Capture Index Cooling-Performance Metric
- Unlike temperature-based metrics, Capture Index (CI) is solely a function of airflow. There are two kinds of CI:
- Cold Aisle CI: the fraction of air ingested by the rack which originates from local cooling resources (e.g. perforated floor tiles or local coolers)
- Hot Aisle CI: the fraction of air exhausted by a rack which is captured by local extracts (e.g. local coolers or return vents)
- CI measures effectiveness of supplying cooling air to rack inlets or scavenging heated air from rack exhausts on a 0% (bad) to 100% (good) scale.
- CI is defined in terms of local cooling resources (airflow from tiles, local coolers, local extract vents, etc.) and it measures the robustness and scalability of a grouping of equipment.
The Cold Aisle Capture Index of the top-middle rack is 84%. In other words, 84% of the airflow drawn in by that rack originated from the perforated floor tiles. The remaining 16% of inlet air comes from other sources including the room ambient and recirculation from the subject rack and others.
The Hot Aisle Capture Index of the bottom-right rack is 66%. In other words, 66% of the exhaust airflow from this rack is captured by the local coolers while the additional 34% escapes, heating the room ambient and, potentially, entering rack inlets.