Estudo das pressões máximas no evaporador de uma bomba de calor de expansão direta à R744 assistida por energia solar

Abstract

The use of heat pumps to heat water instead of electric heaters is a way to reduce energy consumption and consequently greenhouse gas emissions. In this context, carbon dioxide (CO2 or R744) as a refrigerant has drawn the attention of several researchers in the field of refrigeration. Several works in the literature evaluated the performance of the heat pump, economic performance, energy performance, exergy performance, influence of the geometry in the solar evaporator, but no works were found that presented the behavior of the pressure in the evaporator of a heat pump at R744 in the cycle transcritical. In this context, this work presents a mathematical model for the heat pump evaporator (DX-SAHP) that evaluates the behavior of the pressure in the evaporator when it is not operating, but exposed to the sun, and the impacts of these pressures on the structural integrity of the components, considering a mass amount of R744 trapped inside the evaporator varying between 8% and 12%. The meteorological data for solving the mathematical model were taken from the INMET website, studying data from Belo Horizonte since 2012 and in the other four regions of Brazil, focusing on the year 2022. The maximum pressure of R744 for 12% of mass inside the evaporator was of about 12.2 MPa while the maximum working pressure in the evaporator recommended by the tube manufacturer is 13.2 MPa.