Why is testing, adjusting and balancing (TAB) essential?

When the installation of a mechanical system is complete, the system may appear to be working. Fans turn, pumps run, rooms heat up or cool down to some extent. But this does not mean that the system is working as designed. Testing, adjusting and balancing (TAB) is a systematic process that measures the actual performance of the installation and brings it to the design values.

What is TAB?

TAB is the work of measuring air and water distribution systems, adjusting them to the design values and verifying that the control system works correctly. It is carried out with calibrated measuring instruments and according to a defined procedure. The results are documented in a report showing the design and measured values for each measurement point.

TAB is not an installation item but an independent verification step. It is therefore important that the team taking measurements on site is knowledgeable and competent. In Türkiye, the TAB certificate issued by ISKAV is a recognised qualification in this field; on international projects, the procedures of organisations such as NEBB or AABC may also be taken into account.

What happens in an unbalanced system?

Air and water follow the path of least resistance. In a system that has not been balanced, spaces close to the source receive too much flow while distant spaces receive too little. The consequences we often see on site are:

• Some rooms get too cold while others never reach the desired temperature.
• Thermostat settings are constantly changed in response to user complaints.
• Pumps and fans are run at higher speeds than necessary, increasing energy consumption.
• Noise occurs at valves and air terminals.
• Pressure relationships are disrupted in spaces such as cleanrooms, hospitals or laboratories.

Most of these problems are solved not by replacing equipment, but by correct adjustment and balancing.

What does the TAB process involve?

The process begins with a review of the design documents. The accessibility of measurement points, balancing valves and dampers is checked. Systematic measurement and adjustment is then carried out on site. A typical TAB scope covers the following steps:

• Air side: Total airflow and static pressures of air handling units and fans, and airflow at grilles and diffusers, are measured; dampers are adjusted.
• Water side: Pump flows and heads, and flows at branches and terminal units, are measured; balancing valves are adjusted.
• Equipment checks: Motor currents, speeds and directions of rotation are checked.
• Room measurements: Temperature, humidity and differential pressure values are recorded in the spaces where required.

Balancing is usually carried out using a proportional method. The aim is to bring the system to design flows with the lowest total resistance, without unnecessary throttling. This also means pump and fan energy is not wasted. Once balancing is complete, valve and damper positions are marked, so that any setting changed by mistake later can be easily spotted. Acceptable tolerances between measured and design values are agreed with the project team at the start of the work. Points where a deviation cannot be corrected are noted separately in the report, together with the reason.

Relationship with automation

In today's facilities, flows, temperatures and pressures are largely managed by the automation system. In variable-flow systems, control loops tuned without balancing do not operate stably. TAB is therefore planned together with automation commissioning.

• Sensor readings are compared with measurements taken with calibrated instruments.
• Fully open and fully closed positions of valve and damper actuators are verified.
• Differential pressure and flow set points are determined according to the balancing results.
• Alarm and safety functions are tested on site.

Without this work, the automation system makes decisions based on incorrect data. While everything looks normal on screen, comfort and energy problems may persist on site. That is why we recommend that automation commissioning records are also handed over together with the TAB report.

When should TAB be planned?

TAB should not be seen as an afterthought at the end of installation. For measurement and adjustment to be possible, the necessary components must be provided for in the installation from the outset. At the design and installation stage, we pay attention to the following:

• Balancing valves with test points and regulating dampers on branches
• Sufficient straight lengths and test holes in ducts and pipes for measurement
• Access panels in suspended ceilings for valves and dampers
• Duct leakage tests and pipe pressure tests completed before TAB

System cleaning, filter installation and connection of automation points should also be completed before TAB. Otherwise, measurements have to be repeated and the schedule slips.

Why is a TAB report valuable for a facility?

A TAB report is a measured snapshot of the system's condition at handover. It matters to the facility owner and technical manager in several ways. It allows an objective assessment at handover acceptance. It serves as a reference for later alterations and capacity changes. It makes it easier to find the source of a problem that arises during operation. In critical facilities such as hospitals and cleanrooms, it is an important part of the validation process.

In short, TAB is the final step that shows the investment works as designed. When this step is skipped, problems usually surface during operation, at a higher cost. At Ekura, under the direction of our ISKAV TAB-certified engineer, we can carry out this work on the systems we install and in existing facilities.