Heat cycle system and method of operating heat cycle system

Abstract

A heat cycle system, comprises a working fluid, which is cycled through a circuit comprising a compressor (10), a condenser (11a, 11b), an expander unit (130), and an evaporator (14). The expander unit (130) is configured to generate a rotating mechanical motion. The expander unit (130) is connected between an outlet of the condenser (11a, 11b) and an inlet of the evaporator (14). A working fluid pressure drop over the condenser is less than about 5 bar.

Description

[0001] HEAT CYCLE SYSTEM AND METHOD OF OPERATING HEAT CYCLE SYSTEM

[0002] Technical field

[0003] The present disclosure relates to a heat cycle system, for application in a cooling system, and to a method of operating a heat cycle system.

[0004] Background

[0005] Heat cycle systems operating according to cyclic heat processes, such as a Carnot process, are used in many applications.

[0006] In some applications, the objective is to provide heat, such as in heat pump systems that are used to heat a space by picking up heat from ground, bedrock, water or air and supplying the heat to a heating system for the space.

[0007] In other applications, the objective is to remove heat, i.e. to cool something, such as in air conditioning systems or in cooling / refrigeration systems, the objective is to remove heat from a space or from an object.

[0008] In the Carnot process, energy is input in the form of heat Q picked up by the evaporator and in the form of mechanical energy W supplied by the compressor. The mechanical energy may be provided by a conversion of electric energy by an electric motor. Furthermore, energy is output in the form of heat QH provided by the condenser. A heating coefficient of performance (COPH) is defined as QH / W and a cooling coefficient of performance (COPC) is defined as OC / W.

[0009] Fig. 1 schematically illustrates a conventional heat cycle system, in which is circulated a working fluid.

[0010] The system comprises a compressor 10 having a compressor input where the working fluid is in a first state with a first pressure Pl, a first temperature T1 and a first enthalpy Hl, and a compressor output where the working fluid is in a second state with a second pressure P2, a second temperature T2 and a second enthalpy H2.

[0011] The compressor 10 is configured to increase the pressure of the working fluid, such that P2>P1.

[0012] The compressor may be electrically powered.

[0013] The system further comprises a condenser 11 having a condenser input which is connected to the compressor output to receive the working fluid in the second state, and a condenser output, where the working fluid is in a third state P3, T3, H3.

[0014] The condenser 11 may be configured to exchange heat with a heat delivery circuit 12, wherein heat is delivered from the condenser 11, whereby the temperature of the working fluid may be reduced, such that T3<T2 and the enthalpy of the working fluid is reduced, such that H3<H2. At least part of the working fluid turns from vapour state to liquid state.

[0015] As an alternative, the condenser 11 may be configured to deliver heat to an airflow, or to merely dissipate heat to surrounding air, as could be the case in a refrigeration system.

[0016] The heat delivery circuit 12 may be e.g. a heating circuit for providing heating to a space, such as one or more dwellings or an automobile interior. In other applications, heat may be used in a drying process, or the like.

[0017] The system further comprises an expansion valve 13, which is connected to the condenser output.

[0018] The expansion valve 13 is configured for isenthalpic expansion, to allow the working fluid to expand to a fourth state P4, T4, H4, such that the working fluid, at an expansion valve output has a lower pressure than the third state, such that P4<P3.

[0019] The system further comprises an evaporator 14, which may be configured to exchange heat with a heat supplying circuit 15, such that the working fluid undergoes evaporation, wherein heat is received by the evaporator 14, whereby the enthalpy of the working fluid will increase, such that H1>H4. Also the temperature may be increased, such that T1>T4.

[0020] The heat supplying circuit 15 may be a cooling circuit in a cooling device or an air conditioning device. Alternatively, the heat supplying circuit 15 may be configured to pick up heat from e.g. air, ground, bedrock or water in a heat pump system.

[0021] An evaporator input is connected to receive the working fluid in the fourth state from the expansion valve 13. An evaporator output is connected to the input of the compressor 10.

