Data Center Airside Economizer Upgrade in Phoenix

Scenario

A Tier III colocation facility in Phoenix upgraded its airside economizer system to increase free-cooling hours. The new design routed 100% outdoor air through extended ductwork (including two 90° elbows and a high-efficiency MERV-14 filter) to serve 14 server aisles. Thermal load density (≥5 kW/m²) demanded tight airflow control—TESP accuracy directly impacted fan energy use and cooling reliability during 45°C summer peaks.

Given Data

• Duct Length: 68 m (including equivalent length for fittings: 60 m straight + 8 m for elbows)
• Duct Diameter: 0.55 m (newly installed spiral-wound aluminum duct)
• Airflow Rate: 8.7 m³/s (required for 22,000 cfm cooling load)
• Component Pressure Drops: [180 Pa (MERV-14 filter), 35 Pa (motorized dampers), 25 Pa (economizer enthalpy wheel), 15 Pa (diffusers)] → total = 255 Pa
• Duct Roughness: 0.02 mm (manufacturer spec for smooth aluminum liner)

Calculation

Using the Fan TESP Calculator:

1. Friction loss: Re ≈ 410,000 (turbulent), ε/D = 0.00002/0.55 ≈ 0.000036 → f ≈ 0.015 → ΔP_friction = 0.015 × (68/0.55) × (0.6 × 8.7²) ≈ 148.3 Pa
2. Component losses: Sum = 180 + 35 + 25 + 15 = 255 Pa
3. Total TESP = 148.3 + 255 = 403.3 Pa (reported as 403.30 Pa)

Result and Decision

The TESP (403.30 Pa) fell within the operating range of the existing EC plug fan—but only at 82% speed. To meet ASHRAE TC 90.1 fan power limits (<0.9 W/cfm), the engineering team specified a new ultra-efficient EC centrifugal fan (Model ECO-FAN-900) with integrated pressure sensors and adaptive speed control. Commissioning confirmed 401.2 Pa measured TESP and 18.2% lower fan energy vs. baseline.

Lesson

In high-airflow data center applications, even minor duct roughness reductions (e.g., smooth aluminum vs. standard galvanized) yield measurable TESP savings—justifying material upgrades when lifecycle energy cost dominates capital cost.