Study On Heat Transfer Characteristic Of Low-Temperature Radiant Floor Cooling And Heating System

The human body exchanges heat with the surrounding environment by the convection, radiation and evaporation. The necessary condition for thermal comfort is the body's thermal equilibrium. According to researches, when the human body reaches the thermal equilibrium, heat flux by the convection accounts for about 25% ~ 30%, the radiation accounts for 45% ~ 50% and the feeling evaporation through breathing accounts for 25% ~ 30%. The sufficient condition for body's thermal comfort is meeting the appropriate proportion of heat transfer modes. In recent years, because low-temperature radiant floor heating technology meets the human body requirements for thermal comfort better, it is used widely in the residential building and some public buildings in northern China.However, although the radiant floor cooling technology heats transfer in the same way of radiation, the condensation on the cooling floor surface arises easily in the high humid environment. It limits the application of radiant floor cooling technology. Abroad, the radiant ceiling cooling systems integrated the replacement ventilation and supplying air below the room are used commonly. By monitoring the indoor air temperature to control the supply water temperature, keep the cooling surface temperature is higher than the air dew-point temperature to prevent the condensation. In China, the radiant floor heating system is designed for winter and another traditional air-conditioning system is also designed for summer. It causes the inefficient resource utilization rate.Beijing belongs to the cold regions. The air-conditioning characteristic all the year is longer heating periods in winter (11.1 ~ 3.15) and relative shorter cooling periods in summer (6.1 ~ 8.30). And the outdoor air temperature and relative humidity are both lower than the South China of high humidity. So Beijing has the better climatic condition for using low-temperature radiant floor cooling and heating technology. In this paper, the feasibility and adaptive conditions of low-temperature radiant floor cooling and heating system for the office building in Beijing were researched. And the related studies of the following aspects were investigated.In order to know the heat transfer process of low-temperature radiant floor cooling and heating system better by the experimental methods, a set of low-temperature radiant floor cooling system for the test was builded. And using the test, the thermal performance of radiant floor heat exchanger can be experimented at the summer cooling conditions and winter heating conditions.The cooling condition in summer was taked as the target in this study. The condensation condition on the floor surface and control methods for office buildings in Beijing were mainly researched. The body's thermal comfort conditions were analyzed and a large number of useful experimental data and results were gained.According to the basic theory of heat transfer and the calculation methods of ASHRAE (American Society of Heating Refrigerating and Airconditioning Engineers) about the convection and radiation between the floor surface and the room, the two-dimensional simplified calculation model of radiant floor heat exchanger was developed. Eexperimental results verified the validity of the model.Based on the two-dimensional simplified calculation model, the influences on the thermal characteristics of radiant floor heat exchanger were analyzed and researched by the experimental study and MATLAB's PDE Toolbox, such as the tube space, the supply water temperature, flow rate and thickness of filler layer.It provide a valuable reference for the further study.