Rainwater harvesting: model-based design evaluation

Transcription

1 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 Rainwaer harvesing: model-based design evaluaion S. Ward*, F. A. Memon and D. Buler Cenre for Waer Sysems, School of Engineering, Compuing and Mahemaics, Universiy of Exeer, orh Park Road, Exeer, EX4 4QF, UK *Corresponding auhor, sw278@exeer.ac.uk ABSTRACT The rae of upake of rainwaer harvesing (RWH) in he UK has been slow o dae, bu is expeced o gain momenum in he near fuure. The design of wo differen new-build rainwaer harvesing sysems are evaluaed using a sae-of-he-ar coninuous simulaion modelling approach. The RWH sysems were shown o fulfill beween 36% and 46% of WC demand. I was found ha design mehods based on simple approaches (such as used in hese wo cases) generae ank sizes subsanially larger han he simulaion model. Comparison of he acual ank sizes and hose calculaed using he simulaion model esablished ha he acual anks insalled are oversized for heir associaed demand level and cachmen size. The imporance of cachmen size was demonsraed, a facor negleced in he simpler mehods commonly used in pracice. Financial analysis revealed ha RWH sysems wihin large commercial buildings may be more financially viable ha smaller domesic sysems. A recommendaion for a ransiion from he use of simple ools o simulaion models is made. KEYWORDS Rainwaer harvesing; ank sizing; susainabiliy; waer conservaion, waer demand managemen I TRODUCTIO The upake of rainwaer harvesing (RWH) in he UK has been slow o dae. Neverheless, his is se o change, paricularly in he souh-eas of England where despie relaively high annual rainfall, here is a low waer resource per capia. Furhermore, RWH is now explicily menioned in he Building Research Esablishmen s Environmenal Assessmen Mehod (BREEAM, 2007a) and he Code for Susainable Homes (DBERR, 2007). The laer, alhough volunary, is se o become mandaory in he fuure. Addiionally, he recen waer sraegy, Fuure Waer (DEFRA, 2008) and waer company Sraegic Direcion Saemens (OFWAT, 2008), idenify ha RWH has a par o play in urban waer managemen sraegies. A number of facors have so far conribued o he lack of progress. Ambiguiy in he financial viabiliy of RWH sysems is a key reason; lack of experience and he absence of well-run demonsraion sies is anoher. Alhough some echnical guidance is available (CIRIA, 2001), he cosing informaion provided is skechy and here is limied advice on he appropriae sysem sizing mehods o use. The oucome is ha sakeholders such as local auhoriies and developers, are sill relucan o implemen RWH sysems in new developmens (or indeed, o rerofi hem). Neverheless, here has been a rise in he number of RWH sysems being implemened in new commercial buildings and in schools. Ward e al. 1

2 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 RWH sysem suppliers and oher waer indusry-based sakeholders ofen use rule-of-humb or simple mass balance approaches. However, resuls provided by hese ools lack he accuracy and deail o properly size RHW sysems and can resul in he calculaion of unrealisic pay-back-periods or overly opimisic whole life cos scenarios. (Roebuck and Ashley, 2006). A number of deailed models, capable of simulaing RWH sysem design and/or performance have been developed and published and hese are summarised in Table 1. Several of hese models are eiher freely available or available o purchase. However, rarely do non-academic sakeholders uilise such ools, due o an apparen lack of awareness of he availabiliy and capabiliies of hese ools. Table 1. Exising models for analysing RWH sysems Model Developer RWH only? Funcionaliy DRHM Dixon (1999) Yes Mass balance wih sochasic elemens for demand profiling, simulaes quaniy, qualiy and coss Rewapu Vaes and Berlamon Reservoir model, rainfall inensiy-duraion-frequency Yes (2001) relaionships and riangular disribuion RWIN Herrmann and Schmida Hydrological-based high resoluion (5 minue) rainfallrunoff model No (KOSIM) (1999); ITWH (2007) PURRS Coombes and Kuczera Probabilisic behavioural, coninuous