Automated Aerosol-Sealing of Building Envelopes
Dr. Mark Modera | University of California, Davis
Objectives of the Demonstration
The objective of this project was to validate an aerosol sealing application method for sealing building shells as a cost-effective means to meet the U.S. Army Corps of Engineers (USACE) tightness requirement for military facilities. The project involved several demonstrations on various building types and in multiple climates to show the ability of the technology to be applied on a large scale.
The aerosol envelope sealing process involves pressurizing a building to normal testing pressures while applying an aerosol “fog” to the interior. As the air escapes through leaks in the shell of the building, the aerosolized sealant is transported to the leaks, and seals them as the particles try to escape from the building. This technology uses commercially available blower doors to positively pressurize the building during installation, as well as to provide real-time feedback on sealing progress, allowing the air-tightness to be tracked during the sealing. The entire process is controlled from outside the building and is capable of simultaneously measuring, locating, and sealing leaks in a building envelope, while also providing verification of building tightness.
The results of the demonstrations were expected to facilitate the adoption of the aerosol sealing method for other Department of Defense (DoD) installations by providing several demonstrations on multiple building types and in multiple climate zones. Prior work has demonstrated excellent results showing the ability to seal 80% of the building leakage in less than two hours. Very few retrofit demonstrations have been performed which was the focus of this project. These demonstrations validated the performance of the sealing technology as an effective solution for retrofit installations.
This project demonstrated that the aerosol envelope sealing technology is very effective at sealing building leakage on DoD facilities. Ultimately, over 75,000 cfmat 75 Pa was sealed over the sixteen demonstrations cutting the air leakage of the buildings in half. Figure 1 presents the overall percent air leakage reduction for each demonstration. The most successful demonstration sealed 80% of the building leakage and three of the demonstrations brought the buildings to within the USACE specification for envelope leakage. This was impressive considering two of these buildings were in poor condition and scheduled for demolition.
Durability testing was performed to assess the strength and longevity of the seals created using the aerosol sealing process. Seals were created under different humidity conditions to determine the sensitivity of seal strength to this parameter. Multiple tests were conducted on seals formed on test plates in the laboratory, including pressure cycling at medium and low pressures, temperature cycling at medium pressure, and holding high pressure for one hour.
In summary, there were no seal failures during the lab testing of seal durability in which the seals were subjected to pressures up to 5,000 Pa (equivalent to a wind speed of more than 200 miles per hour). There was a gradual increase in leakage rates when subjected to prolonged pressures above 800 Pa. Cyclic tests at more reasonable pressures of 100 Pa showed that after 1,900 pressure cycles the overall change in leakage flow between the first and last 100 cycles was 0.067 scfm for the six sealed leaks tested. This translates to an increase in leakage area of approximately 0.004 in2. For six sealed leaks each measuring about 1.2 in2, this represents an overall increase of less than 0.1% in the sealed leakage area, indicating very little change over the course of the testing.
Modeling of facility energy saving and associated payback as a result of applying aerosol sealing to reduce infiltration showed long payback periods exceeding 20 years in some climate zones. Only in very cold climates was the payback calculated to be five years or less. However, when accounting for reduced outdoor airflow to meet a pressurization target in a building, simple payback periods were much shorter with most scenarios modeled paying back in less than five years. Clearly the impact of reducing infiltration is much more significant in pressurized buildings. Lastly, this analysis does not account for improved indoor air quality and improved safety in the buildings
The most significant challenge that was met during the demonstrations was the presence of significant leakage that was too large for the aerosol to address. This leakage was discovered at the roof-to-wall connection which is a common location for building air leakage since it attaches to continuous air barrier sections. The aerosol sealing process is still advantageous in this situation even though it does require supplemental manual sealing. Future aerosol sealing installations in commercial buildings should assess the roof-to-wall connection to determine if manual sealing work is required.
Another issue that came up during the demonstrations arose from the fact that most people are not familiar with the aerosol sealing process which led to questions about the safety of its application. Environmental, Safety, and Occupational Health (ESOH) staff at one base was questioning whether the material being applied could potentially have an environmental impact. After providing the safety data sheet and explaining that the amount of material applied to the building is small the ESOH staff were satisfied and allowed the demonstration to move forward. It is critical to work with ESOH staff to familiarize them with the process prior to performing the work in order to answer questions about the safety of its application.
Points of Contact
Dr. Mark Modera
University of California, Davis
Energy and Water
SERDP and ESTCP