[0022] There is a general desire to increase performance of heat cycle systems, and thus to improve the coefficient of performance. It is known from e.g. W02013141805A1 to include in a heat cycle system an energy converter for converting the energy of a pressurized fluid into mechanical energy, which may then be used for generating electric energy.

[0023] There is still a general need for improving heat cycle systems, in particular in terms of efficiency and / or production of electric energy.

[0024] It is an objective of the present disclosure to provide a heat cycle system capable of producing electric energy and preferably also having improved efficiency.

[0025] A particular objective is to provide a heat cycle system and method of operation which is suitable for so-called water-water systems and for water-air systems, i.e. for systems where the external heat source is a liquid, such as water and where the external heat sink is a liquid or a gas.

[0026] A particular objective includes the provision of a heat cycle system that is suitable for use as a cooling system, for cooling a space or a body of material.

[0027] The invention is defined by the appended independent claims, with embodiments being set forth in the dependent claims, in the following description and in the drawings.

[0028] According to a first aspect, there is provided a heat cycle system, comprising a working fluid, which is cycled through a circuit comprising a compressor, a condenser, an expander unit, and an evaporator, wherein the expander unit is configured to generate a rotating mechanical motion, wherein the expander unit is connected between an outlet of the condenser and an inlet of the evaporator. The working fluid pressure drop over the condenser is less than about 5 bar.

[0029] In a normal heat cycle system, the working fluid pressure drop over the condenser will be on the order of at least 6-7 bar.

[0030] However, by providing a condenser which is adapted to provide a lower pressure drop, it is possible to increase the system's cooling capacity.

[0031] Hence, the system may be a dedicated cooling system, i.e. a system that is not reversible so as to be useful for both cooling and heating.

[0032] The working fluid pressure drop over the condenser may be about 0.50-0.75 bar; about 0.75-1.00 bar; about 1.00-1.25 bar; about 1.25-1.50 bar; about 1.50-1.75 bar; about 1.75-2.00 bar; about 2.00-2.25 bar; about 2.25-2.50 bar; about 2.50-2.75 bar; about 2.75-3.00 bar; about 3.00-3.25 bar; about 3.25-3.50 bar; about 3.50-3.75 bar; about 3.75-4.00 bar; about 4.00-4.25 bar; about 4.25-4.50 bar; about 4.50-4.75 bar; or about 4.75-5.00 bar.

[0033] The heat cycle system may further comprise a subcooler, connected between an working fluid outlet of the condenser and an inlet to the expander unit, wherein said subcooler is configured to transfer heat to the working fluid at a point between a working fluid outlet of the evaporator and an inlet to the compressor.

[0034] The heat cycle system may further comprise a first condenser and a second condenser, connected in parallel with the first condenser, and a condenser distributor configured for distributing a working fluid flow between the first and second condensers.

[0035] By using a pair of condensers, which are connected in parallel, it is possible to reduce the risk of liquid working fluid plugging the condenser. Condenser capacity may be dynamically controlled, as requried, e.g. due to a selected operating mode of the heat cycle.

[0036] Hence, a heat cycle system configured as claimed finds particular application in connection with heat pump systems for capturing heat from ground or water, or for capturing waste heat.

[0037] The condenser distributor may comprise a pressure sensor configured to detect a pressure at an inlet of a first one of the condensers and a controllable valve, configured to control a flow into a second one of the condensers based on said pressure.

[0038] The heat cycle system may further comprise an expander bypass for at least partially bypassing the expander unit to provide a connection between a expander inlet and a expander outlet.

[0039] The expander bypass may comprise a control valve for controlling a flow in the expander bypass.

[0040] The expander bypass may be provided with at least one control valve, that may be configured to control a working fluid distribution between the expander unit and the expander bypass.

