This question is so easy to answer in my mind, but when the answer has to be in written format, I find it to be almost overwhelming. I do believe however, that after more than 35 years of design experience, I am qualified to answer. My answer is based on my own work experience and knowledge I have accumulated throughout my career. The following explanation could be expanded upon to include many other duties and responsibilities, but my intent is to present generalities and not be all inclusive. Other engineers may have parallel or different career experiences which would make their answer unlike mine. To each his own.
An HVAC Engineer is a mechanical engineer who has elected to specialize in the heating, ventilation and cooling of buildings, processes and specialized applications. The fact that the description is so general is what really makes this job interesting- It applies to so many applications.
The Design Process Simplified:
At the core of the job is designing HVAC systems for a wide range of building types. Office buildings, medical buildings, industrial buildings are a few of the types I have designed. Each has its own operational parameters, esthetic considerations, system types and other unique requirements. Before any design starts there is research required to determine the general system size, system types, equipment placements, budget constraints and other considerations as well as getting to know the design parameters used by the architect, structural engineer, civil engineer and other design team members. The HVAC design has to compliment not only the building, but the systems installed by other design professionals. The process is indeed a team effort.
After the general research and understanding of the building has been completed, the HVAC Engineer begins to perform a thermal load calculation for the facility based on prevailing weather conditions, building construction components, occupancy and other influencing factors. The production of the load calculation produces the HVAC model of the building. Bear in mind that the other design professionals will be changing and altering their approach to the building design such that it affects other disciplines. In that sense, the HVAC model will need constant updating. Typically, there are many load calculation iterations required during this initial phase. As the design team solidifies building features, recalculation of the thermal loads begins to minimize until all disciplines are in agreement of the physical and esthetic parameters. The HVAC engineer will take the final model and determine the system types and select equipment to satisfy the load requirements.
System types and equipment selections are complimentary and generally determined by senior HVAC Engineers. Some of the major system types are implicitly implied by the load model, but other systems are selected based on a number of criteria. Budget, owner preferences, operations and maintenance are at the top of the list but there are others.
Once the load and systems have been established, the HVAC Engineer begins the actual design of the HVAC system. This is possibly the most challenging part of the job. Placing of equipment, routing of ductwork and piping, coordination with other disciplines, compliance with building codes and calculations to support equipment sizing are a few of the tasks. Design drawings convey the ideas and intents of the HVAC Engineer and have to compliment the drawings produced by the other members of the design team. The process of designing buildings is normally broken down into submittal levels, typically in percentages, i.e., 35%, 90%, 100%. There are also other ways to express this such as pre-final, final, etc. At each of these levels the design team will confer (by meetings or exchanging drawings) to coordinate and mesh the individual discipline designs with their own design. This is how the building design develops such that the many design components are coordinated and present a coherent design package. Specifications for the design are also developed by the design team and further define the project requirements that are not included on the drawings. These are normally published in book form. The drawings and the specifications become the contract documents used in the bidding process.
The Bidding and Construction Process Simplified:
During bidding, The HVAC Engineer will be required to respond to questions and suggestions submitted by the bidding contractors. Most of these responses are simple clarifications to the contract documents assuming that the design team has adequately coordinated their efforts and presented a comprehensive design.
Once the bidding process is completed and a contractor is selected to execute the project, the construction phase of the project begins. The HVAC installation is typically started after the building construction is complete enough to keep the weather out of the building, however some systems have to be partially installed prior to this. During this phase, the HVAC Engineer is called upon to assist the owner by making site visits, construction observation and working out other installation issues as required to assure that the design intent is met by the installing contractor. Assistance during construction is an integral part of the HVAC Engineers job such that most firms employ a field engineer to respond to many of the requests for information made by the contractor. It may seem as the construction site is busy with the trade contractors all going in different directions, but in almost all projects the general contractor knows the progress of each trade contractor and is able to predict and coordinate construction efforts to assure all trades are moving forward towards completion.
The Commissioning Process Simplified:
When construction is almost complete, building commissioning begins in some form. Commissioning is the process of verifying that building systems designed by the HVAC Engineer, Electrical Engineer, Plumbing Engineer, etc. operate in accordance with design intent. For the HVAC Engineer, water and air flow rates are verified, control system operation is verified, energy consumption/savings are verified, etc. Verification of the systems performance requires the commissioning agent to document all operations involved in start-up, shut-down and sequencing of equipment as designed by the HVAC Engineer. Upon successful competition, the HVAC Engineer acknowledges to the owner (as well as the commissioning agent) that the building performs as designed.
As your abilities grow you will also become more educated in other aspects of building design. Most mechanical engineers are also knowledgeable in plumbing design. More experienced engineers know general requirements for sprinkler design, building egress, electrical requirements and other design disciplines that directly interact with HVAC design. The HVAC Engineer, just like other design professionals, is constantly learning during their career to keep abreast of the latest code requirements, design methods and available systems related to HVAC engineering.
The more you know makes you aware of how much more there is to learn.
Feel free to offer comments related to this post. Other points-of-view are invited.