The procedures of residential hvac design see figure 1 are covered in detail by a series of publications produced by the air conditioning contractors of america acca, which in turn. Principle of duct design in hvac systems cedengineering. Air and gas ducts for fossil fuel power stations and industrial boiler applications are unique structures, yet structural analysis and design of ductwork are not currently referenced or governed by any national code or design standard. The procedures of residential hvac design see figure 1 are covered in detail by a series of.
This method relies on the fact that all the energy losses due to friction in ducts and shape resistance due to separations in fittings are. Asce has a publication that i have used for designing industrial ductwork. Air ducts spreadsheet template the velocity method. Deficiencies in duct design can result in systems that operate incorrectly or are expensive to own and operate. The pressure drops are calculated for this velocities for respective branches and main duct. Duct material roughness duct material roughness refers to the inside surface of the duct material. Identify code requirements regarding sizing, design, and selection of hvac equipment and ducts explain how the acca manual j, s and d load calculation standards are used to determine appropriate sizing and design of ducts and hvac equipment describe the role the hvac system plays in moisture control and the effect. The loop is fed by four or more ducts radiating out from the central plenum. Compute the necessary air volume flow m 3 s, cfm in every room and branch of the system. Calculate the pressure loss of the duct fitting in a 600mm w x 200mm h duct with a radius of 600mm and a 90 bend angle.
Ceiling plenums, duct chases, and obstructions such as walls and beams often dictate that a certain size duct be used, regardless of whether or not it is the best size from a. Pdf process exhaust duct system design using dynamic. Jun 09, 2017 it would be helpful if duct design 5 sizing the ducts contained the duct size formulas for round steel, rectangular, and flex ducts, similar to how you included the friction rate formula in duct design 4. The manufacturer will not only recommend the size, shape, and type of the required perforated duct, but also the. Number one is the heating and cooling load calculation using a protocol like accas manual j or the ashrae handbook of fundamentals.
Very large installations concert halls, airports and industrial. Entering an air friction chart at 27 ft3 min flow quantity and a velocity of 900 ft min at the air handler outlet, gives a friction loss of. Highvelocity hv duct systems are characterized by air velocities in the range of 2500 to 3500 fpm. Materials, equipment, and construction methods must be carefully chosen to achieve the most advantageous balance between both initial and life cycle costing considerations. It is basically laid out around the perimeter of the structure next to the edge of the slab. It delivers an schematic drawing of the duct system including locations and sizes of trunklines, branch ducts, outlet registers, an inlet grilles. Use 1 to compute the total air volume m 3 s, cfm in the main system. The velocity reduction method can be used when sizing air ducts. Design of flexible duct junction boxes analysis method computational fluid dynamics cfd potential alternative to physical testing used to determine pressure loss of box configurations calculates pressures within system consisting of inlet duct, junction box and outlet ducts designs were reconfigured and measured to determine variations in. Chapter layout and fabrication of sheet metal and. Duct design fundamentals static pressure ps measure of the static energy of air flowing air which fills a balloon is a good example of static pressure equally exerted in all directions the atmospheric pressure of air is a static pressure 14. Larger volumes or higher static pressures should be. Duct design methods velocitymethod equalfrictionmethod staticregainmethod.
Air flow problems have plagued the hvac industry for years. The duct size are determined for assumed velocities and known quantities of air to be supplied through the respective ducts. Keep in mind that those studies showing 20% to 35% duct system leakage were not cases of contractors testing for leakage during construction and having someone signing off that it was okay to leak that much. All information provided in this document is to be used as a guideline only. This report assists structural engineers in performing the structural analysis and design of ductwork. The purpose of residential ductwork design is to properly distribute the airflow, produced by your heatingcooling system, to your house. Small hvac system design guide new buildings institute. Ansismacna 0062006 hvac duct construction standards. This method is the most accurate but take lots of time for calculation. Compare installed hvac and duct systems to outputs of manual j, s, and d. As a result of these tests, swim recommends for design 4.
