Data Centres and Renewable Energy Project
PowerUse in Data Centres
Where is Energy used in data centres?
Data centres use energy in three main areas (1):
- Powering the IT equipment – servers, storage and communications
- Infrastructure – power conditioning units, uninterruptible power supplies (UPS) and backups, lighting, humidity control
- Cooling – air handling, heat exchangers and chilling. This has to be capable of removing all the energy used for IT and the infrastructure
Growth in IT power density and total power
As servers have become more powerful, and more packed together, not only has the total IT demand of a typical data centre increased, the power density has become more and more concentrated as well. The power density of data centres is generally measured in terms of either:
- Power per rack, W/rack. A rack is a standard metal housing for IT equipment, 19” high and 36” deep and up to 88” high.
- Power per unit IT area, W/m2. IT area is often referred to as ‘raised floor area’ because the traditional method of cooling involves blowing air round the racks through a mesh floor
The Lawrence Berkeley Laboratory of the University of California carried out a number of benchmarking studies of existing data centres in 2004 (2). The highest energy density they reported had an average around 0.60kW/m2 (3) and individual racks ranged from 0.75-4kW (4). The highest total IT power was under 0.5MW in a data hall of 690m2.
Three years later, Intel was able to describe a power of 6.6kW/rack as ‘low density’ in a paper advocating the cost benefits of high density racks (4). They described a typical new build data centre as having 4MW total IT load in a 2500 m2 data hall.
In 2009 Telecity, a data centre hosting company, opened a new unit in London aimed at high-power users (5). This can accommodate 10MW of IT power in racks which take between 4-20kW each. The first unit in the newly opened Cambridge Data Centre has around 6MW in 3700 m2, at an average of 4.7kW/rack (6).
Measuring energy performance:
Energy performance is generally measured in terms of Power Usage Effectiveness (PUE), defined as (7):
Therefore, the closer the PUE gets to 1.0, the more efficient the data centre.
The US Environmental Protection Agency carried out an extensive data centre benchmarking exercise in 2008/09 (7). 121 data centres collected their energy use data over 11 months; the centres comprised old and new, stand-alone and co-located in offices. The average PUE was just over 1.9, with some very inefficient centres still in the 3.0-4.0 range. A handful were very efficient, with a PUE between 1.1 and 1.5. The availability standard or Tier of data centre was not found to affect energy efficiency (8).
A study on energy efficiency carried out on behalf of some of the biggest data centre operators in 2008 concluded that if all the infrastructure best practices were to be implemented in one place it should be possible to achieve a PUE of 1.36 in a legacy building and 1.27 in a new build (9).
Developments in energy efficiency:
Although historically energy efficiency was not a consideration in designing data centres, rising energy prices, increasing Carbon emission legislation and climate change concerns have brought it into increasing focus (1).
Outside the scope of this project, but very importantly, a great deal of development is taking place to make servers more energy efficient, and to use their capacity to the full through virtualisation and cloud computing (1), (9).
More efficient power equipment design includes reducing standby losses (2), ensuring that the power supply is the right size for the facility rather than too big (10), using UPS systems with flywheels or fuel cells rather than batteries (9) and looking at reducing the power conditioning losses as incoming AC current is converted to DC and then back again.
The biggest area for efficiency savings is however in cooling, with a 5:1 difference between least and most efficient (2). This area is covered further in the section on Cooling.
Use of renewable energy
There is much interest in reducing carbon footprints through using renewable energy, although so far only a limited implementation. Some data centres use some renewable energy: i/o Datcentres Phoenix One facility has a 4MW solar PV array as part of its 80MW power (11). The Cambridge data Centre will meet about half its 72MW power from an on-site biomass plant (6). The proposed Lockerbie data centre will make use of local wind and biomass plants, although this will be via the grid (13). Only one data centre operator, AISO, claims to be 100% powered by renewables, in this case solar PV (12)
Waste heat as a by product of the centre is also starting to be used; Telecity provide district heating for nearby homes from their data centre in Amsterdam, and they heat a commercial greenhouse beside their Paris facility (14).
References used in this page:
(1) EPA 2007: Report to Congress on Server and Data Centre Energy Efficiency, Public Law 109-431, EPA US, August
(2) Greenberg, S; Mills, E; Tschudi, B; Rumsey, P; Myatt, B 2006: Best Practices for Data Centres: Lessons Learned from Benchmarking 22 Data Centres ACEEE Summer Study on Energy Efficiency in Buildings vol 3 pp76-87
(3) Tengfang, X; Greenberg, S 2008: Data centre Energy Benchmarking Part 2: Case Studies on two Co-Location Data Centres (no 18 and 19) Lawrence Berkeley National Laboratory 23 May
(4) Tengfang, X; Greenberg, S 2007: Data centre Energy Benchmarking Part 1: Case Studies on two Co-Location Data Centres (no 16 and 17) Lawrence Berkeley National Laboratory 1 Aug
(4) Patterson, M K; Loeffler, M 2007: Data Centre TCO: a comparison of high-density and low-density spaces Intel White Paper, submitted to THERMES, Santa Fe Jan-07
(5) Telecity Powergate 2010: London - Central London Data Centre http://www.telecitygroup.com/colocation-data-centre-central-london.htm, accessed 20 Feb 2010
(6) Cambridge Data Centre 2010 Website of Elean Data, http://www.eleandata.com/, accessed 10 February 2010
(7) EPA Energy Star 2009 Data Center Infrastructure Rating Development Update http://www.energystar.gov/ia/partners/prod_development/downloads/ 29 September; accessed 10 February 2010
(8) EPA Energy Star 2009: Data Center Infrastructure Rating Development Update http://www.energystar.gov/ia/partners/prod_development/downloads/ 12 November; accessed 10 February 2010
(9) SLVG 2008: Silicon Valley Leadership Group: Data Centre Energy Forecast, August
(10) Rasmussen, N 2008: An Improved Architecture for High-Efficiency, High Density Data Centres APC White Paper no. 126
(11) Phoenix ONE: http://www.iodatacenters.com/data-centers/data-center-power.php
(12) AISO Solar Power http://www.aiso.net/company-vision.html
(13) Lockerbie Data Centre 2009: Peelhouses Data Centre & Sustainable Village: Masterplan Document, March 2009 http://www.lockerbiedatacentres.co.uk/, accessed 2 Feb 2010
(14) Telecity Green data Centres 2010: Environment http://www.telecitygroup.com/environment.htm, accessed 20 Feb 2010