Abstrict A process using a cascade desiccant air-conditioning/air drying
apparatus having cold thermal energy storage means is used to produce
a major increase in the system's thermal coefficient of performance.
The latent heat of vaporization from the water separation occurring
in desiccant regeneration is recovered in the heating process for
desiccant regeneration in the next stage. This energy recovery results
in a major improvement in thermal coefficient of performance in
air-conditioning or air drying processes. Values greater than 1.0
are expected to be common and values greater than 2.0 are possible.
Presently most thermal driven air-conditioning systems have a thermal
coefficient of performance less than 1.0 with an average value less
than 0.7.
Claims What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A cascade desiccant air-conditioning process for conditioning
an air flow utilizing a plurality of desiccating means, comprising:
desiccating said air flow by removing moisture therefrom to produce
a desiccated air flow, wherein said step of desiccating said air
flow further comprises passing said air flow through said plurality
of desiccating means such that said moisture of said air flow is
absorbed by said plurality of desiccating means;
cooling said desiccated air flow to produce a cooled, desiccated
air flow by passing said desiccated air flow through heat exchanging
means;
chilling said cooled, desiccated air flow to produce a conditioned
air flow, wherein said step of chilling said cooled, desiccated
air flow further comprises injecting water into said cooled, desiccated
air flow such that said water is adiabatically evaporated by said
cooled, desiccated air flow to lower a temperature of said cooled,
desiccated air flow;
exhausting said conditioned air flow; and
desorbing said moisture absorbed by said plurality of desiccating
means as steam in a cascade manner wherein a first steam produced
by desorbing serves as an energy source for subsequent desorbing
to produce a second steam such that a major increase in a thermal
coefficient of performance of said cascade desiccant air-conditioning
process is effected by recovering a latent heat of vaporization
of said moisture through desorption of said moisture from said plurality
of desiccating means as said first and second steam.
2. A cascade desiccant air-conditioning process as claimed in claim
1 wherein said step of desorbing said moisture further comprises:
passing a high temperature fluid through first heat exchanging
means cooperating with first desiccating means of said plurality
of desiccating means to desorb moisture absorbed by said first desiccating
means as a first steam having a first temperature; and
passing said first steam through second heat exchanging means cooperating
with second desiccating means of said plurality of desiccating means,
said first steam condensing in said second heat exchanging means
to desorb moisture absorbed by said second desiccating means as
a second steam having a second temperature and wherein said second
temperature is less than said first temperature.
3. A cascade desiccant air-conditioning process as claimed in claim
1 wherein said step of desorbing said moisture absorbed by said
plurality of desiccating means further comprises regenerating said
plurality of desiccating means to generate a plurality of zero loss
cold thermal energy storage means such that air flowing through
said plurality of zero loss cold thermal energy storage means is
chilled without an additional energy input.
4. A cascade desiccant air drying process for conditioning an air
flow utilizing a plurality of desiccating means, comprising:
desiccating said air flow by removing moisture therefrom to produce
a desiccated air flow, wherein said step of desiccating said air
flow further comprises passing said air flow through said plurality
of desiccating means such that said moisture of said air flow is
absorbed by said plurality of desiccating means;
cooling said desiccated air flow to produce a cooled, desiccated
air flow by passing said desiccated air flow through heat exchanging
means;
exhausting said cooled, desiccated air flow; and
desorbing said moisture absorbed by said plurality of desiccating
means as steam in a cascade manner wherein a first steam produced
by desorbing serves as an energy source for subsequent desorbing
to produce a second steam such that a major increase in a thermal
coefficient of performance of said cascade desiccant air drying
process is effected by recovering a latent heat of vaporization
of said moisture through desorption of said moisture from said plurality
of desiccating means as said first and second steam.
5. A cascade desiccant air drying process as claimed in claim 4
wherein said step of desorbing said moisture further comprises:
passing a high temperature fluid through first heat exchanging
means cooperating with first desiccating means of said plurality
of desiccating means to desorb moisture absorbed by said first desiccating
means as a first steam having a first temperature; and
passing said first steam through second heat exchanging means cooperating
with second desiccating means of said plurality of desiccating means,
said first steam condensing in said second heat exchanging means
to desorb moisture absorbed by said second desiccating means as
a second steam having a second temperature and wherein said second
temperature is less than said first temperature.
