Multi-system power generator

A geothermal power system utilizes a fluid refrigerant capable of changing phase between liquid and gaseous states. The system includes a heat exchanger exposed to a heat source such as earth, water, air, or industrial waste for vaporizing the fluid in the heat exchanger. The heat exchanger includes at least two compartmentalized heat exchanger cells. Each of the heat exchanger cells is disposed in a portion of the naturally occurring heat source, the portions being sufficiently spaced apart such that a temperature of any one portion is substantially unaffected by a temperature of any other portion. The vaporized fluid is directed to a turbine or energy extraction means wherein the gas is expanded and energy is re)eased in the form of mechanical rotation of a shaft. The turbine shaft may be coupled to a generator for converting the mechanical rotational energy to electrical power. The gas discharged from the turbine is cooled/condensed and circulated into an accumulator, with a sensor and a controller for continuously maintaining the optimum amount of refrigerant flowing in the system under particular heat source/heat sink conditions. The liquid refrigerant is then recirculated to the heat exchanger, and the process is performed continuously. A compressor and sensored and controlled accumulator may be utilized in a second and separate refrigerant heat exchange loop with compartmentalized heat exchanger cells if necessary to maintain continuous output from the geothermal power system under all temperature conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a power generation system which utilizes naturally 
occurring low grade heat energy at or near the earth's surface to produce 
mechanical or electrical power. 
2. Prior Art 
Systems for generating power convert the thermal energy difference between 
a heat source and a heat sink to useful power by driving a generator or 
other power output while transferring heat energy from the source to the 
sink. Such systems are most efficient where the difference in the 
temperature between the source and sink is the greatest. Geothermal power 
generation systems are known which rely on heat from high temperature 
sources, located in an area of volcanic activity and/or far below the 
earth's surface, generally at depths of from 100 to 30,000 feet. The heat 
is extracted from maqma or superheated rock, and carried to the surface by 
water, brine, etc. The heat is then extracted at the surface, and various 
uses can be made of the heat, including operating a turbine or other 
device coupled to an electric generator. Whereas the surface temperature 
is always lower than such high temperature sources, the heat extraction 
technique can be used to generate power. 
A power generation system of this type may use a circulating coolant which 
is changed between a liquid phase and a gas phase in each pass around the 
circulation loop, the changes being a result of the temperatures 
encountered at the source and at the sink. For example, pressurized liquid 
coolant is heated and phase changed into a gas on the hotter side of a 
circulation loop, and after driving a turbine-generator or the like at 
which the heated coolant is allowed to expand and cool, the now-gaseous 
coolant is condensed and depressurized to the liquid phase on the cooler 
side of the circulation loop, proceeding again around the loop to the 
hotter side. The coolant is circulated continuously around the loop, 
generally using the temperature difference between the hotter and cooler 
sides as the power source for driving the turbine. 
Apart from direct association with volcanic activity, the underground 
temperature of the earth near the surface, where insulated from day to day 
surface temperature variations, is a relatively stable temperature in the 
mid 50.degree. Fahrenheit range. However, at any particular time of the 
year the temperature at the surface, specifically the surface air 
temperature, may be higher or lower than the temperature of the earth 
beneath the surface. The earth's underground temperature also increases 
roughly 88.degree. Fahrenheit per mile of depth. 
It is known to use the temperature difference between a heat source or sink 
at a temperature nearly equal to the surface air temperature to move heat 
energy into or out of a building or other heating/cooling load, by use of 
a similar circulating coolant system known as a heat pump. The coolant is 
heated (or cooled) at a heat exchanger located outside of a building and 
the heat is extracted (or the coolant extracts heat) at a heat exchanger 
disposed in the building, one or both heat exchangers normally being 
associated with fans for moving air over the heat exchanging surfaces. 
Such systems do not produce mechanical or electrical energy from the 
temperature difference. The systems simply extract heat or sink heat 
between the building and the outside heat exchanger, using electrically 
powered fans and pumps. 
Known systems for tapping the ever abundant heat source of the earth below 
the surface, for the purpose of generating power, typically convert water 
into steam for driving a turbine or operating a refrigeration plant. For 
example, see U.S. Pat. Nos. 4,091,623; 4,142,108; 4,189,923; 4,255,933; 
and 4,388,807. The systems require passages leading deep into the earth. 
Drilling expenses, passage obstruction problems, shifting of the earth 
associated with volcanic activity, and other expenses or technological 
problems generally render these ostensibly good ideas economically 
unrealistic and infeasible. 
