Cooling efficiency of a spot-type personalized air-conditioner

Publication date: 15 August 2017
Source:Building and Environment, Volume 121
Author(s): Shengwei Zhu, Daniel Dalgo, Jelena Srebric, Shinsuke Kato
This study defined Cooling Efficiency (CE) of a Spot-type Personalized Air-Conditioning (SPAC) device as the ratio of the additional sensible heat removal from human body induced by SPAC and the device's cooling capacity. CE enabled the investigation of SPAC performance on the occupant's sensible heat loss (Q s ) and thermal sensation by its quantitative relation with the change of PMV level (ΔPMV). Three round nozzles with the diameter of 0.08 m, 0.105 m, and 0.128 m, respectively, discharged air jets at airflow rates from 11.8 L s⁻¹ to 59.0 L s⁻¹, toward the chest of a seated or standing human body with a clothing of 0.48 clo. This study developed a validated CFD model coupled with the Fanger's thermoregulation model, to calculate Q s in a room of 26 °C ventilated at a rate of 3 ACH. According to the results, Q s , CE and draft rate (DR) at face had significant positive linear correlations with the SPAC device's supply airflow rates (R ² >0.96), and a negative linear correlation for ΔPMV. With DR = 20% at face, CE was always under 0.3, and ΔPMV was around −1.0-1.15. Interestingly, both CE and ΔPMV had the least favorable values for the air jet produced by the nozzle with the diameter of 0.105 m independent of body posture. In conclusion, although SPAC could lead to additional Q s by sending air at a higher airflow rate from a smaller nozzle, the improvement in cooling efficiency and thermal sensation had a limit due to draft risk.