The present invention related to cooling systems. More specifically, the present invention relates to a system for cooling one or more parts of a building and or processes comprising a compressor, a condenser having an inlet and an outlet and a plurality of condenser cooling fans, a receiver, a liquid refrigerant pump, an expansion device, an evaporator, the evaporator being surrounded by a chiller barrel having a cooled water return and a chilled water supply line, and refrigerant line means interconnecting the compressor, condenser, expansion device and evaporator in series, in a closed loop for circulating refrigerant therethrough; means for switching the cooling system between free cooling and mechanical cooling and means for actively floating the head pressure in both mechanical and free cooling modes.