Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B49/00—Arrangement or mounting of control or safety devices
  • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
  • F25B49/027—Condenser control arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B41/00—Fluid-circulation arrangements
  • F25B41/30—Expansion means; Dispositions thereof
  • F25B41/31—Expansion valves
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B41/00—Fluid-circulation arrangements
  • F25B41/30—Expansion means; Dispositions thereof
  • F25B41/39—Dispositions with two or more expansion means arranged in series, i.e. multi-stage expansion, on a refrigerant line leading to the same evaporator
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/19—Pressures
  • F25B2700/195—Pressures of the condenser
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/21—Temperatures
  • F25B2700/2116—Temperatures of a condenser
  • F25B2700/21161—Temperatures of a condenser of the fluid heated by the condenser
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/21—Temperatures
  • F25B2700/2116—Temperatures of a condenser
  • F25B2700/21163—Temperatures of a condenser of the refrigerant at the outlet of the condenser

Definitions

• the disclosure relates to a refrigerant circuit for control based on the condenser approach. It also relates to a method of operating a refrigerant circuit.
• a refrigerant circuit for example for a HVACR (Heating, Ventilation, Air Conditioning and Refrigeration) system, or for a transport climate control system, with one or more expansion valves for regulating refrigerant flow around the refrigerant circuit.
• HVACR Heating, Ventilation, Air Conditioning and Refrigeration
• Well established valve arrangements for controlling a refrigerant circuit include the use of a thermal expansion valve or electronic expansion valve to control expansion of refrigerant between a condenser and evaporator in order to maintain a target superheat of refrigerant gas returned to a compressor. Such control based on superheat avoids return of liquid refrigerant to the compressor.
• a refrigerant circuit may operate more efficiently if refrigerant is sub-cooled upon exit from a condenser.
• a refrigerant circuit comprising, in flow order along a main refrigerant path: a compressor; a condenser configured to transfer heat from a refrigerant side to a secondary fluid side; a main expansion valve; and an evaporator, the refrigerant circuit further comprising: a thermal expansion valve disposed downstream of the condenser and upstream of the main expansion valve; wherein the thermal expansion valve comprises a remote sensing bulb mounted to the condenser for thermal communication with the secondary fluid side of the condenser.
• the thermal expansion valve is configured to regulate refrigerant flow along the main refrigerant path responsive to variation of a condenser approach temperature, the condenser approach temperature being a difference in temperature between a condenser refrigerant exit temperature and a condenser secondary fluid inlet temperature.
• the refrigerant circuit may further comprise a liquid receiver or flash tank downstream of the thermal expansion valve and upstream of the main expansion valve along the main refrigerant path.
• the thermal expansion valve comprises a pressure equalisation port in fluid communication with (i) an outlet of the thermal expansion valve upstream of the main expansion valve (e.g., to provide an internally compensated thermal expansion valve) or (ii) a portion of the main refrigerant path upstream of the main expansion valve (e.g. to provide an externally compensated thermal expansion valve).
• the portion of the main refrigerant path may be upstream of the main expansion valve and downstream of the thermal expansion valve (which may include an internal pressure equalisation port in fluid communication with an outlet of the thermal expansion valve).
• the pressure equalisation port is in fluid communication with (i) an outlet of the thermal expansion valve upstream of a liquid receiver or flash tank as defined above (e.g., to provide an internally compensated thermal expansion valve) or (ii) a portion of the main refrigerant path upstream of the main expansion valve (e.g. to provide an externally compensated thermal expansion valve).
• the pressure equalisation port may be in fluid communication with the respective portion of the main refrigerant path for monitoring a pressure of refrigerant at the respective portion of the main refrigerant path.
• pressure equalisation port originates from the conventional use of thermal expansion valves for superheat control, whereby an actuator of the thermal expansion valve (e.g. a diaphragm) is exposed: (i) at one side to a pressure of a secondary refrigerant charge associated with the sensing bulb, which is a function of a temperature of a refrigerant of the refrigerant circuit as monitored by the sensing bulb at a monitoring location, and (ii) at an opposing side to a pressure of a refrigerant along a main refrigerant path of the refrigerant circuit at the same or a corresponding monitoring location.
