Reliable Forced Air Cooling for Telecommunications Equipment

Free convection cooled equipment racks used by British Telecommunications plc (BT) have an effective limit for system power dissipation density of approximately 2 W/litre. Power densities in excess of this which result from increased levels of system integration are most conveniently cooled by forced convection but the possible problems of reliability, maintenance, acoustic noise and capital cost must first be considered. Theoretical and practical work undertaken at British Telecom Research Labs (BTRL) has addressed these ¿roblems and a prototype rack has been designed and tested which allows power densities of up to 20 W/litre. This system utilizes independent fan modules used in parallel, together with replicated monitoring and alarm circuitry. Reliability calculations suggest a cooling system MTBF of 1200 years. Fan control electronics allows acceptable performance to be maintained at minimum battery voltage or when individual elements of the cooling system have failed. Optimised airflow design minimises acoustic noise and fan power requirement.