The following duct sizes are based on a fraction drop of. The static balance duct network can easily identify the critical zone of highest pressure loss. You can specify sizing for sections of duct using friction andor velocity, equal friction, or static regain sizing methods. With this method, the air speed in the duct is reduced near each branch or diffuser so that the dynamic. This equation is used to calculate the leakage rate through a unit of duct surface for constant. Pdf process exhaust duct system design using dynamic. The ashraefundamentals handbook contains hvac design criteria for most countries around the world. Static regain improved this design methodology sizes the supply duct system to obtain uniform static pressure at all branches and outlets. 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 method has been partially modified brooks,1995 to compensate for some of these problems.
Measured in inches of water column inwc, it acts equally in all directions and is independent of velocity. Deficiencies in duct design can result in systems that operate incorrectly or are expensive to own and operate. Environmental protection agency in the past, variable air volume vav supply air systems have consisted of pneumatically actuated mechanical inlet vanes or discharge dampers which maintain constant duct static pressure. See if static regain will increase your next projects profit margins. No part of this work may be reproduced or used in any form or by any means graphic, electronic, or mechanical, including photocopying. I have done 10 case studies of comparing friction method ducting to static regain. It is sufficient to design the main duct for complete regain. A realistic duct design problem was solved by using both this method and the static regain method. A novel method for resetting duct static pressure for.
Static regain design provides a cost savings by efficently moving air. Larger volumes or higher static pressures should be. Static regain supply air only decrease in velocity pressure. To use the duct sizing dialog to specify duct size, the ductwork must be. This paper explores the design methods for process exhaust duct systems, including velocity method, the equal friction method, the static regain method and the t. Types of ducts, duct fittings, dampers, types of diffusers, flexible ducts etc. Explain typical performance characteristics of a duct system. Duct design methods velocitymethod equalfrictionmethod staticregainmethod. Popular traditional duct design methods, including equal friction and static regain ashrae, 1997, provide engineers with design tools. This information should be consulted to ensure that the proper type and location of duct system is selected for the structure in question. The relationship between energy and volume flow rate through the normal range of volume control is shown in table 1.
The static regain method claims to create equal static pressures at successive takeoff points along a main duct thereby causing equal air flow in branches that are identical. Installation time is reduced compared to rectangular ductwork. Discharge cones may be used on the duct fans to adapt to larger diameters see fig. We have chosen to keep it simple with an equalfriction comparison. Sizing choices can be verified using a ductulator type device. Duct velocities are systematically reduced over the length of the distribution layout, which allows the velocity pressure to convert to static pressure, offseting. Design air conditioning ducts using velocity method, equal friction method or static regain method. In this method the static pressure is maintained same before each terminal or branch. 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. An equation that describes leakage as a function of leakage class and static pressure is presented in the duct design chapter of the 1993 ashrae handbook.
This method is commonly used for high velocity systems with long duct runs, especially in large systems. In general only the proposed method succeeded in designing a system that ensures exact total pressure balancing at the design airflows. 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. Design supply ductwork using the static regain method. Hvac airside design package includes over 23 programs and forms that include. Determine the maximum acceptable airflow velocity in the main duct. Principle of duct design in hvac systems cedengineering. Table 2 shows the amount of additional static pressure capability, which results from using the discharge. The velocity reduction method can be used when sizing air ducts. Further considerations duct sizing methods there is no single duct sizing method that will inherently give the best duct design. Associated with the above, are the higher noise levels requiring additional attenuation. Exhaustreturn design methods design considerations 1.
The equal friction method for sizing air ducts is often preferred because it is quite easy to use. Ducts reducer selection duct gauge selection and number of sheet calculation duct designing methods manual calculations using. Take the velocity of air in the main duct a as 8 ms for both the methods. Sizing can be applied to sections of ductwork or to an entire system. Table 1 in accas manual j lists design con ditions for locations in the u. The static regain principle and duct static pressure control. Velocity in the main duct leaving the fan is selected first. Ducts are looped together, which cause the air to selfbalance and minimize the pressure loss across the duct network. 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. Problems with the static regain method sciencedirect. Select suitable velocities for main and branch ducts from the table below. Any duct system over 3000 ls must be tested at minimum 10% of each system at 1. In the following sections, both the equal friction and static regain design methods are explored.
You can select a dynamic sizing method for the ductwork for the duct systems in a project using the duct sizing dialog. Ideally, ductwork should be sized based on lifecycle costs, balancing rst costs with lifecycle energy costs, with constraints due to noise and space considerations. Compute the necessary air volume flow m 3 s, cfm in every room and branch of the system. The static regain method of duct sizing is based on bernoullis equation, which states that when a reduction of velocities takes place, a conversion of dynamic pressure into static pressure occurs. Design of an effetive low pressure vav air distriution system in the case of the fixed aperture outlet, m and v change at the same rate as flow and therefore it can be seen that energy changes with the cube of the volume flow rate. Dynamic losses in duct 1 pressure losses due to enlargement 2 pressure loss due to contraction 3. Clearly, there is no intrinsic value to having the same. The friction method ducting is contorted due to the vav box requirements. Ratings shown in this bulletin are for duct fans with inlet and outlet ducts of the same diameter as the fan. Use duct sizing revit products 2017 autodesk knowledge.
Tsal and behls 1 argued that, irrespective of equal static pressures, it is impossible to have equal flows because total pressure balancing is violated. Equal friction and static regain are nonoptimizing methods, and the tmethod is a practical optimization method. This study introduces a static balance duct design method for a temperature dependent variable air volume system. Use 1 to compute the total air volume m 3 s, cfm in the main system.
Find the sizes of main and branch ducts from the air flow rates and the velocities by using. Much more complex than equal friction, static regain can be used to design systems of any pressure or velocity. Static pressure is the outward push of air against duct surfaces and is a measure of resistance when air moves through an object like duct work. Static pressure is the pressure that causes air in the duct to. Duct design methods duct design methods for hvac systems and for exhaust systems conveying vapors, gases, and smoke are the equalfriction method, the static regain method, and the t method. This equalfriction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. 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 lower energy consumption. A novel method for resetting duct static pressure for variable air volume systems robert j. Design the duct system using a velocity method, and b equal friction method. A pragmatic solution to optimise the conflicting elements in duct design. Duct design methods for hvac systems and for exhaust systems conveying vapors, gases, and smoke are the equal friction method, the static regain method. Static regain method duct design static regain method this method is commonly used for high velocity systems with long duct runs, especially in large systems. I have never designed or even seen a duct that gets larger at the end of a run.
The static regain method has been shown to have a number of deficiencies tsal and behls, 1988. It is possible to design long run as well as short run for complete regain. The velocity reduction method can be used for sizing air ducts. Calculate our quick test and see what you come up with. Duct system design guide first edition 2003 mcgill airflow corporation mcgill airflow corporation one mission park groveport, ohio 43125 duct system design i notice.16 298 118 1171 40 29 1151 351 101 51 1428 323 1409 15 675 1207 853 527 39 618 790 1423 738 129 497 958 693 1340 1512 71 176 540 281 222 1281 392 369 105 675 923 531 1122 1477 551