A specialist VRF air conditioning system has been developed for the Crossrail project to provide high resilience cooling for its new underground facilities. The system was developed by a project team made up of representatives from Toshiba Air Conditioning UK and Crossrail engineering staff, which provided the solution for contractor Laing O’Rourke. It will be used to provide a high quality temperature-controlled environment in ticket halls, station control centres and equipment rooms.
Key design challenges were meeting London Underground’s strict fire safety requirements, and integrating refrigerant leak detection and management systems to ensure the safety of workers and the public. Also important was the ability to deliver fine control of temperatures to ensure a stable environment for people and equipment, with low power draw on equipment start-up. After analysing the required specification, and identifying variances with existing standard air conditioning systems, the partners developed and tested a bespoke system to meet the precise requirements. The London Underground fire-prevention code places strict limits on the use of plastics below ground. The team carried out a detailed evaluation of all components in Toshiba’s indoor units. It resulted in the drain pan being replaced with an all-metal version, and several other components – such as fans, motors, controls and insulation – being replaced with non-plastic alternatives.
The system is equipped with Toshiba’s new integrated LD2 refrigerant leak detection and management technology, which constantly monitors refrigerant charge in relation to performance. In the unlikely event of a leak, it sends an alarm signal and automatically isolates the site of the leak, preventing further loss.
Low power draw on start-up is ensured by the use of Toshiba’s inverter system, which allows the system to be controlled in fine increments of just 0.1Hz. With the use of Toshiba’s twin rotary compressors, this also enables the system to operate at very low loads, when cooling demand is low. This suits the demand profile of the equipment rooms in which the systems are installed, which was a focus of Crossrail’s engineering team. The equipment was tested and certified to CE standard at a third party facility.
The result is a unique VRF system for use in underground and sensitive applications. In the Crossrail projects, the VRF condensing units connect to bespoke floor / wall-mounted and ceiling-suspended indoor units. Toshiba is supplying some 30 of the specialist units to Laing O’Rourke, to be installed by contractors Conair UK Limited and Skyline Air Conditioning Limited. It is believed to be the only VRF air conditioning system currently available that meets the strict requirements for use on London Underground.