Reduction of rooftop-mounted air-conditioning condensing unit noise for a multi-family residential building using an iterative approach

In comparison to other building HVAC equipment, residential air-conditioning condensing units are small and relatively quiet. While they do produce noise and vibration, it can be easily controlled if noise is considered when placing condensers and if basic noise and vibration control strategies are incorporated into the building and HVAC system design. However, perhaps because they are small, relatively quiet, and ubiquitous, and because many multi-family residential building design teams do not include an acoustical consultant, the noise and vibration that these condensing units produce is often not considered when the building is being designed, resulting in noise complaints after the building is occupied. For a recent project, this situation and the general contractor's need to mitigate the noise for minimum cost, lead to an iterative approach to reducing condensing unit noise transmission into the building. This paper presents that iterative approach and the benefit that was realized with each step. The as-built conditions are described, followed by the progressive measurements and analysis that guided the noise mitigation steps to a conclusion in which the recommended noise level criteria was achieved for the condominium owners living below the condensing units.