Abstrict A high efficiency air conditioning system is proposed, in which,
while operating on a batch system, desiccant regeneration and process
air dehumidification can be carried out simultaneously with a simple
configuration. The air conditioning system comprises at least two
desiccant members, a process air passage for providing a process
air to one of the desiccant members for dehumidification of the
process air, and a regeneration air passage for providing a regeneration
air to the other of the desiccant members for regeneration of the
regeneration air. The desiccant members are movable with respect
to the process air passage and the regeneration air passage to alternatingly
switch each of the desiccant members from one of the regeneration
air passage and the process air passage to another.
Claims What is claimed is:
1. A desiccant assisted air conditioning system comprising:
a cylindrical desiccant body comprised by two semicylindrical desiccant
members joined together via a partition member;
a process air passage for providing a process air to one of said
desiccant members for dehumidification of said process air;
a regeneration air passage for providing a regeneration air to
the other of said desiccant members for regeneration of said desiccant
members; and
a rotating device for rotating said desiccant body so as to alternately
switch each of said desiccant members from one of said regeneration
air passage and said process air passage to another.
2. A system according to claim 1 wherein said desiccant body is
encased in a casing for defining at least two parallel air passages
therein.
3. A desiccant assisted air conditioning system according to claim
1 further comprising:
a heat pump including a high temperature heat source and a low
temperature heat source, said high temperature heat source being
disposed in said regeneration air passage for heating regeneration
air, said low temperature heat source being disposed in said process
air passage for cooling of process air; and
a sensible heat exchanger for exchanging heat between process air
which has passed through said one desiccant member and regeneration
air which has not yet entered into said other desiccant member.
4. A desiccant assisted air conditioning system according to claim
3 wherein said heat pump is a vapor compression heat pump.
5. A desiccant assisted air conditioning system according to claim
3 wherein said heat pump is an absorption heat pump.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to air conditioners, and
relates in particular to an air conditioning system having a continuous
air processing capability by alternately treating the process air
through at least two desiccant members.
2. Description of the Related Art
FIG. 6 shows a prior art example of desiccant assisted air conditioning
system same as the system disclosed in a U.S. Pat. No. 4430864.
The system comprises: a process air passage A; a regeneration air
passage B; two desiccant beds 103A, 103B; and a heat pump device
200 for desiccant regeneration and cooling of process air. The heat
pump device 200 utilizes heat exchangers, embedded in the two desiccant
beds 103A and 103B, as high and low temperature heat sources. In
each of the thermal medium passages, there are opposingly disposed
expansion valves 240A, 240B and one-way valves 241A, 241B, which
are arranged parallel to the expansion valves 240A, 240B respectively,
and the direction of compression of the compressor 230 can be switched
by a four-way valve 250.
In the technology described above, cooling and dehumidifying processes
can be explained with reference to a psychrometric chart shown in
FIG. 7. The process air (state K) is withdrawn by a blower 102 through
a passage 110 raised in pressure, and is forwarded to the one desiccant
bed 103A through the passage 111 and the four-way valve 105 and
passage 112A, where the moisture in the process air is adsorbed,
to lower its humidity ratio and raise its temperature by the effect
of the heat of adsorption. Because the desiccant bed 103A is cooled
by the heat pump 200 through the heat exchanger 220 the adsorption
heat is absorbed and the temperature of the process air does not
rise too much, and after saturating (state L), the process air is
dehumidified along iso-relative humidity line. The process air which
has been dehumidified and maintained at the temperature (state N)
is supplied to the conditioning space through the passage 113A,
the four-way valve 106 passage 114. An enthalpy difference .DELTA.Q
is thus produced between the return air from the conditioning space
(state K) and the cooled process air (state N), to provide cooling
of the conditioning space.
The regeneration process of the desiccant is performed as follows.
Regeneration air (state Q) is withdrawn into the blower 140 through
the passage 120 raised in pressure, and is forwarded to the other
desiccant bed 103B through the passages 121 122 the four-way valve
106 and the passage 113B. The desiccant bed 103B is heated by the
heat pump 200 by way of the heat exchanger 210 so its temperature
is raised, and the relative humidity is lowered (state R). The regeneration
air which now has a lowered relative humidity passes through the
desiccant bed 103B to remove the moisture from the desiccant material
(state T). The regeneration air which has passed through the desiccant
bed 103B passes through the passage 112B, four-way valve 105 and
the passage 124 and is discharged to an outside environment.