6. A cascade desiccant air drying process as claimed in claim 4
wherein said step of desorbing said moisture absorbed by said plurality
of desiccating means further comprises regenerating said plurality
of desiccating means to generate a plurality of zero loss cold thermal
energy storage means such that air flowing through said plurality
of zero loss cold thermal energy storage means is chilled without
an additional energy input.
7. A cascade desiccant air-conditioning/air drying apparatus for
conditioning an air flow, comprising:
first flow ducting means for conducting said air flow therein;
first and second desiccating means operatively associared with
said first flow ducting means for removing moisture from said air
flow wherein said moisture in said air flow is desorbed therefrom
by circulating said air flow through said first and second desiccating
means to produce a desiccated air flow;
second flow ducting means operatively associated with said first
and second desiccating means for receiving said desiccated air flow;
cooling means associated with said second flow ducting means for
cooling said desiccated air flow to produce a cooled, desiccated
air flow and wherein said cooled, desiccated air flow is subsequently
exhausted from said second flow ducting means;
first heat exchanging means adapted to cooperate with said first
desiccating means for desorbing moisture therefrom;
second heat exchanging means adapted to cooperate with said second
desiccating means for desorbing moisture therefrom;
steam piping means interconnecting said first desiccating means
to said second heat exchanging means for conducting a first steam
produced in said first desiccating means to said second heat exchanging
means;
exhausting means operatively associated with said second desiccating
means for removing a second steam produced in said second desiccating
means; and
isolating means operatively associated with said first and second
desiccating means and first and second flow ducting means for alternately
isolating said first and second desiccating means from said first
and second flow ducting means and wherein
when said isolating means isolates said first and second desiccating
means from said first and second flow ducting means a high temperature
fluid flowing through said first heat exchanging means desorbs moisture
absorbed by said first desiccating means as said first steam having
a first temperature, and said first steam is conducted through said
steam piping means to said second heat exchanging means and condenses
therein to desorb moisture absorbed by said second desiccating means
as said second steam having a second temperature less than said
first temperature, and said second steam is removed from said second
desiccating means by passing through said exhausting means and wherein
a major increase in a thermal coefficient of performance of said
cascade desiccant air-conditioning/air drying apparatus is effected
by recovering a latent heat of vaporization of said moisture through
desorption of said moisture from said first and second desiccating
means as said first and second steam.
8. A cascade desiccant air-conditioning/air drying apparatus as
claimed in claim 7 further comprising:
moisture injecting means associated with said second flow ducting
means for chilling said cooled, desiccated air flow prior to subsequent
exhaustion from said second flow ducting means.
9. A cascade desiccant air-conditioning/air drying apparatus as
claimed in claim 8 wherein said first and second desiccating means
further comprise:
first and second containers operatively associated with said first
and second flow ducting means;
first and second desiccants disposed in said first and second containers,
respectively.
10. A cascade desiccant air-conditioning/air drying apparatus as
claimed in claim 7 wherein said first and second desiccating means
further comprise:
first and second containers operatively associated with said first
and second flow ducting means;
first and second desiccants disposed in said first and second containers,
respectively.
