By Gary Mann
I am often asked “Why is a Duct size not available in the Ducting Program?”. The answer is that it probably is, but it is not a BS EN 1506 recommended size. If you are not aware of this long running industry initiative, please see the following article.
MEPworx is designed so that only the 14 preferred sizes from BS EN 1506 are selected by default. If you want to use “Non recommended” imperial sizes then you will have to double-click on the duct to display the “Duct Details” dialog above, tick “Fix Duct Size” and scroll past the recommended sizes and choose from the Imperial Sizes (6”, 12” etc.) or other sizes, that belong to no published standard, which are below the Imperial list. So, sizes that are existing and need to be modelled, can be actioned, but you should be aware that a proposed new system consists not only of straight duct but also connectors, tees, elbows, flexibles, volume control/fire dampers, grilles, diffusers, fans, supports etc. and every single size range takes up valuable space of a trade counter shelf or warehouse. Non-standard sizes will also take a hit on delivery times and increase costs unnecessarily.
If you want to use a Ø150 duct, or any other non-preferred size extensively on a project, open the Duct Database and rename to reflect the project to which it will be used on e.g. Imperial Hse.DBD and replace the Ø160 instance with Ø150 or Ø180 and Save. Use Edit>General to use on the current project. Do not “Re-order2 Sizes.
What is also not helping in this initiative is the current CIBSE Guide C’
Figure 4.2 Pressure drop for air in galvanised circular ducts (ñ = 1.2 kg·m–3; T = 293 K)
The familiar CIBSE Duct sizing chart has circular duct sizes from 50mm to 3000mm in 25, 50, 100 & 200mm increments. Of the 29 sizes listed on the chart, only 7 coincide with BSEN 1506, 4 align with the Imperial not recommended and 4 coincide with the sizes belonging to no standard. If this chart is re-drawn with only the recommended sizes, there would be less than 50% of the sizes displayed, resulting in increased clarity and total avoidance of non-recommended duct sizes. See the equivalent ASHRAE Metric Duct Design chart:
Manufacturers are keen to supply whatever the customer asks for, but a look through their product catalogue highlights sizes they are often asked for, but are not keen to supply.
I hope you found this interesting.
Let me know if you have any questions.