HVAC Displacement System Noise Control – A New Method to Quantify Noise Control Performance

Abstract

For most of the 20^th century, performing arts venues and other rooms were ventilated with overhead supply systems.  In the early 21^st century, displacement systems seem to have taken over both in performing arts centres and offices.  They are thought by some as a new thing but their pedigree goes back to Roman times and perhaps beyond.  There are currently no recognised calculation or measurement procedures to calculate displacement system noise control.  This paper will try to address this issue.  It will focus on performing arts centres because that is what the author is most familiar with.  A typical displacement system for a performing arts auditorium or an office has a room or chamber below the occupied room.  The floor of the room above is then is either perforated with a series holes, or ventilation grills allowing the supply air to slowly ventilate upwards.  The existing air is displaced by the conditioned air, hence the name.  A new method has been developed to predict and quantify the combined behaviour of the chamber and the openings in the floor.  The concept is to consider near and far field components, combined in the same way that one might study direct and reverberant sound fields.  Measurements have been performed in three auditoria, two with acoustically lined chambers and one without.  The chamber and floor openings, combined, introduce approximately 20 to 30 dB of noise control isolation, although there are some pipe resonance issues around 200 to 400 Hz.  The new method was first implemented on Toronto’s Four Seasons Centre for the Performing Arts, with encouraging results.