Utilizing raised floor system to facilitate cable management becomes a trend in modern intelligent buildings. Underfloor ventilation systems, which make use of the sub-floor plenum below the raised floor for conditioned air distribution, are also gaining popularity. The ductless operating principle of the underfloor ventilation system enhances space flexibility. Supplying conditioned air from the floor level also inherents advantages in improving indoor air quality and energy saving. Two types of the underfloor ventilation systems are commonly found including the top-level return type (TR) and the floor-level return type (FR). Thermal comfort and indoor air quality aspects of both the TR and the FR. underfloor systems were experimentally investigated in the present study. The most commo...[ Read more ]

Utilizing raised floor system to facilitate cable management becomes a trend in modern intelligent buildings. Underfloor ventilation systems, which make use of the sub-floor plenum below the raised floor for conditioned air distribution, are also gaining popularity. The ductless operating principle of the underfloor ventilation system enhances space flexibility. Supplying conditioned air from the floor level also inherents advantages in improving indoor air quality and energy saving. Two types of the underfloor ventilation systems are commonly found including the top-level return type (TR) and the floor-level return type (FR). Thermal comfort and indoor air quality aspects of both the TR and the FR. underfloor systems were experimentally investigated in the present study. The most commonly used straight vane type floor supply diffusers were used in the experiments. The performance of traditional ceiling-based system with widely adopted 4-way spread type supply diffusers was also determined under the same conditions for comparison purpose. A controlled experimental room was developed to facilitate the experiments.

High risk of draught was observed near the supply outlet of the underfloor ventilation systems. However, draught discomfort can be reduced by the underfloor system compared to the ceiling based system. Similar to the traditional ceiling based system, vertical temperature differences in the occupied region were lower than 3°C under all the tested conditions for the TR system. Temperature variations higher than the international comfort standards were observed with the FR system when Archimedes number (Ar) was higher than 0.03. Lower Predicted Mean Vote (PMV) values were resulted with both types of underfloor ventilation systems compared to the ceiling-based one. Lower cooling effect should be provided when using the underfloor systems to avoid overcooling to the occupants.

The age of air experiments showed that the ceiling-based system maintained a uniform distribution of ventilation in the space. Compared to the ceiling-based system, improvements in ventilation were achieved with the use of TR or FR system in regions near the floor supply outlet. In spaces that were far away from the floor supply outlet, the ventilation performance of the FR system deteriorated. The performance of the TR system was found similar to the ceiling based system at far distance. The TR system was the most efficient one in removing smoke particles inside the whole room. The FR system removed particles in the lower part of the room better than the ceiling-based system. Improvements in particle concentration in the sitting person breathing level were achieved by the FR system.