Oil-free air source heat pump system and apparatus

Abstract

In at least one embodiment, the present disclosure provides an oil-free air source heat pump apparatus and system having at least one source heat exchanger in fluid communication with at least one load heat exchanger to create a closed heat exchange loop, each of the at least one source heat exchanger and the at least one load heat exchanger having an inlet, an outlet and a heat exchange section, the inlet adapted to receive a working fluid, the working fluid passing through the heat exchange section and exiting through the outlet, at least one expansion device in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger, at least one first variable frequency drive operably connected to at least one oil-free compressor, each oil-free compressor in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger and adapted to compress the working fluid, at least one second variable frequency drive operably connected to at least one fan, each fan operable to direct and induce flow of external ambient air through the at least one source heat exchanger over the heat exchange section of the at least one source heat exchanger, and a control module adapted for electronically controlling the at least one first variable frequency drive and the second variable frequency drive.

Description

[0001] OIL-FREE AIR SOURCE HEAT PUMP SYSTEM AND APPARATUS

[0002] FIELD

[0003] The present invention relates to heating and cooling equipment for residential, commercial, industrial and institutional applications. More specifically, the present disclosure relates to methods and apparatuses providing an innovative oil-free Air Source Heat Pump (ASHP) offering improved efficiency, reliability, and sustainable cost-effective design.

[0004] BACKGROUND

[0005] Existing Air Source Heat Pump (ASHP) systems face several limitations that can impact their efficiency, reliability and sustainability. One significant limitation is poor performance at part-load conditions, as traditional systems often operate inefficiently at partial loads which leads to higher energy consumption and reduced operational efficiency.

[0006] Additionally, many conventional ASHPs rely on fixed-speed compressors, which cannot adjust to varying demand, further exacerbating energy inefficiency. At full load, the use of an oil-free centrifugal compressor enhances system efficiency compared to traditional oil-lubricated compressors, as it eliminates friction losses that can be associated with oil lubrication.

[0007] Another limitation with known prior art solutions is that oil-lubricated compressors can be prone to wear, require regular maintenance and increase the risk of oil leaks. These issues can lead to higher maintenance costs, decreased reliability, and a shorter lifespan for the overall system. Oil-lubricated compressors, such as those in scroll- or screw-type systems, also tend to produce more noise and vibration, which can be disruptive in certain environments.

[0008] Environmental concerns can also arise from the use of high Global Warming Potential (GWP) refrigerants and the potential for oil contamination in traditional systems. The use of these refrigerants contributes to a larger carbon footprint, while oil leaks can contaminate the surrounding environment.

[0009] The present oil-free ASHP system design addresses these limitations by incorporating several advanced features. The use of dedicated Variable Frequency Drives (VFD) to rotatably power each compressor(s) and fan(s) allows precise control of compressor and fan speeds according to thedemand. This ensures the system operates efficiently across both full-load and part-load conditions, significantly improving energy efficiency and reducing overall energy consumption. It is further contemplated that each variable frequency drive is adapted to adjust to varying conditions, ensuring energy is used only when necessary, which traditional systems often fail to achieve.

[0010] It is further contemplated that the present oil-free ASHP design eliminates the need for lubricants in the compressor, reducing mechanical components and, consequently, the risk of failure. This results in a more reliable, lower-maintenance system that requires fewer repairs and replacements. In some embodiments, the use of one or multiple oil-free centrifugal compressors also reduces noise and vibration, offering a quieter and more comfortable operation compared to traditional oil-lubricated compressors.

[0011] Furthermore and as noted above, in some embodiments the present oil-free ASHP design supports the use of low-GWP refrigerants, significantly reducing the system's environmental impact. The lack of oil in the system eliminates the risk of contamination and leaks, thereby promoting greater sustainability and minimizing the overall environmental footprint.

[0012] Depending on the application, the present oil-free ASHP can be designed either as a packaged unit or as a modular system composed of multiple stacked modules. Additionally, it may feature one or more circuits, each equipped with either a single oil-free compressor, load heat exchanger, source heat exchanger and fan or multiple oil-free compressors, load heat exchangers, source heat exchangers and fans each of which can be tailored to meet the specific requirements of the end-user application.

[0013] Accordingly, it is contemplated that the present oil-free ASHP design overcomes the limitations of existing systems by improving efficiency at part-load, reducing maintenance and environmental impact, and ensuring quieter and more reliable operation, leading to a more sustainable and cost-effective solution for a wide variety of applications.

[0014] As discussed in further detail herein, known oil-based systems face challenges such as contamination risks from seal degradation and leaks, reduced efficiency from friction and heat transfer losses, and increased compressor failure risks due to oil traps. It will be appreciated that these systems require complex oil management systems, leading to higher maintenance needs, increased costs, and reduced reliability compared to oil-free designs.Accordingly, it is contemplated that the present disclosure provides an innovative oil-free Air Source Heat Pump (ASHP) system that improves efficiency, reliability, and sustainability by eliminating the use of oil within the system. For example, existing oil-based ASHPs with fixed speed vapor injection (VI) scroll compressors have lower part-load efficiency and struggle to maintain precise Leaving Fluid Temperature (LFT) control, often relying on frequent cycling to meet the required demand.

