Chiller Interview Q&A
Category: Chiller Systems
Style: Detailed + Explanation
Part 1 – Q1 to Q50
1. What is a chiller?
A chiller is a mechanical device used to remove heat from a liquid through a refrigeration cycle. The chilled water produced is circulated through heat exchangers to cool air or equipment in commercial and industrial HVAC systems.
2. What is the main function of a chiller in HVAC?
The main function of a chiller is to maintain required temperature by absorbing heat from the process or space and rejecting it to the atmosphere or condenser water system.
3. Explain the working principle of a chiller.
A chiller operates on the vapor compression refrigeration cycle. It consists of four major components: compressor, condenser, expansion valve, and evaporator. Refrigerant absorbs heat in the evaporator, gets compressed, rejects heat in the condenser, and expands through the expansion valve to repeat the cycle.
4. What are the main types of chillers?
The main types are air-cooled chillers, water-cooled chillers, absorption chillers, centrifugal chillers, screw chillers, scroll chillers, and reciprocating chillers.
5. Difference between air-cooled and water-cooled chillers.
Air-cooled chillers reject heat through ambient air using condenser fans, while water-cooled chillers use cooling towers and condenser water to dissipate heat, offering higher efficiency.
6. What is COP in a chiller?
COP (Coefficient of Performance) is the ratio of cooling effect produced to the power consumed by the chiller. Higher COP indicates better efficiency.
7. What is EER in chiller systems?
EER (Energy Efficiency Ratio) is the ratio of cooling capacity to input power, usually expressed in BTU/hr per watt.
8. What is chilled water temperature range?
Typical chilled water supply temperature ranges from 6°C to 7°C, with return temperature around 12°C to 13°C.
9. What is Delta T in a chiller?
Delta T is the temperature difference between chilled water supply and return. It indicates the system heat absorption efficiency.
10. What is the function of an evaporator?
The evaporator absorbs heat from chilled water by allowing refrigerant to evaporate, thereby cooling the water.
11. What is the function of a condenser?
The condenser rejects heat absorbed in the evaporator and compressor and converts refrigerant vapor into liquid.
12. What is superheating?
Superheating occurs when refrigerant vapor temperature rises above its saturation temperature after evaporation.
13. What is subcooling?
Subcooling is the process of lowering the liquid refrigerant temperature below its saturation point.
14. What causes low suction pressure?
Low suction pressure can be caused by refrigerant undercharge, clogged expansion valve, dirty evaporator, or restricted flow.
15. What causes high discharge pressure?
High discharge pressure results from dirty condensers, overcharge of refrigerant, high ambient temperature, or poor cooling water flow.
16. What is short cycling in chillers?
Short cycling is frequent starting and stopping of the chiller, usually caused by improper load matching or faulty sensors.
17. What is surge in centrifugal chillers?
Surge is unstable compressor operation caused by low load and high pressure difference across the compressor.
18. What is oil return and why is it important?
Oil return ensures lubrication of compressor components and prevents compressor failure.
19. Function of expansion valve.
The expansion valve reduces refrigerant pressure and regulates flow into the evaporator.
20. What is a flooded evaporator?
A flooded evaporator maintains excess refrigerant around the coil to maximize heat transfer efficiency.
21. What is a dry expansion evaporator?
It allows refrigerant to fully evaporate before reaching the compressor suction line.
22. What is chiller tonnage?
Chiller tonnage measures cooling capacity. 1 TR equals 12,000 BTU/hr or 3.517 kW.
23. What is approach temperature?
It is the difference between chilled water outlet temperature and refrigerant evaporation temperature.
24. What is lift in chillers?
Lift is the temperature difference between condenser and evaporator saturation temperatures.
25. Explain compressor types used in chillers.
Centrifugal, screw, scroll, and reciprocating compressors are used depending on capacity and application.
26. What causes compressor overheating?
Low refrigerant, high suction temperature, poor lubrication, or blocked airflow.
27. What is condenser fouling?
Accumulation of dirt or scale on condenser tubes reducing heat transfer efficiency.
28. What is chiller efficiency improvement method?
Regular maintenance, proper water treatment, cleaning heat exchangers, and VFD installation improve efficiency.
29. What safety devices are used in chillers?
High-pressure cut-out, low-pressure cut-out, oil pressure switch, phase protection, and motor overload protection.
