Postal Service Shared Energy Savings Partnership Successful in Atlanta Upgrade
February 1, 2002
The Atlanta District of the U.S. Postal Service recently completed construction on a $3.2�million shared energy savings project at the Bulk Mail Center (BMC) in Atlanta, Georgia. The Postal Service's regional headquarters in Memphis, Tennessee, awarded a contract for the project to Municipal Electric Authority of Georgia (MEAG). MEAG, an Atlanta-based electrical cooperative, selected Custom Energy, LLC, an energy services company, to provide comprehensive turnkey, design-build, construction, energy, and financial services for the shared energy savings project. By implementing the MEAG/Custom Energy project, the BMC and the Postal Service are enjoying a significant reduction in facility operating costs, an increase in facility production, and a greatly improved working environment for employees.
MEAG addressed concerns regarding the Postal Service's aging central chilled water plant. Only one of the facility's two 900-ton centrifugal chillers was operational, and both used CFC-11, a banned and increasingly scarce refrigerant. The chillers were contaminated by asbestos from the cooling towers, as were the towers themselves (asbestos was used as the fill material in the original towers). The original controls for the plant's HVAC systems were also defunct, requiring that all of the equipment be operated manually.
The Postal Service's shared energy savings performance contracting approach offers several advantages— primarily it eliminates the up-front expense involved in the analysis, design, and construction phases. The customer incurs no expense until the work is complete and operational. The performance contractor (MEAG) funds the project, including long-term financing for a period of up to 10 years. The project is designed so that the facility's monthly energy savings amount is at least as much as the finance payments, and any excess is an immediate benefit for the customer.
The BMC project began with a preliminary energy audit, which outlined a number of potential energy projects and provided estimated energy savings and implementation costs. The Postal Service evaluated a detailed feasibility study that provided investment grade estimates of energy savings and guaranteed project pricing, and selected promising projects. It was apparent early in the process that the cost savings generated by the new chillers would not be sufficient to pay for their installation in the 10-year period. Fortunately, the Postal Service was able to "buy down" the chiller plant payback period using funds earmarked for CFC replacement.
Custom Energy investigated a variety of chiller plant options, including gas-fired absorption and engine-driven chillers as well as conventional electric machines. The best solution was found to be an all-electric system of three centrifugal chillers of 525�tons each and one rotary screw chiller with a capacity of 250 tons. This combination offered an excellent combination of efficiency (0.6�kilowatt per ton) and operating flexibility, as well as a level of redundancy desired by the Postal Service. Custom Energy also converted the facilities' original chilled water pumping system from constant to variable flow, using a primary/secondary layout with four new primary pumps and a new 100-horsepower secondary pump. The facility is now outfitted with a new secondary pump and its two existing secondary pumps were converted to variable speed operation with the installation of three adjustable frequency drives.
Custom Energy also made extensive modifications to the 28 single-zone and three multi-zone air handling units at the BMC. Other upgrades to the facility include the replacement of supply fan motors with new, energy-efficient motors equipped with adjustable frequency drives, converting the systems from constant to variable air volume. All of the chilled water and hot water control valves have been replaced with new valves with electric operators. A state-of-the-art direct digital energy management and control system is being installed that will provide total HVAC system control.
In addition, Custom Energy retrofitted the lighting systems in the three-story office portion of the facility. More than 3,300 fluorescent fixtures were converted from the existing T12 lamps and magnetic ballasts to T8 lamps with high-frequency electronic ballasts.