REFRIGERATION

&
AIR CONDITIONING

REFRIGERANTS

AJAY KUMAR YADAV, PhD

Assistant Professor
Department of Mechanical Engineering
National Institute of Technology Karnataka, Surathkal
❖Introduction, definition of Ton of refrigeration, COP
❖Refrigerant properties,
❖nomenclature

✓ Food processing, preservation

✓ Chemical and process industries
✓ Pharma industries, preservation of blood, cells,
medicines
✓ Comfort air-conditioning
✓ Aircraft air-conditioning
✓ Cryogenics
Cooling, Refrigeration, Air-conditioning, Cryogenics

Cooling: A process of removing heat at any temperature. Ex.: cooling of liquid

metal at 1000 °C to 800 °C.
Refrigeration: A process of cooling of bodies or fluids to temperatures lower
than the surroundings (upto -150 °C).
“All refrigeration processes involve cooling, but all cooling processes need not
involve refrigeration”
Air-conditioning: A process of conditioning of air (temperature, humidity,
quality, velocity etc.). It may involve cooling or heating based on the
requirements. Ex: Winter air conditioning may require heating, whereas
summer air conditioning may require cooling.
Cryogenics:
KRYO +
VERY COLD GENERATION

A branch of science deals with the production and effects of very low temperatures
i.e., below 123 K. 3
 Heat engine, Refrigerator and Heat Pump
10-1

Objectives
The objective of a refrigerator is to remove heat (QL) from the cold medium;
the objective of a heat pump is to supply heat (QH) to a warm medium

(fig. 10-1)

TH

QH

QL

TC

Heat engine Refrigerator Heat pump

Some definitions
Ton of refrigeration: It is a heat removal capacity of a refrigeration plant which
is equivalent to produce one tonne of ice at 0 °C from water at 0 °C in 24 hours.
COP (Coefficient of Performance):
It measures the performance of a system, and widely used for refrigeration system
and heat pump.

𝐷𝑒𝑠𝑖𝑟𝑒𝑑 𝑜𝑢𝑡𝑝𝑢𝑡
COP = 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑖𝑛𝑝𝑢𝑡

For a heat engine,

𝑁𝑒𝑡 𝑤𝑜𝑟𝑘 𝑜𝑢𝑡𝑝𝑢𝑡

COP = = ƞ (named as efficiency)
𝐻𝑒𝑎𝑡 𝑖𝑛𝑝𝑢𝑡

For a refrigeration system,

𝑅𝑒𝑓𝑟𝑖𝑔𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑟 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑒𝑓𝑓𝑒𝑐𝑡 𝑅𝑒 𝑜𝑟 𝑄𝐶

COP = =
𝑁𝑒𝑡 𝑤𝑜𝑟𝑘 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑊

For a heat pump,

ℎ𝑒𝑎𝑡 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑟𝑜𝑜𝑚 𝑄𝐻
COP = 𝑁𝑒𝑡 𝑤𝑜𝑟𝑘 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑
= 𝑊
5
 10-3
Ordinary Household Refrigerator

(Fig. 10-4)
Çengel
Boles
Thermodynamics

Third Edition

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998

 Refrigerants
Classification:

7
Refrigerant nomenclature

8
Refrigerant nomenclature…

9
Refrigerant nomenclature…
Unsaturated hydrocarbon (alkene: CnH2n)

R 1XYZ:
1: for alkene
C = X+1
H = Y-1
Z=F
Remaining Chlorine/Bromine

Example:
HFO (Hydro-fluoro-olefin)
R1234:
C = 3; H = 2; F = 4, Cl = 0
Chemical formula will be: C3H2F4

R1234yf: CH2=CFCF3

R1234ze: CH2=CFCF3
 Refrigerant nomenclature…

HFO-1234yf
2,3,3,3-Tetrafluoropropene, HFO-1234yf, is a hydrofluoroolefin (HFO) with the
formula CH2=CFCF3. It is also designated R-1234yf as the first of a new class
of refrigerants, it is marketed under the name Opteon YF by Chemours and
as Solstice YF by Honeywell.
HFO-1234yf has a global warming potential (GWP) of less than 1, compared to
1,430 for R-134a and 1 for carbon dioxide.

