Efficient work environment ventilation.

A breakthrough in ventilation research was made once it was realized that ventilation principles based on mixed flow patterns are not optimal and that further energy savings can be achieved if an alternative technique could be developed. Several researchers, particularly in the Nordic countries, have shown by theoretical studies that replacing mixed ventilation flow by displacement flow increases ventilation efficiency. This also results in decreased air supply volumes and thus decreased energy requirements. In addition, lower air velocities may reduce problems of comfort and noise. Soon, however, practical experience showed that a displacement ventilation system must be very carefully designed in order to work as theoretically expected. Not all systems were successful initially and difficulties were encountered in implementing the new technology. This paper discusses the design basics for practical displacement ventilation systems. An example is taken from a plastics industry, where horizontal displacement ventilation is applied to a real work environment situation. Field measurements are made. Results of the field measurements, carried out in the plastics industry, are surprisingly good. For a channel flow ventilation situation, an air change efficiency of around 80 % has been achieved. It is also shown that worker exposure to styrene vapor can be kept within acceptable limits. The results are affected by the room geometry and the nature of the air supply. The energy gains from high air change efficiencies are discussed, particularly with regard to cold climates where there are large heating requirements.