Data centre achieves PUE of under 1.1 with evaporative cooling
Evaporative cooling for a new data centre at Cambridge University has helped achieve a PUE (power usage effectiveness) of less than 1.1. It is the second data centre completed by EcoCooling for the Department of Engineering and uses the latest fresh-air and evaporative-cooling techniques and technology. The data centre is currently achieving a PUE of 1.06, but is not yet fully populated.
Four evaporative coolers provide 90 kW of cooling with n+1 redundancy. Air is delivered into the cold aisle of this first-floor data centre, which is populated with high-density racks. EC axial fans supply and extract air and use less than 5 kW at full load, so they add no more that 0.05 to the PUE
At present, the data centre is only partly populated, which can be exploited by the EC fans. The current energy use is less than 2% of the IT cooling load.
Air is supplied to a ceiling void and then filtered through G4-grade cartridges, enabling a large number of filter elements to be installed with minimum cost and space requirements. This is said to be the first installation of its kind to be used with a fresh-air system to provide a dust-free environment at a fraction of the cost of normal filters.
The control system was designed by EcoCooling using a Schneider Crouzet PLC to control airflow, humidity and temperature. There are also links to the fire-alarm system. These controls directly interface with a Honeywell Trend BMS for data and fault reporting.
This data centre is run at the lower end of the ASHRAE temperature standard at 18.5°C. It costs more to achieve, but gives a more comfortable environment for operators and also reduces temperature-related failures. Internal temperatures may rise up to 24°C on the very hottest days, but this is within ASHRAE guidelines.
Colder temperatures which could result in servers shutting down are prevented by mixing return air with supply air.
The control system controls the supply-air setpoint to control RH at ASHRAE-compliant conditions of 20 to 80%.