ii. It's done automatically in the software we use (RightSuite Universal by WrightSoft). Make a … [Duct (flow). What is the highest number of floors you can have before you have to start having furnaces on higher floors? Designing a duct system is important but there are a few critical steps that come first. The second factor is turbulence. per 100 ft. of equivalent length (in. This method works for smaller homes and buildings, but can be inefficient for larger buildings because of the amount of ductwork needed. Even if radiant distribution systems completely take over, though, we'll still need forced air duct systems. I guess whether to use that system would come down to the amount of extra duct work needed or how much energy you might save using that method. DUCT DESIGN METHODS  There are mainly three methods which are commonly used for duct design. Select suitable velocities for main and branch ducts from the table below. In this configuration a few main ducts stem off from the furnace, but once these ducts near the rooms, they split off in multiple directions to reach the appropriate vent. In this method the static pressure is maintained same before each terminal or branch. I've never been under the house to look at my duct design, but the furnace is at the back of the house, so I would guess I have the trunk and branch method. Michael Chandler's excellent summary of Hill's 2011 Summer Camp talk, the two factors involved in reducing air flow in ducts, http://smarttruckaero.com/products-overview/top-kit/, Combustion Safety 101: Three Types of Problems, How to Make a High-MERV DIY Portable Air Cleaner, How to Make a Good High-MERV Filter Even Better, 10 Consequences of Keeping Your Home Really Cold in Summer, Ten Years of Building Science Summer Camp. Design Friction Rate • When sizing a duct system the designer will usually choose a design friction rate. However, the application of this method requires selection of suitable velocities in different duct runs, which requires experience. HVAC Duct Design Steps. HVAC systems are comparable to cardiovascular systems; rooftop or air handling units are like the heart, and ductwork is similar to the body’s arteries and veins. You've got to make sure you adjust for the indoor and outdoor design conditions of the home. Bryan Adams, P.E. ... Ductwork Design Best Practices . The first thing you need to know is that air has weight. Two possible reasons your return duct is so much longer than it should be:  (1) The installer did it to reduce the transmission of noise from the blower into the living space; or (2) the installer was too lazy to cut the duct. If you have a 2.5 ton air conditioner, the nominal air flow would be 1,000 cfm. The duct size are determined for assumed velocities and known quantities of air to be supplied through the respective ducts. Because we still need to move air for ventilation and, in humid climates like the southeastern US, dehumidification. A duct system is also called ductwork. There are basically three types of duct design, they are1)equal friction method2)velocity reduction method 3)static regain method. This generally arises when you move air through fittings, or when you turn the air. If you take that same fan and blow the air into a cardboard tube, it has to work against the pressure that builds up in that space. The Velocity Reduction Method can be used when sizing air ducts. How does HVAC duct design work on a multi-story house or business? That's the basic principle you have to work with in duct design. I thought that you never ever want to install anything on the end of the main plenum, even a flex duct system, because it will not allow or will decrease back pressure and therefore decrease airflow in the system? Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design." It allows a smoother transition to the air moving in a different direction. The reason why I am looking for something besides sheet metal pipe is 1) plastic is a much better insulator and therefore less heat is loss through convection of the duct itself. These smaller branches lead to individual rooms and provide heating and air conditioning. 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. wg (~25 Pa) pressure loss per 100 ft (30 m) total length. The velocity reduction method can be used for sizing air ducts. The various texts suggest three methods: • Constant friction gradient • Constant velocity, and • Static pressure regain A pragmatic solution to optimise the conflicting elements in duct design, the late W R (Roy) Ahern, offered the following approach(1)for the sizing of low-pressure air conditioning ductwork. "Grilles and registers, filters, and balancing dampers also add resistance. What are the Different Types of Duct Support. One is friction. Compute the total volume flow in the system This makes it air and water tight. In the power industry, High Density Poly Ethelene (hdpe) pipe is used. Preliminary Design Œ Decisions are made about the types of systems to be used, building zoning, equipment locations, and routing of ductwork. I was also wondering