GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Aynsley, Richard M. North Queensland Community Housing, Townsville.

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1 PART 8 Appendix THE BIOCLIMATIC-ZONES CONCEPT Landscape Design Strategy for Site Planning in Hot Arid Climates Attia, S., The Bioclimatic-Zones Concept: Landscape Design Strategy for Site Planning in Hot Arid Climates, SASBE2009, 2009 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Upadhyay, A. K. XXXV IAHS World Congress on Housing Science, Melbourne, Australia., September 4-7, 2007 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Aynsley, Richard M. North Queensland Community Housing, Townsville. November, 2006 LOW-ENERGY DESIGN IN THE UNITED ARAB EMIRATES DRIVERS AND URBAN DESIGN PRINCIPLES Peter St.Clair. BEDP Environment Design Guide, DES 29. February, 2009 MICROSCALE VEGETATION EFFECTS ON OUTDOOR THERMAL COMFORT IN A HOT-ARID ENVIRONMENT Limor Shashua-Bar, David Pearlmutter, Evyatar Erell, Blaustein Institues for Desert Research, Ben Gurion University of the Negev, Israel. The seventh International Conference on Urban Climate. Yokohama, Japan,29 June - 3 July 2009 ENVIRONMENTAL TECHNOLOGY Prelgauskas, E. Renewable Systems, Viewed March 16, 2011, TOWN OF PORT HEDLAND MUNICIPAL INVENTORY OF HERITAGE PLACES Laura Gray, Heritage and Conservation Consultant, TOWN OF NEWMAN MUNICIPAL INVENTORY OF HERITAGE PLACES Shire of East Pilbara Municipal Heritage Inventory, 1999 TOWN OF ONSLOW MUNICIPAL INVENTORY OF HERITAGE PLACES Shire of Ashburton Municipal Heritage Inventory 1999 TOWN OF DAMPIER MUNICIPAL INVENTORY OF HERITAGE PLACES Heritage Council of Western Australia, 2011 LIST OF RECOMMENDED PLANT SPECIES FOR THE PILBARA Pilbara Vernacular Handbook / Part 9-379

2 THE BIOCLIMATIC-ZONES CONCEPT: LANDSCAPE DESIGN STRATEGY FOR SITE PLANNING IN HOT ARID CLIMATES Attia, Shady. Bioclimatic Landscape Design Strategy: Bioclimatic-zone Concept for site planning in arid climates, Smart and Sustainable Built Environment. Delft, The Netherlands, June This paper explores the use of landscaping for improving the micro-climate of an urban space in a hot-dry climate. It presents the bioclimatic-zones concept as an strategy for achieving this. This concept is based on creating a set of zones; each linked to a group of design guidelines that can improve that particular environment. The paper includes a case study of the Helwan University Campus, explaining and assessing the improvements that could be made through applying the bioclimatic-zones concept. This paper is applicable to urban design in the Pilbara as it illustrates how vegetation can be used to substantially improve the comfort of a specific urban environments in a hot-dry climate. The Bioclimatic-Zones Concept suggests landscape features that can be used to improve particular climate issues. In brief these strategies are: Shelterbelt: large scale trees and shrubs can be used as a buffer to activities on other sites and provide wind and dust protection Oasis: palm groves can be used to funnel wind up and provide a buffer to sand storms. An oasis can reduce temperature/solar radiation, wind speed and dust Desert Landscape: succulent and drought tolerant plants can be used stabilise soil and provide a soft barrier - reducing dust, wind speed and encouraging plant growth Gateways and Entries: entries need to be designed to avoid wind tunneling. Vegetation/water surfaces can be used to lower temperature and humidity Parking and Roads: The earth can be shaped to block solar radiation and winds. Trees can provide shade. To reduce large areas of impervious paving, parking should be located under planted roofs and/or broken into smaller groups of bays. Permeable pavement should also be considered Building Interface: Screens, rooftop greening, green ground cover, trellis, pergolas, ramadas, tents, canopies, car ports and canopy trees can be used to improve the thermal comfort/energy use in and around buildings and reduce glare Inner Gardens and Courtyards: Shading, green ground cover and water surfaces create a cool reservoir that lowers temperature/solar radiation, increases air speed and cleans the air Drought-resistant vegetation should be used. Establishing the Bicoclimatic-Zones The Bioclimatic-Zone for hot arid areas identifies broad climatic zones defined primarily on solar radiation, wind airflows and evaporation. These zones correspond with potential, but not necessarily existing, vegetation boundaries. Both the type and location of plant material can have a substantial effect on micro- climate (Jusuf, 2006). The use of arid plants has been emphasised for its ability to withstand extended periods of drought. The location of plant material in relation to structures and other site elements can have an equally important influence on plant-climate relations. Plants in an exposed, windy location will require many times more water than plants located in protected areas, such as under overhangs or behind walls. It is important therefore, to identify the micro-climate or Bioclimatic-Zones for various plant types that might be chosen for any site. In this concept, seven climatic zones are determined. Each zone is linked to a landscape-design strategy. Fig. 1 is an abstract representation for the Bioclimatic-Zones Concept. Based on the cause-and-effect relations of climate and landscape-design elements, a thorough analysis have been made to define and locate vegetation, water bodies and other landscape design elements for each bioclimatic zone (Olgyay, 1963). The success of each zone should be verified through measuring the climatic impact for every design decision. Table 1 was developed based on Givoni s classification for the climatic parameters that influence thermal comfort in outdoor areas in hot arid areas as listed below (Givoni, 1992, Givoni, 1991). Fig 1: Bioclimatic-Zones Concept illustration for the Northern hemisphere assuming N-S prevailing wind 1. Solar radiation (radiation control, heat control, albedo control and glare control) 2. Wind airflows (dust control, soil erosion control and natural ventilative cooling) 3. Evaporation (evaporative cooling and diurnal cooling) Therefore, the Bioclimatic-Zone concept is vital in site planning during the conceptual phase. The landscape-design decisions for the site planning are interrelated between the expected climatic impact and landscape design elements including vegetation. Each of the listed zones was first examined extensively and intensively on the site scale. The Bioclimatic-Zones Concept is based on the design inventory and analysis phase, followed by the generation of alternatives based on the potential bioclimatic zoning in the site. The listed climatic impacts for each zone, in table 1, help Pilbara Vernacular Handbook / Part 9-380

3 THE BIOCLIMATIC-ZONES CONCEPT: LANDSCAPE DESIGN STRATEGY FOR SITE PLANNING IN HOT ARID CLIMATES Table 1: Bioclimatic-Zones Concept: Decisions and Impacts matrix designers to identify areas most suitable for the establishment of each bioclimatic zone. During the process of site planning, designers have to find areas of suitability. The areas of suitability are used in the final determination of the bioclimatic composite. Next, we will find seven zones that correspond to this concept. Therefore, the Bioclimatic-Zone concept is vital in site planning during the conceptual phase. The landscape-design decisions for the site planning are interrelated between the expected climatic impact and landscape design elements including vegetation. Each of the listed zones was first examined extensively and intensively on the site scale. The Bioclimatic-Zones Concept is based on the design inventory and analysis phase, followed by the generation of alternatives based on the potential bioclimatic zoning in the site. The listed climatic impacts for each zone in table 1 help designers to identify areas most suitable for the establishment of each bioclimatic zone. During the process of site planning, designers have to find areas of suitability. The areas of suitability are used in the final determination of the bioclimatic composite. Next, we will find seven zones that correspond to this concept. Zone 1: Shelterbelt The edge of the property, often the most exposed, typically represent the most arid zone on the site. Because this zone is usually a low use area, it should be planned accordingly as a low maintenance area. Climatically, the Shelterbelt Zone lends itself well to large-scale trees and shrubs that serve either as a buffer to activities on adjacent sites or to reduce wind velocity. One of the primary functions of the shelterbelt is to create protected leeward side areas and protect the site from encroaching dunes. This Zone should be planted with the most drought tolerant plants forming narrow shelterbelt that allows the wind to reduce its speed but still flows over (Miller, 1980 ). Figure 2a: Section in the Shelterbelt Zone Figure 2b: Section in the Oasis Zone Pilbara Vernacular Handbook / Part 9-381

