An investigation of Cooling Unit Performance on the London Underground Railway Network

In 2012 London Underground successfully installed two new innovative cooling technologies at Green Park and Oxford Circus. These cooling systems utilise bespoke platform air handling units (AHU’s) designed by London Underground for specific application in a tunnel environment. The units intake warm air dissipated by the trains as they stop at the stations. The air is cooled as it passes through specially designed water based cooling coils and then exhausted from the units directly onto the platforms where passengers are waiting. Building on this initial success London Underground has implemented a new R&D project to assess design options for the next generation of AHUs with the focus being on reducing whole life costs of future installations. One particular aspect of this R&D project was to investigate cleaning of the internal components of the units, which are subjected to air borne dust particles and therefore prone to performance losses. The aim of this investigation was to identify design options which reduce the maintenance requirements of the units and the need for regular track access, whilst maintaining the high cooling performance, thus providing significant cost savings to London Underground. The study of differences between dust accumulation patterns on various heat exchanger coil configurations and the resultant impact of the air side fouling on the coil heat exchange performance is the subject of this paper.