simulaion, No (2001) evaluaes sources conrol sraegies RCSM Fewkes (2004) Yes Behavioural, coninuous simulaion, deailed analysis of ime inerval variaion and yield-before/afer-spill MUSIC CRCCH (2005) No Coninuous simulaion, modelling waer qualiy & quaniy in cachmens (0.01 o 100km²) Aquacycle Michell (2005) No Coninuous waer balance simulaion using a yield before-spill algorihm RSR Kim and Han (2006) Yes RWH ank sizing for sormwaer reenion o reduce flooding, using Seoul as a case sudy RainCycle Roebuck and Ashley Excel-based mass balance model using a yield-afer-spill Yes (2006) algorihm and whole life cosing approach HWCM Liu e al (2006) No Objec-based behavioural,coninuous simulaion using Simulink This paper invesigaes he design of wo new RWH sysems; one wihin an office building and he second being a series of communal sysems wihin a housing developmen. The aim is o evaluae he insalled sysems based on a comparison beween he design daa, wo simple mehods and a commercial ool represening he sae-of-he-ar in RWH sysem design. The impac of he use of differen rainfall daa resoluions and he effec of analysing a group of communal sysems as a whole or as pars will also be evaluaed. METHOD Models Three mehods are used wihin he design evaluaion, wo of which are based on he approach developed by Fewkes (1999), which buil on an original concep devised by Jenkins e al (1978). The core of his approach is a waer mass balance in he form: V = V 1 + Q D Subjec o 0 V S Where: 2 Rainwaer harvesing: model-based design evaluaion

3 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 V Q D S = (Rain) Waer in sorage a end of ime inerval, = Inflow during ime inerval, = Demand during ime inerval, = Sorage capaciy From his he yield-afer-spill and yield-before-spill (YBS) operaing rules were developed (Fewkes and Buler, 2000), which ake he form (for YAS and YBS respecively): Y D = min V 1 V V 1+ Q = min S Y Y Y D = min V 1+ Q V V = min S 1+ Q Y Where: Y = Yield from sore during ime inerval The YAS and YBS rules deermine he posiion of supply, demand and overflow in he calculaion of sorage volume. Fewkes and Buler (2000) underook exensive analysis of he YAS and YBS algorihms which led o he derivaion of capaciy-demand and cachmenrainfall raios (called he demand fracion and sorage fracion, respecively). From his research i was concluded ha he YAS operaing rule (wih an hourly or daily rainfall ime series) provided he mos accurae, conservaive resuls. Fewkes (1999) and Fewkes and Warm (2000) exended his work and developed a se of generic performance (waer saving efficiency, E T ) curves for RWH in he UK. They also esablished a mahemaical relaionship for esablishing a suiable ank size; an inpu raio for he desired RWH sysem is calculaed using: AR / D Where: A = Cachmen area (m²) R = Average annual rainfall (mm) D = Average annual demand (l) This is used o locae a desired performance level (E T ) and he number of days sorage (X) from he design curves. The ank size can hen be calculaed using: S = XDd Where: X = Number of days sorage D d = Average daily demand (l), i.e. D/365 Wihin he presen sudy, Mehod 1 is based on he YAS approach in he form of a coninuous simulaion using daily rainfall and demand ime series, represening he sae-of-he-ar in RWH sysem design. Mehod 2 is a simplified version of he AR/D approach, which simply akes a user-defined number of days sorage (raher han being seleced using he AR/D raio) Ward e al. 3

