Design considerations The first one being the shape of the ductwork.
Duct Sizing Chart How To Size AndIn this article well be learning how to size and design a ductwork system for efficiency.Duct Sizing Chart Full Worked ExampleWell include a full worked example as well as using CFD simulations to optimise the performance and efficiency using SimScale.Duct Sizing Chart Free SimScale AccountScroll to the bottom to watch the FREE YouTube video tutorial Create a free SimScale account to test the cloud-based CFD simulation platform here: 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.
Discover more than 50 free on-demand webinars on different topics, from ventilation or data center design and wind load analysis to aerospace, F1, and sports aerodynamics here: Read more about the benefits of using cloud-based engineering simulation and the SimScale Community here: Find thousands of ready-to-use simulation templates created by SimScales users which you can copy and modify for your own analysis: Methods of ductwork design There are many different methods used to design ventilation systems, the most common ways being: Velocity reduction method: (Residential or small commercial installations) Equal friction method: (Medium to large sized commercial installations) Static regain: Very large installations (concert halls, airports and industrial) Were going to focus on the equal friction method in this example as its the most common method used for commercial HVAC systems and its fairly simple to follow. Design example The Building Layout So well jump straight into designing a system. Well use a small engineering office as an example and we want to make a layout drawing of the building which well use for the design and calculations. This is a really simple building it has just 4 offices a corridor and a mechanical room which is where the fan, filters and air heater or cooler will be located. Building heating and cooling loads The first thing we need to do is calculate the heating and cooling loads for each room. I wont cover how to do that in this article well have to cover that in a separate tutorial as its a separate subject area. Once you have these, just tally them together to find which is the biggest Load as we need to size the system to be able to operate at the peak demand. The cooling load is usually the highest, as it is in this case. Now we need to convert the cooling loads into volume flow rates but to do that we first need to convert this to mass flow rate so we use the formula: mdot Q (cp x t) Calculate air mass flow rate from cooling load Where mdot means mass flow rate (kgs), the Q being the cooling load of the room (kW), cp is the specific heat capacity of the air (kJkg.K) and t being the temperature difference between the designed air temperature and the design return temperature. Just to note that we will use a cp of 1.026 kJkg.k as standard and the delta T should be less than 10C so well use 8c. ![]() If we look at the calculation for room 1, we see it requires 0.26 kgs. So we just repeat that calculation for the rest of the room to find all the mass flow rates. Air mass flow rate calculation for each room Now we can convert these into volume flow rates. To do that we need the specific volume or density of the air. Well specify 21c and assume atmospheric pressure of 101.325 kPa. We can look this up in our air properties tables but I like to just use an online calculator as its quicker. So we just drop those numbers in and we get the density of air being 1.2 kgm3. You see that density has the units of kgm3 but we need specific volume which is m3kg so to convert that we just take the inverse which means to calculate 1.2 to the power of -1. You can just do that in excel very quickly (copy paste this 1.2-1) to get the answer of 0.83m3kg. Now that we have that we can calculate the volume flow rate using the formula: vdot mdot multiplied by v. Calculate air volume flow rate from mass flow rate where vdot equals the volume flow rate, mdot equals the mass flow rate of the room and v equals the specific volume which we just calculated. So if we drop those values in for room 1 we get a volume flow rate of 0.2158m3s that is how much air needs to enter the room to meet the cooling load. So just repeat that calculation for all the rooms. Building air volume flow rates duct sizing Now were going to sketch out our ductwork route onto the floor plan so we can start to size it. Ductwork layout Before we go any further we need to consider some things which will play a big role in the overall efficiency of the system.
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