The HVAC system manages the operation of the Heating, Ventilation and Air Conditioning (HVAC) equipment serving the controlled spaces within a facility.
Normal HVAC control calls for the management and modulation of the temperature and humidity within the conditioned/occupied building space and is one of the important aspects of conditioning for human comfort. Heat and moisture must be supplied to (or removed from) the air of a building to maintain the desired conditions. Normally, this involves providing an air stream at a higher or lower temperature and humidity than that of the space to the degree needed to balance the heat and moisture loads in the conditioned space.
The HVAC control system manages the operation of the HVAC equipment serving the controlled spaces within the facility. This equipment includes a broad assortment of elements ranging from large Chillers, Boilers and Air Handling Units to smaller Roof-Top-Units and Variable Air Volume Boxes and assorted dampers and fans. While this equipment is normally controlled with the specific purpose of maintaining desired comfort levels in the various areas of the facility, many of these devices serve a dual purpose when exposed to emergency conditions.
Smoke Control is considered an emergency condition which can take advantage of the existing HVAC equipment to create barriers to the undesired migration of smoke when a fire emergency exists in a facility. In addition to performing containment functions, the HVAC equipment also serves to facilitate movement (exhausting) of smoke from the affected areas with the goal of maintaining a tenable environment within the defined escape routes such as stairwells and spaces adjacent to the affected fire areas. This maintenance of a tenable space in proximity to the affected areas also serves to help in fighting the fire in the affected areas and reduces smoke damage in other areas of the facility.
An HVAC system designed for non-dedicated smoke control will perform normal comfort and time scheduled control until an alarm situation is detected and/or an FSCS override is activated. The Fire Alarm Panel (FAP) will provide the HVAC/Smoke Control system with an indication of an alarm condition when it detects fire or smoke in a particular area/zone in the facility.
The smoke control system will receive the alarm indication through one of two avenues:
1) Using discrete contact outputs from the FAP directly wired to the discrete inputs on the Smoke Control, I/O modules or the controllers in the MS/TP family described here. The SmartStruxure Solution smoke control system can interface with any UL 864 Listed Fire Alarm Panel providing zoned alarm contact outputs.
2) Using a BACnet/IP protocol interface between the FAP and Smoke Control Servers assigned to provide FAP interface and alarm management functions. This FAP alarm management may frequently be combined in the same Smoke Control Servers managing the FSCS panel. In such arrangements, all automated smoke control functions (alarm initiated) and manual override (FSCS initiated) are originating from a common controller. The SmartStruxure smoke control system can interface with any UL 864 Listed Fire Alarm Panel that includes a BACnet/IP interface within the scope of the listing.
An example FAP with a UL 864 Listed BACnet interface is the Simplex BACpac Ethernet Portal modules- Models 4100-6069 or 4010-9915 used with their Listed compatible fire alarm control panels (currently listed as 4100ES, 4100U, 4010ES and legacy 4100/4100+ and 4120 Series). The Smoke Control Server assigned as the FAP controller managing the BACnet/IP interface will continuously monitor the status information provided by the FAP and the detection of the first active alarm signal will be processed as defined in the paragraphs that follow.
Both contact and protocol interface methods produce the same basic function of providing the HVAC smoke control application with the indication of an alarm. The FAP contact inputs, or protocol defined alarm signals are each interpreted and assigned a zone number. The zone numbers will correlate with the defined smoke/fire zones created by the arrangement of HVAC equipment and applications, coupled with the design of smoke barrier components and dedicated system equipment.
The FAP controller monitors the incoming alarm information and will initiate the appropriate alarm response based on the zone indicating an alarm. Typically, this will include activation of exhaust equipment/applications in the alarming smoke zone and the presssurization of surrounding zones along with activation of the pressurization of escape corridors such as stairwells.
In larger facilities, the serial protocol interface provides a more efficient means of access to signal information from the larger number of alarm zones. The BACnet/IP interface also provides supervision of the communications to the FAP interface. This supervision takes place during normal and alarm conditions and provides immediate indication of fault conditions on the FSCS panel when a problem is detected. For more information, see the FAP protocol interface discussion that follow.
