Refrigeration system

#This application claims priority to European Patent Application No. 19218293.9, filed Dec. 19, 2019, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of which in its entirety are herein incorporated by reference.

#The present invention relates to a refrigeration system and a method for operating a refrigeration system.

#As is well known, refrigeration or heating can be provided by a refrigeration system making use of the refrigeration cycle, in which a refrigerant fluid is compressed, cooled, expanded and then heated. In one common usage, where such a refrigeration system is used for satisfying a cooling load, the cooling of the refrigerant fluid is done via a heat rejection heat exchanger rejecting heat to the atmosphere and the heating of the refrigerant fluid is done via a heat absorbing heat exchanger that absorbs heat from an object to be cooled, such as a refrigerated space for low temperature storage, or an interior of a building to be occupied by people. In this way the refrigeration system can transfer heat from within the building to outside of the building even when the interior is cooler than the atmosphere. Alternatively, a refrigeration system can be used as a heat pump to satisfy a heat demand. In that case by the heat absorbing heat exchanger is used to absorb heat from a low temperature source, with the refrigeration circuit then rejecting heat to a higher temperature object that is to be heated. Once again this may be the interior of a building. In both cases a full or partial phase change of the refrigerant fluid can be used to increase the possible temperature differential between the heat rejection and heat absorption stages.

#Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

#FIG. 1 is a schematic diagram for a refrigeration system using a main refrigeration circuit and a buffer tank connected to the main refrigeration circuit; and

#FIG. 2 shows example plots of efficiency against charge level for various operating conditions.

#As seen in FIG. 1, a refrigeration system includes a compression device 12, a heat rejecting heat exchanger 14, an expansion device 18 and a heat absorbing heat exchanger 16 that together form a main refrigeration circuit. The main refrigeration circuit contains a refrigerant fluid and circulation of the refrigerant fluid via the compression device 12 enables the refrigeration system to utilise a refrigeration cycle (or heat pump cycle) to satisfy a cooling (or heating) load. In this example the compression device 12 is a compressor 12 for compression of gaseous refrigerant fluid, the heat rejecting heat exchanger 14 is a condenser for at least partially condensing the refrigerant fluid, the expansion device 18 is an expansion valve for expanding the refrigerant fluid, and the heat absorbing heat exchanger 16 is an evaporator for at least partially evaporating the refrigerant fluid. The refrigeration system may advantageously be arranged so that the fluid is fully condensed at the condenser 14, and fully evaporator at the evaporator 16. In many cases it is beneficial to avoid the presence of liquid at the inlet to the compressor 12.

#The example refrigeration system further includes a buffer tank 20 attached to the main refrigerant circuit in parallel with the expansion device 18. The buffer tank 20 provides a receiver/reservoir for the refrigerant fluid and is connected to the main refrigeration circuit via a first valve 22 for controlling flow to or from a higher pressure point on the refrigerant circuit and a second valve 24 for controlling flow to or from a lower pressure point on the refrigerant circuit. As shown in FIG. 1, in this example the buffer tank 20 is connected to the main refrigeration circuit in parallel with the expansion device 18, with fluid connections via the first valve 22 to a higher pressure point prior to expansion, and via the second valve 24 to a lower pressure point after expansion.

#The valves 22, 24 are controlled by a controller 26 in order to control the flow of refrigerant fluid between the main refrigerant circuit and the buffer tank 20. The controller 26 can also be used for control of other elements of the refrigeration system, such as the compressor 12. The valves 20, 22 are controlled to transfer refrigerant fluid between the main refrigerant circuit and the buffer tank 20 based on a measure of sub-cooling obtained from a sub-cooling sensor 28 in the main refrigerant circuit. In this example the sub-cooling sensor 28 is placed on a refrigerant fluid pathway between the heat rejecting heat exchanger (condenser) 14 and the expansion device (expansion valve) 18.