VISION ISSUE SIX | 2017
Clash Detection: What to Know, What to Look for As technology continues to develop, more and more projects are switching from traditional 2D AutoCAD design to 3D BIM modeling such as Revit. BIM allows the design team to better coordinate construction and their design intent to ensure that costly change orders are minimized during construction. To this effect, one of the many benefits of BIM is the continued development of clash detection software not only within Revit, but also alternative programs such as Autodesk Navisworks. While it may be easy to depict ductwork, piping, and light fixtures within a ceiling cavity, construction tolerances always need to be considered. Modeling piping in a tightly-spaced group is not difficult, but can this piping be supported? Or insulated? While Revit allows both the design and construction teams the ability to review physical clashes between objects, it does not consider construction tolerances. However, Navisworks has been developed to provide a much higher level of review. In this article, we will work to better explain the importance of using Navisworks correctly. Improper use of this software can generate clash detection reports which are both impractical, unhelpful, and misleading to the design and construction teams. What Level of Development Is Used? Level of Development (LOD) can be described as the level of detail which has been incorporated into a model. Higher LODs ensure that a model is considering smaller elements whereas a lower LOD is primarily considering large elements only. Model elements with the highest LOD will be a field verified representation in terms of size, shape, location, quantity, and orientation. Models of this level are typically
part of the construction team coordination; lower LODs are used during design. How Should We Analyze Object Clashes? The Autodesk Navisworks Clash Detective tool allows its users to choose “Clash Rules” as well as tolerances. The tolerance can be defined as the distance between two objects that is permissible. Choosing proper Clash Rules allows the user to avoid highlighting conflicts that are intended, for example, two segments of ductwork which are physically connected. Similarly, using tolerances which are too broad will result in clashes between objects which are not actually in conflict; a tolerance of 6” will be too broad. On the other hand, a tolerance of 1/8" may be so narrow that it is physically impossible to construct. No matter what the tolerance or rules being applied, members of the design team must rely on their own industry knowledge and years of experience to allow adequate tolerances for construction. Is the Same Object Listed Twice? Three Times? More? If a user implements Clash Rules incorrectly within Navisworks, it is possible for the same clash to appear multiple times. For example, when a pipe is in conflict with a segment of ductwork, it may list conflicts such as Duct/Pipe, Duct Insulation/Pipe,
Pipe Insulation/Duct, and so on. This occurrence will inflate the overall quantity of clashes which are indicated, which in turn will make an accurate review more difficult and time consuming. In order to avoid this type of inflated clash reporting, it is critical to implement the correct Clash Detection Rules. Proper implementation is the only way to ensure the generation of truly valuable information for the design team (Duplicates Rule).
Figure 2: Pump vs. Connected Piping Conflict (Pumps should have piping connections.)
Should These Objects Be Connected? Having a basic understanding of MEP systems will give the reviewer the knowledge needed to identify elements that should and should not be connected. Should piping be connected to this object? What about ductwork? Air handling equipment, for example, will often have ductwork and piping connections. Without these continued on page 4
IN THIS ISSUE CFD in Auditoriums
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Maintaining Museum Environment 3 Revit® Corner 3 Figure 1: Instances of the Same Pipe vs. Duct Conflict
ALL TEXT ©2017 KOHLER RONAN, LLC
On the Boards
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Computational Fluid Dynamics in Auditoriums Auditoriums provide the audience with an enhanced visual and audible experience of a performance. To deliver this experience, the creation of the physical space requires a unique approach from the architectural, acoustical, and thermal design perspectives. Auditorium spaces demand nonstandard, complex interior volumes to satisfy the criteria required for functional, acoustical, and visual noninterference. Typically, they have high ceilings, wide spans, and balconies which breaks up the interior volumes while providing unique challenges for designers. The best practice air distribution system for an auditorium is one in which air is supplied via floor vents and returned through ceiling vents. Air is supplied at low velocity close to where the occupants are seated, creating a stratified air-conditioned zone around them. In spaces with high ceilings, this delivery system improves energy efficiency, ventilation delivery, and acoustics while simplifying ceiling coordination. While displacement type distribution is ideal, physical and cost constraints often require the use of conventional, overhead air distribution systems. In a traditional space (flat, low ceiling, non-densely occupied), air terminals/diffusers can typically be adjusted to fit an architectural ceiling pattern without causing thermal discomfort. With high ceiling spaces, however, air needs to be supplied at a higher velocity in order to reach occupants. The increased velocity tends to increase supply air noise, posing a potential acoustical interference. Ceiling layouts are usually driven by architecture, acoustics, and lighting; HVAC diffusers are typically fitted in where they can be best hidden. Additionally, auditoriums have acoustical ratings of NC 20-30 which usually forbid the use of any directional diffusers. These constraints present a challenge when predicting the interactions of the conditioned air within the geometric volume. A computational fluid dynamic (CFD) simulation is a sophisticated airflow and heat transfer process modeling tool used to understand the interactions of thermal processes within a space and evaluate parameters such as velocity, temperature, and thermal comfort. The objective of the CFD
simulation in an auditorium project would be to evaluate the effectiveness of air and ventilation distribution, visualize hot and cold zones, and identify measures for improving the design. Similar to energy analysis, a CFD study follows an iterative design process as shown in the following example.
