| Currently, governments are carrying out energy conservation policies, and China is also identifying the most energy-saving potential field based on the national basic conditions and the energy structure, according to the statistics of energy consumption, building energy consumption shares a larger proportion, and the air conditioning energy consumption accounts for about 50% of building energy consumption, so it is the air conditioning industry development goal to reduce air conditioning energy consumption while the comfort of the person in the room is ensuring. In this context, the radiant cooling system arouses great concern for its comfort, energy saving and other features.According to the researches on the energy efficiency and comfort of the radiant system, it is pointed out that the air conditioning system had broad application prospect, but when the radiant cooling system is used in summer, condensations on the radiant panel prevented the popularization and application of this technology. In summer, when the dew point temperature of the indoor attached layer is higher than the surface temperature of the radiant panel, condensation occurs on the surface of the radiant panel, then it affects on the indoor air quality. The traditional way to prevent condensation is to increase the supply water temperature, but this will reduce the cooling capacity of the radiant cooling system, in order to express the full potential of the radiant cooling system, we must first solve the problem that the radiant panel condenses easily, so it is necessary to grasp the dynamic moisture content distribution properties of the attached layer to solve this problem fundamentally.A combined research method of experiment and numerical simulation was used in this paper to study the dynamic moisture content distribution properties of the attached layer, mathematical and statistical method was used for data analysis. Through experiments we studied and analyzed the surface temperature changes of the radiant panels and the dew point temperature changes of attached layer. Furthermore comparing the experimental data and numerical simulation data to verify the accuracy and feasibility of the numerical simulation model, and the validated model was used to do expand research, the impacts of different factors on the dynamic moisture content distribution were analyzed, the factors include air supply method, air outlet form, the length of the air outlet, the relative distance between air outlet and attached layer, wet source scattered strength and the relative distance between wet source and attached layer. The experimental results show that after the radiant ceiling cooling system runs about 15 minutes, the radiant panels condense under un-pre-dehumidification condition. When the indoor air is pre-dehumidified, the dew point temperature of the attached layer decreases as the moisture content of the attached layer decreases, as the radiant ceiling cooling system operating within 40 minutes, the dew point temperature values almost remain the same with the dew point temperature values after pre-dehumidification, meanwhile, the surface temperature of the radiant panels rapidly decline, but the temperature difference between the radiant panels and the dew point temperature of the attached layer is still greater than the safety temperature difference(1 ~ 2 ℃), so condensation does not occur.The effects of different air supply methods and air outlet forms on the dynamic moisture content distribution properties of the attached layer in pre-dehumidification stage and the dew point temperature of the attached layer in stable stage were analyzed, the results show that in the pre-dehumidification stage and the stable stage, slit-jets air vent form is better than the other two air vent forms. The effect of air velocity and scattered wet strength on the dynamic distribution of the attached layer were analyzed, the results show that in pre-dehumidification stage, the air velocity has little effect on the pre-dehumidification time; and in the stable stage, the dew point temperature of the attached layer gradually reduces until it reaches a steady state, the length of the air outlet has little effect on the steady dew point temperature, but the scattered wet strength has great effect on the steady dew point temperature, the steady dew point temperature increases as the scattered wet strength increases, however the rising of the dew point temperature will increase the risk of condensation of the radiant panel, therefore when the number of person in the room increases, we can increase the water temperature appropriately according to the increased number of person, thus we can prevent condensation while the radiant cooling capacity is maximize. The contribution rate of each factor’s effect on the dew point temperature of the attached layer were analyzed via the SAS statistical software, the results show that the contribution rate of the scattered wet strength is the largest, that is to say, it has the greatest impact on the dew point temperature of the attached layer, the greater factors are the relative distance between air outlet and attached layer and the relative distance between wet source and attached layer, the impact of air velocity is small and it can be ignored, the dew point temperature equation was obtained using regression analysis method after removing the impact of air velocity. The achievements of this paper provide theoretical support for the proposing of the radiant cooling system and anti-condensation control methods, meanwhile it will make due contribution to the promotion of radiant cooling system. |
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