Understanding HVAC Dampers and Flow Rates

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In summary, the conversation discusses the use of HVAC dampers in regulating air flow in duct systems. The person is confused about how dampers work and how they affect the flow rate and velocity. The expert clarifies that the key is the pressure drop across the damper, which can reduce efficiency if too much back pressure is created. Dampers should only be used to balance different areas and keep in mind that less restriction leads to better efficiency. The person asks for more clarification and provides a link to their original post for further discussion.
  • #1
poont2
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Hello guys,

I recently got an internship at a engineering consultant firm doing HVAC work. I am kinda confuse on one thing. How does HVAC dampers work? I have always learned in school the continuity equation Q=AV=AV ,

Q = the volumetric flow rate
A = the cross sectional area of flow
V = the mean velocity

So how do you regulate flow in a duct system using damper when the flow is going to be the same even if you put a damper to block the air space, wouldn't it just make the flow kinda turbulent while the flow rate stay the same? wouldn't the velocity just increase at the damper and decrease after it passes the damper? I am kinda confuse, only way i can think of is it give more pressure making the air handling unit put out less air?

For example, if a pump is connected to A and B pipe. Where A pipe is 1" and B pipe is 5", of course the velocity is going to be larger on the smaller pipe, but the flow rate (Q) would be the same on both pipe rite?

Thanks for your help!
 
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  • #2
Which has the higher flow rate in your wash basin? When the valve is open or closed?
 
  • #3
poont2 said:
...only way i can think of is it give more pressure making the air handling unit put out less air?
That's the answer. The key is the pressure drop across the damper making it harder for the fan to move air.
 
  • #4
A common misconception about HVAC air flow is that you need "back pressure" to make it work. Service techs will often close air dampers just to build pressure because they've been taught that pressure differential is the key to air flow. But efficiency demands mass flow which is reduced with back pressure. In the 70's a lot of homes were built with "high pressure" air distribution systems. This was accomplished by drastically reducing duct diameters. Unfortunately the resultant volume reduction resulted in poor heat distribution and efficiency. So, the less restriction the better and dampers should only be used to balance different areas always keeping in mind that the more open the damper the greater the efficiency.
 
  • #5
I still don't get it. could you please illustrate more
 
  • #6
What, exactly don't you get?
 

FAQ: Understanding HVAC Dampers and Flow Rates

1. What is the purpose of HVAC dampers?

HVAC dampers are used to regulate the flow of air in a heating, ventilation, and air conditioning (HVAC) system. They are typically installed in ductwork and can be manually or automatically controlled to adjust the flow of air to specific areas or rooms.

2. How do HVAC dampers work?

HVAC dampers work by opening or closing to control the amount of air that passes through a specific section of ductwork. This is achieved by using a motor or actuator to adjust the position of the damper blades, which can open or close to varying degrees to regulate the air flow.

3. What are the different types of HVAC dampers?

There are several types of HVAC dampers, including volume control dampers, fire dampers, smoke dampers, and balancing dampers. Volume control dampers are the most common and are used to control the flow of air, while fire and smoke dampers are designed to prevent the spread of fire and smoke in case of an emergency. Balancing dampers are used to balance the air flow in a system to ensure proper distribution.

4. How do I determine the appropriate flow rate for my HVAC dampers?

The appropriate flow rate for HVAC dampers can vary depending on factors such as the size of the space, the type of HVAC system, and the specific needs of the building. It is best to consult with a professional HVAC technician who can assess your specific needs and recommend the appropriate flow rate for your dampers.

5. Can I adjust the flow rate of my HVAC dampers myself?

In most cases, adjusting the flow rate of HVAC dampers should be left to a professional. However, some systems may allow for manual adjustment by the user. It is important to consult the manufacturer's instructions or a professional technician before attempting to adjust the flow rate of your HVAC dampers.

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