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With delta-Ts of 5°F to 14°F, the flow rate of the 2,000-ton chillers varied from 9,600 to 3,430 gpm. Upon further consideration, the delta-T range was changed to 7°F to 16°F (6,800 to 3,000 gpm) to stay below the maximum flow rate allowed by chiller manufacturers and allow the desired 16°F delta-T to develop over time.

Finally, the chillers' capital costs were considered; they did not vary significantly until a delta-T of 8°F was reached. The cost of the chiller then increased, resulting in a premium for design optimization up to this point.

Based on these factors, the project team selected a design delta-T of 10°F, with an operating range between 7°F and 16°F. The Peffley plant is capable of handling lower delta-Ts without limiting its ability to operate at a higher delta-T in the future. With the implementation of a variable primary-flow system and the selected operational delta-T range, the project team estimated a chiller energy savings of 2 to 4 percent.

Free cooling. Another energy-saving measure included the use of a 2,000-ton free-cooling heat exchanger. It allows chillers to be shut down when it is cool outside and the building cooling load is low. The system transfers heat directly from chilled water to condenser water, offsetting the need for operating chillers. Relocated from Ottawa, the heat exchanger utilizes the same chilled-water distribution pumps and condenser water pumps that the chillers employ. Therefore, the additional cooling system required a minimal capital investment for piping, valves, and controls.

LBWL uses the free-cooling system instead of a centrifugal chiller from December through February. The free-cooling system allows LBWL to meet most of the daily chilled-water demand in periodic service runs during late fall and early spring, weather permitting. At a design temperature of 44°F, the system is capable of producing an amount of chilled water equivalent to that produced by an electric centrifugal chiller. The free-cooling system's number of operational hours offsets the need for electrically generated chilled water, saving energy and reducing the building's carbon footprint.

Architectural Considerations
The Peffley plant is located near the heart of downtown Lansing on the Capitol Loop highway, near the state capitol building and several state office buildings. A primary project objective was to integrate the plant into the surrounding architecture.

Because of site space considerations, eight cooling-tower cells were located on the plant's roof. To conceal them, the project team used architectural louver screens, but the screens made the building mass too large. Horizontal and vertical exterior-insulation-finishing-system accents were added to break up the mass. The vertical accents provided an opportunity to include colored light-emitting diodes to accentuate these features during night hours. A combination of decorative masonry block, brick, and glass was used to construct the building.

Budget Control and BIM
The project operated under a very tight budget. To help minimize the possibility of change orders during construction, the project was designed utilizing BIM. This design approach integrates current technology with the design process to improve communication, identify potential problems early, and provide engineers and designers with vital resources.

BIM software modeled the plant in 3D with an interference manager to identify potential conflicts early in the design process. The software produced structural models with analytical features; architectural models for uses such as space planning; mechanical models of equipment, piping, and HVAC systems; electrical models of equipment and cable tray; and a database linked to piping and instrumentation diagrams with information on valves and instruments. The models then were used to produce traditional construction drawings, specifications, and data sheets. The resulting BIM model provided LBWL personnel and the project construction manager with valuable information on the project design and assisted in resolving clarifications.

Change orders totaled less than 2.4 percent of the project contract value, and the project was completed within its $20 million budget.

Maintenance Operations
Despite limited site space, another project objective was to improve accessibility for equipment maintenance. To this end, equipment was arranged to preserve an open-access aisle on the operating floor, which allows equipment removal without interruption of plant operations. Additionally, the operating floor was designed so chillers and heavy electrical equipment could be moved without the need for floor shoring.

To further facilitate maintenance, monorails were provided over each chiller driveline and for each row of pumps. For equipment removal/installation in the basement, a floor access hatch was included. Lastly, piping and equipment design included valve operators at accessible locations wherever practical and ensured those out of reach could be accessed by a lift.

Summary
The redevelopment of downtown Lansing provided LBWL with an opportunity to improve the operation and maintenance performance of its chilled-water system. The project converted the primary-secondary system to a variable primary system and maintained the free-cooling system, reducing energy consumption and carbon footprint. Additionally, LBWL constructed an industrial facility without compromising the aesthetics of the downtown area.

References
1) Nonnenmann, J. (2006, February). Chilled water plant pumping schemes. Paper presented at the International District Energy Association Campus Energy Conference, Albuquerque, N.M. 2) McCauley, G., & Strause, R. (1996, September). Chilled water distribution pumping schemes. Paper presented at the Central Association of Physical Plant Administrators (CAPPA) Annual Meeting, San Antonio, Texas. 3) Durkin, T. (2005). Evolving design of chiller plant. ASHRAE Journal, 47, 40-46.

A senior mechanical engineer and project principal for Stanley Consultants Inc., James J. Nonnenmann, PE, is responsible for business development, mechanical design, and evaluation related to central energy plants, power generation, and building mechanical systems. He holds a bachelor's degree in mechanical engineering from the University of Illinois, Urbana-Champaign. He can be contacted at nonnenmannjim@stanleygroup.com. A principal mechanical engineer and project manager for Lansing Board of Water & Light, Daniel J. Flynn, PE, is responsible for consulting, project management, and design related to the utilities' production and distribution facilities. He holds a bachelor's degree in mechanical engineering from Michigan Technological University. He can be contacted at djf@lbwl.com.

Low-Delta-T Syndrome
Causes of low-delta-T syndrome include:

• Improper coil or control-valve selection.
• Dirty coils.
• Mismatched design conditions.
• Three-way control valves, which allow bypass of chilled water around a coil at part-load conditions, result in lower return-water temperatures for all conditions except design. The mixing of the chilled-water supply and return water results in a lower-than-design delta-T, contributing to low delta-T syndrome.
• Supply/return mixing at building decoupler.
• Arbitrary lowering of supply-air-temperature set point.
• Coil piping configuration. Coils must be piped so water is counterflow to air. If coils are piped in reverse, the coil's heat-transfer efficiency will decrease, resulting in lower chilled-water return temperatures.

Did you find this article useful? Send comments and suggestions to Associate Editor Megan White at mailto://megan.white@penton.com.

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