The History Of Natural Ventilation Environmental Sciences Essay
‘’ we need a system that allows the traditional way of cooperation to work in our society. We must subject technology and science to the economy of the poor and penniless. We must add the aesthetic factor because the cheaper we build the more beauty we should add to respect man’’
One of the current debates in architecture concerns sustainability and environmental design. The sustainability of the built environment aims to conduct human activities in a way that will preserve natural resources for future generation. Environmental sustainability emphasizes reduction the waste of energy in the environment, reducing the production of agents that harms human health, and using renewable resources. Meanwhile sustainability in architectural fields should encourage using minimum energy resources, using renewable materials, preserving existing buildings, and reusing energy without producing pollution. Among all fossil energy consumers, the building industry can be considered as one of the main energy users (Edwards, 1995). Construction uses almost 40% of the world’s energy and is responsible for almost 70% of emitted sulphur oxides and 50% of emitted CO2 (UNCHS, 1993). The amount of energy which has been consumed by the building industry is emitted in any of four stages: firstly, during the process of preparing the materials; secondly, transporting the material, thirdly, building and erecting the buildings and finally the amount of energy required for running and maintaining buildings during their life time. In parallel as a result of increasing family income and population in developed countries, the use of air conditioning systems has also increased which increases the amount of energy being used during the life time of a building (Asimakopoulos and Santamouris, 2005). It is estimated that the volume of air conditioned buildings in Europe will increase four times by the year 2010 compared to 2005 (Asimakopoulos and Santamouris, 2005).
We often underestimate the enormous influence of the introduction of mechanical air-conditioning and heating systems on the evolution of architecture. Such systems have served the relationship between the building and its natural climatic environment. According to green building website both designers and clients have become less concerned about how their buildings relate to factors such as the movement of the sun, direction of the wind and changes in outside temperatures. Mechanical systems, which depend on consume energy, allow for full control of climatic conditions within the building and, therefore, a decision as to whether or not to wrap a building with a curtain -wall glass facade, for example, is unfortunately now most often based on factors unconnected with climatic issues. Obviously, such an approach is neither sustainable nor responsible. The use of mechanical air-conditioning and heating systems further contributes to carbon dioxide gas emission in the environment, thus increasing problems relating to pollution and global warming, it is also economically inefficient and wasteful. An alternative to mechanical cooling system is to make use of passive cooling provided by design elements such as shade, natural ventilation and thermal mass (Givoni, 1998). This research Demonstrate the ability of wind-catchers or Badgirs, as an environmentally friendly element to provide natural ventilation for indoor environments. Since Traditional wind-catchers have been used in areas with higher outdoor temperature than the UK this paper will conclude by demonstration how such traditional design approach can be incorporated into modern buildings in the UK.
Ventilation systems help to provide a comfortable microclimate in the ventilated space (Awbi, 1991). In this context, the microclimate concept involves a thermal environment and air quality (Battle McCarthy Consulting Engineers, 1999). Ventilation is the process of supplying and removing air by natural or mechanical means to and from any space. Ventilation in building is needed to provide fresh air for occupants, to reduce and exhaust pollutants and to provide cooling in summer. Ventilation is also needed for the protection of the building and elements of its construction against moisture. Too little ventilation puts the health and comfort of the occupants at risk, and in the other hand too much ventilation during the heating season will incur an energy penalty. Most people spend majority of their time in buildings, either at work, at home, or pursuing leisure activities. According to Guardian newspaper typically, in the UK, people spend up to 90% of their life indoors.(Gardian, 2011). The quality of indoor air is therefore fundamental to people health and well being. In most parts of the word, the modern approach to dealing with warm weather is to seal up the building envelope and use air conditioning or other forms of mechanical comfort cooling to bring the internal environment to a desired temperature. This option is now extensive in many areas of the word where air condition is within economic reach and is often seen as a necessity for the pursuance of a modern life style. (Holmes, 2007). Air conditions as an adaption to climate change has clear disadvantages, however particularly because of the implications for increased power consumption and CO2 emissions. Mechanical ventilation is the movement of air by mechanical means to and from a space. It is controllable and can be localised, using individual wall or roof fans, or centralised, with ducted distribution. It can incorporate filtration and a heat recovery system to extract heat from exhaust air and use it to pre-heat supply air. Some of the potential harmful effects of air conditioning systems on the environment and human health could be listed as follow:
High electrical energy consumption in summer as a result of wide usage of air conditioning units lead to increased peak electricity demand in the hot season.
