1 Copyright © 2003 by ASME Proceedings of 2003 ASME Summer Heat Transfer Conference July 21–23, 2003, Las Vegas, Nevada, USA HT2003-47271 DESIGN STUDY COMPARISON OF PLAIN FINNED VERSUS LOUVERED FINNED- TUBE CONDENSER HEAT EXCHANGERS Susan W. Stewart Ph.D. Student G.W.W. School of Mechanical Engineering Georgia Institute of Technology Atlanta, GA 30332 Sam V. Shelton Assoc. Professor G.W.W. School of Mechanical Engineering Georgia Institute of Technology Atlanta, GA 30332 ABSTRACT Enhanced fins are widely used in residential air conditioning system finned-tube condenser designs. While this heat transfer augmentation technique increases the heat transfer coefficient in the heat exchanger, it also increases the air side frictional pressure drop. These two effects compete with each other, making it difficult to determine the relative goodness between plain fin versus enhanced fin designs with realistic constraints. In the past, this design tradeoff has been largely determined by experimental trial and error or heuristic figures of merit. No studies are available showing the effect of fin augmentation on overall system performance under consistent cost and frontal area constraints. The residential air conditioning system model calculates all component and system performance parameters. The condenser design requires the specification of approximately ten design parameters. A search method is used to vary these ten parameters and reach an optimum design based on a COP (efficiency) figure-of-merit with condenser cost and other appropriate constraints. It was found that when optimized, louvered fin designs always show better system performance than the optimum plain fin design for the cases studied. However a decrease in system efficiency can result if louvers are merely added to a plain fin optimum design. INTRODUCTION Researchers have been studying the effects of fin surface enhancements for several decades [1-3], and the practice of adding surface enhancements to the fins of finned-tube heat exchangers has become widely used in many products, notably residential space-conditioning air cooled condenser heat exchangers. Many authors have developed experimental correlations to predict the performance of enhanced finned-tube heat exchangers and others have made heat transfer coefficient or friction coefficient comparisons between plain and enhanced fins. However, very few, arguably none, have quantitatively investigated the effects of fin enhancements on total system performance. Adding louvers to a finned tube condenser heat exchanger in an air conditioning system will reduce compressor power by increasing the refrigerant-to-air conductance, but will increase the condenser air fan power. These competing effects make it more difficult to determine the relative goodness of a heat exchanger design. Many different heat exchanger figures-of- merit have been used. Their differences primarily depend on constraints imposed for the analysis. The most common system figure-of-merit for an air- conditioning system is the first law efficiency, which is expressed as the coefficient-of-performance (COP). More specifically, the seasonal COP (COP seas ) measures the average COP over a cooling season. This method is an undisputed technique for comparing the relative energy efficiency of different air-conditioning system designs. However, for a heat exchanger optimization study, care must be taken in fixing the appropriate constraints of the system design for the comparison. The more important ones are generally the system’s desired output; i.e., cooling capacity, physical size, and the equipment cost. In this study the louver fin geometry will be investigated and compared to plain fins. A complete model of a residential air-conditioning system, with great detail in the condenser component, is used to calculate the system COP along with an