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BACKGROUND OF THE INVENTION
Until the nineteen-seventies, solar heating received only scattered,
spasmodic attention because it was not price competitive with the use of
fossil fuels. Renewed interest in solar energy has developed during the
past few years as a result of increasing costs of energy from fossil
fuels, the problems of depletion of resources, and the degradation of the
environment. Although solar energy may be considered as a new and
unconventional resource, it has been used for many centuries for drying
agricultural products, heating water, etc.
Prior art solar heating systems are generally accomplished by placing large
collector plates on the roof and side structure of buildings. Liquids,
such as water, are piped through the collector, heated to a higher
temperature, and subsequently circulated through a building and used as a
space and tap-water heating medium. Such a system may be useful during the
sunlight hours but loses its effectiveness after sundown. In a more
elaborate application of the same principle, it has been suggested to
place large tanks of water, rocks, stones, etc., in the ground and have
heated water from the solar collector fed into the tanks, where the heat
energy is stored and utilized for space and hot water heating. But, during
prolonged cloudy or rainy weather, such a system loses its effectiveness
because of its incapacity to store more than a few days' supply of heat
energy. Furthermore, during the winter period when the heat is most
desirable, the efficiency of the solar radiation is much less than that of
summer months, and heat loss from the collector to the surroundings is
much greater. In short, currently known solar-heating systems must be
installed in addition to, not instead of, conventional heating systems.
The earth, as a thermal storage reservoir, has several interesting
attributes. First, heat capacities are extremely large because of the
large available mass. For example, in a volume of one acre of land, 15
feet deep, at a temperature difference of 50.degree. F. the energy flux is
estimated to be 1.49 .times. 10.sup.9 BTU. The area of one acre is much
larger than an average house. Specifically, it is over 20 to 40 times
larger than the average house of sizes from 2,000 ft.sup.2 to 1,000
ft.sup.2. Assuming a winter heating requirement of 60 .times. 10.sup.6 BTU
for a small house, such a volume of earth would be able to store
sufficient heat to supply approximately 25 homes.
Another attribute of the earth is its extremely low thermal conductivity.
Since the storage system may be unbounded in the downward and sideward
directions as opposed to the confined, insulated and water-proofed
constructions of the conventional designs, the low thermal conductivity of
the earth restricts losses in those directions. It has been approximated
that the total energy in the solar flux over one acre of area, for one
summer season, is 1.2 .times. 10.sup.10 BTU; these are approximately the
heating requirements for 200 houses. It can therefore be seen that the
theoretically available energy from the sun is extremely high.
SUMMARY OF THE INVENTION
The present invention relates to a system for collecting, storing and
utilizing solar energy, and more particularly, relates to a system which
utilizes the earth, or ground, as a long-duration storage for heat energy.
Part of the invention system also relates to a novel heat pipe
characterized by having uni-directional irreversible vapor flow, and
having a unique compact system for moving working fluid from the condenser
section to the evaporator system.
The invention comtemplates a novel system for storing and utilizing solar
energy wherein the system comprises a collector means for collecting solar
energy and changing the solar energy to heat, means for transmitting the
heat from the collector means to a location below the surface of the
ground, and a distributing means disposed within the ground for
distributing the heat from the mentioned location throughout a
considerable volume of the ground for raising the temperature of the
considerable volume of ground to thereby establish a heat reservoir.
For accomplishing for foregoing objective, the invention contemplates the
use of solar collectors, a heat pipe or pipes for transmission of the
solar heat energy to the storage ground, and piping loops for both
transmission and storage of heat in the system, and extraction of heat
from the storage ground for space heating and hot water heating. The heat
pipe functions in the system as a sort of rectifier, for changing solar
flux to heat energy, and allowing the heat energy to flow with the least
possible resistance from the evaporator section of the heat pipe to a
desired depth underground during the period of time when the sun is
shining, but prevents the reverse flow of heat energy when the temperature
above the ground is lower than that of the storage ground.
Accordingly, an important object of the invention is to provide for
long-duration earth storage of solar energy which can be used for both
space heating and hot water heating systems, year-round, in multiple-unit
housing, public buildings such as schools, etc., commercial buildings or
single dwellings.
Another object of the invention is to provide a highly efficient means for
transferring solar energy from solar flux collectors into the ground for
storage of heat through the use of novel heat pipe including an evaporator
section, an adiabatic section, a condenser section and a working fluid,
wick means disposed only in the evaporator section and condenser section,
and pump means for transferring the working fluid, after phase change from
vapor to liquid from the condenser section to the evaporator section.
