![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Figure-1-adaptation-flow-per-speed-control-fan-660x316.jpg\")
Figure 1: Demand-based adjust\u00adment of the air flow enables signif\u00adi\u00adcant energy savings and noise reduc\u00adtion. (Photo: ebm-papst)<\/p><\/div><\/div>\n
Spec\u00adi\u00adfi\u00adca\u00adtions for resi\u00adden\u00adtial build\u00adings<\/h2>\n
For example, DIN 18017-3 applies to exhaust fans in window\u00adless bath\u00adrooms and toilets. According to this, the exhaust air flow may change by a maximum of 15% at a pres\u00adsure differ\u00adence of +\/-40 Pa or +\/-60 Pa. In indi\u00advidual venti\u00adlation systems with a common exhaust air line, a reduc\u00adtion in the exhaust air flow of the lowest unit of a maximum of 10% is permitted when oper\u00adating all units. This is intended to ensure that the exhaust air flow changes as little as possible in the event of external wind forces acting on the building enve\u00adlope.<\/p>\n
There are similar legal require\u00adments for decen\u00adtral\u00adized venti\u00adlation of indi\u00advidual rooms or for central resi\u00adden\u00adtial venti\u00adlation units with heat recovery. DIN EN 13141-8 applies to decen\u00adtral\u00adized systems. Here, the units are divided into three quality classes depending on the resulting change in air flow at a pres\u00adsure differ\u00adence of +\/-20 Pa (Fig. 2).<\/p>\n
![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Figure-2-default-ventilation-systems-660x378.jpg\")
Figure 2: Spec\u00adi\u00adfi\u00adca\u00adtions in DIN EN 13141-8 for decen\u00adtral\u00adized venti\u00adlation systems with heat recovery. (Photo: ebm-papst)<\/p><\/div><\/div>\n
In the case of central venti\u00adlation systems, the exhaust air flow must always be higher than the intake air flow according to the DIBT approval (German Insti\u00adtute for Construc\u00adtion Tech\u00adnology), but the excess exhaust air may not exceed 10%. Satis\u00adfac\u00adtory values can only be achieved here if the air flow of the fans used in the appli\u00adca\u00adtion can be precisely deter\u00admined and regu\u00adlated as needed by adjusting the speed.<\/p>\n
Methods compared<\/h2>\n
In prin\u00adciple, there is wide range of phys\u00adical measuring methods for deter\u00admining a volume or mass flow rate; however, not all of them are suit\u00adable for gases and there\u00adfore for fans. Magnetic-induc\u00adtive measuring methods or those based on Cori\u00adolis force are ruled out, for example, as they only work with elec\u00adtri\u00adcally conduc\u00adtive media or the forces gener\u00adated with gases are much too small. Mass flow measuring methods with thermal sensors are, in prin\u00adciple, suit\u00adable for fans, but only under labo\u00adra\u00adtory condi\u00adtions, as the thin measuring wires are very sensi\u00adtive.<\/p>\n
Not all measuring methods that are possible in prin\u00adciple do not neces\u00adsarily turn out to be prac\u00adtical.<\/span><\/p><\/blockquote>\n
Other measuring methods are highly accu\u00adrate and robust, but rela\u00adtively expen\u00adsive to imple\u00adment and there\u00adfore more suit\u00adable for test rigs. On an ultra\u00adsonic flow meter, two offset detec\u00adtors record the transit-time differ\u00adence of two ultra\u00adsonic waves propor\u00adtional to the average flow speed (Fig. 3).<\/p>\n
Alter\u00adna\u00adtively, flow speeds can be recorded using a vane anemometer or using a vortex gener\u00adator according to the vortex prin\u00adciple (Fig. 3). On a vortex gener\u00adator, the shed\u00adding frequency of the vortices propor\u00adtional to the flow speed is detected. In the case of the anemometer, the speed and air flow are propor\u00adtional.<\/p>\n
Figure 3: Left: speed measure\u00adment using ultra\u00adsound; right: vortex gener\u00adator. (Photo: ebm-papst)<\/p><\/div><\/div>\n
What is prac\u00adtical?<\/h2>\n
Things that are possible in prin\u00adciple do not neces\u00adsarily turn out to be prac\u00adtical. Speed measure\u00adments can be used in the inflow or outflow of a fan in all fan types and the rela\u00adtively small sensors do not cause any rele\u00advant pres\u00adsure losses. In many appli\u00adca\u00adtions, however, the addi\u00adtional costs for the sensors, their instal\u00adla\u00adtion, and the effects of aging or cont\u00ada\u00adm\u00adi\u00adna\u00adtion present substan\u00adtial obsta\u00adcles.<\/p>\n
