Abstrict An improved desiccant air conditioning system includes at least
one heat exchanging desiccant bed having desiccant material surfaces
defining air passageways through the desiccant bed. The desiccant
material surfaces adsorb moisture from building air during an adsorption
phase and desorb moisture into exhaust air during a desorption phase.
The heat exchanging desiccant bed is formed with refrigerant circulating
channels or tubes in heat exchange relationship with the desiccant
material surfaces. A heat pump system is also provided including
an evaporator, compressor, condenser, and metering device operatively
coupled by a refrigerant circulating line for evaporation of refrigerant
and transfer of heat to the refrigerant from air in the evaporator
air passageways during a coincident adsorption/evaporation phase
and for condensation of refrigerant and transfer of heat from the
refrigerant to air in the condenser air passageways during a coincident
desportion/condensation phase. The refrigerant circulating channels
are operatively coupled in the refrigerant circulating line of the
heat pump system so that the heat exchanging desiccant bed comprises
either the evaporator or the condenser or a component element of
the evaporator or condenser. Various combinations of desiccant bed
elements and heat pump elements are described. A heat pump desiccant
bed air conditioning system is also provided by operatively coupling
a heat pump between sources of relatively hot and cold heat transfer
liquid of a non-change of phase heat transfer liquid circulating
heat exchanging desiccant bed.
Claims I claim:
1. An improved method of desiccant bed air conditioning comprising:
circulating heat transfer liquid in liquid circulating channels
in heat exchanging relationship with a desiccant bed having desiccant
material surfaces defining air passageways through the desiccant
bed;
storing relatively hot heat transfer liquid in a first storage
tank;
storing relatively cold heat transfer liquid in a second storage
tank;
alternately coupling the first storage tank for circulating relatively
hot heat transfer liquid and the second storage tank for circulating
relatively cold heat transfer liquid to the liquid circulating channels
of the heat exchanging desiccant bed for alternately operating the
desiccant bed respectively in a desorption mode and an adsorption
mode;
and pumping heat from the second storage tank to the first storage
tank.
2. The air conditioning method of claim 1 wherein the method of
pumping heat uses a heat pump comprising a compressor, an evaporator
heat exchanger, and a condenser heat exchanger with the evaporator
heat exchanger being operatively coupled in heat exchange relationship
with the second storage tank and the condenser heat exchanger being
operatively coupled in heat exchange relationship with the first
storage tank.
3. The method of claim 1 wherein the first and second storage tanks
are insulated and when the step of pumping heat comprises using
a heat pump during off peak hours and storing off peak energy using
said first and second storage tanks.
4. An improved method of desiccant bed air conditioning using a
desiccant bed having desiccant material surfaces defining air passageways
through the bed and heat transfer liquid channel means in heat exchange
relationship with the desiccant material surfaces comprising:
storing relatively high temperature heat transfer liquid in a hot
tank;
storing relatively low temperature heat transfer liquid in a cold
tank;
alternately coupling the hot tank and the cold tank to the heat
transfer liquid channel means of the heat exchanging desiccant bed
for alternately operating the desiccant bed respectively in a desorption
and an adsorption mode;
and pumping heat from the cold tank to the hot tank using a heat
pump operatively coupled in heat transfer relationship between the
cold tank and hot tank for maintaining the temperature differential
of relatively high temperature heat transfer liquid in the hot tank
and relatively low temperature heat transfer liquid in the cold
tank.
5. The air conditioning method of claim 4 comprising pumping heat
during off peak hours and insulating the hot tank and cold tank
for storing off peak energy.
Description TECHNICAL FIELD
This invention relates to desiccant air conditioning systems and
to heat pump systems The invention provides new air conditioning
systems with complementary and integrated desiccant bed and heat
pump technology for reverse cycle cooling and heating, drying and
humidifying, and controlled comfort zone air conditioning generally.
BACKGROUND ART
In desiccant bed air cooling and air conditioning systems, hot
humid air enters the intake side of a desiccant bed. Water vapor
and moisture is adsorbed on the extended desiccant material surface
areas of the bed, drying the air and releasing latent heat of condensation.
The hot dry air may then pass through a heat exchanger giving up
some of the heat to an exhaust air stream. The air is then reconditioned
by evaporative cooling through an evaporative cooling element or
unit where moisture is evaporated back into the air for example
by spraying. It is intended by this final evaporative cooling step
to achieve a desired temperature and humidity in the comfort zone
range. The desiccant bed is periodically recharged by passing hot
exhaust air through the bed to evaporate or "desorb" moisture
from the desiccant material.
In applicant's pending U.S. patent application, Ser. No. 750932
filed July 1 1985 there is described an improved "Desiccant
Solar Air Conditioning System" incorporating a novel desiccant
bed structure in the form of a liquid-to-air and air-to-liquid heat
exchanging desiccant bed. The desiccant bed is composed of desiccant
material surfaces such as granular extended surface area desiccant
material defining air passageways through the desiccant bed. Fluid
circulating channels are formed through the desiccant bed for circulating
heat transfer liquids such as water in heat exchange relationship
with the desiccant bed.
The desiccant bed structure of U.S. Ser. No. 750932 is provided
by parallel heat conducting metal plates or fins establishing the
air passageways with granular desiccant material such as silica
gel granules or spheres intimately bonded to the heat conducting
surfaces by an adhesive bonding layer. Humid air passes through
the air passageways of the desiccant bed for condensation and adsorption
of moisture on the extended surface area of the desiccant material
during an adsorb cycle or adsorption phase. Coolant liquid circulates
through the fluid circulating channels in heat exchange relationship
with the desiccant bed for efficient removal of latent heat of condensation
and adsorption from the desiccant bed and desiccant material.
During the desorb cycle or desorption phase heated air is passed
through the air passageways of the desiccant bed for evaporating
and removing moisture from the saturated or moisture-laden desiccant
material. At the same time heated liquid is circulated in the circulating
channels in heat exchange relationship with the desiccant bed for
importing heat energy from external sources into the system to provide
latent heat of vaporization. Thus, the desiccant air conditioning
system of U.S. Ser. No. 750932 is an open system which permits
substantial import of energy from external sources and substantial
removal of heat energy from the system.
U.S. Ser. No. 750932 describes a complete air conditioning system
constructed and arranged to provide an adsorb cycle or adsorption
phase for passing air through the desiccant structure for drying
the air for subsequent evaporative cooling, and a desorb cycle or
desorption phase for reactivating the desiccant structure using
imported heat energy. Subsidiary heat exchange closed loops for
both the adsorb and desorb cycles are included in the system to
enhance efficiency. Most important, however, the system for the
first time provides an efficient air to liquid and liquid-to-air
heat exchanging desiccant bed for desiccant air conditioners for
net export and import of heat energy at higher efficiency.
Heat pump systems and units providing combination heating and cooling
are well known, for example described in the handbook, Refrigeration
and Air Conditioning, Chapter 11 of the Air Conditioning and Refrigeration
Institute, Prentice Hall, 1979. Refrigeration equipment is used
in such a way that heat is taken from a heat source and given up
to an air conditioned space when heating is desired. In the reverse
cycle, heat is removed from the space and discharged in exhaust
air when cooling is desired. A standard heat pump system generally
includes an evaporator, compressor, condenser, and metering device.
The evaporator and condenser are typically air t liquid and liquid-to-air
heat exchangers formed with air passageways for passage of air through
the evaporator and condenser. A refrigerant circulating line operatively
couples the evaporator, compressor, condenser, and metering device.
Refrigerant such as Freon (Trademark) expanding through the metering
device such as an expansion valve evaporates transferring heat to
the refrigerant from air and moisture passing through the evaporator
air passageways during an evaporation phase. After compression to
higher pressure by the compressor, the refrigerant vapor condenses
in the condenser transferring heat from the refrigerant to air and
moisture passing through the condenser air passageways during a
condensation phase.
A feature distinguishing the heat pump system from a conventional
refrigeration cooling cycle is that the heat pump system incorporates
a four-way reversing valve for reversing the flow of refrigerant
in the refrigerant circulating lines so that the respective functions
of the evaporator heat exchanger and condenser heat exchanger may
be reversed. To accomplish this, two expansion valves are incorporated
in the refrigerant circulating line, one for each heat exchanger
operative when the heat exchanger is functioning as an evaporator.
A one-way check valve is incorporated in parallel with each expansion
valve or other metering device to bypass the expansion valve when
the respective heat exchanger is functioning as a condenser. A refrigerant
accumulator or reservoir is typically provided as a precaution upstream
from the compressor to capture and prevent any liquid refrigerant
from entering the compressor during the reversal of cycles. A more
complete description of heat pump reverse cycle heating and cooling
systems is found in the Refrigeration and Air Conditioning handbook
reference referred to above.
It has not occurred to those skilled in the refrigeration and air
conditioning field that heat pump technology and desiccant air conditioning
technology might bear a useful relationship. It is not at all apparent
that it would be desirable or possible to relate desiccant bed cycles
and refrigeration cycles. It is a major discovery of the present
invention that in fact the cycles or phases of desiccant bed air
conditioner operation bear a productive complementary and synergistic
relationship to the cycles or phases of heat pump reverse cycle
operation. The present invention develops a new interactive technology
of integrated heat pump desiccant air conditioning systems based
on a complementary synergistic coincidence and interaction of adsorption
and evaporation on the one hand and desorption and condensation
on the other hand. The invention provides complete complementary
reverse cycle operation all achieved by the novel heat pump and
heat exchanging desiccant bed structures of the invention.
