Heat utilization in environmental control systems

Abstract

An environmental control system (110) for heating at least one enclosed space (14) is disclosed. The system (110) includes a heat pump circuit (22) including a compressor (30), a heat output stage, an expansion device, and an evaporator (314) arranged in series along a flow path of a refrigerant. The heat output stage includes a primary heat exchanger (34) and a secondary heat exchanger (36), both configured to transfer heat from the refrigerant to one or more external media in thermal communication with the at least one enclosed space (14). The primary heat exchanger (34) and the secondary heat exchanger (36) are connected in series along the flow path such that the secondary heat exchanger (36) transfers excess heat remaining within the refrigerant after traveling through the primary heat exchanger (34) to the one or more external media.

Description

Technical Field

[0001] This invention generally relates to environmental control systems with heat pump capabilities, such as heating, ventilation, and air conditioning (HVAC) systems. In particular, this invention relates to environmental control systems and methods with improved heating efficiency and coefficient of performance (i.e., the ratio of useful heating energy to work input to the system). Background Technology

[0002] Environmental control systems, such as HVAC systems, have been developed to manage environmental conditions, such as temperature, in enclosed spaces. For example, HVAC systems are commonly used to heat the air in the passenger compartments of public transportation vehicles such as buses or trains.

[0003] Environmental control systems typically include a heat pump circuit comprising a compressor, a heat output stage (e.g., a condenser or gas cooler, depending on the type of refrigerant used), an expansion unit, and an evaporator connected in a loop. The heat pump circuit generally defines a flow path for the refrigerant to transfer the heat absorbed by the refrigerant at the evaporator to the heat output stage, where heat is then released from the refrigerant to heat the enclosed space.

[0004] The refrigerant flow path can be said to begin at the compressor, driven by a prime mover, which compresses the refrigerant to form a superheated refrigerant gas. This superheated refrigerant gas is then conveyed to the heat output stage, which takes the form of a heat exchanger in thermal communication with an enclosed space to be heated. The enclosed space will be relatively cooler than the superheated refrigerant gas, so that the heat energy within the refrigerant is transferred to the enclosed space, thereby heating it. At this point, the refrigerant is either condensed into a liquid or exists as a cooled gas (depending on the type of refrigerant used), and is conveyed from the heat output stage to the evaporator via an expansion device (or a series of devices for reducing refrigerant pressure, including expansion valves and expansion containers for localized refrigerant buildup). The evaporator is in thermal communication with the surrounding environment, which is separated from the enclosed space (e.g., the exterior of a vehicle). As the ambient air circulates on the evaporator, the refrigerant (at this time in the liquid phase) evaporates, absorbing heat energy from the ambient air. To complete the cycle of the heat pump circuit, the refrigerant is conveyed back from the evaporator to the compressor.

[0005] While such a system can meet the heating needs of most enclosed spaces, the heat exchange between the heat exchanger and the enclosed space is such an inefficient process that not all the heat generated by the system is used to heat the enclosed space. This is disadvantageous because it reduces the system's coefficient of performance (i.e., energy efficiency) and can lead to higher operating costs. For example, to meet the heating requirements of the enclosed space, the heat pump loop must work harder than would be required for a more efficient system, and, for example, drive the compressor at a higher speed.

[0006] Therefore, the present invention seeks to improve the heating efficiency of environmental control systems. Summary of the Invention

[0007] According to one aspect, an environmental control system is provided for heating at least one enclosed space. The system includes a heat pump circuit comprising a compressor, a heat output stage, an expander, and an evaporator arranged in series along a refrigerant flow path. The heat output stage includes a primary heat exchanger and a secondary heat exchanger configured to transfer heat from the refrigerant to at least one external medium (e.g., a corresponding external medium) for heating the at least one enclosed space. The primary and secondary heat exchangers are connected in series along the flow path such that the secondary heat exchanger is configured to receive the refrigerant from the primary heat exchanger and transfer any remaining heat in the refrigerant after the primary heat exchanger to the at least one external medium. For example, the invention provides two separate heat sources (in the form of a primary heat exchanger and a secondary heat exchanger) for heating the at least one enclosed space.

