Steam-turbine-driven chillers have been around for almost a century. Now, with a stable supply of low cost natural gas in the United States, steam-turbine-driven chillers are becoming a popular choice, particularly for large combined heat and power (CHP) applications. Steam-turbine-driven chillers also are attractive when the cost of steam is relatively low compared to the cost of electricity.
A conventional utility power plant has an average electrical efficiency of 35 percent. This means that 65 percent of the input primary fuel energy is wasted. In a combined heat and power system utilizing a combustion gas turbine (with typical electrical loads greater than 1 MW), the exhaust gas heat is recovered to produce steam at medium-to-high pressures — useful for heating and cooling. In so doing, the overall system efficiency increases to almost 90 percent, which is maintained year-round. Only 10 percent of the input primary fuel energy is wasted.