How Coating Impact on Heat Transfer Is Tested

The before-and-after method

The most direct test measures the same coil twice: once uncoated and once after coating, in the same test rig at the same air velocity, air temperature and fluid conditions. The change in capacity is the heat-transfer effect; the change in air-side pressure drop shows how much the film narrows the air passages.

Coil test rigs used for rating air-cooling and air-heating coils follow methods such as ASHRAE Standard 33, and the same rigs are used for coating comparisons.

Sample and panel tests

Some coating data comes from small samples rather than full coils. These are useful for comparing coatings with each other but may not reflect a specific coil geometry. PG-S1’s ≤ 1.8% result is to GB/T 8446.2; the report gives the sample and conditions.

Reading the result

A heat-transfer result is only meaningful with the film thickness and coil geometry it was measured on. A 1% result on a coil at 10 fins per inch says little about a coil at 18 fins per inch.

Limits

Test results describe a clean, new coil. In service, the difference between a coated coil that stays clean and an uncoated coil whose fins corrode is usually larger than the initial coating loss.