Popular traditional duct design methods, including equal friction and static regain ashrae, 1997, provide engineers with design tools. Understanding basic residential ductwork design please note. Ductwork sizing, calculation and design for efficiency. The critical paths having maximum pressure loss are addressed by refining flow parameters and fittings in the duct work. Introduction most air conditioning and heating systems require some form of duct work to channel or direct the. It covers material selection, design loads, service conditions, load combinations, plate design and.
As the air moves through a duct, it interacts with the surfaces. Use of the proper materials and methods extends the life of the ducted system, retaining duct efficiency. Duct design presented by dave janquart slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Medium to large sized commercial installations static regain. These techniques are not limited to ductwork, so the processes you learn here can be applied to roofing, flashing, and exterior building siding, to name a few. The basic principles of duct design, part 1 energy vanguard. Introduction to design of industrial ventilation systems. Local pressure losses are caused by the fluid flow through the duct fittings.
The two fundamental concepts, which govern the flow of air in ducts, are the. However, vav systems operate much of the time at an offpeak load condition and the impact of varying airflow rates to the sizing of duct systems has not been considered. It is sufficient to design the main duct for complete regain. Dec 15, 2017 this video will explain how to use friction chart for determining duct diameter and velocity in each duct. Ive written previously about the two factors involved in reducing air flow in ducts. Make semco spiral duct your first choice in performance. Duct sizing and calculation methods revit products 2017. Residential or small commercial installations equal friction 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. There are many different methods used to design ventilation systems, the most common ways being. If you continue browsing the site, you agree to the use of cookies on this website. These systems are notorious for consuming more energy than is necessary to properly heat. The types of fittings to be used based on the designers calculations of fitting losses i. Design the duct system using a velocity method, and b 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 design quick introduction duct sizing tools and methods recommended duct velocities and noise effects duct fitting pressure losses do and donts of duct design duct applications as 4254. Download free mep calculation excel sheets, autocad drawings, and training courses for hvac, firefighting, plumbing and electrical systems design. The equal friction method can be done manual or more or less semi automatic with the spreadsheet template below. Design of large ductwork structural engineering general. This manual is designed to offer both the hvac system designer and installer detailed information on duct design, materials and construction methods. Lowvelocity ductwork design is very important for energy efficiency in air distribution systems. Designing a duct system is important but there are a few critical steps that come first.
This manual provides the hvac system designer detailed information on duct design and u. Take the velocity of air in the main duct a as 8 ms for both the methods. Process exhaust duct system design using dynamic programming methods article pdf available in journal of the chinese institute of engineers 262. Upstream velocity of fitting h height of the duct w width of the duct r radius of the bend. The structural design of air and gas ducts for power stations. The fourth edition of hvac systems duct design presents the basic methods and procedures required to design hvac air distribution systems. Fundamentals distribution systems 2 space availability the sizing criteria will often be defined by the space available to run the ductwork figure 1. Consequently, the total pressure or total energy of air flowing in a duct system is generally equal to the sum of the static pressure and the velocity pressure. Pressure drop calculation revit computes pressure losses in ductwork based on the geometry and roughness of the ductwork, air density, and air dynamic viscosity. Size ductwork using the balance by design or the blast gate method.
Hvac duct design hvac systems duct design smacna hvac duct construction duct design residential duct design duct design methods 20 ashrae duct design ashrae handbook fundamentals duct design advanced strategy guideline. This equalfriction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Related commercial resources ashrae handbook fundamentals chapter. This chapter introduces you to basic sheet metal and fiberglass ductwork fabrication. Exhaustreturn design methods design considerations 1. Here duct sizing is done by varying the velocity in the main and bracnch ducts. Air distribution basics and duct design hvac design hvac proccess design hvac model design hvac controls design hvac control. It would be helpful if duct design 5 sizing the ducts contained the duct size formulas for round steel, rectangular, and flex ducts, similar to how you included the friction rate formula in duct design 4. When proper methods of assembly and sealing are used, the total airflow should satisfy indoor air quality requirements. Dynamic losses in duct 1 pressure losses due to enlargement 2 pressure loss due to contraction 3 pressure loss at inlet and outlet of a duct.
