Thermal comfort in naturally ventilated office spaces equipped with intermittent personalized ventilation

Intermittent personalized ventilation (IPV) has been reported to maintain overall thermal comfort (OTC) for users when used with mixed convection at elevated room temperatures while demonstrating a lower energy consumption compared to steady personalized ventilation (PV). However, the performance of IPV in naturally ventilated office spaces compared to steady PV has not been studied. The IPV may offer enhancement to the OTC due to the interaction between IPV-induced turbulence and natural ventilation (NV) disturbances affecting the thermal boundary around the occupants. The IPV may offer enhancement to the OTC due to the interaction between its turbulence and the disturbances created by natural ventilation (NV). This work aims to investigate the IPV induced turbulence with the disturbances created by NV and study its effect on the OTC of the user. A 3D computational fluid dynamics model of an office space with two seated occupants (one using IPV and one steady PV) was developed and validated experimentally in an outdoor naturally ventilated climatic chamber. A parametric study was conducted at room average temperature of 30.3 °C, IPV supply temperature of 24.8 °C at different IPV frequencies and different turbulent intensities (TI) of the entering outdoor air. The IPV frequency and NV TI influence the rate of entrained room air and the transient convective heat transfer around the occupant head and upper body, and hence affects the OTC. It was found that increasing IPV frequency from 0.5 Hz to 0.7 Hz significantly improved OTC by 39.6 % and 38.3 % for outdoor TI of 40 % and 80 %, respectively However, a further increase in IPV frequency to 1.0 Hz yielded no significant change in OTC for the 40 % TI case, while a slight decrease of 6.2 % in OTC was noted in the 80 % TI scenario. An energy analysis showed that operating IPV at frequencies of 0.5 Hz, 0.7 Hz, and 1.0 Hz saved 20.14 %, 23.97 %, and 26.18 % of energy, respectively, compared to steady PV, achieving equivalent OTC levels.