HVAC interview questions and answers

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 HVAC interview questions and answers


1. What is ASHRAE & ISHRAE? 

American Society of Heating Refrigeration and Air-conditioning Engineers.

Indian Society of Heating, Refrigerating and Air Conditioning Engineers.

2. What is COP and Relative COP?

 COP - Coefficient Of Performance

COP =Net Refrigeration Effect / Work Done Supplied

It is the parameter on which efficiency is compared to air-conditioning units.

It is calculated at 100% load.

Relative COP = ratio of actual COP and Theoretical COP

3. What Is Btu?

BTU = British thermal unit 

It is the unit in which air-conditioning capacity defined.

1 TR = 12000 BTU/hr


4.Explain Refrigeration cycle? Components that make a refrigeration system?.

Watch the video with detailed explanation.




5. What Our Air Conditioning System and its function? and type of air-conditioning system?



6. Which Gas used in  VRF?

R410a

7. What is VRV and VRF? 

http://learnhvac003.blogspot.com/2020/08/vrvvrf-overview.html




8.What is Ventilation and its type? Difference between vane axial and tube axial fan?



9. What are the Air Terminal Devices?



10. What are the Air control Devices?



11. What device measures humidity?

 Hygrometer

12. What type of unit used in the data centre?



13. Name the different types of material used for duct fabrication.



14. Who invented the air conditioner and when? 

Willis Carrier in 1902

15. What is TR?


16. What is a chiller and its type? Working of chiller?



17. What is AHU and its type?


18. What is Aspect Ratio?

It is the ratio between the height and length of the duct.

 Generally, we take 1:2 can vary with space and size up till 1:4.

19. What is VFD?

VFD - Variable frequency drive

it is used to control the speed of the motor by changing the frequency of power supply.

It is used for Chillers, Pump, fan and AHU etc. (use to control the RPM of pumps)


20. Temperature of water in the chilled water system?

It completely depends on design but generally in India we design at 7 to 12 ‘C

The outlet of a chiller - 6-7 ‘C

the inlet of AHU – 7 – 8‘C

The outlet of AHU – 10 - 11‘C

the inlet of Chiller - 13-14‘C


21. What are the primary pumps and secondary pumps?

Primary pump – Pump which supplies water from the chiller to building

Secondary Pump – Pump which supplies water from building to the chiller

22. What are duct heaters and why it is used?

 To provide heating in some specific areas.


23. What is VAV and its working?

 Pressure dependent & Pressure independent: - To control the flow of air and temp. (Variable air volume).

- Pressure dependent: - The volume of air supplied by the terminal unit varies depending upon the static pressure in the primary air duct.

 - Pressure independent terminal units: - have flow-sensing devices that limit the flow rate through the box. They can control the maximum and minimum cfm that can be supplied and are therefore independent of the SP in the primary air duct.


23. What is a 3-way valve and 2-way valve?

Where we will use them and why?

2-way valve = it will regulate the flow as per demand and it will be fitted in the return line.

3-way valve = if the AHU is closed and is running on min load then it will by-pass (Connected to BMS).

24. What are the Securities checking in chillers?

Flow switch, Chiller and Pump interlocking, High Pressure cut-out, Oil Pressure switch, High Suction superheat, Anti-Freez

25.How to find Weight of Duct?

Wt. in Kg = 8.0318 x Thickness x Perimeter = ____Kg.

 Where Perimeter of Duct = (W x D) ²/1000

26. What is CAV and VAV?

CAV - Constant air volume

 In cav , airflow remains constant and the temperature of air varies to meet thermal requirements.

VAV - variable air volume

In vav, airflow is varied to  at constant temperature

27. What is vapour compression cycle?

Vapor-Compression refrigeration or vapour-compression refrigeration system (VCRS), in which the refrigerant passes through phase changes, is one of the many refrigeration cycles and is the most widely used method for air-conditioning of buildings and automobiles.

 28. Types of condensor.

1. Air cooled

2. Water-cooled

3.  Evaporative 

29. What is approach temperature for a cooling tower?

The approach is the temperature of the water leaving the cooling tower minus ambient wet-bulb temperature.

Approach = Cold water temperature (Of cooling tower) - Ambient wet bulb temperature


30. What is Range temperature for Cooling tower.

The range is the difference between the cooling tower water inlet and outlet temperature.

Range = Hot water temperature - Cold water temperature 

31. What is cooling tower efficiency?

Efficiency = (Range / (Range + Approach))x 100

32. What is Kw/ton ?

It is to specify the amount of electrical power that is required for a certain power cooling.

33. What is IPLV?

IPLV indicate for integrated part-load value.

It is a rating by which chiller performance is described. It is developed by AHRI.

Commonly we use COPor EER to describe chiller performance which is calculated at 100% load. But practically if we check, chiller won't run at 100% load every time. It varies based on load. So it is very unfair to use COP or EER to describe the performance.

This is the reason we IPLV to determine the performance of chiller. It is calculated from chiller efficiency while operating at different capacity. It is calculated with chiller operating at 100%, 75%, 50%, 25%.

IPLV = 0.01*(COP at 100% load) + 0.42*(COP at 75% load) 

             + 0.45*(COP at 50%load) + 0.12*(COP at 25%load)

34.What is Fahu?

Fahu - Fresh air handling unit 

It is used to inject fresh air in confines space.


35. At which temperature Fahrenheit and Celsius are same ?

  - 40' C

36.Which gas is used to purge the refrigerant line during brazing ?

Nitrogen

37. How do we measure and control noise level ?

It us measured in DB by DB meter.

It can be controlled by acoustic.

Sound attenuators can also be used to reduce sound level.

38. How to control vibration in AHU, FAN and chiller ?

By using 

Vibration Isolator 

Rubber Pad 

Flexible bellow 


Thanks for giving your valuable time.


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