Figure 1. Step well
Buildings account for an estimated 30 percent of the total energy consumption in India. Furthermore, the absolute figure is rising fast due to booming real estate demand and increasingly affluent lifestyle across various sections of society. In India, there are several showcase buildings such as a solar passive house in hot arid zones in India (Bansal and Minke, 1995) and a passive-cooled building for semi-arid zones (Srivastava et al., 1984) using wind tower, earth berms and evaporative cooling systems. Studying 3 cases where natural ventilation system has replaced/reduced use of mechanical cooling and saved energy. A wind tower is designed for a school building as overcrowded, poorly ventilated classrooms contribute substantially to the spread of infectious diseases, such as colds and influenza. Designed wind tower is for 2 classrooms with capacity of 40 students and area of 72 sq. m. resulted duct sizes for inlet and outlet are 0.20 sq. m. and 0.062 sq. m. respectively.
Over the past few years, concern towards energy efficiency and incorporation of passive cooling systems in buildings has increased. In earlier times, when energy was not available in its most popular form, i.e., electricity, building designers had to rely on natural ways and means for maximizing comfort inside the building envelope. A major difference between ancient times and today's situation is that today, none of the major resources namely, land, money and time are available in abundance. This has led to a situation where passive features must be designed more scientifically and technically as compared to the past.
In India, there are several showcase buildings such as a solar passive house in hot arid zones in India (Bansal and Minke, 1995) and a passive-cooled building for semi-arid zones (Srivastava et al., 1984) using wind tower, earth berms and evaporative cooling systems. The first platinum rated LEED accredited building of India also displays use of passive cooling systems in building design (CII-GBC, 2004). There are also some examples of unsuccessful passive cooling systems. Bakiwala (2002) has prepared a report on non-functional passive features concluding that the failure was primarily due to two reasons: 1) Inadequate design calculations or design by gut-feel 2) Over-expectation from the passive feature. As stated by M. R. Khani, K. Yaghmaeian, and A. R. Dehghani , in hottest months of season, July, when the temperature of water was in the range of 12.7 to13.8°C during the whole summer period whilst the outside ambient temperature was reached up to 35 to 40°C.
The Kyoto Protocol on climate change has come into effect on February 2005. This requires the signatories to reduce emissions of greenhouse gases below 1990's level by the year 2012 in order to contribute towards a more sustainable global environment. It can be predicted that developing countries including India will be demanded to consent to the Protocol in the near future. Thus, it is important and effective to consider the energy saving means in developing countries in the course of its economic development.
The emission cut from the use of air-conditioners in residential areas could be effectively carried out through energy saving efforts, by maximizing the use of natural ventilation. Therefore, the importance of natural ventilation has been increasingly reevaluated partly due to the recent needs of energy saving. A number of studies related to natural ventilation in buildings can be seen over the last few decades. For example, Backer and Standenven (1996) summarized results of the comfort monitoring surveys in order to develop comfort criteria appropriate to natural ventilated buildings. A field survey of thermal comfort in natural ventilated buildings was carried out in the UK by Raja and Humphreys et al. (2001), in Singapore by Wong et al. (2002) and in Indonesia by Karyono (2000).
India's climatic condition requires air condition applications in the summer and round the year in some crowded cities; an unaffordable appliance has to be utilized by people for comfort which can easily be achieved through provision of natural ventilation and optimized design of the buildings considering energy consumption. Reduction in energy consumption (electricity) can be achieved by avoiding or minimizing utilization of air conditioning equipments at least for residential zones. In favorable climates and buildings types, natural ventilation can be used as an alternative to air-conditioning plants, saving 10%-30% of total energy consumption.
Ventilation: Ventilation air, as defined in ASHRAE Standard 62.1 and the ASHRAE Handbook, is that air used for providing acceptable indoor air quality. Ventilation is the movement of air from outside a building to the inside.
Ventilation plays an important role in providing indoor air quality & thermal comfort for occupants.
Natural ventilation: the process of supplying and removing air through an indoor space by natural means.
Natural Ventilation systems rely on natural driving forces, such as wind and temperature difference of a building and its environment. Both work on the principle of air moving from a high pressure to a low pressure zone. Buildings with well-designed natural ventilation systems often provide very comfortable and pleasant indoor environments for the occupants.
Pressure differences can be caused by wind or the buoyancy effect created by differences in temperature or humidity. In either case, the amount of ventilation will depend critically on the size and placement of openings in the building. It is useful to think of a natural ventilation system as a circuit, with equal consideration given to supply and exhaust. Openings through rooms such as transom windows, louvers, grills or open plans are techniques to complete the airflow circuit through a building.
