The modern heating, ventilating, and air conditioning (HVAC) system has been designed efficiently for its specific function. Use of this system for smoke control stresses many of its components.
Central fans can be overloaded, outlet air terminals can hamper or obstruct efforts, and dangerous static pressures can be generated that can hold fire doors open or closed or blow out windows. Efforts to provide fresh air can cause freezing damage to critical central equipment.
This paper discusses the various problems without providing a specific course of action. The Summary is a checklist of considerations if the HVAC system is to be part of a smoke control system. The primary suggestion is that smoke control be part of the initial specifications to assure that certain safety factors are considered.
Specifications should consider: 1. Control fan load limiting controls. 2. Compressed air fuses to keep the system operating despite damaged lines. 3. Compressed air interlocks to abort smoke management efforts if all control fails. 4. A means to protect equipment from freeze damage in northern climates. 5. Positive position terminals, either fail open or fail closed depending on the concept selected. 6. Interlocks on self-contained terminals to drive open or closed. 7. Programmed control of terminals as opposed to “kill the main” approaches. 8. Matching pressurization areas to fan capacity. 9. Pressure testing of the system after completion, including fan load and forces on doors. 10. Possible use of dedicated fans on each floor (not part of the HVAC system) for pressurization and for exhaust.