An HVAC system

Abstract

An HVAC system is provided, comprising: a fluid circuit for transporting refrigerant; a compressor for compressing refrigerant; three heat exchangers defining an evaporator, an outdoor exchanger and a heat recovery exchanger arranged along the fluid circuit; an expansion valve arranged along the fluid circuit; and a tank connected in parallel to the expansion valve, wherein an injection valve is located between the tank and an upstream connection of the expansion valve and a discharge valve is located between the tank and a downstream connection of the expansion valve; wherein the fluid circuit comprises a plurality of valves configured to be controlled based on a selected operating mode such that at least one of the outdoor exchanger and the heat recovery exchanger is connected to a discharge line of the compressor and in series with one of the remaining heat exchangers connected to a suction line of the compressor, the expansion valve being arranged between the heat exchangers; wherein the injection valve and the discharge valve are configured to be controlled to store a volume of refrigerant in the tank.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to HVAC systems, in particular to four-pipe HVAC systems with variable refrigerant capacity. BACKGROUND

[0002] Four-pipe HVAC systems comprise separate heating and cooling sections, each having its own heat exchanger coil with a supply and return pipe. The heating and cooling sections can be operated independently, enabling the four-pipe system to provide both heating and cooling at the same time.

[0003] Four-pipe systems have multiple modes based on the required operation. The effective volume of the system varies depending on the mode of operation used (e.g. based on the volume of the heat exchangers used in the mode of operation). Therefore, the volume of refrigerant in the system (i.e. the refrigerant capacity) is typically a compromise for providing optimal overall performance.

[0004] However, it is desirable to provide a four-pipe system with improved performance. SUMMARY

[0005] According to a first aspect, there is provided an HVAC system comprising: a fluid circuit for transporting refrigerant; a compressor for compressing refrigerant; three heat exchangers defining an evaporator, an outdoor exchanger and a heat recovery exchanger arranged along the fluid circuit; an expansion valve arranged along the fluid circuit; and a vessel connected in parallel to the expansion valve, wherein an injection valve is located between the upstream connection of the vessel to the expansion valve and a discharge valve is located between the downstream connection of the vessel to the expansion valve; wherein the fluid circuit comprises a plurality of valves configured to be controlled based on a selected mode of operation such that at least one of the outdoor exchanger and the heat recovery exchanger is connected to a discharge line of the compressor and in series with one of the remaining heat exchangers connected to a suction line of the compressor, the expansion valve being arranged between the heat exchangers; wherein the injection valve and the discharge valve are configured to be controlled to store a volume of refrigerant in the vessel to provide an effective refrigerant capacity in the fluid circuit corresponding to the selected mode of operation.

[0006] The evaporator and / or the heat recovery exchanger can be a refrigerant-water heat exchanger and / or the outdoor exchanger can be a refrigerant-air heat exchanger.

[0007] The internal volume of the outdoor exchanger can be greater than the internal volume of the heat recovery exchanger and / or the evaporator.

[0008] The operating modes can be selected from one or more of: a chiller mode in which the outdoor exchanger is connected to the discharge line and the evaporator is connected to the suction line; a heat pump mode in which the heat recovery exchanger is connected to the discharge line and the outdoor exchanger is connected to the suction line; a defrost mode in which the outdoor exchanger is connected to the discharge line and the heat recovery exchanger is connected to the suction line; a heat recovery mode in which the heat recovery heat exchanger is connected to the discharge line and the evaporator is connected to the suction line; and a partial heat recovery mode in which both the heat recovery exchanger and the outdoor exchanger are connected to the discharge line and the evaporator is connected to the suction line.

[0009] The effective refrigerant capacity required for the chiller mode can be greater than the effective refrigerant capacity required for the heat pump mode; and / or the effective refrigerant capacity required for the defrost mode can be greater than the effective refrigerant capacity required for the heat pump mode; and / or the effective refrigerant capacity required for the heat pump mode can be greater than the effective refrigerant capacity required for the heat recovery mode.

[0010] In the partial heat recovery mode, a hot gas bypass valve upstream of the heat recovery exchanger can divert refrigerant to the outdoor exchanger to control heat recovery at the heat recovery exchanger.

[0011] The plurality of valves can include a four-way valve configured to connect one of the outdoor exchanger and the heat recovery exchanger to the discharge line and to connect the other of the outdoor exchanger and the heat recovery exchanger to the suction line via a bypass leg.

[0012] The fluid circuit can include a liquid line connected between the expansion valve and each of the heat recovery exchanger and the outdoor exchanger, wherein the liquid line is disposed on an upstream side of the expansion valve.

[0013] The fluid circuit can include a return line connected between the expansion valve and each of the heat exchangers, wherein the return line is disposed on a downstream side of the expansion valve.

[0014] The plurality of valves includes a valve disposed along each of the return lines to allow connection of a heat exchanger connected to the suction line of the compressor to the expansion valve.

[0015] A drain line with a pressure reducing valve can be disposed between the return lines and the liquid line.

[0016] The drain valve can be connected to the return line downstream of the container.

[0017] The HVAC system can further include a suction line heat exchanger connected to a portion of the fluid circuit upstream of the expansion valve and to the suction line.

[0018] A bypass line can be provided across the suction line heat exchanger on the portion of the fluid circuit upstream of the expansion valve; wherein a valve is provided for controlling the flow of refrigerant through the bypass line to bypass the suction line heat exchanger.

[0019] The HVAC system can further include a pressure line connecting the discharge line to the reservoir and having a pressure relief valve disposed between the compressor and the reservoir.

[0020] The HVAC system can further include a desiccant upstream of the expansion valve.

[0021] The HVAC system can further include a controller that controls the plurality of valves in response to a selected mode of operation.

