Abstrict A desiccant dehumidifier is provided in which a desiccant material
is applied to a first end of a heat pipe heat exchanger. During
the sorption phase, a supply air stream is exposed to the desiccant
material on the first end of the heat pipe heat exchanger and a
second air stream, which could be ambient atmosphere, is exposed
to the second end of the heat pipe heat exchanger. The moisture
from the supply air stream is transferred to the desiccant material.
However, the heat pipe heat exchanger acts as a heat sink and adsorbs
the heat generated by the moisture transfer and transfers it to
the second end of the heat pipe heat exchanger. At the second end
of the heat pipe heat exchanger, the heat is transferred to the
second air stream. As a result, both the supply air stream and the
desiccant material remain at a substantially constant temperature
during the sorption phase. During the desorption phase, a heated
air stream is exposed to the second end of the heat pipe heat exchanger,
and a regeneration air stream is exposed to the first end of the
heat pipe heat exchanger. The heat from the heated air stream is
transferred to the heat pipe heat exchanger, and then from the heat
pipe heat exchanger to the desiccant material. As a result, the
surface vapor pressure of the desiccant material rises, and the
moisture from the desiccant material is transferred to the regeneration
air stream. In addition, in accordance with a further embodiment,
after the heated air stream is cooled as it is transfers heat to
the heat pipe heat exchanger, it is also used as the regeneration
air stream.
Claims What is claimed is:
1. A dehumidifier comprising:
a supply air stream passage, a second air stream passage, a third
air stream passage, and a heated air stream passage;
a heat pipe heat exchanger having a first end and a second end,
the first end of the heat pipe heat exchanger having a desiccant
material applied thereon;
a drive mechanism coupled to the heat pipe heat exchanger, the
supply air stream passage, the second air stream passage, the third
air stream passage, and the heated air stream passage, the drive
mechanism operating, during a sorption process, to expose the first
end of the heat pipe heat exchanger to the supply air stream passage
and the second end of the heat pipe heat exchanger to the second
air stream passage, and operating, during a desorption process,
to expose the first end of the heat pipe heat exchanger to the third
air stream passage and the second end of the heat pipe heat exchanger
to the heated air stream passage.
2. The dehumidifier according to claim 1 wherein the supply air
stream passage includes a supply air stream inlet for receiving
a supply air stream and a supply air stream outlet for outputting
a dehumidified supply air stream, the dehumidified supply air stream
having substantially the same temperature as the supply air stream.
3. The dehumidifier according to claim 1 wherein the second air
stream passage includes a second air stream inlet for receiving
a second air stream and a second air stream outlet for outputting
the second air stream, the second air stream adsorbing the heat
generated during the sorption process.
4. The dehumidifier according to claim 1 wherein the heated air
stream passage transmits a heated air stream having a temperature
in the range of 100.degree. F. to 150.degree. F.
5. A dehumidifier comprising:
a plurality of heat pipe heat exchangers, each of the plurality
of heat pipe heat exchangers including a first end and a second
end, the first end of the heat pipe heat exchangers having a desiccant
material applied thereto, the plurality of heat pipe heat exchangers
arranged to form a tubular wheel having a first end and a second
end which correspond to the first and second ends of the heat pipe
heat exchangers;
a plurality of partitions arranged around the tubular wheel, the
plurality of partitions forming at least a first chamber and a third
chamber around the first end of the wheel and a second chamber and
a fourth chamber around the second end of the wheel, the first chamber
having an input for receiving a supply air stream and an output
for outputting a dehumidified supply air stream, the second chamber
including an input for receiving an air stream and an output for
outputting the air stream, the third chamber including an input
for receiving a regeneration air stream and an output for outputting
the regeneration air stream, the fourth chamber including an input
for receiving a heated air stream and an output for outputting the
heated air stream;
a drive mechanism coupled to the tubular wheel, the drive mechanism
rotating the tubular wheel relative to the plurality of partitions
so that any given point on the second end of the wheel sequentially
traverses the first and third chambers and any given point on the
second end of the wheel sequentially traverses the second and third
chambers.
6. The dehumidifier according to claim 5 wherein the supply air
stream maintains substantially the same temperature as it passes
from the supply air stream input to the supply air stream output.
7. The dehumidifier according to claim 5 wherein the heated air
stream has a temperature in the range of 50.degree. F. to 150.degree.
F. as it enters the heated air stream input of the fourth chamber.
8. The dehumidifier according to claim 5 wherein the output of
the fourth chamber is coupled to the input of the third chamber.
9. The dehumidifier according to claim 5 wherein the inputs of
the third chamber and fourth chamber are coupled to a common air
stream.
10. The dehumidifier according to claim 5 wherein the desiccant
material is permanently bonded to the first end of the heat pipe
heat exchangers.