[0015] In contrast, it is contemplated that in at least one embodiment the present system utilizes at least one oil-free centrifugal compressor with Variable Frequency Drives (VFDs) and advanced controls to enhance energy efficiency, overall reliability, and environmental sustainability.

[0016] In at least one embodiment, it is contemplated that an economizer can be utilized to improve efficiency and overall system capacity at low ambient temperatures. Alternatively, it is contemplated that the system can be designed with multiple compressors in a common circuit or in separate parallel circuits, either with or without an economizer. In some embodiments, it is contemplated that the use of multi-speed or variable speed fans can enhance efficiency, reliability, and sustainability by providing precise speed control, reduced noise, lower energy consumption, and a simplified overall design.

[0017] Moreover, at least one embodiment of the present system comprises control logic employed by a suitable control module and a mechanical framework contemplated to ensure functionality at both low- and high-pressure ratios (PR) in both cooling and heating modes.

[0018] In some embodiments, it is contemplated that an advanced defrost strategy is employed to ensure effective and reliable defrosting of the unit. It is contemplated that the control logic can enhance defrost functionality by ensuring proper triggering of the defrost mode, preventing trips during the defrost process, optimizing defrost efficiency, and ensuring a smooth exit from defrost mode.

[0019] It will be appreciated that designing an oil-free ASHP system to operate with stability, reliability, and efficiency demands innovative approaches to system design, mechanical engineering, and control logic development. This is especially important for oil-free centrifugal compressors, which can be prone to surge, choke (from both low suction pressure and / or high-pressure ratios), overheating, and carryover - particularly during transient operating modes.As such, it is contemplated that the present design significantly improves efficiency, reliability, and environmental sustainability by simplifying maintenance through its oil-free and low-maintenance structure. By eliminating the need for oil management systems, it reduces operational costs and minimizes the risk of system failures, ensuring long-term reliability.

[0020] Additionally, compatibility with low-GWP refrigerants further enhances the eco-friendliness of the present system, thereby reducing its environmental impact and contributing to global sustainability efforts. The streamlined design also optimizes energy consumption, providing higher efficiency across various operational loads, while minimizing noise and vibration for a quieter, more comfortable environment.

[0021] BRIEF DESCRIPTION

[0022] It is contemplated that the present disclosure provides an oil-free air source heat pump that provides optimized energy consumption, provides higher efficiency across various operational loads, and which can minimize noise and vibration for a quieter, more comfortable operating environment.

[0023] In at least one embodiment, the present disclosure provides an oil-free air source heat pump apparatus and system having at least one source heat exchanger in fluid communication with at least one load heat exchanger to create a closed heat exchange loop, each of the at least one source heat exchanger and the at least one load heat exchanger having an inlet, an outlet and a heat exchange section, the inlet adapted to receive a working fluid, the working fluid passing through the heat exchange section and exiting through the outlet, at least one expansion device in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger, at least one first variable frequency drive operably connected to at least one oil-free compressor, each oil-free compressor in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger and adapted to compress the working fluid, at least one second variable frequency drive operably connected to at least one fan, each fan operable to direct and induce flow of external ambient air through the at least one source heat exchanger over the heat exchange section of the at least one source heat exchanger, and a control module adapted for electronically controlling the at least one first variable frequency drive and the second variable frequency drive.

[0024] DETAILED DESCRIPTION OF THE FIGURESThe present disclosure will be better understood in connection with the following Figures, in which:

[0025] FIGURE 1 is a diagram of a simplified air source heat pump operating in a heating mode;

[0026] FIGURE 2 is a diagram of a simplified air source heat pump operating in a cooling mode; and

[0027] FIGURE 3 is a simplified diagram of an oil-free air source heat pump system according to one embodiment of the present invention.

[0028] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] It is contemplated that the present disclosure provides an oil-free air source heat pump system engineered to deliver efficient, low-noise, and reliable operation in heating and cooling modes for residential, commercial, and industrial applications. It is further contemplated that the system ensures stable and seamless operation during mode transitions, as well as providing consistent performance in cooling and heating modes within the operational condition range.

[0030] Moreover, recognizing the sensitivity of oil-free centrifugal compressors to various compressor limitations such as surge, choke, low- and high-pressure ratios (PR), it is contemplated that some embodiments of the advanced system design can include sophisticated control logic implemented by a suitable control module to deliver reliable and smooth functionality.

[0031] In the context of the present invention, it will be appreciated that the present oil-free air source heat pump will be understood as a reversible air source heat pump system that is operable to transfer heat from an ambient source environment (i.e. outdoors) to a load environment (i.e. indoors) when operating in a heating mode and operable to transfer heat to an ambient source environment (i.e. outdoors) from a load environment (i.e. indoors) when operating in a cooling mode, as will be readily understood by the skilled person.

[0032] As such, it is contemplated that the present oil-free air source heat pump includes at least two heat exchangers, each of which is reversibly operable as both a condenser or an evaporator depending on whether the system is in a heating mode or a cooling mode, as discussed in further detail herein.