30. What is refrigerant migration?
Refrigerant moving to compressor during off-cycle causing oil dilution.
31. What is pump down cycle?
A process that removes refrigerant from evaporator before shutdown to avoid liquid slugging.
32. Causes of low Delta T syndrome.
Improper flow rate, coil fouling, bypassed valves, or incorrect setpoints.
33. What is chilled water balancing?
Equal distribution of chilled water across all circuits to ensure uniform cooling.
34. What is cavitation in pumps?
Formation of vapor bubbles due to low pressure causing pump damage.
35. What is BMS role in chiller operation?
BMS monitors and controls chiller parameters for optimized performance.
36. What is part load performance?
Efficiency of chiller when operating below full capacity.
37. What is economizer cycle?
It improves efficiency by reducing compressor workload.
38. Difference between single-stage and multi-stage compressor.
Multi-stage compressors provide better efficiency with reduced pressure ratio per stage.
39. What is refrigerant glide?
Temperature change during phase change in blended refrigerants.
40. Why is water treatment important?
Prevents scaling, corrosion, and microbial growth in condenser water circuits.
41. What is load mismatch?
Occurs when chiller capacity is greater or lesser than actual cooling load.
42. What is chiller startup sequence?
Pump start → Flow confirmation → Compressor start → Monitoring operation.
43. What is chiller shutdown sequence?
Compressor stop → Pump delay → System stop.
44. What is pressure drop in evaporator?
Loss of pressure due to friction or flow resistance inside coil.
45. What is the difference between primary and secondary chilled water system?
Primary handles chillers directly; secondary distributes chilled water to loads.
46. What is variable primary flow system?
Chiller adapts flow rate based on cooling demand.
47. What is staging of chillers?
Sequential operation of multiple chillers based on load demand.
48. What is free cooling?
Use of ambient cool air or water to reduce compressor usage.
49. What is evaporator icing?
Freezing of moisture on coil due to low refrigerant temperature.
50. What is thermal load calculation?
Determining cooling capacity required based on heat gain sources.
Chiller Interview Q&A Scripts (Pure English Technical)
Category: Chiller Systems
Style: Detailed + Explanation
Part 1 – Q1 to Q50
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1. What is a chiller?
A chiller is a mechanical device used to remove heat from a liquid through a refrigeration cycle. The chilled water produced is circulated through heat exchangers to cool air or equipment in commercial and industrial HVAC systems.
2. What is the main function of a chiller in HVAC?
The main function of a chiller is to maintain required temperature by absorbing heat from the process or space and rejecting it to the atmosphere or condenser water system.
3. Explain the working principle of a chiller.
A chiller operates on the vapor compression refrigeration cycle. It consists of four major components: compressor, condenser, expansion valve, and evaporator. Refrigerant absorbs heat in the evaporator, gets compressed, rejects heat in the condenser, and expands through the expansion valve to repeat the cycle.
4. What are the main types of chillers?
The main types are air-cooled chillers, water-cooled chillers, absorption chillers, centrifugal chillers, screw chillers, scroll chillers, and reciprocating chillers.
5. Difference between air-cooled and water-cooled chillers.
Air-cooled chillers reject heat through ambient air using condenser fans, while water-cooled chillers use cooling towers and condenser water to dissipate heat, offering higher efficiency.
6. What is COP in a chiller?
COP (Coefficient of Performance) is the ratio of cooling effect produced to the power consumed by the chiller. Higher COP indicates better efficiency.
7. What is EER in chiller systems?
EER (Energy Efficiency Ratio) is the ratio of cooling capacity to input power, usually expressed in BTU/hr per watt.
8. What is chilled water temperature range?
Typical chilled water supply temperature ranges from 6°C to 7°C, with return temperature around 12°C to 13°C.
9. What is Delta T in a chiller?
Delta T is the temperature difference between chilled water supply and return. It indicates the system heat absorption efficiency.
10. What is the function of an evaporator?
The evaporator absorbs heat from chilled water by allowing refrigerant to evaporate, thereby cooling the water.
11. What is the function of a condenser?
The condenser rejects heat absorbed in the evaporator and compressor and converts refrigerant vapor into liquid.
12. What is superheating?
Superheating occurs when refrigerant vapor temperature rises above its saturation temperature after evaporation.
13. What is subcooling?
Subcooling is the process of lowering the liquid refrigerant temperature below its saturation point.
