Buildings globally are responsible for about 40% ofall energy consumption. In the US, air conditioning(a.c.) alone consumes approximately 16% of allelectricity, but is responsible for 43% of the peak load(Hawken and Lovins, 1997). The demand for airconditioning is a major reason for current supplyproblems on the west coast of the US, CO2 emissionsfrom air conditioning world-wide make a significantcontribution to greenhouse gas emissions; but airconditioning also uses refrigerants, and commonlyused refrigerants (such as R134a and R22) are between1300 and 1700 times more potent per molecule thanCO2 in contributing to global warming.

The stratospheric ozone layer is the world’s UVradiation shield. UV affects photosynthesis and killsphytoplankton (the basis of oceanic food chains).Refrigerants (both CFCs and HCFCs) are responsiblefor the ‘holes’ appearing in the ozone layer. CFCs areextremely stable and (in spite of the MontrealProtocol) are still being manufactured in China andIndia. The black market for CFCs in the US is said torival that for narcotics. HFCs continue to be used, ofcourse, throughout the world, although the searchfor less damaging alternatives is bearing fruit.Alternative refrigerants may be part of the answer,but there is now strong interest in more radicalalternatives to air conditioning.

Last year the Carrier Corporation and Toshiba soldover US $8 billion worth of air-conditioningequipment worldwide. They are the major players ina market that continues to expand. Expandingdemand for a.c. is a major driver for new centralgenerating plant (power stations) because of its

impact on peak load demand, and of course this inturn leads to greater demand for fossil fuels. Thesecharacteristics are common throughout the world,and many countries (including Japan & the US) arefinding it hard to construct new generating capacityfast enough to keep up with the increase in demand.

The Carrier Corporation has realized that theowners and occupiers of buildings don’t necessarilywant air conditioning per se, they want thermalcomfort (Hawken and Lovins, 1997), and they havenow started to offer ‘coolth services’, and to advisecustomers on how they can reduce their coolingrequirements. While this is welcome, expandingglobal sales of cooling equipment underline thecontinuing negative impact of this technology onthe environment, and the need for more radicalalternatives.

Cooling without air conditioning.The tradition of ‘cooling without air conditioning’,which incorporates a range of design responses toclimate apart from evaporative cooling, has itsorigins in ancient Egypt; it subsequently spreadeastwards through the Middle East and Iran to northIndia with the Moghul empire, and westwards acrossnorth Africa to southern Spain.

In the Middle East there is a long tradition of usingvarious techniques to encourage evaporative coolingboth within and between buildings. Bahadooridescribes cooling systems in Iran (incorporatingwind-catchers, porous water pots and salsabil) whichhave been effective for several centuries (Bahadoori,1978). In this tradition, wind-catchers guide outside

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Air conditioning is now recognized as a significant factor in globalwarming and climate change. In the search for alternatives, passivedowndraught evaporative cooling (PDEC) is proving to be bothtechnically and economically viable in different parts of the world.Brian Ford describes the principles and current practice of thisinnovative approach to cooling in the hot dry regions of the world.

Passive downdraughtevaporative cooling:principles and practiceBrian Ford

Practice addressWSP EnvironmentalBuchanan House24–30 HolbornLondon EC1N 2HSUnited KingdomBrian.Ford@WSPGroup.com

environmental design

air over water-filled porous pots, inducingevaporation and bringing about a significant drop intemperature before the air enters the interior [Figs.1a and b]. More recently, this tradition has beentaken up by Hassan Fathy and others, and developedfor cooling schools and other buildings. Often, theair flow rate is enhanced by catching and redirectingthe prevailing wind. Fathy comments on designstrategies to exploit these effects not only withinbuildings but in external spaces as well (Fathy, 1986).

In north India, the Moghul palaces and gardensexploited evaporative cooling to delight the eye andother senses as well as providing thermal relief. Thinwater chutes (salsabil) and other evaporative coolingtechniques were features of Moghul architecturefrom the thirteenth to the seventeenth centuries[Fig. 2]. The intense dry heat and dust of the summerin north India calls for the creation of an internal‘refuge’ or haven from the extremes of the externalworld. The diurnal swing in temperature is‘dampened’ by the mass of stone and earth, and theair is further cooled by the evaporation of water inthe ventilation air flow path. This is exemplifiedperfectly in the beautifully atmospheric ‘Rai PravinaMahal’ in Orchaa (Ford and Hewitt, 1996) [Figs. 3a and b].

