Duct sizing methods

What are the different methods for HVAC duct sizing? How to size your ductwork? The velocity reduction method can be used for sizing air ducts Select suitable velocities for main and branch ducts from the table below. Find the sizes of main and branch ducts from the air flow rates and the velocities by using eq.

From velocities and duct dimensions.

Revit provides standard methods for sizing duct : Friction. About Duct Sizing Methods Pressure Drop Calculation Revit computes pressure losses in ductwork based on the geometry and roughness of the ductwork , air density, and air dynamic viscosity. The equal friction method for sizing air ducts is easy and straightforward to use 1. Compute the air volume in every room and branch. Determine maximum acceptable airflow velocities in the main ducts.

Existing Duct Sizing Methods. Both methods were developed as expedient practical procedures and neither addresses optimization. Available computer programs are simply automated versions of these manual procedures.

To size the ducts you’re going to need a duct sizing chart. You can obtain these from ductwork manufacturers or from industry bodies such as CIBSE and ASHRAE. If you don’t have one, you can find them in the following links. These charts hold a lot of information.

Air volume in cfm can be calculated by multiplying the air velocity by the cross-sectional area of the duct in square feet. The volume of each room should be expressed as a percentage of the total volume of the structure. Duct systems in small buildings are generally sized using the equal friction or modified equal friction method. A third method for HVAC duct sizing involves using a device called a ductulator.

This is a device that allows the user to input certain calculations about the areas where HVAC ducts will be installe such as air volume and air velocity, and uses that information to output proper supply and return duct sizes. Duct sizes are calculated using either the equal friction method or constant velocity method. For more information, see Specifying a Calculation Method for Duct Sizing.

Each duct segment in the run can pass on the flow values for all outlet devices that are downstream from it. This section describes the various duct sizing methods and tools in AutoCAD MEP toolset. Velocity Reduction Method : Here duct sizing is done by varying the velocity in the main and bracnch ducts.

Static regain method : Here the total frictional drop and fitting pressure drop is calculated for the ducts, and the line with the biggest pressure drop is taken. This method is the most accurate but take lots of time for calculation. This will provide the knowl-edge necessary to recognize possible design errors and understand the effects of various design decisions.

Once properly covere use of Carrier’s Duct Calculator for equal friction sizing will be presented. Regarding the long duct runs you see in the schematic at the top of this article, we do that for a good reason. Yes, extra duct surface area hurts when the ducts are in unconditioned space.

Total pressure method—a method of duct sizing that allows the designer to determine all friction and dynamic losses in each section of a duct system (including the total system) Equal friction method—a method of duct sizing in which the duct friction loss (pressure drop) value is used constantly throughout the design of a low pressure system. Ductulator is an engineering tool to calculate air duct dimensions based on given inputs including air-flow, duct material roughness and either air pressure static loss (friction method) or air velocity (velocity method).