[0033] In the context of the present disclosure, it will be appreciated that a suitable source heat exchanger and load heat exchanger will be understood to be any suitable heat exchanger arrangement (commonly referred to as an air source heat pump) where the source heat exchanger is adapted totransfer heat between a circulating working fluid, such as a refrigerant, and the external ambient environment where the source heat exchanger is located and the load heat exchanger is adapted to transfer heat between a circulating working fluid, such as a refrigerant, and the load environment where the load heat exchanger is located.

[0034] In the context of the present invention, it will be appreciated that the source heat exchanger and load heat exchanger are collectively operable to transfer heat from the external ambient environment to the load environment (in a heating mode) and from the load environment to the external ambient environment (in a cooling mode) depending on the end-user application of the present disclosure, as discussed in further detail herein and as will be appreciated bythe appropriately skilled person. Each heat exchanger has an inlet, a heat exchanger section (which can be, but is not limited to, heat exchange coils or heat exchange plates) and an outlet, and is adapted for reversible operation as both a condenser and an evaporator, depending on the end user application under consideration.

[0035] It will be further appreciated that, in some embodiments, the source heat exchanger will also be appreciated as an “outdoor”, “external”, “air-side”, or “ambient” heat exchanger that is operable as a condenser or an evaporator in the external ambient environment, depending on the operating mode of the present system, as will be readily appreciated by the skilled person.

[0036] Similarly, it will be appreciated that a load heat exchanger, in some embodiments, will also be appreciated as an “indoor” or “internal” heat exchanger that can operate as an evaporator or a condenser in the load environment, depending on the operating mode of the present system, as will be readily appreciated by the skilled person.

[0037] It will further be appreciated that the load heat exchanger may communicate with the load environment by way of an additional closed circulation loop of a second working fluid (such as refrigerant or water) in a manner commonly known as an “air-to-water system” or byway of additional fans that are adapted to induce airflow (and, by extension, heat transfer) through the load heat exchanger to the load environment by way of convective airflow in a manner commonly known as an “air-to-air system”. In this way, heat energy can be transferred to or from the load heat exchanger to the load environment based on the needs of the specific end user application.

[0038] In the context of the present disclosure, it will be appreciated that a suitable variable frequency drive will be understood as any suitable electric rotary power source that can be electronically controlledby the control module to provide rotary power at variable and / or multiple rotational speeds, as will be readily appreciated by the appropriately skilled person.

[0039] In the context of the present disclosure, it will be appreciated that a suitable oil-free compressor will be understood to be any suitable oil-free compressor adapted to compress a working fluid (such as but not limited to a refrigerant or a low-GWP refrigerant) without requiring any oil to lubricate the moving components of the oil-free compressor. In at least one embodiment, a suitable oil-free compressor can be an oil-free centrifugal compressor, however other arrangements are also contemplated as will be appreciated by the appropriately skilled person.

[0040] In the context of the present disclosure, it will be appreciated that a suitable fan will be understood to be any suitable rotary fan that is adapted to operate at variable and / or multiple speeds to direct air flowthrough a heat exchanger to assist with the transfer of heat from a working fluid (such as but not limited to a refrigerant, low-GWP refrigerant and / or water) circulating through the heat exchangers to the surrounding environments, as will be readily understood by the skilled person. Suitable fans can include, but are not limited to, coolingfans, outdoorfans, air-side fans and ambient air fans, as will be readily appreciated by the skilled person.

[0041] In the context of the present disclosure, it will be appreciated that suitable expansion devices will be understood to be any suitable mechanical component adapted to permit and control the expansion and flow of a circulating working fluid, such as a refrigerant, between a compressed liquid state and an expanded vapour state, as will be readily understood by the appropriately skilled person.

[0042] Moreover, it is contemplated that in the context of the present invention a suitable expansion device can be a heating expansion device or a cooling expansion device, depending on the operating mode of the present system, as will be readily appreciated by the skilled person. In some embodiments, it is contemplated that a suitable expansion device can be controlled to suction superheat to improve the performance and efficiency of the overall system, as will be readily appreciated by the skilled person.

[0043] In the context of the present disclosure, it will be appreciated that a suitable distributor will be understood as a mechanical component adapted to control flow of a working fluid, such as a refrigerant, to at least one of the source heat exchanger and the load heat exchanger in order tomaintain appropriate working fluid flow to the appropriate heat exchanger to enable efficient heat exchange through the heat exchanger, as will be readily understood by the skilled person.

[0044] In the context of the present disclosure, it will be appreciated that a suitable economizer will be understood as a dedicated heat exchanger adapted to assist with the transfer of heat to and / or from the circulating working fluid, depending on the particular end user application of the presently disclosed system and depending on the operational mode selected as discussed in further detail herein.

[0045] In the context of the present disclosure, it will be appreciated that a suitable control module will be understood as a suitable electronic control system adapted to electronically control the variable speed drives and related mechanical components of the presently disclosed system, depending on the operational mode selected as discussed in further detail herein.

[0046] In the context of the present invention, it will be further appreciated that the source heat exchanger and load heat exchangers are in fluid communication in order to enable the circulation of a working fluid (such as a refrigerant) therebetween in a closed heat exchange loop.