The novel change of phase heat exchanging desiccant bed structures
of the present invention function alternately as adsorption bed
and desorption bed as part of a functional desiccant air conditioning
system at the same time that as heat exchangers they function alternately
as evaporator and condenser as part of a reverse cycle heat pump
heating and cooling system. By the simultaneous operation of this
novel structure as an adsorption bed and evaporator on the one hand
and as a desorption bed and condenser on the other hand, the synergism
of the heat pump technology and desiccant bed air conditioning technology
provides a total enthalpy heat pumping system for transfer of both
latent and sensible heat with greater efficiency and with potentially
near complete utilization of the cycled heat energy. A new method
of enthalpy matching air conditioning by coacting adsorption and
evaporation and coacting desorption and condensation is provided.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a
new reverse cycle heating and cooling system combining the benefits
of desiccant air conditioning systems with heat pump systems.
Another object of the invention is to provide an integrated air
conditioning system integrating the absorption phase of a desiccant
bed with the evaporation phase of a heat pump heat exchanger on
the one hand and integrating the desorption phase of a desiccant
bed with the condensation phase of a heat pump heat exchanger on
the other hand. A complete enthalpic heat transfer pump is therefore
provided, for example, transferring latent heat of adsorption and
condensation from moisture adsorbed on the desiccant material surfaces
and sensible heat of air in the air passageways to latent heat of
vaporization and sensible heat of refrigerant in the desiccant bed
circulating channels; and transferring latent heat of condensation
and sensible heat from refrigerant in the desiccant bed circulating
channels to heat of vaporization of moisture on the desiccant material
surfaces and sensible heat of air in the air passageways for desorption
of the desiccant bed.
A further object of the invention is to provide new desiccant bed
structures for desiccant bed air conditioning systems which incorporate
the heat exchange functions of change of phase refrigerant heat
pump heat exchangers. The objective is to provide an integrated
desiccant bed structure which incorporates both desiccant air conditioning
technology and reverse cycle heat pump technology in a complementary
and matching relationship.
It is also an object of the invention to provide new air passageway
arrangements, refrigerant circulating arrangement, and respective
controls for simultaneous reversal of functions between adsorption
and desorption phases on the one hand and evaporation and condensation
phases on the other hand so that adsorption and evaporation remain
coincident and complementary while desorption and condensation remain
coincident and complementary during reverse cycle heating and cooling
by the novel heat exchanging desiccant bed structures. The invention
achieves "enthalpy matching" and thermal enthalpic impedance
matching in the transfer of latent and sensible heat across the
desiccant bed structure between the processes of adsorption and
desorption at the desiccant material surfaces and the processes
of evaporation and condensation in the refrigerant circulating channels.
It is intended that the invention be applied for complete stand
alone combination heating and cooling systems and for retrofitting
systems for adding on to existing air conditioning, heating, and
cooling systems.
DISCLOSURE OF THE INVENTION
In order to accomplish these results the invention provides an
improved desiccant air conditioning system having at least one desiccant
bed comprising desiccant material surfaces defining air passageways
through the desiccant bed. The desiccant material surfaces adsorb
moisture from building air passing through the desiccant bed during
an adsorption phase and desorb moisture into exhaust air during
a desorption phase. According to the invention, a heat pump system
is also provided including an evaporator, compressor, condenser,
and metering device such as an expansion valve. The evaporator and
condenser heat exchangers are formed with air passageways for passage
of air through the respective evaporator and condenser. A refrigerant
circulating line operatively couples the evaporator, compressor,
condenser, and metering device for evaporation of refrigerant and
transfer of heat to the refrigerant from air in the evaporator air
passageways during an evaporation phase and for condensation of
refrigerant and transfer of heat from the refrigerant to air in
the condenser air passageways during a condensation phase.
The desiccant bed, according to the invention, comprises a heat
exchanging desiccant bed having refrigerant circulating channels
in heat exchange relationship with the desiccant material surfaces
of the desiccant bed for transfer of both latent and sensible heat
energy across the bed. The refrigerant circulating channels are
operatively coupled in the refrigerant circulating line of the heat
pump system so that the heat exchanging desiccant bed comprises
either the evaporator or the condenser. The heat exchanging desiccant
bed may comprise either the evaporator or condenser in its entirety
or comprise one element of the condenser or evaporator coupled in
series with traditional evaporator or condenser heat exchangers.
In the preferred example embodiment first and second heat exchanging
desiccant beds are incorporated in the system, each with refrigerant
circulating channels operatively coupled in the refrigerant circulating
line of the heat pump system. One of the heat exchanging desiccant
beds functions as the evaporator heat exchanger or a heat exchanging
element of the evaporator while the second heat exchanging desiccant
bed functions as the condenser or a heat exchanging element of the
condenser. The integrated heat pump desiccant bed air conditioning
system incorporates controls operatively controlling circulation
of refrigerant in the refrigerant circulating line and passage of
air in the desiccant bed air passageways so that the adsorption
phase on the desiccant material surfaces of the heat exchanging
desiccant bed structure coincides with the evaporation phase in
the refrigerant circulating channels of the structure. Similarly,
the desorption phase on the desiccant material surfaces of the heat
exchanging desiccant bed structure coincides with the condensation
phase of the refrigerant circulating channels inside the structure.
A feature and advantage of this arrangement is that latent and sensible
heat energy is exchanged between the processes of adsorption and
evaporation in one direction while latent and sensible heat energy
is transferred in the other direction between condensation and desorption,
resulting in a total latent and sensible heat pump. The total latent
and sensible heat energy is referred to herein as "enthalpy".
The system is arranged for "enthalpy matching" across
the heat exchanging desiccant beds between the desiccant material
surface processes of adsorption and desorption and the refrigerant
heat pump processes of evaporation and condensation.
The reversing controls include a four-way reversing valve in the
refrigerant circulating line for directing refrigerant flow in opposite
directions from the compressor. Similarly, directional vanes may
be included in air ducts connecting the air passageways of the desiccant
beds for diverting and redirecting flow of air through the air passageways.
According to further embodiments, reversing fans are provided adjacent
to the desiccant beds in association with upstream and downstream
one-way louvers in the air ducts for directing building air in one
direction through desiccant bed air passageways while directing
exhaust air in the opposite direction.
According to the invention, a variety of combinations and permutations
of heat exchanging desiccant beds and heat pump systems in interactive
combination are provided. For example, in a conventional air conditioning
system the condenser alone may comprise a heat exchanging desiccant
bed in a split system in which the condenser is located outside
the house. The desorption phase of the desiccant bed coincides with
the condensation phase of the air conditioner for transfer of latent
heat of condensation from the refrigerant to latent heat of desorption
and evaporation of moisture on the desiccant material surface. A
second heat exchanging desiccant bed operates simultaneously for
drying building air and adsorbing and accumulating moisture from
the building air onto the desiccant material surfaces. The refrigerant
circulating line is alternately coupled between the first and second
heat exchanging desiccant beds for alternately operating one bed
as the condenser, desorbing and recharging the desiccant bed while
the other bed is decoupled from the refrigerant circulating line
for adsorbing moisture from building air.
According to another alternative combination, the evaporator of
a heat pump system may incorporate a heat exchanging desiccant bed
in the air circulating system only with an air duct operatively
coupling the air passageways of a conventional evaporator heat exchanger
and the air passageways of the desiccant bed for both cooling and
drying the air. The desiccant bed may include heat transfer fluid
circulating channels in heat exchange relationship with the desiccant
material surfaces for transfer of sensible heat energy, for example,
by circulating water for cooling the desiccant bed. Alternatively,
the heat exchanging desiccant bed may incorporate refrigerant circulating
channels fully incorporated in the refrigerant circulating line
of the heat pump system for full operation as a component of the
evaporator for transfer of both latent and sensible heat energy
referred to herein as enthalpy.
The heat exchanging desiccant beds of the present invention may
be integrated in a variety of refrigerant, air conditioning, and
heat pump systems including single cycle and reverse cycle heating
and cooling systems. Thus, the heat exchanging desiccant beds may
comprise either one or both of the evaporator or condenser of such
systems or component heat exchanging elements of the evaporator
or condenser and may be incorporated for either circulation of change
of phase refrigerant for enthalpic heat pump operation or for circulation
of a single phase heat transfer liquid such as water as previously
described in applicant's pending U.S. patent application Ser. No.
750932 referred to above. The heat exchanging desiccant beds are
adapted for reverse cycle operation alternately operating between
adsorption and desorption phases at the desiccant material surfaces
of the desiccant air passageways. A feature and advantage of this
reverse cycle operation according to the invention is that it complements
and coincides with the reverse cycle operation of evaporation and
condensation of refrigerants circulating in refrigerant circulating
channels within the desiccant bed for full latent and sensible heat
pumping between the air and refrigerant. Significantly, the invention
provides "enthalpy matching" or thermal enthalpic impedance
matching in the enthalpic heat energy transfer across the heat exchanging
desiccant bed.
The invention contemplates a variety of air conditioning system
structural arrangements for both independent self-contained operation
and for retrofitting existing air conditioning systems. For example,
the air ducts for passage of air through the system may incorporate
bypass airways around the heat exchanging desiccant beds with bypass
dampers operatively arranged for controlling the proportion of air
in the air duct passing through the bypass airway and passing through
the heat exchanging desiccant bed air passageways. The bypass dampers
afford additional control over the temperature and humidity of the
resulting air in the downstream mixture. Conventional evaporator
and condenser heat exchangers with air passageways may be incorporated
in the air ducts operatively coupled in series with the air passageways
of the heat exchanging desiccant beds or in parallel. In the latter
application, for example, the conventional condenser and evaporator
heat exchangers may be incorporated in the bypass airways around
the heat exchanging desiccant beds. In the preferred form and arrangement
of the invention, a conventional evaporator heat exchanger is placed
in series in the air duct upstream from the air passageways of the
heat exchanging desiccant bed. A second conventional evaporator
heat exchanger may also be placed in series downstream from the
heat exchanging desiccant bed. A conventional condenser heat exchanger
is positioned in series in the air duct upstream from the air passageways
of the heat exchanging desiccant bed.
