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Air cooling

Data centers generate heat through the operation of electronic equipment, resulting in increased temperatures, therefore cooling mechanisms are needed to control de temperatures and keep them in the optimal operational range (18°C to 27°C), as per ASHRAE recommendations[1].

Air cooling is a form of heat dissipation that uses low temperature air as a medium to reduce the temperature the equipment by heat convection.
Server rack density is increasing with the growth of machine learning, Artificial Intelligence and other high-performance computing. This is also changing how temperature is managed across major data center markets, which are adopting solutions that are more efficient at removing heat, but also because close temperature control is critical to the system reliability[2].

A growing demand

Currently, up to 98% of the European data centers are based on air cooling, but this can be impacted by the climatic conditions, particularly in summer, which will increase drastically with global warming. As an example, in the summer of 2022, the data centers of Google, Oracle, and London-based Guy’s and St Thomas’ NHS Foundation Trust all experienced outages that lasted more than 24 h due to the heatwave that affected the UK[3], [4].

The large demand for data center cooling drives the requirement for higher efficiency. Phase-change heat transfer using HFOs/ HCFOs provides high efficiency in energy utilization while maintaining adequate performance and system reliability. The data center industry is growing rapidly as an increasing number of applications require data computing and storage, driving a corresponding rapid increase in energy and water use in data center facilities. Data centers are estimated to be responsible for up to 3% of global electricity consumption today and are projected to touch 4% by 2030. The average hyperscale facility consumes 20-50MW annually – theoretically enough electricity to power up to 37,000 homes[5].

The challenge of energy efficiency

Energy use for data centers was one of the themes of the European Commission Communication ‘Shaping Europe’s digital future’ (19.2.2020 COM(2020) 67 final). “Yet it is also clear that the ICT sector also needs to undergo its own green transformation. The environmental footprint of the sector is significant, estimated at 5-9% of the world’s total electricity use and more than 2% of all emissions. Data centers and telecommunications will need to become more energy efficient, reuse waste energy, and use more renewable energy sources. They can and should become climate neutral by 2030.”[6]

Waste heat from data centers can be used for local heating requirements for offices, facilities, greenhouses, and housing. In March 2022, Fortum, a state-owned energy company in Finland, has announced a deal with Microsoft to use waste heat from two new data centers to heat homes and businesses in Helsinki[7].

These function on vapor-compression cooling, using HFOs[8] and it was estimated to reduce the annual emissions of Microsoft by 400000 MT CO2. Similarly, data centers residual heat is recovered in Sweden, Denmark and The Netherlands, using a combination of refrigerants, water and air[7]. Where vapor compression cooling is used, waste heat use is more attractive due to the higher temperatures of the waste heat.

Where vapor compression cooling is used, waste heat use is more attractive due to the higher temperatures of the waste heat.
Cutting edge technologies, such as Indirect Thermosyphon Cooling[9] can provide an efficient solution for data centers. It uses the waste heat from the data center and a combination of gravity and a syphon effect, to drive a refrigeration cycle capable of operating without pumps or compressors, providing remarkable levels of energy efficiency. Systems have been designed for use with HFO refrigerants[8].
The global data center cooling market was valued at USD 10.96 billion in 2022, and it is forecasted to grow at a CAGR (compound annual growth rate) of 13.76% over the next five years, reaching USD 21.42 billion in 2028[10].