Abstrict A hybrid air conditioning system which simultaneously dehumidifies
and cools air using standard vapor-compression equipment and aqueous
solutions of liquid desiccant. By using a circulating liquid desiccant
and an adiabatic humidifier, a more efficient refrigerant cycle
is utilized. Moreover, conditioned air can be delivered at the same
temperature and absolute humidity as conventional vapor-compression
systems but without overworking the compressor.
Claims What is claimed is:
1. A hybrid air conditioning system comprising:
a refrigerant;
a liquid desiccant;
an evaporator for receiving liquid desiccant, refrigerant, and
warm moist air, and for absorbing moisture to the liquid desiccant
and expelling the liquid desiccant, the refrigerant, and cool dry
air:
a condenser for receiving liquid desiccant, refrigerant, and dry
air, and for desorbing moisture from the liquid desiccant and expelling
hot moist air, liquid desiccant, and refrigerant;
each of said evaporator and condenser having a heat and mass exchanger
comprising:
(I) a plurality of horizontally extending refrigerant tubes extending
the length of said condenser or evaporator through which refrigerant
is circulated;
(II) a plurality of substantially planar fins extending the height
of said condenser or evaporator, the planar surface of each fin
being perpendicularly traversed by said plurality of refrigerant
tubes;
(III) a horizontal air flow path extending perpendicular to said
horizontally extending refrigerant tubes and along the planar surface
of each said planar fin;
(IV) a distribution media configured above said refrigerant tubes
and said fins for distributing said liquid desiccant vertically
down and across the surface of said fins;
(V) a sump configured below said refrigerant tubes and said fins
for receiving downward flowing liquid desiccant;
means for circulating said refrigerant within the horizontally
extending refrigerant tubes and between said condenser and evaporator;
and
means for pumping said liquid desiccant within said evaporator
and within said condenser and between the sump of said evaporator
and the sump of said condenser.
2. The hybrid air conditioning system of claim 1 wherein said
distribution media configured to gravitationally deliver liquid
desiccant downward and perpendicular to said horizontal air flow
path.
3. The hybrid air conditioning system of claim 1 wherein said
refrigerant is circulated between said evaporator and said condenser
by a compressor.
4. The hybrid air conditioning system of claim 1 wherein liquid
desiccant in the sump of said evaporator is partially distributed
to the distribution media of said evaporator and partially distributed
to the sump of said condenser.
5. The hybrid air conditioning system of claim 1 wherein liquid
desiccant in the sump of said condenser is partially distributed
to the distribution media of said condenser and partially distributed
to the sump of said evaporator.
6. The hybrid air conditioning system of claim 1 wherein said
refrigerant tubes and planar fins constructed of corrosion resistant
materials with acceptable heat transfer characteristics.
7. A hybrid air conditioning system comprising:
a refrigerant;
a liquid desiccant;
an evaporator for receiving liquid desiccant, refrigerant, and
warm moist air, and for expelling the liquid desiccant, refrigerant,
and cool dry air, said evaporator including a first heat and mass
exchanger;
first entrainment separator means for capturing liquid desiccant
suspended in the cool dry air expelled from said evaporator;
a condenser for receiving liquid desiccant, refrigerant, and dry
air, and for expelling liquid desiccant, refrigerant, and hot moist
air, said condenser including a second heat and mass exchanger;
second entrainment separator means for capturing liquid desiccant
suspending in the hot moist air expelled from said condenser;
evaporator blower means for drawing warm moist air into one end
of said evaporator to contact with said first heat and mass exchanger
and for drawing dry cool air from opposite end of said evaporator;
condenser blower means for drawing dry air into one end of said
condenser to contact with said second heat and mass exchanger and
for drawing hot moist air from an opposite end of said condenser;
a first and second sump for collecting liquid desiccant captured
by said first and second entrainment separator means respectively;
a distribution means for distributing liquid desiccants down and
across the surfaces of said first and second heat exchangers whereby
said liquid desiccant is collected in first and second sumps, respectively;
means for circulating said refrigerant between said evaporator
and condenser; and
means for pumping said desiccant within and between said evaporator
and condenser.
