The three branches within the main duct now receive equal air flow making a significant improvement to the design. Create a free SimScale account to test the cloud-based CFD simulation platform here: https://www.simscale.com/ With 100,000+ users worldwide, SimScale is a revolutionary cloud-based CAE platform that gives instant access to CFD and FEA simulation technology for quick and easy virtual testing, comparison and optimization of designs in several industries, including HVAC, AEC, and electronics. This is because an additional branch now feeds the three smaller branches allowing some of the air to smoothly break away from the main flow and feed into these smaller branches. My question is on the selection of the unit size Do I use the total cooling load to select the size of my machine or I have to use the also the data on the duct friction loss to select the unit. In the guides we find two tables the one you use depends on the direction of flow, we’re using the straight direction so we locate that one and then look up each ratio to find our loss coefficient. May you do more lessons similar to this series on BMS, SCADA, DCS and its interaction with HVAC systems in the smart buildings. A series of equations is used to determine this, including duct cross sectional area, air flow rate and air speed. They also offer free webinars, courses and tutorials to help you set up and run your own simulations. For the main duct G we just sum branches L and I. We can compare the performance of different ductwork designs, quickly and easily using CFD or computational fluid dynamics. The equal friction method is straightforward and easy to use and gives an automatic reduction of air flow velocities through the system. To limit the noise in this section we’ll specify that it can only have a maximum velocity of 5m/s. Thank you very much for your great work. So just add that to the table. This website uses cookies to improve your experience while you navigate through the website. You can obtain these from ductwork manufacturers or from industry bodies such as CIBSE and ASHRAE. I would like it as well if you can finish the illustration with diffusers, grills and flexible ducts. Do that for all the ducts and branches on the table. Use the actual heat, cooling or air quality requirements for the rooms and calculate required air volume flow - q. 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. If we look at the calculation for room 1, we see it requires 0.26 kg/s. The size of each room that will need a duct must be taken into consideration, along with the way the ducts need to be … We’ll specify 21*c and assume atmospheric pressure of 101.325 kPa. Now find the total duct losses for each duct and branch, that’s very easy to do simply multiply the duct length by the pressure drop per meter, in our example we found it to be 0.65pa/m. We'll assume you're ok with this, but you can opt-out if you wish. Determine the maximum acceptable airflow velocity in the main duct, Determine the major pressure drop in the main duct, Use the major pressure drop for the main duct as a constant to determine the duct sizes throughout the distribution system, Determine the total resistance in the duct system by multiplying the static resistance with the equivalent length of the longest run, en: equal friction method air ducts sizing dimensions. Note! Pls help me team on this , do we need this much CFM for less than a ton cooling. Repeat that last process for all the remaining ducts and branches until the table is complete. All rights reserved. Drain Cleaning & Video Camera Pipe Inspection, Will My Air Conditioning Work Better with Dehumidification, AC As a Safety Feature in the Home: A Tip From Horsham. In this example we can see the coefficient comes out at 0.11. Round duct is by far the most energy efficient type and that’s what we’ll use in our worked example later on. We already know all these values so if we drop the figures in we get an answer of 0.718 pascals. Only emails and answers are saved in our archive. Before we go any further we need to consider some things which will play a big role in the overall efficiency of the system. Sizing Ducts. You also have the option to opt-out of these cookies. Typical values used for friction loss are 0.1 in H2O/100 ft (0.85 Pa/m) for supply ducts and 0.08 in H2O/100 ft (0.65 Pa/m) for return ducts. At this intersection we draw a line to find the velocity and we can see that it falls within the lines of 3 and 4m/s so we need to estimate the value, in this case it seems to be about 3.6m/s so we add that to the chart. There are three methods used for most modern duct sizing. Then we use the bend table for the tee section, again its between the values listed in the table so we have to find the numbers using bilinear interpolation. So add this figure into the chart. The 12V lead acid car battery. AddThis use cookies for handling links to social media. For example use long radius bends rather than right angles as the sudden change in direction wastes a huge amount of energy. In general though, the velocity method allows contractors to determine the appropriate size and layout of ducts based on their application (residential, commercial, industrial or high speed) and their position (main or branch ducts). Equal friction method: (Medium to large sized commercial installations) 3. For D that’s just the sum of L I and F and for duct A its then the sum of L, I, F and C. so just enter those into the table. Duct sizing for air conditioning is a complex process using one of three methodologies.