U.S. patent application number 13/043993 was filed with the patent office on 2011-06-30 for method and apparatus for accumulating, storing, and releasing thermal energy and humidity.
Invention is credited to Ronald M. Wexler.
Application Number | 20110154737 13/043993 |
Document ID | / |
Family ID | 44185771 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110154737 |
Kind Code |
A1 |
Wexler; Ronald M. |
June 30, 2011 |
METHOD AND APPARATUS FOR ACCUMULATING, STORING, AND RELEASING
THERMAL ENERGY AND HUMIDITY
Abstract
A method and apparatus for supplying heat and humidity to gas
filled spaces by the addition of water to a dehydrated material
that releases heat upon exposure to water, exposing the hydrated
material to dry contacting gas which results in loss of water from
the hydrated material to the contacting gas, the contacting gas
being heated and humidified by such exposure, and subsequent
dispersal of the added heat and humidity to the gas filled space.
This sequence also results in regeneration of the dehydrated
material so that these steps may be repeated. By limiting the
amount of water addition to the dehydrated material within a cycle
of the process, less time and/or energy is required to regenerate
the dehydrated material and finer control of resultant living space
humidity may be possible.
Inventors: |
Wexler; Ronald M.;
(Rochester, NY) |
Family ID: |
44185771 |
Appl. No.: |
13/043993 |
Filed: |
March 9, 2011 |
Current U.S.
Class: |
48/197R |
Current CPC
Class: |
B01J 20/0281 20130101;
F24D 2220/10 20130101; Y02E 60/142 20130101; B01J 20/045 20130101;
B01J 20/048 20130101; C09K 5/063 20130101; B01J 20/0237 20130101;
F28D 20/003 20130101; B01J 20/046 20130101; B01J 20/0244 20130101;
Y02E 60/14 20130101; B01J 20/043 20130101; B01J 20/3433 20130101;
F28D 20/02 20130101; Y02E 60/145 20130101 |
Class at
Publication: |
48/197.R |
International
Class: |
C10J 3/46 20060101
C10J003/46 |
Claims
1. A method of supplying heat to a gas filled space, comprising: a)
adding a quantity of water to a dehydrated material in solid form
that releases heat upon exposure to water, producing a hydrated
material, b) exposing the hydrated material to dry contacting gas,
releasing heat and water vapor from the hydrated material to the
contacting gas and regenerating the hydrated material back to
dehydrated material; and c) dispersing the heated contacting
gas.
2. The method of claim 1 further comprising: d) when at least a
selected percentage of the water added in step (a) has been removed
by exposure in step (b), repeating the method from step (a).
3. The method of claim 2, in which the selected percentage is
85%.
4. The method of claim 2, further comprising the step, before
repeating, of removing any remaining water from the material by
exposing the hydrated material to vacuum.
5. The method of claim 1 further comprising: e) measuring the water
vapor in the heated contacting gas from step (b) as the water vapor
of the heated contact gas first increases, then reaches a peak
value, then declines as the water is removed from the hydrated
material; and f) when the water vapor of the heated contacting gas
stops declining after it has begun decreasing, repeating the method
from step (a).
6. The method of claim 1, further comprising the step of removing
heat from the hydrated material and dispensing the removed heat to
the gas filled space by passing a gas through a conduit in thermal
contact with the hydrated material.
7. The method of claim 1, further comprising controlling humidity
in the gas filled space by dispersing the heated contacting gas
into the gas filled space to raise humidity and dispersing air from
a conduit in thermal contact with at least one of the hydrated
material or the heated contacting gas to maintain or lower
humidity.
8. The method of claim 7, in which the controlling is done by
switching between a conduit carrying the heated contacting gas and
a bypass conduit carrying gas from a source of gas, in thermal
contact with at least one of the hydrated material or the heated
contacting gas.
9. The method of claim 1, further comprising the step of condensing
at least a portion of the water from the contacting gas and
recycling the condensed water as part of the water added in step
(a) of claim 1.
10. The method of claim 1, in which the material is contained in a
chamber, and further comprising the step of contacting at least a
thermally conductive portion of the chamber of the material with
the source gas prior to step (b) of claim 1.
11. The method of claim 1, in which the dry contacting gas is
generated from a source gas by heating the source gas.
12. The method of claim 1, further comprising the step of drying
the source gas by contacting the source gas with a desiccant,
resulting in a dry contacting gas.
13. The method of claim 1, wherein the quantity of water added in
step (a) is selected such that a percentage of the water and
material mixture that is solid, by volume, is greater than 50%
following the water addition.
14. The method of claim 1, wherein the quantity of water added in
step (a) is in a range of 5% to 50% of the dehydrated material by
weight.
15. The method of claim 1, wherein the quantity of water added in
step (a) is in a range of 15% to 35% of the dehydrated material by
weight.
16. The method of claim 1, further comprising maintaining the
material in step (b) at a temperature no higher than an equilibrium
phase transition temperature of the hydrated material throughout
the process.
17. The method of claim 1, wherein water is added in step (a) at a
rate of greater than 0.1 weight percent of dehydrated material per
second.
18. The method of claim 1, wherein water is added in step (a) at a
rate of greater than 10 weight percent of dehydrated material per
second.
19. The method of claim 1 in which the hydrated material comprises
one or more materials selected from a group consisting of magnesium
sulfate heptahydrate, magnesium sulfate hexahydrate, magnesium
sulfate pentahydrate, sodium carbonate decahydrate, sodium
carbonate heptahydrate, sodium sulfate decahydrate, sodium
tetraborate decahydrate, sodium thiosulfate pentahydrate, sodium
thiosulfate dihydrate, copper sulfate pentahydrate, zinc sulfate
heptahydrate, zinc sulfate hexahydrate, potassium aluminum sulfate
dodecahydrate, trisodium phosphate dodecahydrate, disodium hydrogen
phosphate dodecahydrate, disodium hydrogen phosphate heptahydrate,
sodium dihydrogen phosphate dihydrate, tri-(sodium metaphosphate)
hexahydrate, calcium chloride tetrahydrate, calcium acetate
dihydrate and magnesium acetate tetrahydrate.