• an actuator of the thermal expansion valve e.g. a diaphragm
• the secondary refrigerant charge associated with the sensing bulb is generally selected to have the same or similar thermodynamic properties to the refrigerant of the main refrigerant path, so that the relationship between temperature and pressure is similar for both the secondary refrigerant charge and the refrigerant of the refrigeration path. Therefore, in such conventional implementations the pressures acting on the actuator generally equalise when the temperature of the refrigerant is equal to the saturation temperature - i.e., there is no superheat.
• the remote sensing bulb is configured to monitor a temperature of the secondary fluid side of the condenser (corresponding to a temperature of a secondary fluid in use), whereas the pressure equalisation port is in fluid communication with a portion of the main refrigerant path upstream of the main expansion valve (corresponding to a pressure and thereby a temperature of the refrigerant), whether this may be along the liquid line (e.g., to provide an externally compensated thermal expansion valve) or in internal fluid communication with the outlet of the thermal expansion valve (e.g., to provide an internally compensated thermal expansion valve), which is itself along the main refrigerant path and upstream of the main expansion valve.
• the liquid line e.g., to provide an externally compensated thermal expansion valve
• the outlet of the thermal expansion valve e.g., to provide an internally compensated thermal expansion valve
• the thermal expansion valve i.e., by the remote sensing bulb and the pressure equalisation port respectively
• two different properties of the same fluid i.e., (i) refrigerant temperature and (ii) refrigerant pressure as a proxy for saturation temperature). Therefore, it may be that in the invention as described herein, the pressure equalisation port does not serve to equalise pressure forces across an actuator of the thermal expansion valve at a particular reference condition of the refrigerant (e.g., when there is no superheat as described above).
• a "pressure equalisation port” may be a conventional physical feature of a thermal expansion valve among those skilled in the art, it may interchangeably be referred to herein as a main refrigerant pressure port, and may be configured for internal compensation (e.g., internally coupled to the outlet port of the thermal expansion valve) or configured for external compensation (e.g., providing an external port on the expansion valve, for connection to a portion of the liquid line).
• the thermal expansion valve comprises an actuator configured to move in response to a pressure force balance between two sides, wherein the actuator is exposed to a pressure associated with the pressure equalisation port on one side and a pressure of a secondary refrigerant charge associated with the remote sensing bulb on the other side.
• the portion of the main refrigerant path as defined above may interchangeably be referred to as a refrigerant pressure monitoring location. Accordingly, the pressure associated with the pressure equalisation port may otherwise be referred to as a refrigerant pressure at the refrigerant pressure monitoring location.
• the thermal expansion valve is configured to regulate refrigerant flow to maintain a saturation temperature corresponding to a monitored refrigerant pressure at the pressure equalising port above a temperature monitored by the remote sensing bulb.
• the remote sensing bulb is mounted to the condenser for thermal communication with the secondary fluid side of the condenser to monitor a temperature of the secondary fluid side of the condenser.
• the remote sensing bulb is mounted to the condenser to monitor a temperature of the secondary fluid side of the condenser.
• the pressure equalisation port is in fluid communication with the respective portion of the main refrigerant path for monitoring a pressure of refrigerant at the respective portion of the main refrigerant path (also referred to herein as the refrigerant pressure monitoring location), the pressure being associated with a saturation temperature of the refrigerant.
• the thermal expansion valve comprises a pressure equalisation port in fluid communication with a refrigerant pressure monitoring location along the main refrigerant path which is upstream of the main expansion valve, to monitor pressure at the refrigerant pressure monitoring location.
• the remote sensing bulb is mounted to the condenser to monitor a temperature of the secondary fluid side of the condenser.
• the thermal expansion valve is configured to regulate refrigerant flow so that a saturation temperature corresponding to the monitored pressure is above the temperature monitored by the remote sensing bulb.
• the refrigerant pressure monitoring location may be along the main refrigerant path upstream of a liquid receiver or flash tank (where present, as defined above), and downstream of the thermal expansion valve.
• the refrigerant pressure monitoring location may be at or immediately downstream of the thermal expansion valve (e.g. with no intervening components which may impart a pressure drop).
• the thermal expansion valve comprises a secondary refrigerant charge within a volume extending from the remote sensing bulb to a body of the thermal expansion valve.
• the refrigerant circuit comprises a main refrigerant charge along the main refrigerant path.
• the secondary refrigerant charge and the main refrigerant charge have different refrigerant compositions.