[0022] The evaporator can include a cold water supply conduit and a cold water return conduit, and the heat recovery exchanger can include a hot water supply conduit and a hot water return conduit. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of an HVAC system according to an embodiment of the present application operating in a chiller mode;

[0024] Figure 2 shows the HVAC system operating in a heat pump mode;

[0025] Figure 3 shows the HVAC system operating in a thaw mode;

[0026] Figure 4 shows the HVAC system operating in a heat recovery mode;

[0027] Figure 5 is a schematic diagram of an HVAC system according to another embodiment of the present application operating in a chiller mode;

[0028] Figure 6 shows the HVAC system operating in a heat pump mode; Figure 5 of the present application;

[0029] Figure 7 shows the HVAC system operating in a thaw mode; Figure 5 of the present application;

[0030] Figure 8 shows the HVAC system operating in a heat recovery mode; Figure 5 of the present application; and

[0031] Figure 9 shows the HVAC system operating in a partial heat recovery mode; Figure 5 of the present application. DETAILED DESCRIPTION

[0032] Figures 1 to 4 All show a schematic view of an HVAC system 2 according to embodiments of the application. The HVAC system 2 comprises a plurality of compressors 4 arranged in parallel; but in other arrangements, only a single compressor 4 can be used. The discharge (or exhaust) ports of the compressors 4 are connected via a manifold to a common discharge line 6. The discharge line 6 is connected to a first (discharge) port of a four-way valve 8.

[0033] The HVAC system 2 further comprises three heat exchangers, which form an evaporator 10, an outdoor exchanger 12 with a fan 9, and a heat recovery exchanger 14. The heat exchangers are arranged in parallel. The evaporator 10 comprises a cold water supply conduit 11 and a cold water return conduit 13. The heat recovery exchanger 14 comprises a hot water supply conduit 15 and a hot water return conduit 17.

[0034] A second port of the four-way valve 8 is connected to a first side of the outdoor exchanger 12, a third port of the four-way valve 8 is connected to a bypass branch 20, and a fourth port of the four-way valve 8 is connected to a first side of the heat recovery exchanger 14.

[0035] A second side of the outdoor exchanger 12 is connected to a first liquid line 22, which is connected to a dryer 24 and an electronic expansion valve (EXV) 26 arranged in series (but other expansion valves can be used). Similarly, a second side of the heat recovery exchanger 14 is connected to a second liquid line 28, which is also connected to the dryer 24 and the EXV 26. In the arrangement shown, the first liquid line 22 and the second liquid line 28 are formed as a common portion close to the dryer 24, which is then split into a first portion and a second portion connected to the outdoor exchanger 12 and the heat recovery exchanger 14, respectively.

[0036] An outlet of the EXV 26 is connected to a first return line 30, which feeds into a first side of the evaporator 10. A second side of the evaporator 10 is connected to a suction line 16 extending between the evaporator 10 and the compressors 4. The bypass branch 20 joins the suction line 16 between the evaporator 10 and the compressors 4. Thus, the bypass branch 20 connects to the suction line 16 downstream of the evaporator 10. A reservoir 18 is provided along the suction line 16.

[0037] A second return line 32 extends from downstream of the EXV 26 and connects to the first liquid line 22 close to the outdoor exchanger 12. A third return line 34 extends from downstream of the EXV 26 and connects to the second liquid line 28 close to the heat recovery exchanger 14. In the arrangement shown, the second return line 32 and the third return line 34 are formed as a common portion, which branches off from the first return line 30, and then splits into a first portion and a second portion, which join the first liquid line 22 and the second liquid line 28, respectively.

[0038] Valves 36, 38, and 40 are installed along the first return line 30, the second return line 32, and the third return line 34, respectively. Check valves 42 and 44 are also installed along the first liquid line 22 and the second liquid line 28, respectively.

[0039] A container line 46, including container 48, is connected between the first liquid line 22 and the second liquid line 28 and the second return line 32 and the third return line 34. Specifically, container line 46 is coupled to the common portion of the first liquid line 22 and the second liquid line 28 and the common portion of the second return line 32 and the third return line 34. An injection valve 50 is provided along container line 46 on a first side of container 48, and a discharge valve 52 is provided along container line 46 on a second side of container 48. Injection valve 50 is located between the first liquid line 22, the second liquid line 28 and container 48, while discharge valve 52 is located between container 48 and the second return line 32 and the third return line 34. Therefore, container line 46 is arranged in parallel with EXV 26 and connected to either side of EXV 26, with injection valve 50 on the upstream high-pressure side and discharge valve 52 on the downstream low-pressure side. Therefore, a pressure difference exists across container line 46.

[0040] Figure 1 The HVAC system 2 is shown in cooler mode. In cooler mode, the four-way valve 8 connects the first port to the second port, causing the exhaust line 6 to be connected to the outdoor heat exchanger 12. In this mode, the outdoor heat exchanger's fan 9 is running. The four-way valve 8 also connects the third port to the fourth port, but these ports are not used in this mode, as described separately below.

[0041] In cooler mode, valve 36 on the first return line 30 is set to the open position, while valve 38 on the second return line 32 and valve 40 on the third return line 34 are set to the closed position.

[0042] Refrigerant, in the form of hot compressed gas, is discharged from compressor 4 into discharge line 6. The hot compressed gas reaches outdoor heat exchanger 12 through four-way valve 8. In outdoor heat exchanger 12, the hot compressed gas is cooled by outdoor air flowing through the coils of outdoor heat exchanger 12 by means of fan 9. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then leaves outdoor heat exchanger 12 via first liquid line 22 and reaches EXV 26 through dryer 24. EXV 26 reduces the pressure of the refrigerant, thereby also lowering its temperature. Pressure and temperature transducers can be used to control the amount of subcooling applied to the refrigerant in outdoor heat exchanger 12.

