hydronic heating systems

addition of thermostatic valves

chilled water systems

wet-side economizer

Air-water induction systems

replacement with fan-powered VAV terminals

*Requires replacement of air-handling unit

*Requires replacement of air-handling unit engines or even by steam or gas turbines. Natural gas engine-driven equipment sized from 50 to 800 tons of refrigeration are available and in some cases are used to replace older CFC-refrigerant centrifugal chillers. These engine-driven chillers are viable when natural gas costs are sufficiently low. Part-load performance modulates both engine speed and compressor speed to match the load profile, maintaining close to the peak efficiency down to 50 percent of rated load. They can also use heat recovery options to take advantage of the engine jacket and exhaust heat.

Turbine-driven compressors are typically used on very large equipment with capacities of 1200 tons or more. The turbine may be used as part of a cogeneration process but this is not required. (For a detailed discussion of cogeneration, see Chapter 7.) If excess steam is available, in industry or a large hospital, a steam turbine can be used to drive the chiller. However the higher load on the cooling tower due to the turbine condenser must be considered in the economic analysis.

Small water chillers, up to about 200 tons of capacity, may utilize reciprocating or screw compressors and are typically air-cooled instead of using cooling towers. An air-cooled chiller uses a single or multiple compressors to operate a DX liquid cooler. Air-cooled chillers are widely used in commercial and large-scale residential buildings.

Other types of refrigeration systems include liquid overfeed systems, flooded coil systems and multi-stage systems. These systems are generally used in large industrial or low-temperature applications.

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