4 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 and muliplies i by an average daily demand. Curren bes pracise recommends selecion of a number of days sorage of no less han six days (CIRIA, 2001) and so his was used when applying Mehod 2. The final mehod, Mehod 3, is based on a differen approach recommended by he Environmen Agency (EA) (2008). This is a simple rule-of-humb mehod, which sizes he ank based on a user-defined percenage of average annual rainfall or demand (whichever is he lower). The equaion for his approach akes he form: S = PAC f FR Where: P = User-defined percenage (curren bes pracise recommends 5%, i.e. 0.05) C f = Runoff coefficien F = Sysem filer efficiency (R would be replaced by D if he annual demand was he lower of he wo) However, he applicaion of his approach is recommended for smaller RWH sysems only, such as domesic sysems, as larger sysems require a more rigorous analysis due o he complexiy of demand paerns (EA, 2008). Analyses were underaken using an Excel/VBA-based modelling ool, RainCycle (Roebuck and Ashley, 2006). This ool implemens he above hree mehods and also includes he faciliy o calculae he whole life cos, pay-back-period and cos-benefi of a RWH sysem (wih mains op-up) in comparison wih an equivalen mains waer supply (wihin Mehod 1). Approach The hree previously described mehods were used o calculae ank sizes for wo case sudy developmens. This was done in order o compare calculaed ank sizes wih he acual ank sizes designed and insalled by RWH sysem suppliers. As previously menioned, he modelling ool also permis whole life cos and cos-benefi analyses. As he RWH sysems used wihin his sudy are wihin new developmens no operaing coss have ye been accrued. Furhermore, expeced mainenance regimes and heir associaed coss were no available a he ime of analysis. For hese reasons no whole life cos analyses could be performed. However, capial cos informaion was available; being 15,500 per sysem (sorage ank plus associaed piping, pumping and conrols) and his was used wihin Mehod 1 analyses o yield a pay-back-period for boh sies. In addiion, a cos-benefi analysis is given, by comparing he financial savings of using a RWH sysem (plus mainswaer op-up) wih using he mains waer supply alone. Savings ( ) per year figures indicae he poenial financial savings made by using rainwaer via he RWH sysem, compared o he cos of supplying waer via he mains waer supply. Wihin Mehod 1 coninuous simulaions, an analysis period of 25 years was used, as his duraion is ofen quoed as being he minimum expeced lifespan of RWH sysem anks and componens (Pushard, 2004; WPL, 2007). Sie Characerisics Sie 1 - Innovaion Cenre Phase 2 (ICP2) Building. The ICP2 on he Universiy of Exeer s Sreaham campus is an office building (Figure 1), which achieved he BREEAM Excellen 4 Rainwaer harvesing: model-based design evaluaion

5 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 raing. The single RWH sysem wihin he building is used o supplemen mains waer and supplies WCs via a large underground sorage ank and wo header anks. Addiional sie characerisics are summarised in Table 2. The building has recenly been compleed and is he process of being occupied. A programme of RWH sysem monioring is in place, which will include meering waer usage, waer qualiy sampling and a user percepion survey. Sie 2 Broadclose. The Broadclose housing developmen is locaed near Bude in Cornwall, souh-wes England, and is a new-build projec involving The Guinness Trus, Norh Cornwall Disric Council, he Wescounry Housing Associaion and Midas Homes Ld. The need for waer efficiency measures was considered righ from beginning of he design and planning phases and he homes currenly achieve he EcoHomes very good raing; EcoHomes is he domesic dwelling equivalen of he BREEAM (BREEAM, 2007b). Broadclose conains 173 homes divided across 13 home zones (HZ), each of which has a communal RWH sysem, collecing runoff from souh facing roofs, which is used for WC flushing. Addiional sie characerisics are summarised in Table 2. The mix of housing ypes wihin a paricular HZ varies, bu can include 1-bed flas, 2/3/4-bed houses and 2/3-bed bungalows, as illusraed in Figure 2. Consequenly, he main sorage ank for each HZ is a differen size; runoff colleced and demand experienced will vary depending on oal roof cachmen area and HZ occupancy. Eigh properies in differen HZs will be meered as par of a monioring programme o assess waer conservaion and financial performance and user percepion surveys will be conduced across he enire developmen. Figure 1. Souh-facing facade of he Innovaion Cenre Phase 2 building (Sie 1) Figure 2. Houses and bungalows a Broadclose (Sie 2) Ward e al. 5

