Thermally Enhanced Cascade Cooling System

Abstract

A cascade cooling system that uses low-grade thermal and other energy input sources to provide refrigeration and air conditioning in stationary and mobile applications. A two-loop embodiment includes a heat-powered first loop incorporating a vapor-jet compressor and a second loop based on a mechanical compressor powered by an electric motor or other source of rotational torque. The system uses waste heat, solar thermal or a fuel-fired heat source to partially or fully offset mechanical/electrical energy input. The system can also operate entirely on thermal, electrical or mechanical input. The ability to use multiple energy sources in any combination maximizes energy efficiency, performance and reliability. The system is well suited to making beneficial use of waste heat in vehicle applications. In stationary applications, solar thermal and/or waste heat from industrial processes can be used to improve the efficiency of conventional cooling systems.

Description

BACKGROUND

1. Field

This application relates to a cascade cooling system, specifically one incorporating a jet ejector compressor and a mechanical compressor.

2. Prior Art

Air conditioning and refrigeration are among the most energy consuming processes in the developed world. Historically, the terms referred to the application of a colder material, such as ice or water, to absorb heat from a hotter area. Today cooling is more often accomplished using a chemical or mechanical process to forcibly move heat from a colder region to a hotter region. These processes are always energy intensive and become more so as the temperature difference between the colder and hotter areas increase.

Both the need for cooling, and the cost of cooling, increase proportionate to the temperature of the external environment. Given this fact, it is understandable that much effort has been made to find better ways to use heat as an input energy source for cooling systems. While the economic logic behind a heat-powered cooling system is irrefutable, the technology has proven problematic. Heat-powered cooling systems fall broadly into four categories. Absorption systems use heat to separate two chemicals which, at lower temperatures, have a natural affinity strong enough to create a pressure reduction in a sealed system. Desiccant systems use heat to regenerate moisture absorbing chemicals. Vapor expander systems use heat to create a high pressure vapor which, in turn, is used to drive a mechanical compressor. Ejector systems use heat to generate a high pressure vapor which is directed through a venturi ejector to create a low pressure evaporating region. Because the subject invention is related only to the last two technologies, this prior art review ignores absorption and desiccant systems.

The coefficient of performance (COP) describes the overall efficiency of a system. In the case of a cooling system it may be defined as the effective cooling divided by the input energy using the same unit of measure. For example, a cooling system that consumed 500 w of power to transfer 1 kw of heat would have a COP of 2 (1,000/500=2). In general, a high COP is better than a low COP as it means less energy input is required to accomplish the desired cooling. By such measure, heat-powered cooling systems typically fall short of their electrically or mechanically driven counterparts. However, system COP does not describe the economic picture of operating systems which use different types of input energy at different costs. If a heat-powered system is able to use input energy that would otherwise be wasted, then the amount of energy it consumes becomes irrelevant from a financial standpoint so long as the initial purchase price of the equipment required to harness that energy is reasonable.

It is clear that heat-powered cooling systems can make financial sense when a suitable heat energy source is sufficiently plentiful and low in cost. It is not surprising that the primary commercial market for these systems is in manufacturing plants that continuously and reliably generate a large amount of waste heat as a byproduct of other manufacturing processes. Like industrial plants, vehicles powered by internal combustion engines also produce a large amount of waste heat. However, in the case of vehicles, the variable nature of the temperature and quantity of that heat has historically proven to be difficult to economically transform to cooling capacity.

Ejector cooling systems have been beneficially applied for over 100 years to provide cooling in both air conditioning and industrial processes. Early steam-powered trains tapped steam from the motive boiler and directed it though a venturi ejector to create air conditioning for the luxury train cars. The systems were simple and effective although not very energy efficient. With the decline is steam locomotion and an increased awareness of energy efficiency, the ejector systems were eventually replaced by systems using engine-driven or electro-mechanically driven compressors.

All ejector cooling systems require a highly stable source of moderate vapor pressure and temperature. Although there are many ejector-based vehicle air conditioning systems in the prior art. The intermittent and highly variable nature of the waste heat generated by an internal combustion propulsion engine has prevented their wide scale commercial success. Today, mechanical systems which make no use of waste heat at all, remain the dominate method of cooling all types of mobile vehicles.

Stationary applications have the potential to provide the stabile source of motive vapor required by ejector cooling systems. However, the poor energy efficiency of the systems has prevented widespread use of the technology in many of these applications as well. One exception is in factories where industrial processes produce a large amount of waste heat which can be used by the ejector system boiler. In these situations, given that the availability and cost of motive heat is not a restraining factor, ejector systems are both economic and highly versatile. By configuring several ejectors is series (i.e. one ejector as the vacuum source to the outlet of another ejector) multi-stage systems can be created to provide virtually any temperature and capacity desired. The prior art shows many designs for individual ejectors and combinations of ejectors for these applications.

Vapor expander systems are essentially steam engines driving a mechanical compressor. Like ejector systems, they generally have lower energy efficiency than their electrically-driven counterparts when only the amount of energy entering the system and the cooling output is considered. However, in applications such as vehicles, where the cost and inefficiency of producing electrical power is exceptionally high or where the low reliability of belt-driven systems can be very costly, vapor expander systems can be the most cost-effective. The ability of expander-based cooling systems to operate successfully on highly variable vapor pressure and temperature makes them particularly compatible with vehicular application. This ability to operate at high temperatures and pressure, means that they are usually more energy efficient than ejector systems when high-temperature waste heat is available. Yet another advantage is that, when vapor expanders are coupled to positive displacement compressors, they are better able to provide reliable cooling when condensing temperatures are high. These advantages have also made them a preferred choice on higher temperature waste heat applications and concentrated solar thermal-powered industrial sites.

