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Modeling a fan energy consumption in an AHU
 
  
 
  
 
 
 
 
 
 
    
        
        asked Dec 25  
 
 tomer@urecsys.com's avatar  
 
 
 
 
 
I wanted to ask about modeling a fan energy consumption, my current model looks at a 100% OA  AHU with a VAV system.
 
I tried to look at the hourly fan energy consumption in relation to the CFM supplied. when i looked on the results from a fan modeled using DesignBuilder\Energy+ engine i saw a discrepancy from what i assumed will be the theoretical consumption.
 
I assumed the following :
image description
 
but looking at the result from the model i get that a power of 1.7 fits better with the simulation engine prediction, why is that ?
 
fan consumption in red is power 3 and in green its power 1.7 blue is the original e+ model predictions
 
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        answered Jan 3  
 
 PmP's avatar  
 
 
 
 
 
In design builder the fan electricity consumption for a VAV in partial load is defined by a cuadratic curve. In the AHU to see it you have to click in the AHU then in the particular fan. (https://designbuilder.co.uk/helpv7.0/...)
 
I graphed your estimations vs some curves and one of them overlaps, so you probably have the fan curve set at the ASHRAE curve (which I think is the default):
 
image description
 
Select a curve that you consider adequate for your use case, I personally use good static pressure reset (Good SPR) because I was getting way too much fan consumption and it just so happens to be closer to your estimation of ideal variable speed fan.
 
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        Asked:  Dec 25  
 
 
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        Last updated: Jan 07 
 
 
 
 
 
 
 
 
 
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