Troubleshooting Guide: Insufficient performance of an industrial cooling system

1. Description of the problem and scope of application

This manual is designed to systematically diagnose and troubleshoot industrial refrigeration systems that are underperforming. Inadequate performance of the cooling system can manifest itself as a constantly elevated temperature of the coolant despite the rated load, excessive consumption of electrical energy by compressors and pumps, as well as frequent tripping of protective devices due to overload or abnormal operating parameters. Typical equipment to be diagnosed includes chillers (air and water cooled), cooling towers, fluid heat exchangers (plate, shell and tube), industrial process cooling systems, and cold rooms.

Classification of the severity of the problem:

• Critical: The temperature of the cooled liquid exceeds the permissible limits, which leads to the stoppage of the technological process or the risk of damage to the equipment. Requires immediate diagnosis and elimination.
• Basic: The system is operational, but with increased temperatures, reduced efficiency, and significant power consumption. Affects product quality or equipment life. Requires quick intervention.
• Minor: Small deviations from the nominal parameters, which are not critical for the process, but indicate the beginning of system degradation. Requires scheduled diagnostics.

2. Precautions

CAUTION: Before beginning any diagnostic or repair work on industrial cooling systems, ALWAYS follow standard Lockout/Tagout procedures to isolate all energy sources (electrical, pneumatic, hydraulic). Make sure that all stored energy (pressure, electrical charge of capacitors) is discharged to a safe level. Use appropriate personal protective equipment (PPE): safety glasses (DSTU EN 166:2017), chemically resistant gloves (DSTU EN 374-1:2003), protective shoes (DSTU EN ISO 20345:2019) and overalls. Work with refrigerants should be performed only by certified personnel (according to EN 13313:2018) in well-ventilated rooms or using ventilation systems and gas analyzers. Refrigerants can cause frostbite on contact and asphyxiation in high concentrations. Follow the requirements of DSTU ISO 45001:2019 regarding occupational health and safety management systems.

3. Necessary diagnostic tools

It is critical to use calibrated tools for accurate diagnosis and troubleshooting.

4. Initial evaluation checklist

Before starting a detailed diagnosis, conduct a visual inspection and collect basic data. This will allow you to localize possible problems.

5. Scheme of systematic diagnostics

The following diagram provides a structured approach to identifying the root cause of underperformance.

1. Symptom: The temperature of the cooled liquid is constantly higher than the set value.
   1. Step 1: Estimate the heat load.
      • Diagnosis: Compare the actual heat load of the process with the calculated value. Measure fluid flow (m³/h) and temperature drop (°C) on heat consumers. Calculate the actual heat load (kW) using the formula Q = m * C * ΔT, where Q is the thermal power, m is the mass flow rate, C is the specific heat capacity of the liquid, and ΔT is the temperature difference.
      • If actual load > chiller rated capacity:
        • Probable cause: System overload.
        • Skip to section 7.1.
      • If actual load < chiller rated capacity:
        • Proceed to Step 2.
   2. Step 2: Checking the coolant flow rate through the evaporator.
      • Diagnosis: Measure the fluid flow rate (l/min) through the evaporator using an ultrasonic flowmeter. Compare with the passport data of the chiller manufacturer. Check the pressure drop across the evaporator and filters.
      • If flow < minimum recommended or pressure drop > nominal:
        • Probable cause: Insufficient fluid flow (clogged filters, pump failure, closed valves).
        • Skip to section 7.2.
      • If the consumption is normal:
        • Proceed to Step 3.
   3. Step 3: Assess heat transfer efficiency.
      • Diagnosis: Measure the refrigerant and refrigerant temperatures at the evaporator inlet and outlet, and the refrigerant and cooling water/air temperatures at the condenser inlet and outlet. Calculate the temperature differences.
      • If the liquid/refrigerant temperature difference in the evaporator < nominal or the refrigerant/water/air temperature difference in the condenser < nominal:
        • Probable cause: Contamination of the heat exchangers (evaporator or condenser) or failure of the fans/pumps of the cooling circuit.
        • Skip to section 7.3.
      • If the heat exchange efficiency is normal:
        • Proceed to Step 4.
   4. Step 4: Checking the charge of the refrigerant and the operation of the refrigeration cycle.
      • Diagnostics: Connect the pressure gauges for the refrigerant. Measure suction and discharge pressure. Measure the temperature of the suction line (gas) and the liquid line after the condenser. Calculate superheat (subtraction of boiling point by suction pressure from actual gas temperature at suction) and subcooling (subtraction of actual liquid temperature by condensing temperature by discharge pressure).
      • If low suction pressure, high superheat, low subcooling:
        • Probable cause: Insufficient refrigerant charge (leakage).
        • Skip to section 7.4.
      • If high discharge pressure, low superheat, high subcooling:
        • Probable cause: Refrigerant overcharge or non-condensable gases.
        • Skip to section 7.4.
      • If the pressures and temperatures deviate from the norm in other ways:
        • Probable cause: Malfunction of the compressor, TRV (thermoregulating valve) or other components of the refrigeration cycle.
        • Skip to section 7.5.

