Analyses the main malfunctions of HVAC systems and represents some design principles to ensure room non-positive pressure in the worst case, namely the exhaust system breaking down and the standby exhaust equipment switched on automatically.

• 分析了系统运行中的主要故障，给出了最不利状况即排风系统停机故障、排风设备自动切换时，避免房间出现正压的部分设计原则。