11. The dehumidifier according to claim 5 wherein the plurality
of partitions include a housing which surrounds the tubular wheel,
a horizontal partition which extends inward from the housing and
through a rotational axis of the tubular wheel, and a vertical partition
which extends inward from the housing in a direction perpendicular
to the rotational axis of the tubular wheel, the horizontal partition
separating the first chamber from the third chamber and the second
chamber from the fourth chamber, the vertical partition separating
the first chamber from the second chamber and the third chamber
from the fourth chamber.
12. The dehumidifier according to claim 11 wherein the housing
is rectangular.
13. A dehumidifier comprising:
a plurality of heat pipe heat exchangers, each of the plurality
of heat exchangers including a first end and a second end, the first
end of the heat exchangers having a desiccant material applied thereto,
the plurality of heat pipe heat exchangers arranged to form a matrix
having an inner surface and an outer surface, the matrix further
having a first end and a second end which correspond to the first
and second ends of the heat pipe heat exchangers;
a plurality of partitions arranged around the matrix, the plurality
of partitions forming at least a first chamber around the first
end of the matrix and a second chamber around the second end of
the matrix, the first chamber having an input for receiving a supply
air stream and an output for outputting a dehumidified supply air
stream, the second chamber including an input for receiving an air
stream and an output for outputting the air stream, the first chamber
further including a regeneration air output, the second chamber
further including a regeneration air input;
a translating plenum extending over the first and second ends of
a portion of the matrix, the translating plenum including a first
upper translating plenum coupled to the regeneration air output
and arranged over the first end of the upper surface of the portion
of the matrix and a second upper translating plenum coupled to the
regeneration air input and arranged above the second end of the
lower surface of the portion of the matrix, and a lower translating
plenum arranged below the first and second ends of the lower surface
of the portion of the matrix,
a heated air supply coupled to the second upper translating plenum
for transmitted a heated air stream through the second upper translating
plenum, through the second end of the matrix, into the lower translating
plenum, through the first end of the matrix, through the first upper
translating plenum, and out through a regeneration air outlet, the
translating plenum periodically traversing the matrix to regenerate
the desiccant on the first ends of the plurality of heat pipe heat
exchangers.
14. The dehumidifier according to claim 13 wherein the matrix
is a rectangular matrix including M.times.N heat pipe heat exchangers.
15. The dehumidifier according to claim 13 wherein the matrix
is formed as a tubular wheel.
16. The dehumidifier according to claim 13 wherein the supply
air stream maintains substantially the same temperature as it passes
from the supply air stream input to the supply air stream output.
17. The dehumidifier according to claim 13 wherein the heated
air supply has a temperature in the range of 50.degree. F. to 150.degree.
F.
18. An adiabatic desiccant humidification process, comprising the
steps of:
performing a sorption process by applying a supply air stream to
a first, desiccant coated end of a heat pipe heat exchanger while
applying a second air stream to a second end of the heat pipe heat
exchanger to dehumidify the supply air stream while maintaining
a substantially constant supply air stream temperature;
performing a desorption process by applying a heated air stream
to the second end of the heat pipe heat exchanger while applying
a regeneration air stream to the first end of the heat pipe heat
exchanger in order to maintain a temperature of the desiccant on
the first end of the heat pipe heat exchanger at a substantially
constant temperature.
19. The adiabatic desiccant humidification process of claim 18
further comprising the step of heating the heated air stream to
a temperature in a range of 50.degree. F. to 150.degree. F. prior
to applying the heated air stream to the second end of the heat
pipe heat exchanger.
Description FIELD OF THE INVENTION
The present invention relates to the field of desiccant dehumidifiers.
BACKGROUND OF THE INVENTION
Desiccant dehumidifiers as well as cooling-based dehumidifiers
are known. Cooling-based dehumidifiers operate to cool an incoming
air supply in order to cause condensation of the moisture in the
air, resulting in a dehumidification of the air. In contrast, desiccant
dehumidifiers, utilize a desiccant material to attract moisture
from the incoming air supply by creating an area of low vapor pressure
at the surface of the desiccant. Since the pressure exerted by the
water in the air is higher than the pressure at the surface of the
desiccant, the water molecules move from the air to the desiccant
and the air is dehumidified.
Most solid materials can attract moisture in the above manner.
For instance, nylon can absorb up to 6% of its dry weight in water
vapor. The oxide layer on metal surfaces attract and hold water
vapor under the right conditions.
Desiccants designed for water vapor collection, in contrast, generally
attract and hold from 10 to 10000 percent of their dry weight in
water vapor. Desiccants are characterized by their low surface vapor
pressure. If the desiccant is cool and dry, its surface vapor pressure
is low, and it can attract moisture from the air, which has a relatively
high vapor pressure when it is moist. If the desiccant becomes moist
and hot, its surface vapor pressure is high, and it will give off
water vapor to the surrounding air. Vapor moves from the air to
the desiccant and back again depending on the vapor pressure differential.
Desiccant dehumidifiers control vapor pressures to dry air continuously
in a repeating cycle. Initially, the desiccant is relatively cool
("state 1"), and therefore has a low surface vapor pressure.
