Developing strategies for better internal environments

David Mowatt of Lareine Engineering, discusses the dual roles of daylighting & ventilation in creating healthy and safe internal environments.

Every building, whatever its purpose, must provide a controlled internal environment that is protected from the variable and uncontrollable external climate.

The requirements of the internal environment will depend on the intended use of the building and this will naturally determine the requirements for the building envelope.

Generating and maintaining a controlled internal environment is a complex process and the design of the building envelope is an important factor in determining comfort levels and safety of occupants within the building, as well as the energy performance of the building itself.

Appropriate levels of daylight and fresh air are crucial to the success of a building and a balanced, holistic approach to design and specification of daylighting & ventilation systems will generally provide the best results.

Common pitfalls of poor daylighting & ventilation design are: poor energy utilisation, inadequate control of internal temperatures, poor air quality, glare and very importantly, compromised safety of building occupants. So it makes sense to consider all of these factors at an early stage of the building design.

Every sector provides specific challenges to the design and specification of daylighting and ventilation systems and every building needs to be considered independently.

The key advantage of a holistic approach is that system components can be specified to perform dual functions. Rooflights, for example, may be specified with integrated ventilators. Single-point supplier responsibility can also provide advantages in terms of cost and project co-ordination.

Natural comfort ventilation – naturally effective

Natural ventilation is the preferred solution for today’s buildings in many sectors, due to its energy efficiency. Natural ventilation requires no mechanical energy, which is why it’s such an attractive option to those looking to reduce their carbon footprint and save on power costs.

In addition to low running and maintenance costs, key benefits of effective natural ventilation include:

  • Improved wellbeing and increased productivity of building occupants
  • Improved environment for IT and production/manufacturing equipment, resulting in reduced maintenance costs
  • Pleasant internal environments support increased building usage and property values
  • Improved conditions for products and goods resulting in longer shelf life with fewer rejects

Natural ventilation falls into two broad categories, which may operate together or independently of each other:

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 low pressure side.

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.

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.

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

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.

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.

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.

Residential apartment buildings
…can be greatly enhanced by introducing high levels of daylight to public areas. They also present specific challenges for ventilation system design, with many dividing internal walls and high demands for safety, privacy and security of individual units.

  1. Louvred ventilators allow clean fresh air to be drawn in to replace stale air
  2. Roof ventilation terminal to exhaust stale air and fumes
  3. Central pyramid skylight delivers daylight to stairwell – with built-in AOV (automatic opening vent) panels for smoke ventilation is case of fire

 

Shopping malls and office complexes

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

  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

David Mowatt is director at Lareine Engineering