May 12, 2021

Determine the return of a centrifugal fan

Centrifugal fans

Last week we were busy again for our clients. One of our potential clients called. The issue? Supplying manure drying systems to poultry farms. So we got to work.  

The customer

The customer told me that in autumn and winter it is very important to get your best dry compost because dry manure weighs less. And that, of course, reduces costs.  

How does this customer dry the compost? By using centrifugal fans. He uses the fans to blow air in. After our conversation, this customer was immediately interested in learning more about Slingerland Techniek: centrifugal fans are an important part of this customer’s drying system. 

We then had extensive email contact. Including a link to our centrifugal fans. The customer searched through our selection tables and sent me the following message not long after: 

Dear Steven, 

Thanks for your mail. 

Just scrolling through the sheets, I don’t actually come across a 7.5KW centrifugal fan that gives 15,000m3h at 2500 pascal.  

Do you know which one I should have then? 

The solution

The customer could not find the alternative with us. Hmm, how is this possible?  That creates a challenge. So I started looking in our tables myself and indeed: I came up with more in the direction of a 15 or 18.5kW model.  I then made a friendly email explaining why this is absolutely impossible. 

Hello Sir,  

I have studied you request for a while, but I think this is indeed impossible. If someone else can supply you with these fans though, I would like to order 10 of them as well. Because these fans are so efficient that they generate power. To determine the return of a centrifugal fan we need to look at the following: 

Absorbed power you calculate with the following formula: 

Air volume x total pressure : 3600 : (efficiency x 10) = power consumption.  

If I fill this in with the air and pressure data you provide and with the assumption that this fan has 87% efficiency I come up with the following data:  

15000 m3/h x 2500 Pa :3600: 870 = 11.97 kW….  

So with a fan that has 87% efficiency you have 11.97kW of power consumption.  

Now if I enter the same formula with 110% efficiency (practically impossible because then the machine is actually generating energy) I get the following data:  

15000 m3/h x 2500 Pa :3600: 1100 = 9.46 kW….  

So even with this efficiency you won’t make it below 7.5kW. 

With this explanation, the client was of course willing to send me the curves of the competition. Very nice! After studying the curves, I noticed that the numbers were slightly different. In the curves there were the following numbers:  

Het rendement van een centrifugaal ventilator berekenen grafiek

So in this I saw that it is about 12,000 m3/h at just under 200 mm wg.   

12,000 m3/h x 1900 Pa :3600: 870 = 7.2kW   

That comes down to a pretty efficient fan. But I still don’t actually know if they are talking about dynamic pressure or total pressure. So I started looking some more and finally found drawings of the fan. This fan has an inlet of 285mm. 

If you suck in 11,000 m3/h through this inlet you have a speed of 55 meters per second and a pressure loss of 1800 Pa. So there is almost nothing left for your system. So it is very likely that this fan has its operating point somewhere on the left side of the curve. 

Would you like to know more about the operating point of your fan? Contact us today!   

Do you have a ventilation problem get in touch with us!

Slingerland Techniek understands that it is difficult for companies to indicate exactly what they are looking for. In order to provide companies with the best possible service, we look at the business situation together. Then the possible solutions are discussed so that we can solve your business problem in full consultation.
Do you recognize yourself in this problem and would you like to discuss your own situation with our specialists? Then contact us today!
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