Almost all the electricity a data centre draws leaves it as heat. Removing that heat, rather than supplying the power, is the constraint that governs how such buildings are designed and sited.
Heat sets the density limit
A rack of servers concentrates a great deal of power into a small volume. As chips have grown more capable, the power per rack has risen sharply and the heat with it.
Silicon throttles when it exceeds a temperature threshold, deliberately slowing itself to avoid damage. A facility that cannot keep pace with heat therefore loses performance before it loses uptime.
This is why a hall may sit half empty. The floor space exists, but the cooling capacity to fill it does not, and adding cooling means rebuilding the plant.
Air cooling reaches its ceiling
Traditional halls separate hot and cold air into aisles, pushing chilled air past equipment and capturing the exhaust. The approach is simple and works well up to a point.
Air carries little heat per unit of volume, so higher densities demand impractical air speeds. Beyond a certain power per rack, moving enough air consumes an unreasonable share of the energy.
Operators have pushed the ceiling by allowing warmer inlet temperatures than were once thought safe. Equipment tolerates this better than expected, which removed a large amount of unnecessary refrigeration.
Liquid moves heat far better
Water carries heat far more effectively than air by volume, so bringing liquid closer to the chip solves the density problem directly. Cold plates on processors are the common approach.
Immersion goes further, submerging whole boards in a non-conductive fluid. It removes fans entirely and allows very high density, at the cost of a completely different maintenance routine.
Both methods change the building. Pumps, manifolds and leak detection replace large air handlers, and technicians need training that has little to do with conventional server work.
Water use and heat reuse
Evaporative cooling is efficient because evaporation carries away a great deal of heat, but it consumes water continuously. In dry regions that consumption becomes a planning issue in its own right.
Closed-loop systems avoid the consumption by rejecting heat to the air instead, which uses more electricity. The trade between water and power is decided locally rather than universally.
Waste heat can also be sold rather than discarded. Feeding a district heating network requires the data centre and the network to sit close together and to agree on temperature.
Why siting follows cooling
Cool climates reduce the hours during which mechanical refrigeration is needed at all, which is a large part of the appeal of northern locations for large facilities.
Grid capacity matters equally, since a site is useless without a connection large enough to supply the load. Connection queues now shape site selection as strongly as land price.
Put together, these constraints explain a pattern that looks arbitrary from outside: clusters of facilities in a handful of regions, and long waits for permission everywhere else.