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This work proposes a cascade coupling system to recover low-grade waste heat. The hybrid system performs well in hot summer and cold winter areas of China. The economy, energy, and exergy analysis and multiobjective optimizations are conducted. Nondominated sorting genetic algorithm II is applied to realize the optimization process because of the contradiction between the three objective functions. The Pareto solutions are obtained, and the relationships between two different objectives are analyzed. The final optimal solutions are determined by the technique for order preference by similarity to an ideal solution method and the Shannon entropy method. Four schemes aiming at the maximum coefficient of performance (scheme 1), minimum total annual cost (scheme 2), minimum total exergy destruction (scheme 3), and multiobjective optimization (scheme 4) are studied. The results show that the minimum values of the total annual cost and the total exergy destruction are 57.73 × 10 4 $ and 336.91 kW, respectively. The maximum coefficient of performance is 0.61. The multiobjective optimization solutions achieve a 4.12% higher value than the minimum coefficient of performance, while the total annual cost and the total exergy destruction of solutions are 1.86 and 0.58%, respectively, lower than the maximum values. This work presents a deeper dissection and a multiobjective optimization of the cascade system and provides guidance for the development of low-grade waste heat recovery technologies.

The utilization of geothermal energy is favorable for the improvement of energy efficiency. A hybrid system consisting of a seasonal heating and cooling cycle, an absorption refrigeration cycle and a liquid dehumidification cycle is proposed to meet dehumidification, space cooling and space heating demands. Geothermal energy is utilized effectively in a cascade approach. Six performance indicators, including humidity efficiency, enthalpy efficiency, moisture removal rate, coefficient of performance, cooling capacity, and heating capacity, are developed to analyze the proposed system. The effect of key design parameters in terms of desiccant concentration, air humidity, air temperature, refrigeration temperature and segment temperature on the performance indicators are investigated. The simulation results indicated that the increase of the desiccant concentration makes the enthalpy efficiency, the coefficient of performance, the moisture removal rate and the cooling capacity increase and makes the humidity efficiency decrease. With the increase of air humidity, the humidity efficiency and moisture removal rate for the segment temperatures from 100 to 130 °C are approximately invariant. The decreasing rates of the humidity efficiency and the moisture removal rate with the segment temperature of 140 °C increases respectively. Six indicators, except the cooling capacity and heating capacity, decrease with an increase of air temperature. The heating capacity decreases by 49.88% with the reinjection temperature increasing from 70 to 80 °C. This work proposed a potential system to utilize geothermal for the dehumidification, space cooling and space heating effectively.

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