The objective of this study is reduce the energy consumption for heat source distribution in HVAC systems. We carry out the investigate about building energy reduction method in heat source distribution system and the present tendency of decentralized HVAC systems and equipments. And develop the building energy analysis program to calculate the energy consumption precisely in heat source distribution system. We prepare the sample designs which adoped natural circulation of refregerant and calculate the energy consumption for each sample design. (author). refs., figs., tabs.