[0043] Cold liquid refrigerant enters the evaporator 10 along the first return line 30 through the open valve 36. Water flows into the evaporator 10 via the cold water supply conduit 11. The water is warmer than the refrigerant passing through the evaporator 10, so the refrigerant absorbs heat from the water, thereby reducing the temperature of the water and increasing the temperature of the refrigerant. The temperature of the refrigerant is increased sufficiently to cause the refrigerant to evaporate back to a gaseous form. The cooled water is discharged from the evaporator 10 via the cold water return conduit 13 and can be used to provide cooling to the interior of a building. The water can be cooled to a temperature in the range of -12°C to +20°C.

[0044] Low pressure gaseous refrigerant returns to the compressor 4 along the suction line 16 and via the reservoir 18. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the evaporator 10.

[0045] The outdoor exchanger 12 has a relatively large volume (larger than the evaporator 10 and the heat recovery exchanger 14, as the outdoor exchanger 12 uses air rather than water), so a greater refrigerant capacity is required in the refrigerant circuit during this mode of operation. Therefore, the injection valve 50 and the discharge valve 52 are adjusted to release the full volume of refrigerant from the reservoir 48 to the circuit via the first return line 30.

[0046] The heat recovery exchanger 14 is not used in the chiller mode, so water does not flow through the hot water supply conduit 15 and the hot water return conduit 17.

[0047] It can be seen that in the chiller mode, the heat of the cooling water is exhausted to the outdoor ambient air through the ventilation.

[0048] Figure 2 The HVAC system 2 is shown in the heat pump mode. In the heat pump mode, the four-way valve 8 connects the first port to the fourth port, so that the discharge line 6 is connected to the heat recovery exchanger 14. The four-way valve 8 also connects the second port to the third port, so that the outdoor exchanger 12 is connected to the bypass branch 20.

[0049] In the heat pump mode, the valve 36 on the first return line 30 and the valve 40 on the third return line 34 are set in the closed position, while the valve 38 on the second return line 32 is set in the open position.

[0050] The refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the heat recovery exchanger 14. Water flows into the heat recovery exchanger 14 via the hot water supply conduit 15. The water is colder than the refrigerant passing through the heat recovery exchanger 14, and therefore the water absorbs heat from the refrigerant, thereby increasing the temperature of the water and decreasing the temperature of the refrigerant. The heated water is discharged from the heat recovery exchanger 14 via the hot water return conduit 17, and can be used to provide heating to the interior of a building. The water can be heated to a temperature in the range of 25 °C to 60 °C.

[0051] Thus, in the heat recovery exchanger 14, the hot compressed gas is cooled by the water flowing through the heat recovery exchanger 14. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then leaves the heat recovery exchanger 14 via the second liquid line 28, and passes through the dryer 24 to the EXV 26. The EXV 26 reduces the pressure of the refrigerant, and thereby also decreases its temperature. A pressure and temperature transducer can be used to control the amount of sub-cooling applied to the refrigerant in the heat recovery exchanger 14.

[0052] The cool liquid refrigerant passes along the second return line 32 through the open valve 38 and into the outdoor exchanger 12. The fan 9 is activated to draw ambient air through the outdoor exchanger 12. The air is warmer than the refrigerant passing through the outdoor exchanger 12, and therefore the refrigerant absorbs heat from the air, thereby decreasing the temperature of the air and increasing the temperature of the refrigerant. The temperature of the refrigerant is increased sufficiently to cause the refrigerant to evaporate back into a gaseous form. Thus, the outdoor exchanger 12 acts as an evaporator in this mode of operation.

[0053] The low pressure gaseous refrigerant passes through the four-way valve 8, and along the bypass branch 20 and via the reservoir 18 back to the compressor 4. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the outdoor exchanger 12.

[0054] Because the outdoor exchanger 12 is operating as an evaporator in the heat pump mode and therefore receives liquid refrigerant, less refrigerant capacity is required during this mode of operation compared to the chiller mode described previously. Therefore, the injection valve 50 and the discharge valve 52 are adjusted to allow the refrigerant to partially inject into the vessel 48 to ensure that the correct refrigerant capacity is present in the circuit.

[0055] It can be seen that in the heat pump mode, heat is removed from the ambient air and transferred to the hot water loop.

[0056] Figure 3The HVAC system 2 is shown in a defrost mode. This mode is used after the heat pump mode to defrost the outdoor exchanger 12, which acted as an evaporator during the heat pump mode. In the defrost mode, the four-way valve 8 connects the first port to the second port so that the discharge line 6 is connected to the outdoor exchanger 12. In this mode, the fan 9 of the outdoor exchanger is not running. The four-way valve 8 also connects the third port to the fourth port so that the heat recovery exchanger 14 is connected to the bypass branch 20.

[0057] In the defrost mode, the valve 36 on the first return line 30 and the valve 38 on the second return line 32 are set in the closed position, while the valve 40 on the third return line 34 is set in the open position.

[0058] Refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the outdoor exchanger 12, thereby defrosting any ice that has formed on the outdoor exchanger 12. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then exits the outdoor exchanger 12 via the first liquid line 22 and passes through the drier 24 to the EXV 26. The EXV 26 reduces the pressure of the refrigerant, thereby also reducing its temperature. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the outdoor exchanger 12.

[0059] The cold liquid refrigerant passes along the third return line 34 through the open valve 40 and into the heat recovery exchanger 14. In the defrost mode, water does not flow into or out of the heat recovery exchanger 14 via the hot water supply conduit 15 and the hot water return conduit 17. In the heat recovery exchanger 14, the temperature of the refrigerant is raised sufficiently to cause the refrigerant to evaporate back into a gaseous form. Thus, in this mode of operation, the heat recovery exchanger 14 acts as an evaporator.

