DEVELOPMENT OF A SUSTAINABLE COOLING AND VENTILATION SYSTEM FOR HOT-ARID CLIMATE REGIONS

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1 DEVELOPMENT OF A SUSTAINABLE COOLING AND VENTILATION SYSTEM FOR HOT-ARID CLIMATE REGIONS Nasim Karizi Arizona State University Herberger Institute for Design and the Arts Tempe, AZ nkarizi@asu.edu Prof. Rudolf Wienands Technical University of Munich Architecture Department Arcisstrasse Munich abstract It is fascinating, how the architects of the past learned to decrease the impact of extreme climatic conditions from arid to cold climate zones by applying simple, but very intelligent building elements. These elements are what lead to the development of sustainable and energy efficient architecture. The architecture in hot-arid climate regions all over the world has many distinguishable elements in common that provide a higher level of thermal comfort in the living environment. Unfortunately, there seems to be common mistakes made in the design by application of inappropriate building techniques that does not take the climate condition aspects into account. This has led to extremely high energy consumption of the buildings. This paper presents the traditional natural cooling and ventilation building elements in hot-arid climate zone in central Iran and their enormous impact on indoor environment of the buildings. In addition, it demonstrates the design of a school building as a part of the thesis that is based on these traditional technologies and operates with minimal energy consumption. The application of moderated elements in the building saved up to 85% of the cooling energy during the summer season. The collected data confirm that traditional passive techniques deserve further investigation into gaining a higher level of understanding and should be utilized in more architecture of today and the future. 1. introduction To decrease the impact of extreme climatic conditions from arid to cold climate zones, the architects of the past learned to apply simple, but very intelligent building elements. These elements are what lead to the development of sustainable and energy efficient architecture. The architecture in hot-arid climate regions all over the world has many distinguishable elements in common that provide a higher level of thermal comfort in the living environment. Unfortunately, there seems to be common mistakes made in the design by application of inappropriate building techniques that does not take the climate condition aspects into account. This has led to extremely high energy consumption of the buildings. In this paper, it is emphasized, that traditional passive techniques deserve further investigation into gaining a higher level of understanding and should be utilized in more architecture of today and the future. Fig. 1: Historical alleys in Yazd, Central Iran. 1

2 2. traditional architecture in central iran As an example of hot-arid climate, city Yazd in Central Iran is one of the best cases to investigate the traditional building principles in these climate regions. Yazd is one of the most historical cities in Iran and is the best place to find the traditional building elements. 2.1 Hot -Arid Climate in Central Iran Climates regions in Iran can mainly be divided into four regions: Mild and Humid, Cold, Hot and Humid, Hot and Arid. The Hot-Humid and Hot- Arid regions of Iran have a hot long summer including dramatic changes in temperature between day and night. Without an effective cooling process inside houses and closed buildings, uncomfortable temperatures would be annoying for the inhabitant. Figure 2 shows the hot-arid climate zones in Iran and the location of Yazd, (1). Yearly outside temperature and relative humidity values in Yazd are shown in figures 3 and comfort zones for natural ventilation based on temperature and humidity are shown in figure 4. The white part in the graph indicates to the comfort zone that could be achieved through natural ventilation and adiabatic cooling/heating. 2.2 Traditional Building Principles in Yazd To moderate the extreme climate conditions in Yazd, some simple but very intelligent solutions are applied in architecture, landscape architecture and building services. Such solutions consist of building principles and elements, Important cities Hot and arid zone Fig. 2: Hot and arid climate zone in central Iran. which cooperate perfectly together and constitute the best appropriate natural cooling and ventilation systems for this kind of climate. Some of these principles and elements are: high density in city planning, narrow alleys, special building materials like adobe, atrium principle, summer and winter residence in a house, dome shaped roofs, walls with two layers, wind catchers and wind canals, openings, water basins and water fountains, plants in courtyard, daylighting, basement principle, (2), (3), (4) and (5) Outside daily average temperature [ C] Relative Humidity [%], ( the top line) A ußentemperatur (Tagesdurchschnittstemperatur) [ C ] R elative Luftfeuchtigkeit [% ] [ C ] HOT TEMPERATE COLD FREEZING Yazd, Ta Yazd, RH Fig. 3: Outside temperature and relative humidity diagram in Yazd based on Meteonorm. [% ] RH [%] RH [%] FREEZING COLD adiabat. adiabatic adiabat. Erwärmung heating Erwärmung dry dry TEMPERATE 4,5g/m³ 4,5g/m³ Trockenerwärmungskurve Trockenerwärmungskurve comfort comfort Natural ventilation Erwärmung Erwärmung Mechanical heating + zusätzliche Befeuchtung + zusätzliche and humidification Befeuchtung HOT HOT Luftkühlung nur Luftkühlung mit Mechanical technischen nur cooling Mitteln mit (Luftentfeuchtung) and technischen humidification Mitteln (Luftentfeuchtung) humid humid 14g/m³ 14g/m³ Trockenkühlungskurve Trockenkühlungskurve adiabatic adiabat. adiabat. Kühlung cooling Kühlung Temperature [ C] o C Temperatur [ C] Fig. 4: Comfort zone diagram according to outside temperature and relative humidity values in Yazd. 2

