ATC 105 test requirements

To perform an official thermal acceptance test that contractually binds the manufacturer, you can't just pick any day, clip on a couple of sensors, and record the data.

The Cooling Technology Institute (CTI) ATC-105 code establishes strict criteria for the test environment, the stability of the plant during the test, and the mechanical readiness of the tower.

These "test day" requirements are broken down into three major pillars: Envelope Limits, Stability Limits, and Pre-Test Physical Conditions.

1. The Boundary Envelope (Allowable Deviations)

The test code recognizes that you will rarely get a perfect "design day" during commissioning. However, the weather and plant conditions must still fall within a reasonable "envelope" around your original design specifications for the mathematical correction curves to remain valid.

The average values recorded during the test window must meet these criteria:

💡 Connecting this to your specification: Notice that your project spec is actually more generous than the CTI standard for flow rate ($\pm20\%$ vs CTI's $\pm10\%$). Because your contract specifies $\pm20\%$, that contractual agreement overrides the standard CTI envelope for that parameter.

2. Constancy and Stability Limits

Even if you are inside the envelope above, you cannot test while the plant is wildly fluctuating. Before and during the 1-to-2 hour data-collection window, the system must achieve a steady thermodynamic state.

CTI ATC-105 requires the parameters to stay within these tight stability brackets:

• Circulating Water Flow: Must not fluctuate more than $\pm 2\%$ during the test.
• Heat Load & Cooling Range: Must remain within $\pm 5\%$.
• Inlet Wet-Bulb Temperature: Must not drift or change faster than $2^\circ\text{F}\ (1.1^\circ\text{C})$ per hour.

3. Pre-Test and Equipment Conditions (CTI PGT-156)

Before the testing agent sets up their instruments (like calibrated psychrometers and pitot tubes), the physical tower must be prepared and checked.

1.Film Fill Conditioning:1,000 Hours Minimum.

If your IDCT uses plastic film fill, it must be operated under heat load for at least 1,000 hours (roughly 6 weeks) before the test. New plastic fill has manufacturing oils that cause water to bead up; conditioning allows it to break down so the water sheets out cleanly for proper heat transfer.

2.Cleanliness Inspection:Pre-test.

The water distribution nozzles must be completely clear of debris. The drift eliminators and the fill itself must be clear of scale, algae, oil, or silt.

3.Mechanical Alignment:Pre-test.

Fans must rotate in the correct direction. Fan blade pitch angles must be uniform across all blades, set to pull power within the allowable $\pm15\%$ of the motor's design limit.

4.Isolate Basin Hydraulics:During test.

The cold water basin must be at normal operating height. Make-up water and blowdown valves should ideally be isolated (shut off) during the test loop so cold mains water doesn't skew the temperature readings.

What happens if the plant can't provide enough heat load on test day?

This is the most common issue in new plants. If your IDCT has multiple cells (e.g., a 4-cell tower) and the plant is only running at 75% capacity, CTI ATC-105 explicitly allows you to isolate cells. You can block off one cell entirely and divert all the water and air through the remaining 3 cells. As long as the flow and heat load per cell fall back into the allowable $\pm10\%$ and $\pm20\%$ envelopes, the test is fully code-compliant.