St Paul Travellers building was served by a Carrier Moduline VAV system, installed over 20 years ago. The system comprised a 12 meter long variable air volume air handling unit, complete with supply and recirculation fans, each of which incorporated motorised inlet vanes to vary the air volumes. Cooling was supplied by two Carrier air cooled water chillers, utilising the refrigerant R22, incorporating semi-hermetic, reciprocating compressors.

The AHU was suffering severe corrosion, and required urgent replacement. In addition, the client had specific requirements, due to the construction of a new computer room facility, requiring roof space for a large electrical generator, and the reconfiguration of electrical power supplies for this facility.

We therefore recommended that the two air cooled water chillers be replaced by one Daikin twin screw machine, having the same footprint as one of the original water chillers, but with increased height, therefore leaving sufficient space to install the new electrical generator in the space occupied by the second original water chiller.

The high level, chilled water pipework was reconfigured into one single circuit, enabling the removal of a number of unsightly gantries.

The new AHU incorporated new inverter drives to the supply and recirculation fans, as well as all new motorised dampers, chilled water and heating control valves. The existing control panels were modified to accept the new controls and inverters. Power wiring was revamped, giving some 150 amps per phase back to the client for other uses.

As this was a fully occupied building it was essential that the downtime of air conditioning plant was kept to an absolute minimum. The old equipment was turned off on a friday afternoon. The new AHU was providing fresh air on the monday morning and the water chillers came on line on the wednesday. Therefore the entire change-over was carried out in under five days.

Change-over completed in 48 hours.