Further, the invention provides such a heat pipe wherein the pump means
includes a fluid line extending from the condenser section to the
evaporator section and a pump is connected in the fluid line.
A further, and important, object of the invention is to provide such a heat
pipe wherein the pump is disposed at a location remote from the condenser
section.
A still further object of the invention is to provide a novel heat pipe
wherein the evaporator section and the condenser section each include an
outer casing formed of heat conductive material, and the adiabatic section
has at least a portion thereof formed of a poor heat conductive material
for precluding transfer of heat by conduction between the condenser
section and the evaporator section.
A further object of the invention is to provide a large thermal storage
reservoir in the unprepared earth and to utilize the stored energy for
year-round space heating and hot water heating substantially or completely
without the aid of conventional heating systems.
A still further object of the invention is to provide a solar heating
system which need not be an integral part of the solar heated home, if so
desired, thus having no adverse impact on the esthetics of the home.
A still further object is to provide an efficient means to collect and
store an abundance of solar energy during the summer season for subsequent
winter use when the efficiency of collecting solar energy is extremely
low.
Further objects and advantages of my invention will become apparent from an
understanding of the following detailed description of preferred
embodiments of my invention.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic sectional view of a system for collecting, storing
and utilizing solar energy in accordance with the present invention.
FIG. 2 is a diagrammatic vertical section of a heat pipe constructed in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, the novel collection, storage and utilization system,
generally indicated by the numeral 10, includes a conventional solar
collector 12 (shown in broken lines) which collector 12 may be planar,
parabolic, or any other type of collector, for collecting solar energy and
transferring the heat energy thereof to a heat pipe 14. The heat pipe
includes an evaporator section 16, adiabatic section 18, and a condenser
section 20. The particular details of construction for the heat pipe 14
will be later described in connection with the showing in FIG. 2. Briefly,
however, energy is absorbed by the evaporator section 16 and transferred
through the adiabatic section 18 down to the condenser section 20, which
section 20 may be, depending upon circumstances, located at a depth below
the earth's surface a distance of approximately 5 feet to 30 feet, or
more.
At a location 22, represented by a volume of earth encompassed within the
broken line rectangle, heat is absorbed from the condenser section 20,
where the phase change from vapor to liquid is taken place. Heat energy is
transmitted in all directions from this location 22, thereby cooling the
condenser section 20 and causing the heat energy to be transferred to the
surrounding earth. One important feature of the present invention is to
surround the condenser section 20 with material which has a higher
coefficient of heat conductivity than the normal soil. One such manner is
illustrated by the provision of a relatively small volume of granular sand
24, and the like, which may have the moisture content thereof increased by
piping water, or the like, through a control valve 26 downwardly through a
supply pipe 28 and outwardly through a series of holes 30. It will be
understood that the moist sand 24 will aid in transmitting heat outwardly
from the location 22 to the surrounding unprepared earth soil, generally
designated by the numeral 32. It is understood that other types of heat
conductive material, such as metal and the like, which may also be in the
form of fins extending outwardly from the condenser section 20 may be be
used instead of, or in combination with, the moist sand 24.
In addition to the foregoing described manner of transmitting heat energy
from the condenser section 20 to the surrounding soil 32, the present
invention also includes the provision of an expanding array of pipe (or
pipes), generally indicated by the numeral 34. The pipe 34 is comprised of
a closed loop in which is located a pump 36 and a two-way valve 38 having
a vane 40 shown by solid lines located in a first position 42. In order to
transmit heat energy from the location 22 throughout the soil 32, the pipe
34 is completely filled with heat transfer fluid, such as water and the
like, the heat transfer fluid being circulated within the pipe 34
downwardly from the pump 36 and spirally about the condenser section 20
throughout the location 22. During this time, the heat transfer fluid
picks up heat and then carries it throughout the expanding array of pipe
34 to distribute the heat throughout a large volume of the earth's soil
32. This distibution of the heat is generally indicated by the plurality
of the arrows 44. It will be appreciated that after the system has been
operating for a period of time, the temperature of the sand 24, the soil
32, and beyond, will be elevated to a sufficiently high degree such that
adequate heat supply may be later extracted for subsequent use.
