Optimizing Data Center Cooling: TCO And Design Comparisons Between Single-Phase And Two-Phase

Author: Lucas Baron, Director of Product Marketing, Accelsius Collection: 2025 OCP Global Summit - Expo Hall Sessions

Summary

Accelsius, a two-phase direct-to-chip (D2C) liquid cooling company and OCP startup member, presents a TCO analysis comparing single-phase and two-phase D2C cooling for a 10 MW data center. Working with Jacob's Engineering, Accelsius created two reference designs for single-phase and two-phase facilities, each with 64 racks at 136 kW (78% liquid cooled, 22% air cooled), using isothermal chip temperatures and universal cold plates to ensure fair comparison. The facility was designed with operational limits of 5 to 40 degrees C for heat rejection infrastructure and concurrent maintainability requirements.

The TCO analysis, based on a data center in Austin, Texas, reveals that chip-to-chiller CapEx is essentially neutral between the two approaches (single-phase: $10,385,576 vs. two-phase: $10,381,534). However, two-phase D2C delivers 35% lower annual OpEx ($678,640 vs. $1,043,799) due to warmer facility water utilization, reduced CDU pumping power, and lower maintenance costs. Over a 5-year period, two-phase achieves approximately 12% TCO savings ($13,774,735 vs. $15,604,571). Additionally, two-phase's lower peak PUE enables deploying 5% more GPUs (67 vs. 64 IT racks) within the same power envelope, generating approximately $7 million in additional annual revenue. The presentation also introduces Accelsius's product line under the "NeuCool" brand: the IR80 (in-rack, 80 kW, for enterprise/colo), the MR250 (in-row, 250 kW, the industry's largest two-phase CDU, announced for general availability at OCP), and LSS/TSR simulation sleds for testing and commissioning.