Abstrict A compact and energy efficient air conditioning system is operated
with a desiccant material having a high differential adsorption
capacity even at lower regeneration temperatures than those in the
conventional system. The desiccant assisted air conditioning system
comprises a process air path (A) for flowing process air to adsorb
moisture from the process air by a desiccant member, and a regeneration
air path (B) for flowing regeneration air heated by a heat source
to desorb moisture from the desiccant member (103). The desiccant
member is arranged so that the process air or the regeneration air
flows alternatingly through the desiccant member. The desiccant
member is arranged so that the process air or the regeneration air
flows alternatingly through the desiccant member. The desiccant
member comprises an organic polymer material, the organic polymer
material comprising an amphoteric ion exchange polymer having an
anion exchange group, a cation exchange group and bridging ligands,
thereby exhibiting a high differential adsorption capacity.
Claims What is claimed is:
1. A desiccant assisted air conditioning system comprising: a process
air path for flowing process air to adsorb moisture from said process
air by a desiccant member; and a regeneration air path for flowing
regeneration air heated by a heat source to desorb moisture from
said desiccant member, said desiccant member being arranged so that
said process air or said regeneration air flows alternatingly through
said desiccant member; wherein said desiccant member comprises a
desiccant material which is an organic polymer material, said organic
polymer material comprising an amphoteric ion exchange polymer having
an anion exchange group, a cation exchange group and bridging ligands,
thereby exhibiting a high differential adsorption capacity.
2. A system according to claim 1 wherein said organic polymer
material is obtained by reacting an acrylonitrile homopolymer or
copolymer with a hydrazine or hydrazine homologue to provide an
anion exchange group followed by hydrolyzing residual nitrile group
to provide a cation exchange group.
3. A system according to claim 1 wherein said organic polymer
material includes said anion exchange group at a concentration of
0.01.about.5.0 meq/g and said cation exchange group at a concentration
of 2.about.11 meq/g.
4. A system according to claim 1 wherein said desiccant material
is regenerated at a temperature of not more than 70.degree. C.
5. A system according to claim 4 wherein a heat pump is provided,
and dehumidified process air is cooled by a low-temperature heat
source of said heat pump, and pre-desiccant regeneration air is
heated with a high-temperature source of said heat pump.
6. A method for operating a desiccant assisted air conditioning
method comprising: flowing a process air through a process air path
to adsorb moisture from said process air by a desiccant member;
and flowing a regeneration air through a regeneration air path for
heating said regeneration air by a heat source and for desorbing
moisture from said desiccant member, said desiccant member being
arranged so that said process air or said regeneration air flows
alternatingly through said desiccant member; wherein said desiccant
member comprises a desiccant material which is an organic polymer
material, said organic polymer material comprising an amphoteric
ion exchange polymer having an anion exchange group, a cation exchange
group and bridging ligands, thereby exhibiting a high differential
adsorption capacity.
7. A method according to claim 6 wherein said organic polymer
material is obtained by reacting an acrylonitrile homopolymer or
copolymer with a hydrazine or hydrazine homologue to provide an
anion exchange group followed by hydrolyzing residual nitrile group
to provide a cation exchange group.
8. A method according to claim 6 wherein said organic polymer
material includes said anion exchange group at a concentration of
0.01.about.5.0 meq/g and said cation exchange group at a concentration
of 2.about.11 meq/g.
9. A method according to claim 6 wherein said desiccant material
is regenerated at a temperature of not more than 70.degree. C.
10. A method according to claim 9 wherein a heat pump is provided,
and dehumidified process air is cooled by a low-temperature heat
source of said heat pump, and pre-desiccant regeneration air is
heated with a high-temperature source of said heat pump.
Description TECHNICAL FIELD
The present invention relates in general to dehumidifying air conditioning
systems, and relates in particular to a desiccant assisted air conditioning
system to provide continuous processes of desiccant-assisted dehumidification
and desiccant-regeneration using a heat source.
