Quantification of aerosol losses in mechanical exhaust and balanced air flow ventilation systems

Abstract

Highly-efficient balanced air flow ventilation systems increased from 5 to 50% in markets hare within six years for new residential buildings in The Netherlands. This success is based on the contribution of the system to energy performance in combination with cost effectiveness. Occupants¿ complaints indicate that installation and maintenance quality need further improvement. One of the complaints relates to particle deposition. For better understanding of the impact of ducted air on particle distribution, experiments were performed with a full scale system in a test chamber. The presented results focus on aerosols deposition in the heat recovery unit and in the ducts, including components like dampers, sound attenuators, tees and bends. The deposition was measured under different ventilation scenarios, for the particles of size range 0.7-15 micrometers. The results show high deposition rate: 10-40% for total number concentration and with over 80% deposition of the larger particles. The ventilation unit and the air transport components function as one large filter, even in a scenario when no filter was applied. The overall effect is that the air at inlet dampers in the chamber contains less particles, especially in the larger size ranges (>PM1). A remarkable but preliminary result is that in components with large variation in air velocity, for instance in sections with turbulent flow, the particle concentration is higher. The deposition is not stable: aerosols are both deposited and released, possibly as a result of these turbulent flows. This effect raises questions about the location of filters. As filters and ducts seem to have a similar effect on aerosols concentration, and filters at the air intake location do not prevent deposition in the ducts, the deposited layer still influences air quality. The recommendation is to give attention to filter systems in the inlet dampers in the occupied space as well.