20. The method of claim 1, in which the hydrated material has an
equilibrium phase transition temperature in a range of 30.degree.
C. to about 100.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to energy collection
and distribution and more particularly to improved methods and
apparatus for accumulation, storage and controlled release of
thermal energy.
[0003] 2. Description of Related Art
[0004] In recognition of the ecological and cost impact of fossil
fuels and other conventional energy sources, significant effort has
been expended in developing and optimizing sources of energy that
are more environmentally benign, including solar, wind, and
geothermal energy sources. While these sources show considerable
promise in helping to meet future energy needs, significant
problems prevent more effective utilization of these types of
energy sources.
[0005] One problem inherent to these types of sources relates to
the timing and location of energy supply and demand. With energy
sources such as solar, wind, and geothermal sources, the relative
rates of energy supply and demand are not readily matched in terms
of time and/or location. For example, for those living above
certain degrees of latitude in parts of the northern or southern
hemispheres, solar energy collection is not practical year-round
and higher rates of energy are typically generated when energy
demands themselves tend to be at lower levels. Wind energy is often
limited by timing considerations; while wind energy can occur any
time of day or any season, it is not controllable either in terms
of timing or intensity. As with solar energy systems, many
geothermal energy systems are similarly constrained by location
considerations. So called "low temperature" geothermal energy
systems still require proximity to extremely high temperature
resources such as geologically hot rocks and hot springs which are
often limited to areas near tectonic plate boundaries. Thus, there
is a need for an economical means of storing the energy for
effective utilization of energy sources in which the rates of
energy supply and demand, timing, and location, are not generally
well matched. Also, there is a need for economical and efficient
means of utilizing energy sources that are well matched to the time
and location of their use. In addition, there are also advantages
to systems that can take advantage of waste energy from combustion
or other sources.
[0006] A number of methods used for heat storage apply energy to
increase the temperature of a medium, typically to high temperature
levels that exceed acceptable levels for safe direct use and for
human or animal contact, and maintain that elevated temperature
until the stored heat can subsequently be used. With some
approaches to the problem, only short-term storage is feasible,
such as using sufficiently large water reservoirs with
correspondingly costly insulation for energy storage. With solar
collection, special and therefore costly solar collectors can be
used if long-term storage is required, since in this case the high
temperatures usually encountered are considered necessary for
regeneration of the storage medium. In addition, regeneration of
such a long-term store is in practice only possible in the summer
months with strong direct solar radiation, so that the storage
medium must have capacity that extends through the months in which
heating is used.
[0007] Various chemical storage media have also been proposed for
storing and releasing energy using hydration/dehydration cycles and
similar techniques at high temperature. While such methods may
provide large amounts of thermal energy for subsequent use, the
regeneration of the storage medium also consumes large amounts of
energy, amounts that may be difficult to obtain from the most
desirable sources, particularly for use in low temperature
conditions. High amounts of stored heat can also be generated from
the storage media when releasing the stored energy, although it is
generally at temperatures in excess of what is generally considered
to be safe and comfortable for habitable spaces, for example. Thus,
current practice often requires the use of heavily-insulated
containers or conduits, which are expensive and can result in large
losses of heat energy even during short periods of storage or
distribution. Because of high levels for generated heat, current
methods of heat storage can also require a good measure of
isolation between the storage location and the location of use by
occupants of a home, workplace, or other facility.
[0008] Goals for improved methods and apparatus for accumulating,
storing, and releasing thermal energy for living quarters, work
environments, and other habitation include the following: [0009]
(i) Capability for energy accumulation and storage at moderate
temperatures. Energy storage using lower temperatures would enable
storage to be accomplished with less time between energy storage
and use in addition to offering reduced risk of scalding or other
injury to nearby inhabitants. This also allows for use of higher
relative humidity source gas for energy storage. [0010] (ii)
Capability for reversible cycles of energy storage and release.
This relates to overall cost of operation by decreasing heat
requirements for energy storage and/or increasing the speed of
energy storage, environmental impact, and usability. [0011] (iii)
Capability for self-regulation with respect to temperatures reached
by the storage medium in each cycle. It is beneficial for
controlling the rate at which heat is generated to be inherently
limited by the materials used. This provides greater flexibility in
the delivery of heat in a safe manner, as well as providing a
control on the amount of humidity provided. [0012] (iv) Capability
for providing controlled added humidity. The level of ambient
humidity can affect the relative comfort level of a house,
workplace, or other habitation at a particular temperature. In
addition, when appropriately controlled, ambient humidity can have
health benefits and preserve the integrity of building components
and contents that are susceptible to damage under low or high
humidity conditions. Also, a higher level of relative humidity
allows lower temperatures to be more acceptable and more
comfortable for building occupants during the heating season, for
example. At the same time, it is desirable to control the humidity
level even during the heating season to avoid condensation on cold
surfaces such as windows and creating environments conducive for
undesirable organisms. Therefore, it is also beneficial to limit
the amount of added humidity. In addition, it is desirable to add
humidity during the heating season without the cooling effect that
can occur upon water evaporation. [0013] (v) Environmentally
benign. It would be advantageous for any type of storage material
or system to use components that are not toxic, not detrimental to
the environment and do not undergo chemical transformation upon
exposure to components of living environments such as air and
water. [0014] (vi) Capable of locating the energy generation and
energy storage components in the same place, without requiring that
energy storage be provided at a separate facility or location. At
the same time, it would be advantageous to also provide a solution
that allows storage of energy to be performed at a location that is
different from locations where energy is released. [0015] (vii) Low
cost and complexity. The storage system should require as little
added energy as possible for heaters, compressors, pumps, and other
equipment requiring large amounts of external power. In addition,
the high cost of such complex equipment would be undesirable.
[0016] A number of solutions have been proposed for energy storage
and release using dehydration and hydration of metal salts.
However, none of these solutions appears to satisfy the
requirements listed in (i) to (vii) above.
[0017] For example, U.S. Pat. No. 4,303,121 entitled "Energy
Storage by Salt Hydration" to Pangborn describes storage of solar
energy or waste heat for later use using endothermic/exothermic
cycles of dehydration/hydration of inorganic salts. The Pangborn
'121 solution, however, is intended for and describes only high
heat and high temperature applications and falls short of what is
needed for goals (i), (iii), and (iv).
