There are 160 million buildings in the European Union, which consume more than 40% of all energy in Europe. Thus, energy use in buildings is one of the main factors affecting the fossil fuel consumption and CO2 emissions. Under the Kyoto Protocol, the European Union has to reduce emissions, but it should be noted that the amount of energy used in building services is increasing. Ventilation and air conditioning systems today are complex and highly automated systems that are able to maintain required internal air characteristics and quality. But together with system’s complexity and automation level power consumption grows as well and sometimes may reach up to 40% of the total building energy consumption. Due to the regulation of 2010/31/EU directive that starting from the 2020th all new built and reconstructed buildings should be "nearly zero energy buildings", this article aims to clarify the energy-efficient ventilation system development strategy as well as overview of detailed indoor climate simulation applications.