Study On Humidity Control Of Liquid Desiccant Air Conditioning System In Hot Summer And Warm Winter Zone

Liquid desiccant air conditioning system is based on temperature and humidity independent control method, takes humidity control as first, can effectively avoid the humidity control ability insufficiency and reheat loss caused by overcooling in the traditional air conditioning systems, enhance the thermal comfort of air-conditioned room and air conditioning system's energy efficiency. Combined the features of annual outdoor conditions in hot summer and warm winter zone and the operation characteristics of liquid desiccant air conditioning system's air handling equipments, the annual conditions division and control schemes of liquid desiccant air conditioning system in hot summer and warm winter zone are put forward in this paper.Annual humidity is high in hot summer and warm winter zone. Set an example of Guangzhou, the time of outdoor air humidity ratio higher than the upper limit of summer indoor design point(12.6g/kg) is up to 5135 hours, about 58.6% of the time throughout the year. These climate features make a higher demand of air conditioning system's dehumidification capacity and continuous operation under various conditions. Liquid desiccant air conditioning system is divided into temperature control and humidity control two sub-systems, sets the air-conditioned room's temperature and humidity adjustment apart, ensures the air conditioning system's dehumidification capacity in various operating conditions.Before the analysis of liquid desiccant air conditioning system's control schemes, based on the features of annual outdoor conditions in hot summer and warm winter zone, the performance of liquid desiccant air conditioning unit was tested. The results show that supply air relative humidity maintains about 65% in various operating conditions, liquid desiccant air conditioning unit has higher dehumidification capacity. When fresh air condition is 33.5℃,21.3g/kg, the unit is full load, supply air temperature and humidity ratio is about 20℃and 10g/kg, there is no need to reheat to reduce supply air temperature difference. With the reduction of supply air volume and the addition of supply air humidity ratio, Unit's energy efficiency ratio(EER) is integrally upward. The maximum of Unit's EER is 7.864, minimum is 1.725. In order to improve air conditioning system's overall energy efficiency and achieve energy saving, the control of unit's inlet parameters should make full use of humidity ratio value, reduce supply air volume.Based on the features of annual outdoor conditions in hot summer and warm winter zone and the characteristics of liquid desiccant air conditioning system, annual operating conditions of liquid desiccant air conditioning system is divided into five divisions. And air handling processes, operation adjusting methods and operating mode transition conditions are analyzed. On these bases, system control schemes and judging logic are proposed in various conditions. The preliminary study of system control schemes' implementation is carried out, the block diagrams of air handling equipments'operating mode logic judgment controller and temperature and humidity control systems are proposed. In order to verify liquid desiccant air conditioning system's humidity control schemes, humidity pretreatment process were selected and the experiment investigation were carried out. The experimental results show that with the reduction of supply air volume and the addition of initial indoor air humidity ratio, the required time of pretreatment process extends correspondingly. Taking the affection of system operation's stability and indoor thermal comfort caused by pretreatment process into account, the air handling speed of pretreatment process should take precedence over the performance of liquid desiccant air conditioning system.