2. REFRIGERANT
A refrigerant is a substance used in refrigeration systems
to absorb heat in the evaporator, by changing state from a
liquid to a vapour and rejects this heat in the condenser as
it changes back to a liquid.
In principle, any fluid can be used as a refrigerant.
Air used in an air cycle refrigeration system can also be
considered as a refrigerant
3. Refrigerant selection criteria:
Selection of refrigerant for a particular application is based
on the following requirements:
Thermodynamic and thermo-physical properties
Environmental and safety properties, and
Economics
5. ODP & GWPOzone Depletion Potential (ODP):
Relative value that indicates the potential of a substance to destroy
ozone gas as compared with the potential of chlorofluorocarbon-11
(CFC-11) which is assigned a reference value of 1. Thus, a substance
with ODP of 2 is twice as harmful as CFC-11.
According to the Montreal protocol, the ODP of refrigerants
should be zero, i.e., they should be non-ozone depleting
substances
Global Warming Potential (GWP):
GWP of a refrigerant is an indicator of its potency to warm the
planet by action as a greenhouse gas
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.
6. SECONDARY REFRIGERANT Secondary refrigerants allow the amounts of
environmentally harmful primary refrigerants to be
minimized and contained in a restricted area.
Examples of secondary refrigerants include water, air,
hydrocarbons, ammonia and carbon dioxide, which are
more environmentally safe than traditional refrigerants
such as HCFCs.
They are safer (some are even incombustible and non-toxic)
and generally suitable for refrigeration systems.
7. Secondary refrigerants absorb heat and change temperature in
order to transfer heat from the substance or product to be
cooled.
They usually do not change state in the cooling cycle but
change temperature by absorbing sensible heat.
Secondary refrigerants should have a low freezing point, a low
viscosity, a high specific heat, and a high thermal conductivity.
Brines are often chosen as secondary refrigerants for large
refrigeration systems, such as those supplying supermarkets,
the most common brines being water-glycol solutions, water-
ethanol solutions and acetate solutions.
8. Solutions of salts in water, called refrigeration brines, are used
as secondary refrigerants.
Sodium chloride brine is employed for temperatures down to –
15°C;
Magnesium chloride brine, down to – 27°C;
Calcium chloride brine, down to – 45°C.
Antifreezes and Freons are used in low-temperature
refrigerating systems.
Aqueous solutions of propylene glycol are employed for
temperatures down to – 47°C;
Aqueous solutions of ethylene glycol, down to – 60°C;
Freon-30, down to – 90°C and Freon-11, down to – 100°C.
10. ECO-FRIENDLY REFRIGERANTS In the aftermath of the Montreal protocol HFC’s have
predominantly replaced CFC’s and HCFC’s.
Due to their high GWP, HFC’s are not a good replacement
solution.
The solution are the natural refrigerants :
Ammonia, Hydrocarbons and Carbon dioxide
ozone depleting
substance
developed countries developing countries
CFCs phased out end of 1995 total phase out by 2010
halons phased out end of 1993 total phase out by 2010
HCFCs total phase out by 2020 total phase out by 2040
11. HYDRO CARBONS Very promising non-halogenated organic compounds with
no ODP and very small GWP values
Their efficiency is slightly better than other leading
alternative refrigerants
Dominant in domestic market like household refrigerators
and freezers
Growing use in very small commercial systems like car air-
conditioning system and window air conditioners of low
charge
Examples: R170, Ethane, C2H6
R290 , Propane C3H3
R600, Butane, C4H10
R600a, Isobutane, C4H10
12. AMMONIA(NH3) ODP = 0
GWP = 0
Excellent thermodynamic characteristics: small molecular mass,
large latent heat, large vapour density and excellent heat
transfer characteristics
High critical temperature (132C) : highly efficient cycles at high
condensing temperatures
Its smell causes leaks to be detected and fixed before reaching
dangerous concentration
Relatively Low price
13. Some draw backs are,
Toxic
Flammable ( 16 – 28% concentration )
Not compatible with copper
Temperature on discharge side of compressor is higher
compared to other refrigerants
14. CARBON DIOXIDE (CO2)
ODP-0
GWP-1
Excellent thermophysical properties, leading to high heat transfer;
Efficient compression and compact system design due to high volumetric capacity;
Non-flammable and low toxicity;
Widely available at low cost.
Its high operating pressure provides potential for system size and weight reducing
potential.
Drawbacks:
Operating pressure (high side) : 80 bars
Low efficiency
