Ceiling radiation cooling that used well water as a heat source and air conditioning were jointly applied to a test house with high airtightness and insulation, and data obtained through a long-term survey at the test house were analyzed. Based on such values as COP, PMV and SET^*, comfort and energy-saving depending on operating methods were examined. The effectiveness of use of well water was investigated to find the degree of dependence on electric and natural energy. Data gained in the laboratory were compared with those obtained in the test house. It has been discovered that the joint use of air conditioning and ceiling radiation panels was most effective in terms of energy-saving and comfort. It has also been found that the use of well water was effective and that data from the test house were similar to the past data gained in the laboratory. This report shows that the ceiling radiation cooling system using well water is more effective than the conventional air conditioning system in terms of energy-saving and comfort.