Experimental vapor expander cooling systems have been developed that use waste heat from an internal combustion propulsion engine as a thermal energy source for the boiler. In these systems, high pressure refrigerant vapor drives a small turbine which is connected by a shaft to a centrifugal compressor. Turbine expanders have the advantage of small size but they are unsuited to the low temperature heat of the engine cooling circuit. Therefore, in these systems only the relatively small portion of the waste heat released through the exhaust system can be used. The experiments have not yet provided a system which is commercially viable.

Another system attempts to improve the energy efficiency of the ejector cooling cycle by using a hydrocarbon refrigerant that provides decreased entropy under decreasing pressure. The reliability and stability of the heat source is also improved with the inclusion of a thermal storage means. However, no means is incorporated to provide cooling during extended periods with insufficient thermal input energy. Also, no energy source other than heat can be used to power the system.

Certain cooling technologies perform well in one set of conditions and other technologies perform better in different conditions. Research has been conducted into how different types of cooling technologies can be combined in a single system which performs well in a wider range of conditions. When successful, these systems have a superior energy efficiency and performance in a wider range of applications.

One system on a motor vehicle attempts to offset the advantages and disadvantages of various types of cooling technologies by operating a ejector cooling system in parallel with an engine-driven mechanical compressor system. The ejector side of the system uses waste heat from the propulsion engine to provide air conditioning to the vehicle cabin. When the engine is cold or an insufficient amount of waste heat is available, the engine-driven mechanical system provides the needed cooling power. Such a system would be unsatisfactory for industrial applications since the system input power is limited to the rotary and thermal energy produced from an internal combustion engine power source. Also, while the system does offer reliable and sufficient cooling power, the design does not improve the energy efficiency of either the ejector or the mechanical compressor operation.

Other systems exists which combine a mechanical compressor and an ejector compressor in a common refrigerant circuit in what is know in the industry as a “two-stage” configuration. The ejector compressor applies its vacuum directly to the discharge of the mechanical compressor to reduce its power consumption. In some of these systems the mechanical compressor is electrically powered, in other systems it is engine-driven and in still other systems it is driven by a vapor expander. In all of the systems, both compressors operate from a shared refrigerant charge. This common refrigerant charge eliminates the possibility of optimizing the high-temperature ejector performance and the low-temperature mechanical compressor performance by using different types of refrigerants.

Investigation into the combined use of ejector compressors and mechanical compressors has focused on the use of one compressor in series connection with the other within a common refrigeration circuit—a two-stage system. In some cases, as described above, the mechanical compressor is placed between the vacuum port of the ejector and the system evaporator. In this position, the mechanical compressor boosts the refrigerant vapor from the evaporator pressure to a non-condensing intermediate pressure. vapor at the intermediate pressure enters the vacuum port of the ejector compressor which, in turn, further boosts the pressure to the condensing pressure.

Further research has described a variation in which the role of the ejector and the mechanical compressors are reversed. As with the previously described configuration, the compressors are connected in series within a common refrigerant circuit and therefore, remain a two-stage system. However, in this alternate configuration, the ejector compressor is placed between the evaporator and the suction inlet of the mechanical compressor. The ejector compressor boosts the vapor from the evaporator pressure to a non-condensing intermediate pressure. The mechanical compressor receives all vapor exiting the ejector, including the evaporator vapor and the ejector motive vapor and boosts it to a condensing pressure before discharging it to the condenser.

In none of these systems is it possible to use one type of refrigerant to optimize the performance of the heat-powered compressor and a different type of refrigerant to optimize the performance of the mechanical compressor. As with all two-stage configurations, these systems suffer an additional disadvantage in that extra steps must be taken to ensure that the refrigerant does not condense between compressors. A condensing refrigerant would harm system efficiency and mechanically damage the receiving compressor.

Another vehicle system uses two separate air conditioning systems to cool the vehicle cabin. An ejector system operates from the waste heat of the propulsion engine. A mechanical system is driven directly from the propulsion engine in the typical manner. The evaporators of the two systems are co-located but remain separate. The advantage of this system is that the vehicle can be cooled by waste heat, when sufficient waste heat is available, or by the mechanical system. Also, unlike the two-stage systems which have been previously described, it is possible use different refrigerants in the ejector and mechanical systems. However, there is a serious disadvantage in this approach. In a typical operating condition where both systems are in use at the same time, the cooling power of one system reduces the evaporator pressure/temperature of the other system. A reduction in the evaporator pressure increases the differential pressure across the compressor thereby reducing the energy efficiency and capacity of the entire system. Therefore, in this system the COP would be lower than in the other systems of the prior art.

In view of the limitations of the prior art, there remains a need for an improved cooling system that operates reliably and efficiently from a variety of thermal and non-thermal input energy sources.

SUMMARY

A thermally enhanced cascade cooling system is comprised of two separate refrigerant circuits—a primary cooling loop and an ejector boosting loop. The two loops are thermally connected such that the evaporator of the ejector cooling loop cools the condenser of the primary cooling loop. This configuration is generally know in the industry as a “cascade” system. The motive input energy for the ejector cooling loop is heat. In the various embodiments this heat may be waste heat from an internal combustion engine, industrial process or other electronic or chemical process which releases heat as a by-product. The heat source may also be solar energy collected through concentrating or non-concentrating collectors. In certain embodiments the heat source may also include fuel-fired boilers in which the heat generated in not waste heat. The exemplary embodiment accommodates a plurality of heat sources operating at a plurality of temperatures.

The primary cooling loop includes a mechanical compressor which receives motive energy input from a variable-speed electric motor in the exemplary embodiment. In other embodiments, the input energy may be an internal combustion engine, vapor expander, hydraulic motor, wind turbine, or other source of torque. The mechanical compressor may be reciprocating, scroll, screw, turbine, rotary piston, Wankel, centrifugal, liquid ring, or other known type.

An evaporator in the primary cooling loop is positioned to remove heat from a compartment. The condenser of the primary cooling loop, being in thermal communication with the evaporator of the ejector cooling loop, transfers heat into the working refrigerant of the ejector cooling loop. Under certain conditions, such as when no heat is available to power the ejector cooling loop, a second air-cooled condenser is positioned in the primary cooling loop.

