Many design firms in the heating, piping and air-conditioning industry are evaluating the cost/benefit relationship of moving into the world of 3-D design. This is a major policy decision because it has a direct effect on short-term productivity and profitability, which must be balanced against the long-term gains expected. Poorly implemented, the shift to 3-D modeling can consume considerable resources with negligible results. Properly done, it can result in wide-ranging benefits.
WHY DESIGN IN 3-D?
We live in a 3-D world. Systems are physically constructed in three dimensions. Two-dimensional drafting was developed as a means to convey three-dimensional information simply because, at the time, the tools did not exist to produce designs in 3-D.
In documenting existing facilities, the designer had to mentally translate the three-dimensional environment into two dimensions on his sketchpad. He then would develop the modifications mentally in three dimensions and translate that concept back into two dimensions on the drawing board. The contractor then would have to take this two-dimensional representation and make it happen in the real, 3-D world. Representing a 3- D object in two dimensions requires multiple, independently drawn pictures of the same object showing a plan, matching sections, elevations, etc.
All too often, conflicts and inconsistencies between the many separate 2-D representations of the same portion of a project are found in the field, rather than on the drawing board, resulting in costly change orders and project delays. In complex piping system design, 3-D scale models are constructed for conceptualization and communication to minimize such problems. However, these physical models are costly, time-consuming, and difficult to rearrange if design changes occur.
While there is no doubt that incorporating 3-D techniques into our workflow required a significant learning curve, our firm decided the following advantages made the effort worthwhile.
• Efficiency. Let us say that we are designing a pumping system. In 2-D computer- aided design (CAD), a system would be represented with a large-scale plan view and one (or, in some cases, many) elevation views. Each of these views is drawn from scratch as a separate, unrelated drawing. This requires much checking back and forth to ensure that each elevation view is an accurate and The long-term advantages of 3-D computer-aided design
will outweigh the short-term cost of transition consistent portrayal of the plan view.
With 3-D modeling, our designers become virtual pipe-fitters and millwrights. Full-scale, three-dimensional equipment models are developed and installed in their proper location and orientation. Piping, valves, supports, etc., also depicted to scale and three dimensionally, then are fit up. The model can include indication of valve handwheel orientation.
This is performed once in the model with precision and consistency. Now let us say that, for some reason, the system has to be rearranged. In the 2-D CAD example, each individual drawing representing a view would require manual modification of every element.
In the 3-D case, the model is updated once and all related views are automatically updated because they are truly “views” of the model rather than separate, manually created drawings.
In addition to greatly reducing redesign costs, this leads to more accurate drawings that ultimately will decrease contractor confusion. This means more accurate, competitive bidding and less chance for costly change orders in the field.
A decade ago, there was debate with respect to the advantages of manual drafting versus those of CAD. The cost of remaining in the 2-D world today is that it is inherently less efficient than 3-D modeling.
• More utilities. Two-dimensional CAD drafting is merely a graphical representation of a system, requiring much manual checking for interferences and constructability reviews. In 3-D design, interference and constructability issues are discovered and resolved in the design
process because the system is being virtually constructed. In addition to this builtin quality-control utility, other utilities may be added to the 3-D design.
• Bill of material takeoffs. There are add-on piping design packages that allow you to specify the schedule of pipe, class of valve, etc., and link this intelligence to CAD entities. This allows the designer to quickly extract an accurate, detailed bill of materials takeoff for estimating purposes.
If the piping design changes, a new bill of materials takeoff can be generated instantly and the cost estimate can be updated without a great deal of rework.
• Piping-stress analysis. Designing piping runs in 3-D allows the piping-system geometry to be input directly into most thermal pipe-stress analysis programs. In some cases, this link is bi-directional.
This means that not only does the stressanalysis software accept data from CAD, but if a support or anchor location is modified in the stress-analysis software, the CAD file is updated.
• Virtual modeling. The design can be viewed and manipulated as a virtual model. Just like hand-constructed scale models, virtual models are an aid in conceptualization, visualization, and communication.
This can be a valuable aid in communicating the design to a client who may be unfamiliar with reading plans.
• New field-measurement options. Working in 3-D allows the user to take advantage of newer options to the laborious task of obtaining field measurements of existing conditions. Obtaining field measurements requires skill and experience. It is an art that is fast losing its practitioners in a shrinking labor market.
Designing in 3-D actually relieves this burden somewhat through the further use of technology. When our firm first began designing piping systems in 3-D, we took a notebook computer loaded with CAD software into the field. One person took measurements and called them out to the CAD operator, who built the existing model. This method, in effect, gives you a 3-D sketchpad. Using this method, we were able to leave the field with a verified existing 3-D CAD model. This system worked well for small- to medium-sized mechanical-equipment rooms.
In larger plants where the preceding system had obvious limitations, we developed laser-based, modified surveying techniques to improve the accuracy of our measurements. This electronic distance- measurement technology obtains about one measurement per minute and results in a cloud of points. The CAD operator then “connects the dots” to create a 3-D model. The accuracy of this method has been proven to be plus or minus .5 in. from an absolute reference point.
Our most recent iteration is the use of high-speed laser scanning (See “Attacking As-Builts,” HPAC Engineering, October 2000). Objects are measured directly at a rate of 1,000 measurements per second using a reflectorless electronic-distance measuring laser. The accuracy of each measurement is plus or minus 6 mm at 50 meters. This technology has become our firm’s measurement system of choice.
Certainly, there are disadvantages to designing in three dimensions; otherwise, acceptance would occur quickly and universally. Disadvantages include:
• Time and money. Investing in 3-D design requires a significant personal, as well as financial, commitment to staying abreast of new technology. Procedures and protocols have to be developed and learned. This is a non-billable overhead function.
As with nearly all computer technology, the financial investment in acquiring the hardware and software and then staying current is substantial and seemingly endless. Fortunately for some, and unfortunately for the rest, this is a fact of living in our technological era. To ignore advances in technology and retrench is a comfortable, short-term temptation.
CAD operators have to leave their comfort zone. The shift from 2-D CAD to 3-D modeling is similar to the transition from manual drafting methods to CAD. There was much resistance to that transition, which spanned from, “This will never catch on,” to, “I can draft by hand much more quickly than I can with CAD.”
It is worth noting that it is now rare to find a competitive firm still producing designs on the drafting board.
IS 3-D NEEDED?
Decisions relative to production are critical and directly affect the viability of a firm. So they have to be taken with due consideration to staying competitive. Many firms do not perceive a need for designing in 3-D. Their clients are not requesting, let alone requiring, that their designs be performed in 3-D. They have established their procedures and protocols for two-dimensional drafting and their people are trained to pursue and produce projects.
It is difficult to argue this point from a near-term business perspective. However, firms must also anticipate the day when the client does require 3-D design, and prepare accordingly.
After evaluating all the options, our firm decided that making the move to
3-D CAD will set us apart from the competition.
Kevin H. Rhodes, PE is vice president, and Frederick W. Betz, PE is executive vice president of ZBA Inc. (www.zbainc.com). ZBA is a 43-year-old, full-service mechanical and electrical engineering firm with expertise in the areas of central cooling and heating, HVAC, utility distribution, master planning, and project management. Since joining ZBA in 1998, Rhodes has led the development and implementation of modified land surveying techniques and high-speed laser-scanning technology. Betz has more than 30 years of experience in the mechanical engineering field performing analysis, studies, and design. He is an active member of ASHRAE and serves as the regional vice chairman for chapter programs