Absorption refrigeration cycles (ammonia-water, lithium bromide – hydrogen – water and others) are a thermally powered alternative to vapour compression refrigeration cycles. Unlike vapour compression cycles, absorption cycles do not rely on mechanical compressors, which are costly and require electricity to operate.
Absorption refrigerators have been in widespread use for many years. In fact, almost all early gas powered refrigerators were based on an absorption cycle. Nowadays, they are only commonly used in applications where electricity is scarce or supply is unreliable, such as propane powered fridges in caravans and mobile homes.
Vapour-compression cycles replaced absorption cycles in terrestrial refrigeration and air conditioning, as electricity (rather than gas) became the standard means of energy distribution.
There is renewed interest in absorption cycles for solar powered, and other thermally powered refrigeration and air conditioning systems, in the quest for lower fossil fuel consumption, and ‘off grid’ refrigeration, particularly in developing countries.
Some absorption cycles operate at two very different pressures, and employ a powerful pump to move liquid refrigerant from the low to the high pressure region. Although this pump is usually electric, it requires much less power than a compressor in a vapour-compression refrigeration cycle. Other absorption cycles operate intermittently, or at a single pressure, and only require a pump to circulate refrigerant.
In either case, NIFTE devices are particularly well suited to perform these tasks as they are also thermally powered, cheap to produce and highly reliable.