In smaller facilities, it may be more efficient to use one (or more) of the MS/TP controllers or I/O modules to receive the contact closure alarm indications from the FAP.
The contact interface is not supervised and the FAP contact to controller/module interface must be run in conduit for a length less than 20 feet. For more information, see the section that follows on FAP contact interfaces.
The configuration of the FAP zone alarm contact connections and/or the programming in the Smoke Control Server must be arranged to exclude or ignore zone alarms originating from a manual pull-box. If the FAP zone alarm signals are received via the BACnet/IP protocol interface, then the Smoke Control Server program should ignore pull-box initiated alarms. The pull-box alarm signals are excluded because of the high probability that the pull-box alarms are being initiated by persons observing fire and/or smoke in other areas of the building. Such an alarm signal would produce an inappropriate response from the smoke control system.
A control system response to a pull-box alarm from a zone outside the fire/smoke area could aggravate the smoke/fire situation. The only exception is where the only automated response is the pressurization of stairwells or other escape corridors regardless of where the smoke/fire is detected. In that case, the activation of the common response from a pull-box would be acceptable.
When the Smoke Control Server managing the FAP receives a fire/smoke zone alarm via contact or protocol, the Smoke Control Server will activate the initial Automated Response to the smoke control system based on the first received alarm.
The smoke control system will initiate an automatic response to the FIRST alarm originating from the FAP. Typically, the automated response will attempt to contain and exhaust the fire/smoke zone. For more information, see Fundamentals of Smoke Control .
The smoke control system should be designed to provide an automated response (within a single building) to the first zone alarm. Subsequent alarms may be produced by the FAP due to smoke migration from the original area/zone, or the spread of fire in the facility. Typically, the smoke control system will be programmed to ignore alarm signals after the first alarm. The automated smoke response will be latched into effect based on the first alarm zone and stay active until the alarm has been reset by the FAP system. Depending on the special building and equipment circumstances, the local AHJ may approve alternate schemes such as a continued automated response to additional zone alarms.
The system designer will define the response for each possible smoke zone alarm based on the objective of containing the smoke and limited by the available HVAC equipment, dedicated equipment applicable to the situation and physical space segmentation (zoning) of the facility. The smoke response algorithms will typically be configured to pressurize adjacent zones (above, below and to the side) to the zone producing the alarm and will exhaust the air from the alarming zone. The system may also pressurize areas such as stairwells and other areas of the building.
The smoke control Automated Response takes priority over any and all normal modes of operation associated with the equipment called upon to affect the pressurize and exhaust functions. Regardless of current comfort levels and associated setpoints which the HVAC equipment is attempting to achieve or maintain, the controller applications associated with smoke control will accept their alarm response direction from the Smoke Control Server managing the FAP and hold the equipment in the specified automated response condition until the following events occur:
The alarm zone signal is extinguished, typically by the acknowledge and reset actions on the FAP. The first alarm response is latched by the FAP interface controller, or Smoke Control Server, and will hold the alarm response until the zone alarm signal deactivates. If the initial/latched alarm signal extinguishes, but other alarm signals are still active, the system will typically be configured to transition the automated response to an operating condition applicable to the next active zone alarm signal starting from zone 1 in numeric order.
The current automated alarm response is overridden by manual override direction (commands) originating from the Firefighters Smoke Control Station (FSCS). Override control direction from the FSCS panel must be configured to have the highest priority and will override normal and automated response operation.
A smoke control system compliant with the UL UUKL system listing will include an FSCS. As the name implies, the FSCS panel provides the firemen arriving at a facility with a means to override the current state of selected, non-dedicated HVAC and dedicated smoke control equipment. After the initial automated response, this assists the firemen with override control of equipment containing and exhausting smoke from the facility. For more information, see FSCS Basics .
