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Nowadays, energy consumption and global warming are the biggest challenges face up to the planet. Most of 20th century buildings in hot climate are not suitable even for present conditions. Generally, buildings in these regions cannot adjust to their climate unless by using electricity and mineral fuels to provide indoor thermal comfort for their occupants. The best way to find a solution for this problem is to focus and study on traditional buildings and architecture that is more adaptable to the currently concern and sustainability in environment. Many traditional technologies are energy efficient and sustainable, although some of them are no longer properly functioning because of changed cultural and environmental situations. In this paper tried to introduce and review traditional passive cooling techniques particularly in hot dry climates to find the extent to how traditional passive techniques are viable and useable ,and can help to optimize the energy use.
Keywords: Traditional architecture, Passive cooling, Passive techniques, Hot and arid regions.
Nowadays, energy consumption and global warming are the biggest challenges face up to the planet. In accord to Kyoto protocol signed in December 1997, most of the countries around the world have committed themselves to reducing the emission of the greenhouse gases. Energy is a primary part of every aspect of life in the modern world. Energy efficiency has become a main concern for the most energy policies. Building industry are known as a most significant energy consumer. since Demand for energy is rising rapidly, sustainable design and construction strategies must be apply much more than before. Climate has a major effect on the performance of the building and its energy consumption. The most important function of a building is to provide a comfortable indoor environment. Traditional buildings of previous times had many architectural features for achieving comfort. animals and birds build their shelters naturally and adapt themselves to environmental changes, but man consider various resources to build shelters for protection from heat, cold ,rain and other natural disaster . They are shaped and planned to take maximum advantage of the climate and surroundings. Gradually, as newer materials and techniques of construction developed, traditional built techniques evolved to provide a pleasant balance between buildings, climate and people s lifestyle. Studying traditional techniques to understand the sustainable strategies used in hot climate should make a valuable contribution to the field. In this paper tried to introduce and review traditional passive cooling techniques particularly in hot dry climates. The main objectives are to find the extent to how traditional passive techniques are viable and useable ,and can help to optimize the energy use.
2. Research Methodology
The paper conducted in two main stages:
2.1 Use of secondary data
The first stage consists of a broad review of recent related literature, the definition and selection of prior case studies, design of research instruments and field work. This stage is a mixture of theoretical (literature review) and practical (field-work) activities, that have done by another researchers to investigation and evaluate:
? The principles of passive cooling techniques in traditional architecture.
? The strategies, used in traditional architecture, adapted to the local climate.
? passive-cooling system s designs and elements in traditional architecture in the hot-dry climate particularly in Yazd to achieve how they can be useful and functional.
To achieve the aforesaid objectives, relevant data and information collected from existing book, essay, article, dissertation, exegesis and use of World Wide Web (internet resources) and also discuss and interview to previous researchers and investigators.
2.2 Case study
The second stage accomplished, through direct in-situ observations and impression of a traditional house in the area located in middle of Iran in old an ancient city call Yazd, and also talk to the native occupant in case study area and who has experienced to live in same building as case study also taking photos of building could help to achieve the research aspects. Case-study building chose from a range of traditional passively-cooled and air-conditioned buildings according to criteria such as size, layout, design, ventilation type, current functionality and the physical condition of the building. Traditional house building selected as case study, because house is a primary and most important necessity of the human, and also housing sector as mentioned before is a major part of energy consumer in the world.In the second stage thermal comfort, physical and cultural aspects in Lariha house are assessed to identify how the application of traditional passive techniques to new and existing buildings could improve their performance, cut their energy consumption and running costs and adapt them to climate change, would, it is hoped, break new ground.
3. Energy consumption and issues
Energy demand and cost, green-house gas emissions, air pollution levels and thus heat-related illnesses and mortality rise. Hence there is a need for urgent action, and in such action buildings are the front line of our resistance and must be designed to protect us from the effects of climate change and global warming (Roaf et al, 2004).
