16 October 2002
A terrorist-resistant air-conditioning concept that engineers said will cost less to install in new construction will be more energy efficient and cheaper to operate than the current industry standard.
"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," said Dr. Stanley A. Mumma, P.E., Penn State professor of architectural engineering and developer of the concept. "Forced-air systems can also expose occupants throughout a building to odors and cold viruses or contribute to 'sick building' problems."
"By decoupling 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, called a Dedicated Outdoor Air System (DOAS), couples an independent fresh air supply with radiant cooling panels. The radiant panels, which use cool circulating water and can be part of a building's fire sprinkler system, have a 15-year history of success in Europe.
Mumma said the DOAS/radiant approach does not use recirculated air. Consequently, noxious agents released inside do not go to other parts of the building by the air-conditioning system. Instead, the system dilutes them and then exhausts them 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, the system needs less air and can then treat and dehumidify the air at lower cost. The exiting "used" air can also run through an energy recovery system to provide further savings.
The Penn State researcher noted that careful control of dehumidification creates a healthier environment by eliminating damp spots in ceiling tiles, insulation, and 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. Fresh air enters through overhead forced-air vents. Radiant cooling panels supply cooling. Wall radiators supply heat.
He noted that because 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.
The Penn State researcher estimated that his approach will save $2 per square foot in new construction. Operating costs could be less than 60% to 70% of the cost of all-air systems. Mumma's analyses are at www.DOAS.psu.edu, along with detailed descriptions of the system.
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