High electrical energy consumption in air conditioning systems increase the consumption of fossil fuel and then high consumption of fossil fuel lead to increased atmospheric pollution and finally climate changes.
Heat rejection during the production and consumption process has a detrimental effect on the environment.
CFCs and HFCs used in air conditioning units lead to Ozone layer depletion.
Indoor air quality
Applying mechanical ventilation system can result in sick building syndrome. Occupants feel dissatisfied in such buildings.
As natural sources are limited, this leads to the political and economical dependency of countries with limited amounts of natural sources to the countries with higher amount of natural sources.
Installation and maintenance of air-conditioning units results in extra costs.
Therefore, applying renewable energy such as wind and solar energy to provide an acceptable indoor air quality and solve the problems of mechanical ventilation systems are vital (Liddament, 1996). As in natural ventilation fossil dependency is much less than mechanical ventilation systems, hence Natural ventilation is often considered to be the most energy efficient and healthy solution.
A rather sophisticated traditional approach for natural ventilation is the use of Badgirs. Wind catchers or Badgirs are sustainable energy systems which traditionally have been used in the Middle East for ventilation and cooling purposes. They are only relying on natural forces to provide thermal comfort and fresh air (A'zami, 2005). Badgirs are often tall structures that extend above the roofs of buildings. They have openings on one or more sides, depending on the direction of the prevailing winds and breezes. Wind towers catch the wind or breeze and direct it into the interior of the building. Due to the high thermal capacity of their walls, they cool off at night but also remain relatively cool in the daytime. Air cools off when it comes in contact with the walls of these towers and then enters the building. If there was no wind, the Badgirs would still cool off the building as a result of the chimney effect. Wind-catchers can be divided into ‘’one-sided, two-sided, three-sided, four sided, hexahedral, and octahedral, both of the shaping and regional point of view’’(Ahmadkhani Maleki,2011).
The structure of a badgirs
Badgirs must rise above the roof to transport the desired wind currents to interior spaces of the house. To fulfil this purpose the ratio of its length and its width to its height is important. The height of a wind catcher in hot-dry climates is more than in the hot- humid ones, due to the lower temperature and higher velocity of the wind at greater heights. In hot- humid areas the desired wind is at a lower level, due to the breeze coming from the ocean. The components of badgirs, either functional or ornamental, are as follows from top to bottom:
A roof. Badgirs generally have a flat roof to prevent rain penetration. However, pitched or domed roofs have been used, as well.
An upper air canal with openings, which can be square, rectangular, circular, or octagonal. The tower head might have openings on one to four sides, but will at least have one located toward the predominant wind direction. In older time, the builder had to have enough expertise to recognize the suitable wind direction in order to choose which sides of the badgir should be open to receive the cooler wind and not to allow dust to enter the air canal. The tower head of the badgir is also where the most ornaments, which are formed through recesses and projections of bricks, can be seen.
A lower air canal, or the shaft of the badgir, is located between the upper canal and the main roof of the building and determines the height of the wind catcher. The master builder would estimate the height of the shaft based on the geographical location and the required height to catch the wind. On the whole the taller the badgir was built, there was more distance between the air entrance and exit, therefore the difference between air pressures at the top and bottom of the shaft would increase, as well as air speed in the badgirs ,(According to Bernoulli’s rule, which states that air rate will be increased when air passes through narrow sections), hence the badgir would be more efficient. ( Soflaee, 2005)
The function of Badgir
In natural ventilation, temperature reduction is not the only effective factor in thermal comfort, the increase in wind speed is also effective, due to the cooling effect of perspiration evaporation and to the increase of oxygen.
Badgirs are used to transfer the wind flow to the interior spaces of buildings in order to provide comfort for occupants. The shafts of a badgir provide a combination of inlet and outlet openings. Specifically, in four- sided badgirs one of the shafts constantly receives the breeze, and the other three shafts work as outlet air passages. They deliver the stuffiness out of the living space by the stack effect. The difference in temperature between the interior and exterior of a building creates a pressure difference, which results in air currents. This effect is the main factors in natural ventilation. When wind strikes a building, the air pressure in front of the building will increase and become positive, while the air pressure in behind the building will decrease and become negative. In this way the badgirs act both by sucking the cold air into the buildings and by discharging the hot and polluted air from the building. The difference of wind pressure on various surfaces of buildings depends on:
The form of buildings
The surrounding environment and the location of the building on the site; trees and other obstacles can influence the wind speed. Plants and trees inside courtyards act as a natural cooling system, due to the low heat capacity of the air. Unlike the surrounding thick brick walls of courtyards, which have a high heat capacity and act like a thermal condenser, plants serve as a reservoir of coolness, gathering it during the night and releasing it gradually during hot day.
