Standby
48 Ah
A different kind of system
These are signal systems, not flow systems — so we organise by subsystem. But the design discipline is identical: Role → Design method → Worked numbers → Software → Code. The unifying theme in a tall building is integration: fire, BMS, security, lifts and power all talk to each other and to the fire command centre. Symbols & conversions used in the worked examples
| Symbol | Unit | What it is |
|---|---|---|
| Isup / Ialarm | amps (A) | Standby (quiescent) current / alarm current — from the device schedule. |
| tstandby / talarm | hours | Required standby (e.g. 24 h) & alarm (e.g. 5 min = 0.083 h) periods — set by code/AHJ. |
| derating | 1.25 | Battery ageing/safety factor. |
| bitrate | Mbit/s | Camera stream rate (CCTV storage). |
Key formulas: battery Ah = (Isup·tstandby + Ialarm·talarm) × 1.25 · daily storage GB/day = bitrate × 86,400 s ÷ 8 ÷ 1000 (÷8 converts bits→bytes; 86,400 = seconds in a day)
5.1 System architecture
ELV (Extra-Low-Voltage) systems share a backbone: distributed equipment/telecom rooms up the tower, a structured-cabling network, and head-ends in a control/security room and the fire command centre. The fire-alarm system is separate and listed, but interfaces with everything for cause-and-effect.
Figure 5-0 · ELV/FA architecture — independent subsystems, integrated for control. (Original schematic.)
5.2 Fire detection & alarm
Role: detect fire early and initiate alarm + cause-and-effect. An addressable Fire Alarm Control Panel (FACP) runs loops of devices: smoke/heat detectors, multi-sensors, manual call points, beam & aspirating detectors for big volumes, plus interface modules to plant.
Worked example 5.2 · Smoke-detector coverage
Given: open floor 1,000 m², smooth flat ceiling; spot smoke detector nominal coverage ≈ 81 m² (≈9.1 m / 30 ft spacing).
Detectors ≈ 1,000 ÷ 81 = 12.3 → ≥ 13, then adjust for beams, partitions and HVAC airflow (high air change reduces spacing).
~13+ detectors before adjustment; add detection in voids, ducts (duct smoke detectors for HVAC shutdown), and per-room devices in hotel/residential. Loop loading kept below the panel's device limit.
Code
Detection & spacing: NFPA 72; duct detection & HVAC shutdown: NFPA 72/90A; under SBC 801 & Civil Defense.5.3 Voice evacuation & mass notification
Role: in a tall building you cannot evacuate everyone at once — you use phased/voice evacuation with intelligible voice messages by zone, controlled from the fire command centre, following a cause-and-effect matrix (what each alarm triggers: messages, smoke control, lift recall, door release, etc.).
| Design point | Target |
|---|---|
| Speech intelligibility | STI ≥ 0.50 (or CIS ≥ 0.70) in occupied areas |
| Evacuation strategy | Phased (alarm floor + above/below first), managed from FCC |
| Survivability | Circuit integrity / fire-rated cabling so the system works during the fire |
Code
Voice/MNS & intelligibility: NFPA 72 (Ch. 18/24); egress strategy: NFPA 101; SBC 801 / Civil Defense.5.4 Fire-alarm standby power (battery sizing)
Role: the FA system must survive a mains failure — batteries (or generator + batteries) sized for a supervisory period plus an alarm period.
Fire-alarm battery sizing (NFPA 72)
The standby battery carries the quiescent (supervisory) load for the required standby period, then the alarm load for the alarm period (5 min here), with a derating factor (~1.25) for ageing and temperature.
Quiescent draw of the panel + all devices.
Required standby (24 h typical; 60–72 h for some occupancies).
Full-alarm draw (notification appliances) for 5 min.
Alarm
0.7 Ah
Required ×1.25
61 Ah
Pick a battery
Required battery vs supervisory current for the chosen standby period (alarm 5 min × 1.25 derating), with your operating point marked.
Worked example 5.4 · Battery capacity
Given: supervisory current 2 A; alarm current 8 A; standby 24 h; alarm 5 min (0.083 h); derating 1.25.
Ah = (2 × 24 + 8 × 0.083) × 1.25 = (48 + 0.67) × 1.25 = 60.8 Ah.
Select sealed batteries ≥ 61 Ah (next standard up). Voice/MNS and some AHJs require longer standby/alarm — confirm the required periods.
