By Kirstie Nugent
In the past, existing building renovations were executed by using existing drawings and field verification to document design. These designs could only be as accurate as the corresponding as-built drawings, and required a decent amount of time in the field, verifying the conditions. But today, 3D scans have changed the way renovation projects can be approached, designed, phased and budgeted. These scans have proven to be most beneficial in mechanical spaces of mission-critical facilities — healthcare facilities, for example.
In healthcare facilities, with restrictive occupant schedules on critical MEP systems, shutdown periods have been a major design hurdle in the renovation projects. Sometimes the work can be completed over a weekend, but in other instances the shutdown period has had to be limited to just a matter of hours in the middle of the night. This constraint requires the design team to develop highly accurate, coordinated design drawings and phasing to get the work completed in a very small window of time, with little to no room for error.
Critical facilities often have very complex systems and layouts in place. When phasing a renovation project, it is important to not only accurately model the systems in question, but also everything around them. There are two issues frequently encountered in these spaces. First, the as-built drawings do not match the existing conditions. Second, some of the components are located so far off the catwalk, field verification becomes a safety risk to anyone in the space and the spaces below. 3D scans have been the solution to these issues on many recent renovation projects.
When developing the project proposal, the design team must decide whether or not to use a 3D scan. If they are hiring an outside firm to complete the scan, the design team will need to clearly outline the scope of work (i.e., what area is being scanned and what the expected deliverables will be). The building owner will then need to coordinate the best time for the scanning team to visit the site. In just one visit, the entire area of work can be scanned using a laser scanner at a series of points in the space. The scans taken from these points are then brought together to create a complete 3D model of the space. The initial model can be ready within a few days. Essentially, this model digitally recreates the space for the engineer. When looking at this preliminary model, it is as if you are actually in the space. Everything looks the way it would if you were physically there. You can accurately measure from one component to another. You can read the labels on the piping and ductwork. This model eliminates days or even weeks of fieldwork for the design team. Additionally, the firms specializing in creating these scans can also provide a Revit model of the existing conditions. The engineer can then take this complete Revit model of the existing conditions and move directly into modeling the demolition and new work for the project.
While the 3D scans are extremely beneficial in terms of the quality of work, there are some drawbacks. For an engineer or owner looking to get the complete Revit model of the scan, there is a long lead time that must be accounted for in the project timeline. While the initial scan can be ready within a few days, the Revit models take longer to create due to the time it takes to model everything from the scan. The upfront cost of the scan should also be considered when creating or adhering to a budget. Both of these factors will be impacted by the size and complexity of the scan. Conversely, the increased size or complexity of the project area increases the benefits of having the scan. A larger project area means more points will need to be scanned. For the initial scan, this will not necessarily have a large impact on the timeline or the budget. When using the Revit model, this will potentially mean adding manpower to lessen the impact to the project timeline, or incorporating lead time from the start of the scan to the point where the engineer can begin designing. Either way, a larger scan will mean additional cost.
The complexity of the scanned area will have the same impact with regards to modeling. More time will be needed to create an accurate model, meaning more cost to the owner. When having an outside firm do the scan model, that firm’s drafters will model exactly what they see in the scan. This means they do not account for insulation when modeling ductwork or piping. The drafters also do not always correctly model the piping and ductwork systems, meaning they may not differentiate between supply, return, and exhaust ductwork. The engineer will have to take these factors into account when looking at the Revit model. For instance, if it is supply ductwork, they will need to subtract the thickness of the insulation in order to get the actual duct size. The same goes for any piping. This is why it is important to have the initial scan show the space as though being physically there. This scan provides the ability to see the insulation on each component and any system labels.
The high upfront costs of 3D scanning should not discourage an owner or engineer from utilizing the technology. It simply means they should be selective when deciding where to use 3D scans. These scans have proven to be most beneficial in mechanical spaces where accurate fieldwork is more difficult and the systems are more complex. These are the areas where the benefits, most apparent during construction, strongly outweigh the costs. Projects using 3D scans have a higher quality of design coordination than those without them, resulting in fewer challenges arising during construction.
Nugent is a mechanical designer at RMF Engineering with experience in designing HVAC, plumbing, and medical gas systems. Her project experience includes assessment of existing conditions, building information modeling/coordination, as well as contract document production. Nugent has experience in coordinating designs with all disciplines including MEP, architectural, structural, and specialty systems. She currently hires and manages all of the co-ops for the Raleigh, NC office Mechanical Buildings Department and was a co-op for RMF before being hired as a full-time employee.