At our recent webinar on the ventilation solutions for overheated corridors in apartment buildings webinar, I received some excellent questions during the Q&A section. Here you can see my answers to these questions, slightly edited for clarity.
There is also a recording of the webinar available.
Can you recommend a fire rated attenuator?
There is no standard fire rated attenuator that we are aware of. Our general approach is to apply some special spray coating or external cladding to a standard attenuator so as to provide that fire rating.
Do you have a formula for calculating battery standby capacity - depending on the number of variable operations of an AOV?
Yes. This is not based on the number of variable operations, but on the total Ampere rating of the ventilators on the system. The battery back-up unit is sized to charge the battery and to give an output sufficient to operate all ventilators together and the batteries are sized to give 1 hour of continuous operation on loss of mains power (when fully charged).
Is there any standard the smoke exhaust vents have to comply with?
This is the EN 12101 series of standards. EN 12101-2 covers natural ventilators and EN 12101-3 covers mechanical ventilators, so fan systems. There are also other parts of the EN 12101 system which cover ducting and power supplies, controls etc., so there is a lot of standardization in terms of ensuring that the products are suitably rated.
To prevent birds from getting into a building, is it possible to fit bird guards?
Yes, it is perfectly possible to fit bird guards and insect guards. Most manufacturers will have those available as standard options for their natural ventilators.
How disturbing might noise levels be at night?
Generally when we are looking at a new build, there will be a planning requirement which gives maximum external noise levels during both day time and night time. Those levels are normally designed in order to not significantly increase the existing minimum noise levels. So if we know what those noise levels are, we simply design the ventilation system so as not to exceed those noise levels, so effectively there is no disturbance at all, simply because the noise levels do not increase.
What is the longest corridor you can provide smoke ventilation and validate the design with CFD modelling?
The limitation is actually not the CFD modelling and the validation, since you can probably provide validation for any length you like. The limitation is actually in terms of what is likely to be accepted by Building Control, and generally it has been accepted in the UK that 30m would be the absolute maximum. In most cases people tend to limit themselves to about 20 to 25m but I think it would be very unlikely, certainly in the UK, that anything longer than 30m would be accepted by the Building Control.
Is it possible to predict fan performance for a fire rated fan when operating at normal temperatures?
Yes, we do know what its performance is at ambient temperatures. The volume flow rate does not change with temperature (although the mass flow rate does). In fact we select the fan based on duct pressure drop at ambient temperature as this requires the maximum motor power.
When all AOV’s close except on the fire floor and the stair vent, can other vents above the fire floor be opened in addition to those on the fire floor?
No: the last thing we ever would want to do is open ventilators on more than one floor. There are various reasons for this.
If we have a natural ventilation system, then there is a risk that we will spread smoke between floors, because we have no real control over where the smoke goes once it is in the shaft if we have various ventilators open.
If we have a mechanical system, then if we open more than one ventilator, then we will be in a situation where the flow is then shared between however many ventilators we open and therefore the flow on the fire floor, which is what we really need, will be much reduced.
So, no it is not acceptable and the system will always be designed so that we only ever have the one ventilator open. Of course the Fire Brigade can then come along and close that ventilator and open another one if they decide to as a manual operation.
Download the whitepaper which looks at the various solutions to combat overheated corridors.
If you missed our recent CPD-accredited webinar on this topic, you can watch a recording here.
Paul Compton is Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.