[0047] As will be readily appreciated by the skilled person, it is further contemplated that the closed heat exchange loop can include, in some embodiments, a number of additional mechanical components including, but not limited to, expansion devices, economizers, distributors, working fluid (i.e. refrigerant) pumps, accumulators, receivers, reversing devices, staging valves, hot gas bypass valves, isolating suction valves (of the compressor) and other isolating valves, depending on the operational mode selected as required by the end user application of the presently disclosed system, as discussed in further detail herein and as will be readily appreciated by the skilled person.

[0048] In at least one embodiment, it is contemplated that the present disclosure can employ a variablespeed oil-free centrifugal compressor which offers energy efficiency in full load and part loads by adjusting speed for load demands, thereby reducing noise and operational costs. This provides an environmentally friendly result with no oil use, enhancing system reliability and durability. The quiet operation can improve workplace conditions, and this arrangement is versatile, as it is suited for low-GWP refrigeration, air conditioning, and industrial cooling applications. Depending on the application, it is contemplated that the present system may utilize one or multiple such oil-free compressors, depending on the end user’s needs.In at least one embodiment, it is contemplated that the present disclosure can employ at least one source heat exchangerthat is configured to transfer heat between the external ambient environment and the circulating working fluid and can function as either a condenser or an evaporator, depending on the unit's intended operating mode.

[0049] In heating mode, it is contemplated that the at least one source heat exchanger operates as an evaporator, absorbing heat from the air and transferring it to the working fluid, as will appreciated by the skilled person. In cooling mode, it is contemplated that the at least one source heat exchanger operates as a condenser, releasing heat to the environment and thereby cooling the working fluid, as will be appreciated by the skilled person.

[0050] In at least one embodiment, it is contemplated that a distributor is provided to ensure an even working fluid flow during heating mode when the heat exchanger operates as an evaporator, thereby enhancing energy efficiency, system durability, and overall performance.

[0051] In at least one embodiment, it is contemplated that the present disclosure employs at least one load heat exchanger that is adapted to transfer heat between the circulating working fluid and the load environment and which can function as either a condenser or an evaporator, depending on the unit's operating mode.

[0052] In heating mode, it is contemplated that the at least one load heat exchanger can efficiently transfer heat from the working fluid to the load environment. In cooling mode, it is contemplated that the at least one load heat exchanger facilitates effective heat transfer from the load environment to the circulating working fluid.

[0053] In some embodiments, it is contemplated that a dual or plural heat exchanger configuration may be used where the present air source heat pump employs a plurality of source heat exchangers and / or a plurality of load heat exchangers to enhance energy efficiency, system capacity, and reliability, while providing compactness and cost-effectiveness to optimize overall system performance, as will be appreciated by the skilled person.

[0054] In at least one embodiment, it is contemplated that the present oil-free air source heat pump system can include at least one expansion device to control the working fluid mass flow to the heatexchanger that is functioning as an evaporator in the respective heating and cooling modes under consideration.

[0055] In cooling mode, it is contemplated that the load heat exchanger functions as the evaporator, and a cooling expansion device can regulate working fluid flow to optimize heat absorption. In heating mode, it is contemplated that the source heat exchanger acts as the evaporator, with a heating expansion device controlling working fluid flow for efficient heat transfer from the external ambient environment.

[0056] It is further contemplated that, in some embodiments, these provided expansion devices can be controlled by suction superheat to ensure optimal superheating, improving system efficiency and avoiding compressor failure.

[0057] It is contemplated that the present system design ensures reliable operation across all modes, including during mode transitions through the use of carefully selected components in the refrigerant circuits that are aligned with the provided control logic to ensure the overall intended functionality of the system.

[0058] As such, it is contemplated that properly designed and selected mechanical components such as an accumulator, receiver, reversing device, staging valve, hot gas bypass valve, and isolating valves, for example, can minimize overall risks when switching between heating and cooling modes and thereby ensuring system stability, efficiency, and reliability under varying conditions.

[0059] Depending on the application, it is contemplated that the present system can incorporate one or multiple air source hat pumps, with each air source hat pump featuring either a single or multiple oil-free centrifugal compressor(s), source heat exchanger(s), load heat exchanger(s) and fan(s), as required by the particular end user application and as discussed in further detail herein.

[0060] In at least one embodiment, it is contemplated that the present oil-free air source heat pump system can further employ a control module that plays an important role in ensuring efficient, stable, and safe operation across all conditions.

[0061] It is contemplated that through intelligent electronic management of the presently disclosed system components and operating parameters, the provided control module can optimize performance and enhances reliability of the presently disclosed oil-free air source heat pump.More specifically, it is contemplated that the control module can electronically monitor system parameters such as, but not limited to, pressure, temperature, and compressor data (such as but not limited to discharge pressure, suction pressure and inverter temperature) in real time to ensure the heat pump operates within predefined safety and efficiency thresholds.

[0062] It is contemplated that potential advantages that the present control module can provide in various embodiments of the present disclosure include, but are not limited to:

[0063] • Efficient, stable, reliable and safe operation at all operating conditions including during mode transitions;

[0064] • Stable and optimum operation at low- and high-pressure ratios (PR) under various ambient and load conditions;

[0065] • Effective expansion device control for efficient operation in cooling and heating modes.