[0018] U.S. Pat. No. 4,291,755 entitled "Method and Apparatus for
Accumulating, Storing, and Releasing Thermal Energy and Humidity"
to Minto describes a heat storage system that employs polyvalent
metal salts to generate heat that is used for drying grain.
However, embodiments described in Minto '755 utilize compressed
steam and heated oil in hydration and dehydration, providing a
system that handles high temperatures, failing to satisfy (i)
above, risks uncontrolled temperature elevation and heat evolution,
failing to satisfy (iii) above, introducing some environmental
concerns relative to (v) above, and not compatible with goal (vi)
above. The efficiency of such a system is questionable, making it
difficult to satisfy goal (vii) above.
[0019] U.S. Pat. No. 4,484,617 entitled "Method of Using and
Storing Energy from the Environment" to Sizmann describes heat
storage using materials such as silica gel or zeolite, with applied
water vapor for heat generation. However, some method of vapor
generation must be included as part of the system, making it
difficult to satisfy goal (i) above and along with large complex
equipment, falling short of meeting goal (vii) above.
[0020] U.S. Pat. No. 4,179,493 entitled "Dehydration Process" to
Sadan describes the production of dehydrated or anhydrous salts
from higher hydrates of the same salt using solar energy. However,
embodiments described in Sadan '493 utilize aqueous solutions and a
solar pond to obtain the dehydrated or anhydrous salts failing to
satisfy (ii) above since no energy release is performed and would
require complex separation equipment to obtain the potentiated
material for energy release, failing to satisfy (vii) above. In
addition, (iv) and (vi) above are not satisfied as humidification
cannot be controlled nor can energy generation and storage be
co-located or conveniently moved.
[0021] Other solutions such as that described in U.S. Published
Patent Application 2009/0020264 entitled "Method of Heat
Accumulation and Heat Accumulation System" to Morita, and
references therein, involve formation of and storage of liquid salt
solution phases and require the use of complex and costly equipment
such as vacuum pumps and compressors, thereby failing to satisfy
(iv) and (vii) above.
SUMMARY OF THE INVENTION
[0022] In embodiments of the present invention, thermal energy is
stored in a medium which can be maintained in a relatively high
potential energy state for indefinitely long periods of time in
uninsulated or partially insulated containers, and can be
controllably liberated at another time or another place, while also
being able to be used at or near the same location and used very
shortly after storage of the energy, and the heat storage medium
thereafter recharged or reactivated by the application of heat
and/or dry air to the medium.
[0023] The invention provides an improved method of accumulating,
storing and controllably releasing thermal energy with a storage
medium at moderate temperatures in the 10-75.degree. C. range and
wherein the medium can be indefinitely recycled by regenerating the
medium.
[0024] The invention uses a process that is self-regulating with
respect to the maximum temperature reached by the medium. Apparatus
of the present invention can be used to store energy from a range
of sources including solar, wind, hydroelectric, nuclear, wave and
geothermal energy. Additionally, energy sources from other
processes, such as waste heat from a furnace or furnace ducts,
oven, stove, clothes dryer, washer or fireplace, or waste engine
heat may be used.
[0025] The present invention supplies heat and humidity to gas
filled spaces by the addition of water to a dehydrated material
that releases heat upon exposure to water, exposing the hydrated
material to dry contacting gas which results in loss of water from
the hydrated material to the contacting gas, the contacting gas
being heated and humidified by such exposure, and subsequent
dispersal of the added heat and humidity to the gas filled space.
This sequence also results in regeneration of the dehydrated
material so that these steps may be repeated. By limiting the total
amount of water addition to the dehydrated material within a cycle
of the process, less time and/or energy is required to regenerate
the dehydrated material and finer control of resultant living space
humidity may be possible.
BRIEF DESCRIPTION OF THE DRAWING
[0026] FIG. 1 is a concept diagram that shows the cycle of
hydration and dehydration.
[0027] FIG. 2 is a graph that compares temperature and mass
percentage of material for energy storage using the method of the
present invention and a prior art approach.
[0028] FIGS. 3A to 3C are schematic diagrams showing components of
a system for thermal energy storage and release.
[0029] FIGS. 4a-4d are schematic diagrams showing variations for
providing outside air in exemplary embodiments of the present
invention.
[0030] FIG. 5 is a schematic diagram showing parts of an alternate
embodiment of a system for thermal energy storage and release.
DETAILED DESCRIPTION OF THE INVENTION
[0031] It is to be understood that elements not specifically shown
or described herein may take various forms well known to those
skilled in the art. Figures provided herein are given to show
overall function, operation, and relationships and are not drawn
with the intention of showing components or elements to scale.
[0032] Various terms are used in the art to describe the process by
which energy can be stored using materials that exhibit heat of
hydration. In the context of the present disclosure, the term
"dehydration" is used for the storage process and is considered to
be essentially equivalent to the terms "regeneration" or
"potentiation" that are sometimes used in the art.
[0033] Embodiments of the present invention utilize dry air or
other type of dry gas as the gas that contacts hydrated material in
order to perform dehydration. By "dry gas" is generally meant a
contacting gas having sufficiently low moisture content to effect
drying when it moves past a material that is at least partially
hydrated. Roughly speaking, such dry gas should have a moisture
content of less than about 10 grams per cubic meter and preferably
less than about 6 grams per cubic meter. The less moisture content,
that is, the lower the water vapor pressure, the faster the drying.
As is well known, moisture content is a factor in determining
relative humidity (RH), along with temperature.
[0034] The "equilibrium phase transition temperature" for salt
hydrates is defined as the temperature at and above which a salt
hydrate releases water such that a liquid phase forms under
equilibrium conditions. The present invention, which operates at
least partially under the non-equilibrium condition of low water
vapor pressure above the salt during dehydration, enables
dehydration to occur at temperatures at or below the equilibrium
phase transition temperature.
