Bio-climatic Chart for Different Climatic Zones of Northeast India

Transcription

1 Proceedings of 3 rd International Conference on Solar Radiation and Day Lighting (SOLARIS 27) February 7-9, 27, New Delhi, India Copyright 27, Anamaya Publishers, New Delhi, India Bio-climatic Chart for Different Climatic Zones of Northeast India Manoj Kumar Singh, 1 Sadhan Mahapatra 2 and S.K. Atreya 1 1 Instrument Design and Development Centre, Indian Institute of Technology Delhi, New Delhi , India 2 Department of Energy, Tezpur University, Tezpur , India Abstract: This article examines and analyses the climates of Northeast India with respect to building design parameters: temperature, relative humidity, wind velocity/direction and solar radiation, with a view to providing passive solar design potential for the achievement of physiological comfort. It presents the work on development of bio-climatic zones for the region. The major climatic types of the region are warm and humid, cool and humid and cold and cloudy zones. A bio-climatic approach is adopted in which the comfort zone and 12 monthly climatic lines are determined and plotted on the psychrometric chart for each climatic zone. From these bioclimatic charts, the potential use of passive design strategies such as solar heating, natural ventilation, thermal mass, thermal mass with night ventilation and evaporative cooling are assessed. A total of five passive design strategies are considered. It is expected that this study will help in explaining the different passive features, which are present in traditional buildings of the region and also help the architects to design modern climate responsive energy efficient buildings in the region. Keywords: Energy efficient buildings, Bio-climatic, Passive features, Natural ventilation. Introduction Thermal comfort and acceptability are not precisely defined by the ASHRAE Standard 55 code for thermal environment conditions for human occupancy. It is commonly agreed within the thermal comfort research community that the combination of indoor space environment and personal comfort requirements will create acceptable thermal environmental conditions for the occupants within a space [1]. Human body requires a constant internal temperature around 37 ±.5 C for maintaining healthy conditions. Thermal environment is the outcome of a number of parameters and, therefore, can be defined as a point in multi-dimensional space [2]. These topological relationships may change as one moves along any particular dimensions of the multidimensional space. Actually, there are at least six parameters which give these multi-dimensions to any unique thermal conditions; two of these, activity level and clothing (specific to human) and other four are characteristics of the environment itself, such as air temperature, humidity, velocity and solar radiation. Moving one step closer Fanger and Sayigh [3, 4] have given the energy balance between human (per unit body surface area) and environment. Out of the various factors that affect architectural design, climate control is of prime importance as it involves maintaining comfortable conditions inside the building. If this objective is disregarded discomfort

2 Bio-climatic Chart for Different Climatic Zones of Northeast India 195 will prevail, resulting in lower productivity and psychological stress. Simultaneously, the energy cost of maintaining comfort conditions will rise. Hence, it is desirable to design climate responsive buildings incorporating appropriate passive features. To get the maximum benefit, these aspects should be considered at the planning and design stage itself [5, 6]. Now we are moving towards the era of intelligent buildings that will support advanced hardware, such as building and personnel management system, as well as accommodate future technologies and the anticipated level of long-term user requirements. This must also deal with environmental conditions, such as thermal comfort, visual perception, air control, acoustic etc. [7]. In this article, 12 monthly lines are represented on psychrometric charts for a number of representative places of Northeast India in each climatic zone to estimate the passive solar strategie, potential. Bio-climatic Approach The weather of any place represents an integrated effect of all atmospheric variables over a brief period of time. Climate is the average weather over a period of many years and is generally known as the macroclimate. Both weather and climate are described by the climatic factors like solar radiation, ambient temperature, air humidity, precipitation, wind and sky condition [8]. Based on these climatic factors, Northeast India is mainly divided into three climatic zones namely, warm and humid, cool and cloudy and cold and cloudy [9]. The researchers working in the field of thermal comfort over past few decades have been trying to develop a systematic approach to incorporate the prevailing climatic conditions so that the thermal comfort conditions will be maintained inside the building, at the design stage itself. But well before that it is required to have clear understanding about the design strategies that will be of worth for a particular climatic zone. Olgyay [1] in 195 used the bio-climatic chart where the effects of dry bulb temperature, relative humidity, mean radiant temperature, wind speed and solar radiation were taken into account. This work was further carried on by Milne and Givoni [11] and more recently by Szokolay [12] leading to the development of building bio-climatic charts based on typical psychrometric charts. There is, however, very little work done on climatic analysis and bio-climatic based design strategy for different climates in Northeast India [13]. In the present work the relevant data such as temperature (both maximum and minimum of monthly averages for 3-year normal data), humidity (3 years normal of monthly average data at 8.3 hrs and 17.3 h), rainfall (3 years normal of monthly data) and wind data (3 years normal of the percentage of winds in particular direction) were collected for 3 stations in the region by Regional Meteorological Centre, Guwahati, India (Fig. 1). Fig. 1. Data collecting stations. Analysis of Bio-climatic Charts The first step in the determination of the passive solar design strategy involves the division of the region into meaningful different bio-climatic zones. The region is classified into three major zones namely: warm-humid, cool-humid and cold-cloudy (Fig. 2). The climate of a given location is analysed in its own terms and the analysis leads to certain passive solar design strategies. The monthly climatic lines are drawn on the psychrometric

