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Diagnosis and resolution of insufficient performance of industrial cooling systems: hydraulics, heat exchange and refrigerant

Technical analysis: Troubleshooting industrial cooling system insufficient capacity: heat load calculation, flow balance

Diagnosis and resolution of insufficient performance of industrial cooling systems: hydraulics, heat exchange and refrigerant

1. Problem Description and Area of Application

< ступінь серйозності: Critical (threat of stopping technological equipment or emergency release of protection) >

This manual is intended for reliability engineers, workshop managers, and shift mechanics of Ukrainian industry enterprises (metallurgy, machinery manufacturing, chemical industry, food industry, and energy). The manual covers industrial cooling systems (chillers, cooling towers, plate and shell-and-tube heat exchangers, cooling circuit pumping stations).

Main symptom under consideration: insufficient cooling capacity of the system, which is manifested by the inability to reach the required process temperature, increased temperature of the return medium above permissible limits (more than +15 °C for technological circuits or +7 °C for air conditioning systems), or periodic shutdown of the equipment according to the high pressure refrigerant relay signal or compressor overload protection.

Insufficient cooling capacity leads to emergency stops of stamping lines, thermoplastic injection machines, laser systems and compressor equipment. Successful diagnosis requires sequential elimination of factors: deviation of liquid flow rate, contamination of heat exchange surfaces, disruption of refrigerant balance and increase of heat dissipation in the cooled object.

2. Safety Measures

WARNING! DANGER OF HIGH PRESSURE AND TOXIC SUBSTANCES. Before starting any work, perform the procedure Lockout/Tagout (LOTO). Turn off the power supply to the compressors, pumps and fans at the main distribution board, lock out the input and hang warning tags in accordance with the requirements of NPAOP 0.00-1.28-10.

Personal Protective Equipment (PPE): Safety goggles with side protection (EN 166), chemically resistant gloves (nitrile or neoprene when working with glycols and refrigerants), protective footwear with steel toe (EN ISO 20345), respirator or gas mask with appropriate filter when working with ammonia or freon in enclosed spaces.

WARNING: ENERGY RETENTION: Cooling circuits under pressure may contain liquid and gas under pressure up to 25 bar. Before disconnecting flanges or fittings, close the shut-off valves and release the residual pressure through pressure ports. Do not allow liquid refrigerant to come into contact with exposed skin — this may cause cryogenic burns.

3. Required diagnostic tools

Tool Name Specification / Model Measurement range Purpose
Digital manifold Testo 550s or equivalent (CE) -1 to 60 bar, -50 to +150 °C Pressure measurement of condensation/boiling, superheat and subcooling of refrigerant
Ultrasonic flow meter Fugita / Flexim Fluxus (or similar) 0.1 – 20 m/s, pipes DN15–DN1000 Actual Coolant Flow Rate Control in the Circuit
Thermovisor (Thermal imager) Fluke Ti401PRO / Testo 883 -20 to +650 °C, sensitivity < 0.05 °C Detection of fouling zones in heat exchangers, bearing overheating, bypass flow rates
Portable vibration analyzer VMI / Fluke 810 10–10000 Hz, vibration velocity 0.1–200 mm/s Condition Monitoring of Pump and Compressor Bearings
True RMS Multimeter Fluke 87V 0–1000 V AC/DC, 0–10 A (up to 400 A with terminals) Voltage check, power consumption of compressors and pumps
Refractometer Digital Brix/Glycol Refractometer 0–80% glycol concentration, -50 to 0 °C Determination of freezing point and concentration of propylene glycol/ethylene glycol aqueous solution

4. Initial Condition Assessment Checklist

Parameter for checking Normative value (Permissible) Alarm value (Fault) Actual value
Water temperature at the inlet to the cooler +10 °C to +14 °C +18 °C [ ] Record
Water temperature at the cooler outlet +5 °C to +7 °C +10 °C [ ] Record
Pressure drop on the evaporator / heat exchanger According to the OEM passport (0.5 – 1.5 bar) Deviation over 30% from the nominal value [ ] Record
Suction side refrigerant overheating of the compressor 5 K – 8 K < 3 K (ризик заливу) або > 12 K [ ] Record
Overcooling in the condenser 3 K – 5 K < 1 K (нестача фреону) або > 8 K [ ] Record
Compressor current consumption (L1, L2, L3) Within the nominal value on the nameplate (±5%) 105% of nominal or asymmetry > 2% [ ] Record
Concentration of glycol in the system According to the mode map (e.g. 30%) 45% (viscosity increase, heat capacity loss) [ ] Record

