Power Distribution in Immersion Environments: Challenges and Opportunities

Author: Oriol Chavanel (Submer, Ecosystem Tech Lead) & Kevin Gero (Murata, Senior Product Marketing) Collection: 2024 OCP Global Summit - Cooling Environments & Immersion

Summary

This presentation reports on the OCP Power Distribution in Immersion workstream, which is drafting a base specification for integrating ORV3 (Open Rack Version 3) power infrastructure into single-phase immersion tanks. The work adapts the existing ORV3 air-environment standard to address mechanical, electrical, and safety requirements unique to fluid-submerged operation. The workstream covers five system elements: immersion tanks, busbars, power shelves, PSUs (power supply units), and ancillary components such as fuses, connectors, and cables.

The central performance finding is that immersion cooling dramatically improves power component thermal performance: PSUs operating at 54 kW load inside Submer immersion tanks show internal temperatures below 60°C, enabling a 3.6 kW PSU to be pushed toward 6–7 kW capacity — nearly double its air rating. Busbars rated for 150A in air can handle at least 300A (2x) in immersion due to the superior cooling at the tank bottom. Similarly, ORV3 connectors have been validated to carry more than twice their air amperage rating in immersion. Thermal simulations show ORV3 busbars at 1200A total load reaching only 26.95°C max temperature rise at 52°C ambient with 2.05 m/s airflow equivalent convection, confirming immersion busbars are not the thermal bottleneck.

Key specification requirements being codified include: power shelves must not exceed 4U height; AC input connectors and PS-controllers must be accessible above the fluid line; single-phase PSUs must be deployed in groups of three to balance three-phase input; and busbar temperature rise must not exceed 30°C at full load current. Outstanding open items include fuse behavior in immersion (a fuse may not blow at rated current if immersion cooling prevents it from reaching trip temperature) and a mechanical polarity-locking mechanism to prevent reverse-polarity server installation.