3 2.3 Natural Cooling and Ventilation Systems Figures 5 and 6 illustrate the cooperation and the function of natural cooling and ventilation elements in a traditional house in Yazd. The hot and arid air is caught by the high adobe wind catcher and is led into the house. On its way through the long adobe chimney and with the help of evaporation principle, the air becomes moist and cool. Through the adobe wind canals inside the house, a part of the air is led into the basement and the other part into the summer residence and courtyard. The first part passes through the basement s adobe wind canals under the courtyard and absorbs moisture from the canal walls. Accordingly, it blows to the courtyard through the small openings on the surface. The whole evaporation and air circulation processes cause a more comfortable climate inside the building and also in the courtyard. The trees in the yard are also elements of the natural cooling system. They provide a better air quality and more shadow in courtyard. Furthermore, their roots keep the basement s wind canals moist. This fact increases the evaporation process on the air flow in the basement, (2), (3) and (4). Fig. 5: Operation of two different type of wind catchers. Wind catcher pulls the hotarid air inside the house The exhaust indoor air gets to the courtyard and goes up and causes more air circulation in the house. A part of the air from the wind catcher blows into the courtyard and by passing over the water basin gets moist and cooler The cool air layer in the lower layer of the courtyard beneath the trees and over the water basin. The adobe walls of basement canals are the real cooling machines. Through the plant-roots, they stay permanently moist and so increase the evaporation process on the air flow. Fig. 6: Function of different natural cooling and ventilation elements in a traditional house. 3

4 3. Application of the principles on a building design The goal of the research was to design a sustainable new building in Yazd that operates with the minimal energy consumption and is based on the traditional building technologies of these regions. Based on this fact, a school building on the North-West part of the city is planned. There is an exhausted air duct in each class room, which drains off the extracted air. In order to avoid the exhausted air into the supply air ducts the exhausted air canals are not as high as supply air canals. The wind caps on the top of the exhausted air canals rotate in the opposite of wind direction to increase the negative pressure (succession) and produce a faster conduction of exhausted air. 3.1 Modified Natural Cooling and Ventilation System The building is designed to be an elementary school (1 students capacity with 24 classrooms) but the ventilation system is designed to be applicable for different type of buildings in the same climate zone. As shown in figures 7 to 11, the school building has 4 supply air- and 12 exhaust air ducts. There are special wind rotation caps on the top of these ducts (wind catchers), which are equipped with wind lead sheets to rotate in direction (or by the exhausted air ducts in the opposite direction of) the wind. The hot outside air is caught more effectively through these caps and led to the basement. The wind catchers and basement-canals consist of adobe material and functioning based on the absorbing and releasing the humidity. In order to increase the absorption of humidity, the supply air wind catchers are divided into smaller canals, (figure 12). By dint of evaporation, the hot air gets cool and moist. The cooling effect is more efficient by spraying the adobe walls with water and keep them extra moist most of the time, (figure 13). Fig. 7: Roof view Fig. 8: Air movement in basement s wind canals during summer. In the second step, the air flows through the underground canals around the courtyard. Because of irrigating the plants in the courtyard, the yard ground and therefore the underground canals are moist. In this way, the air gets another evaporation opportunity. Finally, the air arrives in the divider terminal room and is sent to the three building stories, (figures 8 and 9). Fig. 9: Air ducts plan, spreading the supply air into the classrooms. Fig. : Wind circulation through the building is an important principle of natural cooling. 4