[0035] Embodiments of the present invention contemplate an improved
method and apparatus of handling thermal energy in which a metal
salt or mixture of metal salts having different states of
hydration, is utilized as a heat storage medium.
[0036] The sequence diagram of FIG. 1 shows the cycle of steps used
in embodiments of the present invention. Heat is generated in a
hydration step 10, in which water 14 is added to a heat storage
medium 12 to effect hydration of the medium and generate heat that
is removed and applied to its desired use. In an energy storage
step 20, the heat storage medium 12 in a low energy, at least
partially hydrated state is dried with dry air or other gas 16 to
effect dehydration of the storage medium and to separate water of
hydration therefrom. Though not shown in FIG. 1, gas 16 may also be
used to remove or provide heat at the same time as effecting
dehydration. The water of hydration is reversibly removable from
the hydrated salt, such as in a stepwise manner, progressing from a
higher state of hydration, with lower potential or stored energy,
to one or more lower states of hydration, with inversely higher
potential energy.
[0037] Conventional approaches using heat of hydration, such as
those noted above in the Description of Related Art, for example,
attempt to maximize heat output. Such an approach, however, also
consumes considerable energy in order to store energy for future
use. The Inventor, however, has adopted an alternative approach to
energy storage, operating over an energy range that neither
delivers the peak amounts of heat energy possible from hydration of
the material, nor requires higher temperatures and overall energy
input for the purpose of storing energy by dehydration. By working
over a more moderate energy storage/output range, methods of the
present invention can take advantage of lower energy requirements
and simpler equipment configurations in order to affect energy
storage.
[0038] By way of example, the difference between the solutions
proposed in the present invention and those taught in the Morita et
al. '264 disclosure are illustrated in the comparative graph of
FIG. 2. For reference, the energy transition utilized in the Morita
et al. '264 method is represented in dashed line form. A hollow
circle 90 shows the hydrated state of magnesium sulfate
(heptahydrate) with its heat content spent at 20.degree. C. A
filled circle 92 shows the dehydrated state of the magnesium
sulfate monohydrate in equilibrium with a saturated solution of
magnesium sulfate. In order to store energy and move from the
hydrated to the dehydrated state using this prior art method, a
considerable amount of heat is required, raising the temperature
above the phase boundary equilibrium phase transition temperature
between the two phases, as shown by a line 94 in the graph.
[0039] In contrast, the energy transition used in the present
invention does not require this energy input, as shown by a solid
line 96 with starred endpoints. As the graph of FIG. 2 shows, the
method taught in Morita et al. '264 uses the transition between
monohydrate plus saturated solution and heptahydrate forms of the
salt medium. By comparison, the method of the present invention
operates primarily over the transition between higher levels of
hydration, such as empirical compositions of tetrahydrate,
pentahydrate and hexahydrate shown in FIG. 2, rather than
predominantly monohydrate form obtained by Morita, et al. '264. By
doing so, inputting the latent heat necessary for the phase
transition to liquid is minimized or avoided. Thus, although the
energy output is lower, the amount of energy required for storage
is much lower than that of the earlier approach.
[0040] For the process used herein, the degree of dehydration that
is attainable is a direct function of the temperature to which the
salt is subjected and is an inverse function of the partial
pressure of water vapor in the fluid (typically air) that is in
contact with the salt. The applied fluid can be some other gas than
air, for example nitrogen, oxygen, argon, neon, helium or carbon
dioxide may be used.
[0041] Particularly useful in the dehydration is warming of outdoor
air having a temperature below about 20.degree. C. prior to
warming. Such warming may occur by methods such as earth-air heat
exchange or through the use of another renewable energy source.
Similarly, cool indoor air which has gone through warming from a
furnace, radiator or other space heating apparatus may also be
particularly useful.
[0042] During the dehydration, supplemental heat may be applied by
a heater or heat from some other source. Preferably, unlike other
methods that have been described in the art, such as that taught in
the Morita et al. '264 application that require dehydration above
the equilibrium phase transition temperature of a hydrated salt,
dehydration is done with the temperature of the hydrated salt at or
below its equilibrium phase transition temperature in embodiments
of the present invention, as was shown with reference to FIG. 2.
This helps to minimize energy consumption in the dehydration step
and allows for use of permeable materials (e.g., mesh, fabric or
yarn) to support the storage medium.
[0043] However, the process of the present invention may
alternately be used in conjunction with a process in which the
storage medium temperature is brought slightly above the
equilibrium phase transition temperature during some part of the
process and/or utilize vacuum for a portion of the dehydration
step. Use of vacuum for the dehydration step may be particularly
useful at times when additional humidification of the surroundings
or nearby living spaces is not desired. In such a case, it may be
possible to increase the rate of dehydration. Once sufficient water
is removed, the storage medium temperature may be decreased to at
least the equilibrium phase transition temperature and the current
inventive process may be continued.
[0044] In energy storage step 20 of FIG. 1, water of hydration is
extracted from the salt and removed from its presence and the
dehydrated storage medium 12 may then be used at or near the same
location or stored for later use at or near the same location, or
may be stored and/or used at a remote location. The heat potential
may be liberated subsequently in a controllable manner by adding
water 14 (preferably liquid water) to the dehydrated salt storage
medium 12. The temperature at which the heat is liberated from the
salt may be a function of the temperature of the storage medium and
water, the amount of liquid water 14 added to the salt, the rate at
which heat is removed from the medium 12 for use in another
process, and the temperature at which the hydrated salt storage
medium 12 undergoes a phase transition to the dehydrated salt and
saturated solution of the salt.
[0045] Referring to FIGS. 3A, 3B and 3C, in accordance with the
present invention, the hydrated salt is subjected to the action of
a dry contacting gas 16 which acts to sweep away released water
vapor 18. The gas that is used as contacting gas 16 may be air, for
example. In such a case, the air may even originate from a
relatively cold source, such as from outdoor air during the winter
that may act as source gas 15. Even though this air may have a high
relative humidity (RH) at a lower outdoor temperature, the same
air, when heated to room temperature, can serve as dry gas for the
function of acting as contacting gas 16.