[0008] By providing a secondary heat exchanger connected in series with and downstream of the refrigerant outlet of the primary heat exchanger, the heating capacity or thermal energy remaining in the refrigerant after heat exchange at the primary heat exchanger can be utilized at the secondary heat exchanger to heat the at least one enclosed space. For example, an environmental control system can utilize the thermal energy (generated by the heat pump circuit) that would otherwise be wasted or lost within the system. Therefore, the heat pump circuit (e.g., a compressor) can operate with a higher coefficient of performance and can meet a given heating requirement in one or more enclosed spaces with lower power consumption.

[0009] Furthermore, by having two heat exchangers in the heat output stage, the present invention provides a more versatile system that can be more easily adapted to maximize system efficiency. For example, the dimensions (in terms of the area of ​​the heat transfer surface) and / or the positions (relative to one or more enclosed spaces) of the primary and secondary heat exchangers can be independently set and customized during manufacturing to implement the system in a configuration that maximizes system efficiency.

[0010] The at least one external medium can be any one or more heat-conducting media outside the heat pump loop itself. More than one medium may be present, for example, one medium for each of the primary and secondary heat exchangers. When more than one medium is present, it can be in thermal communication with the same enclosed space or multiple different enclosed spaces to heat the enclosed space(s).

[0011] Each of the primary and secondary heat exchangers can operate as a condenser and / or a gas cooler, depending on the type of refrigerant used in the heat pump circuit. For example, in an arrangement using a commonly used refrigerant (e.g., so-called "R407C"), one or more of the primary and secondary heat exchangers can condense the refrigerant from the gas phase to a liquid as it releases energy to the external medium. However, other refrigerants may not undergo a phase change from gas to liquid as they flow through the primary and / or secondary heat exchangers, and in this case, the primary and / or secondary heat exchangers can be referred to as gas coolers.

[0012] The primary heat exchanger and the secondary heat exchanger may be downstream of the compressor and upstream of the evaporator in the direction of refrigerant flow (around the heat pump loop during the heat pump cycle).

[0013] The primary heat exchanger and the secondary heat exchanger may be the first two active components downstream of the compressor in the direction of refrigerant flow.

[0014] The primary heat exchanger and the secondary heat exchanger may be upstream of the expansion device in the direction of refrigerant flow. The expansion device may be, for example, a thermal expansion valve operable to control the amount of refrigerant released into the evaporator. The expansion device itself is upstream of the evaporator in the direction of refrigerant flow.

[0015] The primary heat exchanger and the secondary heat exchanger can be of different types.

[0016] The primary heat exchanger can be a refrigerant-to-liquid heat exchanger. In other words, the heat exchanger can be configured to transfer heat from the refrigerant to a liquid medium outside the heat pump loop.

[0017] The secondary heat exchanger can be a refrigerant-to-gas heat exchanger. In other words, the heat exchanger can be configured to transfer heat from the refrigerant to an external gaseous medium, such as air within the at least one enclosed space.

[0018] The primary heat exchanger and the secondary heat exchanger can be configured to transfer heat from the refrigerant to a corresponding external medium, wherein both external media are used to heat the at least one enclosed space.

[0019] As will become clearer in the following detailed description, the arrangement of the primary heat exchanger being a heat exchanger from refrigerant to liquid and the secondary heat exchanger being a heat exchanger from refrigerant to gas can be particularly advantageous in maximizing the amount of refrigerant heat capacity utilized by the heat output stage, and thereby maximizing the coefficient of performance of the system.

[0020] The primary heat exchanger may be part of a first heat distribution loop that is in thermal communication with a first enclosed space to be heated. In the case that the primary heat exchanger is a refrigerant-to-liquid heat exchanger, the first heat distribution loop may include one or more distribution lines that define a flow path for the liquid medium to flow between the primary heat exchanger (where the liquid medium will gain heat) and one or more convection heaters, for example, located in the enclosed space to be heated (where the liquid medium will release heat).