[0041] The expander bypass may comprise an expansion valve, which is operable based on a condition downstream of the evaporator and upstream of the compressor. The heat cycle system may further comprise an expansion valve which is connectable in series with the expander unit and downstream of the expander unit.

[0042] The expansion valve may be operable based on a condition downstream of the evaporator and upstream of the compressor.

[0043] An expansion valve bypass valve may be connectable in parallel with the expansion valve.

[0044] The heat cycle system may further comprise a control valve, connected in series with the expansion valve and in parallel with the expansion valve bypass valve for controlling a flow to the expansion valve.

[0045] The condenser may be configured to exchange heat with a first external working fluid in the form of a liquid.

[0046] The first external fluid may comprise, consist or consist essentially of, water, optionally with an additive, such as an anti-freeze agent.

[0047] The condenser may be configured to exchange heat with a first external working fluid in the form of a gas.

[0048] The first external fluid may comprise, consist or consist essentially of, air.

[0049] The evaporator may be configured to exchange heat with a second external working fluid in the form of a liquid.

[0050] The second external working fluid may comprise, consist or consist essentially of, water, optionally with an additive, such as an anti-freeze agent.

[0051] This second external working fluid may be configured to exchange heat with a space or a body of material that is to be cooled, such that the heat cycle system is used as a cooling system.

[0052] The heat cycle system may further comprise an auxiliary heat exchanger connected between an evaporator outlet and a compressor inlet, said heat exchanger configured to transfer heat from a third external working fluid to the working fluid.

[0053] The provision of additional heat at this stage may increase evaporation of the working fluid, whereby the work required in the compressor may be reduced.

[0054] The third external working fluid may comprise, consist or consist essentially of, water, optionally with an additive, such as an anti-freeze agent.

[0055] The heat cycle system may be configured to be operated as a non-reversible cooling system for cooling a space or a body of material. A space may be a building interior, a vehicle interior, or the like. A body of material may be an ice rink, or the like. Hence, the heat cycle system may be configured to only cool the space or body of material, while not being reversible to, instead, heat the space or body of material.

[0056] According to a second aspect, there is provided a method of operating a heat cycle system, wherein the heat cycle system comprises a working fluid, which is cycled through a circuit comprising a compressor, a condenser, an expander unit, and an evaporator, wherein the expander unit is configured to generate a rotating mechanical motion, wherein the method comprises operating the compressor to receive the working fluid in a first state, with a first pressure, a first temperature and a first enthalpy, and to compress the working fluid to a second state with a second pressure, a second temperature and a second enthalpy, operating the condensing arrangement to receive the working fluid in the second state, and to condense the working fluid to a third state with a third pressure, a third temperature and a third enthalpy, operating the expander unit to receive the working fluid in the third state, and to expand the working fluid to a fourth state with a fourth pressure, a fourth temperature and a fourth enthalpy, operating the evaporator to receive the working fluid in the fourth state, and to evaporate the working fluid to the first state. The method comprises reducing a working fluid pressure by less than 5 bar across the condensing arrangement.

[0057] The method may further comprise operating a distributor to distribute the working fluid in the modified second state between at least one first condensor and at least one second condensor.

[0058] The expander unit may be at least partially bypassed via an expansion valve.

[0059] The method may further comprise further expanding the working fluid in an expansion valve downstream of the expander unit.

[0060] The expansion valve may be at least partially bypassed via an expansion valve bypass valve.

[0061] The method may further comprise providing additional heat to the working fluid between the outlet of the evaporator and the inlet of the compressor.

[0062] The condenser may be caused to exchange heat with a first external working fluid in the form of a liquid. The condenser may be caused to exchange heat with a first external working fluid in the form of a gas.

[0063] The evaporator may be caused to exchange heat with a second external working fluid in the form of a liquid.

[0064] The heat cycle system may be operated as a non-reversible cooling system for cooling a space or a body of material.

