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Top HVAC Basic Interview Question and Answers (With PDF File)



What is refrigerator?
Ans :- Refrigerator is a equipment used to producing and maintaining the temperature in a closed space below the surrounding atmospheric temperature.

What is refrigerant?
Ans :-Refrigerant is the working fluid in a refrigerator.
It will absorb heat at a lower temperature and rejects the heat at a higher temperature in the form of latent heat.

What are the Properties of refrigerants ?
Ans :-
1. Low Boiling Point .
2. Low Freezing Point.
3. High Latent heat Evaporation.
4. High Co-efficient of performance.
5. Odourless and colourless.
6. In-flammability.
7. Non-corrosiveness.


What are the Type of refrigerant gases ?
Ans :-
1. Freon gases.
a) R12, R21, R22, R502 (Non Eco friendly gases)
b) R134a, R404a, R410a, R407a, R407C, R507a (Eco friendly gases)
2. Ammonia (NH3).
3. Carbon Di-oxide (CO2)
4. Air.
Notes:-
1. Freon gases - Its used for industrial HVAC Equipment like Chiller, PAC, Split and Windows A/C (Its mainly used for vapour compression system).
2. Ammonia (NH3) - Its used in the ice manufacturing and cold storage plants.(Its mainly used for vapour absorption system plants.)
3. Carbon Di-oxide(CO2) - Its used in the Marine refrigerator .
4. Air:- Its used in the aircraft.

What is Air conditioning system?
Ans :-It is defined as the simultaneous control of the temperature of air, Humidity of air, purity of air and motion for the purpose human comfort, food processing and other industrial purposes.
A/C Cyclic Order :-
1. Compressor.
2. Condenser.
3. Expansion Valve.
4. Evaporator. 

What are the Types of Compressor's ?
Ans :-
1. Centrifugal Compressor.
2. Screw Compressor.
3. Scroll Compressor.
4.Reciprocating Compressor.
5. Rotary Compressor.
Note :- 
a) Centrifugal,Screw,Scroll these are all high capacity and high energy efficiency compressor.
b) Reciprocating and Rotary these are all low capacity and low energy efficiency compressor.

Name Few Compressor Oil's ?
Ans :-
1.P.O.E (Polyolester Oil)
2.It's a type of synthetic oil used in refrigeration compressor that is compatible with the refrigerants like R134a, R410a , R12 etc...

What are the Types of Condenser's ?
1.Air cooled Condenser
2.Water cooled Condenser.

What are the Types of Expansion valve's ?
Ans :-
1. Automatic Expansion Valve(Solenoid valve).
2. Thermostatic Expansion Valve.
3. Capillary Tube.
4. Float Valve.


What are the Types of Evaporator ?
Ans :-
1. Vertical falling film evaporator.
2. Horizontal film evaporator.
3.Atmospheric forced draft evaporator.
4. Low temperature vacuum evaporator.
5. Mechanical vapour recompression (MVR) evaporator.
Based on the construction :-
1. Bare tube evaporator.
2. Plate type of evaporator.
3. Finned evaporator.
4. Shell type evaporator.
5. Tube type evaporator.

What are the Types of A/C Filters ?
Ans :-
1. Pre Filter.
2. Hepa Filter.
3. Ulpa Filter.
4. Fine(Microvee) Filter.
5. Mini Pleat Filter.
6. Carbon Filter.
7. Bag (Packet) Filter.
8. Micron Filter Etc..

Materials used to make Filter Frame ?
Ans :-
1. MS Painted 
2. G.I
3. Aluminium.
4. Wooden
5. Carton.
6. PVC
7. Stainless Steel etc...

What is Humidity ?
Ans :-Humidity is defined as the moisture content present in the atmospheric air. The atmosphere always contains some moisture in the form of water vapour.

Humidity Types ?
Ans :-
1. Relative humidity.
2. Specific or Absolute Humidity.

How to control Humidity at atmosphere ?
Ans :-The control of humidity of air means the increasing and decreasing of moisture contents of air during summer and winter respectively.

What is Temperature Index (T.H.I) ?
Ans :-It is also termed as discomfort index.Its expresses in numeric values the relationship between comfort or discomfort temperature and humidity. It is felt that T.H.I at 20° provides a comfortable atmosphere.

What is Dry Bulb Temperature (D.B.T) ?
Ans :-Dry bulb temperature is the atmospheric air temperature recorded by a thermometer whose bulb is exposed to the atmosphere.

What is Wet bulb Temperature (W.B.T) ?
Ans :-It is defined as temperature of air measured by a thermometer when its bulb is covered with wet cloth and is exposed to a present of air.


General Types of Air Conditioners ?
Ans :-
1. Direct Expansion :-
a) PAC
b) Split A/C.
c) Windows A/C.
Note :- Its using cooling medium is refrigerant gases like R12,R22,and R410a etc.
2.Indirect Expansion :-
a) AHU.
b) Chillers.
Note :- Its using cooling medium is water.

Types of Refrigerating System ?
Ans :-
1. Vapour Compression refrigeration system.
2. Vapour absorption refrigeration system.

Vapour compression refrigeration system :-

S- Suction line
D – Delivery line.
Vapour compression refrigeration system :-


What is Air Handling Unit (AHU) ?
Ans :-It is take's in outside air then after recondition it and supply it as fresh air to a Building.
Construction and working :-
Image pending
Note :-
AHU Inlet temp - 12°c.
AHU Oulet Temp - 14°c.
AHU Inlet Pressure - 3.5Kg/cm2
AHU Outlet Pressure - 4.5 Kg/Cm2




What is Chiller ?
Ans :-It is machine which is used to removing heat from a liquid via vapour compression or vapour absorption refrigeration cycle.



Notes :-
Chiller Inlet temp - 8°
Chiller Outlet temp - 12°
Chiller Inlet Pressure - 60 Psi
Chiller Outlet Pressure - 160 Psi
These Compressor is a heavy duty chiller compressor this is having a temperature cut in-cut out setting of 8°C-12°C when the compressor is running it is having a suction pressure of 60 Psi and discharge pressure of 160 Psi but as soon as it cuts off discharge pressure equalizes with the suction pressure and comes to 120 Psi .

Basic Calculation & Formulas :-
1. º C = 5/9(ºF-32) = 33.80ºF
2. ºF = 9/5 C+32 = -17.22 º C
3. 1METRE = 3.281 FEET
4. 1 FEET = 0.3048 METRE
5. 1Inch = 2.54cm
6. 1Inch = 25.4mm
7. 1K.JOULE = 0.9478 BTU
8. 1 K.WATT = 1.341 HP
9. 1 WATT = 3.415 BTU/Hr
10. 1 calorie/sec = 14.286 BTU/hr
11. 1 K.PASCAL = 4.0186 IN H2O = 0.3349 FT H2O  = 0.145 Psi = 0.01 bar
12. 1 metre2 = 10.764 ft2
13. 1 metre3 = 35.3146 ft3
14. 1 metre/sec = 196.85 FPM
15. 1 metre3/sec = 2119 CFM
16. 1m/hr = 0.5886 CFM
17. 1 Litre/ sec = 2.119 CFM
18. 1 Litre/ sec = 15.85 GPM
19. 1 Kg = 2.205 lbs
20. 1 TR = 12000 Btu/hr=3.517 kw= 3000 k cal/ hr


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