The geographical spread of this tradition fromnorth India to southern Spain is remarkable. TheMoorish Islamic tradition in southern Spainincorporates extremely subtle design strategies,which must have developed empirically, to moderateconditions both inside and outside buildings. A mid-summer visit to the ‘Casa de Pilatos’ in Seville [Fig. 4a]provides an experience of what can be achieved. Acentral paved courtyard, searingly hot in the middleof the day, is surrounded by narrow sectionbuildings that are linked by large openings to greengarden courts beyond. Heat rising from the pavedcentral court pulls cooler humidified air from theshaded garden courts across the narrow rooms,where the occupants appreciate both the lowertemperatures and the air movement.

Many aspects of the tradition outlined above werereviewed by the designers of the Expo site in Sevillefor the 1992 World Fair (Alvarez, 1991). This includedthe 30m high ‘cool towers’ of the Avenue of Europe,which employed high-pressure water mistingnozzles (micronizers) to induce downdraught

cooling [Fig. 4b]. This technique of passivedowndraught evaporative cooling (PDEC) has onlyrecently been applied to buildings, but hasenormous potential to displace the need forconventional air conditioning.

What is PDEC ?In the twentieth century, evaporative cooling wasapplied in buildings throughout the world inconjunction with a mechanically driven air supply(known widely as ‘Desert’ coolers). Recently,attention has returned to the potential of exploitingthe benefits of direct evaporative cooling whileavoiding mechanical assistance by using buoyancy orwind forces to drive the air flow.

When water evaporates within a stream ofambient (outside) air, the temperature of the air islowered and its moisture content is elevated, whileits ‘wet bulb’ temperature remains constant. Thecooling of the air is also reflected in an increase indensity, sufficient to drive a downdraught of airthrough a building. In the late 1980s, a number ofsuccessful experiments were undertaken whichtested the evaporation of water within adowndraught tower, hence the term PassiveDowndraught Evaporative Cooling (PDEC).

The cooling effect of a PDEC tower is the product ofthe temperature drop and the volumetric air flowrate. The principal factors that influenceperformance are therefore the characteristics of theclimate (ambient dry bulb and wet bulbtemperatures), the height of the tower and the cross-sectional area of the air inlets (including theirresistance to air flow). As a result of the potentiallyhigh air-flow rates generated by a PDEC system, theinternal air and surface temperatures are governedmainly by the temperature of the cooled air, and thelevel of internal heat gains. Indoor air temperaturesin a well insulated building may be only 1 to 2°Cabove the temperature of the air exiting from theevaporative cooler. The high air movement and lowair and surface temperatures can yield significantimprovements in thermal comfort conditions, andsignificant reductions in energy demands comparedwith equivalent air-conditioned buildings.

Contemporary applicationsIn an experimental building in Tucson, Arizona in

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1a 1b

1986 (Cunningham and Thompson, 1989), adowndraught tower incorporating wetted cellulosepads demonstrated the effectiveness of directevaporative cooling in driving a substantial air flowthrough the building [Figs. 5a and b]. Givoni, inanalyzing the test data, confirmed the effectivenessof this strategy (Givoni, 1990). From a sample of thepublished results it is interesting to note that the exitair temperature from the cooling tower wasmeasured at 24°C when the outdoor dry bulbtemperature (DBT) reached 41°C and the wet bulbtemperature (WBT) was 22°C. The large drop intemperature through the cooling tower, coupledwith high air change rates (in this case believed to beinduced by buoyancy alone), indicates not only thesignificant cooling potential of this technique, butalso that it drives the ventilation air through thebuilding. Since this experimental work, a number ofsmall buildings in Arizona have been designedincorporating cool towers with wetted cellulosepads.

