Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Thermodynamic modeling of a two-stage air-conditioning system with an economizer
Submission Author:
Leonardo Grous Franco , SP
Co-Authors:
Leonardo Grous Franco, Guilherme Borges Ribeiro, Izabela Henriques
Presenter: Leonardo Grous Franco
doi://10.26678/ABCM.COBEM2021.COB2021-2293
Abstract
An extremely high external ambient temperature brings several issues for a proper operation of a vapor-compression refrigeration system. The decrease of the lubricating oil viscosity, reducing the compressor lifespan, and the reduction of the cooling capacity, and the increase of power consumption are key effects found in a refrigeration system when subjected to high ambient temperatures. With a focus on these aspects, this paper describes a thermodynamic modeling and comparative study between a single-stage refrigerating system and a two-stage refrigeration system with an economizer, operating at high ambient temperatures. The comparison of the coefficient of performance (COP) between these two cycles, changing external ambient temperatures and refrigerant fluids, are part of the analysis. As a baseline for this study, an air-conditioning unit for military purposes with a cooling capacity of 1.5 TR (tons of refrigeration), and using R-407c as refrigerant fluid, is applied. Moreover, other refrigerants are assessed, like R-32, R-1234yf, R-410a, and R-1234ze(E). The models consider the global thermal conductance of the heat exchangers and the total heat exchanger area is divided into corresponding fluid phases. The prediction of the latent heat transfer rate is performed using the Lewis analogy. A two-stage scroll compressor is modeled based on curve regression presented in the literature. Through the successive substitution method and the bisection method, a solution for the cycle operation is achieved under several internal and external conditions. With the analysis of the output data, a higher COP can be found for the two-stage system with economizer, regardless of the refrigerant fluid, due to the presence of the intermediate pressure, yielding a reduction of compressor power input, and an increasing of the COP and cooling capacity. These results are intended to be used as a tool for the design of efficient air conditioning systems under extreme high ambient temperatures, reducing the carbon footprint and the global warming impact of the air conditioning system.
Keywords
Economizer, vapor compression, air conditioning, Refrigerant, High temperature
