An underfloor air conditioning system was developed and introduced into a high technology "smart" building in Tokyo. Experiments and numerical simulation studies were carried out prior to the introduction of the system, to preestimate its thermal comfort and energy saving effects. After the construction of the system, field measurement of the indoor environment and occupant surveys helped assess whether the system actually achieved its anticipated performance. The floor diffuser design was improved to prevent draught and local cooling of feet observed under the high cooling load condition. The results of these studies demonstrated that the indoor environment provided by the underfloor air conditioning system with the improved type of outlet meets thermal comfort requirements recommended by ASHRAE Standard 55-92 and maintains good indoor air quality (IAQ). Moreover, these studies revealed that, compared with a conventional ceiling diffuser system, the underfloor air conditioning system not only promotes exhaust heat removal with higher efficiency but also increases the use of natural energy. Possibilities to apply underfloor air conditioning to "task/ambient" or personalised systems were also discussed. The studies suggest that the system should be considered as an appropriate choice available for air conditioning systems in future smart buildings.

KEYWORDS: year 1995, underfloor, air conditioning, intelligent buildings, Japan, performance, thermal comfort, occupiers, measuring, temperature distribution, air flow, air quality, indoor, questionnaires, energy conservation, natural ventilation, energy storage