The county of San Diego is always looking for ways to reduce electrical usage and demand; and particular interest involved the HVAC system (last upgraded in 1998).
The county's Juvenile Hall Complex is made up of the Juvenile Court, Juvenile Hall and the Juvenile Probation Center. The three facilities encompass 52,405 square feet, 136,000 square feet and 65,807 square feet, respectively. Pre-retrofit chillers
The central plant is made up of two eight-year-old centrifugals (300-ton and 450-ton centrifical chillers, both equipped with variable frequency drives). The performance of the 450-ton chiller was monitored during the first two weeks of October 2005. The entering condenser water temperature was reset based on outdoor wet bulb temperature and was observed between 65 degrees to 72 degrees F; while leaving the chilled water was maintained at 46 degrees F. The chiller consistently operated between 0.71 kW/ton and 2.0 kW/ton and averaged 0.935 kW/ton for the two-week period. Recommendation
The existing chillers had considerable operating problems (high energy usage, consistent high lift alarms, surging and difficulty staging and automatically bringing another chiller online). Also, because of the primary-secondary-tertiary system, significant mixing occurred in the decouplers and miscellaneous three-way valves, making it impossible to fully load any one of the chillers (significant low delta T syndrome). Noticing the inefficient operation of the two centrifugal chillers as well as documenting the operating problems listed above, the San Diego Regional Energy Office (SDREO) convinced the county of San Diego to retrofit both machines with Turbocor compressors.
Three TT300 Turbocor compressors (90 tons each) were installed on the 300-ton chiller. The savings with these TT300 compressors have been well documented and several retrofits have been successfully operating in San Diego. For the 450-ton machine, the TT400 compressor (three compressors at 150 tons each) was selected.
Total savings for the entire Turbocor retrofit project was estimated at $60,000 to $70,000 per year. As part of this project, the all-variable speed Hartman Loop control strategy was also implemented. The decoupler was removed and variable frequency drives were installed on all condenser pumps, chilled water pumps and cooling fans. The savings from this retrofit was estimated at an additional $42,000 per year. Conclusion
Benefits and points of interest include: ¥ Low-load performance was greatly improved (70 percent - 90 percent less energy) ¥ Surging and high-lift alarms were eliminated ¥ Sequencing of chillers was automated; operator hassles and maintenance were reduced ¥ Oil-less compressor technology (reducing dependency on foreign oil while increasing efficiency of the machines ¥ Variable condenser and evaporator flow was easily implemented with the oil-less chillers ¥ Noise was greatly reduced ¥ Significant portion of the central plant upgrade was covered by incentives
To learn more about the advances of this amazing technology along with any other services (service/maintenance for commercial and industrial; tenant improvements and special projects, plumbing services and installation, energy retrofit and/or controls), contact Alpha Mechanical Service & Engineering at (858) 279-1300 or visit www.alphamechservices.com.
Submitted by James Egan of Alpha Mechanical Service & Engineering and the San Diego Regional Energy Office