This paper investigates the problem of converting a conventional building to nearly zero energy building (nZEB) and a novel methodology is proposed. This is realized by properly manipulating several variables that depend on potential constructional interventions, correct selection of the power of the thermal unit according to the needs of the house, proper selection of the renewable energy sources (RES) and energy storage system (ESS), as well as, considering the potential re-duction in the electric energy consumption that can be attained by an energy management system of the building microgrid. The proposed methodology is based on a flow of actions that their proper implementation is decided by a system of several evaluation parameters that consider the investment cost, the operational cost and the depreciation cost as well as the optimal utilization of the electric energy in the house. The final decision is obtained by minimizing a cost function that depends on the above parameters considering some predefined weighting factors that are provided by the residents of the house or the supervisor of the energy management system. The feasibility and the effectiveness of the proposed methodology for converting a conventional building to nZEB are validated by a simulation model that utilizes data obtained by measurements from a real building.