As supply air passes over the desiccant, moisture from the air is
attracted to the desiccant. This is often referred to as the sorption
process. However, movement of the moisture from the air causes an
increase in the temperature of the air. This increase in temperature,
in turn, increases the temperature of the desiccant. Eventually,
the vapor pressure at the surface of the desiccant approaches that
of the surrounding air because it becomes moist and warm ("state
2"). Once the vapor pressure at the surface of the desiccant
equals the vapor pressure of the surrounding air, the desiccant
will cease collecting moisture.
The desiccant is then taken out of the moist air and placed into
a different, heated air stream. The hot air heats the desiccant
and causes the vapor pressure on the surface of the desiccant to
be higher than the vapor pressure of the moisture in the heated
air stream, thereby causing the moisture to leave the desiccant
surface ("state 3"). This is often referred to as the
desorption process, or regeneration process. At this point, the
desiccant is dry, but relatively hot. The desiccant is then cooled
returning it to its initial condition ("state 1", cool
and dry) completing the cycle so that the desiccant can begin collecting
moisture once again. This is often referred to as the cooling process.
Thermal energy drives this cycle. The desiccant is heated to drive
moisture off its surface (state 2 to state 3) and cooled to restore
its low vapor pressure (state 3 to state 1). The heating of the
desiccant from state 1 to state 2 is caused by the heating of the
conditioned air as water molecules in the gaseous phase are changed
to water molecules in a stationary condition, attached to the surface
of the desiccant. The efficiency of the process improves when the
desiccant has high moisture capacity. In addition, since the desiccant
must be heated to drive off moisture, the use of a low mass desiccant,
which requires less energy to heat, also improves the efficiency
of the process.
SUMMARY OF THE INVENTION
One use for desiccant dehumidification is to condition air for
"space air conditioning," a market currently dominated
by mechanical air conditioners. However, since, in a desiccant system
the process air is heated as it dries during the sorption process,
additional hardware is needed to remove the heat from the process
air before it can be delivered to the space. Such hardware, may
include, for example, air-to-air heat exchangers, direct evaporative
coolers, mechanical cooling coils, indirect evaporative cooling,
or a combination thereof. Therefore, there is a need for a desiccant
dehumidification system in which the process air experiences little
or no temperature increase as it transfers moisture to the desiccant
material.
Another undesirable effect of the sensible temperature rise of
the process air during the sorption process is that the desiccant,
because it is surrounded by the process air, also rises in temperature
along with the process air. This is disadvantageous because a higher
desiccant temperature results in a higher desiccant surface vapor
pressure. The higher the desiccant surface vapor pressure, the less
moisture the desiccant can adsorb during the sorption process.
However, if the temperature rise at the surface of the desiccant
can be avoided, then the desiccant will be able to adsorb more water
for any given amount of desiccant. In addition, with a lower desiccant
temperature during the sorption phase, the desiccant can be regenerated
at a lower temperature during the desorption or regeneration process.
This is because the desiccant must be heated during the regeneration
process in order to create a higher vapor pressure at the surface
of the desiccant than in the surrounding air. If the desiccant enters
the regeneration process at a lower temperature, it is not necessary
to add as much heat in order to create the requisite pressure differential.
In accordance with the present invention, a desiccant material
is applied to a first end of a heat pipe heat exchanger. During
the sorption phase, a supply air stream is exposed to the desiccant
material on the first end of the heat pipe heat exchanger and a
second air stream, which could be ambient atmosphere, is exposed
to the second end of the heat pipe heat exchanger. The moisture
from the supply air stream is transferred to the desiccant material.
However, the heat pipe heat exchanger acts as a heat sink and adsorbs
the heat generated by the moisture transfer and transfers it to
the second end of the heat pipe heat exchanger. At the second end
of the heat pipe heat exchanger, the heat is transferred to the
second air stream. As a result, both the supply air stream and the
desiccant material remain at a substantially constant temperature
during the sorption phase. These two parameters are also influenced
by the state of the entering, second air stream.
During the desorption phase, a heated air stream is exposed to
the second end of the heat pipe heat exchanger, and a regeneration
air stream is exposed to the first end of the heat pipe heat exchanger.
The heat from the heated air stream is transferred to the heat pipe
heat exchanger, and then from the heat pipe heat exchanger to the
desiccant material. As a result, the surface vapor pressure of the
desiccant material rises, and the moisture from the desiccant material
is transferred to the regeneration air stream. In addition, in accordance
with a further embodiment of the present invention, after the heated
air stream is cooled as it is transfers heat to the heat pipe heat
exchanger, it is also used as the regeneration air stream. Finally,
when the desiccant is once again exposed to the supply air stream,
it will cool to the temperature of the supply air stream and then
the sorption process will begin again.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a-c) (Prior Art) are illustrative graphs showing the sorption,
desorption, and cooling processes.
FIG. 2 is an illustrative psychrometric chart showing the adiabatic
sorption process.
