The Architecture of Natural Cooling

Brian Ford, Rosa Schiano-Phan, Juan A. Vallejo

• Editore: Routledge
• Anno: 2019
• ISBN:
  9781351809993
• Edizione: 2
• Argomento: Architecture
• Categoria: Architecture General

Overheating in buildings is commonplace. This book describes how we can keep cool without conventional air-conditioning: improving comfort and productivity while reducing energy costs and carbon emissions. It provides architects, engineers and policy makers with a 'how-to' guide to the application of natural cooling in new and existing buildings. It demonstrates, through reference to numerous examples, that natural cooling is viable in most climates around the world.

This completely revised and expanded second edition includes:

• 
  
  

• An overview of natural cooling past and present.
• Guidance on the principles and strategies that can be adopted.
• A review of the applicability of different strategies.
• Explanation of simplified tools for performance assessment.
• A review of components and controls.
• A detailed evaluation of case studies from the USA, Europe, India and China.

This book is not just for the technical specialist, as it also provides a general grounding in how to avoid or minimise air-conditioning. Importantly, it demonstrates that understanding our environment, rather than fighting it, will help us to live sustainably in our rapidly warming world.

PART 1

Chapter 1

Origins and Opportunities

The natural cooling of buildings developed empirically over many centuries, based on an understanding of seasonal and diurnal changes in the local climate, and through a process of trial and error, to provide relief from the extreme heat of summer. Different techniques developed in response to local conditions, often reflecting a profound understanding of the local environment. Anecdotal evidence of how these buildings worked has been available for many years, but it is only recently that significant research has contributed to a more detailed understanding worldwide. This increased interest in the origins of climate-responsive architecture is reflected in the many journal papers on this tradition, in the annual PLEA Conferences, and in recent books (see Weber & Yannas, 2014; and Hawkes, 2012). This research is not just of academic interest, as the move to a low carbon future is now a major driver among design professionals globally. Many buildings now demonstrate that a ‘climate aware’ approach to design is both practical and cost effective. At the very least it can reduce dependency on mechanical air-conditioning, and in many locations can be completely avoided.

1.1. Origins

The tradition of ‘Natural Cooling’, which incorporates a range of design responses to climate, has its origins in Egypt, where frescoes from the 13th century BC (fig. 01) depict buildings with a ‘malqaf’ (traditional windcatcher) used to help ventilate and cool the interior (figs 02–03) (Fathy, 1986). This approach subsequently spread eastwards as part of the Islamic tradition through the Middle East and Iran to north India (with the Mo-ghul empire), and westwards across North Africa to southern Spain with the Moors.

This tradition, which has been largely overlooked, is characterised by dramatic achievements. Travelling through the Iranian desert on his journey to China in the 13th century AD, Marco Polo commented on his being offered fruit flavoured water-ices to relieve the summer heat. The creation and storage of ice in the desert was made possible at the time through the construction of huge natural refrigerators. These typically consisted of a shallow pool, protected and shaded on its south side by a huge earth brick wall, and connected to a domed ice storage pit (figs 04–05). These shallow pools were provided with water from man-made underground water conduits ‘qanat’ bringing water sometimes hundreds of miles from surrounding mountains to the desert ‘caravanserai’ along the silk-route to China (Beazley & Harverson,1986).

01. Wall painting from the tomb of Nebamun. Egyptian Dynasty 18, about 1475 BC.

02. Traditional windcatcher malqaf, Dubai.

03. Section through the Qã’a of Muhib Ad-Din Ash-Shãf’i Al-Muwaqqi, showing how the malqaf and wind-escape produce internal air movement. All wind and airspeeds are given in metres per second.

Under the clear night sky of the desert, long wave radiation from ground to sky causes surface temperatures to drop low enough to freeze a thin layer of water, introduced to the shallow pool from the qanat. On successive nights the depth of ice built up until it was about 300mm thick. The ice was then cut up and stored below ground level in a massive domed ice house. The temperature of the surrounding walls of the ice pit, although several degrees above freezing, were low enough and sufficiently stable to store the ice for many months. In this way, the extremes of the environment were turned to the advantage of the people living there. This reflects an attitude of respect and symbiosis between people and their environment, working with it rather than against it, to enhance the quality of their lives.