4 THE BIOCLIMATIC-ZONES CONCEPT: LANDSCAPE DESIGN STRATEGY FOR SITE PLANNING IN HOT ARID CLIMATES Zone 2: Oasis In ancient times, people survived desert storms by hiding in oasis. The dense grid of palm trees provided a kind of protection by influencing the micro-climate. Palm oases are most probably famous for standing the extremes of temperature, tolerating alkaline soils and salt, resist drought and lifting up the wind. The climatic definition of the desert oasis effect refers to the cooling effect cause by vegetation and water (Givoni, 1991, Kai, 1997). In this study the Oasis Zone is aiming to create a lee that funnels the wind up and faces sand storms as shown in Fig. 2b. Growing an oasis will prevent desertification and fight sandstorms besides reducing temperature, direct radiation and moderation of wind velocity (Potcher, 2008). Another major significant role of the Oasis Zone is dust control. In general, plants prevent sand and dust from being carried away by the wind because of the difference of the land-surface characteristics such as particle size distribution, plant vegetation and surface soil moisture content and so on (Rizvi, 2006). Zone 3: Desert Landscape The desert landscape is also part of the Bioclimatic-Zones Concept. Designing this zone aims to stabilise the soil and offers a soft barrier. Succulent and drought tolerant are planted to create a boundary layer. Less sand movement creates more favorable environment for plants such as salt bush and indigenous grasses that can germinate in the created zone (Abohassan, 1978). Zone 4: Gateways and Entries Entries and gateways create critical gaps in site planning. They require to be especially treated as separate bioclimatic zones. Since gaps within a shelterbelt reduce its effectiveness. Gaps can result in an increase in wind speed due to the Figure 3a: Section in the Parking and Roads Zone Figure 3b: Section in the Building Interface Zone wind accelerating as it funnels through the gap within the shelterbelt. This effect is often called wind tunneling. Therefore, the location of entries and gateways needs to be determined based on climatic background. A solution for such gaps could be a design for small strips of shelter in front of the gap or creating an angled gap that can overcome this problem (Robinette, 1983). Zone 5: Parking and Roads The level of use of the Parking and Roads Zone, a transitional zone, is moderate. Here we find roads for pedestrians and vehicles in addition to parking areas. Zone 5 is in charge of creating a safe and comfortable environment for pedestrians and vehicles. Landscape-design should provide comfortable and shaded pedestrian and bicycle paths. Trees should be planted in regimen for ease and efficiency of water use, canopy production and shade delivery. Also the earth should be shaped to block undesirable solar radiation and winds. Effects are most useful within five times the height of berm away from windbreak (Robinette, 1983). Significant areas of sites are typically devoted to the parking of automobiles. The current provision of large areas of impervious asphalt or concrete leads to elevated surface temperatures during the summer and heat island effect. Preferably, parking should be located under planted roofs. Otherwise, parking lots should be broken into many small bays, small bays, parking pockets and planted with canopy trees and/or shade structures. Perimeter berming and planting enhance human comfort and thermal performance in these areas. Also soil-biofiltration should be considered through permeable pavement. Generally, lowmaintenance deciduous trees in parking lots require little water, they can take the heat, and they do not lose their leaves. See Fig. 3a. Zone 6: Building Interface The Building Interface Zone is very important because it has a direct impact on thermal comfort and energy conservation in and around buildings. This zone includes elements such as screens, light structures, rooftop greening, grass and canopy trees. Robinette and many others pointed to locating vertical shade screens on the most solar exposed facades of the buildings to impede solar heat gain (Robinette, 1983). Also shades and isolative dead air areas can reduce the delivered energy to cool the spaces behind these facades. Vegetation can satisfy the need of glare reduction as long as reduced thermal gains on buildings. Akbari proofed that urban vegetation reduces the energy needed for indoor climate control (Akbari, 1997). Cool air reservoirs around buildings, such as fountains and pools of water, have a great cooling effect and can reduce the harshness of the micro-climate. Trellis, pergolas, ramadas, tents, Figure 4: Inner Gardens landscape canopies, car ports and other elements are also an essential design element for the Building Interface Zone. In general, large paved areas should be broken up with shaded areas or with zones of vegetation and ground cover (Reynolds, 2002). Excessive large areas of paving should be located on the leeward side of structure so that any heat build-up will be blown away from buildings. Planting roof gardens will minimise solar impacts on buildings and improve the surrounding microclimate. Habitable roofs can also be used in conjunction with vegetated ones (Attia, 2006 ). See Fig. 3b. Zone 7: Inner Gardens and Courtyards Zone 7 affords the most protection from wind and sun. Structural overhangs, walls shade trees, fences, pergolas, and atriums provide an environment more suitable for high-water consumption vegetation than either Zone 1 or 5. If tender exotics are planted, this is the zone where they are most likely to survive. The level of use and the visual interest of zone 7 are high. Accordingly, the exotics, potted plants, and annuals suitable for this zone will capture the attention and provide impetus for the maintenance is generally easier due to the proximity to utilities. Despite the scarcity of water and difficulty of providing large water pools to increase humidity and create air current, elements such as fountains, cascades or spray at least on a seasonal basis. Pilbara Vernacular Handbook / Part 9-382

5 THE BIOCLIMATIC-ZONES CONCEPT: LANDSCAPE DESIGN STRATEGY FOR SITE PLANNING IN HOT ARID CLIMATES The last zone of the Bioclimatic-Zones Concept, shown in Fig. 6, seeks to create relatively cool enclosed air reservoir through intensive landscape (canopy trees and water elements) in contrast to an open hot extensively planted area. CASE STUDY: HELWAN UNIVERSITY Introduction Helwan University Campus is 30 km south of Cairo on a plateau enclosed on the southwest and southeast by steep El Mokattam limestone hills and lying some 50m above the Valley of the Nile, 3km away. Since its establishment in 1975, Helwan University is considered to be under construction. The campus covers an area of 147 hectares and comprises 18 colleges as well as 50 research centers and productive units while many open spaces are left empty. It has a warm, dry desert climate with more than 330 days of sunshine per year. The SOM office was involved in the design of the Master Plan during the seventies; however, many buildings were designed and constructed later by local architects without maintaining a certain Landscape Master Plan. The existing landscape at the campus is a group of scattered patches that were designed by the commissioned architects during the process of designing the different buildings. Comparing Two Scenarios The study verifies the Bioclimatic-Zones Concept through two scenarios for the same site. The first scenario will keep the existing site without any change. The second scenario will adapt the Bioclimatic-Zones Concept all over the site. It is important to mention that applying the Bioclimatic-Zones Concept in this case is more difficult because the site already includes several buildings and landscape patches. However, a landscape amalgamation will occur in the site respecting the physical built environment. Finally, the estimated changes in micro-climate, for both scenarios, will be compared through simulations and field measurements. Field Measurements Two instruments measuring temperature, humidity and air speed (operating range -50o to +700 C, 0.44 to 67 MPH and RH accuracy ±5.4%) were used in this study. Measurements were taken at intervals of every 30 minutes on a height of 1.5 m from the floor. The field measurements were taken on hot days from 16th 20th July The measurements were deployed in four areas with respect to their different shading and greenery distribution conditions. The four measurements were selected to represent four bioclimatic zones as shown in Fig. 5.b. As shown in Fig. 6, measurements prove that there are differences in temperature, humidity and air speed among the estimated zones. ENVI-MET simulation ENVI-Met is a three-dimensional non-hydrostatic urban climate model. It provides detailed environmental conditions, for instance, air temperature and humidity, for each landscape patch within each square within a grid system (Bruse, 2004 ). This information is especially valuable for the present study, in which one wants to evaluate the effects of vegetation in each Bioclimatic-Zone on thermal environment of the various locations of the Campus. The model input parameters used are shown in table 2. Several simulations were produced for this case, including different types of vegetation covers and various atmospheric background conditions. Simulations are briefly summarised in the findings and discussion. Figure 6: Measurements of four different zones FINDINGS AND RESULTS Simulations are reported here, and relevant results obtained from simulations. Fig. 7 shows temperature profiles throughout Helwan University Campus environment at In condition a-daytime, the areas are hot as indicated by yellow and red color representation. In contrast, case b-daytime has a higher presence of dense green areas. The Bioclimatic-Zones Concept, clearly contribute to low ambient temperatures. The same effect can be illustrated by blue and green color during night. DISCUSSION The Bioclimatic-Zones Concept can help landscape designers to handle several various guidelines. The Bioclimatic-Zones Concept is a passive landscape-design strategy that provides designers with a framework for site planning in hot arid climates. In the field of passive landscape-design, there is much research that is concerned with technical and science based knowledge. However, there is a lack of clear and tangible design strategies that guide the designer in establishing passively planned sites that can improve the micro- climate. Therefore, the author provides designers with a valid strategy that can lead to micro-climate improvement and energy conservation. The Bioclimatic- Zones Concept presents a road-map for landscape designers to take the guidelines into account creatively and use them on a bioclimatic solid and classified basis. The concept embraces Pilbara Vernacular Handbook / Part 9-383

6 THE BIOCLIMATIC-ZONES CONCEPT: LANDSCAPE DESIGN STRATEGY FOR SITE PLANNING IN HOT ARID CLIMATES Figure 7: Temperatures comparison (existing condition map - source: Google Earth) local parameters for outdoor spaces such as wind speed, temperatures, humidity etc. To achieve the human comfort in outdoor spaces the Bioclimatic Zones Concept was verified through measurements and simulations using ENVI-Met. The simulation showed encouraging results and demonstrated the potential use of such a model to investigate in detail the possible impacts of the Bioclimatic-Zones Concept in hot arid areas, and to help planning the landscape design elements to improve the micro-climate in outdoor areas. This concept might not always function through the year and most importantly, it functions only in combination with buildings and solid masses. However, the presented study does not deny other design guidelines for site planning in hot arid climates. There are several other guidelines that need to be addressed and considered for site planning such as integrating existing vegetation, topography, waterways and wadis, in addition in integrating the potentials of existing soil. The presented Bioclimatic-Zones Concept should be considered as a landscape-design strategy that crowns the previously mentioned guidelines for site planning. More importantly, the reclamation of the site under this concept requires a deliberate water efficient irrigation and adequate plant selection. It is fundamental, to think comprehensively and acknowledge the necessity to preserve water resources. Drought-tolerant vegetation must be chosen for landscapes over high water-demanding exotic species. In summary, proper design and evaluation measures of environmental factors in the planning phase of sites in hot arid climates can achieve considerable environmental and energetic benefits to occupants and operators of outdoor environment. CONCLUSION This study presents a theoretical concept that helps landscape designers and site planners to design in hot arid climates based on the classified bioclimatic zones. The concept has a great value, although its utility needs to be empirically tested and verified. The simulations presented in this paper emphasise the important role of landscapedesign on micro-climate in site planning. Vegetation can substantially affect the wind, temperature, moisture and precipitation regime in site planning. This concept has very important practical consequences for example heating and cooling requirements of buildings and dispersion. Observation and field measurements were used to compare some of the model results. Even though only approximate atmospheric conditions and land-surface characteristics were used to initialise the model, it appears that the basic structure air temperature and humidity and wind convergence were simulated correctly. These encouraging results demonstrate the potential use of such a concept to investigate in detail the possible impacts of vegetation in campus and to help planning the development of vegetation and water bodies. Then next step will be the commencement of a detailed empirical study. Pilbara Vernacular Handbook / Part 9-384

7 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Upadhyay, A. K. (2007) XXXV IAHS World Congress on Housing Science 2007, September 4-7, Melbourne, Australia. This report highlights the importance of rigourous climate analysis in the design of sustainable architecture and sets out a framework for analysing relevant climate data. Using Perth City as an example, the report illustrates how climate data can be analysed and applied to the selection of climatically suitable and energy efficient design solutions. This is especially relevant in the Pilbara Region as the isolation and extreme climate faced by these towns stresses the importance of considering design options that are site-appropriate and able to perform efficiently. HOUSING DESIGN STRATEGIES Bio-climatic charts and Mahoney tables are effective tools for analyzing thermal comfort and identifying design strategies that can be used to achieve comfortable conditions in an area s specific climate CASE STUDY: PERTH Climate data for the purpose of this paper is obtained for Perth Airport. Climate data over a period of 63 years have been used for analysis. Perth experiences a Mediterranean climate, characterised by hot, dry summers and mild, wet winters. These seasons extend into autumn and spring months, which are transitional periods between the two main seasons. Mean monthly air temperature ranges from 32 C in February to 18 C in July. The highest temperature ever recorded is 46.7 C in February; however, the temperature exceeds 40 C only three days per year on an average. The average minimum temperature ranges from just 8 C in July and August to 17 C in January and February. The lowest temperature ever recorded is 1.3 C in June. Usually humidity is expressed in percentage i.e. relative humidity. Relative humidity is the ratio of the water vapor pressure to the vapor pressure of saturated air at the same temperature. The moisture-holding capacity of air increases with air temperature. In this paper humidity comfort zone has been expressed in specific humidity i.e. the ratio of the mass of water vapour (gm) to the mass of dry air Pilbara Vernacular Handbook / Part 9-385

