secondary air return

• 二次回风

secondary air return的用法和样例：

例句

1. For a typical single duct air system there will be one zone supply air path and one zone return air path.
   对于典型的单管空调系统，一般由一条区域送风路径和一条区域回风路径组成。
2. Building humidification may not be required if return air contains sufficient humidity to satisfy winter requirement.
   如果回风含有足够的湿度来满足冬季需求的话，建筑则不需要加湿。