To avoid the need to operate in-chassis fans to cool rack-mounted servers in a data center, the data center is arranged into a hot aisle and a cold aisle. The cold aisle is adjacent to a first side of the rack mounted servers and receives cold air from a cold air supply unit. The hot aisle is adjacent to a second side of the rack-mounted servers and has a lower pressure than the cold aisle. Because of the pressure difference between the cold aisle and the hot aisle, cold air flows through the rack-mounted servers, cooling electronic equipment therein, into the hot aisle. Control systems are used to obtain sufficient cooling.