Heating and cooling buildings needs too much energy consumption; thing that is becoming more expensive. Internal thermal comfort is essentially evaluated according to bioclimatic conditions and energy consumption. So the aim of the study is to reach optimum thermal comfort conditions with less energy consumption according to orientation factor in a semi arid climate. In order to point out the relationship between orientation and energy consumption a site investigation is undertaken in Constantine new urban extension called “Ali Mendjeli”. It concerns readings of air and surface temperatures and relative humidity that are compared to thermal comfort limits for such climatic conditions. Moreover, a simulation using TRNSYS (Version 14.1) is done to validate site findings comfort more ever to the search of optimal building orientation which improves internal thermal conditions with economy in energy is tested. The results confirm that taking into consideration the orientation factor reduces building energy consumption and makes it participating in the optic of new conception: Energy conservation buildings.