Last edited 13 Dec 2014

Absorption refrigeration in buildings

Refrigerants are used in buildings:

For heating, ventilation and air conditioning (HVAC) systems.
To provide cooling for refrigeration.
To provide cooling for industrial processes.

They provide cooling in a process that is essentially the same as that used in domestic fridges, based on either compression or absorption.

Absorption and compression refrigeration both work on a similar basis, in that a refrigerant boils at a low temperature and pressure, and is then is then pressurised, and condensed at a higher temperature and pressure. The process of condensing releases heat which is rejected.

In ‘conventional’ compression systems, a liquid refrigerant with a low boiling point absorbs heat from the body that is being cooled and boils in an evaporator to form a gas. The resulting gas is then compressed, which increases its temperature further. The gas is then condensed, releasing its latent heat which is rejected. The process then repeats.

However, whilst in compression refrigeration, the compression and refrigerant flow is achieved by an electrical compressor, in absorption refrigeration, compression is achieved by heating, and circulation is achieved absorbing the refrigerant into and absorber and by an electrical pump. This pump uses much less energy than a compressor.

The liquid refrigerant absorbs heat from the body that is to be cooled (in buildings this may be water that once cool is circulated back to the building) and the refrigerant evaporates at low pressure (in the ‘evaporator’). It is then absorbed into an absorber fluid and the refrigerant / absorber mixture is heated (in the ‘generator’). The refrigerant evaporates again, this time at higher temperature and pressure. The refrigerant is then condensed (in the ‘condenser’) and the heat rejected. The process is then repeated.

Double-effect absorption cooling repeats the process of heating and condensing with as second generator and condenser to increase cooling capacity.

The heat in absorption refrigeration can be gas powered, but absorption refrigeration is particularly suited to situations where ‘waste’, or other low-cost heat supply is available, such as; surplus heat from combined heat and power plant (CHP), heat from industrial processes, district heating, geothermal or solar thermal energy and so on.

Absorption refrigeration was first developed in France in 1850’s, but it was not commercially exploited until the 1920’s.

The most common combinations of refrigerant and absorbent fluid are:

Water absorbent and ammonia refrigerant.
Lithium bromide absorbent and water refrigerant.

Ammonia is not an ozone depleting gas or a global warming gas. However it is flammable and toxic so additional precautions are necessary in design and use.