Read here about traditional Building Management type control systems and programmable logic controllers (PLCs): do they deliver on all the functionalities you need?

1. Can HVAC control systems be effective for smoke ventilation?
As the building industry has evolved, the need has
arisen for sophisticated control systems with highly
complex sequences of operation for smoke
ventilation schemes. In the search for effective
solutions, a debate has arisen about whether
existing systems designed for other purposes can
be adapted to perform effectively for smoke
ventilation.
Having looked at the use of fire alarm control
systems for smoke ventilation in a previous post,
today I am turning my attention to traditional
Building Management type control systems and
programmable logic controllers (PLCs): do they
deliver on all the functionalities you need?
Yes
 HVAC Control systems can be extremely flexible and offer a high degree of programmability,
which is always very useful when designing systems with a complex operation sequence.
 There are a high number of systems available with varying degrees of capability
No
 HVAC systems can be temperamental when not continuously in use. A smoke ventilation
system may be left alone for long periods with little or no attention (although they should be
tested regularly) and only be expected to operate if smoke is detected, but importantly it must
work first time, every time. An HVAC system is not designed to be used only occasionally. As
a consequence, it may not be sufficiently reliable for smoke ventilation control purposes.
 The I/O devices are rarely designed for operation at elevated temperatures.
 These systems often do not perform basic error checking routines to enable fault or
communication error diagnostics to be reported across the network.
 Some BMS or PLC based control systems are more prone to spurious errors caused by
background ‘interference’ from other electrical devices in the building and are too sensitive for
smoke control purposes.
© Colt UK

2.  HVAC systems are not very good at remembering what they were supposed to do if, for any
reason, they lose contact with the main panel. The interface devices out on the network (I/O
devices) rarely have any programmability and therefore have no designated failsafe state.
This is crucial – if the device loses communication with the main panel and is controlling the
extract fans on a life safety system, the fans must continue to run. With a BMS or PLC based
control system, this may not be the case. A smoke control system is reliant on a degree of
failsafe capability from the system which controls it.
The Verdict
Adapting HVAC systems for smoke ventilation control presents significant difficulties. Primarily, they
are not as reliable and robust as they need to be, and their inability to acquire a degree of failsafe
operation can be major obstacle, which needs careful adaptation and rigorous testing to ensure that
these are overcome.
While adequate for simple applications, neither fire alarm nor HVAC control systems deliver on all the
functionalities needed for more complex schemes. What is the answer? A control system designed
specifically for smoke ventilation. In my next post I will write about the approach we adopted at Colt, to
give you an example of how it can work out.
Feel free to continue the discussion by posting a comment below. Alternatively, please join the new
smoke control group on LinkedIn:
Associated blogs:
 Open or closed protocol? It’s a bit of both really
Conor Logan is a Technical Manager of Colt UK, Smoke and Climate
Control Division. Conor is also Chairman of the Smoke Control
Association.
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