8. The hybrid air conditioning system of claim 7 wherein said
evaporator blower means comprises:
an evaporator housing defining a primary air flow path through
said evaporator from a first opening placed at one side of said
evaporator and through a second opening placed at the opposite side
of said evaporator, said warm moist air entering said first orifice
and said cool dry air exiting said second opening;
a fan mechanism placed within said primary air flow path configured
near the second opening, said first entrainment separator means
being placed within said air flow path between said second opening
and said fan mechanism.
9. The hybrid air conditioning system of claim 7 wherein said
condenser blower means comprises:
a condenser housing defining a secondary air flow path through
said condenser from a first opening placed at one side of said condenser
to a second opening placed at the opposite side of said condenser,
said dry air entering said first opening and said hot moist air
exiting said second opening;
a fan mechanism placed within said air flow path configured near
the second opening, said second entrainment separator means being
placed within said air flow path between said second opening and
said fan mechanism.
10. A hybrid air conditioning system comprising:
a refrigerant;
a liquid desiccant;
an evaporator for receiving liquid desiccant, refrigerant, and
warm moist air, and for expelling liquid desiccant, refrigerant,
and cool dry air;
an evaporator housing having a first and second opening defining
a horizontal evaporator air flow path through said evaporator;
a first fan mechanism placed within said evaporator air flow path
near said second opening for horizontally drawing warm moist air
into the evaporator at said first opening and for horizontally drawing
cool dry air from the evaporator at said second opening;
a first entrainment separator configured within said evaporator
air flow path near said second opening, said first entrainment separator
having means for separating liquid desiccant from air within said
evaporator air flow path;
a humidifier configured within said evaporator air flow path between
said first entrainment separator and said first fan mechanism, said
humidifier having means for adding moisture to air within the horizontal
evaporator air flow path;
a condenser for receiving liquid desiccant, refrigerant, and dry
air, and for expelling liquid desiccant, refrigerant, and hot moist
air;
a condenser housing having a first and second opening defining
a horizontal condenser air flow path through said condenser;
a second fan mechanism placed within said condenser air flow path
near said second opening for horizontally drawing dry air into the
condenser at said first opening and for horizontally drawing hot
moist air from the condenser at said second opening;
a second entrainment separator configured within said condenser
air flow path near said condenser, said second entrainment separator
having means for separating liquid desiccant from air within said
condenser air flow path;
each of said evaporator and condenser having a heat and mass exchanger
comprising:
(I) a plurality of horizontally extending refrigerant tubes extending
the length of said condenser or evaporator through which refrigerant
is circulated;
(II) a plurality of substantially planar fins extending the height
of said condenser or evaporator, the planar surface of each fin
being perpendicularly traversed by said plurality of refrigerant
tubes;
(III) a horizontal air flow path extending perpendicular to said
horizontally extending refrigerant tubes and along the planar surface
of each said planar fin;
(IV) a distribution media configured above said refrigerant tubes
and said fins for distributing said liquid desiccant vertically
down and across the surface of said fins;
(V) a sump configured below said refrigerant tubes and said fins
for receiving downward flowing liquid desiccant;
means for circulating said refrigerant within the horizontally
extending refrigerant tubes and between said condenser and evaporator;
and
means for pumping said liquid desiccant within said evaporator
and within said condenser and between the sump of said evaporator
and the sump of said condenser.
11. The hybrid system of claim 10 said humidifier comprising:
a humidifying media through which water is distributed;
water distribution means for distributing water to a top of said
humidifying media;
a water sump for collecting water runoff from the bottom of said
humidifying media;
a pumping mechanism configured to deliver water from said water
sump to said water distribution means.
12. The hybrid system of claim 11 wherein said humidifying media
is constructed of an air and water porous material.
13. A process for converting warm moist air into cool dry air comprising
the steps of:
providing compressed and expanded refrigerant;
providing absorbing, concentrated liquid desiccant and desorbing,
diluted liquid desiccant;
passing air in contact with said absorbing, concentrated liquid
desiccant and in simultaneous thermal contact with said expanded
refrigerant to produce cool dry air, desorbing, diluted liquid desiccant
and warm expanded refrigerant;
passing air in contact with said desorbing, diluted liquid desiccant
and in simultaneous thermal contact with said compressed refrigerant
to produce warm moist air, absorbing, concentrated liquid desiccant
and cooled compressed refrigerant;
circulative said absorbing, concentrated and desorbing, diluted
liquid desiccants;
compressing said expanded refrigerant to produce said compressed
refrigerant;
expanding said compressed refrigerant to produced said expanded
refrigerant; and
selectively humidifying said cool dry air.
