Lesson 1 – What is HVAC design really
Lesson Objective
In this lesson, you will understand the real meaning of HVAC design and how it differs from calculations and analysis.
You will also learn why many HVAC problems happen even when calculations are technically correct.
Design vs Analysis
Most engineers are trained to solve analysis problems.
In analysis, all inputs are known, and there is usually one correct answer.
HVAC design is different.
Design problems are often incomplete, uncertain, and allow multiple acceptable solutions.
HVAC design, the question is not: “What is the correct answer?”
The real question is: “What is the most appropriate solution for this project?”
Why HVAC Design Is Not About One Correct Solution
Two HVAC systems can both meet the same cooling load and still lead to completely different results in operation, cost, comfort, and maintenance.
Design quality is not binary (right or wrong), it exists on a scale from poor to excellent.
Example 1 – Same Building, Different Systems
Consider an office building with the same cooling load:
- Engineer A selects a VAV system
- Engineer B selects Fan Coil Units with a DOAS system
Both systems can handle the load and both can meet comfort requirements.
However:
- One system may be cheaper to install
- The other may be easier to operate
- One may generate noise complaints
- The other may require skilled maintenance staff
Both designs are technically correct — but only one may be correct for the client.
Design as an Iterative Process
HVAC design does not move in a straight line.
Design decisions are reviewed, adjusted, and sometimes reversed as new information appears.
Architectural changes, budget limits, and operational requirements all influence HVAC choices.
For example, a designer may initially select large glazing areas.
Later, the HVAC engineer highlights the impact on cooling load and energy use. The design team may then reduce glazing or improve its performance.
This back-and-forth process is normal in real projects.
Example 2 – Oversizing Due to Late Decisions
In many projects, HVAC engineers are involved too late.
By the time HVAC design starts:
- Façade design is fixed
- Ceiling heights are fixed
- Equipment locations are restricted
The result is often oversized equipment, high noise levels, and inefficient operation.
The calculations may be correct — but the design context is wrong.
Key Takeaway
HVAC design is not about finding one correct answer, it is about selecting the best possible solution within real project constraints.
Good designers think in terms of context, trade-offs, and long-term performance — not just numbers.
Reflection Question
Think about a recent project you worked on.
Was the HVAC system chosen because it was the best solution — or because it was the easiest option at the time?