Simulation Research On Heat Transfer Characteristics And Optimization Of Compound System In A Passive Residential Building In Severe Cold Area

In recent years,passive buildings in Germany have been widely applied in China.The enclosure structure of passive buildings has good thermal insulation performance,and the indoor environment and thermal comfort have been attracted much attention.This paper use numerical simulation to analyze the indoor environment in a passive residential building in Harbin which is a typical city of the severe cold area in winter.The passive buildings uses a radiant heating / cooling-displacement ventilation composite system.And propose effective suggestions for improvement.First of all,the heat transfer model of ceiling radiant heating of the passive building was established,and the surface temperature distribution under the conditions of water supply temperature of 30℃,31℃ and 32℃ is simulated respectively,and compared with the experimental values to verify the reliability of the model.Secondly,the design problem of the passive building is analyzed,using the established radiant ceiling heat transfer model,the temperature distribution on the ceiling surface of the return-type pipe arrangement and the snake-type pipe arrangement method was compared.In the layout,the maximum temperature difference on the ceiling surface is 6.5℃of the snake-type,the maximum temperature difference on the ceiling surface is 1.7℃of the return-type.It is recommended that the passive buildings adopt the return-type method in the design.At the same time,the effects of water supply temperature,pipe spacing,pipe diameter,pipe velocity and pipe depth on the heat transfer characteristics of ceiling radiant heating / cooling system were studied,and the sensitivity analysis of the influencing factors was carried out.It was found that the water supply temperature had the greatest influence on the heating quantity,followed by the pipe diameter and the flow velocity in the pipe.Thirdly,a coupled heat transfer model of radiant heating / cooling-displacement ventilation composite system was established.The indoor thermal environment and thermal comfort were compared of the three composite systems: floor heating + displacement ventilation(system 1),ceiling heating + displacement ventilation(system 2),floor + ceiling heating + displacement ventilation(system 3).The results show that: the horizontal temperature field of system 1 is more uniform;the vertical temperature difference of system 1 is lower,but the vertical temperature difference of the personnel activity area of the three composite systems does not exceed 3℃;There will be a blowing sensation above the system personnel;the difference in average radiant temperature at different locations is very small,within the range of thermal comfort;The gradient of the PMV value of system 1 is smaller,and the overall PMV value of system 3 is larger.Finally,using orthogonal experiments,selecting water supply temperature,supply air temperature,and supply air speed as the influencing factors,and PMV as evaluation index.The indoor thermal environment of the composite system was simulated and optimized,and the optimal plan was selected,and discussed the temperature of the radiation ceiling and floor surface.The results show that the optimal scheme combination of system 1 in winter is: water supply temperature 28℃,supply air temperature 18°C,supply air speed 0.35m/s,and the optimal scheme combination in summer is: supply water temperature 20°C,supply air temperature 25°C,supply Wind speed 0.5m/s;system 2 winter optimal combination plan is: water supply temperature 28℃,supply air temperature 18℃,supply air speed 0.35m/s,summer optimal plan combination is: water supply temperature 20 ℃,supply air temperature 25 ℃,the air velocity is 0.5m/s;for this passive buildings,the recommended surface temperature of the radiant floor is 23～ 26 ℃,and the recommended surface temperature of the radiant ceiling is 24～ 26℃.