01 / The basicsWhite space and grey space
Every data centre divides into two worlds. White space is the IT floor, where racks, cabling and in-row infrastructure live. Grey space is everything that supports it: UPS, switchgear, generators, chillers and air handlers.
White space is where capacity is sold and filled, so the whole purpose of its design is to fit the most usable, powered and coolable rack positions into the room, with the headroom to grow. Grey space matters just as much, but it is back-of-house and not the subject of this guide.
White space is the IT floor
Racks, rows, aisles, containment, structured cabling and in-row power. It is measured in rack positions and kilowatts delivered, not just square metres.
Grey space is the support
The mechanical and electrical plant that powers and cools the white space: essential, but behind the scenes.
Usable, not just big
A large room laid out badly yields fewer real rack positions than a smaller one designed well. Aisles, containment, pathways and clearances all take floor; planning is what turns area into capacity.
Density changed the brief
White space used to be planned by the square metre. Now a single rack can draw what a whole row once did, so it is power and cooling per rack, not floor area, that sets the real limit.
02 / The anatomyThe building blocks of a data hall
A well-designed hall is a repeating pattern: rows of racks arranged front to front and back to back, so cool supply air and hot exhaust never mix. Around that sit the floor, the containment and the pathways that feed power and connectivity to every cabinet.
- 01
The rack and the row
The 42U or 48U cabinet is the unit. Rows of them, front to front, create the alternating cold and hot aisles that make airflow management possible.
- 02
Raised floor or slab
The classic raised floor is a cold-air plenum and a cable route. High-density halls increasingly go slab-on-grade with overhead distribution: heavy racks and liquid loops do not suit a void.
- 03
Pathways, over or under
Power (busway) and data (cable basket) run overhead or underfloor. Overhead is now the default: it keeps the floor clear, eases changes and suits high density.
- 04
Power to the rack
Busway overhead, rack PDUs in the cabinet and A and B feeds for resilience, sized for the density and metered so capacity can actually be managed.
03 / The plannerSize a hall, live
Floor area, power, cooling and rack count are all linked: change one and the rest move. Set a rack count and a density and watch the white space size itself, from the IT load and the floor area to the layout and the cooling that density demands.
- AirContainment, up to ~10 kW
- Air, fully containedNear its ceiling at ~30 kW
- Rear-door HXLiquid assist at the rack
- Direct-to-chipLiquid to the silicon
Indicative only. Area uses ~3 m² a rack, rows hold ~12 racks, and energy uses a representative PUE for the density and £0.20/kWh as an illustration.
Real layouts depend on rack footprint, aisle widths, clearances, the cooling approach and code. The point the planner makes is the relationship: as density rises, the same compute fits in less floor but demands more from power and cooling, which is why modern white space is designed around kilowatts, not square metres.
04 / AirflowContainment and airflow management
The biggest and cheapest win in white space is simple: do not let cold supply air and hot exhaust mix. Every degree of cold air that slips into a hot aisle, or hot air that recirculates to a rack inlet, is cooling you paid for and wasted. Switch between the three arrangements below.
No containment. Supply air goes where it likes. Some bypasses the racks and returns unused; hot exhaust loops over the top and back into the inlets. Both create hot spots and force you to over-cool the whole room.
Cold-aisle containment. The cold aisle is enclosed, so supply air reaches only the rack inlets. Simple and effective; the rest of the room runs warm.
Hot-aisle containment. The hot aisle is enclosed and its exhaust ducted straight back to the cooling. Often preferred for high density, because the working space stays cool.
Blanking and sealing
Blanking panels in empty U-space, brush grommets on cable cut-outs and sealed floor edges. Cheap parts that stop the bypass and recirculation that wreck efficiency.
Run warmer, safely
With containment right you can raise supply temperatures into the upper end of the ASHRAE band, run economisers for more of the year and bring PUE down without risking inlet temperatures.
It is the highest-return discipline in the white space, and it is mostly about rigour rather than capital.
05 / Designing to scaleDesigning for density, growth and change
White space is never finished. It fills, densifies and gets re-laid over a decade. The best designs anticipate that: modular, aware of headroom, and able to take a mix of densities, and one day a liquid loop, without tearing the room apart.
