![\"1_inflow-with-turbulence\"](\"https:\/\/ebmpapst-7237.kxcdn.com\/en\/files\/2014\/04\/1_inflow-with-turbulence.jpg\" "\\"Photo")
<\/a>Figure 1: Typical inflow in customer device with turbu\u00adlence<\/p><\/div><\/div>\n
Heat pumps and air condi\u00adtioners are installed in different ways, with varying dimen\u00adsions and designs. For example, differ\u00adences occur in the posi\u00adtioning of the open\u00adings required for venti\u00adlation, in the heat exchanger surface and in the packing density. The air flow that enters the fan is there\u00adfore influ\u00adenced by the other compo\u00adnents such as the heat exchanger, in addi\u00adtion to being influ\u00adenced by the instal\u00adla\u00adtion situ\u00ada\u00adtion. Depending on the appli\u00adca\u00adtion, the inflow to the fan is subse\u00adquently highly uneven and contains non-stationary compo\u00adnents. For example, the housing walls of rectan\u00adgular heat exchangers exhibit back\u00adflow regions with corre\u00adsponding circu\u00adla\u00adtion \u2013 that is, air turbu\u00adlence (figure 1). These in turn are then directed towards the loca\u00adtions with the least amount of clear\u00adance between the fan and the housing wall. It is here that the turbu\u00adlence from both sides is combined, causing \u2018vortexes\u2019 that generate high levels of turbu\u00adlence. This causes major fluc\u00adtu\u00ada\u00adtions in the pres\u00adsure and speed at the front edge of the blade, which can some\u00adtimes lead to dras\u00adti\u00adcally increased levels of addi\u00adtional noise, partic\u00adu\u00adlarly in the low-frequency range. This gener\u00adates broad\u00adband noise and narrow\u00adband, tonal frequency compo\u00adnents, also referred to as tonal noise.<\/p>\n
The tonal noise consists of the blade-passing noise and its harmonics. The formula for this is f=n*z*k<\/i>. The frequency of the blade-passing noise f<\/i> is calcu\u00adlated from the product of the speed of the fan n<\/i> and the number of blades z<\/i>. The harmonics of the blade-passing noise are the multiple of this, desig\u00adnated as k<\/i>. Accord\u00adingly, an axial fan with five blades and 1,200 rpm (20 rps), for example, would result in a blade-passing noise at a frequency of 100 Hz. We are all familiar with the unpleasant \u2018humming\u2019 noises that are typi\u00adcally gener\u00adated as a result.<\/p>\n Figure 2: The air inlet grille dras\u00adti\u00adcally reduces the noise-gener\u00adating disrup\u00adtions to the inflow and is equally effec\u00adtive with both axial and centrifugal fans. It has virtu\u00adally no effect on power input and air perfor\u00admance<\/p><\/div><\/div>\n The addi\u00adtional noises gener\u00adated by heat exchangers and air condi\u00adtioners are not only unde\u00adsired, they are intol\u00ader\u00adable. This is partic\u00adu\u00adlarly the case in resi\u00adden\u00adtial envi\u00adron\u00adments, although elim\u00adi\u00adnating these noises is far from easy. It is not possible to compen\u00adsate for disrup\u00adtions to the inflow by opti\u00admising the fan. Providing addi\u00adtional insu\u00adla\u00adtion for the housing also brings little success in prac\u00adtice, as corre\u00adsponding insu\u00adla\u00adtion panels are typi\u00adcally only effec\u00adtive as of higher frequency levels. The fan specialist ebm-papst Mulfingen there\u00adfore took a different approach: if you improve the inflow of air to the fan, this reduces the turbu\u00adlence and there\u00adfore also reduces the unpleasant low-frequency noises that are caused by this.<\/p>\n With this in mind, the Mulfingen engi\u00adneers devel\u00adoped the special Flow\u00adGrid air inlet grille which has a straight\u00adening effect on the inflowing air (figure 2). This dras\u00adti\u00adcally reduces the noise-gener\u00adating disrup\u00adtions to the inflow and is equally effec\u00adtive with both axial and centrifugal fans. In the case of a condenser fitted with an axial fan, for example, the deploy\u00adment of the air inlet grille reduces the noise level by 3.9 dB(A) and the tonal noise by 16 dB. With regard to a low profile air condi\u00adtioning device (diam\u00adeter 250 mm), the Flow\u00adGrid reduces the noise level by 2.5 dB(A) and reduces the tonal noise by 9 dB. Figure 3 shows the actual results of a noise measure\u00adment performed on an example condenser.<\/p>\n Figure 3: The air inlet grille achieves a signif\u00adi\u00adcant reduc\u00adtion in the sound pres\u00adsure level and consid\u00ader\u00adably weakens tonal noise. The figure shows the actual results of a noise measure\u00adment performed on a condenser<\/p><\/div><\/div>\n The use of the air inlet grille reduces the sound pres\u00adsure level and consid\u00ader\u00adably weakens the tonal noise. There\u00adfore, there is signif\u00adi\u00adcantly less need for insu\u00adla\u00adtion and noise protec\u00adtion. The air inlet grille is made of injec\u00adtion-moulded plastic and satis\u00adfies various fire protec\u00adtion classes up to UL94-5VA. You can use screws to quickly and easily secure the Flow\u00adGrid to axial and centrifugal fans, and it is possible to imple\u00adment any neces\u00adsary appli\u00adca\u00adtion-specific adjust\u00adments while securing the Flow\u00adGrid. Depending on the design of the end device, it is even possible to retrofit the Flow\u00adGrid, for example in the course of any upcoming service work. In the case of a size 800 axial fan, the air inlet grille requires only around an addi\u00adtional 15 cm of instal\u00adla\u00adtion space in the axial direc\u00adtion, which is typi\u00adcally avail\u00adable in the appli\u00adca\u00adtions.<\/p>\nPutting an end to \u2018humming\u2019 noises<\/h2>\n
<\/a><\/a>A further option for acoustic improve\u00adment<\/h2>\n