What is driving this sudden increase in demand four decades after these systems first came to market? While environmental concerns may be a factor behind the growing popularity of other gas cooling technologies like absorption chillers, this is not the case with gas engine chillers. Unlike absorption cooling, which uses water as the refrigerant, compressor-driven chillers – whether they are powered by an electric motor or a gas engine – use HCFC or HFC refrigerants. Although not as harmful as CFCs, these compounds are certainly not benign, and have subsequently come under the watchful eye of environmental interests and legislators. Also, the internal combustion engine, with it's wide variety of harmful emissions has never been the paragon of environmental friendliness. To be fair, however, natural gas engines have lower emissions than gasoline-powered engines do. The main reason the demand for gas engine chillers is growing is one of the main reasons that all gas cooling technology is becoming more popular – the cost of electricity. Rising, unstable electricity prices are making natural gas-powered chillers much more attractive from the standpoint of operating costs if not from the standpoint of purchase price. The Engine A gas engine chiller has an internal combustion engine similar to the one you'd find in most cars, except it has been modified to run on natural gas. Some chillers employ purpose-designed industrial engines while others use engines that have been derived from mass-produced automobile engines. The automotive derivative engines typically cost far less due, at least in part, to the higher economies of scale in the automobile industry. Unlike electric motors which can reside inside the compressor housing, gas engines must be mounted external to the compressor in a open-drive configuration. The Compressor There are five types of compressors than can be used in compressor-driven chillers: reciprocating, centrifugal. rotary, screw and scroll. (For an explanation of how the different compressors work, see the article "Passing Gas") Gas Engine Chillers vs. Electric Chillers • Wide range of operating speeds makes gas engine chillers more efficient than electric chillers at partial loads. On average, chillers operate at peak loads only about 1% of the time. • Gas engines are capable of exceeding rated outputs for brief periods, sometimes allowing for the selection of a somewhat smaller unit that will still be able to handle peak loads. The engine itself generates heat which can be recovered and utilized for other purposes, such as for heating water. • Gas engine chillers require more maintenance than electric chillers due to the mechanical complexity of the engine, although reports show natural gas engines need less maintenance than gasoline engines do. • A study by the Georgia Institute of Technology shows that a gas engine chiller can have an equipment cost that is three times higher than that of an electric chiller of equal capacity but can have just over half the annual energy costs. A pay-back period of several years is typical. Gas-Electric Hybrids For those who want the best of both worlds, at least one manufacturer is offering a gas-electric hybrid chiller which comes equipped with both a natural gas engine and an electric motor. Hybrid chillers are capable of switching between the engine and the electric motor to drive the compressor. Hybrid systems enable operators to respond virtually instantly to changing electricity prices and also to avoid peak demand charges, therefore minimizing operating costs. To learn how gas engine chillers work, click here. back to PilotLight online