- 01
Design in pods
Repeatable rack, row and containment modules let you fit out in phases, keep cost in line with demand and standardise the install.
- 02
Plan for mixed density
Not every rack is 80 kW. Zone the room so low and high-density kit each get the right power and cooling, rather than designing everything for the worst case.
- 03
Headroom, deliberately
Power, cooling and pathways planned with spare, so the next deployment is a patch and a PDU, not a redesign. Stranded capacity is waste; no headroom is a wall.
- 04
Liquid-ready
Even an air hall today should allow for water tomorrow: floor loading, pathways and space for CDUs, so going liquid later is an upgrade, not a rebuild.
- 05
Pathways for change
Generous, accessible cable and power routes keep moves, adds and changes quick and safe. Congested pathways turn every change into a risk.
- 06
Documented and managed
An accurate floor plan, labelling and capacity records in DCIM, so decisions about what goes where are made on real data.
White space is where several of our guides meet: the structured cabling that feeds it, the AI and GPU density reshaping it, the liquid cooling that density needs, and the operations that run it once it is live.
06 / Our softwareDesigned in our Whitespace Builder
We do not sketch white space in slides. We model it in Whitespace Builder, our own design tool, where a single scene model drives the 3D view, the 2D drawings and the rack, power and cabling counts at once. Change the model and every output updates together. The hall below is a real, anonymised design built in it, running live in your browser. Drag to orbit, scroll or pinch to zoom.
Live 3D model built in Optronix Whitespace Builder. One scene model drives the 3D, the drawings and the counts.
One model, every output
The 3D, the floor-plan drawings and the quantities all come from the same model, so they never drift out of step.
Counts straight off the model
Rack positions, power per row, containment runs and cabling counts are read directly from the design, which is how we cost a fit-out in under 48 hours.
What you see is what we build
Tender-stage models become the build. The design you sign off, layout, densities and containment, is the one our engineers install.
07 / How Optronix helpsFrom a drawing to a working hall
White-space design and fit-out is at the centre of what we do. We take a room, or a drawing, and turn it into a working data hall: layout, containment, power distribution, pathways and the structured cabling that ties it together, for hyperscale, colocation and enterprise clients across Europe, North America, the Middle East and APAC. Our own engineers, end to end.
A costed design in under 48 hours
We turn a client drawing into a costed, model-derived white-space design, with rack layout, densities, containment, power and cabling counts, in under 48 hours. The counts come straight off the model, so what you approve is what we build.
Pods, mixed density and headroom
Halls planned in pods, for mixed density and with the headroom and liquid-readiness to grow, so the white space you fit out today still works when the kit going into it changes.
- 01
Design and model
Layout, density zoning, containment, power and pathways, modelled and costed from your drawing.
- 02
Fit out and install
Racks, containment, busway, power distribution, overhead pathways and the cabling plant, installed by our own engineers.
- 03
Commission and certify
Airflow and containment verified, cabling tested and certified, and the documentation handed over.
- 04
Operate and evolve
Moves, adds and changes, capacity management and phased expansion as the hall fills and densifies.
Related services
White space
Send us the space and your target densities.
We will come back with a costed, model-derived white-space design: layout, containment, power and cabling, built to scale.
Sources and notes
- ASHRAE TC 9.9 thermal guidelines: the recommended inlet-temperature band (18 to 27°C) and airflow management practice.
- Uptime Institute and common industry practice for white-space layout, containment, raised floor vs slab, and capacity planning.
- White-space area per rack (about 2.5 to 4 m² including aisles and access) is a planning rule of thumb; real figures depend on rack footprint, aisle widths and clearances.
- Cabling per TIA-942 and ISO/IEC 11801; high-density and liquid considerations per our structured cabling, AI/GPU and liquid cooling guides.
General guidance, not a design specification. Area, load, layout and energy figures from the planner are indicative and rounded; real designs depend on rack footprint, aisle and clearance requirements, the cooling approach, redundancy and local code. Energy uses a representative PUE for the density and £0.20/kWh as an illustration. Confirm against an engineered design.