Power generation systems have also been developed to utilize temperature 
differentials due to the cooling of ocean water at depth, or as provided 
due to prevailing currents. Generally, ocean water near the surface, which 
is warmed by the sun, provides the heat source, and colder deeper ocean 
water provides a significantly cooler temperature differential, enabling 
the generation of mechanical and electrical power. See, for example, U.S. 
Pat. Nos. 4,087,975; 4,189,924; and 4,302,682. Oceanic thermal difference 
energy conversion systems are theoretically attractive for generating 
power, however their application is obviously limited to ocean areas and 
the cooler-side heat exchanger must be very deep to obtain a substantial 
temperature difference compared to the surface temperature. As with the 
deep well geothermal systems, from a practical standpoint these proposed 
power generation systems are quite large, as considered necessary to be 
economically feasible in many applications. Also, major potential problems 
remain, including weather problems (e.g., hurricanes and typhoons), tides, 
shipping traffic, barnacles, corrosion due to long-term exposure to sea 
water, etc. 
In U.S. Pat. No. 4,290,266, a coolant or refrigerant line is placed 
sufficiently deep for geothermal heat to convert gravity drained liquid 
refrigerant into a gas under high pressure for use in driving a turbine. 
The concept of using a phase changing coolant or refrigerant other than 
water is the same as that of changing water into steam and back for 
driving a turbine in a geothermal system. However, the refrigerant is 
normally chosen such that it has a boiling point suitable for the 
temperature levels of the system design and thus is readily changed in 
phase by the temperatures encountered on the hotter and cooler sides of 
the loop. On the other hand, the refrigerant concept has significant 
operational problems when one attempts to apply it to geothermal power 
generation due to the requirement for substantial vertical conduit lengths 
between the surface and the subsurface heat exchangers. For example, there 
is no ready means to force the refrigerant dependably under power around 
the circulation loop, due to the phase differences between the heavier and 
less compressible liquid and the lighter and more-compressible gas phases. 
Once gravity fed liquid refrigerant is phase changed into a gas, it is 
difficult to force it further downward, because the low density gas tends 
to rise in the higher density liquid refrigerant. In short, it is 
difficult to move the refrigerant in a loop to a sufficiently hot 
subterranean depth, prior to phase change, for naturally producing the 
pressures needed for significant power generation. Once the liquid 
refrigerant changes phase from a liquid to a gas, the effects of gravity 
flow are substantially diminished. Inasmuch as the most remote point in 
the circulation loop may be far below the surface, such gravity flow 
refrigerant systems ultimately suffer from poor system equilibrium and 
periods of in operation. Other problems include inability of the system to 
operate in a reverse direction, inability to recover geothermal heat on 
the heat extraction side after extended operating periods, and typically, 
high costs and associated problems encountered with deep wells. 
Another approach for a refrigerant type power generation system is 
disclosed in U.S. Pat. No. 3,995,429 (Peters). This patent describes the 
production of a pressurized vapor via selective utilization of temperature 
differentials in two of three or more heat sources or sinks, each of which 
varies in temperature over time. A fluid pump is powered by an electric 
motor for moving liquid refrigerant around a loop including selected ones 
of the sources and sinks. Controls and valves are provided for switching 
between heat and heat sink sources having the most efficient (highest) 
naturally occurring temperature differential. The disclosure of the patent 
teaches heat sources including a solar energy absorber, a radiator placed 
in the earth or in water, and an atmospheric heat exchanger. One obvious 
problem with this system, as noted in the patent, is that under certain 
conditions there is no sufficient temperature difference between any two 
of the heat, or heat sink, sources, whereupon all action stops. This 
results in a lack of continuous and dependable power. Moreover, 
refrigerant equilibrium problems and imbalances in refrigerant quantities 
occur and must be accurately and consistently controlled to effect 
appropriate refrigerant phase changes under varying load and temperature 
differential conditions and to effectively generate power. For example, 
Peters neglects to provide a means to overcome the negative effects which 
will operationally be realized when the vaporized refrigerant encounters 
pressure resistance from the turbine and exerts a back pressure against 
and/or into the liquid refrigerant exiting the liquid refrigerant pump 
and/or source. Such back pressure can severely hamper system operational 
efficiency, ultimately placing as much of a power drain on the circulating 
pump as the turbine is able to produce from the coolant. This back 
pressure can result in system equilibrium loss and shut down. Further, the 
Peters invention neglects to provide for a coolant accumulator/dispenser 
system which will automatically sense conditions and adjust the amount of 
refrigerant contained in the circulation loop at any given time to 
maintain optimum conditions for the particular heat source/heat sink 
system being utilized for power generation. Such a refrigerant supply 
control is critical for optimum system operation under varying temperature 
conditions. For example, when operating under relatively colder 
temperature conditions, a larger quantity of refrigerant is required to 
achieve optimum performance than when operating under relatively hotter 
temperature conditions. If refrigerant quantities in the system are not 
controlled and reduced when operating between the warm sun and warm air 
and/or warm water and/or warm earth in the summer, as opposed to colder 
identical heat and heat sink sources in the winter, pressures may become 
so high or so low as to result in pump and/or generator burn out or 
malfunction. 