Description BACKGROUND OF THE INVENTION
This invention relates to a vapor-compression air conditioning
system embodying a liquid desiccant for simultaneously cooling and
dehumidifying conditioned air.
Liquid desiccant system can provide cooling where no active cooling
is available by drying the air to a level below that required for
comfort conditions, exchanging heat with the ambient environment,
and then injecting moisture into the system. However, desiccant
systems requires low ambient wet bulb temperatures to produce the
requisite cooling. In contrast, vapor-compression systems must actively
cool the air below the dew point of the air entering the evaporator
in order to dehumidify the air by condensation. The vapor-compression
system thereby requires that evaporator temperature be driven to
a level much lower than required to achieve sensible cooling.
Hybrid vapor-compression, liquid desiccant systems combine the
benefit of both desiccant systems with vapor-compression systems.
Hybrid systems combine active, sensible cooling inherent in vapor-compression
systems with passive, latent cooling inherent in desiccant dehumidification
systems. The hybrid system need not be supercooled in order to remove
moisture from the system. Consequently, energy is not wasted over-conditioning
the air because moisture is sorbed rather than being condensed from
the air being conditioned.
Hybrid vapor-compression, liquid desiccant systems operate by sensibly
cooling the air and sorbing the moisture from the air. Sensible
cooling occurs by circulating compressed and expanded refrigerant
between an evaporator and condenser found in a standard vapor-compression
system. Dehumidification occurs by contacting air with a desiccant
on mass exchange surfaces. The mass exchange surfaces are sprayed
with a liquid desiccant as outdoor air, air returning from the conditioned
space, or a mixture of both, are drawn or blown through the mass
exchange surfaces. The mass exchange surfaces described in prior
art are separated from the heat exchange surfaces of the vapor-compression
system. Conventional mass exchange surfaces often require a separate
heat exchange surface for pre-cooling or pre-heating desiccants
prior to being sprayed into the mass exchanger. The problems associated
with separate heat and mass transfer surfaces are increased costs
required to purchase separate heat and mass exchangers and reduced
thermal and mass transfer efficiencies.
In the dehumidification process, moisture is sorbed from conditioned
air by spraying and cooling a desiccant contacting the air in a
sorbing mass exchanger or sorber. Water is sorbed in direct contact
with sprayed droplets of desiccant entrained with air or on falling
films of desiccant covering part or all of the mass exchange surface
of the sorber. Conventional spraying techniques are inefficient
methods for dehumidifying air because spraying creates an adiabatic
sorbing process which increases the temperature of the sorbent,
thereby reducing mass transfer. Thus, conventional spraying means
require cooler exchange surfaces and produce a less efficient system
because cooling is required to remove the heat of condensation,
the heat of solution, and the sensible heat transferred from the
air being conditioned. Conventional hybrid system waste energy by
also having to transfer heat by heat exchange means external to
the heat exchanger surfaces of the vapor-compressor system, or by
circulating the desiccant through the heat exchange surfaces of
the vapor-compression system.
During heat exchange, the desiccant solution is diluted with water
and falls by gravity to a sump or reservoir placed within or below
the sorber. To maintain a dehumidification process, the diluted
desiccant must be desorbed, i.e., regenerated. Regeneration accomplished
by spraying and heating the diluted desiccant in contact with air
expelled from a desorbing mass exchanger or desorber. Consequently,
a portion of the diluted desiccant in the sump of the sorber is
pumped to the desorber for concentration. Water is desorbed from
the sprayed droplets of desiccant entrained with air or by falling
films of desiccant covering part or all of the mass exchanger surfaces
of the desorber. Heating is required to provide the heat of vaporization
necessary to evaporate water from the desiccant solution and to
heat the air contacting desiccant solution. The heat is provided
by a primary energy source such as natural gas or electricity, or
a renewable energy source such as solar, waste heat or any combination
of these sources. When waste heat from the vapor-compression system
is reclaimed, the heat is transferred by heat exchanger means external
to the heat exchange surfaces of the vapor-compression system, or
by circulating the desiccant throughout the heat exchange surfaces
of the vapor-compression system. The desiccant solution is concentrated
during this process and falls by gravity to a sump within or below
the desorber. Continuous dehumidification is facilitated by pumping
the same mass flow rate of desiccant from the sump of the desorber
to the sorber as was sent from the sump of the sorber to the desorber.
