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USING AIR CONDITIONING TO DEMONSTRATE 1ST AND 2ND LAW ANALYSIS

Frank Wicks Union College Schenectady, New York

ABSTRACT In contr~ 2nd Law efficiency is best described as the ratio of actual to ideaI performance. The 2nd Law analysk techniques have the advantage isentropic efficiency of a turbine, pump, or of demonstrating the lost work associated with each compressor is the 2nd Law efficiency of a process, non-ideal process in an engine or the extra work while the ratio of the actual efficiency of an engine to associated with each non-ideal proo%s in an air the ideal efficiency of an engine with the same heat conditioner, but the existing text books do not source and sink describes the 2nd Law eftkiency of a provide good examples of the applications of these cycle. techniques. Thus, a paper was presented and published for the 1995 conference to demonstrate the Simiiarly, two methods can also be defined for use of these techniques for fuel burning Carnot and evaluating the overall performance of a cycle. The Rankine cycles. This paper presents similar fwst method can be defined as a 1st Law method examples of the use of these techniques for air because it examines the 1st Law energy balance for conditioning analysis. each process and for the total cycle, from which the ratio of desired energy achieved (i.e., the net work 1. Introduction from engine) to what is supplied (i.e., the fuel) can be directly determined. Rwog&ing that we live on a ftite planet with limited fuel resources in the ground and with limited The second method requires the 2nd Law and atmosphere to absorb the products of Combustio% thus is called a 2nd Law method. This method starts engineers will be continually and increasingly by determining the ideal performance of a cycle and challenged to make our expanding modern society then applies the 2nd Law to determine the more energy efficient. irreversiiities of the individual processes. If it is an engine or power producing cycle, the irreversibtities This means that all energy conversion processes represent lost work. If it is an air conditioning or and cycles should be continuously examined to refrigeration cycle, the irreversibfities are the extra establish how much fuel is being consumed and for work that must be supplied. the potential of improving efficiency with better cycles, heat exchangers and any other improved While both the 1st and 2nd Law methods should technologies. give the same net efficiency or performance, the 2nd Law method provides additional information since it A fkn understanding of thermodynamics is the quantities the lost work or extra work associated with prerequisite for deftig existing eftlciencies and the each less than ideal process. Thus, the 2nd Law opportunities and limits for such improvements. It is technique provides better guidance in terms of which also noted that overall fuel consumption is typically of the processes represent the largest loss, and thus a complicated function of many related effkiencies, the best opportunities for improving performance. which can be classified in various ways. Some thermodynamic text books describe the 1st Law et%ciencies can be described as the required principles, but do not provide good ratio of the useful energy achieved to the energy that numerical examples to demonstrate their application. must be provided. The effkiency of a boiier or Thus, it is the author’s goal to develop and present furnace represents a 1st Law efficiency of a proces some such examples for inclusion in future text while the net efficiency of a power plant is the 1st books. Law efficiency of a cycle.

{’ti!ij 1996 ASEE Annual Conference Proceedings ‘O,+,pylj .

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Wicks, F. (1996, June), Using Air Conditioning To Demonstrate 1st And 2nd Law Analysis Paper presented at 1996 Annual Conference, Washington, District of Columbia. 10.18260/1-2--6371