After the air conditioning process has been carried out for sometime
and the moisture content in the desiccant becomes higher than a
certain value, the four-way valve is operated to be switched, so
that the air passages for the desiccants and cooling/heating of
the heat pumps are interchanged. Thus, the operation is carried
on so that the regenerated desiccant is used to continue air conditioning
operation while the other desiccant is being regenerated. Therefore,
it can be seen that the processes of adsorption and regeneration
are conducted in a batch type system.
In the technology described above, heat exchange of the low temperature
heat source of the heat pump and the desiccant for adsorption are
embedded into a unit, and heat exchange of the high temperature
heat source of the heat pump and the desiccant on the regeneration
side are embedded into a unit. So, the cooling effect .DELTA.Q is
provided by a direct thermal load on the heat pump (refrigeration
device), which means that it is not possible to generate more cooling
than that allowed by the capacity of the heat pump acting as a refrigeration
device. Therefore, this configuration does not provide any advantages
worthy of making the apparatus complex. In addition, there has been
required two four-way valves, one for reversing the operation cycle
of the heat pump and the other for interchanging the passages of
the process/regeneration air, which further makes the configuration
of the apparatus complex.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high efficiency
air conditioning system in which, while operating on a batch system,
desiccant regeneration and process air dehumidification can be carried
out simultaneously with a simple configuration.
The object has been achieved in a desiccant assisted air conditioning
system comprising: at least two desiccant members; a process air
passage for providing a process air to one of the desiccant members
for dehumidification of the process air; and a regeneration air
passage for providing a regeneration air to the other of the desiccant
members for regeneration of the regeneration air, wherein the desiccant
members are movable with respect to the process air passage and
the regeneration air passage to alternatingly switch each of the
desiccant members from one of the regeneration air passage and the
process air passage to another.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is schematic representation of a first embodiment of the
basic configuration of the air conditioning system of the present
invention;
FIG. 2 is a schematic representation of a first embodiment of the
other configuration of the air conditioning system of the present
invention;
FIG. 3 is a psychrometric chart of the air conditioning cycle in
the first embodiment;
FIG. 4 is an illustration of the movement of heat in the present
air conditioning system;
FIG. 5 is a partially perspective view of a second embodiment of
the basic configuration of the air conditioning system of the present
invention;
FIG. 6 is a schematic representation of a conventional air conditioning
system; and
FIG. 7 is a psychrometric chart of the air conditioning cycle in
the conventional air conditioning system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, preferred embodiments will be presented with
reference to the attached drawings.
FIGS. 1 and 2 relate to the first embodiment of the air conditioning
system, which comprises: a process air passage A; a regeneration
air passage B: two desiccant beds 103A, 103B; and a heat pump device
200 for performing regeneration of the desiccant and cooling for
the process air. Though any type of heat pump device can be used,
in the embodiment, a vapor compressor type heat pump device disclosed
in a U.S. patent application Ser. No. 08/781038 filed by the inventor
is used.
Process air passage A starts from a process air inlet (usually
an interior air intake), and reaches a process air inlet of a casing
302 which houses the desiccants beds 103A, 103B, through the blower
102 and passage 111 and further reaches a process air outlet of
the casing 302 by way of one of the desiccant beds 103A, 103B. The
process air outlet of the casing 302 is communicated through the
passage 113 with a process air inlet of a sensible heat exchanger
104 heat-exchangeable with regeneration air, a process air outlet
of the sensible heat exchanger 104 is communicated a heat exchanger
220 serving as the low temperature heat source for the heat pump
device 200 through the passage 114. Then the process air passage
A reaches the process air outlet through the passage 115.
Regeneration air passage B starts from a regeneration air inlet
(usually an exterior air inlet), and, proceeds to the passage 120
the blower 140 the passage 121 a heat exchanger 104 heat-exchangeable
with the process air, a heat exchanger 210 serving as the high temperature
heat source for the heat pump device 200 and one of the passages
124A, 124A, to reach one of two regeneration air inlets of the casing
302 which can be shut and opened by shutters 301A, 301B in coordination
with the desiccant beds 103A, 103B. Regeneration air passage B further
proceeds to the one of the regeneration air outlets 125A, 125B of
the casing 302 by way of the desiccant beds 103A, 103B to reach
the regeneration air outlet through the passage 126.
The desiccant beds 103A, 103B can be moved inside the casing 302
by a motor 303 through a pulley-belt mechanism so that the desiccant
beds 103A, 103B are arranged as shown in FIG. 1 when the desiccant
103A is in the absorption process and the desiccant bed 103B is
in the regeneration process, or arranged as shown in FIG. 2 when
the desiccant 103A is in the regeneration process and the desiccant
bed 103B is in the absorption process. In an interlocking manner
with the desiccant bed 103A, 103B, the shutter 301A is operated
to shut the inlet connected to the passage 124A as shown in FIG.
