Feature sponsored by Test & measurement
Anu Kätkä, Vaisala
Keith Dunnavant, Munters
DATA CENTRE INNOVATION
HOW MEASUREMENT ACCURACY ENABLES ENERGY EFFICIENCY
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he global demand for electricity is about 20,000 terawatt hours; the ICT (Information and Communications Technology) sector uses 2,000 terawatt hours and data centres use approximately 200 terawatt hours, which is one per cent of the total. Data centres therefore represent a significant part of most country’s energy consumption.
It has been estimated that there are over 18 million servers in data centres globally. In addition to their own power requirements, these IT devices also require supporting infrastructure such as cooling, power distribution, fire suppression, uninterruptable power supplies, generators etc. In order to compare the energy efficiency in data centres, it is common practice to use ‘power usage effectiveness’ (PUE) as the measure. This is defined as the ratio of total energy used in a data centre to the energy used by IT only. Optimally the PUE would be one, which would mean that all energy is spent on IT, and the supporting infrastructure is not consuming any energy. So, to minimise the PUE, the objective is to reduce the consumption of the supporting infrastructure such as cooling and power distribution. The typical PUE in traditional legacy data centres is around two, whereas big hyperscale data centres can reach below 1.2. The global average was approximately 1.67 in 2020. This means that, on average, 40 per cent of total energy use is non-IT
In the following article, Anu Kätkä from Vaisala and Keith Dunnavant from Munters describe recent trends in the data centre sector, and discuss the impact of HVAC measurements on energy efficiency. With spiraling energy costs and governments urgently seeking greenhouse gas emissions reduction opportunities, data centre energy efficiency is the focus of international scrutiny.
consumption. However, PUE is a ratio, so it does not tell us anything about the total amount of energy consumption, which means that if the IT devices are consuming a high level of energy in comparison with the cooling system, the PUE will look good. It is therefore important to also measure total power consumption, as well as the efficiency and the lifecycle of the IT equipment. Additionally, from an environmental perspective, consideration should be given to the way in which the electricity is produced, how much water is being consumed (both in generating the electricity and at the site for cooling), and whether waste heat is being utilised.
The PUE concept was originally developed by the Green Grid in 2006 and published as an ISO standard in 2016. The Green Grid is an open industry consortium of data centre operators,
cloud providers, technology and equipment suppliers, facility architects, and end-users, working globally in the energy and resource efficiency of data centre ecosystems striving to minimise carbon emissions.
PUE remains the most common method for calculating data centre energy efficiency. At Munters, for example, PUE is evaluated at both a peak and annualised basis for each project. When computing PUE metrics, only the IT load and cooling load are considered in the calculation of PUE. This is referred to as either partial PUE (pPUE) or mechanical PUE (PUEM). The peak pPUE is used by electrical engineers to establish the maximum loads and to size back-up generators. The annualised pPUE is used to evaluate, and compare with other cooling options, how much electricity will be consumed
March 2023 Instrumentation Monthly
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