ACR-News

THE key to reducing the cooling load in server rooms is to integrate the best technology in the most efficient way, says George Hannah, development manager of Airedale
Keeping a server room running 24hrs/day is critical to business survival yet operators face constant pressure to do more with less, without risking uptime.

On top of this, every kilowatt of power consumed by the computer can produce up to 1kW of heat. Since stable temperatures are required for computers to function reliably, this heat must be managed. Humidity is also key for reliable operation and both of these operations use yet more power.

Typically cooling accounts for around 58% of a data centre power usage. One kW power saved every hour on one unit alone, becomes significant in the operation of a data centre, representing a saving over a year of £700 (£0.08/kWh) or over 4 tonnes of CO2.

High efficiency cooling combined with advanced controls enables us to create solutions that integrate free-cooling chillers with precision ac systems and rack level products. The latter are even more efficient in the IT environment because they deal with heat closer to the source and are ideal for coping with hot spots.

Reacting to changing heat loads

Faced with the variable load conditions of the server room, traditional close control units are relatively inefficient compared with latest systems which often work at part load and vary the amount of cooling to avoid unnecessary waste of power.

By incorporating for example 30-90Hz inverter driven scroll compressors in high efficiency CRAC units, it achieves precise and efficient cooling from 25-100% when operating at part load. By applying the Turbocor compressor to an air-cooled chiller, load requirements can be matched exactly. Typically this gives a reduction in running power of up to 20% compared with a high efficiency screw chiller.

Fan efficiency is pivotal to reducing energy consumption, particularly in part load applications. By matching air volume in CRAC units, in response to changes in room demand, system power consumption can be significantly lowered. The high efficiency of the EC fan in part load applications further enhances power reduction. On a chilled water unit where air volume can be matched to load, the EER can increase from 26 to 100.

Free-cooling using ambient air

Since free-cooling can operate with as little as 1ºC differential between ambient and return fluid temperatures, the 24/7 operation and the high temperatures of a server environment mean that a free-cooling opportunity is increased and the chiller will use very little mechanical cooling. A chiller with simultaneous mechanical and free-cooling will always use free-cooling first before initiating mechanical cooling. Selected high efficiency precision ac units now include dual cool options with a free-cooling variant which uses 46% less energy than a standard air cooled DX system.

Using heat to cool

In dealing with a higher grade heat and subsequent higher processor air-off temperatures of a server room, the free-cooling threshold can be increased so that a larger proportion of the year is spent in free-cooling mode. By operating at higher temperatures there is also more opportunity for dew-point control and without liquid on the coil surface, there is greater scope for higher volume airflow and hence more capacity from the system.

When monitoring the room load and automatically adjusting chilled water setpoints to match this load, we see a significant increase in plant energy efficiency at higher water temperatures.
Significant power can be saved by managing air volume to the space across multiple airside units by sharing airflow duty between run and standby units. The more units, the greater is the benefit. By running three airside units instead of two, gives a 70% saving in power of 5.3kW.

A web of multiple cooling products can be integrated so that they interact, communicate and are managed and optimised via a single BMS to reduce energy costs through combined efficiencies. Such a BMS is specifically designed for data centres and is fail safe, with two-way communication, alarm handling and an IP address that can sit on an existing Ethernet and browsed remotely.

Airedale
0113 239 1000