In order to get the ideal amount of air from your HVAC system, it is important to have the right duct size. Duct system is used to appropriately allocate air through a building. Ducts which are not well-designed outcome in uneasiness, high energy charges, and bad air quality, and increased noise levels. Selecting the right-sized duct is vital to maintaining suitable air flow in the system. The major mistake made when sizing a duct in a residential HVAC system is not understanding how airflow over the duct affects and is affected by the whole system. You cannot properly size one duct without getting to know the load and airflow of the whole system. Changing one duct can alter the airflow in all ducts. Whether it is for a new home, an energy upgrade, getting an accurate heating and cooling load calculation is important for HVAC system design. The design of an HVAC system impacts the home’s construction costs, air quality, and comfort and energy efficiency. The consequences for selecting a wrong-sized system can be severe, noisy, inability to keep you comfortable, failure to maintain proper moist control and a system breakdown.
Techniques Used For Duct Sizing
There are three approaches which are used to determine the size of the duct. The first technique is the Velocity Method which takes into account the speed at which the air moves through the ducts centered on their overall size. A series of calculations are used to determine the speed, including the duct cross-sectional areas, the rate of air flow and speed. This technique allows contractors to decide the precise size and design of the ducts based on their applications (commercial or residential) and their location. Constant Pressure Loss and Static Pressure Recovery approaches can also be used to design the ductwork for your HVAC system. The CPL technique tends to outcome in more components but offers a correct reading of the actual pressure loss in the based on the material being used and the design of the ductwork. Static pressure recovery method emphasizes on confirming the similar pressure level is attained at all vents and inlets for the system. It is the most complex sizing methods, though it is seldom used for residential installations.
The Process
The process used while duct sizing involves:
- Determine CFM (cubic feet per minute) for every room by using Manual J load calculations. This takes into account the Room Load x Equipment CFM. The entire house should be measured and load calculations must be completed before this can be finished.
- Determine the Friction Loss Rate which is available static pressure x 100 / Effective Length.
- Lastly, the contractor will use a duct sizing chart or a software to select the ductwork based on the resistance loss and CFM calculated in the first step.
The objective of all these calculation is to ensure that the system fitted is just as large as is essential to distribute heated or cool air to the entire house. Wrong measurements outcome in improper delivery of air and a system which doesn’t get the job done.