Heat enters the ejector cooling loop from the primary cooling loop via the evaporator, and from the motive fluid of the ejector via the boiler. All heated vapor is mixed in the ejector and discharged to a condenser. The condenser is positioned to sink the heat to an air, water or geothermal medium. In certain embodiments, heat may be released into a thermal storage medium which holds it in reserve for later use as a motive heat source.

Of the total motive energy required by the system, the percentage with is directed to each loop is variable. A control system regulates amount and source of input power received by each cooling loop to achieve optimum energy efficiency and cooling performance. This control is made relative to the amount and cost of the various input energy sources which are available at a given time and to the amount of cooling power required. The control system also prevents excess power being drawn from any one energy source.

According to one exemplary embodiment, an ejector cooling loop and a primary cooling loop are thermally connected such that the evaporator of the ejector cooling loop cools the condenser of the primary cooling loop. The ejector cooling loop includes a boiler which receives thermal input energy and boils a liquid refrigerant to a vapor at a motive pressure and temperature. The motive vapor follows two paths. One path directs a portion of the vapor to the high-pressure inlet port of a venturi ejector. The other path directs a portion of the motive vapor to a vapor expander. The vapor expander is operably coupled to a mechanical compressor connected within the primary cooling loop. An variable-speed electric motor/generator is operably positioned so as to transform electric input power into rotational torque which can rotate the vapor expander and the mechanical compressor. Conversely, when sufficient input heat energy is available, the vapor expander can rotate the motor/generator to produce an electrical output and rotate the mechanical compressor. The vapor expander is a reciprocating type but could also be a rotary, scroll, Wankel, turbine, or other known type.

No fluid communication exists between the ejector loop and the primary loop. The two loops are in mechanical communication at the point that the vapor expander is coupled to the electric motor and mechanical compressor. The two loops are in thermal communication at the point where the evaporator of the ejector cooling loops is thermally coupled to a first condenser of the primary cooling loop.

This embodiment is able to operate in a plurality of modes. In one operating mode, heat energy enters the ejector cooling loop through the boiler and refrigerant is boiled to a motive vapor. A portion of the motive vapor from the boiler activates the ejector compressor creating cooling effect through the creating a low pressure zone in the evaporator. A further portion of the motive vapor flows to the vapor expander where it is expanded to create a torque force. This rotational torque rotates the motor generator to produce an electrical voltage and further rotates the mechanical compressor to produce a cooling effect in the primary cooling loop.

In a second operating mode, the operation of the system is the same as described in the previous mode except that electric power is input to the motor/generator to create a supplemental rotational torque. In this operating mode, the ratio of electric input power to thermal input power is continuously variable.

In a third operating mode, no thermal energy enters the ejector cooling loop. An intelligent control system positions electric refrigerant flow controls so that refrigerant flowing in the ejector cooling loop bypasses the ejector compressor. Electric input power flows to the variable-speed motor/generator which, in turn, provides a rotation force to the vapor expander and the mechanical compressor. The intelligent control system reconfigures the inlet and discharge valves of the vapor expander such that it now functions as a mechanical compressor. In this all-electric mode, the two separate loops perform as a two-stage compressor system. The now electrically-powered ejector cooling loop continues to cool the condenser of the primary loop. The control system optimizes system performance by adjusting the rotational speed of the two compressors and altering the inlet and discharge timing on the valves on the expander/compressor.

Various embodiments of the present invention provide a thermally enhanced cascade cooling system which,

• (a) cools a human-occupied or other enclosure using motive input power in the form of waste heat energy delivered over a wide range of temperatures.
• (b) provides a separate thermally-powered circuit and a separate mechanically-powered circuit thereby allowing each circuit to be performance-optimized by using a different refrigerant.
• (c) accepts thermal and mechanical input energy including electrical, mechanical, hydraulic, and pneumatic in any proportion.
• (d) generates its own electric power from thermal or other non-electric power input sources.
• (e) functions as a two-stage mechanical cooling system in an all-electric mode.
• (f) allows the output of a solar thermal power source to be variably balanced again other thermal sources such as a gas-fired boiler as well as non-thermal sources such as electric power from a photovoltaic array and/or the commercial utility grid.
• (g) improves the efficiency and reduces the power consumption of an engine-driven or electric compressor by using heat to reduce the condensing temperature of a primary cooling circuit.

DRAWINGS—DESCRIPTION

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawing. which are briefly described below.

FIG. 1 is a block diagram of a thermally enhanced cascade cooling system according to a first embodiment.

FIG. 2 is a block diagram of a thermally enhanced cascade cooling system according to a second embodiment.

FIG. 3A is a block diagram of one embodiment of a high temperature loop in a mobile vehicle application.

FIG. 3B is a block diagram of one embodiment of a high temperature loop in a stationary application.

FIG. 4 is a block diagram of a thermally enhanced cascade cooling system according to a third embodiment.

FIG. 5A is a block diagram of one embodiment of a direct expansion primary cooling loop.

FIG. 5B is a block diagram of one embodiment of a primary cooling loop incorporating a liquid chiller.

FIG. 6 is a block diagram of a thermally enhanced cascade cooling system according to a fourth embodiment.

FIG. 7 is a control logic flow chart for a high temperature loop in a mobile vehicle application.

FIG. 8 is a control logic flow chart for a high temperature loop in a stationary application.

FIG. 9 is a control logic flow chart for heating control according to one embodiment of a high temperature control loop.

FIG. 10 is a control logic flow chart for boiler superheat control according to a first embodiment of a thermally enhanced cascade cooling system.

FIG. 11 is a logic flow chart for chart for certain aspects of input power control according to a fourth embodiment of a thermally enhanced cascade cooling system.

FIG. 12 is a logic flow chart to control valve timing in a vapor expander.

FIG. 13 is a logic flow chart to control valve timing of a vapor expander operating in compressor mode.