1 or the shutter 301B to shut the inlet connected to the passage
124B as shown in FIG. 2.
Next, the operation of the first embodiment system having the heat
pump device serving as the heat source, will be described with reference
to a psychrometric chart shown in FIG. 3. The operation is according
to the system setup shown in FIG. 1 which shows the desiccant beds
103A, 103B are positioned so that the desiccant bed 103A communicates
with the process air passage A and the desiccant bed 103B communicates
with the regeneration air passage B.
Process air (state K) is admitted into a process air inlet, and
is withdrawn into the blower 102 through the passage 110 raised
in pressure, and is forwarded, through the passage 111 and the regeneration
air inlet of the casing 302 to one desiccant bed 103A where the
moisture in the air is adsorbed to lower its humidity ratio, and
the temperature is raised by the heat of adsorption (state L). The
air which has been dehumidified and raised in temperature is supplied
to the sensible heat exchanger 104 through the passage 113 and
is cooled in the sensible heat exchanger 104 by heat exchange with
the regeneration air (state M). The air which has been dehumidified
and cooled is forwarded to the heat exchanger 220 serving as the
low temperature heat source for the heat pump device 200 and after
being cooled, it is finally supplied to the conditioning space through
the passage 115 (state N). An enthalpy difference .DELTA.Q thus
produced between the return air (state K) and the supply air (state
N) provides cooling to the conditioning space.
During the same cycle, the other desiccant 103B performs a regeneration
process as follows. Regeneration air (state Q) is withdrawn into
the blower 140 through the passage 120 raised in pressure, and
is forwarded to the sensible heat exchanger 104 through the passage
121 and cools the process air while its own temperature is being
raised (state R). The regeneration air then flows into the heat
exchanger 210 acting as the high temperature heat source of the
heat pump device 200 through the passage 122 and is heated by the
refrigerant to about 60.about.80.degree. C., and its relative humidity
is lowered (state S). The regeneration air having a lowered relative
humidity is introduced into the casing 302 through a regeneration
air inlet thereof and then passes through the desiccant bed 103B
to remove the moisture in the desiccant bed (state T). The regeneration
air which has passed through the desiccant bed 103B reaches the
regeneration air outlet through the passage 125B and the passage
126. Since the regeneration air inlet connected to the passage 124A
is shut by the shutter interlockingly with the desiccant beds 103A,
103B, the regeneration air does not pass through the passage 124A.
When the water content of the desiccant bed exceeds a predetermined
level after a certain period of air conditioning operation, the
desiccant beds 103A, 103B are moved by the motor 303 through the
pulley-belt mechanism so that the desiccant 103A communicates with
the regeneration air passage B and the desiccant bed 103B communicates
with the process air passage A. FIG. 2 shows the air conditioning
system in which the desiccant bed 103A, 103B are moved relatively
to the casing 302 so that the desiccant 103A communicates with the
regeneration air passage B and the desiccant bed 103B communicates
with the process air passage A. The regeneration air passes through
the passage 124B and the passage 125B is shut. The detailed description
of the operation thereof is omitted since the action of the apparatus
is similar to that shown in FIG. 1.
As described above, the system is operated by repeating the process
of alternating cycles of dehumidification and cooling of each desiccant
bed 103A, 103B. Incidentally, it has long been a wide practice to
recycle the return room air as regeneration air, and in this invention,
this approach may also be used to achieve the same end results.
Further, since the system described above does not require the four-way
valve for reversing the operation cycle of the heat pump and for
interchanging the passages of the process/regeneration air, the
apparatus can be made simple.
In the present air conditioning system, the cooling effect produced
by the heat pump device is represented by .DELTA.q, a differential
enthalpy between the state M and state N shown in FIG. 3 which
is significantly less than the cooling capacity for the entire system,
.DELTA.Q. In other words, the system can generate a cooling effect
which surpasses the capacity of the heat pump device, thus enabling
to produce a compact unit and lower the manufacturing cost.
The thermal flow in the heat pump device of the present system
is illustrated in FIG. 4. The heat input, represented by a sum of
the heat introduced from the low temperature heat source of the
heat pump and the power for the compressor, is given to heat the
regeneration air. The temperature lift of this type of heat pump
device can be estimated to be at least 55.degree. C., in extracting
heat from evaporator at 15.degree. C. and raising it to 70.degree.
