A data center chiller is a cooling system used in a data center to remove heat from one element and deposit it into another element. Chillers are used by industrial facilities to cool the water used in their heating, ventilation and air-conditioning (HVAC) units. Round-the-clock operation of chillers is crucial to data center operation, given the considerable heat produced by many servers operating in close proximity to one another. Without them, temperatures would quickly rise to levels that would corrupt mission-critical data and destroy hardware.
The development of powerful chillers and associated computer room air conditioning (CRAC) units has allowed modern data centers to install highly concentrated server clusters, particularly racks of blade servers. Like many consumer and industrial air conditioners, however, chillers consume immense amounts of electricity and require dedicated power supplies and significant portions of annual energy budgets. In fact, chillers typically consume the largest percentage of a data center's electricity.
Manufacturers also have to account for extreme conditions and variability in cooling loads. This requirement has resulted in chillers that are often oversized, leading to inefficient operation. Chillers require a source of water, preferably already cooled to reduce the energy involved in lowering its temperature further. This water, after absorbing the heat from the computers, is cycled through an external cooling tower, allowing the heat to dissipate. Proximity to cold water sources has led to many major new data centers being sited along rivers in colder climates, such as the Pacific Northwest. The chillers themselves, along with integrated heat exchangers, are located outside of the data center, usually on rooftops or side lots.
Manufacturers have approached next-generation chiller design in a number of ways. For large-scale systems, bearingless designs significantly improve power utilization, given that the majority of chiller inefficiency results from energy lost through friction in the bearings. Smaller systems use smart technologies to rapidly turns a chiller's compressor on and off, letting it work efficiently at from 10% to 100% of capacity, depending on the workload. IBM's "Cool Battery" technology employs a chemical reaction to store cold.
To maintain uptime, data center managers have to ensure that chillers have an independent generator if a local power grid fails. Without a chiller, the rest of the system will simply blow hot air. While any well-prepared data center has backup generators to support servers and other systems if external power supplies fail, managers installing UPS and HVAC systems must also determine whether a facility provides emergency power to the chiller itself. Data center designers, for this reason, often include connections for an emergency chiller to be hooked up. Multiple, smaller chillers supplied with independent power supplies generally offer the best balance of redundancy and efficiency, along with effective disaster recovery preparation. As recent major outages at hosting providers like Rackspace have demonstrated, however, once knocked offline, chillers may take too long to cycle back up to protect data centers, during which time servers can quickly overheat and automatically shut down.