By Kristin Lang
You have the architectural model, structural model, and your MEP model set up. You have your loads and equipment selections from your engineer. Now it’s time to start design. Revit, as we know, is not much different than CAD with the exception of all items being in a 3D environment. This can take some getting used to when you are just starting out as a Revit user. If you’re like me, you will come to love designing in Revit for the 3D aspect and knowing without a doubt that what you have designed will fit.
Here are some steps (and tips) for getting started in Revit.
- Load all of your families into Revit.
Most items can be found in the BIM object library. For all equipment, I recommend asking your local equipment reps or checking their website for families if these aren’t readily accessible through the BIM object library. Sometimes you may have to wait a short while to get some families especially if they are modular equipment that is a special build.
- Begin with a Design Development level, single line, layout either by hand or in CAD.
Personally, I do this to get my thoughts on paper and to have a starting plan. Once I have this and have reviewed the general layout with the engineer I will start “Revit-ing.” I layout all equipment that effects other disciplines, electrical, plumbing, architecture, etc. I then set equipment in place and share this information and equipment selections with other disciplines. Once equipment is located you can start to route duct mains. (Pro Tip: Always keep pressure loss in mind when routing duct.) Fittings and offsets in ductwork affect pressure loss in the entire system. The more level and straight you can keep the duct, the less pressure loss you will have. Thus, the smaller fan motor you will need to push the air ultimately saving in energy cost. (Pro Tip: Keep no more than a 4:1 duct size ratio.) Because of the noise factor, at a ratio greater than 4:1, the air noise in the duct will get loud resulting in occupant discomfort.
- Start locating air devices.
There are many factors to think about when locating air devices. Always keep in mind the throw capability of each device type. If you locate supply air devices too close together, this will create turbulent air resulting in occupant discomfort, thermally and from noise. If you have low ceiling heights (7′-6″ – 9′-0″) in a space with a large occupant load, work with your engineer or even an air device rep when selecting the air devices. If you have very high ceilings (11′-0″ or more), try to opt for low wall return to help pull the air to the floor. This will help with stratification and occupant comfort. (Pro Tip: Know your air device styles and manufacturer’s. There are many on the market and thus, a good understanding of the options is essential.) Finally, always keep this question in mind when laying out air devices, “How will this perform in heating vs. cooling?” If you’re not sure, ask your engineer.
- If you have terminal boxes to layout, now is the time to start locating them.
If not, I will proceed with extending branch ducts from the mains to the air devices.
- Start keynotes for any specific design elements that need explanation.
Once you have 75% of components located, start annotating. (Pro Tip: If the design starts to get very busy, decide if you need sections or enlarged plans to help depict the design.)
- Export 3D views into Navisworks to do walkthroughs for visually fitting, especially if space is very tight.
Navisworks has proven to be a valuable tool to use when designing in Revit. This is also useful for the engineers in assisting with the duct take-offs for static pressure calculations.
- To prevent model crashes, consider separating disciplines into their own models at the start of the project and link them into one another.
We all know how devastating a model crash can be. (Pro Tip: We have found that separating our disciplines allows us to view another disciplines design, but not alter it.) It is all too easy to select a model component of another discipline and move or delete it unintentionally if all disciplines are working in the same central model.
Kristin Lang, LEED GA is a Mechanical Designer with Kerr-Greulich Engineers, Inc.