Heat pump able to operate with very low external temperature

A heat pump comprising

• first and second absorption devices each having an evaporator (1;1A), an absorber (2;2A) containing a steam absorbing liquid to form a dilute solution, a generator (3;3A), a heating element (11;11A) for boiling absorbing liquid in the generator with the formation of steam and a condensing heat exchanger (11;13, E15) for condensing the steam, whereby the pressure present in the first generator (3) is less than the pressure present in the second generator (3A)
• means for maintaining within the evaporator (1) and absorber (2) of the first device a pressure less than that within the evaporator (1A) and absorber (2A), respectively, of the second device, comprising a first syphon connected between the evaporators (1,1a) and second syphon connected between the absorbers (2,2A),
• a fluid conduit for withdrawing the liquid present in the second evaporator (1A) by a pump (P7), passing it through a heat exchanger (5A) for absorbing heat and returning it to the second evaporator (1A),
• a fluid conduit for withdrawing dilute solution from the absorbers (2,2A), mixing a portion thereof and feeding the mixed dilute solution by a single pump (P1) to the second generator (3A) and to the first generator (3) in succession,
• fluid conduits for returning the condensed liquid from the condensing heat exchangers (11;13,E15) to the evaporators (1,1A),
• fluid conduits for connecting the generators (3A) and to the first generator (3,3A) to the absorbers (2,2A) to feed them with the concentrated absorbing liquid after cooling it in heat exchangers (10,10A) in which the dilute liquid originating from the absorbers (2,2A) is heated,
• an external heat source for the second heating element (11A) an
• a solution of low freezing point in the first evaporator (1).