BACKGROUND ART
FIG. 10 shows a conventional dehumidifying air conditioning system
having a process air path for dehumidifying air by passing the air
through a desiccant, and a regeneration air path for desorbing moisture
from the desiccant by passing heated air through the desiccant,
arranged in such a way to flow the process air and regeneration
air alternatingly through the desiccant. The system comprises: a
process air path A; a regeneration air path B; a desiccant wheel
103; two sensible heat exchangers 104 121; a heater 220; and a
humidifier 105. Process air is dehumidified in the desiccant wheel
103 and, in this process, is heated by the heat of adsorption of
moisture in the desiccant member, and is cooled next by passing
through a first heat exchanger 104 by exchanging heat with the regeneration
air. Process air is further cooled in the humidifier 105 before
being supplied to the conditioning space (room) supply air SA. In
the meantime, outside air (OA) serving as regeneration air is admitted
into the first sensible heat exchanger 104 which raises the temperature
of regeneration air by transferring heat from the dehumidified process
air, and the heated regeneration air is further heated by a heat
source 200 in the heating device 220 to lower its relative humidity,
and is passed through the desiccant wheel 103 to desorb the moisture
from the desiccant member. In the conventional system, sensible
heat portion in the post-regeneration regeneration air is recovered
by heat exchange with unheated regeneration air in the second sensible
heat exchanger 121 before exhausting the regeneration air to outside
(EX). This type of system is known as a desiccant-assisted air conditioning
system, and is an important practical technique to provide control
over conditioning space humidity.
Desiccant materials which can be used in such desiccant-assisted
air conditioning systems are known to include silica-gel and zeolite
(known as molecular sieve), which are classified as a modified zeolite
in Breuner type 1. It is said that those materials having an isothermal
separation factor in the range of 0.07.about.0.5 are most suitable
as a desiccant member which is used in those systems designed to
carry out desiccant regeneration by using some combustible gas as
heat source. U.S. Pat. No. 3844737 mentions zeolite as a desiccant
material in air conditioning systems using combustible gases for
heating regeneration air, but, no prior publications give any suggestions
regarding the suitable adsorption characteristics of zeolite. Although
lithium chloride has also been used as a moisture adsorbing material,
its use has gradually been discontinued because of deliquescence
tendency when exposed to high humidity to fall out from a rotating
frame of the desiccant wheel.
In air conditioning technologies based on combustible gas heating
of regeneration air, as mentioned above, regeneration temperature
is reported as 101.degree. C. (215.degree. F. ) or 143.degree. C.
(290.degree. F.). It is said that zeolite is suitable for regeneration
at such temperatures, and in particular, zeolite having an isothermal
separation factor R between 0.07.about.0.5 as exemplified by R=0.1
in FIG. 11 is most suitable. However, if other types of heating
sources are considered for desiccant regeneration, lower regeneration
temperatures (65.about.75.degree. C.) offer more available choices,
such as waste heat and solar heating. But, in such a case, zeolite
materials in Breuner type 1 class and having a separation factor
in the range of 0.07.about.0.5 are not always an optimum material
for desiccant. The reason will be explained with reference to FIG.
11.
FIG. 11 is an adsorption isotherm of conventional zeolite. When
outdoor air is used as regeneration air in a desiccant-assisted
air conditioning system, humidity ratio in summer is estimated to
be about 20.about.21 g/kg (g moisture/kg air) for design purposes.
When such an air is heated to a desiccant desorption temperature
of 110.degree. C. mentioned above, its relative humidity drops to
about 3.0%. On the other hand, relative humidity of process air
to be dehumidified can be estimated to be about 50% based on general
room conditions where dry-bulb temperature is 27.degree. C. and
wet-bulb temperature is 19.degree. C. as specified in JIS(Japanese
Industrial Standard)-C9612 for example. The desiccant member thus
alternatingly contacts process air and regeneration air, respectively,
at 50% and 3% relative humidity. Equilibrium moisture content in
zeolite in contact with regeneration air at 3% relative humidity
is found to be X=0.236 from FIG. 11 using a functional relation
X=P/(R+P-R.times.P) for a separation factor R=0.1 and P=0.030.