[0021] The secondary heat exchanger may be part of a second heat distribution loop that is in thermal communication with the second enclosed space to be heated and / or the first enclosed space. In the case where the secondary heat exchanger is a refrigerant-to-gas heat exchanger, the second heat distribution loop may include one or more air ducts defining a flow path for a gaseous medium (e.g., air within the first and / or second enclosed space) to flow between the secondary heat exchanger (where the gaseous medium will gain heat) and the enclosed space to be heated (where the gaseous medium will release heat).

[0022] The refrigerant can be carbon dioxide (CO2) or a CO2-based refrigerant. CO2 or CO2-based refrigerants may be superior to other known refrigerants (e.g., R407C) because they operate at higher superheated gas temperatures, which increases the degree of heat transfer in the heat exchanger. Furthermore, CO2 is naturally occurring and has a global warming potential (GWP) equal to 1.

[0023] This invention is applicable to heating any type of enclosed space. However, it may be particularly advantageous when used to heat enclosed spaces within a vehicle. Therefore, according to another aspect, a vehicle is provided that includes an environmental control system as defined in any of the foregoing statements.

[0024] In such an embodiment, at least one enclosed space (e.g., the first enclosed space and / or the second enclosed space described above) may include the passenger compartment of the vehicle. The primary heat exchanger and the secondary heat exchanger may be configured to heat the same passenger compartment of the vehicle.

[0025] A vehicle can be any type of movable body used to transport people or goods. For example, a vehicle can be a public transport vehicle, such as a bus or a train car.

[0026] In an embodiment that combines a refrigerant-to-air heat exchanger with a refrigerant-to-liquid heat exchanger in public transport vehicles, the applicant deviates from the long-standing industry practice of not using refrigerant-to-air heat exchangers for heating such vehicles. Typically, to meet the heating requirements of public transport vehicles, refrigerant-to-air heat exchangers need to be large, which is impractical and too heavy for use in such vehicles. For example, the additional size and weight associated with a larger heat exchanger significantly increases the energy required to power the drivetrain of such vehicles. However, by providing a combination of a refrigerant-to-air heat exchanger and a refrigerant-to-liquid heat exchanger, the vehicle's heating requirements can be met while reducing the overall size and weight of the heat output stage, compared to the hypothetical arrangement using only a refrigerant-to-air heat exchanger.

[0027] According to another aspect of the invention, a method is provided for heating at least one enclosed space using the aforementioned environmental control system. The method includes using a compressor to drive a refrigerant flow along a flow path defined by a heat pump circuit, wherein the refrigerant flows from the compressor through a primary heat exchanger of a heat output stage in the refrigerant flow direction, and then through a secondary heat exchanger of the heat output stage, such that the secondary heat exchanger transfers the heat remaining in the refrigerant after the primary heat exchanger to at least one external medium.

[0028] The at least one enclosed space may be located within the vehicle as described above. Attached Figure Description

[0029] The invention will now be described by way of example with reference to the accompanying drawings, in which:

[0030] Figure 1 This is a schematic diagram of an exemplary vehicle in which the environmental control system of the present invention can be used;

[0031] Figure 2This is a block diagram schematically illustrating an example embodiment of an environmental control system;

[0032] Figure 3 This is a schematic diagram illustrating the heat pump circuit and heat distribution system of an environmental control system according to an embodiment of the present invention;

[0033] Figure 4 It is an illustrative representation of the use Figures 1 to 3 A flowchart of a method for using an environmental control system to heat the enclosed space of a vehicle; and

[0034] Figure 5 It is shown schematically in Figures 1 to 3 A graph showing the available heat capacity versus refrigerant temperature during the operation of the environmental control system. Detailed Implementation

[0035] Figure 1 An exemplary vehicle 10 is shown that can use the environmental control system of the present invention. Figure 1 In the illustrated embodiment, vehicle 10 is a public transport bus that transports passengers (not shown) between destinations. However, the invention described herein is more generally applicable to any type of vehicle or virtually any type of transport unit (e.g., a container on a flatbed, a transshipment container, a truck, a van, etc.) having an enclosed space where environmental control is possible. The system can be used, for example, in a train carriage.