Studies have indicated that natural ventilation has the potential to reduce the energy cost significantly, required for mechanical ventilation of buildings. These natural ventilation systems may reduce both original and operating costs compared to mechanical ventilation systems while maintaining ventilation rates that are consistent with acceptable indoor air quality. Also, some studies have indicated that occupants reported less fever symptoms in buildings with natural ventilation compared to buildings with mechanical ventilation. If natural ventilation can improve indoor environmental conditions, such improvements can also potentially increase occupants productivity by reducing absenteeism, reducing health care costs, and improving worker productivity.
Natural ventilation in ancient building proposes and introduces some strategies for the modern architecture while representing the natural ventilation as a sustainable cooling system in traditional Iranian architecture (M. Mahmoudi Zarandi)
According to an accepted definition of sustainable development that is taken from the Brunt land report, the objectives for an agenda of urban design in a regime of sustainable development would emphasize conservation of both the natural and built environments. We do not have to search far for ideas for sustainable building: they are all pervasive in our lost constructional traditions.
Few of the ancient monuments provide a glimpse of proper natural ventilation systems which were used to avoid discomfort from the heat i) A step-well from Gujarat, ii) Cooling system-Diwan e-Khas, Red Fort, Delhi, iii) Pleasure garden built in a lake at Amber and iv) Iranian cooling system using wind tower, underground funnel.
Figure 1. Step well
Figure 2. Red Fort
Figure 3. Pleasure Garden
Figure 4. Iranian cooling system
Figure 5. Vikas Appartment, TN
Building oriented so as to catch the summer day & night wind. Oriented longitudinally along east-west axis with shaded openings along north-south for cross-ventilation & reducing summer gains. Natural cross ventilation is improved by increasing the wind velocity with the help of pier walls oriented at 45 degrees to the predominant wind direction. Solar chimneys are integrated with the building structure to create a natural draft that is especially refreshing at night .The basement floors, being only 1.2m underground, receive a lot of daylight & at the same time remain cool in summer.
A material used for walls and chimney is stabilized earth blocks and stainless steel non power wind driven roof extractor, for ventilating a room of 41m3 having 4.0x3.2 and of height 3.2 M. four holes in the dome opening into chimney have been provided which suffice ventilation need for comfortable living. 0.6x0.6 M size chimney has been provided right from basement to the terrace.
Figure 6. Detailed Arrangement of Dome and Movement of Air
Figure 7. Torrent Research Center, GU
A passive downdraft evaporative cooling (PDEC) system has been selected wherein vertical shafts acts as a cooling tower with smaller exhaust shafts which are placed at strategic locations. Mircronisers installed at the top of the cooling towers react automatically to temperature & humidity conditions to produce a fine mist that cool the air which causes the air to sink and flow into the corridors and hopper windows. The system operates differently in different seasons.
An active system is integrated with the passive design. The operation of the motorized dampers and exhaust fans is used to induce ventilation so that a consistent comfortable environment can be provided. The resultant architectural form dominated by the ventilation towers with shading devices to articulate the facade.
Figure 8. Details of Wind Tower and Photograph of Research Center Showing Number of Wind Towers
The Institute building has a unique environmental friendly architectural design and has used environment friendly materials for its construction. The plan is based on the traditional Maharashtrian Wada style with a central open-to-sky courtyard. Wind direction has been studied to circulate air through the complex. A series of water tanks channels and fountains have been incorporated into the design, which is reminiscent of Mogul gardens. The water is circulated through the channels by a fine spray fountain, which increases the moisture levels to produce a cooling effect in the building. The circulation device is operated by a special pump that uses solar energy. The building has composite walls of white Gokak and brick for a cooling effect and is aesthetically appealing for a building that housed an Environment Institution.
Figure 9. Auditorium
The Institute has a unique environmentally friendly auditorium. The floor of the auditorium forms a giant wind catcher, which is blowing air through the flooring. On one side there is a large water sprinkler system, which moisturizes the air for summer days when Pune is very dry. On the other side, there is a complex exhaust ducting system. It uses an environmentally friendly wind powered impeller device, which sucks air out of the auditorium without using electricity. The auditorium has no fans and no AC. This new structure has also incorporated measures for rainwater harvesting. This auditorium is used not only for the students programs but also for organizing School Environment Education Programs, in the form of Audio–Visual shows for schools at least four or five times a week. Similarly NGOs interested in environmental protection and Forest Department also use it for their programs.
