Sustainable Cooling of High Density Racks at BT | Pure Thermal


British Telecom (BT) is an internationally leading provider of communications solutions, and markets itself as a business partner for digitalisation.

BT started operating in Germany in 1995 and has since become a preeminent supplier of global network and IT services, focussing on solutions with challenging demands on IT infrastructure and security. BT has many prominent customers such as Allianz, BASF, Commerzbank, DHL, Volkswagen and Media-Saturn. The German operation is a 100 percent subsidiary of London-based BT Group.

Over 200 data centres are connected to BT’s international network, 48 of which BT runs itself. BT is currently investing in future-orientated cloud computing scenarios against the background of a new generation of cloud services securely connected to the global network. Two of these are the data centres in Hamburg and Berlin where the project described below was implemented.

Project and implementation

At its data centres, BT offers room-in-room solutions for high-density racks which place gruelling demands on the technical infrastructure due to the concentrated power density. These “cubes” can be scaled modularly, each in a power range of 40 to a maximum 100 kW IT load. Uniformly water-cooled in-row chiller units with hot-aisle housing are used for cooling. With temperatures of 22-25°C 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 – which allows highly efficient cooling.

The “cubes” are connected up to existing central DC infrastructures and existing chilled-water or cooling-water systems. Cooling-water networks are available for this at the BT locations in Hamburg and Berlin. An additional, modularly scalable chilled water preparation system was needed which was to maximise efficiency, provide failsafe redundancy and support relatively high system temperatures – the optimal area of application for the eChiller.

Three eChillers per cube feed a buffer tank with chilled water. An energy-management application decides on the number of eChillers 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 all the relevant operating and performance data. efficient energy (EE) can proactively analyse the installation’s process parameters at all times and avoid malfunctions via the installed remote-maintenance channel. In addition to this, storage of the log data allows uncomplicated evaluation of system-operating and -efficiency metrics.

The EE service contract provides for regular system maintenance. As the eChiller has a 1-year maintenance period, the effort and costs are very low compared to other chillers.

The three-month installation time for a cube – from awarding the assignment to final commissioning – could be met for all cubes, also thanks to the excellent technical support provided by efficient energy.


An eChiller has already been running since 2017 in a one-year-plus field trial at a BT location in Munich. The trial demonstrated the eChiller’s excellent reliability, extremely stable chilled water preparation (with a target chilled-water flow temperature of 16°C), and maximum efficiency under realistic load conditions.

BT has currently implemented three of the above-mentioned cubes using eChillers. The first of these has meanwhile been running at the Hamburg site for over a year. Since then, the infrastructure has operated fault free, and with impressive efficiency.
A further major benefit of the eChiller is its use of water as a refrigerant, as this is almost cost-neutral and poses no risks for the climate or for health. In addition to this, operators are not subject to the requirements of DIN EN378 or the F-Gases Regulation.

BT project manager Jens Fischer draws a final conclusion: “Use of the eChiller for chilled water preparation in this data-centre application has proven itself over the long term. It has ensured both operating reliability and extremely high energy efficiency. We have not suffered a single system malfunctions to date.”

Refrigeration capacity (kW) 3x45kW
Target temperature 18 °C
Refrigerant R718 (Wasser)
Cooling Water/Glycol; 40/45 °C
Cooling water inlet 40 °C


  • Operational reliability
  • Redundancy
  • High efficiency, partial-load behaviour
  • Innovation
  • Use of a natural refrigerant

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