Code
Secondary power & battery calc: NFPA 72 (24 h + 5/15 min); NFPA 110/111 where generator/UPS backs FA.5.5 BMS / BAS — building management
Role: monitor and control the mechanical/electrical plant (HVAC, pumps, chillers, energy metering, lighting control) to optimise comfort and energy and to report faults. Architecture: field sensors/actuators → DDC controllers → network → head-end/graphics, on BACnet (ISO 16484).
- Points list — every monitored/controlled point (AI/AO/DI/DO) is scheduled per plant item; the count sizes controllers and network.
- Sequences of operation — written control logic (chiller staging, CHW/condenser-water reset, optimum start, demand-controlled ventilation, pump DP control).
- Integration — to power meters, lifts, FA (read-only for smoke control), generators.
In the software
The points list & sequences are documented (often in vendor tools — Siemens Desigo, Honeywell, JCI Metasys) and the energy benefit of resets/optimisation proven in the HAP/energy model. Network architecture drawn in Revit/Visio. Code
BACnet/interoperability: ISO 16484-5; control strategies & DCV: ASHRAE 90.1 & 62.1 / SBC 601.5.6 Structured cabling & ICT
Role: the building's data backbone — telecom rooms (TR) per floor/zone, vertical backbone (fibre) and horizontal copper to outlets, supporting IT, Wi-Fi, BMS, security and PA over a converged IP network. Data centres follow TIA-942.
Worked example 5.6 · Horizontal channel length
Given: TIA-568 limits a copper horizontal permanent link to 90 m (+10 m patch/equipment cords = 100 m channel).
→ Telecom rooms must be located so no outlet's cable route exceeds 90 m. On a large floor plate that fixes the number & position of TRs.
Place a TR per zone/floor so every workstation is ≤ 90 m of cable route; backbone between TRs and to the main equipment room is fibre.
Code
Cabling: ANSI/TIA-568, -569 (pathways), ISO/IEC 11801; data centre: TIA-942; BICSI TDMM; telecom regulator (e.g. CITC).5.7 Security — CCTV, access control, intrusion
Role: protect people & assets: IP CCTV (cameras, VMS, storage), access control (readers, controllers, electric locks integrated to FA for fail-safe egress), and intrusion detection — all on the converged network.
Worked example 5.7 · CCTV storage
Given: 200 cameras at 4 Mbit/s each (H.265), recording 24/7 for 30 days retention.
Per camera/day = 4 Mbit/s × 86,400 s ÷ 8 = 43,200 Mbit = 5.4 GB/day → ×30 = 162 GB; ×200 cameras ≈ 32 TB (×~1.2 overhead ≈ 39 TB).
~40 TB usable storage for 30-day retention; size the recording servers/SAN accordingly and the network bandwidth (200 × 4 = 800 Mbit/s).
Code
CCTV: IEC 62676 / EN 50132; access & egress release interlocked to FA: NFPA 101 / 72; security authority requirements (e.g. HCIS for major KSA projects).5.8 In-building coverage & public address
Role: reliable wireless and broadcast inside a structure that blocks signal: DAS (distributed antenna system) for cellular & first-responder radio coverage (often mandated by Civil Defense), Wi-Fi, public address/background music, and IPTV. First-responder radio coverage is a life-safety requirement in tall buildings.
Code
First-responder radio coverage: NFPA 1/72 & AHJ; PA/VA overlaps NFPA 72; telecom: CITC.5.9 Integration & network architecture
Role: tie it together so the building behaves as one system in an emergency — the cause-and-effect matrix is the master document: an alarm at a device triggers voice messages, smoke-control fans, lift recall, door release, AHU shutdown/damper action, and signals the FCC. Subsystems integrate over IP/BACnet with a clear, cyber-secure network design and redundancy.
The cause-and-effect matrix
This single matrix is the heart of tall-building life safety — it must be agreed with Civil Defense and proven by an integrated test before occupancy. Code
Integration & survivability: NFPA 72; integrated testing: NFPA 4; cyber/network: ISA/IEC 62443 (OT security) where applicable.5.10 Installation, accessories & field tricks
| Item | Field rule / trick |
|---|---|
| Dedicated ELV containment, segregated from power | Keep data/FA away from power cables (min separation) to avoid EMI; separate fire-alarm containment. |
| Fire-rated / fire-survival cabling | FA, voice, smoke-control & firefighting-lift control on circuit-integrity cable. |
| Firestopping & fire-rated TR doors | Seal every penetration; telecom/equipment rooms fire-rated & cooled (a heat load to HVAC). |
| Labelling, testing & certification of cabling | Every link tested & certified (e.g. Fluke) and labelled to TIA-606. |
| Earthing/bonding of racks, trays, DAS | Proper ELV earthing for safety & signal integrity. |
| Spare capacity | Spare TR space, containment fill & panel loop capacity for future devices. |
| Device location coordination | Detectors clear of supply diffusers; call points/strobes per code height; coordinate in BIM. |
Code
Cabling install/test: TIA-568/606, BICSI; fire-survival cable: BS/IEC; firestop: UL/NFPA; separation: SBC 401/TIA.5.11 Commissioning
- FA: 100% device test, battery/standby test, voice intelligibility (STI) survey, and the full cause-and-effect verification with smoke control, lifts & power — witnessed by Civil Defense.
