Estudo experimental sobre o desempenho de uma bomba de calor a CO2 assistida por energia solar de expansão direta para aquecimento de água para uso residencial

Abstract

The expansion of energy consumption, the depletion of fossil resources and the poor efficiency of energy systems, have led many countries to invest in sustainable energy solutions and ways of diversifying the energy matrix. In this context, at a national level, it is possible to highlight electric showers that are responsible for significant amount of residential electricity consumption. The present work presents an experimental analysis of the performance of a CO2 small size direct expansion solar assisted heat pump for residential water heating, as an efficient alternative to replace electric showers. The variation of parameters such as: water inlet temperature, ambient temperature, solar radiation, humidity, expansion valve opening, water mass flow rate are analyzed. For higher solar radiation condition the CO2 DX-SAHP results in a COP cycle about 2.9, and for lower solar radiation the COP is approximately 1.9. The decrease of the relative humidity reduces the performance of the system. Considering the same operation parameters, the COP decreases 6% for a relative humidity changed of 55.8% to 31.57%. The augment in the water mass flow rate, causes an increase of the theoretical performance in about 60%. On the other hand, if the water inlet temperature increases form 15°C to 35°C reduce the cycle COP in approximately 32%. In addition, it is observed that independently of the solar radiation flux, there is an optimum opening of the expansion valve (2 turns), which could be replaced by fixed devices of lower cost for small systems like this one. Differently from the others correlations present in the literature, the new correlation of the correction coefficient proposed for the expansion valve allows to estimate the mass flow rate for heat pump operating with solar energy and CO2. The relative deviation is less than ± 15% for all of the data.