton for each nstalled applance. Occupant load varatons durng a da throughout a week were surveed. Most of the ntervewees were the occupants stang at home the longest tme. Durng the ntervew, the were asked to provde nformaton of the applance usage patterns on the da pror to the ntervew, and the hourl usage patterns on weekdas, Sundas and holdas. The average tme between applance demands was nvestgated. The average flow rates of water taps nstalled at the snk, washbasn, shower and bath were measured wth some smple operatons b the occupants; the dscharge and refllng tmes of each WC cstern were measured as well. Floor area of each apartment was obtaned from the facltes management, drect measurement, or record drawngs of ppng arrangements. Results and Dscusson The surveed annual water consumptons (m 3 r ) of the sample apartments n a ear aganst the apartment occupant load N p (persons) were shown n Fgure. It was

5 33 Water Consumptons noted that the domestc seawater consumpton for WC flushng was not ncluded n ths surve. Accordng to the Hong Kong global data, the per capta annual seawater consumpton was about 36 m 3 hd r and the per capta annual fresh water consumpton was m 3 hd r (5). Comparng wth the latter, the surve average of the domestc sector ( Y = 6. m 3 hd r, s = 4.5 m 3 hd r ) represents 45-65% of the Hong Kong total. The UK annual domestc water consumpton s also shown n Fgure for reference, the surve average was sgnfcantl hgher (p < 0.000) than the UK average (40 m 3 hd r ) (4). Unlke the mnor ncrease as n UK, ths stud showed a sgnfcant non-lnear ncrease n the consumpton wth the household sze (p < 0.000). Ths could be explaned b the fact of behavoral dfferences between regons that water consumptons for number of showers taken everda n ths ct, not fllng a teapot n some UK ctes, accounts for the major water consumpton. It was reported that the annual water consumpton would be correlated wth the occupant load N p (R = 0.65; p < 0.000). Predcted consumptons for alternate p- values from 0. to 0.9 are shown n Fgure for llustraton. Wth these predctons and a standard error of 4.5, the surveed consumpton for a sample could be expressed b, 0.8 = 77.8 (4) N p Yearl consumpton (m 3 r ) ? Surve 004 Hong Kong average? 005 Hong Kong average? UK (4) Occupant load N p (persons) p = Fg. : Annual water consumpton per household

6 34 Wong, Mu and Law enchmark (%) % confdental ntervals X? Surve Per capta earl water consumpton (m 3 hd r ) Fgure 3: Domestc water consumpton benchmarks The water consumpton benchmarks and the correspondng dstrbutons ~ for certan water consumpton were evaluated b Monte Carlo smulatons wth Equaton (3), takng σ ~ σ and µ ~ µ as descrbed n Equaton (3). The smulaton results showed that the standard devaton of the benchmarks s would correlate wth the mean benchmark µ (R = , p < 0.000), µ 0.00µ ; 0 < µ < 00 σ = (5) 0 ; µ = 0; µ = 00 The benchmarks for consumpton n the surveed range (4.4-5 m 3 hd r ) are shown n Fgure 3, wth specfed 95% confdence ntervals shown. For an example apartment wth a per capta earl water consumpton of 40 m 3 hd r (.e. X n the fgure), the mean benchmark would be µ = 9 wth the 95% confdence ntervals of and 6 as llustrated. The water consumpton benchmarks of the surveed apartments were determned and shown n Fgure 3. Concluson Sustanablt of some apartments n Hong Kong was examned n the lght of per capta water consumpton. In partcular, a smple benchmarkng model for domestc water consumptons was proposed usng Monte Carlo smulatons. The model was tested n a case based on a surve of the average water consumpton dstrbuton of 60 tpcal apartments n Hong Kong, and water consumpton benchmarks were

7 35 Water Consumptons developed for resdental premses n the regon. The surve results showed that annual domestc water consumpton would be correlated wth the occupant load of an apartment. Through the developed benchmarkng model, hgh as well as low water consumpton samples could be dentfed and further evaluaton of ther sustanablt could be proposed. It would be partcularl useful for evaluatng the benchmarks of water consumpton that s under contnuous montorng. Ths stud also presented a template for formulatng water consumpton benchmarks for resdental premses elsewhere. References. Hong Kong Water Servces Department: Annual Report, Atken, C. K., Duncan, H. and McMahon, T. A. A cross-sectonal regresson analss of resdental water demand n Melbourne, Australa, Appled Geograph () pp , Edwards, K. and Martn, L. A methodolog for surveng domestc water consumpton, Journal of the Chartered Insttuton of Water and Envronment Management 9(5) pp , ale, R. J., Joll, P. K. and Lace, R. F. Domestc water use patterns, Water Research Centre, ucks, UK, Hall, J., Hooper,. D. and Postle, S. M. Domestc per capta water consumpton n South West England, Journal of the Chartered Insttuton of Water and Envronment Management (6) pp , Mukhopadha, A., Akber, A. and Al-Awad, E. Analss of freshwater consumpton patterns n the prvate resdences of Kuwat, Urban Water 3(/) pp. 53-6, Lgman, K., Hutzler, N. and ole, W. C. Household wastewater characterzaton, Journal of the Envronmental Engneerng dvson 00(EE) pp. 0-3, Cheng, C. L. Evaluatng water conservaton measures for green buldng n Tawan, uldng and Envronment 38() pp , Lazarova, V., Hlls, S. and rks, R. Usng reccled water for non-potable, urban uses: a revew wth partcular reference to tolet flushng, Water Scence and Technolog: Water Suppl 4(4) pp , 003

8 36 Wong, Mu and Law 0. Mu, K. W. and Wong, L. T. Water consumpton benchmarks for resdental buldngs n Hong Kong, Proceedngs of the 5th Internatonal Conference on Sustanable Energ Technologes, 30 August September 006. Department of Industral Management and Engneerng, Unverst of Padova, Stradella S. Ncola, 3 Vcenza, Ital, pp. 57-6, 006. HK-EAM Socet: Hong Kong buldng envronmental assessment method - An envronmental assessment for new buldng (verson 4/04), 004. Corral-Verdugo, V., echtel, R.. and Frajo-Sng,. Envronmental belefs and water conservaton: an emprcal stud, Journal of Envronmental Pscholog 3(3) pp , Hnes, W. W., Montgomer, D. C., Goldsman, D. M. and Conne, M.. Probablt and statstcs n engneerng, 4 th Edton, Wle, New York, Wong, L. T. and Mu, K. W. Determnng the domestc dranage loads for hgh-rse buldngs, Archtectural Scence Revew 47(4) pp , Wong, L. T. and Mu, K. W. Determnaton of domestc flushng water consumpton n Hong Kong, Facltes 3(/) pp. 8-94, 005