FIG. 3 shows an illustrative prior art heat pipe heat exchanger
which is suitable for use with the present invention.
FIG. 4(a) is a view of the non-adiabatic dehumidifier according
to a first embodiment of the present invention.
FIG. 4(b) is the dehumidifier of FIG. 4(a) shown with the process,
regeneration, and heated air steams.
FIG. 4(c) is another view of the dehumidifier of FIG. 4(a) showing
the heat pipe heat exchangers in cross-section.
FIG. 5 is an illustrative graph showing the sorption, desorption,
and cooling processes for the dehumidifier according to the present
invention.
FIG. 6(a) shows a dehumidifier according to a second embodiment
of the present invention.
FIGS. 6(b,c) shows a portion of the dehumidifier of FIG. 6(a) in
more detail along with the process, regeneration, and heating air
streams.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1(a)-(c) illustrate the sorption, desorption, and cooling
processes of conventional desiccant dehumidifiers. While conventional
desiccant dehumidifiers have a variety of constructions, they share
a common functionality. A desiccant material is sequentially exposed
to a supply air flow, a regeneration air flow, and a cooling air
flow. FIGS. 1(a)(c) illustrate the moisture content and vapor pressure
of a desiccant material of a conventional desiccant dehumidifier
in three states, numbered 1 through 3.
Referring to FIG. 1 (a), in its initial state 1 the desiccant
is relatively cool and dry. Then the desiccant is exposed to the
process air. Since the surface vapor pressure of the desiccant is
lower than the vapor pressure of the process air, a sorption process
occurs, transferring the moisture from the process air to the desiccant.
Eventually, the vapor pressure of the process air will equal the
surface vapor pressure of the desiccant, and the sorption process
will cease. As illustrated in FIG. 1(a) at state 2 the sorption
process results in an increased moisture content in the desiccant.
However, as the moisture leaves the air, this reaction liberates
heat, increasing the temperature of the air. The increased air temperature,
in turn, heats the desiccant as shown in state 2. Referring to FIG.
2 the increase in the temperature of the process air flow during
dehumidification is directly proportional to the amount of moisture
removed from the air.
After the desiccant reaches state 2 it is then exposed to the
regeneration air stream of relatively hot, dry air. Since the regeneration
air stream has a vapor pressure which is much lower than the surface
vapor pressure of the desiccant at state 2 a desorption process
occurs, transferring the moisture from the desiccant to the regeneration
air stream. Once the vapor pressure of the regeneration air stream
equals the surface vapor pressure of the desiccant, the desorption
process will cease. As illustrated in FIG. 1(b), at state 3 the
desorption process has resulted in a decrease in the moisture content
of the desiccant. In addition, while the temperature of the regeneration
air stream has been reduced due to its absorption of the moisture
from the air, the temperature of the regeneration air stream will
still be above the state 2 temperature of the desiccant. Therefore,
as shown, in FIG. 1(b), at state 3 the desiccant exhibits a decreased
moisture content, but also an increased temperature.
At state 3 the desiccant has a sufficiently low moisture level,
but because of to its high temperature, has too high a surface vapor
pressure to adsorb moisture. Therefore, the desiccant must be exposed
to a cooling source, such as a heat exchanger connected to a chilling
system or cooling tower, until it returns to state 1 as shown in
FIG. 1(c). This completes the cycle. Alternatively, the desiccant
will be cooled as it is exposed to the process air during the beginning
of the sorption process.
As stated above, desiccant dehumidification has potentially broad
application in the conditioning of air for "space air conditioning,"
a market currently dominated by mechanical air conditioners. However,
since, in a desiccant system the process air is heated as it dries
during the sorption process, additional hardware is needed to remove
the heat from the process air before it can be delivered to the
space. Such hardware, may include, for example, air-to-air heat
exchangers, direct evaporative coolers, mechanical cooling coils,
indirect evaporative cooling, or a combination thereof. Therefore,
there is a need for a desiccant dehumidification system in which
the process air experiences little or no temperature increase as
it transfers moisture to the desiccant material.
Another undesirable effect of the sensible temperature rise of
the process air during the sorption process is that the desiccant,
because it is surrounded by the process air, also rises in temperature
along with the process air. This is disadvantageous because a higher
desiccant temperature results in a higher desiccant surface vapor
pressure. The higher the desiccant surface vapor pressure, the less
moisture the desiccant can adsorb from the process air during the
sorption process. Therefore, it is desirable to reduce the sensible
temperature rise of the desiccant, or even to cause the temperature
of the desiccant to decrease, as the moisture is removed from the
process air.
In addition, if the temperature of the desiccant is lowered, the
desiccant can adsorb considerably more water per unit of desiccant
because the surface vapor pressure of the desiccant will be lower.
Moreover, with a lower desiccant temperature, the supply air could
be dried to a much lower level because the lower surface vapor pressure
of the desiccant would permit a greater volume of moisture to be
removed from the process air.
