Optimization of NTUm allocation between dehumidifier and regenerator in liquid-desiccant air-conditioning system.

• Allocation principle of NTU m in the HPLDAC system is theoretically deduced. • The nonlinearity of the iso φ line of air affects the allocation principle. • Only when the total NTU m below 10, does the allocation principle matter. • This study suggests equal allocation cannot always lead to the optimal performance. Heat and mass transfer capacities of dehumidifier and regenerator significantly affect the performance of a heat pump driven liquid desiccant air-conditioning (HPLDAC) system. When the dehumidifier and regenerator have the same air flow rates, an equal allocation of the total usable number of mass transfer units (NTU m) between the dehumidifier and regenerator is an intuitive choice. However, whether the equal allocation can result in the optimal system performance is still a pending question. Thus, the optimization principle of NTU m allocation between dehumidifier and regenerator in the HPLDAC system is theoretically deduced and illustrated in this study. The results reveal the equal allocation is recommended when the nonlinearity of the iso φ line is insignificant, whereas allocating more NTU m to the dehumidifier than regenerator is recommended when the nonlinearity of the iso φ line is significant. When the NTU m values of the dehumidifier and regenerator are large enough, further increases of the NTU m values show limited effect on performance improvements of the dehumidifier and regenerator. Only when the total NTU m is below 10, does the NTU m allocation optimization play an important role in the system performance improvement, and is a pre-estimation necessary for achieving the optimal system performance. [ABSTRACT FROM AUTHOR]