What Are The Challenges Of Modeling In Ductwork

1. What A What Are The re The Challenges O Challenges Of f M Modeling I odeling In Ductwork n Ductwork Mechanical, Electrical and Plumbing design can be intricate and require a significant amount of coordination activity in order to create the necessary detail and design components to install systems effectively. The challenges that BIM modelers face in Revit 3D BIM modellingnot only involve issues involved with software deficiencies, the challenge of coordinating with ductwork against ductwork but also coordinating locations of components with reference to other disciplines, and in some cases creating design information for third parties who may wish to integrate with other software. As we know, building services projects can be complex and they require a high level of detail to make sure everything is built exactly as designed. The globally accepted Level of Development (LOD) standard has helped somewhat to define the extent of detail required for ductwork as well as other services but the challenges within the software itself or the experience of the BIM modeller are still variables that have to be overcome. The extent of detail can of course affect the time taken to complete the design but more detail means that elements such as cost estimating in which Revit can generate automatic quantity take offs, can be added to the scope. So for example a well detailed project will allow for Revit quantity take offs for quantities for duct, insulation and other materials are created. Turning to software initially, it is certainly true that Revit MEP modelling is now becoming the standard for ductwork modelling. However, this has not always been the case as early versions of the software omitted various components such as ductwork shoes, flanges or even circular ducts. Of course, these elements could have been created using the family set up, but that is both time consuming and costly. The latter versions of Revit have improved considerably and the tool is now becoming a defect to standard in the design industry. With the software constantly improving the challenge then moves on to the specification and project definition, knowledge of the ductwork systems and the software skills of the users. BIM modelers face a constant challenge as they need to provide a much higher level of detail in the BIM era. Higher levels of detailing and modeling require time and effort and also a good understanding and experience of using Revit. Specific mechanical units and the associated ductwork may be unique in design that must be modeled as generic boxes, and ducts. Mechanical BIM modelers can model generic duct elements as place holders for coordination but these generic ducts may not illustrate the proper weight of a duct and that will affect the cost of material and other take-off data. Examples such as duct socks cannot be created from the fabric and therefore place holders can be modeled to coordinate locations with other disciplines. Whilst unique ductwork can be created, it adds challenges as it relies on the creation of customised families. Complex routing can also be a challenge because of possible multiple elevation changes with elbows. This routing may be created using a window of various views to see elevations and plans at the same time. These views can show how duct changes as you edit them in the model. Routing that requires different sizes along the route can be troublesome because individual runs with similar sizes need to be changed independently, however fitting may be hard to select with the various elevation changes. As models are developed and a high level of detail is generated, coordination knowhow and experience is necessary to avoid clashes while maintaining an installable solution. Mechanical engineers coordinate with plumbing and electrical engineers to provide water and electricity to HVAC units and exhausts. Projects that involve engine rooms require coordination due to the large number of pipes and ducts that may create clashes due to limited space. Clash detection in Revit or using a tool such as Navisworks can be executed however it requires time to develop the reports and also require time to learn the process. Of course, without detail some clashes cannot be seen due to non-existent components such as small ducts or duct components that are not modelled. Smaller ducts may not be modeled because the detail is described by other means, which can result in potential problems with model. The BIM Modeller also has to give due consideration to lagging and insulation which can add 50mm (2 inches) to the width of a duct and could therefore result in