• the secondary fluid side of the condenser is bounded by an external wall for enclosing a liquid secondary fluid, wherein the remote sensing bulb is mounted to the external wall for thermal communication with the secondary fluid side by conduction through the external wall, and wherein the remote sensing bulb is provided with insulation to inhibit heat transfer with an ambient fluid outside of the external wall.
• the secondary fluid side of the condenser defines a secondary fluid path for an unbounded and/or gaseous secondary fluid flow, and wherein the remote sensing bulb is disposed in the secondary fluid path.
• the remote sensing bulb for the secondary fluid path is not provided with insulation, so as to promote heat transfer with the secondary fluid path.
• the condenser defines a condenser refrigerant path from a condenser refrigerant inlet to a condenser refrigerant exit, wherein the condenser refrigerant exit temperature is a temperature of refrigerant at the condenser refrigerant exit. It may be that the condenser defines a secondary fluid path from a secondary fluid inlet to a secondary fluid exit, wherein the condenser secondary fluid inlet temperature is a temperature of secondary fluid at the condenser secondary fluid inlet.
• the refrigerant circuit may comprise a flash tank disposed downstream of the thermal expansion valve and upstream of the main expansion valve along the main refrigerant path. It may be that the refrigerant circuit further comprises a vapor injection line between the flash tank (or a receiver) and the compressor.
• a method of operating a refrigerant circuit comprising: the thermal expansion valve regulating refrigerant flow to maintain a predetermined condenser approach temperature; wherein, during operation of the refrigerant circuit over a range of operating conditions, a subcooling of the refrigerant at a condenser refrigerant exit of the condenser varies while the thermal expansion valve maintains the predetermined condenser approach.
• the thermal expansion valve maintains a saturation temperature corresponding to a pressure of refrigerant at the pressure equalising port above a temperature of secondary fluid monitored by the remote sensing bulb.
• FIG. 1 shows a refrigerant circuit including a valve for controlling a condenser approach.
• This simplified circuit substantially corresponds to that shown in Fig. 1a of paper referenced at (i) in the background section above.
• the refrigerant circuit comprises a compressor 10, a condenser 12, a valve 14, a receiver tank 16, a main expansion valve 17 and an evaporator 19.
• the receiver tank may function and be referred to as a flash tank.
• the valve 14 between the condenser and receiver tank is an electronic expansion valve EEV comprising a controller 14a configured to receive signals from sensors 15, and a valve body 14b controlled by the controller 14a.
• EEV electronic expansion valve
• the sensors include a secondary fluid temperature sensor 15a configured to monitor a temperature of a secondary fluid associated with the condenser (i.e., a process fluid to which heat is transferred by the condenser, from the condensing refrigerant), a refrigerant temperature sensor 15b downstream of the condenser and upstream of the valve body 14b, and a pressure sensor 15c at the same location.
• a secondary fluid temperature sensor 15a configured to monitor a temperature of a secondary fluid associated with the condenser (i.e., a process fluid to which heat is transferred by the condenser, from the condensing refrigerant)
• a refrigerant temperature sensor 15b downstream of the condenser and upstream of the valve body 14b
• a pressure sensor 15c at the same location.
• the main expansion valve 17 is a thermal expansion valve configured to control refrigerant flow therethrough to maintain a target superheat of refrigerant along a suction line (the line between the evaporator 19 and the condenser).
• the main thermal expansion valve 17 is provided with a sensing bulb 18 thermally coupled to the evaporator outlet or the suction line, such that a temperature and pressure of a refrigerant charge in the sensing bulb and communicatively coupled to the main thermal expansion valve 17 responds to a temperature of refrigerant in the suction line. This corresponds to a well-established means of controlling superheat in a refrigerant circuit.
• the compressor 10 is operated to cause refrigerant flow around the circuit and to compress the refrigerant.
• the main thermal expansion valve 17 regulates the flow of refrigerant to maintain a target superheat.
• the valve 14 further regulates the flow of refrigerant to maintain a predetermined condenser approach, which is the temperature difference between the refrigerant discharged from the condenser (as monitored by the temperature sensor 15b) and a temperature of the secondary fluid of the condenser (as monitored by the temperature sensor 15a).
• a thermal expansion valve can be used for controlling expansion immediately upstream of the evaporator to maintain a superheat of the refrigerant exiting the evaporator.
