Do Spatially Distributed Sensor Measurements Provide Better Representation of Indoor Environment than Single Sensor Measurements? A Mechanically Ventilated Office Space Case Study

Most existing office buildings are equipped with indoor environmental quality (IEQ) sensors that are connected to the Building Management System (BMS) and provide feedback to the heating, ventilation and air-conditioning (HVAC). Unfortunately, they are often installed in locations selected based on practical reasons rather than for reliable representation of IEQ at actual workplaces. This leads to a difference in the IEQ sensed by the BMS and the occupants, resulting in increased complaints and decreased occupant satisfaction. This paper investigated whether additional sensors spatially distributed in mechanically ventilated office spaces provided a better representation of IEQ than originally installed BMS-connected sensors providing single sensor measurements. Two mechanically ventilated office spaces were equipped and monitored with additional sensors from January to May 2019. Indoor temperature and CO2-concentration were measured with sensors located at the perimeter and the interior of the office spaces. Statistical analysis (confidence intervals and p-value) was used to determine whether the difference in sensor measurements between the two locations was significant. The results showed that the temperature measured at the perimeter was significantly lower (1-1.7 degrees C) than the temperature measured at the interior of the office space. Overall, the difference in the measured CO2-concentration at the monitored locations was statistically insignificant (< 162 ppm). The results suggest that whereas one CO2 sensor seems sufficient to adequately represent IEQ at the office spaces, at least two temperature sensors should be deployed in 20 - 210 m(2) office spaces with mixing ventilation and a 0.33 window-to-wall ratio. Additional analysis showed that accounting for the actual IEQ at the office spaces can be associated with increased energy demand. Using the sensor measurements at the perimeter for HVAC control can increase heating energy use by 0.4 - 40%, depending on the climate zone and building type.