For instance, ASHRAE 62-1989, “Ventilation for Acceptable Indoor Air Quality,” for meeting ventilation requirements through air leakage calls for much greater air flow than that called for by the standard for mechanical ventilation ASHRAE 62.2 2010, “Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings.” Essentially, if a building is leaky enough, it is not required to have mechanical ventilation, but if the building is tightened beyond a certain point, then—for health and safety reasons—mechanical ventilation must be installed.
Air leakage is, by definition, the uncontrolled exchange of conditioned and unconditioned air. If we substitute mechanical ventilation for air leakage, we are then controlling the exchange and can utilize heat-recovery ventilators and/or energy-recovery ventilators to minimize the energy loss. We also can control the source of the incoming air and thus the pollutants that are being drawn into the building.
Residential vs. Commercial Code
The residential building industry has been addressing air-infiltration issues for some time. All versions of the residential code, beginning with the International Energy Conservation Code (IECC) 2009, require testing of the building shell and duct system to demonstrate reduced air leakage. In fact, under IECC 2009 and later versions of the code, the requirements for shell tightness are so strict that mechanical ventilation must be installed under ASHRAE 62.2 1989. (Note: The tightness requirements of IECC 2012 also apply to
additions and substantial rehabilitation projects. It will be interesting to see how this requirement plays out in the future; difficulties will most certainly arise in the enforcement and testing of only certain areas of a building.)
To give examples of the disconnect between residential and commercial construction codes and practices in regard to testing for and quantifying air leakage, the older 2009 version of the IECC required shell testing for residential construction, but the newer
and more progressive 2012 version still doesn’t require it for commercial and high-rise construction. The LEED for Homes program requires air-leakage testing as a prerequisite to certification, but LEED 2009 for commercial buildings does not offer standard energy and atmosphere points for demonstrating reduced air leakage.
Not addressing air infiltration in the commercial side of the codes is misguided because the taller a building is, the greater the pressures exerted on it by wind and stack effect, and the greater the potential for air flow. The amount of air leakage through a building shell will be defined by the cumulative size of the holes in the shell and the difference in air pressures from one side of the air barrier to the other. In other words, for a hole of any given size in an air barrier, if there is no pressure difference from one side of the hole to the other, air won’t flow, no matter how big the hole. Conversely, if the pressure differential is increased, then, given the same-size hole, air flow will increase. In addition to naturally occurring pressures, like wind and stack effect, mechanical equipment typically pressurizes tall buildings for fire-safety purposes, leading to even greater pressure differentials and thus greater air leakage for a given-size hole.
Currently, only certain “stretch codes,” a term generally applied to voluntaryor “beyond the norm” codes, require commercial building-shell testing. For instance, the International Green Construction Code has a provision for air-infiltration testing. The Washington-based U.S. Department of Defense has a requirement that its new construction and major renovation projects undergo air-leakage testing under an “Army Corps of Engineers Standard.” This standard is by far the most progressive in the country, and the DoD remains proactive in requiring tighter buildings. Washington state also requires air infiltration testing for all new buildings and major rehabs.
One of the reasons for the disconnect between residential and commercial air-infiltration testing seems to stem from a lack of information in the marketplace and industry regarding the relative ease with which commercial tests can be conducted. In the not-too-distant past, buildings would have been tested with large trailer-mounted engine-driven fans. This was in contrast to the hand-carried fan (commonly called a blower door) used in residential testing. The perception in the marketplace is that commercial testing is complex, intrusive, expensive and unwieldy. However, fan technology and software have advanced dramatically. The days of the trailer-mounted fans are all but over. Advanced computer control software and fan technology allow for any number of smaller hand-carried fans to be connected together, allowing relatively easy testing on buildings of almost any size. Six or seven of these hand-carried fans have about the same capacity as one of the old trailer-mounted blowers.
As commercial building codes continue to evolve, we will see more attention placed on the deleterious effects of air infiltration on our buildings. Tighter building envelope design will most assuredly become one of the next green-building best practices that becomes commonplace for architects and engineers. As building owners become aware of the benefits of reduced air infiltration, including energy savings and more productive work environments, the current indifference to air infiltration will rapidly become history.