Hybrid vapor-compression liquid desiccant systems that reclaim
waste heat for partial or full generation of the desiccant are more
efficient systems than those that use primary energy or alternative
energy for regeneration. Furthermore, hybrid vapor-compression liquid
desiccant systems that are configured for low-temperature regeneration
are more efficient than those systems that regenerate at higher
temperatures. Conventional hybrid systems incorporating spray delivery
means require higher regeneration temperatures, thereby reducing
thermal efficiency of the system. Moreover, conventional hybrid
systems which do not combine heat and mass exchange surfaces on
a single surface are less efficient and require more operation energy.
SUMMARY OF THE INVENTION
The present invention simultaneously dehumidifies and cools air,
using standard vapor-compression equipment and aqueous solutions
of liquid desiccants. The invention is a hybrid air-conditioning
system embodying a standard compressor, evaporator, condenser, and
refrigerant. In addition, liquid desiccant and refrigerant are simultaneously
circulated between the evaporator and condenser for cooling and
dehumidifying air forced therein. The evaporator and condenser each
having a plurality of tubes for receiving circulated refrigerant,
and a distribution media for receiving liquid sorbent. Liquid sorbent
or desiccant is gravitationally distributed over planar surfaces
of fins configured perpendicular to the refrigerant tubes for contact
with air forced along the surface of the planar fins.
In operation, warm moist air from, for example a space to be air
conditioned, is circulated by a blower through the evaporator. Simultaneously,
liquid sorbent and expanded, cooled refrigerant act as dehumidification
and cooling agents which convert the warm moist air drawn into the
evaporator resulting in cooled dry air expelled back into the conditioned
space. The liquid desiccant becomes diluted with water during dehumidification
and must be reconcentrated. To accomplish this, a portion of the
diluted desiccant is routed through the condenser, whereby thermal
heat from the condenser reconcentrates the liquid desiccant which
is then recirculated back through the evaporator. The condenser
is naturally heated by compressed, hot refrigerant entering the
condenser wherein thermal heat cast from the condenser desorbes
moisture from the liquid desiccant and expels the moisture from
the system via warm moist air exiting the condenser.
The present invention uses aqueous solutions of glycol or brine
as the liquid desiccant. Although any form of desiccant solution
can be used as long as it can sorb and desorb moisture from the
conditioned air without causing undue corrosion to the conditioning
equipment. As the liquid desiccant circulates between the cooled
evaporator and hot condenser, the chosen desiccant transports thermal
energy and moisture and transfers that energy and moisture throughout
the hybrid system. The mass transfer characteristics of the liquid
desiccant helps maintain a more energy-efficient system. By sorbing
rather than condensing moisture from air, the evaporator does not
have to be maintained at a temperature below the dew point temperature
of the air delivered. Therefore, the temperature of the evaporator
can be raised to improve the operating efficiency of the hybrid
system. Furthermore, the moisture sorbed by the desiccant solution
is circulated to the condenser where it evaporates on contact with
a hot condenser causing the condenser to cool. Since the evaporator
temperature is raised and the condenser temperature is lowered during
operation, higher compressor capacities and coefficients or performance
result. The increased efficiencies is a direct product of the circulating
diluted/concentrated liquid desiccant. Because of the circulating
liquid desiccant, the present invention operates more efficiently
and can use down-sized conventional vapor-compression equipment.
Along with smaller compressors, and in some cases smaller evaporators
and condensers, comes increased efficiency. Finally, because the
present system uses biostatic liquid desiccants, the humidity of
the conditioned space can be lowered while mitigating the microbial
contamination of the air-conditioned space.
Although the present invention is intended to be used as a cooling
and dehumidifying air-conditioner, this invention can also be operated
with an adiabatic humidifier, adding moisture while cooling the
air. During humidification periods, the air provided can be adiabatically
saturated and delivered at the same temperature and relative humidity
as that obtained from a conventional vapor-compression system. A
saturator or humidifier is provided within the air flow path of
the evaporator, enabling the consumer to obtain more dehumidification
or more cooling by simply flipping a switch. Therefore, the consumer
can selectively choose either (1) dehumidification with cooling
by enabling the hybrid system without the saturator, or (2) cooling
and adiabatic humidification by enabling the hybrid system with
the saturator. Because the temperature as well as the humidity level
can be selectively controlled by the consumer, it is anticipated
that homes in which the present invention are installed will be
more comfortable.
