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              Email:    Dr. Stanley A. Mumma,
   Ph.D., P.E



   Since February 15, 2001

DOAS and Environmental Safety after 9-11:

Recent exposure of humans working in buildings to anthrax has caused all of us in the industry to re-evaluate the way we design building heating, ventilating and air conditioning systems. The intent of this document is to share some thoughts on the issue of indoor environmental safety in buildings served by the DOAS/radiant approach taken at this web site.

Historically, naturally occurring microbes grew within building materials and mechanical system due to moisture. The microbes have been largely responsible for sick building problems and reduced worker productivity. Generally, moisture was the result of either water leaks or condensation. Because of the DOAS system's ability to completely decouple the space sensible and latent loads, condensation problems and related sick building syndrome problems are virtually eliminated.

Further, the DOAS system does not use any recirculated air. Consequently, any biological or chemical agents accidentally or intentionally released inside the building (as has been the case thus far with anthrax) are not transported to other parts of the building by the mechanical system, rather they are diluted and exhausted from each individual space. However some have questioned the carryover potential at the enthalpy wheel.  The issue is addressed at the following two links:
   *  National Cancer Institute E Coli Phage Biological Carryover report
   *  Georga Tech Research Institute Biological and Particulate Carrover results
Since there is essentially no carryover with the proper enthaly wheel selection and no system wide recirculation, this is an overwhelming advantage of the DOAS approach over conventional all air systems.

Finally, consider biological agents accidentally or intentionally released in the vicinity of the fresh air intakes. Conventional filters, with dust spot efficiencies greater than 20% will take out more than 90% of spore size particles (such as anthrax). In new design, better filters could be used (with a first and operating cost penalty) capable of particle filtration efficiencies up to or greater than 99.999%. Biological agents not removed by the filters could be killed with ultraviolet light. Since the quantity of air that must be treated with the DOAS approach is generally less than 20% that of conventional all air systems, the DOAS approach again holds an overwhelming advantage.

As more information on this important subject becomes available, links to credible sites will be provided. Currently several good sites are:

WBDG: Chemical, Biological, Radiation Safety (CBR).  6/22/05
Penn State press release: Economical Terrorist-Resistant Air Conditioning Concept, 10/14/02

ASHRAE Report:  Building Health and Safety under Extraordinary Incidents, 1/26/03
LBL Secure Building Website
The Right to Healthy Indoor Air, WHO.  May 2000

In conclusion, ventilation will continue to be required to dilute indoor generated contaminants. Owners and operators must not consider closing the OA openings, or sick building problems will cause devastation to the occupants' health and productivity. In new construction, there is no question in my mind that the DOAS approach is the best option.

S. A. Mumma, Ph.D., P.E., Fellow of ASHRAE Prof. of Arch. Engineering.

Please visit the Papers section of this site for more information on
      Dedicated Outdoor Air Systems and Radiant Ceiling Panels.

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Copyright 2001 Bob Hedman.