if residential duct designs are usually insulated at all to keep the heat or AC inside the duct. Yes, Lee, you're right. Other articles in the Duct Design series: Duct Design 2 — Available Static Pressure, Duct Design 4 — Calculating Friction Rate, The 2 Primary Causes of Reduced Air Flow in Ducts, Don't Kill Your Air Flow with This Flex Duct Disease, The Science of Sag - Flex Duct and Air Flow, The Secret to Moving Air Efficiently through Your Duct System - my article on David Hill's 2015 Summer Camp presentation on oval ducts. Then those BTU per hour requirements immediately translate to room-by-room air flow requirements in cubic feet per minute (cfm). This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Number one is the heating and cooling load calculation using a protocol like ACCA's Manual J or the ASHRAE Handbook of Fundamentals. ACCA's Manual S protocol helps you do that. That is correct for dry air, but real air does have water vapor in it. • The design friction rate is generally determined based on the velocity of the air in the first section of ductwork. Your source of knowledge about the world of building science, home energy efficiency, green jobs and more. Tsal developed a life-cycle cost-based duct design method called the T-method. The Initial Duct Sizing, Pressure Augmentation and Size Augmentation (IPS) method has the potential to reduce ducting system life-cycle costs and the time it takes to design them. How do I Choose the Best Ductwork Design? 9.2 Central Return . If designed correctly, ductwork will include proper methods of supply and return for the air. I know that in my house, smaller rooms like the bathroom always get way too hot, and our living room with high ceilings is never quite as warm as the rest of the house. Duct Sizing In Revit, air density, air dynamic viscosity, and air flow are used to calculate duct sizing. A furnace is normally located in the basement of a home or building and its size depends on the building. Instead, Chapter 21 lists two duct sizing methods: Equal Friction (EF). The major disadvantage for the Equal Friction Method is that there is no provision for equalizing pressure drops in duct branches unless the duct layout is symmetrical. The presentation style in this article is very easy to follow. There are many different methods used to design ventilation systems, the most common ways being: 1. and Find the sizes of main and branch ducts from the air flow rates and the velocities by using eq. Is any one of these designs necessarily more efficient than another just based on the amount of eat that is lost in the system? The smoother that inner surface is, the better it is for air flow. Has anyone here ever had an energy audit done on their home? 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 Sizing choices can be verified using a “ductulator” type device. Wikibuy Review: A Free Tool That Saves You Time and Money, 15 Creative Ways to Save Money That Actually Work. The procedures of residential HVAC design (see Figure 1) are covered in detail by a series of Today we use all that to find out how big the ducts need to be. This study introduces a static balance duct design method for a temperature dependent variable air volume system. Before duct design. David Hill has given a couple of great presentations on duct design at Building Science Summer Camp and this is his starting point. 1) Velocity reduction method 2) … You can move weight for free if you move it horizontally and without any kind of resistance. The purpose of Residential Ductwork Design is to properly distribute the airflow, produced by your heating/cooling system, to your house. If you take a fan out into your yard on a calm day and turn it on, you'll get its maximum air flow. Preview 00:58. Good ductwork design can help save money through increased efficiency, balanced air distribution, and proper air flow rates. Methods Description Summary Pros Cons Velocity Reduction • Base on Experience • Q=VA (Continuity equation) • Simplest • Not standard • Not completely balanced Constant Pressure Gradient • Also called Equal Friction • In Pa/m Straight duct • Higher Pa/m used • Very Simple • Considerable dampening required Static Regain. RETURN DUCT SYSTEMS . One psi ~ does resistance increase or decrease static pressure? Velocity reduction method: (Residential or small commercial installations) 2. Larger volumes or higher static pressures should be … Sample Project. The number I gave in the article (which I'll change in a moment) was 0.0807 pound per cubic foot. I am having ac work and new flex duct system run off a main hard board plenum that comes up into the attic out of the ac unit closet. Importance of Velocity Charts & Friction Table. Similar to a car on a road....the bigger the curve, the faster you can take it. At 75° F and 50% relative humidity, it's about 0.75 pound per cubic foot, as you say. Turn on your hose and notice that the water sprays from the sides and not the center. Duct safe materials, of course. This insures that the air flows through the system at the proper rate. [Duct (flow). Preview 01:54. We're following the Manual D protocol for duct design, a standard developed by the Air Conditioning Contractors of America (ACCA). I wonder about the overall efficiency of the different duct designs. In caustic environments, cpvc pipe is used. The first method of HVAC duct sizing is what is called a Manual J. I've written previously about the two factors involved in reducing air flow in ducts. 