[0060] The low pressure gaseous refrigerant passes through the four-way valve 8 and along the bypass branch 20 and back to the compressor 4 via the reservoir 18. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the heat recovery exchanger 14.

[0061] The refrigerant capacity requirement for the defrost mode is comparable to the chiller mode, as the outdoor exchanger 12 acts as a condenser in both modes and the evaporator 10 and the heat recovery exchanger 14 have substantially similar volumes. Thus, like the chiller mode, the defrost mode requires sufficient refrigerant so that the container 48 is completely discharged of refrigerant. In the defrost mode, the injection valve 50 can be closed and the discharge valve 52 adjusted to slowly release the full volume of refrigerant from the container 48 to the circuit via the third return line 34, thereby improving the defrost efficiency.

[0062] The evaporator 10 is not used in the defrost mode, so water does not flow through the cold water supply conduit 11 and the cold water return conduit 13.

[0063] Figure 4 The HVAC system 2 is shown in a heat recovery mode. In the heat recovery mode, the four-way valve 8 connects the first port to the fourth port, so that the discharge line 6 is connected to the heat recovery exchanger 14. The four-way valve 8 also connects the second port to the third port, but these ports are not used in this mode, as described further below.

[0064] In the heat recovery mode, the valve 38 on the second return line 32 and the valve 40 on the third return line 34 are set in the closed position, while the valve 36 on the first return line 30 is set in the open position.

[0065] Refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the heat recovery exchanger 14. Water flows into the heat recovery exchanger 14 via the hot water supply conduit 15. The water is cooler than the refrigerant passing through the heat recovery exchanger 14, so the water absorbs heat from the refrigerant, thereby raising the temperature of the water and lowering the temperature of the refrigerant. The heated water is discharged from the heat recovery exchanger 14 via the hot water return conduit 17, and can be used to provide heating to the interior of the building.

[0066] Thus, in the heat recovery exchanger 14, the hot compressed gas is cooled by the water flowing through the heat recovery exchanger 14. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then leaves the heat recovery exchanger 14 via the second liquid line 28, and passes through the desiccant 24 to the EXV 26. The EXV 26 reduces the pressure of the refrigerant, thereby also lowering its temperature. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the heat recovery exchanger 14.

[0067] The cool liquid refrigerant passes along the first return line 30 through the open valve 36 into the evaporator 10. Water flows into the evaporator 10 via the cold water supply conduit 11. The water is warmer than the refrigerant passing through the evaporator 10, so the refrigerant absorbs heat from the water, thereby lowering the temperature of the water and raising the temperature of the refrigerant. The temperature of the refrigerant is raised sufficiently for the refrigerant to evaporate back into a gaseous form. The cooled water is discharged from the evaporator 10 via the cold water return conduit 13, and can be used to provide cooling to the interior of the building.

[0068] The low pressure gaseous refrigerant passes along the suction line 16 and returns to the compressor 4 via the reservoir 18. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the evaporator 10.

[0069] As previously mentioned, the evaporator 10 and heat recovery exchanger 14 have a smaller volume than the outdoor exchanger 12, such that in the heat recovery mode the refrigerant charge requirement is at its minimum. Thus, in this mode the charge valve 50 is opened and the discharge valve 52 is modulated such that the vessel 48 is charged with refrigerant until it is almost full. This reduces the effective refrigerant charge in the circuit, thereby ensuring efficient operation.

[0070] The outdoor exchanger 12 is not used in the heat recovery mode, so the fan 9 is not activated.

[0071] It can be seen that in the heat recovery mode the heat of the cooling water is recovered on the hot water loop.

[0072] The settings of the HVAC system 2 can be controlled using a suitable controller (e.g. the controller 3 shown in Figures 1 to 4 Figure 1). In particular, the controller 3 is able to control the positions of the various valves and other components in response to the current mode of operation and feedback from the various sensors. The controller 3 can be a wired unit or a wireless unit. As previously mentioned, the discharge of refrigerant from the vessel 48 can be used to provide a desired refrigerant liquid subcooling. Thus, the subcooling can be used to measure whether the vessel 48 is to be charged or discharged (e.g. based on a comparison between the current subcooling and a subcooling setpoint), thereby avoiding the need for any liquid level sensors in the vessel 48. Alternatively, the vessel 48 can have a liquid level sensor for directly determining the volume of refrigerant present in the vessel 48. Alternatively, the volume of refrigerant can be determined based on the flow through the charge valve 50 and the discharge valve 52.

[0073] Figures 5 to 9 Figures 2 and 3 each show a schematic diagram of an HVAC system 102 according to a further embodiment of the application. The HVAC system 102 generally comprises the components previously described in relation to the HVAC system 2, and those components are indicated by corresponding reference numerals in Figures 5 to 9 Figures 2 and 3. Furthermore, those components are arranged in the same manner in the HVAC system 102, so Figures 5 to 9 the following description will focus on the additional components and functionality included in the HVAC system 102.

[0074] The HVAC system 102 also includes a suction line heat exchanger (SLHX) 54. The SLHX 54 is connected along the suction line and the liquid return line. In particular, the SLHX 54 is connected on the liquid return line between the dryer 24 and the expansion valve 26, and on the suction line 16 between the evaporator 10 and the compressor 4. A three-way valve 56 is provided upstream of the SLHX 54 and is connected with a bypass line 58. The three-way valve 56 can be controlled to modulate the liquid through the SLHX 54, as well as to completely bypass the SLHX 54, as will be described further below.