5 Wind catchers Main supply air ducts to the first and second floors Underground air canals Supply air openings to the classrooms Technical plant room Fig. 11: Wind catchers, wind canals and air ducts in the building in one view. Fig. 12: Details of the modified wind catchers. Water sprayer Adobe walls Rough textured sponge Porous stones Fig. 13: Simple humidifier systems to be installed in wind catchers to increase the evaporation process. 3.2 Energy Efficiency of the System As shown in figure 3, based on yearly temperature and relative humidity values in Yazd, in July, the maximal temperature value during the day is about 38oC with 12% to 26% relative humidity which is beyond the comfort zone and in hot area of diagram 3. In this case, there is a big opportunity to cool down the air through evaporation process and provide a more comfortable indoor temperature. In the transition period (April and October) the temperature and relative humidity are in comfort zone. That means there is no need for cooling. At the end of October, the relative humidity declines to 12%, so the need for moisturizing rises. Figure 13 illustrates very simple but effective moisturizing systems to install inside the wind catcher in order to increase the evaporation process and also moisturize the arid air in winter period. In this design, a very fine water sprayer is installed inside the wind catcher, (figure 12). 5

6 Outside temperature Air temperature in summer Soil temperature in summer 18oC Soil temperature in winter oc Air temperature in winter Length of the canal Fig. 15: Soil temperature diagram for Yazd. (6) In the second step of natural cooling process, the air flows through the adobe wind canals in the basement around the courtyard. Based on the soil temperatures in Yazd, which are between 16o C and 24oC in summer, the air gets cooler after it flows through the underground canals. Depending on the length and depth of these canals, the air temperature approaches the soil temperature. Diagram 15 presents the connection between the length of the canals and soil temperature in summer as well as in winter period, (6). Fig. 14: Molier-h-x diagram for Yazd in hottest and driest day during summer. T= oc RH= % Outdoor temperature Exhaust air T= 23oC RH= 50% T= 18oC Soil temperature T= 26oC RH= 50% Wind canals in the basement Fig. 16: Temperature course diagram in the natural cooling system in a hot summer day. T= 23oC RH= 50% Supply air temperature 6

7 4. conclusions The goal of the research was to design a sustainable building in Yazd that operates with the minimal energy consumption and is based on the traditional building technologies of these regions. In order to achieve this, a school building on the North-West part of the city is planned. Furthermore, the investigated cooling and ventilation elements were modified and applied to the school building. Based on some experiment results by implementation of the proposed system on an existing wind catchers in one of the historical houses in Yazd, a temperature decrease of 15 o C is achieved. In summer when the air achieves the underground canals, only through the first part of the cooling system (wind catcher) a temperature drop of 14 o C to 15 o C is obtained. After the air passes through the underground canals (second part of the system), which are about 25 m long and 7m deep around the building, its temperature drops 3 o C additionally. These results indicate that through the proposed cooling and ventilation system, in extreme hot and arid days ( o C and 12% relative humidity) the air could be cooled down up to 23 o C ( 50% relative humidity). Due to this fact and based on the weather data in Yazd during the summer season, 85% of the required mechanical cooling energy could be saved. 5. References (1) Iran climatic provinces, Projection, Cartography, Lithography and printing by: Geographc &Drafting Institute, No. Tehran/ Iran. (2) Hamid Bagheri, Wohnungsbau in Heiß-Trockenen Gebieten des Iran, Am Beispiel der Stadt Yazd, Faculty of Architecture and Urban Planning, University of Stuttgart, (3) Ali Ghafar-Sedeh, Grundlagen und Gestaltungsprinzipien der traditionellen Städte Zentral Irans, Urban Planning Institute, University of Stuttgart, (4) Hassan Fathy, Natural Energy and Vernacular Architecture, The University of Chicago Press, Chicago and London (5) Kambiz Haji Ghasemi, Ganjnameh, Yazd Houses, Faculty of Architecture and Urban Planning, Shahid Beheshti University, Iran, 04. (6) Dirk U. Hinrichs and Klaus Daniels, Plusminus o / o Latitude, Sustainable building design in tropical and subtropical regions, SCHÜCO, Bielefeld, 07. 7