Top 25 HVAC Interview Questions – With Answers pdf

✅ Top 25 HVAC Interview Questions – With Answers

🔹 Core Concepts

1. What is the refrigeration cycle and name its components?
   ✅ It consists of Evaporator → Compressor → Condenser → Expansion Valve, forming a closed loop to remove heat from indoor air.
2. What is 1 TR (ton of refrigeration) and how is it calculated?
   ✅ 1 TR = 12,000 BTU/hr ≈ 3.517 kW. It’s the cooling needed to freeze 1 ton of water into ice in 24 hours.
3. What is the difference between air-cooled and water-cooled chillers?
   ✅ Air-cooled uses air to reject heat; water-cooled uses cooling tower water. Water-cooled is more efficient but needs more infrastructure.
4. What is delta-T in HVAC, and why is it important?
   ✅ Delta-T = Supply temp – Return temp. Shows how much heat is removed; affects chiller/pump performance.
5. Explain the function of the expansion valve in a refrigeration system.
   ✅ It drops refrigerant pressure and temperature before it enters the evaporator, enabling cooling.

🔹 System Types & Design

6. What is the difference between AHU and FCU?
   ✅ AHU is a large air-handling unit connected to ductwork; FCU is compact, installed in rooms, and serves individual zones.
7. What is a VAV system and where is it used?
   ✅ Variable Air Volume system adjusts airflow based on demand. Used in offices, malls, and hospitals.
8. What are the components of a ducted HVAC system?
   ✅ AHU/FCU, ducts, diffusers/grilles, dampers, and controls.
9. How do you perform cooling load calculations for a room?
   ✅ Based on area, orientation, occupancy, equipment, lights, and ventilation. Result is expressed in TR or kW.
10. Explain the difference between DX and VRF systems.
    ✅ DX uses refrigerant directly inside evaporator; VRF uses multiple indoor units with inverter outdoor unit, modulating refrigerant flow.

🔹 Piping & Pumps

11. What is the function of a decoupler in a chilled water system?
    ✅ It separates primary (chiller) and secondary (building) loops to prevent flow conflict.
12. What is the ideal velocity for chilled water in piping?
    ✅ Main line: 8–10 ft/s; branch line: 4–6 ft/s to reduce noise and erosion.
13. How do you size a chilled water pipe?
    ✅ Based on flow rate, velocity, and pressure loss using charts or software.
14. What is the difference between static and dynamic balancing?
    ✅ Static: manual valve setting; Dynamic: automatic valve adjustment (e.g., PICV).
15. What is a PICV (Pressure Independent Control Valve)?
    ✅ A valve that ensures constant water flow regardless of system pressure changes.

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