[0065] According to a third aspect, there is provided a heat cycle system, comprising a working fluid, which is cycled through a circuit comprising a compressor, a condenser, an expander unit, and an evaporator, wherein the expander unit is configured to generate a rotating mechanical motion, wherein the expander unit is connected between an outlet of the condenser and an inlet of the evaporator. The heat cycle system comprises a first condenser and a second condenser, connected in parallel with the first condenser, and a condenser distributor configured for distributing a working fluid flow between the first and second condensers.

[0066] The condenser distributor may comprise a pressure sensor configured to detect a pressure at an inlet of a first one of the condensers and a controllable valve, configured to control a flow into a second one of the condensers based on said pressure.

[0067] Fig. 1 is a schematic diagram of a conventional heat cycle system.

[0068] Fig. 2 is a schematic diagram of a modified heat cycle system.

[0069] Fig. 3 is a table showing test data according to the claimed invention in respect of four different scenarios.

[0070] Fig. 4 is a table showing comparative data for a commercially available system in respect of the same four scenarios.

[0071] Fig. 5 is a schematic diagram of an alternatively modified heat cycle system.

[0072] Detailed description

[0073] Referring to fig. 2, there is provided a schematic diagram of a modified heat cycle system. Components in the modified heat cycle system of fig. 2 which correspond to components of the conventional heat cycle system illustrated in fig. 1 are indicated by the reference numerals. The system shown in fig. 2 differs from that shown in fig. 1 in that the expansion valve 13 has been replaced by a rotatable expander 130 and the evaporator 14 replaced by one with larger capacity. Additionally, it may be advantageous to reduce pressure drop in the evaporator 14, and make the connection between the output of the rotatable expander 130 and the evaporator 14 as short and straight as possible. Thus, a pressure drop over the evaporator may be less than about 5 bar, preferably less than about 4 bar, less than about 3 bar, less than about 2 bar or less than about 1 bar. Preferably, a pressure drop over the evaporator may be about 0.5 bar.

[0074] Hence, in fig. 2 there is illustrated a heat cycle system in which is circulated a working fluid, as indicated by the arrows.

[0075] The system comprises a compressor 10 having a compressor input where the working fluid is in a first state with a first pressure Pl, a first temperature T1 and a first enthalpy Hl, and a compressor output where the working fluid is in a second state with a second pressure P2, a second temperature T2 and a second enthalpy H2.

[0076] The compressor 10 is configured to increase the pressure of the working fluid, such that P2>P1.

[0077] The compressor may be electrically powered.

[0078] The system may further comprise a condenser 11 or a pair of condensers 11a, lib, which is / are arranged downstream of the compressor 10 and which will be described in more detail later.

[0079] The condenser or condensers should be modified in order to minimize the working fluid pressure drop over the condenser. Hence, the working fluid may be caused to pass through the condenser divided into several pipes, which may have fewer bends and / or which may have larger cross sectional area than conventional condensers.

[0080] It is preferred to provide condensers having a pressure drop below about 5 bar, even more preferred to have pressure drops below about 4 bar, below about 3 bar, below about 2 bar or below about 1 bar.

[0081] The condensers 11a, lib exchange heat with a cooling arrangement 12a, 12b, which comprises a medium that acts as cooling medium for the condensers 11a, lib. This cooling medium may in some embodiments be a liquid, such as water, brine, oil, or the like, which may be circulated in a cooling cirquit. In other embodiments, the cooling medium may be a gas, such as air, which may be circulated in a cooling circuit, or which may be applied to the condensers by means of a fan.

[0082] The system further comprises a rotatable expander 130, which replaces the expansion valve 13 (fig. 1) and which may have the form of e.g. a turbine, a scroll type expander or a GE rotor type expander. Hence, the rotatable expander 130 replaces the expansion valve 13 (fig. 1) which would otherwise be provided at this stage in the heat cycle process. An outgoing rotatable axle of the rotatable expander 130 may be mechanically connected to a generator configured to produce electricity.

[0083] An expander input is connected to receive the working fluid in the third P3, T3, H3 state from the condenser 11a, lib.