The need to minimize operational energy in the running of active systems has focused attention on two sets of factors, the demand side and supply side efficiency. Supply side efficiency comes from the elements of the building that drive the need for power in the building whilst the demand side efficiency is related to elements that use power. The first important way to save energy is to use less of it, so the first goal is to cut demand, and second goal is to supply power in a manner that is benign, using renewable energy sources (solar power, hydro power, wind power and etc) (Hyde, 2000).The successful design of buildings relies on an appropriate understanding of the climate. In hot climates, most of 20th century buildings are not suitable even for present conditions. They are dependent on air-conditioning systems and electricity, reliant on fossil fuels and increasingly unable to adapt to a warming climate. A large proportion of these modern buildings are poorly designed for the prevailing climate, leading to extreme use of electrical equipment and energy to maintain desired indoor conditions. These buildings, without enough insulation, un-shaded, over-glazed and tight-skinned and with inefficient air conditioning, are using vast amounts of energy to provide thermal comfort, especially when the weather conditions are harsh and extreme.
4.The principles of traditional passive solar design
4.1Climate and its impacts
Since human activities do not generally occur under natural conditions, the problem of creating a comfortable interior environment with the point of meeting needs is as old as the human history. One of the main principles of architecture is to establish artificial environments that provide comfortable spaces for human life. A building, which is the produce of architecture, is a physical environment that is created in line with these requirements. Therefore, one of the expected functions of a building is to provide an interior environment that is controlled in terms of climatic comfort. Effects of climate conditions on a building are certainly one of the most important natural factors that shape architectural studies.A number of passive solar methods were approved in traditional architecture in a range of climatic zones since, control of the microclimate around the building was all the time a vital design consideration while planning a town, care was taken to orient the streets keeping the effects of sun and wind in mind.
4.2 Passive solar design
With mass production of air-conditioners it has allowed houses to be kept unnaturally cool as long as occupants were willing to pay the electricity bills. It relies upon the design or architecture of the building itself to ensure climate control by way of natural thermal conduction, convection and radiation. The rudiments of solar passive design were developed and used through the centuries by many civilizations across the globe; in fact, many of these early civilizations built dwellings that were better suited to their climatic surroundings than those built today in most developed and developing countries. Traditional buildings in the desert are prepared with thick high walls, wind catchers, courtyards, ponds, rich gardens and domed rooms, according to principles developed over many generations. These principles consist of physical performance, aesthetic, low-energy use, comfort, durability and in general seen to be well modified to local climate conditions and are frequently considered a proper base for environmental design. Although its importance, traditional architecture and its techniques and strategies, are failed to realize and unused in new constructions. In particular, the use of traditional passive design strategies aims at minimizing operational energy demand in buildings and therefore optimizing demand side efficiency whilst the use of low-energy technologies aims at optimizing the increased use of renewable energies in the energy supply, thus reducing the circumstances for enhanced greenhouse gas emissions and resource depletion (Hyde, 2000). Traditional passive cooling systems use simple, low-cost techniques to provide summer comfort in warm climates for people and animals in buildings. Such systems can also be used to keep food, liquids, and other materials at temperatures that will prevent spoiling or other deterioration.
4.3 Passive concepts
However comfortable indoor environment cannot achieve in intense climatic conditions by traditional passive design and techniques only, but by applying these certain tested and established concepts to a design in such climatic conditions, are able to largely satisfy the thermal comfort criteria. By employing passive cooling techniques in existing or new modern buildings however, it can often eliminate the need for mechanical cooling or at least significantly reduce the size and cost of the equipment. Generally, traditional passive solar cooling consist of two basic concepts that are composed of some subsequence features in table 1 and also some objectives of heat gain control and the rejection of unwanted heat are accomplished by the different principles in table 2 (Halacy, 1986).
