NTUm-based optimization of heat or heat pump driven liquid desiccant dehumidification systems regenerated by fresh air or return air

Abstract

Liquid desiccant (LD) dehumidification systems have received significant attention in recent years owing to their effectiveness in humidity control and great potential for energy saving in buildings. The optimization of these systems, considering the relevant influencing factors, is thus an important research purpose. This paper focuses on the optimization pf area distribution among the packing towers, under a fixed total area, in the liquid desiccant dehumidification systems. Two typical LD dehumidification systems are analyzed and optimized. One system is regenerated by fresh air and the other system is regenerated by return air, with total heat recovery and the dehumidification modules. The input heat for the heat driven pattern and the input work for the heat pump driven pattern are adopted as the optimizing indexes. It is indicated that for the first system, the square ratio of the optimum NTUm of the dehumidifier to that of the regenerator is equal to the ratio of the enthalpy difference between the fresh air and supply air to that between the fresh air and exhaust air. For the second system, the optimum NTUm of the total heat recovery module accounts for about 30% of the total NTUm. The heat-cold offset takes a great proportion of the input heat, and the NTUm distribution development based on the optimum input work with the heat pump driven pattern is consistent with that based on the optimum input heat with the heat driven pattern. Therefore the optimization of input heat is important for LD systems and can be the representative criterion for their NTUm-based optimization.