Optimum Window Area for Residential Buildings in Ardabil and Tehran

Solar gain through windows compensate for their thermal weakness in building envelope. Free solar gains in this way have a significant effect on reducing heating load of the building. Then not only thermal comfort during cold season is obtained, but also the pollution induced by burning fossil fuels will be reduced. One of the simplest passive solar elements is south window which is vastly used in traditional and newly built buildings. In contrast to traditional ones, there is no specific size introduced for these windows in modern buildings so that designers may be able to apply them. Many researches have been carried out concerning windows, which cover up various subjects. Researches so far done mostly concentrate on specifications of the glass, day lighting from windows and optimum window area for passive solar heating. As Iran is situated in the solar belt of the earth, traditional buildings in this country mostly relied on passive solar heating through windows. In modern buildings also the same strategy for passive heating of interior spaces can readily be applied. In this paper the optimum window area for residential buildings of Ardabil (cold climate) and Tehran (hot-arid climate) is studied in order to obtain part of building's annual heating energy need by solar incidence through windows. The research is carried out by simulation. Two softwares were used, EnergyPlus for simulation and calculating hourly inside temperatures and heating load of the building and Ecotect as graphical interface. A typical room in each above mentioned cities was selected. The room under study has a south orientation. It was supposed that the room is surrounded by spaces having similar temperature and only its south wall with window contributes to heat transfer. There is no heating system in the room in order to see the effect of solar incidence inside. The window area was changed from 5% to 50% of the floor area in five steps intervals. The simulation was carried out considering three different window types and walls: no insulation with single glazing window, insulated south wall with single glazing window and insulated south wall with double glazed window. After selecting the proper window area, two typical residential buildings one in Ardabil and the other in Tehran were simulated considering four different cases, first with the building and the window area as it is and the other three cases with the optimum window area and the previously mentioned window and wall types. The results showed that by applying the optimum window area, heating load will significantly decrease. When the building is insulated according to Code No. 19 (Energy Conservation in Buildings), to prevent overheat during mild period of the year the window area should be decreased. Overall this study indicates that there are optimum window areas for buildings with and without insulation which by applying them heating load decreases and energy conservation will be met during cold period of the year, and also there will be thermal comfort inside within mild seasons.