Powerplus Engineering

The Challenge
To house 2 off 2000 kVA diesel powered standby generator sets within a limited space on the first floor of a prestigious office building in the heart of London. The location within the building was space commandeered from an active first floor office. This meant low noise level requirements in the adjoining office space to two sides, in the floor above, the floor below and externally to the building façade which faced residential flats.

Engine exhaust emissions were a concern due to the close proximity of pedestrian routes and limited access to a high level discharge

City of London required that the noise emissions from Moore House did not exceed the prevailing background levels at the nearest noise sensitive receiver by more than 1 dB. It was determined that to achieve this the noise emitted from the plantroom should not exceed 65 dBA at 1 metre from the cooling air inlet and discharge louvres with both generators running together at full load.

The Solution
In close collaboration with its client, Powerplus Engineering designed a bespoke acoustic enclosure complete with acoustic base which was also bunded to ensure no fuel or coolant leakage from the generator engines could affect the integrity of the building. The enclosure, base and cooling air attenuators were manufactured for on-site assembly as access was severely restricted. Cooling air attenuation was achieved within the space constraints by using two stage splitter type silencers, the main assemblies being attached directly to the enclosure with the secondary units attached directly to the building ventilation apertures. Because of height restrictions, the exhaust silencers were also fitted in two stages, one within the enclosure and one between the primary and secondary cooling air attenuators. Exhaust emissions were taken care of by fitting 2 stage catalytic exhaust purifiers and a flue dilution system between the cooling air outlet and the weather louvres.

The Result
External to the building at 15 metres distance from the cooling air inlet and outlet louvres the background level was measured at 59 dB. The same level was measured with both generators running on load proving them to be inaudible in normal operation. Within the building levels measured did not exceed NR 45 either in areas adjacent to or on the floors above and below.