[0036] like Figure 1 As shown, vehicle 10 includes a frame 12, an enclosed space defined by the frame 12 for a passenger compartment 14, and wheels 16. Although not shown, vehicle 10 includes a propulsion system configured to drive the wheels 16 and a drivetrain (not shown). The propulsion system (e.g., prime mover, engine, etc.) can be an internal combustion engine or an alternative power source (e.g., a battery pack) for powering a motor coupled to the drivetrain of vehicle 10. Vehicle 10 may have a hybrid propulsion system including an internal combustion engine and a power source, which can be selectively used to power the drivetrain.

[0037] An environmental control system 110, particularly an HVAC system, is provided on the roof 18 of the vehicle 10. This environmental control system is configured to control one or more environmental conditions, including but not limited to the temperature of the passenger compartment 14 (but the environmental control system may also, or alternatively, control the conditions in additional or alternative enclosed spaces within the vehicle 10).

[0038] Figure 2 This is a more detailed schematic diagram of the environmental control system 110.

[0039] The environmental control system 110 includes a programmable controller 20. The controller 20 may include a single integrated control unit (not shown) or a distributed network of control elements (not shown). The controller 20 may include a processor, memory, a clock, and input / output (I / O) interfaces (not shown).

[0040] The environmental control system 110 also includes a closed heat pump circuit 22 and a heat distribution system 24 in thermal communication with the heat pump circuit 22. The heat pump circuit 22 includes a compressor, a heat output stage, an expansion device (e.g., a valve), and an evaporator, which are operable under the control of the controller 20 to transfer heat to the heat distribution system 24. The heat distribution system 24 is in thermal communication with the passenger compartment 14 and thus transfers heat received from the heat pump circuit 22 (particularly the heat output stage of the heat pump circuit) to the passenger compartment 14. For this purpose, the heat distribution system 24 includes at least one heat distribution loop (not shown) that defines a flow path for a heat-conducting fluid medium to pass between the heat output stage and the relatively cool passenger compartment 14, whereby the fluid medium absorbs heat from the refrigerant and releases heat to the passenger compartment 14.

[0041] Controller 20 controls the heat pump circuit 22 of the environmental control system 110 to achieve a desired state (i.e., temperature) for the passenger compartment 14. Specifically, controller 20 can be wired or wirelessly connected to one or more sensing devices for measuring multiple operating conditions of the environmental control system 110, such as the internal temperature of the passenger compartment 14, the ambient temperature, and operating parameters of the environmental control system 110 (such as evaporator temperature, pressure, etc.), to allow controller 20 to draw conclusions about what actions must be taken to achieve the desired state. For example, controller 20 can compare the current state (e.g., passenger compartment temperature and ambient temperature) with a target state (e.g., setpoint temperature of the passenger compartment 14) and adjust the current heating capacity delivered by the environmental control system 110 accordingly. This can be accomplished by sending control signals to various passive control devices of the environmental control system 110, such as refrigeration throttle valves, dampers, etc., which control the movement of refrigerant through the heat pump circuit 20.

[0042] The environmental control system 110 further includes a power compartment 26 that houses an internal combustion engine (e.g., a diesel engine) that can provide power to drive the compressor and other components of the heat pump circuit 22. The power compartment 26 may also, or alternatively, house an on-board electric motor that can replace the internal combustion engine to provide power to drive the compressor and other components.

[0043] The controller 20 itself is powered by a power module (not shown), which may include one or more power sources. The power source receives electricity from a generator machine (e.g., a belt-driven alternator, a direct-drive generator, etc.), which is mechanically driven by the prime mover of the electric motor or internal combustion engine of the power compartment 26. However, in other embodiments, components of the power compartment 26 and / or the power module may be integrated with one or more components of the vehicle 10's propulsion system. For example, in the case where the vehicle 10's propulsion system is a hybrid or all-electric system, the onboard electric motor of the power compartment 26 and / or the controller 20 of the environmental control system 110 may be powered by a power source configured to power the vehicle 10's drivetrain.

