We are using trane companys varitrane equal friction duct sizing software for the design. There is no single duct sizing method that will inherently give the best duct design. This may increase the system cost compared to other methods. The dynamic loss coefficients for the outlets may be taken as 1. A study on the duct design of hvac system using the equal friction method and the t method article pdf available in journal of the society of naval architects of korea 464. Duct system design guide first edition 2003 mcgill airflow corporation. In this notebook, three methods for positive pressure design will be addressed. Dimensions for linear duct for the section are computed from flow and velocity. Total air pressure loss calculation using the equivalent resistance when the head loss corresponding to a certain airflow rate is known, the following equations may be. These singlestep design ap proaches result in designs that are work able but are not cost efficient.
Published on october 22, 2015 october 22, 2015 563 likes 68 comments. Pdf a study on the duct design of hvac system using the. The ducting from our air handling units goes all the way to the vavs and from there to the diffusers. This is the most widely used method of sizing lower pressure, lower velocity duct systems. The equal friction method can be done manual or more or less semi automatic with a spreadsheet as shown in the table below.
Determining the coefficient of friction succeed in physical science static friction is the force that holds back a stationary object up to the point that it just starts moving. Standard test method for static and kinetic coefficients of. In this method the duct designed in such a way that the velocity decreases as flow proceeds. Five easy steps to estimate external static pressure drop in hvac ducts using equal friction method. Are 346p hvac project comparison of revit mep automatic duct sizing and equal friction method manual calculations name. The lowvelocity systems occupy more space and have higher first costs. Note that sometimes n is used instead of r for the normal contact force. The equal friction method is utilized to compute the velocity through each section based on the constant friction loss and the divided flow rates through the system. Duct design methods there are mainly three methods which are commonly used for duct design. According to one option in the software, we can input the data of all the duct sections till the vav. This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.
Jun 21, 2014 much more complex than equal friction, static regain can be used to design systems of any pressure or velocity. Are 346p hvac project comparison of revit mep automatic. Determining the coefficient of friction succeed in physical science object of weight w on incline of angle a the force required to overcome friction fr equals the coefficient of friction u times the cosine of the incline angle cosa times the weight of the. No part of this work may be reproduced or used in any form or by any means graphic, electronic, or mechanical, including photocopying. In the authors opinion, the ef method offers only this benefit. The equal friction method, as its name implies, is based on maintaining the same pressure drop per unit of duct length or friction rate throughout the system. Equal friction method duct flow ventilation architecture scribd. Friction velocity equal friction static regain friction and velocity methods when just the friction or the velocity sizing method is selected, sizing can be based on only the one method, or a logical combination of the friction andor velocity methods. Select a suitable frictional pressure drop per unit length the combined initial and running costs are minimized. A study on the duct design of hvac system using the equal friction method and the tmethod article pdf available in journal of the society of naval architects of korea 464. Oct 25, 2015 equal friction method the equal friction method of sizing ducts is recommended because it does not require a great deal of experience in the selection of proper velocities in the various sections of the duct system. Duct system design guide first edition 2003 mcgill airflow corporation mcgill airflow corporation one mission park groveport, ohio 43125 duct system design i notice. The equal friction sizing method works iteratively between the minimum and maximum velocity limits to determine a duct size that results in the specified pressure loss per unit length.
Equal friction this design methodology sizes the supply duct system for a constant pressure loss per unit length. Prima usaha sheet metal duct sizer by friction for equal friction method instruction 1 enter friction loss per 100 of. Duct velocities are systematically reduced over the length of the distribution layout, which allows the velocity pressure to convert to static pressure, offsetting friction losses in the succeeding section of duct. About duct sizing methods revit products 2017 autodesk. Air flow problems have plagued the hvac industry for years. Dec 15, 2017 how to use friction chart for duct design thermal science.
