Field study of the impact of a desktop task/ambient conditioning system in office buildings.

A field study was carried out to assess the impact of installing a desktop task/ambient conditioning (TAC) system at 42 selected workstations within three San Francisco office buildings occupied by a large financial institution. In this study, field measurements, including subjective surveys and physical monitoring, were performed both before and after the TAC system installation to evaluate the impact of the TAC system on occupant satisfaction and thermal comfort, as well as the thermal environments within the office buildings. For comparative purposes within each building, a control group, consisting of workers who did not receive a desktop TAC unit, was studied concurrently. During the follow-up field tests, performed three months after the TAC system installation, measurements were repeated under three different room temperature setpoint conditions (normal, set-up, and set-down) to investigate the ability of the occupants to use the desktop TAC units to control their local environment in response to a wider range of ambient temperatures. Survey results show that among the six building assessment categories investigated, installation of the desktop TAC system provided the largest increases in overall occupant satisfaction for thermal quality, acoustical quality, and air quality. In terms of specific environmental factors, increased occupant satisfaction levels among the TAC group were strongly significant in comparison to changes within the control group for both temperature and temperature control. A large majority of the workers in the control group indicated a preference for higher air movement at operative temperatures of 73°F (23°C) and above. The percentage preferring higher air movement within the TAC group was significantly lower. Workers in the TAC group had the ability to use their TAC units to adjust the air movement in their workstations in response to changes in the ambient temperature. Over the range of operative temperatures covered by this field study, air movement preference and thermal sensation votes by workers in the control group indicated that they were more than twice as sensitive to changes" in temperature as those in the TAC group.