Abstrict A desiccant assisted air conditioning system, incorporating desiccant
members in each of separate passages for process air and regeneration
air, is presented to significantly improve the cooling efficiency
to utilize the low and high temperature heat sources of a heat pump
device. While one desiccant is dehumidifying so that moisture in
the process air is being adsorbed in the one passage while the regeneration
air is removing moisture from the desiccant in the other passage.
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.
Claims What is claimed is:
1. A desiccant assisted air conditioning system comprising: a process
air passage for dehumidification of process air and a regeneration
air passage for regeneration of a desiccant material; at least two
desiccant members, one desiccant member being disposed in said process
air passage and other desiccant member being disposed in said regeneration
air passage; a sensible heat exchanger; and a heat pump device,
wherein a high temperature heat source of said heat pump device
is disposed in said regeneration air passage for heating regeneration
air, a low temperature heat source is disposed in said process air
passage for cooling of process air, and said sensible heat exchanger
exchanges 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.
2. A desiccant assisted air conditioning system according to claim
1 wherein an additional sensible heat exchanger is provided for
transferring heat between regeneration air which has passed through
said other desiccant member and regeneration air which has not yet
entered into said high temperature heat source.
3. An air conditioning system according to claim 1 wherein said
heat pump is a vapor compression heat pump.
4. An air conditioning system according to claim 1 wherein said
heat pump is an absorption heat pump.
5. An air conditioning system according to claim 1 further comprising
a switching valve for alternatingly switching said desiccant member
from one of said regeneration air passage and said process air passage
to another.
6. An air conditioning system according to claim 1 wherein said
regeneration air passage and said process air passage are arranged
in a manner that regeneration air and process air flow in reverse
directions to each other in said desiccant member.
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 units of desiccants.
2. Description of the Related Art
FIG. 7 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. 8. 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 satulating (state L), the process air is
dehumidified along iso-relative humidity line. The process air which
has been dehumidified and maintained at a temperature (state N)
is supplied to the conditioning space through the passage 113A,
the four-way valve 106 passage 114. An enthalpy difference DQ 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 DQ 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.
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.
The object has been achieved in a desiccant assisted air conditioning
system comprising: a process air passage for dehumidification of
process air and a regeneration air passage for regeneration of a
desiccant material; at least two desiccant members, one desiccant
member being disposed in the process air passage and other desiccant
member being disposed in the regeneration air passage; a sensible
heat exchanger; and a heat pump device, wherein a high temperature
heat source of the heat pump device is disposed in the regeneration
air passage for heating regeneration air, a low temperature heat
source is disposed in the process air passage for cooling of process
air, and the sensible heat exchanger exchanges heat between process
air which has passed through the one desiccant member and regeneration
air which has not yet entered into the other desiccant member. Accordingly,
the heat pump device is used as a heat source for conditioning of
the desiccant material to achieve higher thermal efficiency as well
as using the heated process air to provide increase the temperature
of the regeneration air to achieve even higher thermal efficiency.
An aspect of the system is that a sensible heat exchanger is provided
for transferring heat between regeneration air which has passed
through the other desiccant member and regeneration air which has
not yet entered into the high temperature heat source. Accordingly,
the heat from the spent regeneration air is used to preheat the
regeneration air before it is allowed to go into the high temperature
heat source, thereby fully utilizing available heat from the system.
Another aspect of the system is that the heat pump device is a
vapor compression heat pump.
Another aspect of the system is that the heat pump device is an
absorption heat pump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a first embodiment of the
basic configuration of the air conditioning system of the present
invention.
FIG. 2 is a psychrometric chart of the air conditioning cycle in
the first embodiment.
FIG. 3 is an illustration of the movement of heat in the present
air conditioning system.
FIG. 4 is a schematic representation of a second embodiment of
the basic configuration of the air conditioning system of the present
invention.
FIG. 5 is a schematic representation of a third embodiment of the
basic configuration of the air conditioning system of the present
invention.
FIG. 6 is a psychrometric chart of the air conditioning cycle in
the third embodiment.
FIG. 7 is a schematic representation of a conventional air conditioning
system.