5. Systematic Diagnostic Block Diagram

  • SYMP TOM: Insufficient cooling capacity (process temperature higher than setpoint)
    • STEP 1: Check the total heat load on the object.
      • IF heat load exceeds design (increase in machine/power plant capacity by >15%) OR ambient temperature higher than calculated (according to DIN EN 14511) $ ightarrow$ Cause: Overloading of the cooling system by heat flow.
      • If the thermal load is within normal limits $ \rightarrow $ Proceed to STEP 2.
    • STEP 2: Measure the cooling fluid flow rate using an ultrasonic flow meter and check the pressure drop.
      • IF the flow is below the nominal value by >20% $ ightarrow$ Check the position of the balancing valves, the condition of the dirt filters and the pump operating point. $ ightarrow$ Cause: Hydraulic imbalance or flow restriction.
      • IF pressure drop across the heat exchanger is higher than >40% at nominal or reduced flow $ \rightarrow $ Cause: Fouling (scale, biofouling, sludging) of heat exchanger surfaces.
      • If the consumption and hydraulic resistance are within normal limits $ \rightarrow $ Proceed to STEP 3.
    • STEP 3: Connect the digital manifold and check the refrigeration circuit parameters (boiling pressure, condensation pressure, superheat, subcooling).
      • IF subcooling < 1 K AND температура на рідинній лінії нижча за норму AND є бульбашки у смотровому склі $ ightarrow$ Cause: Insufficient refrigerant charge (leak).
      • If condensation pressure exceeds the calculated value by >4 bar AND air/water temperature at the inlet to the condenser is normal $ \rightarrow $ Cause: Condenser fouling or presence of non-condensable gases in the circuit.
      • IF overheating at suction > 12 K AND position of electronic/thermostatic expansion valve (TXV/EV) closed $ \rightarrow $ Cause: Faulty TXV/EV or clogged filter-drier.

6. Fault Matrix and Causes

Symptom Likely causes (in order of likelihood) Diagnostic test Expected result upon confirmation of the cause
High outlet water temperature, LP/HP protection activation 1. Scale fouling on the plate evaporator.
2. Reduced flow due to clogging of the mesh filter.
3. Freon shortage (leak).		 Measure the temperature difference of the water and the pressure drop on the evaporator. Take a thermogram of the heat exchanger. Pressure drop higher than nominal by 50%. Thermogram shows uneven temperature distribution (flow stagnation).
The compressor is running continuously, but there is no cooling 1. Refrigerant leakage.
2. Filter-dryer clogging.
3. Compressor performance loss (valve wear).		 Check the inspection glass for the presence of moisture/bubbles. Measure overheating and undercooling. Boiling of the viewing glass (bubbles). No undercooling (< 1 K). Перегрів > 15 K.
Frequent cyclic shutdown of the compressor (Short Cycling) 1. False relay operation.
2. Incorrect thermostat settings.
3. Insufficient buffer tank capacity.		 Close relay contacts for the flow (temporarily for testing). Check the cycle operating time using SCADA or a stopwatch. When the relay is forced to close, the compressor stabilizes the operation (sensor flow fault confirmed).

7. Root Cause Analysis for each failure

7.1. Contamination of heat exchange surfaces (Scale and sludge)

Why it occurs: The use of unprepared or poor quality water in open cooling towers or open circuits leads to the precipitation of hardness salts (calcium carbonate, magnesium) upon heating of the heat exchange surface. In closed circuits, corrosive sludge and degradation products of glycol accumulate.

Як підтвердити: Гідравлічний опір теплообмінника зростає на 30–50% при номінальній витраті. За допомогою тепловізора фіксується висока температурна нерівномірність на корпусі пластинчастого теплообмінника (зональні температурні плями).

Наслідки: Зменшення коефіцієнта теплопередачі ($k$), зростання температурного напору, зростання тиску конденсації, перевантаження компресора, ризик механічного пошкодження пластин.

7.2. Hydraulic imbalance and drop in fluid flow rate

Why it occurs: Filter clogging (Y-shaped filters), wear of the pump impeller (cavitation, erosion), closure of shut-off valves after maintenance work, or incorrect balancing of the piping systems.

Як підтвердити: Ультразвуковий витратомір показує витрату на 25–40% нижче проєктного значення (згідно з ISO 5167). Манометри до і після фільтра показують критичний перепад (понад 0.8 bar).

Consequences: Laminar flow character instead of turbulent flow in the heat exchanger, local freezing in the evaporator (if the boiling temperature is below 0 °C), activation of the freeze protection (anti-freeze thermostat).

7.3. Deficiency or excess of refrigerant

Cause: Microleaks through rolling connections, solder joints, valve seals or Schrader valves due to vibrational loads (according to standards EN 378).

Як підтвердити: Маніфольд показує зниження тиску кипіння та конденсації. Переохолодження падає нижче 1 K. Наявність вказівок на вологу та газ у смотровому склі рідинної лінії.

