Abstract: A heat pump system includes a compression device 12, a heat rejecting heat exchanger 14, an expansion device 18 and a heat absorbing heat exchanger 16; wherein the expansion device 18 provides a controllable degree of expansion. The heat pump system is operated in accordance with a method including determining a temperature indicative of frosting conditions on an exterior surface of the heat absorbing heat exchanger 16; operating the heat pump system in a first mode if the temperature indicative of frosting conditions is above a threshold value, and operating the heat pump system in a second mode if the temperature indicative of frosting conditions is within a range of temperatures that is below the threshold value.

Abstract: A heat pump system includes a compression device 12, a heat rejecting heat exchanger 14, an expansion device 18 and a heat absorbing heat exchanger 16; wherein the expansion device 18 provides a controllable degree of expansion. The heat pump system is operated in accordance with a method including determining a temperature indicative of frosting conditions on an exterior surface of the heat absorbing heat exchanger 16; operating the heat pump system in a first mode if the temperature indicative of frosting conditions is above a threshold value, and operating the heat pump system in a second mode if the temperature indicative of frosting conditions is within a range of temperatures that is below the threshold value.

Abstract: Compressor systems for compression of refrigerant fluid are described. The compressor systems include first and second compressor elements each having a housing. An equalization line fluidly connects the first and second housings at suction sides in order to allow for equalization of pressure between the housings as well as flow of lubricant between the housings. An equalization valve on the equalization line is used to open and close the connection between the first and second compressor element housings. The compressor system is arranged for full load operation using both the first and second compressor elements as well as for part load operation in which one of the compressor elements is not utilized. The equalization valve is opened during full load operation and is closed during part load operation to thereby prevent movement of lubricant and/or refrigerant fluid between the first and second compressor element housings during part load operation.