Efficient Cooling for Data Centers

With the exponentially increasing volume of data and the associated heightened demand for centralized computing power, more and more powerful data centers are being operated. The servers, storage devices, and network components require energy and constantly generate heat that needs to be dissipated. Traditionally, the energy consumption of data centers has often been neglected. However, with rising energy costs and environmental regulations, efficiency is increasingly gaining importance. To effectively reduce the energy consumption of data centers, it is important to identify the main consumption areas. Cooling and rack operation account for a significant portion, followed by data processing and storage, unnecessary energy losses, and network operation. The metric PUE (Power Usage Effectiveness) describes the energy efficiency of data centers and makes them comparable.

The cooling of data centers is a crucial factor for the energy efficiency and sustainability of IT infrastructure. The concept for cooling a modern data center is redundantly designed to ensure reliability. The generated heat is dissipated in different ways depending on the concept. Different systems interact depending on local conditions and outside temperatures:

INDIRECT AND DIRECT AIR COOLING 

In direct air cooling, heat is directly expelled outside through fans in the server racks and additional ventilators over a raised floor. The airflow is designed with ducts to avoid short circuits. This variant is used up to an outside temperature of 18°C.

In indirect air cooling, a heat exchanger absorbs the heat, transfers it to a medium (brine), and transports it to a condenser or evaporator outdoors. The condenser variant is used up to an outside temperature of 22°C. If an evaporator is used instead of a condenser, higher outside temperatures can be accommodated. The possible outside temperature then depends on the weather-dependent wet bulb temperature.

AIR COOLING WITH ADDITIONAL REFRIGERATION SYSTEM 

If outside temperatures continue to rise, indirect cooling is no longer sufficient. Now, the warm water from the brine circuit is cooled with a chiller. This ensures constant and reliable temperatures when needed. The warm air from the server racks is absorbed through registers. Brine circulates in the register and transports the heat through pipes to the chiller. The chiller works like a traditional refrigeration system and releases the heat to the surroundings.

Given challenges such as the phase-down scenario of the F-gas regulation, the associated limitation of CO2 equivalents of refrigerants, and the scarcity of refrigerants, innovative approaches must be developed. Synthetic refrigerants are becoming less prominent for this application, and natural refrigerants are becoming more appealing. For cooling capacities of approximately 600 kW and above, for example, ammonia chillers become an economically attractive option. These systems are characterized by their high efficiency and offer the additional advantage:

• no ozone depletion potential (ODP = 0) 
• no direct greenhouse effect (GWP = 0) 
• This significantly reduces environmental impact. 

LIQUID COOLING 

Liquid cooling does not involve a refrigeration system or chiller. Water or brine circulates through the server racks and directly absorbs heat from the CPUs and electrical devices. Temperatures of up to 60°C of water are transported and dissipated outdoors via condensers or hybrid coolers. This application is most interesting for the energy efficiency of a data center because a slight decrease in the recovered heat is possible.

UTILIZING THERMAL ENERGY 

Simply releasing and wasting the generated heat to the environment is neither efficient nor necessary. This heat can be used for heating or providing hot water to adjacent office spaces or for feeding into a district or local heating network.

Configuring Settings Safe and future-proof chillers and heat pumps with ammonia Industrial heat pumps can be used here. The 60-degree brine is brought to a temperature level of up to 130°C and fed into the nearby district heating network. By optimizing energy consumption and effectively utilizing heat with connected heat pumps, data center operators can not only save costs but also make a valuable contribution to environmental protection.