On the other hand, equilibrium moisture content in zeolite in contact
with process air exhausted from a room can be found, similarly,
to be X=0.910 for separation factor R=0.1 and P=0.5. Therefore,
in the case of heating the regeneration air to 101.degree. C. for
desorbing zeolite, the amount of moisture which can be adsorbed
by the desiccant member is 0.169 kg/kg, which is obtained by multiplying
the difference in the relative adsorbed amount (0.910-0.236=0.674)
with the maximum uptake 0.25 kg/kg (kg water per kg zeolite). If
a material such as silica-gel is used, whose characteristic adsorption
isotherm is linear (isothermal separation factor R=1), the difference
in desorption and adsorption is the same as the difference in the
relative humidity values, 0.500-0.030=0.470 and a corresponding
value drops to 0.140 kg/kg, which is obtained by multiplying the
maximum uptake (usually 0.3 kg/kg for silica-gel) with 0.470. Therefore,
zeolite is more effective in this case. This example shows that,
when the desorption temperature is as high as 101.degree. C. as
in the conventional air conditioning apparatus, the use of zeolite
is clearly more advantageous. However, when similar calculations
are performed for the range of desorption temperatures of 50.about.70.degree.
C. as desired in the present invention, superiority of zeolite is
not certain and the differential adsorption capacity (difference
in desorbed/adsorbed amount) is significantly decreased. This will
be explained in more detail below with reference to FIG. 12.
FIG. 12 shows the configuration of a desiccant-assisted air conditioning
system disclosed the inventor, comprised by a process air path for
dehumidifying and a regeneration air path for flowing air which
is first heated in a heating source before desorbing moisture from
the moisture-laden desiccant member 103 arranged in such a way
that regeneration air and process air alternatingly flow through
the desiccant member 103. Dehumidified process air is cooled in
a low-temperature heat source 240 of a heat pump, and pre-desiccant
regeneration air is heated in a high-temperature heat source 220
of the heat pump. FIG. 13 shows a psychrometric chart to show the
operation of the system shown in FIG. 12.
Accordingly, by cooling the dehumidified process air in the low-temperature
source 240 of the heat pump, the temperature of supply air SA (state
N) can be lowered below that of the room (state K) as shown in FIG.
13. Therefore the humidifier 105 used in the conventional system
shown in FIG. 10 becomes unnecessary so that dehumidified cooled
process air and supply air SA have the same humidity ratio, thus
providing a higher cooling effect than the conventional system.
Those skilled in the art know that, for summer air conditioning,
supply air is generally at less than 8 g/kg (moisture per kg of
air), therefore, by setting the humidity ratio of the supply air,
i.e., dehumidified process air at 7 g/kg, the process air changes
its state from the room state along an isenthalpic line until it
reaches 7 g/kg where a relative humidity is 20%, as shown in FIG.
13 (when the adsorption heat is high as in zeolite, relative humidity
of 20% is reached at a slightly higher humidity ratio value of 8
g/kg).
It is known by those skilled in the art that the relative humidity
of dehumidified process air is equal to the relative humidity of
regeneration air before regeneration (for example, refer to reference
material p23.about.25 of TC 3.5/short course seminar, US ASHRAE
Society Annual Meeting, 1997). Therefore, outdoor air can be heated
to a temperature to lower its relative humidity so as to be used
as regeneration air to regenerate the desiccant member.
In other words, humidity ratio in summer is generally about 15
g/kg, therefore, such an air, when heated to 50.degree. C. having
a 20% relative humidity, can be used as regeneration air. Humidity
ratio can reach a value of 20 g/kg on rare occasions, but even such
an air can be heated to 55.degree. C. and used for dehumidifying
the process air to less than 8 g/kg moisture. Therefore, it is desirable
for such an air conditioning system to have a desiccant material
which provides a high moisture removal capacity at regeneration
temperature of 50.about.70.degree. C., but the conventional zeolite
shows a low capacity for moisture content difference between its
absorption and desorption state. Thus, low capacity must be compensated
by increasing the mass of the desiccant. This will be explained
in more detail below.
When the regeneration air at humidity ratio of 15 g/kg is heated
to 50.degree. C., its relative humidity is about 20% (18.9% accurately).
Therefore, equilibrium moisture content of zeolite of separation
factor R=0.1 in contact with regeneration air is X=0.71 for P=0.2
when relative humidity is 20% as shown in the graph in FIG. 11.
On the other hand, equilibrium moisture content of zeolite in contact
with spent process air exhausted from the room is X=0.91 at P=0.5
as before. Therefore, by flowing regeneration air heated to 50.degree.
