Increasing the efficiency of existing cooling systems by integrating efficient chillers with the natural refrigerant water

Prof. Dr. Christian Schweigler
Energy and Building Services Engineering, Department 05

In the course of digitalisation, the demand for computing power is growing rapidly and the corresponding electrical energy demand of data centres in Germany has been rising steadily for years. Although newly built data centres are very efficient in terms of their infrastructure, the majority of existing systems exhibits high potential for optimization. Around 40 to 50 % of the energy provided in existing data centres is required for air conditioning and for uninterruptible power supply; there is considerable potential for increasing energy efficiency in this area. In particular, the optimisation of air conditioning may lead to substantial savings of electricity.

Cooling of small and medium-sized commercial data centres with cooling capacities up to 50 kW is usually provided by direct expansion cooling units in split design. The room air is cooled while passing through the indoor units, operating as evaporators. The outdoor unit contains the compressor and the condenser heat exchanger of the refrigeration circuit. Due to the direct heat transfer from the room air to the refrigerant of the air-conditioning system, there is no possibility of using free cooling with these systems.

In future, supply air temperatures of 27 °C and higher can be used to cool IT in data centres. Thus, the power requirement for data centre cooling can be significantly reduced through the use of suitable refrigeration units which operate with improved efficiency when the temperature of the cooling supply is raised. In addition, so-called free cooling can be used under cooler ambient conditions, in which the waste heat from the data centre is dissipated directly into the environment, i.e. without the use of active refrigeration.

Within the project, a concept and the implementation of a test plant for the energy-efficient cooling of data centres is to be developed and tested. The focus is on upgrading the system technology of existing data centres and of systems which are currently expanded within so-called retrofit measures. For the investigation of these measures, the following concept is pursued:

• Increasing the available cooling capacity by using a turbo chiller with the refrigerant water, which can be operated with variable temperature of the cooling supply and increased energy efficiency. The refrigerant water also reduces the direct greenhouse effect caused by common refrigerants.
• Continued operation of existing direct evaporating split air conditioning units, with conversion of the cooling supply via a water circuit.
• Optimised use of all cooling devices in a network.
• The conversion to a cold water system opens up the possibility of free cooling via the heat rejection unit - without the use of active cooling.

The following figure shows the basic structure of the integrated cooling system.