Maximising space with multi-storey data centres
Traditionally, data centres were located away from urban centres, taking advantage of cheap development land to construct large, single-storey buildings, which would often be grouped together on a common campus. However, increasing demand for data centres within urban environments and the scarcity of suitable development land with access to power, fibre, and other utility services is driving the industry towards multi-storey designs.
Building upwards, rather than outwards, offers a practical solution in dense urban areas, but comes with its own set of challenges.
Tackling spatial constraints
In a hi-rise data centre, key design considerations are the availability of plant space – particularly for heat rejection, service distribution, plant replacement strategy, safety, and the provision of vertical circulation routes. The building's hi-rise form dictates a different servicing approach and presents unique challenges not found with single-storey schemes.
These hi-rise urban facilities are typically located on constrained plots of land, so must maximise the efficient use of space. This often means that ancillaries, such as generators, electrical transformers, and fuel and water storage tanks normally situated in external plant compounds, must be accommodated within the building footprint.
These practical constraints dictate building stacking. Ancillary areas, including security and main entrances, fire control rooms, loading docks, and points of entry for utilities, must be at ground level for accessibility. However, heavier items such as water and fuel storage tanks will either be buried beneath external roadways or situated within a basement – if one is provided.
For larger data centres, the building will require an electrical substation that must be accommodated on the ground floor to facilitate utility company access, cable entry, and plant replacement. Point of presence (POP) rooms, the demarcation points for external and internal grade fibre, and the location of internet service providers' equipment will also ideally need to be located on the lower levels of the building.
Designing for verticality
When designing a hi-rise data centre, vertical circulation routes must be considered. These routes are essential for moving IT equipment and installing or replacing plants, people, and firefighting resources. High-capacity goods lifts are typically required, and the location of stair and lift cores, smoke shafts, and vertical services risers will significantly impact the floor layout.
Given the premium on space, electrical distribution via medium voltage (MV) can bring the benefit of smaller cable risers and allow for the strategic stacking of low voltage (LV) and uninterruptible power supply (UPS) rooms. This is one method to maximise floor space and ensure the LV distribution is carried out horizontally to on-floor data halls. This avoids the need for larger LV cables to rise through the building, which would require larger service shafts.
However, accommodating larger plant items such as generators, UPS and battery banks, chillers, and heat rejection plants usually presents the greatest challenge.
The challenge with generators, energy storage and cooling
The integration of generators into multi-storey data centres presents unique challenges. Unlike traditional data centres, where generators are housed in external yards with tall buildings, there is often no alternative but to incorporate them within the building envelope. In doing so, data centre developers can maximise the use of the available land to accommodate a larger building. A further advantage is the opportunity to reduce the length of power distribution routes, minimising cable lengths and conductor sizes. However, this approach may require structural reinforcement due to the weight of the generators and a more complicated fuel distribution system.
Some of these issues can be overcome by locating generators on the ground floor of the building. This approach requires careful planning to ensure adequate airflow for combustion and cooling purposes and lends itself to adopting a centralised generator system utilising medium voltage distribution.
One solution to help minimise the airflow issues is remote radiators, which can reduce the volume of cooling air needed within the generator hall. However, this option is complicated by congested roof spaces, often filled with mechanical cooling and heat rejection equipment. Installing remote radiators on the roof of a tall building may also necessitate hydraulic segregation between the generator's water-cooled engine and the remote radiator/heat-rejection system due to the static head imposed by the height of the building.
Additionally, the design of energy storage banks also needs to be adapted to suit deployment within a hi-rise data centre. Lithium-ion (Li-ion) batteries are often preferred over valve-regulated lead-acid (VRLA) batteries for their smaller footprint and lighter weight. However, along with these advantages, Li-ion batteries also increase fire risk, which must be considered in the design. Enhanced sprinkler protection may be needed to extinguish a lithium-ion battery fire, and consideration must also be given to safely venting toxic fumes and hydrogen that a reaction between water and lithium can create.
Due to the growing demand for artificial intelligence and HPC, data centres have a greater need for high-capacity cooling systems. Integrating this infrastructure into hi-rise facilities requires understanding the constraints from an early stage of the design. A fundamental issue is the availability of space for a heat rejection plant. On a tight urban site, external plant compounds of the sort often seen on hyperscale campuses are unlikely to be feasible. However, accommodating a large amount of space on the roofs of buildings is not without its challenges. With multi-storey designs, adding successive floors of technical space increases the demand for the cooling system. Still, the roof area where the plant will be accommodated remains unchanged. Taller buildings can limit the facility's capacity, not by the availability of power but by the number of heat rejection plants crammed onto the roof.
On several multi-storey DC projects, Cundall has addressed this conundrum by shifting the plant away from the roof and housing it on external gantries built onto the side of the building. This approach can relieve pressure on roof space and allow a taller building to fully utilise the available power supply. However, great care is needed at the design stage to assess and control air movement from the heat rejection plant. Intake and discharge airflows must be segregated to avoid interaction between the plant on adjacent building levels, as this could lead to significant de-rating of the plant.
Designing for safety and connectivity
Safety, fire risk and means of escape are paramount in designing multi-storey data centres. Although operational data centres are sparsely occupied, the design and layout of stair and lift cores must still allow for code-compliant means of escape and fire brigade access. Wet or dry rising fire mains, fire-fighting lifts and smoke extract systems may all be required. The need for smoke vent shafts may increase the size of cores.
Data centres are typically very well protected by extensive smoke detection and alarm systems and the provision of fire suppression to high-risk areas. However, in a multi-storey context, sprinkler systems can present additional risks themselves; without an effective, high-capacity catchment and drainage system, water released by the activation of a sprinkler head on an upper level of the building can spill down to the levels below, causing extensive damage to IT equipment and electrical distribution and switch rooms. The cost of this damage and the associated facility downtime could easily exceed the cost of the fire damage that triggered the original discharge. A well-thought-out containment and drainage strategy can prevent such incidents.
Another important consideration is plant installation and replacement. In a facility containing multiple data halls, phased fit-out is the norm. This means the plants must be positioned on the roof or in plant gantries that may be significantly above ground. If mobile cranes are to be utilised for plant erection, adequate hard standing and off-loading must be considered in the design. The input of a cranage specialist is usually required to support the development of a plant installation and replacement strategy. Another approach is to incorporate cranage into the design of the building. This adds significant up-front costs and regular maintenance and certification costs. However, for some buildings, it may be the only solution.
The underground services will become more challenging as the data centre is built further above ground. Managing incoming fibre and medium/high (MV/HV) power supplies and ensuring diverse routes become increasingly complex, with limited space for buried distribution routes and connection points. Ensuring reliable connectivity and diverse routing requires meticulous planning and coordination with local utilities and service providers. 3D coordination of below-ground service routes to ensure adequate separation of cable and fibre ducts with other elements, such as below-ground drainage and rainwater attenuation tanks, is essential.
As land constraints persist, multi-storey data centres are set to become more common, especially in urban environments. While they come with benefits, their design brings construction complexities and additional costs. These projects demand the expertise of a multi-disciplinary design team. Integrating architectural, structural, mechanical, electrical, and fire safety systems means close coordination between disciplines, as the data centre needs to operate holistically. A team experienced in navigating these complex designs is vital to ensure the building is efficient, reliable and meets the required safety and sustainability standards.