11. A cascade desiccant air-conditioning/air drying apparatus for
conditioning an air flow, comprising:
first and second flow ducting means for conducting said air flow
therein;
first and second desiccant spraying means operatively associated
with said first and second flow ducting means, respectively, for
removing moisture from said air flow wherein said moisture in said
air flow is desorbed therefrom by injecting said air flow with first
and second liquid desiccant sprays from said first and second desiccant
spraying means, respectively, to produce a desiccated air flow;
first and second cooling means associated with said first and second
flow ducting means, respectively, for cooling said desiccated air
flow to produce a cooled, desiccated air flow and wherein said cooled,
desiccated air flow is subsequently exhausted from said first and
second flow ducting means;
first and second collecting basins operatively associated with
said first and second flow ducting means, respectively, for collecting
first and second moisture-laden liquid desiccants, respectively,
after said first and second liquid desiccant sprays have passed
through said air flow and absorbed said moisture therefrom;
first and second high pressure pumping means operatively associated
with said first and second collecting basins, respectively, for
pumping said first and second moisture-laden liquid desiccants from
said first and second collecting basins, respectively, and wherein
said first and second high pressure pumping means are adapted to
operate such that said first moisture-laden liquid desiccant is
pumped from said first collecting basin by said first high pressure
pumping means at a first predetermined pressure and said second
moisture-laden liquid desiccant is pumped from said second collecting
basin by said second high pressure pumping means at a second predetermined
pressure and wherein said first predetermined pressure is greater
than said second predetermined pressure;
first and second containers operatively associated with said first
and second high pressure pumping means, respectively, for receiving
said first and second moisture-laden liquid desiccants, respectively;
first heating means operatively associated with said first container
for desorbing said first moisture-laden liquid desiccant by heating
thereof such that a first liquid desiccant and a first steam having
a first predetermined temperature are produced in said first container;
second heating means operatively associated with said first and
second containers for desorbing said second moisture-laden liquid
desiccant by condensing said first steam in said second heating
means such that a second liquid desiccant and a second steam having
a second predetermined temperature are produced in said second container
thereby recovering a latent heat of formation of said first steam
by generating said second steam;
water separator means operatively associated with said second container
for removing said second steam therefrom; and
first and second cycling means operatively associated with said
first and second containers, respectively, and said first and second
desiccant spraying means, respectively for transferring said first
and second liquid desiccants to said first and second desiccant
spraying means, respectively, such than an operating cycle for said
cascade desiccant air-conditioning/air drying apparatus is maintained
continuously.
12. A cascade desiccant air-conditioning/air drying apparatus as
claimed in claim 11 further comprising first and second water injecting
means operatively associated with said first and second flow ducting
means, respectively, for chilling said cooled, desiccated air flow
prior to subsequent exhaustion from said first and second flow ducting
means.
Description BACKGROUND OF THE INVENTlON
1. Field of the Invention
The present invention relates to air-conditioning systems and more
particularly to an air-conditioning system having a cold thermal
energy storage capability to reduce the direct thermal energy required
for operation of the system.
2. Description of the Prior Art
The principle of using desiccants for air conditioning is widely
known and numerous patents, such as U.S. Pat. Nos. 516313 (November
1931), 2138684 (November 1938), 2138690 (November 1938), and
3844737 (October 1974), are found in the prior art. U.S. Pat.
No. 246626 covering desiccant absorption was granted in November
1881. A number of these patents also note the application of desiccants
for direct air drying. Numerous other patents utilize the principle
for air conditioning/air drying which has been known since the early
1900's and before. The last patent mentioned makes use of a regenerative
zeolite desiccant wheel and a sensible heat exchanger (heat wheel).
It provides a viable continuous stream of cool air. The system has
been referred to in numerous papers on solar air-conditioning. Many
of these presentations used solar energy plus the addition of thermal
energy from gas combustion or resistance heating. The problem with
these systems is that the thermal coefficient of performance is
poor, normally 0.6 or lower. The thermal coefficient of performance
is defined as COP.sub.Thermal =Q.sub.L /Q.sub.IN where
Q.sub.L is air-conditioning energy provided by the system, and
Q.sub.IN is thermal energy required to operate the system. The
energy units of both values are identical. The basic conventional
absorption cycles, such as water and lithum bromide, have thermal
coefficients of performance limited to approximately 0.76.
The low coefficient of performance of these systems limits the
use of direct thermal energy to produce air-conditioning economically.
This is true for gas sytems, solar systems, electrical systems,
and other thermal energy addition systems. However, by doubling
the thermal coefficient of performance, a 50 percent reduction in
the solar collector area, the major capital cost in a solar system,
is possible. Reducing energy input by 50 percent or more in any
air-conditioning system is obviously beneficial. This is particularly
true as fossil fuel costs rise.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a simple, economical
process and apparatus for air-conditioning or air drying having
a major increase in the thermal coefficient of performance with
respect to present systems.
Another object of this invention is to provide a cascade air-conditioning/air
drying process and apparatus having a cold thermal energy storage
capability.
Yet another object of this invention is to provide an air-conditioning/air
drying process and apparatus which utilizes the latent heat of vaporization
stored in the desiccant for subsequent regeneration of other desiccants
to reduce the direct thermal energy required to operate the system.