HFO-1234ze

1,3,3,3-Tetrafluoropropene (HFO-1234ze(E), R-1234ze) is a hydrofluoroolefin. It

was developed as a "fourth generation" refrigerant to replace fluids such as R-134a,
as a blowing agent for foam and aerosol applications, and in air horns and gas
dusters. The use of R-134a is being phased out because of its high global-warming
potential. HFO-1234ze(E) has zero ozone-depletion potential (ODP=0), a very low
global-warming potential (GWP < 1 ), even lower than CO2, and it is classified by
ANSI/ASHRAE as class A2L refrigerant (lower flammability and lower toxicity).
11
 Refrigerant selection criteria/Refrigerants properties
Selection of refrigerant for a particular application is based on the following
requirements:
i. Thermodynamic and thermo-physical properties,
ii. Environmental and safety properties, and
iii. Economics

Thermodynamic and thermo-physical properties:

The requirements are:

a) Suction pressure: At a given evaporator temperature, the saturation pressure

should be above atmospheric for prevention of air or moisture ingress into the
system and ease of leak detection. Higher suction pressure is better as it leads to
smaller compressor displacement.

b) Discharge pressure: At a given condenser temperature, the discharge pressure

should be as small as possible to allow light-weight construction of compressor,
condenser etc.

c) Pressure ratio: Should be as small as possible for high volumetric efficiency and
low power consumption
12
 Thermodynamic and thermo-physical properties…

d) Latent heat of vaporization: Should be as large as possible so that the required mass
flow rate per unit cooling capacity will be small.
e) Isentropic index of compression: Should be as small as possible so that the temperature
rise during compression will be small.
f) Liquid specific heat: Should be small so that degree of subcooling will be large leading
to smaller amount of flash gas at evaporator inlet.
g) Vapour specific heat: Should be large so that the degree of superheating will be small.
h) Thermal conductivity: Thermal conductivity in both liquid as well as vapour phase
should be high for higher heat transfer coefficients.
i) Viscosity: Viscosity should be small in both liquid and vapour phases for smaller
frictional pressure drops.
j) The freezing point of the refrigerant should be lower than the lowest operating
temperature of the cycle to prevent blockage of refrigerant pipelines.
13
 Environmental and safety properties:

a) Ozone Depletion Potential (ODP): According to the Montreal protocol, the ODP of
refrigerants should be zero, i.e., they should be non-ozone depleting substances.
Refrigerants having non-zero ODP have either already been phased-out (e.g. R 11, R
12) or will be phased-out in near-future(e.g. R22). Since ODP depends mainly on the
presence of chlorine or bromine in the molecules, refrigerants having either chlorine
(i.e., CFCs and HCFCs) or bromine cannot be used under the new regulations.

b) Global Warming Potential (GWP): Refrigerants should have as low a GWP value as
possible to minimize the problem of global warming. Refrigerants with zero ODP but a
high value of GWP (e.g. R134a) are likely to be regulated in future.

c) Total Equivalent Warming Index (TEWI): The factor TEWI considers both direct
(due to release into atmosphere) and indirect (through energy consumption)
contributions of refrigerants to global warming. Naturally, refrigerants with as a low a
value of TEWI are preferable from global warming point of view.

d) Toxicity: Ideally, refrigerants used in a refrigeration system should be nontoxic.

However, all fluids other than air can be called as toxic as they will cause suffocation
when their concentration is large enough.
 Environmental and safety properties…
e) Flammability: The refrigerants should preferably be non-flammable and nonexplosive.
For flammable refrigerants special precautions should be taken to avoid accidents. Based
on the above criteria, ASHRAE has divided refrigerants into six safety groups (A1 to A3
and B1 to B3). Refrigerants belonging to Group A1 (e.g. R11, R12, R22, R134a, R744,
R718) are least hazardous, while refrigerants belonging to Group B3 (e.g. R1140) are most
hazardous.
Other important properties are:
f) Chemical stability: The refrigerants should be chemically stable as long as they are
inside the refrigeration system.
g) Compatibility with common materials of construction (both metals and nonmetals)
h) Miscibility with lubricating oils: Oil separators have to be used if the refrigerant is not
miscible with lubricating oil (e.g. ammonia). Refrigerants that are completely miscible with
oils are easier to handle (e.g. R12). However, for refrigerants with limited solubility (e.g. R
22) special precautions should be taken while designing the system to ensure oil return to
the compressor.
i) Dielectric strength: This is an important property for systems using hermetic
compressors. For these systems the refrigerants should have as high a dielectric
strength as possible.
j) Ease of leak detection: In the event of leakage of refrigerant from the system, it should
be easy to detect the leaks.
 Economic properties:
The refrigerant used should preferably be inexpensive and easily available.

Comparison between different refrigerants:

Comparison between different refrigerants:

17
Comparison between different refrigerants:

18
References:
1. M. Ramgopal, NPTEL Lecture on Refrigeration and Air-conditioning, IIT Kharagpur, India.
2. Thermodynamics- An Engineering Approach in SI units by Yunus A. Cengel, Michael A.
Boles, TATA McGraw Hill.
3. Engineering Thermodynamics by P.K. Nag, TATA McGraw Hill.
4. Fundamentals of Thermodynamics by Sonntag, Borgnakke and Van Wylen.
5. Internet resources.

Dept. of Mech. Engg., NITK

BAZ

19