This paper describes the analysis of cooling operation data for an office building with multiple air-conditioning heat sources, and the estimation of energy saving effect of cooling water temperature relaxation.1. BEMS data of an office building in Tokyo was analyzed to reveal the cooling operation of the air-conditioning heat source. Furthermore, chilled water temperature characteristic equations were created.2. A study using a simulation model of the heat source that incorporates the chilled water temperature characteristic equations confirmed that more energy-saving potential from further relaxation of the temperature for the mid-term period.