The orientation of the walls of the wind towers is determined by the direction of the wind. for instance if the desired winds blow from the northwest, the long sides of windcatchers , should orientate towards the northwest for the maximum cooling effect of the wind on buildings.
Partitions divide the tower into small shafts to increase air motion, in accord with the Bernolli effect. Such an arrangement provides more surfaces in contact with the flowing air, so the air can interact thermally with the heat stored in the mass of these partitions.
The material of the badgir also plays an important role. At night when the temperature is low, the badgir, which is made of mud brick, become cool through radiation and convection. The mud brick has 7 to 9 hours of response time. In the morning the mud brick begins to exchange heat with the internal air; because the cooler air has higher density than warm air, the cool air flows down into the rooms. The wind shaft gets warm during daytime, and at night it works as a solar chimney, the walls release their heat to the air, and the internal air density decreases, creating air circulation.
A traditional Badgir, perform mainly in the following three ways to optimize thermal comfort:
And providing the ventilation for the internal environments.
The fourth function of badgirs is the establishment of an environmental stability or steadiness. Badgirs and their climatic function are very appropriate in terms of preservation and longevity of the building itself. Badgirs have been used to increase the relative humidity (RH) level for human comfort. However, moisture should not reach the point that it damages the durability of the structure. At the surface of finished interiors, materials would remain air dry with a RH not exceeding approximately 70% or 50% in the basement. (A'zami, 2005).
Sue Roaf described the usage of windcatcher in Yazd ( a city in Iran) as follow:
‘In contrast to the Western approach to comfort and design in which the individual chooses the climate for a room, the People of Yazd( name of the City in Iran) living in a traditional house selects a room for its climate. Such choice and movement around a house during a day constitutes a behavioural adjustment that has been an essential adaptive strategy evolved by the people of such hot desert regions, enabling them to inhabit a seemingly hostile environment with some degree of comfort. In the heat of the Yazdi summer, starting out from sleeping on the roof, they will migrate to the courtyard, which provides shade and relative cool in the morning and, thence, to the cellar to rest through the hottest hours of the day. Towards evening they will come out into the relative heat of the courtyard, which may initially be cooled a little by water thrown on to the hot surfaces, and will then grow cooler as night draws near. In late autumn, a different migration occurs, horizontally from the shaded north-facing summer wing, to the south-facing winter rooms of the courtyard, deliberately warmed by the sun’. (Roaf, 1988).
It is necessary to remember sustainable aspects of traditional building methods and then adapt them to current needs through technological advances. By illustrating the benefits of functioning badgir, traditional experience and knowledge will be passed on to new generations; otherwise this concept and technology will be lost. Currently new forms of windcatcher have been applied in the UK. In 1999 the investigation of Building Research Establishment (BRE) proved that this type of technology can provide the sufficient ventilation rate in a building (BRE, 1999). The design of contemporary wind-catchers although based on the design of traditional ones, have some differences, which some of them will be discussed. As the interest to apply environmentally friendly features is increasing, applying wind-catchers in the UK is also becoming popular. Some buildings which are using wind-catchers for cooling or ventilation purposes in the UK could be listed as follows: (Battle McCarthy Consulting Engineers, 1999)
Bluewater Shopping Centre, Dartford, Kent,
Ionica Headquarters , Cambridge,
Queens Building, Leicester,
Regent Park Health Centre, London
Kidderminster College, Kidderminster
the Primary Centre at St Joseph’s College
Modern designs of wind-catcher take advantage of traditional wind-catchers’ principle and adapt and improves them into the new generation of wind-catcher. In the modern windcatcher same as the traditional one, outlet and inlet have been placed in the same features which are allows the system to introduce fresh air and exhaust polluted air in the same time. As mentioned previously there are some differences between the traditional and contemporary Windcatchers, some of these differences are as follow:
In traditional wind-catcher hatches were the only control devices for users but the modern design of wind-catcher provides more possibility for users to control the windcatchers. Monodraught wimdcatcgers units can be controlled individually or by a central control panel, which can be fitted with a spring, summer, autumn, and winter switch to ensure that dampers open for night time cooling only during summer months.
By entering air from outdoor in natural ventilation devices, noise also enters. In the wind-catcher usually openings are located at higher areas so it is less likely traffic or outdoor noise enters into the building. However in the modern design of wind-catcher, by applying acoustic lining in to the air paths, the system become more insulated against outdoor noise in comparison to the traditional design.
