The Performance Analysis And Optimal Design Of The Air-conditioning System Combining Radiant Cooling With Liquid Desiccant Dehumidification

Compared to the conventional all-air conditioning system, the air-conditioningsystem combined the radiant cooling and liquid desiccant dehumidification (called“Joint System”) can deal with the sensible and latent load independently. It has theadvantage of “improving indoor air quality and comfort, energy saving andenvironmental protection”, and so on. However, there are still some problems neededto be solved in the development process of the radiant cooling technology and liquiddesiccant dehumidification technology. These problems are as follows: theinappropriate structure of the existing radiant cooling ceiling leads to the dewformation on the surface of radiant cooing panels and the comparatively low coolingcapacity of the radiant cooling system when applied in hot-humid areas; in theresearch of the liquid desiccant dehumidification system, some research directionshave not attracted sufficient attention, such as system design and optimization ofstructural parameters and operational parameters, which are important in improvingthe performance of the liquid desiccant system. In order to solve those problems, thispaper carried out the following studies:Firstly, the structure of the radiant cooling panel is modified. On the basis ofsummarizing the unsuccessful experience of the existing radiant cooling panel, theauthor considers to weaken the heat conduction but to enhance the heat convectionand heat radiation between the inner copper pipes and the board of the panel. Thesemeasures make the temperature distribution quite evenly on the panel surface, so as toopen the way to solve the condensation formation on the radiant cooling panel surface.According to this new idea, the author guided the partners in producing the newstructure radiant cooling panel products, which have been used successfully in theair-conditioning system projects in Hong Kong. This paper also has analyzed the heattransfer effect, and summarized the reasons for the success of the new product.Following that, the air-conditioning system applying the new radiant coolingpanel is studied by experiment. The main research content includes four aspects asbelow: analysis of condensation problem of radiant cooling panel, change of allrelated outdoor and indoor parameters in case of different running mode of the systemin summer, indoor thermal comfort when using the system and the heat transferequation of the radiant cooling panel. Secondly, based on the existing system, a new set of liquid desiccantdehumidified fresh air system is proposed and modeled. In accordance with themathematical model, the simulation program, which is useful to study the liquiddesiccant system performance, is developed by using C++language. Then, the firstlaw and second law of thermodynamics are used to analyze and compare the twostructures of the comprehensive performance of the liquid desiccant system.Thirdly, on the basis of simulation program, this paper analyzes the structuralparameters and the operational parameters by using the statistics analysis method. Thefirst step is factor analysis, to filter out the important influence factors and todistinguish whether there are any significant interactions among these factors. Thesecond step is do orthogonal experiment on the filtered important factors, to find outthe optimal level combinations of structural parameter for different indexes and to setup a data table of optimal level combinations of operational parameter.Finally, a preliminary analysis on the performance of the “Joint System” iscarried out, which includes three aspects: system energy efficiency, systemcontrollability and its scope of application. This section focuses on the optimizationcontrol, with the aim of meeting the human comfort requirement by adjusting theindoor temperature and humidity in energy-saving control strategy. Based on theoptimization control strategy and the PMV index, the “Joint System” controls thesupply air parameters and the surface temperature of the radiant cooling panel, inother words, to control the ratio of the cooling capacity provided by radiant coolingpanels to the total cooling capacity provided by the “Joint System”ω ceiling. At last,this paper concludes the relationship between the ratioω ceilingand the indoor PMVindex, and provides theoretical basis for the optimal operation of the “Joint System”.