DATA CENTRES COOLING
The amount of water and electricity consumed in the ATP can be manipulated by raising or reducing the point at which evaporative cooling is activated
cooling will be reduced. However, even if the outside air enters the unit saturated and at a low temperature, evaporative cooling will still occur when the air is heated as it passes over the heat exchanger; this raises its dry-bulb temperature and enables it to hold more moisture. The unit also includes a direct expansion
(DX) unit to provide a small amount of additional cooling for days when outside air temperature and humidity is exceptionally high. Heat from the DX unit is rejected into the scavenger exhaust air stream, avoiding the need for additional plant outside the facility. In cool, northern European climates, run-time for the DX unit will be minimal. Research by consultant Cundall Johnston and Partners predicts that for a typical year at London Heathrow airport, DX cooling will be required for fewer than 50 hours. Even in hot, humid environments with the DX unit running, the Air-to-Air solution will show significant running cost-savings over a refrigerant-cooled data centre. To enable the unit to work cost-effectively anywhere in the world, the amount of water and electricity consumed in the ATP can be manipulated by raising or reducing the point at which evaporative cooling is activated. In northern Europe, where water is plentiful and energy is relatively expensive, it is set up to maximise the benefits from evaporative cooling. By contrast, in locations where water is relatively expensive and energy plentiful, as in the Middle East, the DX unit minimises
58 CIBSE Journal September 2013
the water use in the evaporative cooler. The energy efficiency of the Air-to-Air solution is demonstrated by its power usage effectiveness (PUE), which is a measure determined by dividing the overall power that a building uses by the energy used in the white space alone. On a conventional data centre, the PUE ratio can be as high as two, which means that computer equipment accounts for only 50% of energy. The Air-to-Air ATP, however, will help to deliver a PUE ratio of less than 1.1. In other words, less than 10% of the energy used by the data centres is spent keeping them cool. An additional benefit of the energy efficiency of the system is that a smaller power supply is needed for the site. This reduces the utility costs of getting power to site and makes more sites viable. In addition, transformer and generator ratings can be reduced, along with switchgear and cable sizes. The ATP also has a low rate of water consumption, as water is collected in a sump at the base of the unit and returned to the sprays (the unit automatically refreshes the sump water when it becomes dirty). And, unlike misting systems, it does not need a cleaned or sterilised water supply, instead using harvested rainwater, switching to mains water if the tank falls to a minimum reserve level. Another major advantage of using evaporative cooling is that it enables the white space to be sealed and positively pressurised. As a result, the Air-to-Air data centre can incorporate the DigiPlex DeOx innovative fire prevention system. This environmentally friendly technology actively eliminates the possibility of equipment catching fire – in stark contrast to systems such as gas suppression, which are triggered only after a fire has occurred. The DeOx system works by compressing
the air, drying it and then passing it through a molecular filter to reduce the proportion of oxygen molecules from 21% to 15%. This means there is sufficient air for humans to work normally, but insufficient oxygen to enable a fire to ignite. To ensure quality and to speed construction, every module is built off site. They are available in widths of 2.4m or 2.9m so they are easily transportable by road. All the cooling equipment and controls are factory-installed, providing a ready-made, sustainable and economic solution that can be tailored to meet the demands of any location in the world. CJ
www.cibsejournal.com
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