Today, the operator of a Data Center basically has two fundamental concerns: firstly, reliability, i.e. Data Center availability; secondly, energy efficiency, particularly in this age of rising energy prices.
In most cases, larger Data Centers continue to use closed-circuit air conditioning units. These so-called CW units basically consist "only" of an air/water heat exchanger, fans, air filters, control valves and the necessary electrical components, plus a controller. The cooled water supply to these units is provided by a centralized chiller.
To remove the heat load from the Data Center, a certain airflow is required, the amount of which depends on the air-side temperature difference. This airflow is supplied by the closed-circuit air conditioning units.
A certain level of so-called "redundancy" of air conditioning units is created, depending on the size and desired reliability level, to ensure reliable Data Center air conditioning. In other words, more units are installed (standby units) than are actually required for air conditioning. Normally, these units are only brought (automatically) into operation if a running unit switches off due to a fault (passive redundancy).
The latest closed-circuit air conditioning units make use of EC fans for ventilation. These fans are considerably more energy efficient than the older versions with AC motor. Another major advantage of these fans is that as the fan speed decreases, the motor's power consumption does not decline in a linear fashion as a function of the speed, but by the power of three.