How do you silence a sewage-pumping station in a growing urban neighborhood? Just ask BKL.
Take the Royal Avenue Pumping Station in New Westminster, BC, for example. Originally built in 1977, the station was upgraded and finished in the winter of 1995 by the Greater Vancouver Sewerage and Drainage District. The project’s prime consultants, Kerr Wood Leidal, oversaw the design of a visually pleasing, tree-encircled station that features an activated charcoal odour-control system and a 125 kW emergency generator. BKL was tasked with designing noise-control measures that would meet the City of New Westminster’s stringent bylaw and keep the neighbours happy. That meant reducing generator noise—measured at 104 dBA inside the generator room—to less than 55 dBA at the nearest property line, 10 metres away. Also, the odour control and building ventilation systems, which operate 24 hours a day, couldn’t exceed 45 dBA. Adding to the challenge, space requirements limited potential solutions.
Emergency Generator Set
First, BKL identified the primary noise sources related to the emergency generator set: the cooling air intake, the cooling air exhaust, and the combustion exhaust. Because the genset’s radiator fan can accommodate very little static pressure, a large attic plenum space was designed to curtail noise from the cooling air intake. To reduce noise levels from the cooling air exhaust, BKL commissioned two specially-designed acoustical elbow silencers that were installed between the genset’s radiator and the building exhaust louvres. These silencers have very low pressure drop with an acoustical insertion loss matched to the specific genset. The combustion exhaust was also fitted with an acoustical muffler.
Odour Control and Ventilation
The odour control system consists of a high static pressure fan between a wet well and a carbon bed. Although the carbon reduces exhaust noise, BKL recommended a silencer between the outlet of the carbon bed and the building exhaust louvres. To meet the rigorous noise bylaw, BKL’s design also included sound seals on all doors, acoustically constructed ceilings and exterior walls, and silencers for the building ventilation exhaust.
Outcome
With BKL’s noise-control design installed, the sound level measured one metre from the exterior exhaust was 64 dBA—a substantial 40 dBA reduction. At the property line 10 metres away, the resulting noise level was below the ambient level. The final inspection attests to the overall success of the design—and specifically, BKL’s contributions—noting that the “… noise reduction measures are extremely successful. With the genset operating, no noise is detectable on north, east and south sides of the building, while at the west property line (the side where the exhaust louvres are located), only a faint hissing noise is audible.”
* Photos courtesy of Kerr Wood Leidal Associates Ltd.