When modernising a city centre underground car park’s ventilation system, the owner wanted to improve air quality and improve efficiency to reduce energy costs. To achieve this, the new system needed to provide a dynamic response to actual vehicle movements.

The fume extraction ventilation system consisted two centrifugal extraction fans located in a common plenum chamber of a chiller room and two axial supply fans in an adjoining corridor area. Both sets of fans operated in duty, standby configuration.
Two ABB 37 kW drives were used for the fume extract fans, and two 22 kW drives for the supply fans. All were rated at IP54. The two extract fans are supplied with separate mains power from a new junction box installed outside the plenum chamber in the chiller room. A motorised damper was controlled from a relay controlled from within the duty VSD.

Carbon monoxide sensors

Once the damper has opened, a start command is then sent to the VSD. A carbon monoxide (CO) Once the damper has opened, a start command is sent to the VSD. A carbon monoxide sensor is installed adjacent to each VSD. This detects the CO level in the plenum chamber and sets the speed of the drive proportional to the CO level, with 50 ppm being 25 Hz and 100 ppm being 50 Hz. If the detected CO is below this level, the duty fan will operate at a fixed frequency of 20 Hz.

A 4-20 mA frequency dependant control signal is derived from each VSD running the extract fans. These signals are transmitted via the original cables to the new junction box and from there again via existing cables to the supply fan VSDs. Firstly, the signal is used to operate a supervision relay to start the VSD via the digital input. This signal is also used to tell the VSD how fast to run to match the extract fan speed.

When complete, the system had achieved all the objectives set by the owner. Ventilation was improved, and overall energy consumption reduced. In addition, noise levels in the chiller room were also reduced.

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