FIG. 14 shows input and output functions of an intelligent control system according to some embodiments of a thermally enhanced cascade cooling system.

DETAILED DESCRIPTION

Unlike the present invention, systems known in the prior art are not cascade systems. Specifically, they do not use an thermally-powered ejector cooling loop to reduce the condensing temperature of a separate mechanically-powered cooling loop. Also, the prior art does not show a cooling system including an ejector cooling loop which further includes a vapor expander which can also function as a mechanical compressor when no external heat source is available. Also, no thermally enhanced system is seen in the prior art which includes an intelligent controller which optimizes the system performance by changing the temperature of the evaporator in an ejector cooling loop to alter the condensing temperature of a mechanical primary cooling loop.

According to various exemplary embodiments, a thermally enhanced cascade cooling system may use input thermal energy supplied from a variety of different sources. In some embodiments, the thermal energy input reduces the amount of electric power required to drive an electrically powered mechanical compressor. In other embodiments the heat energy is used to reduce the amount of drag induced on an engine powering an engine-driven compressor. In still other embodiments the system may be operated entirely from heat energy through the use of a vapor expander connected to a motor/generator and a mechanically-powered compressor. In the temporary absence of thermal input energy, some embodiments can operate entirely from electric energy input.

The thermally enhanced cascade cooling system is comprised of two or more separate cooling loops. The refrigerant from one cooling loop does not mix with refrigerant in another. This allows different refrigerants to be used in each loop to optimize the system to receive input thermal energy at a wide range of temperatures and to provide cooling at a wide range of temperatures. For example; in a vehicle application, the thermal input to the ejector cooling loop may be waste heat from an engine at 95 degrees C. and a fuel-fired heater at 110 degrees C. In an stationary industrial application, the thermal input to the ejector cooling loop may be waste heat from a manufacturing process at 250 degrees C. and from a concentrated solar thermal array at 220 degrees C. In such applications it may be desirable to use a refrigerant such as R245fa in the ejector cooling loop of the vehicle application and water in the ejector cooling loop of the stationary industrial application.

Similarly, the refrigerant used in the primary cooling loop may be altered according to the type of cooling to be done and the evaporator temperatures encountered. For example; in a vehicle application you may have a primary cooling loop providing cabin air conditioning with an evaporator temperature of 5 degrees C. You may also have an additional primary cooling loop on this same system or on a different system which provides freezing to a food storage area using an evaporator temperature of −40 degrees C. In such cases, in may be desirable to use R134a as the refrigerant in the primary cooling loop for the air conditioner and R-404a as the refrigerant in the freezer primary cooling loop.

In some embodiments, the mechanical compressor in the primary cooling loop is powered by a variable-speed electric motor and also by a vapor expander. In these embodiments, the vapor expander is in fluid communication with the ejector cooling loop and in mechanical communication with the mechanical compressor in the primary cooling loop. In an embodiment so equipped, it is possible to operate the entire system using heat energy as the only input motive power. The heat boils refrigerant in the boiler in the ejector cooling loop to create a vapor at a motive pressure and temperature. This motive vapor is supplied to the ejector compressor to provide cooling in the ejector cooling loop, and to the vapor expander which turns the mechanical compressor in the primary loop to provide cooling. The vapor expander also turns a motor/generator to produce the electrical power required to operate controls, fans, valves, pumps and other electrically-powered components of the system. An intelligent control system alters various aspects of the system to maximize efficiency and meet other operating requirements. For example, the intelligent control system may alter that percentage of motive vapor that flows to the ejector compressor relative to the amount which flows to the vapor expander.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, a first exemplary embodiment of a thermally enhanced cascade cooling system is comprised of two refrigerant loops.—an ejector cooling loop and a primary cooling loop. The ejector cooling loop operates in two modes—a first mode when thermal energy is available and a second mode when no thermal energy is available. In the first operating mode, when thermal energy is available, the ejector cooling loop performs an active cooling function. In the second operating mode, the ejector cooling loop performs a passive cooling function in the manner of a pumped refrigerant thermosyphon. FIG. 10 shows a control logic flow applied by an intelligent control system 24 to govern various aspects of the primary cooling loop. The following explanation will describe system operation in the first operating mode. Following that explanation will be a description of the second cooling mode.

Still referring to FIG. 1, the ejector cooling loop includes a boiler 1 which, in a first operating mode, receives heat from a thermal energy source and boils a suitable liquid refrigerant to a motive vapor at a motive temperature and motive pressure. Boiler 1 may be a tube-in-tube, tube-in-shell, heated plate or other type and construction and may be either a flooded or flash type boiler. The thermal energy source may be any source of heat energy which is at least 20 degrees C. higher in temperature than the heat sinking temperature of condenser 5. Suitable heat sources include the cooling system of an internal or external combustion engine, the exhaust of an internal or external combustion engine, a fuel-fired heater, a solar thermal collector, electronic components, an electric motor, an electric generator, a geothermal source, a thermal byproduct of a fuel-burning process, a thermal byproduct of a chemical process, a thermal by-product of a manufacturing process, a thermal byproduct of a power generation process, a thermal byproduct of a emissions control process, or a thermal byproduct of a solid waste reduction process.

Motive vapor leaves boiler 1 and passes through a solenoid valve 2 which is an electronically controlled valve constructed of heat-resistant materials and of a capacity which allows full vapor flow with minimal restriction. The motive vapor enters an ejector compressor 3 and is accelerated to a near-sonic to super-sonic speed through an internal orifice and further through a venturi mixing port so that a region of vacuum pressure is created on a vacuum inlet port. A working refrigerant vapor at an evaporator pressure leaves an ejector loop evaporator 9 and enters the vacuum inlet port of ejector compressor 3 and is mixed with the motive vapor in the venturi mixing chamber.

