Water-coupled carbon dioxide microchannel gas cooler for heat pump water heaters: Part I - Experiments

An experimental and analytical study on the performance of a compact, microchannel water- carbon dioxide (CO2) gas cooler was conducted. The gas cooler design under investigation used an array of serpentine refrigerant microchannel tubes wrapped around water passages containing offset strip fins, resulting in a generally counterflow configuration between the two fluids. Part I of this two-part paper addresses the experimental aspects. Data were obtained using an experimental heat pump facility at varying inlet conditions for three gas coolers of the same design, but different sizes. Measured heating capacity for the three gas coolers ranged from 1.5 to 6.5 kW. The results of this study are used in the companion paper (Part II) to develop a predictive heat exchanger model to optimize gas cooler design over a wide range of operating conditions, eliminating the need for expensive prototype development and testing.