[0066] Specifically, in some embodiments control of multiple heating expansion devices is provided based on the designed capacity of the overall system;

[0067] • Defrost functionality to avoid low-pressure (LP) trips and working fluid carryover at successful defrost trigger, efficient defrost cycles and termination of defrost cycles and moving back to the heating mode;

[0068] • Low PR control including control of fan and working fluid pumps to guarantee reliable and stable operation;

[0069] • Providing smooth staging up and staging down of the compressors through the proper control of a provided staging valve;

[0070] • Improved compressor safety by ensuring compressor shutdown when running outside of predetermined operating parameters; and

[0071] Ensuring reliable system control during transitions between various modes, such as cooling modes, heating modes, and defrost modes.It will be further appreciated that transitioning between various modes requires precise coordination of each of the provided system components such as but not limited to reversing devices, expansion devices, isolating suction valves (of the compressor), compressor staging valves and fans.

[0072] It is further contemplated that the presently disclosed control logic can ensure seamless transitions between the various modes disclosed herein by managing timing and synchronization of the disclosed system components, thereby avoiding disruptions and maintaining overall system reliability.

[0073] In at least one embodiment, it is contemplated that modular design concepts can be employed to address wide system capacity ranges, match system loads more precisely when in operation and introduce redundancy to the overall system so that if any individual modules fail, standby modules can operate instead to provide uninterrupted operation.

[0074] In at least one embodiment, it is contemplated that the present system can employ high-efficiency variable or multi-speed fans that are adapted to adjust airflow based on load and ambient temperature in both cooling and heating modes, thereby ensuring stable and efficient functionality.

[0075] It is further contemplated that by controlling these variable or multi-speed fans and dynamically optimizing airflow through the present system, it serves to enhance heat dissipation in cooling mode and heat transfer in heating mode, thereby improving overall system performance and energy efficiency while reducing overall operational costs.

[0076] In at least one embodiment, it is contemplated that a working fluid pump can be provided to deliver and pressurize the circulating working fluid in the cooling line which can be used to effectively address low PR scenarios, ensuring stable running in cold ambient temperature conditions.

[0077] Additionally, it is contemplated that sophisticated control logic can be provided and electronically enabled by the control module that can further enhance operational reliability by dynamically adjusting operational parameters in real time. This approach prevents disruptions and ensures efficient system operation under challenging environmental conditions, particularly during low PR scenarios, contributing to overall system stability and energy efficiency.In at least one embodiment, it is contemplated that an economizer can be integrated into the present system to boost efficiency and performance especially when the present oil-free air source heat pump is employed in a heating mode at low ambient temperature.

[0078] It is further contemplated that in some embodiments the economizer can be adapted to subcool the working fluid, thereby reducing compressor workload. This increases capacity, lowers energy consumption, and reduces operating costs. In other embodiments, the system can be designed without an economizer, as will be readily appreciated by the skilled person.

[0079]

[0080] Cooling Mode:

[0081] In at least one embodiment, it is contemplated that the presently disclosed oil-free ASHP system defaults to cooling mode and operates in a manner similar to a conventional vapor-compression chiller. In this embodiment, it is contemplated that the present system is contemplated to ensure reliable and efficient performance across a wide range of operational conditions, including both low and high ambient temperatures.

[0082] In these embodiments, it is contemplated that advanced control logic can be electronically implemented by the control module, enabling the unit to maintain stable and optimal performance under all operating conditions.

[0083] Additionally, the present design addresses potential compressor trips caused by the high sensitivity of the oil-free centrifugal com pressor to working fluid carryover and low-pressure trips due to working fluid migration in low ambient conditions. As will be appreciated by the skilled person, key design considerations include, but are not limited to, optimized piping, a properly designed accumulator, advanced fan control, and strategically placed isolating valves.

[0084] Heating Mode:

[0085] In embodiments where heating is required, the system can operate in a heating mode byway of a provided reversing device. Additionally, a plurality of additional motorized valves can be adjusted during mode changes to direct the circulating working fluid in an appropriate direction.Unlike conventional oil-based air source heat pump systems, which are less sensitive to low suction pressure, the present system employs oil-free centrifugal compressors that are more susceptible to risks when coil frosting occurs, as it will be readily appreciated that frosting reduces heat transfer effectiveness and requires a lower saturated suction temperature (SST). Therefore, in these embodiments special attention is needed when designing the present oil-free air source heat pump system to address an appropriate defrost trigger at a suitable time, thereby ensuring reliable operation.

[0086] Defrost Mode:

[0087] As noted above, in a standard air source heat pump system, defrosting is essential when frost or ice accumulates on the outdoor coil of the source heat exchanger during heating mode, particularly in cold weather.

[0088] To prevent performance degradation due to ice buildup, in some embodiments the present oil-free air source heat pump system activates a defrost cycle that ensures frost on the source heat exchanger will be successfully melted.

[0089] As discussed herein, while oil-free centrifugal compressors are advantageous in many aspects, it will be readily appreciated that these types of compressors are less capable of handling high pressure ratios (PR) when compared to scroll-type compressors. This limitation impacts the system's ability to achieve the required reduction in suction saturation temperature (SST) to successfully initiate a defrost cycle.