Baseline
Baseline The Baseline case features a grid of linear ceiling diffusers aligned in parallel to each other and a lighting grid (not shown) running perpendicular to the air diffusers to present a clean architectural layout. This case shows stratified cold (blue) and warm (yellow) air zones which could lead to thermal discomfort.
Case 1
Case 1 The overall airflow in the space is reduced by 15% in the Case 1 scenario. This eliminates the cold zones, but introduces a warm zone in the center of the space (red). Case 2 The airflow is reset back to 100% and distribution is revised; more air is supplied at the back than at the front. Case 2 reduces the extent of the cold and warm zones.
Case 2
The observations from the three simulations are that the parallel diffusers create channels of cold and warm zones due to the buoyancy forces of air. Since acoustical standards would not allow directional diffusers, the only option is then to introduce turbulence from diffusers aligned perpendicular to the current grid.
Case 3
Case 3 Ceiling diffusers perpendicular to the light are introduced to create a mixed air volume and comfortable interior conditions within the design parameters. A CFD simulation is highly beneficial when attempting to understand thermal patterns in space–especially when working with nonstandard geometries or internal load conditions. Although running the simulation is computationally intensive, multiple iterations with incremental changes can be run fairly easily and with significantly less effort and expense than creating physical models. Auditoriums and assembly spaces are ideal projects for this type of analysis due to their complex geometries and advanced acoustical, visual, and thermal comfort requirements.
Professional Development Kohler Ronan, LLC is a registered provider of AIA Continuing Education Credits. Our professionals have prepared several presentations on relevant and timely industry topics. In the coming months, we will be available to visit your offices and share these presentations. To learn more, or to schedule a visit, please contact Joe Lembo at (203) 778-1017 or via email at krce@kohlerronan.com
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Maintaining a Museum Environment While Avoiding Condensation Natural daylight is a feature of modern museum design and can be provided via skylights, a sloped curtain wall, or via traditional window openings. Environmental conditions within a museum pose specific challenges for glazed surfaces, particularly in the Northeast. In most other buildings, the relative humidity can be reduced to a sufficient level in order to avoid condensation, while in museums, the HVAC systems are actively adding humidity. Allowing for seasonal variations in humidity levels can greatly reduce instances of condensation, but this is usually not practiced due to collections management and art sensitivity. Therefore, the typical indoor museum environment experienced in winter months is 70°F and 50%RH. This environment almost always results in condensation unless specifically addressed. Condensation occurs on glazed surfaces when the surface temperature of the glazing is colder than the dew point of air (indoor room air). Selecting glazing with exceptional thermal performance is the
REVIT® CORNER
first step in combating condensation, but mechanical systems are usually required to further eliminate or reduce instances of condensation. Kohler Ronan studied a variety of glazing systems for use in a recent museum project. It is important to note that window U-values are provided as an average value and the U-value is typically much higher at the framing components, where condensation is likely to originate. We found that (at 75°F/50%RH interior) utilizing double pane glazing with an average U-value of 0.38 and the highest component U-value of 0.92 resulted in condensation forming when the outdoor temperature dropped to 45°F. Condensation formed on triple pane glazing with an average U-value of 0.18 and the highest component U-value of 0.58 when the outdoor temperature reached 35°F. These results indicate that condensation will form in museum environments on most high performing glazing systems during winter months.
