Other cycles
Absorption chillers and heat pumps- ammonia-water systems. Technology

The cycles described above all require a pump to circulate the rich solution from the low-pressure part (evaporator/absorber) to the high-pressure part (desorber/condenser). As a result, these systems all consume electrical energy, albeit in small quantities (around 5% of cooling power), but requiring the presence of an on-site power source. To eliminate the need for a pressurizing pump, H. Geppert proposed in 1899 (US Patent 666.690) to add an inert gas (he suggested air) in the low-pressure section, in order to equalize the total pressures prevailing in the "evaporator/absorber" and "desorber/condenser" assemblies. Circulation of the rich solution from the absorber to the desorber, and then of the lean solution from the desorber to the absorber, can then be achieved...