The present invention is directed to an air-conditioning system
which utilizes moderate temperature thermal energy for operation,
has a built in zero loss thermal energy storage capability, requires
a minimum of moving parts, is economical and provides a major increase
in thermal coefficient of performance compared to present systems,
and can similarly be used as a highly efficient system for direct
air drying.
In accordance with the present invention there is disclosed an
air-conditioning process and apparatus having a high thermal coefficient
of performance by the use of two sets of equipment for completing
the process, and using solar or conventional energy. By eliminating
the last step in the air-conditioning phase, direct air drying is
accomplished. In accordance with the method of the present invention,
ambient air and/or internal environment (inside) air is circulated
over a desiccant and thereby dried. The desiccant can be silica
gel, an absorbent molecular sieve with a high affinity for water,
a liquid desiccant, or other similar absorbents. Silica gel, for
example, can absorb 50 percent of its own weight in water mass and
molecular sieves can absorb 30 to 60 percent of their mass in water
mass depending upon the sieve. The dried air and desiccant undergo
an increase in temperature due to the heat generated as a result
of the drying process. The heated, desiccated air is cooled in a
heat exchanger to as low a temperature as possible without using
a chiller. The temperature could approach ambient temperature or
possibly a lower temperature if water from a cooling coil is utilized
in this cooling step. Liquid moisture is then added to the dried
air. Adiabatic evaporation of the added water reduces the air temperature
and humidity to acceptable values for air-conditioning. Heated,
desiccated air at a temperature of 95.degree. F., for example, by
the adiabatic evaporation of the added water, can be cooled to 55.degree.
F. This is the temperature goal for conventional home or commercial
air-conditioners. If only dried air is desired, this water addition
step in the process is eliminated. The operation of this system
will, after a time, render the desiccant too wet to perform. The
desiccant must then be regenerated.
To regenerate the absorbent material the desiccant is sealed from
the flow of ambient or inside air and then heated by an external
means. Heating can be accomplished by applying heat to the outside
of the container holding the desiccant or by running sealed tubes
with hot water or steam through the desiccant. The addition of heat
regenerates the desiccant and produces water vapor or steam within
the desiccant-holding holding container. This water vapor or steam
is then transferred to another container of desiccant where regeneration
is required. This second unit is also sealed and again steam is
produced. This process can continue to third, fourth, fifth, etc.
desiccant units. A large part of the energy used in regeneration
is recovered and used in a subsequent desiccant unit. Of particular
importance is the fact that since succeeding desiccant stages are
at lower temperatures, the steam which is generated under pressure
condenses and not just sensible heat is recovered but also the latent
heat of vaporization. A cascade regeneration process is thus formed.
Possible temperatures for a three stage system could be 350.degree.
F., 300.degree. .F, and 250.degree. F. for each stage, respectively.
The first stage is heated and saturated steam is produced at between
300.degree. to 350.degree. F. Due to the high pressure in the first
stage, the steam condenses in the second stage at 300.degree. F.
giving up sensible heat and the heat of vaporization. The process
is repeated at the third stage at a lower temperature and pressure.
Since only part of the input energy to a stage is recovered, each
succeeding stage must be physically a little smaller than the preceding
stage.
lf each stage has an independent thermal coefficient of performance,
and 90 percent of the energy is recovered, and if each succeeding
stage is 90 percent of the size of the last stage, then the overall
thermal performance is:
a. 0.5 for one stage
b. 0.95 for two stages
c. 1.36 for three stages
d. 1.72 for four stages
e. etc.
The systems use energy recovery, including latent heat of vaporization
recovery, for successive desiccant regeneration.
In order to form pressurized steam, the desiccant must collect
a large percentage of its mass in water and regenerate the water.
For example, if Linde 13.times. molecular sieve is used as the desiccant,
a mass of water equivalent to over 30 percent of its mass can be
absorbed. If this water is transformed to saturated steam at 350.degree.
F., the container can physically contain only 10 percent of the
steam. This means the remaining 90 percent of the steam must be
forced out of the container to the next unit. With higher mass percentage
absorption and/or lower temperatures and pressures, a higher percentage
of steam is forced from the container. If the temperature of the
next unit is lower, the steam will condense in the heat exchanger
coils. The condensation of the steam is a critical requirement of
this invention. The condensation requirement necessitates that the
desiccant units be well charged prior to regeneration.