Duct sizing by equal friction method using varitrane software duct sizing by equal friction method using varitrane software solidspaces mechanical op 23 oct 15. Newtons laws, maximum static friction, kinetic friction, coecients of friction. Many times, systems are sized to operate at a certain pressure or not in excess of a certain pressure. The output tension is equal to the input tension plus the product of the coefficient of friction with the normal force caused by the two tensions. But there is no way to relate friction rate to lifecycle costs other than. Duct friction chart is prepared on which scale duct sizing and pressure loss calculation pdf duct sizing table by equal friction method equal. View prima usaha acmv duct sizing table 2017 locked. Total pressure loss for the length of each duct is computed.
May 11, 2019 the equal friction method is straightforward and easy to use and gives an automatic reduction of air flow velocities through the system. Using the mcquay duct sizing formula i can simply put in the the amount of airflow ls and the external static pascalspm and it will spit out the velocity and equivalent round duct size. Duct sizing by equal friction method using varitrane. Duct sizing equal friction method engineering toolbox. The most popular duct sizing method equal friction is covered in detail. Principle of duct design in hvac systems cedengineering. Larger volumes or higher static pressures should be dealt with on an individual job basis.
Appendix b logger pro objective to measure and analyze the coecients of friction s and kbetween a wood block and wood plane. Air volume equivalent round air volume cfm 4 6 8 10 12 duct inches cfm 50 6 x 4 550 75 6 x 4 675 100 8 x 4 6 x. Duct designer supports both the equal friction and static regain methods of duct design. The equal friction method creates an initial guess for duct sizing by establishing a constant pressure loss per unit of duct length. The main disadvantage of this method is that there is no equalization of pressure drops in duct branches unless the system has a symmetrical. Gpm friction loss in 100 1001 psi 1502 psi 2004 psi 2506 psi 3009 psi 35012 psi 40016 psi 45020 psi 50025 psi. Estimate friction loss in main and branch ducts from the charts below.
Minor pressure loss coefficients must be summarized for for the actual applications. This equalfriction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Lets try a flow of 350 gpm, 3 x 4 equals 12, which is the friction loss in 100 feet of 3 hose. Scribd is the worlds largest social reading and publishing site. Compute the necessary air volume flow m 3 s, cfm in every room and branch of the system. In this article we will follow a worked example using the equal friction method of calculation. Higher pressure at the same volume flow rate means that more energy is required from the fan, and this will raise the operating cost.
Modified equal friction, incorporating many of the benefits of static regain, is presented in the related tdp505, duct design, level 2. The reduced velocities are in general within the noise. The equal friction method for sizing air ducts is often preferred because it is quite easy to use. Equal friction method the equal friction method of sizing ducts is recommended because it does not require a great deal of experience in the selection of proper velocities in the various sections of the duct system. Select a suitable frictional pressure drop per unit length. Use 1 to compute the total air volume m 3 s, cfm in the main system.
When both are selected, the size of the duct must comply with both the friction and velocity. The velocity method can be done manual or more or less semi automatic with the spreadsheet template below. Explain typical performance characteristics of a duct system. Design air conditioning ducts using velocity method, equal friction method or static regain method. Method for determining friction head loss along elastic pipes article pdf available in irrigation science 325. One question please, if i want to calculate the pressure drop on the system, should i just multiply the friction loss by the length of the duct from. Thus, the static coefficient of friction concerns the force restricting the movement of an object that is stationary on a relatively smooth, hard surface. You can use the friction model to determine whether a body will slide, what. The brake torque is a function of th e maximum normal force, which is.
Calculation of duct sizing by equal friction method en5kv68pgpno. The reduced velocities are in general within the noise limits of the application environment. Equal friction method same friction loss per foot of ductwork most commonly used method accomplished by use of a ductulator requires less balancing important to have balance dampers at each outlet results in reasonable duct sizes 17. Jul 11, 2014 equal friction method same friction loss per foot of ductwork most commonly used method accomplished by use of a ductulator requires less balancing important to have balance dampers at each outlet results in reasonable duct sizes 17. Take the velocity of air in the main duct a as 8 ms for both the methods.
