Faculty of Architecture and Planning Thammasat University AR/IA 241 LN 231 Lecture 7: Site Planning Author: Asst. Prof. Chalermwat Tantasavasdi 1. Effects of Microclimate As we all know, there are four major climatic zones according to the world s climatic categorization cold, temperate, hot-humid, and hot-dry. They can further be divided into 11 subclimatic zones. These climatic and sub-climatic zones possess distinct differences in environmental parameters, consequently resulting in different approaches of built environments. However, local settings known as microclimates could share some impact, or even alter environmental parameters. Microclimate includes humidity and cloud conditions, land forms, water bodies, vegetation, and urban conditions. Humidity and cloud conditions Local humidity level and cloud affect the nocturnal radiative cooling. Therefore, they have influence on the air temperature. 1
Land forms Altitude affects a number of parameters: Air temperature decreases at a rate of 1 º C per 100 m increase in altitude. Solar radiation level: in northern hemisphere, a south-facing slope would be warmer than a north-facing slope. Local wind directions: cool air is denser than warm air. At night, the radiative loss cools the ground surfaces. Cool air then flows toward the lowest points, e.g. valleys. The flow reverses during the day when the ground surfaces warm up. Humidity level on the windward side is generally higher than the leeward side. Water bodies On/offshore breeze: water has a higher specific heat than the land. Therefore, large water bodies, e.g. seas, rivers, lakes, and large ponds have more stable temperatures than adjacent lands. During the day, warmer air on the land surfaces rises, drawing cooler air from water, and creates onshore breeze. At night, the flow reverses. The land surfaces cool off because of the nocturnal radiative loss, creating offshore breeze. Air temperature decreases, while the humidity increases when an air mass flows through a water body because of the evaporation. 2
Vegetation Air temperature and humidity are influenced by plants natural photosynthesis process, similarly to the effect of water bodies. Plants also provide shade to the ground that further reduces air temperature. Wind direction and speed could be altered by plants. Vegetation can act as a windbreak to block the wind or wind channel to enhance the wind speed. Urban conditions Densely built areas create urban heat island that has many impacts. Air temperatures in urban areas are generally higher than rural environments. Man-made surfaces reflect more solar radiation during the day and release heat at night. The effect is worsen by the lack of evaporation due to the reduced plant cover. Humidity near the ground level in urban areas is lower than the rural areas. However, at higher altitudes above the city, more clouds are expected because of the urban heat island effect. Wind speeds within a city are generally lower than the rural areas due to the friction created by buildings. 2. Site Planning Process Site planning represents one of the first processes in built environmental design. It is the process that can save a large amount of energy and other natural resources, and reduce impacts on natural environments. Understanding the effects of climate and microclimate would help the designers in properly planning the built environments and making full use of natural advantages. In general, the process includes the followings. 3
Site analysis in terms of effects of climate and microclimate that involve the sun path, local wind direction, topography, effects from neighboring buildings, and existing natural elements i.e. water bodies and vegetation. Building and open space location selection and landscape design in relation to the site and advantage that can be taken from the prior procedure. Building shape, form, and orientation selection that are proper to the site and its natural forces. Space planning that includes orientation and location of the space, location and types of openings, and furniture. 3. Site Planning Strategies for Hot-Humid Climates In hot-humid climates, the design objectives should involve improving thermal comfort for occupants and reducing energy consumption for cooling of buildings. A number of site planning strategies for such climates in the northern hemisphere such as Thailand include creating cool microclimate, minimizing solar heat gain of buildings, and promoting natural ventilation. Creating cool microclimate Locating buildings on the south and west part of the site to create building shade for open spaces. Providing areas on the north and east of buildings for outdoor activities to maximize the benefit from building shade. Keeping and creating plants, especially plants with large canopy. Keeping and adding water elements on the windward side of the site, especially for airconditioned buildings. Using natural ground covers instead of hard-surface paving materials. Minimizing solar heat gain of buildings Selecting long building shape where most of the facades are facing north and south for naturally ventilated buildings. Selecting compact shape for air-conditioned buildings. Providing external shading to all openings that may include using parts of a building to shade other parts of the building, placing large-canopied plants closed to the building, and creating sun-shading elements. Placing main functions on the north and south sides of the buildings to avoid solar penetration. Minimizing opening on east and west while placing service areas on these sides to create solar buffer zones. Promoting natural ventilation Using plants and landforms to channel prevailing wind into the buildings. Locating buildings as far apart as possible. Selecting elongated building forms with maximum openings. 4
Placing main functions on the windward sides of the buildings. Providing semi-outdoor spaces as integral parts of living spaces. 4. Space Planning Considerations for a Single-family House A single-family house represents one of the simplest typical buildings that require response to the climate. Space planning for such building, therefore, needs to give attention climatic factors including prevailing wind and sun path. Functionally, space in this small residential building can be categorized into four types: Public space: living space Eating & cooking space: dining space, pantry, kitchen Sleeping space: bedroom Space for hygiene: restroom, bathroom, laundry Climatically, design considerations for each of the aforementioned function includes the followings: Orientation and location of the space Location and type of openings Furniture Space Living Space Dining Space Pantry & Western Style Kitchen Thai Kitchen Bedroom Bathroom Laundry Orientation & Location windward side, avoid morning & afternoon sun need ventilation, avoid afternoon sun need ventilation, need leeward side, need windward side, avoid afternoon sun leeward side, need leeward side, need Design Considerations Openings Furniture large openings, avoid E sofas receives & W ventilation medium openings, dining set receives avoid W ventilation medium openings esp. stove on leeward side at sink as open as possible stove on leeward side medium openings but bed receives ventilation avoid openings at the but avoid head of bed, avoid W medium openings receive ventilation & morning as open as possible receive ventilation & The table above presents only guidelines for typical buildings. Design for actual buildings require further analysis and considerations in terms of human s environmental needs that specifically occur on each site. These include thermal comfort, air quality & hygiene, and visual & acoustic comfort. 5
Thermal comfort consideration could still be divided into physical and psychological aspects. Users behavior, microclimate, and mode of building operation (air-conditioned, naturally ventilated, or hybrid systems) represent considerations on the physical side. Volume of space, color, texture, and contrast are the examples of the psychological side. Air quality & hygiene, and visual & acoustic comfort are other major areas but are not further discussed here. Bibliography Daniels, K. (1997). The technology of ecological building: Basic principles and measures, examples and ideas. Boston: Birkhauser. Givoni, B. (1998). Climate considerations in building and urban design. New York: Van Nostrand Reinhold. Moore, F. (1993). Environmental control systems: Heating cooling lighting. Singapore: McGraw- Hill. Ruano, M. (1999). Ecourbanism: Sustainable human settlements: 60 case studies. Barcelona, Spain: Editorial Gustavo Gili, SA. Yeang, K. (1999). The green skyscraper: The basis for designing sustainable intensive buildings. New York: Prestel Verlag. 6