Performance Study Of Absorption/Mechanical Hybrid Heat Pump Cycle

A heat/power hybrid heat pump cycle, which integrates an absorption heat pump cycle with a booster compressor, can improve the condensation pressure and temperature or reduce generation pressure and temperature. In this thesis, a hybrid heat pump cycle with the compressor between the generator and the condenser for distributed heating is simulated and analyzed. The interrelation between the two sub-cycles of thermal compression and mechanical compression and the hybridization principle have been explored. The theoretical analysis is demonstrated with a H2O/LiBr based hybrid cycle simulation with Aspen Plus software.Calculation results suggest that there exists an ultimate state for the absorption heat pump cycle, and the cycle coefficient of performance (COP) exhibits a sharp deteriorations when the cycle approaches to its ultimate state; and the hybrid cycle has a higher ultimate temperature lift and thus can upgrade the input low-grade heat to a higher temperature level, for example from 30℃ to up to 90 ℃ for space heating or process heating and drying purpose. By examining two different hybridization schemes, it is concluded that hybrid cycle can achieve an improved performance only when hybridization deviates the thermal compression away from its ultimate state. Compared with a compression heat pump cycle and an absorption heat pump cycle, coefficient of performance (COP), exergy efficiency and heat driven COP of the hybrid cycle is improved by 10.15%、12.24% and 16.59%, respectively.When the condense temperature is constant, the cycle COP first increases rapidly to a maximum, and then drops gradually with the increase of the pressure ratio. Parametric sensitivity study was conducted to investigate the influence of some key parameters, including the pressure ratio ε and the lithium bromide concentration X, on the cycle thermodynamic performance. It indicates that there exist optimal ε values around 1.3 and X around 0.622 which maximize the cycle efficiencies.A study was also carried out to reveal the energy saving mechanism in the hybrid system as compared with an individual absorption heat pump and a simple vapor compression heat pump working within the same temperature regions utilizing 1gP-T diagram and T-h diagram. The results indicates that replacement of a part of the mechanical work with low-grade heat makes the hybrid cycle achieves not only significant energy saving of high-quality mechanical work, but also the better use of low-grade waste heat because of the cascade use of the two energy inputs.In order to further improve the thermal performance of hybrid cycle, a new type of double pressure hybrid heat pump cycle was proposed with cascade utilization of surplus heat. Compared with the absorption heat pump cycle and the single pressure hybrid heat pump cycle, the heat yield increase by 6.8% and 7.0%, respectively.This paper provids theoretical support to the design and integration of absorption /compression hybrid heat pump.