3 196 SINGH, MAHAPATRA AND ATREYA chart. The two end points of the climatic lines are given by the mean minimum temperature and mean minimum relative humidity, and mean maximum temperature and maximum relative humidity. The proportion of the monthly lines falling within a particular passive design strategy zone indicates (in terms of percentage) the potential use of that passive design (Table 1). In determining the percentage of potential use, the 12 monthly climatic lines were grouped into the colder half (October-March) and warmer half (April-September) of the year. The first group is for assessing the potential use of passive solar heating, and the latter is for assessing the design strategies for passive solar cooling. To provide a more holistic view, active design strategies, namely conventional/active heating and air-conditioning are also shown on the bio-climatic chart. Table 1. Passive design strategies potential S. No. Place Passive design strategies potential (% of the year) AC Comfort NV PSH CH Cold and cloudy Warm and humid Cool and humid Highland climate Fig. 2. Bio-climatic zones of Northeast India Guwahati Dhubri Agartala Tezpur Tura Imphal Halflong Aijal Zero Shillong Kohima Cherrapunji AC: Air-conditioning; NV: Natural ventilation; PSH: Passive solar heating/cooling; CH: Conventional heating. Guwahati Guwahati is located in the Northeastern part of India (26 6 N, E and altitude 54 m). Figure 3 represents the bio-climatic chart for the place. This city has annual average temperature of C and relative humidity remains above 7% most of the time throughout the year. From the bio-climatic chart it can be concluded that for 3.3% of time of the year, convention heating is required. Most of the monthly lines lie in the conventional air-conditioning region which is 53.75% of time of year. Comfort condition exists for about 14.17% time of the year, that too in the winter and early summer months. Here, the potential of the use of passive solar heating and natural ventilation is 12.1 and 16.7%, respectively. It must be noted that these figures represent the potential energy usage and saving potential but these figures are likely to change depending upon the building design orientation and surroundings. Agartala Agartala is the capital city of state Tripura (23 53 N, E, and altitude 16 m) with annual mean temperature C and humidity above 7% for most of the time of year. Same as Guwahati, 55.4% time convention airconditioning is required. Passive solar heating and natural ventilation potentials are 8.3 and 17.92%, respectively (Fig. 4).

4 Bio-climatic Chart for Different Climatic Zones of Northeast India 197, Fig. 3. Bio-climatic chart for Guwahati Fig. 4. Bio-climatic chart for Agartala. Halflong Halflong (25 1 N, longitude 93 1 E, altitude 682 m) falls under cool and humid climate zone. The entire region is evenly heavily vegetated with uneven topography. Figure 5 shows the bio-climatic chart for Halflong. Halflong has potential of 5.83% of conventional heating during December, January and February. Comfort zone is 26.67% time of the year. It has potential for passive solar heating and natural ventilation is of 17.8 and 1%, respectively. Rest 4.4% time of the year conventional air-conditioning is required for maintaining the comfort. Aijal Aijal, also like Halflong, is under cool and humid climatic zone. Figure 6 shows the bio-climatic chart of Aijal % time of year comfort prevails and rest 36.25, 18.8, and 7.8% time of year conventional air-conditioning, passive solar heating and natural ventilation can maintain the comfort condition Fig. 5. Bio-climatic chart for Halflong Fig. 6. Bio-climatic chart for Aijal. Zero This place lies in cold and humid zone. Figure 7 shows the bio-climatic chart of Zero. In the figure, we can envisage that most of the monthly lines fall in conventional heating and passive solar heating zone with a

5 198 SINGH, MAHAPATRA AND ATREYA potential of 33.8 and 38.3%, respectively. Artificial air-conditioning requirement is almost zero. Comfort prevails and 9.6% for natural ventilation of the year. Shillong This place lies in the same climatic zone as Zero. Figure 8 shows the bio-climatic chart of Shillong. From this we can notice that this place has conventional heating, passive solar heating and air-conditioning potential of 2.83, 33.8 and 14.2% time of the year, respectively. Comfort persists for around 3% time of the year Fig. 7. Bio-climatic chart for Zero Fig. 8. Bio-climatic chart for Shillong. Conclusion Entire Northeast India is now on the development track. In this development process, housing sector will have a major share and will consume a substantial amount of energy. Here, we have considered 12 representative places across the three climatic zones and a total of five design strategies: solar heating, natural ventilation, thermal mass, thermal mass with night ventilation, and evaporative cooling are assessed. In the region, the relative humidity level is always at high value throughout the year, so evaporative cooling is not very effective. But for passive design strategies like thermal mass, thermal mass with night ventilation and natural ventilation can save a substantial amount of energy used for conventional air-conditioning. The warm and humid climatic zone has and 15.2% potential for passive solar heating and natural ventilation, respectively and 15.75% time of the year comfort conditions persist. But 55.1 and 2.23% time of the year conventional air-conditioning (summer months) and conventional heating (winter months) are also required to restore the comfort. In cool and humid climate, 41.3 and 5.63% time of the year have to depend on conventional air-conditioning and conventional heating, respectively. Passive solar heating and natural ventilation have got the potential of and 1.85% time of the year, respectively. Comfort prevails for 26.35% time of the year. For cold and cloudy climate, comfort prevails for 23.86% time of the year. Passive solar heating and natural ventilation have got the potential of and 3.5%, respectively. Conventional heating system has potential of 21.2 and 18.46% time of year on air-conditioning, to restore comfort conditions. It is hoped that the present work would help builders, architects, and engineers to assess the passive design strategies during the initial planning stage of buildings. This work is limited to only 12 places of the region but detailed study is required for all the places and also on low energy intensive building construction materials.

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