The present invention overcomes these problems by providing a geothermal 
power system and method which utilizes a low grade, naturally occurring 
heat source found at or near the surface of the earth. The invention 
provides a heat exchanger having two or more compartmentalized heat 
exchanger cells in contact with the naturally occurring heat source for 
vaporizing a liquid refrigerant. The heat exchanger cells are spaced 
apart, and switchable valves are provided for selectively controlling 
refrigerant flow through the individual cells so that the heat source in 
the vicinity of each cell can alternately be given time to naturally 
recover heat after being drawn down by refrigerant vaporization. An 
accumulator/dispenser is provided with means to monitor and control 
refrigerant quantities in the system in order to maintain optimum system 
temperatures and pressures and to prevent dangerous system overpressures 
or underpressures. A supplemental design utilizing two separate 
refrigerant loops may also be used, with the first loop utilizing a 
compressor for circulating the refrigerant, and for pressurizing and 
heating the vaporized refrigerant returning from the underground heat 
source, to a suitable temperature for ensuring a phase change in the 
secondary refrigerant loop for operating a turbine, reciprocating engine 
or other power extraction device which expands the pressurized gas and 
assists in converting the pressurized refrigerant back into the liquid 
phase. The turbine or other engine may be coupled to a generator for 
producing electricity. Alternatively, it can be used to provide mechanical 
power. The mechanical or electrical energy can be stored via compression 
of gas or hydraulic fluids, electrolysis, batteries, etc., for later use. 
Expansion valves and condensing cells are provided as necessary to 
maintain operational temperature/pressure differentials in the system. For 
the system with two separate refrigerant loops wherein the refrigerant in 
the first loop is continuously circulated by the compressor, the system, 
unlike Peters, is operational with extremely modest temperature 
differentials between the heat source and the heat sink. 
The invention is particularly applicable to a ground source heat exchanger 
having temperature exchange coils which are buried in an array near the 
earth's surface, especially just below the frost line or heat line. For 
example, a sinuous pattern of copper or other thermally conductive tubing 
can be mounted along the walls of a simple backhoe trench to provide the 
subsurface heat exchanger. Similarly, a bored cylindrical hole can be 
lined with a helical pattern of heat exchange coils, rested along the 
sides of the hole before backfilling. The subsurface heat exchanger can be 
operated in conjunction with heat exchangers for the opposite side of the 
loop, including water based and ambient air heat exchangers, thus 
providing a versatile system for extracting power from naturally occurring 
temperature differences. The apparatus can be provided simply as a power 
generation device, or alternatively can be operated in a power generation 
mode only when not in use as a building HVAC heat pump system. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a power generation system which 
is relatively simple to construct, operate and maintain. 
It is another object of the invention to provide a power generation system 
which is cheaper to construct and operate than conventional systems. 
It is a further object of the invention to provide a power generation 
system which can be built on either a small or large scale at almost any 
location. 
It is yet another object of the invention to provide a power generation 
system which efficiently provides mechanical or electrical power with 
little or no damage to the environment. 
It is still another object of the invention to provide a power generation 
system which utilizes naturally occurring heat sources having relatively 
small temperature differentials. 
