Research On Cooling Characteristics And Operation Strategy Of Floor Radiation Terminal

With the social and economic development,the improvement of people’s living standards,the requirements of indoor comfort is also getting higher and higher.Compared with other air-conditioning systems,the radiant air-conditioning system has many advantages such as high thermal comfort,energy saving,and low noise.The radiant floor heating system has been widely used in winter,while the application range of radiant floor cooling system in summer has been affected due to the immature regulation strategy.Therefore,aiming at the problems of condensation on the surface of radiant panel and long response time of the terminal,this paper studies the condensation characteristics on the surface of radiant panel and the heat transfer process of radiant terminal,which provides a theoretical basis for the cooling operation strategy of floor radiant terminal.First of all,this paper studies the influence of air side parameters on condensation.Through the theoretical analysis of condensation mechanism,it is found that certain supercooling degree of radiant panel surface temperature is the prerequisite for condensation.By establishing a wet air condensation model,the delay time of condensation on radiant panel surface corresponding to different supercooling degree under different environmental conditions is studied.It is found that the delay time of the condensation on the surface of the radiation plate is inversely proportional to the condensation rate of the wet air,which is affected by the supercooling on the surface of the plate,the moisture content of the air and the flow rate in a large range.The lower the supercooling degree of the plate surface,the lower the moisture content of the wet air,and the lower the air flow rate,the longer the condensation delay time,and the less likely condensation will occur on the radiation plate surface.Secondly,this paper analyzes the influence of water supply temperature,water supply velocity and concrete layer thickness on the surface temperature distribution and terminal response time of radiant panel through the cooling experiment and numerical simulation research of floor radiant terminal.From the three aspects of speeding up the response time of the terminal,effectively adjusting the surface temperature of the radiation plate and maintaining the thermal uniformity of the plate surface,the water supply temperature is determined as the regulating parameter of the system operation.Then,combined with the law that the cold storage capacity of the terminal structure layer gradually decreases,this paper proposes a radiant terminal cooling operation strategy with a step change in water supply temperature,that is,at the initial stage of operation of the system,low temperature water is used to reduce the surface temperature of the radiant panel and shorten the response time of the terminal.After that,the temperature of the water supply is adjusted and the surface temperature of the radiant panel is maintained by high temperature water.Finally,based on the heat transfer model of floor radiant terminal,this paper studies the influence of low water supply temperature on terminal response time,and the influence of water supply temperature step change time and step temperature on the fluctuation amplitude and delay time of floor radiation terminal surface temperature.Combined with the research of dew condensation delay time of radiant panel surface,the results show that: When the step change strategy of water supply temperature is adopted at the floor radiant cooling terminal,creating a dry indoor environment with less air disturbance or adopting higher initial water supply temperature and the step change time of timely adjusting water supply temperature can reduce the response time of the terminal and prevent the condensation on the surface of radiant panel.When the air temperature is 28℃ and the relative humidity is less than 60%,7℃ can be used as the initial water supply temperature at the beginning of the operation of floor radiant terminal to shorten the response time of the terminal without causing condensation on the surface of the radiant panel.Compared with the water supply temperature kept at 15℃,the response time of the terminal can be shortened by more than 56.6%.When the relative humidity of the air is greater than 70%,in order to operate the system more reliably and prevent condensation on the surface of the radiant panel,it is recommended to use the initial water supply temperature of 11℃ as a minimum.Compared with the water supply temperature kept at 15℃,the response time of the terminal can be shortened by more than 39.3%.