In the U.S., traditional ventilation systems supply a mixture of outside and recirculated air in high velocity jets so that the indoor air in rooms is often well mixed. This can be an inefficient method of delivering outside air to an occupant. Task-ambient conditioning (TAC) systems are a ventilation technology with the potential for improved ventilation to the occupant. TAC systems may supply air from the floor, desk, or partitions and enable occupants to adjust the supply flow rate, direction, or temperature so that thermal conditions can be tailored to meet the individual's requirements.
 

Figure 6a. Desktop-based System

Figure 6b. Below Desktop System

Figure 7. Floor-based task ventilation systems
See also the Center for the Built Environment at the University of California, Berkeley, Underfloor web site. Underfloor Air Technology.

Mixing ventilation
Supply of air through ceiling-mounted diffusers or high-wall supply grilles and removal of air through ceiling-level or high-wall return grilles is conventional practice in US office buildings. Air is supplied in high velocity jets that entrain room air, promoting mixing. Complete mixing of the indoor air is the usual design goal. Indoor temperature control is achieved by regulation the supply temperature, supply flow rate, or both of these parameters. A thermostat controls the regulation of supply temperature. Generally, there are more occupants than thermostats and occupants are not able to adjust the thermostat setting.

Task or Personalized Ventilation

• What is task or personalized ventilation?

Task or personalized ventilation is a method for providing occupants with control of a local supply of air so that they can adjust their individual thermal environment. Controlled variables could be the supply-air temperature, velocity, direction, the ratio of room air to outside in the supply air, and the radiant temperature. These systems may provide all or part of the conditioned air to the occupied space. Task or personalized ventilation systems also have the potential to improve ventilation at the occupant's breathing zone because they can provide supply air preferentially toward the breathing zone. Supply air from these systems usually contains a high percentage of outside air, which generally does not contain a high concentration of indoor-generated pollutants. The air supply outlets of current task or personalized ventilation systems are located at the floor, mounted on the desk, or incorporated within the workstation partitions.

• How do task ventilation systems perform?

We have measured the air change effectiveness (ACE) of several task ventilation systems. The ACE is the ratio of the effective ventilation rate at the breathing zone divided by the effective ventilation rate that would occur with perfect mixing while at the same ventilation rate. With most commercial task ventilation technologies, the ACE was typically slightly greater than unity, for example, 1.0 to 1.2. We are presently developing a new air supply technology that can yield an ACE of 2.0.

Our colleagues at the University of California, Berkeley have shown that commercial task ventilation systems can enable occupants to adjust thermal conditions to meet their individual preferences. Center for the Built Environment.

For more information on publications concerning novel ventilation technologies see the Publication and Reference pages.