These and other objects are accomplished by a power generation system which 
utilizes a refrigerant fluid suitable for changing phase between liquid 
and gaseous states. In the first design, a heat exchanger absorbs heat 
from a low grade, naturally occurring heat source such as shallow earth, 
shallow water, air, solar or industrial waste heat. The heat exchanger 
includes two or more heat exchanger cells and selector valves for 
controlling refrigerant flow through each cell. The cells in any one 
naturally occurring heat source are sufficiently spaced apart so that each 
cell draws down heat from its local area with negligible effect on the 
heat content of the local area of any other cell. The individual heat 
absorption cells are permitted appropriate time to recover heat and gasify 
the liquid refregerant in them by shutting off and isolating the liquid 
refrigerant supply and the gaseous discharge until sufficient gas pressure 
is reached. The liquid refrigerant passes into one of the heat exchanger 
cells and is vaporized into a pressurized gas. Once sufficient gas 
pressure is reached, a valve opens and permits the pressurized gas to 
enter a turbine or reciprocating engine. The gas is expanded in the 
turbine, thereby giving up energy in the form of powered mechanical 
rotation of the turbine. The mechanical energy thus developed can be 
converted to electrical energy in a generator coupled to the turbine 
and/or stored via batteries, electrolysis, hydraulic or pneumatic fluids 
or gases, potential energy (e.g. by lifting a quantity of water), etc., 
for later use. After exhausting from the turbine, the expanded gas would 
be converted to a liquid in a condenser, which condenser can comprise one 
or more of the coolest compartmentalized heat exchange cells, to maintain 
system operating parameters. The liquid is then circulated back to the 
heat exchanger and the process is repeated. A pump may be provided for 
maintaining the liquid refrigerant flow to the heat exchanger cells A 
liquid refrigerant accumulator and control means such as valves are 
provided for directing the quantity and flow of the refrigerant through 
the system at optimum quantities, temperatures and pressures. Preferably 
the valves are solenoid valves coupled to outputs of a microprocessor 
controller which is also coupled to temperature and pressure sensors along 
the circulation path, and programmed to optimize system parameters by 
controlling the valves and refrigerant supply as appropriate to present 
sensed conditions. 
A secondary design utilizes two separate refrigerant loops. The first loop 
utilizes a compressor for circulating the refrigerant through a condensing 
cell, which cools and liquifies the refrigerant, and through a heat source 
which heats and vaporizes the refrigerant. The compressor pressurizes and 
superheats the gaseous phase-changed gas exiting the heating source. The 
second loop operates in the manner as described hereinabove in the first 
design, except the heat source for the second power generation loop is the 
heat generated via the first refrigerant loop achieving refrigerant 
circulation by means of a compressor. 
The compressor is a beneficial part of the invention. The compressor 
maintains refrigerant flow in the system even during periods of low 
temperature differentials, thereby overcoming the problem of the prior art 
systems which become inoperative in the event of low temperature 
differentials. Further, refrigerant flow is maintained at a sufficient 
velocity to prevent separation of lubricating oil out of suspension in the 
refrigerant. The compressor also provides a means of condensing and 
accelerating the effects of even modest temperature differentials, thus 
enabling the system to operate to take advantage of whatever temperature 
differences are available even when the differences are relatively small.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A power generation system according to the invention utilizes a suitable 
fluid which changes phase from liquid to gaseous states at relatively 
modest temperatures and at pressures which are maintained in the system as 
hereinafter described. In particular the fluid is chosen to undergo a 
liquid to gas phase change readily at the temperatures encountered in a 
heat exchanger disposed in contact with a low grade, naturally occurring 
or waste heat source, and is pressurized according to the invention such 
that the phase change from liquid to gas occurs at a point in the 
circulation loop where the phase change can be used to drive a mechanical 
means for extracting energy, i.e., at a turbine or other engine which 
extracts mechanical energy by allowing pressurized gas to expand to a 
larger volume. The gas may be a commonly used refrigerant such as Freon 12 
or Freon 22, or ammonia, or another known refrigerant. The fluid is 
communicated throughout the system by conduit means such as pipe or tubing 
connected between successive stages in the system. 
According to a first embodiment of the invention, one or more heat 
exchangers is disposed in thermal communication with a heat source. As 
illustrated schematically in FIG. 1, heat exchangers 11, 12, 13, 14, 15 
are disposed in thermal communication with a naturally occurring or waste 
heat source such as geothermal, water, air, solar energy, or an industrial 
waste heat source, respectively. The, for example, geothermal heat 
exchanger should be placed sufficiently below the earth's surface to 
provide a dependable source of heat at least at the typical subsurface 
temperature of 55.degree. F., and where available may be placed in thermal 
communication with a warmer temperature source. 
