How Are Air and Waterside Economizers Designed for Data Centers?

Airside economizers are designed with intake/exhaust louvers, filtration, and mixing dampers plus humidity control; waterside economizers with plate heat exchangers, tower/dry-cooler capacity, and chiller-bypass piping. Both need control sequences for changeover, integrated partial operation, and edge-case protection — designed and commissioned as a primary operating mode. The design discipline that separates good economizer projects from disappointing ones is treating the economizer as the plant's normal state rather than a bonus mode. In a favorable climate, the plant will spend most of its hours in some degree of economizer operation. Designing the sequences, setpoints, and maintenance access for a system that's 'rarely used' guarantees it will perform like one.

Airside design is an air-handling engineering exercise at large scale: louver sizing for the full economizer airflow with acceptable pressure drop and rain and snow management, filtration banks selected for the site's air quality with pressure-drop monitoring and maintenance access, and damper sections — intake, exhaust, and recirculation — with actuators and controls capable of precise mixed-air control. Humidification or dehumidification capacity covers the moisture swings of outdoor air. Waterside design is a hydronic exercise: plate-and-frame heat exchangers selected for the approach temperatures the free cooling hours require, cooling tower or dry-cooler capacity that can produce the needed water temperatures in cold weather (including freeze protection for the tower), and piping with the valving to run the loop through the exchangers, around the chillers, or in integrated configurations. Strainers and water treatment protect the exchangers, because a fouled economizer heat exchanger quietly erases the savings.

Economizers repay careful design many times over in energy savings. Here's what I make sure is covered. Design the mode you'll live in.

• Equipment selected for the actual climate and air quality — filtration, freeze protection, and capacity matched to the site
• Control sequences for changeover, integrated partial operation, and edge cases, written as primary operating logic
• Humidity control strategy for airside systems: the moisture consequences of outdoor air, designed not discovered
• Heat exchanger protection waterside: strainers, treatment, and maintenance access so performance doesn't degrade silently
• Commissioning across the operating range with trend-data verification that economizer hours match the design prediction