C., the desiccant can adsorb moisture of 0.05 kg/kg, obtained by
multiplying the differential adsorption capacity 0.20 (=0.91-0.71)
with the maximum uptake of 0.25 kg/kg for zeolite. Comparing this
value 0.05 with the previous value 0.169 kg/kg, gives a ratio as
1/3.4 which means that the size of the zeolite desiccant needs
to be 3.4 times larger.
FIG. 14 is a graph, calculated from the adsorption isotherm of
FIG. 11 showing the relationship between adsorption capacity of
zeolite and temperature of air in contact therewith for various
parametric values of the humidity ratio of the air. Point A is the
adsorption-start point where the moisture content of zeolite is
in equilibrium with process air, and points D50 and D70 are the
desorption- or regeneration-start points where the moisture content
of zeolite is in equilibrium with regeneration air at 50 and 70.degree.
C., respectively. This graph also shows that the differential adsorption
capacity is 0.05 and 0.11 kg/kg, respectively, for 50.degree. C.-regeneration
and 70.degree. C.-regeneration. These values confirm that the desiccant
size must be increased by 1.5.about.3.4 times the size of a desiccant
regenerated at higher temperatures.
On the other hand, if a material such as silica-gel is used, whose
adsorption isotherm is linear (separation factor R=1), the differential
adsorption capacity is 0.3 (=0.5-0.2) for 50.degree. C.-regeneration
(relative humidity 20%), similarly to the differential relative
humidity, so that, adsorbed amount is 0.09 kg/kg, obtained by multiplying
0.3 with the maximum uptake of 0.3 kg/kg for silica-gel. For 70.degree.
C.-regeneration (relative humidity 7.5%), the adsorbed amount is
0.127 kg/kg, obtained by multiplying the differential adsorption
capacity 0.425 (=0.5-0.075) with the maximum uptake of 0.3 kg/kg
for silica-gel. These values (0.09 0.127) are higher than those
for zeolite type 1 (0.05 0.11), but even in these cases, it is
clear that the desiccant size must be increased compared with the
high-temperature regeneration process which produces an adsorption
amount of 0.14 kg/kg.
It can be seen, therefore, that the conventional desiccant technology
is not adaptable to low-temperature regeneration (50.about.70.degree.
C.), and the necessity for a larger desiccant leads to a large air
conditioning system and high operating cost.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a compact and
energy efficient air conditioning system that is operated with a
desiccant material having a high differential adsorption capacity
even at lower regeneration temperatures than those in the conventional
system.
A desiccant assisted air conditioning system comprises: a process
air path for flowing process air to adsorb moisture from the process
air by a desiccant member; and a regeneration air path for flowing
regeneration air heated by a heat source to desorb moisture from
the desiccant member, the desiccant member being arranged so that
the process air or the regeneration air flows alternatingly through
the desiccant member; wherein the desiccant member comprises an
organic polymer material, the organic polymer material comprising
an amphoteric ion exchange polymer having an anion exchange group,
a cation exchange group and bridging ligands, thereby exhibiting
a high differential adsorption capacity.
An air conditioning system using such a desiccant material permitting
regeneration at relatively low temperatures (50.about.70.degree.
C.) enables to provide a compact and energy efficient air conditioning
system.
The organic polymer material is obtained by reacting an acrylonitrile
homopolymer or copolymer with a hydrazine or hydrazine homologue
to provide an anion exchange group followed by hydrolyzing residual
nitrile group to provide a cation exchange group.
The organic polymer material thus produced can be used as a desiccant
material in the air conditioning system that is energy conserving
and compact because the desiccant medium can be regenerated at 50.about.70.degree.
C.
The organic polymer material may include the anion exchange group
at a concentration of 0.01.about.5.0 meq/g and the cation exchange
group at a concentration of 2.about.11 meq/g.
The desiccant medium having the properties so defined exhibits
a high deferential moisture adsorption capacity, to enable a compact
high energy efficiency system.
The desiccant material may be regenerated at a temperature of not
more than 70.degree. C.
Because the desiccant medium allows regeneration at low temperatures,
heat pump can be operated at relatively low temperatures, thereby
enabling to provide a compact and high efficiency air conditioning
system.
Dehumidified process air is cooled by a low-temperature heat source
of a heat pump, and pre-desiccant regeneration air is heated with
a high-temperature source of the heat pump.