Methods and devices used to measure friction in rolling j jeswiet1, m arentoft2, and p henningsen2 1 department of mechanical engineering, queens university, kingston, canada 2 department of manufacturing engineering and management, dtu, lyngby, denmark the manuscript was received on 5 january 2005 and was accepted after revision for publication on 5 october 2005. Residential duct sizing guide the following duct sizes are based on a friction rate of. The answer is 4 which is the friction loss in 100 feet of 3 hose. Most of the time however, the round size is known, and the designer wants to determine one of the dimensions of the rectangular or flat oval section. Air volume equivalent round air volume cfm 4 6 8 10 12 duct inches cfm 50 6 x 4 550 75 6 x 4 675 100 8 x 4 6 x 6 6 100. Five easy steps to estimate external static pressure. Calculation of duct sizing by equal friction method. Special issue paper 49 methods and devices used to. Duct sizing by equal friction method using varitrane software. Theory friction is the force that resists the relative. Driver operator manual chapter 3 fireground hydraulics. Modified equal friction, incorporating many of the benefits of. Fundamentals distribution systems 1 introduction this technical development program tdp covers the fundamental principles of duct system design for commercial building applications. Pdf method for determining friction head loss along elastic.
It is necessary to select the main duct velocity consistent with good practice from a standpoint of noise for. Whilst most people are aware of the constant pressure gradient, constant velocity and static regain methods, there is a further method known as the balanced pressure drop method and yet another more recent method known as the t method optimisation. The equal friction method is straightforward and easy to use and gives an automatic reduction of air flow velocities through the system. Generate a proposed layout of the air distribution system. The equal friction method can be used for the design of supply and extract duct systems. Pressure or pressure loss is important to all duct designs and sizing methods. Air flow and friction loss from a diagram is added. Two engineers given the same desired friction rate will design ducts roughly the same size. The duct size is based on the flow rate through a particular section of duct, and design value for the friction rate.
Fundamentals distribution systems 1 introduction this technical development program tdp covers the fundamental principles of duct sys tem design for commercial building applications. Are 346p hvac project comparison of revit mep automatic duct sizing and equal friction method manual calculations. Also called equal friction in pam straight duct higher pam used very simple considerable dampening required static regain supply air only decrease in velocity pressure branch or fitting offsets friction loss in succeeding section of duct fixing 1st segment with methods above lower system pressure loss. This length is taken for the critical path, considering the longest branch in an air distribution system, and possibly have the highest sum of total pressure loss on. There are a couple of difficulties being encountered. The equal friction and static regain methods are nonoptimizing meth ods that rely on heuristics that do not account for prevailing local economic conditions. Design the duct system using a velocity method, and b equal friction method. Standard test method for static and kinetic coefficients of friction of plastic film and sheeting1 this standard is issued under the.
Equal friction method in this method the frictional pressure drop per unit length in the main and branch ducts. Example equal friction method the equal friction method can be done manual or more or less semi automatic with a spreadsheet as shown in the table below. In most cases the air in a duct is assumed to be incompressible, an assumption that overlooks the change of air density that occurs as a result of pressure loss and flow in the ductwork. If you have been using the ductulator to design your duct runs, you are already familiar with the equal friction method. In the previous article the various methods used to calculate the pressure loss through ducts were briefly described. Determine the maximum acceptable airflow velocity in the main duct. Much more complex than equal friction, static regain can be used to design systems of any pressure or velocity. Are 346p hvac project comparison of revit mep automatic duct. Equal friction method part 30 in the previous article the various methods used to calculate the pressure loss through ducts were briefly described. Duct design method used on high velocity systems supply onlybased on bernoullis equationsizes the ducts so that the increase in static pressure at each branch offsets the friction loss in the succeeding section of the duct.
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