C., which is 22% higher than a typically achievable temperature
lift of 45.degree. C. in conventional heat pump devices, and the
pressure ratio is also somewhat higher than the conventional heat
pump devices. Therefore, when designating the heat output from the
compressor as one heat unit, the coefficient of performance (COP)
can be designed up to a value of 3 units. It follows that the input
heat from the evaporator is 3 and the output heat is a total of
1+3=4 and all of this heat output is available to heat the regeneration
air for use in the desiccant assisted air conditioning system.
The value of COP to show the energy efficiency as a single unit
of the present system is given by dividing the cooling effect .DELTA.Q
shown in FIG. 2 by the input regeneration heat .DELTA.H. In the
conventional technology shown in FIG. 6 the cooling effect is obtained
only from the heat pump action (.DELTA.q in FIG. 2) while in the
present system, there is a contribution (.DELTA.Q-.DELTA.q) from
the sensible heat exchanger 104 operating between the process air
and the regeneration air. The numerator is increased by this amount
and a higher value of energy efficiency is thus achieved.
The value of COP (.DELTA.Q/.DELTA.H) of desiccant assisted cooling
system is generally reported in a range of 0.8.about.1.2 at best.
Assuming a value of 1 for COP of the desiccant assisted cooling
system, the cooling effect of the air conditioning system is 1.
Assuming a value of 1 for the heat input from the compressor, the
total available thermal input for operating the present system is
4 which means that the cooling effect of 4 is obtainable from the
heating of the regeneration air. In the present system, there is
an additional cooling effect of 3 contributed by the low temperature
heat source, thus providing a total of 7 for the cooling effect
of the present system. The overall system COP is given by:
and it can be seen that this value is significantly higher than
a value of "4 or less" typical of the conventional system.
In the above embodiment, the desiccant beds 103A, 103B are moved
by using the motor and the pulley-belt mechanism. However, as long
as the desiccant bed 103A, 103B are linearly moved with respect
to the casing 302 various mechanism can be employed in the above
embodiment, which includes a diaphragm-piston mechanism utilizing
a static pressure of the blower for the regeneration air or the
process air, a cylinder-piston mechanism utilizing air pressure,
an electric rack-and-pinion mechanism, a recirculating ball mechanism
using a spiral screw or a link mechanism.
FIG. 5 shows a second embodiment of the present invention where
switching is embodied by a rotating action to switch the process
air passage and the regeneration air passage whereas, in the first
embodiment, the desiccant beds are linearly moved with respect to
the casing. In the second embodiment of the present invention, two
desiccant beds 103A, 103B are joined through a partition wall 107
to form a cylindrical desiccant body. The cylindrical desiccant
body is arranged in a cylindrical casing 302 and is rotatable about
its own axis therein by a motor (not shown). Inside the casing 302
two hollow spaces are formed at both ends by partition walls 304
305. One space is connected to the passages 111 113 for the process
air passage A and the other space is connected to the passages 124
125 for the regeneration air passage B. According to the second
embodiment of the present invention, when the water content of one
desiccant bed exceeds a predetermined level, the cylindrical desiccant
body is rotated by the motor to switch the process air passage and
the regeneration air passage.
In the above embodiments, a vapor compressor type heat pump device
was used for the heat pump device 200 however, any type of heat
source can be used so long as it provides a heat pump action. For
example, an absorption type heat pump disclosed in U.S. patent application
Ser. No. 08/769253 can be used to produce the same benefits.
Summarizing the significant features of the present desiccant assisted
air conditioning system, two switchable desiccant beds are provided
to alternately treat the process air and regeneration air so that
moisture in the process air is adsorbed in the one passage while
the regeneration air is regenerating the desiccant in the other
passage. Since the system does not require four-way valve arrangement,
the configuration of the apparatus can be simple. The high temperature
heat source of the heat pump device is placed in the regeneration
air passage to heat the regeneration air while the low temperature
heat source is placed in the process air passage to cool the process
air. This arrangement enables to utilize the heat pump device to
not only act as a heat source for desiccant regeneration but also
to utilize the sensible heat exchanger between the process air and
regeneration air to enhance thermal efficiency. The combined effect
of this arrangement enables to produce cooling effect in excess
of the cooling capacity of the heat pump device, and to achieve
a significantly higher energy efficiency for operating the air conditioning
system.
Although certain preferred embodiment of the present invention
have been shown and described in detail, it should be understood
that various changes and modifications may be made therein without
departing from the scope of the appended claims. |