Typically, the FSCS consists of a wall-mounted panel providing a graphical presentation of the building and the equipment which is monitored and controlled from that panel. The FSCS provides indicators showing the current state of the equipment used for smoke control, in addition to providing switches that the fireman can use to override the current state.
Control directions to the equipment from the FSCS panel take top priority over normal environmental control and also over the automated initial alarm response. Although the automated FAP response may have been the correct response at the time of the alarm, the situation can vary and the firemen in the facility will use the FSCS to further refine the use of non-dedicated HVAC equipment and dedicated equipment to manage the smoke situation and facilitate the evacuation of the facility and fighting of the fire.
For the HVAC equipment, the normal position for the FSCS override switches is the automatic position. The HVAC equipment will follow the automatic comfort controls from the normal HVAC control applications. When a switch is taken out of the normal/automatic position, it will be moved to the ON or OFF position such as fans, or OPEN and CLOSE for dampers. When the switch is moved from the auto position, the Automation Server or AS-P managing the FSCS will send an override command to the associated controller(s). The individual controller(s) managing the overridden equipment will direct the equipment to the requested state regardless of normal environmental control strategies. If the FSCS switch is changed, the system will again direct the equipment to the requested override state.
If the equipment override switch on the FSCS is returned to the Normal or Auto position, then the control of the equipment will return to the normal environmental control applications. An exception to this occurs if the equipment is associated with a currently latched automated response algorithm that has not yet been cleared (Reset). When the FSCS is used to override equipment currently controlled by an automated FAP response, the equipment will return the associated, automated response state when the FSCS override switch is returned to the Auto position.
In addition to providing override control of the selected HVAC equipment in the facility, the FSCS panel must also provide indications for the detection of equipment trouble conditions. Equipment trouble represents the failure of the overridden equipment to reach the override state or condition as sensed by the managing controller using various methods for proofing the state of the equipment.
At a minimum, the FSCS must provide a Master Equipment Trouble (or Equipment Fault) indicator. This master trouble indication will illuminate (and sound audible) when the proofing status from any of the supervised pieces of equipment indicates a trouble/fault condition. Providing an individual trouble indicator for each of the equipment items controlled from the FSCS is a preferred option, but it is not required for UUKL compliance. Omitting individual trouble indications does not relieve the requirement for the FSCS to provide individual indications of equipment status such as ON, OFF, Open, Closed, etc.
The equipment trouble indications serve to warn the FSCS operator when the equipment responding to smoke control commands (FAP or FSCS) has failed to respond as directed. This allows the FSCS operator to judge the potential need to make further equipment overrides or institute alternate responses to compensate for potential equipment failures. Obviously, the indication of individual equipment faults presents much better visibility into the current operation of the equipment and areas where alternate override control may be applicable.
Regardless of whether or not individual, trouble indications are provided on the equipment, the NFPA guidelines require that a summary indication be provided. The summary indicator must be programmed to illuminate when trouble is detected on any individual pieces of equipment.
Communications are required between all controllers participating in the smoke control application. A loss of communications will prompt a failure of some portion of the smoke control system. The smoke control system must be configured and programmed to continuously monitor the integrity on all communications paths required for the smoke application. This requires that each of the communications paths be supervised. The supervision on the MS/TP RS-485 busses should be performed by the Smoke Control Server managing the bus.
All of the Smoke Control Servers will supervise the communications to all connected MS/TP controllers (b3 or MNB series) that are participating in smoke control applications. The Smoke Control Server programming must create a variable which indicates when any supervised MS/TP controllers have failed to deliver their supervision heartbeat for the defined timeout period. Upon detecting a failure to receive the MS/TP heartbeat, the Smoke Control Server program must indicate the fault in the supervision status information that is continuously being sent to the Smoke Control Server managing the FSCS (under a BACnet COV subscription).
That FSCS Smoke Control Server application program will at a minimum provide a summary LED and audible indication on the FSCS when any controller on any bus in the smoke control system is reported with a communications fault.
All communications channels used for the smoke control applications are designated as UL 864 Class C pathways. The operational capability is continuously verified via end-to-end communication. Loss of communications shall result in annunciation of a trouble signal on the FSCS.
