Distribution park plant replacement, East Midlands

The challenge

A fit-out contractor was replacing the building services plant at two large units on an established distribution park, four new units in total, capable of running around the clock. Planning needed a noise assessment before the application went in.

The timing was the difficulty. The council publishes no numerical guidance for plant noise, so there was nothing to design to. And the equipment had not been chosen yet, so there was nothing to assess. The contractor did not want a compliance test run after the units had been ordered and installed, which is when a problem becomes expensive. They wanted the acoustic envelope defined up front, as a constraint the mechanical designer could buy against.

What we did

We monitored at two positions over two days, deliberately placing the equipment no closer to the main roads than the nearest homes are. That biases the measured background downwards, which makes the resulting limit tougher than it strictly needs to be, which is the right way round to be wrong.

With no local criterion to adopt, we set a conservative one ourselves: the plant should sit clearly below the background already present, rather than merely matching it.

The useful step was then running the calculation backwards. Instead of reporting a limit at the neighbours, which no supplier can quote against, we converted it into the single number the equipment has to meet at ten metres, the figure that appears on a datasheet.