CHILLER TECHNOLOGY | WATER AS REFRIGERANT operating fully. At these temperatures, it has an energy efficiency ratio (EER) of 3.4. When the ambient temperature drops, the second compressor modulates, increasing the efficiency. For example, at an ambient temperature of 21C the EER increases to 7.4. When the ambient temperature drops to a level where the cooling water from the dry cooler is at least 2K colder than the return water from the chilled water/cooling circuit, the first stage also switches off. This allows the system to direct the water solely through the chiller without mechanical cooling, achieving free cooling, which delivers an EER of more than 20. Actual efficiency is subject to the cooling load profile of each individual project. However, this mix of mechanical and free cooling results in a system delivering a very high seasonal EER (SEER) in excess of 11 (in representative northern German climatic conditions). Above: High cooling-density server enclosure Left: New technology chiller and integration/buffer tank system Below: Drawing of the internal configuration of the cooling unit BT case study An installation has been operating since 2017 at a BT location in Hamburg. At its data centres, BT offers room-in-room cube solutions for high-density server racks, which place gruelling demands on the technical infrastructure because of the concentrated power density. These cubes can be scaled modularly, each in a power range of 40kW to a maximum 100kW IT load. Uniformly water-cooled, in-row chiller units with hot-aisle housing are used for cooling. With temperatures of 22-25C required on the intake side of the racks (cold aisle), large temperature differences arise between the supply and discharge air at a simultaneously high temperature level. The cubes are connected to existing central DC infrastructures and existing chilled-water or cooling-water systems. Coolingwater networks with adequate capacity are not available for this additional cube load at the locations in Hamburg and Berlin. As such, an additional modular, scalable, chilled-water production system was needed to maximise efficiency, provide fail-safe redundancy and support relatively high system temperatures the optimal area of application for the new technology chiller. Three chillers per cube feed a buffer tank with chilled water. An energy-management system controls the number of chillers, which should operate in parallel, depending on the load. This ensures evenly distributed operating times and high operational reliability. The systems are connected to a building-control system for monitoring relevant operating and performance data, while the manufacturer can actively analyse the installations process parameters at all times and avoid malfunctions via an installed remote-maintenance interface. In addition to enabling maintenance intervention, the storage of recorded data allows straightforward evaluation of the system operation and its efficiency. The installation at Hamburg has demonstrated the reliability of this new technology application, stable chilled-water delivery temperatures of 16C, and maximum efficiency under realistic load conditions. BT has installed three highdensity cube systems using eChillers. The first of these has been running at the Hamburg site for two years, and since commissioning the system has operated fault free. CJ G ARRY BROADBENT is director at Green Thermal Energy 58 February 2020 www.cibsejournal.com CIBSE Feb20 pp57-58 eChiller.indd 58 24/01/2020 15:10