Cooling – Steam Turbine Chillers
Steam turbine centrifugal chillers, like vapor compression and absorption chillers, rely on a vapor compression cycle to produce cooling. In electric and gas chillers, an electric motor or gas engine drive the compressor, and heat drives the thermal compressor of the absorption chiller. In steam turbine chillers, medium pressure steam—usually 100 to 200 psig—drives a turbine, which operates the compressor. Like other chillers discussed in this module, heat is rejected to cooling water in the condenser. Heat is absorbed in the evaporator to provide the cooling effect for the conditioned space.
Two types of steam turbines are available—condensing and back pressure. In condensing models, the entering steam is fully condensed in a dedicated steam condenser and heat is rejected via a cooling tower or river water. In back pressure systems, steam leaving the turbine enters the steam distribution system for use in an industrial process or for heating.
Steam cooling can be a cost-effective cooling option. If the cost of electricity is sufficiently high relative to the cost of steam, especially steam produced from on-site power generation or a boiler plant, a steam chiller can offer a lower life-cycle cost despite a higher first cost. Since cooling demands peak in the summer months when boiler heating demands are lower, it can be economical to maintain boiler operation through the summer and produce steam for cooling. A hybrid chiller plant operating steam chillers in tandem with electric chillers can also contribute to overall energy savings.