13 December 2021
A data centre
Post-Cop26 and in the face of an energy crisis, data centre managers face the dual challenge of keeping their facilities cool while minimising electricity consumption.
Tom Merton, technical specialist at flexible equipment insulation material and engineered foams manufacturer, Armacell, explains how data centre air conditioning and refrigeration systems can be managed to help achieve both.
Why data centres need to be kept cool
Typically, data centre managers strive to maintain an ambient temperature within their premises of the ASHRAE-recommended 18-27o. This is regarded as the optimal operating temperature for the equipment within, preventing overheating and automatic shut-down.
Why energy efficiency matters
As technology evolves to incorporate higher density chips and rack densities increase, the amount of heat generated within data centres is growing, placing more pressure on the air conditioning and refrigeration systems used to keep the facilities cool.
Left unchecked, this can result in increased energy consumption, but economically and environmentally, this is not an option. In 2020, the Journal of Science found that data centres account for 1% of total energy use worldwide. Arguably, this is already too high, and most managers will already be working towards stringent organisational sustainability targets.
As energy prices continue to rise - in October, Cornwall Insight research predicted that in 2022, energy bills could increase by 30% - the goal of achieving maximum data centre power usage effectiveness (PUE) now comes with an added financial incentive.
Hot aisle containment
Historically, data centres were cooled via a system whereby the space beneath the floor was pressurised, and the resulting cold air was transmitted upwards into the room through perforated tiles. While an effective means of maintaining a low temperature, it was unfocused and inefficient.
A more energy efficient method involves the installation of a hot aisle containment computer room air conditioning (CRAC) system. Using a predefined “hot aisle”, cold air is targeted at the warmest parts of the room, pulled through the server racks to remove heat and then returned it to the CRAC unit.
Insulation
CRAC system insulation is the least expensive means of achieving a high degree of PUE. Insulation prevents a scenario whereby warm air escapes from pipes and back into the room, forcing the system to work even harder to maintain a cool ambient temperature and utilising more energy.
Flexible elastomeric foam (FEF) is easier to install and seals the system more efficiently than phenolic, polyisocyanurate (PIR) and expended polystyrene (XPS) rigid insulations and closed-cell FEF is superior to open-cell materials.
The advantages of closed-cell FEF
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.
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 requires replacement, while it goes without saying that data centre equipment must not come in to 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.
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, can further support the goal of sustainable data centres.