[0084] The rotatable expander 130 is configured to allow the working fluid to expand to a modified fourth state P40, T40, H40 such that the working fluid, at an expander output has a lower pressure and enthalpy than the third state, such that P40<P3 and H40<H3.

[0085] The rotatable expander 130 may be characterized as operating close to isentropic, which causes not only a pressure loss but also a loss in enthalpy, such that in the fifth state modified fourth state P40, T40, the enthalpy H40 is less than that (H3) of the third state.

[0086] The system further comprises an evaporator 14, which may be configured to exchange heat with a heat supplying circuit 15, wherein heat is received by the evaporator 14, whereby the enthalpy of the working fluid is increased and the working fluid is vaporized, such that H4O<H1.

[0087] The heat supplying circuit(s) 15a, 15b may be one or more cooling circuit in a cooling device or an air conditioning device. Alternatively, the heat supplying circuits 15a, 15b may be configured to pick up heat from e.g. air, ground, bedrock or water in a heat pump system.

[0088] An evaporator input is connected to receive the working fluid in the modified fourth state from the rotatable expander 130. An evaporator output is connected to the input of the compressor 10. A expander bypass 131 is provided for bypassing the expander 130 by providing a direct connection 1311 between the outlet of the condenser 11a, lib and the inlet of the evaporator 14.

[0089] The expander bypass 131 may be provided with an expansion valve 1312, which may be configured to operate based on the conditions at the outlet of the evaporator 14 in a per se known manner.

[0090] Consequently, the expander bypass 131 results in the rotatable expander being connectable in parallel with the expansion valve 1312.

[0091] The expander bypass 131 is provided with a control valve 1313, which may be configured to regulate the flow in the expander bypass 131. The regulation may be binary (on / off), stepwise or continuous between on and off states.

[0092] Service valves 1314, 1315 may optionally be provided on upstream and downstream sides of the rotatable expander 130 to allow for easy deconnection and / or exchange of the rotatable expander 130. Service valve may be binary (on / off) valves, while control valves may be binary, stepwise or continuous between on and off states.

[0093] The modified heat cycle system may optionally comprise a pair of condensers 11a, lib, which are connected in parallel, and provided with a regulator 110 for distributing the working fluid between the condensers 11a, lib.

[0094] The condensers 11a, lib thus receive the working fluid in the second state P2, T2, H2.

[0095] In the illustrated example, the regulator 110 comprises a pressure sensor 1101 configured to determine pressure at the inlet of a first one of the condensers 11a, lib and a controllable valve 1102 configured to open an inlet of a second one of the condensers 11a, lib, such that working fluid is only directed to the second condenser lib when the pressure at the inlet of the first condenser 11a exceeds a predetermined value.

[0096] The evaporator 14 is configured to transfer heat from a first external fluid circuit 15a to the working fluid.

[0097] The modified heat cycle system may optionally comprise an additional heat exchanger 140, which is connected between the outlet of the evaporator 14 and the inlet of the compressor 10. The additional heat exchanger is configured to transfer heat from a second external fluid circuit 15b to the working fluid. This additional heat exchanger 140 may be configured to transfer further heat from the same external fluid circuit 15a as the evaporator, or from a different external fluid circuit. In particular, the second external fluid circuit 15b may be configured to pick up waste heat or to pick up heat from e.g. solar panels.

[0098] The auxiliary heat exchanger 140 may be selected and designed in accordance with a type of external medium that is available for heat exchange, as well as the amount and rate of said external medium.

[0099] The heat cycle system illustrated in fig. 2 may be operated in various modes, as will be described in the following.

[0100] A subcooler 150 may be provided in order to transfer heat from the working fluid exiting the condenser 11a, lib to the working fluid exiting the evaporator 14. The subcooler 150 may be embodied as a heat exchanger.

[0101] Test

[0102] A water-air test system, wherein the evaporator was heated with a water based brine and the condenser was cooled with an air flow, was built comprising a compressor 10 in the form of a Maneurop IlkW.