8 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN (Kg). It is generally accepted that humidity ratio of 4-12 g/kg is considered as a comfortable humidity level (Szokolay, 1986). The morning and afternoon humidity levels in Perth are found within the comfort zone. Summer months are hot and winter months are cold but humidity levels are always in the acceptable range across seasons. Of the annual mean rainfall of 767 mm, which is approximately 87 days of rainfall, about 70% usually fall between May and September. It rains more frequently during winter with 150 mm rainfall in an average of 14 rainy days in a month. In contrast, the total summer rainfall is just 35 mm with an average of 2 rainy days in a month. Hence, it is not unusual in Perth to have extended dry periods during summer. Perth is one of the sunniest Australian cities and enjoys an annual average of 8.8 hours of sunshine per day. In predominantly clear days of summer, the average daily sunshine duration exceeds 11 hours. As winter months get substantial rain, the sky in winter is cloudy for about 12 days in a month. In summer, horizontal solar radiation is the highest. Cloudy conditions and low sun angle, results in low winter horizontal solar radiation in Perth. Requirements of heating or cooling are best described by heating/ cooling degree hours. Heating/ cooling degree hours are the sum of every hour, multiplied by the number of degrees the outside temperature is above or below the comfort temperature. Upper comfort temperature is set according to the neutral temperature (Szokolay, 1982) for each month to respond to the changing characteristics of the climate. Lower comfort temperature has been taken 18 C for the year round. Pilbara Vernacular Handbook / Part 9-386

9 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Summer and early autumn months require cooling; from mid autumn to spring, heating demand is very high in Perth. In total, 85% of the time has heating demand and 15% of time has cooling requirements. Wind is mainly easterly in the morning due to the effect of land mass; and south westerly in the afternoon due to afternoon sea breezes. Winter morning wind comes from the north and changes its course towards the west and south-west in the afternoon. The westerlies are associated with the bulk of the annual rainfall. The average wind speed in winter is considerably lower than in summer. The wind effect is described in detail in the later section of the paper. COMFORT ANALYSIS AND STRATEGIES FOR COMFORTABLE CONDITIONS Evaluating the human-comfort condition is a complex process. There are various environmental and physiological factors that affect the comfort condition of an individual. The effect of climate is evaluated considering the physiological condition of a normal individual. Various climatic parameters are combined to form the thermal index to express their effect on man. In this study, the Bioclimatic chart (Olgyay, 1962) and Building Bioclimatic chart (Givoni, 1976) are used to evaluate the comfort condition and to formulate strategies to respond to it. Bioclimatic approaches to architecture are attempts to create comfortable conditions in buildings by understanding the microclimatic characteristics and resulting design strategies that include natural ventilation, daylight, and passive heating and cooling. The Bioclimatic chart proposed by Olgyay (1962) is very effective for analyzing the comfort condition. The chart checks if a particular temperature humidity relationship falls into the comfortable zone; and also reveals strategies to achieve comfortable conditions. It provides recommendations on, for example, need of radiation under a cold condition, and wind flow or humidification with wind flow under a hot condition. However, the Bioclimatic chart is limited in its applicability, since the analysis of physiological requirements is based on outdoor climate. Later, Givoni (1976) used the Psychrometric chart as the basis for defining the comfort zone and stretched out the probable extent of outdoor conditions under which certain passive control techniques could ensure indoor comfort. The Building Bioclimatic chart derived by Givoni (1976) provides suggestions for building design considering the local climatic conditions. Various control strategies, which ultimately lead to a climate-sensitive design, are suggested. Szokolay (1986) defined control -potential zone to describe the range of outdoor atmospheric conditions within which indoor comfort could be achieved by the various passive control techniques. In the Psychrometric chart different zones are plotted to indicate different strategies depending upon the monthly temperature humidity relationship. To identify the comfort condition for Perth, the climatic data of all months are plotted in both the Bioclimatic chart and Building Bioclimatic chart, as shown in Fig.7 and 8. Two points of each line represent mean minimum temperature with the 9 AM relative humidity and the mean maximum temperature with the 3 PM relative humidity. Both the comfort charts clearly indicate that buildings in Perth require cooling for four months from December to March, as the lines cross the comfort range. In January and February, wind speed up to 2.5 m/s can create a comfortable condition in daytime. Pilbara Vernacular Handbook / Part 9-387

10 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Similarly, thermal mass is also helpful in cooling building from December to March. Night temperature remains just below the comfort range and are usually pleasant in summer months. Over all, building design strategies should make provisions for thermal mass and air movement for that period. The daytime temperature-humidity relationship shows that April, May, October and November are comfortable, but the nighttime temperature falls below the comfort limit. Passive solar heating strategies are suggested to offset nighttime falling temperature. Similarly, June, July, August and September are colder months and require some sort of heating to make the situation comfortable. During this period, passive solar heating strategies help to maintain room temperature within comfortable range. In short, buildings in Perth need to adjust to a large range of thermal conditions which includes utilizing both heating and cooling. It can be achieved through the judicious use of radiation and wind effects along with thermal mass. WIND ANALYSIS Wind is the motion of air relative to the surface of Earth and is one of the most highly variable climatic elements, both in speed and direction. General wind patterns are defined by the atmospheric pressure distribution, but locally wind can be strongly affected by several factors, such as, time of day (e.g. sea breezes), height above the ground and the surrounding terrain. Wind roses are used to represent wind information. They give wind direction, wind speed at varying intensities and the percentage of time wind blows from a certain direction. For the purpose of this study, hourly (more generally every three hours starting from midnight) wind speed record from Bureau of Meteorology, Australia has been used in preparing wind roses for corresponding hours. Earlier, wind data represented wind pattern into sixteen directions but the latest equipment make it possible to record data to the resolution of one degree. For building design purposes, however, eight directions and seasonal wind roses give all the information necessary for a designer. Perth experiences three distinct wind patterns during a day in summer, autumn and spring. Morning wind is largely dominated by breeze coming from the land in the east. Wind direction starts to change towards south and west during noon; and constant strong wind blows from southwest direction in the afternoon. The afternoon wind is caused by sea breeze and can be used to cool off buildings. This south westerly wind in Perth is well known by the name of Fremantle Doctor. This westerly wind changes its course towards south by 9 PM. Winter wind is relatively less intense and dispersed into all possible directions. The wind roses clearly show that the intensity of wind is much stronger in summer than in autumn and spring. Although the general requirement of wind is already suggested by the Bioclimatic and Building Bioclimatic charts, those charts do not specify the time of the day at which the wind is required. Hence, hourly temperatures for different months are generated with the help of maximum and minimum temperatures, considering that the maximum temperature occurs at 3 PM and minimum temperature occurs at 5 AM (Krishan, et al., 2001). Shaded areas in the hourly temperature table indicate the time when cooling may be needed. The cooling temperature is set to the lower comfort limit, which is 18 C temperature higher than these may require cooling. Pilbara Vernacular Handbook / Part 9-388

11 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN To facilitate the ventilation for cooling, wind is necessary at almost all times in summer, morning to evening in autumn and noon to evening during spring months. From the analysis attained cooling in summer and autumn can be assured by having openings towards east, south-west, and south. Morning wind comes from east, afternoon wind comes from south-west and night wind blows from south direction. In spring, south-west wind needs to be secured for noon to evening cooling. In winter, cold wind coming from north and west needs to be blocked as outdoor temperature is already below the comfort level. DESIGN RECOMMENDATIONS FROM MAHONEY TABLES The Mahoney tables (Koenigsberger, et al., 1973) provide results of thermal comfort analysis using primarily temperature and humidity, and make recommendations for pre- design guidelines. Combination of temperature and humidity helps to identify the thermal stress conditions i.e. comfortable, hot and cold, for mean temperatures within, above and below the thermal stress comfort limit, respectively. Once the local climatic conditions have been analyzed and the indoor comfort limits classified, remedial actions or strategies are suggested to arrive at acceptable pre-design conditions for better indoor climate. The Mahoney tables involve six indicators i.e., three humid indicators and three arid indicators. The Mahoney tables indicate remedial action involving air movements for humid conditions. Excess downpours may affect the building structure, so adequate rain protection is also advised. Similarly, for hot and arid conditions, thermal capacity is one of the options for making the indoor space comfortable. Climatic zones with nighttime temperature above the comfort limit are advised to make a provision for outdoor sleeping. An arid climate with lower temperature needs protection of the building from cold wind. The design specifications from Mahoney tables which are very useful for architects and planners in the initial building design stages for Perth are: Layout: A building will benefit from winter solar radiation for heating if it is oriented on north and south axis (long axis on east-west). Spacing: Compact layout of estates with adjoining houses for mutual sheltering. Air movement: Mahoney tables suggest air movement if there is high level of humidity. Perth has got humidity in comfort range so air movement is provisional. Openings: Small openings with 15 25% of wall area are enough to maintain ventilation without substantial heat gain through openings. Position of openings: Openings should be in windward side at body height and also in the internal walls to facilitate ventilation in the rooms on the leeward side of the prevalent wind flow. Protection of openings: Openings should be protected from sun in overheated period in summer and also from rain. Walls and roofs: Extreme diurnal temperature variation and heating requirement in the evening and at night time needs heavy external and internal walls and roofs with time lag of more than eight hours. Outdoor sleeping: Summer months need provisions for outdoor sleeping. These preliminary recommendations are further elaborated combining wind, solar radiation and rainfall parameters to come up with design strategies specifically for Perth. DESIGN STRATEGIES The design strategies are formulated considering the comfort analysis and preliminary recommendations from Mahoney tables. Design strategies are meant to be comprehensive and schematic in helping the design process so that no major opportunities are missed, at the same time, they have to be few such that they can be easily memorise. Following are the specific design recommendations for Perth: Street layout Orientation and layout of streets have significant effects on accessing sun and wind in buildings. To maximise cross ventilation and air movement in streets, primary avenues in Perth should be oriented towards 25 degree west of south. It helps to secure both prevailing afternoon wind and night breezes in summer; and winter solar exposure on the north facade. Major street orientation within the angle of approximately degree on either direction of the prevailing breezes is highly recommended (Brown and DeKay, 2001). Securing neighborhood sunshine Buildings in Perth require solar radiation in winter months. An ideal organisation of streets, open spaces, and building for solar utilisation at maximum density is to elongate buildings in the east west direction and spacing in the north south direction. This placement allows buildings facing north to collect sun, and they are far enough apart not to shade each other. However, because of the topography or pre-existing conditions, many streets do not have an east west orientation so the Fig.s 11, 12 and 13 show several variations in buildings and open space layout, along with their implication for solar access. Pilbara Vernacular Handbook / Part 9-389