[0075] The HVAC system 102 also includes a pressure relief valve 60 (configured at, for example, 6 bar) disposed along a pressure line 62 connected between the discharge line 6 and the vessel 48.

[0076] Another pressure relief valve 64 (configured at, for example, 36 bar) is disposed along a discharge line 66 connected between the liquid return lines 30, 32, 34 and the second liquid line 28. The pressure relief valve 64 allows for the release of liquid refrigerant when the system is not in use to avoid reaching burst pressure when refrigerant is trapped between the EXV 26 and the check valves 42, 44 or the EXV 26 and the valves 36, 38, 40.

[0077] An evaporator gas valve 68 is disposed on the second side between the evaporator 10 and the SLHX 54 proximate the evaporator 10. The evaporator gas valve 68 prevents freezing of the evaporator 10 when the heating demand is off and water is not being supplied to the evaporator 10 when in the heat pump mode. Similarly, an outdoor gas valve 70 is disposed on the first side between the outdoor exchanger 12 and the four-way valve 8 proximate the outdoor exchanger 12 for the case where the outdoor exchanger 12 is not in use.

[0078] The HVAC system 102 also includes a hot gas bypass valve 72 disposed along a bypass line 74. One end of the bypass line is connected between the four-way valve 8 and the heat recovery exchanger 14 and the other end is connected between the outdoor exchanger 12 and the four-way valve 8 (or more specifically, between the outdoor exchanger 12 and the gas valve 70).

[0079] Figure 5 The HVAC system 102 is shown in the chiller mode. In the chiller mode, the four-way valve 8 connects the first port to the second port so that the discharge line 6 is connected to the outdoor exchanger 12. In this mode, the fan 9 of the outdoor exchanger is running. The four-way valve 8 also connects the third port to the fourth port, but these ports are not used in this mode as described further below.

[0080] In the chiller mode, the valve 36 on the first return line 30 is disposed in the open position, while the valve 38 on the second return line 32 and the valve 40 on the third return line 34 are disposed in the closed position. The gas valve 68 and the gas valve 70 are also disposed in the open position. The hot gas bypass valve 72 is closed.

[0081] Refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the outdoor exchanger 12. In the outdoor exchanger 12, the hot compressed gas is cooled by outdoor air which is caused to flow over the coils of the outdoor exchanger 12 by means of the fan 9. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then leaves the outdoor exchanger 12 via the first liquid line 22 and passes through the dryer 24 to the EXV 26 via the three-way valve 56 and the SLHX 54. The EXV 26 reduces the pressure of the refrigerant, thereby also reducing its temperature. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the outdoor exchanger 12.

[0082] The cool liquid refrigerant passes along the first return line 30 through the open valve 36 into the evaporator 10. Water is caused to flow into the evaporator 10 via the cold water supply conduit 11. The water is warmer than the refrigerant passing through the evaporator 10, so the refrigerant absorbs heat from the water, thereby reducing the temperature of the water and increasing the temperature of the refrigerant. The temperature of the refrigerant is increased sufficiently to cause the refrigerant to evaporate back into a gaseous form. The cooled water is discharged from the evaporator 10 via the cold water return conduit 13 and can be used to provide cooling to the interior of a building.

[0083] The low pressure gaseous refrigerant passes along the suction line 16 and via the reservoir 18 back to the compressor 4. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the evaporator 10. Further superheating of the refrigerant is provided in the suction line 16 as the gaseous refrigerant passes through the SLHX 54 with the hot liquid refrigerant flowing to the EXV 26. The SLHX 54 therefore minimises the amount of liquid droplets in the refrigerant returning to the compressor 4 via the suction line 16. The reservoir 18 can therefore be omitted in some arrangements. The three-way valve 56 can be adjusted to allow some liquid refrigerant to bypass the SLHX 54 via the bypass line 58 to provide the desired superheat.

[0084] As described for the HVAC system 2, the outdoor exchanger 12 has a relatively large volume (larger than the evaporator 10 and the heat recovery exchanger 14, as the outdoor exchanger 12 uses air rather than water), so a greater refrigerant capacity is required in the refrigerant circuit during this mode of operation. The refrigerant circuit is therefore arranged to provide a greater refrigerant capacity in the cooler mode than in the heating mode. Figure 5 In the example shown, the injection valve 50 is closed and the discharge valve 52 is open so as to release the full volume of refrigerant from the container, but in other arrangements the injection valve 50 and the discharge valve 52 can be adjusted as shown so as to release the required volume and provide the desired subcooling. Figure 1 In the example shown, the injection valve 50 is closed and the discharge valve 52 is open so as to release the full volume of refrigerant from the container, but in other arrangements the injection valve 50 and the discharge valve 52 can be adjusted as shown so as to release the required volume and provide the desired subcooling.

[0085] The heat recovery exchanger 14 is not used in the cooler mode, so water does not flow through the hot water supply conduit 15 and the hot water return conduit 17.

[0086] In the chiller mode, with the outdoor ambient air temperature below the evaporator temperature, the pressure reducing valve 60 is activated and gas is supplied from the compressor 4 to the vessel 48.

[0087] Figure 6 The HVAC system 102 is shown in the heat pump mode. In the heat pump mode, the four-way valve 8 connects the first port to the fourth port so that the discharge line 6 is connected to the heat recovery exchanger 14. The four-way valve 8 also connects the second port to the third port so that the outdoor exchanger 12 is connected to the bypass branch 20.

[0088] In the heat pump mode, the valves 36 on the first return line 30 and 40 on the third return line 34 are set in the closed position, while the valve 38 on the second return line 32 is set in the open position. The evaporator gas valve 68 is set in the closed position, while the outdoor gas valve 70 is set in the open position. The hot gas bypass valve 72 is closed.