Further objects, features, and advantages of the present invention
will be apparent from the following detailed description when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a hybrid vapor-compression/liquid desiccant air-conditioning
system of the present invention.
FIG. 2 is a cut-away view of a heat and mass exchanger apparatus
housed within a condenser or evaporator of the present invention.
FIG. 3 is a graph of dry bulb temperature versus absolute and relative
humidity showing a vapor-compression/dehumidification cooling cycle,
and a vapor-compression/dehumidification cycle with adiabatic humidification.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, FIG. 1 is a hybrid vapor-compression/liquid
desiccant air-conditioning system 10 having evaporator 12 and condenser
14. Evaporator blower 16 draws warm moist from, for example, a conditioned
air space and into an opening at one end of evaporator 12. As the
warm air enters evaporator 12 it is filtered by air filter 18 configured
within the air flow path at one end of evaporator 12. As the warm
moist air is drawn through evaporator 12 it is cooled and dehumidified
by liquid desiccant and refrigerant circulated within evaporator
12.
Liquid desiccant is circulated throughout hybrid system 10 including
circulation within evaporator 12 and condenser 14. When hybrid system
10 is activated, evaporator pump 20 and condenser pump 22 operate
to simultaneously draw liquid desiccant from evaporator sump 24
and condenser sump 26 respectively. Beginning at evaporator 12
liquid desiccant is pumped from the evaporator sump 24 and, by means
of a series of globe valves 28 and 30 liquid desiccant is routed
through recuperator 32. Globe valve 30 functions to meter or regulate
the amount of liquid desiccant flowing into recuperate 32. Desiccants
not pumped into recuperate 32 is metered into desiccant distributor
34 by globe valve 28. The liquid desiccant contained in evaporator
sump 24 is diluted with water absorbed by liquid desiccant emitted
from desiccant distributor 34 and evenly dispersed throughout evaporator
12 via distribution media 35. Liquid desiccant flows gravitationally
downward contacting horizontally forced moist air as it traverses
evaporator 12. Thus, the liquid desiccant collects water on its
path downward leaving a diluted desiccant solution in evaporator
sump 24. To remove the unwanted water from the liquid desiccant,
a portion of the diluted desiccant is routed to the condenser sump
26 by globe valve 30. On its way to the condenser sump 26 recuperator
32 thermally heats the diluted desiccant through heat exchange means.
The warmed, diluted desiccant is then added to the desiccant within
the condenser sump 26. From condenser sump 26 the diluted liquid
desiccant is circulated by a condenser pump 22 through globe valves
36 and 38. Globe valve 36 functions to meter a portion of liquid
desiccant to desiccant distributor 40. Desiccant distributor 40
then deliver the diluted liquid desiccant to distributor media 42
which evenly distributes the diluted mixture down the hot surfaces
of condenser 14. As the diluted mixture contacts the heated surfaces
of the condenser 14 moisture is desorbed and the liquid sorbent
is reconcentrated as it collects in condenser sump 26. The desorbed
water is carried from condenser by scavenger air drawn through air
filter 44 and condenser 14 by condenser blower 46. The water is
then expelled through warm moist air cast from hybrid system 10.
Globe valve 38 delivers the dried, concentrated liquid desiccant
back to evaporator sump 24. The concentrated liquid desiccant, routed
to evaporator sump 24 helps maintain a moisture sorbing environment
which dehumidifies air cast back into the conditioned air space
via evaporator blower 16.
To cool the dried conditioned air exiting evaporator 12 a refrigeration
loop of a standard vapor-compression system is used. The present
invention utilizes conventional vapor-compression equipment (evaporator,
condenser, compressor, and refrigerant) incorporated into the aforementioned
liquid desiccant circulation system. The present hybrid system 10
using refrigerant (e.g., R22) and having a refrigerant circulation
loop comprising a compressor 48 which circulates refrigerant throughout
hybrid system 10 between condenser 14 and evaporator 12. Compressor
48 compresses the refrigerant and circulates the compressed refrigerant
into condenser 44. Under principles of fluid thermodynamics, the
compressed refrigerant remains hot causing condenser 14 to be heated
such that diluted desiccant is naturally desorbed with thermal heat
generated by compressed refrigerant circulated therein. The condensed
refrigerant exits condenser 14 and enters expansion valve 50 whereby
the refrigerant is expanded and cooled as it enters evaporator 12.
