Air-Side Pressure Drop Testing After Coating
Key facts
| What to ask for | Why it matters |
|---|---|
| Face velocities tested | Pressure drop rises steeply with velocity |
| Dry or wet coil | Condensate changes the result on cooling coils |
| Fin pitch and coil depth | Dense and deep coils are most sensitive |
| Film thickness on the test coil | The result applies to that thickness only |
| Before and after values | The change, not the absolute value, shows the coating effect |
How the test is done
The coil is mounted in a duct with pressure taps upstream and downstream. Air is drawn through at several face velocities, and the static pressure difference is recorded at each. The coil is then coated and tested again in the same rig. Coil test methods such as ASHRAE Standard 33 describe the rig and measurements.
Wet and dry
A cooling coil in service is wet. Condensate on the fins narrows the passages further and may bridge them, so the surface properties of the coating affect wet pressure drop. Ask whether the result was measured dry, wet, or both.
Reading the result
Compare the change at the face velocity the coil will run at. A thin film with no bridging should change pressure drop very little; a large change points to bridging or excess film build.
Limits
The result applies to the tested geometry and film thickness. Microchannel coils and dense fins are more sensitive than open fin patterns.
Is pressure drop tested wet or dry?
Both matter for cooling coils. Dry tests show the film effect alone; wet tests show how the coated surface handles condensate.
Do PG systems have pressure-drop data?
Not as a published figure. Tests on a comparable coil can be arranged for projects where pressure drop is critical.
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