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INDICATOR LIGHTS

A firefighters' smoke-control system (FSCS) has status-indication lights in addition to manual hand-off-auto switches. The lights allow for verification of damper position and override status. They can be initiated from auxiliary switches on an actuator, damper-blade switches, or proximity switches.

Actuator switches often are preferred, as they are as reliable as blade-switch indication. The linkage between actuator jackshaft and damper is more robust than the typical coat-hanger connection from damper blade to switch package.

Fully engineered smoke-control systems exist in about only 10 percent of applications. Firefighters have control of dampers in these systems. Indicator lights show the systems' status.

Figure 3 shows a simple method of indicator-light wiring. The lights could be in a panel or local junction box, which could be located in the ceiling. An FSCS panel also would have an amber light indicating fault. If the damper were closed, the red light would be on. If the damper were open, the green light would be on. A variety of wiring methods are possible.

In some jurisdictions, the red light means “fire” or “problem,” while the green light means “OK.” In other areas, green means “on,” and red means “off,” particularly for fans. Although rare, some dampers normally are open when not powered, and the red and green lights could be switched. This can confuse a firefighter during the commotion of a fire. Indication lights should be discussed with a local fire department to ensure correct operation.

PROPORTIONAL DAMPER CONTROL

Figure 4 shows two proportional applications. The pressure in a stairwell or duct may need to be controlled at a certain set point. A smoke damper is required if a wall also is part of a smoke barrier. Given typical space constraints, one damper and actuator are technically and economically superior to two (or three, if a wall also is a fire barrier).

There are two ways to provide proportional damper control:

• No proportional electric actuator meets Uniform Building Code (UBC) criteria for 15 sec of operation. These actuators cannot be installed in UBC regions (which currently are California and a few outside cities). In these cases, two dampers are required. A two-position fire and smoke damper sits in the rated wall. A standard proportional damper and actuator are installed in series.

• In International Building Code regions, a proportional fire and smoke damper and actuator can be installed because the code (based on Underwriters Laboratories 555S, Standard for Smoke Dampers) requires a 75-sec maximum for operation. Actuators that meet the 75-sec requirement (20 sec to spring closed, 75 sec to drive open) are available.

CONCLUSION

The type of damper used depends on the application. Actuation is provided for smoke-control dampers and combination fire and smoke dampers. Containment systems are the most common, while reopenable dampers provide fire departments with more options.

By following the wiring diagrams in this article and comparing them with the sequence of operation, one can gain an understanding of the operation requirements for interfaces between mechanical and control systems.

Codes and practices differ geographically. One should consult local inspectors, contractors, and representatives with specific questions. The methods shown in this article are typical, although practices may vary.

For past HPAC Engineering feature articles, visit www.hpac.com.

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Larry Felker is a product manager for Belimo Americas. He is a member of the International Code Council, the National Fire Protection Association, and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). He serves on ASHRAE Technical Committee (TC) 1.4: Control Theory and Application and is a corresponding member of ASHRAE TC 5.6: Control of Fire and Smoke.

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