[0103] A pair of condensers 11a, lib was provided in the form of gas (typically air) cooled condensers, in which case it is possible to use a pair of 600x800x3 lamellae coils with 3 / 8" connectors. The condensers presented a pressure drop of about 0.5 bar. A fan in the form of a Ziehl-Abegg FB063-6EK.4 from available from Ziehl-Abegg, Germany, was used to drive cooling air across the condensers.

[0104] The fan was controlled based on the condensation pressure as measured in the liquid line at K6. A fan speed control in the form of a P15ST-9100 from Johnson Controls was used in the test setup.

[0105] A scroll type expander 130 was provided in the form of a DENSO SCSA06C 447220-6572 HFC134a. The scroll type expander was modified by removal of its nonreturn check valve and by increasing the flow area of the expander input to a diameter of about 14 mm. The expander was connected to a brake, in the form of a Delta AC Servo Modell ECMA-J11330R4 kW 3,0 / 3000 rpm from Delta Electronics (Sweden) AB, which was used to emulate a generator connected to the outgoing axle of the rotatable expander 130. An evaporator 14 was provided in the form of a brazed plate heat exchanger M29-60 LG from Multichannel AB, Landskrona, Sweden . The evaporator presented a pressure drop of about 0.5 bar.

[0106] Piping in the form of 5 / 8 inch pipes was used from the expander to the evaporator and in the form of 7 / 8 inch from the evaporator to the compressor.

[0107] At the first condenser 11a, a pressure sensor 1101 was provided in the form of a Penn P77AAW-9350, 6-30 bar from Johnson Controls. A controller was set to engage the second condenser lib when a pressure exceeding 1.5 bar above the nominal set point was detected at the inlet of the first condenser 11a, and to disengage the second condenser lib when a pressure equal to the nominal setpoint was detected.

[0108] An expansion valve 1312 was provided, as was a control valve 1313, configured to control the flow to the expansion valve 1312.

[0109] In a first series of tests, the evaporator was configured to exchange heat with a first liquid (brine - water based) and the condensers were configured to exchange heat with air. Tests were made with the following combinations of incoming and outgoing water temperatures at the evaporator:

[0110] The following measurement points were provided:

[0111] Temperatures and pressures were measured as per the table above, as was torque (%M) and rpm (RPM) for the expander units 130. In the table below, Pex is the power produced by the expander unit 130; Qo is the cooling effect on the water, Pc is the power consumed by the compressor and COP* is the resulting cooling efficienty.

[0112] The results of the various runs of the various scenarios appear from the table provided in fig. 3.

[0113] As a comparison, corresponding measurements were made in the same scenarios for a reference system in the form of an ARGO R32, Model AG4HP163PH (10.2 kW, power input 2.13 kW, EER W / W: 4.79). Corresponding measurement points were provided. The results of the various runs of the various scenarios appear from the table provided in fig. 4.

[0114] As can be seen from the test data, the mofidied system achieves a substantailly higher COP* value as compared to the reference system. Hence, it is concluded that by introducing at least some of the modifications disclosed with reference to fig. 2, it is possible to achieve a heat cycle system having improved efficiency.

[0115] With reference to Fig. 5, there is disclosed a system which corresponds to the one disclosed in fig. 2, but wherein the expansion valve 1312 is connected in series downstream of the expander unit 130, upstream of the evaporator 14, and wherein an expansion valve bypass valve 1316 is provided, such that the working fluid exiting from the expander unit 130 can be distibuted between the expansion valve 1312 and a direct connection to the evaporator 14. This arrangement effectively provides a way of controlling the pressure drop over the expander unit 130.

[0116] Preliminary tests have shown that this arrangement provides a potential for increasing efficiency, in particular with respect to the heat cycle itself. It is understood that the systems disclosed herein may be used in a heating system, i.e. a system that is used primarily for supplying heat to a heat sink, such as a space or a body by extracting heat at the condenser.

