Empirical and human response studies of personalized ventilation combined with underfloor air distribution system

Abstract

This doctoral research is aimed at exploring the use of Personalized Ventilation (PV) system in conjunction with an Under Floor Air Distribution (UFAD) system (PV-UFAD) with focus on improvement of occupants? thermal comfort and inhaled air quality in an energy efficient manner. The problem of ?cold feet? and ?warm head? in conventional UFAD systems employed for cooling applications are well documented in the literature. In the present study, it is hypothesized that PV air will reduce the uncomfortable sensation of ?warm head? by providing fresh air at the facial level while the UFAD system operates with a warmer supply air temperature, thereby addressing the ?cold feet? issue. The experimental conditions for the overall research project, including the physical and human response measurements involved different combinations of UFAD supply air temperature (22 ?C and 18 ?C) and PV supply air temperature (22 ?C and 26 ?C) as well as three experiments at reference conditions without PV, i.e. UFAD with supply air temperature at 22 ?C and 18 ?C as well as ceiling supply mixing ventilation (CSMV) air diffuser. The PV air flow rate was tested with 10 L/s and 5 L/s which result in 0.7 m/s and 0.3 m/s facial velocity respectively. Objective measurements and subjective assessments were employed in this research to investigate the thermal and IAQ performance of UFAD-PV and to assess the acceptability of the UFAD-PV system by tropically acclimatized subjects. A breathing thermal manikin was employed for the objective measurements. Temperature and velocity parameters were measured as well. Subjective responses were collected by means of a questionnaire survey. The results of the manikin measurements reveal that the warmer UFAD supply air temperature can result in a warmer thermal environment in the lower space of the occupied zone. Subjective responses also showed that the warmer thermal environment created by the warmer UFAD supply air temperature has a positive effect on the thermal sensation and acceptance of air movement at feet level. The performance characteristics of combining PV with UFAD revealed that the use of PV provides cooler thermal sensation at face and improves the whole body thermal comfort and the acceptability of air movement in comparison with use of the UFAD or CSMV alone. By granting the occupants opportunity to choose the PV flow rate, more occupants could make themselves comfortable with the air movement. The measured inhaled air quality and perceived inhaled air quality were also improved by elevated PV air flow rate. Furthermore, the potential to save energy using the PV-UFAD system is explored by comparing with the conventional mixing ventilation system. Heat removal abilities were found 20% ~40% improved by using UFAD-PV system when compared with that of CSMV system. Moreover, by incorporating the heat-pipe unit into the PV Air Handling Unit (AHU) the energy savings from pre-cooling and reheating was up to 35.6% of total energy consumption of the cooling the outdoor air when compared with a conventional system. The most demanding conditions for the PV supply air temperatures could be achieved by using less reheat energy when the heat pipe was involved. In view of increased acceptability of perceived air quality and low risk of thermal discomfort combined with the enhanced benefits of PV system (such as increased personal exposure effectiveness), the present study identified that a combination of UFAD and PV consisting of a warmer UFAD supply air temperature (22 ?C), higher PV flow rate and cooler PV air temperature (10 L/s and 22 ?C) would be ideal in a hot and humid climate.