6 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 Table 2. Characerisics of Sie 1 and Sie 2 Unis Sie 1 Sie 2 Type of developmen Office building Housing developmen Size (approx occupancy) Type of sysem Single sie Communal Use of RWH sysem WCs (oiles) WCs (oiles) Sandard average annual rainfall (30- mm 807 (Exeer) 881 (Bude) year) near sie Toal (roof) cachmen area m (22.5/propery) Roof cachmen characerisics Fla, smooh Piched, iled Toal sorage ank volume m Average daily demand m (working day) a 0.36 (holiday) a a Toal yearly demand m b 7270 a a = calculaed wihin RainCycle; b = calculaed by RWH sysem supplier RESULTS A D DISCUSSIO Design Evaluaion: Sie 1 The RWH sysem was supplied by Sormsaver, a UK-based supplier. An Excel ool based on he AR/D approach was used by he supplier o design he sysem. The ool uses parameers including local annual rainfall (based on a Me Office 40 year figure), roof area, esimaed annual demand, number of days required sorage, filer and runoff coefficiens and sysem efficiency. The parameer values used in he RWH sysem supplier design are summarised in Table 3. Alhough he sysem manual quoes he pre-ank filer as being able o achieve 95% efficiency, he figure used in he design was 90%, so his has been used in he simulaions. Table 3. RWH sysem supplier 1 design parameers and values for Sie 1 Parameer Unis Value used by RWH sysem supplier Local rainfall mm 764 Roof area m² 1500 Building occupancy 300 Esimaed annual demand m Days required sorage 6.8 Demand days 250 Filer coefficien 0.9 Runoff coefficien 0.6 Analysis period years 25 Analysis. The RWH sysem supplier recommended a sorage ank size of 25 m 3, which could yield an annual waer saving of 816 m 3 (60% of he demand), represening annual financial savings of 1,469 (compared o he mains waer supply). The hree mehods were applied using he same parameer values. Mehod 1 simulaion resuls suggesed ha o achieve a similar level of waer and financial saving (619 m 3, 46% and 1,459 per year, respecively), a 9 m 3 ank would be he opimum size o mee demand. Mehods 2 and 3 indicaed sorage ank sizes of 25 and 31 m 3 respecively. As previously menioned Mehod 3 should no generally be applied o larger sysems; he resul is included o show how i compares o he oher mehods. Rainfall resoluion. In order o invesigae he impac of differen emporal resoluions of rainfall daa, i was decided o use a 30-year sandard average annual rainfall figure and a monhly rainfall profile (insead of he non-sandard 40-year figure used by he RWH sysem supplier). This is in line wih EA sandard procedure. The 30-year sandard average ( Rainwaer harvesing: model-based design evaluaion

7 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, ) annual rainfall for Exeer was idenified as being 807 mm (DCC, 2005), however monhly averages for Exeer were no available a he ime of analysis. In order o use monhly daa, 30-year sandard average monhly figures for Teignmouh (26 km from Exeer) were obained from he Me Office (Figure 3). Teignmouh has a 30-year sandard average annual rainfall of 820 mm and experiences he same rain shadow effec from Darmoor as Exeer (DCC, 2005) Jan Feb Mar Apr May Jun Jul Aug Sep Oc ov Dec Figure year sandard average monhly rainfall daa for Teignmouh (Me Office, 2007) Simulaions were run using Mehod 1 for he annual 30-year sandard averages for Exeer (Simulaion 2) and Teignmouh (Simulaion 3) and also he monhly 30-year sandard average profile for Teignmouh (Simulaion 4). Resuls of hese simulaions and a comparison wih he firs are summarised in Table 4. Using a 30-year sandard average monhly rainfall profile raher han a non-sandard annual average increased he percenage of demand me by 4%. As can be seen in Table 4, he increase in rainwaer uilised also decreased he annual sysem cos, hereby increasing he oal long-erm (25 year) savings. Addiionally, he Mehod 1 recommended ank size increases from 9 o 10 m 3. Table 4. Mehod 1 resuls using differen rainfall daa for Sie 1. Unis Simulaion 