Penn Stateengineers have developed a terrorist-resistant A/C concept that they estimate costs less to install in new construction, is more energy efficient, and is cheaper to operate than the current industry standard. Dr. Stanley A. Mumma, P.E., professor of architectural engineering and developer of the concept, says, "Currently, if an anthrax-laden letter is opened in an office, a standard, forced air, cooling system can carry the airborne spores to other locations in the building. Forced air systems can also expose occupants throughout a building to odors and cold viruses or contribute to 'sick building' problems."

"By de-coupling the process of supplying fresh air to a building's occupants from the cooling and heating functions of the air conditioning system, we've developed an approach that is not only cheaper to install and operate but also provides superior cooling comfort."

The new approach is called a Dedicated Outdoor Air System (DOAS). It couples an independent fresh air supply with radiant cooling panels. The radiant panels, which use cool circulating water and can be installed as part of a building's fire sprinkler system, have a 15-year history of success in Europe.

Mumma explains that the DOAS/radiant approach does not use recirculated air. Consequently, noxious agents released inside are not transported to other parts of the building by the A/C system. They are diluted and exhausted from each space. In conventional all-air systems, there is a nearly 80% carryover of recirculated air.

In addition, because the fresh air supply is independent from the cooling and heating function, less air is needed and it can be treated and de-humidified at lower cost. The exiting "used" air can also be run through an energy recovery system to provide further savings.

The Penn State researcher notes that careful control of dehumidification creates a healthier environment by eliminating damp spots in ceiling tiles, insulation, carpets, and behind vapor barriers where biocontaminants can breed. He has designed a special humidity detector for his prototype system that shuts the cooling panels system down if the regular controls fail when the humidity becomes too high.

Mumma's prototype is in an architecture design studio on campus where 40 students work on senior projects. Fresh air enters through overhead forced air vents. Radiant cooling panels supply cooling. Wall radiators supply heat.

He notes that since humans generate the most heat from their head, having the cooling panels up above makes the room occupants feel more comfortable than the standard forced air delivery approach. Mumma estimates that his approach will save $2 per sq ft in new construction. Operating costs could be less than 60% to 70% of the cost of all-air systems. His analyses are posted on his website at along with detailed descriptions of the system.