Advanced computer control soft- ware and fan technology allow for any number of smaller hand- carried fans to be connected together, allow- ing relatively easy testing on buildings of almost any size.
warm moist air is allowed to contact a suffi ciently cooler surface, moisture will condense on the cooler surface. If we can stop the air from fl owing (leaking through the building shell), we can stop the continued condensation within the exterior wall cavities.
Along with limiting mold problems,
a tighter building shell will save energy because conditioned air is no longer lost to the exterior. The heat that rides along with the air that actually fl ows to the outside is called “convective” heat loss. The Washington, D.C.-based U.S. Depart- ment of Energy estimates nearly 30 per- cent of the energy used for heating and cooling our buildings is lost because of air leakage. It should also be mentioned most types of insulation and building materials will lose their insulating abil- ity if they get wet (from condensation) or are subjected to a constant fl ow of air through or over them. The reduced R- value of the insulation leads to another type of heat loss that is referred to as
“conductive” heat loss. The conductive heat loss is separate from and occurs in addition to convective heat loss.
AIR LEAKAGE VS. MECHANICAL VENTILATION Historically, most builders have argued against constructing buildings that were tight for fear of creating the dreaded “sick building syndrome.” This mindset is being rapidly reversed. We now have the means with which to reliably eliminate the risks of creating such problems. For example, advance- ments have been made in blower-door and duct-tightness testing equip- ment, and new testing protocols and straightforward ASHRAE ventilation standards are available. Building owners often are quizzi-
cal about testing and tightening their buildings to virtually eliminate air leak- age and then installing a fan to bring in outside unconditioned air. However, because the volume of air leakage is de- pendent upon many factors, including temperature differential from inside to outside, wind speed, the height of the structure, etc., the actual amount of air coming into the structure at any given time is hard to estimate. For instance, ASHRAE 62-1989,
“Ventilation for Acceptable Indoor Air Quality,” for meeting ventilation requirements through air leakage calls for much greater air fl ow than that called for by the standard for me- chanical 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
Air leakage is, by defi nition, the uncontrolled exchange of conditioned and unconditioned air.
50 RETROFIT // March-April 2013
safety reasons—mechanical ventila- tion must be installed. Air leakage is, by defi nition, 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 rehabilita- tion 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 certifi cation, but LEED 2009 for commercial build- ings does not offer standard energy and atmosphere points for demonstrating reduced air leakage. Not addressing air infi ltration in the