The velocity reduction method can be used for sizing air ducts. However, these methods involve some engineering judgment and extensive manual recalculations, so air distribution systems designed by different engineers for identical situations will turn out to have. Small hvac system design guide overview 1 overview this design guide focuses on packaged heating, ventilation and air conditioning hvac syst ems up to 10 tons per unitthe most common hvac systems for small commercial buildings in california. Jul 11, 2014 air velocity in duct design as air velocity increases noise increases increasing air velocity causes more turbulence recommended velocity 700900 fpm 8. Further considerations duct sizing methods 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. Handbook of heating, ventilation and air conditioning. Current duct design methods for variable air volume vav systems are based on the use of peak constant airflow. The course concludes with the basic instructions for filling out a manual d speedsheet. Our manual d calculation service, is a complete custom duct design for your residential project. Select suitable velocities for main and branch ducts from the table below. Modified equal friction, incorporating many of the benefits of static regain, is presented in the related tdp505, duct design, level 2. The summary of loss coefficient run in tandem with duct sizing summary. Getting a complete manual d hvac design done on your property plans is the best way to ensure that your heating and cooling system will deliver maximum comfort at high efficiency. In this method the duct designed in such a way that the velocity decreases as flow proceeds. The following duct sizes are based on a fraction drop of.
Youve got to know how much heating and cooling you need for each room in btuhr. Design air conditioning ducts using velocity method, equal friction method or static regain. A comprehensive duct layout indicating sizes, design airflows, pressure class, and routing of the duct system. May 11, 2019 the method can increase the numbers of reductions compared to other methods and often a poorer pressure balance in the system require more adjusting dampers. It is necessary to select the main duct velocity consistent with good practice from a standpoint of noise for a particular building or application. It is possible to design long run as well as short run for complete regain.
The equal friction method for sizing air ducts is often preferred because it is quite easy to use. Remember to keep safety as the main focal point on any jobsite. Lowvelocity design will lead to larger duct sizes, but it may be worth since, doubling of duct diameter. May 25, 2017 thats the basic principle you have to work with in duct design. Duct design clicking on a companys name will take you to their web site. The rougher the surface, the higher the friction loss. The velocity method can be done manual or more or less semi automatic with the spreadsheet template below. Pressure or pressure loss is important to all duct designs and sizing methods. You will be introduced to the tools needed to work the sheet metal. The most popular duct sizing method equal friction is covered in detail. The duct sizing utility is designed to follow the equal friction method workflow in computing losses.
Students or novice designers should read and study this material thoroughly before proceeding with the design sections. The structural design of air and gas ducts for power stations and industrial boiler applications. Larger volumes or higher static pressures should be dealt with on an individual job basis. What are the methods that are used for duct design. Find the sizes of main and branch ducts from the air flow rates and the velocities by using. In comparing duct performance, two elements should be equal in the related designs. Oct 10, 2019 the air tightness of hvac duct begins with the proper specification written by a design engineer. Design of ducts with side junctions side duct junctions.
The manual d is a complete schematic drawing of the duct system including locations and sizes of trunklines, branch ducts, outlet registers, an inlet grilles. Determine the maximum acceptable airflow velocity in the main duct. Increased friction rate in compressed flexible duct. The fundamentals of duct system design mcgill airflow. Total duct leakage and percentage duct leakage test 5. Introduction to design of industrial ventilation systems course no. This and a companion paper introduce an optimum duct design proce. Armed with knowledge from real job examples, you can make informed decisions on product selection and scope resulting in more efficient, less expensive duct systems. Duct sizing in revit, air density, air dynamic viscosity, and air flow are used to calculate duct sizing. Decisions are made about the types of systems to be used, building zoning, equipment locations, and routing of ductwork. Heat conduction and thermal resistance for steady state conditions and one dimensional heat transfer, the heat q conducted through a plane wall is given by.
To get the maximum pressure loss in the system, determine the longest run of duct. Lowvelocity ductwork design is very important for energy efficiency in. This document is not a procedural stepbystep set of instructions on how to create a duct design. The base sheet should be prepared chapter 11 as soon as the architects floor plan is received.