In some form of modern designs the wind-catcher’s structure is accompany with auxiliary tools such as a fan or water supply to improve wind-catcher’s performances.
Due to economic and aesthetic reasons the height of modern wind-catchers in the UK is less than the height of wind-catcher in the Middle East. Therefore they are less likely to benefit from stack effect. (Harwood, 1998).
Reliance on night cooling
As the temperature difference between day and night in the UK climate is small, modern wind-catchers in UK have less possibility to take advantage of night cooling (Harwood, 1998). However, in summer time a volume control damper is applied to allow fresh air to enter the room during night time.
The materials that have been used in the modern design of wind-catcher are thin plastic
and metal sheets. Also the materials used in modern windcatchers are lighter than traditional ones and usually 3ply glass fibre with Class 0 fire retardant resin has been used in modern designs (Monodraught, 2003)
Form of louvres
The form of the wind-catcher’s louvres is highly affected by climate situation. In traditional design of wind-catchers, as usually they have been used in the hot and dry area, wind-catchers have big vertical vents. However as in the UK rain plays a very significant role on architecture, modern wind-catchers in the UK have several oblique horizontal louvres which could affect the wind-catcher’s performance.
Monodraught have exploited this traditional architectural design into commercial natural ventilation devices. The modern Monodraught windcatchers are made of thin plastic and metal sheets, so they are compact, light and have lower elevation above the roofs. The Monodraught windcatcher deal with the issue of air movement and, through that, also with air temperature.
NGS ( the National Green Specification) describes the product as follows: ‘’ The Monodraught Windcatcher system has proved to be the most effective method of providing natural ventilation to any commercial building, by encapsulation the prevailing wind from any direction. Clean fresh air, relatively free from contamination or traffic pollution, is entrained at roof level and is carried down to the rooms below, through a controlled damper arrangement. The ventilation effect is similar to displacement ventilation.’
Night time cooling is achieved without compromising the security of the building. Warm, stale air is exhausted by the passive stack quadrants of the Monodraught system and replaced by cool fresh air, taken in from roof level. The new generation of Windcatchers works in the following way, wind movement striking the Monodraught system is captured by the louvers serving the quadrants. Internal turning vanes on the windward side move the air through 90 degree. The force of the wind is then driven down into the room or space below and, having a greater density than the internal air, this cooler incoming air flows down to floor level, while the less dense, warmer internal air rises and exits through the passive stack quadrants as a form of displacement ventilation. (Monodraught, 2006). As the wind changes direction at rooftop level, the system quadrants use a 40W solar panel to switch their function to continually provide incoming air and extract stale air from the building, without consuming electricity.
The Primary Centre at St Joseph’s College
Designed by Wincer Kievennar Charted architect, the Primary Centre at St Joseph’s College in Ipswich is a 1550 square metre, housing up to 200 children. The architect has provided the building with a clear statement of environmental intent by using Monodraught windcatchers to naturally ventilate the 125 square metre hall, a circular library and series of interlinked shared spaces.
Located in the grounds of Birkfield House near the centre of Ipswich, the collage has undergone an extensive programme of refurbishment and re organisation since May 2000. Won in competition in 2006 and completed in September last year, the Primary Centre occupies the western corner of the 17 hectares campus and is situated adjacent to the college chapel. The decision to naturally ventilate the building proved relatively straight forward in the classroom using a combination of high and low level opening lights coordinated by an automatic control system with integrated temperature and carbon dioxide sensors. But the main inboard spaces comprising the hub, shared areas and hall posed a number of problems. The nature and type of glazing used in both the turrets and hub disallowed the use of opening lights. Added to this, the area of glazing in the turrets was thought to be insufficient to provide adequate summer ventilation. In the hall, safety and security issues severely limited the size, positioning and opening possibilities of the windows. The solution was to use Monodraught’s windcatcher system of ‘topdown’ ventilation system. The roof mounted units, comprise a series of external louvers linked to internal turning vanes, designed to catch the wind from any direction. The flow of fresh air into the building is controlled using a damper system fitted to the base of the unit. Warm internal air is expelled out through the same route. Project architects Paul Hammond explains that the decision to use windcatchers to naturally ventilate the building was taking for several reasons. First, the windcatchers can be designed and sized to meet the exact needs of the individual spaces, without relying on elements such as opening windows and vents. Second, the system can provide night time cooling during the summer, a key aspect of many natural ventilation strategies, without the attendant security risks of having to leave windows open. Third, the windcatchers themselves are inherently reliable, being designed to operate at comparatively low wind speeds, containing few moving parts, and requiring little or no maintenance. (Monodraught, 2006). From the outset the architect worked closely with environmental engineer and Monodraught to develop a detailed natural ventilation design, During occasional periods of little or no wind, air movement is still achieved by stack effect, warmer and less dense air is dispersed at roof level and replaced by cooler, denser air outside. The air change rate itself is calculated using factors such as room size, number of occupants, and predicted heat gains from windows, IT equipment, lighting etc. Later in the design the team decided to use a programmable Cylon panel in order to control the ventilation automatically. (Monodraught, 2006). The units are connected to the panel using a combination of temperature and carbon dioxide sensors.