12 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Building orientation In Perth, building should be oriented to maximise solar access in winter months and to facilitate wind flow in summer months. Building running long on east west axis with 25 degree orientation towards east of north ensures winter solar access and is able to cut off unwanted solar gain in the north façade during summer months. This orientation angle facilitates both afternoon and evening wind flow across building. Building Structure Perth requires cooling in summer months and heating in winter months. The large range of thermal conditions requires utilisation of both radiation and wind effects, as well as, protection from them. Hence, dual role is required of the structure. Thermal mass helps to store daytime heat during the day and release it at night to balance room temperature in winter months. Thermal mass can be used to absorb heat from a room during the day and to cool off the radiated heat at night with ventilation in summer months. For this, there must be enough mass in the building to absorb the heat gains, and the mass must be distributed over enough surface area so that it can absorb the heat quickly and keep the interior air temperature comfortably low. The opening must be large enough to allow cool outside air to flow past the mass to remove the heat accumulated during the day and carry it outside the building. Roof design Summer horizontal solar radiation is very high in Perth and longer hours of sunshine impart maximum heat flux from roof. Double roof with outer layer lightweight, highly reflective surface, insulated from inside, helps to keep the heat out from entering the building envelope. Ventilation between two layers will dissipate the heat trapped in the gable space. Slope roof is beneficial to collect rainwater and also to provide shade for windows and protection from rain. Windows and ventilation Ventilation during daytime in summer must be kept to the minimum, as the outside air is hot and dry; but good cross ventilation is preferable at night. Medium sized openings are needed to ensure good cross ventilation during summer and to permit the penetration of sun in winter. Windows should face north and south to prevent low angle sun and the openings on these directions also help to facilitate night cooling breezes moving inside the building. Building should be preferably single banked; if double banked, adequate provision must be made for good cross ventilation. Outdoor spaces In summer months, outdoor spaces towards south are very useful as prevailing evening breeze comes from south west in Perth. Outdoor sleeping is recommended in Perth for two months in summer. Winter months require sun tempering as daytime temperature remains below comfort range. Outdoor space towards the eastern part of a building, securing solar access from north and protecting it with westerly breezes is very useful. Pilbara Vernacular Handbook / Part 9-390

13 UNDERSTANDING CLIMATE FOR ENERGY EFFICIENT OR SUSTAINABLE DESIGN Shading devices Shading devices are required on the openings to protect from extreme solar radiation during summer months, but these devices should let in winter radiation in a living area. Vertical and horizontal shading devices can be used for the purpose. Deciduous trees can also be good for shading, allowing winter sun to the living areas but blocking the summer sun. In Perth, prevailing summer wind comes from south west so north façade can be effectively shaded by plantations. Courtyard option Courtyard arrangement is an option for shading in summer and protection from cold winds in winter. Inward looking layout can benefit from microclimatic advantages. In summer months, courtyard with water feature helps in cooling the surroundings. CONCLUSION Climate has an obvious impact on building design and planning. Energy efficient and sustainable design practice should be able to integrate the natural energies (i.e. solar radiation and wind) as parts of its design features. Consideration of the climate starting as early as, in layout of the streets, allocation of building lots, orientation of buildings and in day to day operation of the building, helps to maximise the use of natural energy to achieve comfort conditions. This study reveals specific planning and building design ideas for Perth which can make use of natural energies to achieve comfortable living condition in a building. Winter and nighttime heating can be met by incorporating solar energy and use of thermal mass while summer cooling can be achieved with the use of cool breezes. Wind direction at different time across seasons help designers/ urban planners to orient building and openings to catch the cooling breezes. Pilbara Vernacular Handbook / Part 9-391

14 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Aynsley, Richard M. North Queensland Community Housing, Townsville. November, 2006 TROPICAL HOUSING IN AUSTRALIA Frequent nostalgic references are made to Queenslanders and Darwin s Top Enders as the houses of the good old days. The Queenslander The good features of the Queenslander were their breezy verandahs and elevation, on tall stumps above the termites and local flooding, to catch the breeze. The interior rooms of the Queenslander had few openings in their walls which severely restricted cross ventilation. The dark coloured roof paints of the time on the corrugated iron roofing caused overheating in interior rooms during the day despite the provision of roof vents described by R. Sumner from James Cook University in her study in While they were hot during the day their light weight construction cooled down quickly after sundown. The Top Ender Top Enders in Darwin, also raised on stumps and built with Cypress Pine to deter termites, had the benefits of verandahs on all sides, screened for privacy with close spaced battens fixed vertically over insect screening (Freeman, 1992). The internal rooms had large doorways in opposite walls to encourage indoor air flow. Despite these desirable features, the interiors of these houses were still hot. The corrugated iron roofs, often unpainted, got hotter than painted roofs but had ridge vents to exhaust hot indoor air. CONTEMPORARY HOUSES IN AUSTRALIA S TROPICS Many houses recently built in Australia s tropics reflect designs for temperate regions and are inappropriate for the climate because of: Large areas of poorly shaded glass Large areas of unshaded masonry walls which absorb and store large amounts of heat Large areas of unshaded concrete paving and driveways which absorb and store heat Dark coloured roofs and walls that absorb large amounts of solar energy Lack of shaded outdoor living space Uninsulated roofs Little opportunity for cross ventilation Low ceilings and lack of ceiling fans or ceiling ventilation Dependence on air conditioning for indoor thermal comfort People arriving in the tropics for the first time recognise these houses as similar to those had in southern temperate climates and buy them not realizing that they are inappropriate for the humid tropics. DESIGN STRATEGIES FOR TROPICAL HOUSES In humid tropical climates along the coast, during the hotter months, indoor air movement can be very effective at cooling occupants. At night when winds often decrease, ceiling fans are beneficial to indoor thermal comfort, particularly in bedrooms. Light-weight construction, with timber framing clad with timber or fibre-cement and metal roofing has the advantage of cooling quickly in less than 1 hour after sundown. If this type of construction has a radiant barrier in the roof, shading of walls and windows, and cross ventilation, then indoor air temperatures are rarely more than one or two degrees Celsius above outdoor shade temperature. Concrete slab floors on the ground will rarely exceed 30 C if kept shaded. As long as they are not covered with insulating material such as carpet, they help cool interiors. When summer indoor air temperatures exceed outdoor shade air temperatures by more than say three degrees Celsius, in naturally ventilated houses, the designer has failed. Heavy-weight masonry construction of houses in Australia s tropics was uncommon until the introduction of concrete masonry after World War II. Over the past few decades there has been a significant increase in tiled roof, brick veneer and concrete block construction on concrete slab floors. These types of construction, when exposed to direct sun, absorb large amounts of heat during the day and release it for 3 to 9 hours later at night. This undesirable situation can be overcome by shading walls, choosing lighter colours to reflect heat, or installing external insulation on the exterior surface of masonry walls. In locations where the difference between maximum daytime, and minimum night time air temperature is more than 7 C, masonry houses can be ventilated with a whole house attic fan at night to cool the house for the next day. Up to around midday, this can keep the house cooler inside than outside, if windows are closed shortly after sunrise. Later in the day when indoor temperatures reach outdoor shade temperatures the windows should be opened to benefit from indoor air movement. Small battery powered indoor/outdoor thermometers now available from retail electronic hobby stores for a few dollars can be used to compare indoor and outdoor air temperatures. Thermal Energy Storage The capacity of building materials to store thermal energy depends on their weight and thermal conductivity. Thin metal building components absorb heat quickly, from solar radiation or hot air and distribute it quickly throughout the material. They also lose heat just as quickly, usually a matter of minutes when the source of heat such as sunshine is removed. Concrete and masonry materials are relatively heavy materials but are poorer thermal conductors than metal sheeting. Thick slabs or walls absorb heat from solar radiation and hot air and distribute the heat slowly through the material. Pilbara Vernacular Handbook / Part 9-392

15 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Fixed/adjustable shading Recessed windows can improve natural ventilation Typical window applications for cross ventilation (right) They lose this heat slowly when the surrounding environment cools, usually over a number of hours. This means that heat absorbed during the hottest time of the day is still being released late at night. In locations where night time air temperatures regularly fall more than 7ºC from daytime temperatures to night time temperatures, the coolness of the night air can be used to cool concrete or masonry by night time ventilation. The storage of coolness or coolth can be used to maintain lower morning indoor temperatures for at least a few hours if windows and doors are closed at sunrise. When indoor air temperatures reach outdoor air temperatures windows and doors should be opened to benefit from ventilation and air movement. Outdoor Living in the Humid Tropics During the warmer months, the most comfortable space is usually a shaded outdoor living space that catches the prevailing breeze. In many ways this space can improve thermal comfort and energy efficiency in houses in humid tropical climates more than any other feature of house design. It is important that roofing over such space be insulated to stop heat radiating downward from the hot roof. During the evening, breezes often subside and ceiling height should be sufficient to allow ceiling fans to be installed to improve thermal comfort and deter flying insects. Indoor Air Flow Energy consumed by indoor cooling for thermal comfort can be reduced significantly by providing ceiling fans to provide air flow of around 1 metre per second. This level of air flow has a cooling effect on occupants of up to 3.5ºC, reducing the requirement for cooling indoor air by the same amount. There are some months in tropical regions when outdoor conditions are thermally comfortable. During these months, houses with cooling and heating equipment can be switched off and external windows and doors can be opened to take advantage of energy savings from natural ventilation. Minimise the indoor resistance to air flow between windward and leeward walls by limiting the number of openings through which the air flow has to pass from windward to leeward openings. Avoid hallways which force indoor air flow to change direction abruptly thereby increasing resistance to air flow. Having bedrooms open directly off a family room is a common means of avoiding hallways. Pilbara Vernacular Handbook / Part 9-393