• the operating principle of a thermal expansion valve permits an approximately constant superheat to be maintained, even while the saturation temperature and absolute temperature of the refrigerant varies.
• Superheat is the temperature difference above the saturation temperature (boiling temperature) to which a vapour is superheated.
• the saturation temperature is a function of pressure, which may change at different operating points of a refrigerant circuit.
• Superheat can therefore be determined by monitoring a pressure (which determines saturation temperature), and monitoring an absolute temperature of the refrigerant.
• a thermal expansion valve permits superheat control mechanically.
• the thermal expansion valve 20 comprises a valve body 21, valve head 22, refrigerant inlet port 23, refrigerant outlet port 24 and a movable valve element 25 configured to vary an orifice opening between the inlet and outlet ports.
• the valve element 25 is biased by a biasing element (e.g. a spring 29 as shown in Figure 2 ).
• the valve element is actuated by a diaphragm 26 within the valve head 22, which is exposed to a charge of refrigerant for a sensing bulb 27 at one side, and exposed to refrigerant from the refrigerant circuit at an opposing side, with fluid communication to a refrigerant line of the refrigerant circuit via a pressure equalising port 28.
• the pressure equalising port 28 may be configured for internal communication with the outlet port 24 (referred to as “internal compensation” in the technical field, as indicated at 28'), or configured for external communication with a downstream refrigerant line (referred to as “external compensation", as indicated at 28).
• the refrigerant charge for the sensing bulb 27 may be selected to be the same, similar or have similar thermal properties to a refrigerant of the associated refrigerant circuit, such that the refrigerant charge exhibits a similar relationship between pressure and temperature as the refrigerant of the refrigerant circuit.
• a refrigerant charge which is similar or having similar thermal properties may have minor differences (e.g., in composition) relative to the refrigerant of the associate refrigerant circuit, that allow to control superheat in different ways as a function of the operating pressure.
• the sensing bulb 27 may be placed in thermal communication with an evaporator outlet coupled to a suction line of the refrigerant circuit (i.e.
• the refrigerant line extending from the evaporator to the compressor), and the pressure equalising port 28 may be in communication with refrigerant in the evaporator outlet (e.g. for external compensation), or in internal communication (i.e., within the thermal expansion valve) with pressure at the outlet port 24 of the valve.
• the refrigerant charge in the sensing bulb is such that the pressure in the sensing bulb and the respective side of the diaphragm is approximately the same as the saturation pressure for the absolute temperature at the sensing bulb, as is conventional in the artK.
• a pressure balancing point of the thermal expansion valve is configured and can be adjusted by a biasing force (e.g., a spring force) applied to the movable element 25.
• a biasing force e.g., a spring force
• the higher the spring force the higher the superheat that the valve will maintain.
• This operating principle provides a natural self-regulating control for superheat, with the thermal expansion valve being particularly configured to respond to variations from saturated conditions, irrespective of the particular saturation temperature or pressure.
• This operating principle relies on three conditions (i) the sensing bulb being thermally connected to the refrigerant flow passing through the valve, (ii) the outlet port (and any pressure equalising port for external compensation) of the thermal expansion valve being connected to the low pressure region of the refrigerant circuit where the refrigerant is at evaporating saturation conditions (in particular, two-phase flow for entry to the evaporator), and (iii) the refrigerant charge in the sensing bulb has similar thermal properties to the refrigerant flow that it is thermally coupled to (i.e. the refrigerant in the evaporator outlet).
• These three conditions enable the thermal expansion valve to serve as a main expansion valve in a refrigerant circuit, automatically regulating flow rate to maintain superheat.
• the inventor has departed from the above-described use of a thermal expansion valve (for superheat control), and has re-purposed a thermal expansion valve to implement the control methods proposed in the papers referenced above (at (i) and (ii)), rather than using an expensive electronic expansion valve that requires a controller and sensors, as will be described below.
• Figure 3 shows a refrigerant circuit 30 similar to the refrigerant circuit 10 described above with respect to Figure 1 , but comprising a thermal expansion valve 32 between the condenser 12 and receiver 16 (which may be referred to as a liquid line thermal expansion valve, since it is provided on the liquid line of the refrigerant circuit), instead of the electronic expansion valve of Figure 1 .
