Sense and sensibility – The utility of HVAC sensors for large zones

Abstract

Utility of deploying environment/occupancy sensors in buildings is well studied. However, the settings in the existing works are limited in scope and hence the observations may not be generalizable. This paper proposes an approach to quantify the utility of sensing in generic zone setups. The usefulness of sensing temperature and occupancy is quantified in terms of ‘information-utility’ and ‘actuation-utility’. The information-utility is quantified as the minimum number of sensors required to reconstruct the ground truth within a tolerable error; and the actuation-utility is the energy savings due to sensor deployment from a baseline, subject to acceptable occupant comfort. A thermal model based on thermodynamic principles is used to model the zone responses while quantifying the sensing utility.The approach is evaluated through data from a real-world office building. Key findings include: (1) sensing population accurately requires higher number of sensors than sensing temperature. (2) Under steady-state, maximum actuation-utility of sensing at finer spatial resolutions increases with number of actuators. (3) For a real-world case, the maximum actuation-utility was ∼30%. After accounting for system inertia, the maximum and average actuation-utility of sensing were 22% and 5% respectively. This suggests that frequently occurring occupancy patterns influence the average utility of finer-sensing.