Once the desiccant is regenerated, the system can provide air-conditioning
according to the above described process without energy addition
until the desiccant is again near saturation. During this period
the desiccant is providing cold thermal energy storage without thermal
losses. The quantity of the thermal energy storage is determined
by the mass of the desiccant.
By utilizing two or more complete systems as described hereinabove
the air-conditioning process can be made to operate continuously.
While one or more systems are being regenerated, the other systems
can be used for regeneration. Sizing each system of the two or more
systems so as to provide 24 hours of air-conditioning would allow
solar energy to be used for regeneration. lf insolation is not available
during a given day, the system could be regenerated with lower priced
electricity during off-peak hours.
A system using conventional thermal energy, such as natural gas,
would use smaller units and possibly recycle thereby regenerating
the desiccant every thirty minutes. A continuous operating system
using liquid desiccant is also a possibility.
The invention can more than double present thermal coefficients
of performance, is simpler than most present systems, and has a
lower capital cost than most present systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other objects, features and attendant advantages of the
present invention will be more fully appreciated as the same becomes
better understood from the following detailed description when considered
in connection with the accompanying drawings in which like reference
characters designate like or corresponding parts throughout the
several views and wherein:
FIG. 1 is a cross-sectional view, partially in schematic form,
of a cascade air-conditioning/air drying system having a cold thermal
energy storage capability in accordance with the invention;
FIG. 2 is a schematic of an application of the cascasde air-conditioning
system and cold thermal energy storage system of the present invention
to a home using conventional energy or solar energy with a conventional
energy backup source;
FIG. 3 is a schematic depicting the cascade air-conditioning/air
drying process for a continuously operating system using liquid
desiccant in accordance with the present invention; and
FIG. 4 is a schematic depicting a cascading arrangement for regenerating
liquid desiccant in the cascade air-conditioning/air drying process.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown in cross-section, partially
in schematic form, a cascade desiccant air-conditioning/air dryer
system 100 in accordance with the present invention. The system
100 consists of three chambers 5 6 7 filled with desiccants 18a,
18b, 18c, respectively. These chambers 5 6 7 would normally be
cylindrical tanks having tapered ends. The desiccant 18 can be silica
gel, molecular sieves, activated carbon, or other getters. The desiccant
18 can be in the form of pellets, spheres, and other shapes, or
a cindered porous mass. Most of these substances are commercially
available in various size pellets and spheres. One-eighth and one-quarter
inch diameters are common sizes for pellets and spheres. The desiccants
18a, 18b, 18c must allow air to pass through with a minimum pressure
loss. If small desiccant particles are used, screens 8 are required
at each end of chambers 5 6 7 to constrain the desiccant particles.
At each end of the chambers 5 6 7 a sealing means 26 such as
an air tight valve or plug, is required so that each chamber 5
6 7 can be sealed air tight. The chambers 5 6 7 and sealing means
26 must be able to withstand and seal appreciable pressures, for
example, 70 Psig if a maximum temperature of 300.degree. F. is utilized.
This becomes more obvious in the regeneration part of the cycle
which is discussed later. Inside of each chamber 5 6 7 is a heat
exchanger 36. In most cases the heat exchanger 36 will consist of
tubing 36a through which water or steam can flow. A possible heat
exchanger 36 configuration has coil-shaped tubing 36a extending
from one end of the chambers 5 6 7 through the chambers 5 6
7 to the other end thereof. To enhance heat transfer, the heat exchanger
tubing 36a must be placed in a geometry where oscillating temperatures
do not cause large stresses in the tubing 36a. At the entrance and
exit of each heat exchanger 36 are valves 34 which can be shut off.