14. What causes low suction pressure?
Low suction pressure can be caused by refrigerant undercharge, clogged expansion valve, dirty evaporator, or restricted flow.
15. What causes high discharge pressure?
High discharge pressure results from dirty condensers, overcharge of refrigerant, high ambient temperature, or poor cooling water flow.
16. What is short cycling in chillers?
Short cycling is frequent starting and stopping of the chiller, usually caused by improper load matching or faulty sensors.
17. What is surge in centrifugal chillers?
Surge is unstable compressor operation caused by low load and high pressure difference across the compressor.
18. What is oil return and why is it important?
Oil return ensures lubrication of compressor components and prevents compressor failure.
19. Function of expansion valve.
The expansion valve reduces refrigerant pressure and regulates flow into the evaporator.
20. What is a flooded evaporator?
A flooded evaporator maintains excess refrigerant around the coil to maximize heat transfer efficiency.
21. What is a dry expansion evaporator?
It allows refrigerant to fully evaporate before reaching the compressor suction line.
22. What is chiller tonnage?
Chiller tonnage measures cooling capacity. 1 TR equals 12,000 BTU/hr or 3.517 kW.
23. What is approach temperature?
It is the difference between chilled water outlet temperature and refrigerant evaporation temperature.
24. What is lift in chillers?
Lift is the temperature difference between condenser and evaporator saturation temperatures.
25. Explain compressor types used in chillers.
Centrifugal, screw, scroll, and reciprocating compressors are used depending on capacity and application.
26. What causes compressor overheating?
Low refrigerant, high suction temperature, poor lubrication, or blocked airflow.
27. What is condenser fouling?
Accumulation of dirt or scale on condenser tubes reducing heat transfer efficiency.
28. What is chiller efficiency improvement method?
Regular maintenance, proper water treatment, cleaning heat exchangers, and VFD installation improve efficiency.
29. What safety devices are used in chillers?
High-pressure cut-out, low-pressure cut-out, oil pressure switch, phase protection, and motor overload protection.
30. What is refrigerant migration?
Refrigerant moving to compressor during off-cycle causing oil dilution.
31. What is pump down cycle?
A process that removes refrigerant from evaporator before shutdown to avoid liquid slugging.
32. Causes of low Delta T syndrome.
Improper flow rate, coil fouling, bypassed valves, or incorrect setpoints.
33. What is chilled water balancing?
Equal distribution of chilled water across all circuits to ensure uniform cooling.
34. What is cavitation in pumps?
Formation of vapor bubbles due to low pressure causing pump damage.
35. What is BMS role in chiller operation?
BMS monitors and controls chiller parameters for optimized performance.
36. What is part load performance?
Efficiency of chiller when operating below full capacity.
37. What is economizer cycle?
It improves efficiency by reducing compressor workload.
38. Difference between single-stage and multi-stage compressor.
Multi-stage compressors provide better efficiency with reduced pressure ratio per stage.
39. What is refrigerant glide?
Temperature change during phase change in blended refrigerants.
40. Why is water treatment important?
Prevents scaling, corrosion, and microbial growth in condenser water circuits.
41. What is load mismatch?
Occurs when chiller capacity is greater or lesser than actual cooling load.
42. What is chiller startup sequence?
Pump start → Flow confirmation → Compressor start → Monitoring operation.
43. What is chiller shutdown sequence?
Compressor stop → Pump delay → System stop.
44. What is pressure drop in evaporator?
Loss of pressure due to friction or flow resistance inside coil.
45. What is the difference between primary and secondary chilled water system?
Primary handles chillers directly; secondary distributes chilled water to loads.
46. What is variable primary flow system?
Chiller adapts flow rate based on cooling demand.
47. What is staging of chillers?
Sequential operation of multiple chillers based on load demand.
48. What is free cooling?
Use of ambient cool air or water to reduce compressor usage.
49. What is evaporator icing?
Freezing of moisture on coil due to low refrigerant temperature.
50. What is thermal load calculation?
Determining cooling capacity required based on heat gain sources.
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✅ Next: Q51 to Q100 available on request. Just say: "Continue Chiller Q&A Part 2"
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Part 2 – Q51 to Q100
51. What is condenser water temperature range?
Typically, condenser water enters at 30°C to 32°C and leaves at 35°C to 37°C, depending on ambient conditions and cooling tower performance.
