| As the process of urbanization and modernization in China is accelerating,the contradiction between increasing building energy demand and limited energy supply capacity will become even more prominent.How to use renewable energy to reduce air-conditioning energy consumption is of great significance for establishment of energy-saving,low-carbon,green ecological,intensive and efficient building energy consumption systems.Hybrid displacement ventilation can ensure thermal comfort and indoor air quality with minimum energy consumption by maximizing utilization of stack ventilation.The key to the successful implementation of hybrid displacement ventilation is the calculation of ventilation rate,its influencing factors and the formulation of ventilation control strategies,however,the design methods available for engineering applications are not yet complete,this paper has studied these issues.Firstly,using basic equations and theories of fluid mechanics such as energy equations,continuity equations,orifice flow equations and so on,based on the previous studies and taking thermal stratification and non-adiabatic wall conditions into account,the ventilation rate calculation formula,thermal stratification height calculation formula and ventilation mode conversion point calculation formula of hybrid displacement ventilation,supply fan mode and exhaust fan mode were derived respectively.Secondly,through the parameters contained in the ventilation rate calculation formula,the key factors influencing ventilation effect were identified and the influence of these factors on ventilation rate was analyzed.When the conditions are consistent and the area of top opening is constant,for exhaust fan mode hybrid ventilation system there are:(1)The key factors affecting composite ventilation rate are opening area ratio and mechanical ventilation rate.When the mechanical ventilation rate is constant,the composite ventilation rate increases as the opening area ratio decreases.When the opening area ratio is constant,with the increase of mechanical ventilation rate,the composite ventilation rate also increases,and in stack dominant mode the increasing slope is fast firstly and then slow,but when convert to fan dominant mode,the slope increases suddenly and remains unchanged,after this time,composite ventilation rate is equal to mechanical ventilation rate.(2)When the opening area ratio is greater than 1,the composite ventilation rate of supply fan mode is larger.When the opening area ratio is less than 1,the compositeventilation rate of exhaust fan mode is larger.When the opening area ratio is equal to 1,the composite ventilation rate of supply fan mode is equal to exhaust fan mode.(3)The composite ventilation rate calculation model of this paper is consistent with the results of quadratic superposition model.The maximum relative error is 20% when the opening area ratio is 0.5,with the reduction of opening area ratio,the relative error will be smaller.Therefore,when the opening area ratio is less than 0.5,the quadratic superposition model can be used to estimate the composite ventilation rate,but when the opening area ratio is greater than 0.5,the relative error is comparatively large.Thirdly,the author designed and built a experiment platform of hybrid displacement ventilation,tested the ventilation rate and the temperature distribution in the ventilation chamber by the tracer gas method and other experimental methods,verified the accuracy of the theoretical formula of composite ventilation rate.The experimental results showed that the measured values of the composite ventilation are identical with the theoretical values,and the maximum relative error between them is9.4%.In hybrid ventilation system,when in stack dominant mode,the air enter from lower opening and discharge from upper opening,the room is in the displacement ventilation state,the indoor temperature distribution has thermal stratification phenomenon;when in fan dominant mode,the air enter from upper and lower opening at the same time,the room is in a mixing ventilation state without obvious thermal stratification phenomenon.Finally,according to the applicable environment of thermal comfort model and the climate characteristics of Chongqing region,a thermal comfort assessment model suitable for non-air-conditioning environment in Chongqing region was selected,combined with the deduced theoretical formula and experimental results,a control strategy of hybrid displacement ventilation applied in Chongqing was proposed. |
