All Steamed Up

When planning power-plant upgrades, more schools are investigating cogeneration as a means to cut costs while increasing efficiency.

At a time when budget cuts are reducing the funds available for education, many schools are looking for methods of lowering operating expenditures. One of those methods is cogeneration--the simultaneous production of electrical power and useful thermal energy--which first sparked in the 1970s when the oil embargo sharply increased utility costs. Although gas lines and off-the-chart utility bills may be a distant memory, cogeneration still is an attractive alternative for any campus with a constant demand for both forms of energy.

Today, the ability to generate energy can reduce costs substantially while freeing the school from dependence on the utility company. But the decision to invest in cogeneration must be based on careful consideration of many issues.

As with any project, a financial evaluation provides justification for implementing cogeneration. The financial analysis starts with a realistic cost estimate of the project, which is based on experience in the design and construction of similar systems and project-specific factors that could affect final cost.

The output of the financial analysis is normally presented in two formats. A simple payback analysis shows the investment recovery resulting from the first-year savings divided into the estimated installed cost of the system. A cash-flow analysis also is performed based on the applicable net present value for the life of the system and the displaced cost for the out-years of system operation (i.e., the costs of operating the present system, which will be displaced by the cogeneration system).

Finally , a cost-sensitivity analysis is performed using the base financial analysis as the norm. Estimates are made on the cost of electric power, steam, fuel and maintenance to evaluate their impact on net savings. If replacement of aging equipment also is a factor, cogeneration becomes an even more attractive alternative.

Optimum design The design of the system and selection of equipment are project-specific factors based on demand, usage patterns, growth projections, capabilities of operations and maintenance staff, as well as other factors. Administrators must decide if the school is going to declare total independence from the utility or maintain a backup connection. Independence requires that the school build in redundancy in case the main system goes down, which can increase the project cost considerably.

The amount of redundancy built in depends on the extent to which the campus can afford to sustain outage without compromising safety and security of users and residents, as well as electronic and research data. A system that sheds non-critical users can reduce the cost of redundancy. Severing all connections with the utility also requires a level of confidence in the capabilities of the in-house maintenance and operations staff.

On the other hand, the benefits of maintaining a connection with the utility also are balanced by cost. For example, in the event of equipment outage, the rates charged for backup power will be much higher than if the school were a customer all year. That must be balanced with the additional costs of installing and maintaining backup equipment for complete independence.

Another major decision is whether to renovate the existing boiler plant or build a new facility, and if it is to be a new facility, where it should be sited. Renovation may or may not be practical. Often it is not feasible due to the cost, as well as the inability to provide steam to the campus during a renovation. The existing facility usually must remain in operation while the new plant is being built.

The key in siting a new plant is often accessibility of connection with the existing steam loop. A site adjacent to the existing plant is ideal, but it is not essential, provided the connection can be made cost effectively. Disruption during any excavation and construction must be factored in, along with the distance from the new plant to the existing infrastructure.

Although the building envelope will be a smaller part of the overall budget than in a usual campus building, it is important to pay attention to design. Whether the building is a showcase of this new technology or a background support facility will have an impact on the design-time cost and construction dollars. Decide early to establish the budget range to meet the design intent and to map out the review and approval process for design development.

Coordination with nearby buildings will have an effect on material selection and the level of detail. Inclusion of office and support areas may mean adding windows, and life-safety and code upgrades. If the building is to be a showcase with equipment on display, large-scale windows may be added. Even simple background buildings need to be built of materials that reduce the transmission of sound to the surrounding area, while using pragmatic and straightforward components to comply with building and energy codes.

Permitting the project The cogeneration facility will have to meet local, state and federal regulations with respect to air emissions and noise levels. Air permitting for a cogeneration plant is initiated at the inception of the design. Meet with the state department of environmental conservation or protection to discuss issues related to the plant and its proposed location. Gather manufacturers' equipment emissions data for all elements of the proposed system. Then, submit a permit application, which includes an evaluation of net emissions (i.e., a comparison of current emissions with projected emissions from the new cogeneration plant), best available technology (BAT) and a monitoring/recordkeeping summary.

The state also may require an initial, or screening, model, or a more detailed air model to assess dispersion of emissions. After the application is reviewed, the state or local agency may require clarification or additional information. Before the operating permit is issued, actual plant emissions must be tested to determine if they comply with emissions detailed in the application.

Noise generated by the new facility is a key issue when obtaining approval. State and local guidelines will dictate maximum noise levels at the property boundary for various times of the day. Engineers will use calculations based on manufacturers' equipment noise data to design a facility that meets these guidelines. They may enclose noise-generating equipment, for example, or use other techniques to reduce noise emissions.

Finally, if the new plant's storm-water discharge is subject to a National Discharge Elimination System Permit requirement, this permit application must be prepared and submitted.

When the existing coal-fired boiler plant at the State University of New York (SUNY) at Buffalo was reaching the end of its useful life, the university decided to build a new cogeneration plant. A financial and engineering analysis showed that cogeneration would enable the university to meet the campus' current and future energy demands cost effectively and free it from dependence on the local utility company.

The first consideration was to determine the savings that would be realized by cogeneration and the optimum mix of steam- and electrical-generating equipment to meet current and future energy demands. Because the university sought total independence from the utility company, the cogeneration facility required both electrical- and steam-generating redundancy to enable the plant to meet demand even if the largest prime generating unit were temporarily out of service.

The study evaluated several configurations of cogeneration systems, utilizing a heat-recovery steam generator, combustion turbines, reciprocating engine generators, steam turbines and diesel generators in various combinations. On the basis of the study and load demands, the system selected was a simple cycle cogeneration configuration comprising two 5.1 MW gas turbines with heat-recovery steam generators rated at 70,000 lbs/hour at 125 psig saturated steam; two 800 kW gas-engine generators; a 70,000-lbs/hour steam generator; and three 1,750 kW diesel engines. The steam generator and diesel generators will be used in case of failure of one of the prime generators.

Three primary factors were considered in executing the design of the cogeneration plant: -Integrating the new plant into the existing steam loop. -The aesthetics of the building in the campus environment. -Adherence to all government regulations.

The university's south campus currently is on a steam loop feeding directly from the boiler house. The key in siting the new plant was accessibility of connection with the existing steam loop. Renovation of the plant was not feasible due to the estimated cost and the non-availability of steam to the campus during a renovation. The area immediately adjacent to the plant was already in use. Therefore, the new cogeneration plant is sited on a playing field 700 feet from the original plant and connected to the steam loop through a pipe tunnel.

The new facility is functional and architecturally appropriate to the campus environment. The building comprises a 13,000-square-foot cogeneration plant and a 2,700-square-foot support/administration area. Ample windows on the north face of the building enable students and other passersby to view the operations of the plant while providing abundant natural light to staff. The exterior of the building is covered with a combination of ground and split-face block and precast concrete panels, which reflect the style of the neighboring building.

TAGS: Energy HVAC
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