Ventilation Technologies

Ventilation is essentially the replacement of stale or noxious air with fresh air. This can be done by just mixing the air so that the contamination is reduced; by directing an airflow across the premises or by pushing the air upwards in the premises. Some common terms are:

Mixing ventilation - This is standard ventilation whereby fresh air is brought into the premises and stale air is taken out. The fresh air quickly dilutes the contaminants in a well designed system. Siting the supply and extraction points closely together can make this much less effective, as the airflow goes straight from one point to the other failing to effect most of the rest of the room. This is commonly called ‘short circuiting’.

Directed ventilation - This brings in fresh air at one side – or in one part - of the premises and extracts it at the other side or part. This can work well for small premises but may not be possible in larger premises due to the resistance of the air in the middle of the room. In these cases air cleaners or ceiling fans seem to help the distribution and effectiveness – but this then becomes essentially mixing ventilation. It is important in smaller premises to distribute the air evenly so that draughts are not created.

Fabric diffusers can be a very good way of avoiding draughts. These ‘spread’ the airflow out, increasing its effectiveness and reducing its speed. ‘Four-way’ supply diffusers are commonly used and fabric diffusers (essentially ducts make from fabric rather than steel) can be very effective especially in smaller spaces.

This technique can be highly effective at preventing smoke drift into non-smoking areas as can be seen in the Black Dog study.

Displacement ventilation - This system usually integrates the heating and cooling into the air quality system rather than running in parallel to the ‘wet’ (radiator) system. This idea is to bring slightly cooler air in at ground level and extract the warmer air towards the ceiling. The air warms as it rises taking the contamination with it.

A common problem is that rooms have one or more extract fans but no supply ventilation, and so are quite ineffective. If some supply ventilation is added the systems will create a much better airflow carrying contaminants towards the extracts and replacing them with fresh air.

The aim is to replace the air in the room a number of times an hour (‘air changes’) with fresh air – the higher the level of smoking the greater rate of air change required. In reality ventilation does not work as simply as this as the distribution of the air (where it is sent from, and to) can be as important as the amount of air.

To see some different types of ventilation and their costs, please click here to read case studies based on UK pubs.