At midnight the dampers open fully for night time cooling. This has the effect of removing the building of stale air while cooling the structure and fabric to below daytime temperature. The dampers are programmed to automatically close during this process if the internal temperature drops to below 16 C. In terms of CO2 levels, the dampers open to 40 percent for 15 minutes and then close for 30 minutes if levels rise above 1500ppm, the cycle is repeated until CO2 falls below 1400ppm. (Monodraught, 2006). In the winter, the dampers are either closed or set to five percent open to provide required ventilation. Manual overrides located on the sensors allow stuff to fine tune comfort levels. The override is linked to a timer, which resets the system to its original position after a specified period. Facilities manager at St Joseph’s College, Commented that system has worked well since it was commissioned last year and is proving highly efficient. (wincer kievenaar architects, 2009).
It is concluded that, there is little need to justify the drive to minimise the energy consumed by HVAC systems. Motivation may now appear to have moved from the desire to reduce costs and save scarce resources towards minimising the production of carbon dioxide which in terms of necessity is of much greater importance. It is however economic forces that will always dominate. Furthermore, the trend towards more ambitious architectural designs is stretching the ability of engineers to provide robust low-energy design solutions ( Holems 2007). In recent years there has been a reaction against total mechanically ventilated or air-conditioned buildings, largely on the grounds of energy efficiency. It seems certain now that we have embarked on a series of increasingly warm and humid summers. All attempts to reduce our level of carbon consumption will fail if we become increasingly dependent on air conditioning systems, hence as a result of the harmful effects of air conditioning systems on the environment applying environmentally friendly features has became more popular. Environmentally friendly features take advantage of renewable energies, such as wind and solar power to run the system. Windcatchers or Badgirs, are environmentally friendly energy systems that are not only reliable and sustainable, but highly cost effective particularly in comparison with air conditioning and mechanical ventilation systems. As previously mentioned, the design of traditional wind-catchers has inspired the design of a new form of wind-catcher in the UK. Traditional wind-catchers have been used in areas with higher outdoor temperature than the UK; but they can provide acceptable indoor air condition. However as the climatic condition in the UK and Middle-East are totally different, it is impossible to use identical wind-catchers in the UK. These climatic differences have influenced the design of contemporary wind-catcher in the UK.
The form of openings are the main differences between traditional and modern wind-catchers. The form of windcatcher openings are highly affected by climate condition. In traditional design of wind-catchers, as been used in the hot and dry regions, this traditional device have big vertical vents. But as in the UK because of rain issues, modern windcatchers have several oblique horizontal louvres which affect the wind-catcher’s performances.
Perhaps the problems which are associated with applying the windcatcher in modern buildings are heat lost in winter, and inefficiency of system to providing acceptable amount of fresh air in summer. To overcome heat lost modern windcatchers are equipped with dampers and some research has been done to optimise the angle and the size of dampers by (Hughes and Ghani, 2009). However, it seems that little research has been done to increase the total amount of air entering to the room. In modern wind-catchers to increase the total amount of fresh air introduce to the building, usually the size and the number of wind-catchers are increased. As air enters a windcatcher through louvres, the form and size of louvres have a direct influence on the efficiency of system. As mentioned before, the form of the louvres is one of those main differences between traditional and modern wind-catcher. Modern wind-catchers take advantage of louvres instead of vertical secondary partitions in traditional ones which provide better protection against rain, dust, birds, and increase the security of buildings. There is a limit to the extent of research and analysis that can be conducted within the context of a 5,000-6,000 words dissertation. If I was undertaking a more involved piece of work I see opportunities on how I could take this topic further. This for example, might involve assessing a greater number of building case studies including possibly within different climatic conditions around the world; and also conducting interviews or questionnaires with users and maintainers of mechanical, natural and combined ventilated buildings in order to come of further conclusions on the benefits and disbenefits of each system and therefore come to an even stronger view on the hypothesis.