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Define fan spec at loaded point

* Generally we use fans at loaded condition. But by now small fans performance spec is mentioned under no loaded condition. This way isn`t a correct way of fan estimation.
* To develop Ecology fan SEPA proposes new fan spec definition that measures fan spec at operating point.  SEPA determined system impedance curve by analyzing small electric components.


Current : No loaded condition New proposal : Loaded condition
* Free air condition * ISO 10302 1/4 size plenum
* Fan load can change by slider plate opening

Measured Noise analysis

Green:Plenum 52.2 dBA@10cm Red:Free air  44.6dBA@10cm
* This noise data is a comparison of two kind of measuring condition at no load. (Plenum slider plate is fully open)
* Noise value is quite different.
Free air condition 44.6dBA@10cm
Plenum condition 52.2dBA@10cm
* The difference of noise canceling mechanism maybe the reason. Existence of separator plate of air in and air out will block noise canceling.
* But in the case of real fan using, there is a separator plate always. So measuring noise with plenum is closer real system condition.