{"id":14454,"date":"2020-09-01T09:11:44","date_gmt":"2020-09-01T07:11:44","guid":{"rendered":"https:\/\/mag.ebmpapst.com\/en\/?p=14454"},"modified":"2026-05-06T09:12:18","modified_gmt":"2026-05-06T07:12:18","slug":"air-handling-unit-ahu-efficiency-axial-centrifugal-fans","status":"publish","type":"post","link":"https:\/\/mag.ebmpapst.com\/en\/industries\/refrigeration-ventilation\/air-handling-unit-ahu-efficiency-axial-centrifugal-fans_14454\/","title":{"rendered":"AHUs: The issue of effi\u00adciency"},"content":{"rendered":"\n

Every fan\u2019s air perfor\u00admance, noise and effi\u00adciency depend on the geom\u00adetry of the impeller, the housing compo\u00adnents, the speed and the diam\u00adeter. Theo\u00adret\u00adi\u00adcally, both centrifugal and axial fans can be used in air handling units (AHUs). In both designs, the air is drawn parallel to the axis of rota\u00adtion. While the outflow for axial fans is primarily parallel to the axis, the air in centrifugal fans mainly escapes outwards and radi\u00adally from the center, i.e. centrifu\u00adgally.<\/p>\n\n\n\n

In both designs, the air flow is also directly propor\u00adtional to the speed, while the pres\u00adsure increase rises with the square of the speed. Which is the better choice depends on the appli\u00adca\u00adtion involved. The instal\u00adla\u00adtion and oper\u00adating condi\u00adtions are impor\u00adtant factors for the fan to work at optimum effi\u00adciency and with minimal noise emis\u00adsions.<\/p>\n\n\n\n

Axial fans: a sensible solu\u00adtion?<\/h2>\n\n\n
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Fig. 1: Differ\u00adences in the char\u00adac\u00adter\u00adistic curves of centrifugal and axial fans. (Graph | ebm-papst)<\/figcaption><\/figure>\n<\/div>\n\n\n

Axial fans work most effi\u00adciently when they convey air \u2013 for example via a heat exchanger \u2013 into the open at low back pres\u00adsures. To achieve the best possible effi\u00adciency, an axial fan\u2019s impeller should be posi\u00adtioned in a fan housing that has been aero\u00addy\u00adnam\u00adi\u00adcally opti\u00admized. Together with a front plate, this ensures the correct flow control and provides the sepa\u00adra\u00adtion required between the intake and outlet sides.<\/p>\n\n\n\n

The char\u00adac\u00adter\u00adistic curve of a typical axial fan is marked in blue in Fig. 1. There\u00adfore, axial fans achieve optimum effi\u00adciency at high air flows and do so with minimal noise emis\u00adsions. Axial fans are sensi\u00adtive to inflow fluc\u00adtu\u00ada\u00adtions without addi\u00adtional measures, such as an upstream guide vane. It is also often useful to have a discharge vane on the outlet side to opti\u00admize effi\u00adciency, which means more mechan\u00adical effort during the assembly and an increased overall length.<\/p>\n\n\n\n

The outflow char\u00adac\u00adter\u00adis\u00adtics of axial fans are very focused compared to centrifugal fans, which is a disad\u00advan\u00adtage when applying air to down\u00adstream filters or heat exchangers. However, if the outflow goes directly into a duct network, this can be advan\u00adta\u00adgeous (Fig. 2).<\/p>\n\n\n\n

Centrifugal fans: the better choice<\/h2>\n\n\n\n

Centrifugal impellers are intrin\u00adsi\u00adcally less sensi\u00adtive to influ\u00adences on the inflow and outflow sides. The devel\u00adop\u00adment of RadiPac centrifugal fans from ebm-papst, specially designed for instal\u00adla\u00adtion in AHUs, not only involved opti\u00admizing the energy effi\u00adciency and noise emis\u00adsions of the impeller, motor, control elec\u00adtronics and housing: it also involved consid\u00adering the actual instal\u00adla\u00adtion condi\u00adtions in AHUs. The result is clear: this choice of fan does not require large reserves to be prepared for instal\u00adla\u00adtion losses. Further\u00admore, centrifugal fans without a scroll housing are partic\u00adu\u00adlarly flex\u00adible when it comes to outflow vari\u00adants out of the AHU. Since the fans apply air to a pres\u00adsure chamber (pres\u00adsure plenum), it is possible to connect to a duct network in virtu\u00adally all direc\u00adtions without signif\u00adi\u00adcant losses.<\/p>\n\n\n\n