Cunningham and Thompson’s experimentsdemonstrated that buoyancy forces alone canachieve very high air change rates (30 airchanges/hour were recorded in their experimentalbuilding). This is significant if applied to a building,because fans normally required to drive air aroundthe building can be avoided. Fan power can represent30–40% of the electrical energy required by a

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1 The tradition ofcooling without airconditioning spreadfrom ancient Egyptthrough the MiddleEast and Iran tonorth India and thenacross north Africato southern Spain.This example is ofthe Qa’a of MuhibAd-Din Ash-Shaf I Al-Muwaqqi, Irana Section showingthe malqaf andcentral location ofthe qa‘ab Section showingpattern and velocityof air movement

2 Salsabil (waterchute) in Moghul

gardens of the RedFort, Delhi

3 Intense summer heat in north Indiais resisted by aninternal refugewhere the diurnaltemperature swing isdampened by themass stone and earthand the air cooled bywater evaporation asin the Rai PravinaMahal at Orchaaa Section throughsummer roomshowing spotmeasurements taken on 18 April 1995b Plan of summerroom

4 The Moorish Islamictradition uses verysubtle designstrategies whichwere reviewed forthe ’92 Expoa Casa de Pilatos,Seville, Spain. Plan.Heat rising from thepaved central courtpulls coolerhumidified air fromthe shaded gardencourts across narrowroomsb The Cool Towers(left) in the Avenueof Europe at Expo ’92in Seville employedhigh-pressure watermisting nozzles toinduce downdraughtcooling

conventionally air-conditioned building. Theinnovation in relation to contemporary buildings istherefore not the use of evaporative cooling per se,but rather the rediscovery that it can drive the airflow through the building. Typically, in a new air-conditioned office building in southern Europe thismight represent a saving of 70–80kWh/m2 per year(35–45kg/m2 per year).

The first large-scale application of PDEC was in theTorrent Research Centre in Ahmedabad [Figs. 6a–c].Designed by Abhikram Architects and completed in1998, this project demonstrated that this approachto cooling could be applied to a large, complexlaboratory building (Ford et al, 1998). The briefrequired over 17,000m2 of pharmaceutical researchlaboratories, including ‘unclean’ areas like chemicalsynthesis laboratories, and ‘very clean’ areas liketissue culture, molecular biology and drug designareas. Conventional wisdom would suggest that over50% of such a new laboratory building would require

refrigerant-based air conditioning, in order to meetthe environmental requirements within thelaboratories.

Typically, laboratories and offices are arranged onthree levels either side of an open concourse, whichallows the circulation of people between spaces [seeFig. 6b and c]. This arrangement allows evaporativelycooled air to be introduced to the occupied spaces ateach level, and exhausted via perimeter stacks. Inthis way, the working areas are both physically andthermally buffered from the external environment.

Measurements of air temperature and relativehumidity in different parts of the building in April1998 revealed that very significant cooling and highair change rates were achieved. Peak temperatures of27°C in the ground floor laboratory, and 29°C at firstfloor, were achieved when the external maximumreached 38°C. Over the same period, air change ratesof 9 per hour on the ground floor and 6 per hour atfirst floor were recorded. The staff reported thatduring the summer (February – June) thelaboratories are comfortable without fans and arenot stuffy or smelly, as most chemistry labs are, evenwhen air conditioned. During the monsoon (July –September), the evaporative cooling system is notoperated, of course, so ceiling fans are used toenhance comfort for these two to three months.

In the first year since its occupation, the TorrentResearch Centre was reported to have usedapproximately 64% less electrical energy than theequivalent conventionally air-conditioned building.Expenditure on M&E plant was reduced by 36%,which also provides further savings in maintenancecosts.

The wider contextOf course the context of both construction andenergy use is very different in India compared withEurope or the US. In India, construction costs aregenerally approximately one tenth of costs inEurope, while energy costs are relatively muchhigher. This situation is compounded by the fact thatenergy supply in India is unreliable, so majorbusinesses very often invest in expensive dieselgenerators to guarantee their supply. This all adds upto a major incentive to reduce the base loadelectricity requirement. Recent power shortages andprice rises in California, are having a similar effectthere, although the reaction of the Bushadministration has been to encourage furtherexploitation of fossil fuel reserves, rather thanaddress the demand side of the equation andpromote energy efficiency.

It has been argued (Hawken and Lovins, 1998) thatimprovements in ‘resource efficiency’ can result in asimultaneous increase in market value (of cooling forexample) and reduction in non-renewable resourceconsumption. Just as BP are announcing that theyhave gone ‘Beyond Petroleum’, companies likeCarrier may embrace ‘Cooling without AirConditioning’. This may sound far-fetched, but itspotential is reflected in the considerable researcheffort into the new market for PDEC in Europe, aswell as signs of real change in the US.