When it is desired to use some of the heat that has been stored in the soil
32, the valve vane 40 is moved to the dotted line position 50. As one
example of apparatus for using the storage heat, a heat exchanger 52 is
connected across the valve 38 and the pump 36 by pipes 54 and 56 so that
the heat transfer fluid does not pass directly from the valve 38 to the
pump 36 through a connecting pipe 58. It is, of course, to be understood
that the hot water in pipe 54 gives up its heat energy as it passes
through the heat exchanger 52, becomes cooler, and passes downwardly
through the pump 36 into the array of pipe 34 to become heated and again
return to the heat exchanger 52.
In order to increase the efficiency of the heat storage system, a layer of
insulating material 60 is disposed about on the surface of the earth, and
preferably, the insulating material 60 is covered by a sheet, or sheets,
of black plastic 62, or the like, to serve as a vapor barrier and also to
aid in collecting additional heat from the solar flux and transmitting
such heat into the soil 32 and in absorbing more heat because black
materials characteristically have the highest heat absorbtivities.
While the foregoing description of the invention has been limited to only a
single array of pipe 34, it will be readily understood that multiple
arrays of pipe 34 and additional heat pipes 14 may be connected to the
system through a valve 64.
FIG. 2 illustrates the constructional details of a preferred heat pipe 14
which is utilized in the system 10 of FIG. 1. The heat pipe 14 includes an
evaporator section 16, an adiabatic section 18, and a condenser section 20
as well as containing a working fluid (not illustrated). The evaporator
section 16 is lined with a wick 70 and the condenser section 20 is lined
with a wick 72. It is to be noted that the adiabatic section 18 is not
lined with any similar wick. The wick 70 and 72 may be metal, such as wire
screen, sintered metal powder or fiber, or perforated sheets, or it may be
a non-metallic material such as felt, cloth, or fiber glass. The working
fluid may be water, ammonia, acetone, fluorocarbons (refrigerants),
alcohols, and various liquid metals. However, only enough working fluid to
saturate the wick is introduced into the heat pipe. The choice of
container, wick material, and working fluid combination is based on the
operations and design criteria of the heat pipe application.
In evaporator section 16 heat energy, indicated by the arrows 74, is
received from the solar collector 12 (FIG. 1) and is transferred by
conduction through the outer wall of the evaporator section 16. The heat
energy 74 causes the working fluid to vaporize, as indicated by the arrows
76. The vaporized working fluid then flows downwardly through the
adiabatic section 18 to the condenser section 20 where the vapor condenses
and the heat energy is transmitted outwardly to the wick 72 through the
wall of the condenser section 20, all as is indicated by the arrows 78. It
is to be understood this heat, as indicated by the arrows 78, is the heat
given up in the location 22 of FIG. 1.
In order that heat pipe 14 operates in a continuous manner, it is necessary
that the working fluid condensate in the condenser section 20 be returned
to the evaporator section 16. This return of working fluid is provided by
the provision of a return line 80 which is connected to a port 82, at the
bottom of the condenser section 20, and connected to a pump 84 which is,
in turn, connected to a port 86 at the evaporator 16. While the pump 84 is
indicated as being a reversible pump, so that the heat pipe 14 is useful
in other modes of operation, it is to be understood that when the heat
pipe 14 is used in the environment of the system 10, of FIG. 1, the pump
84 is operated only in the direction to return working fluid from the
condenser section 20 to the evaporator section 16. This is an important
part of the system 10 so that, when the collector 12 is not operating and
the ambient temperature around the evaporator 16 is lower than the ground
temperature around the condenser section 20, the heat pipe 14 is
irreversible; in other words, heat energy is not transmitted upwardly
through the adiabatic section 18 and lost to the atmosphere through the
evaporator section 16.
When the solar energy is not available, or during extremely cold weather,
the pump 84 will be shut off automatically by a thermostatic control (not
shown). This prevent the reverse vapor flow in order to avoid heat losses
from the earth reservoir to the surrounding environment. As an additional
measure to prevent heat loss by axial conduction of heat upwardly through
the heat pipe 14, the adiabatic section 18 is made of a poor heat
conductive material. Thus, the condenser section 20 is insulated from the
evaporator section 16.
While a preferred system and a preferred heat pipe for use in such system
has been illustrated and described, it is to be understood that various
changes and arrangement of parts may be made without departing from the
spirit and scope of the invention as defined in the appended claim subject
matter.
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