Smoke exhaust – it’s serious
looking into the electrical aspects of the systems — it is time
to explore EN 12101 Part 10.
The important aspect with electrically powered
equipment required to operate in a fire condition is the
requirement for the electrical current to be supplied to the
equipment. Yes, it sounds obvious; however, insufficient
attention is often paid to this aspect of the system. The selection of the control panel is not an isolated
decision — the requirement exists for the control panel to
suit the equipment being powered. The SHEVS equipment
manufacturer needs to give the panel designer sufficient
information to ensure that the equipment can be operated in
an emergency situation. Matching equipment that works as
certified is critical to a successful system.
4.1 General
If a smoke and heat control system fails to the fire operational
position on loss of power, only one power source shall be required.
For non-fail-safe smoke and heat control systems there shall
be at least two power sources: the primary power source and
the secondary power source. The primary power source shall
be designed to operate from the public electricity supply or an
equivalent system. The secondary power source, for example
batteries of a generator, shall be permanently available, tested and
maintained.
[EN 12101-10: 2006; p. 10] 6. 2.2
Note 1: To allow for possible failures of equipment or of the
incoming mains supply, the secondary supply should be capable of
maintaining the system in operation for at least 72h, unless provision
is made for immediate notification of failure, either by local or
remote supervision of the system, and a repair contract is in force
giving a maximum repair period of less than 24h. In this case the
minimum standby capacity may be reduced from 72h to 30h or may
be further reduced to 4h if spares, repair personnel and a standby
generator are available on site at all times.
Note 2: At the end of the maximum standby period if dead lock
is required, the residual power should be capable of operating the
system (including deadlock) in accordance with the requirements of
EN 12101-9.
[EN 12101-10: 2006; p. 15]
Every system designer should
safeguard against equipment
without certified documentation
supporting the claims relating to
the equipment performance.
Should the system designer select fail-safe equipment, it
should be noted that fusible link ventilators do not meet the
requirements of ‘fail safe’ — there is no requirement for a
secondary power source. Fail safe come with their own set of
unique challenges and are no longer the first-choice solution
for most designers. The installation of power closed / power
open ventilators has many challenges, which we discover
as we work through this portion of the code. A pertinent
question would be the integrity of the electrical reticulation
system between the SHEVS control panel and the ventilator’s
actuators. It is important when solving a problem, that
associated new problems relating to power closed / power
open systems are not ignored. Batteries and generators
forming part of the secondary power source must comply
with the code requirements.
Part 10 delves into the requirements relating to pneumatic
systems, which do not form part of this topic. In South Africa,
pneumatic ventilators are seldom a requirement; I am not
aware of a locally produced EN 12101:2-certified ventilator in
South Africa.
www.hvacronline.co.za
I want to explore this somewhat: Should a power failure occur
and the actuators on the ventilators are isolated, is the control
panel consuming power? The panel is definitively consuming
power, but this does not mean that the secondary power
source, if batteries, are not being discharged. The electrical
control consumes power once the system goes live. The
internal control circuit constantly monitors the fire signal, LEDs
consume micro amounts of power, and the batteries drain.
All these possible scenarios form part of the certification
and testing. The designer needs to ensure diligence when
specifying; checking during commissioning that the system
contains all the correctly specified components and plug-in
items — as an example, batteries when the certification was
achieved. Every certificate issued comes with a complete set
of detailed certified results, which give a complete equipment
and component breakdown of the certified product. All claims
relating to current usage and performance after the 72-hour
‘power off’ scenario are detailed and tested; this requires
checking before specifying. If the supplier is unwilling/unable
to produce the test results and the components tested, the
designer will struggle to mitigate his or her decision to use the
equipment as part of the SHEVS system.
Addressing the monitoring of the cabling going into the
field should be a question raised when selecting control
panels to power ventilators using power closed / power
open actuators. A damaged cable that is unmonitored
cannot be brought to the attention of the building
RACA Journal I January 2019
73