[0046] The contacting gas 16 may optionally be obtained by warming,
using heater 44a, of source gas 15 with naturally derived heat such
as from solar energy or geothermal sources, from heat pumps or by
waste heat sources, such as suitable flue gas ducts, furnace ducts,
ovens, stoves, fireplaces, washing machines, or clothes dryers, or
by electric heaters including those whose electricity is derived
from solar photovoltaic, wind, hydroelectric, nuclear energy, or
stored in electrical batteries, which may be rechargeable or single
use, or fuel cells, and may be used directly, or along with any
other source of gas.
[0047] Alternatively, the source gas 15 may be derived from a
storage cylinder of compressed dry gas which may be used either
directly without warming or, optionally with application of heat
from a heat source, to become the dry contacting gas 16.
[0048] This process may be used either in a continuous flow or a
batch mode of operation. In a continuous flow operation, the source
gas may be dried by causing the gas to contact a strongly
hygroscopic or desiccant material (41 in FIG. 4a) such as anhydrous
calcium chloride or anhydrous magnesium chloride prior to
contacting the storage medium, while in a batch mode, the gas that
is to be used as contacting gas 16 may be dried by simultaneous
contact with such strong hygroscopic materials and the storage
medium. Additionally, in accordance with the present invention,
room air from a living area may be used for at least some part of
the dehydration process.
[0049] During hydration of the dehydrated material, the total
amount of water that is added is limited to that which favorably
generates heat with little or no excess liquid solution formed
after the water addition. The volume percentage of the
water/storage medium mixture that is solid should be greater than
50% following the water addition, preferably it is greater than 90%
and most preferably greater than 99%. For the preferred materials,
the amount of water added to the dehydrated material should be less
than about 60% by weight and often can be less than about 35% by
weight.
[0050] However, for the most preferred cases, the weight percentage
of water added to the dehydrated storage medium 12, such that
little or no excess liquid solution forms, is dependent upon the
chemical composition of the storage medium and the extent to which
it has been dehydrated. Thus, if the dehydrated storage medium has
a composition approximating sodium carbonate monohydrate, anhydrous
sodium sulfate, sodium tetraborate pentahydrate or magnesium
sulfate tetrahydrate, the weight percent of added water to the
dehydrated storage medium should most preferably be less than about
50%, 20%, 35%, or 30%, respectively.
[0051] Additionally, if too little water is added or if the rate of
water addition is too slow, insufficient storage medium heat
generation temperature increase is obtained. The minimum weight
percent of added water to the dehydrated storage medium should be
at least about 5%, preferably at least about 10% and most
preferably at least about 15%.
[0052] The minimum rate at which water should be added to the
dehydrated material is greater than about 0.1 weight percent per
second based on the dehydrated material, preferably greater than
about 1 weight percent per second based on the dehydrated material,
and most preferably greater than about 10 weight percent per second
based on the dehydrated material.
[0053] It will be understood that where the term "weight
percentage" is used herein, what is meant is a weight of water
being added as a percentage of the weight of the solid material to
which it is being added at that time. Any additional material which
is isolated from the material to which the water is being
added--whether by having the other material in one or more separate
containers, or by isolating the material with some kind of barrier
within the same container, such that the added water does not reach
the other material--would not be considered when the "weight
percentage" was being determined within the teaching of the
invention.
[0054] The schematic block diagrams of FIGS. 3A, 3B, and 3C show
hydration and energy storage steps, respectively, for a thermal
energy storage and release system in a gas filled area 30 according
to various embodiments of the present invention.
[0055] The system is comprised of a storage medium 12 that may be
held in trays or otherwise supported by fine wire mesh, fabric or
yarn. Furthermore, the storage medium 12 may be free standing or
surrounded by a chamber 36 that may be partially thermally
insulating and partially thermally conductive or entirely thermally
conductive.
[0056] A water supply 32 provides water for hydration. Although
droplets are shown in FIGS. 3A and 3B, a continuous application or
stream of water may also be used. Also, application of water may
occur from a water distribution source that provides water from
below or within the storage medium. Consistent with an embodiment
of the present invention, water is in liquid form, allowing the
direct use of tap water or water from a reservoir, water line, or
other convenient source. To initiate hydration and release of
thermal energy, a valve 34 can be manually or automatically
actuated to introduce water into a chamber 36 that contains heat
storage medium 12.
[0057] As the dashed line indicates, both hydration for releasing
energy and dehydration for storing energy can be executed within
the same environment 30, such as the same room, building or general
area. The use of non-hazardous materials enables the system of the
present invention to be used within a habitat, such as a house,
office building or workplace, for example. Alternately, using the
appropriate support components, hydration for heat generation can
be done at one location, with dehydration performed at a different
site.
[0058] After water addition is completed, source gas 15 can be
drawn from outside the area 30 through an outside inlet or conduit
64, or an optional valve 40 can allow drawing some or all of the
source gas 15 through an inside inlet 104 within the area 30. A
blower 42 draws the gas in, and propels it into the chamber 36
where the dry contacting gas 16 flows across and contacts the
material 12. It should be noted that source gas 15 and blower 42
may be replaced by a cylinder of compressed gas and a valve.
Preferably, source gas 15 has a temperature of less than about
20.degree. C.
[0059] Heat generation can be used to heat the ambient room air
surrounding storage medium 12 or to heat another transport medium.
In the embodiment shown in FIG. 3A, an optional air duct 100
provides an air path that is in thermal contact with heat storage
medium 12 or with chamber 36 for distributing heat due to hydration
by routing heated air 110 to the room or other area without having
the air 110 pick up humidity 18 from the hydrated material 12. Air
duct 100 is particularly useful for diverting the air flow during
water addition so that heat may be transferred to the desired
location without impacting the water addition. Valve 101 allows
control of air flow through the chamber 36 or through the bypass
conduit 100, or a mixture of flows.
[0060] Dry contacting gas 16 removes moisture from hydrated storage
medium 12. The water content of the dry gas increases as it
contacts the hydrated form of storage medium 12.
[0061] Optionally, a heater 44a can be provided for heating the
source gas 15 to form the dry contacting gas 16, or heater 44b can
be provided for heating the hydrated storage medium 12 which may
also cause heating of the source gas 15 and/or dry contacting gas
16.