The refrigerant circulating line is coupled on the condenser side
to flow first into the condenser heat exchanging desiccant bed and
then into the conventional heat exchanging element which is upstream
in the air flow. On the evaporator side the refrigerant circulating
line is coupled for flow of refrigerant first into the conventional
evaporator heat exchanger and then into the evaporator heat exchanging
desiccant bed which is also downstream in the air flow. The conventional
evaporator heat exchanger cools the incoming air and increases relative
humidity for more efficient moisture adsorption in the evaporator
desiccant bed. A second conventional evaporator heat exchanger downstream
can provide additional air cooling. The conventional condenser heat
exchanger preheats exhaust air for more efficient desorption of
moisture from the condenser heat exchanging desiccant bed desiccant
material surfaces.
The invention provides a variety of heat exchanging desiccant bed
structures in addition to those set forth in applicant's U.S. patent
application, Ser. No. 750932. For example, the desiccant bed may
be a radiator of parallel vertical metal plates and at least one
fluid circulating channel tube passing through the plates in multiple
passes perpendicular to and contiguous with the plates. The refrigerant
circulating channel tube is sufficiently long and sinuous with multiple
passes for complete evaporation of refrigerant in an evaporator
desiccant bed. A layer of granular desiccant material such as silica
gel granules or spheres is bonded to surfaces of at least some of
the metal plates of the radiator. For example, the desiccant material
may be bonded by a layer of bonding adhesive to alternate sides
only of the metal plates of the radiator, or every other metal plate,
to expose metal surfaces for more efficient transfer of heat through
the radiator.
The desiccant bed may also be constructed from tubes with adjoining
and projecting fins known as tube fins. The fins may be attached
to the tubes. The layer of granular desiccant material may be bonded
to all exposed metal surfaces or to one side only of the fins or
to every other tube fin to enhance heat transfer between the air
and refrigerant or heat transfer fluid circulating in the channels
of the desiccant bed. Tube plates may also be used for the desiccant
bed. Metal particles or granules may also be mixed with the granules
of desiccant material to enhance heat transfer between air passing
through the desiccant bed and circulating fluid or refrigerant in
the circulating channels of the desiccant bed. The desiccant bed
may also be provided with two sets of fluid circulating channels,
one for a non-change of phase heat transfer fluid and the other
for a change of phase circulating refrigerant. A desiccant bed may
be manufactured by spraying silicone rubber glue on the exposed
metal surfaces or selected surfaces of the radiator, tube fins,
or tube plates and then rolling silica gel spheres onto the surfaces
for adhesion and bonding to those surfaces coated with the silicone
rubber glue.
In the assembled heat pump desiccant air conditioning system, according
to the present invention, the desiccant beds may be used to adsorb
moisture without use of the heat pump components by using the fan
only. Or the heat pump components including the conventional evaporator
and condenser heat exchangers may be used alone of reverse cycle
heat pump heating operation for heating and humidifying a building
space.
The invention also provides a novel heat exchanging structure with
conventional heat exchangers and a heat exchanging desiccant bed
integrated into a single unitary structure for both evaporators
and condensers. According to this aspect of the invention an elongate
heat exchanging framework is provided with air passageways defined
by fins or plates for passage of air in the elongate direction through
the framework. At least one elongate "serpentine" refrigerant
channel or tube winds through the framework in heat exchange contiguity.
Such a framework may be provided, for example, by stacked arrays
of folded tube fins with serpentine refrigerant channel tubes winding
in heat exchange relationship with the fins throughout the framework.
Stacks of elongate tube plates or an elongate radiator structure
may also be used. Along a central band of the framework, the fins
or plates are coated with silicone rubber glue or similar bonding
adhesives and a layer of granular desiccant material such as silica
gel granules or spheres is bonded to the surfaces throughout the
central band. A central heat exchanging desiccant bed is therefore
provided bounded on either side in the air flow by a conventional
metal surface liquid-to-air heat exchanger all in a unitary structure
designated HX/DB/HX. The unitary "banded" multiple heat
exchanger structure can serve as a complete evaporator or condenser.
A feature and advantage of the enthalpic heat pump desiccant air
conditioning system of the present invention is the energy savings
achieved over conventional air conditioners. In conventional air
conditioners approximately 30% or nearly one third of the system
energy is lost at the condenser in exhaust air from the condensation
phase or cycle. According to the present invention, the normally
wasted heat energy is substantially recovered in the desorption
and recharging of the desiccant material surfaces of the heat exchanging
desiccant bed condenser. That is, the desorption or recharging phase
coincides with the condensation phase utilizing the latent heat
of condensation for the latent heat of desorption or vaporization
with a consequent savings of approximately 30% of system heat energy
or enthalpy. The recharged desiccant bed is available for drying
and cooling air in the absorption and evaporation phase to effect
this saving of energy.
Additionally, the combination of desiccant air conditioning with
heat pump or refrigerant air conditioning according to the invention
provides building air with lower specific humidity and moisture
content for greater flexibility in the final conditioning of the
air to parameters in the desired comfort zone range. For example,
at the lower moisture content higher air temperatures are tolerated
in the comfort zone. Alternatively a final stage of evaporative
cooling or chilling can return a specified level of moisture content
and humidity while substantially lowering the air temperature. The
structures and systems of the invention thereby afford substantial
energy savings and far greater conditioning flexibility in comparison
to conventional air conditioners.
Other objects, features, and advantages of the invention are apparent
in the following specification and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic side cross-section view of an upright
enthalpic heat pump desiccant bed air conditioning system according
to the present invention with complementary desiccant beds for operation
alternatively in the coincident adsorption and evaporation phase
and the coincident desorption and condenser phase looking in the
direction of the arrows on line C--C of FIG. 2.
FIG. 2 is a diagrammatic top cross-section view of the complementary
desiccant beds and bypass airways in the direction of the arrows
on line A--A of the heat exchanging desiccant bed air conditioning
system of FIG. 1.
FIG. 3 is a diagrammatic side cross-section view of the heat pump
desiccant bed air conditioning system in upright position and rotated
90.degree. from the view of FIG. 1 in the direction of the arrows
of line D--D of FIG. 4 and showing one of the desiccant bed modules
operating in the absorption phase.
FIG. 4 is a diagrammatic cross-section view looking down on the
fan of the desiccant bed of FIG. 3 in the direction of the arrows
on line B--B of FIG. 3.
FIG. 5 is a diagrammatic side cross-section view of the other heat
pump desiccant bed of FIG. 3 operating in the desorption phase.
FIG. 6 is a diagrammatic side cross-section view of an upright
desiccant bed air conditioning system similar to FIG. 1 but with
the conventional heat exchangers in a different configuration and
location.
FIGS. 7 and 8 are simplified or generalized schematic diagrams
of the refrigerant circulating line of the heat pump desiccant bed
air conditioning system of the invention operating respectively
in the evaporation and condensation cycles, phases, or modes.
FIG. 9 is a detailed schematic diagram of a refrigerant circulating
line for another heat pump desiccant bed air conditioning system.
FIG. 10 is a fragmentary end view and FIG. 10A is a fragmentary
plan view of one arrangement of fin tubes for a heat exchanging
desiccant bed (HXDB).
FIG. 11 is a diagrammatic perspective view of an elongate multiple
element or multiple stage heat exchanger structure according to
the invention incorporating both conventional metal surface heat
exchangers and a heat exchanging desiccant bed in a unitary "banded"
(HX/DB/HX) structure.
FIG. 12 is a schematic diagram of another generalized enthalpic
heat pumping desiccant bed reverse cycle heating and cooling air
conditioning system according to the invention.
DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND BEST
MODE OF THE INVENTION
A heat pump desiccant bed air conditioning system 10 composed of
two reverse cycle complementary heat pump desiccant beds 12 and
14 for full-time operation is illustrated in FIGS. 1-4. FIGS. 1-4
illustrate the air flow and air passageway elements of the system
for showing the desiccant bed cycle operation in the adsorption
and desorption phases. FIGS. 7-10 described subsequently illustrate
the refrigerant lines and circuits showing the coincident and complementary
heat pump cycle operation in the evaporation add condensation phases.
Referring to FIGS. 1-4 the desiccant bed unit 14 is shown operating
in the adsorption phase, cycle, or mode, while the desiccant bed
unit 12 is operating in the desorption cycle. Operation of the desiccant
bed unit 14 in the adsorption phase is described with particular
reference to FIGS. 1 3 and 4.
During adsorption, warm, moist, house air is drawn into the desiccant
bed unit 14 through the entrance duct 15 by a three-speed reversible
fan and drive motor 16. The one-way shutters or louvers 18 open
inwardly in the entrance duct 15 to admit the high humidity house
air for adsorption. This air is drawn into the fan 16 and blown
or pushed through desiccant bed modules 21 22 23 and 24 and also
through a bypass duct 25 between the desiccant bed modules 22 and
23. A liquid-to-air heat exchanger 26 is positioned at the end of
the bypass duct 25 for cooling the bypass air which is constrained
to pass through the heat exchanger 26.