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5a

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5 An experimentalbuilding with a cooltower in Tucson,Arizona in 1986demonstrated theeffectiveness ofdirect evaporativecooling in driving airflow

a Sketch view ofexperimental buildingto show pattern of airmovementb Measured data from experimentalbuilding byCunningham andThompson

PDEC for a speculative office in SevilleDesign studies for a speculative office building inSeville in southern Spain (completed as part of arecent EC funded research project) resulted in abuilding which met the British Council of Offices(BCO) criteria, providing both open-plan and cellularoffice space without compromising the PDEC system.(Similar design studies for a site in Catania, Sicily, byMario Cucinella Architects were also part of the ECresearch project.)

The proposed office building in Seville dealssimultaneously with the commercial requirementsof the brief, the constraints of the urban site andgeometrical implications of the PDEC strategy. Thedesign attempts to achieve an essentially ‘deep plan’office floor plate (overall width 27m) incorporatingsubstantial (6m wide) light wells, which also serve asthe ‘transitional space’ through which evaporativelycooled air is distributed to each floor [Figs. 7a–g]. Theopen shafts in the centre of the building aresurrounded by open-plan offices, with cellularoffices and meeting rooms around the perimeter.

Offices on the south (street) side of the building areprotected from noise and pollution by exhaustingair via perimeter shafts which allow stale air to eitherfall (in still air conditions) or rise (in windyconditions). Since the prevailing wind is also fromthe south-west, this approach avoids the potentialproblem of positive pressure on exhaust air vents.Exhaust air from open-plan offices passes through abulkhead duct located in the perimeter cellularoffices, and out via automatically controlled tophung ventilators into the perimeter shaft. Theseshafts, expressed fully in the Torrent building, aredeliberately suppressed in the Seville office building,terminating in a relatively low continuous parapet.

The performance of the final design was evaluatedin great detail in terms of both cost (by the DavisLangdon Consultancy) and thermal performance.Performance analysis undertaken at De MontfortUniversity (Lomas, 1999) revealed that while PDEC canachieve satisfactory conditions for 85% of the time,the wet bulb temperature is sometimes too high inSeville to rely on PDEC for cooling. Mixed modeoperation is therefore proposed for this officebuilding to maintain internal air temperaturesbelow 26°C. Nevertheless, simulation results indicateenergy consumption approximately 75% below thatrequired for the air-conditioned reference building.

The cost analysis revealed that the PDEC buildingcould be built for 6% less than the equivalent air-conditionedbuilding. This is extremely significant for the widertake-up of this approach. Not only are air-handlingunits, ductwork, suspended ceilings and relatedcontrols avoided, but also building fabric savings canbe achieved because floor to floor heights can bereduced. It is a popular misconception thatenvironmental responsibility in architectureinevitably results in higher costs. The Seville officebuilding demonstrates that there can also besignificant capital cost savings as well as the revenuebenefits of reduced maintenance and energy costs,associated with adopting PDEC.

The Seville project also addresses the problems of

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6 The first large-scale application of PDEC was in theTorrent ResearchCentre,Ahmedabad, India, designed by AbhikramArchitects andcompleted in 1998a Typical laboratoryblock b Site plan c Section throughtypical laboratoryblock

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7 Design studies for aspeculative officebuilding in Sevilleprovides both open-plan and cellularoffices withoutcompromising thePDEC systema Site planb Site sectionc Aerialphotomontage d Diagramatic

section showingPDEC ventilationstrategy,preliminaryproposale Section with CFDplot of air velocityvectors, DeMontfort Universityf Section, finalproposalg Model ‘slice’ offinal proposal

city centre noise and air pollution [Figs. 7e–g]. Thefacades of the building are sealed, buffering theoffice interior from the noise and pollution of thebusy commercial street on its south side. Air isintroduced to the building at high level, where theconcentration of pollutants is significantly lowerthan at street level. It then enters the separate officefloors via light well and vent shafts. Balancing the airvolume flow rate at each level is achieved by reducingthe open area (and therefore resistance)progressively down the building. The design allowsfor perimeter cellular offices as well as central open-plan areas, allowing flexibility in office layouts asoccupancy changes.

Mixed-mode downdraught cooling systems.The research project also investigated the widerapplication of this technique within southern

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8 Application of PDECto a large publicspace: diagram ofcooling strategysubmitted as part ofthe InternationalCompetition for thenew ConstitutionalCourt,Johannesburg, SouthAfrica

9 Map of the worldshowing thegeographicapplicability of PDEC

Europe, generating maps of applicability related tothe governing criterion of wet bulb temperature.These maps indicate that while PDEC may beapplicable in much of southern Europe, it is rarelyapplicable for 100% of the time (simply because attimes the wet bulb temperature is too high).Therefore, some form of back-up cooling may berequired, depending on location, building type, andinternal heat gains. Clearly the back-up systemcannot be a conventional a.c. system as this wouldimply a duplication of costs.

