Center for the Built Environment

During recent years an increasing amount of attention has been paid to air distribution systems that individually condition the immediate environments of office workers within their workstations. As with task/ambient lighting systems, the controls for the “task” components of these systems are partially or entirely decentralized and under the control of the occupants. Typically, the occupant has control over the speed and direction, and in some cases the temperature, of the incoming air supply. Variously called “task/ambient conditioning,” “localized thermal distribution,” and “personalized air conditioning” systems, these systems have been most commonly installed in open-plan office buildings in which they provide supply air and (in some cases) radiant heating directly into workstations. A large majority of these systems have included a raised access floor system through which underfloor air distribution is used to deliver conditioned air to the space through floor grills, or in conjunction with the workstation furniture and partitions.

The purpose of this document is to present and discuss engineering and application guidelines and recommendations that encourage the intelligent design, installation, and operation of task/ambient conditioning (TAC) systems in commercial buildings. A well designed TAC system should take maximum advantage of the potential improvements in thermal comfort, ventilation performance, indoor air quality, and occupant satisfaction and productivity, while minimizing energy use and costs. The development of these guidelines is based on a compilation of available information, including (1) TAC system design experience described in the literature, (2) laboratory experiments on several TAC systems, (3) field studies of TAC systems installed and operated in buildings, (4) computer simulations of whole-building energy use with and without TAC systems, (5) a survey of heating, ventilating, and air-conditioning (HVAC) engineers and manufacturers about TAC systems, and (6) the results of the Workshop on Task/Ambient Conditioning Systems in Commercial Buildings, May 4-5, 1995, held in San Francisco, California [Bauman 1995]. Since experience with TAC systems is still rather limited, the recommendations and guidelines contained in this guide represent our best estimates at this time of sound engineering judgment. As more information and experience becomes available, we expect to periodically revise and improve this document. The guide is intended for use by design engineers, architects, building owners, facility managers, equipment manufacturers and installers, utility engineers, researchers, and other users of TAC technology.