The silica gel bed modules 21 22 23 and 24 operate to dry the
portions of air which flow through the modules. The desiccant bed
modules 21-24 are constructed, for example, from tube fins, tube
plates, or radiators all as hereafter described, defining air passageways
in the elongate direction through the modules. Extended surface
area desiccant material such as silica gel beads or granules are
intimately bonded to the heat conducting surfaces of the fins, plates,
or radiators by an adhesive bonding layer such as silicone rubber
glue. The modules are constructed with refrigerant liquid or heat
transfer liquid circulating tubes and channels on heat exchange
relationship with the extended surface area desiccant material through
the fins, plates, and radiators for export of heat energy from the
desiccant bed during the adsorption phase and import of heat energy
from external sources to the desiccant bed during the desorption
phase as hereafter described. The refrigerant circulating tubes
or tortuous channels through each of the desiccant bed modules is
accessed through header pipes 28 which function either as inlet
headers or outlet headers for the tubes or channels depending upon
the phase in the cycle of operation.
The relative proportion of the inflowing warm and humid building
air passing through the heat exchanging or heat pumping desiccant
bed modules 21-24 for adsorption and drying of the air and the relative
proportion of inflowing building air passing through the bypass
air passageway 25 and air-to-liquid heat exchanger 26 for cooling
the air is controlled by the rotatable vein or shutter 30. This
relative proportion or ratio may be controlled to achieve the desired
relative humidity and temperature of the combined air flows at the
outlet to achieve desired air parameters in the comfort zone range.
At the same time, outside air is prevented from being drawn in by
the fan 16 through the exhaust air outlet 32 by one-way shutters
or louvers 34 which are constrained so that they may open only in
the outward direction.
Conditioned air exiting from the heat exchanging or heat pumping
desiccant bed modules 21-24 and bypass air passageway 25 and heat
exchanger 26 mixes in the conditioned air return duct or outlet
35 through one-way outlet louvers 36. From the return dutt and outlet
35 the conditioned air may be subjected to a further evaporative
cooling step to achieve the final parameters in the comfort zone
range before return to the building or house distribution air ducts.
The conditioned air is prevented from exiting through the outside
air inlet 37 by means of one-way louvers 38 which are oriented for
opening only in the inward direction.
While condensation of moisture from humid building air on the desiccant
material surfaces releases latent heat of condensation heating the
desiccant bed from the outside surfaces, evaporation of refrigerant
expanding in the refrigerant circulating tubes or channels in heat
exchange relationship with the inside surfaces of the desiccant
beds carries away latent heat of vaporization in the circulating
refrigerant gas. At the same time sensible heat from the adsorbing
air flow is transferred across the desiccant bed to the circulating
refrigerant gas by the refrigerating action of the heat pump. Therefore
both laten heat and sensible heat energy are transferred across
the heat exchanging desiccant bed surfaces by the coincidence of
adsorption and condensation of moisture on the outside surfaces
of the desiccant bed modules in the air passageways and evaporation
of refrigerant inside the refrigerant circulating tubes or channels
of the desiccant bed modules. It is this synergistic coincidence
and coaction of desiccant bed adsorption and heat pump evaporation
which permits matching of latent heat and sensible heat energy flow
across the heat exchanging desiccant bed surfaces referred to herein
as "enthalpy matching". That is, both latent heat of condensation
and sensible heat are transferred to the desiccant bed by moisture
adsorbing and condensing on the outside of the desiccant material
surfaces and adsorbing air flowing in the air passageways while
both latent heat of vaporization and sensible heat are carried away
from the desiccant bed by refrigerant gas expanding and evaporating
in the refrigerant circulating tubes or channels. This "enthalpy
pumping" or "enthalpy matching" resulting from the
coincidence of adsorption and evaporation across the desiccant bed
surfaces greatly enhances the efficiency of operation of the air
conditioning system.
While the desiccant bed unit 14 is operating in the adsorbing or
adsorption phase of the air conditioning cycle, desiccant bed unit
12 is being recharged in the desorption phase or desorbing mode
of operation. A diagrammatic side cross-section through the center
of desiccant bed unit 12 during the desorption phase is illustrated
in FIG. 5. For desorption, evaporation, and removal of moisture
from the extended desiccant material surfaces of the desiccant bed
modules 41 42 43 and 44 the rotation of fan 20 is reversed so
that outside air or air from an outside source such as hot attic
air or solar heated air is drawn through the outside air entrance
or inlet 57 through the one-way louvers or shutters 58. Building
air is prevented from being drawn by the fan through the conditioned
air outlet 55 by the one-way shutters or louvers 56 which are oriented
for opening only in the outward direction. All of the desorbing
air is constrained to pass through the desiccant bed modules 41-44
by closing the shutter 50 so that none of the air passes through
the bypass air passageway 45 and liquid-to-air heat exchanger 46.
The construction of the air conditioning desiccant bed unit 12
is identical to that of the air conditioning desiccant bed unit
14 and desiccant bed module 41-44 are similarly heat exchanging
or heat pumping desiccant beds composed of fins, plates, or radiators
covered with extended surface area desiccant material with tortuous
circulating tubes or channels for heat exchange fluid or refrigerant
fluid accessed through the inlet and outlet headers 48.
The outside air or desorbing air passing through the desiccant
beds 41-44 and laden with moisture and humidity desorbed or evaporated
from the desiccant bed desiccant material surfaces is pushed, blown,
or forced out of the system by the fan 20 through the exhaust air
outlet 52 through the exhaust outlet one-way shutters or louvers
54. The 100% humidity moisture-laden air is prevented from entering
the house or other building through the building air entrance duct
or inlet duct 60 by the one-way louvers or shutters 62 which are
constrained for opening only in the inward direction.
During the cycling operation of the parallel reversing cycle heat
pump desiccant bed air conditioning system 10 the heat pumping,
heat exchanging desiccant bed units 14 and 12 are operating alternatively
in the adsorbing and desorbing operating modes. When one of the
desiccant bed units, e.g., desiccant bed unit 14 is operating in
the adsorption phase as a desiccant bed air conditioner, it is also
functioning as the evaporator of a heat pump circuit as hereafter
described. At the same time the other heat pumping, heat exchanging
desiccant bed unit 12 is operating in the desorption phase recharging
the desiccant bed while at the same time functioning as a condenser
in the heat pump refrigeration circuit hereafter described. When
the desiccant bed modules 21-24 of the desiccant bed unit 14 are
saturated with moisture in excess of 40% by weight of the desiccant
material of the desiccant bed modules, the system reverses and the
desiccant bed unit 14 cycles through a desorption phase recharging
the desiccant bed modules while at the same time functioning as
a condenser in the refrigerant heat pump circuit. The system 10
is capable of full-time operation as an air conditioning system,
however, because the desiccant bed unit 12 then cycles through the
adsorption phase drying and conditioning the building air while
at the same time functioning as an evaporator in the refrigerant
heat pump circuit. The two reverse cycle parallel complementary
desiccant bed units 12 and 14 of the system are separated by the
partition 64 to isolate heat transfer between the parallel units.
As warm, moist house air passes through the desiccant bed modules
21-24 of desiccant bed unit 14 during the adsorption phase for drying
the air, moisture condenses on the extended surface area of the
silica gel granules releasing the latent heat of condensation which
heats the silica gel bed. At the same time, refrigerant liquid such
as Freon (TM) refrigerant expands and evaporates in the refrigerant
tubes or channels of the desiccant bed modules absorbing or picking
up latent heat of evaporation from the desiccant bed transferring
the heat away in the refrigerant vapor through the headers 28 of
the desiccant bed modules. As a result, greater condensation and
greater moisture capacity is achieved at the surfaces of the desiccant
material. The refrigerating effect of the desiccant bed modules
functioning as an evaporator in the heat pump circuit also cools
the air passing through the desiccant bed modules by removing and
carrying away sensible heat. The heat exchanger 26 may be coupled
in series with the desiccant bed modules 21-24 in the refrigerant
line of the heat pump circuit upstream from the modules, therefore
also functioning as an evaporator for refrigerating and cooling
air passing through the bypass air passageway 25.
The heat exchanger 26 may also be reconfigured as a larger surface
area heat exchanger 27 and also positioned upstream in the air flow
from the desiccant bed modules 21-24 as illustrated in FIG. 6.
An advantage of this configuration is that the liquid-to-air heat
exchanger 27 functioning as a component of the evaporator of the
heat pump circuit cools the warm humid air approaching the desiccant
bed modules so that the building air approaches and reaches saturation
as it is cooled by evaporation of the refrigerant in the circulating
lines or channels of the heat exchanger 27. By this important expedient,
removal of water vapor from the house air by condensation on the
desiccant bed silica gel surfaces is maximized. By way of example,
when the relative humidity of the building air entering the silica
gel desiccant beds is increased to 100% relative humidity or saturation
and beyond that to super-saturation, the silica gel beads or granules
of the desiccant bed are capable of capturing, absorbing and condensing
over 50% by weight of the water exceeding the 40% by weight capacity
limit of the extended surface areas of the silica gel desiccant
material. Thus, with super-saturation moisture and water vapor in
the building air may be condensed over the outside of the silica
gel beads or granules. At the same time, the desiccant bed modules
functioning as evaporators carry away the heat of condensation in
the vaporization or evaporation of the refrigerant in the circulating
tubes or channels of the desiccant bed modules functioning as evaporators
in the heat pump cycle.
