From a cooling perspective, the various electronic components inside servers and other IT equipment can be viewed as small but powerful heaters that convert almost all of the electrical power that they draw into heat – each processor is similar to a 100W incandescent light bulb, each server is similar to an “electric bar heater”, each rack of servers may be equivalent to a domestic heating boiler. The role of data centre cooling is simply to continuously and reliably transport the heat from the points of origin deep inside each server to a location outside the computer facility where it can no longer do harm (or, possibly, where it can be harnessed for other uses such as building heating).
The problem is that air, which is typically used to capture and transport the heat within the IT room, is actually quite an effective insulator (which is why it can be used in the “void” in double glazed windows). Because of this the air must be chilled to low temperatures and blown at high velocities around the room. This requires air conditioning plant (CRAC units) and fans and usually, because the required air temperature is typically below the ambient air temperature outside the data centre, chiller plant. The combined electricity cost of operating this cooling equipment, which is shown in the figure below, may be 30% or more of the data centre running costs.
Figure 1: Typical heat transfer path in “air cooled” data centre (simplified). Air stages shown in pink, water stages shown in blue.
A typical air cooled data centre with around 1000 servers would require approximately 1 megawatt of electricity to operate, of which around 300 kilowatts would be used on cooling. The typical 3 year cooling cost would therefore be around $788,400.