Abstract: Methods are disclosed for defrosting an air source heat pump having a plurality of outdoor evaporators each comprising a number of coils each comprising fins and pipes. The heat pump comprises a defrost system that applies a defrosting medium to provide thermal energy to defrost the coils. The method includes: a) using at least one temperature sensor measuring at least one temperature of at least one of the coils of at least one of the outdoor evaporators; b) activating the defrost system and hereby performing several defrost processes each having a duration (Tdefrost) separated by a pause (Tpause) without defrosting, when the at least one temperature is below a predefined temperature value; c) using at least one temperature sensor to measure at least one outdoor temperature; and d) determining a maximum allowable pause time (Tpause, max) depending on the at least one outdoor temperature.

Abstract: A CO2 based system, such as a heat pump system or a refrigeration system, is disclosed. The system comprises a plurality of ejectors arranged in parallel. Each of the ejectors comprises a motive port and a suction port. Each of the ejectors has a fixed geometry. A first actuated ball valve is arranged in front of the motive port. A second actuated ball valve is arranged in front of the suction port. The system comprises a control unit arranged and configured to control the activity of the ball valves on the basis of one or more predefined criteria.