DISCUSSION ON PRINCIPLES OF EXERGY ANALYSIS APPLIED TO HVAC SYSTEMS

摘要

Exergy is another name of available energy that measures the ability of the energy source to produce useful work. This article provides an analytical review of some pertinent works in HVAC application. Some general conclusions can be obtained. Exergy efficiency is more rational than energy efficiency; exergy analysis is more helpful than energy analysis for locating and evaluating available energy saving potentials, identifying opportunities for improvements in system design, establishing cost effective system maintenance programs. In addition, an unusual selection of dead-state novel to HVAC applications is suggested, which simplifies the exergy analysis by eliminating the necessity of calculating the exergy of water at ambient temperature (T_0). Such a selection will also make it easier to evaluate the precooling capacity of moist air (such as outdoor air or exhaust room air as secondary air). In this paper, the authors also suggest a functional classification to break down HVAC project in a hierarchy structure for exergy analysis. The HVAC system is considered as an energy service system that provides exergy for pure consumption in energy consumer system such as conditioning space. Energy service system can be further broken down into different components. Energy flows are also classified according to their functions as source energy flow and service energy flow to assist the evaluation of the performance of the systems or components. Relevant principles of exergy analysis are discussed. Finally, an imagined but typical case is calculated to demonstrate the application and the reasonability of the above propositions.