Sizing power and cooling before the hardware arrives

A recurring pattern in this trade: the hardware arrives on schedule and then sits in a room for six weeks because the switchgear did not. Electrical work runs on its own calendar, and that calendar is longer than any hardware lead time. The sizing has to be settled before the order, not after it.

Start at the wall, not the spec sheet

Manufacturers quote a nominal wall power with a tolerance band, often several percent, and that figure assumes rated ambient conditions. Real draw drifts above nominal on hot days and with older units. Size the electrical chain on the top of the tolerance band, not the middle of it, and add headroom on top of that.

A practical rule: take nominal wall power, add the manufacturer's stated tolerance, then plan the circuit at no more than 80 percent continuous load. For a 3,500 W machine with a 5 percent band that means budgeting roughly 4,600 W of circuit capacity per unit. It feels wasteful on paper and it is the difference between a site that runs and a site that trips.

The electrical chain

• Service and transformer. The total in kilowatts, plus growth. Upgrading a transformer after the fact is the single most expensive mistake on this list.
• Distribution and breakers. Sized per the 80 percent continuous rule, with the phase balance worked out across the whole fleet rather than per row.
• Voltage and phase. Air cooled units are typically single phase at 200 to 277 V, hydro units three phase at 380 V and up. Mixing both on one site means two distribution schemes, decided in advance.
• PDUs and connectors. Count outlets per rack against machines per rack and confirm the connector type before shipping. Adapters bought in a hurry are a fire risk.
• Cable runs. Voltage drop over distance is easy to underestimate in a long building.

The thermal chain

Whatever goes in as electricity comes out as heat, near enough all of it. A 1 MW site is a 1 MW heater. The cooling question is not whether you can absorb that heat but how fast you can move it out, and the answer is a volume of air or liquid per unit of time.

For air, the working figure is airflow per kilowatt at a given temperature rise. Higher permitted rise means less air to move, but it also means hotter machines and a real efficiency penalty when the chips throttle. Most operators land between a 10 and 15 degree rise across the room and size fans and openings from there.

• Separate hot from cold. Containment matters more than raw fan capacity. Recirculating exhaust into the intake is the most common cause of unexplained derating.
• Filtration is a maintenance choice. Finer filters mean cleaner machines and more frequent changes. Pick deliberately rather than discovering it.
• Design for the worst week, not the average. Ambient peaks and hashprice peaks do not coordinate with each other.
• For liquid routes, the loop is a construction project. Manifolds, pumps, leak detection and a dry cooler sized for the same worst week.

Headroom is cheaper before than after

Every operator we talk to who expanded within two years wishes they had run one size larger on the service, the loop and the exhaust. Adding capacity to a live site means downtime on the machines that already earn. Adding it during construction means a slightly larger invoice from the electrician.