Capture Index: The Cooling Efficiency Metric You Need to Know

1. Capture Index: The Cooling Efficiency Metric You Need to Know “If you can’t measure it, you can’t manage it,” is an old business school maxim that’s just as applicable to data center cooling. Data center managers need to measure cooling efficiency if they’re going to manage it effectively, and Capture Index (CI) is one of the best metrics they can use. CI is a measurement of airflow from local cooling resources, such as nearby tiles in a raised-floor environment, nearby return vents in a hot-aisle containment system, or an in- row cooling unit. CI is calculated in two ways. Cold-air CI is the percentage of air ingested by IT equipment that is supplied by local cooling resources, while hot-air CI is the percentage of exhaust air that is captured and neutralized by local cooling resources. The higher the CI value the better the cooling performance. Most other metrics are based upon temperature, and don’t provide a complete view of cooling efficiency. If the room temperature is set low enough, rack inlet temperatures might be satisfactory even if airflow patterns are poor and there’s a lot of mixing of hot and cold air. CI can identify these kinds of problems. What’s more, CI is measured at the rack level, making it useful for determining where to place enclosures to optimize airflow and best meet the requirements of the equipment. Cold-air CI is used in traditional raised-floor facilities that rely upon computer room air conditioner (CRAC) units. As the name implies, CRAC units are designed to cool the entire data center, regardless of the location of IT equipment or the IT load. Exhaust air is not captured locally and must return to the CRAC unit. Therefore, you use cold-air CI to measure the delivery of chilled air to the equipment. Hot-air CI is used in environments with local coolers that capture exhaust air. The goal is to prevent hot exhaust air from entering the data center, so there is no net heating of the room. You

2. don’t have to worry about the delivery of chilled air because all IT equipment receives air at a consistent temperature. The hot-air CI metric can be used to prove the efficiency of in-row cooling units. In-row cooling brings chilled air closer to the equipment so that exhaust air is neutralized before it can mix with the surrounding air in the room. While in-row cooling units can be suspended from the ceiling or placed on top of a cabinet, the highest CI value is achieved with rack-sized units that are installed directly in an aisle or distributed throughout a pod. Even greater efficiencies can be gained with units that vary cooling capacity and fan speeds according to the IT load. Enconnex in-row cooling units, for example, are 45U high, 1200mm deep and available in 600mm and 900mm widths. They fit comfortably in any data center environment yet can deliver more than 100kW of cooling capacity to address today’s heat loads. Available in condensate water, chilled water, and DX air- and water-cooled configurations, they feature a wall of variable-speed, hot-swappable fans, dual power supplies, and an intuitive, touch-screen interface. Macro-level measurements based on temperature don’t provide the data you need to effectively manage cooling efficiency. Rahi’s experts can help you calculate the CI of your environment and leverage in-row cooling from Enconnex to improve airflow and reduce costs.