Thermodynamic analysis of cooling and heating systems for energy recovery
Abstract All energy systems that produce waste heat that is above the ambient temperature, must be coupled to other thermal equipment in order to increase the benefits of the primary source and, like this, reduce pollution. By means of the first and second law of thermodynamics, this work analyses waste heat recovery of a Two Stage Vapour Compression System (R123) for an Absorption Heat Transformer (H2O/LiBr). Both systems are evaluated in an individual and comprehensive manner, considering an evaporation temperature of 235.15 K in the condenser of the cooling system and different absorption temperatures in the heating system. The cooling system (by means of the condenser) is capable of reaching the temperatures required to activate the heating system (through the evaporator); however, its energy performance decreases and exergy destruction increases in the high-pressure circuit. Two relationships are proposed to quantify the performance of the coupled machines, where recovered heat and its temperature play an important role. Under this analysis scenario, it is possible to reach performance values of the coupling from 0.711 to 0.927, when the difference in the absorber and evaporator temperatures decreases by 18 K at an interchange temperature of 343.15 K.