1 Simulaion 2 Simulaion 3 Simulaion 4 Difference (1 and 4) Demand me % Pay-back-period Years RWH sysem cos /year 3,087 2,970 2,935 2, Mains supply cos /year 4,547 4,547 4,547 4,547 - Savings /year 1,459 1,576 1,611 1, Toal savings /25 36,482 39,408 40,292 40, Recommended ank size yrs m Design Evaluaion: Sie 2 Analysis. The communal RWH sysems wihin Sie 2 were designed and supplied by a second RWH sysem supplier, again using an adapaion of Mehod 2. The parameers used in he analysis are summarised in Table 5. Consrucion of Sie 2 is due o finish in Augus 2008, herefore acual occupancy figures are no ye available. As such i was decided o use he curren average household occupancy rae of 2.4 (DCLG, 2006), leading o a oal occupancy of 415. A monhly 30-year sandard Ward e al. 7

8 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 average ( ) rainfall profile was obained for Bude (Me Office, 2007), which has an annual oal of 881 mm. As runoff is only colleced from souh facing roofs, he average per propery roof size (45 m 2, derived from sie plans) was halved and hen muliplied by he number of properies (173) o yield an approximae oal cachmen area. Table 5. RWH sysem supplier 2 design parameers and values for Sie 2. Parameer Unis Value used by RWH sysem supplier Toal local rainfall mm 881 Roof area m² 3893 Occupancy 415 Esimaed annual demand m Days required sorage 6.8 Demand days 365 Filer coefficien 0.9 Runoff coefficien 0.85 Run duraion years 25 An iniial simulaion was carried ou using he values for he developmen as a whole (raher han by HZ). Mehod 1 resuls revealed ha 36% of he WC demand would be me using RWH, yielding an average annual saving of 756 (compared o he mains waer supply) or 4.37 per propery, wih a pay-back-period of 23 years. Furhermore, Mehod 1 indicaed he available sorage (255.5 m 3 ) was no fully uilised, being empy on a large number of days and recommended a oal sorage capaciy for he developmen of 12 m 3. Mehod 2 and Mehod 3 calculaed ank sizes were 120 and 131 m 3, respecively. Cachmen Area. A limiing facor in meeing demand appeared o be he size of he roof cachmen area uilised. Using boh norh and souh facing roof faces wihin Mehod 1 indicaed ha 72% of demand could be me wih a revised ank size of 34 m 3. This could yield average annual savings of 9,571, or 55 per propery, wih a pay-back-period of 11 years. Mehod 2 and Mehod 3 yielded ank sizes of 120 and 262 m 3, respecively, for he increased cachmen area, which are in line wih he acual oal capaciy. The figure for Mehod 2 does no change, as he mehod only uses he number of days sorage; i does no accoun for changes in cachmen area size. Mehod 1 indicaed he overall ank volume o be subsanially oversized. Neverheless, a poenial benefi of over-sizing he sorage anks is he availabiliy of exra sorage capaciy o reduce runoff during periods of heavy rainfall (depending on he deailed design of he sysem). This could prove beneficial in relaion o climae change; projecions indicae an increase in winer (already some of he wees monhs) precipiaion of beween 5 and 15% (SWCCIP, 2003). This would complemen oher SUDS echniques in use a Broadclose, such as swales and surface ponds. To furher explore he level of savings and o invesigae he sizing of individual HZ sorage anks, he mehods were applied separaely o each HZ. These simulaions used individual ank sizes and calculaed he occupancy and cachmen area based on he number of properies wihin each HZ. Table 6 summarises he ank sizing comparison resuls for each mehod for each HZ, along wih he associaed financial savings. The oal volume previously calculaed for he whole developmen using Mehod 1 was 12m 3, ye he aggregae of he 13 individual HZs ank size analysis is 30m 3. Furhermore, here is a subsanial difference beween he acual ank sizes and hose calculaed using he hree mehods. Tank sizes calculaed using Mehod 1 are beween 200% and 600% smaller han 8 Rainwaer harvesing: model-based design evaluaion

