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Home » Smoke exhaust – it’s serious – Power supplies for SHEVS systems

Smoke exhaust – it’s serious – Power supplies for SHEVS systems

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By Ron Burns

When technical and/or sales advice is given, particularly regarding smoke and heat exhaust ventilation systems (SHEVS), how diligently is that information checked?

Ron Burns - Bio

When is a door not a door? I suggest we explore that a little later …

The manner in which suppliers present information into the market comes in many shapes and forms, in an attempt to gain and enjoy market share.

“Cognisance of all possible system faults must be addressed when selecting equipment and components to deliver a working SHEVS system.”

What if I were to extend an open invitation to any reader to join me for a ride in my car, promising that it would be a once-in-a-lifetime experience? I wonder how many volunteers I would have. Having read Lewis Hamilton’s book on how to drive a racing car at high speed, I think my credentials are great for this endeavour. I would offer one lucky person the opportunity to be my passenger as I drive my car at 237km/h in accordance with Hamilton’s book. I have read the book, checked the oil levels and tyre pressure, and I imagine the queue is forming to take me up on this.

Then I step up to my Atos 1 100cc and suddenly, I am met with many a puzzled look. The first question is: how is he going to get that car to 237km/h? Not a problem, I say; we are going to drive down a mine shaft, cornering won’t be an issue, and there will only be one bump, right at the end. The car is specifically prepared: airbags removed to lighten the load and to increase the possibility of reaching the desired speed. At this point, I imagine there is a lot of head-shaking and mutterings that cannot be put into print. The fact is, what I do ‘in accordance with’ anything, is useless. Who is really interested in ‘according to’ when an independently tested and certified component exists? (I do like my car and I am holding thumbs no one wants the driving experience.)

When technical and/or sales advice is given, how diligently is that information checked?

I am currently inundated with quotations claiming that control panels are ‘certified EN 12101-9 control panels’. My search on the BSI website returns a message informing me they are unable to match my search — the code has not been promulgated. I had a discussion with this specific contractor four weeks ago; he asked for the weekend to get me the information. Weekends have come and gone, and a certificate is yet to be produced. Shall I use the panel on the strength of the quotation? Would I be able to explain away a failure should the system experience one when required to operate?

A door is not a door when it is ajar. Would the control panel offered be a jar? An empty vessel when I require performance? Most definitely a childish approach, carefully playing on words. However, this practice is rife in our industry with many customers happily purchasing components that have been marketed as ‘certified’, ‘in accordance with’, or (in this instance) without the code referred to even being promulgated.

Over the past five years, the SHEVS ventilators have received the lion’s share of the scrutiny while other system components have sailed under the radar. I would like to start 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.

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]

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.

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.

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]

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 maintenance engineer; this can render the entire system unserviceable, depending on where the cable fault occurs. Cognisance of all possible system faults must be addressed when selecting equipment and components to deliver a working SHEVS system.

“Every system designer should safeguard against equipment without certified documentation supporting the claims relating to the equipment performance.”

One would never try to fill a 150mℓ wine glass with a 750mℓ bottle of wine; how is it possible for a designer to select a 12-amp panel to power a 16-amp ventilator load? It does not have any bearing on the information produced by the supplier indicating internal testing regimes. The panel needs to be certified to meet the claims made. Live system testing in a workshop is not comparable to testing in a certified test house. The impact is worse when making assumptions without certification when it comes to large-scale fan exhaust systems where cable performance in live commissioning tests at ambient temperatures negate the effect of elevated temperatures on the current-carrying capacity of the same cable at elevated temperatures. The excessive volt drop impedes current flow, which causes excessive lower voltage being supplied to the motor, resulting in motor failure. Caution and diligence are required for all things electrical.

Every system designer should safeguard against equipment without certified documentation supporting the claims relating to the equipment performance. Time constraints leading to hasty, inadequately researched solutions always find enough time to nitpick at decisions made, after an event. Additional time spent ensuring fit for purpose, suitably certified equipment saves disasters from occurring and hours of unproductive time.