A back-up system that mimics the downdraughtoperation of PDEC (i.e. no fans) is required. Engineerssuggested that chilled water cooling coils, locatedhigh in the supply air shafts, could perform this role.While requiring chilling equipment, the use ofcooling coils has many of the advantages of the PDECsystem (i.e. avoids the need for air-handling units,ductwork, suspended ceilings and so on).

The combination of PDEC and cooling coils toprovide downdraught cooling under both dry andmore humid conditions, has been included in thedesign for the new Stock Exchange in Malta byarchitects Architecture Project. This project involvesthe refurbishment of an eighteenth-century churchto provide office accommodation on three levelsaround a central atrium. In dry conditions, air willbe supplied at high level via ridge vents, andmicronizers will induce downdraught cooling,driving air through the atrium and exhausting atlow level. In more humid conditions, the ridge ventsare closed, and downdraught cooling is induced bycooling coils located just below the ridge.Performance simulation indicates that PDEC willoperate for about 25% of the summer period inMalta, and the cooling coils will cut in when theinternal relative humidity exceeds an agreedthreshold.

Risks and remedies So far, this review has concentrated on the benefitsof PDEC. However, there are a number of associatedtechnical problems and disadvantages. Hardness ofthe water is significant in terms of the potentialbuild-up of scale, and therefore water quality has tobe good otherwise nozzles will block. High pressures(>40Bar) are required to minimize water droplet sizeand maximize evaporation, which implies moreexpensive pumps and plumbing. The risk of micro-biological contamination of the water supply to themisting nozzles must also be minimized. This can beaddressed by a combination of design measures(including the use of UV filters in the supply line tothe micronizers), regular maintenance, and testing,but it would clearly be better if this was not an issue.

In many parts of the world the potentialdisadvantages of using micronizers (risks of micro-biological contamination, blockage of micronizers,high-pressure stainless-steel plumbing fittings etc.),are a powerful disincentive. ‘Low-Tech’ solutions maybe more appropriate in locations where waterquality is poor, or where high-pressure plumbing isunfamiliar. The practical integration of such systemswithin the building envelope is fundamental to the

feasibility of this approach. If simpler techniquescurrently under investigation do prove technicallyand financially viable, the market potential could besignificant.

The market potential for PDEC in southern EuropeAn investigation (under the EC Altener programme)of the market potential for PDEC within southernEurope, has recently started. Data on the buildingstock in different countries will be reviewed in thecontext of the technical constraints of PDEC toestablish a model of applicability. This research willhelp those involved with the procurement of newbuildings and the refurbishment of existingbuildings, to assess the potential strategic value ofPDEC to their investment decisions. A preliminaryassessment within Spain and Italy suggests that themarket for new office and commercial buildingscould benefit by capital cost savings of 40 millionEuro/year, and energy cost savings of 8.4m Euro/year,if there is a 10% take up of PDEC. If such savings canbe achieved in 10% of all new non-domestic buildingsin Spain and Italy, capital cost savings could amountto over 2 billion Euro/year. Such savings are apowerful incentive to the take up of PDEC insouthern Europe.

The market for PDEC in the USWith the current attitude of the Bushadministration to energy use, PDEC would seemunlikely to find a market in the US. However, thenews that adiabatic cooling has been applied in thenew law court building by Richard Meier in Phoenix,Arizona (Meier R., 2001) is very encouraging. Itdemonstrates confidence in the approach, both interms of being a viable passive cooling technique inhot dry climates and in being able to resolve thepotential risks and disadvantages.

The courtrooms and administrative offices arearranged on six levels, and are accessed via a huge(107 × 46m) atrium which runs the full length of thebuilding. The atrium is a glass box, intended torepresent the ‘transparency’ of the judicial process,and to a provide the major public space in thebuilding. At first sight, this solution seemsquestionable, even crazy, given its desert location.However, the extensive use of shading and theapplication of passive evaporative cooling, haveenabled the designers to achieve comfort conditionsfor most of the year, without the use of mechanicalconditioning.