[0062] Water vapor 18 is expelled from chamber 36 to a valve 50
that can direct the output moisture either to an outlet 111 in the
same room 30 that contains the thermal energy storage and release
system or to a different room, or to the outside 112. One or more
optional sensors 46 are used in one embodiment, to sense the
humidity of the expelled gas.
[0063] Sensor 46 (or a second such humidity sensor) may also be
used to measure the relative humidity (RH) of the ambient air in a
room or building 30, to determine whether or not to control valve
50 to direct moist gas back into the room or building or expel the
moisture to the outside or other room 112 or repeat the method. For
example, measuring the water vapor in the heated contacting gas
with sensor 46, the water vapor may first increase, then reach a
peak value, then decline. When the water vapor level stops
declining after it has begun decreasing would provide an indication
that the process may be repeated. Alternatively, if it is found
that at least 85% of the water added in the hydration step has been
removed during dehydration, for example by sensing the weight
change of the storage medium, the process may be repeated.
[0064] An optional filter 52 helps to inhibit the emission of salt
particles into the surrounding environment. Optionally, water vapor
expelled during dehydration that is not needed for increasing room
humidity is condensed and re-used for subsequent hydration or other
use.
[0065] FIG. 3B also shows a room temperature and humidity sensor
47, which can be used to control the valves 40, 50, and 101 and
blower 42. The sensor 47 may be in wired or wireless communication
with the valves and/or blower such that when room humidity and/or
temperature level are at various levels relative to a desired set
point, the valves and blower may be adjusted to allow for: [0066]
a) heating only of room air, obtained by actuating valve 101 to
direct inlet air 15 through bypass conduit 100 and 110 into the
room 30. Valve 50 could be set in this mode to exhaust contacting
gas 16 to the outside 112. [0067] b) heating and humidifying room
air, obtained by operating valve 101 to direct inlet air 15 to
contact the storage medium 12 directly and setting valve 50 to
output contacting gas 111 to the desired room 30. [0068] c) heating
only by contact of room air with exterior of chamber 36, obtained
by closing valves and/or turning off the blower.
[0069] The operation of both valves 50 and 101 could also be set,
if desired, to allow a blend of contacting gas 111 and heated
bypass air 110 to flow into the room 30 in modes a or b, above.
Valve 40 could be set in modes a or b to allow some or all of the
intake air 15 to be drawn from the room 30.
[0070] Dry air serves as the drying agent in one embodiment of the
present invention. The air that is in communication with blower 42
or other type of air mover may be obtained in any of several
ways.
[0071] FIGS. 4a to 4d show a number of options for providing air
that is at suitable temperature and humidity levels.
[0072] In FIG. 4a, an air input subsystem 60 receives outside air
as source gas 15 directly through a conduit 64, shown being
directed through a wall 62 into the habitable area or other room
that contains storage medium 12. Conduit 64 may be insulated and
may optionally pass through a window or door, for example. A
desiccant material canister 41 can optionally be put in the conduit
64 line to dry the air 15 before use.
[0073] As shown in FIGS. 4b-4d, air input subsystems 68, 70, and 78
use geothermal energy, or some other readily available heat source,
to heat the outside air 15, then directs the air through, within,
or past wall 62 into the room or other habitable area. Geothermal
energy is obtained, for example, by routing the incoming air
conduit 64 to a sufficient depth into the earth 76. Conduit 64 may
be insulated, especially downstream of the buried horizontal run,
The air does not necessarily need to be heated further and can be
used at relatively low temperatures, such as temperatures of at
least about 10 to 15.degree. C. in some cases.
[0074] The rate of dehydration and consequent energy storage is a
function of both the temperature and relative humidity of the dry
contacting gas 16. Advantageously, embodiments of the present
invention do not require extreme temperatures in order to provide
energy storage, but can efficiently store energy even using dry air
as the source gas at temperatures that are at or below room
temperature. In one embodiment, shown as air input subsystem 60 in
FIG. 4a, valve 40 is set to draw ambient air 115 through input 104
from within the room or other habitable area is itself used as
input for dehydrating heat storage medium 12.
[0075] The schematic diagram of FIG. 5 shows an embodiment in which
air input 81 and output 83 are near a window 80. Weather-stripping
82 and insulation 84 are provided, with tubing extending through
the insulation 84. Again, heater 44a is optional, but can be useful
for decreasing the relative humidity of the drying air. An optional
condensation tank 102 is provided to take advantage of cooler
temperature against window 80 for condensation, if valve 50 is set
to route output air partially or entirely to outlet 106 instead of,
or in addition to, outside outlet 83. The collected water can then
be used for hydration, for example, by recycling the water through
a line 105 back to the water source 32. Source gas may be provided
from room air by means of valve 40. An optional valve 54 allows
moist heated air from chamber 36 to be output within the room or
other area after it has contacted the storage medium in the chamber
36 (not shown).
[0076] There are a number of options for providing heat storage
medium 12. In one embodiment, chamber 36 is a replaceable canister
or other easily removable container that can be used to generate
heat for a room or other location. Once the canister has been
hydrated and its stored heat obtained, the canister may be removed
and returned to a recharging site at which dehydration takes place.
This type of arrangement makes it possible, for example, to take
advantage of higher energy sources than might be usable near human
habitation or than might be available at the time and/or location
of its use for generating heat. An example of such use would be to
move the canister of hydrated storage medium 12 to a furnace area
of a building for dehydration. When dehydration is complete, the
canister can be brought back to a room for hydration and heat
evolution. Such a replaceable canister may contain one or more
trays or other support means for the storage medium 12.
[0077] Optional heating devices 44a and 44b used with embodiments
of the present invention can use heat from any of a number of
sources, in addition to heating elements. Waste heat from
combustion, such as from a furnace, radiator, hot water heater,
fireplace, stove, oven, clothes washer or dryer, or excess heat
from a nuclear or industrial process can be used, for example. The
heat used for heating the source gas 15 or for heating the heat
storage medium 12 can be from a renewable source, such as solar
thermal, geothermal, wind, or hydroelectric power, for example.