The mixed motive vapor and working refrigerant vapor exit ejector compressor 3 and pass through a heat exchanger 4 which may be a tube-in-tube, shell-in-tube or other suitable gas-liquid heat exchanger. Heat energy is recovered from the mixed vapor and transferred to liquid refrigerate being pumped to boiler 1. The cooled, mixed vapor enters an ejector loop condenser 5 which condenses the vapor to a liquid by transferring heat to air which is outside the compartment being cooled. In some embodiments, ejector loop condenser 5 may transfer heat to a material other than air such as water or a phase-change material. In some cases the heat so transferred may be stored and, at certain times, be used as a source of thermal input energy to boiler 1.

Upon exiting ejector loop condenser 5, the liquid refrigerant at a condensing pressure, follows two paths. A first path leads to an expansion valve 8 which is an electronically-controlled stepper expansion valve capable of accurately regulating the flow of liquid refrigerant and further capable of closing off the flow of refrigerant. Expansion valve 8 meters liquid refrigerant into an ejector loop evaporator 9 which is in thermal communication with, and receives heat from, a primary loop condenser 19. In one embodiment, ejector loop evaporator 9 and primary loop condenser 19 are two different circuits in a tube-in-tube heat exchanger. In other embodiments, they may be a different type of heat exchanger or may be two separate heat exchangers. For example; in an embodiment where is was desirable to be able to easily physically separate the primary cooling loop from the ejector cooling loop, ejector loop evaporator 9 and primary loop condenser 19 could be separate components which bolt or snap together to provide thermal communication.

Liquid refrigerant following the first path enters ejector loop evaporator 9 and, upon absorbing heat from the primary cooling loop via primary loop condenser 19, boils to a vapor at a ejector loop evaporator temperature and pressure. The ejector loop evaporator temperature is typically a temperature which is 3 degrees to 10 degrees C. below the condensing temperature of the primary cooling loop. The ejector loop evaporator pressure, will be the vapor pressure of the refrigerant in the ejector cooling loop that corresponds to this temperature. Once vaporized, the refrigerant returns to the vacuum port of ejector compressor 3 where it is mixed in the venturi mixing chamber with the motive vapor.

Liquid refrigerant leaving ejector loop condenser 5 and following a second path leads to a refrigerant pump 7 which is a variable-speed, sealed electric pump suitable to pump liquid refrigerant from a condensing pressure to a motive pressure. Liquid refrigerant leaving refrigerant pump 7 passes through a 3-way refrigerant valve 6—an electrically controlled sealed refrigerant valve—and is returned to the inlet of boiler 1 where it receives heat from the thermal energy source and boils to a motive vapor at a motive temperature and motive pressure. This concludes the description of the first operating mode of the ejector cooling loop of a first exemplary embodiment.

When no heat energy is available, the ejector cooling loop functions in a second operating mode. In this mode, the ejector loop cools the condenser of the primary loop but, unlike in the first operating mode, it does not cool it to a temperature lower than the heat sink temperature of the ejector loop condenser. Having a second operating mode for the ejector cooling loop provides a way for the heat from the primary cooling loop to be dissipated through the condenser of the ejector cooling loop. This eliminates the need to have an auxiliary condenser in the primary cooling loop. In some embodiments, the second operating mode is eliminated and an auxiliary primary condenser is added.

When operating in a second mode, 3-way refrigerant valve 6 is positioned so that liquid refrigerant discharged from refrigerant pump 7 flows directly into ejector loop evaporator 9. As in the first operating mode, heat from the primary refrigerant loop is discharged in primary loop condenser 19 and passes by thermal communication to ejector loop evaporator 9 and vaporizes the liquid refrigerant therein. The vaporized refrigerant passes through ejector compressor 3 and heat exchanger 4 to enter ejector loop condenser 5. No further substantial compression or heat transfer is imposed on the vapor between the outlet of ejector loop evaporator 9 and the inlet of ejector loop condenser 5.

Upon entering ejector loop condenser 5, the refrigerant vapor transfers heat to air which is outside the compartment being cooled and condenses to a liquid. As in the first operating mode, the liquid refrigerant leaving ejector loop condenser 5 enters refrigerant pump 7 for continued circulation. The concludes the operational description of the second operating mode of the ejector cooling loop.

Continuing to refer to FIG. and turning attention to a primary cooling loop as shown in detail in FIG. 5A, which includes a mechanical compressor 10 operably coupled to an electric motor 11. In one embodiment mechanical compressor 10 is a variable-speed rotary piston compressor but in other embodiments may be single speed and/or variable capacity in design and may be a scroll, rotary vane, gerotor, reciprocating piston, oscillating, centrifugal, scotch yoke, swash plate, screw, turbine, Wankel, or other known type. In one embodiment, motor 11 is a variable-speed synchronous permanent magnet motor but in other embodiments may be a single speed motor and may also be an induction motor, a switched reluctance motor, a permanent magnet BLDC motor, or another rotating electric machine. In still other embodiments, motor 11 may be a source of torque energy other than an electric motor such as an internal combustion engine, a hydraulic motor a wind turbine, a pneumatic motor, a vapor expander, or a rotating shaft or axle of a machine.

Refrigerant vapor is compressed by mechanical compressor 10 to a primary condensing pressure which is a pressure equal to the vapor pressure of the refrigerant in the primary cooling loop at the primary condensing temperature. The primary condensing temperature is a temperature which is typically 3 degrees to 10 degrees C. above the evaporator temperature of the ejector cooling loop. From the compressor, refrigerant vapor enters a primary loop condenser 19 which is in thermal communication which, and rejects heat to, ejector loop evaporator 9. From primary loop condenser 19, the liquified refrigerant flows to an expansion valve 8 and is metered to a primary loop evaporator 12.

In one exemplary embodiment, primary loop evaporator 12 is a parallel flow aluminum air-refrigerant heat exchanger which absorbs heat from the air of a compartment to be cooled. In other embodiments it may be a liquid chiller, a serpentine coil, a plate type heat exchanger, a heat exchanger incorporating thermosyphons, a heat exchanger incorporating heat pipes, a coil within a tank containing a thermal storage material, a heat exchanger removing heat from a chemical process, a heat exchanger removing heat from an electrical process, a heat exchanger removing heat due to solar exposure, or another suitable type of heat exchanger.

