U.S. patent application number 12/788631 was filed with the patent office on 2011-12-01 for thermally enhanced cascade cooling system.
Invention is credited to Gerald Allen Alston.
Application Number | 20110289953 12/788631 |
Document ID | / |
Family ID | 45020946 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110289953 |
Kind Code |
A1 |
Alston; Gerald Allen |
December 1, 2011 |
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.
Inventors: |
Alston; Gerald Allen;
(Oakland, CA) |
Family ID: |
45020946 |
Appl. No.: |
12/788631 |
Filed: |
May 27, 2010 |
Current U.S.
Class: |
62/238.6 ;
62/335; 62/500 |
Current CPC
Class: |
B60H 1/32 20130101; Y02A
40/963 20180101; Y02A 40/967 20180101; F25B 1/08 20130101; F25B
27/02 20130101; Y02A 30/274 20180101; F25B 7/00 20130101; Y02A
40/966 20180101 |
Class at
Publication: |
62/238.6 ;
62/500; 62/335 |
International
Class: |
F25B 27/00 20060101
F25B027/00; F25B 7/00 20060101 F25B007/00; F25B 1/06 20060101
F25B001/06 |
Claims
1. A cascade cooling system comprising; a source of thermal energy
and, a primary cooling loop including; a mechanical compression
means which uses mechanical energy to compress a refrigerant gas
from an evaporator pressure to a condensing pressure and, an
evaporator located to cool a compartment by using heat from the
compartment to evaporate a liquid refrigerant and, a refrigerant
flow regulator to create a differential pressure and to regulate
the flow of liquid refrigerant into the said evaporator a condenser
in thermal communication with an evaporator of an ejector boosting
loop such that heat from the primary cooling loop is transferred to
the ejector boosting loop and, an ejector boosting loop comprising;
a boiler in which heat from said source of thermal energy converts
a motive refrigerant from a liquid state to a vapor having a motive
pressure and motive temperature and, a refrigerant flow regulator
to receive and regulate the flow of a portion of the said motive
refrigerant into an evaporator, the said evaporator in thermal
communication with, and operably positioned to receive heat from,
the said primary cooling loop condenser and, an ejector compression
means having a high pressure port, a low pressure port and a
discharge port and a venturi mixing chamber and further configured
to receive the said vapor at a motive pressure and temperature in
the high pressure port, and to further receive refrigerant vapor
from the said evaporator in the low pressure port and to mix and
discharge vapor out the discharge port and, a condenser located to
transfer heat from the vapor exiting the discharge port of the
ejector compression means, to an area outside the compartment to be
cooled and, wherein the operation of the ejector boosting loop
improves the energy efficiency of the primary cooling loop by
reducing the pressure differential imposed on the mechanical
compression means.
2. The system of claim 1 which further includes an electric motor
operably coupled to provide motive power to the said mechanical
compression means.
3. The system of claim 2 in which the electric motor receives
electric power from one or more of a listing including electric
storage battery, fuel cell, photovoltaic solar panel, wind-powered
generator, engine-driven generator, or utility power grid.
4. The system of claim 2 wherein the electric motor is a
variable-speed motor.
5. The system of claim 1 wherein the said source of thermal energy
may be a plurality of sources.
6. The system of claim 5 wherein the said plurality of sources
includes one or more of an internal combustion engine cooling
system, heated gas from a combusted fuel, a fuel-fired heater, a
solar thermal collector, an electric propulsion motor, motor
control electronic components, an electro-chemical process, a
chemical process, a geothermal source, biofuel combustion, or the
thermal byproduct of electric power generation.
7. The system of claim 1 which further includes an intelligent
control system which adjusts the rotational speed of various motors
and the position of various valves to maximize the performance and
efficiency of the system.
8. The system of claim 1 wherein the cooled compartment is the
cabin of a vehicle.
9. The system of claim 1 wherein the cooled compartment is a
building.
10. The system of claim 1 wherein the cooled compartment is used
for holding one or more items from a list including food,
chemicals, plants or animals.
11. The system of claim 1 wherein the cooled compartment is an
enclosure for a chemical or electrical process.
12. The system of claim 1 wherein the cooled compartment is a
plurality of compartments.
13. A three-loop heat transfer system comprising; a heat input loop
including; a source of input heat energy and, a fluid path
including heat transfer liquid and, a pump positioned to circulate
the heat transfer liquid so as to transfer heat energy from the
said source of input heat to a boiler and, an ejector cooling loop
including, a boiler in thermal communication with the heat input
loop which boils a liquid refrigerant in an ejector cooling loop to
create a vapor at a motive pressure and motive temperature and, an
ejector compressor which, operating on the venturi principle, uses
the said vapor at a motive pressure and motive temperature to
create a low pressure zone and, a condenser which condenses the
refrigerant vapor exiting the ejector compressor by transferring
heat from the vapor to an area outside a cooled compartment and, a
liquid pressure pump which receives liquid refrigerant from the
condenser and circulates it to the said boiler and to an
evaporator. an evaporator in fluid communication with the said low
pressure zone of the ejector compressor and, in thermal
communication with the said primary cooling loop, such that the low
pressure causes liquid refrigerant to be evaporated thereby
absorbing heat from the primary cooling loop and, a primary cooling
loop including, a gas compressor receiving input energy from a
rotating shaft and, a condenser in thermal communication with the
said evaporator in an ejector cooling loop such that, heat in the
vapor discharged from the said gas compressor is transferred to
refrigerant in the ejector cooling loop thereby vaporizing
refrigerant in the ejector cooling loop and liquefying refrigerant
in the primary cooling loop and, an evaporator positioned to
receive liquid refrigerant from the condenser and boil it to a
vapor by extracting heat from a compartment to be cooled.