6. Malfunction-cause matrix

This matrix systematizes typical symptoms, probable causes, and methods of confirming them.

7. Root cause analysis for each malfunction

7.1. System overload

Explanation: Overload occurs when the actual heat load applied to the cooling system exceeds its nominal cooling capacity. This can be caused by the expansion of production, a change in the technological process without upgrading the cooling system, or an incorrect initial calculation of power. Long-term overload leads to constant operation of compressors at maximum capacity, increased wear, increased temperatures and pressures, which shortens the service life of the equipment.

How to confirm: Compare the calculated heat load (kW) from all sources (technological processes, equipment, heat inflows through insulation) with the nominal capacity of the chiller. Measure the actual electrical power (kW) consumed by the compressors and compare with the rated power. If the ratio of the actual thermal load to the nominal capacity of the chiller exceeds 0.95, the system is operating at the limit.

Consequences: Constant overheating of the coolant, increased operating temperatures and pressures of the refrigeration cycle, excessive energy consumption, premature failure of compressors due to wear, frequent tripping of protective devices.

7.2. Insufficient fluid/air flow

Explanation: For efficient heat exchange in both the evaporator and the condenser, an adequate flow rate of the working fluid (water/glycol) or air is critical. Insufficient flow can be caused by clogging of filters, malfunction of pumps or fans, incorrect adjustment of balancing valves, or accumulation of deposits (sludge, corrosion) in pipelines and channels of heat exchangers.

How to confirm:

• For the liquid circuit: Measure the liquid flow rate with an ultrasonic flow meter (allowable deviation from nominal < ±5%). Measure the pressure drop across the filters and evaporator; a significant increase in pressure drop (> 0.5 bar from normal) indicates clogging. Check the current of the pumps; a reduced current may indicate cavitation, and an increased current may indicate a mechanical malfunction.
• For the air circuit (condenser): Check the current of the fan motors; abnormal values ​​indicate a malfunction. Inspect the fan blades for damage and contamination. Measure the air velocity with an anemometer at the inlet/outlet of the condenser.

Consequences: Decreased heat transfer coefficient, local overheating, increased discharge pressure (for the condenser) or decreased suction pressure (for the evaporator), which leads to a decrease in cooling capacity and increased energy consumption.

7.3. Fouling of heat exchangers

Explanation: Contamination of heat exchange surfaces (evaporator, condenser) significantly reduces their efficiency. In the evaporator, it can be biological fouling, sludge, corrosion products; in the condenser - dust, fluff, fat (air) or mineral deposits (scale), biological fouling (water). The contamination layer creates additional thermal resistance, preventing efficient heat exchange between the refrigerant and the cooled/cooling medium.

How to confirm:

• Visual inspection: Examine the surfaces of the heat exchangers. For air-cooled chillers – condenser radiators, for water-cooled ones – inner surfaces of pipes/plates (after dismantling).
• Measuring temperatures: Use a thermal imager to detect cold or hot areas on the heat exchanger, indicating inefficient heat transfer.
• Temperature difference: For the evaporator: an increase in the difference between the boiling temperature of the refrigerant and the temperature of the cooled liquid at the outlet (more than 5-7 °C). For the condenser: an increase in the difference between the condensing temperature of the refrigerant and the temperature of the cooling medium at the outlet (more than 5-7 °C).
• Pressure drop: A significant increase in the pressure drop across the heat exchanger (more than 0.3-0.5 bar from the clean state) indicates internal contamination.