In the desorption phase exemplified by heat pump desiccant bed
unit 12 shown in FIGS. 1 5 and 6 hot air drawn from an external
source through the outside air inlet 57 and louvers 58 is constrained
to pass through the air passageways of desiccant bed modules 41-44
with the rotating shutter 50 closed. The hot desorbing air may be
derived for example from attic air or other solar heated air. Water
from the moisture-laden and saturated desiccant material surfaces
of the desiccant bed modules 41-44 evaporates into the desorbing
air flow which subjects the desorbing modules to evaporative cooling,
carrying away the heat of vaporization.
In the configuration of FIG. 6 a conventional liquid-to-air type
heat exchanger 47 extends across the entire air passageway at the
ends of the desiccant bed modules 41-44. During the desorption phase
this conventional heat exchanger 47 is positioned at the downstream
end of the desiccant bed modules and therefore does not perform
any substantial additional function of transferring heat to the
desorbing exhaust air. The circulating tubes or channels of the
heat exchanger 47 are coupled in series in the refrigerant flow.
According to an alternative example embodiment of the invention
hereafter described, a conventional metal surface liquid-to-air
heat exchanger similar to heat exchanger 47 may be placed upstream
from the desiccant bed modules in the desorbing air flow for preheating
the desorb air to increase the efficiency of desorption and evaporation
of moisture from the desiccant bed for recharging the desiccant
material surfaces.
At the same time, however, the modules are functioning as condensers
in a heat pump circuit delivering latent heat of condensation from
hot compressed refrigerant gas condensing in the refrigerant circulating
tubes or channels of the heat exchanging desiccant bed modules 41-44.
Transfer of latent heat of condensation from the refrigerant to
the desiccant beds from the inside of the desiccant beds is therefore
matched with transfer of latent heat of vaporization away from the
outside surfaces of the desiccant bed by moisture evaporating into
the desorbing air flow. Sensible heat is also transferred across
the desiccant bed from the hot refrigerant liquid to the desorbing
air flow. There is thus total enthalpy transfer across the heat
exchanging desiccant bed surfaces with "enthalpy matching"
in the transfer of both latent heat and sensible heat on both sides
of the desiccant bed heat exchanging surfaces by reason of the complementary
coincidence of desorption on one side in the air passageways and
condensation on the other side in the refrigerant circulating channels
as hereafter described. It is this synergistic coincidence and coaction
of desorption and condensation which permits the transfer of both
latent heat and sensible heat energy across the heat pumping, heat
exchanging, desiccant bed surfaces. This delivery of latent heat
and sensible heat energy to the desiccant bed by condensation on
one side and the carrying away of both latent heat energy and sensible
energy by desorption on the other side is referred to herein as
"enthalpy matching".
Simplified diagrams of the heat pump cycle showing the refrigerant
circuit and refrigerant line flow during reverse cycle operation
are shown in FIGS. 7 and 8. The heat exchanging desiccant bed units
12 and 14 with respective fans 20 and 16 are showing simplified
block diagram form and the heat pump cycle corresponding to FIG.
1 is illustrated in FIG. 7. In this cycle, heat exchanging desiccant
bed unit 14 is operating in the adsorption phase in the air conditioning
passageways and as an evaporator in the heat pump refrigerant line.
On the other hand, heat exchanging desiccant bed unit 12 is operating
in the desorption mode in the air conditioning air passageways while
functioning as a condenser in the refrigerant circulating line of
the heat pump. Referring to FIG. 7 the compressor 70 delivers hot
compressed refrigerant gas such as Freon (TM) gas at a temperature
in the range of, for example, 200.degree.-250.degree. F. (93.degree.-121.degree.
C.) and a pressure in the range reversing valve 72 to the refrigerant
circulating tubes or channels through desiccant bed unit 12 operating
in the desorption phase and functioning as a condenser in this heat
pump cycle. Passing through the heat exchanging desiccant bed unit
12 the hot refrigerant gas condenses giving up latent heat of condensation
and sensible heat energy to moisture on the desiccant material surfaces
evaporating into the desorb air flow. The condensed liquid refrigerant
still on the high pressure side of compressor 70 passes out of the
condenser heat exchanging desiccant bed 12 at a temperature in the
range of, for example, 90.degree.-120.degree. F. (32.degree.-49.degree.
C.) and bypasses the reverse cycle metering device or expansion
valve 74 through one-way check valve 75. The expansion valve 74
can pass liquid refrigerant in only one direction and operates as
the metering device or expansion valve during the reverse cycle
hereafter described with respect to FIG. 8. The one-way operation
of expansion valve 74 may be controlled by a thermostat associated
with the input line to desiccant bed unit 12.
The passage of refrigerant through the condenser desiccant bed
unit 12 lowers the temperature below the triple point of Freon (TM)
with the transition from the gaseous phase to liquid phase typically
at 120.degree. F. (49.degree. C.). The drop in temperature of the
refrigerant from 200.degree.-250.degree. F. (93.degree.-121.degree.
C.) to 100.degree.-120.degree. F. (38.degree.-49.degree. C.) represents
the typical 30% loss in energy during cooling operation of a conventional
heat pump refrigeration system. According to the present invention
this energy difference is substantially entirely utilized for recharging
the desiccant bed by desorption for use in drying, cooling, and
conditioning the building air during the adsorption air conditioning
phase when the heat exchanging desiccant bed unit also functions
as an evaporator in the heat pump circuit. The coacting coincidence
and synergism of the desiccant bed air conditioning phases of adsorption
and desorption with the heat pump cycles of evaporation and condensation
according to the present invention therefore affords an increase
in efficiency of substantially 30% over conventional reverse cycle
heat pump systems.
Referring again to FIG. 7 the condensed liquid refrigerant at
a temperature in the range of, for example, 100.degree.-120.degree.
F. (38.degree.-49.degree. C.) is metered, sprayed, and expanded
through the heat pump cooling or evaporating cycle metering device
or expansion valve 76 into the refrigerant circulating tubes or
channels of heat exchanging desiccant bed unit 14 which is operating
in the adsorption phase in the air conditioning air passageways
and functioning as an evaporator in the heat pump circuit. One-way
check valve 78 constrains the condensed liquid refrigerant to flow
during the forward cycle or first cycle through the expansion valve
76. As the refrigerant expands and evaporates through the channels
of desiccant bed unit 14 it cools the desiccant bed carrying away,
in the latent heat of vaporization and sensible heat of the refrigerant
gas, the latent heat of condensation of moisture adsorbed from humid
building air on the desiccant bed desiccant material surfaces and
sensible heat from the air passing through the air passageways of
heat exchange desiccant bed unit 14. Upon passing through the metering
device or expansion valve 76 and heat exchanging desiccant bed unit
14 functioning as an evaporator, the refrigerant gas, for example
Freon (TM) gas, is typically at a temperature of 50.degree.-60.degree.
F. (10.degree.-15.degree. C.) and at a pressure of 50-60 psi (3.6-4.3
kgs/cm). The refrigerant then passes through four-way reversing
valve 72 through the accumulator 80 and back into the compressor
70. Accumulator 80 serves to trap any remaining liquid refrigerant
so that only refrigerant gas or vapor re-enters the compressor 70.
For operation of the heat pump circuit of FIG. 7 according to the
desiccant bed configuration of FIG. 6 a conventional metal surface
liquid-to-air type heat exchanger 27 of FIG. 6 would be interposed
on the evaporator side of the refrigerant line, for example upstream
from the heat exchanging desiccant bed 14 for pre-cooling building
air before it enters the air passageways of desiccant bed unit 14.
Such pre-cooling of the building air has the advantage as previously
described of increasing the relative humidity of the air and therefore
increasing the adsorption and condensation of moisture from the
air on the desiccant material surfaces of desiccant bed unit 14.
Similarly, a conventional metal surface liquid-to-air type heat
exchanger may be placed upstream on the condenser side of the heat
pump upstream in the refrigerant line from the heat exchanging desiccant
bed 12 for preheating desorption air passing through the air passageways
of desiccant bed unit 12 for greater desorption and evaporation
of moisture from the desiccant material surfaces during recharging
of desiccant bed unit 12.
The reverse cycle heat pump operation is illustrated in FIG. 8.
When the desiccant material surfaces of desiccant bed unit 14 have
been saturated during the adsorption phase, four-way reversing valve
72 is actuated and rotated so that heat exchanging desiccant bed
12 operates in the evaporation cycle or phase while desiccant bed
unit 14 is recharging. At the same time that reversing valve 72
is actuated the reversing fans 16 and 20 are reversed for reversing
the adsorption and desorption phases of the desiccant bed air passageways
as described with reference to FIGS. 1-6.
The provision of two parallel complementary heat exchanging desiccant
bed units 12 and 14 with reversing fans and reverse cycle operation
in the adsorption and desorption phases in a heat pump circuit with
the desiccant beds coinciding with the evaporator and condenser
of the heat pump circuit capable of reverse cycle operation in evaporation
and condensation phases coincident with the adsorption and desorption
phases, the heat pump desiccant bed air conditioning system is capable
of full-time operation with one side of the system always conditioning
building air while the other side of the system is recharging.
The reverse cycle capability further permits substantially complete
utilization of the system energy without the 30% loss of system
energy normally experienced by conventional heat pump systems by
utilizing what would ordinarily be waste heat energy for recharging
one side of the system while the other side is air conditioning.
The two complementary sides of the heat pump desiccant bed air conditioning
system cycle back and forth between the coincident adsorption and
evaporation phases on the one hand and the desorption and condensation
phases on the other hand.
