Numerical Research Of Natural Ventilation Of Civil Residence In Winter In Cold Zones

The outdoor temperature is low and the temperature fluctuation is large between day and night in winter in cold zones. People usually close the windows for a long time to keep indoor temperature constant. But the indoor air quality has been seriously contaminated due to the emitting pollutants from human body, floors, walls and furniture. So, how to ensure the heating temperature and indoor air quality simultaneously has become a hot issue in the study field of HV&AC. In this paper, natural ventilation of a typical civil residence of Lanzhou was simulated to explore the reasonable way of natural ventilation in winter in cold zones. The thesis mainly includes:(1) Physical model of civil residence which meets the standards of energy-saving 65% in cold zones(Lanzhou) was established. The data of the outdoor temperature, solar radiation intensity and hourly average dry bulb temperature in all directions were counted when the outdoor average temperature is less than 5℃ in winter in Lanzhou. The unsteady heat transfer method was adopted to calculate wall temperature, heat flux and indoor heat gain under the double disturbances of outdoor temperature and solar radiation intensity.(2) The laminar mathematical model was used to numerically analyze the pollutant(C7H8) releasing from the floor of the closed room for 1h, 6h, 12 h, and 15 h, respectively. The pollutant distributions of horizontal plane Z=1.1m(breathing height) and the crossing section Y=3m were dynamically monitored. And the pollutant diffusion profiles were obtained.(3) Comparing the numerical results with the experimental results of references, the Realizable k-ε turbulence model was chosen to simulate the three-dimensional fields of indoor airflow velocity, air temperature and C7H8 concentration of the civil residence. The numerical results of 12 natural ventilation conditions at different airflow velocities and different area ratios of inlet and outlet were compared subsequently from indoor temperature uniformity,concentration of C7H8, PMV and ventilation efficiency. The results show that the inlet airflow velocity has significant effect on indoor temperature and the concentration of C7H8. On the one hand, higher inlet airflow velocity corresponds shorter time of natural ventilation for the limit of necessary heating temperature. On the other hand, higher inlet airflow velocity will lead the indoor pollutant concentration decrease more quickly. Under lower airflow velocity(0.4 m/s), if the inlet area is too small(width×height = 0.1m×1.5m), the C7H8 concentration decrease more slowly, which will extend the time of indoor personnel exposed to polluted air,this is disadvantageous for resident’s health. Choosing appropriate inlet area and locating the inlets in a scatter way can ensure the indoor thermal comfort and indoor temperature uniformity. In addition, the ratio of inlet and outlet area has great influence on the indoor temperature. It is advantageous to maintain the indoor temperature when the inlet area islarger than the outlet area.(4) Three reasonable working conditions(condition 10, 11 and 12) were chosen from twelve natural ventilation working conditions and the airflow velocity field, temperature field and C7H8 concentration field were analyzed simultaneously. The results show that the indoor C7H8 concentrations of the three working conditions are lower than the limit value of indoor air quality standard(GB/T18883-2002), but condition 12 is the most ideal condition due to the most superior indoor thermal comfort and the best uniformity of temperature distribution of all conditions. Analysis of the condition 12 shows that the average concentration value of C7H8 is the highest one in room 2#, the next one is room 3#, and room 4# has the lowest value of average concentration. Room 4# has the highest average value of temperature, the next one is room 3#, and room 2# has the lowest average value of temperature. According to the above analysis, Room 4# is the most suitable room for resident to stay for a long time while room 2#is the not most suitable one for people to stay for a long time.The study is a basic attempt to probe natural ventilation modes in winter in cold zones,which may provide active reference for designing ideal natural ventilation mode in some special climatic conditions and it is full of theoretical meaning for improving indoor air quality dynamically. Of course, the factors relative to the natural ventilation in winter are variable and complicated, which means there is a lot of constructive works to do to obtain more applicable and accurate results.