Specifiedatthetemperatureofuse,notthetemperatureonthedatasheet.
Almost every thermal product on the market is quoted at 35 °C ambient. The design ambient here is 50 °C, with peaks to 55 °C. Every thermal component is specified on net sensible capacity at 50 °C — nominal ratings are treated as marketing figures and are not accepted as design inputs.
- 7.5 kW
- Net sensible @ 50 °C
- 18–25 °C
- Internal band held
- 10 kW
- Online UPS, double conversion
- +55 °C
- Condenser rating
Thermal design
A closed-loop cycle. The air inside never leaves.
Precision DX, not comfort AC — a tight setpoint held against a 50 °C exterior. Internal air circulates in a sealed loop; heat leaves through a refrigerant circuit, not through a vent.
- 01
Supply
18–25 °CConditioned air is delivered upward across the equipment intake face by EC fans in the rack-mount evaporator.
- 02
Load
~7.5 kW absorbedThe air passes through the GPU, CPU and power stages, absorbing roughly 7.5 kW of heat on a single pass.
- 03
Return
sealed plenumHeated air leaves the top of the equipment stack into a sealed internal plenum — it never touches outside air.
- 04
Reject
to +55 °C ambientThe plenum returns air to the evaporator, where heat transfers to refrigerant and is rejected outside by a high-ambient condenser rated to +55 °C.
Why the loop stays closed
The cooling unit is described by function only — component selection is finalised at build.
Zero air exchange
No outside air enters the cabinet, so dust, sand, salt and humidity never reach the electronics. Filter maintenance in the field is eliminated.
Precision DX
An inverter-driven compressor with EC fans modulates to load rather than cycling, holding a tight setpoint as GPU utilisation swings.
High-ambient condenser
The outdoor unit is rated to +55 °C and roof-mounted with vertical upward discharge, so rejected heat is not re-ingested.
Insulated, reflective shell
PIR sandwich panel over mineral insulation — low conductivity, closed-cell, no moisture uptake, under a UV-stable C4+ coating.
Sealed penetrations
Every cooling, power and data cut-out is gasketed and sealed so the IP55 rating survives integration, not just the empty cabinet.
Fail-safe on cooling loss
High-temperature alarm, staged GPU power capping, automatic graceful shutdown and emergency door release if the setpoint cannot be held.
Power architecture
Solar first, grid behind it, UPS across the gap.
Two independent sources, one automatic transfer switch, and an online UPS that hides the transfer from the node.
Automatic transfer switch
Continuously monitors both sources and holds the load on the solar-fed inverter while it stays in tolerance. On undervoltage, frequency excursion or source loss it transfers to grid, and back again once solar recovers — automatically, with no attendance.
Rack-mount online UPS, 10 kW
True double conversion: the node is always fed from the UPS inverter, so the ATS break — typically tens of milliseconds — is never seen by the load. Transfer time is effectively zero.
Ride-through and ordered shutdown
Battery autonomy covers cloud transients, inverter restarts and grid events. If both sources stay down, the UPS signals the HMI, which triggers a graceful GPU and OS shutdown before the batteries are exhausted.
Two sources, one transfer switch, five protected circuits.
| Way | Protection | Load | Supply |
|---|---|---|---|
| W1 | 32 A 3P | Online UPS 10 kW → RPDUs → AI compute node | UPS-backed |
| W2 | 20 A 3P | Precision DX cooling unit | Utility fed |
| W3 | 6 A 1P | Fire suppression unit | Utility fed |
| W4 | 6 A 1P | HMI / DCIM panel | Utility fed |
| W5 | 16 A 3P | Outdoor condenser (ODU) | Utility fed |
Single line diagram EXN-EL-001 Rev A · 400 V 3φ+N 50 Hz · TN-S earthing · 63 A main. Cooling load (~2.5–3.5 kW) sits downstream of the ATS on utility power — deliberately not on the UPS, to preserve UPS autonomy for the compute node. Aggregate design load ~11 kW. Ratings indicative, subject to a licensed electrical engineer review before issue for construction.
Fire detection & suppression
A sealed cabinet is the ideal place to put out a fire.
No air exchange means smoke concentrates early and extinguishing agent stays where it is discharged. The payload is a dense concentration of high-current electronics and lithium energy storage in a confined, unattended volume — so protection is internal to the rack.
Detect
Sensors confirm an event in the return-air path. In a sealed volume the products of combustion are not diluted by room air, so an incipient fault is picked up early and unambiguously. Alarm is raised locally and signalled remotely.
Isolate
Cooling fans and compressor stop and dampers close, so circulating air cannot dilute the agent or fan the fault — and the loop stops feeding oxygen to it.
Warn
A short pre-discharge delay with audible and visual warning permits abort if a person is present at the cabinet.
Discharge
Clean agent is released directly into the sealed volume from the self-contained rack-mount unit. It is electrically non-conductive, leaves no residue and requires no post-discharge clean-up.
Hold
The sealed envelope retains extinguishing concentration for an extended hold time without room-scale agent volume.
Interlock
Power to the node is interlocked off, the door is secured, and status is annunciated locally and northbound.
Why hold time is the sealed enclosure’s advantage
Suppression fails far more often through loss of concentration than through insufficient initial discharge — agent escapes through leakage paths before the fire is fully extinguished, and re-ignition follows. A room-scale system spends significant effort on enclosure integrity testing for exactly this reason. A cabinet already sealed to IP55, with closed dampers and stopped fans, retains concentration by construction.
Agent selection criteria
- Clean agent
- Electrically non-conductive and non-corrosive, zero residue.
- Environmental
- Zero ozone depletion potential, low global warming potential.
- Occupant safety
- Discharge concentration safe for normally occupied areas.
- Self-contained
- Detection, control and agent in one rack-mount unit.
The agent is specified against properties rather than by product. Suppression fails far more often through loss of concentration than through insufficient initial discharge — a cabinet already sealed to IP55, with closed dampers and stopped fans, retains concentration by construction.
Monitoring & control
A 7-inch HMI is the node’s DCIM.
A standalone outdoor node has no building management system, so it provides its own. Every subsystem reports to one door-mounted touchscreen — and to your central platform.
21.4°C
Supply
38.7°C
Return
6.42kW
Node load
Solar
Source
Online
UPS mode
Armed
Fire system
Representative screen layout
Thermal
Supply and return temperature, delta-T across the load, internal humidity, setpoint and deviation, compressor and EC fan state, condenser status, and derived cooling capacity margin.
Power
Active source, input and output voltage, current, kW and kWh, power factor, UPS mode, battery state of charge and remaining runtime.
Safety
Fire system armed / alarm / discharged, door position, smoke and heat sensor state, leak detection, intrusion.
Compute
Node power draw and GPU telemetry surfaced from the platform’s own management interfaces.
Northbound integration
Modbus TCP, SNMP v3 and MQTT to a central DCIM or NOC, with local trending, event logging and remote alerting. Operators can adjust setpoints, acknowledge alarms and trigger a graceful shutdown from the panel or remotely.