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Filtering out virus from the air-stream t this time is not readily identifiable in test standards due to its sub-micron size. Laws of physics have shown that removal of these particles is actually higher than the mechanical removal capabilities of the filters.
RECOMMENDATIONS FOR FACILITIES Looking at the total system of air conveyance in buildings is vitally important. Identifying the most vulnerable areas of potential insult and addressing them first will reduce the possibility of danger. Administrative procedures implemented and practiced should always be the first steps for any facility.
OUTSIDE AIR First and foremost recognize that the best protection for any building is to remain positive pressured to the outside environment. If all outside air supply is stopped the exhaust systems will draw air into the building in all possible sources.
Outside air should be filtered with as high a MERV value as possible (Minimum MERV 11) within the HVAC design capability. The filtration must be on the suction side of the air handler to prevent leakage into mechanical room spaces and ultimately the building environment.
Exhaust fans can be shut off in the case of a known outside event to help the pressurization of spaces. This will help prevent infiltration into the building.
Gas Phase filtration should be considered where potential for chemical disaster is a risk. If gas phase filtration is installed consideration must be given to “single pass removal” efficiency as the air only passes once through outside air systems.
RETURN AIR Improving efficiency of return air in HVAC systems will continue to reduce concentrations of all particulate including bio-organisms. The air recirculation will remove particulate on each pass through the filter system. A minimum of MERV 10 is recommended.
SYSTEM INSPECTION In all air conveyance systems attention should be given to seal all possible bypass. This includes gasketing of filters as well as gaps in framing systems. A fact of physics is that the higher the pressure drop the more bypass will leak around gaps in filters.
MAIL ROOMS Current events have shown that one of the biggest threats is from inside insult of a property through mail. Evaluate the mailroom in regard to pressure relationship to the rest of the building. If mail has entered the facility contaminated, it is advisable to contain it within the space. This can be accomplished by negative pressure relationship to adjoining areas. Filtered air cleaning devices can create this environment economically while cleaning potentially harmful organisms from the air environment.
CONCLUSIONS Any upgrades invested in by facilities should be done with the idea of long-term improvement to Indoor Air Quality. Improving the filtration efficiency will only help the overall reduction of microbial organisms as well as particulate from the air conveyance system. ASHRAE 52.2 will allow a measuring tool for the level of improvement.
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