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Beneficial Microbes in Building Air

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If you perform blower-door tests, there may be some new strategies coming. Blower-door testing, for those not familiar with it, is a method of measuring the airtightness of a building by correlating it to the amount of airflow required to change the building’s static pressure with respect to outside pressure. Obviously, the higher the airflow, the higher the number of air changes per hour (ACH) at a given pressure (for residential testing, generally 50 pascal), and the higher the number of air changes, the greater the amount of leakage in the building envelope. The name itself comes from the device, typically a variable-speed fan (“blower”), a manometer, and a method of mounting the fan in a door or window. The idea, of course, is for buildings to be as tight as possible to prevent infiltration of unconditioned air into conditioned spaces or, conversely, exfiltration of conditioned air to the outside. Here in Florida, homes generally are desired to have no more than five ACH; anything over 10 gets very expensive with our high number of cooling degree days.

So, from an energy-efficiency standpoint, tighter clearly is better. It may not, however, be healthier. In the August 2016 issue of Trends in Microbiology, in the article “Buildings, Beneficial Microbes, and Health,” two Yale University researchers—Jordan Peccia and Sarah E. Kwan—make the case that we may want to start designing to intentionally allow exposure to certain microbes in buildings, including our homes. According to the article, we spend more than 90 percent of our time indoors. The microbes in the air in our buildings come from the occupants—human and animal—and from outside-air infiltration and ventilation. Because normal activities cause dust and microbes from elevated surfaces to become resuspended, the concentrations of bacteria and fungi in indoor air often are higher than those outside, especially in the case of poorly ventilated buildings. The adverse health effects of poor ventilation are well-established. The idea of improving ventilation by adding certain microbes to fresh air is a paradigm shift.

Peccia and Kwan point out the association of beneficial indoor microbes and disease prevention, using as an example the lower rates of asthma among children on Bavarian and Amish farms who grow up in homes in close proximity to livestock. They also cite recent research that shows dust in homes in which there are dogs may improve airway immunity to allergens, asking if dog ownership could be the urban equivalent to growing up on an Amish farm. This leads to their hypothesis that, although it’s not yet feasible, in the future, the intentional design of buildings to promote beneficial-microbe exposure may be desired. Maybe the next emerging business opportunity in HVAC will, instead of T&B, be TB&B: test, balance, and bacteria.

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