[0089] Refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the heat recovery exchanger 14. Water flows into the heat recovery exchanger 14 via the hot water supply conduit 15. The water is colder than the refrigerant passing through the heat recovery exchanger 14, so the water absorbs heat from the refrigerant, thereby raising the temperature of the water and lowering the temperature of the refrigerant. The heated water is discharged from the heat recovery exchanger 14 via the hot water return conduit 17 and can be used to provide heating to the interior of a building.

[0090] Thus, in the heat recovery exchanger 14, the hot compressed gas is cooled by the water flowing through the heat recovery exchanger 14. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then leaves the heat recovery exchanger 14 via the second liquid line 28 and passes through the desiccant 24 to the EXV 26 via the three-way valve 56 and the SLHX 54. The EXV 26 reduces the pressure of the refrigerant, thereby also lowering its temperature. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the heat recovery exchanger 14.

[0091] The cool liquid refrigerant passes along the second return line 32 through the open valve 38 and into the outdoor exchanger 12. The fan 9 is activated to draw ambient air through the outdoor exchanger 12. The air is warmer than the refrigerant passing through the outdoor exchanger 12, so the refrigerant absorbs heat from the air, thereby lowering the temperature of the air and raising the temperature of the refrigerant. The temperature of the refrigerant is raised sufficiently for the refrigerant to evaporate back into a gaseous form. Thus, the outdoor exchanger 12 acts as an evaporator in this mode of operation.

[0092] The low pressure gaseous refrigerant passes through the four-way valve 8 and along the bypass branch 20 and back to the compressor 4 via the SLHX 54. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the outdoor exchanger 12. Further superheat of the refrigerant is provided in the suction line 16 as the gaseous refrigerant passes through the SLHX 54 with the hot liquid refrigerant flowing to the EXV 26. Thus, the SLHX 54 minimizes the liquid droplets in the refrigerant returning to the compressor 4 via the suction line 16. The three-way valve 56 can be adjusted to allow some liquid refrigerant to bypass the SLHX 54 via the bypass line 58 to provide the desired superheat.

[0093] As described for the HVAC system 2, since the outdoor exchanger 12 is operating as an evaporator in the heat pump mode and thus receives liquid refrigerant, less refrigerant capacity is required during this mode of operation than in the chiller mode described earlier. Thus, the injection valve 50 and the discharge valve 52 are adjusted to allow the refrigerant to partially inject the reservoir 48 to ensure the correct refrigerant capacity is present in the circuit.

[0094] Figure 7 The HVAC system 102 is shown in the defrost mode. In the defrost mode, the four-way valve 8 connects the first port to the second port so that the discharge line 6 is connected to the outdoor exchanger 12. In this mode, the fan 9 of the outdoor exchanger is not operating. The four-way valve 8 also connects the third port to the fourth port so that the heat recovery exchanger 14 is connected to the bypass branch 20.

[0095] In the defrost mode, the valve 36 on the first return line 30 and the valve 38 on the second return line 32 are set in the closed position, while the valve 40 on the third return line 34 is set in the open position. The evaporator gas valve 68 is set in the closed position, while the outdoor gas valve 70 is set in the open position. The hot gas bypass valve 72 is closed.

[0096] Refrigerant in the form of hot compressed gas is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the outdoor exchanger 12, thereby defrosting any ice that has formed on the outdoor exchanger 12. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then exits the outdoor exchanger 12 via the first liquid line 22 and passes through the drier 24 to the EXV 26. In this mode, the three-way valve is closed so that all of the refrigerant is transmitted along the bypass line 58, thereby completely bypassing the SLHX 54. The EXV 26 reduces the pressure, and thus the temperature, of the refrigerant. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the outdoor exchanger 12.

[0097] The cold liquid refrigerant passes through the open valve 40 along the third return line 34 and into the heat recovery exchanger 14. In the defrost mode, water does not flow into or out of the heat recovery exchanger 14 via the hot water supply conduit 15 and the hot water return conduit 17. In the heat recovery exchanger 14, the temperature of the refrigerant is raised enough to cause the refrigerant to evaporate back into gaseous form. Thus, in this mode of operation, the heat recovery exchanger 14 acts as an evaporator.

[0098] The low pressure gaseous refrigerant passes through the four-way valve 8 and along the bypass branch 20 and back to the compressor 4 via the reservoir 18. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the heat recovery exchanger 14.

[0099] As described for the HVAC system 2, the refrigerant capacity requirement for the defrost mode is comparable to the chiller mode, as the outdoor exchanger 12 acts as a condenser in both modes, and the evaporator 10 and the heat recovery exchanger 14 have substantially similar volumes. Thus, like the chiller mode, the defrost mode requires enough refrigerant so that the container 48 is completely discharged of refrigerant. In the defrost mode, the injection valve 50 can be closed and the discharge valve 52 adjusted to slowly release the full volume of refrigerant from the container 48 to the circuit via the third return line 34, thereby improving the defrost efficiency.

[0100] The evaporator 10 is not used in the defrost mode, so water does not flow through the cold water supply conduit 11 and the cold water return conduit 13.

[0101] Figure 8 The HVAC system 102 is shown in the heat recovery mode. In the heat recovery mode, the four-way valve 8 connects the first port to the fourth port, so that the discharge line 6 is connected to the heat recovery exchanger 14. The four-way valve 8 also connects the second port to the third port, but these ports are not used in this mode, as described further below.

[0102] In the heat recovery mode, the valve 38 on the second return line 32 and the valve 40 on the third return line 34 are set in the closed position, while the valve 36 on the first return line 30 is set in the open position. The evaporator gas valve 68 is set in the open position, while the outdoor gas valve 70 is set in the closed position. The hot gas bypass valve 72 is closed.

