This project demonstrated the performance and life-cycle cost benefits for U.S. Department of Defense (DoD) building energy efficiency by using dynamic windows, a new type of advanced “Smart Window” product, as compared to existing single pane windows or low-emissivity (low-e). These smart windows can automatically tint and untint throughout the day to minimize solar heat-gain in the summer, maximize passive heating in the winter, and maximize the use of natural daylighting throughout the year. The project was intended to facilitate future technology transfer across all DoD building stock, while providing a direct benefit to the host base in terms of reduced energy consumption, reduced life-cycle cost, and improved occupant comfort. Specific project objectives included:
- Install dynamic windows in a demonstration site on a DoD installation.
- Monitor energy consumption, peak-load, and occupant comfort before and after installation.
- Develop detailed energy models for the site, calibrated against baseline and experimental energy results.
- Use the calibrated models and historic weather data to predict the life-cycle energy savings (and resulting greenhouse gas [GHG] and energy cost savings) at the site.
- Use calibrated models to estimate reductions in peak-load energy use and improvement in occupant comfort to propose the ability to down-size the heating, ventilation, air-conditioning (HVAC) capacity and eliminate blinds/shades in future new construction and major renovation projects.
- Quantify improvements in occupant comfort and satisfaction.
- Quantify the total predicted life-cycle cost-, energy- and GHG-savings relative to state-of-the-art low-e windows at the site and across the entire DoD building stock.
- Develop guidance documents and tools to assist with technology transfer across DoD.
To accelerate the transfer of technology throughout the DoD, the project team also engaged with major DoD Energy Service Companies, including Johnson Controls Inc. (JCI) and Noresco, to enable and accelerate future installation through Energy Savings Performance Contracts (ESPC). The collaboration with these companies in concert with this demonstration project will allow Federal agencies to implement dynamic windows without upfront capital costs and without the need for special Congressional appropriations.
View’s dynamic windows technology represents a significant advancement over the current state-of-the-art in energy-efficient windows. The product operates by the electrochromic effect, reversibly changing color when a charge is applied. While electrochromic glass is not new, View’s approach results in a product that consumes 2x less energy and costs 4x less than the electrochromic glass available during the initiation of the demonstration project. These benefits make it a viable energy-efficiency technology for military installations.
The project demonstrated a reduction in HVAC energy consumption of 29% compared to the existing windows baseline, corresponding to 2.2x greater energy savings than if the team had upgraded to state-of-the-art low-e windows. Lighting energy was reduced by 62%, corresponding to 2.4x enhanced savings over upgrading with low-e windows. Total building energy savings was 28%, a 2.4x enhancement over upgrading with low-e windows. Economic assessment of this project estimates a payback of upgrading to View dynamic windows over state-of-the-art low-e windows of less than 3 years and a lifetime savings-to-investment ratio of 4.3. All performance objectives were met or exceeded, and the host site has been enthusiastic and pleased with the impact on comfort in their building.
Inefficient windows in buildings represent one of the biggest energy problems in the military today. If broadly adopted, View’s dynamic windows technology could reduce global DoD energy consumption from buildings by 15% and GHG emissions by 24%, representing an annual savings of approximately $680 million. At the same time, replacing existing windows with dynamic windows can reduce total facilities peak load by up to 25%, reducing strain on local electrical grid infrastructure, further improving energy security.
During this project, no significant implementation issues were encountered. Two minor issues were encountered. First, a very small population of the building occupants (two of them) found the glare at the 4% tint state was still too high for their personal comfort during direct, full sunlight. In response, the software drivers were modified to reduce the maximum tint state to 1%. There were no further complaints following this upgrade, and will future windows will be shipped with this as a default setting. Second, the team found that it was important to accurately set occupant expectations upon conversion to dynamic windows. The glass is designed to predictively tint and clear to maximize comfort. This is a gradual process that may occur infrequently throughout the day. However, some occupants expected the glass to transition quickly and often in response to non-comfort or energy conditions. This resulted in some concern, although it did not impact performance.