Research On Principle Of Heat Transfer And Water Condensation Of Radiant Cooling Panels And Match Characteristic Empolyed In Solar Air-conditioning

Energy crises and environmental pollution are two serious problems that humanbeings are facing. About30%of our total energy is consumed by buildings. This value willbe higher in the future with the development of the global economy and people’s livingstandard. Consequently, it is important to use renewable energy to save energy; it will meetthe sustainable development demand of architecture, energy and the environment.The solar powered lithium bromide-water absorption cooling system adopts solarenergy to generate cooling for air conditioning. There is no primary energy consumed andonly a litter electric power was used to drive the pumps which resulted in energyconservation. Solar cooling can reduce the amount of electric power consumption insummer days. Besides, lithium bromide-water was used as the refrigerant of the systemcould avoid the emission of greenhouse gas comparing with the conventional electriccompression refrigerator. It is kind of environment friendly refrigerant.The radiant cooling panels and supply air system were selected as the indoor airconditioning endings. The radiant cooling panels were used to handle the indoor sensiblecooling load and the entire latent cooling load was removed by the supply air system. theradiant cooling system was cooled by the solar cooling system, which could provide hightemperature chilled water. In thus, the performance of the solar cooling system could beincreased in the increase of the evaporation temperature. And the indoor thermalcomfortable level was also improved due to the use of radiant cooling. The process ofsupply air was separated into two steps, firstly the supply air was cooled by the pre-coolerwhich connected with the solar cooling system, and then the supply air was cooled by theelectric compression refrigerator. Through the two steps cooling system, the solar coolingwas as much as used in the air conditioning system and the electric power was saved. Theradiant cooling system used as the cooling endings in air conditioning system could notonly benefit the performance of the solar cooling system, but also improve the indoorthermal comfortable. However, the insufficient cooling capacity and condensation problemof the radiant cooling panels restrict the wide spread application in the domestic airconditioning market. So the performance of heat exchange and water condensation of the radiant cooling panels was detailed investigated in this paper. The research mainly focuseson the following contents:（1）The cooling capacity of the radiant cooling endings was mainly impacted by thewater velocity inside the tube, chilled water temperature, indoor environment temperatureand relative humidity. For the capillary tube with inner diameter of2.7mm, suitablevelocity of the chilled water was found to be0.45m/s. With the decreas of the watertemperature and the increase of the indoor environment temperature, the cooling capacityof the radiant cooling endings was shown increasing.（2）The water condensation phenomenon would not arise on the tube surfaceimmediately while the inlet chilled water temperature right decrease to the indoor dewpoint temperature, due to the exist of temperature difference astride the capillary tube. Thesub-cold drgee concept was used in the paper to assist analysis the water condensationphenomenon. The use of the sub-cold degree in the water condensation control system wasable to increase the cooling apacity of the radiant cooling panel while the watercondensation phenomenon was successful avoid. The results shown that the sub-colddegree of the three radiant cooling panels were3.2oC、5.4oC and6.5oC, repectively.（3）Comparied with the all air system, radiant cooling system was normally mountedintegrate with the building envelope. The heat storage performance of the buildingenvelope could reduce the volatilily of the radiant cooling temperature. Especially for thesolar cooling system, the chilled water temperature was unstable because of the variationof the solar energy. So, the big dimention heat storage water tank was always employed inthe solar cooling system. Hence, the radiant cooling system was able to reduce thedimention of the hot water tank. Meanwhile, the indoor air temperature could be mentainedat the similar temperature for78min due to the heat storage performance of the buildingenvelope.（4）Radiant cooling system make heat transfer with the indoor items directly whilethe all-air system transfer cooling to the air dirst and then to the people. It could enhancethe heat transfer efficiency and then save energy. The performance of the solar coolingsystem was also impacted by the indoor air conditioning ending, the COP and coolingcapacity of the solar cooling system were0.22and3.62kW, respectively, for the fan coilsendings,0.31and4.6kW for the radiant cooling panels. Meanwhile, the indoor thermalcomfort level was improved while the radiant cooling system was employed.