In addition, with a lower desiccant temperature during the sorption
phase, the desiccant can be regenerated at a lower temperature during
the desorption or regeneration process. This is because the desiccant
must be heated during the regeneration process in order to create
a higher vapor pressure at the surface of the desiccant than in
the surrounding air. If the desiccant enters the regeneration process
at a lower temperature, and therefore a lower surface vapor pressure,
it is not necessary to add as much heat in order to create the pressure
differential.
For example, if the regeneration temperature could be lowered to
a level where waste heat is generally available, then air conditioning
could be performed with no process energy cost. In addition, if
the regeneration temperature could be lowered to 50.degree. F. to
150.degree. F., solar heated air could be used for regeneration.
This is a significant advantage because solar energy is most abundant
when cooling is required, i.e., in the summer.
Conventionally, a heated regeneration air stream is caused to flow
over the regeneration portion of the desiccant system in order to
trigger the desorption process. The combination of air flow and
initial temperature must result in an air flow stream with sufficient
energy so that when the desorption process takes place, an energy
balance exists between the sorptive process and the desorption process.
In other words, the desorption process must generate enough energy
to remove all of the moisture adsorbed by the desiccant during the
sorptive process. The energy balance, in simplified form, is (SCFM.times..DELTA.T).sub.sorptive
=(SCFM.times..DELTA.T).sub.desorption, where SCFM is the mass flow
of the air stream, and T is temperature of the air stream. Therefore,
there either must be a high temperature and lesser desorption air
stream flow or a lower temperature and larger desorption air stream
flow. Neither is desirable. Creating high temperatures is generally
expensive, and creating high air flow requires equipment which is
both large and expensive.
Therefore, it is desirable to provide a desiccant dehumidifier
which utilizes low air mass flow and low temperature during the
regeneration process. In accordance with the present invention,
this is accomplished by heating the desiccant during the regeneration
process from within by its own internal heat source. By heating
the desiccant from within, the energy balance between the sorptive
and desorptive processes can be achieved with a much lower temperature
heat source because the desiccant can be maintained at a nearly
constant temperature. Normally, as the regeneration air stream cools
during the desorption process as a result of evaporative cooling,
the desiccant cools down as well. In addition, in conventional systems
the regeneration air must enter at a temperature high enough so
that sufficient moisture is removed during the regeneration process
despite the evaporative cooling of the air stream. If the energy
for desorption comes from within the desiccant, then the temperature
of the desiccant can be controlled so that the temperature change
of the regeneration air flow is negligible. Therefore, untempered
ambient air, exhaust air from a building, or the cooled heated air
steam, can be used as the regeneration air flow to carry off the
moisture from the desiccant. Moreover, instead of having the temperature
of the regeneration air decrease as it traverses the desiccant (thereby
inhibiting the air's ability to adsorb moisture), its temperature
increases (thereby enhancing the air's ability to adsorb moisture).
Therefore, air having a relatively low temperature, for example,
120.degree. F., can be used as the regeneration air flow and maintained
at this temperature during the entire desorptive process.
In accordance with the present invention, a desiccant dehumidifier
is provided which utilizes a low air flow and low temperature for
the regeneration air stream. In accordance with the present invention,
a desiccant material such as silica gel, molecular sieve, or a polymer
is applied to a first end of a heat pipe heat exchanger. FIG. 3
shows an illustrative prior art heat pipe heat exchanger which is
suitable for use with the present invention. The heat pipe heat
exchanger 10 is formed of a tube 101 containing a liquid/vapor heat
transfer medium 105. The tube 101 includes fins 30. Since the medium
105 in the tube 101 exists in liquid vapor equilibrium, the entire
length of the tube exhibits substantially the same temperature.
During the sorption phase, a supply air stream is exposed to the
desiccant material on the first end of the heat pipe heat exchanger
and a second air stream, which could be ambient atmosphere, is exposed
to the second end of the heat pipe heat exchanger. The moisture
from the supply air stream is transferred to the desiccant material.
However, the heat pipe heat exchanger acts as a heat sink and adsorbs
the heat generated by the moisture transfer and transfers it to
the second end of the heat pipe heat exchanger. At the second end
of the heat pipe heat exchanger, the heat is transferred to the
second air stream. As a result, both the supply air stream and the
desiccant material remain at a substantially constant temperature
during the sorption phase.
During the desorption phase, a heated air stream is exposed to
the second end of the heat pipe heat exchanger, and a regeneration
air stream is exposed to the first end of the heat pipe heat exchanger.
The heat from the heated air stream is transferred to the heat pipe
heat exchanger, and then from the heat pipe heat exchanger to the
desiccant material. As a result, the surface vapor pressure of the
desiccant material rises, and the moisture from the desiccant material
is transferred to the regeneration air stream. In addition, since
the heated air stream is cooled as it is transfers heat to the heat
pipe heat exchanger, this air stream, having been cooled to a lower
vapor pressure, can be used as the regeneration air stream. When
the desiccant is once again exposed to the supply air stream, it
will cool to the temperature of the supply air stream and then the
sorption process will begin again.
