Citi recently designed an award-winning 100,000 square foot datacenter that achieves greater than Tier IV reliability and which also aims for a gold accreditation through the US Green Building Council's LEED scheme.
Citi has an ambition to significantly reduce its greenhouse emissions by 2011 and so has designed the new facility to minimise its environmental impact, for example it incorporates an optimised cooling design to produce 8,183 hours of free cooling per annum (93% of the time). Overall, the new facility provides a total saving of 11,700 tonnes of CO2 per annum compared to a typical datacenter.
One of many innovative solutions employed by the design team was the use of the state of the art simulation capabilities of 6Sigma DC and the Virtual Facility┬® to evaluate and improve the airflow management within the datacenter at each stage from concept design onwards.
Future Facilities Ltd, a UK company with specialised computational fluid dynamics (CFD) expertise for datacenters and mission critical facilities, has applied its extensive knowledge and experience to create 6Sigma DC, a unique virtualisation package specifically for the sector
Citi applied the Virtual Facility┬® to make decisions regarding the following aspects of the new datacenter:
1) Under floor airflow management
Ôé¼. Perforated diffusion baffles are attached to floor jacks in front of CRAC units, this converts the
high air velocity into an even static pressure in the active area of the data hall.
Ôé¼. Variable speed drive fans automatically maintain the even pressure in the event of CRAC
failure.
2) High Level data cabling
Ôé¼. High level data cabling eliminates underfloor cable dams, which cause low air flow and local
hot spots in a typical datacenter.
Ôé¼. High level data cabling also removes the need for cable penetrations in the raised floor which
unless completely sealed are a cause of waste of cool air and therefore a source of inefficiency.
3) Above floor airflow management
Ôé¼. Open network frames are interleaved with server racks to reduce length of data cabling. A
novel Hot-Aisle/ Cold-Aisle/ Cold-Aisle layout overcomes overheating problems in the open
frames.
Ôé¼. Hot exhaust air is captured in the ceiling plenum, reducing mixing of hot and cold air and
therefore protecting the equipment.
4) Recapturing the hot exhaust air
Ôé¼. Hot exhaust air is captured in a ceiling plenum; reducing mixing of hot and cold air and
protecting equipment from high inlet air temperatures.
Ôé¼. A well designed false ceiling provides the effectiveness of high-level return ductwork whilst
offering flexibility throughout the life of the facility: ventilation grilles can be simply moved to
accommodate changes to rack layout and changing ventilation strategies of free-standing kit,
whereas ductwork need to be re-designed for each layout change.
Good airflow management enables the datacenter to be designed to achieve greater than Tier IV reliability despite experiencing internal air temperatures that are considerably higher than in a typical facility.
By modelling operations using the Virtual Facility┬®, a high internal air temperature can safely be set as follows: CRAC supply at 20├ï┼íC (5-7├ï┼íC higher than a typical datacenter) and CRAC return between 27-29├ï┼íC (also 5-7├ï┼íC higher). In turn this leads to high chilled water temperature in the coils: Flow is 10├ï┼íC (3├ï┼íC higher than typical) and return is 18├ï┼íC (6├ï┼íC higher than typical).
At Citi the 2 coils in the CRAC units are linked to free cooling heat exchangers providing free cooling and free pre-cooling from 17ËšC external WBT, which equals 8,183hrs per annum (93% of the time) or 8,486 MWhr per annum. At the same time the design is highly resilient; 2 coils provide a 2N cooling system at the CRAC (> Tier IV standard.) and free cooling increases 3N system redundancy during the winter period (also exceeding the Tier IV standard).