Fig. 37-55 Performance Curve for 2,500 hp Steam Turbine Applied with Centrifugal Compressor. Source: Tuthill Corp. Murray Turbomachinery Division.

the specific annual cooling load profile of the facility, the application-specific thermodynamic performance of each system under actual load conditions, long-term electricity and fuel cost rates as they apply to the specific load profile and time of use, installed costs for the complete system, and long-term OM&R costs. Careful consideration must also be given to the host facility's requirements for redundancy and reliability. First cost alone thus provides insufficient indication of economic performance. Instead, life cycle cost analysis with focus on total cost of service is required.

First cost, size, familiarity, simplicity of operation, and minimal service and maintenance requirements typically make electric motors the most common choice for vapor compression system applications. The capital cost of prime mover-driven vapor compression systems is usually significantly greater than that of conventional electric-driven systems, with the premium ranging anywhere from $200 to $800 per ton ($50 to $225 per kWr) of installed cooling capacity. On the low end of this range are back-pressure steam turbines, in the middle are moderate-speed reciprocating engines and condensing steam turbines, and on the high end are gas turbines and low-speed reciprocating engines.

The capital cost differential would move higher or lower for each technology, depending on capacity and site-specific conditions. Generally, as chiller capacity is increased, the cost per ton (or kWr) differential between prime mover-driven chillers and electric-driven chillers drops, since economies of scale are reached with the prime mover itself and the coupling of the driver to the compressor. The differential is also reduced when compared with electric motor-driven systems featuring premium efficiency motors and/or VFDs.

In new installations, the costs associated with gas or oil, exhaust, and waste heat piping for reciprocating engine- and gas turbine-driven units, or steam piping for steam turbine-driven units, will add to capital costs as will costs for air permitting and emissions control. Electric service (i.e., wiring, transformers, and switchgear), a large unit's motor starter, and the cost of extensive conduit runs will elevate the cost of an electric-motor drive unit. In cases where a facility would need to install additional electric service capacity to support the installation of a new electric system, the cost can be substantial. Depending on the logistics of the facility and the location and available utility substation capacity, these costs can often offset a portion or, in an extreme case, all of the installed capital cost premium for a prime mover drive.

Another potential cost factor is the need for standby electric generation capacity to support critical cooling loads. In these cases, the combined cost of the electric cooling equipment and the standby prime-mover generator set may be equal to or even greater than the cost of the prime mover-driven vapor compression system. In some cases, an electric generator may be mounted in line with the compressor on a prime mover-driven system. This allows the prime mover to serve the dual function of providing emergency power to the facility for other (non-cooling) loads in the event of a utility outage.

Operating cost generalizations are difficult to make given the wide range of fuel and electricity prices and differing utility rate structures found across the country. Fuel prices are an important factor with simple-cycle prime mover-driven systems. It is less critical for systems operating on cogeneration cycles, which will generally produce net energy operating costs of $0.01 to $0.03/ton-h ($0.002 to $0.008/kWr). Even so, when electricity prices are extremely low, it is difficult to generate sufficient operating cost savings to overcome the capital cost differential on a life-cycle basis. The increased OM&R cost requirements also reduce savings potential.

Generally, the relationship between the facility load requirement curve and the electric rate structure are the key influences on operating costs. The trend toward higher peak electricity pricing, either on a commodity basis (such as the case with real-time pricing) or on the basis of high demand charges, places an operating cost premium on electric motor-driven units operating during peak periods. Given the common coincidental relationship between peak facility cooling requirements and high peak electricity pricing, peak or near-peak capacity operation for relatively few hours can dramatically drive up annual operating costs. This is, however, counterbalanced when systems also operate extensively in lower cost off-peak or intermediate rate periods.

Stratified electric rate structures also provide an opportunity to achieve operating cost optimization through use of mixed (hybrid) systems, featuring both electric motor- and prime mover-driven systems. For larger facilities, particularly those that require some measure of system redundancy, mixed systems allow for a variety of operating strategies driven by the dynamic changes in facility load and electricity pricing.

Chapter Thirty-Eight

Absorption Cooling Systems

Chapter Thirty-Eight

Absorption Cooling Systems

■ he use of absorption cycle technology has varied JL since its introduction in the late 19th century, depending on the relative cost of fuel and electricity and on improvements to mechanical compression and absorption technology. In recent years, seasonal pricing of electricity and fuel, improvements in absorption technology, heat recovery applications, utility promotion, and environmental concerns over halocarbon-based refrigerants have driven a resurgence of absorption cooling applications.

In response to market demand, U.S. manufactures have all introduced expanded lines of direct-fired and steam-powered absorption chillers and chiller/heaters ranging from 3 tons (11 kWQ to more than 1,500 tons (5,000 kWr). This chapter presents detail on a wide range of absorption technologies and applications.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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