DESIGN INTERVENTIONS FOR RESIDENTIAL BUILDINGS FOR PREVAILING WEATHER TRENDS

Abstract

Climate change vis-à-vis the rise in global air temperatures (approximately 0.6 ± 0.2°C) because of increasing carbon emissions is the hot-topic of interests among most institutions, research scholars and governments. This is very evident in the manner of occurrence of erratic climate/ weather events like frequent elevated temperatures, erratic distribution of rainfall etc. are being experienced on a higher frequency. Sustained duration of elevated temperatures can cause aggravate health issues and lead to enhanced financial burden. And this can all start, and to an extent stop, at the house that we inhabit. The case being made here is that in case of erratic weather phenomenon, the house, if designed suitably can help to weather this trend or aggravate it. This fact is supported by WHO in their report on the international workshop on housing, health and climate published in 2010. The study tries to establish and interpret how a weather trend creates an impact on the house using the composite climate context of Roorkee as a demonstrative case. The study uses a 41-year daily temperature data for maximum, minimum and mean temperature of Roorkee (1976-2016) to establish a trend in the three variables, the results of which are: - - rising trend observed in days where maximum temperature is above 35°C - rising trend in the average annual mean temperature - rising increasing trend in the number of days in a year when the daily mean temperature is above the average annual mean temperature. The increasing trend highlights to an extension of the overall period with warmth experienced in a year since in the last 41 years. Based on this trend analysis, representative decadal weather files have been created for the period of 1976-1985, 1986-1995, 1996-2005, 2006-2016 as Roorkee does not have a weather file of its own. Representative months for each decade have been obtained by using the least range of standard deviation obtained from the difference between daily and average temperatures for both daily maximum and minimum temperatures. The weather files were then simulated against documented residential buildings from two study areas in Roorkee, Awas Vikas Colony and Solani Puram. It was attempted to document maximum number of residential buildings for this study, but as a result only 5 buildings from each study area have been documented and studied. An initial simulation of these buildings | Design Interventions for Residential Buildings for Prevailing Weather Trends | P a g e | vi was conducted for the weather file of Saharanpur (nearest weather station) followed by weather files of Roorkee. The results obtained have been analysed in terms of number of comfort hours on the Tropical Summer Index comfort model. The results from comfort hours indicate that although the number of hours with hot severity(TSI>34°C) are increasing with every decade (ranging between 0.5-1.5%), there are comparatively more number of hours (ranging between 22-26%) under cold severity(TSI<19°C) for all the documented cases. The comfort hours (TSI 25-34°C) are rising and range between 24-26%. Based on the comfort hours obtained, the analysis focussed on locating exact causes due to which such number of hours are being obtained. The simulation results show that the opaque envelope elements – 230mm thick brick wall (U-Value – 2.084 W/m2K) and 150mm thick R.C.C roof with 150-175mm brick bat-coba terracing (U-Value – 2.251W/m2K) are the major sources from where heat gains and losses take place rapidly. High thermal transmittance values for both the wall and roof lead to rapid heat loss and gains with very less time-lag (4-6 hours approximately), eventually causing minimum heat gains inside the structure during winters and maximum during summers, creating hours of discomfort during both peak winter and summer seasons. The results obtained above have been used to find possible passive-design solutions. A basecase has been selected based on the maximum number of hours of thermal comfort achieved. Options explored have been created as energy conservation measures and then simulated individually for the best performing base-case. The energy conservation modules created are:- S.no Series Name Type of ECM Modules Outcome 1. ECM – Series -1 Orientation 8 Best orientation 2. ECM – Series -2 Projection factor of windows with shade 16 Configuration of shading device with location of shading projection 3. ECM – Series -3 Wall Thickness 4 Optimum thickness for thermal resistance and effective time lag 4. ECM – Series -4 Wall Assembly 7 Thermal resistance and effective time lag | Design Interventions for Residential Buildings for Prevailing Weather Trends | P a g e | vii 5. ECM – Series -5 Double Glazed Windows 4 Regulation of heat gains 6. ECM – Series -6 Roof Insulation 5 Thermal resistance and effective time lag 7. ECM – Series -7 Roof Canopy with Orientation 3 Effect of roof shading to control heat gains 8. ECM – Series -8 Combination of ECM’s 4 Selection of best performing strategies to assess combined effect on thermal comfort 9. ECM – Series -9 Combination of ECM’s with spatial intervention 6 -Introduction of an atrium which is ventilated at the top -Enclosed staircase shaft as a ventilation shaft The ECM modules are simulated to quantify maximum number of thermal comfort hours. The simulation results show that an atrium implemented in the design of the structure supplemented by appropriate opening and closing of windows according to seasonal changes helps to facilitate natural ventilation inside the structure. It has helped to achieve 36% of total hours as comfort hours (TSI – 25-30°C) and 12% of total hours with cold severity(TSI<19°C) as compared to the base case. Design strategies that have helped to achieve thermal comfort hours for the study context of composite climate include: - - wall and roof assembly having low thermal conductivity and higher time lag - ventilation of the structure through an atrium - skylights covered during summer season and open during winter season. - application of reflective and high albedo surface finishes to reduce heat gains inside the structure.