Cooled refrigerant temperatures translate to cool air circulated
through evaporator 12. Once the cooled, expanded refrigerant leaves
evaporator 12 it is routed back through compressor 48 which transforms
the refrigerant to compressed, hot refrigerant ready to again enter
condenser 14.
The advantage in combining the liquid desiccant circulation system
with the refrigerant circulation system is to maintain a lowered
pressure differential throughout the refrigerant system. When the
diluted liquid desiccant solution is circulated to condenser 14
water in the solution evaporates on contact with the hot condenser
causing condenser 14 to cool. Moreover, since absorption rather
than condensation is used by the hybrid system to extract water,
evaporator 12 need not be operated at a temperature below dew point.
The result is an evaporator 12 operating at a higher temperature
and a condenser 14 operating at a lower temperature. Thus, the combined
effect is to reduce the temperature difference between the cool
evaporator 12 and warm condenser 14 such that the pressure differential
within the refrigerant system is minimized. A lower pressure differential
allows compressor 48 to operate more efficiently by not having to
as much energy compressing the refrigerant. Also, since evaporator
12 need not expend additional energy to cool air below dew point,
evaporator 12 operates more efficiently. Thus, the present hybrid
system 10 costs less to operate than conventional vapor-compression
system. An added benefit of a more efficient operating system is
that evaporator 12 and compressor 48 can be down sized, thereby
also reducing the initial investment cost of the present invention.
The present invention hybrid system 10 can further reduce the temperature
of air supplied to the conditioned space by adding moisture to the
air. When air leaving evaporator 12 is dry, but not cool enough
to maintain an acceptable temperature within the conditioned space,
the air can be humidified with a water saturated humidifying media
52 configured within evaporator air flow path. Humidifying media
52 is made principally of cellulose material and becomes saturated
with water by pumping water from humidifier sump 54 by humidifier
pump 56. Humidifier pump 56 delivers water into humidifier distributor
58 which in turn evenly distributes the water down humidifying media
52. As water detaches from the bottom of humidifying media 52 it
is collected in humidifier sump 54 ready to be recirculated back
into the humidifier distributor 58. The humidifying apparatus can
be activated or deactivated by simply flipping a switch. If during
the operation of the hybrid system 10 the consumer wishes more
or less humidity in the air, he or she can activate or deactivate
the humidifying system independent of the hybrid system 10. Water
can be periodically flushed from the humidifier sump 54 through
globe valve 60. A makeup line 62 with shut-off float control 64
is used to refill the humidifier sump 54 with fresh water free of
microbial contamination.
Humidifying media 52 is placed between evaporator blower 16 and
evaporator entrainment separator 66. Evaporator entrainment separator
66 functions to entrap liquid desiccant entrained in the evaporator
12 air flow path. As cool dry air contacts evaporative entrainment
separator 66 the liquid desiccant is collected upon the surface
of entrainment separator 66. As liquid desiccant collects upon the
surface it is gravitationally drawn downward and deposited in the
evaporator sump 24 for recirculating back into the system. Condenser
entrainment separator 68 functions similar to evaporator entrainment
separator 66. By collecting and depositing liquid desiccant into
the condenser sump 26 the condenser entrainment separator 68 assures
that minimal amounts of costly liquid desiccant leave the hybrid
system 10. Likewise, evaporator entrainment separator 66 insures
that minimal amounts of liquid desiccant are circulated within the
conditioned air space. In small concentrations, the type of liquid
desiccant chosen for the presentation invention is relatively nontoxic.
Evaporator entrainment separator 66 ensures that high concentration
levels in the air conditioned space will never be achieved.
The present invention uses an aqueous solution of glycol or brine
as the liquid desiccant. Although trietheleyne glycol or calcium
chloride is preferred, other forms of liquid desiccant can also
be used, including, e.g., lithium chloride and lithium bromine.
Each form of liquid desiccant having its own advantages and disadvantages.
When considering which form to use, factors such as safety, corrosivity,
heat and mass transfer potential, and cost must be considered. Table
I represents a weighted summary of all four forms based on the above
factors.