9 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 hose calculaed using Mehods 2 and 3. I should be noed ha had he number of days sorage used wihin Mehod 2 been increased, ank sizes calculaed would have also been higher (perhaps closer o he acual ank sizes insalled). A comparison of acual ank sizes and hose calculaed using he various mehods is illusraed in Figure 4 (for a selecion of HZs, represenaive of ank sizes presen in he developmen). Table 6. Comparison of resuls for each HZs in Sie 2 using each mehod. HZ # % Demand Savings Cachmen Acual ank Mehod 1 Mehod 2 Mehod 3 PBP Me /year area size ank size ank size ank size Unis m 2 m 3 m 3 m 3 m N/A N/A N/A N/A N/A N/A N/A b Toal Acual ank size Mehod 2 Calculaed Mehod 1 Calculaed Mehod 3 Calculaed Tank Size (m 3 ) Home Zone Figure 4. Differences in HZ ank sizes derived using differen mehods, for Sie 2. I was also idenified ha alhough he same annual financial savings were achieved, he disribuion of he savings was highly variable across he HZs; some susaining annual savings of 451 and ohers losses of 263 (compared o he mains waer supply). Ward e al. 9

10 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 CO CLUSIO S A D RECOMME DATIO S The design of wo RWH sysems in wo disinc new-build developmens has been evaluaed using a sae-of-he-ar model and wo simpler mehods. The main findings were: (1) Design mehods based on a simplified AR/D approach (used by RWH sysem suppliers) and he EA approach generaed ank sizes subsanially larger han he saeof-he-ar YAS-based coninuous simulaion. Tanks wihin he case sudies presened are considered o be oversized for he specified demand levels and cachmen sizes; (2) WC demand levels of beween 36% (for a group of communal domesic sysems) and 46% (for a commercial sysem) could be me using RWH; (3) Despie overesimaing ank sizes, he demand levels and financial savings calculaed by he RWH sysem suppliers were similar o hose using he sae-of-he-ar model; (4) Modelling several communal RWH sysems as a whole raher han as separae sysems can have implicaions for ank sizing resuls; (5) Levels of demand aained were limied by he cachmen area size, which also had implicaions for financial savings. This indicaes ha no enough consideraion is given o he cachmen size when designing a RWH sysem; (6) The use of a non-sandard rainfall ime-series resuled in an underesimaion of he demand aained and he associaed savings from implemening a RWH sysem; (7) Financial savings made were greaer for a large commercial building han for a series of communal sysems wihin a housing developmen. Based on hese conclusions he following recommendaions are made: (1) A ransiion from using simple ools based on single calculaions o more sophisicaed coninuous simulaion ools is necessary. This can be faciliaed by increasing sakeholder awareness of he availabiliy and capabiliies of such ools; (2) Designers, planners and archiecs considering implemening RWH wihin a developmen need o be aware of he imporance of sizing he roof collecion area supplying a RWH sysem, in addiion o appropriaely sizing he sorage ank; (3) RWH indusry professionals should be made aware of using and promoing he use of long-erm sandard average rainfall daa (ideally wih a monhly profile) in order o promoe consisency in analysis, wheher using simple or complex design mehods. ACK OWLEDGEME TS This work was carried ou as par of he Waer Cycle Managemen for New Developmens (WaND) projec (Buler e al., 2006) funded under he Engineering & Physical Science Research Council s Susainable Urban Environmen Programme by EPSRC, UK governmen and indusrial collaboraors. REFERE CES BREEAM (2007a) BREEAM: BRE Environmenal Assessmen Mehod websie, hp:// visied 03 Augus BREEAM (2007b) BREEAM: Ecohomes websie, hp:// visied 03 Augus Buler, D., Balmforh, D., McDonald, A., Ashley, R., Sharp, E., Kay, D., Packman, J., Jeffrey, P. and Savic, D. (2006) Managing he urban waer cycle in new developmens. In: Delecic, A. and Flecher, T. (eds): Proceedings of he 7h Inernaional Conference on Urban Drainage and 4h Inernaional Conference on Waer Sensiive Urban Design, Melbourne, Ausralia, 2-7 April 2006, Volume 2, CIRIA (2001) Rainwaer and greywaer use in buildings: Bes pracice guidance. CIRIA Publicaion C539. Coombes, P. & Kuczera, G. (2001) Rainwaer ank design for waer supply and sormwaer managemen. Sormwaer Indusry Associaion 2001 Regional Conference. Por Sephens, NSW, Ausralia. 10 Rainwaer harvesing: model-based design evaluaion