According to the invention, the heat exchangers 11, 12, 13, 14, 15 need not 
be, but could be, in thermal communication with a high temperature heat 
source. The invention can utilize heat retained in shallow earth, shallow 
water, air or other substance at moderate temperatures. For example, the 
geothermal heat exchanger 11 preferably comprises a plurality of 
substantially horizontal tubes disposed in the earth at a distance of one 
or two feet below the frost line for the geographic locality of the 
system, in order to minimize the depth of excavation required for 
subterranean placement of the heat exchanger while preventing the tendency 
of the tubes to become displaced due to frost heaving or to become 
inefficient due to proximity to cold surface conditions. A suitable heat 
exchanger is disclosed in patent application Ser. No. 725,962, filed Jul. 
5, 1991, entitled MODULAR TUBE BUNDLE HEAT EXCHANGER AND GEOTHERMAL HEAT 
PUMP SYSTEM, hereby incorporated by reference. Alternatively, the heat 
exchanger may be disposed in shallow water or in air, or exposed to heat 
from solar energy or industrial waste heat, provided the heat exchanger is 
disposed to be heated relative to the temperature of the expanded (cooled) 
refrigerant which has been passed through the turbine or other mechanical 
energy extraction means. Only modest temperatures are required for 
operation of the system according to the invention, however, it is 
advantageous to employ the maximum temperature differential which is 
available, for best efficiency. 
Each of the heat exchangers includes at least two compartmentalized heat 
exchanger cells designated a and b and placed in different locations 
having potentially different temperatures. The different locations can be 
in different portions of one source of heat, the portions being 
sufficiently spaced apart that a temperature of any one portion is not 
substantially affected by a temperature of any other portion. Thus, the 
cooler fluid refrigerant flowing into one of the heat exchanger cells 
draws heat from the portion of the heat source associated with that cell, 
but does not draw down any substantial amount of heat from the portion of 
the heat source associated with any other cell in the heat source as a 
whole. The use of spaced apart heat compartmentalized heat exchanger cells 
allows the refrigerant to be contained in one of the cells for a time 
sufficient to permit complete vaporization and appropriate pressurization 
of the refrigerant in the one cell while allowing the other cell time to 
discharge its already heated and pressurized gas into the turbine 30. 
Temperature sensing means associated with each of the heat exchanger cells 
11,12,13,14,15 are coupled to a control device which senses the 
temperature for each portion of the heat source having a heat exchanger 
cell. The control device, which may comprise a programmed microprocessor 
coupled to sensors associated with the respective heat sources or 
portions, determines the temperatures available and chooses the highest 
temperature and greatest temperature differential of the respective heat 
source portions. Via controllable valves coupled to the circulation 
passages the control device selects and switches the circulation loop to 
traverse one or more of the available heat exchanger cells. In this manner 
the control device avails the system of the particular heat source portion 
which has the greatest heat reserve and/or the greatest capacity and 
highest difference in temperature. U.S. Pat. No. 3,995,429 to Peters 
discloses a suitable sensing means and switching means for selecting among 
different heat sources, and the disclosure is hereby incorporated for the 
particulars of sensing and control arrangements which can select among 
plural sources to obtain the greatest available thermal energy difference. 
It is also possible to arrange a similar function using, for example, 
other mechanical controls and/or a microprocessor coupled to suitable 
temperature sensors and valve actuators. As shown generally in FIG. 1, 
control valves 33, 34 are provided at the inlet and outlet of each of the 
heat exchanger cells to selectively arrange the fluid circulation loop to 
include whichever of the heat exchanger cells will provide the greatest 
heat source, as determined by the sensing and control means. This valving 
arrangement can direct the fluid to traverse more than one of the heat 
exchanger cells, for example to take advantage of the possibility that 
more than one of the heat exchanger cells is at a usefully tapped 
temperature. 
The refrigerant fluid is maintained within the respective heat exchanger 
cells a, b where it receives heat from the heat source portion in which 
the heat exchanger cell is in thermal communication. The refrigerant in 
the respective heat exchanger cells is changed into its gaseous phase and, 
once a sufficient pressure is reached, the pressurized refrigerant gas 
opens a pressure valve, or is released from the cells via timed sequence 
valves or a pressure sensor. The individual, compartmentalized heat 
exchanger cells provide the advantage of permitting retention of the 
refrigerant in one cell so that it has time to absorb sufficient heat to 
vaporize and pressurize the refrigerant completely, while simultaneously 
permitting release of the refrigerant which has been vaporized and 
pressurized in another cell so that pressurized refrigerant is kept 
available for operating a turbine means as hereinafter described. The 
individual compartmentalized heat exchanger cells further provide the 
advantage of eliminating back pressure against and/or into the liquid 
refrigerant and against a liquid refrigerant pump hereinafter described, 
which back pressure would otherwise substantially undermine system 
operational efficiency and/or result in system equilibrium loss and 
shutdown. 
