Data Center Refrigeration System Design: 40 Q&A on Safety, Operation, and Troubleshooting

1. Safety conditions for reliable refrigeration system operation

(1) Refrigerant pressure must never exceed abnormal high pressure to avoid equipment rupture. (2) Wet‑stroke, liquid‑slug, or liquid‑hammer must be prevented to protect equipment. (3) Moving parts must be free of defects and fasteners must be secure.

2. Definition of evaporation temperature

Evaporation temperature is the temperature at which the refrigerant boils and vaporizes in the evaporator under a specified pressure.

3. Definition of condensation temperature

Condensation temperature is the temperature at which the refrigerant gas condenses into liquid in the condenser under a specified pressure.

4. Definition of sub‑cooling (over‑cooling) temperature

Sub‑cooling temperature is the temperature of the liquid refrigerant after condensation that is lower than the condensation temperature.

5. Definition of intermediate temperature

In a two‑stage compression system, the intermediate temperature is the saturated temperature of the refrigerant in the intermediate cooler at intermediate pressure.

6. How to detect and control compressor suction temperature

Suction temperature is measured with a thermometer placed before the suction valve; it is typically 5‑10 °C higher than the evaporation temperature, and can be adjusted by changing the liquid supply.

7. How to detect compressor discharge temperature and influencing factors

Discharge temperature is measured on the discharge pipe; it is proportional to the pressure ratio and suction temperature. Higher suction over‑heat or higher pressure ratio raises discharge temperature.

8. What is “liquid carry‑over” (liquid hammer)?

Liquid carry‑over occurs when liquid refrigerant or wet vapor is drawn into the compressor due to insufficient evaporation heat absorption.

9. Causes of liquid carry‑over

1) Failure of the liquid‑level controller in the separator or low‑pressure tank. 2) Excessive or rapid liquid supply; leakage or excessive opening of the throttling valve. 3) Excess liquid in the evaporator or separator, low load, or rapid startup. 4) Sudden load increase or failure to adjust the suction valve after defrost.

10. Consequences of liquid carry‑over

For piston compressors, liquid entering the cylinder damages oil film, causes oil pressure instability, leads to piston damage, and may result in catastrophic mechanical failure. For screw compressors, it causes vibration, noise, and potential equipment damage.

11. Handling liquid carry‑over

Immediately close the suction cutoff valve and throttling valve, stop liquid supply, reduce load, and use crankshaft friction heat to evaporate residual refrigerant. Repeat until the crankcase is free of liquid, then gradually restore normal operation.

12. Causes and remedies for excessive discharge pressure

1) Excess mixed gas in the high‑pressure side – vent air. 2) Scaling or fouling in condenser water side – clean with high‑pressure water. 3) Excess condensate or oil in the condenser – open drain valves and clean. 4) Damaged condenser end‑cap gasket – replace.

13. Compressor start‑up failures and solutions

1) Electrical faults – repair. 2) Pressure or oil‑pressure relay failure – check and adjust contacts. 3) Excessive crankcase or intermediate pressure – service discharge valve or reduce pressure. 4) Piston‑type unload mechanism failure – repair.

14‑16. Common piston‑compressor issues (knocking sounds, low oil pressure, oil‑pump failure) and corrective actions

Check for valve‑seat wear, loose bolts, excessive clearances, oil‑pump wear, clogged filters, and adjust oil pressure or refill oil as needed.

17‑22. Causes of high suction over‑heat, high discharge temperature, and related remedies

Insufficient refrigerant, poor evaporator heat absorption, inadequate insulation, high water temperature, and improper valve settings are typical causes; solutions include adjusting throttling valves, increasing liquid supply, cleaning heat exchangers, and verifying system pressures.

23‑24. Low suction pressure and abnormal vibration causes

Clogged liquid‑supply or suction filters, insufficient refrigerant, excess oil, or low load can cause low suction pressure. Vibration may stem from loose foundation bolts, misaligned shafts, pipe resonance, or excess oil/liquid ingestion.

25‑30. Screw‑compressor specific problems (capacity loss, noisy operation, high discharge/oil temperature, etc.) and fixes

Improper slide‑valve position, clogged suction filters, excessive wear, high pressure loss, insufficient oil cooling, and leakage are addressed by cleaning, adjusting valves, repairing bearings, and ensuring proper cooling water flow.

31‑34. Oil‑separator and oil‑system issues (oil‑level rise, leakage, low oil pressure) and mitigation

Oil returning to the compressor, excessive refrigerant dissolved in oil, blocked return lines, or worn seals cause oil‑level rise; venting, heating oil, or cleaning lines resolves the issue. Low oil pressure is corrected by adjusting the pressure regulator, repairing leaks, cleaning filters, or replacing oil.

35‑40. Maintenance scheduling for piston and screw compressors (major, intermediate, minor overhauls)

Major overhauls: ~8000 h for piston compressors, component inspection, cleaning, and replacement as needed. Intermediate overhauls: 3000‑4000 h, focus on clearances and wear. Minor overhauls: 1000‑1200 h, routine cleaning of filters, oil change, and inspection of fasteners. For screw compressors, component‑specific intervals (motor 2‑3 yr, oil separator 2 yr, oil cooler 6 mo, etc.) are recommended.