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Has BIM Changed MEP Design Workflow?

The MEP design and installation workflow involves a number of stakeholders and parties that are collectively responsible for overseeing a series of stages that will result in the building engineering (or building services) to be planned, designed, spatially coordinated, fabricated, installed, commissioned and maintained. Typically, the building services design stage follows the initial architectural design, from which point it can usually be designed in parallel with further architectural as well as structural design changes.

The engineering teams that typically design building services solutions are usually in one of two groups. The first group is typically the building designer, also known as the consultant engineer or the design engineer. It is the role of the design engineer to work closely with the architect to develop the overall building engineering elements including lighting, cooling, heating, drainage, waste, fire prevention and protection services. Traditionally, the design engineer will not be involved in the detailed spatial design of these services. Instead the detailed spatial design and installation would normally be handled by the second party, known as the MEP contractor (M&E contractor) or trade contractor. The MEP or trade contractor is responsible for evolving the initial consultant design into a workable and installation-ready building services solution.

In some instances, there is also a third party involved – the fabricator, who will be responsible for creating MEP components such as ductwork or pipework elements or in some cases pre-fabricated solutions that consist of pipework, electrical ladder, plumbing, ductwork and sprinkler within a frame (module) that is delivered to site for installation in risers, plant rooms and corridors.

This article is concerned with the role of the MEP designer and MEP contractor, specifically, the focus for this article is to discuss how BIM (Building Information Modelling) has influenced the MEP design workflow between the designer and the contractor.

Current MEP BIM Workflow Options

Essentially there are five different MEP design workflow scenarios that currently exist and these will be discussed in the article. They are as follows

  1. Traditional 2D design and 3D BIM coordination
  2. 3D MEP design and 3D BIM coordination
  3. Designers 3D BIM design and coordination
  4. Contractor 3D BIM design and coordination
  5. General contractor 3D model coordination

Traditional 2D Design and 3D BIM Coordination

Considering the traditional MEP approach first, this is where a consultant will create 2D design outputs, which include 2D plan layouts, 2D sections and MEP (M&E) schematics. This will indicate the design intent for the building based on the use specified by the architect. Once the consultant has completed this design information he will pass on the information to an MEP contractor who will be responsible for creating the MEP coordinated solution. This article assumes that the contractor will create a spatially coordinated 3D BIM model using BIM tools such as Revit MEP and Navisworks. The contractor will use the design information and create an installation-ready solution which takes into account installation, efficiency of pipe runs or duct bends, space for lagging and hanging the services, access for post install maintenance and so on. This traditional MEP approach, from a 2D design to a 3D model has existed for the past couple of decades and allows the contractor to add additional information into the model that can be used by him and by facilities management companies after the installation. The use of the 3D tool such as Revit is of course useful as it is an intelligent model, with parametric components and therefore, as well as allowing the contractor to identify and resolve clashes before any time is spent on site, it has other uses and applications where model ‘information’ is used and relied upon.

3D MEP Design and 3D BIM Coordination

The second workflow method is more directly influenced by BIM. As the MEP designer, one will use BIM tools to create a 3D model and associated drawings during his initial design phase (rather than a 2D design) before this information is handed across to an MEP trade contractor. The MEP design engineer will typically create a 3D model due to customer specifications and requirements for a BIM model, as in many cases a federated model (which combines the other disciplines in a single model) is needed by the client for a weekly review and hence the MEP consultant cannot simply provide a set of 2D drawings. In this workflow, the BIM model is effectively a 3D representation of what would otherwise be a 2D deliverable. It will therefore consist of areas where further changes are still needed by a trade contractor. Such examples include the use of library items rather than specific MEP trade contractor procured elements that may be used in the model. The creation of a 3D BIM model at this stage by the consultant is also subject to multiple architectural and structural model changes. These have a knock-on effect on the MEP solution as it is effectively a work-in-progress model for MEP with constant architectural and structural changes and therefore will never have the same level of efficiency, in terms of layout of services, compared to an MEP model where the architectural and structural models are frozen. The downside of this workflow method is of course the extra time taken to create a BIM model by the consultant team. Added to this issue is the fact that 3D modelling expertise and skills within a consulting engineering team can sometimes be limited. Once the consultant completes his model and passes it to the MEP contractor, the decision as to whether the contractor should adapt the model or start the modelling process from the start is really based on the quality of the model to start with. In reality both scenarios will exist, in some cases the MEP trade contractor is better off starting the BIM model again using only the 2D design drawings that are created by the consultant from his BIM model, while in some rare cases the trade contractor will use the consultants MEP BIM model and adapt and modify it with his changes, to make the model ready for installation. In both scenarios, the MEP contractor will always look to make value engineering additions and changes to the model as well as procurement led model changes.

