The aim of this work was to determine the optimal parameters of the energy renovation of the building envelope for an existing family house located in the area of the Northern Adriatic and to determine the optimal operating parameters of the heating, cooling, ventilation and hot water preparation system. The main goal was to reduce energy consumption for heating and cooling and achieve nearly zero energy building. In order to achieve this, energy renovation measures were implemented for the building envelope, which included the installation of insulation on exterior walls and the replacement of existing windows and doors. Also, the existing heating system with a fuel oil boiler was replaced with a more energy-efficient thermo-technical system with the use of renewable energy sources. The computer program TRNSYS was used to carry out the simulations. In the first part of the work, an analysis of the energy renovation of the building envelope was carried out, which included the calculation of the annual energy consumption for heating and cooling for different insulation thicknesses of exterior walls and for different glazing characteristics. The optimal solution is determined on the basis of the minimum total costs consisting of investment costs and operating costs for the considered period of 20 years. The insulation of the external walls with 5 cm thick mineral wool was chosen as the optimal measure which achieved a condition that meets the currently valid regulations. In the second part, the analysis of the chosen concept of the thermo-technical system was carried out. A new technical system is planned, which includes mechanical ventilation with heat recovery, an air-to-air heat pump, solar thermal collectors and photovoltaic panels. Simulations of the produced energy for heating and cooling and the electricity consumption were carried out, and the optimal parameters were determined based on the calculated specific consumption of primary energy and investment and operating costs. With the energy renovation of the house and the implementation of an energy-efficient thermo-technical system with the use of renewable energy sources, nearly zero energy consumption was achieved. Also, it is evident from the results that when applying energy-efficient systems, the investment return period is long.