Effects: Increased condensing pressure (for the condenser) and reduced evaporation pressure (for the evaporator), resulting in increased compressor load, reduced cooling capacity, excessive energy consumption, and increased wear and tear.

7.4. Insufficient/excess refrigerant charge

Explanation: The exact amount of refrigerant is critical for optimal operation of the refrigeration cycle. An insufficient charge (usually due to a leak) leads to insufficient filling of the evaporator and a decrease in its efficiency. Overcharging leads to increased condensing pressure, compressor overload and risk of water hammer. Non-condensable gases (air, nitrogen) entering the system also act as an excess charge, increasing the pressure.

How to confirm:

• Undercharge: High overheating (over 10 °C for most systems) and low or zero subcooling. Low suction pressure. Bubbles in the liquid line (if there is a sight glass). Reduced current of the compressor (due to a decrease in the density of the refrigerant).
• Excess charge/non-condensable gases: High discharge pressure, low superheat, high subcooling (above 10 °C). If the discharge pressure with the compressor off is significantly higher than the saturation pressure for the ambient temperature, this indicates non-condensable gases.

Consequences: Reduced cooling capacity, increased energy consumption, compressor overheating, risk of compressor failure (due to lack of lubrication at low charge or water hammer at excessive charge).

7.5. Malfunction of components of the refrigeration cycle

Explanation: Malfunctions in components such as the compressor, TRV (thermoregulating valve), receiver, solenoid valves, or check valves can significantly affect the efficiency of the cycle. A compressor malfunction (reduced compression, mechanical wear) will lead to the inability to create the required pressure drop. Incorrect operation of the TRV (too open/closed, jamming) will disrupt the supply of refrigerant to the evaporator, which will affect overheating.

How to confirm:

• Compressor: Measure the motor winding current (phase-phase) with a multimeter. Compare with rated current. Reduced current at high intake pressure indicates insufficient compression. Listen to the compressor for extraneous noises (knocking, grinding).
• TRV: Measure the temperature at the inlet and outlet of the TRV. A significant temperature drop (icing) on ​​the TRV when the evaporator is not completely filled indicates a closed TRV. The absence of an appreciable drop in pressure or temperature through the TRV may indicate that it is jammed in the open position. Calculate the overheating.
• Solenoid/check valves: Check the electrical signal on the solenoid valve. Check the pressure drop across the valve; a significant pressure drop across an open valve indicates an internal blockage or malfunction.

Consequences: Decreased cooling capacity, increased operating temperatures, increased wear, complete shutdown of the system.

8. Step-by-step troubleshooting procedures

CAUTION: Follow all precautions listed in section 2.

8.1. Elimination of system overload

1. Step 1: Calculate the actual heat load. Collect data on all heat sources served by the system.
2. Step 2: Compare with chiller data sheet. If the actual load is > 95% of the nominal load, consider optimizing the process or upgrading/add-on cooling equipment.
3. Step 3: Optimization of the technological process. If possible, reduce the temperature of heat sources before entering the cooler or reduce the number of simultaneously operating equipment.
4. Verification: After optimizing or upgrading, re-measure coolant temperature and system power consumption. The parameters must correspond to the calculated values.

8.2. Restoration of normal fluid/air flow

1. Step 1: **Isolation and LOTO.** Isolate the pump/fan and related circuits. CAUTION: Before working with pumps or fans, make sure that there is no power supply and that moving parts are fixed.
2. Step 2: Check and clear the filters. Replace clogged filters according to manufacturer's recommendations. The pressure drop across a clean filter should not exceed 0.1 bar.
3. Step 3: Check the pumps. Diagnose the pump according to the manufacturer's manual: check the impeller for clogging/damage, condition of bearings, seals. Measure the pump motor current and compare with the rated current. To detect mechanical malfunctions, use a vibration analyzer (ISO 10816-1:2018); permissible vibration level for industrial pumps is up to 4.5 mm/s (root mean square value).
4. Step 4: Check the fans (for air cooling condensers). Clean the blades from dust and dirt. Check the engine, bearings. Measure the air speed using an anemometer at the outlet of the fan; it must correspond to passport data (tolerable deviation < ±10%).
5. Step 5: Check thread balancing. Use an ultrasonic flow meter to measure the fluid flow in each circuit and adjust the balancing valves to achieve the calculated flow rate.
6. Verification: After the flows are restored, check the pressure drop across the heat exchangers, fluid/air flow and operating temperatures.

