Mechanical Monitoring Glossary — COP, Delta-T, EWMA, CUSUM, dB
A short, accurate glossary of the terms that show up in chiller, pump and AHU monitoring reports — written for asset owners, not for vibration engineers.
Every mechanical monitoring report in the UAE includes a handful of terms — COP, delta-T, EWMA, kW/TR — that the report writer assumed the reader knew. Most don't. This page is the reference.
Each entry has a definition, a 'why it matters' line, and the typical range for a UAE Grade-A tower. If a term you need isn't here, it is probably worth adding — the page is updated as new ones come up in client conversations.
| Term | Definition (short) | Why it matters | Typical UAE range |
|---|---|---|---|
| COP | Coefficient of Performance — cooling output / electrical input | Headline chiller efficiency | 5.5 – 6.5 (water-cooled) |
| kW/TR | Kilowatts of electrical input per ton of refrigeration delivered | Inverse of COP; what utilities quote | 0.55 – 0.65 |
| Delta-T | Temperature difference across a coil or loop | Drift indicates load or fouling | 5.5 – 8°C (chilled water) |
| Approach temp | Difference between leaving water and refrigerant condensing temp | Rising approach = condenser fouling | 1.5 – 3°C |
| EWMA | Exponentially Weighted Moving Average — drift-detection statistic | Catches slow degradation | Used as control statistic |
| CUSUM | Cumulative Sum control chart — small-shift detection | Catches step-changes the eye misses | Used as control statistic |
| mm/s RMS | Vibration severity (ISO 10816 / 20816) | Bearing health indicator | Zone B: 1.12 – 2.8 (Class II) |
| RMS current | Root-mean-square of three-phase current at the motor | Drift indicates load, wear or imbalance | Per nameplate per asset |
| Phase imbalance | Asymmetry between the three current phases | > 5% indicates motor or supply issue | ≤ 2% healthy, > 5% flag |
| Suction-line drift | Pipe-clamp thermal drift on the compressor suction line | Rising suction-line temp = under-charge | Stable on a healthy circuit |
How to use this page
Treat it as a lookup. When a monitoring report mentions a term, find it here. Most entries have a 'why it matters' line that connects the definition to a decision an asset owner would actually make.
Why COP and kW/TR are the same thing, sort of
COP is the dimensionless ratio of output to input. kW/TR is the inverse, scaled to the units utilities care about (kilowatts of electricity per ton of refrigeration). A COP of 6.0 is equivalent to kW/TR of 0.586. The industry uses kW/TR because it converts directly into a DEWA bill.
Why EWMA and CUSUM appear in vibration reports
EWMA and CUSUM are the two standard statistical-process-control techniques for catching small shifts in a noisy time series. They are not Novek's invention — they have been industrial-quality tools since the 1950s. Their value in vibration analysis is that they pick up the early degradation curve weeks before a threshold alert would fire.
ISO 10816 thresholds — see the dedicated page
The vibration severity zones (A/B/C/D) and the four equipment classes deserve their own page; see the ISO 10816 vibration analysis explainer for the full table and consequences.
What is a 'good' COP for a UAE chiller?
Water-cooled: 5.5–6.5 is healthy. Air-cooled: 3.0–3.5 is healthy. The numbers are lower on hot days; what matters is whether the figure trends down over months.
Why does delta-T matter so much?
Delta-T tells you whether the chilled-water loop is doing useful work. A delta-T that falls below design indicates bypass, low load or coil fouling — each with a different fix.
What is EWMA actually?
A moving average where recent points are weighted more heavily than older ones. It is the standard way to smooth a noisy signal while still being responsive to genuine drift.
Why are vibration thresholds in mm/s, not g?
ISO 10816 standardised on velocity (mm/s) for severity assessment because it correlates best with bearing damage across a wide frequency range. Acceleration (g) is used for diagnostics, not severity.
What does phase imbalance tell me?
Imbalance above 5% on a three-phase motor indicates supply quality, motor winding degradation, or a drive issue. Sustained imbalance shortens motor life materially and is one of the cleanest early signals you can get from current alone.
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