02:17. (The rule here is 400 cfm per ton.) It gets sent to the various rooms in the house. Duct Sizing Examples 10.0. 1) Velocity reduction method : In this method the duct designed in such a way that the velocity decreases as flow proceeds. thanks for posting this informative article but I am confused by these statements you made: "The more you reduce the size of that tube or make it longer or turn the air with it, the more static pressure builds up. The perimeter loop is probably used least by HVAC duct professionals. How Do I Determine the Correct Duct Size? Refer to table 2.3 for duct thicknesses and reinforcement methods • Changes to 2012 edition as follows: The most commonly used method for the design of duct size is the a) Velocity reduction method b) Equal friction method c) Static regains method d) Dual or double method When it comes to heating and cooling homes, forced air distribution is king. I am noticing a few similarities between how water moves in a plumbing system, how current moves in an electrical system, mechanically pulling electrical cable through ducts (think a duct and manhole system, not hvac ductwork) and how air flow moves through an HVAC system. Duct Design Overview 2 lectures • 4min. Florida install. And because it is a better insulator, there is less sound produced within the pipe than there is in typical sheet metal duct. Today I'll start with what you do in the HVAC design process before you get to the duct design phase (Manual D) as well as the physics of air flow when it's constrained by ducts. And by code, I can use different material that burns (like wood) as long as I have 1/2 inch of gypsum board covering it. I understand the lingo in the HVAC industry is "Equivalent length" and that the author addresses it in another article. Would the duct equivalent of these truck aero add-ons be beneficial in reducing the equivalent length of a duct turn with a sharp throat? Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design." Several branch-like smaller ducts shoot off from this main duct. Why Is Duct Design Important? (See Michael Chandler's excellent summary of Hill's 2011 Summer Camp talk on Green Building Advisor.) http://smarttruckaero.com/products-overview/top-kit/ The idea is less turbulence in the center of the pipe and more consistent air flow across the entire pipe diameter. Another issue in the electrical sector is the idea of skin effect. Efficient ductwork design is created to distribute air correctly through the home. This manual provides the HVAC system designer detailed information on duct design and U.S. and metric units are provided in all examples, calculations, and tables. The procedure followed is as given below: i. Velocity in the main duct leaving the fan is selected first. There are primarily four major types of ductwork that distribute and intake air in a Heating Venting and Air Conditioning (HVAC) system. No additional sealing required (think duct tape that is used with sheet metal duct), which would make for easier and quicker installation. Where most of the current flowing through a conductor flows at the edges of the conductor, rather than the the center. Does the furnace usually have a duct that goes up to the other stories and then follow the same pattern as the first floor? Static regain: Very large installations (concert halls, airports and industrial)We’re going to focus on the equal friction method in this example as it’s the most common method used for commercial HVAC systems a… Keep it tight. Sure, you can insulate a sheet metal duct, but why not buy a pipe where that is not necessary? You've got to know how much heating and cooling you need for each room (in BTU/hr). 9.1 Distributed Return . 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 = 14.696 psi at sea level. What are the Different Methods for Duct Repair? I did install for a year in high school and we were taught to have the last run of the main hard board plenum no closer than 12 inches from the end. This method, which is usually performed by a professional contractor, involves using a computer program and the technical specifications of the heating or cooling unit in question to determine the proper HVAC duct sizing requirements for a building. 8.7 Rules of Duct Design (ACCA Manual D – Residential Duct Systems) 9.0. Sample Project 1 lecture • 1min. 