Energy Efficiency Evaluation Of Especial Type Of Iranian Residential Building With Vast Western And Eastern Wall

The building envelope is one of the most important systems affecting energy efficiency of a building. Comprehensive analyses and researches of heat loss through the envelope are vital for design of energy efficient buildings. Generally, it is regarded that heat is mainly lost by conduction. In addition, the gradient between indoor and outdoor temperatures highly influences the energy consumption in the arid regions.Influence of western and eastern walls in energy consumption of especial residential buildings have been investigated in this study. Mentioned type of mid-rise residential buildings has evolved in the big cities of Iran (such as Mashad) over last two decades and located between one story houses. Every years more than 90% of new constructed residential buildings applying hollow clay blocks with poor thermal properties for exterior walls in Mashad. According to the Iranian Islamic architectural rules, these apartments cannot have any view to the one-story houses, which are located in their neighborhood (eastern and western parts of apartment). Hence, these apartments have no window on their vast eastern and western walls and the average of window to wall ratio in these apartments is around 10-20 percent. Here, a comprehensive research has been performed on heat transfer through the walls of mid-rise residential buildings, to investigate the impact of different factors and possibility of performing various approaches on reduction of energy consumption in the mentioned buildings. In this case, the effects of a suggested construction method using insulation materials instead of conventional construction method (hollow clay block wall) on decreasing the consumed energy of the walls were studied. For this purpose, two apartments with different construction methods (conventional and suggested methods) of walls are selected in Mashad-Iran and the amount of energy consumption in these apartments were investigated by simulation and in situ measurement methods. To investigate the behavior of these apartments, CFD software PHOENICS was applied to simulate wind velocity around and inside the building in intermittent air conditioning with natural ventilation and determine the amount of ACR of building in natural ventilation condition during summer. The simulations on wind velocity distribution inside of buildings exhibited that most of apartment area (about 95%) was comfortable zone, and ACR was reach up 23 times per hour. In addition, building walls were investigated by simulation software (e.g. K-Value and Therm-6) and laboratory measurements (by Hot Box). The results of simulation and measurements showed that applying suggested wall instead of conventional wall reduced about 59% and 45% of heat fluxed through wall, respectively. The evaluation also showed good similarity for results of "time lag"and"decrement factor"by simulation and measurement methods. In addition, two studied apartments were simulated by DeST-h (annual dynamic energy simulation software) to evaluate the effects of various factors on the building cooling-heating loads. The results of indoor temperature of studied buildings indicated applying natural ventilation could decrease about 80-90% of requirement time for air-conditioning during summer. The results also implied that the important factors in the energy loss in the conventional building are eastern wall, western wall, roof and floor, and their shares for energy consumption are about 19, 18, 14 and 7%, respectively. To approach real condition, in situ measurements are performed on two full-scale apartments in Mashad. Therefore, the amount of energy consumption and heat flux through wall in these apartments during long and short terms in-situ measurements were determined and the results were evaluated. The evaluations indicated that not only total energy consumption of conventional apartment were 43% more than suggested apartment, but also total heat flux through western and eastern wall of conventional apartment was 94% more than suggested apartment. Finally, simulation and measurement methods showed good similarity in case of cooling and heating loads and indicated applying suggested wall instead of conventional decreases energy consumption of studied buildings. The results of cooling loads showed about of 29, 24% reduction, and results of heating loads present about of 34, 30% reduction for simulation and measurement methods, respectively.In general, due to similar construction time and cost of conventional and suggested walls and the impact of suggested walls on improvement of energy conservation of residential buildings, applying the new insulated wall is one step toward sustainable building hence the developed construction method has merit to be replaced with conventional method for the studied residential buildings to reduce energy demand with constant cost.