Development of a ductless air supply system using low temperature air.

This paper proposes a new ductless air supply system with a ceiling plenum chamber using low temperature air as a secondary HY AC system for an ice thermal storage system. The proposed air supply system mixes low temperature air with return air from a room using a mixing fan unit (MFU), pressurizes a plenum chamber with the mixed air and supplies the air to the occupied room from diffusers on the ceiling. The purpose of this study is to develop a new HY AC system to utilise low temperature air, to prevent cold draught and dew condensation, to keep thermal comfort in the room and to save fan energy consumption. Room temperature is fed back to controllers that regulate fan motors of an air handling unit and an MFU with inverters. Low temperature air from an air-handling unit is controlled at 10°C by regulating flow rate of chilled glycol. A 7m and 10m and 3m height room is provided to evaluate the proposed system. 24-hour time series data are obtained by data loggers. Vertical temperature distribution is within set point ± 1K and horizontal temperature is controlled between 25.7 and 26.2°C  at l.5m height above floor. Time-averaged PMV at the centre of the room is +0.24 and PPD is 6.2%. 24-hour time-averaged temperature is 26.2°C at the sensor for control and the root mean square error is 0.18K. Temperature difference between mixed and room air is averaged to 9K. It prevents cold draught due to low temperature air supplied directly to the room from ceiling mounted _air diffusers. Air velocity at the centre of the room is averaged to 0.22m/s and turbulence intensity is 8.6%. The results meet IS07730- l 994. This system is also expected to reduce the fan energy consumption by 70%. In addition, use of night electric power for ice storage systems saves energy cost of a chiller. The ductless air supply system using low temperature air is appreciated satisfactory for thermal comfort and energy saving.