HFCs and HFOs are widely used for data centre cooling, with large refrigerant charges for high capacity centrifugal chillers. The safety (low toxicity and mildly or non-flammable) and performance properties of these fluorocarbon refrigerants make them particularly suitable for use in large chillers. Even though refrigerant losses are very low with modern well-designed chillers, HFOs with their very low GWPs provide further reductions in GHG emissions.
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Large data centres use massive amounts of energy to process and store data. Similar quantities of energy can be required for cooling to maintain the required data operating temperature. The Internet of Things (IoT) cloud computing and smart technology are expanding data centre installations. Blockchain and high-frequency trading systems are processor and energy intensive. The large demand for data centre cooling drives the requirement for higher efficiency. Free cooling is clearly the most energy efficient option, but due climatic conditions it cannot be used in all locations throughout the year, which means that most data centres have a close control air conditioning system to maintain the required temperature range particularly in summer. High system reliability and close temperature control are critical.
Chillers, using HFC refrigerants such as HFC-134a, are widely used for data centre cooling and are designed to minimise energy consumption while delivering reliable cooling over a wide temperature range. Water-cooled or air-cooled chillers are available, but water management is critical in some locations, limiting the use of water-cooled chillers. Chillers, using HFOs such as HFO-1234ze(E), are being installed due to the very low GWP of the HFOs. Indirect Thermosyphon Cooling can provide an efficient solution for data centres. It uses the waste heat from the data centre 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.
Waste heat from data centres can be utilised for local heating requirements for offices, facilities, greenhouses and housing. Some data centres, in Scandinavia, transfer the waste heat using heat pumps for district heating. For example, HFO-1234ze(E) is used for the heat pumps at a data centre in Finland to provide cooling for the data centre and utilise the waste heat. Where vapour compression cooling is used waste heat utilisation is more attractive due to the higher temperatures of the waste heat.