Making Progress in Data Centre Energy Reduction
CPW are supporting 3DReid Architects with the Initiative 'Living with Data - Harvesting the Heat', which aims to reduce carbon emissions (both embodied and operational) associated with Data Centres, and explores the potential for integrating them into existing urban environments.
As with any project that CPW work on, there is never a universal solution when designing data centres. The final solution and service philosophy depend on the density and types of servers to be employed, and the location of the servers.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and server manufacturers have a number of criteria with differing requirements, however, the most onerous limit is ‘A1: Operating temperatures should be between 15°C to 32°C’. There are bands that allow higher temperatures, however at the onset of a project we choose to design for ‘A1’ which ensures that the room is suitable for all equipment. If more accurate detail becomes available, there is always opportunity to revisit the design if appropriate.
We therefore target 20°C to 27°C in normal operation, with occasional excursions to a maximum of 32°C (when extreme outside temperatures coincide with the maximum load for IT equipment, which is a rare occurrence). The advantage of these temperatures in the UK climate is that we can serve a data centre all year, without the need for high energy mechanical cooling systems, by using evaporative cooling to reject the heat. This will maintain 20°C to 27°C over 95% of the time, and always less than 32°C.
Evaporative cooling can be achieved in evaporative cooling banks or indirect air handling units, and can bring the Power Usage Effectiveness (PUE) down to 1.05-1.15, dependant on the size and other equipment utilised. A typical data centre using downflow cooling units and chillers would have a PUE in the order of 2.0, so evaporative cooling yields an improvement of between 41-47%.
Taking a step further, if the energy centre was to be co-located with facilities that need heating (especially if said facilities require heating all year), then there is the opportunity to use the waste heat from the data centre rather than losing it. This approach would mean we use the energy twice: once in the form of electrical energy to perform computations, and again as that energy is emitted as heat and can be used to heat another space. This process saves primary energy that would otherwise be used to provide heating.
Once the largest energy consumer (the cooling) has been addressed, focus then needs to be placed on the remaining systems to ensure that they are as efficient as possible.
For instance, a rotary uninterruptable power supply (UPS) can be far more efficient than a traditional battery UPS. Inverters for the UPS can also be optimised for efficiency.
Lighting, small power and ventilation are all areas that should be considered carefully to ensure that optimum efficiency is obtained, as long as cost remains reasonable.
Insulation of external walls of the data centre must be carefully considered and modelled as the likelihood is that a lower-than-normal insultation level will result in a lower energy demand over the year. Key areas in this are ensuring good permeability and water tightness / security of the data centre itself. In addition, a heavyweight mass in the building construction can help delay solar gain and flatten out the cooling demand for the space, again reducing demand and increasing efficiencies.
The solutions must be a result of close collaboration, as operation and day-to-day management of the data centre will play a key role in ensuring that the servers run effectively and obtaining optimum efficiency. As such, areas that must be discussed and agreed include:
Server density in racks and in the room as a whole
Air-flow management within racks
Direct in-rack cooling
Legacy equipment
Equipment monitoring
The more information that can be gathered from the end-user at design stage, the more effectively we can design the services for efficiency and carbon reduction. We can also then provide support to the other members of the design team with a greater accuracy of information surrounding areas such as fabric or air permeability limits.
Where this information is not available there runs a risk of inefficiency, mainly in having an oversized plant and associated equipment which will not be operating at peak efficiency. Having a scalable solution, where additional cooling can be added to a live data centre as it develops over time, can allow modules to be added where required. This approach allows for correct sizing for likely loads, rather than peak anticipated loads at some point in the future. It has the added benefit of minimising initial capital cost, and provides a level of flexibility for growth so that over the life of the data centre it can take advantage of new, more efficient plant as it is developed.
To find out more about 3DReid Architects and their initiative ‘Living with Data - Harvesting the Heat’, go to https://www.3dreid.com/living-with-data-harvesting-the-heat/ .