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DAYLIGHTING & VENTILATION 3 Wind-driven (or wind-induced) cross ventilation, where pressure differences between one side of the building and the other draw air in on the high pressure side and draw it out on the 1 low pressure side.

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Buoyancy-driven stack ventilation (the stack effect), where cool air enters the building at low level, is heated by sources inside the building (people, equipment, heating systems etc), becomes less dense and therefore rises through the building to be ventilated to the outside at the top The design of natural ventilation systems can be complex because of the interaction between wind ventilation and the stack effect, as well as the effect of building geometry and the distribution of openings. This can require analysis using computational fluid dynamics.

central atriums to control the flow of smoke into the mall or atrium.

Shopping malls and office complexes

Maintaining a clear layer below the smoke is another critical factor. It needs to be high enough to keep escape routes clear. This can have a bearing on the design of smoke barriers which can affect building usage.

...are busy and often multi-level buildings requiring high levels of natural daylight and often with complex requirements for smoke and heat exhaust ventilation.

Natural ventilation can also be influenced by occupant behaviour, for example, a person near to a window choosing to close it. For this reason it can be beneficial to automate natural ventilation systems, or to provide training for occupants.

Ensuring a supply of replacement air is another essential aspect of system design. As smoke and gases are extracted, sufficient fresh air needs to be introduced to take their place. Without this fresh air supply, the building will become depressurised and the smoke ventilation system will be ineffective.

Integrated smoke ventilation systems Natural ventilation systems can also be designed to incorporate smoke and heat exhaust ventilation systems (SHEVS) to remove smoke from the building in the event of fire. SHEVs allow low level escape routes to be kept clear of smoke as well as reducing damage to the building. System design must take a variety of factors into account which will be specific to the building. With large roof spaces, for example, it’s important to limit the spread of smoke. This requires high level smoke barriers to divide the roof space into individual smoke containment reservoirs. Smoke barriers are also often used in shopping centres and buildings with

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Mar/Apr 2017

1. Louvred ventilators allow clean fresh air to be drawn in to replace stale air 2. Fixed louvres and roof ventilation terminals to exhaust stale air and fumes 3. Dual purpose louvred ventilators can provide both smoke & natural ventilation and can be integrated into rooflights

It should be noted that when considering any smoke ventilation system design, it is important that it carries full BS EN12101 Certification. Beware of terms like ‘in accordance with BS EN12101’. These claims do not necessarily mean that a product or system has actually been tested to BS EN12101 – and that in turn can mean that a specification made in good faith could actually be non-compliant and therefore potentially dangerous. To safeguard yourself, your client and your client’s building occupants, you need to be 100% certain of compliance. www.lareineengineering.com

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DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

DAYLIGHTING Magazine issue 3 March/April 2017  Daylighting magazine mar apr 2017:2  

The bi-monthly magazine for architectural specifiers and technicians, building contractors and anyone interested in the provision of natural...

Profile for bb2b