This project incorporated Building Integrated Solar Technology (BIST) systems including solar thermal and solar electric (photovoltaic or PV) systems along with additional insulation, air barrier improvements, above sheathing ventilation (ASV), rainwater harvesting, and a retrofit roofing system. The overall objective was to determine if the dynamic integrated retrofit metal roofing system could reduce energy and water consumption, mitigate the building’s environmental impact, lower construction and operating costs, and reduce the building’s overall energy intensity.
A holistically designed retrofit metal re-roofing system creates an air space by adding structural subframing atop the existing roof and then installing a new metal roof over the assembly. This air space provides the opportunity to add high-performance insulation and solar thermal air and water heating and cooling systems between the two roofs. It then enables solar electricity and rainwater collection systems to be installed on the topside of the new metal roof. This innovative assembly of well-accepted roofing components is referred to as a "fully integrated retrofit metal roof system."
This project will demonstrate the synergy of these technologies when integrated into the overall retrofit roof assembly. Energy savings from these technologies will improve the energy efficiency of the building and lower the electrical energy demand from the grid and on fossil fuels for water heating and space conditioning. In addition, the incorporation of a rainwater harvesting system will reduce the demand for fresh water.
In an unfortunate turn of events, the building was converted to a data center after the baseline data collection period was established, substantially compromising the project’s ability to gather data. The experimental design did not include sufficient data collection to analyze the impact of adding approximately 9-12 KW load to the building’s baseline load in conjunction with the complex roof assembly that was installed, pinpoint the effects of the many factors interacting on the building (the effect of ASV on the solar thermal system, variations in performance of the ASV system with varying wind loads), and distinguish the true source of energy savings (insulation vs. ASV technology, insulation vs. solar thermal energy systems, etc.).
The facility used more electricity during the post-construction monitoring period than it did in prior years, despite the PV system producing 59,039 kWh of solar electricity in FY 2013. The natural gas consumption in FY 2013 was 32.2 thousand cubic feet of natural gas (KCFNG) less than FY 2012 of which 27.0 KCFNG was offset by the hydronic solar thermal system. The thermal energy savings totaled less than 10% of the savings projected. Additionally, the installation personnel reported that the rainwater harvesting system was not utilized because of issues with the irrigation system maintenance and a general ban base-wide on irrigation due to excessive drought conditions.
Though the building’s change in use drastically altered the course of this project, the basic principles of energy savings through retrofit roofing, which encompasses insulation enhancements and renewable energy systems, were demonstrated.
The high performance retrofit metal roofing system demonstrated in this project should be considered as one of a number of possible retrofit roofing designs that are adaptable to the current DoD building stock, particularly on those buildings that have metal roofs.
Key lessons learned from this project are as follows:
Implementation sites should be surveyed for suitability, i.e., is the building in need of a new metal roof, and if so, implementation schedules should prioritize those buildings that will deliver a maximum rate of return on the investment.