Comparative Study On Radiant Floor Cooling Systems With Various Ventilation Conditions

Due to the characteristics of high comfort,high energy efficiency ratio and space saving,the floor radiation cooling system has been gradually promoted.However,when calculating and selecting the floor radiant cooling system,the same cooling capacity calculation method is often used.Insufficient consideration is given to the different forms of ventilation system and heat sources combined with it,which makes it difficult for the system to meet the cooling demand or waste the cooling capacity.Therefore,it is very important for the design and selection of the composite system to fully analyze the thermal comfort and cooling performance of the floor radiant cooling system combined with different ventilation systems.In this paper,the model verification of ANSYS Fluent simulation was carried out according to the floor radiation cooling experiment of Yakup Karakoyun in the closed room and the radiation effect experiment of Yuguo Li in the displacement ventilation room,and the simulation settings and boundary conditions of the simulation experiment were determined.By comparing the indoor thermal environment and the floor temperature distribution,the authenticity and reliability of ANSYS Fluent’s simulation of the experiment are verified.The three-dimensional room model of the combination of displacement ventilation system,stratum ventilation system and mixing ventilation system with floor radiant cooling system was established respectively.The simulation analysis without ventilation condition is carried out.The results show that:The vertical stratification of indoor air temperature is obvious,and the distribution of temperature and velocity is uniform.The introduction of cooling loads on the roof and different external walls has different effects on the total heat transfer coefficient of floor cooling.When calculating the cooling capacity of the floor only considering the cooling load of one South exterior wall,the total cooling capacity,radiation cooling capacity and convection cooling capacity of the floor are 6.182（Top0.6-Ts）,4.966（AUST-Ts）and0.311（Ta1.1-Ts）,respectively.According to the simulation of a floor radiant cooling room with an external wall and indoor heat source height of 0.5m under displacement ventilation,the simulation results are compared with those without ventilation.The results show that the displacement ventilation system makes the total heat transfer coefficient fluctuate in a certain range,the radiation heat transfer coefficient is less affected,and the convection heat transfer coefficient increases with the increase of the reference temperature difference（the temperature difference between the average air temperature at 1.1m height and the average floor surface temperature）.In this kind of cooling environment,when calculating the cooling capacity of the floor,the total cooling capacity and radiation cooling capacity are 5.988(T_op0.6-T_s)and 4.921（AUST-T_s）,respectively.The model of the combination of three different ventilation systems and floor radiant cooling system is simulated and analyzed.The results show that:in terms of indoor thermal comfort.The cooling capacity provided by the composite system under the condition of displacement ventilation system is mainly used for cooling the air in the lower part of the room.There is a large vertical temperature gradient.There is a high risk of thermal discomfort in the upper part of the human body.The effect of gravity flow of stratum ventilation and mixing ventilation on thermal comfort is significant.The effect of ventilation form on the minimum temperature of floor surface is not significant.In terms of the cooling capacity of the floor.Under the same working environment,the total cooling capacity of the floor of the displacement ventilation system is low,and the radiation cooling capacity accounts for the largest proportion,which has better energy-saving characteristics.The elevation of indoor heat source height can not only reduce the total cooling capacity of the floor,but also improve the proportion of radiant cooling capacity,and also improve the thermal comfort of the human body.In terms of cooling coefficient,stratum ventilation has the highest total heat transfer coefficient,and mixing ventilation has the highest radiation heat transfer coefficient and convection heat transfer coefficient.The introduction of cooling loads on the roof and different external walls and the height change of indoor heat source make all kinds of floor heat transfer coefficients of different ventilation systems change in different degrees.In addition,considering the relationship between comfort and total cooling capacity,when selecting the floor radiant cooling composite system,the local comfort index has great limitations on the total cooling capacity and system applicability,and the vertical temperature difference is one of the most important local comfort indexes.