In this thesis, a heating and cooling system of a reference near zero energy family house (nZEB) for continental Croatia has been modeled and optimized. A gross surface of the house is 236 m2 (od which 177 m2 is heated and cooled) with heating demand of 22 kWh/m2, and cooling demand of 88 kWh/m2. Data on the energy required for heating and cooling was previously calculated in the PE Project. The system consists of a heat pump as a production system and fan coils. Using the data for energy demand, a model for the calculation of the system’s electricity consumption has been made on an hourly basis for a referent meteorological year. The water supply temperature for heating has been modeled using a heating curve, while the supply water temperature for cooling has been set as constant 7°C. The values of the COP and EER of a heat pump, needed for the calculation of the electricity consumption, have been determined by interpolating manufacturers’ data for different working conditions. The annual electricity consumption for the operation of the heating and cooling system is 5235 kWh (30 kWh/m2). The optimization of the supply water temperature was also done, with the purpose of lowering the energy consumption. As a result of the optimization, the annual electricity consumption has been reduced to 4646 kWh (26 kWh/m2), which is a reduction of 11%. The consumption of a domestic hot water (DHW) heating system has also been calculated. The system consists of a solar collector and a tank with an additional electric heater. The required water temperature in the tank is 60°C. Energy demand for DHW has been calculated in accordance with the HRN EN 15316-4-3:2008 standard and amounts 2894 kWh, out of which 1770 kWh (61%) can be provided by the solar collectors.