[0044] In traditional environmental control systems, the heat output stage comprises a single heat exchanger, typically a refrigerant-to-liquid heat exchanger, used to transfer heat from the refrigerant to the external liquid medium within the heat distribution system. However, the heat exchange process in this arrangement is not entirely efficient, such that not all available heat energy within the refrigerant is transferred via the heat distribution system to the liquid medium and thus to the passenger compartment. Furthermore, in the refrigerant-to-liquid heat exchanger, the refrigerant temperature is always significantly higher than the temperature of the liquid medium and the air temperature within the passenger compartment.

[0045] A refrigerant-to-gas heat exchanger can be used instead of a refrigerant-to-liquid heat exchanger. In such an arrangement, theoretically, any temperature difference between the refrigerant and the gaseous medium at their respective outlets can be eliminated, allowing most of the available heat capacity of the refrigerant to be transferred to the heat distribution system. However, in reality, only very large heat exchangers can achieve this, which are typically too bulky and heavy for practical and cost-effective applications (e.g., in vehicles). Therefore, on a scale suitable for vehicle integration, a refrigerant-to-gas heat exchanger will output refrigerant at a temperature higher than that of the gaseous medium and thus higher than the temperature of the passenger compartment.

[0046] The applicant has recognized that in the two arrangements described above, where the temperature of the refrigerant at the outlet of the heat exchanger is higher than the temperature of the fluid medium in the heat distribution system and therefore higher than the temperature of the crew compartment, there is idle thermal energy and heat capacity within the refrigerant. Therefore, the present invention aims to utilize at least some of this available heat capacity to transfer additional thermal energy to the heat distribution system. This is achieved by providing a heat output stage having two separate heat exchangers arranged in series within a heat pump circuit, specifically a primary heat exchanger and a secondary heat exchanger. The heat exchangers are arranged in series such that the secondary heat exchanger receives refrigerant from the primary heat exchanger, which itself is downstream of the compressor. In this way, the secondary heat exchanger can be configured to utilize the excess heat remaining after the refrigerant has traveled through the primary heat exchanger.

[0047] Figure 3 The illustration schematically shows an exemplary embodiment of the present invention. Figure 2 The heat pump circuit 22 and the heat distribution system 24.

[0048] The heat pump circuit 22 includes a compressor 30, a compressor discharge line 32, a primary heat exchanger 34, a secondary heat exchanger 36, an output line 38, an expansion device (e.g., an expansion valve) 310, an evaporator inlet line 312, an evaporator 314, and a suction line 316 connected in series. The heat pump circuit 22 generally defines the flow path for the refrigerant, which in this embodiment may be CO2 or a CO2-based refrigerant, such as so-called "R-744" or "R-455A" refrigerant or similar refrigerants.

[0049] Primary heat exchanger 34 and secondary heat exchanger 36 are the first two active components located downstream of compressor 30 in the refrigerant flow direction 318. Heat exchangers 34 and 36 are referred to as "active" because they are configured to transfer heat between two heat-conducting media (i.e., the refrigerant and an external fluid medium). This contrasts with the passive components of circuit 22 (such as valves or containers), which are not configured to exchange heat between different media.

[0050] In this regard, it should be understood that the heat pump circuit 22 (e.g., output line 38 and / or suction line 316) may contain any number of passive components, such as shut-off devices, check devices, or expansion devices (valves), and / or containers for localized refrigerant build-up or other purposes. Additionally or alternatively, the heat pump circuit 22 may include one or more internal heat exchangers that provide refrigerant-to-refrigerant heat exchange within the heat pump circuit 22 itself. It should be understood that the internal heat exchangers differ from the primary heat exchanger 34 and secondary heat exchanger 36 in that the internal heat exchanger is configured to exchange heat between refrigerants located at different points along the flow path of the heat pump circuit 22 itself, while the primary heat exchanger 34 and secondary heat exchanger 36 are external heat exchangers configured to transfer heat from the refrigerant to separate heat-conducting media outside the refrigerant flow path.

[0051] In this embodiment, the primary heat exchanger 34 is in the form of a refrigerant-to-liquid heat exchanger that operates to transfer heat present in the refrigerant after the compressor to an external liquid medium, such as ethylene glycol or a water-based liquid. The primary heat exchanger 34 can be any type of known heat exchanger suitable for transferring heat from the refrigerant to the liquid medium, including brazed-plate heat exchangers, tube-in-tube heat exchangers, shell-and-tube heat exchangers, or similar heat exchangers known in the art.