[0103] The refrigerant, in the form of hot compressed gas, is discharged from the compressor 4 into the discharge line 6. The hot compressed gas passes through the four-way valve 8 to the heat recovery exchanger 14. Water is flowed into the heat recovery exchanger 14 via the hot water supply conduit 15. The water is cooler than the refrigerant passing through the heat recovery exchanger 14, so the water absorbs heat from the refrigerant, thereby raising the temperature of the water and lowering the temperature of the refrigerant. The heated water is discharged from the heat recovery exchanger 14 via the hot water return conduit 17 and can be used to provide heating to the interior of the building.

[0104] Thus, in the heat recovery exchanger 14, the hot compressed gas is cooled by water flowing through the heat recovery exchanger 14. This causes the refrigerant to condense into a liquid form. The liquid refrigerant then exits the heat recovery exchanger 14 via the second liquid line 28 and passes through the dryer 24 to the EXV 26 via the three-way valve 56 and the SLHX 54. The EXV 26 reduces the pressure of the refrigerant, thereby also reducing its temperature. A pressure and temperature transducer can be used to control the amount of subcooling applied to the refrigerant in the heat recovery exchanger 14.

[0105] The cool liquid refrigerant passes along the first liquid line 30 through the open valve 36 and into the evaporator 10. Water flows into the evaporator 10 via the cold water supply conduit 11. The water is warmer than the refrigerant passing through the evaporator 10, so the refrigerant absorbs heat from the water, thereby reducing the temperature of the water and increasing the temperature of the refrigerant. The temperature of the refrigerant is increased enough to cause the refrigerant to evaporate back into a gaseous form. The cooled water is discharged from the evaporator 10 via the cold water return conduit 13 and can be used to provide cooling to the interior of the building.

[0106] The low pressure gaseous refrigerant passes along the suction line 16 and returns to the compressor 4 via the SLHX 54. A pressure and temperature transducer can be used to control the amount of superheat applied to the refrigerant in the evaporator 10. Further superheating of the refrigerant is provided in the suction line 16 as the gaseous refrigerant passes through the SLHX 54 with the hot liquid refrigerant flowing to the EXV 26. Thus, the SLHX 54 minimizes the liquid droplets in the refrigerant returning to the compressor 4 via the suction line 16. The three-way valve 56 can be adjusted to allow some liquid refrigerant to bypass the SLHX 54 via the bypass line 58 to provide the desired superheat.

[0107] As described for the HVAC system 2, in the heat recovery mode, the refrigerant capacity demand is at its minimum amount. Thus, in this mode, the injection valve 50 and the discharge valve 52 are adjusted so that the tank 48 injects refrigerant until it is almost full. This reduces the effective refrigerant capacity in the circuit, thereby ensuring efficient operation.

[0108] Figure 9 The HVAC system 102 is shown in a partial heat recovery mode, which can be used when the heat recovery demand is lower than the cooling demand. The partial heat recovery mode corresponds to the heat recovery mode, except that the hot gas bypass valve 72 is adjusted to allow some of the hot gas to divert from the heat recovery exchanger 14 and instead flow to the outdoor exchanger 12.

[0109] In the outdoor exchanger 12, the hot compressed gas is cooled by outdoor air that flows through the coil of the outdoor exchanger 12 by means of the fan 9 (which can run at a slower speed compared to the cooling mode). In the heat recovery exchanger 14, the hot compressed gas is cooled by water that flows through the heat recovery exchanger 14. This causes the refrigerant to condense into a liquid form in both the outdoor exchanger 12 and the heat recovery exchanger 14. By diverting some of the hot compressed gas to the outdoor exchanger 12, the temperature rise of the water flowing through the heat recovery exchanger 14 is reduced.

[0110] The liquid refrigerant then leaves the outdoor exchanger 12 via the first liquid line 22 and, as in the heat recovery mode, leaves the heat recovery exchanger 14 via the second liquid line 28 and passes through the desiccant 24 to the EXV 26 via the three-way valve 56 and the SLHX 54.

[0111] As in the heat recovery mode, the cold liquid refrigerant enters the evaporator 10 along the first return line 30 through the open valve 36 and is used to cool the water flowing through the evaporator 10.

[0112] As the refrigerant also passes through the outdoor exchanger 12 in the partial heat recovery mode, the required refrigerant capacity is greater than for the heat recovery mode. Therefore, in the partial heat recovery mode, the injection valve 50 and the discharge valve 52 are adjusted so that the vessel 48 is partially injected, although it stores less refrigerant than in the heat recovery mode.

[0113] As described, the refrigerant capacity required for optimal performance varies significantly based on the operating mode that is currently being used (specifically due to the larger internal volume of the outdoor exchanger 12 compared to the evaporator 10 and the heat recovery exchanger 14). The HVAC system 2, 102 allows for easy control of the effective refrigerant capacity present in the circuit based on the current operating mode. This ensures that the refrigerant capacity is optimized in all operating modes, providing improved performance. The circuit is arranged so that the refrigerant always flows in the same direction through the EXV 26. Furthermore, the vessel line 46 is arranged so that the injection valve 50 is always at a higher pressure compared to the discharge valve 52. Therefore, the vessel line 46 is always able to inject and discharge the vessel 48 in all operating modes. The release of refrigerant from the vessel can also be used to control refrigerant liquid subcooling.

[0114] As the system is able to precisely control the effective refrigerant capacity in the system, the volume of the vessel 48 does not need to be precisely sized and can be larger than the required volume. Likewise, the total refrigerant capacity (i.e. including the refrigerant present in the vessel) can be larger than the required amount. Therefore, as the volume of refrigerant does not need to be precisely measured, the vessel arrangement saves time when establishing the system.

