Note that the blower door tool, used here for a single classroom, is an excellent diagnostic tool for discovering air leakage for an entire building. (Whole building pressurization testing is now being required by some states for new construction.) It can give you an accurate idea of the overall airtightness of your building and, combined with theatrical smoke and thermal imaging, can help locate the holes.
Thermal Imaging
Do not overlook a simple, low-tech solution for finding and closing holes. For example, in a relatively new medical facility, the owner couldn’t keep patient rooms much above 65 F on the coldest winter days and was inclined to blame the HVAC system designer, the energy model and the load calculations. But, diligently, he also consulted an enclosure specialist. Our consulting team followed a systematic evaluation process that began with the design drawings. The design looked sound and a survey of the building exterior exhibited no clues to difficulties. (See Images 6 and 7.)
A thermal imaging survey with an infrared (IR) camera, including areas above interior ceilings, revealed a plume of 38 F air descending into patient rooms where the exterior walls met the attic (see Images 8a-b). Closer inspection revealed key pieces of the air barriers had been omitted during construction, allowing the cold air to compromise comfort for the patients.
IR surveys are immensely valuable but you need a temperature differential between inside and outside for them to work; these surveys may not be effective in the mild seasons. Interpreting IR images requires training. You should ask for at least a level-2 certification from the Columbus, Ohio-based American Society for Nondestructive Testing for the technicians on your project. Be careful you don’t receive a false impression from the bright contrasts of the images. Always insist on a color scale. The dramatic colors you see may represent only a few degrees of temperature variation.
Much has been written about air leaks and the need for tighter buildings. Don’t let the fog of technical data about permeability and vapor retarders obscure the impressive truth that 10 times as much moisture can move through a 1-square-inch hole than can diffuse through 10 square feet of the cheapest vapor retarder the builder may have installed.
Retrofit for Today’s Energy Standards
We always want to keep an eye on moisture movement in walls. What happens when we change walls that have been functioning well historically but no longer meet the owner’s goals? I worked with an owner who wanted to repurpose a historic masonry power plant into a college student center (see Image 9). The existing walls were solid brick, 12-inches thick, but uninsulated. How would we best retrofit to modern energy standards while keeping the risk of damage from freeze-thaw low? To solve this problem, our consulting team used two computer simulation tools to predict how walls should and could perform. The THERM model results, Image 10, estimate interior surface temperatures within the wall to compare different insulation retrofit methods and help the HVAC engineer confirm the comfort level of the occupants in different heating and cooling schemes.
In Image 11, a 2-dimensional WUFI model charts the relative humidity and temperature within the brick to try and predict freeze-thaw damage.
As with the IR camera tool, you must try to gauge the skills of the WUFI or THERM user. These models can be misleading and the dynamics of freeze-thaw damage to brick is complex.
The study showed the bricks to be robust enough to insulate, and the improved wall thermal barrier had a dramatic effect on the selection of the HVAC to be installed.
PHOTOS: dbHMS