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The case for thermal insulation

Tom Merton

Tom Merton

Technical Specialist at Armacell
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Thermal Insulation
Image credit: Armacell

As organisations across the UK unite to help honour the pledges made by the Government at the COP26 United Nation Climate Change Conference to limit temperature increases above pre-industrial levels, data centre managers face the dual challenge of keeping their facilities cool while limiting energy consumption and their carbon footprint.  

A 2020 study published in the Journal of Science found that data centres account for 1% of total energy use worldwide; according to a 2021 Techerati report, they are also responsible for up to 2% of global CO2 emissions.

Server rooms must be kept cool in order to provide optimal operating temperatures for the electrical equipment within, allowing it to function safely and reliably. If computers get too hot, they automatically switch off to avoid damage. The industry tends to work to the ASHRAE guideline of an ambient temperature of 18-27°C. As the equipment itself generates a vast amount of heat – especially as new technologies feature higher density chips and rack densities increase – refrigeration and air conditioning systems are deployed to provide intensive data centre cooling around the clock.

This year, steep hikes in energy prices make the issue of energy-efficiency particularly pressing, with the research firm Cornwall Insight predicting in October 2021 that UK energy bills could rise by as much as 30% in 2022 if the cost of gas and electricity continues to soar.

Hot aisle to cool down

A widely used energy-efficient means of data centre cooling is the use of hot aisle containment computer room air conditioning (CRAC) systems, which channel cold air to specific areas of the room, pulling cool air through the server racks and removing heat from the equipment before returning it to the CRAC unit via a predefined ‘hot aisle’ route.  

This is a more sustainable technique than the traditional method of data centre cooling, which involves the pressurisation of space below a raised floor and transmission of cold air through perforated tiles into the main data room space.

But data centre managers can go one step further than deploying an energy-efficient hot aisle CRAC solution to improve power usage effectiveness (PUE) and meet stringent sustainability regulations, by taking care to insulate it properly, both to prevent heat gains as warm air escapes from the system back into the room and to guard against the condensation that can form on the surface of cool pipes.  Insulation is the least expensive method of reducing CO2 emissions.

Closed-cell insulation

It is widely known that flexible elastomeric foam (FEF) is a more practical insulation than rigid materials such as phenolic, polyisocyanurate (PIR) and expanded polystyrene (XPS), which are difficult to fit securely to provide a fully sealed system.  But when it comes to energy-efficiency, not all FEFs are equal and closed-cell insulation is the best.

Closed-cell FEF insulation comprises millions of tightly packed, closed air filled cells, each bonded to those around it, creating an impenetrable barrier to both air and moisture, precluding the need for an external water vapour block.  

The rate of thermal ageing – the process by which materials lose a percentage of their thermal resistance over time – in closed-cell insulation is extremely slow when compared to open-cell alternatives; a low level of thermal conductivity is maintained, allowing the CRAC system to operate energy-efficiently long-term.

In recent Armacell research conducted by the Fraunhofer Institute for Building Physics in Stuttgart, it was found that over a period of 10 years, the thermal conductivity of our closed-cell FEF insulation, AF/ArmaFlex Class 0, rose by only around 15%; over the same period, that of open-cell mineral wool rose by 77% and polyurethane (PUR) by 150%. As a result of the poor performance of mineral wool in particular, its use on refrigeration pipes is restricted in some European countries, including Germany and Belgium.

An accessible alternative

Closed-cell FEF also prevents condensation forming on the pipework that carries cooling liquid or refrigerant. Condensation is the enemy of insulation for several reasons, not least because when it’s damp, it does not insulate properly and the CRAC system needs to work overtime to maintain a cool ambient temperature.

It can also corrode the insulated pipes to the point where they fail to function safely and efficiently and require replacement, and it goes without saying that data centre equipment must not come into contact with dripping water. Open-cell insulations are more prone to condensation as their structure allows air to reach the surface of cooler pipes, so they require the application of external water vapour barriers.

A further advantage of closed-cell insulation is its hygiene, and this is vital as data centres are ‘clean room’ environments where insulation must not release dust or fibres that could interfere with the performance of the equipment.

There are many unique data centres around the world that utilise ingenious sustainable methods of maintaining a constant temperature, ranging from those based under water, in nuclear bunkers, in 19th century cathedrals and in the Arctic Circle.  These options are not available to the majority of organisations, but the judicious insulation of CRAC systems with closed-cell material provides an accessible and cost-effective alternative. 

The selection of products such as pipe supports featuring recycled material, requiring less energy to manufacture and generating less CO2 as compared to conventional structural materials, and can further support the goal of sustainable data centres.

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