In addi\u00adtion, flow speeds measured \u201clocally\u201d \u2013 i.e. in one place \u2013 require precise knowl\u00adedge of the oper\u00adating point or instal\u00adla\u00adtion-depen\u00addent speed distri\u00adb\u00adu\u00adtion in the cross-sectional area through which the flow passes or corre\u00adsponding unit-specific cali\u00adbra\u00adtion to deter\u00admine the air flow.<\/p>\n
The measuring accu\u00adracy at low air flows is signif\u00adi\u00adcantly reduced by the pres\u00adsure drop or pres\u00adsure differ\u00adence methods.<\/span><\/p><\/blockquote>\n
On the other hand, volume flow control systems based on measuring the pres\u00adsure drop or pres\u00adsure differ\u00adence are now found rela\u00adtively frequently in air condi\u00adtioning systems or venti\u00adlation units (Fig. 4). A sensor is also required here for pres\u00adsure measure\u00adment. However, in many cases the measuring points can be applied in such a way that the speed is not measured purely locally, but instead that enables at least an approx\u00adi\u00admate \u201cinte\u00adgral\u201d measure\u00adment of the air flow to be taken via the pres\u00adsure signal.<\/p>\n
In addi\u00adtion, there are normally no addi\u00adtional pres\u00adsure losses and the processes are rela\u00adtively inde\u00adpen\u00addent of the inflow and outflow and the oper\u00adating point. The greatest disad\u00advan\u00adtage of the pres\u00adsure drop or pres\u00adsure differ\u00adence methods is that the measuring accu\u00adracy at low air flows is signif\u00adi\u00adcantly reduced by the quadratic rela\u00adtion\u00adship between air flow and pres\u00adsure. In addi\u00adtion, there are appli\u00adca\u00adtion-specific prob\u00adlems: for example, if the pres\u00adsure differ\u00adence across a heat exchanger or filter is used in a resi\u00adden\u00adtial venti\u00adlation unit, the measuring signal is heavily depen\u00addent on cont\u00ada\u00adm\u00adi\u00adna\u00adtion and bypass flows.<\/p>\n
Figure 4: Left: pres\u00adsure differ\u00adence measure\u00adment at the inlet nozzle of a centrifugal impeller in an air condi\u00adtioning system; right: pres\u00adsure drop measure\u00adment in a resi\u00adden\u00adtial venti\u00adlation unit. (Photo: ebm-papst)<\/p><\/div><\/div>\n
Sensor\u00adless control<\/h2>\n
If there is a clear rela\u00adtion\u00adship between power consump\u00adtion and air flow at a constant speed, an oper\u00adating point can be deter\u00admined by measuring the motor current and the speed. These char\u00adac\u00adter\u00adistic curves are only found for forward-curved centrifugal impellers. The term \u201csensor\u00adless\u201d control is often used in the context of elec\u00adtron\u00adi\u00adcally commu\u00adtated blowers because only internal motor vari\u00adables are used and no external pres\u00adsure or speed sensors are required.<\/p>\n
Various ebm-papst blowers use sensor\u00adless control inte\u00adgrated into the elec\u00adtronics for constant volume control (Fig.\u20095). To deter\u00admine the oper\u00adating point, this relies on a blower-specific and, in some cases, also unit-specific cali\u00adbra\u00adtion poly\u00adno\u00admial. However, the rela\u00adtion\u00adship between power consump\u00adtion and air perfor\u00admance which is cubic in the first approx\u00adi\u00adma\u00adtion leads to signif\u00adi\u00adcantly increasing control inac\u00adcu\u00adra\u00adcies, even in this approach at low air perfor\u00admances. In addi\u00adtion, a change in the air density results in an error in air flow deter\u00admi\u00adna\u00adtion.<\/p>\n
Figure 5: Sensor\u00adless constant volume control of a forward-curved ebm-papst centrifugal fan. (Photo: ebm-papst)<\/p><\/div><\/div>\n
Effi\u00adcient solu\u00adtion for back\u00adward-curved centrifugal fans<\/h2>\n
