What do Mechanical Engineers do?
April 18, 2020
By: Lisandro Vazquez, PE
Mechanical Engineering is such a diverse field that you’d practically need a novel to cover the full spectrum of its different types of jobs and specialties. From machining components for the medical industry, designing high-tech heat exchangers & turbines for refineries, to commissioning energy management systems for power plants, campuses, and manufacturing facilities Mechanical Engineers work in almost every line of engineering.
So to keep things manageable, I’ll share with you my own experiences as a Mechanical Engineer. And though the field is wide-ranging, there are many similarities between my job and the other innumerable niches within the industry.
My specific field of mechanical engineering involves HVAC (Heating, Ventilation, and Air Conditioning) and plumbing design for a wide range of commercial buildings and multi-family residential projects in addition to energy code compliance determination.
So, what do I do?
Using architectural drawings and/or 3D modeling, information collected from site-visits, and input from the client, owner, and other applicable stakeholders, I design the HVAC and plumbing systems for new construction or renovations to best meet the project’s specific goals while adhering to the local jurisdiction’s building code requirements.
For HVAC Design:
The first part of my design process is called Schematic Design1. During this phase, I map out the general areas of the building, explore each space’s intended use and occupancy, and seek to understand the overall expectations of the project stakeholders with respect to performance and costs. At this point, I work with my team to build a basic draft of which types of HVAC systems should be employed and sketch a preliminary draft on how conditioned air will be conveyed to all required zones of the facility. We’ll investigate the need for exhaust, combustion air for gas powered equipment, and potential locations for interior and exterior heat exchangers in addition to identification of mission critical and/or sensitive areas such as server rooms, operating rooms, or spaces with sensitive occupants such as surgery patients or infants. Usually, we’ll send this initial proposed strategy to the Architect for a first review before moving ahead.
Once I’ve received feedback on the Schematic Design I’ll proceed with the next phase called Design Development. During this phase, I’ll complete the initial modeling of the heating and cooling needs for a building by inputting the walls, ceilings, building materials, number of people & corresponding levels of physical activity, and required ventilation air into a program which calculates how much heat gain the structure experiences in the summer and how much heat it loses in the winter.
I then take the output reports of the heating/cooling load calculation software and match them with specific models & configurations of HVAC equipment. Depending on the size and scope of design, I’ll either work directly with equipment manufacturers to select major equipment and systems or I will choose these items myself (based on project needs). Equipment includes air conditioners, chillers, ventilation & exhaust fans, pumps, valves and dampers. The selections process involves review of fan curves, pump curves, motor efficiencies, heat capacities, fluid pressures, flow rates, and temperature differentials to name just a few of the parameters.
In addition to determining all the required equipment specifications I write the sequences of operations which describe how the different HVAC machines should operate in their particular applications. I find the operations sequencing aspect very interesting because you have to run through all the scenarios of how the building’s HVAC equipment is supposed to operate given varying conditions and then write the sequence of operations for the controls contractor or mechanical contractor to input into the Building Automation System (BAS) or the specific equipment’s local controller.
Calculations for airflow requirements, duct sizing, and heating/cooling zoning are done by me and reviewed by a senior Mechanical Engineer at multiple stages of the design process. I do not use computational fluid dynamics (CFD) to model the fluid flow for the projects which I work on; however, it is absolutely vital to understand the mechanics of fluid flow because inadequate layouts for duct design can lead to excessive turbulence, vibration & noise, and a significant energy bill for the building owner (these are the “minor” consequences of poor design).
ASHRAE (American Society of Heating Refrigeration and Air Conditioning Engineers) has published a series of references which reduce the complex fluid dynamics equations into algebraic expressions to meet the design parameters of the most common building systems. These design manuals and standards are like textbooks except way more detailed and VERY specific to my HVAC work. (To learn more about professional engineering societies such as ASHRAE, check out “What is a professional engineering society and why should I join?”)
To make the “blueprints” (actually called the “plans” in the building construction industry) I draft the equipment, ducts, and air terminal devices (like grilles) in either AutoCAD (I use the 2D version only) or REVIT (BIM – Building Information Modeling… it’s 3D) dependent upon the project. While there are other CAD (Computer Aided Design) programs, AutoCAD and REVIT are the most prevalent in my particular field. Most of the time I do my own drafting, but sometimes other engineers will take certain portions of the design or experienced Mechanical Designers will step in to assist.
