Holocene: National Naval Medical Center

In June, Holocene commissioned a 50-collector commercial solar water heating system at the new Warrior Transition Unit facility in Bethesda, Maryland. Part of the National Naval Medical Center, the Warrior Transition Unit supports wounded soldiers who require at least 6 months of rehabilitative care and complex medical management. The system was designed to provide more than 30% of this facility’s annual hot water demand for kitchen use, showers and laundry services.

One of Holocene’s principal challenges was coordinating the installation within a dynamic and fast-paced construction environment. Impressively, Holocene was the first contractor to successfully commission its system on the project. Comprehensive training of the Naval Facilities Engineering Command maintenance staff was a key component of system commissioning.

The collector array is configured in banks of five collectors in parallel, which are plumbed into the main collector supply and return piping. This approach minimizes system temperature differentials and increases overall system efficiency. Because the system relies on drainback for freeze protection, careful attention was given to the proper installation of the supply and return piping.

The 2,500-gallon Fluid Handling System (FHS), manufactured by Holocene Technologies (a subsidiary of Holocene, LLC), is located in the facility’s basement. The component’s hot water exchange and storage approach is based on a design developed in the 1970s by Ben Gravely, Holocene’s director of technology. The FHS utilizes a nonpressurized, insulated steel tank and has no heat exchanger between the collectors and the tank.

“The FHS contains specified pumps, heat exchangers, controls and monitoring components in one integrated package. Factory-built storage systems provide greater quality control and lower installation costs, and are very well suited for commercial water heating installations.”

—Ben Gravely, PhD, Holocene

Overview

DESIGNER: Ben Gravely, PhD, director of technology, Holocene, holocene-energy.com, solarhotwater-systems.com
LEAD INSTALLER: Terry Holthaus, project manager, Holocene
DATE COMMISSIONED: June 29, 2011
INSTALLATION TIME FRAME: 45 days
LOCATION: Bethesda, MD, 39°N
SOLAR RESOURCE: 3.9 kWh/m2/day
ANNUAL HEATING DEGREE-DAYS: 4,101, base 65°F
RECORD LOW TEMPERATURE: -5°F
COLLECTOR ARRAY AREA: 2,000 sq. ft.
AVERAGE ANNUAL PRODUCTION: 480 MBtu (141 MWh)

Equipment Specifications

COLLECTORS: 50 Alternate Energy Technologies (AET) AE40, 40 sq. ft. each
HEAT EXCHANGER: Power Plus International, custom
PUMP: Goulds 5SV4
STORAGE: 2,500-gallon Holocene Technologies Fluid Handling System with embedded heat exchanger, pump and controls
CONTROLS: Goldline GL30 Delta-T controller, autofill system with ASCO solenoid valve
FREEZE CONTOL: Drainback configuration
COLLECTOR INSTALLATION: Lowslope roof, bituminous roofing material, custom collector array mounts, 180° azimuth, 35° tilt
SYSTEM MONITORING: Badger 228BR flow meter with 3060 transmitter on DHW exchanger

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