As the relevant codes and standards (CSA, ASHRAE) don't require 100% OA (at least in most areas), I've been interested in the history behind 100% OA and recirculation in the health care setting. I did a little searching into the old handbooks at our office and was able to go back as far as the 1971 Applications Handbook which states that:
"Until recent years, available air filter media could remove only a relatively small percentage of the pathogenic organisms in an air stream as compared with the high-efficiency air filter media available today. Because of this low efficiency, past authorities believed it was better to use all outdoor air which contained very few pathogenic organisms than to reuse by recirculation the more contaminated air from within the hospital for the ventilation of operating rooms and similar sensitive areas. Today, however, it has been demonstrated that properly designed air systems using high-efficiency air filter media can deliver air equally free of bacterial contamination, whether it be outdoor air or air recirculated from within the area."
So it looks like ASHRAE has had the belief that recirculation systems with proper filtration can deliver air equally free of bacteria since at least the early 1970's.
Do the energy savings benefits of recirculation systems outweigh the potential health benefits of 100% OA systems? What are your thoughts?