From the Field: CEE Staff Conduct Air Leakage Tests on Large Buildings
Contributing authors: Dave Bohac and Josh Novacheck
Leaks in a building’s envelope allow conditioned air to escape, directly increasing its energy consumption for heating and cooling. Some studies have estimated that proper air sealing can save up to 30 percent of building energy use. But it’s challenging to identify and seal each of the small gaps and cracks that comprise a building’s overall air leakage. Weather conditions and building occupancy and HVAC operation also affect air infiltration and energy savings opportunities.
Senior Building Analyst Jim Fitzgerald, Research Analyst Josh Novacheck, and Director of Indoor Air Quality Dave Bohac recently traveled to Madison, WI to perform air leakage tests on a 121,000 square foot office building. The tests were part of an ASHRAE-funded research project to characterize the leakage of newer US buildings.
Researchers perform several different tests to locate air leaks and to quantify the rate of air loss through the building envelope.
First, staff depressurize the building with blower door fans and measure the in/outside pressure difference. A building this size normally requires about eight fans, but this one was so tight that only four were required: three on the bottom floor, and one on the upper floor. They also set up pressure gauges and tubing on each side of the building at the ground level and roof to obtain a more accurate measure of the building in/outside pressure difference. These measurements will also be analyzed to help determine outdoor tube locations and monitoring duration necessary for reliable tightness measurements for various wind and outdoor temperature conditions.
While the building is pressurized, staff perform infrared scans that highlight “hot spots” of heated air being forced out of the building. On the evening of the test, it was 40 degrees outside and 68 degrees inside, so leaks were easy to spot. The IR image to the right shows leakage at the wall/roof joint, which is common for larger buildings.
After identifying likely leaks with the IR scans, the team verifies them with a “smoke puffer.” This tool sends out a stream of smoke that runs “like water from a hose” if there is a pressure difference between indoors and outdoors. This helps determine the severity of the leak
Insight from the field: you can learn a lot about building dynamics when you’re pressurizing and depressurizing a huge building. Simple construction errors have huge energy consequences. And even new and relatively “tight” buildings can have significant air leakage under certain weather and occupancy conditions.
The ASHRAE project focuses on buildings constructed since 2000, to learn how building envelopes have gotten tighter with new construction practices. CEE has helped test buildings in Champaign, IL; Duluth, GA; the Twin Cities; and a second building in Madison. We are arranging to test one or two buildings in Duluth this summer.
Our air leakage research also includes the CEE project Capturing Energy Savings From Large Building Envelope Leakage Reduction.