Safety is a factor since the liquid desiccant will be in direct
contact with the air delivered to the conditioned space. Therefore,
a liquid desiccant must be chosen which will not demonstrate adverse
effects of ingestion, inhalation or skin contact. All four forms
are relatively nontoxic with trietheleyne glycol being the least
toxic of the group. Corrosive liquid desiccant should be avoided
so as to maintain longevity and reliable operation of the present
invention. Corrosion rates in inhibited trietheleyne glycol, are
low for most metal surfaces including aluminum, copper, and steel.
The thermal conductivity of the liquid desiccant solution is representative
of its heat transfer potential. The liquid desiccant must be capable
of transferring heat fairly quickly as the desiccant circulates
between the cooled evaporator and heated condenser. Thermal conductivity
of calcium chloride and lithium chloride are somewhat better than
the other forms. Mass transfer of all four forms is relatively equal.
Costs of the four forms of desiccant range from cheaper calcium
chloride and lithium chloride to the more expensive lithium bromide.
Contained within evaporator 12 and condenser 14 is a heat and mass
exchanger 70 illustrated in FIG. 2. FIG. 2 is cut-away view of the
exchanger 70 comprising a plurality of planar fins 72 and refrigerant
tubes 74. Liquid desiccant is dispersed evenly on the top of exchanger
70 via distribution media 35 or 42 illustrated in FIG. 1. Liquid
desiccant flows as thin falling films 76 on both sides of the planar
surfaces of each fin 72. Each fin 72 is spaced equal distance from
the adjacent fin to allow air movement along the wetted planar surfaces.
By placing the exchanger 70 directly within the air flow path and
configuring the planar surface of each fin parallel to said air
flow path, efficient heat and mass transfer is achieved. The fins
72 can be either cooled or heated by cold or hot refrigerant circulated
throughout the refrigerant tubes 74 traversing each fin. Because
of the larger area of fins 72 the temperature of fins 72 and the
vapor pressure of water in the falling films 76 can be rapidly and
efficiently transferred to air entering exchanger 70. Both the fins
72 and refrigerant tubes 74 are made of non corrosive material such
as copper which will not degrade when brought in contact with liquid
sorbent and water flowing downward and across the outside surfaces
of fins 72 and refrigerant tube 74. The downward flowing liquid
desiccant is collected in evaporator sump 24 or condenser sump 26
for reuse in the system.
FIG. 3 illustrates the process paths of the conditioned air in
the disclosed invention versus the process path of the conventional
vapor-compression air conditioner. The graph of FIG. 3 is taken
using 26.7.degree. C. air at 50% relative humidity as the benchmark.
The conditioning of air by a conventional vapor-compression air
condition is shown by path 1-3. Dry bulb temperature as well as
absolute humidity, is reduced by standard vapor-compression techniques
incorporating condensation dehumidifying techniques. In order to
condense the moisture prior to removal, it is necessary to cool
the air to a point below dew point, such dew point temperature being
lower than the desired temperature of point 3. A lower condensation
temperature of the evaporator refrigerant requires additional work
to be done by the compressor of a conventional vapor-compression
system. Thus, to arrive at point 3 a conventional air conditioning
system must cool the air below that shown in point 3 and then a
reheating process is sometimes used to bring dry bulb temperature
back to point 3. The supercooling and reheating process is very
inefficient and demonstrates lower coefficients of performance.
On the other hand, conditioning of air in the hybrid system 10 of
the present invention is represented by path 1-2 with the humidifier
pump 56 not activated, and by path 1-2-3 if the humidifier pump
56 is activated. By simply flipping a switch, humidifier pump 56
can be turned off thereby providing dry cool air along path 1-2.
Absolute humidity is reduced by the liquid desiccant sorption process.
The air need not be supercooled as in the conventional dehumidification-by-condsensation
process of conventional air conditioners. If the consumer wants
cooler humidified air, he or she can simply flip a switch at any
time during hybrid system 10 operation, thereby activating humidifier
pump 56. An activated humidifier pump 56 functions to add moisture
to the cool dry air along path 2-3. Thus, the same temperature and
relative humidity at point 3 can be selectively obtained from the
hybrid system 10 as from a conventional air conditioning system
but without having to supercool the air and thereby wasting energy.
While the present invention has been described with reference to
a preferred embodiment, one of ordinary skill in the art will appreciate
that additions, modifications, or deletions can be made without
departing from the scope of the invention. |