The vaporized refrigerant flows through conduit 26 to a turbine means such 
as turbine 30, or any other rotary, reciprocating, stirling, inertial or 
scroll engine. In the presently preferred turbine embodiment, the gas is 
directed through nozzles to impinge on a plurality of blades connected to 
a rotatable shaft. The gas acting on the blades is expanded at the nozzles 
and energy thereby extracted from the pressurized gas is converted into 
rotational (mechanical) energy of the turbine shaft. The shaft may be 
coupled to any apparatus which can appropriately utilize the mechanical 
energy, and preferably is arranged to store the energy by mechanical, 
electrical or chemical means. For example, the shaft may be coupled to an 
electric generator means 40 for generating electrical power, which can be 
utilized by coupling to the electric mains via an inverter, or stored in 
batteries. The system may be operated for electrical power generation via 
direct current generation and/or via alternating current generation, with 
constant output and/or turbine speed and/or generator load maintained via 
use of an eddy current clutch and/or via controlling areas exposed to the 
low grade heat source and/or via introduction of pressurized gas in 
subatmospheric operation. The mechanical or electrical power can be also 
be used or stored, for example, by raising a fluid or other weight, by 
pressurizing a reservoir, by electrolysis, etc. 
After expansion and energy extraction, the refrigerant gas is circulated 
back through conduit 27 to one of the heat exchangers 11, 12, 13, 14, 15 
acting as a condenser in a relatively cooler one of the potential heat 
sources which now acts as a heat sink. The control valves 33, 34 are 
operated by the sensing and control device to admit the refrigerant gas to 
whichever of the heat exchangers is disposed in the greatest and coldest 
heat sink source. The refrigerant is cooled and liquified in the heat 
exchanger acting as the condenser, thereby reducing the pressure in the 
coolant conduit 27 on the downstream side of the turbine or other engine. 
If necessary, the refrigerant gas could be isolated and maintained in the 
compartmentalized heat exchanger cells for a period of time so that 
excessive heat would have adequate time to be removed in each cooling 
cell, for reducing the pressure in this area of the loop. 
After release from the condenser, the liquid refrigerant flows to an 
accumulator/dispenser 65 having means for sensing and adjusting an optimum 
amount of liquid refrigerant in the system. The refrigerant released from 
the accumulator/dispenser 65 is pumped via liquid refrigerant pump 72 back 
into whichever of the heat exchangers is disposed in the greatest heat 
source, as determined by the sensing and control device, and the process 
is repeated. Thus, the power generation system according to the invention 
comprises numerous potential refrigerant loops for generating mechanical 
or electrical energy, with sensing, control and valve means for 
circulating refrigerant through an active loop which includes the isolated 
and compartmentalized heat exchangers disposed in the greatest heat source 
and the greatest heat sink at any given time. 
The liquid refrigerant accumulator/dispenser 65 is used for automatically 
sensing and adjusting, via mechanical controls and preferably via a 
procedure of calculations or parameter look-up functions supervised by a 
micro-processor, the proper amount of refrigerant to be utilized at any 
given time under the particular refrigerant supply/pressure requirements 
necessitated via the particular temperature differentials and pressure 
conditions existing between the particular heat source/heat sink portions 
selected as active at the time. Absent continuous and correct adjustment 
of the refrigerant supply to the active loop, based upon actual 
operational temperature differentials, it is difficult or impossible to 
achieve efficient, or even actual, refrigerant phase change, as needed to 
optimize operational efficiency. 
The power generation system may be microprocessor controlled to achieve 
optimum temperatures and pressures for best system efficiency. A flash 
evaporating system, with a subatmospheric pressure range turbine, may be 
utilized to optimize performance below atmospheric pressures. Whereas the 
system operates by providing a phase change in the refrigerant between the 
hotter and cooler sides of the circulation loop, together with stepping up 
the pressure of the refrigerant gas preceding the mechanical energy 
extraction means, it is possible selectively to operate the system at 
different points in the pressure/temperature/phase chart which 
characterizes the particular coolant chosen. 
