Center for the Built Environment

This study assesses the impact of sensor number and placement on the energy needed to condition a typical office using several likely variants of an underfloor air distribution system (UFAD). The study uses an empirical-based room stratification model developed from full-scale tests of UFAD systems. Annual energy consumption is calculated for an interior zone using outside air temperature bin data. The comfort criteria are taken from ASHRAE standard 55-92. The simulations indicate that there are benefits derived from using more than one temperature sensor to control conditions in the occupied zone of a room. Among these are: 1. By adjusting both supply air temperature and volume to maintain the maximum allowable thermal gradient in the occupied (lower) part of the room, an optimal supply air condition can reduce energy use (relative to the best arrangement of a single sensor) while maintaining comfort; 2. Discomfort caused by stratification can be detected by having one of the sensors located at foot level; 3. For the simulated UFAD interior zone of a typical office building in Sacramento, an overall energy saving of 8%/24% (VAV/CAV respectively) can be achieved when two sensors as opposed to one are used to control room conditions.