2. clashes. Reducing the lagging or insulation is not really an option as that can affect cooling or heating capacity. One final obstacle to overcome is the duct hanging system. In some cases the brackets and hangars are modelled but in many cases, the BIM modeler has to allow for hanging and allow that in his layout/model. As the model is detailed, essential information is developed for engineers. Modelers may be required to supply a high level of detail with duct in order to provide values for calculations. Providing essential information is challenging because it add responsibilities to model to a large level of development and requires modeling components such as ductwork to be precise based off manufacturing information. If the information is not correct then the ductwork can be under or oversized. Oversized ducts can create a lack of space in possible tight quarters or undersized ducts can lead to poor performance and circulation. Ultimately, modeling ductwork has several challenges. The level of detail, coordinating with other disciplines, the challenges of the software itself and specifying information can create challenges but the benefit of BIM modeling can and does add more value to a project when the project is well planned and the level of design detail specified. Using Revit MEP for Ductwork Modelling and Ductwork Fabrication Revit is a useful tool in the AEC industry since it was introduced. It has effectively enabled organisations to minimise the possible on-site concerns and helped to lower the overall project cost. Revit MEP covers of all of the main services including ductwork modelling which is the subject of this particular article and specifically how it is used for modelling and how it is now being used for fabrication. Focusing firstly on ductwork as a discipline, ductwork is a core feature of MEP design projects as it facilitates heating, ventilation and air conditioning (HVAC) for regulating the air flow and to maintain acceptable indoor air quality as well as thermal comfort. Duct work essentially comes in three types of shape – circular, elliptical and rectangular and they are designed to be fitted at varied elevation levels. Revit has provided an array of options in its latest update for design ductwork models, yet there are many challenges when modelling ductwork in Revit. Ductwork is unique in design for each of the structures and all element expose different challenges while designing. BIM services modellers must create ductwork models to accommodate customised frames, windows, fittings and complex routings. Specific outlets are also required to be designed for ductwork to fit in the outlets as well as to leave adequate space for electrical and plumbing requirements. As well as different shapes, ductwork has to modelled in different sizes as well, to suit the design requirements along with the factors such as flow of air and mode of discharge or exhaust. An oversized duct may pose design challenges such as failing to accommodate the electrical and plumbing requirements and under sized duct may result in a serious design flaw and may not be able to hold the desired amount of air flow. Ductwork modellers typically model to a high level of detail (LOD), typically at LOD 300 and increasingly at LOD 350. Although it is only a component of MEP design ductwork modelling does require expert inputs and precise layout plans to create a clash free duct network for building and engineering projects. This can seamlessly accommodate plumbing and electrical lines without causing costly design changes at construction level. Pre-Revit, the industry used AutoCAD MEP, a 3D tool, as well as other specialist tools and add-ons such as CAD Duct to create ductwork models. When Revit was introduced it had a number of shortfalls and incomplete areas for mechanical services and indeed for ductwork. However later versions have addressed earlier shortfalls and the tool is at a stage where it can be used for detailed design to address the challenges and requirements detailed above but also for interfacing with fabrication level detail, which will be discussed further below. As well as modelling capability, Revit also provides other advantages such as providing quantity take- offs at an early stage, which helps to avoid costly design changes in the later part of the design process and provides accurate quantities for ductwork, insulation and other materials. Even though seamless ductwork models are prepared using Revit, the functionality of the design files across other

3. platforms had remained limited. For instance, when the ductwork model files designed in Revit had to be used for fabrication purposes on related software, due to its incompatibility on these softwares, the duct layouts had to be re-modelled leading to time delays and a more expensive fabrication process, resulting in fabrication errors which can have negative implications while assembling the ductwork. To overcome the limitations for fabrication, Autodesk updated Revit features for ductwork modelling in its latest version - Revit 2017. Revit 2017 now has tools to design duct fabrication which are included within the package. This enables designers and modellers to create the ductwork models, layouts and designs for the entire project lifecycle, including fabrication teams. The files which have wider compatibility for fabrication tools such as FABMEP help designers and modellers to design ductwork seamlessly over various platforms and save the project in a single file without affecting the actual design. Historically, this level of interoperability has not been experienced from design, detailing and finally through to fabrication and in the future - facilities management. In summary, Revit MEP is an established tool for ductwork modeling and it does address the core elements of a ductwork system and allow a reasonably sound set of design drawings to be issued. The challenge for fabrication from Revit was always a concern and as briefly discussed, Autodesk have now started to address this and we are seeing fabrication interoperability at last. Added to this is the fact that Revit is working more closely with fabrication tools in its own right and therefore the fabrication (manufacturing) industry is now starting adoption of Revit models in a way that has not previously been experienced. The end game will surely mean accurate designs, delivered faster and therefore more efficiently - helping to reduce costs and improve timescales in the engineering and building industry.