DATA CENTRES & CABLE MANAGEMENT


Ultra-efficient reverse osmosis improves data centre sustainability


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Ben Hazard, Process Engineer, at Te-Tech Process Solutions explains how a new ultra-efficient batch reverse osmosis technology can help improve data centre sustainability


ata centres are packed with information communication technology (ICT) hardware – servers, central processing units (CPUs) and graphics processing units (GPUs) – that


use enormous amounts of electricity, most of which is converted into heat. To keep them working they must be cooled to about 27°C. Small data centres use air cooling – effectively air conditioning – but in hyperscale centres, with more than 5,000 servers and areas larger than 1,000m2, this is simply not practicable. In these facilities, liquid immersion technology has become the norm. It’s more efficient because liquids have a higher specific gravity than air and it’s also easier to control because liquid flow can be readily diverted to where it is needed by automatic valves. The relentless demand for cooling consumes vast amounts of both energy and water, which has a significant environmental impact.


Where does water come in?


The heat is removed from the ICT units into a coolant, typically an organic refrigerant, which is recirculated to a refrigeration unit. This, in turn, is cooled by cooling water in a recirculatory system with an evaporative cooling tower. The metric for water consumption in data centres is the water usage effectiveness (WUE), which is defined as the site water usage divided by the ICT energy consumption, and is typically about 1.8 L/kWh. Hyperscale centres for “cloud” applications can use as much as 80 MW which can mean water consumption as high as 2000 m3/day, so there is a drive to reduce this figure to conserve water resources. One major initiative is the EU’s Climate Neutral Data Centre Pact, which aims to reduce WUE to a maximum of 0.4 L/kWh by 2030.


Reduced water consumption, how can it be achieved?


One way of minimising water consumption in recirculatory cooling systems is by increasing the cooling tower concentration factor, which is limited by water chemistry. Reducing the total dissolved solids concentration of the cooling tower make-up water by reverse


SAM50, designed by Salinity Solutions and available in the UK from Te-Tech Process Solutions under a new manufacturing partnership


osmosis allows concentration factors to be increased by up to 10 times, reducing blowdown and helping to minimise scale, corrosion and microbiological problems.


Isn’t reverse osmosis expensive?


Traditional reverse osmosis systems use a lot of energy, but newly developed RO technology, SAM50, can typically reduce energy consumption by 50%. It can also achieve high recovery, reducing wastewater by up to 80%, compared to traditional reverse osmosis systems. Developed by University of Birmingham spin out Salinity Solutions and is available in the UK from Te-Tech Process Solutions under a new manufacturing partnership.


That sounds impressive, how does it work?


It’s a fully automatic batch RO system consisting of a high-pressure feed pump, a recirculation pump, an RO module, a free-piston pressure exchanger and three automatic valves as shown in the flow diagram:


SAM50 Pressurisation Phase (left) and Purge & Refill Phase (right)


In the first phase of the cycle, the pressurisation phase, the feed pump applies pressure to the feed side of the pressure exchanger, matching the minimum osmotic pressure of the water in the batch. This pressure is transferred to the batch of water that is being processed via the free moving piston.


The batch then passes through the membrane module, producing permeate and a reject stream. The reject stream is then recirculated into the pressure exchanger via the recirculation pump. During this process no additional feed


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is added, so the concentration inside the recirculation loop increases over time. As a result, the feed pump generates a higher


pressure to overcome the increasing osmotic pressure, causing the piston to slide to the right. This allows for the average pressure of the cycle to be lower than in conventional RO technology, thus reducing the energy demand. When the piston reaches the end of its travel, the pressurisation phase ends, the automatic valves change position and the purge-and-refill phase begins.


During this phase, concentrated reject brine is discharged to waste and the free piston moves to the left back to its original position. This cyclic operation not only reduces energy consumption but also allows a much higher water recovery and, hence, reduced waste.


Why is this important?


With some 30 billion devices online, data centres are increasing both in numbers and size, creating a vast demand for water. With rising energy costs and a growing demand for water to supply a growing world population, a low energy batch RO system with high recovery can help to reduce WUE towards 0.4 L/kWh and make a valuable contribution to reducing operating costs and water conservation.


BUILDING SERVICES & ENVIRONMENTAL ENGINEER AUGUST 2023 7


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