[0052] The primary heat exchanger 34 and the liquid medium form part of a heat distribution system 24 of the vehicle 10, particularly a first heat distribution loop 320 of the heat distribution system 24. This first heat distribution loop 320 includes one or more distribution lines (e.g., pipes) configured to receive a heated liquid flow from the liquid outlet of the primary heat exchanger 34 and to deliver the heated liquid flow to a location within the vehicle 10 requiring heating before returning the liquid to the liquid inlet of the primary heat exchanger 34. In the example shown, the first heat distribution loop 320 includes at least one convection heater 322 located within the passenger compartment 14 of the vehicle 10 to heat the air within the passenger compartment 14. The first heat distribution loop 320 may also be in thermal communication with one or more other compartments within the vehicle 10 (e.g., compartments housing electronic components such as batteries requiring heating).

[0053] The secondary heat exchanger 36 is in the form of a refrigerant-to-gas heat exchanger that operates to transfer excess heat remaining in the refrigerant after the primary heat exchanger 34 to an external gaseous medium, in this case, the air within the vehicle's passenger compartment. The secondary heat exchanger 36 can be any known heat exchanger suitable for transferring heat from the refrigerant to the external gaseous medium, such as a finned-tube heat exchanger or a microchannel heat exchanger.

[0054] The secondary heat exchanger 36 and the gaseous medium (air) form part of a second heat distribution loop 324 of the heat distribution system 24. This second heat distribution loop 324 includes one or more conduits for guiding air between the passenger compartment 14 and the secondary heat exchanger 36. Specifically, the air inlet of the secondary heat exchanger 36 is in fluid communication with the passenger compartment 14 via one or more conduits to receive air to be heated from the passenger compartment 14. The air inlet of the secondary heat exchanger 36 may also be in fluid communication with fresh air from outside the vehicle 10. Accordingly, one or more conduits may be configured to guide heated air exiting the air outlet of the secondary heat exchanger 36 into the passenger compartment 14. Similar to the first heat distribution loop 320, this second heat distribution loop 324 may also, or alternatively, be in thermal communication with one or more other compartments within the vehicle 10 (e.g., compartments housing electronic components such as batteries that require heating).

[0055] By providing a secondary heat exchanger 36 downstream of the primary heat exchanger 34, the heat pump circuit 22 is able to use the available heat capacity within the refrigerant leaving the primary heat exchanger 34 to heat the crew compartment 14.

[0056] In this regard, the heat capacity of the heat exchangers can be readily determined using conventional techniques known in the art. Furthermore, the dimensions of each heat exchanger in the heat exchangers can be customized, for example, regarding the area of ​​their heat transfer surfaces, to ensure that the heat exchangers can achieve the desired heat capacity for a given application, i.e., meet the heating requirements of the passenger compartment 14. The system controller 20 can also manage the refrigerant flow through the heat exchangers, for example, by using one or more passive components (e.g., valves) to control and optimize the heating performance between the primary and secondary heat exchangers. In other words, the amount of heat capacity used at the primary heat exchanger can be controlled to ensure optimal allocation of the total available capacity (i.e., in the refrigerant leaving the compressor) between the primary and secondary heat exchangers based on actual system requirements. In this way, an environmental control system can be designed to maximize the system's coefficient of performance.

[0057] Figure 4 This is a schematic illustration of operation during a heat pump cycle. Figures 1 to 3A flowchart of a method for heating the enclosed space of a vehicle using an environmental control system.

[0058] The method begins at box 40, where the refrigerant in the flow path is compressed by compressor 30 to form a superheated refrigerant gas, which is then transported in the flow direction 318 along compressor discharge line 32 to the downstream refrigerant inlet of primary heat exchanger 34.

[0059] like Figure 5 As best illustrated, the refrigerant in heat pump circuit 22 will be at its highest temperature T3 essentially immediately after being discharged from compressor 30. Furthermore, the refrigerant temperature will be significantly higher than the air temperature T1 within passenger compartment 14, and correspondingly higher than the temperature of the liquid medium within the first heat distribution loop 320. Therefore, the available heat capacity within the refrigerant will be at its maximum value C3 at that point.

