Air conditioning which is powered by solar thermal is another “green” alternative solution to the regular compressor air conditioning system which is costly and not eco-friendly. In fact for a regular compressor air conditioning unit we are going to incur more cost on electricity bill than the cost of the unit itself.

There are two types of technologies which could use solar thermal as the power source which are absorption cooling and adsorption cooling. Not limited to air conditioning system, both absorption and adsorption cooling technologies also could be used for freezer or refrigerator. Another benefit of these types of air conditioning systems is low noise comparing to the compressor air conditioning unit or refrigerator.

Absorption Air Conditioning or Cooling System

In absorption cooling system, any heat source could be used as its power sources either solar thermal, gasoline, diesel or waste heat from industries. Absorption cooling is not something new, the technology have been used for 150 years to make ice before the electric bulb was invented.

However as people are more conscious about environment, clean technology and renewable energy, the system is becoming more popular. The absorption air conditioning system has been installed in a number of green buildings around the world. It is also being installed in Masdar City, a green city in the UAE. Readers who might miss an article about green architecture or green building could read it at this link, The 5 Concepts of Green Architecture or Green Building.

Working Principle

Refrigerant with a very low boiling temperature, approximately less than −18 °C (or 0 °F) is used either in absorption or compressor air conditioning system. When refrigerant evaporates, heat is taken away and provides cooling in both systems. Refrigerant then changes back to liquid and the cycle is repeat providing continuous cooling effect in both systems.

Gas -> Liquid -> Gas …..

The main differences of absorption vs. compressor in cooling mechanism are:

• Refrigerant changes its form from gas to liquid need just heat and no moving parts.
• Compressor cooler (air conditioning) normally use an HCFC or HFC, while absorption refrigerators typically use ammonia or water.

The table below is the comparison of absorption vs. compressor air conditioning system.

Absorption Air Conditioning	Compressor Air Conditioning (Conventional)
Quiet	Noisy
Free renewable energy such as solar thermal or waste heat from industrial	Expensive electricity
Refrigerant changes its form from gas to liquid need just heat and no moving parts.	Noisy compressor
NH3 and H2O or Ammonia and WaterWater and Lithium BromideWater and Lithium Chloride	Typically CFC and HCFC  or other such as R22…(Ozone depletion potential and Global Warming issues)

The working principle for air conditioning and refrigerator is similar. The diagram below illustrates the process of the absorption cooling mechanism. The absorption cooling cycle can be described in three segments:

Evaporation

A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from the system.

Absorption

The gaseous refrigerant is absorbed and dissolved into another liquid. Then reducing its partial pressure in the evaporator and allowing more liquid to evaporate.

Regeneration

The refrigerant-laden liquid is heated, causing the refrigerant to evaporate out. It is then condensed through a heat exchanger to restock the supply of liquid refrigerant in the evaporator.

In the next article we are going to see more about other solar air conditioning system. Thanks for reading.