A more detailed system diagram of an alternative arrangement for
the heat pump desiccant bed air conditioning system showing the
heat pump refrigerant circuit is illustrated in FIG. 9. In this
diagram the solid arrows represent the refrigerant flow during the
cycle of operation when heat exchanging desiccant bed unit 14 is
operating in the adsorption phase in the air conditioning air flow
and functioning as an evaporator in the refrigerant line while heat
exchanging desiccant bed unit 12 is operating in the desorption
phase in the air conditioning air flow while functioning as a condenser
in the refrigerant line thereby corresponding to the cycle of operation
illustrated in FIGS. 1 and 7. The reverse cycle operation corresponding
to FIG. 8 is shown in dashed arrows.
However in the system of FIG. 9 conventional metal surface liquid-to-air
type heat exchangers 82 and 84 have been positioned in the air conditioning
air flow upstream from the respective heat exchanging desiccant
beds 12 and 14. On the other hand in the refrigerant circulating
line the heat exchangers (HX) 82 and 84 are upstream in the refrigerant
circulating line from the respective heat exchanging desiccant beds
(HX) 12 14 when the HX is functioning as an evaporator, and downstream
in the refrigerant circulating line when the respective HX is functioning
as a condenser.
Referring to FIG. 9 and the cycle of operation represented by solid
arrows, the compressor 85 forces high temperature and pressure refrigerant
vapor or gas such as Freon (TM) vapor for example at 250.degree.
F. (121.degree. C.) and 300 psi (21 kgs/cm) through oil trap 86
and reversing 4 way valve 87 in the channel direction represented
by solid lines through the 4 way valve 87. The hot pressurized refrigerant
vapor flows into the circulating tubes or channels of desiccant
bed unit 12 functioning as a condenser in the refrigerant circulating
line while desorbing its desiccant bed desiccant materials surfaces
in the exhaust air passageway.
The high pressure Freon (TM) refrigerant exits the circulating
channels of desiccant bed 12 partially condensed liquid and partially
vapor at a temperature for example 120.degree. F. (49.degree. C.)
and pressure of 300 psi (21 kgs/cm) and approaches the on/off valves
88 and 89. In this cycle of operation valve 89 is closed and valve
88 is open passing the hot refrigerant through conventional heat
exchanger 82 which serves to preheat the desorbing exhaust air passing
through the air passageways of desiccant bed unit 12. For example
desorb air entering heat exchanger 82 at a temperature in the range
of for example 85.degree.-90.degree. F. (29.degree.-32.degree. C.)
is preheated by the 120.degree. F. (49.degree. C.)Freon (TM) refrigerant
and at the same time the condensation of refrigerant to liquid at
a temperature for example 100.degree. F. (38.degree. C.) is complete.
The system components are configured so that the refrigerant enters
the top of heat exchanger 82 and the fully condensed liquid exits
at the bottom. The liquid refrigerant cannot pass through expansion
valve 90 and therefore by passes around to dryer 92 for removal
of water, site glass 93 to expansion valve 94. At expansion valve
94 the liquid refrigerant is released and expanded into the low
pressure side of the refrigerant circuit. During this cycle of operation
on/off valve 95 is closed and valve 96 is open so that the refrigerant
flows partially expanding into the bottom of heat exchanger 84 at
a temperature for example 45.degree. F. (7.degree. C.) at a pressure
of 60 psi (4.3 kgs/cm). Heat exchanger 84 which is positioned upstream
in the air conditioning air flow through desiccant bed unit 14 pre-cools
the warm building air to increase its relative humidity and thereby
increase the adsorption of moisture on the desiccant material surfaces
of heat exchanging desiccant bed 14. Because the refrigerant picks
up heat in heat exchanger 84 it exits the top of heat exchanger
84 at a temperature for example 50.degree. F. (10.degree. C.) and
50 psi (3.6 kgs/cm).
The refrigerant then flows into the bottom of HXDB 14 expanding
into the circulating tubes or channels cooling the desiccant bed
desiccant material surfaces as it evaporates thereby carrying away
the latent heat of condensation from moisture adsorbing on the desiccant
material surfaces exposed to the air passageways. Sensible heat
is also transferred to the refrigerant across the heat exchanging
desiccant bed from building air flowing in the HXDB air passageways.
The vaporized refrigerant leaves the top of HXDB 14 at a temperature
in the range of 55.degree.-60.degree. F. (12.8.degree.-15.degree.
C.) and pressure of 50 psi (3.6 kgs/cm) for return through four-way
reversing valve 87 to accumulator 96. Any liquid refrigerant is
trapped in accumulator 96 for revaporization before return to the
inlet of compressor 85 for recycling.
When the desiccant material surfaces of the desiccant bed modules
in HXDB 14 have adsorbed moisture to their full capacity (e.g. 40%
by weight of silica gel granules or beads) the reverse cycle is
initiated. A humidity sensor in the building air flow at the outlet
of the HXDB may be used for this purpose. To reverse the cycle of
operation the four way reserving valve 87 is changed manually or
automatically in response to a humidistat so that the Freon (TM)
or other refrigerant flow follows the paths of the dash lines in
valve 87. The refrigerant circulation then follows the path of the
dashed arrows so that the system operates identically in reverse
with HXDB 14 functioning as a condenser in the heat pump circuit
while HXDB 12 functions as an evaporator. At the same time the reversing
fans 16 and 20 in the air flow and corresponding shutters and louvers
are reserved so that the HXDB 12 operates in the adsorption phase
adsorbing moisture from humid building air, while HXDB 14 is recharging
and desorbing moisture from the desiccant material surfaces into
an exhaust air flow.
One construction arrangement for the desiccant bed modules 21 through
24 and 41 through 44 is illustrated in FIGS. 10 and 10A as set forth
in applicants co-pending U.S. patent application Ser. No. 750932
for DESICCANT SOLAR AIR CONDITIONING SYSTEM filed July 1 1985.
According to this embodiment, each desiccant bed module 101 is formed
by a stack of side-by-side two sheets or tube fins 102. Each tube
fin comprises a liquid coolant or refrigerant circulating tube or
channel 104 of liquid confining thermally conducting material such
as copper. A fin 105 of heat conducting metal such as aluminum is
soldered, welded or otherwise intimately bonded to the tub 104 for
good thermal conductivity. The ends of fins 105 are folded over
providing spacers 96 for spacing the tub plates or tub pins in substantially
parallel relationship from each other and for defining the air passageways
108 between the fins 105. The substantially equal spacing of the
tub fins 102 and fins or plates 105 substantially equalizes the
pressure gradient over the desiccant bed for equalizing flow of
air through the bed during the adsorb and desorb cycle.
The desiccant material and extended desiccant surface area throughout
the desiccant bed of the module is provided by silica gel granules
such as commercial silica gel, for example in the form of spheres
110 intimately contacting and bonded over the surfaces of the tube
fins 102. For adhesive bonding of the silica gel spheres 110 to
the surfaces of the tubes 104 and fins or plates 105 a thin layer
of an adhesive bonding glue which also forms a good heat conducting
layer is applied over the surfaces of the circulating tube 104 and
fins or plates 105. An adhesive bonding material or glue such as
silicone rubber glue provides the advantages of intimate bonding
and good thermal conductivity. To enhance the thermal conductivity
of the adhesive layer, metal particle filler may be added to the
silicone rubber glue or other glue. Such metal particle fillers
may also be incorporated in the silica gel to improve thermal conductivity.
The silica gel spheres 110 are then spread over the surface and
pressed through the layer of silicone rubber glue until they actually
touch the aluminum fins or plates 105 and tube 104. An advantage
of using aluminum for the fins, sheets or plates 105 is that the
pores in aluminum facilitate adhesive bonding.
While the preferred example embodiment is described with reference
to silica gel spheres, other granule size forms of silica gel such
as crushed pieces, pellets, etc. may also be used but in the preferred
granular size range greater then power size, that is, in the mesh
size greater than U.S. or Tyler Standard Mesh Size 50 and preferably
from mesh size, for example, 20 up to mesh size 4 and greater. Thus,
the diameter of the granules, pieces, pellets or spheres is in the
optimum range of for example 132 inch to 1/4 inch (0.08 to 0.65
cm). While silica gel is the preferred desiccant material other
desiccants may also be used such as activated alumina or aluminum
oxide and zeolite. Other construction details and features are set
forth in applicant's co-pending patent application Ser. No. 750932
referred to above.
Other parallel plate structures with heat conducting surfaces and
circulating tubes or channels may also be used for in the construction
of the desiccant bed modules such as for example tube sheets and
radiators. Tube sheets are two sheets of metal, welded, bonded,
or laminated together with air space channels between the sheets
defining liquid circulating channels. Radiators of course provide
tortuous liquid circulating tubes or channels with parallel radiator
fins extending from the tubes or channels such as in an automobile
radiator. The radiator fins or tube sheets are then coated with
a layer of granular silica gel as defined above. It is advantageous
in the structure of the desiccant bed modules to incorporate liquid
coolant or refrigerant circulating tubes and channels which are
tortuous, folding back on themselves to provide extended passes
through the desiccant bed module in heat exchange relationship with
the fins, plates, or radiators for complete evaporation or condensation
of refrigerant circulating through the desiccant bed modules.