FIGS. 4(a-c) show a dehumidifier according to a first embodiment
of the present invention. A plurality of heat pipe heat exchangers
10 form a wheel 130. A vertical divider 80 a horizontal divider
85 and a pair of outer partitions 40 are encased in a housing 1
to form four quadrants A, B, C, and D. In quadrants A and C, a desiccant
material is integrally bonded to the fins 30 of the heat exchangers
10. The wheel 130 is rotated by rollers 12 driven by a motor (not
shown). Seals 50 insure that air will not flow between quadrants.
A supply air inlet 90 and supply air outlet 110 are connected to
quadrant A. A regeneration air inlet 140 and regeneration air outlet
150 are connected to quadrant C. A heated air inlet 111 and heated
air outlet 112 are connected to quadrant D. A cooling air inlet
114 and cooling air outlet 113 are connected to quadrant B.
In accordance with a further embodiment of the present invention,
the fins 30 are preferably made from 0.004-inch aluminum, coated
with a desiccant material, and spaced 14 fins to the inch. The fins
could be manufactured with collared holes for the heat pipe heat
exchanger to pass through, and with radial ribs to insure that air
flows radially between heat pipes.
FIG. 5 shows an illustrative psychrometric chart for the dehumidifier
of FIGS. 4(a-c). In this example, the supply air stream 100 begins
as "outdoor" air at 95.degree. F. dry bulb and 116 grains
of moisture as it enters quadrant A (point 1A). During operation,
as supply air stream 100 passes through quadrant A, the desiccant
on the heat pipe heat exchangers are relatively cool and dry with
a low surface vapor pressure. Since the supply air has a higher
vapor pressure, moisture travels from the air to the desiccant,
and the supply air is dried to 40 grains of moisture. However, because
of the heat pipe heat exchanger, the heat generated by this condensation
is adsorbed by the heat pipe heat exchanger, transferred to quadrant
B, and then to the cooling air stream 200. Therefore, the temperature
of the supply air stream 100 decreases slightly to 90.degree. F.
The cooling air stream 200 (point 2a-2b), also begins from an outdoor
air source (95.degree. F. dry bulb and 117 grains of moisture).
In this example, the cooling air stream 200 has water sprayed into
it and onto the heat pipe heat exchangers in quadrant B as the cooling
air stream 200 traverses quadrant B. Due to evaporative cooling,
the heat transferred from quadrant A to quadrant B is dissipated
as the water sprayed on the heat pipe heat exchangers in quadrant
B evaporates into the cooling air stream, leaving the cooling air
stream 200 at 90.degree. F. dry bulb and 206 grains of moisture.
Moreover, since in this example the mass flow of stream 200 is equal
to the mass flow of stream 100 the enthalpy (energy in BTU/lb)
gain between points 2a-2b are equal to the enthalpy decrease between
points 1a-1b.
If the dehumidifier were to be used in a creature comfort application,
it may be desirable to further sensibly cool the supply air stream
100 from point 1b to point 1c. This could be accomplished as follows.
An additional component, an air to air heat exchanger with an indirect
evaporative cooling feature could be provided. The air to air heat
exchanger includes a supply air passage having a supply input connected
to the supply air stream output 110 and a supply output connected
to the space to be cooled. The air to air heat exchanger further
includes an exhaust air passage having an exhaust input connected
to the space to be cooled and an exhaust output connected to outdoor
air. Water is sprayed into spent, stale air leaving the space to
be cooled as it passes through the exhaust air passages of the air-to-air
heat exchanger, which in turn, cools the process air in the supply
air passage of the heat exchanger. This process cools the air to
67.degree. F. and 40 grains of moisture. Further cooling could be
achieved by passing the process air through a direct evaporative
cooler to obtain a final temperature of 55.degree. F. and 60 grains
of moisture (points 1c to 1d). In this condition, the energy of
the process air is sufficient to cool the space and control the
relative humidity of the space.
Referring again to FIG. 4(a,b), in order to provide a continuous
dehumidification process, the wheel 130 rotates in order to allow
regeneration of the desiccant. As the wheel rotates, for example,
at 5 to 15 revolutions per hour, the desiccant covered heat pipe
heat exchangers which were initially in quadrant A during the sorption
process, rotate into quadrant C in order to undergo desorption.
Referring to FIGS. 4a,b, a heated air stream 400 enters quadrant
D via heated air inlet 111 passes over heat pipe heat exchangers
10 and exits via the heated air outlet 112. As the heated air passes
over the heat pipe heat exchangers 10 in quadrant D, the heat is
adsorbed by the heat pipe heat exchangers and transferred to the
desiccant coated fins 30 in quadrant C. The heat raises the surface
vapor pressure of the desiccant, and causes the moisture from the
desiccant to evaporate into the regeneration air stream 300. The
constant supply of heat from the heated air stream 400 to the desiccant
allows quadrant C to remain at or near a constant temperature as
the moisture evaporates from the desiccant.
