1. Field of the Invention
This invention relates generally to enhancing the efficiency of converting oil, gas, steam or other fuels to cooling using a compressor and, more particularly, to a system for improving the operating efficiency by connecting to the power grid a motor which can operate as a cogenerator.
2. Description of the Background
Large cooling systems such as central, industrial or district cooling, are increasingly important as efficient and environmentally beneficial alternatives to producing cooling within individual buildings. Such systems involve large chillers typically driven by large induction motors or steam turbines, which use electric or steam power generated elsewhere. They seldom use prime movers like gas turbines or reciprocating engines, which generate power directly, because the economics of the short cooling season discourage investment in these more expensive prime movers. Although chiller systems with prime movers that generate power directly are known to be more efficient, two problems have hindered the rapid development of this concept. First, gas turbines or condensing steam turbines used to drive chilling compressors lose power under the very conditions in which the compressor requires maximum power, that is, when ambient temperature and resulting space cooling requirements are highest: in the summer months and during the daylight hours. Second, even if the power output of the prime mover is constant at higher ambient temperatures, as is the case with reciprocating engines, the chiller needs more power at those times. Conventionally, one must either purchase an oversized prime mover at significant capital cost or accept insufficient chilling output during periods of peak requirement. If the prime mover is oversized, its efficiency will drop during the cooler periods because it will operate at partial load.