PUE-fecting data centres
A key metric used by the data centre industry to understand how efficiently data centres use energy is Power Usage Effectiveness (PUE). Bradley Stone, Data Centre Vertical Manager (UK and Ireland) at Carrier, highlights how efficient HVAC systems can help this energy-hungry sector reduce running costs and carbon footprints.
Rising energy costs and the need to meet sustainability goals means that data centres are under constant pressure to improve efficiency.
Data centres play a significant role in an increasingly digital world but with approximately 3.5 quintillion bytes (3.5 million terabytes) of data created daily, the energy needed to consume this information is huge.
The energy consumption required by data centres is driven by the need to power and cool servers and other infrastructure required to store, process and transmit data. Data centres account for 1% of the world’s electricity consumption and 0.5% of carbon dioxide emissions.
Calculating PUE
A key metric used by the data centre industry to understand how efficiently data centres use energy is Power Usage Effectiveness (PUE). It can identify opportunities where efficiency can be improved over time.
The formula used to calculate power usage is Total Facility Energy divided by IT Equipment Energy.
IT Equipment Energy covers the energy consumed by the core IT equipment within the data centre, including servers, switches, storage devices and networking infrastructure. It encompasses the energy required for data processing, computation, and transmission.
Total Facility Energy is a combination of everything else that requires power in the data centre, such as non-IT equipment, lighting and cooling systems.
Non-IT equipment can include security, backup power devices during utility outages and power distribution infrastructure such as transformers, switchgear, power distribution units (PDUs), and cabling. These elements are all susceptible to electrical resistance and inefficiencies.
Energy consumed by lighting may seem minimal, but cumulative energy consumption can impact on the overall PUE significantly.
Data centres also generate substantial heat because of the operational intensity of IT equipment. Maintaining stable temperatures and ensuring equipment doesn’t overheat is crucial to a data centre’s smooth and safe running. This is where HVAC systems play their part.
However, heating and cooling systems consume around 30% to 40% of the overall energy in a data centre facility.
The ideal PUE ratio is 1.0, as it signifies that every unit of power consumed is utilised solely by the IT equipment. In reality, however, most data centres fall within the range of 1.2 to 1.4 as a result of factors such as suboptimal equipment efficiency or inefficient cooling systems.
Although HVAC systems consume a considerable amount of energy, it is possible for data centre operators to optimise their PUE ratio by enhancing their energy efficiency, maximising free cooling and using systems operating on low Global Warming Potential (GWP) refrigerants.
Enhancing energy efficiency
One approach to enhancing energy efficiency is the use of hot aisle/ cold aisle containment systems.
By segregating hot and cold airflows and preventing mixing, these systems enable more precise cooling, reducing the workload on HVAC systems. Advanced monitoring and control systems can also be employed to fine-tune operations.
Machine learning algorithms and artificial intelligence can analyse vast amounts of data from devices and sensors then adjust cooling based on workload and environmental conditions. These intelligent systems optimise energy usage and maximise efficiency without compromising performance.
Free cooling
Free cooling in HVAC systems involves using the cooler outside air to directly cool the water or other heat transfer fluid. This can be achieved through various methods, such as air-side economisers, evaporative cooling or heat exchangers.
Free cooling can provide cooling capacities that exceed the requirements of the design, allowing for optimisation of multiple chillers. Multiple chillers can be operated in parallel or independently, depending on the cooling load, to further enhance efficiency and flexibility.
As an example, Carrier’s AquaForce® 30XF air-cooled screw chiller, designed specifically for data centres, operates between 100% hydronic free cooling, hybrid (free/mechanical) cooling and 100% mechanical cooling to maximise the efficiency of the system.
Data centres situated in cold climates or even underwater can reduce the amount of mechanical cooling needed to dissipate the heat generated by servers, increasing energy savings further.
Low GWP refrigerants
Many modern chiller and heat pump systems operate on lower GWP refrigerants. With the emergence of F-gas regulations in 2020, refrigerant blends such as R-1234ze are now being utilised. These refrigerants provide a sustainable solution and are compliant with regulations.