• the thermal expansion valve 32 is provided in addition to the main thermal expansion valve 17 between the receiver 16 and the evaporator 19.
• the liquid line thermal expansion valve may have a similar configuration and working principle to a conventional thermal expansion valve, such as that described above with respect to Figure 2 .
• the liquid line thermal expansion valve 32 has a sensor bulb 33 which is thermally exposed to the secondary fluid inlet to the condenser 32 (i.e., the fluid to which heat is rejected by the condenser, from the refrigerant flowing therethrough), which is a departure from condition (i) described above.
• the outlet port of the of the liquid line thermal expansion valve 32 is in communication with a high pressure portion of the refrigerant circuit (i.e. the region downstream of the condenser 12 and upstream of the main expansion valve 17 (that controls refrigerant flow through the evaporator 19)) and in this example is in fluid communication with the portion of the liquid line extending from the liquid line thermal expansion valve 32 to the receiver 16, where the refrigerant is 100% saturated liquid rather than two-phase. This represents a departure from condition (ii) as described above.
• the liquid line thermal expansion valve 32 is configured to be responsive to changes in the condenser approach (as described above: the difference in temperature between the refrigerant discharged from the condenser, and the secondary fluid inlet to the condenser).
• the charge of fluid associated with the sensing bulb 33 provides a pressure force on one side of the diaphragm which is a function of the secondary fluid temperature, whereas the pressure on the opposing side of the diaphragm is the saturation pressure of the refrigerant at the receiver 16, is in fact a function of the absolute temperature of refrigerant discharged from the condenser.
• the respective operating region for the refrigerant as described above is the subcooled region, which can be described with respect to a pressure-enthalpy diagram, as shown in Figure 4 .
• Pressure-enthalpy diagrams are available for refrigerants of different types and typically have a form as shown in the representative example of Figure 4 (noting that individual pressure-enthalpy diagrams are produced under copyright).
• the Y-axis is pressure (logarithmic scale)
• the X axis is enthalpy.
• the solid line is the saturation line 41 for the refrigerant, demarcating a zone where the refrigerant is at saturated temperature for the respective pressure condition.
• the saturation line represents 100% liquid refrigerant (0% vapor quality)
• the saturation line represents 100% vapor refrigerant (100% vapor quality)
• the area enclosed by the saturation line is the saturation region, where the refrigerant is two-phase and varies from 100% liquid to 100% gaseous. Accordingly, the region to the left of the saturation line (i.e., the part of the saturation line to the left of the critical point) and below critical pressure corresponds to subcooled conditions for a refrigerant, and may be referred to as the subcooled region 43.
• Figure 4 shows two dashed isothermal lines, which are example isothermal lines for representative temperatures.
• the isothermal lines are lines on the pressure-enthalpy plot of constant temperature.
• the example lines are substantially vertical in part of the subcooled region which corresponds to suitable operating conditions for the respective part of a refrigerant circuit (e.g., from an exit of the condenser to an inlet of a main expansion valve), when below critical pressure.
• This corresponds to a substantially constant specific heat (and therefore substantially constant temperature) over a pressure range in the subcooled region.
• the rate of change of temperature or specific heat with pressure is close to zero or substantially zero in the respective part of the subcooled region.
• Isothermal lines generally become more non-vertical within the subcooled region towards the critical point, with increasing enthalpy as pressure increases.
• the inventors have found that for realistic and feasible operation of a refrigerant circuit as shown in Figure 3 , subcooled refrigerant discharged from the condenser tends to be in the part of the subcooled region corresponding to substantially vertical isothermal lines as described above.
• Figure 4 shows example refrigerant conditions at selected parts of the refrigerant circuit 30 of Figure 3 , with reference to points A, B, C and D.
• point A is downstream of the condenser 12 and upstream of the liquid line thermal expansion valve 32.
• Point B is downstream of the liquid line thermal expansion valve 32 and upstream of the receiver 16.
• Point C is downstream of the receiver 16 and upstream of the main thermal expansion valve 17.
• Point D is downstream of the main thermal expansion valve 17 and upstream of the evaporator 19.
• Figure 4 provides arrows which approximate the various stages of the refrigerant circuit and extend through points A-D.
• point A is sub-cooled, since it is to the left of the saturation line.
