Aurora Energy: Talbot County Public Safety Center

Fluctuating hot water demand presents an interesting challenge for commercial water heating system design. In the Talbot County Public Safety Center, the average inmate population is approximately 100, but the maximum population can reach as high as 157. To solve the design challenge posed by this wide swing in demand, Aurora Energy developed a rooftop heat dissipation system to prevent system overheating during periods of low usage.

The array consists of 32 evacuated-tube collectors, with 30 tubes each, plumbed in two parallel banks of 16 collectors. A ballasted, nonpenetrating mounting system secures the collectors to the roof surface. Each of the two collector loops is coupled with an equivalent number of fin-tube heat dissipaters that are controlled by thermostatic diverting valves.

The system’s pump station was built at the site and consists of two pumps and one micro-bubble separator for each loop. Each pump has a dedicated controller. The first pump runs at a lower temperature gradient between collector inlet and outlet. The second pump starts at a higher temperature gradient and serves as a backup if the first pump fails. In addition, the second pump increases flow rate during periods of high solar insolation. The system’s heat exchangers and pumps are located close to the collector arrays to keep the glycol-circuit piping as short as possible.

“Manipulating tube numbers to manually increase and decrease the active capacity of the collector field to match inmate population would have placed an undue burden on the facility staff. The solution was a heat dissipation system that automatically matches solar hot water production with consumption, thereby eliminating the potential for system overheating.”

Mike Kabler, Aurora Energy

Overview

DESIGNER: Fariborz Mahjouri, PE, CEO, Aurora Energy, aurora-energy.com
LEAD INSTALLER: Mike Kabler, project manager, Aurora Energy
DATE COMMISSIONED: June 2012
INSTALLATION TIME FRAME: 23 days
LOCATION: Easton, MD, 39.2°N
SOLAR RESOURCE: 4.6 kWh/m2/day
ANNUAL HEATING DEGREE-DAYS: 4,707
RECORD LOW TEMPERATURE: -21.7°F
COLLECTOR ARRAY AREA: 1,686 sq. ft.
AVERAGE ANNUAL PRODUCTION: 153 MWh

Equipment Specifications

COLLECTORS: 32 Solar Panels Plus SPP-30A evacuated tube, 52.7 sq. ft. each
HEAT EXCHANGERS: Advanced Industrial Components L-Line LA 14-50
PUMPS: 4 Grundfos UPS 26-99 FC
STORAGE: Existing 1,500-gallon tank
CONTROL & MONITORING: Thermo Technologies USDT 2005
FREEZE CONTROL: Closed-loop antifreeze, DOWFROST HD heat transfer fluid
COLLECTOR INSTALLATION: Nonpenetrating ballast mount on TPO roofing, 180° azimuth, 38° tilt

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