Abstract
In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather low; thus the quest for more appropriate technologies. Solar-assisted air-conditioning is also discussed, outlining the possibilities and the constraints.
Highlights
The most recent surveys ascertain that the demand for building cooling has been increasing in the past few years and will continue to do so dramatically in the near future
With electric chillers being dominant, the concern is about electricity consumption and, more importantly, black-out risks which may occur in large urban areas, when several thousands of small and large size air-conditioning units are likely to be activated almost simultaneously during the hottest hours of the day in the summer season
A quite different picture appears when one looks at the problem from a second law perspective. In this case we have to judge the technologies on the basis of the exergy efficiency, defined as the ratio of the exergy required by the end-use to that exploited to drive the system
Summary
The most recent surveys ascertain that the demand for building cooling has been increasing in the past few years and will continue to do so dramatically in the near future. Looking at these results one may conclude that current technologies for cooling are quite acceptable, and in certain cases (for PER > 1), apparently able to provide the user with a cooling energy even greater than the exploited PE. A quite different picture appears when one looks at the problem from a second law perspective In this case we have to judge the technologies on the basis of the exergy efficiency, defined as the ratio of the exergy required by the end-use to that exploited to drive the system. Detecting the most responsible processes and/or components for thermodynamic inefficiencies will give us the opportunity either to improve the design or to find new technologies
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