Arlington County, Virginia
Currently experiencing a population boom, Arlington County is facing massive growth in the next decade and is seeking to add half a million square feet in educational facilities. During competitive design procurement for Discovery, one of the teams suggested a zero energy goal could be accomplished within the given budget. Proponents at the district level who had been championing energy efficiency were receptive, but were skeptical that it could be done within the budget aimed at LEED Silver. Not only did the project end up coming under budget including the solar array, the building is more efficient than the originally predicted. Now Discovery saves $100,000 per year in utility costs, enough to cover the salaries of two teachers.
5241 N. 36th St., Arlington, VA
Typical Number of Permanent Occupants
GENERAL FLOOR AREATotal Gross Floor Area 98,000 ft²
BUILDINGBuilding unit or complex: Described project is a single building
DATE OF OCCUPANCY/COMPLETION August 2016
SUSTAINABLE MATERIALS AND RESOURCES USED IN THE CONSTRUCTION AND LANDSCAPING
ARCHITECTURAL MEASURE USED TO MEET A HIGH-LEVEL OF ENERGY PERFORMANCE
Discovery was built adjacent to an existing middle school on a portion of the site that was previously considered unusable because of a sloped hillside. Even with those constraints, the design team experimented with various shapes and orientations for the new 630-student school. Every version was analyzed for energy efficiency and described in terms of how many solar panels it would take to offset the energy load. The model that performed best was actually rejected. It was too compact and did not have enough sun exposure for daylighting.
During design, an engineering firm that had successfully designed several zero energy schools in Kentucky was brought onto the team. The firm had experience with designing and modeling exterior wall assemblies constructed with insulated concrete forms—a construction technique that is rarely used in Virginia but that offers high R-value, high thermal mass, and good air sealing. Add LED lighting and geothermal wells for a ground-source heat pump system, and they had the main ingredients for a highly efficient school.
Discuss goals that were met and goals that were not achieved, and the reasons for these outcomes
For the project team, the lessons learned from Discovery have been about tracking performance and understanding maintainability. Most sustainability programs are based on predicted energy use, but zero energy requires proven performance. And part of tracking actual performance means the design team is more in touch with problems that crop up during operations. The team learned that making things simpler to operate—rather than automating everything in a way that gets overridden when occupants complain—was one key to success.
How the Project was Financed
Total Project Cost$32,305,800
Property Acquisition Costs$0
Project CostsBuilding only: $26,690,000 PV: $1,510,000 Sitework: $4,106,000
Estimated payback time of any investment in measures needed to reach zero net energy
Simple payback on the photovoltaic system at Discovery is estimated to be 13 years. However, analyzing the financing from a whole-project perspective, the cost savings from the building being energy efficient (approximately $100,000 per year) more than make up for the bond payment on the solar array. Furthermore, the array generates income when the building is energy positive, so the system was actually cash flow positive from day one.
Incremental costs related to building envelope, lighting, HVAC, and renewable energy technologies incurred to achieve net-zero energy
Typical site EUI for the district is 69. The energy model predicted an EUI of 21, but actual performance is closer to 16.
Building Envelope Thermal Performance and Mechanical Systems
Insulated concrete forms (8 in. concrete core and 2 in. polystryrene form walls)
Geothermal wells and small, distributed floor-mounted heat pumps, demand control ventilation
1,700 photovoltaic panels, 496 kW
Aspects of the project that were included in balance calculations
- Plug Loads
Energy Generation Source Locations
- Generate renewable energy within its footprint (e.g. solar PV on the roof)?
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