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Fans are tested and certified in laboratories under ideal conditions—that is, conditions intended to facilitate maximum performance. The conditions under which fans ultimately are placed into service, however, can be far from ideal. The resulting degradation in air performance can be attributed to a phenomenon known as system, or installation, effect.
At the inlet of a fan, an improperly placed fitting, such as an elbow, an inlet box, or a heat exchanger, can produce a vortex, or turbulent non-homogeneous velocity area. This less-than-optimum airflow condition leads to a reorganization of flow inside of the fan’s impeller and, thus, a deterioration of the fan curve.
At the outlet of a fan, an improperly connected fitting, such as an elbow, a damper, or a duct branch, can produce non-uniform flow profiles. This degraded flow will increase pressure loss across the fitting. When an outlet obstacle is close to the fan’s impeller, the flow pattern inside of the impeller may be disturbed, causing a deterioration in performance.
This presentation will show how fan performance is affected by both inlet and outlet connections. It will summarize the main points of International Organisation for Standardisation (ISO) Technical Report 16219, “Fans – System Effects and System Effect Factors,” which was published in September 2020. The paper will explain the origin of system effect, present ways to quantify system effect, describe typical examples of system effect taken from a series of tests, and provide practical advice for mitigating system effect.
The paper also will discuss AMCA Publication 201, Fans and Systems, which introduced the concept of system-effect factor many years ago and is being updated with new test data.