Special Issue: Conference Proceeding of i-CON-2016 Global Journal on Advancement in Engineering and Science (GJAES) Vol. 2, Issue 1 : March-2016, ISSN (Print): 2395-1001 S. Mandal (Editor), GJAES 2016 © GJAES Page 117 Original Research Work To Study the Impact of Temperature Boundary Conditions for Overall Heat Transfer Coefficient Measurement Suitable for Adaptation in Tropical Climate for Energy Efficient Building Debrudra Mitra 1 , Subhasis Neogi 2 School of Energy Studies, Jadavpur University, India Email: debrudramitra@yahoo.com 1 , neogi_s @yahoo.com 2 Abstract: Building sector is one of the major energy consumers in most of the developed countries. To design energy efficient building systems heat transfer through the building components needs to be calculated which depends on the overall heat transfer coefficient or U value. Guarded Hot Box Test Facility is used to determine the U value for a specified temperature difference. Due to wide range of weather conditions, more than one set point temperatures are required to measure the U value. Temperature difference of 10°C and 20°C are required to determine the U value of building component in Guarded Hot Box Test Facility. Keywords: U value, Guarded Hot Box, Temperature difference, Weather Condition I. Introduction Buildings energy consumption accounts for a 20–40% of total energy use in developed countries and it is more than industry and transport sector in the European Union and the United States of America [L. Pérez-Lombard et al, 2008]. In India, building sectors consume 33% of total energy produced nationally [S. Kumar et al, 2010]. Therefore, it is important to develop techniques that can reduce the building energy consumption. To design energy efficient building system heat flow through the building components should be minimised. For doing this, the thermal performance of any building material should be evaluated. Amount of heat transfer through a component depends on the overall heat transfer coefficient (U value) of that component. Heat transfer through building component increases with the increase in U value of the material. The U-value of a building material can be determined by the Guarded Hot Box Test Method [BS 874: Part 3: Section 3.1:1987]. The method described in the International Standards measures the total magnitude of heat transferred from one side of the specimen to the other side for a given temperature difference. The U value depends upon the temperature difference between the hot and cold side of the sample [Xiande Fang, 2001]. As the temperature difference across the sample increases, U value also increases. So for calculating the U value it is important to specify the proper temperature difference across the sample [BS EN ISO 8990:1996]. The British standard [BS 874-part 3-section 3.1:1987] has recommended maintaining a minimum difference of 20˚C between the air temperatures in the hot and the cold sides for obtaining accurate thermal transmittance. According to American standard ASTM C1058 “It is recommended that thermal properties of insulation materials be evaluated over a mean temperature range that represents the intended end use. For this situation, the lowest and greatest mean temperatures need to be within 10°C of the maximum and minimum mean temperature of interest.” “For building envelopes in moderate climates with an anticipated exterior temperature range of 0°C to 50°C [30°F to 120°F]), recommended mean temperatures are 4°C, 24°C, and 43°C [40°F, 75°F and 110°F].” Defined mean temperatures for evaluating thermal properties of building envelope are -4°C, 4°C, 10°C, 24°C, 38°C and 43°C i.e. 25°F, 40°F, 50°F, 75°F, 100°F and 110°F. [ASTM C1058]. But there are no specified set point temperatures for U value measurement in the Guarded Hot Box Test Facility for tropical climate countries like India. The objective of this study is to define the temperature differences across the test sample for Indian climatic condition. II. British and American Set Point Temperatures Great Britain consists of England, Northern Ireland, Scotland and Wales. In England summer accounts a temperature from 20.9°C to 11.7°C (July) and during winter the temperature ranges from 7.2°C to 1.1°C (February) .The yearly maximum and minimum temperatures are 13.5°C and 5.9°C respectively. In Northern Ireland summer has a temperature from 18.4°C to 10.6°C (July) and during winter the temperature ranges from 6.7°C to 1.2°C (February).The yearly minimum and maximum temperatures are 12.2°C and 5.2°C respectively. In Scotland summer accounts for a temperature from 16.9°C to 9.3°C (July) and during winter the temperature ranges from 5.0°C to -0.2 °C (January) .The yearly maximum and minimum temperatures are 10.5°C and 4.0°C respectively. In Wales summer accounts a temperature from 19.1°C to 10.9°C (July) and during winter the temperature ranges from 6.6°C to 1.1°C (February) .The yearly maximum and minimum temperatures are 12.3°C