Static Pressure in HVAC System

Static pressure creates resistance against air movement in the ducts of an HVAC system, and air handling units must overcome this pressure to provide heating and cooling. The static pressure and airflow are the two main factors that determine how a fan operates, and also its power consumption. For these reasons, static pressure calculation is a very important step in the HVAC design process.
Air ducts are used in many types of HVAC systems, and their design has an impact on temperature control and energy efficiency. For example, packaged rooftop units (RTU) and fan coil units (FCU) are normally connected to an air duct system. To specify these components correctly, and accurate static pressure calculation is necessary.
Air Duct Design: A Brief Overview
Before designing air ducts, HVAC engineers must calculate heat load and airflow according to ASHRAE standards. They must also find optimal locations for diffusers, air handling units and HVAC equipment. Finally, the air duct layout can be designed according to the space available.
During the ductwork design process, it is very important to avoid clashes with other building systems, such as electrical and plumbing installations. However, BIM software can detect these issues automatically, and engineers can correct them before construction.
The following are some useful guidelines from HVAC experts when designing air ducts:
Reduce the pressure loss in air ducts as much as possible. This also reduces the fan horsepower required, improving energy efficiency.
Avoid sudden changes in direction when designing the air duct layout, and provide turning vanes to minimize pressure drop.
Minimize noise and vibration, since they cause discomfort and distraction for occupants. Vibration also shortens the service life of equipment, leading to expensive repairs.
Focus on cost-effective design: Save space and materials whenever possible, without affecting HVAC performance.
Design air ducts with an aspect ratio as close to 1 as possibl