International Research Journal of Engineering and Technology (IRJET) Volume: 04 Issue: 02 | Feb -2017
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e-ISSN: 2395 -0056 p-ISSN: 2395-0072
DESIGN OF DUCT FOR A THREE STOREY RETAIL SHOP Mr. Virendra V. Khakre1 Dr. AvinashWankhade2 Prof. M. A. Ali3 1 PG
student, Department of Mechanical Engineering, B.N.C.O.E. Pusad. and Head, Department of Mechanical Engineering, B.N.C.O.E. Pusad. 3 Associate Professor, Department of Mechanical Engineering, B.N.C.O.E. Pusad. ---------------------------------------------------------------------***--------------------------------------------------------------------2. Duct Sizing Abstract - In this paper importance of duct designing has 2 Professor
been analyzed which create an impact on system performance. In this a duct system for a three storey retail shop has been designed, the main purpose of this is to make proper calculation of supply air quantity and to decide size of duct by using Equal Friction method so person in the shop can feel comfortable. In equal friction method, the frictional pressure drop per unit length of the duct is maintained constant throughout the duct system. This paper attempt to formulate a methodical approach to select the perfect duct design for a given situation.
The main goal of designing HVAC duct systems is to use the lowest cost (read smallest) duct sizes that can be used without violating certain sizing constraints. First and operating cost considerations in dictate that duct systems should be designed to operate at the lowest possible static pressure. The most widely used method to size duct is constant friction loss method. The other methods are velocity reduction method and static regain method.
2.1 Equal friction method
Key words: Duct design, Equal Friction Method
Duct systems in small buildings are generally sized using the equal friction or modified equal friction method. 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. The duct size is based on the flow rate through a particular section of duct, and design value for the friction rate. Each section is sized using the design friction rate criterion, and the total pressure drop for each run is simply the sum of the pressure drop of each individual section. The duct sections pressure drop includes straight duct friction loss, pressure losses through fittings such as elbows, takeoffs, and registers and /or diffusers. In the sections entering and leaving the HVAC unit, pressure losses associated with the flow transitions entering the leaving the unit (the system effect) are also included. The unit fan speed is selected to provide the design cfm and produce enough pressure difference to overcome pressure losses in the supply and return branches having the greatest pressure drop. Note that duct systems designed using the equal friction method is not self-balancing. Balancing dampers must be installed in lower pressure loss branches to balance the system.
1. Introduction In the present day, the human being needs more comfort because of inferior environment (like light, sound, machine which produce heat). Sound, light and heat affect human comfort a lot. They may adversely affect the human comfort positively or negatively. The field of air conditioning design is more technologically challenging than ever before. Today the emphasis is no more on understanding air conditioning ‘products’ but on creating ‘solutions’ and not just solutions , but ‘customized solutions’. One of the important modules in the process is the duct design. The efficient duct design process enables the proper supply of air quantity, equal distribution of air at every corner of the Air conditioned space. The efficiency of air distribution systems has been found to be 60-75% or less in many houses because of insufficient and/or poorly installed duct insulation and leaks in the duct system. Properly designed and installed duct systems can have efficiencies of 80% or more for little or no additional cost. Duct systems that are undersized, are pinched, or have numerous bends and turns may lead to low air flow rates and high air velocities. Low air flow rates cause the heating and cooling equipment to operate inefficiently and the high air velocities increase noise.
2.2 Velocity Reduction Method The velocity criterion for sizing duct is fairly simple and straightforward. With this method, the ducts are sized fixing the speed in the duct immediately downstream from the delivery fan and empirically reducing this speed over subsequent duct trunks, normally close to each branch. Velocity limits are commonly used as a surrogate for limiting duct breakout noise. Many argue it is a poor indicator since noise is more likely to result from turbulence than velocity; e.g., a high velocity system with smooth fittings may make
A three storey retail shop has been selected for calculation of cooling loads on the basis of floor area, temperature of heat sources, humidity, climate structure, occupancy and location. These results will help in determining the duct design. The rectangular cross-section of the duct is selected as they are easy to fabricate.
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