[0115] In other examples, as with the HVAC system 2, the SLHX 54 (and the three-way valve 56) and the hot gas bypass valve 72 (and its bypass line 74) can be omitted.

[0116] In both the HVAC system 2 and the HVAC system 102, the valves 36, 38, 40 can be step motor valves. The valves 36, 38, 40 can have sufficient leakage rates such that check valves need to be provided between the valve 36 and the evaporator 10, between the valve 38 and the outdoor exchanger 12, and between the valve 40 and the heat recovery exchanger 14. The leakage through the valves 36, 38, 40 can mean that the pressure relief valve 64 and the discharge line 66 of the HVAC system 102, which are provided to release retained refrigerant, can be omitted.

[0117] While the valve 60 has been described as a pressure relief valve, it can instead be a solenoid or other actuated valve. Such a valve can provide sufficient leakage to allow liquid refrigerant to flow back to the discharge line 6, avoiding excessive pressure when the valve is closed and the tank 48 is full of liquid.

Claims

1. An HVAC system comprising: a fluid circuit for conveying refrigerant; a compressor for compressing refrigerant; three heat exchangers defining an evaporator, an outdoor exchanger and a heat recovery exchanger arranged along the fluid circuit; an expansion valve arranged along the fluid circuit; a reservoir connected in parallel to the expansion valve, wherein an injection valve is located between the reservoir and an upstream connection of the expansion valve and a discharge valve is located between the reservoir and a downstream connection of the expansion valve; a plurality of valves configured to be controlled based on a selected operating mode such that at least one of the outdoor exchanger and the heat recovery exchanger is connected to a discharge line of the compressor and is in series with one of the remaining heat exchangers connected to a suction line of the compressor, the expansion valve being arranged between the heat exchangers; and a controller to control the plurality of valves in response to the selected operating mode; wherein the injection valve and the discharge valve are configured to be regulated to store a volume of refrigerant in the reservoir and to slowly release a volume of refrigerant from the reservoir to provide an effective refrigerant capacity in the fluid circuit corresponding to the selected operating mode, and wherein the selected operating mode is selected from a plurality of operating modes including a partial heat recovery mode in which both the heat recovery exchanger and the outdoor exchanger are connected to the discharge line and the evaporator is connected to the suction line.

2. The HVAC system of claim 1, wherein, The evaporator and / or the heat recovery exchanger is a refrigerant-water heat exchanger and / or the outdoor exchanger is a refrigerant-air heat exchanger.

3. The HVAC system of claim 1 or 2, wherein, An internal volume of the outdoor exchanger is greater than an internal volume of the heat recovery exchanger and / or the evaporator.

4. The HVAC system of claim 1, wherein, The plurality of operating modes includes the partial heat recovery mode and one or more of: a chiller mode in which the outdoor exchanger is connected to the discharge line and the evaporator is connected to the suction line; a heat pump mode in which the heat recovery exchanger is connected to the discharge line and the outdoor exchanger is connected to the suction line; a thaw mode in which the outdoor exchanger is connected to the discharge line and the heat recovery exchanger is connected to the suction line; and a heat recovery mode in which the heat recovery heat exchanger is connected to the discharge line and the evaporator is connected to the suction line. An effective refrigerant capacity required for the chiller mode is greater than an effective refrigerant capacity required for the heat pump mode; 5. The HVAC system of claim 4, wherein, and / or wherein an effective refrigerant capacity required for the thaw mode is greater than an effective refrigerant capacity required for the heat pump mode; and / or wherein an effective refrigerant capacity required for the heat pump mode is greater than an effective refrigerant capacity required for the heat recovery mode. In the partial heat recovery mode, a hot gas bypass valve upstream of the heat recovery exchanger diverts refrigerant to the outdoor exchanger to control heat recovery at the heat recovery exchanger.

6. The HVAC system of claim 4 or 5, wherein, ​ 7. The HVAC system of claim 1, wherein, The plurality of valves includes a four-way valve configured to connect one of the outdoor heat exchanger and the heat recovery heat exchanger to the discharge line and to connect the other of the outdoor heat exchanger and the heat recovery heat exchanger to the suction line via a bypass branch.

8. The HVAC system of claim 1, wherein, The fluid circuit includes a liquid line connected between the expansion valve and each of the heat recovery heat exchanger and the outdoor heat exchanger, wherein the liquid line is disposed on an upstream side of the expansion valve.

9. The HVAC system of claim 1, wherein, The fluid circuit includes a liquid line connected between the expansion valve and each of the heat recovery heat exchanger and the outdoor heat exchanger, wherein the liquid line is disposed on an upstream side of the expansion valve.

10. The HVAC system of claim 9, wherein, The plurality of valves includes a valve disposed along each of the liquid lines to allow connection of a heat exchanger connected to the suction line of the compressor to the expansion valve.

11. The HVAC system of claim 1, further comprising: A suction line heat exchanger connected to a portion of the fluid circuit upstream of the expansion valve and the suction line.

12. The HVAC system of claim 11, wherein, A bypass line is disposed across the suction line heat exchanger on the portion of the fluid circuit upstream of the expansion valve; wherein a valve is provided to control flow of refrigerant through the bypass line to bypass the suction line heat exchanger.

13. The HVAC system of claim 1, further comprising: A pressure line connecting the discharge line to the vessel and having a pressure relief valve disposed between the compressor and the vessel.

14. The HVAC system of claim 1, further comprising a desiccant upstream of the expansion valve.

15. The HVAC system of claim 1, wherein, The evaporator includes a cold water supply conduit and a cold water return conduit and the heat recovery heat exchanger includes a hot water supply conduit and a hot water return conduit.

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