Nowadays, with high energy costs and increasing environmental concerns, many of these simpler techniques are once again becoming attractive. The applicability of each system depends on the climatic conditions. Some of the most common traditional passive cooling components applied in hot-dry climate are as follow:
? Passive downdraught cooling
? Earth cooling tubes
? Earth-sheltered buildings
? Evaporative cooling
? Wind tower
? Water reservoir
? Qanat, Aqueduct or Kareez
? Ice builder/Ice house
5. Lariha house as a case study
5.1 The urban structure of Yazd
Yazd province is located in the central part of Iran, The neighboring deserts, as well as a scanty rainfall give the province a dry climate. In the course of history due to its distance from important capitals and its harsh natural surrounding, Yazd remained immune to major troops' movements and destruction from wars, therefore it kept many of its traditions, city forms and architecture until recent times. The urban form of traditional city of Yazd is the extremely centralized or innermost looking (Fig. 1). Definitely, the orientation and relation to the environment has been of high importance in the planning of city. The high radiation and temperature in the summer, seasonal differences from dry, hot summer to cold, dry winter, low humidity, daily variation of temperature, limited water supplies and the dusty winds are the most important features in forming the urban structure of Yazd. Concentrated urban texture reduces penetration of dusty wind into complex as far as heat influence on the building surfaces. Covered passageways and narrow alleys with long walls in clay make the shade and thermal comfort conditions in the hot summers. Furthermore, their direction is in a way to avoid hot summer sun rays and stormy winds. The organic network of ways (passage, alley) has been prepared in accord to ground slope and the underground water canals.
Lariha house was chosen for the reason that most of the Persian architecture elements are collected and applied in this house and also is a big sample scale of the common yazdi houses.
Khan-e Lari, or Lariha House, is one of the historical houses of the Qajar era. It is located in the heart of the historical part of the Fahadan district in central of the old city of yazd some 130 years ago (1878)(Fig. 2 and 3).
The area of the land is about 1700 Sqm, and the built area is about 1200 sqm. Like most historical houses in Yazd, it has a central courtyard. Typically, there are rooms with 3 doors (Sedari) and rooms with 5 doors (Panjdari), a central hall with a wind tower, a kitchen and a cellar. In addition, there are decorative areas consisting of a mirror room and stalactite work.
Orientation of the land and building as referred, is an important factor, actually the best orientation in this climate condition is the south-north direct because of the sun radiation and also wind flow that explained in previous chapter. Moreover Specific orientation facing toward and away from Mecca that is south-west in Iran.
House has tree entrance doors, the first one opens to the private place and provides easy access for the residents without going across the yard and public area to go out and come in the house. The second or middle door plays the role as a main iterance, that provide accessing to the courtyard through (Hashti and Dalan-e-vorudi ) the doorway one steps into a small enclosed transitional space called Hashti. Here one is forced to redirect one s steps away from the street and into the hallway, called Dalan e Vorudi. and can use for both parts of the house without making any problem for residents of the house and finally third door that is located in the southern side that usually used for guests and strangers who stays temporary in the house. The majority of the building space is fit in to the first part (Andarooni) that is include courtyard in the middle and the luxury rooms and places around it according to four seasons of the year.
5.6 Privacy in house
Privacy as an important principle which affects all the sides of the human life has formed beautifully in traditional architecture in Iran and also Lariha house, privacy had considerable affects on the spatial character and the way of formation of the various functions beside each others.In fact religion and culture, cause come and go in Iranian house, and for religion reason, house hold female shod secure from eyes of strange men who are guests build up private and guests parts in a house which mentioned, interior (andarooni) and exterior(birooni).And also religion affect on design of door knocks, that it is different for male and female, to make different sound and household can understand sex(Fig. 4).
5.7 Seasonal Usage
It should be said that there is a yearly space in this house, the north part that is called winter portion and the south is summer portion. The residents of the house move to northern part in winter and consequently to the southern part in summer to adapt themselves to regional conditions. The height of summer portion is more in the house thus, the hot weather as ends up and the cooler one replace it in the lower surfaces. For better air ventilation, wind-catcher is located in the southern part of the building of Lariha house. The cellar (sardab) and storage areas of the house are located underground and are all connected via stairways to the courtyard s floor or the corridors leading to them. The underground floor area is almost the same as building area to keep and reserve the food and the stock instrument to keep cool and fresh and also keep out from solar and sun. The eastern side that consist of mirror rooms ,kitchen and another rooms uses in autumn and at the end they used the rooms in the west side in spring as a proper and pleasant place that called Bahar Khaab to sleep and get relax. In Lariha house like most of the houses of hot-arid regions of Iran, wind catcher has a direct connection to parch and this space is used for diversity of functions from morning to noon and inhabitants use the underground in the afternoon and roofs at night, which have colder weather, for sleeping.