• Expansion e.g., isenthalpic expansion
• the liquid line thermal expansion valve 32 causes a pressure reduction while maintaining substantially the same temperature (in the respective region of the pressure-enthalpy diagram), to reach point B.
• Substantially the same pressure and temperature conditions are maintained throughout the receiver 16 and to the second (main) thermal expansion valve 17, such that points B and C are the same on Figure 4 . These points correspond to saturated liquid.
• the pressure equalising port of the liquid line thermal expansion valve 32 is in fluid communication with the part of the liquid line between the liquid line thermal expansion valve 32 and the liquid receiver 16, which is at different thermodynamic conditions to the refrigerant at condenser exit. Further, the pressure sensing bulb is in thermal communication with the secondary fluid of the condenser. Accordingly, neither side of the liquid line thermal expansion valve 32 (e.g., neither of the sides of the diaphragm as described with reference to Figure 2 ) is configured to directly monitor the refrigerant discharged from the condenser.
• the pressure at point B serves as a proxy for the temperature of the refrigerant as discharged from the condenser. More particularly, the pressure at point B is for refrigerant at 100% liquid saturated conditions, whereby the saturation temperature is a function of the pressure. This saturation temperature is substantially equal to the absolute temperature of the sub-cooled refrigerant exiting the condenser at point A, as shown in Figure 4 .
• the pressure of the refrigerant charge in the sensing bulb is a function of the temperature of the secondary fluid. Accordingly, the pressure difference at the liquid line thermal expansion valve is a function of the absolute temperature difference between the sub-cooled refrigerant exiting the condenser, and the secondary fluid inlet to the condenser, which corresponds to the condenser approach.
• the refrigerant charge for the sensing bulb 33 can be selected to provide a suitable pressure variation in response to the monitored temperature of the condenser secondary fluid inlet, thereby providing a suitable response of the thermal expansion valve to the temperature difference between the condenser refrigerant outlet and condenser secondary fluid inlet, allowing therefore the control of a nearly constant condenser approach.
• suitable refrigerants which may include refrigerant blends
• suitable refrigerants for use in a sensing bulb for a desired response is made according to the same principles as conventionally used when using a thermal expansion valve for superheat control. Any number of different combinations of suitable refrigerants may be selected by a person skilled in the art.
• the thermal expansion valve can be configured (e.g., calibrated) to provide a suitable response by adjusting (e.g., by selection) a configuration of a spring of the thermal expansion valve.
• the spring is configured to bias the diaphragm in a direction to close the valve and opposing the sensing bulb pressure (such that the valve opens more as the superheat rises and pressure in the sensing bulb increases).
• the temperature monitored by the sensing bulb is lower than a saturation temperature of refrigerant in the liquid line (i.e.
• the thermal expansion valve may be configured so that the spring biases the diaphragm in a direction to open the valve and opposing the pressure at the pressure equalisation port. Accordingly, if the condenser approach were to temporarily increase because the temperature of the refrigerant exiting the condenser and thereby the saturation pressure at the pressure equalisation port increases, the increased pressure acts against the spring to close the valve, thereby reducing the refrigerant flow rate at the condenser and return the condenser approach to the lower predetermined amount.
• the liquid line thermal expansion valve 32 between the condenser and liquid receiver 16 is configured to operate when the underlying temperature difference between the temperature monitored by the sensing bulb and the refrigerant in communication with the pressure equalising port is negative.
• any sub-cooling at the condenser 12 can only be caused by the associated secondary fluid having a lower temperature. Therefore, the temperature of the secondary fluid as monitored by the sensing bulb is lower than the temperature of the refrigerant exiting the condenser.
• the pressure equalising port is in communication with the low-pressure side of the refrigerant circuit at saturated conditions, with the pressure being a function of the saturation temperature, whereas the sensing bulb is generally in thermal communication with superheated refrigerant at the evaporator outlet.
• the liquid line thermal expansion valve 32 is configured (e.g., calibrated) to operate with such an underlying negative temperature difference.
• the thermal expansion valve 32 may be suitably calibrated by adjusting a bias of the thermal expansion valve 32, for example by installing a suitable biasing spring or other biasing element to pre-load a valve member of the thermal expansion valve, for example by setting a suitable biasing force and/or direction of the biasing force as described above.