Referring again to the illustrative psychrometric chart of FIG.
5 the heated air stream traverses the path from point 4a to point
4b and the regeneration air stream traverses the path from point
3a to 3b. In this example, the mass flow of supply air stream 100
is equal to the mass flow of regeneration air stream 300. Therefore,
the moisture increase of air stream 300 must equal the moisture
decrease of air stream 100 in order to return the desiccant to its
initial state (point 1a). In addition, there must be an energy balance
between regeneration air flow 300 and heated air flow 400. As an
illustration, outdoor air at 95.degree. F. and 117 grains of moisture
can be heated to 140.degree. F. and delivered as equal air streams
300 and 400 shown as points 3a and 4a respectively. As the air
stream 400 transfers heat to the heat pipe heat exchanger 10 and
to the desiccant in quadrant C, it cools sensibly to 116.degree.
F. and 117 grains of moisture. Regeneration air stream 300 evaporates
moisture from the desiccant and cools to 117.degree. F. and 194
grains of moisture (point 3b), thereby removing the 77 grains of
moisture which has been adsorbed by the desiccant during the sorption
process. Thereafter, as the wheel 130 rotates the desiccant back
into quadrant A, the temperature of the desiccant returns to 95.degree.
F. dry bulb, and the sorption process begins again.
FIGS. 6a, 6b show another embodiment of the dehumidifier according
to the present invention. In accordance with this embodiment, the
heat pipe heat exchanger remains stationary, and the heated and
regeneration air streams periodically traverse the heat pipe heat
exchanger in order the perform the desorption process. The dehumidifier
includes an enclosure 1001 a plurality of heat pipe heat exchangers
10 forming a rectangular matrix 131 a stationary divider 2000
and a sliding divider 1100 which define an A side and a B side of
the heat pipe heat exchangers 10. The A side of the heat pipe heat
exchangers 10 are coated with a desiccant material such as silica
gel, molecular sieve, or a polymer. The supply air enters via a
supply air inlet 2200 traverses the A side of the heat pipe heat
exchangers 10 and exits through a supply air outlet 1400. The cooling
air streams enters via cooling air inlet 9000 traverses the B side
of the heat pipe heat exchangers 10 and exits through cooling air
outlet 2300. Dividers 7050 inserted between heat pipe heat exchangers
insure that air flow through the heat pipe heat exchangers is vertical
as shown in FIG. 6b.
The dehumidifier further includes an A-side upper plenum 1700
a B-side upper plenum 1720 and a lower plenum 1750. The A-side
upper plenum 1700 is separated from the B-side upper plenum by stationary
divider 2000. The heated air stream enters via heated air inlet
1000 flows through a flexible duct (not shown), where it enters
the B-side plenum 1720 via a collar 3000. The heated air stream
then traverses through the portion of the B side heat pipe heat
exchangers 10 which are directly below the B-side upper plenum 1720
and into the lower translating plenum 1750. The heated air stream
then traverses the length of the lower translating plenum 1750 and
then travels through the A side of the heat pipe heat exchangers
10 into the A-side upper plenum 1700 through collar 3010 heated
air output duct (not shown), and out the heated air outlet 2100.
A drive 1300 drives a chain or belt 1310 which in turn, rotates
four sprockets 1500 and their respective screws 1501 causing the
translating plenums 1700 1720 and 1750 to traverse the width of
the heat pipe heat exchangers 10. Tension is maintained in the belt
or chain 131 by tensioning/idler roll 1502. The sliding divider
1100 and seal 1200 separate the supply air flow 100 from the cooling
air flow 200 while accommodating the movement of the lower plenum
1750.
In accordance with the embodiment of FIGS. 6(a-c), the desiccant
coated heat pipe heat exchangers 10 covered by the upper and lower
plenums undergo desorption, while the remaining desiccant coated
heat pipe heat exchangers undergo sorption. For example, referring
again to the illustrative psychrometric chart of FIG. 5 the supply
air begins as "outdoor" air at 95.degree. F. dry bulb
and 116 grains of moisture as it enters the desiccant coated portions
(the A side) of the heat pipe heat exchangers 10 (point 1A). During
operation, as supply air flow 100 passes through, the desiccant
on the heat pipe heat exchangers are relatively cool and dry with
a low surface vapor pressure. Since the supply air has a higher
vapor pressure, moisture travels from the air to the desiccant,
and the supply air is dried to 40 grains of moisture. However, because
of the heat pipe heat exchanger 10 the heat generated by this condensation
is adsorbed by the heat pipe heat exchangers 10 transferred to
the B-side of the heat pipe heat exchangers 10 and then to the
cooling air stream 200. Therefore, the temperature of the supply
air flow 100 decreases slightly to 90.degree. F. The cooling air
stream 200 (point 2a-2b), also begins from an outdoor air source
(95.degree. F. dry bulb and 117 grains of moisture). In this example,
the cooling air stream 200 has water sprayed into it and onto the
B-side of the heat pipe heat exchangers. Due to evaporative cooling,
the heat transferred from the A-side to the B-side of the heat pipe
heat exchangers 10 is dissipated as the water spayed on the heat
pipe heat exchangers evaporates into the cooling air stream, leaving
the cooling air stream at 90.degree. F. dry bulb and 206 grains
of moisture. Moreover, since in this example the mass flow of stream
200 is equal to the mass flow of stream 100 the enthalpy (energy
in BTU/lb) gain between points 2a-2b are equal to the enthalpy decrease
between points 1a-1b.
