大空间碰撞射流通风性能优化研究

Improving energy usage is an important issue for energy efficiency in HVAC systems. To enhance thermal comfort and indoor air quality (IAQ) by using least amount of energy is a challenge for building ventilation system. One answer to this challenge is practicable "ventilation strategies". However, it is difficult to balance the requirements between indoor thermal comfort, indoor air quality and energy efficiency in large enclosed space. Displacement ventilation (DV) is a suitable way for providing good indoor air quality and relatively high energy efficiency in summer, but cannot be used for supplying warm air in to the space. Mixing ventilation can be employed for both cooling and warming indoor environment, the energy usage is low among the available ventilation strategies..Impinging jet ventilation (IJV) system is has the advantages of both DV and Mixing ventilation. It is operated by facing the supply terminals toward the floor at appropriate height. The high momentum jet hits the floor, which drastically decreases jet velocity, and then forms air distribution in the lower zone of the space. The velocity near the floor is higher than DV; thus, the momentum is high enough to prevent supplied warm air from floating to the ceiling. Therefore, the heating system can be easily applied. In cooling mode, the stratified layer is preserved because high turbulent flow only occurs near the supply terminal area. Theoretically, the same IAQ as that of DV can be achieved, and it is obviously can be used in large space ventilation. Unfortunately, IJV is less common to many practitioners up to now due to the lacking of studies in many aspects. The flow pattern of IJV is different from the other ventilation modes in principal, and indoor thermal comfort, indoor air quality and energy efficiency are all controlled by indoor air flow. In the present study, impinging jet characteristics in large spaces, terminal configurations, operation conditions and space volume are considered to be investigated both experimentally and theoretically. The study would obtain some predicting models for optimizing impinging jet flow characteristics, indoor particle resuspension and indoor thermal comfort due to the jet's impaction, and the energy efficiency of IJV in large space ventilation will also be evaluated.

提高能量利用率是实现空调系统节能的关键问题。为在低的能耗下改善室内热环境和空气品质，合理的通风方式即为有效方法之一。但在大空间中，很难对热舒适、空气品质与送风能量利用率进行优化处理。置换通风方式虽可实现节能和良好空气品质的目标，但不能用于热风供暖；混合通风虽然可以兼顾供冷与供热的需求，但送风热量的利用率低，不利于节能。.碰撞射流通风同时具有混合通风和置换通风的优点，它利用射流动量将送风气流撞击地面，在速度衰减后向周围扩散，使近地区域具有置换通风的特点，故可供既冷、亦可供热。理论上，这种方式可以获得置换通风的同样效果，故适用于高大空间通风。但这种通风方式在我国还很少使用，也缺乏必要的研究。由于碰撞射流特征不同于其他通风方式，而热舒适、空气品质和送风能量利用率都受控于气流特性，本研究将通过实测与理论分析，研究大空间内碰撞射流通风的性能，给出碰撞射流通风气流运动特性的预测模型并估计其节能效果。

提高能量利用效率是实现空调系统节能最为重要的问题之一。为在低能耗下改善室内热环境和空气品质，合理的通风方式即为有效方法之一。但在大空间中，很难对热舒适、空气品质与送风能量利用率进行优化处理。置换通风方式虽可实现节能和良好空气品质的目标，但不能用于热风供暖；混合通风虽然可以兼顾供冷与供热的需求，但送风热量的利用率低，不利于节能。理论上，碰撞射流通风同时具有混合通风和置换通风的优点，但由于对这种通风方式缺乏必要的理论分析基础，故目前还很少使用。本研究通过系统的实测与理论分析，研究了大空间内碰撞射流通风的性能，并给出了相应的优化设计方法与原则。. 本项目通过系统的理论、实验和数值模拟研究，给出了浮力和惯性力综合作用对室内空气温度、流场和污染物扩散的影响作用；分析了碰撞射流通风引发颗粒物再悬浮的风险，并给出了消除碰撞射流通风房间发生再悬浮污染风险的送风速度限值，以及已悬浮颗粒物和二氧化碳浓度的空间分布特征，为碰撞射流通风实现良好空气品质提供了基本设计依据。在考虑满足室内热舒适要求的基础上，分析了碰撞射流通风与传统通风策略下的室内热环境和系统能耗特征，指出高大空间使用碰撞射流供冷时的节能性和空气品质与置换通风类似；碰撞射流用于热风供暖时，比混合通风至少节能20%，其节能率随着房间层高的增大而增加，并且室内的被动式与主动式污染物浓度均明显低于混合通风。另外，利用大量工况模拟计算结果和数学分析方法，得到了碰撞射流热风供暖送风距离的多因素预测模型，并发现碰撞射流热风供暖时，其送风距离存在极大值，这是其他送风方式没有的情况。为此，利用建立的送风距离预测模型，给出了碰撞射流通风设计的优化原则，为碰撞射流通风的设计工作提供了理论依据和计算方法。