Batteries and fuel cells can be used to generate heat, coupled with
various types of resistive or thin-film heating devices. Another
source of heat may be from the addition of water to anhydrous salts
of calcium chloride, magnesium chloride, magnesium sulfate or
sodium carbonate which may also be subsequently dehydrated for
re-use, though under higher temperature conditions than those
employed in the present invention.
EXAMPLES
[0078] In one embodiment of the present invention, heat storage
medium 12 was, initially, fully hydrated sodium tetraborate
decahydrate, commonly known as borax or with the alternative
formula Na.sub.2[B.sub.4O.sub.5(OH).sub.4].8H.sub.2O, in a tray
that was housed within an insulated container. Outdoor air at
-7.degree. C. and 80% relative humidity (RH) was brought through a
conduit through a wall of a room that was at 9.degree. C. and 61%
relative humidity. The tubing was connected to the inlet of a
blower that simultaneously heated the air. The outlet of the blower
was connected to tubing, the end of which was placed at the bottom
of the insulated container. The top of the container was partially
open to allow air, with the added moisture from its dehydrating
action on the hydrated salt, to leave the container.
[0079] The heated outdoor air moved through the container
containing the tray of borax for about five hours, during which
time the temperature of the borax had increased to about 48.degree.
C. After this time, the borax was found to have lost about 23% of
its weight, indicating conversion of the borax from its original
decahydrate to a composition having a similar empirical formula to
sodium tetraborate pentahydrate. Addition of water to the
dehydrated composition in a weight ratio of 1:3.2 at 22.degree. C.
resulted in a temperature rise of the hydrated sodium tetraborate
to about 45.degree. C. with a concomitant rise in the temperature
and humidity of the air in the insulated container.
[0080] Another specific example of the present method with the
above apparatus is similar to that just described, except that the
tray in the insulated container contained partially hydrated sodium
sulfate containing about 13% water, by weight. Dehydration was
carried out with outdoor air that was at -7.degree. C. and 80% RH
brought by intermittent use of a blower, such that the blower did
not heat the outdoor air, through a conduit through a wall of a
room having indoor air at 9.degree. C., 63% RH. With a heater in
contact with a tray containing the partially hydrated sodium
sulfate, the salt temperature rose to about 32.degree. C.,
resulting in a weight loss of about 13% indicating conversion to
predominantly anhydrous sodium sulfate. Addition of water to the
dehydrated composition in a weight ratio of 1:5 at 19.degree. C.
resulted in a temperature rise of the hydrated sodium sulfate to
about 25.degree. C. with a concomitant rise in the temperature and
humidity of the air in the insulated container.
[0081] Another specific example of the present method used
magnesium sulfate heptahydrate, which was converted by dehydration
to magnesium sulfate hexahydrate. This was accomplished using
outdoor air at 2.degree. C. and 88% RH. Continuous blowing and
heating of this air through a conduit surrounded by indoor air at
about 7.degree. C. and 64% RH resulted in air entering the
insulated chamber at about 55.degree. C. and 2% RH. Additional
heating was supplied by a heater in contact with the magnesium
sulfate heptahydrate so that the salt temperature was about
45.degree. C. After a short time the salt experienced a 7% weight
loss, indicating conversion to a composition approximating
magnesium sulfate hexahydrate. Further treatment under the same
conditions resulted in a total weight loss of about 14%, indicating
conversion to a composition with the empirical formula
approximating magnesium sulfate pentahydrate.
[0082] An alternative batch method used to dehydrate magnesium
sulfate heptahydrate was performed in which the magnesium sulfate
heptahydrate was placed in a container with anhydrous calcium
chloride. The air in the container was about 22.degree. C. and 15%
relative humidity prior to heating the magnesium sulfate
heptahydrate in a tray with a heater. Upon heating the hydrated
magnesium sulfate reached about 45.degree. C. and was dehydrated to
a composition approximating magnesium sulfate tetrahydrate as
evidenced by a total weight loss of about 28%. In the absence of
the calcium chloride, addition of water to this dehydrated sample
in a weight ratio of about 1:3.6 at about 22.degree. C. resulted in
a temperature rise of the rehydrated magnesium sulfate to about
50.degree. C. with a concomitant rise in temperature and humidity
of the air in the container.
[0083] Another specific example of the present method with the
above apparatus used partially hydrated sodium carbonate containing
about 25% by weight water which was converted to predominantly
sodium carbonate monohydrate. With intermittent use of the blower
as described above for sodium sulfate, the salt temperature was
about 30.degree. C., with weight loss of about 13%. In this
specific example, the outdoor air was 0.degree. C. at 70% RH and
the indoor air was about 10.degree. C., 50% RH.
[0084] A further specific example of the present method was carried
out using indoor air as the source gas at about 20.degree. C. and
about 20% RH. The air is heated by a hot water radiator that is
part of a home heating system to about 40.degree. C. and 5% RH,
then is blown across a free standing tray holding sodium sulfate,
partially hydrated with water to about 20% by weight, reaching a
temperature of about 30.degree. C. This resulted in about 20%
weight loss from the partially hydrated sodium sulfate. Rehydration
of this material by water addition in a weight ratio of 1 part
water to 5 parts dehydrated sodium sulfate at about 20.degree. C.
led to a temperature rise of the rehydrated sodium sulfate to about
32.degree. C.
Materials
[0085] Preferred materials for use as the storage medium are those
that give off heat when exposed to water and are capable of
releasing water at temperatures well below the boiling point of
water when exposed to dry gas. Such materials include those that
incorporate water into their crystal structures such as inorganic
salts that form hydrates. Such materials include those having an
equilibrium phase transition temperature in the range from above
30.degree. C. to about 100.degree. C., and preferably in the range
of 30.degree. C. to 85.degree. C. Preferably, the hydrated forms of
the salt or salts utilized are capable of efflorescence at moderate
temperatures within the range from about 10.degree. C. to about
70.degree. C. or are capable of dehydration with the release of
heat in this temperature range.
