Potential Estimation And Energy Efficient Evaluation Of Natural Ventilation In Buildings

Natural ventilation is an energy conserving and eco-friendly ventilation method, which is widely used for thousands of years. How to make use of Natural ventilation is now a research focus. However, due to uncertainty of outdoor condition, the prediction of effect of Natural ventilation is still a problem to solve, which leads to difficulty in choosing architecture design plan. Aiming at efficiency and effect evaluation, this paper brings out a set of model to deal with these problems.First of all, this paper analyzed most of the factors influencing natural ventilation effect, including climate, surrounding environment, physical characteristic of walls, human adaptive thermal comfort and related behaviors, required fresh air, outdoor pollution and noise, and so on.Second, by coupling the natural ventilation model with thermal transmission model, the paper reached the potential estimating model energy efficient evaluating model. Major steps are:evaluation of outdoor pollution and noise, input of local climate data, wind environment data, physical parameters of building, calculation of indoor temperature and natural ventilation volume, judging that indoor temperature fulfills occupant thermal comfort request and air change volume satisfies the minimal requirement considering the influence of window opening behavior on air change rate, and finally evaluate energy conservancy.In energy evaluation model, this paper introduced the concept'natural ventilation equipollent saving power', which consists of two parts:first is equipollent mechanical ventilation saving power and second is equipollent air condition saving power, that is, under natural ventilation condition, occupant hot tolerance is larger than that under air condition environment. Finally, the parameters for natural ventilation efficiency and energy conservation evaluation include the following three:yearly natural ventilation hours, yearly natural ventilation volume, and natural ventilation equipollent saving power.Then, this paper carried out the evaluation on single-sided ventilated room. In the model, flow equation utilized the empirical equation of single-sided large opening ventilation coupling the wind and heat pressures. Through analysis of usage ratio the four cities of typical climatic regions, we found that the usage ratios are higher in southern cities in China than that in northern cities. This is partly due to total ventilation flow volume and partly to larger amount of time that when temperature is among the using air condition lower temperature and natural ventilation upper thermal comfort temperature in Guangzhou area, where more energy could be saved.Moreover, this paper analyzed the natural ventilation usage ratio and energy conservation effect of one zone with two openings. In the building model, vertical distance was considered and the opening direction is set as east-west orientation and south-north orientation both ways. In the flow model, not only influence of air velocity around human body and air humidity on comfort temperature of adaptive thermal comfort standard was considered, but also multiple phenomena and multiple solutions considering wind and heat pressure counterwork were considered. Similarly, the analysis on the four cities shows that when the counterwork appears, air stagnancy is an important reason for bad ventilation. The information such as opening area, ventilation hours of different orientation, volume, air conditioning hours, are valuable to preliminary architecture plan choice. Further, this paper built a model for the evaluation of multi-zone building, which was based on the MIX model of large opening ventilation to calculate the indoor temperature and ventilation volume and the energy conservation effect. CFD method was also used in this paper to make modification to wind pressure coefficient parameter to get more accurate results.Finally, through the experiment on window opening behavior, this paper approximated the linear relation between temperature and local window opening percentage as well as window average opening percentage and utilized this function into the model in this paper to correct the air exchange volume and energy conservation effect.On one hand, some building needs little ventilation, on the other, some building should utilize styles that are better for air exchange, especially when the population or air pollution density is high. Moreover, in the process of building design, only considering ventilation effect is not enough. The architecture should make comprehensive consideration of building functions and aesthetic of the buildings and so on. The model in this paper, which provides relatively accurate evaluation of natural ventilation and energy conservation of buildings, can provide valuable reference for preliminary design of building design.