One method for mass producing the desiccant bed module of silica
gel granules on such radiator structures or on stacked tube fins
or tube sheets is to spray silicone rubber glue over the heat transfer
surfaces to be coated and then role silica gel beads over each other
onto the layer of silicone rubber glue until it is fully covered
with granular silica gel. Thus, the silica gel beads are poured
into the slots between the radiator fins after spraying with the
desired layer of silicone rubber glue A suitable radiator structure
for coating in this manner and use in the desiccant bed module is
for example and automobile transmission cooler type radiator. Generally
it is desirable to use such a radiator structure with radiator fin
spacing of 1/2 inch (1.3 cm) to accommodate silica gel beads or
other desiccant beads in the order of 1/8 inch (0.3 cm) on each
surface while still leaving a 1/4 inch (0.6 cm) air passageway gap
between each of pair of desiccant granule coated radiator fins.
Typically the size of each of the desiccant bed modules 21 through
24 and 41 through 44 using stacked tube fins or tube sheets is approximately
4 inches (10 cm) wide with a height and width of length of approximately
22 inches (56 cm) by 20 inches (51 cm) or approximately 2 feet by
2 feet (61 cm by 61 cm). Typical automobile type radiators for use
in the desiccant bed modules typically range in size from 2 to 4
inches (5 to 10 cm) thick with a height and length of width of 16
by 16 inches (41 by 41 cm).
A new integrated heat exchanger desiccant bed structure according
to the present invention is illustrated in FIG. 11. This new integrated
heat exchanging desiccant bed structure example illustrated in FIG.
11 is dimension to replace, for example four of the desiccant bed
modules such as 21 through 24 of FIG. 1. At the same time the integrated
heat exchanger of FIG. 11 incorporates conventional metal surface
liquid-to-air type heat exchangers with a desiccant bed heat exchanger
in an alternating band construction. The integrated heat exchanger
desiccant bed 120 is formed by a stack of tube sheets or folded
tube fins each formed with a tortuous or serpentine liquid coolant
or refrigerant circulating channel 124 which folds back on itself
many times between the inlet and outlet header pipes conduit 125
and 126 at each end of the integrated bed. While the width and length
of the bed is approximately 16 by 16 inches (41 by 41 cm), the height
of the integrated bed provides the elongate dimension of approximately
32 inches (81 cm) and the air flows for adsorption and desorption
are directed through the integrated bed in this elongate direction.
Thus the refrigerant or liquid coolant flows in the serpentine channels
124 is generally perpendicular to the air flow through the elongate
dimension of the desiccant bed.
As illustrated in FIG. 11 only a central band or portion of the
integrated structure is coated with desiccant materials such as
silica gel granules 128 to provide a central heat exchanging desiccant
bed bans or portion 132 sandwiched between two uncoated metal surface
portions constituting outer conventional heat exchanger bands or
portions 130 and 134. The single integrated heat exchanger desiccant
bed structure referred to herein by the symbol designation HX/DB/HX
incorporates conventional liquid-to-air type heat exchangers 130
and 134 on either side of the heat exchanging desiccant bed 132
that is both upstream and downstream relative to the desiccant bed
in the air conditioning adsorption air flow and the recharging desorption
air flow. Furthermore, the conventional heat exchanger bands 130
and 134 further constitute conventional evaporator and condenser
elements on either side of the heat exchanging desiccant bed evaporator
or condenser element in the refrigerant circulating line. This affords
a number of advantages when the integrated heat exchanging desiccant
bed structure 120 is incorporated in air conditioning systems of
the type described for example with reference to FIGS. 1 and 6.
In effect the conventional heat exchangers 26 and 46 of FIG. 1 and
27 and 47 of FIG. 6 have been incorporated as integral elements
of the unitary heat exchanging bed structure.
The integrated unitary heat exchanging desiccant bed structure
HX/DB/HX of FIG. 11 is incorporated in the air conditioning system
with the air flows either desorption or adsorption passing through
the HX/DB/HX structure in the elongate direction. Furthermore, the
headers 125 and 126 of the serpentine refrigerant circulating channels
are coupled into the heat pump refrigerant circuit in the manner
described with reference to FIGS. 7 8 and 9. With the HX/DB/HX
bed 120 functioning as an evaporator in the heat pump circuit and
functioning to adsorb and condition building air in the air flow,
moist building air is first pre-cooled in the conventional heat
exchanger band 130 lowering the temperature of the in flowing air
so that it approaches 100% relative humidity or super-saturation.
Moisture is adsorbed or condensed from the building air as it then
passes through the desiccant bed band 132 releasing the latent heat
of condensation. The latent heat of condensation is carried away
by latent heat of evaporation of refrigerant passing through the
serpentine or tortuous refrigerant circulating channels 124. Finally
sensible heat is removed from the dried building air as it passes
through the final conventional heat exchanger band or portion 134
before exiting to the building air duct. Throughout the adsorption
phase, the integrated heat exchanging desiccant bed 120 is functioning
as an evaporator in the heat pump circuit with conventional heat
exchanger bands 130 and 134 functioning as conventional evaporator
elements while the desiccant bed band 132 functions as a novel enthalpic
heat pump evaporator element because of the matching and complementary
latent heat and sensible heat processes taking place on either side
of the desiccant bed surfaces. Thus in the central desiccant bed
band 132 latent heat of condensation is given up on the desiccant
material surfaces by condensing and adsorbing moisture while latent
heat of vaporization is carried away by expansion and evaporation
of refrigerant inside the refrigerant circulating channels 124 in
heat exchange relationship with the desiccant bed surfaces. At the
same time sensible heat is also transferred across the surfaces
for total enthalpy impedance matching in both latent and sensible
heat transfer.
During the reverse cycle or recharging operation of the integrated
bed 120 after the desiccant material surfaces are saturated to capacity
with water, desorb air enters one end of the elongate integrated
unit such as for example attic air or solar heated air and is preheated
as it passes through the first conventional heat exchanger band
for example band 134. The recharging desorb air is preheated by
the hot pressurized refrigerant gas as both the desorb air and refrigerant
pass through the conventional heat exchanger band or element 134.
Preheating lowers the relative humidity of the recharging air for
evaporation of moisture from the desiccant material surfaces of
the desiccant bed band 132. Latent heat of vaporization for desorbing
moisture from the desiccant bed band 132 is provided by the latent
heat of condensation of hot refrigerant gas condensing in the refrigerant
circulating channels 124 passing through the central band 132 of
the integrated bed. Finally the exhaust air laden with moisture
from the desiccant bed band 132 passes through the final conventional
heat exchanger band 130 for venting to the outside. In the final
conventional heat exchanger band 130 some additional sensible heat
may be given up by the refrigerant circulating in the refrigerant
lines 124 to the exhaust air which undergoes some evaporative cooling
in the desiccant band 132.
By way of example the integrated desiccant bed unit 120 is represented
by the symbolism HXlDDB/HX2 for description of operating examples
during the reverse cycle or condensation/desorption phase. Referring
first to the heat pump circuit refrigerant flow, hot refrigerant
gas at 200.degree. F. (93.degree. C.) passes through the HXl band
preheating the recharging desorb air giving up sensible heat to
the air and cooling the refrigerant. The Freon (TM) refrigerant
then enters the DB band at approximately 160.degree. F. (71.degree.
C.) undergoing condensation and rapid cooling in the central desiccant
bed band while moisture evaporates from the desiccant bed surfaces
into the desorb air. Thus while the band DB is wet and laden with
moisture for enthalpic heat transfer of both latent and sensible
heat across the surfaces of the central band DB the refrigerant
leaves the band DB and enters the portions of the refrigerant circulating
channels in HX2 at approximately 105.degree. F. (41.degree. C.).
While band HX2 is primarily inactive during the reverse cycle or
condensation/desorption phase of operation there is some further
transfer of sensible heat from the refrigerant to the exhaust air
so that the refrigerant exits from the integrated HX1/DB/HX2 unit
120 at a temperature in the range of for example 100.degree.-105.degree.
F. (38.degree.-41.degree. C.) and typically 102.degree. F. (39.degree.
C.).
At the same time recharging or desorb air entering the air passageways
of HX1 at for example 90.degree. F. (32.degree. C.) is preheated
by the Freon (TM) refrigerant to for example 120.degree. F. (49.degree.
C.) as it enters the air passageways of the central band DB. In
desorbing moisture from the desiccant bed surfaces, the recharging
air is subject to some evaporative cooling, emerges from the central
portion DB at a temperature of approximately 100.degree.-105.degree.
F. (38.degree.-41.degree. C.), and exits from the final heat exchanger
band HX2 which is primarily inactive during the condensation/desorption
phase, within the same temperature range. While the desiccant bed
band DB remains laden with moisture during recharging the latent
heat of vaporization of the desorb moisture is matched and supplied
by the latent heat of condensation of refrigerant circulating in
the channels 124 at the same time that sensible heat energy is also
transferred across the surfaces of the desiccant bed band DB. It
is this matching and transfer of both latent and sensible heat energy
that is referred to herein as enthalpic impedance matching and enthalpic
heat pumping and heat transfer which greatly increases the efficiency
of heat pump desiccant bed air conditioning system of the present
invention.
After the desiccant bed band DB has dried, during the reverse cycle
or condensation/desorption phase of operation, the enthalpic heat
energy transfer and matching ceases and the entire integrated HX/DB/HX
sandwich structure functions as a conventional liquid-to-air type
heat exchanger. This is because while the refrigerant gas undergoing
condensation to the liquid state gives up heat of condensation to
the surfaces of the heat exchanger desiccant bed structure, there
is no latent heat of vaporization from moisture on the desiccant
material surfaces to carry away the latent heat of condensation
from the refrigerant. As a result all of the heat given up by the
refrigerant both latent and sensible heat must by converted to sensible
heat of the exhaust air passing through the air passageways. By
way of example, the desiccant bed band DB dry desorb air enters
the first heat exchanger band HX1 at a temperature for example 90.degree.