FIG. 8 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. Any type of heat pump device can be used, but in
this case, a vapor compressor type heat pump device disclosed in
a U.S. patent application Ser. No. 08/781038 filed by the inventors
is used.
Process air passage A starts from a process air inlet (usually
an interior air intake), and reaches the four-way valve 105 through
the blower 102 and passage 111 and further reaches the four-way
valve 106 by way of either: a first passage through the passage
112A, desiccant 103A, passage 113A; or a second passage through
the passage 112B, desiccant 103B and the passage 113B, depending
on the routing chosen by the four-way valve 105. The process air
further progresses through the passage 114 a sensible heat exchanger
104 for providing heat exchange with regeneration air, and a heat
exchanger 220 serving as the low temperature heat source for the
heat pump device 200 to reach the process air outlet.
Regeneration air passage B starts from a regeneration air inlet
(usually an exterior air inlet), and, through 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 the passage 123 reaches
the four-way valve 106. Regeneration air passage B ultimately reaches
the four-way valve 105 by way of either: a first passage through
the passage 113A, desiccant 103A, passage 112A; or a second passage
through the passage 113B, desiccant 103B and the passage 112B, depending
on the routing chosen by the four-way valve 106. The regeneration
air further progresses through the passage 124 to the regeneration
air outlet. Because the four-way valves 105 106 are switched in
a interlocking manner, the process air passage A and the regeneration
air passage B do not cross one another.
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. 2. The operation is according
to the system setup shown in FIG. 1 which shows the four-way valves
105 106 are positioned so that the desiccant 103A operates in the
process air passage and the desiccant 103B operates in the regeneration
air passage.
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 passages 111 the four-way
valve 105 and the passage 112A, 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 four-way
valve 106 passage 114 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 116 (state N). An
enthaly difference DQ thus produced between the processed 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 passages
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
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 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 112B, four-way valve 105 and the
passage 124.
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.
In the present air conditioning system, the cooling effect produced
by the heat pump device is represented by Dq, a differential enthalpy
between the state M and state N shown in FIG. 2 which is significantly
less than the cooling capacity for the entire system, DQ. 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. 3. The heat input, represented by a sum of
the heat released from the evaporator and that generated from 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 per one unit of
the present system is given by dividing the cooling effect DQ shown
in FIG. 2 by the input regeneration heat DH. In the conventional
technology shown in FIG. 7 the cooling effect is obtained only
from the heat pump action (Dq in FIG. 2) while in the present system,
there is a contribution (DQ-Dq) 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 (DQ/DH) of desiccant assited 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 evaporator, 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.
FIG. 4 shows a second embodiment of the present system in which
the process air and the regeneration air in the desiccant bed 103
are circulated in the same direction. The operational diagram of
this embodiment is essentially the same as that shown in FIG. 2
and it will not be repeated.
FIG. 5 shows a third embodiment of the present system. An additional
heat exchanger 107 has been added to the system shown in FIG. 1
for heat transfer between the regeneration air after it has passed
through the desiccant 103B and the regeneration air before it enters
into the high temperature heat source 210 of the heat pump device
200.
The regeneration action of the third system will be described with
reference to the psychrometric chart shown in FIG. 6. 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 107 through the passage 122A,
and is heated further by heat exchange with the regeneration air
which has passed through the desiccant 103B (state S). This regeneration
air enters into the high temperature heat source 210 of the heat
pump device 200 through the passage 122B, and is heated by the refrigerant
to about 60.about.80.degree. C., and its relative humidity is lowered
(state T). The regeneration air having a lowered relative humidity
passes through the desiccant bed 103B to remove the moisture in
the desiccant bed (state U). The regeneration air which has passed
through the desiccant bed 103B flows into the heat exchanger 107
through the passage 112B, the four-way valve 105 and the passage
124A, and transfers heat to the regeneration air before it enters
into the high temperature heat source 210 of the heat pump device
200 to raise its temperature. The spent regeneration air which has
released its heat and has become cooler (state V) is discharged
to outside environment. Because the sensible heat of the spent regeneration
air after regenerating the desiccant is effectively utilized, this
embodiment system produces higher thermal efficiencies than the
first embodiment system.
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, switchable dual passages are provided to
alternately treat the process air and regeneration air through a
pair of desiccant members 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. 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. |