[0060] At frame 42, the superheated refrigerant gas travels through the primary heat exchanger 34 and transfers some of its heat energy to the liquid medium within the first heat distribution loop 320. During this process, and as... Figure 4 As shown, the refrigerant temperature drops to an intermediate temperature level T2 at the refrigerant outlet of the primary heat exchanger 34. The refrigerant temperature T2 at the outlet of the primary heat exchanger 34 will be higher than the air temperature T1 inside the crew compartment 14 (and in fact, the primary heat exchanger 34 can be designed to ensure this). Therefore, the refrigerant leaving the primary heat exchanger 34 will have excess heat capacity C2 that can be used at that point.

[0061] At frame 44, the refrigerant flows downstream and through a secondary heat exchanger 36, which is a second active component downstream of the compressor 30. By allowing the refrigerant to flow through the secondary heat exchanger 36 downstream of the primary heat exchanger 34, the available heat capacity C2 present in the refrigerant leaving the primary heat exchanger 34 is used to heat the passenger compartment 14. In fact, as... Figure 5 As shown, a secondary heat exchanger 36 for refrigerant to air can be designed to utilize, if not all but most of, the remaining heat capacity C2 within the refrigerant, until that remaining heat capacity is exhausted and the temperature of the refrigerant drops to a temperature T1 close to the same temperature as the crew cabin 14.

[0062] It should be understood that by providing a combination of different heat exchangers, particularly a refrigerant-to-gas heat exchanger downstream of the refrigerant-to-liquid heat exchanger, the available heat capacity within the refrigerant can be maximized. Furthermore, by providing a refrigerant-to-gas heat exchanger downstream of the refrigerant-to-liquid heat exchanger, at least some of the heating requirements of the occupant compartment 14 can be met. The remaining heat capacity within the refrigerant can be exhausted using a refrigerant-to-air secondary heat exchanger 36, which is smaller and lighter than the alternative heat exchangers required when the heat output stage includes only a single refrigerant-to-gas heat exchanger. This avoids the size and weight issues associated with refrigerant-to-gas heat exchangers.

[0063] At frame 46, after exiting the secondary heat exchanger 36, the refrigerant, which has been cooled and condensed into a liquid or in the form of a cooled gas (depending on the refrigerant used), is delivered downstream to the evaporator 314 via the evaporator inlet line 312, but through an expansion device (valve) 310 located upstream of the evaporator 314 on the outlet line 38. The evaporator 314 is in thermal communication with the surrounding environment outside the passenger compartment 14 (and, for example, the vehicle). As ambient air circulates on the evaporator, the liquid phase of the refrigerant evaporates, and absorbs heat energy from the ambient air as it passes through the evaporator.

[0064] At frame 48, vaporized refrigerant is transported from evaporator 314 back to compressor 30 along suction line 316 to restart the heat pump cycle.

[0065] Although the invention is described above as being used to heat the same enclosed space, namely the passenger compartment 14 of vehicle 10, different heat distribution loops can be used to heat two separate enclosed spaces (compartments). In fact, another possible advantage of the invention is that the secondary heat exchanger can use the excess heat capacity remaining from the primary heat exchanger for heating applications completely independent of the primary heat exchanger.

[0066] It should also be understood that although the invention is described above as a refrigerant-to-liquid heat exchanger as the primary heat exchanger and a refrigerant-to-air heat exchanger as the secondary heat exchanger, this is not necessary. Instead, the specific order of the heat exchangers can be appropriately selected according to the given application. As mentioned above, the amount of heat capacity utilized at the primary heat exchanger can be controlled to ensure an optimal allocation of the total available capacity between the primary and secondary heat exchangers based on actual system requirements.

[0067] In summary, it can be seen that this disclosure provides an environmental control system that can be advantageously used to maximize heat transfer from the refrigerant in the heat pump circuit to the enclosed space to be heated, and thus make the system highly efficient.

