Co-location centres

Co-location facilities are services packed buildings designed to provide a secure environment for IT and telecommunications equipment. They have evolved to cater for the demand driven by huge growth in the use of the Internet, and the fragmentation of telecommunications markets.

The co-location centre market is however, high risk, and the dramatic fall in confidence in the e-economy has affected the on-going roll-out of these centres. However, some development work is continuing, and the long-term growth prospects are good.

Factors affecting location
Location is a key attribute, as the requirements for co-location centres are specific, including:

• Adjacency to primary fibre optic network nodes to avoid additional costs of laying fibre optics to the site.
  
• Access to large, reliable power supplies.
  
• Noise considerations due to continuous operation.

Central versus modular installation strategies
Developers of co-location centres need to balance their objectives of fast completion and minimal capital outlay, with requirements for high levels of investment in the power supply and cooling capacity that are required on day one. The combination of a flexible infrastructure and the phasing of the development can make an important contribution to the viability of a scheme. There are two main approaches to providing flexibility in the services installation:

• Central distribution involves the installation of most of the primary distribution system at day one, whereas plant is only installed in response to tenant demand. Initial investment in the primary distribution is therefore high, but subsequent disruption within the serviced space is minimised.
  
• Modular services strategies involve the development of localised 'distribution networks'. This approach is adopted on projects where the building itself is designed to be extended on a modular basis. The distribution network includes all plant and primary and secondary distribution. The advantages of this approach include the reduction of initial investment and the need for smaller primary distribution circuits. Disadvantages include the extent of external services required to run to each module, and the higher cost of the completed project.

Primary requirements of services installation
The main selling point of co-location centres is the provision of guaranteed, stable electrical supplies and environmental conditions. Resilience is a critical aspect of the design of a co-location centre. The design will take into account both the potential for internal system failure, through the provision of additional redundant capacity, and also external failure, through the specification of fuel and battery reserves.

Plant specified to provide redundancy is only ever required to operate at full capacity during maintenance or in the event of an emergency. As a result, the level of redundancy specified has significant cost and plant space implications. The standard applied to most re-location centres is N+1, where the total load is supplied by a number of modular plant items, with back up being provided by one additional unit.

Electrical services
The availability, size and security of the power supply are key product differentiators in the co-location centre market. The minimum accepted design standard is 1000 W/m2. This standard represents the maximum theoretical load assuming operation at full capacity. In practice, loads rarely exceed 300-400 W/m2 due to below capacity use of space by tenants, and the diversity of the operation of the servers themselves.

The main design issues associated with the electrical installation are resilience and back-up. The strategy for providing resilience is based on eliminating single points of failure through system duplication. This approach extends from the provision of the high voltage supply to the connections to the individual racks:

• Twin high voltage supplies taken from separate sources, or fed from either end of a common ring main.
  
• Incoming supplies to switchgear, either duplicated (N+N), or independent sections of a common panel connected by an automatic busbar.
  
• Independent transformers supporting both essential and non essential equipment on an N+1 basis. Low voltage distribution based on independent A and B networks.
  
• Dual fed power distribution units, provided with static switches for changeover. Tenants are offered two independent supplies.
  
• Multiple and redundant power feeds using different routes are provided for final distribution.

Requirements for backed-up power supplies are particularly exacting. Virtually the entire electrical load is critical, and no break in supply is permitted.

Standby generator capacity for the full site load at N+1 is required, with a minimum 24 h fuel supply.

Uninterruptible power supply (ups) systems with N+1 diversity are required for most of the load. Battery based static systems remain the preferred option. However, rotary ups systems, which combine battery and generator are becoming more common. These systems cost 5-8% more than the equivalent conventional components, but require less plant room space.

For more details on ups options, refer to 'Back-up Power Supplies' BSJ, March 2001.

Mechanical services
The key issues associated with mechanical services design are:

• The cooling load
  
• Diversity and security of supply
  
• Control of temperature and humidity

IT equipment housed in co-location centres produces large quantities of heat, and is highly sensitive to fluctuations in temperature and humidity. Close environmental control is therefore required, with conditions of 21°C ±1°C and 50% ±5% rh typically being specified. The preferred cooling solution is a centralised chilled water system with close control air conditioning units serving technical spaces.

Requirements for standby capacity are exacting, and redundancy is provided in the centralised chiller plant, chilled water distribution (multiple pressurisation units and pumps, multiple pipe circuits with all pipework welded), and in the numbers of close control units.

Since the technical spaces of co-location centres are generally unoccupied, ventilation is not a key parameter, and minimum permissible air change rates of half to one air change per hour can be specified.

The sensitivity of IT equipment to water damage and the extent of the chilled water system mean that leak detection and prevention is an important consideration. Prevention measures include drip trays and bund walls. Detection systems typically comprise perimeter tape detection and monitoring of high-level drip trays.

Fire detection
Fire detection installations comprise conventional smoke detection and VESDA early warning systems. Both gas suppression and pre-action mist sprinkler systems are specified. Gas systems can be very expensive due to the volumes of the technical spaces served. Although there is some risk of water damage with sprinklers, the pre-action system provides sufficient security to be used in technical spaces. For more information refer to 'Gaseous fire suppression systems', BSJ July 2001.

Security
Security requirements are extensive, including:

• Full cctv coverage to external, plant and technical areas, including surveillance of aisles between equipment racks in technical areas.
  
• Full intruder alarm system at the site, building perimeters and within voids in technical spaces.
  
• Multi-tier card access system to protect technical areas, including the use of 'man trap' features linked to scanners reading identity cards, palms and retina.

Services co-ordination
Co-location projects are engineering led, and the lead contractor is often a services specialist. Detailed design of the services is essential, facilitating the co-ordination of the complex installation. The detailed design should also include a single-point of failure analysis. Other key procurement issues include:-

• Pre-ordering of major plant
  
• Thorough testing and commissioning requirements

Cost breakdown
The cost model is based on a 16 200 m² two-storey development comprising 9700 m² of technical space, 5500 m² of associated plant areas and 1000 m² of support facilities. The cost of the installation does not include for the on floor power feeds to racks from the power distribution units.

Costs are given for two options:

• Full fit-out on day one.
  
• 25% fit-out of technical spaces on day one.

The costs of the part fitted-out option provide an indication of the minimum initial capital cost commitment on a phased development. The '% installed' column indicates the typical proportion of total plant capacity that would be required to support the reduced fit-out. These percentages are provided for illustration only.