52. What is the role of cooling tower in water-cooled chillers?
The cooling tower removes heat from condenser water by evaporative cooling and rejects it to the atmosphere.
53. What is refrigerant flooding?
Flooding occurs when liquid refrigerant returns to the compressor, causing mechanical damage.
54. What is liquid slugging?
When excessive liquid refrigerant enters the compressor cylinders, causing internal damage.
55. What is hot gas bypass?
A method to maintain minimum load by redirecting hot discharge gas to the evaporator.
56. What is chilled water flow switch?
A safety device that ensures proper water flow before compressor startup.
57. What is condenser approach?
Difference between condenser saturation temperature and leaving condenser water temperature.
58. What is evaporator approach?
Difference between chilled water outlet temperature and refrigerant saturation temperature in evaporator.
59. Causes of high compressor ampere draw.
Overload, high head pressure, worn bearings, or inadequate lubrication.
60. What is refrigerant overcharging?
Excess refrigerant leading to high pressure, reduced efficiency, and potential damage.
61. What is refrigerant undercharging?
Insufficient refrigerant causing low cooling performance and evaporator frosting.
62. What is dead band in temperature control?
Range where no control action occurs to prevent frequent cycling.
63. What is soft starter?
A device that reduces inrush current during compressor startup.
64. Role of VFD in chillers.
Controls motor speed to improve energy efficiency and reduce power consumption.
65. What is PLC control in chillers?
Programmable logic controller used to automate and monitor chiller operations.
66. What is chiller capacity control?
Adjusting compressor output based on cooling load.
67. Methods of capacity control.
Slide valve, guide vanes, variable speed drive, cylinder unloading.
68. What is oil separator?
Separates oil from refrigerant discharge gas to ensure proper lubrication.
69. What is crankcase heater?
Prevents refrigerant migration into compressor oil during off cycle.
70. What is chiller design load?
Maximum expected cooling load used for chiller selection.
71. What is redundancy in chiller plant?
Using multiple chillers to ensure system reliability.
72. What is N+1 configuration?
One extra chiller for backup beyond required capacity.
73. What is sequencer control?
Controls operation sequence of multiple chillers.
74. What is condenser tube scaling?
Mineral deposits reducing heat transfer and increasing pressure.
75. What is fouling factor?
Allowance for dirt accumulation in heat exchanger design.
76. What is chiller derating?
Reduction in capacity due to unfavorable conditions.
77. What is ambient temperature effect on chiller?
Higher ambient increases condenser pressure reducing efficiency.
78. What is chilled water pump head?
Pressure required to circulate water through system.
79. What is primary-secondary loop?
Two-loop system separating chiller and distribution flows.
80. What is differential pressure control?
Maintains consistent flow through system.
81. What is glide in blended refrigerants?
Range of temperature change during evaporation and condensation.
82. What is frosting in evaporator?
Ice buildup due to low surface temperature and high humidity.
83. What is load shedding?
Reducing power demand during peak energy usage.
84. What is chilled water reset strategy?
Adjusting supply temperature based on load conditions.
85. What is condenser water reset?
Controlling condenser water temperature to optimize efficiency.
86. What is heat recovery chiller?
Chiller that utilizes rejected heat for domestic hot water.
87. What is adsorption chiller?
Uses solid desiccant material instead of liquid absorbent.
88. What is centrifugal compressor surge control?
Maintains stable operation at low loads.
89. What is pressure relief valve?
Protects system from overpressure conditions.
90. What is refrigerant recovery process?
Collecting refrigerant during maintenance for reuse or disposal.
91. What is thermal expansion?
Change in refrigerant volume due to temperature variation.
92. What is chiller interlock?
Safety mechanism linking components for safe operation.
93. What is chilled water sensor placement?
Ensures accurate temperature measurement.
94. What is system flushing?
Cleaning system to remove debris and contaminants.
95. What is commissioning of chiller?
Testing and verification before system handover.
96. What is transient load?
Short-term sudden increase in cooling demand.
97. What is operating pressure range?
Recommended pressure range for safe operation.
98. What is chiller lifespan?
Typically 15–25 years with proper maintenance.
99. What is energy audit in HVAC?
Assessment of energy usage for optimization.
100. What is performance curve of chiller?
Graph showing efficiency vs load conditions.
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