Drafting the plans is very time consuming and can be quite tedious. To me, this is the least “fun” portion of my job. I enjoy the initial brainstorming and calculations. I enjoy selecting equipment and running through all the pros and cons of doing a design “this way” or “that way,” but the actual drawing of the plans requires lots of time clicking, dragging, and typing. That’s why it is SO IMPORTANT to ask the experienced designers on your team for all the “tricks” and “shortcuts” for whatever CAD program you’re using because IT WILL SAVE YOU TONS OF TIME.
Even though I said drafting is my least favorite part there are still enjoyable aspects of it. At every turn, twist or bend you have to keep in mind what it’ll be like to install and later to maintain your system. Can somebody actually use a screwdriver with the clearances you have provided in your design? Can a valve be reached without a ladder? How would you clean the equipment or change parts? You have to keep these things in mind from the start because many times they will impact how you design the layout.
It’s like solving a puzzle with many right answers and a few very wrong answers.
The plans are reviewed by the Architect at intermediate steps of the design process, and a senior Mechanical Engineer will perform a final project review prior to the signing & sealing of the Construction Documents (the “plans”) for delivery to the client.
I really enjoy this review process. You essentially have to “prove” your design to the senior engineer and answer all sorts of questions on the spot. Most of time you’ll have to make modifications (called “redlines”) prior to completing the project. Some people get upset or defensive during this process, but I like being challenged. If I’m wrong about something, I want to know about it and I want to know WHY I’m wrong so that I can improve. It’s a great—albeit stressful—way to learn.
When the plans are done, they are sealed (you stamp the Professional Engineer’s seal on each sheet), signed by the PE and sent to the Architect and/or client before being delivered to the local building department or Authority Having Jurisdiction (AHJ) for review.
During the AHJ review you’ll likely have to answer formal inquiries from the building department. They may ask for calculations to prove a specific aspect of the design, or they may identify certain—hopefully zero—violations of the building code in your design (hey… nobody’s perfect). Once you’ve satisfactorily addressed the AHJ’s comments your plans will be approved for construction.
From this point forward my work on the project consists of implementing design revisions requested by the client, reviewing the equipment that contractors intend on installing, and going to the building site for periodic inspections (called “site-visits”).
There is SO much more to this whole process but I’ll leave it at that for a brief summary on my work in HVAC design. Now for plumbing!
For Plumbing Engineering:
The design process for plumbing engineering is similar to HVAC; however, in my experience there is far less third-party software used by engineering firms for plumbing as compared to HVAC. A lot of design work (even today) is done with company-specific calculations spreadsheets, or by hand, using published tables of water, sewage, and gas demand load capacities based on pressure, flow and pipe size. This of course varies based on the scope/scale of the project. Larger projects may necessitate use of specialized software for performing plumbing calculations.
Like the early steps of the HVAC design process, I learn the needs of the project and identify the major zones & occupancies of the building. I calculate the water supply needs of the end-users, the sewerage loads, and the gas loads (propane or natural gas). I’ll use these values to arrive at a preliminary pipe size for the main water service line, gas line, and building sewer. These may need to be adjusted later based on the building’s final proposed piping network and the available pressure from the local water supply.
Like the early steps of the HVAC design process, I learn the needs of the project and identify the major zones & occupancies of the building. I calculate the water supply needs of the end-users, the sewerage loads, and the gas loads (propane or natural gas). I’ll use these values to arrive at a preliminary pipe size for the main water service line, gas line, and building sewer. These may need to be adjusted later based on the building’s final proposed piping network and the available pressure from the local water supply.
Next, I sketch a preliminary piping layout in AutoCAD or REVIT based on the locations of plumbing fixtures as determined by the Architect. With this first draft, I perform a rough calculation of the pressure losses in the piping network from the water service entrance to the most remote plumbing fixture. This takes into consideration friction in the pipes and losses due to fittings and changes in elevation.
Sometimes, it turns out that you actually need significantly more pressure to operate that most remote plumbing fixture than is available from the water utility due to all these losses. In these cases, I’ll work with a booster pump manufacturer’s representative to select a pump system that best fits the needs of the building and owner.