Heat from the cooled compartment evaporates the liquid refrigerant which has been metered into primary loop evaporator 12. The resulting vapor, at a primary loop evaporator pressure, returns to mechanical compressor 10 and is compressed to a primary condensing pressure to complete the refrigerant cycle of the primary cooling loop.

Another embodiment is described in reference to the thermally enhanced cascade cooling system shown in FIG. 1. In this embodiment, a potentially hazardous refrigerant is used in the primary cooling loop. The refrigerant may, or may not be a condensing refrigerant at the operating pressures and temperatures required in the application. For example; a high pressure, non-condensing refrigerant such as CO2 is used. In the case of a non-condensing refrigerant and application, primary loop condenser 19 is a non-condensing heat exchanger.

An alternative embodiment of a primary cooling loop which in this case incorporates a liquid chiller is shown in FIG. 5B. In this embodiment, primary loop evaporator 12 is replaced by refrigerant-liquid heat exchanger 27 which is typically a flat plate heat exchanger but may also be a tube-in-shell, tube-in-tube or other suitable type. A liquid pump 17 circulates a heat exchange fluid such as a 40/60 mixture of propylene glycol and water through a closed circuit loop. Liquid-air hear exchanger 28 absorbs heat from a compartment to be cooled and heats the circulating heat exchange liquid which, in turn, is removed by refrigerant-liquid heat exchanger 27. In this embodiment, all refrigerant-containing circuits and components may be placed outside the compartment to be cooled. This is particularly advantageous under certain conditions and when using certain refrigerants to enhance safety.

Referring to FIG. 2, according to a second exemplary embodiment, a thermally enhanced cascade cooling system includes a high temperature cooling loop as shown in FIGS. 3A and 3B. A high temperature loop such as the one diagramed in FIG. 3A is typical of a vehicle application of the present invention and includes an internal combustion engine 16 and a fuel-fired heat source 14. A heat transfer fluid such as a 40/60 mixture of propylene glycol and water is circulated in a liquid loop by liquid pump 17. Liquid pump 17 is typically a variable-speed centrifugal pump which is magnetically coupled to a permanent magnet electric motor. It may also be another type such as a centrifugal or positive displacement pump drive by gear, belt. or chain from an internal combustion engine. In some embodiments the high temperature loop may be the same loop as the internal combustion engine cooling loop and may share the same circulating pump.

The flow of the heat transfer fluid within the high temperature loop is regulated by an intelligent control system 24 which varies the speed of liquid pump 17 and positions 3-way liquid valves 15. A control logic flow for this loop is shown in FIG. 7. By changing the position of 3-way valves 15, the heat transfer fluid may be selectively routed through or around individual heat producing sources. For example; in a condition where the system is activated and cooling is required and where internal combustion engine 16 is cold and/or shut off, a-way valves 15 would be positioned so that fluid discharged from liquid pump 17 would bypass internal combustion engine 16 and flow through fuel-fired heat source 14. Conversely, if internal combustion engine 16 where hot enough to produce all of the required thermal input energy, 3-way valves 15 would be positioned to direct the heat transfer liquid through it and around fuel-fired heat source 14.

Under certain conditions, some thermal energy, but less than the total amount required for operation of the system, is available from internal combustion engine 16. In such a condition, fuel-fired heat source 14 is activated so as to supplement the heat from internal combustion engine 16 so that the correct operating temperature of all devices is maintained and the temperature of the heat transfer fluid entering boiler 1 is sufficiently high to provide the required thermal input energy to the system.

Another embodiment of a high temperature loop is shown in FIG. 3B and represents an embodiment which might be more typical of certain stationary applications. It includes a solar thermal collector 18 as a source of thermal input energy input to the circulating heat transfer fluid in addition to fuel-fired heat source 14. A control logic flow for this loop is shown in FIG. 8. The loop further includes a heat coil 26 which provides thermal communication between the heated heat transfer fluid and the air of a compartment to be heated. Heater coil 26 is typically a parallel flow aluminum heat exchanger but may be another type of liquid-air heat exchanger in other embodiments. Air from a compartment to be heated is circulated over heater coil 26 so that heat is transferred from the liquid heat transfer solution to the air. A control flow logic applied by intelligent control system 24 to the functionality of theater coil 26 is shown in FIG. 9. In some embodiments, heater coil 26 may be of a type and functionally positioned so as to heat a material other than air such as a fluid or solid and may provide heating to aid a process rather than, or in addition to, providing comfort heating.

Referring again to FIG. 2, a thermally enhanced cascade cooling system of the shown embodiment further includes a primary loop auxiliary condenser 13 which is typically an aluminum parallel flow refrigerant-air heat exchanger but may be a different type in other embodiments. Primary loop auxiliary condenser 13 provides thermal communication between the refrigerant vapor discharged from mechanical compressor 10 and air outside the compartment to be cooled. In most application, the heat from auxiliary condenser 13 will be discharge to the same environment as the heat discharged by ejector loop condenser 5. Under certain operating conditions, such as when sufficient thermal input energy is available to provide full cooling capacity in the ejector cooling loop, auxiliary condenser 13 performs no condensing function and all condensing function in the primary cooling loop is performed by primary loop condenser 19. Under other conditions, such as when partial but insufficient thermal input energy is available to provide full cooling capacity in the ejector cooling loop, auxiliary condenser 13 performs a partial condensing function and the remaining condensing function in the primary cooling loop is performed by primary loop condenser 19. Under still other conditions, such as when no thermal input energy is available to provide cooling capacity in the ejector cooling loop, auxiliary condenser 13 performs all of the condensing function in the primary cooling loop.

