Performance investigation of a combined heat pump transformer operating with water/lithium bromide

In the present study, we propose a combined heat pump transformer (CHPT) system operating with a H2O/LiBr working pair, driven by waste heat at medium temperature to supply two types of useful heat. Based on the energy and mass conservation law and phase equilibrium, a computational model is developed in Engineering Equation Solver to investigate performance of the CHPT against the system temperatures, the solution heat exchanger effectiveness, the flow ratio, and the gross temperature lift. The results show that the system efficiency is nearly 100%, and the exergy coefficient of performance (ECOP) is 71.1%, which are 33.2% and 33.1% higher than those in the reference system, respectively. The high-pressure absorber exhibits the highest irreversibility, which accounts for 26% of the total system irreversibility, followed by the low-pressure absorber, the low-pressure generator and the medium-pressure generator; hence, special attention should be paid to these four components. Moreover, an optimal flow ratio or optimal gross temperature lift exists, which results in the largest ECOP for larger energy ratio values. The payback period is approximately 2 years, which is suitable for workshop or industrial park where there is a great requirement for different levels of heat.