According to a second embodiment of the invention as shown in FIG. 2, two 
separate refrigerant circulation loops are provided. Like elements of the 
first and second embodiments are referred to in the drawings by like 
reference numbers. In the first loop of the second embodiment, the 
refrigerant gas exiting at least one selected heat exchanger 11, 12, 13, 
14 or 15 flows to a compressor means 20. The gas enters the compressor 
means at a temperature, for example, if from an earth heating source, 
between approximately 25.degree. and 60.degree. F. and at a pressure 
between about 50 and 100 pounds per square inch (PSI). The compressor 
means compresses the gas and raises its temperature such that the gas 
discharged from the compressor is slightly superheated. The compressor 
means may include, e.g., a reciprocal, scroll, rotary, or inertial type 
compressor. The compressor means not only moves the gas and the liquid 
refrigerant in the first loop, independently of gravity and/or 
independently of a liquid pump 72, as contained in the second loop, but 
more importantly, it provides a means of condensing and accelerating the 
effects of even modest renewable temperature differentials. Consequently, 
it is not necessary to wait for or to rely only upon naturally occurring 
significant temperature differentials. Instead, continuous power is 
provided via the much more dependable modest temperature differentials 
existing due to various thermal energy situations which are virtually 
always readily available. A modest but dependable thermal differential 
exists, for example, between the earth in one's yard and the atmosphere 
directly above it. Various industrial processes produce modest but 
dependable thermal temperature differentials between gaseous or fluid 
effluent and the ambient air or water. These sources/sinks can be 
exploited according to the invention, or the invention may be applied to 
exploit the temperature difference between any two appropriate heat 
sources and sinks which can be placed in thermal communication with a heat 
exchanger. 
The compressor means may include a plurality of serially coupled 
compressors 20 and 21 in order to achieve a sufficiently high gas 
temperature differential for optimum performance of the mechanical energy 
extraction means, which in the preferred embodiment comprises a gas 
turbine. While it would be desirable to utilize only one compressor in 
order to avoid efficiency losses occasioned by additional compressor 
units, more than one compressor may be utilized when marginal conditions 
require that the pressure and/or temperature condition of the compressed 
gas be stepped up via secondary or secondary and tertiary compressors, 
etc. A single compressor may raise the pressure of the refrigerant by an 
amount equivalent to raising the refrigerant temperature as compared to 
the output of the naturally occurring heat source gas temperatures by 
100.degree. F., or more. When higher gas temperatures are necessary to 
effectively operate the turbine or the like, the initially compressed gas 
may be stepped up to a second higher temperature/pressure condition via a 
next compressor, and to a third compressor, and so on, as necessary. The 
gas discharged from the compressor means, if from an earth source, will 
typically have a temperature between approximately 120.degree. and 
200.degree. F., and a pressure between approximately 200 and 325 PSI. 
Two or more compartmentalized heat exchanger cells are preferably 
alternately used with the compressor means in the first closed loop so as 
to allow respective cell heat recovery time when the system is in 
continuous operation. Sensors and valves automatically control refrigerant 
flow through the respective heat exchanger cells. Additionally, as in the 
power generation system of the first embodiment, a controlled liquid 
accumulator/dispenser 65 automatically adjusts the optimum amount of 
refrigerant flowing through the first loop refrigerant system. 
The compressed and superheated refrigerant gas in this first closed loop 
system, which contains the heat energy acquired from the sun, the air, or 
from a ground or water mass, or from industrial waste heat or other 
source, as aforesaid, transfers the accentuated heat energy to a separate 
and second closed loop refrigerant system via thermal coupling means such 
as an isolated and compartmentalized a b refrigerant to refrigerant heat 
exchange coil 55. This method of heat energy transfer eliminates 
efficiency destructive back pressure on the compressor in the first loop. 
The exchange coil 55 includes separate pathways for the refrigerant in the 
first and second loops, such as two tubes spiraled around each other in 
direct contact, or one tube containing the hot gas exiting the compressor 
of the first loop disposed within a separate tube containing cooler liquid 
refrigerant of the second loop. In the exchange coil 55, heat is 
transferred from the hot refrigerant gas exiting the compressor in the 
first closed loop system to the cooler liquid refrigerant in the second 
closed loop system, which refrigerant in the second loop, when heated and 
vaporized to become a pressurized gas, drives the turbine or other motor 
means 30 so as to create mechanical power, which can be used to drive the 
electrical generator 40. At least one of the cells defining a selected 
coldest source is controllable coupled into the conduit on the downstream 
side of the turbine. 
