We have proposed a new floor supply air conditioning system, using phase change material to augment building mass thermal storage. A scale model was constructed for such a system. Granules containing phase change material (PCM), with a phase change temperature of about 20 degrees C, were made from foamed glass beads and paraffin waxes. Results from measurements simulating an air conditioning schedule in office buildings indicate that 89% of daily cooling load could be stored each night in a system that used a 30 mm thick packed bed of the granular PCM. (c) 2005 Elsevier B.V. All rights reserved.