UNDER THE CLEAR NIGHT SKY OF THE DESERT, LONG WAVE RADIATION FROM GROUND TO SKY CAUSES SURFACE TEMPERATURES TO DROP

04. General view of the Ice House in Yazd, Iran.

05. Section and plan of the Ice House in Yazd, Iran.

06. Porous ceramic cooling window in Muscat, Oman.

This understanding is elaborated further in a long tradition in the Middle East of using various techniques to encourage air movement and natural cooling both within and between buildings. Water jars mounted in specially designed window openings in Muscat, Oman (fig. 06), cool the air passing over them into the room by the process of evaporation, at the same time keeping the water at a stable temperature. These windows have a sophisticated design which simultaneously allowed for shading, through the external shading, control of the evaporative cooling effect, through the internal shutters and stack ventilation, through the low and high level openings. In a similar manner, woven ‘khus’ matting suspended over window and door openings are still commonly used in parts of northern India. Khus mats are made from the root of a plant from the Jasmin family, and add a delightful fragrance to the air as it passes into the interior.

Passive cooling and ventilation of buildings in Iran, incorporating wind catchers, porous water pots and ‘salsabil’ (figs 07–08), have been widely applied and very effective for several centuries. In this tradition, wind-catchers guide outside air over water-filled porous pots, inducing evaporation and bringing about a significant drop in temperature before the air enters the interior. Hassan Fathy was also aware of this tradition in Egypt, adapting, developing and re-applying these techniques to cool and ventilate schools and housing projects (Fathy, 1986). In a field study which Fathy describes, on measurements of temperature and air velocity within a house with ‘malqa-fs’, the pattern of airflow and the benefits of enhancing air movement within the building are illustrated.

07. Sloping salsabil in Red Fort, Delhi, India.

08. Salsabil and lotus pool in Red Fort, Delhi, India.

The movement of cool air between adjacent courtyards is remarked upon by Fathy, who refers to the tradition of promoting natural convection between adjacent courtyards having different hygro-thermal properties. This strategy was so effective that a pavilion placed between the two courtyards became a highly desirable location during the heat of the summer day. This space was known as ‘taktabus’ in Arabic and as ‘tablinum’ in the Roman tradition. This natural cooling strategy is embodied in many residences across the southern Mediterranean and north Africa from the 5th century BC to the present day.

In Seville in southern Spain, a sixteenth century house, the Casa de Pilatos, incorporates this strategy within its design (figs 09–10). Seville (latitude 37°N) experiences mild winters and hot dry summers (mean max air temperature of 37°C in July, with relative humidity of 35%). The Casa de Pilatos is a mixture of Italian Renaissance and the Spanish ‘Mudéjar’ tradition (Irwin, 2004). Mudéjar was the term given to the architecture which (after the Moors had been ejected) had inherited Islamic features.

A PAVILION PLACED BETWEEN THE TWO COURTYARDS BECAME A HIGHLY DESIRABLE LOCATION DURING THE HEAT OF THE SUMMER DAY

From the outer court, the visitor passes through a protected arrival gateway into the central formal paved courtyard, around which the building is organised. The whole courtyard is paved, and the visitor naturally keeps to the shade of the cloisters, lined with beautiful tiles ‘azulelos’. Glimpses of green are obtained through grilled openings ‘rejas’ in the narrow rooms surrounding the courtyard, and on entering, the cool of the interior provides relief and where window seats invite a moment of rest to view the adjacent courtyard, full of an almost tropical greenery: palms, citrus trees, flowers and a central fountain (figs 11–12). The seated visitor feels a gentle cooling breeze across face and arms, as air moves from the cool green courtyard to the central paved courtyard. The movement of air and the cooling it induces is not just a happy accident. The building has been designed to exploit this phenomenon.

The central courtyard, being entirely paved, and with no greenery at all, was heating up under the burning sun (the surface temperature of the sunlit paving could reach 50°C+). This caused a plume of warm air to rise from the central courtyard, pulling fresh air from the significantly cooler green co...