Arkansas HVACR NewsMagazine February 2018

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Moisture, mold, and mildew are not your friends. They’ll bite you! Ron Hughes Tight houses with inadequate ventilation can result in moisture, mold, and mildew. Since the “V” in HVAC stands for “Ventilation,” who do you think might be held responsible? HVAC contractors are learning the hard way to not install HVAC in foam encapsulated houses without providing mechanical ventilation. In addition, do not oversize the AC! You can get some slack with a variable speed blower, but an oversized builder-model AC with a one-speed blower in a tight house is begging for trouble. This is not limited to foam encapsulated houses. The combination of a good caulk package and a house wrapped in a ZIP system with all the joints taped can test just as tight as a house encapsulated in foam. This may be the first of several articles to cover why ventilation is important, when do we need to, how best to do it, and how much ventilation may be required. Houses don’t have to breathe, but people do. Ventilation is a health and safety issue, a code issue, and a

liability issue. Houses need ventilation

when code requires it

and when good air quality is a priority. Ventilation must go beyond

a “make-up” air duct from the outside to a return. That behaves more like duct leakage more than ventilation. Ventilation needs to be “controlled” with a motorized damper and controls programmed with run times to satisfy the number of occupants and address humidity. Arkansas’ 2010 Mechanical code requires ventilation of no less than 15 cfm/person if the air leakage of the house is less than 0.35 air changes/hr. which we can expect almost all new homes to be and certainly all that are foam insulated or ZIPPed. I prefer ASHRAE 62.1-2010 which calls for 7.5 cfm/occupant plus 1 cfm for every 100 sf of conditioned space. This means a 2,000 s.f. house with three bedrooms (plus 1 = #occupants) requires 50 cfm running continuously 24/7, or, intermittently at, say, 100 cfm running off and on for 12 hours total during the 24 hour day. Either way, that is 72,000 ft 3