11 11 h Inernaional Conference on Urban Drainage, Edinburgh, Scoland, UK, 2008 CRCCH (Cooperaive Research Cenre for Cachmen Hydrology) (2005) MUSIC User Guide. CRCCH websie, visied 11 Sepember DBERR (2007) Draf Sraegy for Susainable Consrucion: A consulaion paper. Deparmen for Business, Enerprise and Regulaory Reform websie, hp:// visied 03 Augus 2007 DCC (2005) A Warm Response, Our Climae Change Challenge. Sraegy Documen, Devon Couny Council websie, hp:// visied 20 April DCLG (2006) Waer Efficiency in New Buildings: A consulaion documen. Communiies and Local Governmen Publicaions, Weherby, UK. DEFRA (2008) Fuure Waer: The Governmen s waer sraegy for England. DEFRA websie, hp:// visied 08 February Dixon, A. (1999) Simulaion of Domesic Waer Re-use Sysems: Greywaer and Rainwaer in Combinaion. Deparmen of Civil and Environmenal Engineering PhD Thesis. Imperial College of Science, Technology and Medicine, London, UK. EA (2008) Harvesing rainwaer for domesic uses: an informaion guide. EA websie, hp:// visied 01 February Fewkes, A. (1999). Modelling he performance of rainwaer collecion sysems: owards a generalised approach. Urban Waer. 1, Fewkes, A. (2004) The Modelling and Tesing of a Rainwaer Cachmen Sysem in he UK.. Deparmen of Building and Environmenal Healh PhD Thesis. The Noingham Tren Universiy, Noingham, UK. Fewkes, A. and Buler, D. (2000) Simulaing he performance of rainwaer collecion and reuse sysems using behavioural models. Buildings Service Engineering Research and Technology, 21, Fewkes, A. and Warm, P. (2000). A Mehod of Modelling he Performance of Rainwaer Collecion Sysems in he UK. Building Services Engineering Research and Technology, 2, Herrmann, T. and Schmida, U. (1999) Rainwaer Uilisaion in Germany: efficiency, dimensioning, hydraulic and environmenal aspecs. Urban Waer, 1, ITWH (Insiu für echnisch-wissenschafliche Hydrologie) KOSIM-Familie. From ITWH websie, hp:// visied 18 Ocober Jenkins, D., Pearson, F., Moore, E., Sun, J. K. & Valenine, R. (1978) Feasibiliy of rainwaer collecion sysems in California. Conribuion No. 173, Californian Waer Resources Cenre, Universiy of California, USA. Kim, Y. & Han, M. (2006) A Rainfall-Sorage-Runoff (RSR) model for he design of a rainwaer ank effecive for flow conrol in urban drainage pipes. Proceedings of he 2nd IWA Inernaional Rainwaer Harvesing Workshop. Beijing, China, 11 Sepember IWA websie, hp:// visied 15 May Liu S., Makropoulos, C., Buler, D., Memon, F. A. and Fidar, A. (2007). An objec based household waer cycle model: concep and consrucion. Waer Pracice and Technology, IWA online journal, 2 (2), hp:// doi /wp Me Office (2007) averages. Me Office websie, hp:// visied 20 April Michell, V. G. (2005) Aquacycle - user guide. Cachmen modelling oolki websie, hp:// visied 18 Ocober OFWAT (2008) Sraegic direcion saemens. OFWAT websie, hp:// visied 14 January Pushard, D. (2004) Ausin's Zilker Park Showcases Rainwaer Harvesing. HarvesH 2 0 websie, hp:// visied 15 May Roebuck, R. M. & Ashley, R. M. (2006) Predicing he hydraulic and life-cycle cos performance of rainwaer harvesing sysems using a compuer based modelling ool. In: Delecic, A. and Flecher, T. (eds): Proceedings of he 7h Inernaional Conference on Urban Drainage and 4h Inernaional Conference on Waer Sensiive Urban Design, Melbourne, Ausralia, 2-7 April 2006, Volume 2, SWCCIP (2003) Warming o he idea: meeing he challenge of climae change in he Souh Wes. Souh Wes Climae Change Impacs Parnership websie, hp:// visied 20 April Vaes, G. & Berlamon, J. (2001) The effec of rainwaer sorage anks on design sorms. Urban Waer, 3, WPL (2007) Above and Below Ground Rainwaer Harvesing Sysems. WPL brochure websie, hp:// visied 14 Augus Ward e al. 11