- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 18 Sep 2018
To help develop this article, click 'Edit this article' above.
Ventilation is necessary in buildings to remove 'stale' air and replace it with 'fresh' air.
This helps to:
- Moderate internal temperatures.
- Reduce the accumulation of moisture, odours and other gases that can build up during occupied periods.
- Create air movement which improves the comfort of occupants.
Very broadly, ventilation in buildings can be classified as 'natural' or 'mechanical'.
- Mechanical (or 'forced') ventilation tends to be driven by fans.
- Natural ventilation is driven by 'natural' pressure differences from one part of the building to another. Natural ventilation can be wind driven, or buoyancy driven. For more information, see Natural ventilation.
- The building is too deep to ventilate from the perimeter.
- Local air quality is poor, for example, if a building is next to a busy road.
- Local noise levels mean that windows cannot be opened.
- The local urban structure is very dense and shelters the building from the wind.
- Air cooling or air conditioning systems mean that windows cannot be opened.
- Privacy or security requirements prevent windows being opened.
- Internal partitions block air paths.
- The creation of draughts adjacent to openings.
'Trickle ventilation', 'slot ventilators' or 'background' ventilation can be necessary in modern buildings (which tend to be designed to be almost completely sealed from the outside to reduce heat loss or gain), so that problems such as condensation are avoided when openings are closed.
This tendency to 'seal' modern buildings can also adversely affect occupant comfort, as generally, occupants feel more comfortable if there is some air movement (as long as draughts are not created). This situation can be mitigated by heat recovery ventilation (HRV). This permits increased ventilation rates by recovering heat from extract air and using it to pre-heat incoming fresh air using counter-flow heat exchangers. Heat recovery is increasingly common in mechanical ventilation systems. It is also possible, although complicated with some natural ventilation systems.
Ventilation systems may also include heating, cooling, filtration and humidity control. The acronym HVAC refers to Heating Ventilation and Air Conditioning. The phrase 'air conditioning' refers to the process of conditioning the temperature and humidity (and sometimes the quality) of air before using it to ventilate a building. Air conditioning and cooling are not the same, although the terms are often used synonymously by non-professionals.
Rates of ventilation in buildings can be expressed in terms of air change rates (the number of times that the volume of air in a space is changed per hour) or litres per second. The ventilation rate will be determined by the type and size of space and the way it is occupied (for example, the number of occupants, sources of heat, moisture, odour, contaminants, and so on). Ventilation in buildings is regulated by Part F of the Building Regulations.
Whilst there are simple 'rules of thumb' that can be used to design straight-forward ventilation systems, more complex systems may require analysis using environmental design software. Modelling air flow patterns is particularly complex requiring the use of computational fluid dynamics software. This is complicated further by the interaction of ventilation systems with thermal mass, solar radiation, and so on. Whilst there are software packages that can be used for this sort of analysis, the results they produce are very dependent on the way that models are set up, and this requires a great deal of expertise and experience.
 Find out more
 Related articles on Designing Buildings Wiki
- Air change rates.
- Air conditioning.
- Air handling unit.
- Air infiltration.
- Air infiltration testing.
- Approved Document F.
- Background ventilator.
- BREEAM Potential for natural ventilation.
- Computational fluid dynamics.
- Cross ventilation.
- Dew point.
- Displacement ventilation.
- Domestic ventilation systems performance.
- Heat recovery ventilation.
- Indoor air velocity.
- Locating ventilation inlets to reduce ingress of external pollutants into buildings: A new methodology IP 9 14.
- Mechanical ventilation.
- Natural ventilation.
- Passive building design.
- Preventing overheating.
- Retrofit, refurbishment and the growth of connected HVAC technology.
- Stack effect.
- Thermal comfort.
- Underfloor air distribution.
- Vertical riser.
- Whole building ventilation.
Featured articles and news
RIBA launches a consultation on a new Plan of Work for Fire Safety.
This article offers some basic rules to follow when writing your next specification.
The iconic Mackintosh Building will definitely be rebuilt, board chairwoman confirms.
The machinery used to fashion stone has changed dramatically - and so have the products.
This type of pile provides support to the building, as well as acting as a heat source and a heat sink.
Why investors are adopting the SDGs and why civil engineering could be crucial for delivering them.
Read about all the winners from the London ceremony of CIAT's 2018 Architectural Technology Awards.
How do you find the right stone to conserve historic buildings?
Appointment agreements often include a ‘scope of services’ setting out the consultant's performance on a project.
BSRIA study shows an increase of pre-terminated fibre connectivity.
Director of PiP Architecture explores the application of biophilic design principles.