Recently, while reading an interview in MEP Middle East Magazine with several key decision-makers from the HVAC industry in the UAE, one question stood out clearly.

The question was simple but revealing:
“What is the biggest technical problem currently facing HVAC projects?”

Despite differences in project type, company size, and specialization, the response from multiple industry leaders was surprisingly consistent.

Cooling load oversizing.

At first glance, oversizing may not appear to be a critical issue. However, it remains one of the most widespread and costly problems in HVAC design across the region. What makes the issue more complex is that oversizing is often not caused by poor engineering practice, but by a combination of risk management, misunderstood assumptions, and systemic industry behavior.

What Do We Mean by “Oversizing”?

Cooling load oversizing occurs when the selected HVAC system capacity significantly exceeds the actual peak cooling demand of a building or space.

In practice, this typically results in:

• Larger chillers or DX units than required
• Higher airflow rates than necessary
• Oversized ductwork, pumps, and electrical infrastructure
  

While this approach may appear conservative or “safe,” oversizing often leads to several unintended consequences during operation.

• Poor part-load efficiency
• Short cycling of equipment
• Higher capital and operating costs
• Increased energy consumption
• Reduced humidity control and indoor comfort

1. Risk Avoidance and Fear of Undersizing

One of the primary reasons for oversizing is risk avoidance rather than calculation error.

In most projects, undersizing produces immediate and visible consequences, such as occupant complaints or performance issues. Oversizing, on the other hand, tends to reveal its negative effects gradually during operation.

As a result, engineers are often under pressure to ensure that:

• Spaces will never feel warm
• Comfort complaints are avoided
• Systems can handle extreme scenarios

This pressure often leads to the addition of undocumented safety margins. Over time, these margins accumulate and result in systems that are significantly larger than required.

2. Misunderstanding of Safety Factors

A common misconception is that cooling load calculations inherently require an additional safety factor.

In reality, modern calculation methodologies and software already include conservative assumptions related to:

• Outdoor design conditions
• Internal heat gains
• Occupancy patterns

When engineers add further safety margins on top of these built-in assumptions, the result is effectively a double-counting of risk, leading directly to oversizing.

Modern load calculation methodologies, such as those implemented in Carrier HAP and based on ASHRAE Heat Balance principles, already rely on conservative design weather conditions and coincident peak assumptions. Adding informal safety margins on top of these assumptions often results in unintended oversizing.

3. Incorrect Interpretation of Weather Data

Weather data selection plays a critical role in cooling load calculations, particularly in hot climates such as the UAE.

Common issues include:

• Using absolute historical maximum temperatures instead of design conditions
• Confusing the roles of dry-bulb and wet-bulb temperatures

4. Ventilation and Infiltration Confusion

Ventilation and infiltration loads are among the most misunderstood components of cooling load calculations.

Typical problems include:

• Treating infiltration as a constant value rather than a load-dependent one
• Applying conservative assumptions to both ventilation and infiltration simultaneously

In commercial buildings, ventilation loads alone can represent a significant portion of the total cooling demand, making this issue particularly impactful.

5. Treating Software as a Black Box

Load calculation software is an essential engineering tool, but it does not replace understanding.

Oversizing frequently occurs when:

• Default software inputs are accepted without review
• Diversity factors are ignored
• Unrealistic operating schedules are use

Software amplifies engineering judgment. When assumptions are misunderstood, errors become larger—not smaller.

6. Industry Culture and Project Dynamics

Oversizing is also reinforced by common industry practices and project dynamics.

For example:

• Clients rarely complain about excess cooling capacity
• Design reviews tend to focus on compliance rather than optimization

Over time, these factors normalize oversizing and make it a standard practice rather than an exception.

Conclusion: Oversizing Is a Systemic Issue

Cooling load oversizing is not the result of a single mistake or a single party. It is a systemic issue driven by risk perception, misunderstood standards, and project pressures.

As highlighted by industry leaders in the UAE, addressing oversizing requires not only better tools, but a deeper understanding of assumptions, design intent, and system behavior—especially as energy efficiency becomes increasingly critical.

Author’s Note

This article is based on practical engineering experience and public industry discussions. It is intended for educational purposes only and does not represent engineering consultancy or project-specific advice.