The individual Smoke Control Servers in the smoke control system may be configured with I/O modules. For any I/O modules participating in the smoke control system, the Smoke Control Servers must supervise the integrity of the communications to the I/O modules and report the I/O module communications status to the Smoke Control Server managing the FSCS for reporting as described previously.
If the system is using a BACnet/IP interface to the Fire Alarm Panel (FAP), the Smoke Control Server managing that interface must supervise the integrity of the BACnet/IP channel and continuously report the status of the FAP communications to the Smoke Control Server managing the FSCS
The Smoke Control Server managing the FSCS can be the same FSCS used to provide the BACnet/IP management. That is the recommended configuration when using BACnet/IP.
The Smoke Control Server managing the FSCS is also responsible for supervising the Ethernet network communications to all other Smoke Control Servers that are part of the smoke control system. The Smoke Control Server managing the FSCS should be programmed to monitor heartbeat signals from the supervised Smoke Control Servers. The FSCS Smoke Control Server must be programmed to activate the communications fault LED and the audible horn if it detects a communications problem to the other Smoke Control Servers, or it receives signals from the remote Smoke Control Servers indicating a fault on the MS/TP field controllers or I/O modules.
This communications fault LED is a summary indication and a minimum requirement showing that a fault exists at some place in the system beyond the Smoke Control Server managing the FSCS. Optionally, other LEDs can be supplied showing more detail on the location of the fault or the type of controllers producing the fault. Separate communications and equipment trouble indicators facilitate a better understanding of the necessary corrective action and interpretation of the other indicators provided on the FSCS.
The FSCS panel itself must be programmed (by ADI in the Z-Card) to supervise the communications on the Modbus RS-485 channel to the Smoke Control Server managing the FSCS. The processor in the FSCS is acting as the Modbus master and is managing the Modbus communications channel to the Smoke Control Servers. If the Z-Card detects a fault in the RS-485 Modbus communications, the Z-Card will activate a fault LED and horn. It is recommended that a separate LED be used to specify an FSCS communications fault, such as in the example system. For more information, see SmartStruxure Solution .
If this LED is active, it means that the fault is at the top of the reporting tree (at the FSCS) and that all the information on the FSCS cannot be trusted.
Refer to this topic for further discussion on communications supervision and alert requirements. For more information, see FSCS Basics .
Refer also to the discussion on using application programs to achieve communications supervision. For more information, see FSCS Communication Status .
Smoke control systems are composed of dedicated sub-systems, non-dedicated sub-systems, or the more typical combination of both.
A dedicated smoke control system or sub-system is intended only for smoke control. Such a system/subsystem provides separate equipment for air-moving and/or distribution that do not function during normal building operating conditions. When an alarm or FSCS override condition occurs, these systems operate specifically to perform a smoke control function.
The operation and control of dedicated systems tends to be simple and the modification of the controls during HVAC system maintenance is less likely to occur. These dedicated systems are typically not affected by the modification of other building systems.
Dedicated systems tend to be more costly and component failures may go uncorrected since they do not affect normal building operation such as comfort control. Often, they require more space in the facility.
To address the potential undetected failure of dedicated system components, it is necessary to provide periodic (typically weekly) testing of the dedicated control system to confirm proper operation. This periodic testing must be part of the engineered smoke control system.
Non-dedicated systems share equipment components with other facility systems such as the HVAC comfort system. The occurence of a smoke alarm or FSCS override causes the system to change its normal operating mode to achieve the smoke control objectives.
Failures of equipment in non-dedicated systems are less likely to go unnoticed since the equipment is also used for normal, building operation. System costs may be lower due to the shared use of the equipment and reduced space requirements.
Controlling a non-dedicated system may be a little more complex (as compared to a dedicated system) due to the combined normal and smoke control application algorithms. Extra attention must be applied to ensure the smoke control application takes precedence over normal HVAC applications.
Most buildings use a combination of dedicated (for example, stairwell pressurization) and non-dedicated sub-systems.