If the dehumidifier were to be used in a creature comfort application,
it may be desirable to further sensibly cool the supply air 100
fro point 1b to point 1c and then to point 1d in the manner described
above with regard to FIG. 4.
Referring again to FIG. 6b,c, in order to provide a continuous
dehumidification process, the upper and lower plenums 1700 1720
1750 traverse across the width of the heat pipe heat exchangers
in a direction 1790. As the plenums move, the desiccant covered
heat pipe heat exchangers which were initially exposed to the supply
air stream are covered by the plenums 1700 1720 1750 in order
to undergo desorption. Referring to FIG. 6b a heated air stream
400 enters the B-side upper plenum, passes through heat pipe heat
exchangers 10 and into the lower plenum 1750. As the heated air
passes through the B-side portion of the heat pipe heat exchangers
10 the heat is adsorbed by the heat pipe heat exchangers 10 and
transferred to the desiccant coated fins 30 in A-side portion of
the heat pipe heat exchangers 10. The heated air stream 400 then
travels through the lower plenum 1750 and then through the A-side
heat pipe heat exchangers 10 to serve as the regeneration air stream.
The heat transferred to the A-side of the heat pipe heat exchangers
10 raises the surface vapor pressure of the desiccant, and causes
the moisture from the desiccant to evaporate into the heated (regeneration)
air stream 400. The constant supply of heat from the heated air
stream 400 to the desiccant allows the desiccant to remain at or
near a constant temperature as the moisture evaporates from the
desiccant.
Referring again to the illustrative psychrometric chart of FIG.
5 the heated air stream traverses the path from point 4a to point
4b as it passes through the B-side of the heat pipe heat exchangers
10 and then traverses the path from point 3a' to 3b'as it travels
through the lower plenum 1750 and then through the A-side of the
heat pipe heat exchangers 10. In this example, the mass flow of
supply air stream 100 is equal to the mass flow of regeneration
air stream 300. Therefore, the moisture increase of air stream 300
must equal the moisture decrease of air stream 100 in order to return
the desiccant to its initial state (point 1a). In addition, there
must be an energy balance between the energy lost by the heated
air flow 400 as it passes through the A-side of the heat pipe heat
exchangers 10 and the energy gained by the heated air flow as it
passes through the B-side of the heat pipe heat exchangers 10. As
an illustration, outdoor air at 95.degree. F. and 117 grains of
moisture can be heated to 140.degree. F. delivered as equal air
stream 400 shown as point 4a. As the air stream 400 transfers heat
to the B-side of the heat pipe heat exchangers 10 and to the desiccant
in the A-side of the heat pipe heat exchangers, it cools sensibly
to 116.degree. F. and 117 grains of moisture (point 4b). The heated
air stream 400 then passes through the lower plenum 1750 and then
enters the A-side of the heat pipe heat exchangers at point 3a'
(still at 116.degree. F., 117 grains). The heated air stream 400
evaporates moisture from the desiccant and cools to 98.degree. F.
and 194 grains of moisture (point 3b'), thereby removing the 77
grains of moisture which has been adsorbed by the desiccant during
the sorption process. Thereafter, as plenums 1700 1720 1750 move
onto the next section of heat pipe heat exchangers, the temperature
of the desiccant returns to 95.degree. F. dry bulb, and the sorption
process begins again.
In accordance with the embodiment of FIG. 6 the heated air stream
400 is used twice, once to heat the desiccant during the desorption
process, and then again to carry away the moisture which evaporates
from the desiccant during the desorption process. This provides
the advantage of leaving the desiccant at a lower temperature at
the conclusion of the desorption process. This feature can also
be applied to the embodiment of FIG. 4 simply connecting the heated
air outlet 112 to the regeneration air inlet 140. Similarly, separate
heated air streams and regeneration air streams could be provided
in the embodiment of FIG. 6 by dividing the lower plenum 1750 into
an A-side lower plenum and a B-side lower plenum. This would naturally
allow the sliding divider 1100 to be replaced with a stationary
divider. In addition, while the second embodiment has been illustrated
above with regard to a rectangular shaped matrix of heat pipe heat
exchangers 10 it should be clear that a tubular wheel shaped matrix
of heat pipe heat exchangers (such as the wheel 130 of FIG. 4) could
also be used, with the upper plenums 1700 1720 traversing an outer
circumference of the wheel and the lower plenum 1750 traversing
an inner circumference of the wheel. |