Hydronics & Plant Logic | Module 303
Cooling Tower Approach Temperature Performance
Field Status: The “Approach” is the difference between the leaving condenser water temperature and the ambient wet-bulb temperature. As a cooling tower ages, scale accumulation on fill media and fouled drift eliminators physically block airflow. This reduces the tower’s ability to reject heat, causing the approach temperature to rise.
A “design approach” is typically 5°F to 7°F. If you measure an approach of 12°F or higher, the tower is failing to reject heat properly. This forces the chillers to work harder against elevated head pressures, massively spiking kWh consumption.
SYS AUDIT: Approach Vector
APPROACH TEMP: —
TOWER STATUS: —
—
Heat Rejection Fundamentals
A cooling tower is a giant evaporative heat exchanger. The drift eliminators are designed to strip water droplets from the air stream while allowing maximum CFM. If they are dirty, backpressure rises, fan motor amperage increases, and approach temperature drifts upward.
| Approach (°F) | Performance State | Maintenance Protocol |
|---|---|---|
| < 7.0 | Design Optimal | Standard seasonal startup. |
| 7.1 – 10.0 | Moderate Fouling | Chemical fill cleaning cycle. |
| > 10.0 | Critical Failure | Mechanical fill replacement/Eliminator cleaning. |
Diagnostic Gateway Challenge
You audit a tower. The ambient wet-bulb is 75°F. The discharge water leaves the tower at 88°F. The tower is designed for a 7°F approach. What is the efficiency status?