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Fig. 2: Axial and centrifugal fans can be used in air handling units (AHUs). Centrifugal fans (left figure) ensure that the air is applied more evenly to down\u00adstream fittings (filters, heat exchangers) than with axial fans (right figure). The axial speed is presented in color. (Image | ebm-papst)<\/figcaption><\/figure>\n<\/div><\/div>\n\n\n\n

What is the defi\u00adn\u00adi\u00adtion of effi\u00adciency?<\/h2>\n\n\n\n
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<\/figure>\n\n\n\n

Finding the right fan for every appli\u00adca\u00adtion<\/h3>\n\n\n\n

Simply with the new, web-based FanScout selec\u00adtion tool from ebm-papst.<\/p>\n\n\n\n

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Read more <\/i><\/a><\/div>\n<\/div>\n<\/div><\/div>\n\n\n\n

Theo\u00adret\u00adi\u00adcally, effi\u00adciency is defined using the quotient of output over input. In venti\u00adlation tech\u00adnology, the para\u00adme\u00adters are air conveying perfor\u00admance (air flow x pres\u00adsure increase) divided by elec\u00adtrical power consump\u00adtion. However, this infor\u00adma\u00adtion alone does not guar\u00adantee that the manufacturer\u2019s spec\u00adi\u00adfi\u00adca\u00adtions will be compa\u00adrable. First of all, it is impor\u00adtant to deter\u00admine which compo\u00adnents the fan concerned contains. If there is only a fan impeller, the effi\u00adciency values cannot be compared to the values of a complete fan consisting of control elec\u00adtronics (VSD), a motor and a fan impeller.<\/p>\n\n\n\n

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To obtain real\u00adistic infor\u00adma\u00adtion about effi\u00adciency levels, the entire fan unit has to be measured as a whole.<\/p>\n<\/blockquote>\n\n\n\n

Simply multi\u00adplying the indi\u00advidual effi\u00adciency levels of the various fan compo\u00adnents at their optimum point is not enough either. Although this is often done in prac\u00adtice, you cannot expect all the compo\u00adnents used to work at their optimum effi\u00adciency when they are put together, espe\u00adcially consid\u00adering that compo\u00adnent manu\u00adfac\u00adturers often only provide optimum effi\u00adciency values. It is diffi\u00adcult to obtain values for partial load behavior at a reduced speed. To obtain real\u00adistic infor\u00adma\u00adtion about effi\u00adciency levels, the entire fan unit has to be measured as a whole.<\/p>\n\n\n\n

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<\/div>\n\n\n\n

\u03b7Fan<\/sub>\u2260\u03b7max\u2061Motor<\/sub> *\u03b7maxIm\u00adpeller<\/sub> *\u03b7maxCon\u00adtrol elec\u00adtronics<\/sub><\/em><\/p>\n\n\n\n

<\/div>\n<\/div><\/div>\n\n\n\n

Back to the defi\u00adn\u00adi\u00adtion of effi\u00adciency. Air perfor\u00admance is defined by multi\u00adplying the air volume and the pres\u00adsure increase. The air flow, i.e. the air volume, is provided by the air conveying task. The pres\u00adsure increase required is found by deter\u00admining the compo\u00adnents that the air flow passes through, such as filters, heat exchangers and the connected air path. As a sum, this is the overall pres\u00adsure. It is spec\u00adi\u00adfied as static pres\u00adsure and is used to select the fan.<\/p>\n\n\n\n

Nowa\u00addays, the terms total pres\u00adsure and total pres\u00adsure increase are also common. The total pres\u00adsure is the sum of the static pres\u00adsure and the dynamic pres\u00adsure and, there\u00adfore, is always higher than the static pres\u00adsure alone. There\u00adfore, this infor\u00adma\u00adtion should be treated care\u00adfully when comparing the effi\u00adciency of fan systems. Because:<\/p>\n\n\n\n