16 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Airflow between Rooms Ventilation grilles above door frames to ceiling level in naturally ventilated houses, allow hotter air near ceilings to flow through the house to vent through the ceiling into a ventilated roof space with an exhaust fan or wind powered vent. Exposure to Prevailing Breezes Maximum average wind pressure difference across a house with a rectangular plan shape is achieved when the diagonal of the plan is across the approaching breeze. Airflow can be significantly increased by steps in the wall line, recessing windows or doors, or projecting wing walls, below eaves overhangs, which deflect air flow into the openings. For maximum potential for air flow through a house, the air flow should enter and exit a room through openings in opposite walls. Corner lots, with frontages to two streets, are desirable when they increase exposure to prevailing summer breezes. The longest wall of the house should not be inclined by more than 45 to the prevailing direction of summer breezes. L-shaped or U-shaped windward walls, with overhanging eaves, trap prevailing breezes, increasing potential for air flow through the houses. Benefits of cooling summer breezes can be substantially reduced by dense foliage close to the windward side of a house. Benefits of cooling summer breezes can be substantially reduced by adjacent buildings within six building heights of the windward side of a house. Shading Try to shade all doors and windows from direct sunshine with awnings or sunscreens. Recess windows about 600mm back into external walls facing into prevailing breezes to improve shading and air flow. Pilbara Vernacular Handbook / Part Apply sun control tinting film where there are difficulties in fitting sunscreens to windows or glazed doors to control solar radiation. Fit lattice screens over windows increase privacy and provide some sun shading. Paint sheet metal surfaces of sun shading components with white paint to reduce their temperature when exposed to solar radiation by reducing absorption and increasing heat loss by infrared radiation. Further reduce solar heat gain through external glazing by the use of light coloured drapes to reflect solar radiation back out through the glass. Shading Walls of Naturally Ventilated Houses Fully shade south facing walls 2.4 m high between 10.00am and 2.00pm by eaves overhangs for the most southern summer sun path on December 22. Fully shade north facing walls between 11.00am and 1.00pm from May 15 through to July 29 with eaves overhangs. This will allow warming during cooler months at latitudes greater than 15. Avoid two storey walls as they are much more difficult to shade from solar radiation. Try to orientate the longest walls to face North and South. This orientation allows the walls and windows to be shaded by simple eaves overhangs which do not obstruct breezes. Shade walls facing west or east by trees and shrubs to protect them from the sun when it is low in the sky during the morning and late afternoon. Reduce indoor heat gains from solar radiation by up to 10% with appropriate eaves overhangs. External walls higher than one storey are more difficult to shade and should be insulated and glazing to upper floors should be avoided or kept to a minimum. Trees, shrubs, vines on trellis, lattice or other sunscreens can provide effective shade to east or west facing walls and windows but will significantly obscure vision out of windows. Walls inclined toward the East or West can be stepped, so that wall segments with windows face North or South, to improve their solar orientation. Consider the possibility of using the houses on adjacent lots to provide shading to your house from direct sunshine from the East and particularly the West. Sunshading Note that there is sunshine on the south facing wall, at noon, during summer (December). This only occurs in the tropics when the sun is near the Tropic of Capricorn and means that windows in south facing walls need sunshades. Locate living areas on the north to north-east side of the house to allow sunshading with eaves overhangs, covered decks or verandahs. Shelter living and sleeping areas from western sunshine by locating the garage and utility rooms such as bathrooms, water closets, pantry or laundry on the western side of the house. Locate garage on the street frontage side of the house to avoid the need for a long driveway alongside the house which reduces flexibility in site planning. Living or sleeping areas located on the western side of the house may be able to be protected from direct sunshine from the west by shading or from the building on the adjacent lot. Use deep verandahs with a low eaves line and adjustable awnings or blinds to provide protection for walls and windows from western sun where there are desirable views to the west. External walls inclined to the east or west can be stepped to allow windows to face north or south so they are protected from the low angles of the afternoon or morning sun. Reccessed window (internal view) Vertical Shading Elements for Sunshine from East and West Eaves overhangs on north or south facing walls cannot provide sunshading near the ends of walls during low sun angles in the mornings and afternoons. This can be achieved by adding vertical sunshade panels. Solar Orientation and the Frontage to Depth Proportions of Lots North or south facing walls offer the best opportunity for sun shading of windows and walls using eaves overhangs which don t obstruct breezes Lots facing a street running east/west should have long frontage and less depth. Lots facing streets that run north/south should have less frontage to the street and greater depth. Lots facing streets aligned north-west/southeast or north-east/south-west should have equal frontage and depth to allow steps in external

17 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Cocept for Displacement Ventilation - placing air conditioners below window level where cool air is required Concept for perimeter wall-to-floor area ratio walls which provide self- shading to walls from the low angles of the afternoon sun, or rotation of the house plan to orientate long walls to the north and south. Landscaping Landscaping can play an important role in achieving energy efficient houses in tropical regions. Outdoor air temperature around a house has a significant impact on energy use within a house. In the tropics there is no such thing as too much shade. Reduce solar reflection from ground surfaces by shading, planting ground cover or lawn. Reduce solar reflection from adjacent walls and roofs by shading with trees. Avoid continuous concrete or bitumen in favour of mulch and ground covers, light-coloured gravel or block or brick paving to allow evaporative moisture exchange between the ground and the air to minimise ground surface temperatures of ground exposure to the sun. Consider planting or using existing trees and shrubs along the East and West sides of the house for sunshading. Consider a shadecloth-covered orchid house or fernery between the house and Western boundary fence. Glazing While glazing usually has the lowest thermal resistance of any wall component, the main concern in tropical regions is solar heat gain through windows by radiation, which is best controlled by external shading. Double glazing and insulated window frames and sashes are not cost effective in tropical regions as temperature differences between indoors and outdoors are small, unlike cold climates when indoor/outdoor temperature differences are large. Apply tinting film to glass exposed to eastern and particularly western sunshine. Replace glass where visual transparency is not critical, with light coloured metal, plastic or timber louvres or shutters. Reduce window sizes but maximise openable area, particularly in bedrooms, to reduce heat gains while retaining air flow potential. West facing glazing should be kept below 2% of the floor area of the room, or preferably eliminated. East facing glazing should be below 8% of the floor area of the room. Window and Door Type Replace existing sliding windows with louvres or casement sashes, hinged on the side that will enable the sash to catch the prevailing summer breeze to improve air flow Replace sliding doors with hinged or folding doors to improve air flow. Extend window openings as close to ceiling level as possible to encourage venting of hot indoor air. Avoid bay windows unless they are well shaded. Reflection Use light coloured walls to minimising summer solar heat gain by your house from both direct and indirect solar radiation (reflected from the ground and adjacent buildings). Insulation Wall insulation for naturally ventilated dwellings to control indoor radiant heat from solar heat gains should be R1.0 provided west and east facing walls are shaded and indirect solar radiation is controlled. Air Conditioned Houses Energy efficient air conditioned houses in tropical regions require a well sealed and insulated external building envelope (walls - including windows & doors, roofs and floors) with attention to solar orientation and shading. Entry lobbies with two doors, which form an airlock to reduce loss of conditioned air and infiltration of outdoor air, save cooling and heating energy. Differences in time/use of living and sleeping spaces make zonal separation of these areas worthwhile, which means doors to separate these areas. Pilbara Vernacular Handbook / Part 9-395

18 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Vented highlights over internal doors Combined Air Conditioned and Naturally Ventilated Houses Many houses in humid tropical regions have some cooled spaces and some naturally ventilated spaces in the same house. Living areas tend to be naturally ventilated spaces with ceiling fans and sleeping areas the cooled areas. The design of naturally ventilated spaces of such houses should follow the naturally ventilated house guidelines Cooled spaces should follow guidelines for air conditioned houses. Walls separating the naturally ventilated and cooled spaces should be insulated and have doors to limit loss of cooled air. Displacement Ventilation All enclosed buildings require ventilation to provide fresh air and remove stale air. A recent development in energy efficiency in cooling of buildings is displacement ventilation. In the past, air conditioned air was distributed with sufficient velocity through outlets in ceilings to mix with the general air in a room before returning near floor level for filtering, re-cooling and recirculation. Displacement ventilation delivers the filtered and cooled air at lower velocities below window sill level. This fresh air displaces warmed air which rises naturally toward the ceiling from where it is returned to the system for filtering and cooling, leaving the freshest and coolest air in the occupied region within the first 2m above floor level. This accumulation of warm air at ceiling level reduces the temperature difference between the heated roof space and air under the ceiling reducing heat entry into the room. This thermal stratification of indoor air in cooled buildings has been shown to save up to 26% of cooling system energy. If displacement ventilation is adopted ceiling fans should not be operated. CHOOSING A SITE Size of Lots Lots have decreased in size from 1,000m2 to as small as 250m2 Small lots more likely to lose exposure to summer breezes due to obstruction by neighbouring houses. Small lots restrict opportunities to rotate a house plan on the site to achieve better solar orientation. Small lots mean shorter distances between houses which increases potential for visual and noise privacy problems. Elevated Lots for Views and Breezes Lots with elevation above surrounding land and exposure to the direction of approaching prevailing summer breezes are desirable. Elevated lots with views to the west will pose difficult problems in sunshading and solar heat gain through west facing glazing. Elevated lots on the leeward side of hills, without exposure to the prevailing summer breeze, should be avoided as they provide no comfort benefits in summer. Elevated lots can increase exposure to tropical cyclones and require increased attention to site drainage and geological stability, particularly during wet weather. Plan Shape Cooled and warmed (air conditioned) houses in humid, as well as arid tropical locations, should have plan shapes approaching a square, Where feasible plans should be two storeys which can help to minimise area of insulated external walls and roof relative to the internal floor area. Locate outdoor shaded living space with ceiling fans on the East to North-east sides of the house. THERMAL COMFORT ANALYSIS Evaluating thermal comfort is a complex project. There are a variety of environmental and physiological factors that affect an individual s comfort, including temperature, humidity, radiation and air movement, as well as type of activity, clothing and acclimatisation. This report has utilised the following strategies to help identify thermal comfort levels and appropriate design responses. Mahoney Tables Mahoney tables are used to analyse the climate characteristics from which design indicators are obtained. The Mahoney tables involve six indicators: three humid indicators and three arid indicators. From these indicators, a preliminary picture of the layout, orientation, shape and structure of climate responsive design can be obtained. The Mahoney tables relate to the Thermal Comfort Limits and Indicators of requirements for comfort each month tables, which have also been referenced in this report. Thermal Comfort Limits This table indicates the range of temperatures that are likely to be perceived as comfortable at particular levels of relative humidity. These limits assume that there has been no heat loss or gain due to ventilation and insolation. BUILDING BIOCLIMATIC CHARTS Bioclimatic charts compare humidity and temperature to identify design guidelines that can maximise indoor comfort when the building s interior is not mechanically conditioned. The design strategies suggested by this version of the bioclimatic chart are appropriate buildings with small internal heat gains (approx. 20,000 btu per day per person). To identify the comfort condition of these towns, the maximum/minimum temperatures and 9am/3pm mean relative humidities are plotted for each month. One point of each line represents the highest temperature and lowest humidity level experienced, while the other represents lowest temperature and highest humidity. Pilbara Vernacular Handbook / Part 9-396