Walls Being considered as an important element in regional house of hot and dry climate and a major part of the building envelope that receive large amounts of solar radiation. The heat storage capacity and heat conduction property of walls are key to meeting desired thermal comfort conditions. The huge walls in the house have approximately thickness of about 70 cm and built by sun-dried clay brick, mud brick, natural stones and lime, mud brick that are common traditional materials in Iran, especially in desert part(Fig. 5). These materials have thermal resistance, high heat capacity and they absorb the sun radiation by their external surfaces, preventing it from affecting the inside of the building and during the night, in presence of a clear sky, and the building is opened to the cool night-air for the refreshment of walls and roof.
As mention before the walls are thick to do the thermal insulation during the hot days, these thickness walls are also tall and high (about 4.5 m) and hold a thick and flat roof. Same as another houses in Yazd the roofs in Lariha house are flat and paved whit square shapes bricks called paved bricks. This bricks received the most radiations of sun, early in the morning it starts to increase and late in afternoon it decrease gradually. This function causes the change in sun radiation intensity and radiation angle. The roofs are high and cause to let the air movement and natural ventilation come through the rooms to make the indoor conditions more pleasant for their occupants.
According to the plan all the rooms are connected to each others to first, occupants could easily shift through the house under the roof without need to go out side and use courtyard, although courtyard is wooded with leafy trees that prepare a hearty shading inside it, and secondly to achieve a sufficient ventilation throughout the rooms whit prepare an adequate way for wind to be circulate in the house.
Although external walls do not have any windows, there are so many of them on the yard facing internal walls . Passing ventilation is done by these windows in Lariha house , the size and amount of the windows in side the house that open to the courtyard tried to be maximum, cause air flow come through the courtyard to get cool from the water pond and shading of the vegetations in the yard come into the interior space(Fig. 6).
In desert regions the rate of planting depends on water amount and way of accessing to it although nowadays because of the drought, it is difficult and hard to plant and irrigate, but in the past, when this house has built ,condition of planting and drenching was different and in existing courtyard refer to the past studies, there was a full density of trees and vegetations. In Lariha house the herbal space in the courtyard has lots of effects on the surrounding rooms ,it cause to decrease of direct radiation of sunbeams and yard space and also they prepared sufficient shading on the water pool and courtyard space in reason to create a cool place inside the house during the whole of the day. Furthermore these proper planting causes to reduce the amount of dusting that come into the house during windy times and also cause to prevent of undesirable wind speed(Fig. 7). In addition, planting and vegetation increase the humidity and also decrease of temperature in the yard that is a great solution for arid region such as Yazd.
5.13 wind catcher
Typical wind catchers consist of a tower and a head projecting above the roof of the building, there is a tall wind catcher (11 m) in Lariha house which is visible from within the courtyard (Fig. 8). Unusually, this wind catcher is located at a corner of veranda (southwest of the building) rather than the main axis of the courtyard. Wind catchers are often called by direction, such as north-south towers. The desired wind currents in Yazd blow from the east-west. The long sides of wind catchers are, therefore, oriented towards the east-west for maximum usage of the wind to provide cooling for building (Zomorshidy, 1999).The wind catcher in Lariha house is combination of inlet and outlet openings. The tunnel provides cool air for the building while serving as a conduit through which the stuffiness within the building is conveyed through its shaft. This wind catcher is directly connected to the living hall and the biggest room(shah neshin) and also cause connection and opening elements between the whole of the rooms in the building, wind come in from wind catcher, going and circulate into the entire of the building. The tower is divided by two partitions. One of the shafts operates all the time to receive the breeze and the other shaft works as outlet air passage. They convey the stuffiness out of the living space through the flue (chimney) effect. The chimney effect is based on the principle that the air density increases with the increase in temperature. The difference in temperature between the interior and exterior parts of a building and between different regions creates different pressures and result in air currents.
As referred, using the natural air pressure differential between two different elevations by creating towers is called the stack or chimney effect. This causes automatic air movement up and through the chimney which creates a natural air flow. The wind catcher in Lariha house operates as a ventilation-inducing device as a result of the combination of some types of physical mechanisms that brought in table 3 (Allard, 1998).