A power generation system according to the invention, whether a single 
refrigerant loop (as in the first embodiment) or a double refrigerant loop 
(e.g., the second embodiment), can operate in conjunction with a ground 
source heating/cooling system which is either a water-based or direct 
refrigerant exchange type system. Such a ground source heating/cooling 
system is described in U.S. Pat. No. 5,025,634, which is hereby 
incorporated by reference. The invention can either operate independently 
in a separate parcel of land, or immediately adjacent to, or in close 
proximity with the heat exchange coils of a ground source heating/cooling 
HVAC system, especially in warm climates. Furthermore, the system can 
employ at least one of the heat exchangers of an HVAC system when not in 
use. 
Where power generation system heat exchangers and heating/cooling system 
heat exchangers are located in close proximity to one another (typically 
immediately adjacent to one another or within a two foot distance of one 
another), the two separate systems preferably operate in a reverse fluid 
flow arrangement one from the other. This allows each of the systems to 
supplement the other system's efficiency by adding to the temperature 
differentials encountered. For example, in a warm climate, a ground source 
air conditioning system extracts heat from interior air and rejects the 
heat into the ground. A power generation system, with a ground source heat 
exchanger in close proximity to a ground source heat exchanger of the 
heating/cooling system, would extract normal ground heat, as well as waste 
heat dissipated in the ground from the heating/cooling system, and reject 
waste heat into exterior air via a conventional exterior air heat 
exchanger. This process, which is a form of recovery of waste heat, also 
aids the heating/cooling ground source heat exchanger in dissipating waste 
heat, which thus does not accumulate as rapidly in the ground. Operation 
of the power generation aspects of the invention thereby can assist in air 
conditioning efficiency. 
Further, in lieu of placing ground based heat exchange coils from the 
heating/cooling system in close proximity to the ground based heat 
exchange coils in the power generation system, the excess heat from the 
heating/cooling system could be conveyed to the power generation system, 
or vice versa, via a direct heat refrigerant to refrigerant exchange coil. 
The refrigerant to refrigerant heat exchange coil would comprise a "hot" 
refrigerant tube from one of the systems, carrying extra and/or waste 
heat, coiled around another tube with cooled refrigerant from the other 
system Which cooled refrigerant is in sequence to absorb heat and expand. 
The refrigerant to refrigerant heat exchange coil could also consist of a 
tube, with refrigerant from one system, within another tube, with 
refrigerant from the other system, in order to accomplish the same heat 
exchange step. 
Sensors and mechanical and/or microprocessor controls preferably are 
coupled to each of the respective circulation paths, to monitor and 
control proper heat exchange between the two systems such that each system 
operates at the maximum available efficiency under varying ambient 
conditions for each of the heat exchangers. 
For the geothermal power system having a heat exchanger disposed in water 
or in the air, the heat exchanger could include tubing, or rifled tubing, 
having internal or external fins for maximizing heat transfer. Such a heat 
exchanger could be relatively smaller than a heat exchanger having the 
same capacity which is disposed in earth, due to the added factors of 
improved thermal transfer and the existence of convection currents in the 
water. 
Individual tubes of the heat exchangers 11, 12, 13, 14, 15 and the heat 
exchange coils 55 are generally constructed of copper or aluminum or some 
similar highly conductive metal or plastic or material. Copper, however, 
when placed in soil or water, is subject to corrosion in the form of 
oxidation. The chemical reaction behind the oxidation of a metal, such as 
copper, involves a loss of electrons from the metal. To prevent a loss of 
electrons from the tubes of the heat exchangers and heat exchange coils, 
cathodic protection may be provided. The cathodic protection method as 
known in the art involves a sacrificial anode which is electrically 
coupled directly to a tube in each of the heat exchangers and heat 
exchange coils. In a chemical reaction between the copper tubes, the 
sacrificial anode, and the soil or water, the sacrificial anode releases 
electrons which travel to the copper tubing through a wire or other 
electrical coupling device. The copper tubing emits electrons to the soil 
or water which acts as an electron sink. The copper, although losing 
electrons to the soil or water, is continuously supplied with electrons 
from the sacrificial anode. The copper tubing therefore does not 
experience a net loss of electrons and hence does not oxidize and corrode. 
The sacrificial anode does experience a net loss of electrons and will 
oxidize over time, but can easily and inexpensively be replaced. 
The invention having been disclosed, a number of variations will now become 
apparent to those skilled in the art. Whereas the invention is intended to 
encompass the foregoing preferred embodiments as well as a reasonable 
range of equivalents, reference should be made to the appended claims 
rather than the foregoing discussion of examples, in order to assess the 
scope of the invention in which exclusive rights are claimed.