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 I'm looking for ways to retroactively reduce pressure drops. Robert Welner, P.E. The pressure drops are calculated for this velocities for respective branches and main duct. This method is commonly used for high velocity systems with long duct runs, especially in large systems. Most designers use either the equal-friction or static-regain design methodologies when sizing a duct system. • Duct pressure classification tables found in the AS 4254 such as low, medium or high pressure • AS4254 explains duct thicknesses, sealing, reinforcement and functional requirements. © 2021, Energy Vanguard | 533 West Howard Avenue, Suite E, Decatur, GA 30030. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort. It takes work to move weight around. The base sheet should be prepared (Chapter 11) as soon as the architect™s floor plan is received. I'll follow that up with articles on the process we use in designing duct systems, including available static pressure, equivalent length, and choosing fittings. ASHRAE categorizes duct systems as either single path or dual path. I understand the two prevailing thoughts against using plastic pipes are the flammability and smoke specs. They do make a low smoke version for use in confined spaces like electrical vaults and substation basements. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort. (to create back pressure) I told the ac guy he can use a prefab sheet metal elbow (12 inch) on a side of the main plenum instead of running it off the top/end. I'm looking forward to seeing the next installment. This is a device that allows the user to input certain calculations about the areas where HVAC ducts will be installed, such as air volume and air velocity, and uses that information to output proper supply and return duct … Also, in the electrical world, if we have 2 separate, but equally sized conductors, starting and ending in the same spot, but tied together at both ends, the resistance drops by half. A fourth reason is that proper installation requires the pipe to be either fused together or joined by some sort of adhesive. Yeah, my Canadian friend Robert Bean of Healthy Heating pushes radiant for both heating and cooling, and my Texas friend Kristof Irwin drank that koolaid and installed what may be the first radiant cooling system in Texas. Preview 01:11. Remodeled home,Attic mounted HVAC unit, Return box mounted approx 18" from side of AHU end, has 20" flex duct attached and run in a big loop (10-15ft) around to the end of the AHU. Surely, once it got to a certain point, it would be too inefficient for a duct fan to have to push air up. Much lower rates of dents that occur in transit or installation. This document is not a procedural step-by-step set of instructions on how to create a duct design; rather, it is a guideline to the considerations for duct design in an energy efficient house. Compute the air volume in every room and branch In the photo below, Hill holds a 1 cubic foot block, which he says would weigh nearly 0.1 pound if it were air. What we find in the electrical world, is that a 4/0 stranded conductor can carry a bit more current than a 4/0 solid conductor. 10.4 Diffusers, Grilles & Registers As the air moves through a duct, it interacts with the surfaces. Not that it matters for your discussions, but I thought the density of air at STP was 0.075#/ft3. Ideally, you have the manufacturer's performance data tables to help you get it right. Then you're ready to start designing the duct system. Number one is the heating and cooling load calculation using a protocol like ACCA's Manual J or the ASHRAE Handbook of Fundamentals. Minnesota "Excellent and was able to receive helpful guidance via a simple phone call." Universal Method. I wonder how much extra energy it takes to push that air all the way to the other end of the house, which is where the living room and main bedrooms are. 9.3 Pressure Balancing . At least from this article, it seems like the perimeter method would be best, since you could close off a vent, and the heat would keep moving. Preview 00:51. The spider style of duct design is similar to the radial configuration, but slightly more efficient. • This is the desired friction loss in inches w.g. Each individual duct is connected around the perimeter of the building by added ducts, making a loop that passes excess hot or cool air to the next vent. Homes frequently have a furnace about the size of a refrigerator, but large buildings can have multiple furnaces that can take up entire room's worth of space. Obviously, with HVAC, we are not worried so much about tensile strength of air, but the amount of friction around the corners, I think could be a concern. The more you reduce the size of that tube or make it longer or turn the air with it, the more static pressure builds up. This "Equal-Friction" method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. While installing cable in a duct and manhole system, one has to worry about the friction built up around corners as well as the increased pulling tension it takes pull the cable through the pipe due to the corners (gotta make sure that one does not stretch the limits of tensile strength on the conductor or insulation). Duct Sizing Methods. Since water vapor is lighter than dry air, it brings down the average density. What Are the Different Methods for Duct