Ventilation is needed in buildings throughout the year – whether in the height of summer to cool down interiors or in winter to lower humidity in the air.

There are two types of ventilation you can choose from – natural or mechanical – to maintain a minimum of air quality, to remove heat or pollutants from the air and to increase air comfort by providing agreeable and perceptible air movement within interiors.

Ideally, one would opt only for natural ventilation to cut down costs and emissions but comfort and safety regulations in most countries mean that some mechanical system is required, especially in confined spaces without openings, even if used sporadically or left to the discretion of the user.

Natural ventilation can be conditioned also by building type and form, local environment and climate, topography and obstacles – natural or manmade – especially in urban conditions.

The real advantages of having natural ventilation are manifold:

  • LOW running costs
  • NO energy consumption
  • LOW maintenance
  • LOW initial cost
  • HEALTHIER
  • LESS hygiene problems with ducting
  • LESS hygiene problems with filters
  • LESS “unnatural” – psychological effect.

When thinking of natural ventilation, one can generally say that pressure will be positive on the windward side of the building and negative on the roof surface and on the leeward side, although wind-induced pressure distribution can be complex, especially if there are obstacles in the path of the wind.

To take advantage of this and to assist ventilation for the interior of buildings, openings should not only be well distributed and to the correct size but should then be connected to spaces capable of creating flow paths within the building.

Only then can air either be driven in from one side of the building and out through the opposite side,[1] in and out on the same side of the building,[2] or in and up within the building.[3]

There is another way to have natural ventilation circulating through the building and this can be done by humidity, known as cool tower or most commonly by temperature through a stack or Venturi effect.[4]

Cooler air, being denser, will enter from openings lower down the building and the success of this system is dependent upon the volume of air it moves through the building. The higher the stack, the greater the flow, a fact which can be seen in traditional and vernacular buildings where this method has long been used.

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Image Source: Okanagan College Centre of Excellence in Sustainable Building Technologies and Renewable Energy Conservation, 2010

Mechanical ventilation ensures constant air flow through the building and this is done by forcing air through ducting with or without the help of fans, thus using a lot of energy with consequent CO2 emissions.

In the end you might have to opt for hybrid ventilation – a mix of both types – with fans helping natural ventilation where climate conditions are poor.

In order to find out whether ventilation is efficient within your building you must be able to ascertain how many air changes are needed for your space to be comfortable.

This can be easily obtained from manuals relating the volume of air to the area you will be calculating for the number of people expected to be within that space in any one time.

But air flows are difficult things to ascertain with so many variants available, and there is never a perfect mix of all the above ingredients. Air can sometimes take shortcuts and it also can by-pass predicted flow paths and change abruptly direction from obstacles or lack of them.

So controls should be provided for the openings that are available, and preferably those which can be activated manually with or without automatic controls which can sense temperature or air quality, and it is preferable to leave the controls to the individual user.

Human beings are very good at determining their own comfort zones and usually have a pretty good idea how to control their own, and you might be surprised with the results.

By Silvia Pelham


[1] Cross-ventilation.

[2] Single-sided ventilation.

[3] Vertical ventilation.

[4] This occurs when warm air, less dense than cooler air outside, rises to the top of the structure and is expelled at that point.

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