Energy, Vol.120, 209-216, 2017
Adapted computational method of energy level and energy quality evolution for combined cooling, heating and power systems with energy storage units
Current energy quality evaluation indexes mainly focus on depicting energy quality in systems whose character temperature and pressure are higher than environment. However, when the temperature and the pressure are lower than environment, these indexes sometimes fail to properly assess the energy quality of the system. Meanwhile, quoting different references or benchmarks in the calculation of some thermodynamics quantities, one of which is energy quality, may also confuse energy system designers. These situations will thereby result in potentially incomplete or partial evaluation of energy quality in complicated energy systems like combined cooling, heating and power (CCHP) systems. In this research, an adapted computational method of energy level which describes energy quality from thermal and mechanical perspectives has been proposed. In this method, energy quality of all-temperature and all pressure conditions can be quantified without quoting different benchmarks, which allows thorough energy quality analysis for complicated energy systems. Energy quality evolution of a CCHP system with energy storage units (ESUs) has been discussed in terms of the proposed energy levels. The thermal energy quality evolution depicted by thermal energy level indicates that high energy level from waste heat of power generation units will cause large energy quality loss in the absorption refrigerator (AR), since the generation temperature in the AR confines the energy level in the generator to a comparatively low value. In the CCHP power generation unit, thermoacoustic engines prevail over gas turbines in energy quality conservation. Furthermore, mechanical energy level analysis shows that the absorption refrigerator and the absorption cooling storage units have higher mechanical energy levels than other components in CCHP systems due to the high vacuum conditions. Finally, an energy level matching map is provided to suggest matching strategies between waste heat sources and energy storage techniques in CCHP systems. (C) 2016 Elsevier Ltd. All rights reserved.