Accordingly, regeneration air is heated by recycling the heat recovered
from dehumidified process air, thereby enabling to maximize utilization
of output heat from the heat pump, and also enabling to decrease
the temperature lift required for the heat pump, thereby providing
a compact and energy efficient air conditioning system.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph of adsorption isotherm of the high adsorption
polymeric material used as a desiccant in a first embodiment of
the humidity-controlled air conditioning system of the present invention;
FIG. 2 is a graph of moisture adsorption and dry bulb temperature
in contact with the desiccant with parametric absolute humidity
(humidity ratio) of air;
FIG. 3 is a schematic diagram of a second embodiment of the air-conditioning
system of the present invention;
FIG. 4 is a psychrometric chart showing the operational states
in the system shown in FIG. 3;
FIG. 5 is a schematic diagram of a third embodiment of the air-conditioning
system of the present invention;
FIG. 6 is a psychrometric chart showing the operational states
in the system shown in FIG. 5;
FIG. 7 is a graph showing an adsorption isotherm of the high absorption
polymeric material;
FIG. 8 is a schematic diagram of a fourth embodiment of the air-conditioning
system of the present invention;
FIG. 9 is a psychrometric chart showing the operational states
in the system shown in FIG. 8;
FIG. 10 is a schematic diagram of a conventional air conditioning
system;
FIG. 11 is a graph of adsorption isotherm for zeolite;
FIG. 12 is a schematic diagram of another conventional air conditioning
system;
FIG. 13 is a psychrometric chart showing the operational states
in the system shown in FIG. 12; and
FIG. 14 is a graph showing the relation between air contacting
the desiccant and adsorption capacity of zeolite desiccant according
to adsorption isotherm shown in FIG. 11.
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments will be presented in the following with reference
to the drawings.
Preferred embodiments will be explained in the following.
A first embodiment of the humidity-controlled air conditioning
system (such as the one shown in FIG. 12) uses a high adsorption
capacity desiccant material, made from a high polymer material which
is an amphoteric ion exchange polymer having both anion exchange
group and cation exchange group, and bridging legands, produced
by reacting an acrylonitrile homopolymer or copolymer with a hydrazine
or hydrazine homologue to provide the anion exchange group and then
hydrolyzing the residual nitrile group to provide the cation exchange
group. The desiccant material thus produced contains 0.01.about.5.0
meq/g of the anion exchange group and 2.about.11 meq/g of the cation
exchange group. This material was pulverized and the adsorption
characteristics of the powdered material were examined as follows:
FIG. 1 shows a graph of measured adsorption isotherm data of this
high adsorption polymer, in terms of relative humidity on the horizontal
axis and relative adsorption on the vertical axis defined by a ratio
of the measured absorption W to adsorption W.sub.0 at 100% desiccant
humidity (maximum uptake). The separation factor R for this material
is linear (R=1.0) as in silica-gel, but its maximum uptake value
0.98 kg/kg is larger than that for silica-gel.
FIG. 2 shows a relation of air temperature in contact with the
desiccant material and the adsorption value at various values of
humidity ratio of air as a parameter. Point A is the adsorption-start
point for the desiccant material, which is in equilibrium with the
indoor air. Points D50 and D70 refer to desorption-start points
for the dry desiccant materials regenerated at 50 and 70.degree.
C., respectively, which are in equilibrium with the regeneration
air. From FIG. 2 it can be seen that the differential adsorption
capacity of the material is 0.29 kg of moisture per kg of desiccant
material for 50.degree. C.-regeneration and 0.42 kg/kg for 70.degree.
C.-regeneration. The value for 50.degree. C.-regeneration is 1.7
times the value obtained by zeolite regenerated at conventional
regeneration temperature of 100.degree. C., and is 2.1 times the
value for silica-gel. This means that about 60% by weight of the
present material regenerated at lower temperature produce the same
degree of dehumidification as zeolite regenerated at 100.degree.
C.
Next, the operation of the present desiccant assisted air conditioning
system shown in FIG. 12 will be explained using the psychrometric
chart shown in FIG. 13.
Process air (state K) flows through the desiccant wheel 103 which
adsorbs moisture from the process air (state L), and in flowing
through the first sensible heat exchanger 104 transfers heat to
the regeneration air (state Q) and is cooled (state M), and is further
cooled (state N) in the low-temperature heat source 240 of the heat
pump, and returns to the conditioning space 101 as supply air SA.
