Upgrading of the Air-conditioning of the Computer Room in the Computer Centre for the LHC era

Built in the beginning of 1970's, the Computer Centre air-conditioning and cooling systems were designed to be modular and easily adaptable to the unpredictable future needs of computing. The infrastructure of LHC-computing that will be housed in the existing Computer Room with its five Computing farms and over 11000 PC's increases the requirements of cooling and air-conditioning power to a new level. The nominal thermal loads from the equipment rise from the current design maximum of 1MW to estimated maximum of 2MW in the future. This paper presents calculations and proposes solutions to meet the new nominal requirements. The air-conditioning system must also be able to cope with a situation of power cut in the main supply. A calculation of the temperature evolution during the power cut and a justified operation strategy for this scenario is also presented.