1. Problem Description and Scope
This document deals with systematic diagnostics for industrial cooling systems (chillers, water/water exchangers, thermoregulation units) that have insufficient thermal capacity to maintain the setpoint required by machine tools. The problem manifests itself as the inability of the process fluid to drop to operating temperature or thermal fluctuations in the presence of variable loads.
Gravity Classification:
- Critical: Fluid temperature exceeds alarm threshold (e.g. > 45°C for high speed spindles), causing automatic machine tool shutdown and potential damage to precision components.
- Major: Thermal instability that compromises the geometric tolerances of the machined piece.
- Minor: High energy consumption with compressor duty cycles that are too long.
2. Safety Precautions
ATTENTION: ELECTRICAL AND MECHANICAL RISK. Before any intervention, carry out the Lockout/Tagout (LOTO) procedure on the electrical power panels. Refrigeration units contain pressurized refrigerants and moving components. Wear adequate PPE: protective glasses, chemical resistant gloves and safety shoes. In the event of refrigerant leaks, operate only in ventilated environments in compliance with ATEX regulations if applicable.
3. Necessary Diagnostic Equipment
| Tool | Specification/Model | Measurement Range | Purpose |
|---|---|---|---|
| Thermal imaging camera | Resolution min 160x120 | -20°C to +150°C | Thermal gradient analysis on exchangers and components |
| Multimeter | TRUE RMS with current clamp | 0-600V AC, 0-100A | Analysis of compressor and fan absorption |
| Differential pressure gauge | Digitally calibrated | 0-10 bars | Check filter/exchanger pressure drops |
| Flow meter | Ultrasound (clamp-on) | 0-200 L/min | Check actual vs nominal flow rate |
| Gas analyzer | Refrigerant leak detector | Sensitivity > 5g/year | Search for leaks in the refrigeration circuit |
4. Initial Assessment Checklist
| Observation | What to check | Notes |
|---|---|---|
| Alarm status | PLC History | Identify error codes (e.g. high pressure, low flow) |
| Conditions Load | Current heat load | Compare with nameplate specifications (kW) |
| Filters Status | Process side filter | Check differential pressure |
| Environment | Local ambient temperature | Check if the chiller is in environmental overload |
5. Systematic Diagnosis Flow
- Check Fluid Flow:
- Check delivery/return pressure.
- IF deltaP > threshold (see manual): check filters and exchanger cleaning.
- IF flow rate < nominal: check pump status and presence of air in the circuit.
- Heat Exchange Check:
- IF deltaT exchanger < nominal: suspect fouling (encrustations) or internal bypass.
- Check Refrigeration Circuit:
- IF compressor running but no cooling: check refrigerant charge and expansion valve status.
6. Fault-Cause Matrix
| Symptom | Probable Causes (Ranking) | Diagnostic Test | Expected Result |
|---|---|---|---|
| High fluid T | 1. Fouling Exchanger 2. Low Gas Charge | Thermal imaging camera / Pressure gauges | Reduced DeltaT / Low blood pressure |
| Poor range | 1. Clogged filter 2. Worn pump | Diff. pressure gauge | High DeltaP (> 0.5 bar) |
| High Pressure Alarm | 1. Dirty condenser 2. Faulty fan | Visual inspection / Ampere | Fan current > nominal |
7. Root Cause Analysis
Fouling (Encrustations): Accumulation of limestone or biological sediments on exchange surfaces. It drastically reduces the global heat transfer coefficient (U). Confirmation by comparison of fluid input/output deltaT.
Refrigerant Loss: Decrease in circulating mass. Causes compressor overheating and evaporator inefficiency. Confirmation by reading pressures (low pressure too low).
8. Resolution Procedures
- Exchanger Cleaning (Fouling):
- Isolate the user side circuit.
- Use an acid solution specific for the exchanger material (e.g. AISI 316).
- Forced circulation wash for 2 hours.
- Rinse thoroughly and neutralize.
- Refrigerant Refill:
- Locate the leak using an electronic leak detector.
- Recover the residual refrigerant according to current regulations.
- Replace drier filter.
- Deep vacuum (< 1 mbar).
- Load by weight (indicated on the machine plate).
9. Preventive Measures
| Cause | Prevention Strategy | Monitoring Method | Interval |
|---|---|---|---|
| Fouling | Chemical water treatment | Water hardness analysis | Semi-annually |
| Dirt Condenser | Cleaning fins | Visual inspection | Quarterly |
10. Spare parts and components
| Description | Specify | Replacement | UNITEC category |
|---|---|---|---|
| Y filter | 500 micron mesh | If clogged | Circuit Accessories |
| Centrifugal Pump | Stainless steel | After 20,000 hours | Hydraulic Components |
| Expansion Valve | Thermostatic | If it's bad | Refrigeration Components |
To purchase components, consult the online catalogue: https://www.unitecd.com/e-catalog/
11. References
- UNI EN 378: Refrigeration systems and heat pumps.
- OEM technical manuals for process chillers.
- Unitec guidelines on preventive maintenance.
