Research On Cooling Load Decay Characteristic Of Evaporative Cooling Roof

The roof receives the strongest direct radiation from the sun for the longest time compared with other parts of a building around 40% of the heat gain in top floor rooms comes through the roof.In summer the top floor room’s temperature is 2~3℃higher than that of the middle-floor,and the ceiling temperature is 2~4 ℃ higher than the middle-floor’s.The high temperature makes the habitability of these rooms quite poor.Therefore,strengthening and improving roof ability of heat preservation and insulation is conducive to improve the thermal environment of top room,meanwhile,saving energy consumption of air conditioning.In this paper,a special structure of water-retaining roof brick which taking advantage of evaporative cooling technology is advised to existing building roof energy-saving transformation.First of all,it analyze the heat transfer process,evaporative cooling theory,wet migration process and cooling load of the attenuation and delay time of the special structure of water-retaining brick base on the theory,which provides the theoretical foundation for subsequent experimental test.According to the theory,the degree of attenuation and delay time are calculated respectively,and it’s clear that there is a obvious cooling down of cooling load on roof with water-retaining brick compare with ordinary roof.Meanwhile,it also found cooling load attenuation law of water-retaining bricks by the theoretical calculation.Then,selecting one top room which roof lay on the water-retaining bricks in student apartment for experimental testing,and choosing the adjacent room for a comparative test.The test process is divided into two stages of summer and winter,testing the water-retaining roof bricks thermal preservation and insulation performance.Experimental results show that: In the summer,the insulation effect is obvious when roof with water-retaining bricks;In the winter,the performance for roof with water-retaining bricks and ordinary roof is similar.Then,it analyze the influence factors for water-retaining bricks such as shading rate,water storage depth and ventilation etc..The results show that the water-retaining bricks has a better insulation performance when shade in the summer,without shade in winter;The deeper the water depth in the summer and winter,the better insulation in the room,but when the water depth reaches 8cm,insulation effect is improved less noticeable.After comparison,8 cm is recommended to be the optimal level of water;And it’s better to keep the room warm as ventilated in summer and without ventilation in the winter.At the same time,comparing the differences in thermal insulation between roof with water-retaining bricks and traditional ventilation and shading roof.It is found that both can improve the indoor temperature of the top room,but the water-retaining bricks has a better insulation performance.In addition,it found the feature of the moisture transfer that at the entrance of moisture transfer is more obvious than middle through theexperiment testing.Finally,it found energy-saving effect of water-retaining bricks and provide the basis for engineering application.