A third exemplary embodiment of a thermally enhanced cascade cooling system is shown in FIG. 4. This embodiment is a four-loop system comprised of a one ejector cooling loop as previously described, one high temperature loop as previously described and shown in detail in FIG. 3A and FIG. 3B and two primary cooling loops as previously described and shown in detail in FIG. 5A and FIG. 5B. Functionality of this embodiment is as previously described except that ejector loop evaporator 9 is in thermal communication with a plurality of primary cooling loops, each one having a primary loop condenser 19. In this embodiment, the cooling capacity of the ejector cooling loop and the heating capacity of the high temperature loop must be sufficient to transfer all heat from all simultaneously functioning primary cooling loops to and through ejector loop condenser 5. All primary loops remain separate and are able to be charged with a different and optimum type of refrigerant. Additionally, each primary cooling loop may perform the same or a different function. For example; one primary cooling loop might provide air conditioning for a truck cab while a second primary cooling loop may provide refrigeration for truck trailer or cargo area. In this way, the waste heat from the propulsion engine can be used to improve the energy efficiency of both the air conditioning system and the refrigeration system.

In such a system it may be desirable to have one or both of the primary cooling loops easily separated from the other components. For example; in a truck with a detachable trailer, the high temperature loop, the ejector cooling loop and one primary cooling loop might be permanently mounted on the truck cab. This provides a fully functional air conditioning system for the truck cab regardless of whether trailer is attached. A second primary cooling loop might then be mounted on the truck trailer to provide refrigeration. When that primary cooling loop includes a primary loop auxiliary condenser 13 as shown in FIG. 2, it allows full operational functionality even when disconnected from the ejector cooling loop. Once the trailer is attached to the truck cab, the trailer-mounted primary cooling loop is thermally connected to the ejector cooling loop by attaching primary loop condenser 19 to ejector loop evaporator 9 and energy efficiency of the trailer-mounted primary loop system is improved.

A fourth exemplary embodiment of the present invention is shown in FIG. 6. with further power control logic flow as shown in FIG. 11. In this embodiment a vapor expander 21 is operably connected to a motor/generator 20 and further operably connected to mechanical compressor 10. Vapor expander 21 is a reciprocating piston expander but in other embodiments may be a scroll, rotary piston, rotary vane, gerotor, Wankel, centrifugal, turbine, screw or other type of expander which may also be configured to operate as a compressor. Motor/generator 20 is a synchronous permanent magnet rotating machine but may also be a brushless or brushed permanent magnet machine, a dynamo, an alternator, or a field-wound machine. The embodiment operates in two different operating modes—a first mode in which a source of thermal energy is available and a second mode in which only electric energy is available.

In the first operating mode, liquid refrigerant, having been heated in boiler 1 to a motive vapor at a motive pressure and a motive temperature, follows two fluid paths. The first path flows past solenoid valve 2 and into ejector compressor 3 in the manner that has been previously described for other embodiments. Motive vapor following the second path flows to expander inlet valve 23 and enters vapor expander 21 at a motive pressure and motive temperature and is expanded to a lower pressure and temperature. Intelligent control system 24 regulates the operation of these valves as shown in FIG. 12. In the process of expansion, mechanical energy is recovered and transferred as a rotational torque to motor/generator 20 and to mechanical compressor 10.

Expanded vapor exits through expander discharge valve 22 which, like expander inlet valve 23, is a vapor flow control valve whose opening and closing is controlled and timed relative to the position of a vapor expander 21 by an intelligent control system 24. Various operating conditions including vapor and liquid refrigerant temperature, thermal energy input quantity and quality, compressor load are considered by the intelligent control system 24 in determining the optimum positions of system valves, fan speeds, pump speeds and other adjustments. For example; closing expander inlet valve 23 earlier in the expansion stroke of vapor expander 21 will improve system energy efficiency by will also create less rotational torque.

Exiting expander discharge valve 22, the expanded vapor passes through one-way check valve 25 as it follows a fluid path to eventually join and mix with the vapor exiting ejector compressor 3. This intersection is made before the mixed vapor passes through heat exchanger 4 so that heat may be recovered from the vapor and used to pre-heat the liquid refrigerant returning to boiler 1.

When both electrical input energy and thermal input energy are available, and the amount of electrical input energy is equal to the amount required to operate all the electrical components of the system, intelligent control system 24 commands motor/generator 20 to a neutral state so that it neither consumes nor generates electric power.

When both electrical input energy and thermal input energy are available, and the amount of electrical input energy is greater than the amount required to operate all the electrical components of the system, intelligent control system 24 commands motor/generator 20 to a motor state so that the amount of vapor required by vapor expander 21 to turn mechanical compressor 10 is reduced.

When only thermal energy is available or when electrical input energy is available but is insufficient to operate all the electrical components of the system, intelligent control system 24 commands motor/generator 20 to a generator state. In this state, the amount of vapor directed to vapor expander 21 is increased so that it produces a sufficient amount of torque to turn both mechanical compressor 10 and motor/generator 20 and to produce a sufficient amount of electricity to power the electric components of the system.

In the first operating mode, the ratio of thermal input energy to total system input energy can range from 5% to 100%. When a sufficient amount of thermal energy is available, no external source of electric power is required for system functionality.

In the second operating mode, electric input power is available but less than 5% of the total input energy required to run the system is available as thermal input. In this mode, refrigerant pump 7 and ejector compressor 3 are deactivated and solenoid valves 2 are closed. Intelligent control system 24 positions 3-way refrigerant valve 6 so that refrigerant vapor exiting ejector loop evaporator 9 flows directly to expander inlet valve 23. The timing of the opening and closing of expander inlet valve 23 and expander discharge valve 22 relative to the piston position of vapor expander 21 is altered so that vapor expander 21 functions as a compressor. The control flow logic applied by intelligent control system 24 when a compressor mode is shown in FIG. 13. In this valve timing, check valve 25 improves operating efficiency by preventing previously discharged vapor from back flowing into vapor expander 21. In some embodiments, check valve 25 is eliminated by waiting to open expander discharge valve 22 until the internal vapor pressure of vapor expander 21 is equal to or greater than the pressure of the previously discharged vapor.