• the configuration of the liquid line thermal expansion valve 32 may be such that the sides of the diaphragm which are exposed to the refrigerant associated with (i) the sensing bulb and (ii) the main refrigerant path are switched, relative to a conventional thermal expansion valve for superheat control. Additionally or alternatively, the configuration of the liquid line thermal expansion valve 32 may be configured or calibrated by suitable selection of the refrigerant for the sensing bulb in conjunction with the refrigerant for the refrigeration circuit, for example to provide a suitable variation in the pressure difference at the diaphragm of the expansion valve 32 (e.g., to maintain a substantially constant condenser approach).
• the condenser 12 may be an air-to-refrigerant type condenser configured to receive a gaseous secondary fluid.
• the condenser may define a secondary fluid path for an unbounded (e.g. open) flow of a gaseous secondary fluid, such as atmospheric air conveyed by a fan.
• the sensing bulb 33 which is remote from the liquid line thermal expansion valve 32 (and connected by a dedicated refrigerant line therebetween) is disposed in the secondary fluid path for thermal communication with the secondary fluid path.
• the condenser 12 may have a secondary fluid side which is bounded by an external wall for enclosing a liquid secondary fluid, whether for use as a liquid-to-refrigerant type condenser or an air-to-refrigerant type condenser.
• the secondary fluid side may be defined by one or more tubes extending through the condenser.
• the sensing bulb when the secondary fluid is a gas or when the condenser defines a secondary fluid path for an unbounded (e.g., open) flow of gaseous secondary fluid, the sensing bulb may be mounted to a support structure of the condenser or a wall of the condenser for heat transfer between the secondary fluid flow and the sensing bulb.
• the sensing bulb may be disposed in the secondary fluid path and uninsulated on walls of the bulb exposed to the secondary fluid flow, and/or may be insulated on any walls of the bulb that are mounted to a heat transfer surface of the condenser (e.g. a wall between the refrigerant side and the secondary fluid side).
• the sensing bulb may not be disposed in the secondary fluid path, and may be mounted to a wall bounding the secondary fluid side for thermal conduction though the wall with the secondary fluid.
• FIG. 5 shows a refrigerant circuit 50 which is variant of the refrigerant circuit 30 of Figure 3 , configured for intermediate vapour injection into the compressor.
• the refrigerant circuit 50 is identical to the refrigerant circuit 30 of Figure 3 in flow order from the main thermal expansion valve 17 to the receiver 16 (i.e., including the evaporator 19, compressor 10, condenser 32, liquid line thermal expansion valve 32), and the above description of those features is relied upon.
• an economiser arrangement including an economiser heat exchanger 52 along the main refrigerant flow path of the refrigerant circuit (i.e. with the main refrigerant flow path extending through a first side of the economiser heat exchanger 52), and an intermediate line 54 configured to extract a portion of refrigerant from the liquid line between the receiver 16 and the main thermal expansion valve 17.
• the intermediate line 54 is provided with an intermediate valve 56 for expanding the extracted portion of refrigerant, which is then provided through a second side of the economiser heat exchanger 52 to receive heat from the refrigerant in the opposing first side, thereby vaporising the extracted and expanded refrigerant for return to an intermediate pressure port of the compressor 10.
• the intermediate valve 56 may be a thermal expansion valve provided with a sensing bulb 57 in thermal communication with a portion of the intermediate line 54 downstream of the economiser heat exchanger 52, for regulating refrigerant flow along the intermediate line.
• the receiver tank 16 (also referred to as a "receiver") as described above with respect to examples above may function as a flash tank, particularly in configurations where flash vapour from the flash tank is provided elsewhere in the system (e.g. returning to an intermediate pressure port of a compressor).
• a receiver tank according to examples above may interchangeably referred to as a flash tank.
• a flash tank economiser may be provided, for example in place of the economiser arrangement of the refrigerant circuit 50 of Figure 5 .
• the flash tank of the flash tank economiser may replace the liquid receiver 16 of the refrigerant circuit 50 of Figure 5 .
• a flash tank may be provided without an economiser.
• the receiver tank or flash tank 16 may have a liquid line outlet to the valve 17 (e.g., without passing through an economiser 52), and a compressor line may extend from this portion of the liquid line to the compressor, for example via an expansion valve.

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• 2024
  • 2024-03-06 EP EP24161831.3A patent/EP4614089A1/fr active Pending

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