In the meantime, regeneration air is admitted from outdoors (state
Q) into the first sensible heat exchanger 104 to receive heat from
the process air (state L) thereby raising its temperature (state
R), and enters into the second sensible heat exchanger 121 to receive
heat from the post-desiccant regeneration air (state U) thereby
raising its temperature (state S), and is further heated in the
high-temperature heat source 220 of the heat pump to raise its temperature
(state T), and is then flows through the desiccant wheel 103 to
desorb the moisture thereby regenerating the desiccant. Post-desiccant
regeneration air (state U) transfers heat (state V) in the second
sensible heat exchanger 121 to the regeneration air exiting from
the first sensible heat exchanger 104 and is discarded as exhaust.
Accordingly, the desiccant assisted air conditioning system operates
by generating a differential humidity ratio .DELTA.X and a differential
enthalpy .DELTA.Q between the indoor air (state K) and the supply
air (state N) to provide a dehumidification and cooling effect of
the conditioning space. The driving energy for the system is afforded
by the differential heat obtained by subtracting the afore-mentioned
heat .DELTA.Q from the heat input .DELTA.G to heat the regeneration
air so that desiccant regeneration is carried out utilizing the
waste heat generated in a sensible heat treatment process from state
M to state N, thereby providing an excellent energy efficiency for
the system.
In this system, because the supply air temperature (state N) can
be made lower than the indoor air temperature (state K), there is
no need to cool the air using the humidifier 105. On the other hand,
in the conventional air conditioning systems, because it removes
sensible heat from the process air, liquid water is added to the
process air after it is dehumidified to cool the process air, therefore,
it is necessary to remove more moisture than is truly required based
on the difference in the humidity values of supply air and room
air. As can be seen in FIG. 12 humidifier is not used in the present
system, and the net moisture to be removed by the desiccant is low,
and therefore, the same degree of dehumidifying and cooling can
be achieved by using a smaller amount of desiccant member relative
to the amount required by the conventional systems.
Accordingly, in the present system, high capacity desorption can
be obtained even at low regeneration temperatures, and a small amount
of desiccant is sufficient to remove a large amount of moisture,
thereby enabling to use a smaller desiccant wheel. Also, desorption
temperature for regeneration air (state T) can be selected in the
range of 50.about.55.degree. C., and therefore, the operating temperature
(condensing temperature) of the high-temperature heat source 220
of the heat pump can be lowered, and the power required to operate
the heat pump can also be lowered. Present system is overall much
more energy conserving, and is more compact compared with the conventional
systems.
FIG. 3 shows the system configuration in a second embodiment. The
air conditioning system shown in FIG. 3 is a hybrid system combining
a desiccant and a heat pump as in FIG. 12 but without the first
sensible heat exchanger 104 and the desiccant wheel 103 uses the
high absorption polymeric material as in the first embodiment. In
this system, process air and regeneration air do not exchange heat
so that the process air is supplied at higher temperatures. Therefore,
this type of system is most suitable when the use is primarily dehumidification
involving low sensible heat ratios. The operation of this system
will be explained with reference to the psychrometric chart shown
in FIG. 4 related to the system shown in FIG. 3.
Process air (state K) flows through the desiccant wheel 103 which
adsorbs moisture (state L), and is cooled (state M) in the low-temperature
heat source 240 of the heat pump and returns to the conditioning
space 101. In the meantime, regeneration air, which is outdoor air
(state Q), enters into the sensible heat exchanger 121 to receive
heat from the post-desiccant regeneration air (state U) thereby
raising its temperature (state S), and is further heated in the
high-temperature heat source 220 of the heat pump to raise its temperature
(state T), and then flows through the desiccant wheel 103 to desorb
the moisture. Post-desiccant regeneration air (state U) transfers
heat (state V) to the regeneration air in the sensible heat exchanger
121 thereby returning heat to the system and is discarded as exhaust.
Accordingly, the desiccant assisted air conditioning system performs
its functions by generating a differential humidity ratio .DELTA.X
and a differential enthalpy .DELTA.Q between the indoor air (state
K) and the supply air (state M). Compared with the first embodiment,
the temperature of supply air is higher and is close to room air
temperature, and therefore, it is most suitable when the conditioning
load is primarily humidity lowering (latent heat load). If the supply
air temperature is adjusted to 27.degree. C. which is about the
same as room air temperature, the temperature difference between
regeneration air at 50.degree. C. and supply air is only 23.degree.