[0090] In order to overcome this challenge presented by the use of an oil-free centrifugal compressor, the present disclosure provides a method for triggering the defrost cycle for the present system and perform the defrost process with stability, in order to provide reliable defrost triggering, efficient and thorough defrosting and a smooth transition from defrost back to heating mode.

[0091] Transient Mode:

[0092] It will be readily appreciated that when the present oil-free air source heat pump system transitions between operational modes — such as from cooling to heating, heating to cooling, or during defrost cycles — there is potential for various failure modesand risks.As such, the presently disclosed oil-free air source heat pump systems are contemplated to mitigate or eliminate these risks, particularly in embodiments utilizing oil-free centrifugal compressors, which are highly sensitive to fluctuations in, for example, suction pressure, pressure ratios, cooling compressor and refrigerant carryover.

[0093] For example, in an oil-free centrifugal compressor low suction pressure can occur during heating, defrost, or during mode transitions. This condition may also arise when the unit switches from defrost to heating during a sharp drop in suction superheat (SSH), which can cause the heating expansion devices to close.

[0094] Turning to Figure 1, an example of a typical air-source heat pump is depicted wherein the air source heat pump is in a heating mode. In a heating mode, air source heat pump 1 operates as follows. Heat energy is absorbed from the ambient environment in a source heat exchanger 2 (operating as an evaporator), causing a circulating working fluid (such as a refrigerant) to evaporate within the heat exchange section of source heat exchanger 2. The evaporated working fluid is subsequently circulated under pressure to a compressor 6, where the evaporated working fluid is compressed.

[0095] Next, the compressed working fluid is circulated under pressure to load heat exchanger 4 (operating as a condenser), where heat energy is dissipated from the compressed working fluid to the load environment, thereby heating the load environment. Next, the condensed working fluid is circulated under pressure to an expansion device 8, which controls flow of the cooled working fluid back to source heat exchanger 2, where the cycle begins anew.

[0096] Turning to Figure 2, an example of a typical air-source heat pump is depicted wherein air source heat pump 1 is in a cooling mode. In a cooling mode, it will be appreciated that the previously described heating cycle is effectively run in reverse, as follows. Heat energy is dissipated from a compressed working fluid to the ambient environment in source heat exchanger 2 (operating as a condenser), causing the circulating working fluid (such as a refrigerant) to condense within the heat exchange section of source heat exchanger 2. The condensed working fluid is subsequently circulated under pressure to expansion device 8, which controls flow of the cooled working fluid to load heat exchanger 4.

[0097] Next, the cooled working fluid is circulated under pressure to load heat exchanger 4 (operating as an evaporator), where heat energy is transferred from the load environment to the expanded workingfluid, thereby cooling the load environment and evaporating the working fluid. Next, the evaporated working fluid is circulated under pressure to compressor 6, which compresses the working fluid to and circulates the evaporated working fluid back to source heat exchanger 2, where the cycle begins anew.

[0098] Turning to Figure 3, one embodiment of the presently disclosed oil-free air source heat pump is depicted. It will be readily appreciated by the skilled person that Figure 3 depicts a simplified version of the present oil-free air source heat pump, and as such various design choices relatingto the overall piping schematics and ancillary mechanical componentry have been omitted for ease of reference and depiction.

[0099] In this embodiment, oil-free air source heat pump 10 is depicted in a simplified arrangement and includes at least one source heat exchanger 12, at least one load heat exchanger 14, at least one compressor 16, at least one fan 18, at least one variable speed drive 20a / 20b and at least one expansion device 22a / 22b.

[0100] As discussed previously, it will be appreciated that a dedicated variable speed drive is provided for rotatably powering each corresponding fan and each compressor that is provided in the embodiment under consideration.

[0101] Moreover, in this embodiment optional mechanical equipment such as a distributor 40, an economizer 42, a working fluid pump 44 and a reversing device 50 are present, as will be discussed in further detail herein.

[0102] As discussed herein, each of source heat exchanger 12 and load heat exchanger 14 are reversibly operable as a condenser or an evaporator, depending on the operational mode that is employed.

[0103] As such each heat exchanger has an inlet 30 in fluid communication with an outlet 32 and having a heat transfer section 34 in fluid communication therebetween, however it will be appreciated that inlet 30 and outlet 32 are analogous and perform the same function(s) depending on which operational mode is underway, and which direction that a suitable working fluid (such as a refrigerant or a low-GWP refrigerant) is being circulated, as will be readily appreciated in the skilled person.

[0104] Accordingly, oil-free air source heat pump 10 is operable in at least a heating mode and a cooling mode, as noted previously.In the heating mode, oil-free air source heat pump 10 operates as follows. A circulating working fluid (such as a refrigerant or low-GWP refrigerant) circulates clockwise through the provided diagram and enters inlet 30 of source heat exchanger 12 and passes through heat transfer section 34 of source heat exchanger 22.

[0105] Heat energy is absorbed from the ambient environment in heat transfer section 34 of source heat exchanger 12 (operating as an evaporator), causing the circulating working fluid to evaporate within the heat transfer section 34 of source heat exchanger 12. Fan 18 is powered by a dedicated variable speed drive 20b to induce airflow over heat transfer section 34 of source heat exchanger 12, thereby assisting with the absorption of heat by the circulating working fluid from the ambient environment to effectively heat heat transfer section 34 of source heat exchanger 12 and by extension, the circulating working fluid circulating within.

