Improving energy and water usage in data centres

With the growth in demand being placed on UK data centres, electrical usage is a continuing focus in efforts to mitigate climate change. Working alongside data centre specialist, Ian Bitterlin, water pump manufacturer, Wilo UK, has identified how chilled water pumps are key to improving energy and water usage.

The Covid-19 pandemic has caused a surge in demand at data centres in the recent months, with more adults currently working from home and families streaming more content during the day. The implementation of 5G technology and streaming video is also rapidly driving data growth. With users unlikely to reduce their usage, actions such as lowering cooling losses at data centres are important, with better pumps and more efficient controls a key enabler in facilitating this.

There is increasing pressure from the EU for data centres to be powered by renewable energy; however, the first step is to reduce the power consumed by the data centre infrastructure.

The Green Grid, the innovator of the Power Usage Effectiveness (PUE) metric, has recently proposed the introduction of a new data-centre metric, Water Usage Factor (WUF). As PUE expectations drive lower, data centres are now being judged for water consumption as well as electrical energy use.

The majority, 80%, of all data centres utilise chilledwater systems for cooling, 15% use direct-expansion refrigeration systems, and just 5% use air-based evaporative or adiabatic cooling systems.

Consulting Engineer, Ian Bitterlin, commented: “Chilled-water systems (the dominant technology used to date) have continued to evolve technically, with better controls, heat-exchanger technology, variable speed compressors, fans and pumps. They have also developed operationally, with flow water temperatures rising from the legacy 6°C to 18°C (and higher), enabling high percentages of free cooling in suitable climates. Because of this change, an older technology has recently proved more popular – that of evaporative or adiabatic cooling.

“In pursuit of achieving an ever lower PUE, the advent of free cooling solutions brought along with it adiabatic cooling solutions, where water is used to take advantage of the wet-bulb ambient temperature and crucially humidification of high volumes of fresh air. Perhaps for the first time in Europe, water consumption in data-centres is a growing issue.”

Evaporative and adiabatic cooling technology – which dates back to before Roman times in high-status dwellings – use water to increase the humidity of warm, dry air and reduce its temperature from the dry-bulb to the wet-bulb value. For example, in the UK when the external ambient is near the record high of 35°C drybulb, the addition of water vapour can get the air-stream temperature down to 23°C wet-bulb and this can then be used to cool the data centre.

Evaporative and adiabatic cooling systems can save 20-30% of a data centre’s energy (compared to chilled water systems) and do not use pumps. However, they have not proven to be universally popular as they need a lot of space and use a lot of water.

Ian continued: “Despite the potential energy saving of evaporative and adiabatic cooling systems, chilled-water systems are, in my opinion, the way forward as they use hardly any water compared to ‘modern’ evaporative cooling technology. The performance of chilled water systems is much improved by high-quality variablespeed pumps and chillers fitted with evaporative or adiabatic cooling offering total control of internal air temperature and humidity.

“The majority of enterprise and colocation data centres have a partial load, typically <50% at maturity, rarely high and never 100% – this means that for energy-saving reasons the chilled water pumps must be designed for variable speed drives and optimised for operation at 40-50%.

“A pump designed for 100% flow, but only having 30% load, uses 100% power, while the same pump running at 30% flow rate only consumes 2.7% of the energy.”

David Williamson, Director of Wilo UK, commented: “Cooling data centre plants with pumps provides an opportunity to improve on past performance with partial load and variable speed pumping, and offers a high level of control to meet a wide range of systems.

“Through analysis of the hydraulic system and measurement of the power performance of existing and legacy cooling systems, we can select replacement pumps that can achieve the desired system performance while reducing energy use. Often such upgrades further increase data centre resilience and availability.”

The Wilo GIGA range of pumps covers all applications within the data centre environment. The

Atmos GIGA Series has recently been upgraded to provide greater efficiency, and the Stratos GIGA delivers performance greater than IE5 through EC motor technology up to 22kW.

“Cooling data centre plants with pumps provides an opportunity to improve on past performance.”

Far from the perception that evaporative or adiabatic modules are taking over the market, the sales of chilled-water systems have proven to be increasingly resilient, aided considerably by an offshoot of the adiabatic technology; the air-cooled chiller enabled with adiabatic sprayed free cooling coils.

If engineered correctly, chilled water cooling can no longer be considered as wasteful of energy, achieving an overall PUE at full load, with all the other systems included, of 1.2 in northern European city centres.

The final piece of the puzzle is to cater for the endemic partial load and here is where the chilled water pump, allied to variable speed pumps and electronic proportional valves, come into their own. The product that, along with the chiller, was most threatened by air-based direct and indirect adiabatic or evaporative cooling can look forward to a successful future in the data centre industry on which we have come to rely. chevron-

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