| In recent years,the gradual prevalence of capillary radiant air conditioning system existed because constant temperature and humidity to the indoor environment can be provided.When the capillary radiant air conditioning operate,the principle of heat and moisture transfer will occur in the building envelope which can cause condensation on both inside and envelope surface,damage of the structure and insulation board and destroy the aesthetic of the building will be led,increase energy consumption,and effect the indoor air quality.Therefore,the effect of condensation on building enclosure for both internal and surface while using the capillary radiant air-conditioning system mainly are focused on in this paper.the influence of the thickness,location of the insulation board and the relative humidity of the inside air conditioning room and discussed the specific measures for preventing condensation is also analyzed.The main work of this paper are given as:1.The surface condensation of the enclosed structure is simulated: The hot summer and cold winter area as the research object for building in Nanjing is taken as a study case,the heat transfer model of the enclosure structure is established,temperature field of the enclosed structure in using capillary air conditioning system for both summer and winter seasons are calculated by EES programming and the condensation on the surface of the enclosure was analysed.2.The internal condensation of the enclosed structure is simulated: Analyzing the principle of moisture transfer in enclosed structures,building a moisture transfer model for the surrounding structure.The heat transfer and moisture transfer of the enclosure structure are simulated in COMSOL Multiphysics software,the moisture distribution of the enclosed structure when the capillary network is laid down on roof for both summer and winter is studied,and the internal condensation of this enclosed structure for roof is analysed.3.Study of preventive measures for condensation: Simulation study of both inside and outer surface of the enclosed structure,proposed the minimum thickness and position of the expandable polystyrene(EPS)insulation board,and suggested the relative humidity of the conditioned room which prevents the internal condensation of the enclosed structure are studied.The results of this study are given below:1.For preventing surface condensation,the minimum thickness of insulation board depends on insulation material,location of capillary net and wall material.The example of capillary network and EPS insulation plate installed on lower surface of roof is considered.The minimum thickness of 2 mm polystyrene foam EPS is added for 160 mm thickness of inner wall which will prevent the surface condensation of the enclosed structure,the minimum thickness of 8 mm polystyrene foam EPS is required for 120 mm thickness of floor,minimum thickness of 32 mm polystyrene foam EPS is added to roof of 120 mm and similarly the exterior walls of 280 mm with minimum thickness of 2 mm EPS foam is used.2.A risk of internal condensation on the surface of envelope: When the capillary network is laid inside roof,there will be no condensation on both sides of floor.Consider the case of floor between two rooms,there will be no condensation if thickness of 8 mm EPS insulation foam is used on the 120 mm floor in winter,although the condensation occurs between 57 mm~107 mm from the surface of the non radiant air conditioned room due to its low temperature.At this time the condensation occurs in concrete and insulation layer because the saturated vapor pressure is less than water vapor pressure.3.The thickness and position of the insulation board will effect the condensation inside the enclosure.When the capillary is placed on the roof and EPS insulation foam on the inside surface of the exterior wall as an example,after laying 0 mm~5 mm EPS insulation foam on the inside exterior wall in summer,the inner surface of the enclosure structure are not condensed.When the thickness of the insulation foam is greater than 5 mm,the condensation will occured near the insulation foam.Similarly in summer,when the thickness of EPS is greater than 5 mm,the inner surface of exterior wall will not condensed.In winter,2 mm EPS insulation foam is laid on the inner surface of exterior wall,which will prevent condensation on the inner surface of exterior wall.But there is still risk of internal condensation near the isulation foam,when the thickness of the internal insulation foam is increased,When the thickness of internal insulation foam is increased,it is found that the inner wall is more easily exposed with the increase of inner insulation thickness,when the 2 mm EPS insulation board is placed on the outer surface of exterior wall which will prevent condensation on both inner and outer surface.However,there is still moisture in the insulating foam and the brick,when the thickness of the EPS external insulation foam is 5 mm,the relative humidity inside the outer wall is less than 1 due to which condensation will not occur.Concluding that the 5 mm EPS insulation foam should be proposed to use in summer and winter for preventing condensation in the surface and internal structure of the exterior wall.4.Controlling relative humidity of air conditioning room can prevent condensation of enclosed structure.By laying capillary on the roof and EPS insulation foam on the floor as an example,8mm and 7 mm EPS insulation foam is proposed for 120 mm floor and 140 mm floor respectively,the relative humidity of the adjacent room is 85% with the dry bulb temperature of-2 ℃,so the dry bulb temperature of conditioned room is maintained at 22 ℃in winter.When the relative humidity of conditioned room is below 50%,it will prevent the floor condensation,As the relative humidity decreases,it is far away from the dew point.In this study,It is found that condensation occurs not only in summer but also in winter,not only on the surface of the wall,but also inside of the wall.It is necessary to take full consideration of insulation foam material for preventing condensation,the location of capillary network,the thickness of the wall and the material of wall.The results of this paper has provided a significant guidance for preventing condensation in the enclosure of radiant air-conditioned rooms in hot summer and cold winter area. |
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