© Photo | © Tiberius Gracchus

Oper­a­tion geared to require­ments

Fans in AHUs gener­ally operate in the partial load range

Fig. 1: Power consump­tion of an AHU over the course of a week

An office complex with a glass facade, a summer’s day with temper­a­tures of 35 °C in the shade, full of people, maximum demand for venti­lation and cooling and no main­te­nance or servicing due for a long time yet – that would be one way of describing the maximum require­ments for an air handling system.

In commer­cial, munic­ipal and indus­trial appli­ca­tions, maximum load situ­a­tions only ever occur on a few days in the course of a working year (Fig. 1).

But the neces­sary cooling and heating perfor­mance and minimum air exchange rates still have to be reli­ably provided even then. The maximum load situ­a­tion is thus the crucial factor for dimen­sioning of the air handling system and fans – but it is not the most impor­tant when viewed over the entire oper­ating period! 

Oper­ating point and effi­ciency

An infor­ma­tion brochure* issued by the German energy agency dena contains the following recom­men­da­tion: “In the short term, the time of day, produc­tion fluc­tu­a­tions and weather condi­tions may cause the oper­ating point to change.  

Fig. 3a, b, c: As compared to an AC stan­dard motor with converter and the same power rating, the Green­Tech EC motor is roughly 28 % more effi­cient for the load profile under consid­er­a­tion

Over the medium term, changes may come about due to seasonal influ­ences or the degree of manu­fac­turing capacity util­i­sa­tion and in the long term as a result of increasing filter resis­tance etc.

Under such circum­stances it would be wrong to set the design oper­ating point (least favourable condi­tions and maximum perfor­mance require­ment) at the point with the best effi­ciency level.

It is better to have the oper­ating point for the most frequent oper­ating situ­a­tion set here. The ideal solu­tion is to perform opti­mi­sa­tion on the basis of the expected load and select the char­ac­ter­istic curve with the lowest annual energy costs.”

So the key is to have a tech­nology which provides more or less infi­nitely vari­able adap­ta­tion of the air flow to the actual require­ment. This ability is already inte­grated into the RadiPac for oper­a­tion in air handling units. Its capacity for adjust­ment over a broad speed range ensures excel­lent effi­ciency and helps to cut oper­ating costs. This is illus­trated by comparing an AC fan with frequency converter to a Green­Tech EC fan (Fig. 2).

For the load profile shown (Fig. 3a, b, c), the effi­ciency of the EC fan is around 28 % higher. In addi­tion to reduced power consump­tion, other bene­fits include far lower assembly and instal­la­tion costs, less weight and a space-saving design.

Correct values in partial load oper­a­tion

Partial load is thus of consid­er­able impor­tance when plan­ning and oper­ating air handling systems with a view to keeping running costs to a minimum. RadiPac EC centrifugal fans provide an ideal solu­tion.


Fig. 2: System compar­ison between an IEC-E2 motor with frequency converter, sine filter and protec­tive circuitry and a Green­Tech EC motor from ebm-papst

The certi­fied Product Selector makes it possible to real­is­ti­cally simu­late these oper­ating condi­tions because its data­base contains the measured perfor­mance data of the fan. Absolute plan­ning reli­a­bility is thus guar­an­teed.  

Authentic oper­ating condi­tions

Cate­gory A measure­ments with free inlet and free outlet are defin­i­tive for the data given in the product cata­logues and Product Selector and permit direct fan compar­isons (Fig. 4a). The fans in an air handling unit operate in more or less confined spaces. This leads to a reduc­tion in air perfor­mance which has to be taken into consid­er­a­tion when selecting the right fan (Fig. 4b). 


Fig. 4a


Fig. 4b


ebm-papst’s docu­mented values are based on customer require­ments and the possible oper­ating condi­tions involved. When choosing fans, the Product Selector makes it possible to incor­po­rate various factors of influ­ence, including the loca­tion of the air handling system or the avail­able fan instal­la­tion space.

K3G500AP2401_mit Einbauraum mit Originalkurve

Fig. 4c: In the Product Selector the “instal­la­tion situ­a­tion” can be repre­sented by selecting the size of the air handling units

This permits a reli­able assess­ment of energy effi­ciency, as well as oper­ating and life cycle costs, because here again a whole range of correct values provide the foun­da­tion. The real­istic consump­tion and perfor­mance figures supplied by ebm-papst help to ensure that the fore­cast perfor­mance values are actu­ally achieved in prac­tice (Fig. 4c). Selec­tion of the correct fan is thus guar­an­teed.  

*dena guide “Venti­lation Tech­nology for Industry and Commerce”

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