Assessment of design parameter influence on energy efficiency in educational buildings in Tehran's climate

Energy efficiency and comfort consideration in building, contribute to significant energy saving and improvement of spatial quality. According to the importance of energy issues and lack of researches on energy use in educational buildings, climatic variation in the country and huge amount of energy consumption in educational buildings, the need of redefinition environmental design criteria is essential.
The main purpose of this article is to assess the influence of different design variables on comfort condition and energy consumption in the hot-Arid climate of Tehran. Most of the literature concerned with energy performance of school buildings is focused on using saving methods such as utilization of solar energy, constructional issues such as thermal insulation, infiltration, thermal mass, building materials, sun shadings and HVAC performance while assuring thermal comfort and indoor air quality of the building. However, the topic of energy performance and comfort condition of schools located in Iran’s climatic conditions has not been explored.
Nowadays, the subject of energy and optimizing energy consumption in different buildings and different societies is of great importance. On the other hand, energy experts claim that in designing educational buildings, natural energy resources should be used most. This subject is related to the energy consumption of schools. Furthermore, the positive effect of thermal and visual comfort on the quality of students’ education has been confirmed. Educational buildings generally are spaces with different functions.
However, classrooms not only have a central role, but also cover a great part of the school surface. Classrooms are the most fundamental and important units of the educational buildings in terms of energy consumption and thermal comfort. Students spend most of their time in the classrooms. Classrooms are more important, given the relative congestion in comparison with other educational spaces. Due to this fact, proper ventilation is considered necessary. Furthermore, students’ presence as latent thermal energy sources needs special attention in hot seasons. On the other hand, the same thermal sources can play an effective role in creating the comfortable conditions. Therefore, according to the difference of using pattern of these places and their higher internal heat gain, energy saving patterns in designing office and residential buildings cannot meet the needs of designing these buildings.
This research using simulation method is looking forward to realize the influence of different physical variables on energy consumption in educational buildings in Tehran’s climate; the different circumstances that were resumed by diverse variables were assayed. this process took place with the help of E quest energy simulating software and during this process in two separate parts, the independent effect of each variable and the simultaneous influence of applying diverse variables on energy consumption were simulated and its results were compared and discussed in various steps.to enumerate the most essential effective parameters in determining the amount of energy consumption in educational building in Tehran’s climate, we can point out the infiltration rate, heat isolating of the building roof and windows dimension.
To understand the range of influence of each variable on the comfort condition and energy consumption in the classroom, the difference between the maximum and minimum energy consumption obtained for each of the evaluated variables was considered. This difference represents the potential savings that can be achieved by improving a variable within the considered range of values. In this work, the four main orientations were analyzed.to observer the influence of design parameters on energy consumption, a base case classroom was designed and then the absolute and simultaneous effects of different parameters were assessed. The base-case was a common classroom to where all changes were applied and examined. Based on the similar studies, the recommended value for each design variable was determined to achieve a high performance classroom. The fixed parameters of the classroom were its size and height. The thermostat of the heating system was set at 21.1 C while the thermostat of the cooling system was set at 24 C, due to the dissimilarity in the children’s clothing in different seasons. The ventilation system provides a minimum of 4.5 air changes-per-hour (ach) when the classroom is occupied. When there were no children in theclassroom, the ventilation rate will reduce to save energy and the lighting level on the children’s tables was set at a minimum of 300 lux.
The results indicate that by reducing the infiltration rate of the classroom from 4.5 ACH to 0.75 ACH, an energy saving of about 65 KWH/m2.y will achieved. The airtightness of a classroom depends on windows and doors type, quality, and materials as well as on the quality of the construction process. For obtaining infiltration rate of about 0.75 ACH, designers and contractors should give more attention to the quality control of materials and construction and energy performance of the windows and the doors. Meanwhile according to the high amount of sun radiation during the year, roof heat insulation with a 6cm polyurethane layer would reduce the energy consumption by 40 KWH / m2.y in comparison with a roof without any heat insulation. Since the windows have a significant influence on the energy consumption and performance of the classroom, In order to reduce the energy consumption, dimensions and position of the windows should be choose very carefully. It was observed that the recommended size of north and south facing windows is equal to %12 of the classrooms floor area, whilst east and west facing windows should not be exceeds from %10 of the classroom area. If the windows size exceed from %12 of floor area, the glare effect would make visual discomfort for the students. In the simulation process, three types of light control features were evaluated. The results show that with the aid of smart lighting control system, the required electrical energy for lighting would reduce 34 KWH / m2.y. And finally the types of glazing have an important role in energy consumption of the classroom. It is observed that high performance was achieved when using lowemissivity glazing to reduce cooling loads and encourage daylight in classroom. Double glazed windows shows acceptable performance as well, in all directions compared to other alternatives.
Discussion and After analyzing the absolute effect of each parameters on energy consumption and comfort condition in the classroom, the cumulative effect of all parameters were analyzed. It is obvious that by changing of each parameter, the effect of other parameters will be changed. In this case two combination of design variables are assessed in “set-a” and “set-b” in which the annual energy consumption of the classroom is maximum in “set- a” and minimum in “set-b”. Based on the results obtained by simulation, this can be claimed that the proper design of classrooms in hot and arid climate, like the city of Tehran can reduce the amount of energy required for cooling, heating, ventilating and lighting systems from 232 KWH/ m2.y in “set-a” to 104 KWH/ m2.y in “set- b”. It means a %55 reduction in the classroom’s energy consumption. This statics are in conformity with the results achieved by researches in European’s green school which can reduce %55 up to %75 of heating energy consumption and 30 % up to 40 % of electrical energy consumption by using different tricks.