*3.4.3. Computer room air-conditioning units*

A CRAC unit is one type of air-handling unit used for computer rooms or data centers. CRAC units are often located inside the data center and provide cooling to the servers. A typical CRAC unit includes direct expansion coil(s), compressors, supply fan(s), heater(s), and humidifier(s).

The traditional CRAC runs fans and compressors at a constant speed, which consumes extra fan and compressor power at partial load conditions. Application of a VFD converts a CRAC unit to a variable capacity CRAC unit. The VFD can be installed on the supply fan only or both the supply fan and compressors. The supply fan and compressor speeds are modulated to maintain the space temperature set point.

A data center is often a cooling-dominated building type. With the reduction of fan and compressor speeds, a great amount of fan and compressor power is saved.