FIG. 1 shows valves 34 cooperating with the heat exchangers 36 of
chambers 5 6 7. However, the valves 34 are not necessary for the
heat exchanger 36 in chamber 5. This will become obvious during
the later cycle descriptions. Between chambers 5 and 6 and chambers
6 and 7 a steam line 38 connects an air-section 5a of chamber 5
to the heat exchanger 36 of chamber 6 and a steam line 38a connects
an air-section 6a of chamber 6 to the heat exchanger 36 of chamber
7. These steam lines 38 38a have disposed therein on/off valves
32 32a, respectively. Attached to each end of chambers 5 6 7
are air ducts 12 14 16. These ducts 12 14 16 need only withstand
low pressures. The ducts 12 14 16 are attached to an incoming
air duct 10 at one end, and to an exhaust air duct 20 at the opposite
end. Downstream of the exits of the ducts 12 14 16 from chambers
5 6 7 a cooling heat exchanger 22 and a water injector spray 24
are disposed in the exhaust air duct 20. The heat exchanger 22 is
a conventional chilling coil and the water injector 24 functions
to spray water into the conditioned air flowing through exhaust
air duct 20. Leaving the exhaust air duct 20 at location 28 is chilled
air for air-conditioning. If the water injector 24 is deleted, dry
air exits exhaust duct 20 at location 28. Heat exchanger 22 is also
not required for air drying but could be included.
FIG. 1 shows only three chambers 5 6 7. More chambers, however,
could be added in series, as described hereinabove, so that the
present invention is not to be construed as being limited to three
chambers.
The process for this invention is in two phases, the air-conditioning
or air drying phase, and the subsequent regeneration phase.
In the air-conditioning or air drying phase, incoming air enters
through the incoming air duct 10. The incoming air can be either
ambient air or environmentally controlled (recirculated) air or
a combination of the two. The incoming air is divided into three
flow streams entering the inlet ducts 12 14 16 to flow into chambers
5 6 7 via air-sections 5a, 6a, 7a, respectively. Valves 26 are
open on all chambers. Valves 32 32a between chambers 5 and 6 and
between chamber 6 and 7 respectively, are closed. Valves 34 can
be either open or closed. If valves 34 are open, cooling fluid flowing
through heat exchangers 36 will enhance the performance of the air-conditioning
or air drying phase. As the incoming air passes through the desiccants
18a, 18b, 18c, moisture in the incoming air is absorbed by the desiccants
18a, 18b, 18c. In the absorption process, heat is generated. This
heat is removed by the cooling fluid passing through the heat exchangers
36. No cooling is required as the temperature can be allowed to
increase, heating both the desiccants 18a, 18b, 18c and the air
flowing therethrough. However, the process works more efficiently
at lower temperatures. The air leaving the chambers 5 6 7 is desiccated.
For air-drying, the process may stop as the desiccated air enters
the exhaust duct 20 or the air may be further cooled by passing
through cooling heat exchanger 22. For air-conditioning, the air
in the exhaust duct 20 is further cooled by passing through cooling
heat exchanger 22. After the air is cooled, water is added to the
cooled, desiccated air by the water injector 24 such that the temperature
of the cooled, desiccated air drops due to an adiabatic evaporization
process. As the water evaporates, energy equivalent to the latent
heat of vaporization of the water is absorbed from the cooled, desiccated
air. Air properties of the conditioned air equivalent to the exhaust
air properties from conventional air-conditioners can be achieved.
As the incoming air passes through chambers 5 6 7 the desiccants
18a, 18b, 18c become saturated with water and must be regenerated.
In order for this invention to work effectively, the desiccants
18a, 18b, 18c must have absorbed an appreciable amount of water.
Absorption to near the saturation point is most efficient. This
becomes obvious in the discussion on the regeneration phase.
