## 1 Introduction
(**a**) The flow of air inside the main cable. (**b**) Layout of the cable dehumidification system. efficient system was the development direction of the main cable dehumidification system. [PERSON] et al. [20] recommended that, as the cable dried out, the set of the initial RH of the dry air should be increased to reduce long-term running costs. [PERSON] et al. [21] proposed a heat recovery-based anti-corrosive dehumidification system for the main cable, which would recover the waste heat after the roots blower by adding a heat exchanger, and would save about 40% on energy consumption. [PERSON] [22] recommended developing an integrated system using one set of dehumidification plants to provide dry air for all parts of the suspension bridge could significantly reduce construction costs and maintenance costs. [PERSON] et al. [6] suggested that operating dehumidification plants only during specified periods could reduce running costs. [PERSON] et al. [23] set up a heat exchanger auxiliary system in the main cable dehumidification system to preheat the regenerative air with the treated air, which saves about 30% on energy consumption. These studies reduce the energy consumption of dehumidification plants to a certain extent but fail to fundamentally solve the problem of insufficient dehumidification capacity of the existing plants on suspension bridges. The combination of a heat pump drying system (HPDS) and DWDS can effectively improve the dehumidification capacity. Although this has been widely studied in the field of building, it is difficult to apply the existing research results directly to a suspension bridge because there are many differences between suspension bridges and buildings in dehumidification demand. For instance, the temperature and humidity of suspension bridges are more severe and rapidly changing than that of buildings. The total dehumidification capacity required is exceptionally high for suspension bridges compared with buildings. An array of varied outdoor parameters will necessitate the use of sophisticated system controls and strategies. Therefore, currently available dehumidification technologies should be improved to adapt to suspension bridges. In addition, using separated heat pipes to preheat the regenerated air can improve the energy efficiency of dehumidification systems. However, this has been ignored in existing studies. In conclusion, the research aiming at the characteristics of suspension bridges to improve the dehumidification system is not comprehensive. Therefore, it is necessary to study the performance of a hybrid dehumidification system (HDS), which could be a better alternative for corrosion protection of the main cable. Our previous studies [12; 24] explored a potential development of a multi-stage dehumidification system using condensing dehumidification and solid desiccant dehumidification. It could contribute to the multi-stage utilization of waste energy and improve system efficiency. Based on the previous conceptual design, a further numerical study would be followed. Hence, we proposed the HDS adapted for suspension bridge corrosion protection. A numerical model of HDS was first established. Then, the effects of the main operating parameters on HDS were analyzed, and the dehumidification performance of HDS and DWDS was further compared to illustrate the superiority of HDS to apply on a suspension bridge. In addition, the air supply parameter was discussed, and a low-energy operation strategy of HDS in summer cases was proposed. Finally, limitations and adaptations of HPDS and DWDS on suspension bridges were discussed.