The need for Ventilation

Everyone knows that humans need fresh air. Beyond this fundamental understanding, only some people give the subject very much thought. As a result, it tends to be passed over when considering buildings, environmental performance and the myriad issues which drive retrofit practice. Once again, however, building performance evaluation has highlighted how important ventilation is and how intricately related it is to all manner of problems within the industry and the practice of retrofit. Solve ventilation, and you solve, or at least alleviate many other problems.

The 2006 Approved Document F (Building Regulation in England and Wales) contained a handy graph that no longer features but showed clearly why ventilation is needed and the relative importance of the various pollutants noted. For most people, it is no surprise that the most significant reason we need to ventilate is to remove moisture, but it is a surprise that following close behind is the need to remove volatile organic compounds (VOCs) and other gaseous pollutants emitted from the many synthetic and treated elements of a modern house. At roughly half the significance is the need to control body odour and nitrous oxides from cooking and combustion. By far the slightest reason – but important! – is the need to replenish the oxygen we’ve transformed into carbon dioxide by breathing. There are other recognised benefits of ventilation, not least cooling in warm weather and distributing warmth throughout a home. Still, these aspects tend to be considered as secondary to the primary role of extracting pollutants.

The graph is also helpful in reassuring those who believe that building airtight homes will somehow lead to a reduction in oxygen levels for breathing! A house that is so airtight and poorly ventilated is yet to be built that it will lead to life-threatening oxygen levels. Far more important is that many properties have been built or retrofitted which are sufficiently airtight and poorly ventilated that humidity, air quality linked to VOCs, body odour and NOx (cooking) have become serious problems.

A second diagram (above) relates to office buildings. Still, it provides some more insights into ventilation, which are worth mentioning, mainly because of the increased mechanical and often ducted ventilation systems in housing.

The diagram is based on work by Danish building services engineer and researcher Ole Fanger and features the unit known as the “Olf.” Coincidentally similar to Ole Fanger’s name, the word derives from “Olfactory” and describes an amount of air which needs to be removed by the ventilation system to maintain adequate air quality. One ‘Olf’ represents the pollution provided by one person and is an amalgam of moisture generated, body odour, and carbon dioxide. The significance for the ventilation industry is that in any given room, 1 ‘Olf’ needs to be removed for each person in the space. The diagram is based on a typical office in Copenhagen and shows 17 people in a room, so the ventilation system will need to remove 17 ‘Olfs’.

Off-gassing

However, that is only part of the system it must cope with. If everyone in the room smokes, the system capacity has to be tripled to maintain adequate air quality (the work was done in the 1970s and ‘80s when this was more common) while it additionally has to increase capacity again, by almost the same amount, to cope with the off-gassing of synthetic materials and furniture in the building, along with cleaning products etc. Once again, this shows that while most people do not realise the importance of off-gassing of materials, it is a recognised and serious issue and why we emphasise natural and non-toxic materials in this guide. Finally, the punch line is that the ventilation system itself is the source of the largest amount of pollution because the intake ducting is rarely, if ever, cleaned and becomes very dirty, harbouring
an array of pollutants. It must be emphasised that these ventilation systems were air conditioning systems where the air was heated, cooled, humidified and de-humidified. Hence, it is not directly comparable to the simple air ducting of most domestic properties, but the lessons to be learnt are obvious.

Whilst the example is of an office, not a house, and the ventilation is air conditioning, it is hopefully apparent that the risks to health in homes
are similar; people are quite at liberty to smoke in their own homes, all modern buildings contain an equivalent spread of synthetic materials and finishes that off-gas in just the same way, while ducted air systems are becoming more common and maintenance of these is unlikely to be any better. Once again, it shows the importance of maintenance and its complex relationship with energy efficiency and health.

Making it better

A further lesson that can be learnt from this diagram is that if we remove smoking from the equation, use only non-toxic and natural materials and finishes, and either avoid ducted air systems or ensure that they are well cleaned and maintained, then the potential to reduce the need for ventilation – and the associated costs and energy losses – is enormous.