Principles Of Refrigerant Circuit Optimization In Single Row Microchannel Condensers

Automotive HVAC systems manufacturers were the first to introduce microchannel condensers in the comfort airconditioning market. HVAC&R original equipment manufacturers have followed their lead and recently started using microchannel condensers in residential and commercial cooling and heat pump applications. These applications began less than a decade back and their number has been increasing steadily (Mehendale, 2013). The main difference between microchannel condensers used for the automotive and residential / commercial applications is that the latter span a much wider range of coil face areas compared to the former. Considering this fact, there are relatively few well-documented studies in the public domain on the numerical modeling of two-phase heat transfer and pressure drop in microchannel condensers, especially in the size range of interest for residential / commercial climate control applications. More specifically, the principles behind the selection of the correct refrigerant circuit patterns that lead to the optimal thermal-hydraulic performance of microchannel condensers with different sizes is a matter that has not been satisfactorily addressed. In this work, CoilDesigner, an element-by-element heat exchanger model, was employed for simulating a singlerow microchannel refrigerant-to-air condenser consisting of microchannel tubes and multi-louvered fins. Starting with a given microchannel tube design and a fixed multi-louvered fin geometry, the model was exercised to simulate the thermal-hydraulic performance of various two-, three-, and four-pass circuit configurations over a range of coil face areas. Based on the tradeoffs encountered between condenser heat duty and refrigerant pressure drop or pumping power required, recommendations have been provided to help designers and researchers in the HVAC&R field to select the best possible circuiting arrangement.