The technology known as underfloor air distribution (UFAD) is not altogether new. Contractors have been using it for some time to supply cooling in out-of-the-norm situations, such as computer rooms and laboratories.

But today, this once niche technology is slowly moving over into more mainstream commercial applications. In fact, the technology is just one of several that are being studied by researchers at the University of California-Berkeley’s Center for the Built Environment (CBE). The center educates individuals and manufacturers on current trends related to UFAD.

According to the CBE, UFAD technology has a number of benefits contractors can tap into. And although the market for underfloor air is still growing, researchers suggest that in the near future, interest in UFAD will continue to rise.

With an underfloor air distribution system, costs for reconfiguring office space can be reduced because supply outlets are in the floor.


UFAD systems utilize the open floor space between the structural concrete slab and the underside of a raised access floor. Air is then delivered through a variety of supply outlets that can be placed in a number of locations on the floor. These outlets can even be placed in office dividers or partitions. These underfloor supply outlets can also be zone controlled, if desired.

According to CBE, UFAD systems are the same as conventional overhead systems in terms of the types of equipment used at the cooling and heating plants and primary air-handling units (AHUs). Supply air is ducted from the AHU to the underfloor plenum, where it typically flows freely or in combination with a minimum amount of ductwork under the floor to the various supply outlets. The conditioned air that circulates in the environment is then returned through an unducted plenum in the ceiling.

Fred Bauman, P.E., a research specialist and project leader at Berkley’s CBE, says that the installation of an underfloor system is not particularly difficult, but could be somewhat challenging for a contractor with little experience in UFAD technology.

Bauman says that one issue to keep in mind when installing a UFAD system is proper sealing of the underfloor plenum. According to Bauman, because the conditioned air flows freely under the floor, the plenum must be sealed tightly or it could end up wasting energy. He also says that this issue is much like checking for leaky ducts in traditional air conditioning systems.

Finally, he says that contractors must not forget about other important necessities associated with traditional systems, such as humidification, dehumidification, and outside air.


“UFAD technology is not just a fringe practice anymore,” says Bauman.

He explains that consumers and contractors alike are realizing many important benefits of using UFAD in more common applications. Two of the main benefits are energy savings and cost savings.

Bauman says that the CBE has researched the growth and benefits associated with UFAD. Not only is it growing in popularity, but Bauman believes that a well-designed UFAD system can save a great deal of money for consumers over the life cycle of the system.

One reason UFAD can save on energy costs is due to how the conditioned air flows freely through the space. The air is not forced through extensive ductwork as in traditional systems, thereby reducing static pressure and the required fan energy.

Bauman also explains that in a cooling operation, the upward (floor-to-ceiling) movement of air in the room takes advantage of the natural buoyancy of heat gain to the space, producing a vertical temperature gradient. If properly controlled, this stratification can lead to reduced supply air quantities and lower energy used compared to conventional overhead systems. Because air is delivered directly into the occupied zone, for cooling operation, supply air temperatures for UFAD systems must be warmer than that used for conventional overhead systems to avoid overcooling nearby occupants.

The center also believes UFADs can save on building costs, benefiting both the contractor and the consumer. UFAD eliminates the need for large amounts of costly ductwork in the ceiling. All that is needed is a smaller ceiling plenum to accommodate unducted air returns.

By installing the system in a raised access floor, costs associated with reconfiguring building services are reduced. UFAD frees up space for consumers and building owners.

Bauman explains that there is more flexibility in moving panels and partitions. “The underfloor plenum is more accessible,” he says. He also explains that UFAD makes it possible for facility managers and in-house personnel to take care of the building’s air conditioning system.

“For the contractor, the benefits are in the long run,” says Bauman. “It’s easier to work on the floor surface than on the ceiling with ladders.”


CBE has several designers, engineers, architects, and HVACR manufacturers as partners. They are helping to fund various research activities of the center and, in return, learn about new trends and developments associated with indoor environmental technology.

Carrier Corp. is one such company. Ed Gilbert, senior product manager for Carrier’s Commercial Group, says that UFAD is currently in limited use, but the application could very well become more than just a trend.

“It will be growing,” says Gilbert. “Buildings are changing and workspace desires are changing.”

Gilbert explains that more and more building owners are realizing the cost savings associated with UFADs. He says that an increasing number of customers are looking for more high-tech work environments.

For contractors, Gilbert says UFADs provide a number of benefits. There are several opportunities for a system to be installed. One example would be for building renovations, such as a vacant urban building or warehouse. These types of settings can have high ceilings, which can make the installation of ductwork more challenging.

Also, some older buildings may have floors that are not level. In this case, an access floor can be installed with the UFAD system.

Gilbert also suggests that UFAD could be beneficial for environments that require better indoor air quality (IAQ). One example would be a casino, where the UFAD system could remove room tobacco smoke through ceiling returns.

Bauman says that on the West Coast, primarily in California, UFAD is beginning to take off. The application is even more beneficial in locations with dry climates, where air conditioning is almost an everyday necessity.


CBE has begun conducting case studies on various UFAD installations throughout the country. The center’s first case study is the Teledesic Broadband Center in Bellevue, WA. According to CBE, the building was originally a food distribution warehouse and was transformed into office space for a technology company.

The center asserts that UFAD was an obvious choice for the building because of a 25-foot ceiling-to-floor height. The UFAD system was able to promote vertical stratification for the upper levels of the building beyond where individuals work.

CBE says that by installing the air distribution system in the floor, the Teledesic building was able to avoid a cluttered interior.

According to the case study, CBE believes that the UFAD application has so far been a success for Teledesic.

The center says that design for the system was relatively simple. Researchers also report that the UFAD system has created a high degree of temperature uniformity in the building, as well as a lack of employee complaints, low noise, and a limited amount of system adjustment.

CBE just completed another case study on the FNBO Technology Center located in Omaha, NE.

Profiles of several commercial buildings with UFAD systems, including the Teledesic case study, can be found at the CBE underfloor technology website, More information on CBE can be found at (website).

Publication date: 07/29/2002