14. The system of claim 13 which the evaporator in the primary
cooling loop is a refrigerant-liquid heat exchanger positioned to
remove heat from a liquid cooling loop comprising; a fluid circuit
containing a liquid heat transfer fluid and, a heat exchanger
positioned to transfer heat from a compartment to be cooled to the
said liquid heat transfer fluid.
15. The system of claim 13 in which the said primary cooling loop
is a plurality of cooling loops.
16. The system of claim 15 in which one or more of the compartments
to be cooled is a vehicle operator cabin, a vehicle sleeping cabin
or the cargo area of a vehicle.
17. The system of claim 13 in which the mechanical compressor is
driven by an internal combustion engine.
18. The system of claim 13 in which the mechanical compressor is
driven by an electric motor.
19. 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 which cools the air in a compartment by vaporizing a
liquid refrigerant, a first refrigerant condenser which transfers
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, thermal
energy input into the second cooling circuit cools the condenser of
the first cooling circuit and thereby reduces the amount of energy
required by the mechanical refrigerant compressor.
20. The system of claim 19 in which the said mechanical compressor
is a variable-speed compressor.
21. The system of claim 19 which further includes an electric
rotating machine operably coupled to the said mechanical
refrigerant compressor and vapor expander.
22. The system of claim 21 in which the electric rotating machine
is a motor/generator.
23. The system of claim 22 in which the motor/generator uses some
or all of the electrical output energy from a generating mode to
fulfill the electrical power demand from system controls and other
devices.
24. The system of claim 22 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.
25. The system of claim 22 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.
26. The system of claim 22 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.
27. The system of claim 26 in which the intelligent control system
adjusts various operational parameters of the systems to optimize
system efficiency.
28. The system of claim 26 in which the intelligent control system
further adjusts various operational parameters based partially or
entirely on stored historical operational data from previous run
cycles.
29. The system of claim 26 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.
30. The system of claim 26 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.
31. The system of claim 26 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.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] Not Applicable
FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
SEQUENCE LISTING OR PROGRAM
[0003] Not Applicable
BACKGROUND
[0004] 1. Field
[0005] This application relates to a cascade cooling system,
specifically one incorporating a jet ejector compressor and a
mechanical compressor.
BACKGROUND
[0006] 2. Prior art
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] Various embodiments of the present invention provide a
thermally enhanced cascade cooling system which, [0036] (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. [0037] (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. [0038] (c) accepts thermal and mechanical
input energy including electrical, mechanical, hydraulic, and
pneumatic in any proportion. [0039] (d) generates its own electric
power from thermal or other non-electric power input sources.
[0040] (e) functions as a two-stage mechanical cooling system in an
all-electric mode. [0041] (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. [0042] (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
[0043] 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.
[0044] FIG. 1 is a block diagram of a thermally enhanced cascade
cooling system according to a first embodiment.
[0045] FIG. 2 is a block diagram of a thermally enhanced cascade
cooling system according to a second embodiment.
[0046] FIG. 3A is a block diagram of one embodiment of a high
temperature loop in a mobile vehicle application.
[0047] FIG. 3B is a block diagram of one embodiment of a high
temperature loop in a stationary application.
[0048] FIG. 4 is a block diagram of a thermally enhanced cascade
cooling system according to a third embodiment.
[0049] FIG. 5A is a block diagram of one embodiment of a direct
expansion primary cooling loop.
[0050] FIG. 5B is a block diagram of one embodiment of a primary
cooling loop incorporating a liquid chiller.
[0051] FIG. 6 is a block diagram of a thermally enhanced cascade
cooling system according to a fourth embodiment.
[0052] FIG. 7 is a control logic flow chart for a high temperature
loop in a mobile vehicle application.
[0053] FIG. 8 is a control logic flow chart for a high temperature
loop in a stationary application.
[0054] FIG. 9 is a control logic flow chart for heating control
according to one embodiment of a high temperature control loop.
[0055] FIG. 10 is a control logic flow chart for boiler superheat
control according to a first embodiment of a thermally enhanced
cascade cooling system.
[0056] 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.
[0057] FIG. 12 is a logic flow chart to control valve timing in a
vapor expander.
[0058] FIG. 13 is a logic flow chart to control valve timing of a
vapor expander operating in compressor mode.
[0059] 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
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] Hereinafter, various embodiments of the present invention
will be described in detail with reference to the drawings.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] Thus the scope of the embodiments should be determined by
the appended claims and their legal equivalent, rather than by the
examples given.
* * * * *