Data centre power and cooling is the equipment that carries electricity to every rack, keeps the servers running when the grid fails, and removes the heat that the servers produce. The industry calls it data centre infrastructure, or critical infrastructure. Without it, no server in the building could run for more than a few minutes.
Power comes first. Electricity arrives from the state electricity distribution company, the discom, often on two separate high-voltage lines. Transformers lower the voltage. The power then passes through an uninterruptible power supply (UPS), a large bank of batteries with electronics that convert the power. Power distribution units then carry it to each rack. Each server has two power supplies, fed by two separate paths, called A and B. If one path fails, the server keeps running on the other. This is redundancy.
Imagine that the grid fails at 3 p.m. at a data centre in Hyderabad. The UPS batteries take over at once, with no break in power, so no server notices. Within about 10 seconds, the diesel generators start. Within a minute, they carry the whole load, and the batteries stop discharging. The batteries need to last only those few minutes, though they are usually sized for 5 to 10 minutes to be safe. The generators can then run for many hours on the diesel stored on site.
Next comes cooling. Almost all the electricity that a server uses turns into heat. Ordinary racks are cooled by air: cold air is blown in at the front of the racks, and warm air is drawn out at the back. The warm air passes over coils of chilled water from the building's chillers. The extra power that a building uses for cooling and other equipment is measured by power usage effectiveness (PUE). A PUE of 1.5 means that for every 100 kW used by the servers, the building uses another 50 kW.
AI has changed this equipment. An ordinary rack of servers draws perhaps 5 to 10 kW. A rack in an AI cluster can draw 100 kW or more, and air cannot remove that much heat. So cold liquid is piped to a metal plate on top of each chip, called a cold plate, and the warm liquid is piped away. This is called direct-to-chip liquid cooling. In immersion cooling, the servers sit in a tank of a special liquid that does not conduct electricity.
The UPS and the power converters are built with power semiconductors, chips that switch and convert electric current. In a colocation data centre, the operator meters the electricity that each tenant's racks use and bills it every month.