\n
<\/div>\n\n\n\n

qV<\/sub>*pstat<qV<\/sub>*(pstat<\/sub>+pdyn<\/sub>)<\/em><\/p>\n\n\n\n

<\/div>\n<\/div><\/div>\n\n\n\n

There\u00adfore also<\/p>\n\n\n\n

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<\/div>\n\n\n\n

\u03b7stat<\/sub><\u03b7tot<\/sub><\/em><\/p>\n\n\n\n

<\/div>\n<\/div><\/div>\n\n\n\n

There\u00adfore, different fan systems have to be made compa\u00adrable before you can real\u00adis\u00adti\u00adcally compare their energy values. First of all, as described above, this involves how the fans are composed and the defi\u00adn\u00adi\u00adtion of the pres\u00adsures used in the calcu\u00adla\u00adtion. Instead of talking about percent\u00adages of effi\u00adciency, it is better to compare fans for a defined air conveying task using the expected power consump\u00adtion. It is also impor\u00adtant to eval\u00aduate how the fan will react with its surround\u00adings when installed. These vari\u00adables, called instal\u00adla\u00adtion losses (system effects), can become rather impor\u00adtant for different fan types and instal\u00adla\u00adtion condi\u00adtions, and must be added to the required (static) overall pres\u00adsure increase when selecting the fan.<\/p>\n\n\n\n

\n
<\/div>\n\n\n\n
Fig. 3: The figure shows an axial fan\u2019s char\u00adac\u00adter\u00adistic curve with and without a diffuser. (Graph | ebm-papst)<\/figcaption><\/figure>\n<\/div><\/div>\n\n\n\n

Here, axial fans perform much worse with a very high partial speed level than centrifugal fans without a scroll housing. Measure\u00adments by ebm-papst have shown that even the best axial fans on the market do not achieve the overall effi\u00adciency levels or the low noise levels of centrifugal fans (Fig. 3). However, the effi\u00adciency and acoustics of axial fans can be signif\u00adi\u00adcantly improved using combi\u00adna\u00adtions of sound absorbers, diffusers or guide blades mounted on the outlet side. Yet, even with these measures, which signif\u00adi\u00adcantly increase the overall length, you are best off with a common centrifugal fan.<\/p>\n\n\n\n

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Fan selec\u00adtion made easy<\/h2>\n\n\n\n

ebm-papst has a flex\u00adible selec\u00adtion tool to help customers find their optimal combi\u00adna\u00adtion of fans: The FanScout by ebm-papst<\/a> is a powerful, web-based selec\u00adtion tool designed to support plan\u00adners and manu\u00adfac\u00adturers in the HVAC industry in iden\u00adti\u00adfying the ideal fan solu\u00adtion for their specific appli\u00adca\u00adtion. Acces\u00adsible directly via browser without instal\u00adla\u00adtion or updates, it offers an intu\u00aditive inter\u00adface and always works with the latest product data. Users can define up to five appli\u00adca\u00adtion-specific oper\u00adating points and apply a wide range of filters, including voltage, frequency, motor tech\u00adnology (AC\/EC), instal\u00adla\u00adtion space, and permis\u00adsible noise levels. Sustain\u00adability criteria and life\u00adcycle costs can also be factored in. <\/p>\n<\/div><\/div>\n\n\n\n

Centrifugal fans with modern EC tech\u00adnology<\/h2>\n\n\n\n

The power consump\u00adtion values spec\u00adi\u00adfied in tech\u00adnical docu\u00adments are impor\u00adtant when selecting fans. You also need to correctly inter\u00adpret the spec\u00adi\u00adfied effi\u00adciency levels. With axial fans, you also need to consider the fact that the aero\u00addy\u00adnam\u00adi\u00adcally instable oper\u00adating range (stall area) is very close to the fan\u2019s optimum effi\u00adciency. If the system curve changes to higher pres\u00adsures, this can have a devas\u00adtating effect on the device\u2019s oper\u00adating safety and, there\u00adfore, on the entire system.<\/p>\n","protected":false},"excerpt":{"rendered":"

Every fan\u2019s air perfor\u00admance, noise and effi\u00adciency depend on the geom\u00adetry of the impeller, the housing compo\u00adnents, the speed and the diam\u00adeter. Theo\u00adret\u00adi\u00adcally, both centrifugal and axial fans can be used in air handling units (AHUs). In both designs, the air is drawn parallel to the axis of rota\u00adtion. While the outflow for axial fans [\u2026]<\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"wp_typography_post_enhancements_disabled":false,"footnotes":""},"categories":[16,9],"tags":[],"class_list":["post-14454","post","type-post","status-publish","format-standard","hentry","category-fans","category-refrigeration-ventilation"],"acf":[],"_links":{"self":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/14454","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/comments?post=14454"}],"version-history":[{"count":11,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/14454\/revisions"}],"predecessor-version":[{"id":22965,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/14454\/revisions\/22965"}],"wp:attachment":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/media?parent=14454"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/categories?post=14454"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/tags?post=14454"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}