The heat generated by the servers switched and other IT equipment can increase the temperature inside data center and hence it can damage these devices. Thus, to ensure high uptime of the datacentre, a close control unit is used to maintain temperature and humidity at a precise level. CCUs transports heat generated inside the server room to outside with the help of a cooling agent. These cooling agents can be refrigerant, chilled water, or glycol. Based on the cooling agent used in the system, there is two major types of CRAC units; Chilled water (CW) type and Direct Expansion (DX) Type unit.
The initial and running cost of the DX-type units is higher than similar capacity chilled water units. However, its cooling efficiency is always better than the CW unit. Also, depending on the change in the inlet temperature of chilled water, the cooling performance of the chilled water unit might affect. It needs a continuous supply of high-pressure chilled water through pipes that can run inside the data center. Thus, the facility gets exposed to the threat of water leakage.
The DX Air Conditioner system cools air that enters through a supply plenum and returns it to the area that requires cooling via the return. The unit circulates refrigerant effectively through a sequence of condensers and evaporators, where heated air is cooled and sent through the return. Another significant characteristic of DX Packaged units is the ability to house the entire cooling system in a single unit. This enables them to be installed on top of or alongside a building without taking up an excessive amount of space, and they are often less expensive to install.
Chiller units, like DX units, use a vapour expansion/compression cycle to cool liquid refrigerant. The refrigerant is changed continually from a liquid to a vapour and back. This procedure chills the refrigerant as it travels through an evaporator. Warm water is passed over the evaporator via a supply pipe with a radius of 2-5 inches and cooled to the required temperature. The cooled water is typically used to cool existing air handler systems.