Case Study: Effect of mechanical short-circuiting of isolation pads on rooftop equipment noise and vibration transfer to spaces below.

Abstract

The authors conducted investigations into noise from large rooftop air source heat pump (HP) equipment to student housing units below in a new concrete building. The investigation included both airborne noise and vibration measurements on the roof and in the dwelling units below. A total of five, 18-Ton devices were mounted on a foam-filled concrete housekeeping pad resting on an 8-inch thick PT structural slab and isolated by means of spring mounts fitted with neoprene isolation pads below their baseplate. The dwelling units below had exposed concrete at the ceiling, shear walls, and columns. Noise from the HPs were waking residents in the units directly below the equipment. After a number of adjustments to the spring isolation mounts to eliminate bindings and mechanical short-circuits, the investigation showed that vibration was also being transmitted to the building structure from the isolator base plates through the anchor bolts, bypassing the noise pads below the baseplate. Removal of this secondary short-circuit resulted in noticeable reductions in both noise and vibration at the spaces below, highlighting the need for careful adjustment and the provision of additional isolation elements in the installation.