How it works


The Technical Bit


Absorption refrigeration systems have been used for many decades as a simple means of producing silent, low cost, reliable cooling from any available heat source. They are not much used in the present day because the competing Rankine-cycle system is more energy efficient (although it usually requires an electrical supply).


We elected to use an ammonia absorption system, for the following reasons:


  1. •It is able to convert thermal energy to cooling directly, and in the range of temperatures achievable by solar collectors (with some modification).

  2. •It is low cost.

  3. •Very basic materials are used, none of which are in any way likely to be in short supply, even in developing countries.

  4. •It can be manufactured without the need for very expensive production machinery.

  5. •It has no moving parts.

  6. •It uses no electrical power.

  7. •It is very reliable and will work without any maintenance for many decades.

  8. •Globally-available refrigerant (ammonia).


There is only one drawback to the system and that is energy efficiency.  Other absorption systems are more efficient, however they are also larger, more complex, and have many more components, making them more expensive.  Solar-Polar’s system is much simpler and designed to be cheap to produce, giving it a much much lower cost per Watt of cooling, combined with zero carbon emissions.


The operation (Figure 1) is based on an evacuated tube solar collector (shown bottom right). Sunlight enters the transparent envelope of the evacuated tube and is trapped there by the greenhouse effect, and the very effective insulation of the vacuum envelope. Inside the tube is a heat pipe, with an appropriate phase-change material within it. The operation of the heat pipe heats the bulbous end of the pipe and the insulated heat transfer medium surrounding it. The heat transfer medium in turn heats the generator chamber of the ammonia system and boils ammonia gas out of the strong solution in the chamber. Gas and diluted solution are then forced up the exit tube in much the same way as a coffee percolator works. At the top of the tube is a separator chamber where the gas and liquid part company. The hot ammonia gas passes up into a condenser and changes to pure ammonia liquid.




Figure 1 - Basic system operation


The ammonia liquid flows through a gas trap into a hydrogen atmosphere where its partial vapour pressure causes it to evaporate, absorbing heat from the surrounding air through the evaporator. The cold gaseous ammonia descends to a point where it can recombine with the weakened solution from the separator. The resulting strong solution then flows down to a reservoir where it is fed back into the generator.


Surrounding the evaporator is a chamber where a naturally convecting stream of air is cooled by the evaporator. Excess humidity in the air is also removed in the evaporator chamber.