Static Pressure HVAC
Static pressure is called Pst, sometimes called Pfa in the fan curve.
Static pressure is “the pressure exerted by a liquid or gas, especially water or air, at rest.”
This pressure differential across any element in the system. A charcoal filter or heating coil, or between the internal and external atmosphere of the system. Static pressure can be either positive or negative. Understanding HVAC static pressure can help you choose the right fan for your application. Fan selection is typically based on CFM and static pressure. Simply put, static pressure is the pressure when a liquid or gas is not in motion. An example is a pressure inside a balloon. Used to determine fan performance by indicating how much static pressure increases if the fan blows into a closed system. Imagine blowing up a fragile balloon with a fan. A fan with high static pressure inflates the balloon to a much larger size than a fan with low static pressure. Static pressure can provide information about the strength of the fan and how well it overcomes resistance.
Important Facts:
- flow resistance
- identical in all directions
- can be positive or negative
- independent of airspeed
Dynamic pressure HVAC
Dynamic pressure is usually expressed in Pd or Pay.
As the name suggests, this is the pressure created by air movement, which increases with velocity and is always positive. An example is sticking your hand out of the car window while the car is in motion. The hand is pushed back because the pressure on the front of the hand is higher than the pressure on the back. This is because the hand stalls the air, providing a pressure differential equal to the dynamic pressure of the liquid/moving air. The faster the car goes, the higher the dynamic pressure of the air and the greater the pushing force of the hand. Note that increasing speed does not increase static pressure at all. This is because the air remains at the same pressure when at rest.
Total Pressure
The total pressure is usually expressed in Pt or PT. This is the sum of all static elements in the system and the dynamic pressure at the exit. That is the sum of static stress and emotional pressure.
If the hand is out the window in the previous example, the pressure measured in front of the hand is the total pressure, and the pressure behind the hand is the static pressure. The difference is dynamic pressure. Many people confuse total pressure, including only the sum of the static elements, and call this a “total pressure drop.” However, when using the total pressure curve, the dynamic pressure due to velocity at the system’s exit must always be added. B. At 10 meters per second, the discharge velocity Pd is 60 Pascals.
Depending on the application, the difference between total and static pressure may be negligible, but ignoring the difference may lead to costly errors.
For further assistance with system pressure calculations and fan selection, please get in touch with us at https://www.dekkoi.co/