Refrigerant is a working substance in

refrigeration. There are many types of

refrigerants. Each is for a certain specific

purpose. Refrigerants ammonia, R-134a

and air are in common use. Their

selection depends upon many factors. It

should have least ozone depletion

and Global warming potential. An

azeotrope forms from two or more

refrigerants. These posses special

properties. These behave as pure


Q. What is a refrigerant? What are types of refrigerants?

Refrigerant is a working substance in a refrigeration system. It absorbs heat at low temperature. It loses heat to the surroundings at high temperature. Compressor produces this high temperature. The refrigerant is of three types:

(i) Primary refrigerant evaporates, compressed, condensed and expanded in a vapor compression refrigeration system. Ammonia, R-22, R-134 a and air are primary refrigerants 

(ii) Secondary refrigerant cools the products or space. Primary refrigerant cools the secondary refrigerant. Air in a fridge & window air conditioner, brine solution in an ice plant are secondary refrigerants.

(iii) Tertiary refrigerant cools the products or space. Primary refrigerant cools the secondary refrigerant. Secondary refrigerant cools tertiary refrigerant. For example in a central air conditioning system, chilled water is the secondary refrigerant. Tertiary refrigerant is air.


1.    Organic refrigerants

Organic refrigerants are of two types.

(a)  Saturated hydrocarbons and their derivatives: Methane, ethane, propane,

CH3Cl, CH2Cl2, CH3Cl, CH2ClF, CHCl2F etc.

(b)  Unsaturated hydrocarbons and their derivatives

C2H4, C3H6, C4H8, C2H3Cl

2.Inorganic refrigerants

Air, water, carbon dioxide, ammonia

3. Mixed refrigerants

A mixture of two or more components in certain proportion, 50 % of R-22 and 50 % of R-12

4.  Azeotrope

It is a refrigerant consisting of two or more components in a fixed proportion and behaves as a pure refrigerant. It  evaporates and condenses at fixed temperatures. R 500, R-501, R-502& R-503 are azeotropes.


1.Classification on the basis of inflammability by National Refrigeration Safety Code

There are three groups.

(i)  Group 1  —-Safest of the refrigerants like R-113, R-11, R-12,R-22,R-13

(ii) Group 2—–Toxic and somewhat inflammable like R-1130, R-764 & R-717

(iii)Group 3 —–Inflammable refrigerants like R-600, R-601, R-290, R-170, R-50

2.Classification of refrigerants on the basis of toxicity 

It is done by  National Board of Fire Underwriters. There are six classes on the basis of toxicity. Class one is most toxic and class six is least toxic.

(i) Class 1—- Sulphur Dioxide

(ii)Class 2—-Ammonia

(iii)Class 3—Methyl format

(iv)Class 4—R-113, R-160

(v) Class 5—R-744, R-22

(vi)Class 6—R-12, R-134 a, R-500, R-502

Enumerate the desirable properties of refrigerants commonly employed in refrigeration and air conditioning applications.


  1. Lower boiling point 

  2. Higher working pressure 

  3. Lesser specific volume at evaporator pressure


  1. Lower freezing point,

  2. High latent heat,


  1. Non-toxic, Non- inflammable, Non corrosive, Non-decomposable, Inert,

  2. Chemically inert with the material of construction

  3. Inert with the lubricant


  1. Cheap,

  2. Easily available in abundance,

  3. Available everywhere,

  4. Less work input,

  5. Minimum running charges,

  6. High COP,

  7.  Less leaking tendency, 

  8. Leakage easily detectable, Leakage does not spoil the products

  Discuss the detail the various thermo-physical properties of the refrigerants.

 Various thermo-physical properties are

(i)  Lower normal boiling point 

(ii) High latent heat

(iii) Low Specific volume at inlet to compressor

(iv) Pressures in evaporator and condenser must be above atmospheric to avoid vacuum operation.

(v) Less power requirements

(vi)  Lower Viscosity

(vii) High Specific heat of liquid and vapor

(viii) High Thermal conductivity

 List antifreeze solutions commonly used in refrigeration and air conditioning systems.

These do not freeze quiet at very low temperatures. Antifreeze solutions are liquid salt solutions. Various anti-freeze solutions:

  1.  Sodium chloride solution (-30C)

  2. Calcium chloride solution (-55C)

  3. Glycerin solution               (-50C)

Q. Explain CFC refrigerants.

 CFC are Chloro-fluoro hydrocarbons like R-12, R-11.

Less  toxic, non-corrosive, non- flammable and non-explosive

Harmful to environment

 Q. Explain HCFC refrigerants.

 HCFC Refrigerants like R-22

Halogenated methane/ethane with one or more hydrogen.  These Cause less ozone depletion and less global warming. Use these as replacements. As per EPA, phase out these by 2030.

 Q. Explain HFC Refrigerants.

HFC Refrigerants are like R-134a. These contain one or more hydrogen atoms & no chlorine atoms. These have no ozone depletion potential and very little global warming. Use these in new systems specially designed for their use. These use only synthetic lubricating oils.

Q. What do you understand by the term Azeotropes? Compare the performance of Azeotropes with CFCs and HCFCs?

 Azeotropes is a mixture of two or more refrigerants in a certain fixed proportion by mass.  This mixture is the azeotrope. It behaves as a pure substance with better properties. 500 series numbers are for azeotropes. First azeotrope is R-500. Next is R-501, R-502 and R-503.

Components (% by mass)
R-12/R152, (73.8/26.2)
– 33.30C
R-22/R-115   (75/25)

Advantages of Azeotropes

(I) Their normal boiling point less.
(ii) Has more cooling capacity.

Disadvantages of azeotropes

(I) Azeotropes are more costly.
(ii) Freon (CFC mixtures) mixtures behaving as azeotropes have lower latent heat
(iii) Azeotropes do not have advantage over HCFC refrigerants.
(iv) Azeotropes cause Global Warming & Ozone Depletion.

Q. List the safety devices / safety precautions for a refrigeration unit?

Low voltage: Use a low voltage cut out and cut-in.
High voltage: use a high voltage cut-out and cut-in.
Insufficient refrigerant : Check for leakage if any, repair leakage and fill more refrigerant
Voltage fluctuations: Use a voltage stabilizer
High current:  Use Overload protector.
Freezing : use defrosting timer or heater for automatic defrosting after a fixed interval
Moisture in the unit: Use Silica gel
Annual maintenance contract of service for indoor & outdoor units.
 Safe refrigerants
There is risk in using refrigerants in refrigeration. Toxicity, flammability and physical hazards pose risks.   Proper system design and control minimizes the risk.  Take extreme care using it. Propane is highly inflammable. Ammonia is highly toxic. These are cheap. These do not cause ozone depletion and global warming.  Ammonia gives the highest cooling effect too.

Precautions in safe handling of refrigerants

Refrigerants are low boiling substances. In cylinders, these are in liquefied form. These need extreme care as these can cause cold burning. Store refrigerant cylinders in cool place to avoid bursting. There are EPA regulations regarding safe handling of refrigerants.

Mention the salient features of maintenance for the safety of a refrigeration unit.

Lubrication of moving parts like blower & condenser fan
Protection from high humidity
Cleaning of filters
Cleaning of Condenser and evaporator
Clean drain pipes
Do not use straight pipe > 15 m
keep least number of bends and no kinks
Ensure oil return to compressor
Provide adequate  fresh air
Use labelled Flouring
No cross wiring
Top up of refrigerant
Use of nitrogen in brazing
Evacuation and dehydration of entire unit
Pressure testing for leakage with nitrogen

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