Spatial Efficacy of Respiration Monitoring using Doppler Radars for Personalized Thermal Comfort Assessment

Recent research efforts have shown that human thermophysiological features could play a crucial role in inferring occupants’ thermal comfort, which is required for comfort-aware heating, ventilation, and air conditioning (HVAC) operation. Our previous studies have demonstrated that variations of respiration, a representative human thermophysiological feature, can be non-intrusively quantified by a Doppler radar sensor (DRS). However, in pursuit of enabling human-aware rooms in buildings, in this study we have explored the impact of distance and position of the respiration monitoring system to investigate the potential of DRS systems as a ubiquitous apparatus in the real-world scenarios. Through experimental studies, respiration characteristics were evaluated in different locations and angles relative to the location of the measurement device. The measurements were carried out using a DRS system and a respiratory belt for ground truth data collection. The noise artifacts were reduced by applying the Savitzky-Golay method and Hann window, and respiration was identified by selecting the frequency component with the maximum amplitude in the typical breathing frequency range (0.1 to 0.5 Hz). Our analyses demonstrated that the signal from a cost-effective DRS technology without the use of external amplifiers could cover a range, within 1.0m longitudinally and 0.5m laterally, which is sufficient for an individual sensing given a normal office environment. It was also observed that the use of an external amplifier extends the range of the DRS sensing but at the same time accentuates the noise. Therefore, advanced noise removal methods are needed to increase the range of robust sensing. This study contributes to DRS deployment strategies for realization of comfort-aware systems.