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Once everything has been selected, the filter icon is visible in the lower right-hand side of the screen. Upon clicking the icon, a menu will display the objects that have been selected.
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Now, the user can select pipe fittings from the menu. Multiple items may be selected at one time. Remember to click OK after selecting items to be filtered.
THE FILTER TOOL A helpful tool in locating items when working within Revit is the Filter Tool. Found in the lower right of the screen, it can easily be overlooked, but, if used correctly, it can dramatically speed up your search process. Take a look at the Fire Protection view displayed below. Let us assume that the user is looking for a certain type of fitting: A 3" Victaulic 90° fitting. By swiping a window around the whole view, all the objects in the view can be highlighted.
To counteract instances of condensation, mechanical systems must be designed in conjunction with the glazed surfaces. Mechanical systems can include heat or a combination of heat and air movement. The introduction of heat will raise the glazed surface temperature above the dew point temperature. Air movement will promote evaporation and will further reduce instances of condensation. Mechanical solutions may include diffusers directed at the glazed surface, radiant panels, baseboard heaters trenched below the glass, and even heating elements built into the window mullions. In many cases, the mechanical system can be integrated in a way that limits its visibility and will provide a means to eliminate condensation in extreme conditions. While this study was based on a museum environment, other spaces that may require humidity control throughout the winter months may also be subject to condensation forming on glazed surfaces if not properly addressed.
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The filter tool will then highlight all the pipe fittings in the view and nothing else, making it easy to see how many and what type of fittings are present (see image above). Since the system will show all fittings be it 3", 4", or 6", the user will have to click on the fittings individually in order to locate a specific one (the 3" in this case). This is a much less time consuming process than having to search through all the items within an entire project. GOOD LUCK!
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On the Boards
Clash Detection...continued from page 1
connections, the piece of equipment would not function. These types of clashes should not be included in final reports.
Renderings Courtesy of The S/L/A/M Collaborative
Can Highly Detailed Models Create Confusion? 3D content is continually being developed by equipment manufacturers with increasing levels of detail. Is this additional detailing necessary? The majority of times equipment models with manufacturer logos and detailed screws are simply not necessary. In fact, if incorrect Navisworks
Figure 3: Highly Detailed Manufacturer Model Creating Conflicts
Dolan School of Business, Fairfield University | Fairfield, CT
Among Kohler Ronan’s On the Boards projects is the much anticipated Dolan School of Business at Fairfield University. Slated for completion in the fall of 2019, the new building will replace the existing business school facility and provide over 85,000 square feet of state-of-the-art collaborative meeting and event spaces, as well as technologically advanced classrooms. Highlights will include a simulated financial trading floor, data analytics lab, and entrepreneurship center. In addition, the facility will house the Center for Applied Ethics. Kohler Ronan is delighted to be providing comprehensive MEP/FP design for such a prominent campus building.
Clash Rules are utilized, extraneous model details will result in a clash. Illustrating this kind of clash would be equipment control panels or switches mounted to equipment. Knowledge of how class detection information is compiled and how results are formulated gives the design team a better understanding of how to analyze the validity of clash detection reports and lists.
About the Firm Kohler Ronan is a multi-disciplined engineering consultancy dedicated to providing exceptional mechanical, electrical, plumbing, fire protection, and technology design, as well as comprehensive energy analysis, sustainable design, and commissioning services. From our offices in Danbury, Connecticut and New York, New York, our team of over 60 professionals collaborate with prominent architectural firms on a wide array of regional and nationally recognized project assignments. Commissions include those for world renowned museums, fine and performing arts centers, prestigious universities, state-of-the-art educational facilities, luxury residences, and premier recreation establishments. Additionally, we have the privilege of designing specialty systems for landmark sites and historically significant buildings across the country. For more information, please visit our website at www.kohlerronan.com or connect with us on social media. 4
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