Numerical Simulation On Thermal Comfort Of Displacement Ventilation With Radiant Floor Cooling By Using CFD Methods

With the development of economy and the improvement of living standard, people pay more and more attention on indoor air quality. Traditional air conditioning system already hasn’t met the people for indoor comfort demand. The radiant floor cooling and displacement ventilation air-conditioning alone operation has widely application both inland and abroad respectively but inadequate. Displacement ventilation with radiant floor cooling system (complex air-condition system for short),they show many advantages such as energy saving, high thermal comfort, beauty and so on. The complex system had been used in developed western countries’project, this complex system not only applied to some big space and high public buildings but also applied for small space. In this paper, displacement ventilation with floor radiant cooling had been analyzed for thermal comfort and energy saving characteristics by CFD simulation, which could be proved to be correct by experiment.This paper uses a typical office as the prototype, the physical model and the mathematical model are established, and indoor thermal comfort is simulated through the CFD. First of all, system parameters are set according to indoor thermal comfort requirements. Next, the air temperature, speed and the radiant temperature of floor are determined in different working conditions. Velocity field and temperature field distribution are obtained in different conditions. Through the temperature field, velocity field of the human surrounding area and facial area size of air speed are analyzed, then combined with thermal comfort index of PMV-PPD, find out the best combination. The best working condition is verified through the experiment. Then analyzes the influence on indoor height of thermal stratification and thermal comfort when parameter changes. The results of the study show that, the air temperature from 22 to 24℃, the radiant temperature of floor is from 23 to 24℃and the air speed is less than 0.25m/s, which can meet temperature difference less than 3℃from 0.1 m to 1.1 m high, but the comfortable level is different. Thermal stratification height will increase if air temperature or air speed are increased. The largest influence of the temperature gradient is the floor temperature. Air temperature on the influence of the temperature gradient is greater than the air speed. The air conditioning system designed can be guided consequently to choose the best cooling parameters.Radiant floor cooling transforms into cooled ceiling system, then combined with displacement ventilation. The load of ceiling is equal to the floor’s. Compared to the two complex systems in the same supply and return water temperature it concluded that the two complex systems have similar temperature gradient and airflow organization form. But radiant floor has higher comfort than the cooled ceiling. Also the floor cooling system can share pipeline with floor heating system in winter thus save investment. Displacement ventilation with radiant floor cooling system has superiority in the same condition.The simulation method in this paper and through experiment to verify the best working condition can provide the theory basis and reference design for the popularization and application of complex system, guide airflow organization design based on comfort level. Also it has realistic significance for indoor air quality, energy conservation of the building.