Then, the plans are drafted in AutoCAD or REVIT by me or somebody else on my team and the remainder of the design process follows that described in the HVAC segment above.
There are all sorts of intricacies and challenges with plumbing design that don’t manifest in some other engineering design fields, the most obvious of which is the need to ensure sloping of gravity-draining sewage pipes within the building. It may not sound like a big deal but trust me that can be a serious challenge, especially when you consider all the other stuff going into a building (HVAC ducts, electrical conduit, structural beams & columns, and lighting fixtures just to name a few). This is the aspect of plumbing design I really enjoy. It’s like solving a puzzle; and the puzzle is different every time.
Lastly, I’ll model the mechanical (i.e. HVAC) and plumbing systems into energy compliance software which specifically caters to the effective adopted energy efficiency code for the jurisdiction in which the project is located. This is to determine whether or not the project’s overall energy consumption complies with code requirements.
In both HVAC and plumbing design, I must coordinate with other engineering disciplines throughout the entire process. The weight of the HVAC equipment on the roof affects the Structural Engineer. Likewise, the location of structural beams and footings affects where I can route ducts and pipes. The electrical requirements of plumbing & HVAC equipment affect the electrical distribution network and thus must be coordinated with the Electrical Engineer.
On my end, I’ll need to know what voltage/phase the pumps, heaters, and fans should use, where electrical panels are located, and where the lights are mounted. I also communicate with the Civil Engineer for utilities connection points and sometimes food/kitchen service consultants for designing commercial kitchens. As you can see, there is a lot of back-and-forth between the engineering disciplines.
Finally, I correspond with the Architect for a wide range of topics such as timelines, equipment types & locations, costs, aesthetics, resolution of interference, and determination of the owner’s needs/wants. The Architect is typically the point of contact between the owner, contractor, and engineering teams.
Normally, engineers work with an architect rather than directly with the building owner/client. An architect is essentially the overall project manager to include all design & development phases.
So, what exactly am I doing when I “communicate?” Most communication is via email, seconded by phone conversations. I’ll email pictures of equipment, or I’ll sketch something on a PDF and email it, or I’ll send screen shots of an issue/conflict shown in CAD along with a brief typed description of the comment/issue/resolution. Often, I’ll call the recipient of the email to verbally explain the contents of the email and answer any questions they may have immediately.
Some big picture items:
I use math every single day, but surprisingly I can’t remember the last time I did any calculus. Though higher-level mathematics such as integral calculus and differential equations lie at the foundation of the design work I perform, most of it can be simplified into algebraic expressions. Significantly larger projects or those with very tight tolerances may demand higher-level mathematics, but when you need that level of analysis you will likely be using software to model your systems anyways and won’t be doing any calculus yourself.
Spreadsheet software is your friend. I use it ALL the time. I use spreadsheets like Excel as a customizable calculator and as a means to provide documentation of my design calculations.
Engineers get emails ALL THE TIME. Even intra-office communication is typically done via email. Of late, there has been a shift in the industry towards more chat-based programs like Slack or Microsoft Teams, but for now email is still the most prevalent method of communication between project team members.
YAY
EMAILS!
Ask questions early. Fixing a mistake or addressing a potential issue at the BEGINNING of a design is always preferable. Think of this: If a problem is discovered during the design process, some lines on a computer need to be updated (i.e. cost equals the time spent updating the plans); but, if a problem is discovered during construction, the cost equals removing installed equipment, ordering new equipment, materials wastage, delay of critical path items, AND the time spent updating the plans. Don’t be shy… if you aren’t sure about something or if you know there is going to be an issue in the future, bring it up as early as possible.
So there you have it. That’s the general gist of what I do as a Mechanical Engineer in the HVAC and Plumbing Engineering fields. To learn more about what type of environment I work in, how many hours engineers typically work or even how much money you can expect to make, please check out the articles below. Thanks for reading!
What type of environment do engineers work in?
How many hours do engineers work?
Mechanical Engineer Salary: What can I expect?
Sources:
- “Design to Construction, Understanding the Design and Construction Process” https://www.aiaetn.org/find-an-architect/design-to-construction/