19 GUIDELINES FOR ENERGY EFFICIENT HOUSING IN THE TROPICS Montly average Annual average temperature relative humidity (RH)% Over 20ºC 15-20ºC Under 15ºC Day Night Day Night Day Night Indicators of requirements for comfort for each month This table uses maximum/minimum temperatures and relative humidity to indicate design requirements for comfort each month. Source: Metric Handbook: Planning and Design Manual Humid indicators H1 Air movement essential mean monthly maximum temperature above the day comfort limits combined with humidity over 80% or humidity between 30-70% and a diurnal range of less than 10ºC H2 Air movement desirable means monthly maximum temperatures within the comfort limits combined with humidities over 70% Arid indicators A1 Thermal storage required diurnal range of temperatures over 10ºC and humidity less than 70% A2 Space required for outdoor sleeping means monthly minimum temperatures above the night comfort limits and humidity below 50%. Outdoor sleeping may also be indicated where maximum temperatures are above the day comfort limits and diurnal range is above 10ºC with humidities less than 50%. Cold indicators C1 Solar radiation desirable mean monthly maximum temperatures below day comfort limits C2 Additional heating required mean monthly maximum temperature below 15ºC Source: Metric Handbook: Planning and Design Manual Pilbara Vernacular Handbook / Part 9-397

20 LOW-ENERGY DESIGN IN THE UNITED ARAB EMIRATES DRIVERS AND URBAN DESIGN PRINCIPLES Peter St.Clair. BEDP Environment Design Guide, DES 29. February, 2009 Climate responsive design and traditional design elements of the Persian Gulf may provide a basis for low-energy design. Current building models employed in the United Arab Emirates are often unsuited to the region s climate, causing massive cooling loads as a result of inappropriate site planning, orientation and building envelopes with high levels of glazing. The application of an inter-disciplinary design approach that considers urban design, landscape design, architecture and meteorology may provide a more appropriate lowenergy design for such hot and arid climates. This paper forms the first part of two parts, and is to be read with the companion paper: DES 30 Low-Energy Design in the United Arab Emirates Building Design Principles. 1.0 INTRODUCTION 1.1 Summary The United Arab Emirates (UAE) provides a unique opportunity and challenge for architects and other design professionals to develop a new low-energy urbanism and architecture. The UAE is currently the world s largest user of energy on a per capita basis, with 70 per cent of primary domestic energy usage being committed to buildings, primarily in the form of mechanical ventilation (air-conditioning and heating) and artificial lighting (Kazim, AM, 2007). Countries of the Middle East such as the UAE possess a rich architectural legacy based upon climate responsive design. Diminishing oil supplies in some Emirates within the UAE have lead to a diversification of the economy expressed in dramatic levels of building and infrastructure development. This ongoing strategy of economic diversification coupled with a desire by government and developers for market differentiation, the UAE s commitment to the Kyoto Protocol and a changing regulatory framework, are providing the opportunity for the UAE to become a centre of research, experimentation and development of low-energy solutions for building and urban design. This can already be seen in projects such as Masdar, a proposed zero energy city and research hub currently being designed by Sir Norman Foster in Abu Dhabi, based upon traditional planning principles of the walled city (Foster + Partners, 2008, Masdar Initiative, 2008) and the development of sustainability codes and voluntary rating systems in both Dubai and more extensively in Abu Dhabi. Traditional architecture in the Gulf region is based upon a sophisticated response to climate that employs passive techniques for the cooling and heating of urban spaces and buildings. Australia shares a similar hot and arid climate across much of the country and employs many low-energy strategies that originated in the Gulf region, such as the courtyard, or courthouse building model (as they are known in the Middle East and North Africa), can be seen in Australia, which respond to the problems of solar radiation and hot winds. Contemporary buildings in the UAE are often based upon imported building models unsuited to the climate and culture. These solutions can only function through extensive intervention by mechanical air-conditioning leading to disproportionate usage of oil and natural gas reserves and consequently high levels of carbon emissions. This paper identifies passive design strategies and relevant literature that may contribute to a low energy urban design and architecture in the UAE. The severe climate and market expectations within the UAE require the use of HVAC systems in most cases. Building design that responds to the climate can complement active systems through reducing building energy usage and associated carbon emissions, while contributing to an appropriate vernacular architecture and forming a legitimate starting point for architectural expression relating to place and lifestyle. The goal of these guidelines is that they can contribute to the education and awareness of architects and clients and be incorporated into organisation practice management systems. 1.2 Guideline Scope Climate responsive design can be equally applied to all building types and scales and so this guideline is intended to be generic, applying to high-rise and low-rise construction. The design strategies that are considered are those primarily relevant to passive considerations such as floor planning, façade design and orientation and not those driven by engineering solutions such as co-generation. Strategies are focused on the reduction of cooling loads in buildings, as this represents both the bulk of energy usage and the fastest growing energy demand in the UAE, where the cooling season is much longer than the heating season. The research and case studies for low-energy design in the UAE are still developing and so this report draws from a wide range of sources including recent academic papers and media articles in addition to established literature by authors such as Baruch Givoni, (architect and climatologist), Hassan Fathy (noted Egyptian architect) and Richard Hyde (coordinator of architectural and design science discipline at Sydney University) that analyse building in other similar hot and arid climates of the world. 2.0 BACKGROUND 2.1 The Climate of the UAE The Arabian Peninsula is situated in one of the most hostile climatic zones on earth, featuring extremely high summer temperatures, limited fresh water and high evaporation rates. The UAE lies in the arid tropical zone extending across Asia and North Africa and contains at least four climatic zones, with that of principal interest for this guideline being the coastal zone containing Dubai and Abu Dhabi. The climate of this coastal zone is classified as semi-arid to hyper-arid (Boer, 1997). The data demonstrates the climate of the UAE to be primarily hot and dry, while exhibiting some qualities of hot and humid climate with a higher rate of relative humidity than in typical arid climates. The sunshine hours per day are among the highest in the world varying from 8.0 hours in December to 11.5 hours in June. Clear sky conditions result in a high diurnal temperature range of C providing the opportunity for night cooling between November and April (NASA, 2008). Insolation, which is a measure of solar radiation levels, is higher at this latitude than at the equator or equivalent south latitude (Givoni, 1976). The combination of sunshine hours, clear skies, high solar radiation and highly reflective terrain (sand and gravel) lead to extreme temperature and daylight and consequently high evaporation levels. The prevailing winds or Shamal are from the north- west bringing cooler and wetter conditions in the winter time and hot dusty conditions from the deserts of Saudi Arabia, Kuwait and Iran in summer time (Arabianbusiness, 2008). Summer winds also extend from the south east, bringing hot and dry conditions and occasional sand storms. The period between the months of May and November is typified by extreme day time heat and night time temperatures above comfort conditions. The building design focus during this period should be upon reducing cooling loads which can be achieved through increased energy efficiency measures. The period between the months of November and April are, however, typified by night time temperatures below 21 C, Pilbara Vernacular Handbook / Part 9-398