C., so that the temperature lift, i.e., temperature difference between
the low- and high-temperature heat sources of the heat pump will
be 33.degree. C. by adding 10.degree. C. to 23.degree. C. Compared
with the conventional vapor compression type air conditioning systems,
the heat pump can be operated at a much lower temperature lift,
thereby enabling to conserve energy. Because a dew drainage is not
needed, the facility becomes simpler, and as in the first embodiment
system, small amount of desiccant member is needed to treat a large
amount of moisture so that the desiccant wheel can be made compact.
Therefore, the overall system exhibits superior energy efficiency
and a compact arrangement is effective for equivalent performance.
FIG. 5 shows the system configuration in a third embodiment. The
air conditioning system shown in FIG. 5 is also a hybrid system
similar to the one shown in FIG. 3 but the difference is that the
process air is a mixture of outdoor air and indoor return air while
the regeneration air is a mixture of indoor exhaust air and outdoor
air. For this reason, in addition to the system configuration shown
in FIG. 3 a passage 161 and a blower 160 are provided between a
process air passage 107 and an outdoor air admittance passage 124
for mixing outdoor air with return room air, and a passage 162 is
provided between a regeneration air passage 124 and a return air
passage 107 for mixing the return room air with outdoor air. In
such a system, because the humidity ratio of the process air at
the adsorption-start point of the desiccant is higher than that
specified in the Japanese Industrial Standards (JIS) for indoor
comfort, regeneration air must be heated to a higher temperature
in order to maintain the humidity at 7 g/kg as in the previous embodiment;
however, the same benefits as before are accrued using the desiccant
member of the present invention. In the following, the operation
of the system based on the high absorption polymeric material will
be explained with reference to the psychrometric chart shown in
FIG. 6 and the relation of air temperature and moisture adsorption
at varying humidity ratio levels shown in FIG. 7.
Mixed process air (state F) comprised by outdoor air (state Q)
and indoor return air (state K) flows through the desiccant wheel
103 which adsorbs moisture (state L), and is further cooled (state
M) in the low-temperature heat source 240 of the heat pump and returns
to the conditioning space 101. In the meantime, regeneration air
is also a mixture (state G) comprised by outdoor air (state Q) and
return indoor air (state K) enters into the sensible heat exchanger
121 to receive heat from the post-desiccant regeneration air (state
U), thereby raising its temperature (state S), and is further heated
in the high-temperature heat source 220 of the heat pump to raise
the temperature (state T), and flows through the desiccant wheel
103 to desorb the moisture. Post-desiccant regeneration air (state
U) transfers heat to the regeneration air (state V) in the sensible
heat exchanger 121 thereby returning heat to the system and is
discarded as exhaust. Accordingly, the desiccant assisted air conditioning
system performs its functions by generating a differential humidity
ratio .DELTA.X and a differential enthalpy .DELTA.Q between the
indoor air (state K) and the supply air (state M).
Compared with the second embodiment system, this system based on
mixing indoor air with outdoor air is most suitable for maintaining
a certain level of comfort in the indoor environment. Assuming that,
on a typical mid-summer day, indoor air is at 27.degree. C. with
a 50% relative humidity (RH) and outdoor is at 33.degree. C. with
a 63% RH, then, pre-desiccant process air is mixed with outdoor
air having a humidity ratio of 20 g/kg to become process air at
a dry-bulb temperature of 29.degree. C. and a humidity ratio of
13 g/kg as shown in FIG. 6. After being dehumidified by adsorption
in the desiccant member, process air moves along the isenthalpic
line to a humidity ratio of 7 g/kg at state L having a relative
humidity of about 10% (more accurately 11%). Therefore, the temperature
of regeneration air for desorption-start is 65.degree. C., as described
before, according to the intersection point of the relative humidity
line at 10% and the humidity ratio line at 17 g/kg. On the other
hand, pre-desiccant regeneration air is at dry bulb temperature
of 31.degree. C. and a humidity ratio of 17 g/kg because of mixing
with return air having a humidity ratio of 10 g/kg. Therefore, the
desiccant condition at the desorption-start point (state T) is at
a dry-bulb temperature of 65.degree. C. and a humidity ratio of
17 g/kg. The differential adsorption capacity of the desiccant member,
given by the difference between the adsorption-start state F (dry-bulb
temperature at 29.degree. C. and humidity ratio of 13 g/kg) and
the regeneration-start state T (dry-bulb temperature at 31.degree.