The regeneration phase is initiated as the desiccants 18a, 18b,
18c approach their saturation points. The incoming air flow is stopped
by closure means (not shown) in incoming air duct 10 and valves
26 are closed on each chamber 5 6 7. Valves 34 are closed on chambers
6 and 7. Valves 32 32a are opened. A high temperature fluid, normally
hot water or steam, passes through the heat exchanger 36 in chamber
5. The addition of heat regenerates the water which has been absorbed
in desiccant 18a. The regenerated water forms steam at a slightly
lower temperature than the heating fluid. This pressurized steam
passes from the air-section 5a in chamber 5 through the steam line
38 to the heat exchanger 36 in chamber 6. As the steam condenses
in the heat exchanger 36 of chamber 6 the water in desiccant 18b
in chamber 6 is regenerated and again forms steam which is transferred
via steam line 38a to the heat exchanger 36 in chamber 7. As the
steam condenses in the heat exchangers 36 disposed in chambers 6
7 steam-water separators 40 cooperating with the heat exchangers
36 of chambers 6 7 allow the condensed water to drain from the
heat exchangers 36. The steam from the last chamber, chamber 7 in
this case, is discarded. The temperature of the steam generated
in any given stage is less than the temperature of the steam generated
in the preceding stage. A major change in the thermal coefficient
of performance of the system results from the recovery of the latent
heat of vaporization in the water vapor absorbed by the desiccants
18a, 18b, 18c. In other desiccant systems, the water vapor is discarded
with the air flow. A residual quantity of steam remains in the air-sections
5a, 6a, 7a of the chambers 5 6 7 and in the heat exchangers 36
and this fraction of the input energy is lost. This percentage decreases
with an increase in the saturation level of desiccants 18a, 18b,
18c. As a result, regeneration near the saturation point of desiccants
18a, 18b, 18c is more efficient. Minimizing the volume of the heat
exchangers 36 where the latent heat of vaporization of the residual
volume of steam is lost, also maximizes efficiency. The mass of
the chambers 5 6 7 the desiccants 18a, 18b, 18c, heat exchangers
36 and other components absorb sensible heat as the temperature
rises. This energy is also lost in each cycle. Therefore, these
masses must be minimized to ensure maximum performance. Insulation
will cover chambers 5 6 7 piping, etc. to minimize additional
energy losses. These percentage losses become smaller as the system
increases in physical size. Due to energy losses in each stage (chamber
and related equipment), less energy is available for succeeding
stages. As a result, each succeeding stage (chambers and related
equipment) will have to be smaller or have an additional source
of energy. Adding extra energy defeats the purpose of the present
invention. As a result, FIG. 1 shows each succeeding stage slightly
smaller.
At the completion of the regeneration phase, an air-chilling capability,
without any additional energy, exists until the desiccants 18a,
18b, 18c again require regeneration. This results in cold thermal
energy storage system without thermal losses. In a system at 55.degree.
F., for example, heat continuously leaks into the system resulting
in thermal energy storage losses. A zero-loss thermal energy storage
capability is inherent to the present invention.
For a continuously operating system, more than one of the systems
100 in FIG. 1 must be utilized. A first system 100 can be air-conditioning
while other systems 100 are regenerating. FIG. 2 is a schematic
of an application of the cascade desiccant air-conditioning system
having a cold thermal energy storage capability 100 to a home. The
air-conditioning cascade and thermal energy storage systems 100
in FIG. 1 are denoted as systems 102 and 104 in FIG. 2. Different
numbers are assigned so a differentiation can be made between the
operation of the two systems 100. A home environment 106 is air-conditioned
by systems 102 and 104. The controlled environment air from the
home 106 enters inlet duct 50 and is channeled through system 102
or 104 and back into the outlet duct 52 by two-way valves 54. The
system 102 (or 104) which is being used for the air-conditioning
phase is in a regenerated state. The other system 104 (or 102) can
be in the regeneration process. Either a conventional heater 62
or a solar collector 110 is used to provide the hot water. The hot
water is circulated by a pump 60 switched to either the solar collector
110 or conventional heater 62 by valves 64 and then to systems 102
104 by inlet lines 56. Return lines 58 from systems 102 104 complete
the hot water flow circuit. Two way valves 57 in inlet lines 56
and return lines 58 direct the flow of hot water to the system 102
or 104 undergoing regeneration. No solar collector 110 is required
in a conventional system which would use only the conventional heater
62 for energy. In a solar system the conventional heater 62 is used
only for backup when solar energy is not available.
If systems 102 and 104 are sized to contain the quantity of cooling
required for a day's air-conditioning, one system 102 (or 104) can
be used for air-conditioning and the other system 104 (or 102) used
for regeneration in a 24-hour period. If system 102 or 104 is not
regenerated by solar energy during the day, because of a lack of
insolation for example, the system 102 or 104 can be regenerated
at night during off-peak hours. Therefore this solar energy air-conditioner
will not increase the peak load on electric power plants as conventional
solar systems do. The inherent internal cold thermal energy storage
capability contributes to the versatility of the present invention.
Inherent cooling can be accomplished by circulating cool water
to systems 102 and 104. The water can be cooled by a cooling tower
108 circulated by a pump 70 and switched to inlet cooling lines
68 return cooling lines 66 and the system 102 or 104 air-conditioning
by two-way valves 72. The cooling could be provided by ambient air
as in most conventional air-to-air air-conditioners. However, using
the cooling tower 108 to provide near or below ambient temperature
cooling, as in many gas fired absorption air-conditioners, increases
the thermal coefficient of performance.
