Static pressure in Air Handling Unit

AI Thread Summary
If the static pressure in the supply duct is higher than in the return duct of an Air Handling Unit (AHU), there is no direct effect on system performance, as the two pressures are not interrelated. Typically, the static pressure of the return air is lower than that of the supply air due to downstream control and distribution devices. According to Bernoulli's principle, the static pressure in the discharge plenum must always be higher than in the supply duct. Therefore, while variations in static pressure can occur, they do not impact the overall functionality of the AHU. Understanding these pressure dynamics is essential for effective HVAC system design and operation.
cktan22
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what will happen if static pressure in supply duct is higher than the fan compartment in AHU?? or vice-versa
thanks
 
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I'm not very clear on what you are asking. What exactly do you mean by "fan compartment"? Do you mean a discharge plenum? (Note: not all fans have a discharge plenum.) The static pressure in the supply duct cannot be higher than in a discharge plenum. It isn't physically possible as per Bernoulli's principle. The static pressure in the discharge plenum will always be higher than in the supply duct.
 
what i mean is, the static pressure for hot return air ( red colour arrow) and the static pressure for cold supply air ( blue colour) in the AHU as shown in the picture. What is the effect if the static pressure for blue colour arrow is greater than red colour arrow and vice-versa?
thank for reply.
 

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The two are not related to each other, so there is no effect. But it is typical for the return static to be lower (in absolute value) than the supply static because of downstream control and distribution devices in the supply duct.
 
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