An experimental investigation into the pull-down performances with different air distributions

• Pull-down (cooling a room) process for a room to reach a thermal comfort state.
• Experimental investigation to find the time and energy used for pull down.
• Stratum ventilation, mixing ventilation and displacement ventilation are tested.
• Stratum ventilation is found to use much less time and energy.

The purpose of this study is to investigate the loads and lengths of the pull-down periods (the time used to achieve a comfortable thermal environment before a room is ready for occupation) with mixing ventilation, displacement ventilation and stratum ventilation. In a typical classroom in Hong Kong, experiments begin with the same initial hot thermal environment. Based on ASHRAE 55-2010, ISO Standard 7730 and literature, existing indices PMV, PD and ADPI, calculated from measured data, are used as the thermal comfort criteria to determine the end of the pull-down period. The results indicate that stratum ventilation outperforms the other two air distributions during the pull-down period in terms of rapidity and energy consumption. For the rapidity of the pull-down process, mixing ventilation spends a shorter time than displacement ventilation, while stratum ventilation spends less than half of the time the other two spend. The average pull-down load of stratum ventilation is only around a quarter of that of mixing ventilation or displacement ventilation, The exergy consumption of the chilled water used for the pull-down of stratum ventilation is also lower than that of the other two distributions.