[0106] The evaporated working fluid exits source heat exchanger at outlet 32 and is subsequently circulated under pressure to compressor 16, where the evaporated working fluid is compressed.

[0107] Compressor 16 is rotatably powered by a dedicated variable speed drive 20a. Moreover, in this embodiment a reversing device 50 is provided that can direct and redirect working fluid flowthrough the overall system, depending on the operational mode that is being employed. Moreover, in this embodiment an economizer 42 is provided to assist with the transfer of heat to or from the circulating working fluid (depending on the operational mode) in order to improve the overall performance and efficiency of the system.

[0108] Next, the compressed working fluid is circulated under pressure to load heat exchanger 14 (operating as a condenser), where it enters inlet 30 of load heat exchanger 14 and circulates through heat exchange section 34 of load heat exchanger 14. Heat is transferred from the compressed working fluid to the load environment by dissipation from the heat exchange section 34 of load heat exchanger 14, and the subsequently condensed working fluid exits load heat exchanger 14 at outlet 32.

[0109] Expansion device 22a is provided to manage flow of the condensed working fluid. In this mode, expansion device 22a is operating as a cooling expansion device and is used to expand the circulating working fluid, thereby lowering the temperature of the circulating working fluid.In heating mode, it will be appreciated that the circulating working fluid bypasses expansion device 22b, which is an inactive component in the heating cycle.

[0110] Moreover, in this embodiment distributor 40 is provided to manage flow of the expanded circulating working fluid into the inlet 30 of source heat exchanger 12, where the process begins anew.

[0111] In the cooling mode, oil-free air source heat pump 10 operates as follows. The circulating working fluid (such as a refrigerant or low-GWP refrigerant) circulates counterclockwise through the provided diagram and enters outlet 32 of source heat exchanger 12 and passes through heat transfer section 34 of source heat exchanger 12. As discussed previously, all inlets and outlets are analogous mechanical components, with the appropriate nomenclature merely depending on the direction of circulation of the working fluid and the operational mode the system is employing.

[0112] Heat energy is dissipated to the ambient environment in heat transfer section 34 of source heat exchanger 12 (now operating as a condenser), causing the circulating working fluid to condense within the heat transfer section 34 of source heat exchanger 12. Fan 18 is powered by a dedicated variable speed drive 20b and operable to induce air flow over heat transfer section 34 of source heat exchanger 12, thereby assisting with the dissipation of heat from the circulating working fluid circulating within heat transfer section 34 of source heat exchanger 12 to the ambient environment.

[0113] The condensed working fluid is subsequently circulated under pressure to expansion device 22b in order to manage the flow of circulating condensed working fluid. In this mode, expansion device 22b is operating as a heating expansion device and is used to control flow of the circulating working fluid to load heat exchanger 14 (which is nowoperating as an evaporator), as will be readily understood by the skilled person.

[0114] In cooling mode, it will be appreciated that the circulating working fluid bypasses distributor 40 and expansion device 22b, which are inactive components in the cooling cycle.

[0115] Next, the expanded working fluid from expansion device 22b is circulated under pressure and then enters outlet 32 of load heat exchanger 14 (now operating as an evaporator), where it circulates through heat exchange section 34 and heat energy is absorbed by the expanded working fluid from the load environment, thereby cooling the load environment. Next, the subsequently evaporated working fluid is circulated back to compressor 16, which is powered by variable speed drive 20a.As discussed previously, in this embodiment a reversing device 50 is provided that can direct and redirect working fluid flowthrough the overall system as required by the particular operational mode being employed.

[0116] In this embodiment, working fluid pump is 44 is provided to additionally pressurize the circulating working fluid which can be used to effectively address low pressure ratio scenarios, ensuring stable operation, particularly in cold ambient temperature conditions.

[0117] Moreover, in this embodiment an economizer 42 is provided to assist with the transfer of heat from the circulating working fluid in order to improve the overall efficiency of the system.

[0118] Next, the compressed working fluid is circulated under pressure to outlet 32 of source heat exchanger 12, where it circulates through heat exchange section 34 of source heat exchanger 12.

[0119] Heat is transferred from the compressed working fluid to the load environment by dissipation from the heat exchange section 34 of source heat exchanger 12 with the assistance of fan 18 powered by variable speed drive 20b, and the subsequently condensed working fluid exits source heat exchanger 12 at inlet 30, and the process begins anew.

[0120] As such, the present disclosure provides innovative solutions which combine mechanical and electronic control strategies, that have been developed to address these risks and ensure reliable operation. In certain mode transitions (such as, but not limited to, switching from heating to defrost in cold ambient conditions with high fluid temperatures) the oil-free centrifugal compressor may lack sufficient liquid refrigerant for cooling which can in turn lead to a lack of subcooling and potentially causing the compressor to trip. It is contemplated that by employing the advanced mechanical and control systems disclosed herein, adequate subcooling under these conditions can be ensured.

[0121] The embodiments described herein are intended to be illustrative of the present compositions and methods and are not intended to limit the scope of the present invention. Various modifications and changes consistent with the description as a whole and which are readily apparent to the person of skill in the art are intended to be included. The appended claims should not be limited by the specific embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole.