With vapor expander 21 now set to operate as a compressor, the ejector cooling loop now operates as the second stage of an electrically-powered two-stage cascade cooling system. Intelligent control system 24 commands motor/generator 20 to produce sufficient torque to provide a first stage of compression in the primary cooling loop through mechanical compressor 10 and the second stage of compression in the ejector cooling loop through vapor expander 21 operating in a compressor mode.

CONCLUSIONS, RAMIFICATIONS AND SCOPE

Accordingly, the reader will see that various embodiments of the thermally enhanced cascade cooling system which constitute the present invention can be used to cool enclosed compartments to air conditioning, refrigeration and freezer temperatures. A wide variety of stored and non-stored thermal, electrical and mechanical energy input sources may be used. Furthermore, an intelligent control system ensures that the most suitable energy sources are used first and supplemented to the extend required by other, lower priority energy sources. Some embodiments will operate solely from heat or electric power when other energy sources are not available or are less desirable.

Because the design uses multiple, separate refrigerant circuits, the system is easily optimized for various input temperatures and cooling temperatures by using different refrigerants in each circuit. By adjusting the speed and flow rate of fans and pumps and by altering the position of flow control valves, the intelligent control system ensures that each cooling loop functions at optimum efficiency and that the temperature and capacity of each cooling loop is optimized relative to each other.

Some embodiments use one ejector cooling loop to reduce the energy consumption of multiple primary cooling loops. Some or all of these primary cooling loops may include an auxiliary condensing coil so that they can operate in a “stand alone” mode (i.e. without connection to the ejector cooling loop) as well as in a cascade connection to the ejector cooling loop. Also, multiple primary cooling loops in a single system may provide a cooling temperature and/or location identical to or different from each other.

Although the description, drawings and specification includes many specific details, these should not be construed as limiting the scope of the embodiments. Rather, they are provided to illustrate exemplary embodiments and applications. For example, the invention can use the waste heat emitted by electronic devices to prevent overheating of those devices. In such a case, the actual cooling temperature may be lower than, equal to, or greater than the ambient air temperature. In different installations and embodiments, certain parts of the system may be easily separated from other parts of the system and, when separated, these parts may function differently or serve a different purpose than when they are connected together in the manner described herein.

Some embodiments may use fixed speed fans, pumps, motors or compressors to save cost. In other embodiments, some or all of these may be variable speed to maximize energy efficiency and performance. Accordingly, the intelligent control system in one embodiment may control different functions in different ways than in another embodiment. Similarly, many different types of compressors, heat exchangers, vapor expanders, pumps and ejectors can be used.

Thus the scope of the embodiments should be determined by the appended claims and their legal equivalent, rather than by the examples given.

Claims

1. A heat-powered cooling system comprising; a first cooling circuit including; a mechanical refrigerant compressor operably coupled to a vapor expander, said vapor expander receiving a portion of vaporized refrigerant at a first motive pressure from the boiler of a second cooling circuit,a first refrigerant evaporator positioned to cool the air in a compartment by vaporizing a liquid refrigerant,a first refrigerant condenser positioned to transfer heat from the refrigerant of the first cooling circuit to a second cooling circuit,a second cooling circuit including; a venturi ejector compressor which accelerates a portion of the said vaporized refrigerant at a first motive pressure through a nozzle and discharges it to a condenser at a lower second pressure such that a vacuum region at a lowest third pressure is created,a second refrigerant evaporator in thermal communication with the said first refrigerant evaporator, which receives liquid refrigerant from a second refrigerant condenser and evaporates it at the said third pressure using heat extracted from the refrigerant of the said first cooling circuit,a second condenser operably positioned to liquify and cool vaporized refrigerant by transferring heat to an exterior heat sink,a liquid refrigerant pump in fluid communication with the second condenser and a refrigerant boiler.a refrigerant boiler which, upon receiving heat energy from an external heat source, boils liquid refrigerant to create the said vapor at a first motive pressure such that,

2. The system of claim 1 which further includes an electric rotating machine operably coupled to the said mechanical refrigerant compressor and vapor expander so that torque energy may be transferred.

3. The system of claim 2 in which the electric rotating machine is a motor/generator.

4. The system of claim 3 in which the motor/generator uses some or all of the electrical output energy from a generating mode to fulfill the electrical power demand of system controls including, fan, valves, or other system control devices.

5. The system of claim 3 in which the motor/generator uses some or all of the electrical output energy from a generating mode to charge an electric energy storage device.

6. The system of claim 3 which further includes a plurality of electrically configurable flow control valves operably positioned and configurable so as to bypass the said ejector compressor in the ejector cooling loop and further including such refrigerant flow controls as required to enable the said vapor expander to function as a compressor when powered by the said motor/generator.

7. The system of claim 3 which further includes an intelligent control system which adjusts various operational parameters of the systems to identify and optimally use energy input sources according to a predetermined priority or preference.

8. The system of claim 7 in which the intelligent control system adjusts various operational parameters of the systems to optimize system efficiency.

9. The system of claim 7 in which the intelligent control system further adjusts various operational parameters based partially or entirely on stored historical operational data from previous run cycles.

10. The system of claim 7 in which the intelligent control system adjusts the priority of energy input sources or other operational parameters based on information received through sensors or determined by real-time calculations.

11. The system of claim 7 in which the intelligent control system adjusts the priority of energy input sources or other operational parameters based on received data which has been transmitted from external sources.

12. The system of claim 7 in which the said operational parameters include one or more from a list including flow control position, valve timing, valve opening, condenser temperature, evaporator temperature condensing fan speed, evaporator fan speed, motor input voltage, motor commutation, generator output voltage, generator load, liquid pump speed, compressor capacity, vapor expander capacity, flow of motive vapor to the expander, flow of motive vapor to the ejector compressor, boiler temperature, and cooling capacity.