[0117] Furthermore, the systems and methods disclosed herein may be used in a cooling system, i.e. a system that is primarily used for cooling a heat source, such as a space or a body by supplying heat at the evaporator.

[0118] The systems and methods disclosed herein may also be used in a combined energy system, where heat is moved from a heat source (that is thus cooled) to a heat sink (that is thus heated).

[0119] It is further understood that by using the expander unit instead of only an expansion valve, it is possible to use an evaporator having greater capacity. Hence, the evaporator may be overdimensioned as compared to the system with only an expansion valve, by at least 20 %, preferably at least 30 % or at least 40 %.

Claims

CLAIMS1. A heat cycle system, comprising: a working fluid, which is cycled through a circuit comprising a compressor (10), a condenser (11a, lib), an expander unit (130), and an evaporator (14), wherein the expander unit (130) is configured to generate a rotating mechanical motion, wherein the expander unit (130) is connected between an outlet of the condenser (11a, lib) and an inlet of the evaporator (14), characterized in that the working fluid pressure drop over the condenser is less than about 5 bar.

2. The heat cycle system as claimed in claim 1, wherein the working fluid pressure drop over the condenser is about 0.50-0.75 bar; about 0.75-1.00 bar; about 1.00-1.25 bar; about 1.25-1.50 bar; about 1.50-1.75 bar; about 1.75-2.00 bar; about2.00-2.25 bar; about 2.25-2.50 bar; about 2.50-2.75 bar; about 2.75-3.00 bar; about3.00-3.25 bar; about 3.25-3.50 bar; about 3.50-3.75 bar; about 3.75-4.00 bar; about4.00-4.25 bar; about 4.25-4.50 bar; about 4.50-4.75 bar; or about 4.75-5.00 bar.

3. The heat cycle system as claimed in claim 1 or 2, further comprising a subcooler (150), connected between an working fluid outlet of the condenser (11a, lib) and an inlet to the expander unit (130), wherein said subcooler (150) is configured to transfer heat to the working fluid at a point between a working fluid outlet of the evaporator (14) and an inlet to the compressor (10).

4. The heat cycle system as claimed in any one of the preceding claims, wherein the heat cycle system comprises a first condenser (11a) and a second condenser (lib), connected in parallel with the first condenser (11a), and a condenser distributor (110) configured for distributing a working fluid flow between the first and second condensers (11a, lib).

5. The heat cycle system as claimed in claim 4, wherein the condenser distributor (110) comprises a pressure sensor (1101) configured to detect a pressureat an inlet of a first one of the condensers (11a, lib) and a controllable valve (1102), configured to control a flow into a second one of the condensers (11a, lib) based on said pressure.

6. The heat cycle system as claimed in any one of the preceding claims, further comprising a expander bypass (131) for at least partially bypassing the expander unit to provide a connection between a expander inlet and a expander outlet.

7. The heat cycle system as claimed in claim 6, wherein the expander bypass (131) comprises a control valve (1313) for controlling a flow in the expander bypass (131).

8. The heat cycle system as claimed in claim 6 or 7, wherein the expander bypass (131) comprises an expansion valve (1312), which is operable based on a condition downstream of the evaporator (14) and upstream of the compressor (10).

9. The heat cycle system as claimed in any one of claims 1-5, further comprising an expansion valve (1312) which is connectable in series with the expander unit and downstream of the expander unit.

10. The heat cycle system as claimed in claim 9, further comprising an expansion valve bypass valve (1316), which is connectable in parallel with the expansion valve (1312).

11. The heat cycle system as claimed in claim 9 or 10, further comprising a control valve (1313), connected in series with the expansion valve (1312) and in parallel with the expansion valve bypass valve (1316) for controlling a flow to the expansion valve (1312).

12. The heat cycle system as claimed in any one of the preceding claims, wherein the condenser (11a, lib) is configured to exchange heat with a first external working fluid in the form of a liquid.

