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. Especially this knowledge is useful if you are willing to find a job as an HVAC sponsorship specialist.
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.
Even if you have the best air conditioning and space heating equipment in the market, a deficient air duct design can have a negative impact on their performance. The ventilation systems must overcome static pressure, while minimizing noise and vibration. However, the static pressure can also be reduced with smart decisions while designing the air ducts.
External Static Pressure – E.S.P Calculation.
External Static Pressure is the measurement of all the resistance in the duct system that the fan has to work against. Examples are filters, grills, A/C coils and the ductwork. It is the sum of the suction pressure (negative) and discharge pressure (positive) created by the equipment blower.
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:
There are three types of air duct systems, classified based on their static pressure:
A higher static pressure causes more noise and vibration. Ideally, an air duct system must be designed with the lowest static pressure that is technically feasible.
Three main methods are used to design air duct systems:
The equal friction method is the most common in the industry by far, since it uses simple calculations that consume less time. The other two methods are rarely used in modern HVAC designs.
With the equal friction method, air ducts are designed to have a constant pressure drop per unit of length, according to the ASHRAE Fundamentals Handbook. The friction loss of the duct system is described by the average pressure drop per 100 feet of ductwork.
The ASHRAE Handbook allows some design flexibility, providing charts with suggested ranges of air velocity and friction rate. Like with any engineering decision, the optimal friction and velocity depend on project conditions:
All ducts are sized initially, and pressure loss is then calculated individually for all sections. Based on the results, air ducts are resized to balance losses.
When designing air ducts, friction losses are classified by source - losses caused by the ducts themselves, and losses caused by fittings.
When all the losses have been accounted for, HVAC engineers can select a fan that will deliver the required airflow and pressure.
HVAC design is very important in building projects, since it has an impact on operation costs and maintenance expenses in the long run. HVAC also represents the highest energy expense for most residential and commercial buildings, and smart design decisions can reduce power and gas bills. To achieve higher performance, a ventilation system can be equipped with occupancy sensors, and variable-frequency drives (VFD) for fan speed control.
A well designed HVAC system also improves occupant comfort, boosting productivity in business settings. HVAC noise can be reduced by selecting optimal duct sizes, after an accurate static pressure calculation.
Make sure your mechanical installations are code compliant and energy efficient, while getting a 50% faster turnaround. You can contact Nearby EngineersNew York Engineers by email (info@ny-engineers.com) or phone (786) 788-0295212-575-5300.