- BMS: point-to-point verification, sequence functional tests, trend/graphics check.
- ICT/security: link certification, VMS/access functional tests, DAS coverage survey.
Code
Integrated test: NFPA 4; FA acceptance: NFPA 72; commissioning: ASHRAE Gl 0 (BMS); cabling: TIA test standards.Terms & abbreviations
Plain-English meaning of the fire-alarm, ELV and BMS terms used in this module.
| Term | What it means (plain English) |
|---|---|
| ELV | Extra-Low-Voltage — the "signal" systems (alarm, data, controls, security), not power. |
| FACP / addressable loop | Fire Alarm Control Panel; an addressable loop is a wired circuit where every device has its own ID. |
| NAC | Notification Appliance Circuit — drives sounders/strobes that warn occupants. |
| Supervisory (quiescent) current | The small standby current the system draws normally — used to size standby batteries. |
| Cause-and-effect matrix | The master table of what each alarm triggers (voice messages, smoke control, lift recall, door release…). |
| Voice evacuation / PAVA | Public Address / Voice Alarm — intelligible spoken messages instead of just bells, evacuating by zone. |
| MNS | Mass Notification System — broadcasts emergency messages building-wide. |
| STI | Speech Transmission Index — a measure of how intelligible speech is (target ≥ 0.5). |
| Phased evacuation | Evacuating the fire floor and those above/below first, not everyone at once (needed in tall buildings). |
| BMS / BAS | Building Management / Automation System — monitors & controls the mechanical/electrical plant. |
| DDC controller | Direct Digital Control — the field computer that runs control logic for plant. |
| BACnet | The open communication protocol (ISO 16484) that lets different building systems talk to each other. |
| Points list (AI/AO/DI/DO) | Every monitored/controlled signal: Analog/Digital Inputs & Outputs — the count sizes the controllers. |
| Sequence of operation | The written control logic (e.g. how chillers stage, how a valve modulates). |
| Structured cabling | The standardised network of cables/outlets/rooms carrying data, Wi-Fi, security, etc. |
| Backbone / horizontal / channel | Backbone = vertical/main cabling (usually fibre); horizontal = floor cabling to outlets (≤90 m link). |
| TR (telecom room) | The floor/zone room housing network equipment and cable terminations. |
| VMS | Video Management System — records and manages CCTV cameras. |
| Access control | Card/biometric readers & electric locks controlling who enters where (released on fire alarm for escape). |
| DAS | Distributed Antenna System — spreads cellular/first-responder radio signal inside the building. |
| DCV | Demand-Controlled Ventilation — uses CO₂ sensors to supply only the fresh air actually needed. |
References & software map
| Task | Software | Code |
|---|---|---|
| FA design, battery & cause-effect | Vendor tools + battery/voltage-drop calc sheets; matrix in Excel | NFPA 72 / 4; SBC 801 |
| BMS points & sequences | Siemens Desigo / Honeywell / JCC Metasys; energy in HAP | ISO 16484; ASHRAE 90.1/62.1 |
| Structured cabling / ICT | Revit/Visio layouts; link certification tools | TIA-568/569/942; ISO 11801 |
| CCTV/security bandwidth & storage | Manufacturer VMS calculators | IEC 62676 / EN 50132 |
- NFPA 72 (Fire Alarm & Signaling), NFPA 4 (integrated testing), NFPA 101 (life safety); under SBC 801 & Civil Defense.
- ISO 16484 (BACnet/BAS); ASHRAE 90.1 / 62.1 / SBC 601 (control strategies).
- ANSI/TIA-568, -569, -606, -942; ISO/IEC 11801; BICSI TDMM; CITC telecom rules.
- IEC 62676 / EN 50132 (CCTV); HCIS security requirements (major KSA projects); IEC 62443 (OT cyber).
Note
Worked numbers teach the method, not stamped design. Battery periods, intelligibility and coverage are AHJ-governed — confirm with Civil Defense and the project spec.