When One Warm Desk Reveals a Bigger HVAC Problem

If you have ever worked in an office where “most of the space feels fine” but one corner is always uncomfortable, you already know this truth: averages don’t create comfort-consistency does.

This story begins with twelve people sharing a workstation at the farthest end of an office floor. No matter the season or settings, their area felt warmer than the rest of the space. Seats were shuffled. Blinds were adjusted. Complaints surfaced quietly.

On the surface, nothing seemed wrong.

Qpro was appointed as the MEP consultant for the fit-out project. The building already had a full-fledged HVAC setup - chillers, pumps, cooling towers, and smart Air Handling Units (AHUs). Each AHU served an entire floor, with VAVs allowing zone-level control.

Everything looked right. Yet comfort was incomplete.

That contradiction became the starting point of the investigation.

The System’s First Assumption: “The Office Is Already Cool”

The AHU was controlling its fan speed based on return air temperature. A sensor near the AHU room continuously reported temperatures between 19°C and 21°C.

From the system’s point of view, this meant the job was done. But, in HVAC systems, the farthest point from the air-handling unit is where reality shows up first.

What the system didn’t realize was that some of the return air was short cycling returning too quickly without travelling through the occupied office space. The sensor was reading air that was cooler than what people were actually experiencing.

Believing the space was already cool, the AHU slowed down its fan. Slower fan speed meant less air reaching the farthest desks. The people at the edge of the system felt the impact first.

This was the first realization: The problem was not cooling capacity. The problem was perception.

The System’s Second Assumption: “One Sensor Is Enough”

The floor was served by two major supply air duct branches. However, the system measured pressure in only one of them using a Differential Pressure Transducer (DPT).

In simple terms, the AHU was adjusting itself based on feedback from only half the floor.

This led to uneven airflow distribution. One branch could be satisfied while the other struggled. Since both supply and return air temperatures were being sensed at the same limited location, the EC fan controller never received a complete picture of what the floor actually needed.

This was the second realization: The system wasn’t malfunctioning it was misinformed.

The Turning Point: Fixing the Way the System Thinks

At this stage, a common reaction would be to add more cooling, increase fan size, or push the system harder.

But, at Qpro we knew, it was not required.

Once the real issue became clear, our solution followed a simple principle: ‘Don’t make the system work harder. Make it understand better’.

Two key changes were implemented:

System Listening was Improved: Pressure Judgment Solved

First, two DPT sensors were installed one on each major duct branch. This allowed pressure demand from both sides of the floor to be measured accurately.

Second, the control logic was refined. Where the EC fan controller supported it, the average of the two pressure readings was used directly to regulate fan speed. Where it didn’t, a Direct Digital Controller (DDC) was introduced. The DDC processed both signals, calculated an average, and fed a single, reliable input to the fan controller.

Now, the AHU was responding to the entire floor not just a part of it.

Correcting the Root Cause: Return Air Short Cycling

Alongside pressure control improvements, the return air path near the AHU was modified. This eliminated short cycling and ensured the return air sensor sampled air that truly represented occupied areas.

Fresh air is needed for comfort cooling to avoid suffocation or stuffiness. Once this was done, the AHU’s decisions began aligning naturally with how people actually felt in the space.

The Outcome: Comfort Through Clarity

After these interventions, airflow stabilized across the floor. The farthest workstation received adequate cooling. Fan speeds adjusted intelligently. Most importantly, the people using the space felt the difference without adding equipment or increasing energy consumption.

This project highlights a simple but powerful lesson in HVAC engineering:
Most comfort problems are not mechanical failures. They are control and sensing failures.

At Qpro, our approach is rooted in understanding how buildings behave in real life not just how they perform on drawings or dashboards.

Because when systems stop guessing and start listening, comfort follows.

Good HVAC doesn’t work harder. It listens better.