Air infiltration has long been a little-understood factor when it comes to energy efficiency in commercial buildings. But as new energy codes come into play, in particular the International Energy Conservation Code (IECC) 2012 and the International Green Construction Code (IgCC), air infiltration will come to the front and center of efforts to further energy efficiency in high-performance buildings.
How tight or leaky our buildings are has long been an overlooked issue. Most designers understand that the issue is there, but only account for it in the design for the heating and cooling system. Countering a leaky building is tricky and can go beyond one designer’s scope of work. Most mainstream energy-modeling software takes air infiltration into account during load calculations but often defaults to “tight” or “loose” parameters without users fully understanding the implications of excess infiltration. Some studies indicate that as much as 30 percent of buildings' heating and cooling energy comes from combating air infiltration.
The easiest way to measure infiltration for any building is with a blower-door pressurization and depressurization test. Many people are familiar with the concept of the blower-door test from residential applications, and the same concept can be applied to commercial buildings, usually with more fan power. This testing method uses a series of fans that pressurize and depressurize a building to a prescribed level, usually following the ASTM E779 standard or the U.S. Army Corps of Engineers (USACE) standard. The airflow through the building is measured with a manometer and recorded.
The two standards are very different in terms of their intended results and designers need to be aware of which one is required for a particular building. The ASTM standard, which is referenced in the IECC 2012 and the IgCC, requires that a building must have no more than 0.4 cubic feet per minute (CFM) per square foot at a pressure difference of 0.3 inches of water column (75 pascals). The USACE standard is more strict and only allows for a maximum of 0.25 CFM per square foot at a pressure difference of 0.3 inches of water column (75 pascals). This means that a building built to the USACE standard will result in a much tighter building in terms of air infiltration and, in turn, will be more energy efficient. At Energy Finance Analytics, an affiliate company of PM Environmental, own energy modeling with Trace 700 software indicates that an energy savings in the range of 30 to 36 percent in Btu per year for space heating in a cold northern climate can be achieved when tightening up a typical building to meet the ASTM 0.4 CFM-per-square-foot standard. An additional 12 to 15 percent energy savings over the ASTM standard can be achieved by tightening up the building to meet the USACE standard.
Up until recently, air-infiltration testing has often been viewed as something nice to have and was employed only in special situations. Usually a testing rig of this capacity was only brought in by designers for a very high-performance building or for diagnostics and architectural forensic work. However, with the advent of the 2009 American Recovery and Reinvestment Act, any state that received stimulus money for building energy had to agree to update its energy code at a minimum to the IECC 2009 code or equivalent. Some states, such as Illinois, agreed to jump further ahead and adopt the IECC 2012 energy code, while the state of Maryland has adopted the IgCC as an alternative code for use in construction. As more states continue to update energy codes, air-infiltration testing in commercial buildings will continue to hold more sway.
The LEED-certification program will also help drive demand for air-infiltration testing. The USGBC has historically excluded building-shell testing as part of LEED's prerequisites and enhanced commissioning credits. However, for some time now the USGBC has allowed building-shell commissioning to count toward a possible innovation credit in all of its rating systems, and building-shell commissioning is now an elective point in LEED for Healthcare. Its inclusion in the LEED 2012 program, however, is still in discussion.
Change is not going to come easily in the design and construction fields. Developers need to understand that air-infiltration testing is an additional expense and they will need to account for it in preliminary budgets. Cost will vary by project, but testing for a a smaller office building that is 3,000 square feet to 5,000 square feet might cost $2,000 to $3,000. A high-rise office building may cost tens of thousands of dollars to test. Architects and engineers are going to have to update skill sets to understand what it means to design a continuous air barrier in a building. Clear delineation of the air barrier on the construction drawings is important so the contractors are clear of expectations in the field. As the testing standards are updated and more industry groups get involved, personal certifications in these areas will become more prevalent. General contractors and trade subcontractors need to become aware of testing requirements and actions required to fix deficiencies discovered during the testing process. Contract language for all parties needs to clearly state roles and responsibilities and provide the necessary “teeth” to ensure deficiencies are addressed should they come up in the field testing.
Commercial air-infiltration testing is by no means a new concept; it’s been around for a long time. Until now, the industry hasn’t fully embraced the possibilities of energy reduction with air infiltration in a truly meaningful way. As designers continue to strive for higher performing buildings, and as new energy codes begin to mandate, architects and engineers will become more cognizant of the importance of air infiltration and its effects on energy efficiency.
Nate Gillette, AIA, is vice president and director of Energy Finance Analytics, an affiliate company of PM Environmental that provides building-shell testing, commissioning, property assessment, energy modeling and audits, and LEED-certification consulting. efanow.com ,