Air flows, air change rates and air quality
The term ventilation is basically understood to be the removal of old, stale air from a room or a building and its replacement by fresh, clean air. Unfortunately, strong focus is often placed on sizes of air flows and air change rates, when we should really be addressing the question of air quality. The number of air changes normally required to ensure a healthy indoor climate and fresh room air, at least when airborne cooling is used, is considerably fewer than those needed to achieve a good thermal climate.
Two conditions that must always be fulfilled, however, are that the air introduced into the building is as clean as possible and that the building materials are chosen so that undesirable and dangerous emissions are minimized. Materials that are quality assured, i.e. emission-tested, are now widely available on the market. If we cannot master the generation of pollutants indoors, this could mean that the ventilation system will have an impossible task.
We must also master the removal of surplus indoor heat, normally achieved with the help of rather expensive and energy-demanding cooling systems. This is an area that requires the involvement of a number of the players engaged in the building process, not least of the architect. Increased awareness about limited energy resources and the environmental consequences of high energy uses will soon necessitate radical changes in the way in which these issues are addressed. New solutions will undoubtedly arrive on the scene, hopefully, too, for cleaning indoor air.
Air is often associated with a sense of well-being
We have all experienced that feeling of relief, while sitting in a hot plane and waiting for it to take off, when the air starts flowing from the over head nozzle, or that feeling of well-being created by a gentle and soothing breeze on a summer evening.
Ventilation is all about removing polluted air – either literally polluted or air that is just uncomfortably warm – and replacing it with clean, fresh air at the right temperature. Air cannot, however, be freely introduced into a room. For example, to avoid draughts, both its temperature and speed in the occupied zone must be acceptable. This means placing demands on the design engineer and the products used in the ventilation system. In buildings where there is a heat surplus, air will have to be supplied at an under temperature. To do this without causing draughts, the correct types of supply air terminal devices will have to be used. They will also have to be correctly located and properly aligned, so that the discharged air jets cannot collide with obstacles such as light fittings and columns.