Power & Cooling
By increasing the ASHRAE limits, consultants have an opportunity to explore alternative design solutions focusing on reducing the air conditioning energy consumption of the data centre. One solution is to use air side economisers also labelled as “free cooling” economisers. This should not be confused with water based economisers which are also labelled as “free cooling”
economisers. An air side economiser allows large volumes of fresh air to be drawn into the data centre whenever the outdoor conditions are favourable. The outside air is distributed into the server rooms which is then warmed by the servers through heat transfer. Instead of being re-circulated and mechanically cooled, the air is simply expelled out of the building. Water based economisers on the other hand use outdoor air to cool a fluid based cooling system via a heat exchanger. This in turn cools the internal air via another heat exchanger without the use of mechanical cooling. Because the water based economiser uses heat exchangers an air side economiser can provide attractive energy savings. Both designs are not entirely free since some energy consuming components (like fans) are needed to make the design work but can be significantly less than the energy used by traditional mechanical cooling. Both air side and water based
Fig 2
economisers may still require supplementary mechanical cooling when outdoor conditions are not favourable.
Maximising economiser using adiabatics
Air side economisers designs have a further advantage that adiabatic cooling can be used to boost the free cooling hours and reduce any mechanical cooling hours as well as the duty and footprint of the equipment.
Adiabatic Cooling vs. mechanical cooling Adiabatic Humidifier Duty
Adiabatic Cooling Power (Direct Evap. Cooling) Adiabatic Power consumption
Water treatment Power consumption Total Adiabatic power consumption Mechanical Cooling power
Mechanical power consumption (COP =2.8) Energy saving
Table 1 30 | DATA CENTRE SOLUTIONS |
www.datacentresols.com
Value 460
318.24 1.15 1.1
2.25
318.24 113.65 98.02%
Units L/Hr KW KW KW KW KW KW
Adiabatic cooling is the evaporation of water, such as a high pressure spray system, with a corresponding reduction in temperature. Energy to change water from its liquid state to a vapour state is taken directly from the air thus cooling it. Every litre of water evaporated provides 680 Watts of cooling from as little as 5 Watts power. On hot dry days the adiabatic system cools & humidifies the intake air therefore extending the free cooling hours of the air side economiser. Control limits are set to avoid the humidity level increasing beyond the recommended environmental envelope.
Additional savings can be achieved by adding a secondary adiabatic cooler and heat exchanger. Located in the exhaust section the adiabatic cooler can significantly reduce the return temperature on to the heat exchanger which in turn pre-cools the fresh air intake. Since the adiabatic cooler is located within the exhaust section there is no restriction on the humidity level.
February/March 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44