Every little helps

Summary

• UK ambient conditions can support substantial free cooling when chillers and controls are specified for partial-load operation.
• Adaptive cooling strategies can reduce compressor running hours, pumping energy, and mechanical wear.
• Recovered server heat can supply neighbouring users when temperature requirements, network integration, and demand are planned early.

Cooling will always be mission-critical in data centres, accounting for a big proportion of energy and, in some cases, water usage. What’s key for data centre designers and operators is that every effort is made to improve operational efficiency, and in turn reduce the consumption of these essential resources. Tim Mitchell, Sales Director at Klima-Therm, explains how free cooling, intelligent controls and heat recovery can reduce data-centre electricity use, maintenance demands and carbon impact.

Data centres convert almost every watt used by IT equipment into heat, which must then be removed continuously and reliably. Cooling plant is therefore one of the most important controllable elements of operational expenditure. The opportunity is not one of dramatic intervention, but a series of connected gains: use ambient conditions whenever possible; match pumps, fans and compressors to the real load; raise water temperatures where the IT design permits; and recover useful heat rather than rejecting it. Each measure helps Power Usage Effectiveness (PUE).

Behind the operational pressures of individual data centres is a backdrop of changing regulation and climate. Hot summers and low rainfall have caused repeated drought, at odds with using the superior cooling capacities of water-based adiabatic cooling, which is better suited to data centres with the largest demand – i.e. the ones concerned with AI – compared to dry air only cooling.

By adding free cooling into the mix, savings can be made, with direct-to-chip liquid cooling offering some of the greatest efficiencies whilst potentially using no water. Adiabatic systems, which deliver evaporative cooling by spraying fine water mist onto or towards heat exchangers, or running water over pads upstream in the heat-rejecting air streams, will cause a spike in water consumption on the hottest days, whereas the fluid returning from the servers cooled via direct to chip can safely be up to 50°C – significantly warmer than even the record-breaking 40°C some parts of the UK have experienced this summer. This heat can then naturally dissipate into the outside air or be recovered and reused at a more useful temperature than cooler room air.

Air-cooled systems still offer an excellent solution for many data centres. The latest solutions deal better with warmer conditions thanks to hot aisle containment, which raises cooling coil air-on temperatures, allowing chilled water temperatures to increase whilst still delivering the required cooling duty and enhanced efficiency.

Free cooling in the UK

Despite the extremes we have experienced recently, overall, the UK has a temperate climate, giving the ‘free cooling’ approach a valuable head start. With well-managed airflows and appropriately elevated chilled-water setpoints, outside air can reject heat for much of the year without full mechanical refrigeration.

Not all free cooling solutions are equal however, and it’s important that this assertion is investigated fully before investment in new technology. Crucially, the system must be able to operate in partial free cooling mode, not just ‘on and off’, in order to provide savings throughout the year.

Free cooling isn’t just an add-on to a conventional vapour-compression chiller. Instead, a ‘free cooling first’ approach must be central to specification, selecting chillers that maximise ambient heat rejection whenever conditions permit, rather than only at very low outdoor temperatures. How the unit will perform hour by hour over a typical year, based on the site’s location and water-temperature regime, must be understood. As the title of this article states, ‘every little helps’.

Adaptive controls

Effective mixed-mode operation depends on combining the right hardware with an optimised control strategy. Owners should seek designs that can vary the free-cooling contribution without forcing the entire refrigeration circuit to operate within one conservative set of limits. This keeps cooling stable and predictable for the IT load while capturing as much ambient capacity as conditions allow. Isolating unused condenser coil banks, for example, can allow fans to increase free-cooling output without driving an active refrigerant circuit into unstable conditions.

Ultimately, fewer compressor run-hours mean lower electricity consumption and less mechanical wear, with potential reductions in servicing, component replacement and unplanned intervention. We also recommend minimising the use of glycol in the main chilled water circuit. Although it protects against freezing, its higher viscosity increases pumping energy and reduces heat-transfer efficiency. Our non-glycol free-cooling system allows for the protection of glycol but without the cost, environmental impact and inefficiency of having glycol throughout the data halls.

Turn a cooling problem into a heating asset

The next gain comes from treating rejected heat as a useful commodity. Well-planned urban developments place data centres beside ‘heat users’ – homes, hospitals, offices, leisure centres or industrial processes.

As discussed, the thermal output from IT equipment is a consistently high-grade source of low-temperature heat, typically between 30–35°C on the air side and up to 60°C with direct liquid cooling. This can be boosted to around 80°C using high temperature heat pumps, making it viable for a range of applications both domestically and commercially.

For network designers and installers, the key considerations include hydraulic separation between data centre and district circuits, redundancy in heat exchanger and pump selection, and the integration of controls for dynamic heat demand response. The system design should also account for the potential use of modular heat interface units (HIUs) at the point of delivery, and the adoption of smart metering for performance monitoring and billing.

This symbiosis can also improve the data centre’s efficiency – heat rejection into the atmosphere uses more energy than recovery. The carbon saving benefits of this approach should be viewed community wide, however, as there is of course power and equipment needed for the redistribution of heat.

Heat recovery and free cooling in action

In Germany, an ENGIE Refrigeration deployment across ten edge data centres combines nine air-cooled chillers with integrated free cooling, seven water-source heat pumps and three chillers with Green Heat Recovery. The manufacturer reports energy savings of up to 60%, while the installed plant provides 6.75MW of cooling from the free-cooling chillers and 5.25MW of heat-pump output. This example combines cooling efficiency and useful heat delivery in one operating strategy.

Specify outcomes

For data centre developers, specifying outcomes not just technologies, is key. kWh across the expected weather file and load profile must be considered alongside proof of stable partial free cooling. For heat recovery, begin conversations with the local authority, heat-network developer and prospective customers before the cooling architecture is fixed. Confirm return temperatures, seasonal demand, redundancy, connection responsibilities and the carbon-accounting method.

Every efficiency gain matters, compounding over a 24/7/365 operating year. The optimal data centre, therefore, is part of an energy system, designed to minimise what it consumes and maximise what it can usefully return.

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