5.13.1 Material and Texture of Wind catcher
The construction materials used for wind tower in Lariha house based on climate. The choice of materials is made to ensure that the wind tower operates effectively as a passive cooling system. This wind catcher is built of mud brick covered with mud plaster. Mud brick (adobe) passes heat at long time, because soil has got uncompressed volume and mud makes from water and soil.After evaporating, there is made empty pit. It causes that heat and cool can not arrive in molecules of soil and mud brick or adobe into the tower. Mud plaster (kah_gel) is mixture of wet earth with chopped coarse straw. These construction materials have gave the wind tower a coarse texture. The mud plaster covering the facade of a wind tower has a light color and there for reflects rays well(Don, 2010).
5.14 Courtyard (Hayat-e-Markazi)
Publicly, it is a classical Persian layout with heavy emphasis on aesthetics and function. as mentioned, there are two central courtyards in this house. One is private quarters where private members of family such as wives, daughters and kinsfolk people live and the other is an external one where a private people commute. the yard in Lariha house is rectangular and its longitudinal axis lies in an approximately northeast-southwest direction. It is pool-centred and the pool serves as a focus and source of humidity for the surrounding atmosphere.
5.14.1 Elements of Courtyard
Sunlight and its effects were an important factor of structural design in the courtyard. In this yard textures and shapes were specifically chosen by architect to harness the light. Due to the dry heat of Yazd, shade is also very important and without which it could not be usable. According to the principle of the traditional Iranian garden there is a small garden in the middle of the courtyard and trees and trellises which planted in this gardens largely prepare a biotic shade; pavilions and high walls are also structurally prominent in blocking the sun inside the courtyard . Orange trees are the most popular vegetation in the desert Persian courtyard houses, because of it is adapt to dry climate and shortage of water consequently majority of trees are orange in the garden. Light also is so important factor in Lariha house, courtyard reduce glare and sun radiation, and use colorful glass ,stain glass, to make light as a beautiful and useful factor in the house as a desirable element. In the courtyard of Lariha house, pond (howz) is a centrally positioned. The pond is an essential element of the courtyard in traditional Iranian architecture. The water pool takes up a large amount of heat in evaporation and causes significant cooling during the hot days. As a result, during day time area around the water pond are generally cooler than the other place. As referred by having a cover full of plants and trees and naturally evapo ration and sudation the courtyard are acting as a cool and fresh air generator for the yard and surrounding spaces. The floor of the yard is paved with square bricks called paved bricks, which water and broom were used to clean them and it caused the yard space to become cool. As the thermal capacity of air is very low, the temperature of the courtyard air follows very closely to the temperature of the surrounding surface at night, the mass of the walls and floor of the courtyard is cooled by outgoing long wave radiation, and therefore, the surface of the courtyard floor and walls will remain cool by the following morning. In this way, the mass of the walls and floor of the courtyard (and not the air deposited in the courtyard) serves as a reservoir of coolness, even if it is not too large and well shaded. For this reason one may feel cool in two ways, firstly, the courtyard air is cooled in contact with the surrounding surfaces, and secondly, by losing heat through the surrounding surfaces by radiation which is known as radiant cooling. The courtyard in the house also in fluenced the performance of the wind catcher, because air for the wind catcher is drawn from two areas, from the roof and from the courtyard. At the end, it is the place to say, even without modern, mechanical heating or cooling systems and without need to consume fossil energy, Lariha house pro vides a comfortable living environment through sea sonal usage of sections of the structure(Fig. 9).
In an overview, the compact form of city, passive techniques such as, wind catchers, courtyards, orientation of buildings to sun and wind, arrangement of the summer and winter spaces, using local materials and clean energies as the environmental potentials, the narrow and covered passageways, the underground spaces, deep courtyards, thick walls, using the water and plants, reusing the materials are some considerable solutions in old urban and traditional architectural design of hot and arid regions for having the green city even in the actual theme. The principles of passive architecture techniques gathered from traditional architecture demonstrated that ancient cities can be appearance of a culture of sustainability, passing on the baton of urban superintendence from generation to generation in a friendship relation with the nature and energy resources. The main target of this research was to analyze traditional architecture and to recover the bioclimatic design concepts and passive cooling system, which should be used in modern architecture, taking into account the environment and local traditions. Hope this research helps to reduce emissions from burning fossils fuel and participate in making our world cleaner, hence improve the environmental preservations for us and future generations.