An absorption heat pump having a generator, a heat source to heat the generator to drive coolant vapor out of solution, a condenser for cooling the coolant vapor and an expansion valve that expand the coolant fluid as well as an evaporator for at least partial evaporation of the expanded coolant fluid against a medium which is connected to at least one absorber which absorbs the expanded coolant fluid. A hot gas line which branches off from a line for coolant vapor upstream of the condenser and is fluid-connected to the evaporator such that it bypasses the condenser and the expansion valve, a defrosting valve being provided in the hot gas line, by means of which the flow of coolant vapor through the hot gas line can be controlled. The absorption heat pump is operated in a cyclic circulation process.

One aspect presents a controller that comprises a control board, a microprocessor located on and electrically coupled to the control board, and a memory coupled to the microprocessor and located on and electrically coupled to the control board. The controller is configured to receive an operating parameter signal and recalculate a first maximum heating % demand to a second maximum heating % demand that is greater than the first maximum heating % demand, when a value of the operating parameter signal exceeds a predetermined value, and operate the HP system based on the second maximum heating % demand.

Disclosed are embodiments of heat pump systems and methods for operating such systems in the heating mode while a heat pump operating parameter reaches or is equal to a predetermined operating value at which it is not advisable to use conventional heat pump systems for heating an enclosed structure. In addition to ancillary components, the heat pump systems includes indoor, outdoor and auxiliary heat exchangers, reversing and flow diverting valves, compressors, refrigerant superheat controllers, and auxiliary energy sources. During the heating mode of operation, while the heat pump operating parameter reaches or is equal to the predetermined operating value, the flow of liquid refrigerant through the outdoor heat exchangers is inhibited and is diverted to flow through the auxiliary heat exchangers. Thermal energy from the auxiliary energy source is used for evaporating the liquid refrigerant flowing through the auxiliary heat exchangers.