[0068] The terminology used in this specification is intended to describe particular embodiments and not to be limiting. Unless otherwise expressly stated, the terms “a,” “an,” and “the,” as well as “described,” also include the plural form. The terms “comprising” and / or “including” as used in this specification indicate the presence of the listed features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or components.

[0069] Regarding the foregoing description, it should be understood that changes may be made in details, particularly in terms of the constituent materials used and the shape, size, and arrangement of the components, without departing from the scope of this disclosure. In other words, this disclosure is not limited to the embodiments described above, and any feature may be used alone or in combination with any other feature unless mutually exclusive. Furthermore, this disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

[0070] The term "embodiment" as used in this specification may, but does not necessarily, refer to the same embodiment. This specification and the described embodiments are merely examples. Other and further embodiments may be designed without departing from the basic scope of this disclosure, the true scope of which is indicated by the appended claims.

Claims

1. An environmental control system (110) for heating at least one enclosed space (14), the at least one enclosed space (14) being a passenger compartment of a vehicle (10), the environmental control system (110) comprising: a heat pump circuit (22) comprising, arranged in series along a flow path of a refrigerant, a compressor (30), a heat output stage (34, 36), an expansion device (310), and an evaporator (314); wherein the heat output stage comprises a primary heat exchanger (34) and a secondary heat exchanger (36), the primary heat exchanger (34) and the secondary heat exchanger (36) being configured to transfer heat from the refrigerant to at least one external medium for heating the at least one enclosed space (14); wherein the primary heat exchanger (34) and the secondary heat exchanger (36) are connected in series along the flow path, such that the secondary heat exchanger (36) is configured to receive the refrigerant from the primary heat exchanger (34) and to transfer heat remaining in the refrigerant after the primary heat exchanger (34) to the at least one external medium, wherein the primary heat exchanger (34) is a refrigerant-to-liquid heat exchanger, wherein the secondary heat exchanger (36) is a refrigerant-to-gas heat exchanger, wherein the primary heat exchanger (34) and the secondary heat exchanger (36) are configured to transfer heat from the refrigerant to respective external media, wherein both external media are used for heating the at least one enclosed space (14), and wherein an air inlet of the secondary heat exchanger (36) is in fluid communication with fresh air from outside the vehicle (10).

2. The environmental control system (110) of claim 1, wherein, The primary heat exchanger (34) and the secondary heat exchanger (36) are downstream of the compressor (30) and upstream of the evaporator (314) in a flow direction (318) of the refrigerant.

3. The environmental control system (110) according to claim 1 or 2, wherein The primary heat exchanger (34) and the secondary heat exchanger (36) are the first two active components downstream of the compressor (30) in the flow direction (318) of the refrigerant.

4. The environmental control system (110) according to claim 1, 2 or 3, wherein The primary heat exchanger (34) and the secondary heat exchanger (36) are upstream of the expansion device in the flow direction (318) of the refrigerant, the expansion device itself being upstream of the evaporator (314).

5. The environmental control system (110) of any preceding claim, wherein: the primary heat exchanger (34) is part of a first heat distribution loop (320) in thermal communication with a first enclosed space (14) to be heated; and the secondary heat exchanger (36) is part of a second heat distribution loop (324) in thermal communication with a second enclosed space or the first enclosed space (14) to be heated.

6. The environmental control system (110) of any preceding claim, wherein, The refrigerant is CO2 or a CO2-based refrigerant.

7. A vehicle (10) comprising an environmental control system (110) according to any preceding claim.

8. The vehicle (10) of claim 7, wherein, The vehicle (10) is a public transportation vehicle (10).

9. A method of heating at least one enclosed space (14), the method using an environmental control system (110) according to any one of claims 1 to 6, the method comprising: driving a flow of refrigerant along the flow path defined by the heat pump circuit using the compressor (30), wherein the refrigerant flows from the compressor (30) through the primary heat exchanger (34) of the heat output stage, and then through the secondary heat exchanger (36) of the heat output stage, in a flow direction (318) of the refrigerant, such that the secondary heat exchanger (36) transfers heat remaining in the refrigerant after the primary heat exchanger (34) to the at least one external medium.

10. The method of claim 9, wherein, The at least one enclosed space (14) is within a vehicle (10).

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