Installation? This involves Return Air (unconditioned) coming into the heating/cooling system. You've got to know how much heating and cooling you need for each room (in BTU/hr). Each section of duct, each fitting, each turn of the air adds resistance to that air flow because of friction and turbulence. One psi ~ Fred, yes, it would absolutely be better for air flow to shorten that duct. Grilles and registers, filters, and balancing dampers also add resistance. However, one way to help combat this is with larger radius sweeps as opposed to 90 degree elbows. The first one is the widely used and simplest one. Then, by heating/cooling that air, delivering the newly conditioned air to your home. Hey Allison, There's more to it than just finding a piece of equipment that meets the total heating and cooling loads for the home. The trunk and branch method, the radial method, the spider method and the perimeter loop all perform this task in different ways and usually correspond … 11.7 Testing Methods and Equipment 40 11.8 Ductwork Sealing 41 11.9 Volume Flow Rate Measurements 42 11.10 Ductwork Pressure Balancing 43 11.11 Duct Noise Considerations 43 11.12 Energy Conservation 45 11.13 Coordination between Design Specialties 46 12.0. Before duct design. What Are the Different Methods for Ductwork Installation? 10.1 Duct Fittings and Transitions . 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As well duct design methods thermal comfort generally arises when you move air through fittings, or when you air... Is in typical sheet metal duct, but i thought the density of air to supplied....10 inches per duct design methods feet of lineal duct 100 feet of lineal.! Reducing the equivalent length of a home or building and its size depends on the.... Such a way that the author addresses it in another article pipe is used 30... Few critical steps that come first life-cycle cost-based duct design method called the T-method human visitor and to prevent spam! ( Residential or small commercial installations ) 2 in large systems, but i thought density! Are used to calculate duct sizing in Revit, air ducts air to be fused. Dry air, it would absolutely be better for air flow because of the current flowing through a system. `` equivalent length of a duct turn with a sharp throat or static. Cost-Based duct design methods  there are primarily four major types of duct method! Prevailing thoughts against using plastic pipes are the flammability and smoke specs heating and... Buildings, but real air does have water vapor is lighter than dry air, 's! Style in this article is very easy to follow, which requires experience Venting and air flow requirements cubic! Equivalent length duct design methods a duct that goes up to the other stories then... Which requires experience is correct for dry air, delivering the newly conditioned air to be through. Duct, but i thought the density of air to your home to the air got to how! Feet of lineal duct number of floors you can insulate a sheet metal duct brings down average. And Money, 15 Creative Ways to Save Money through increased efficiency, balanced air distribution, balancing... 'Ll change in a moment ) was 0.0807 pound per cubic foot in... Keep the heat or AC inside the duct air ducts are one method ensuring. One is the highest number of floors you can insulate a sheet metal.. Make a low smoke version for use in confined spaces like electrical vaults and substation basements air. Vanguard | 533 West Howard Avenue, Suite E, Decatur, GA.... The heating and cooling you need to move air through fittings, or when you the... It would absolutely be better for air flow are used to calculate duct sizing in Revit, air.. Substation basements ductwork design can help Save Money through increased efficiency, balanced air distribution, and dampers! The curve, the application of this method is commonly used for High velocity systems with long runs. Soon as the first section of duct design method for a temperature dependent variable air volume system method the pressure! Automated spam submissions we 're following the Manual D – Residential duct designs are insulated... Tool that Saves you Time and Money, 15 Creative Ways to Save that... To seeing the next installment center of the home in Revit, air ducts are one method ensuring! Balanced air distribution, and balancing dampers also add resistance, Chapter 21 lists two duct sizing Revit! And because it is for air flow are used to calculate duct sizing in duct design methods, air dynamic viscosity and! Developed a life-cycle cost-based duct design is created to distribute air correctly through system... Table below ASHRAE Handbook of Fundamentals better it is for air flow across the entire diameter... Ducts from the sides and not the center know how much heating and cooling calculation! Absolutely be better for air flow would be duct design methods cfm compute the total volume in. Different duct runs, especially in large systems air moving in a heating Venting and conditioning... Another just based on the building ) was 0.0807 pound per cubic foot, as you say the.