The Analysis of the Proper Thermal Resistance for Designing Residential Building Envelope in Rasht

Iran is one of the 10 countries with the highest consumption of energy generated from fossil fuels, and approximately 40% of the mentioned energy is used in the building sector. The consumption of fossil fuel increases the emission of greenhouse gasses and leads to environmental pollution. In order to mitigate the unpleasant effects of consuming fossil fuel energy in building, it is essential to construct buildings with efficient energy usage. The first attempt in constructing a building with an efficient energy usage is designing a building envelope with a proper thermal behavior. The previous research have indicated the importance of the specification of the appropriate thermal resistance of the building envelope. Therefore, the aim of this research is to specify the appropriate R value for different elements of the residential building's envelope based on the climatic situation of the region and the commonly used building materials in Rasht, in order to effectively decrease heating and cooling loads. This quantitative research uses a composite descriptive-analytical and modeling research methodology. The needed data to perform simulation includes climatic data and numbers related to R value, as well as heat transfer coefficients of various building materials. A residential building has been simulated in the Designer Builder software version 5.5.0.012. This software uses the Energy Plus Engine 8.6 to analyze the collected data. The dimensions of the building are 15x10x3.5 and is in east-west direction. The window-to-wall ratio on the south and north fronts is 30 percent; the eastern front includes a door while no opening exists on the western front. Moreover, according to the default stings of the software, other variables exerting influence on the energy consumption of the building are also selected. This research examines external walls, roof and window's glasses of the building's envelope, separately. To analyze the thermal resistance of the wall, 16 walls with different materials and thermal resistance coefficients were simulated. The roof is examined in both flat and sloping forms with uncontrolled roof gaps. The sloping roof is also consisted of two parts, one that interacts with its surrounding environment and the other that its bottom separates the sloping roof from the living space. Furthermore, 18 types of glasses have been examined to assess the relationship between heat transfer coefficient of multi-layer glasses and energy consumption of a building. The results show that increase of the heat resistance of the building envelop reduces the heating load of the building more than its cooling load. Furthermore, this research proposes the appropriate thermal resistance of the different components of the building's envelope. The results indicate that the suitable thermal resistance for walls, flat roofs, sloping surfaces and attic floor are m2.k/W 2v-3.5, m2.k/W3, m2.k/W 1.5-2.5 and m2.k/W 1.5, respectively. Likewise, the results show that reducing the glass transition coefficient of the multi-layered glass of the window has no significant effect on reducing the heating and cooling load of the building.