Each year, millions of dollars’ worth of energy leaks from the envelopes of U.S. Department of Defense (DoD) buildings due to missing or improperly installed insulation, cracks around doors and windows, thermal bridges in the wall system, and many other deficiencies. Identifying the sources of this wasted energy has historically required manual thermal audits that are typically inconvenient, time-consuming, and prohibitively expensive for large-scale energy analysis. At the same time, Federal agencies are under immense pressure to dramatically reduce the amount of energy consumed by their buildings.
This project demonstrated a unique drive-by thermal imaging process that can enable cost-effective energy efficiency in building envelopes at a much greater scale than other commercially available techniques of measuring energy loss due to thermally inefficient building envelopes. This solution used a multi-sensor hardware device mounted on the roof of a customized vehicle to rapidly scan hundreds of buildings in a short period of time. The gathered data were processed and analyzed at the Contractor’s headquarters (Essess, Boston, MA) to ascertain important building envelope information. The project demonstrated this technology by scanning Marine Corps Base Camp Lejeune, NC (American Society of Heating, Refrigerating, and Air-Conditioning Engineers [ASHRAE] Climate Zone 3) and Scott Air Force Base (AFB), IL (ASHRAE Climate Zone 4) to determine the amount of energy being lost at each installation due to thermally inefficient building envelopes.
The Kinetic Super-Resolution Long-Wave Infrared (KSR LWIR) method uses a multi-sensor hardware device that is attached to the roof of a customized vehicle to rapidly scan hundreds of buildings in a short period of time. The gathered infrared imagery data are merged with Light Detection and Ranging (LIDAR) data, Geographic Information System (GIS) data, and Global Positioning System (GPS) data and then processed and analyzed to ascertain important building envelope information.
In the ESTCP demonstrations, the team scanned at least six buildings at each installation using a forward looking infrared radiometer (FLIR) i7 handheld thermal camera. The FLIR i-Series cameras are specially designed for building diagnostics and commonly used in residential and commercial thermal audits. The scanned images for these cameras are 140x140 pixels with a 29-degree by 29-degree field of view (FOV). The FLIR i7 camera uses a Spotmeter to detect the maximum and minimum temperatures within an image. The Contractor found that each of the buildings scanned by the handheld method required about 25 minutes of imaging work. Part of the extra effort involved in this method is the necessity to manually overlap building components in each frame.
No effort was made to analyze the thermal image data captured by the handheld camera because such an analysis would have required all images to be stitched together, which would have been a prohibitively time consuming effort and would have yielded somewhat uncertain results since they would have required a good deal of analyst interpretation.
By comparison, the KSR LWIR method uses an integrated camera system that captures 640x512 pixels per frame for a 45-degree x 37-degree FOV. Computer vision calculates the temperature of each feature within the image and obtains material emissivity. Using the KSR LWIR drive-by method, it took about 30 seconds to scan each of the 12 buildings (i.e., six buildings at each installation) in the set that were also scanned by the handheld method.
The drive-by KSR LWIR method satisfied its performance objectives for Rapid Scanning and Rapid Analysis with more than 100 buildings scanned per hour and the thermographic image data was analyzed at a rate of approximately 327 buildings per hour. This is at least an order of magnitude faster than could be achieved with handheld thermographic methods.
At Scott AFB, more than 3,000 distinct building feature components (doors, windows, soffits, etc.) were identified on buildings across the base. These features were categorized by type (e.g., brick wall, roof, window glass, window frame) and surface temperature to provide an analysis of each building’s envelope energy profile. An in-depth analysis of 30 buildings including a breakdown of recommended energy conservation measures (ECMs) and the potential return on investment showed more than $300,000 in potential envelope-related savings per year that could be achieved. Over the lifetime of the measures, Scott AFB has the potential to save more than $4 million by investing around $2 million with a simple payback period of roughly 7 years.
At Camp Lejeune, more than 2,500 distinct building feature components were identified across various buildings. Similar to Scott AFB, these features were categorized by type and surface temperature to provide an analysis of each building’s envelope efficiency. An in-depth analysis of 30 buildings including a breakdown of the most notable leaks for each building and remediation recommendations showed that Camp Lejeune could save more than $100,000 per year by implementing ECMs. The total investment would be less than $1 million, but would allow the base to save nearly $1.7 million over the lifetime of the measures with a simple payback period of less than 9 years.
The team found that commercial energy audits that include envelope thermal imaging using handheld thermography typically cost around $0.20/square foot (sq ft) of building area (based on data from local thermal imaging auditors within 100 miles of Scott AFB and Green-Buildings.com). Based on the area of buildings scanned at Scott AFB (4.6 million sq ft) and Camp Lejeune (4.2 million sq ft) using the drive-by method, it would have cost approximately $920,000 and $840,000, respectively, using the handheld method. Essess’ costs to scan, analyze and report results for each installation using KSR LWIR was approximately $200,000 regardless of actual square footage scanned.
Although both Scott AFB and Camp Lejeune have a positive return on investment (ROI), the results showed that Scott AFB has a higher potential savings threshold. This is partially due to the fact that Scott AFB is located in ASHRAE Climate Zone 4, while Camp Lejeune is in ASHRAE Climate Zone 3. Increasing ASHRAE climate zone numbers indicate colder climates. The long-term vision of this work is to help DoD reach its goal of saving energy across all military installations by identifying the best candidate installations for energy-saving improvements to building envelopes, i.e., those with the highest potential savings. It would be possible to combine that priority list with information on optimal building stocks and portfolios of cost-effective improvements to equip DoD to save millions of dollars in annual energy losses.