FOCUS on COOLING
The way that air is pushed – and pulled – around your IT equipment has a big bearing on how efficiently heat gets moved around too
The term ‘air handlers’ denotes a sub-category of the whole Heating, Ventilating and Air Conditioning Equipment (HVAC) world and condition and circulate air as part of such a function. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the building and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork. They are also typically the part of the system where most attention is paid to handling humidity. But they are another very energy-intensive item. An air handler fan is typically the second largest energy user in the entire HVAC system.
There are a number of specialist manufacturers outside of the typical data center component supply industry, from Aaon and Addison to Johnson Controls to Robatherm GMBH. A name that stands out here: Trane (www.trane.com
), which offers a wide range of products in the field used in data centers that it says address such issues as humidity control, energy recovery, special acoustical needs, air filtration and the use of optional fuel sources. Another specialist is AirFlow. There is a well-established rent versus buy model; a player like Aggreko, for example, is happy to rent you anything from a 5 to a 15 ton device that can produce up to 400cfm (cubic feet per minute) of airflow per ton and it can also offer a low-temperature version that can operate down to -29C.
Where possible, look to save the cost of running your handler. The cooler the air you give it to push round, the less juice you should need to burn. Many experts recommend using outside
air as much as possible in partnership with an air-side economiser, especially at (cooler) night hours. Microsoft’s recently opened Dublin Cloud data center uses rooftop-placed air handlers, for example, that take outside Irish air and draw it into the data center for use in the air conditioning system. (If the temperature exceeds the desired range, or external air quality is affected by a nearby fire or contaminants, Direct eXpansion (DX) cooling kicks in instead of expensive chillers.
Close control of fan speed is also essential to curbing use of power/cutting cooling overhead cost. If you can reduce it by just 10%, fan power consumption overall can decreases by up to 27%. Older fans were of course mechanical devices that used pulleys. More modern fans that are more applicable to data center use are so- called plug or plenum fans where the fan motor is connected directly to the fan and the outlet holes are also bigger.
Another key aspect to the efficient use of any air handler is placement. It is recommended that where possible large centralised air handlers are deployed, as they offer the kind of efficiency improvements one can expect from larger pieces of equipment while accommodating a number of controls and configuration efficiency opportunities. A central air handler system can also save energy by running the entire system at a lower pressure drop when areas of the data center are loaded below the design assumptions. A distributed system can only realistically realise lower cost by cutting fan usage on the one or two units serving more lightly loaded areas, assuming the smaller units are equipped with Variable Speed Fans. The reason data centers tend to have so many smaller units is historical. Now when highly concentrated loads are more the norm it is a superior solution to have a bigger system which is centrally managed and controlled so that the overall efficiency is increased.
Another placement ‘trick’ is called the “chimney” approach, in which hot air exiting the rear of the equipment rack is collected above the ceiling, and then routed directly back into air conditioning units at the exterior of the raised floor area. This prevents the hot air from re- entering the rack or re-circulating into any cold aisles you may have set up.
In contexts without raised floors, it may also be possible to look at using variable frequency drives on the air handlers. Instead of running fans at 100% speed, variable frequency drives vary the speed of the fans depending on what’s actually needed to cool the IT equipment on a row-by-row basis. Sensors constantly monitor temperatures and the air handler fan speeds are automatically adjusted to increase fan speeds in hotter areas and reduce them in cool areas. The energy saved by reducing fan speed is exponential: a reduction of 50% in fan speed yields a reduction in power consumption of 87%.
It may be appropriate to talk to a specialist data center airflow management consultancy to help decide if such topography changes would be helpful. One such is Degree Controls Inc (www.degreec.com
), which provides thermal and airflow technologies for the electronics and telecommunications industries. It uses sophisticated thermal analysis and computer simulation to design and manufacture proprietary fan trays and intelligent controllers Its AdaptivCool system is designed to intelligently and actively manage the airflow. AdaptivCool eliminates hotspots and saves up to 30% of cooling energy, via an advanced monitoring and control system. The system dynamically manages the flow of cooling air to the IT racks and exhausts hot air back to the CRAC intake. It then automatically compensates minute-by-minute for changes in cooling and IT load, with the overall result of substantially reducing electrical cost by improving cooling effectiveness (www.adaptivcool.com
| 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