Rack Spacing and Top-Row Thermal Stress

During a thermal pathway audit at an 85-unit farm in Ansan, we measured intake air temperatures 11°C higher on top-row units compared to bottom-row units in a four-tier rack configuration with 35 cm vertical spacing.

The Mechanism

Hot exhaust from lower units rises and gets pulled into the intake fans of upper units when vertical clearance is insufficient. The elevated intake temperature forces fans to spin faster, increasing vibration amplitude. Simultaneously, uneven thermal expansion across the frame — hotter on the exhaust side, cooler on the intake side — creates torsional stress that warps side panels over months of operation.

Measured Outcomes

After increasing vertical spacing from 35 cm to 50 cm on two test racks, top-row intake temperatures dropped to within 3°C of bottom-row readings within 48 hours. Junction temperatures on affected units decreased by an average of 6°C. Frame warp measurements taken 90 days later showed no progression on the re-spaced racks, while control racks with original spacing continued to show measurable panel deflection.

Spacing Guidelines

For air-cooled ASIC units in open rack configurations, we recommend minimum 45 cm vertical spacing and 8 cm horizontal clearance between unit side panels. Facilities using enclosed hot-aisle containment can operate with tighter spacing but require quarterly shroud alignment checks.