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Defining net zero: You can't manage what you don't measure

Critical Systems By Dr Maria-Anna Chatzopoulou, Principal Engineer, Critical Systems – 30 January 2024

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Dr Maria-Anna Chatzopoulou

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Defining net zero and how we look to achieve it in today’s resource stressed climate.

As the move towards achieving net zero carbon gains traction, the data centre industry is facing potentially conflicting demands – on the one hand needing to deal with the rising demand for data processing capacity, while on the other, needing to limit the growth in energy and water consumption, to reduce the stresses being placed upon national infrastructure.

At the same time, the industry is striving to develop appropriate solutions to achieve net zero carbon and to limit, and ultimately reverse, the environmental impact of the sector. However, at present, much of the construction industry is wrestling with a clear definition of what net zero carbon, is and has yet to agree a unified methodology for how it should be measured.

Much work needs to be done to provide clear direction on what is to be included in the net zero target. Operational carbon has been the focus, but embodied carbon is more difficult to quantify. It needs a broader understanding of the entire supply chain carbon emissions, requiring consistent data collection and monitoring to be able to create benchmarks and track them.

Everyone has a role to play in achieving true net zero carbon (vendors, owners, consultants, contractors, and authorities). Over this series of articles, Cundall will take you through some changes they are seeing in their work as designers, pushing the boundaries a little further, to deliver the energy-efficient, resilient digital infrastructure the global community needs, in the net zero carbon era.

How we get to net zero carbon in a resource-stressed environment?

Data centres can play a key part in promoting a circular economy and moving towards net zero carbon by making efficient use of resources, including electricity, water, and land, and by maximising reuse across multiple dimensions.

Heat from the racks can be recovered and re-used in local district heating networks, fulfilling the heating demands of the local community. However, enabling waste heat recovery in a data centre facility, requires some inventive thinking, to ensure that the facility’s resiliency and business continuity are not compromised.

As the designers of the largest data centre waste heat recovery system in Europe, we will examine the challenges and opportunities of such systems in our upcoming articles.

The land-use of the data centre building can be reduced by the adoption of high-density racks and/or by moving towards high-rise data centre buildings.

Cooling of high-density racks, with power densities that may exceed 50 kW per rack, goes beyond the capabilities of conventional air-cooling systems. Liquid-to-chip cooling is a suitable technology for addressing such high loads.

The Facility Water Systems (FWS) that support liquid cooling often operate at elevated temperatures (>40C), relative to the systems that support air cooling. This makes them ideally suited to integration with waste heat recovery and district heating networks in the urban environment.

The potential to exploit free cooling also increases, which may in turn reduce or eliminate the need for evaporative or mechanical, refrigerant-based cooling. This can greatly reduce the energy and water consumption of the facility. In this series of articles, we will share our experience in designing liquid-cooled facilities and highlight the benefits and challenges.

Location, location, location

The development of high-rise data centres is often driven by several factors: primarily the scarcity and cost of suitable development land, particularly in urban areas where the location of the facility may have been selected due to its proximity to a target group of users.

An example of this might be data centres clustered around financial centres. Other factors may also apply, such as the desire to exploit ‘trapped’ capacity in locations where power is available, but only to a site of limited size, such as on a partially built-out DC campus.

The spatial constraints force the developer to build upwards, rather than outwards. In these circumstances, maximising utilisation of the available power supply, and plot footprint is key. High-rise data centres may therefore benefit from increased rack power density, where this is paired with the rights cooling technology.

However, further challenges arise from the need to ensure efficient operation: how can waste heat be effectively dissipated away from the building, and how can heat rejection equipment, mechanical and electrical plant be accommodated in a building, where both the roof space and plot size are limited? We will draw upon experience of designing high-rise data centres across the EMEA and APAC regions, to provide some answers to these questions.

Be water aware

With water becoming a scarcer commodity, water usage effectiveness (WUE) is growing in importance. In projects across multiple regions, lack of an adequate water supply is driving the adoption of waterless heat rejection systems, while PUE still needs to be optimised.

This is forcing designers to re-evaluate other parameters, such as the thermal operating envelope within the technical space. By designing for higher operating temperatures, the period when free cooling is viable may be extended. The incorporation of waste heat recovery may also be beneficial.

However, in many cases, the move away from adiabatic cooling is forcing increased reliance upon mechanical, refrigerant-based cooling solutions, which come with their own set of problems.

The use of zero ODP and low GWP refrigerant is a fundamental requirement for this transition. But while HFOs were initially seen as being the best ‘drop in’ alternatives to HFCs, from both an environmental and energy efficiency perspective, recent research has revealed that they are not as benign as first thought; when some commonly used HFO refrigerants decompose in the atmosphere, they form trifluoroacetate (TFA) – a salt of trifluoroacetic acid.

TFA is harmful to aquatic life, even in low concentrations. It is also virtually non-degradable in the environment and cannot easily be removed from drinking water supplies using any current water purification techniques.

Other research has proposed that one of the breakdown products of a widely used HFO refrigerant is R-23 – which itself, is a highly potent greenhouse gas. Would the use of natural refrigerants be able to overcome these problems? Is the industry ready for such a transition? We will be discussing this topic as part of this article series.

Within Cundall, we have many years of experience in designing efficient data centres. However, the more we learn, the more we come to appreciate how much work is still to be done.

True net zero carbon means engineering-out carbon emission through design, to the greatest extent possible, whether those are the upfront emissions generated from the manufacture, transportation and installation of materials and equipment, or operational energy and water-related emissions. The aim of the upcoming series of articles is to explore the areas where we, as designers, can have the most impact.

Originally published in Data Center Dynamics in October 2023.