Designers 3D BIM MEP Design and Coordination

The third MEP design workflow method is a more pure and direct consequence of BIM and it actually also starts to promote the benefit of BIM more significantly as it gets closer to ‘virtual design and construction’ aims of the industry. In this workflow the approach of design engineer is to create a BIM model that is spatially coordinated and that is using the actual specified components for the project. Typically, the consultant during this phase will have a longer period of time to create the model, allowing him to absorb the changes from structural and architectural disciplines as they progress through the detailing stages. The fact that the model is then coordinated with the structure and architecture as well as other MEP services allows the consultant to create a model that is being created according to an installation standard that is now more usable by an installer or fabricator. When the model in this workflow method is passed on to a contractor, the contractor may still wish to make final changes and adjustments in a round of value engineering. Typically, the contractor will use the same model in this workflow and make changes to the model provided by the MEP design consultant. Additionally, it is probable that the consultant engineer will not have provided invert (height) levels or dimensions from gridlines and walls for the MEP services on his drawings. In such cases the contractor will therefore have to create more detail in the drawings, but again contractor could use the consultant’s drawings and progress them in more detail for his/her use.

Contractor 3D Design and Coordination

The fourth workflow method involves MEP contractors (or trade contractors) taking on the design responsibility as well as the coordination responsibility. Whilst the coordination responsibility is an established skillset with experience of developing detailed and comprehensive vertical and horizontal strategies for coordination being part of the contractor’s core skills, the design responsibility is a new element for the contractor. This was traditionally known as a design and build approach; however, it is now becoming increasingly common especially in cases where companies are seeking to have rapid design and detailed coordination completed. Typically, the components to be used will be specified by the end client, allowing the contractor to design and model before creating his detailed coordinated drawings from the model, to allow installation and fabrication if needed. The reason that this particular workflow method is not the most popular at present is simply due to the volume of work in the market and also the design responsibility that also has to be assumed as in most cases, contractors may not wish to accept this risk or indeed they may not have the resources to complete the design work. For this workflow method to exist at all means that the contractor has to employ design staff directly and provide design liability insurance to allow him to design the MEP solution as well as install it. The benefit of this workflow option is obviously the time efficiency that is realized and therefore the cost benefit, as the cost of utilising contractor resource will usually be lower compared to expensive design engineering firms. However, it does come with some risk as the design expertise that design engineers possess cannot be easily replicated by contractors, even if they do employ in-house teams.

General Contractor 3D Model Coordination

The fifth variant of MEP design workflow is based on creating coordinated MEP models similar to the traditional 2D to 3D approach but for a different customer group. In this workflow method a 2D architectural, structural and MEP design that is to be used by a main contractor (or general contractor) is then progressed into a 3D BIM model by the contractor to assess the validity and completeness of the model. In some cases, some of the design elements from the different disciplines may be presented in 3D while others may be in 2D. It is also possible that different disciplines may provide models in different software that may or may not present software interoperability challenges. In such instances, a team will typically be employed to use the design data from architectural, structural and MEP designers to then create a 3D BIM model based on actual data. The aim is to identify any inconsistencies in the design data by identifying any clashes in the model, allowing the contractor in such a workflow method to effectively mitigate his/her potential risk. Any problems found within the model are usually passed back to the designers to make amendments to their 2D design for subsequent changes to the 3D BIM model which is ultimately owned by the main contractor. This BIM workflow solution is becoming less common now because MEP contractors and designers are creating BIM models themselves.

In summary, BIM has introduced a number of new workflow variants to the MEP design services sector. The previously tried and trusted method of a 2D design, from a designer, that was developed into a 3D coordinated MEP model by contractor is no longer the workflow solution used as firms now have many other variants and alternatives available. Along with BIM Modeling, other developments in the construction sector, including collaborative online working and work sharing have also contributed to the uptake levels for BIM and impacted the changes to workflow.

In terms of the MEP design workflow options, the most popular of these as we move forward will be the third option, which is the consultant creating a BIM model that is spatially coordinated, or the fourth option which is the contractor taking on the design responsibility as well as creating the coordinated BIM model. Both options are effectively a change to the traditional approach for MEP design and both point to a single source for the model and drawings as opposed to the historical two-tier design approach. All options discussed will require competent BIM coordination and MEP modelling teams and resources. XS CAD, with its large MEP coordination team and MEP engineering design team, which consists of mechanical and electrical engineering professionals, is well placed to deal with such projects for companies based in the USA, UK, Canada, Australia and New Zealand. As all are regions where BIM is now the preferred solution, XS CAD, with more than 16 years’ experience and a presence in each market is an ideal option for such companies.

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