In the case of back\u00adward-curved centrifugal fans, sensor\u00adless air flow deter\u00admi\u00adna\u00adtion is not possible due to their char\u00adac\u00adter\u00adistic curve. For this highly effi\u00adcient fan design, the flow special\u00adists at ebm-papst have devel\u00adoped a ready-to-install plug & play solu\u00adtion: a vane anemometer posi\u00adtioned in the outlet nozzle of the scroll housing (Fig. 6). It contin\u00adu\u00adously records the actual air flow without signif\u00adi\u00adcant pres\u00adsure losses or addi\u00adtional noise. The data is trans\u00adferred to the inte\u00adgrated central control elec\u00adtronics of the fan.<\/p>\n
This adjusts the speed of the EC motor to the desired setpoint and regu\u00adlates the air volume of the blower to the spec\u00adi\u00adfied setpoint regard\u00adless of air density influ\u00adences. As the speed of the vane anemometer is no longer quadrat\u00adi\u00adcally, but only linearly depen\u00addent on the air flow and the speed of the EC motor is used as an addi\u00adtional internal correc\u00adtion vari\u00adable, very high control accu\u00adracy can still be achieved even with low air flows. In addi\u00adtion, deter\u00admi\u00adna\u00adtion of the oper\u00adating point is barely nega\u00adtively affected by the effects of instal\u00adla\u00adtion through recording the entire air flow.<\/p>\n
Figure 6: Constant volume control of a back\u00adward-curved ebm-papst centrifugal fan with vane anemometer. (Photo: ebm-papst)<\/p><\/div><\/div>\n
With this very robust and fully inte\u00adgrated constant volume control, an extremely precise and effi\u00adcient solu\u00adtion can be achieved over the entire control range. For resi\u00adden\u00adtial venti\u00adlation units, this means, for example, balanced supply and exhaust air flows all year round. On the one hand, this prevents the unwanted supply of cold outside air; on the other hand, this prevents warm room air flowing outwards in winter through leaks through the building enve\u00adlope, cooling down and thus creating conden\u00adsa\u00adtion in the outer walls.<\/p>\n
The addi\u00adtional impeller does not result in any air perfor\u00admance losses or disrup\u00adtive noise, meaning that the overall perfor\u00admance of the fan remains unchanged. Even cont\u00ada\u00adm\u00adi\u00adna\u00adtion is not a problem, as has been demon\u00adstrated in tests under extreme condi\u00adtions with dust and increased air humidity.<\/p>\n","protected":false},"excerpt":{"rendered":"
In many appli\u00adca\u00adtions, regu\u00adla\u00adtion of the air flow to a spec\u00adi\u00adfied setpoint offers the possi\u00adbility of signif\u00adi\u00adcantly reducing energy consump\u00adtion and noise emis\u00adsions (Fig. 1). First of all, this applies to the fan itself; in many appli\u00adca\u00adtions such as air-condi\u00ad\u00adtioning systems, this also has a posi\u00adtive effect on the energy require\u00adments of other system compo\u00adnents [\u2026]<\/p>\n","protected":false},"author":28,"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":[19,16,9],"tags":[],"class_list":["post-15181","post","type-post","status-publish","format-standard","hentry","category-blowers","category-fans","category-refrigeration-ventilation"],"acf":[],"_links":{"self":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/15181","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\/28"}],"replies":[{"embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/comments?post=15181"}],"version-history":[{"count":6,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/15181\/revisions"}],"predecessor-version":[{"id":21569,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/posts\/15181\/revisions\/21569"}],"wp:attachment":[{"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/media?parent=15181"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/categories?post=15181"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mag.ebmpapst.com\/en\/wp-json\/wp\/v2\/tags?post=15181"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Figure-3-volume-flow-measurement-ultrasonic-vs-vortex-generator-660x370.jpg\")
![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Figure-4-RLT-residential-ventilation-unit-flow-rate-660x257.jpg\")
![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Bild-5-Sensorlose-Volumenkonstanz-Regelung-vwgk-660x438.jpg\")
![](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2021\/05\/Fig_6_constant_volume_control-660x300.jpg\")