Наслідки: Падіння масової витрати холодоагенту через випарник, перегрів обмоток компресора через недостатнє охолодження парами, що всмоктуються, зниження Холодильного Коефіцієнта (COP).

8. Step-by-step troubleshooting procedures

Procedure 8.1. Chemical Cleaning of Plate Heat Exchanger (Evaporator / Condenser)

  1. Perform LOTO blocking for the cooling circuit pumps and refrigeration unit.
  2. Close the inlet and outlet valves of the heat exchanger. Release the pressure and drain the remaining liquid through the drain fittings.
  3. Connect the mobile cleaning station (CIP station) with acid-resistant hoses to the drain ports of the heat exchanger.
  4. Fill the station with an inhibited organic acid solution (sulfanilic or citric acid 5-10% solution, temperature up to +40 °C). It is prohibited to use hydrochloric acid (HCl) for stainless steel AISI 316 due to the risk of pitting corrosion.
  5. Circulate the solution for 2–4 hours. Monitor the pH level (maintain within 1.5–2.5). If the pH rises above 4.0, add acid or replace the solution.
  6. Flush the system with a neutralizing solution (1-2% solution of sodium hydroxide or sodium carbonate), and then with clean industrial water until a neutral pH (6.5–7.5) is achieved.
  7. Remove and clean the mesh filters at the inlet.
  8. Assemble the circuit, fill the chamber, vent the air through the vent valves, and start the pump.
  9. Post-repair check: Measure the pressure drop and water temperature. The pressure drop should return to the nominal value specified in the passport (±10%).

    10. Procedure 8.2. Leak Elimination and Refrigerant Recharge

    1. Connect the digital manifold and the electronic leak detector (sensitivity of 1 g/year) or perform pressure testing with nitrogen at a pressure of 15–18 bar with the addition of a trace amount of indicator gas (hydrogen-nitrogen mixture).
    2. Locate the source of the leak (pipe connections, filter housings, valves, solder joints).
    3. Perform vacuuming of the system using a two-stage vacuum pump to a final pressure not higher than 267 Pa (2 Torr). Maintain the vacuum test for 30 minutes (pressure should not increase).
    4. Charge the system with liquid refrigerant by weight (use electronic scales for charging) according to the compressor-condenser unit nameplate.
    5. Post-repair check: Start the system. Check the overheating parameter (5–8 K) and undercooling (3–5 K). The liquid line sight glass must be completely filled with liquid without bubbles.

    9. Preventive Measures

    Primary Cause Preventive strategy Monitoring method Recommended interval
    Contamination of heat exchangers Water quality control, addition of scale inhibitors, regular chemical CIP cleaning. Pressure drop and temperature differential monitoring through SCADA. Quarterly (or once a year depending on water quality).
    Hydraulic imbalance Cleaning of dirt separators, checking the operation of pumps according to H-Q characteristics. Current control of pumps and flow meter readings. Monthly.
    Refrigerant leakage Vibration control of pipelines, annual inspection using a flow meter according to EN 378. Pressure control sensors for boiling/condensation and presence of signaling. Every 6 months.

    10. Spare Parts and Components

    Description of the part Specification When to replace Category UNITEC
    Plate heat exchanger Stainless steel AISI 316, copper solder, max. 30 bar When the plates are mechanically damaged or when there is critical irreversible contamination. Heat Exchanger Equipment
    Hermetic filter-dryer Under the fitting/adapter, with a zeolite core (series DCL/DML) At each leak of the loop or annually during maintenance. Refrigeration Circuit Components
    Electronic Expansion Valve (ERV) Stepper motor, compatible with R410A / R134a / R404A When the rod is jammed or the sealing element loses its integrity. Control valve
    Y-Strainer (Mesh Filter) Cast iron/stainless steel, mesh 0.5 mm, PN16/PN25 When the mesh is damaged or there is through corrosion of the body. Hydraulic components
    Pressure differential sensor / Flow switch 4-20 mA / 0-10 bar, IP65 During calibration drift or in the absence of an electrical signal. Measuring and control instruments

    Are you looking for reliable European components for the repair and modernization of industrial cooling systems? Familiarize yourself with our range in the section Electronic Catalog UNITEC-D.

    11. Normative References

    • EN 378:2016 — Refrigeration systems and heat pumps. Safety and environmental requirements.
    • DIN EN 14511 — Air Conditioners, Liquid-Cooled Aggregates and Heat Pumps with Electrically Driven Compressors for Heating and Cooling of Rooms.
    • ISO 5167 — Measurement of liquid flow using devices with variable cross-sectional area, installed in filled circular cross-section pipelines.
    • NPAOP 0.00-1.28-10 — Rules for the protection of workers during the operation of refrigeration units.

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