Claims

WHAT IS CLAIMED IS:

1. An air source heat pump comprising:At least one source heat exchanger in fluid communication with at least one load heat exchanger to create a closed heat exchange loop, each of the at least one source heat exchanger and the at least one load heat exchanger having an inlet, an outlet and a heat exchange section, the inlet adapted to receive a working fluid, the working fluid passing through the heat exchange section and exiting through the outlet;At least one expansion device in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger;At least one first variable frequency drive operably connected to at least one oil-free compressor, each oil-free compressor in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger and adapted to compress the working fluid;At least one second variable frequency drive operably connected to at least one fan, each fan operable to direct and induce flow of external ambient air through the at least one source heat exchanger over the heat exchange section of the at least one source heat exchanger, andA control module adapted for electronically controlling the at least one first variable frequency drive and the second variable frequency drive.

2. The air source heat pump of claim 1 , wherein the at least one oil-free compressor is at least one oil-free centrifugal compressor.

3. The air source heat pump of claim 1 or claim 2, further comprising a distributor in fluid communication with the at least one source heat exchanger and the at least one load heat exchanger in the closed heat exchange loop, the distributor adapted to control flow of the working fluid to at least one of the at least one source heat exchanger and the at least one load heat exchanger.

4. The air source heat pump of any one of claims 1 to 3, further comprising an economizer in fluid communication with the at least one source heat exchanger and the at least one heat exchanger in the closed heat exchange loop.

5. The air source heat pump of claim 4, wherein the economizer is adapted to remove heat from the working fluid.

6. The air source heat pump of claim 4, wherein the economizer is adapted to heat the working fluid.

7. The air source heat pump of anyone of claims 1 to 6, further comprising a working fluid pump in fluid communication with the at least one source heat exchanger and the at least one load heat exchanger in the closed heat exchange loop, the working fluid pump adapted to pressurize the working fluid.

8. The air source heat pump of any one of claims 1 to 7, wherein at least one of the at least one expansion device is adapted to be controlled by superheat.

9. The air source heat pump of any one of claims 1 to 8, wherein the control module is further adapted to electronically operate the air source heat pump in an operational mode selected from the group of: a heating mode, a cooling mode, a defrost mode and a transient mode.

10. The air source heat pump of any one of claims 1 to 9, further comprising at least one third variable frequency drive operably connected to at least one second fan, each at least one second fan operable to direct and induce flow of air through and over the heat exchange section of the at least one load heat exchanger.

11. An air source heat pump system comprising:a plurality of air source heat pumps, each of the plurality of air source heat source pumps comprising:at least one first heat exchanger in fluid communication with at least one load heat exchanger to create a closed heat exchange loop, each of the at least one source heat exchanger and the at least one load heat exchanger having an inlet, an outlet and a heat exchange section, the inlet adapted to receive a working fluid, the working fluid passing through the heat exchange section and exiting through the outlet;at least one expansion device in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger;at least one first variable frequency drive operably connected to at least one oil-free compressor, each oil-free compressor in fluid communication with the closed heat exchange loop between the at least one source heat exchanger and the at least one load heat exchanger and adapted to compress the working fluid;at least one second variable frequency drive operably connected to at least one fan, each fan operable to direct and induce flow of external ambient air through the at least one source heat exchanger over the heat exchange section of the source heat exchanger, and a control module adapted for electronically controlling the at least one first variable frequency drive and the second variable frequency drive.Wherein each closed heat exchange loop of each of the plurality of air source heat pumps are in fluid communication with one another.

12. The air source heat pump system of claim 11 , wherein the at least one oil-free compressor is at least one oil-free centrifugal compressor.

13. The air source heat pump system of claim 11 or claim 12, further comprising a distributor in fluid communication with the at least one source heat exchanger and the at least one load heat exchanger in the closed heat exchange loop, the distributor adapted to control flow of the working fluid to at least one of the at least one source heat exchanger and the at least one load heat exchanger.

14. The airsource heat pump system of anyone of claims 11 to 13, further comprising an economizer in fluid communication with the at least one source heat exchanger and the at least one heat exchanger in the closed heat exchange loop.

15. The air source heat pump system of claim 14, wherein the economizer is adapted to remove heat from the working fluid.

16. The air source heat pump system of claim 14, wherein the economizer is adapted to heat the working fluid.

17. The airsource heat pump system of anyone of claims 11 to 16, further comprising a working fluid pump in fluid communication with the at least one source heat exchanger and the atleast one load heat exchanger in the closed heat exchange loop, the working fluid pump adapted to pressurize the working fluid.

18. The air source heat pump system of any one of claims 11 to 17, wherein at least one of the at least one expansion device is adapted to be controlled by superheat.

19. The air source heat pump system of any one of claims 11 to 18, wherein the control module is further adapted to electronically operate the air source heat pump in an operational mode selected from the group of: a heating mode, a cooling mode, a defrost mode and a transient mode.

20. The air source heat pump system of anyone of claims 11 to 19, further comprising at least one third variable frequency drive operably connected to at least one second fan, each at least one second fan operable to direct and induce flow of air through and over the heat exchange section of the at least one load heat exchanger.

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