This is in a hospital. The current configuration is a normally closed loop, with other safeties wired in series. Th GC is stating that no other safeties can be wired in this loop. It must be dedicated as HVAC shutdown, directly to the VFD.
As per NFPA - 72 (2019), 21.7.3 Connections between fire alarm systems and the HVAC system for the purpose of monitoring and control shall operate and be monitored in accordance with applicable NFPA standards.
If the fire alarm control unit actuates the HVAC system for the purpose of smoke control, the automatic alarm initiatingzones shall be coordinated with the smoke control zones they actuate.
Various types of control systems are commonly used for HVAC systems. These control systems utilize pneumatic,electric, electronic, and programmable logic-based control units. All these control systems can be adapted to provide thenecessary logic and control sequences to configure HVAC systems for smoke control functions. Programmable electronic logic-based (i.e., microprocessor-based) control units, which control and monitor HVAC systems as well as provide building control and monitoring functions, are readily applicable for providing the necessary logic and control sequence.
HVAC control panel shall have an interface with marshalling cabinet to have the digital output (DO), which is digital input (DI) to HVAC control panel. Shut down of HVAC system could be done by a signal from marshalling cabinet in case a fire by a voting logic of it.
Addressable control module could also shut down the HVAC system in case a fire, by a logic as required with HVAC control / DDC panel.
"current configuration is a normally closed loop" - Wired relay connection in HVAC equipment(s) is not considerable, relay to relay connection in HVAC control panel and marshalling cabinet (PLC) could be considered to have an interface.
In case a fire, dampers, A.H.U's and other respective(s) will shut down to have a complete HVAC system shut down.
"no other safeties can be wired in this loop" - The loop is; cable from FA field device(s) to marshalling cabinet and from marshalling cabinet to HVAC control panel. OR the cable; from FA devices to addressable fire alarm control panel and addressable FACP to DDC panel of HVAC to refer.
Hope this is helpful.
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