13. The heat cycle system as claimed in any one of claims 1-11, wherein the condenser (11a, lib) is configured to exchange heat with a first external working fluid in the form of a gas.

14. The heat cycle system as claimed in any one of the preceding claims, wherein the evaporator (14) is configured to exchange heat with a second external working fluid in the form of a liquid.

15. The heat cycle system as claimed in any one of the preceding claims, further comprising an auxiliary heat exchanger (140) connected between an evaporator outlet and a compressor inlet, said heat exchanger configured to transfer heat from a third external working fluid to the working fluid.

16. The heat cycle system as claimed in any one of the preceding claims, wherein the heat cycle system is configured to be operated as a non-reversible cooling system for cooling a space or a body of material.

17. A method of operating a heat cycle system, wherein the heat cycle system comprises a working fluid, which is cycled through a circuit comprising a compressor (10), a condenser (11), an expander unit (130), and an evaporator (14), wherein the expander unit (130) is configured to generate a rotating mechanical motion, wherein the method comprises: operating the compressor (10) to receive the working fluid in a first state, with a first pressure (Pl), a first temperature (Tl) and a first enthalpy (Hl), and to compress the working fluid to a second state with a second pressure (P2), a second temperature (T2) and a second enthalpy (H2),operating the condensing arrangement (11a, lib) to receive the working fluid in the second state, and to condense the working fluid to a third state with a third pressure (P3), a third temperature (T3) and a third enthalpy (H3), operating the expander unit (130) to receive the working fluid in the third state, and to expand the working fluid to a fourth state with a fourth pressure (P4), a fourth temperature (T4) and a fourth enthalpy (H4), operating the evaporator (140) to receive the working fluid in the fourth state, and to evaporate the working fluid to the first state, characterised in that the method comprises reducing a working fluid pressure by less than 5 bar across the condensing arrangement.

18. The method as claimed in claim 17, wherein the method further comprises operating a distributor to distribute the working fluid in the modified second state between at least one first condensor and at least one second condensor.

19. The method as claimed in claim 17 or 18, wherein said expander unit is at least partially bypassed via an expansion valve (1312).

20. The method as claimed in claim 17 or 18, wherein said working fluid is further expanded in an expansion valve downstream of the expander unit.

21. The method as claimed in claim 20, wherein said expansion valve is at least partially bypassed via an expansion valve bypass valve (1316).

22. The method as claimed in any one of claims 17-21, further comprising providing additional heat to the working fluid between the outlet of the evaporator (14) and the inlet of the compressor (10).

23. The method as claimed in any one of claims 17-22, wherein the condenser (11a, lib) is caused to exchange heat with a first external working fluid in the form of a liquid.

24. The method as claimed in any one of claims 17-23, wherein the condenser (11a, lib) is caused to exchange heat with a first external working fluid in the form of a gas.

25. The method as claimed in any one of claims 17-24, wherein the evaporator (14) is caused to exchange heat with a second external working fluid in the form of a liquid.

26. A heat cycle system, comprising: a working fluid, which is cycled through a circuit comprising a compressor (10), a condenser (11a, lib), an expander unit (130), and an evaporator (14), wherein the expander unit (130) is configured to generate a rotating mechanical motion, wherein the expander unit (130) is connected between an outlet of the condenser (11a, lib) and an inlet of the evaporator (14), characterized in that the heat cycle system comprises a first condenser (11a) and a second condenser (lib), connected in parallel with the first condenser (11a), and a condenser distributor (110) configured for distributing a working fluid flow between the first and second condensers (11a, lib).

27. The heat cycle system as claimed in claim 26, wherein the condenser distributor (110) comprises a pressure sensor (1101) configured to detect a pressure at an inlet of a first one of the condensers (11a, lib) and a controllable valve (1102), configured to control a flow into a second one of the condensers (11a, lib) based on said pressure.

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