60/Plumbing Engineer April 2019
D
uring college, aspiring engineering students were required to dissect and show work for physics prob- lems. The dissection usually consisted of stating the givens and known information, stating the assumptions, performing the calculation and reporting the results neatly enveloped in a box. Upon graduation and entry into the real engineering world, some of that process remains but even- tually phases out with the discovery of office spreadsheets and overall concept understanding. It is easy to input information into a spreadsheet and declare it complete; however, this does not always allow others to easily understand the calculation intent. There are many situations where calculations and design intent need to be understood: peer reviews, project sharing, owner questions or the transfer of project. The content of a decipherable calculation and document should include a cover sheet, calculation/document and supplemental information. This format is not limited to cal- culations as diagrams and napkin sketches can benefit from being sandwiched between a coversheet and references. High-Level Overview The overall goal is to convey as much information as possible and as clearly as possible to an audience. Most of the time the audience is other engineers. However, situa- tions may arise where the owner, governing agency or other trades may benefit from reviewing the calculation package. The cover sheet plays an important role in the calcula- tion package as this is the piece that explains what is to follow and provides a high-level overview of the results. At a minimum, it should include the project name, number, calculation type, calculation date, phase and status. Engineers can generate several iterations of calculations throughout the life of the project; it is important to have each one documented so there is no confusion between the calculation from design development and construction documents. Following the identifying project information, a purpose statement may be included to answer the question of why this calculation was performed and then follow with the methodology. The methodology is the best place to explain how to use and understand the calculation. It may require some refer- encing back to technical writing class to ensure the steps are clear and concise. At the end of the cover page, it is beneficial to provide the main results from the calculation. For example, include the incoming water service size, water supply fixture units and corresponding flow in gal./min. when providing a cover sheet for a building water supply calculation. Explaining the Calculation The cover sheet provides insight into the calculation; however, the calculation is the technical portion of which the design relies on. Sometimes the calculations are best per- formed by spreadsheet and other times by hand. Regardless of format, the calculation should follow the cover sheet and be as clear as possible. Keys to a good calculation include a graphical representation, color coding, comments (both hidden and visible) and formulas. Graphical representation may not always be possible but when it is, it should be intuitive, giving a general under- standing of how the input and calculated data work with the system. An example of incorporating graphical representa- tion is a basic flow diagram for a booster pump system. The input data would be at points along the flow diagram, such as street pressure, meter and backflow loss, booster pump loss and elevation. This data can be connected to formulas documented in more detail. Color coding helps to identify areas of interest in the calculation. A basic implementation of color coding is to color-code the cells where data should be input and where the cells are calculated, requiring no input. To go into more detail with color coding, use shades of a certain color to identify certain data schemes. Overall color coding should be added where necessary to get the proper information identified for the calculation.
By Emily Koussa, BD & C, CPD
Calculation Clarity
Leaving a trail of breadcrumbs helps others understand your reasoning.
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