Figure 10. Arrangement of Towers in a Bungalow
The Institute building has a unique environmentally friendly architectural design and has used environment friendly materials for its construction. The plan is based on the traditional Maharashtrian Wada style with a central open-to-sky courtyard. Wind direction has been studied to circulate air through the complex. A series of water tanks channels and fountains have been incorporated into the design, which is reminiscent of Mogul gardens. The water is circulated through the channels by a fine spray fountain, which increases the moisture levels to produce a cooling effect in the building. The circulation device is operated by a special pump that uses solar energy. The building has composite walls of white Gokak and brick for a cooling effect and is aesthetically appealing for a building that housed an Environment Institution.
The Institute has a unique environmentally friendly auditorium. The floor of the auditorium forms a giant wind catcher, which is blowing air through the flooring. On one side there is a large water sprinkler system, which moisturizes the air for summer days when Pune is very dry. On the other side, there is a complex exhaust ducting system. It uses an environmentally friendly wind powered impeller device, which sucks air out of the auditorium without using electricity. The auditorium has no fans and no AC. This new structure has also incorporated measures for rainwater harvesting. This auditorium is used not only for the students programs but also for organizing School Environment Education Programs, in the form of Audio–Visual shows for schools at least four or five times a week. Similarly NGOs interested in environmental protection and Forest Department also use it for their programs.
Figure 11. 3D View and Model of Sonhari Bangalow, Mah.
Observations made while studying this bungalow are stated below:
Through overall study of above buildings with respect to use of different alternative methods for natural ventilation wind tower was low cost best option to achieve comfortable internal air quality and environment and was decided to apply the same to a school building. The school building is located in the congested area in Pune; one wind tower was to be designed for two class rooms having strength of 40 students and size of 6.0 x 6.0 M.
O. H. Koenigsberger stated in his book, human consumes oxygen, taken from the air by breathing, & exhale carbon dioxide. An average person, depending on his activity, inhales about 0.5 to 5 m^3/h. In a closed environment oxygen content is reduced & the carbon dioxide content is increased by man's presence. Biologically the limit of existence is 0.5% CO2 content by volume but 0.15% content already gives a used air effect. Body smells, fumes & vapors add to the deterioration of an enclosed volume of air.
Thermal comfort for teachers, students, and administrators should be neither hot nor cold as they teach, learn, and work. Poor school IEQ can cause both short-term (reversible) and long-term (chronic) effects in students and staff. Classrooms and other school spaces must be ventilated to remove carbon dioxide and other pollutants that collect due to occupant breathing, odors, and other sources. In many climates, natural ventilation is an energy efficient method of providing at least a portion of the ventilation needed to cool school spaces and maintain indoor air quality.
To achieve a comfortable indoor environment, natural ventilation should provide an indoor air velocity of 0.4 m/s. The corresponding total area of the inlet and outlet apertures should be about 40% of the total floor area. If the aperture area were decreased 9 to 25%, the indoor air velocity would be 0.3 m/s. A ceiling fan can be used to increase the air velocity in this case (Chalermwat Tantasavasdia, Jelena Srebricb, and Qingyan Chenc)
Q= KVA; Quantity of air forces through openings by wind
Where, Q = volume of air, m3/ hr
A = free area of inlet opening, m2
V = wind velocity, m/ hr = 6000 m/h
K = effectiveness of openings = 0.38
Q= 0.38 x 6000 x A
Q=400
400 = 0.38 x 6000 x A
A = 0.1754 m.sq.
A = as an inlet dimensions can be = 0.42 x 0.42 m. Say 0.45 x 0.45 m.
A = for both outlets = 1/1.5 of A = 0.1754 /1.5
= 0.1170 m2
Area for each outlet = 0.0585 m2
= 0.2412m x 0.2412m
= say, 0.25m x 0.25m
Best Possible Location: The beat possible location for installation or construction of wind tower depends on wind direction in the city or location.
For Pune wind direction is SW – W due to which openings provided or rooms facing in south direction get sufficient wind; whereas rooms facing north are deficit of ventilation even with window openings. So the placement of wind tower should be done to suffice the need of ventilations to the rooms facing north.
Size and Height: Size of the wind tower depends on volume & occupancy. For this school building size designed for two classrooms is 0.42 x 0.42 m as inlet and 0.25 x 0.25 m as outlet.
Construction Material: Ferro cement with minimum thickness of 37 mm, with steel louvers can be low cost solution.
Figure 12. Plan of the School Floor1 and Positions of Wind Tower with Optimisation of Window Sizes for Appropriate Ventilation2