Meeting Sustainability Goals through Integration of Fire Alarm and Building Controls

Issue 66: Meeting Sustainability Goals through Integration of Fire Alarm and Building Controls

By Paul Turnbull

Building owners are increasingly focused on the "green" aspects of their buildings and operations.  They have replaced standard light bulbs with CFL or LED bulbs, they recycle office paper, and they use Energy Star compliant computers and appliances.  But they probably haven't considered the sustainability impact of their life safety systems.  This article looks at ways that integration between a building's fire alarm system and its building control system can be used to help achieve sustainability goals while still complying with code requirements for the life safety systems.

The first question to be answered is why someone would want to integrate their fire alarm and building control systems.  There are many benefits from this integration, including the ability to monitor the status of both systems from one location, or to utilize features of the building control system that may not be available on the fire alarm system, such as remote notification, trending, or maintenance management.  But the biggest advantage is that both systems will cooperate to provide appropriate responses during emergency situations.  These responses could include avoiding detrimental responses, like adding air to a fire, or providing beneficial responses, such as supplying or exhausting air from parts of the building to remove smoke and/or create pressure differences – in other words, to perform smoke control.

Unfortunately, the life safety benefits of a smoke control system can conflict with the goal of operating the building in an energy-efficient manner.  The International Building Code¹ (IBC) requires smoke control systems to be activated weekly to verify they are ready to operate when needed.  During this code-required test, large quantities of conditioned air are exhausted to the outside, while nearly equal quantities of unconditioned air are drawn from the outside.  After the test is completed, additional energy is required to condition the air that was drawn in during testing.  From an energy-efficiency standpoint, that weekly smoke control system test is a waste.

Since testing of smoke control systems is mandated, there is not much that can be done to avoid its associated inefficiencies.  However, sustainability goals go beyond energy-efficiency considerations to include material resource management, which takes into account energy and resources required to produce and transport products to the building site; air quality considerations such as toxins in air exhausted from the building; and waste disposal.  With this broader scope in mind, there are a number of design choices that can be made to provide sustainability benefits that help counteract the negative impact of the code-required testing.

The first sustainability benefit from integrating fire alarm and building control systems is a reduction in the amount of equipment used.  Building control systems include control equipment and control circuits to operate fans and dampers for comfort purposes.  Fire alarm systems often include control equipment and control circuits to override these fans and dampers to provide the intended life safety function.  If the building control system has the appropriate life safety listings, these systems can be integrated, making it unnecessary to duplicate these controls and control circuits.  Instead, a signal from the fire alarm system can cause the building control system to operate the fans and dampers in a manner appropriate for life safety.  Since less equipment is required, less energy and resources were used to produce the products and transport them to the building site compared to what would have been required if the systems had not been integrated.

Another sustainability benefit comes from downsizing the equipment required for smoke control.  Paying attention to workmanship details can allow fan size to be reduced.  Using the equations found in NFPA 92,² an analysis of an 11-story stairwell in a location with a 10 F (-12°C) winter design temperature showed a big difference between the amount of air required to pressurize a tightly constructed stairwell and the same stairwell when loose construction was allowed.  For the example system, approximately 6000 cfm (2.8 m³/s) was required with loose construction; approximately 2600 cfm (1.2 m³/s) was required with average construction; and only about 950 cfm (0.45 m³/s) was required with tight construction.³

By sealing construction cracks, painting walls, making sure doors fit well, and caulking doors and windows, the stairwell pressurization fan could be reduced by over 80%.  This means less electricity is used to run and/or test the smaller fan, less material is used to create the smaller ductwork, and less conditioned air is exhausted and less unconditioned air is brought in during testing.

Some sustainability benefits can be achieved through modification of the smoke control system itself.  Pressurizing a stairwell with unconditioned air, or air conditioned just enough to keep it safely above freezing, provides an energy savings from not conditioning the pressurization air.  This approach also reduces the pressure difference between the top and bottom of the stairwell relative to the outdoors due to stack effect, leading to a reduction in the amount of air needed to pressurize the stairwell.  Using the equations found in NFPA 92,² an analysis of an 8-story stairwell using loose construction techniques in a location with a 10°F (-12°C) winter design temperature was shown to require 3800 cfm (1.8 m³/s) using 72°F (22°C) air for pressurization, but only 3200 cfm (1.5 m³/s) using unconditioned air; a reduction of approximately 15%.⁴ While the reduction in pressurization air is not as large as in the previous example, the sustainability benefits from reducing equipment size are the same as previously described.

Another change to the smoke control system that can lead to sustainability benefits is to divide large spaces into smaller spaces during an emergency, using deployable barriers.  When many floors are connected together using open stairs, the smoke exhaust system must be sized for the combined volume of all connected floors.  Use of deployable barriers reduces the size of each protected space, leading to a corresponding reduction in fan and ductwork sizes for each space.  Operation or testing of these smaller systems uses less energy and exhausts less conditioned air to the outdoors compared to systems using larger equipment.

One last approach for making smoke control systems more sustainable may be unpopular because it requires modification to the building design, but this approach can lead to substantial gains.  In building designs where little volume exists above the highest walking surface, smoke exhaust fans would have to be sized for the inefficiencies of a system that includes plugholing (drawing clean air up through the smoke layer).  Increasing the volume of space above the highest walking surface allows a deeper smoke layer to form, which can reduce the number of exhaust inlets needed to prevent plugholing, and can also reduce the size of the smoke exhaust fans. 

The volume above the highest walking surface could be increased by providing additional building height at the top of the atrium, but other methods that do not affect the building shell can also be used, such as separating the highest floors from the atrium by glass walls or other barriers.  Increasing the building height or adding glass walls will require additional construction materials, which will offset some of the gains made from increasing the efficiency of the smoke control system, but this is a one-time tradeoff, where the efficiency gains are realized every year over the life of the building. 

Increasing the volume above the highest walking surface to extreme proportions can result in the greatest sustainability benefits.  If the volume is sufficiently large that all building occupants can be evacuated before the volume fills with smoke, a passive smoke-filling approach is all that is required.  A passive system is certainly the most sustainable system of all, because it completely removes the need for fans, ductwork, exhaust grilles, etc., and the electricity that would have powered it all.  And because there are no operational parts, the weekly tests that dump conditioned air to the outside and require the associated reconditioning of make-up air are also eliminated.

The previous paragraphs have described methods that can make a smoke control system more sustainable, but it should be pointed out that any smoke control system is more sustainable than no smoke control system.  A smoke control system reduces migration of smoke within a building.  This prevents smoke from damaging building finishes and contents in parts of the building that are not directly involved in the fire, so these finishes and contents do not need to be replaced after the fire.  Protecting something for continued use is much more sustainable than allowing it to be damaged and then having to replace it.

Paul Turnbull is with Siemens Industry, Inc.

1. International Building Code, International Code Council, Washington, DC, 2012.
2. NFPA 92, Standard for Smoke Control Systems, National Fire Protection Association, Quincy, MA, 2012.
3. Klote, J. and Turnbull, P., "SFPE Seminar: Smoke Control Session 1 Student Handout", Society of Fire Protection Engineers, Bethesda, MD, 2012.
4. Klote, J. and Turnbull, P., "SFPE Seminar: Smoke Control Session 1 Student Handout", Society of Fire Protection Engineers, Bethesda, MD, 2010.

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