The global energy context of the year 2018 makes us pessimistic about the future. The geopolitical, environmental and socio-economic aspects are linked to the political tensions of countries that hold and manipulate the global energy market. These countries are haunted by the population growth, the depletion of fossil resources and the global economic crisis. Each country is trying to find reasonable solutions to deal with this crisis. Unfortunately, these solutions always have direct negative repercussions on the population and on the environment. In this paper we present a case study developed in Algeria and inspired by the current and critical socio-economic situation of the country, in particular, the application of energy-saving techniques to an existing building. The investigation was conducted by using both simulation software and real interventions. We analyse some of the major components, such as building’s orientation and exposure to daylight which have significant impact on energy consumption. We present the concept of Building Performance Simulation Analysis, using Autodesk ECOTECT Analysis and COMSOL Multiphysics software, and give full consideration to various ecological energy-saving methods. Using our models, we present a possible solution for retrofitting a building to minimize its energy consumption. The results are useful for both building energy conversation and creating a comfortable living environment in future.