[0086] Included among these materials are hydrates listed in Table
1. The hydrated and dehydrated materials listed below may refer to
empirical compositions that may be mixtures of thermodynamically
stable hydrates or to the thermodynamically stable hydrates
themselves. For example, magnesium sulfate tetrahydrate and
pentahydrate, while described as products of efflorescence, may
also each correspond to a mixture of magnesium sulfate hexahydrate
and monohydrate in the respective appropriate ratio.
TABLE-US-00001 TABLE 1 Fully Potentiated and Fully Hydrated Forms
of Salts Salt Preferred potentiated salt Preferred hydrated salt
sodium sodium carbonate monohydrate sodium carbonate carbonate
heptahydrate sodium anhydrous sodium sulfate sodium sulfate sulfate
decahydrate sodium sodium tetraborate pentahydrate sodium
tetraborate tetraborate decahydrate magnesium magnesium sulfate
hexahydrate or magnesium sulfate sulfate magnesium sulfate
pentahydrate or heptahydrate magnesium sulfate tetrahydrate
[0087] While these salts are among those preferred, compositions
having other degrees of hydration may also be present in the
potentiated and hydrated states of the process and both the
preferred potentiated and preferred hydrated salts may be present
at the same time. Any of a number of types of alternate materials
that exhibit heat evolution upon hydration and loss of water upon
exposure to dry gas can be used, including as hydrated forms of the
materials, sodium thiosulfate pentahydrate or dihydrate; copper
sulfate pentahydrate; zinc sulfate heptahydrate or hexahydrate;
potassium aluminum sulfate dodecahydrate; trisodium phosphate
dodecahydrate; disodium hydrogen phosphate dodecahydrate or
heptahydrate; sodium dihydrogen phosphate dihydrate; tri-(sodium
metaphosphate) hexahydrate; calcium chloride tetrahydrate; calcium
acetate dihydrate; magnesium acetate tetrahydrate or mixtures
thereof. Preferred salts are stable in the presence of water and
air so that they are able to undergo a larger number of cycles
without degradation in performance or formation of undesirable
amounts of impurities.
[0088] The storage medium 12 can be formed so that it provides a
favorable surface for energy transfer at a given rate. In one
embodiment, for example, the medium is provided within chamber 36
as a canister, with the medium formed in a shape in which at least
one dimension is small, such as for example, less than about 0.7
cm, and the other dimensions are longer, such as extending along
the length and width of a canister, for example.
[0089] Liquid water is generally preferred for forming the hydrated
salts, since it can help to release energy more quickly, thus
providing a larger temperature increase of the storage medium 12
and not requiring use of added energy for vaporization, as would be
needed to use water vapor. The water for water supply 32 can be
from gravity or line feed and may be added in drop-wise or in
continuous fashion.
[0090] The method and apparatus of the present invention overcomes
the deficiencies of the methods and mechanisms heretofore proposed
for a number of reasons, including at least the following: [0091]
1. Low temperature energy collection. In embodiments of the present
invention, heat energy may be efficiently absorbed and accumulated
with the hydrated salt at temperatures at or below its equilibrium
phase transition temperature. In one embodiment, such as when
furnace exhaust duct heat is used as a heat source for dehydration,
gas/air temperatures of the dry contacting gas are below about
100.degree. C. throughout the process, more preferably below about
80.degree. C. throughout the process, even more preferably below
about 65.degree. C. throughout the process. In another embodiment,
such as when heated room air from a radiator or forced air duct is
used as a heat source, dry contacting gas/air temperatures are
maintained below about 50.degree. C. throughout the process. [0092]
2. Reduced risk to humans in habitable areas. The heat energy is
used and/or stored in a medium at temperatures that are allowable
in close proximity to, or within, living areas. [0093] 3. Location
flexibility. Because the gas that is used to dehydrate can
originate from air as the source gas at or below about 20.degree.
C., the heat storage may take place at or near the same location to
the source of the gas and the heat may be used within a short time
period from the completion of the dehydration. [0094] 4. Use of dry
gas to dehydrate. After liberating the heat therefrom, the storage
medium may then be dehydrated again by subjecting it to a dry gas.
Heating of the storage medium with a heat source other than the
heated gas can help to speed the storage process, but is optional.
[0095] 5. Indefinite number of cycles. This cycle of dehydration
and heat discharge may be repeated indefinitely. That is, the cycle
of hydration and dehydration itself does not limit the lifetime of
heat storage medium 12. Factors that can influence how many cycles
are feasible include the rate of loss of storage medium 12 over
time and rate of introduction of pollutants and impurities.
[0096] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention as described above, and as noted in the
appended claims, by a person of ordinary skill in the art without
departing from the scope of the invention. Various methods could be
used for drying the air or applied gas.
[0097] Thus, what is provided is an apparatus and method for more
efficient accumulation, storage and controlled release of thermal
energy and humidity.
[0098] Accordingly, it is to be understood that the embodiments of
the invention herein described are merely illustrative of the
application of the principles of the invention. Reference herein to
details of the illustrated embodiments is not intended to limit the
scope of the claims, which themselves recite those features
regarded as essential to the invention.
TABLE-US-00002 Table of Reference Numbers 10. Hydration step 68,
70. Air input subsystem 12. Heat storage medium 76. Earth 14. Water
78. Air input subsystem 15. Source gas 80. Window 16. Contacting
gas 81. Air input 18. Water vapor 82. Weather-stripping 20. Energy
storage step 83. Air output 30. Gas filled area 84. Insulation 32.
Water supply 90. Hollow circle 34. Valve 92. Filled circle 36.
Chamber 94. Equilibrium phase boundary 40. Inside/outside source
valve 96. Line 41. Desiccant canister 100. Bypass conduit duct 42.
Blower 101. Direct/Bypass valve 44a. Heater for source gas 102.
Condensation tank 44b. Heater for storage medium 103. Air outlet
inside room 46. Humidity Sensor 104. Air inlet inside room 47. Room
temperature and 105. Condensate line for recycling humidity sensors
106. Outlet 50. Valve 110. Air from bypass conduit into room 52.
Filter 111. Contacting gas into room 54. Valve 112. Contacting gas
exhausted outside 60. Air input subsystem 114. Chamber temperature
sensor 62. Wall 115. Ambient air from room 64. Conduit
* * * * *