8.3. Cleaning of heat exchangers

1. Step 1: **Isolation and LOTO.** Isolate the relevant circuits and equipment. CAUTION: When chemical cleaning, use PPE (protective suit, gloves, mask) and ensure proper ventilation.
2. Step 2: Mechanical cleaning. For air condensers - wash with water under high pressure (up to 150 bar) in the direction opposite to the air flow. For shell-and-tube heat exchangers – mechanical cleaning with brushes or a hydrojet unit.
3. Step 3: Chemical cleaning. To remove scale or biological deposits, use specialized chemical solutions (such as phosphoric acid scale solutions or biocides for fouling) following the solution and heat exchanger manufacturer's instructions. After cleaning, be sure to flush the system with plenty of clean water and neutralize any remaining chemicals.
4. Verification: After cleaning, check the pressure drop across the heat exchanger (it should return to the nominal value) and the heat exchange efficiency (T_output coolant/air).

8.4. Refrigerant charge adjustment

1. Step 1: **Detecting and repairing leaks.** Use an electronic leak detector (sensitivity up to 3 g/year according to EN 14624) or a UV dye. Eliminate all detected leaks.
2. Step 2: **Vacuum the system.** Fix After leaks, evacuate the refrigerant and evacuate the system to 0.1 Torr (13.3 Pa) vacuum for a minimum of 30 minutes. Check vacuum stability.
3. Step 3: **Top-up.** Use a refrigerant scale to accurately top-up according to the chiller manufacturer's specification (±5% of nominal charge).
4. Step 4: **Removal of non-condensable gases.** If non-condensable gases are suspected, perform a purge through the relief valve while monitoring the pressure and temperature.
5. Verification: After refueling and starting the system, measure overheating and subcooling. For most systems, overheating should be in the range of 5-8 °C, hypothermia - 5-8 °C. Check the pressures and temperatures, they must meet the regulatory parameters for the given refrigerant and operating conditions.

8.5. Repair/replacement of faulty refrigeration cycle components

1. Step 1: **Isolation and LOTTO.** Isolate the compressor or related circuit. ATTENTION: When working with compressors or TRVs, it is necessary to completely release the pressure of the refrigerant from the corresponding circuit.
2. Step 2: Compressor. If a malfunction is detected (reduced compression, mechanical noises), the compressor must be replaced or overhauled. After replacement, perform vacuuming and recharging refrigerant according to procedure 8.4.
3. Step 3: TRV. In case of malfunction of the TRV (jamming, loss of sensitivity of the thermal balloon), it must be replaced. Make sure that the new heat exchanger matches the type of refrigerant and the capacity of the evaporator. After replacement, perform vacuuming and refueling.
4. Step 4: Other valves. Replace faulty solenoid or check valves. Check their operation after replacement.
5. Verification: After replacing the components and refueling the system, start the equipment and check all operating parameters (pressures, temperatures, currents of the compressors), make sure the stability of the refrigeration cycle and the achievement of the required refrigeration capacity.

9. Preventive measures

Regular maintenance is key to preventing underperformance and extending equipment life.

10. Spare parts and components

Timely availability of quality spare parts is critical for quick troubleshooting. UNITEC-D offers a wide range of CE and UkrSEPRO certified components that meet ISO standards.

Find the parts and components you need in the UNITEC e-catalogue: www.unitecd.com/e-catalog/

11. Links

• DSTU EN 378:2018 Refrigeration systems and heat pumps. Safety and environmental requirements.
• ISO 5149:2020 Refrigeration systems and heat pumps. Safety and environmental requirements.
• EN 13313:2018 Refrigeration systems and heat pumps. Staff competence.
• EN 16407:2013 Industrial cooling systems. Cleaning requirements.
• DSTU EN 166:2017 Individual eye protection. Requirements
• DSTU EN 374-1:2003 Protective gloves against chemicals and microorganisms.
• DSTU EN ISO 20345:2019 Personal protective equipment. Protective shoes.
• DSTU ISO 45001:2019 Occupational health and safety management systems. Requirements
• ISO 10816-1:2018 Mechanical vibration. Evaluation of machine vibration by measurements on stationary parts.
• Operation and maintenance manuals from manufacturers of refrigeration equipment.