King County's Trails Maintenance Complex
Background
In 2015, King County set a target to launch at least 10 new county construction or retrofit projects by 2020 that would achieve zero energy or living building status. This goal was part of a broader set of green building and energy performance initiatives outlined in the county’s Strategic Climate Action Plan. King County chose its Parks Division’s North Utility Trail Crew’s maintenance shop to be the first of these net-zero energy facilities, after county project staff determined the complex could achieve zero energy status through a combination of energy savings measures and on-site solar.
The newly-installed rooftop solar PV system, combined with additional building retrofits, is currently producing 45% more energy than the maintenance site consumes - on pace to far exceed King County’s net-zero energy goal.
The North Utility Trail Crew’s maintenance complex serves as the maintenance shop for a 10-person crew that takes care of approximately 60 miles of the county’s highest-use regional trails. Built in 2007, the complex is located in King County’s Marymoor Park and includes an office building, fabrication workshop, and an equipment maintenance and parking “hangar” building. While the complex was LEED Certified at initial construction, the two buildings have good sun orientation and demonstrated the potential for deep energy reductions through the installation of LED lighting and a high-efficiency heat pump system.
Solutions
King County’s project team evaluated the main drivers of energy use on the property and determined that approximately 32% energy efficiency savings combined with on-site rooftop solar would enable zero energy status for the site. Lighting and mechanical equipment upgrades were identified as the most cost-effective strategies capable of delivering the desired energy savings. The implemented retrofit package with solar installation is expected to exceed life-cycle cost-effectiveness and meet the zero energy target, even with increased energy use from the addition of new metal fabrication equipment. The net payback after utility rebates and annual solar production savings is expected to be 12 years.
| Savings Measure | Cost | Annual Savings Achieved | Notes | Incentives Received by County | Expected Payback Period (after incentives) |
|---|---|---|---|---|---|
| Interior and exterior LED retrofit | $7,220 | 5,820 kWh | LED lighting replaced former fluorescent and metal halide lighting | $3,600 utility rebate | Less than 3 years |
| Air source heat pump, 17.4 SEER | $31,880 | 12,000 kWh | New, high-efficiency heat pump replaced resistance heating and wall air conditioning systems | $2,750 utility rebate | 20 years |
| Rooftop solar PV array | $72,990 | 44,690 kWh | Array installed on south roof of one building, east and west roofs of the other. Production is exceeding intial estimates, producing 45% more than the complex needs. | $122,110 in grants and sales tax credits | 9 years |
King County is working to conduct similar high-efficiency heat pump heating system retrofits at other facilities and is examining the remainder of its building portfolio to identify sites with good solar potential.
Other Benefits
Because the solar PV system has been generating 45% more power than the complex needs, the surplus power is being used to offset energy consumption from the park’s tennis court lights. Additionally, staff report that the new heat pump is making the office, workshop, and break areas more comfortable. For more details, check out this informational video on the project.
Image Gallery
Aerial view of the maintenance complex