The invention has been described with reference to a particular
embodiment; however, variations will occur to those skilled in the
art of desiccant air-conditioning or drying systems. A critical
feature of this invention is the recovery of the latent heat of
vaporization of the water vapor regenerated from the desiccant through
a cascade recovery system wherein each succeeding desiccant stage
undergoing regeneration is at a slightly lower pressure and temperature.
FIG. 3 is a schematic of a liquid desiccant system for continuous
air-conditioning/air drying using the cascade process to increase
the thermal coefficient of performance. Two cascade stages 101a,
101b are show; however, any number of stages are possible. In each
of the stages 101a, 101b the following sequence takes place. The
sequence described hereinbelow is for system 101a of FIG. 3. Air
enters at 74 and is dryed by flowing through a desiccant spray 82
to subsequently leave as warm dry air at 76. The warm dry air is
cooled in a cooling coil 77 and leaves as dry cool air at 78. The
cool dry air is injected with water by a water injector 79 and leaves
as cold air at 80. The moisture-laden desiccant spray 82 collects
in a basin 84 is then pumped to a relatively high pressure by a
high pressure pump 86 and is heated in a container 96 by heating
means 88 to regenerate the water as steam from the moisture-laden
desiccant. The steam generated in the container 96 flows through
a line 90 to the next cascade stage (shown as 101b in FIG. 3) and
condenses in the heating means 88a, recovering its latent heat of
vaporization through the regeneration of water as steam in this
stage. Steam generated in container 96 of syste 101b is then transferred
via line 98 to the heating means 88x of a subsequent stage to regenerate
the liquid desiccant contained in the subsequent stage, if desired.
Condensed water in the heating means 88a of system 101b, and subsequent
systems, is released through water separators 91. The desiccant
liquid is cooled by a heat exchanger 94 and passes through a flow
control valve 92 and completes the desiccant cycle by being sprayed
back into the entering air through desiccant spray 82. The quantity
of liquid desiccant allows an inherent cold thermal energy storage
system with a zero loss. The tank 84 holding the liquid desiccant
after regeneration can be used as an active cold thermal energy
storage means with zero loss. The high pressure pump 86 is required
to allow a temperature drop to the next cascade stage. The pressure
is reduced in each successive stage. For example, in a first stage
a saturation pressure of 70 psia assures a steam temperature of
over 300.degree. F. In a second stage, a saturation pressure of
30 psia would guarantee a temperature of regenerated steam of greater
than 250.degree. F. but still assure the condensation of the 70
psia steam. The work input into this high pressure pump 86 is relatively
low.
An alternative to the stages 101a, 101b as complete systems as
shown in FIG. 3 is to limit the stages to the regeneration container
96. FIG. 4 shows a schematic where regeneration container 96 has
been broken into three stages using the cascade principle. The saturated
liquid desiccant leaving the basin 84 is divided into three streams,
pressurized by the high pressure pumps 86 and transferred to containers
196a, 196b, 196c. The desiccant in lower container 196a is at the
highest pressure. External thermal energy is transferred to lower
container 196a and the liquid desiccant contained therein is regenerated
with the water being released as steam through line 90a. This steam
regenerates the desiccant in the next stage or container 196b with
a similar process occurring in container 196c. The regenerated liquid
desiccant leaves the containers 196a, 196b, 196c through pressure
regulators and flow controllers 93. The pressure regulators and
flow controllers 93 control the saturation pressure in the containers
196a, 196b, 196c and thereby control the temperature. The regenerated
liquid desiccant continues through the regeneration cycle as shown
in FIG. 3. The condensed water in the heating means 88x of the second,
third, etc. stages is released through water separators 91. Utilizing
this cascade arrangement allows the latent heat of vaporization
of the regenerated water vapor to be recovered. The steam from the
last stage could be used to preheat the liquid desiccant entering
the various stages thereby saving the latent heat of vaporization
from all stages.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is therefore
to be understood that within the scope of the appended claims, the
invention may be practiced otherwise than as specifically described
herein. |