The cooling and ventilation of the space is drivenby the evaporation of a water ‘mist’ into a stream ofambient air drawn in via openings at high level. Asthe moisture is absorbed, the temperature drops andthe air becomes denser, descending to the floor ofthe atrium. Performance predictions indicate thattemperatures at floor level will not be greater than25°C for most of the year. Some benefit is obtainedfrom ‘spill-air’ from the air-conditioned courtroomsand offices, which escapes into the atrium from thebalconies.

The application of PDEC to a large public spaceattached to courtrooms was proposed in a

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competition entry for the New Constitutional Courtin Johannesburg (Weston and Ford, 1998). This(unbuilt) proposal illustrates the potentialopportunities for PDEC to be applied to very largepublic spaces [Fig. 8], suggesting potential futureapplication to transport interchanges, sports venues,

shopping malls and concert halls.The projects described in this paper illustrate the

range of building types and climatic regions inwhich PDEC can be adopted. It is surely just a matterof time before this approach is applied more widelythroughout the hot dry regions of the world [Fig. 9].

ReferencesAlvarez, S. (1991). A series of papers

including ‘Full scale experiments inEXPO ’92 The Bioclimatic Rotunda’published in Architecture and UrbanSpace, Proceedings of the Ninth PLEAConference, Seville, Spain.

Bahadori, M. N. (1978). ’PassiveCooling Systems in IranianArchitecture’ in Scientific American,p.238.

Beazley, E. & Harverson (1982). Livingwith the Desert – Working Buildings ofthe Iranian Plateau, Aris & PhillipsLtd.

Bunn, R. (2000). TO COME in BuildingServices Journal.

Cunningham, W. A. and Thompson, T.L. (1986). ‘Passive Cooling withnatural draft cooling towers incombination with solar chimneys’in PLEA Conference Proceedings, Pecs,Hungary, The Hungarian Society ofSciences.

Fathy, H. (1986). Natural Energy andVernacular Architecture, University ofChicago Press.

Ford, B., Hewitt, M. (1996). ‘Coolingwithout Air Conditioning – Lessonsfrom India’ in arq 1/4, pp.60–69.

Ford, B., Patel, N., Zaveri, P., Hewitt, M.(1998). ‘Cooling without AirConditioning: The Torrent ResearchCentre’ in the Proceedings of World

Renewable Energy Congress V, Florence,Pergamon.

Ford, B., Diaz, C., Hewitt, M. (2000).‘Passive Downdraught Cooling –Architectural Integration in Seville’in the PLEA Conference Proceedings:Architecture, City, Environment,Cambridge, James & James.

Givoni, B. (1994). Passive and Low EnergyCooling of Buildings, Van NostrandReinhold.

Hawken, P., Lovins, A. B., Lovins, L. H.(1999). Natural Capitalism – The NextIndustrial Revolution, Earthscan,London, p.134.

Meier, R. and Partners (2001). ‘Meier’sGreen Shift’ in Ecotech 3, pp.14–17,Architecture Today.

Von Weisacker, E., Lovins, A. B., Lovins,L. H. (1997). Factor Four – DoublingWealth – Halving Resource Use,Earthscan, London.

Weston, R. and Ford, B. (1998).Competition entry for the NewConstitutional Court,Johannesburg, South Africa –unpublished.

Illustration creditsarq gratefully acknowledges:Abhikram Architects, 6cAuthor, 2, 3a and b, 4b, 6a and b W. A. Cunningham and T. L. Thomson,

5a

Baruch Givoni, 5bHassan Fathy, 1a and b Brian Ford Associates, 7a–e and g, 9Brian Ford Associates with Malcolm

Cook of IESD De MontfortUniversity, 7f

Short Ford Architects, 6dRichard Weston and Brian Ford, 8

AcknowledgementsI would like to acknowledge theassistance of my colleagues CamiloDiaz and Rosa Schiano formerly ofBrian Ford Associates and now in WSPEnvironmental for theircontributions to the work described,to Nimish Patel and Parul Zaveri ofAbhikram for their collaboration onthe Torrent project, and my partnersin the PDEC research project whichwas partially funded by the EuropeanCommission.

BiographyBrian Ford is an architect andenvironmental design consultant.Formerly a partner in Short FordAssociates, and Professor of Bio-climatic Architecture at De MontfortUniversity, he is currently aconsultant and Technical Directorwith WSP Environmental.

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