21 LOW-ENERGY DESIGN IN THE UNITED ARAB EMIRATES DRIVERS AND URBAN DESIGN PRINCIPLES higher humidity, and lower insolation and sunlight hours, providing the opportunity for cooling load reductions through passive cooling strategiessuch as nocturnal ventilative cooling. Humidity levels in summer, although lower than in winter time, are coupled with the extremely high temperatures and produce very uncomfortable conditions. Energy efficiency measures can provide further benefits to both cooling and heating loads in this period. 2.2 Changing to Low-energy Design Movement toward low-energy building design in the UAE may result from the influence of a variety of inter-connected factors including the political context, ethical considerations, design and technological advancements, economic costs and opportunities, risk management and marketability. Architects and design professionals who understand these drivers may be better prepared to provide more strategic and relevant design advice and outcomes for their clients. Drivers include the risk of buildings losing competiveness and asset value in the property market as a result of not matching global drives for sustainability and the decreasing costs of solar energy. The emirates of Abu Dhabi and Dubai are showing strong commitment to sustainability principles (Austrade, 2008, Ecospecifier, 2008) leading to changes in planning and building codes such as Dubai s announcement of a new green building code. The Appendix to this paper lists further drivers and opportunities for the private and government developers and their consultants categorised under the following headings: Political and Economic Regulatory and Voluntary Standards Environmental, Ethical and Corporate Governance Design, Climate and Technology Business and Research Opportunities Design, Climate and Technology 3.0 DESIGN STRATEGIES FOR HOT AND ARID CLIMATES Givoni, who is considered a leading authority on building climatology, classifies passive energy design strategies according to two categories. The first category is the design of buildings to minimise its energy needs through strategies such as building layout, orientation and façade design. The second category is strategies that utilise natural energy sources in the form of passive cooling and heating systems, including ventilative cooling, radiant cooling and evaporative cooling systems (Givoni, 1998). Givoni further classifies passive energy design strategies against scale. The first classification being the urban environment and the second being individual buildings (Givoni, 1998).This classification has been adopted for the following description of strategies. 3.2 Design Strategy Summary The following design strategies can provide low- energy outcomes for low and high rise building types in the UAE. Graham Farmer of the University of Newcastle upon Tyne, describes the most effective way to reduce building energy consumption is to exploit natural means and depend less on mechanical means (Boake, 2008). Traditional and contemporary climate responsive strategies can be adapted to contemporary building programmes and construction techniques and so form the main generator of building design. The strategies below have been drawn from generic writings by authors such as Givoni, Fathy and Baker, complemented by current and regional literature. 3.3 Urban Design Strategies Overview Urban climate varies from the climatic conditions in surrounding rural areas. Givoni states that these differences are a consequence of both climatic factors such as wind speed and cloud cover, as well as the city structure in the form of street layouts and building densities (Givoni, 1998). The major impact affecting human comfort and cooling loads of buildings are air temperatures and wind speeds near street levels, caused by convective heat exchange between the ground and buildings and the air flowing above, and the heat generation within the city. This leads to the Heat Island phenomenon where the average diurnal temperature in a densely built urban area is higher than in the surrounding rural areas. This results in significant temperature elevation at night times. In arid desert regions such as the UAE, this effect may be reversed, whereby the introduction of building shade and vegetation can lower temperatures in comparison to surrounding desert areas. Wind speeds generally increase with additional height, as a consequence of a reduced number of barriers and reduced friction. Urban climate conditions and resultant cooling loads can be modified through urban design strategies Street Orientation The objective in a hot, dry climate is to maximise shading for pedestrians and minimise the solar exposure of building facades along streets whilst maintaining optimum urban and building ventilation. An east west orientation of streets promotes north and south solar exposure to buildings that can be more readily controlled as a result of the greater solar altitude. Narrower streets promote greater shading thus reducing radiant heat gains on ground surfaces and building facades. (Givoni, 1992). Street orientations should allow cooling by ventilation with the prevailing afternoon winds, when the urban temperature reaches its maximum. This is demonstrated by the street design for Masdar in Abu Dhabi, where streets are oriented NW/SE, benefiting from the prevailing NW daytime winds and SE night time winds (Maxmakers, 2009). Building ventilation can be further enhanced by exposing buildings along the streets to differing air pressures on their front and rear facades. This may be achieved in the UAE by orientating streets east west, thereby at an oblique angle of approximately 45 C to the prevailing NW and SE winds (Wind Finder, 2008). Studies completed in the UAE have compared the energy usage of a variety of low rise buildings as a result of building orientation and concluded that street and block orientation and lot dimensions can impact the energy required for cooling. Building clusters orientated within 30 C of north perform considerably better when combined with the correct orientation of short and long elevations and window to wall ratio (Aboulnaga, et al, 2000, Givoni, B, 1989) Urban vegetation Urban planting in the form of parks and planting around buildings can significantly reduce the heating loads of buildings by lowering air temperature next to the building facades and thus reducing radiant heat gains reflected from the ground (Givoni, 1991, 1989). The percentage of total solar radiation that reaches the area below a tree is typically only per cent in summer. This leads to cooler surface temperatures below the trees, which in turn reduces the heat transmitted into buildings or re-emitted into the atmosphere. Pilbara Vernacular Handbook / Part 9-399

22 LOW-ENERGY DESIGN IN THE UNITED ARAB EMIRATES DRIVERS AND URBAN DESIGN PRINCIPLES Green roofs and green walls (or living walls ) can further reduce cooling loads by shading and insulating the building envelope and removing heat from the air through evapo-transpiration. The temperature of a conventional rooftop can exceed the surrounding air temperature by up to 50 CC, whereas a vegetated rooftop can be cooler than the surrounding air. While planting and green roofs should not be used as a substitute for conventional insulation, and should be considered carefully in the UAE where water is scarce, they can contribute to building insulation, improve the site micro-climate and reduce the heat island effect on the surroundings (US Environmental Protection Agency, 2009) Building density and type Urban density and building heights are a major determinant of urban ventilation and thus building cooling loads. Tall, long buildings of similar height will limit air movement and should be avoided, whilst buildings of varying heights with long facades, oblique to the wind, enhance urban ventilation. Streets and urban spaces such as street courtyards which have a higher height to width ratio can provide reduced external air temperatures when associated with tree shading. This is achieved by reducing solar radiation exposure and thus absorption in the same way traditional narrow streets limit solar access to ground and wall planes (Shashua-Bar, Hoffman, 2004, Givoni, 1989, 1994). An understanding of traditional city planning aimed at developing favourable micro-climates, coupled with the application of sustainable precinct design tools such as United States Green Building Council (USGBC) LEED rating tool for Neighbourhoods, the new Abu Dhabi Estidama Pearl Design System for New Communities, Urban Centres and Neighbourhoods may support the design of energy efficient precincts and cities in the UAE. 4.0 CONCLUSION The traditional building design practices of the Gulf region, based upon an understanding of climate, provide a foundation for low-energy buildings in the UAE today that is appropriate to the environment and results in reduced carbon emission. This may also lead to an appropriate vernacular architecture replacing imported building models that have contributed to a dramatic rise in energy usage and a proliferation of culturally non-specific building forms (Bouman, Khoubrou, Koolhaas, R (eds), 2007). Significant generic literature exists to support education in the design of low-energy buildings in hot and arid climates, complemented by regional journals and research papers that have measured the benefits of traditional design strategies and the poor performance of imported models, in particular those incorporating curtain glass facades. The dramatically different climatic conditions of the Gulf region mean these imported solutions can only function through extensive intervention by mechanical air conditioning. Strategies for low-energy design extend beyond buildings to include urban design strategies such as correct street and building orientation to promote urban ventilation and shading and the use of urban parks to promote a cool island effect. Buildings can be designed to operate in mixed mode (that is the ability to use air-conditioning or outside air, when it is appropriate), thereby satisfying contemporary market expectations for air-conditioning, while benefiting from passive strategies during the winter and transition seasons. The rate of development in the UAE has demonstrated the economic and lifestyle opportunities that exist within the region, despite the harsh climate. Architects such as Rem Koolhaus see the UAE as a unique opportunity for urban designers and architects stating in Al Manakh. Figure 1: Narrow, deep streets reduce radiant heat gains (Adapted from Givoni, 1998) Table 1 Climatic data for Dubai (Adapted from Aboulnaga, 2006, Club Air Travel, 2008, NASA, 2008, Weather Network Statistics, 2008, Wind Finder, 2008) Pilbara Vernacular Handbook / Part 9-400

23 MICROSCALE VEGETATION EFFECTS ON OUTDOOR THERMAL COMFORT IN A HOT-ARID ENVIRONMENT Limor Shashua-Bar, David Pearlmutter, Evyatar Erell Blaustein Institutes For Desert Research, Ben Gurion University of the Negev, Israel The effect of irrigated vegetation on human thermal stress in a hot-arid region was tested in two semi-enclosed urban spaces with varying combinations of mature trees, shading mesh, lawn and paving. The Index of Thermal Stress was calculated hourly from measured data to evaluate thermal comfort in the spaces, and was expressed on a scale of thermal sensation. While thermal stress in a paved unshaded courtyard was severe during mid-day hours, both grass and shading, either by trees or by mesh, contributed significantly to thermal comfort. A combination of the two strategies resulted in comfortable conditions at all hours though trees alone provided more efficient cooling in terms of water use, as measured by the rate of evapotranspiration. The main effect of both grass and shade was to reduce radiant loads, while differences in air temperature were small. Key words: thermal stress, evapotranspiration, microclimate, landscape, urban design 1. INTRODUCTION Irrigated vegetation may have a profound impact on the climate of urban areas, and the relative lack of vegetation in many cities has been cited as one of the main causes of the urban heat island. Yet in arid regions this situation may theoretically be reversed, with a relative abundance of irrigated landscaping within the built-up area creating a cool island in the midst of sparsely vegetated natural surroundings. Observations in desert cities have shown that such an urban cool island may indeed develop, though largely as a daytime, rather than as a nocturnal, phenomenon (Brazel et al. 2000). The primary mechanism to which this type of urban cooling is attributed is evapotranspiration, by which radiant energy driving the surface energy balance is converted into latent, as opposed to sensible heat. Recent studies in Israel s Negev desert using an open-air scaled urban surface (the OASUS model) showed that the proportion of dissipated latent heat is directly related to the complete vegetated fraction, or the ratio between the total vegetated area and the complete threedimensional urban surface area (Pearlmutter et al. 2009). This indicates that evaporative cooling depends not only on the extent of urban green spaces, but also on the height and density of buildings within the urban fabric. In addition, the thermally moderating effect of vegetation is not just evaporative but also radiative, due to the lower temperatures of shaded and vegetated ground surfaces and the direct shading of pedestrians. Thus the cooling effects of urban vegetation may be highly localised, with individual cool islands of limited spatial extent forming within an otherwise overheated built-up area. When the vegetated area is small and turbulent mixing of air in the urban canopy is efficient, air temperature reductions within the green patch may in fact be negligible though it has been shown repeatedly that the effects of shading and cooler surfaces moderate significantly the overall thermal stress experienced by pedestrians (Pearlmutter et al., 1999; Ali-Toudert and Mayer, 2006; Johansson, 2006). Notwithstanding its benefits, the use of vegetative landscaping in arid regions relies on water resources for irrigation, which in many cases are scarce since precipitation is far outweighed by potential evapotranspiration. This balance between water consumption and the amelioration of urban heating is examined in the present study, which employs observations in a well-defined urban space to model the micro-scale influence of various landscape treatments on pedestrian thermal stress. 2. EXPERIMENTAL SETUP The landscape strategies examined include six combinations of ground cover (dry paving and irrigated grass) and overhead treatment (exposed, shade trees, and shading-mesh). A controlled experiment was conducted in two adjacent courtyard spaces (Fig. 1), which are nearly identical in their material attributes and geometry (15 x 6 m; long axis N-S; H/W = 0.5) but differentiated by the existence of three mature trees in one of the spaces (grass sod units were added to each space subsequently). The site is located at the Sde-Boqer campus in the arid Negev Highlands of southern Israel (30.8 N, 500m elevation). The courtyards were monitored in hot-dry conditions during July- August 2007, with measurements made in each landscape configuration for a period of at least 3-4 successive days. Ambient temperatures were typically in the range of C, with low daytime relative humidity and strong north-westerly winds in late afternoon. Dry- and wet-bulb temperatures were measured in each courtyard (between two Prosopis Juliflora trees in the planted courtyard and at the same central point in the exposed one) using copper-constantan thermocouples in aspirated psychrometers. Temperatures of the various built and vegetated surfaces were measured in both courtyards using shielded ultra-fine thermocouples and an IR thermometer. Wind speed was measured within the courtyards, and other climatic data corresponding to the measurement days were also obtained from a nearby meteorological station for comparison and analysis purposes. Water use for grass irrigation was estimated using custom-made mini- lysimeters, which consisted of rectangular metal pans embedded in the grass-soil layer. The evapotranspiration rate was determined from the periodic change in lysimeter weight, measured hourly with a high- resolution electronic scale starting from the daily time of irrigation. Transpiration from the trees was measured by the sap flow method, which relates the transpiration rate to the rate of sap flow in the tree trunk. The method uses pairs of cylindrical temperature probes inserted in the sapwood, with the upper probe heated by the Joule effect at a constant rate and the lower (reference) probe unheated. A more detailed description of the monitoring setup is given by Shashua-Bar et al. (2009a; 2009b). 3. MODELING THERMAL STRESS AND THERMAL SENSATION Pedestrian thermal stress was quantified using the Index of Thermal Stress (ITS), which expresses the overall energy exchange between a pedestrian s body and its surroundings under warm conditions. Expressed in watts of equivalent latent heat, the index is a measure of the rate at which the body must secrete sweat in order to maintain thermal equilibrium accounting for radiation Rn and convection C as well as the body s internal heat generation (based on metabolism M and work W) and the efficiency of sweat evaporation f, as limited by atmospheric humidity: ITS=[Rn +C+(M-W)]/f The instantaneous exchanges of energy by radiation and convection are computed in W m-2 of body surface using a vertical cylinder to represent a standing pedestrian in the center of the space (Pearlmutter et al. 1999). The body s net radiation balance is composed of absorbed direct, diffuse and reflected short-wave components, long-wave absorption from the sky and other downward-radiating elements, horizontal ground surfaces and vertical wall surfaces, and longwave emission from the body to the environment. The absorption of short-wave radiation is based on measured global and diffuse radiation, shading and view factors (a function of courtyard Pilbara Vernacular Handbook / Part 9-401

