I. First Confirm "Whether It Really Dropped"
Rule out measurement error: Are the thermometers calibrated? Is the air volume measured accurately? Often "efficiency drop" is instrument drift. After confirmation, troubleshoot in the following order.
II. 7-Item Troubleshooting Checklist (by probability)
| No. | Cause | Typical signal | Countermeasure |
|---|---|---|---|
| 1 | Surface ash/dust accumulation | Rising pressure drop, insufficient outlet temperature | Clean, blow ash |
| 2 | Water-side scaling | High wall temperature, K drops | Descale, water treatment |
| 3 | Abnormal flow velocity | Fan/pump VFD turned down | Restore to design velocity |
| 4 | Reversed flow direction | Cold-end temperature cannot rise | Check parallel/counter-flow arrangement |
| 5 | Bypass/internal leak | Two fluid temperatures abnormally close | Check valves, plate seals |
| 6 | Design margin exhausted | Load exceeds original design | Expand capacity or parallel |
| 7 | Insulation damage | High shell temperature, large heat loss | Repair insulation layer |
III. Priority Recommendations
- Look at pressure drop first: Rising pressure drop = clogged, 80% is item 1 or 2;
- Then look at flow velocity: Changed operating parameters is most common; recovery takes effect immediately;
- Finally look at structure: Flow direction and bypass are installation/retrofit issues requiring shutdown inspection.
Don't panic when efficiency drops; 80% of cases are "dirty" or "flow velocity turned down"—a wash and an adjustment bring it back.