Solar Refrigeration

Prepared by M.Devakumar

What is Refrigeration?Refrigeration is a process in which work is done to move heat from one

location to another.

Where it is uses:To provide refrigeration for food and medicine preservation. To provide comfort cooling.

Solar Refrigeration:

Refrigerator which runs on electricity provided by Solar Energy is known as solar refrigeration.

Solar-powered refrigerators may be most commonly used in the future generation.

Developing the world to help mitigate poverty and climate change.

Types of Refrigeration:

Refrigeration systems is broadly classified into two types:

• Vapour Compression Refrigeration (VCR)(uses mechanical energy).

• Vapour Absorption Refrigeration (VAR)(uses thermal

energy).

Vapour Compression Refrigeration:

• Highly compressed fluids tend to get colder when allowed to expand.

• If pressure high enough,

Compressed air hotter than source of cooling

Expanded gas cooler than desired cold temperature

Condenser

Evaporator

High Pressure

Side

Low Pressure

Side

CompressorExpansion Device

1 2

3

4

Refrigeration cycle

Type of refrigerant:

• Refrigerant determined by the required cooling temperature.

• Chlorinated fluorocarbons (CFCs) or freons: R-11, R-12, R-21, R-22 and R-502.

Two advantages:• Lot of heat can be removed (lot of thermal energy

to change liquid to vapour)

• Heat transfer rate remains high (temperature of working fluid much lower than what is being cooled)

Vapour absorption Refrigeration:

• The vapor absorption refrigeration system comprises of all the processes in the vapor compression refrigeration system like compression, condensation, expansion and evaporation.

• In the vapor absorption system the refrigerant used is ammonia, water or lithium bromide.

• The refrigerant gets condensed in the condenser and it gets evaporated in the evaporator.

• The refrigerant produces cooling effect in the evaporator and releases the heat to the atmosphere via the condenser.

Condenser Generator

Evaporator

AbsorberCold Side

Hot Side

Refrigeration cycle

Advantages of vapour absorption cycle:

(i) Moving part is pump(ii) Reduced vaporization pressure & temperature(iii) Load variation does not affect performance(iv) Capacity > 1000 T, 30TR 91% electricity saves.

Disadvantages of vapour absorption cycle:

(a) Efficiency is low(b) Takes long time to produce cooling effect(c) Kerosene/oil/gas flame gives bad smell.

Solar Refrigeration:

Refrigerator which runs on electricity provided by Solar Energy is known as solar refrigeration.

Solar-powered refrigerators may be most commonly used in the future generation.

Need of solar refirgeration:

• Need refrigeration in areas not connected to power grid• Need to minimize environmental impact and fuel cost• Evaluate potential of solar energy to meet these needs• Evaluate efficiencies of three types of solar refrigeration

Types of solar refrigeration:

• Photovoltaic Operated Refrigeration Cycle• Solar Mechanical Refrigeration• Absorption Refrigeration

Solar cooling can be considered for two related processes:

To provide refrigeration for food and medicine preservation and

To provide comfort cooling.

Photovoltaic Operated Refrigeration Cycle:

Vapor compression cycle with power input from Photovoltaic cells.

DC electric power output from PV runs the compressor of a conventional cycle

Considerations:Must match voltage imposed on PV array to the motor

characteristics and power requirements of the refrigeration cycle For given operating condition (solar radiation and module

temperature), single voltage provides maximum power output.Must find compressor motor closely matched to the electric

characteristics of the PV module.

Schematic view of a conventional vapor compression cycle driven by solar photovoltaic:

Solar Mechanical Refrigeration

Vapor compression cycle with power input from solar Rankine cycle.

Considerations:

• Efficiency optimization based on delivery temperature• Efficiency of Rankinecycle increases with increased heat

exchanger temperature • Efficiency of solar collector decreases with increase in

temperature.

Solar driven mechanical power cycle:

Absorption Refrigeration:

• Condenser, throttle, evaporator function exactly the same way.

• Replaces compressor with “thermal compression system”.

• Ammonia is working fluid

• Minimal mechanical power input (pump instead of compressor).

• Absorption into water solution allows it to be pumped.

• Desorbed in generator (rectifier required to separate out water).

• Heat into generator provided by solar collectors.

• The pressurisation is achieved by dissolving the refrigerant in the absorbent, in the absorber section.

• Subsequently, the solution is pumped to a high pressure with an ordinary liquid pump.

• In this way the refrigerant vapour is compressed without the need of large amounts of mechanical energy that the vapour-compression air conditioning systems demand.

• This system greatly increases complexity.

Schematic view of a absorption refrigerator driven by heat from solar radiation:

Benefits:• Environmentally friendly• Longevity• Scalable

Application of solar refrigeration:

• Solar energy should be given a chance if we want to protect the environment. • We own it to our children, our grandchildren

and the generations to come.• Refrigerators• Freezers• Ice-makers• Coolers• Building air-cooling systems

Conclusion:

• COP for solar refrigeration systems is low• Better metrics: size, cost• Complexity of solar ref. systems requires

more size, bulkiness• Low operating costs do not outweigh high

initial investment• Advantage is that they don’t rely on

power grid (PV is most practical for small scale)

Thank you for your attention,any questions please….....