24 MICROSCALE VEGETATION EFFECTS ON OUTDOOR THERMAL COMFORT IN A HOT-ARID ENVIRONMENT geometry), and the albedo of built and vegetative surfaces and of the body itself. Long-wave absorption from surfaces is calculated on the basis of view factors, measured surface temperatures, and estimated emissivity values for all relevant materials. Downward long-wave emission from the sky dome was taken as the residual in the measured net radiation balance above the building roof (with incoming short-wave measured, roof albedo estimated, and outgoing long-wave computed from the measured roof surface temperature and estimated emissivity) and emission from the body is based on a constant skin-clothing temperature. Convective energy exchange is a function of the skin-air temperature differential and of an empirical heat transfer coefficient based on wind speed, which was measured along with air temperature in the courtyards. To calculate the level of thermal stress from the radiative and convective environmental loads, component flux densities are multiplied by the DuBois body surface area to yield fluxes in watts, and summed with the net metabolic heat gain. The evaporative cooling efficiency is computed from an empirical relation based on the vapor pressure of the surrounding air, as well as on wind speed and a clothing coefficient. The level of physiological stress represented by the ITS has also been correlated with subjective thermal discomfort, on a thermal sensation scale ranging from comfortable to very hot (Givoni 1963; Pearlmutter et al. 2007). According to this scale, a limit to comfort is found at an ITS value of approximately 160 W, with the thresholds for warm and hot conditions occurring at successive increments of 120 W each. While climatic conditions were relatively consistent throughout the summer monitoring period, minor differences were accounted for Figure 1. Thermal images of courtyards with trees and grass (top) and with paving and mesh (bottom). by normalizing the results from individual days relative to a reference dataset taken from the adjacent meteorological station. For each landscape configuration, a representative daily cycle was selected and hourly ITS values were adjusted proportionally based on the ratio between the equivalent value computed from simultaneous measurements at the open site of the meteorological station, and the average of reference values for that hour over the set of selected days. 4. RESULTS AND DISCUSSION In Fig. 2, normalised hourly daytime (6:00-20:00) values of thermal stress are shown for the six courtyard configurations as well as for a pedestrian in an open space, with the latter calculated on the basis of measured data (air and ground temperatures, short-wave radiation, wind speed and vapor pressure) from the adjacent meteorological station. In this open situation, ITS values representing thermal discomfort (>160 W) prevail for nearly all daytime hours. In a paved courtyard with no shading (Exposed-Bare), heat stress is only slightly shorter than this in duration and in fact is more severe at mid-day, reaching a higher peak of about 520 W. The introduction of irrigated ground cover (Exposed-Grass) in place of paving and bare soil reduces the level of thermal stress significantly, such that it is nearly confined to the warm category throughout the mid-day hours. This overall result is mainly due to the lower radiative surface temperature of the grass and reduced emission of long-wave radiation, and only in small part to its lower albedo (moderating reflected short-wave radiation) and evaporative cooling of the air above (slightly increasing convective heat removal). In the cases with overhead shading either by trees or mesh but without grass, the attenuating effect on pedes- trian thermal stress during midday hours is more pro- nounced than that observed with exposed grass. It may also be seen that the vegetative shading treatment (Trees-Bare) results in fewer hours of discomfort than Mesh-Bare, owing largely to the high radiant temperatures (45-50oC) of the mesh s bottom surface relative to the underside of tree canopy, which remained close to the courtyard air temperature of up to about 35oC (see Fig.1). Adding grass under the trees or under the mesh produces a modest further reduction in stress, but a crucial one since these combinations of shading and green ground cover result in a thermal state defined as comfortable during all hours of the day. Once again a small advantage is seen during daytime for the purely vegetative configuration (Trees-Grass) compared with Mesh-Bare, meaning that the fully green space is the one in which the peak pedestrian thermal stress is lowest. It is of interest to note that a substantial reduction of thermal stress was obtained with all landscape treatments in spite of a relatively small reduction in air temperature the shade mesh alone even created a small increase in temperature (Shashua- Bar et al., 2009a) and a significant decrease in wind speed that was created by the trees (and to a lesser extent, by the mesh). This highlights the importance of radiant exchange in thermal comfort in outdoor spaces, especially in hot-dry climates. The daily irrigation of grass and trees (metered separately for grass sprayers and tree drippers, with polyethylene sheeting for mutual isolation between the two types of irrigated soil) was designed to offset as closely as possible the water loss due to evapotranspiration over the same daily period. Fig. 3, which compares the water use for each of the vegetative treatments both in Pilbara Vernacular Handbook / Part 9-402

25 MICROSCALE VEGETATION EFFECTS ON OUTDOOR THERMAL COMFORT IN A HOT-ARID ENVIRONMENT Figure 2. Normalised ITS values during summer daytime hours for non-shaded spaces (left) and for courtyard configurations with overhead shading by either trees or mesh (right), with corresponding levels of thermal sensation terms of the water volume provided and the water volume lost (i.e. ET, measured with lysimeters and sap-flow probes), shows that that a close match between irrigation and actual (non-normalised) ET was in fact achieved for the tree transpiration as well as for the grass, when the grass was shaded by either trees or mesh. Exposed grass was under-irrigated relative to its actual evapotranspiration of about 650 liters per day, through oversight rather than design. This rate was higher than that of any other configuration, including the total ET of trees and shaded grass combined. It is notable that overhead shading lowered the grass ET by about one third to just over 400 liters/day in the case of the mesh, and to just below that figure in the case of trees. The lowest water use is seen for the treatment with drip irrigated trees only, which transpired approximately 200 liters daily. Table 1 gives a summary of the daily water use for each land- scape treatment normalised relative to pan evaporation at the reference site in terms of the equivalent latent heat represented by evapotranspiration from the vegetation. This value (QE, in kwh) is derived as the product of the water volume evaporated and the latent heat of vaporisation. Also in Table 1, the landscape strategies are evaluated in terms of their daily cooling effect (ITS). This calculation is based on the hourly difference between each courtyard s associated ITS value and that of the non-treated base case courtyard (Exposed-Bare), and is computed in kwh as a daytime total (from 6:00 to 18:00). By taking the ratio between the reduction in heat load on a pedestrian (quantified here for one person only) and the water required to provide it (i.e. the latent heat energy of evapotranspiration), a measure of cooling efficiency is generated as a percentage for each landscape treatment, as shown in the last column of Table 1. It is clear from the relative values that the deployment of shade trees achieves by far the highest efficiency of any vegetative treatment with a value that is 2.5 times as high as that of the tree-shaded grass (which in turn is slightly higher that of mesh-shaded grass). While exposed grass does have a significant cooling effect, its high water consumption gives it the lowest efficiency, only half that of the shaded grass. 5. CONCLUSIONS Findings from the controlled experiment, which compares a series of urban-space landscape configurations in terms of pedestrian thermal comfort and cooling efficiency of vegetation, lead to a number of general conclusions: Each of the landscape treatments made a clear contribution to improved comfort, with the greatest reduction in mid-day thermal stress provided by a combination of shade trees and grass. The vegetative treatment achieving the highest cooling efficiency in terms of water usage was the configuration of shade trees alone. The additional cooling provided by irrigated grass was far outweighed by its high water demand, which was much higher still when exposed to the sky rather than shaded by either trees or mesh. Intermediate-level moderations of thermal stress were made by single landscape elements (grass, trees or mesh) used in isolation indicating their usefulness on the one hand, and on the other hand showing the synergetic value of combined strategies in terms of thermal comfort as well as water-use efficiency. Vegetation may make a substantial contribution to human thermal comfort even when its effect on air temperature is negligible. Table 1. Summary of daytime reduction in thermal stress, latent heat of daily water loss and cooling efficiency for each of the landscape treatments Pilbara Vernacular Handbook / Part 9-403