C. and humidity ratio at 17 g/kg) is 0.44 g/kg as indicated in FIG.
7 for this material. The moisture adsorption capacity is as large
as what was shown in FIG. 2. The operation of the various devices
for process air and regeneration air is the same as in the second
embodiment, and will not be repeated.
As demonstrated in this embodiment, even when it is necessary to
raise the regeneration temperature slightly about 65.degree. C.
because of mixing with outdoor air, differential adsorption capacity
of the material remains high so that a small amount of material
is needed to perform an equal degree of dehumidification, thereby
enabling to provide a compact desiccant wheel. Also, the temperature
of regeneration air can be set low (state T), so that the operating
temperature (condensation) of the high temperature heat source 220
of the heat pump is lowered, thereby lowering the drive power for
the compressor of the heat pump. The overall system is thus energy
efficient and compact.
FIG. 8 shows the system configuration in a fourth embodiment of
the invention. This system is similar to the so-called desiccant-assisted
air conditioning system without the heat pump shown in FIG. 10.
The difference is that dehumidified process air is cooled in the
heat exchanger 104 by means of heat exchange with the outdoor air
which is humidified in a humidifier 105 thereby eliminating heat
exchange between process air and regeneration air. In the conventional
systems, regeneration air is first humidified to lower its dry-bulb
temperature and is then subjected to heat exchange with process
air, but in such a process, humidity ratio of the regeneration air
becomes elevated, and in order to attain the same level of relative
humidity in the regeneration air as in the dehumidified process
air, it is necessary to heat the regeneration air to a high temperature.
But the present system avoid this difficulty by providing a separate
cooling path for cooling the process air. The operation of the system
shown in FIG. 8 will be explained using a psychrometric chart given
in FIG. 9.
Process air (state K) flows through the desiccant wheel 103 and
is removed of its moisture (state L), and is further cooled (state
M) in the cooler 104 by the humidified outdoor air and returns to
the conditioning space 101. In the meantime, regeneration air is
admitted from outdoors (state Q) and enters into the sensible heat
exchanger 121 to receive heat from the post-desiccant regeneration
air (state U) thereby raising its temperature (state S), and is
further heated in the heater 220 (state T), and then flows through
the desiccant wheel 103 to desorb the moisture. Post-desiccant regeneration
air (state U) transfers heat, in the sensible heat exchanger 121
to the incoming regeneration air (state Q), and the cooled regeneration
gas (state V) is discarded as exhaust. In a separate thermal circuit,
cooling air which is outdoor air (state Q) is admitted into the
humidifier 105 so that its temperature is lowered (state D) by
the heat of evaporation of water, and then it is mixed in the heat
exchanger 104 to remove heat from the process air (state L) to produce
supply air (state M), and the warmed cooling air (state E) is discarded
as exhaust.
Accordingly, a humidity ratio difference DX is generated between
room air (state K) and supply air (state M) to provide a dehumidifying
effect. Compared with conventional systems, because the supply air
temperature is lower and is closer to the room air temperature,
sensible heat load of the room air is not increased, so that the
system is suitable when a conditioning load requires primarily dehumidification
(latent heat load). Outdoor summer temperature is generally around
28.degree. C., which is not much different than indoor air temperature,
so that room dehumidification can be achieved without increasing
the sensible heat load by using the present system in which no humidifier
is provided in the process air passage. Therefore, latent heat load
can be processed by using low temperature heat source at 50.about.70.degree.
C. such as waste heat or solar heating instead of using vapor compression
cycle type cooling system. As in the first embodiment system, a
small amount of desiccant member is sufficient to process a large
amount of moisture, thereby providing a compact desiccant wheel.
Therefore, compared with the conventional system, the present system
offers superior energy efficiency with a compact air conditioning
system.
INDUSTRIAL APPLICABILITY
The present invention is advantageous as an air conditioning system
used in general dwelling houses or larger buildings used as a supermarket
or business offices. |