F. (32.degree. C.) and is preheated passing through the first band
HXI to a temperature of for example 120.degree. F. (49.degree. C.).
Passing through the central desiccant bed band DB the exhaust air
continues to pick up heat from the condensing refrigerant in the
form of sensible heating of the air emerging from the central band
DB at a temperature of for example 130.degree. F. (54.degree. C.).
The air remains approximately at the same elevated temperature exiting
the final heat exchanger band HX2. At the same time the effect on
the refrigerant with the desiccant bed band DB dry is as follows.
Hot pressurized refrigerant vapor, for example Freon (TM) vapor
enters the circulating channels of the first heat exchanger band
HX1 at temperature of 200.degree. F. (93.degree. C.) giving up heat
to the exhaust air and entering the central desiccant bed band DB
at a temperature of for example 160.degree. F. (71.degree. C.).
In this example with desiccant bed DB dry the central band DB functions
as a conventional heat exchanger able to carry away heat from the
refrigerant only in the more limited form of sensible heating of
the air temperature and the refrigerant emerges from the central
band DB at a temperature for example 140.degree.-150.degree. F.
(60.degree.-66.degree. C.). It is in this example that the final
heat exchange band HX2 performs an active condensing function in
further cooling the refrigerant to the condensation temperature
range.
The stacked tube plates of the integrated HX/DB/HX bed of FIG.
11 can be manufactured or formed in a variety of ways. According
to one method, tube fins of the type illustrated in FIG. 10 are
simply folded back and forth with sections of the fins removed at
the turns so that the fins abut against each other and form a substantially
continuous plate joined by the serpentine tube or channel as illustrated
in FIG. 11. According to another method the tube plates of FIG.
11 are manufactured in the same manner as tube sheets in which flat
pieces of metal are bonded together leaving an unbonded tortuous
or serpentine strip which is inflated at for example 400 psi (28.6
kgs/cm) to form the sealed internal tube or channel between the
flat parallel bonded plates. The tubes are approximately 1/4 to
3/8 inch (0.6 to 1 cm) in diameter and the tube plates are stacked
with approximately a 1/4 inch (0.6 cm) gap between the tubes. In
the example of FIG. 11 approximately 25 plates 32 inches (81 cm)
in height and 16 inches (41 cm) wide are stacked to provide the
integrated bed. Before the plates are stacked the silicone rubber
glue is spread over approximately the middle third of the plates
on both sides and the desiccant material such as silica gel granules
are spread over and pressed into the bonding layer of glue.
The invention also contemplates a number of variations in the desiccant
bed structures to enhance heat transfer across the desiccant bed
surfaces. For example with desiccant bed modules of the type illustrated
in FIG. 10 some of the surfaces may be left uncoated. Thus every
other tube fin may be left uncoated by desiccant material exposing
the metal surfaces for greater heat transfer and heat conductivity.
Alternatively one side of the tube fins may be left exposed or one
side of alternative tube fins may be left exposed for direct metal
to air contact. Similarly in the integrated HX/DB/HX heat exchangers,
some of the surfaces of the central band DB may be left uncoated
with desiccant material to expose metal surfaces to air flowing
through the air passageways. Another expedient is to mix metal particles
or pieces with the desiccant bed material to enhance heat transfer
across the layer of desiccant material. The stacked tube sheets,
tube plates and tube fins can be made removal and replaceable for
varying the area of desiccant material surfaces or the area of exposed
metal surfaces according to the application such as summer cooling
or winter heating. For example for winter heating applications it
may be desirable to minimize or eliminate the desiccant material
surfaces for maximizing heat transfer and delivery of heat from
heat transfer liquid circulating in the channels or tubes. On the
other hand for summer cooling it may be desirable to maximize the
desiccant bed desiccant material surface area.
The invention contemplates a variety of permutations and combinations
of the adsorb and desorb desiccant bed elements and the evaporator
and condenser elements of the heat pump. The invention also contemplates
various combinations of the foregoing identified elements with non-change
of phase heat transfer liquid circulating heat exchanging desiccant
bed elements of the type described in applicant's co-pending patent
application Ser. No. 750932 referred to above. For example, according
to the present invention the evaporator of the heat pump desiccant
bed air conditioning system may comprise two elements with separate
parallel circulating lines. One element is a conventional meta surface
liquid-to-air type heat exchanger which functions as an evaporator
element having change of phase refrigerant such as Freon (TM) flowing
through it while the heat exchanging desiccant bed comprises an
evaporator element having non-change of phase heat transfer liquid
such as liquid circulating through it. The two evaporator elements
are placed in series in the air conditioning building air flow with
the conventional heat exchanger upstream in the air flow from the
heat exchanging desiccant bed for pre-cooling moist building air
before it passes through the desiccant bed. The refrigerant circuit
for the conventional heat exchanger evaporator element is of the
type described, for example, with reference to FIGS. 7 8 and 9
while the non-change of phase heat transfer liquid circulating system
is of the type described in U.S. Ser. No. 750932.
The invention also contemplates split unit air conditioners combining
a heat pump with a conventional heat exchanger evaporator inside
the house for cooling the house air and a pair of heat exchanging
desiccant beds performing the condenser function outside the house.
In this arrangement, one of the pair of heat exchanging desiccant
beds on the outside is always functioning as the condenser for the
heat pump refrigerant circuit while the other HXDB is decoupled
from the heat pump circuit and serves only to dry air drawn into
the building through the air passageways defined by the desiccant
material surfaces. In this manner the HXDB functioning as the condenser
is always able to have moisture-laden desiccant material surfaces
to carry away the latent heat of condensation of refrigerant in
the circulating tubes in the latent heat of evaporation of moisture
on the desiccant material surfaces. When the desiccant material
surfaces have dried out the HXDB's are switched so that the wet
or moisture-laden HXDB becomes the condenser and the dry HXDB is
used for adsorbing moisture from outside air drawn into the building.
A much greater efficiency and coefficient of performance of the
split unit air conditioning system is thereby achieved.
According to another combination, a heat pumping heat exchanging
desiccant bed structure may be provided for example as illustrated
in FIGS. 10 and 11 but having two sets of parallel circulating channels
or tubes in heat exchange relationship with fins, plates, sheets
or radiators bearing desiccant material surfaces. One of the two
sets of tubes or channels may be coupled in a non-change of phase
heat transfer liquid circulating system or circuit such as a water
circulating system while the other set of tubes or channels is coupled
in a heat pump refrigerant circulating system of circuit. By this
expedient the heat exchanging desiccant bed may operate to import
heat energy into the system or export heat energy out of the system
using either a non-change of phase heat transfer liquid, a change
of phase refrigerant liquid, or both, according to the available
external energy sources.
In each of the heat exchanging desiccant bed air conditioning systems
it may be advantageous to include conventional heat exchangers either
upstream in the air flow from the HXDB, downstream in the air flow
from the HXDB or both upstream and downstream as exemplified in
the HX/DB/HX integrated heat exchanger of FIG. 11. Furthermore,
the heat transfer liquid or refrigerant may circulate through the
upstream heat exchanger first for greater pre-cooling of building
air during the adsorption phase, or may circulate through the downstream
heat exchanger first for greater after-cooling.
It is also noted that in each of the described and illustrated
example embodiments of the invention and in the various combinations
and permutations of the invention, there is generally a final evaporative
cooling step, not shown, applied to the conditioned building air
exiting from the coincident adsorption and evaporation phase. Thus,
the building air processed through the heat exchanging desiccant
bed and any subsidiary heat exchangers is dry, partially cooled
air, which is then further cooled and humidified of achieve desired
parameters in the comfort zone range by a final evaporative cooling
step, not shown. Such evaporative cooling methods are well known,
for example using a so-called "swamp cooler" or spray
moisturizer.
Another expedient, according to the invention, to increase the
work efficiency of the system as described, for example, in U.S.
Ser. No. 750932 is to further moisturizer or humidify warm humid
building air upstream from the HXDB which is operating in the coincident
adsorption and evaporation mode. Such moisturizing, for example,
by spray moisturizing or using a swamp cooler amounts to an evaporative
cooling step upstream from the adsorption bed which cools the building
air in the direction of the desired temperature range and makes
greater use of the desiccant bed to remove the excess added moisture.
Basically, the work of the adsorption desiccant bed is used to achieve
a lower temperature of the building air by evaporative cooling of
the building air upstream from the desiccant bed all as further
explained in U.S. Ser. No. 750932.
In another embodiment of the invention, the desiccant bed air conditioning
system and heat pump refrigerant system are combined in another
coacting configuration. According to this embodiment, a heat exchanging
desiccant bed air conditioning system of the type described in co-pending
U.S. patent application Ser. No. 750932 is provided. Hot and humid
air to be conditioned passes through the air passageways of a first
heat exchanging desiccant bed for adsorption of moisture on the
extended surface area of the desiccant material during an adsorb
cycle. At the same time, a coolant liquid such as water is circulated
through the circulating channels of the HXDB in heat exchange relationship
with the desiccant material surfaces for efficient removal of latent
heat of condensation from the desiccant bed. The cooling liquid
circulating through the HXDB during the adsorb cycle is derived
from a cold tank or cold water storage tank and returns to the tank
in a closed circuit.
At the same time hot recharge air flows through the air passageways
of a second heat exchanging desiccant bed in the desorb phase or
cycle for evaporating and removing moisture from the saturated or
moisture-laden desiccant material surfaces. A heating liquid such
as water circulates through the circulating channels of the HXDB
in heat exchange relationship with the desiccant bed for importing
heat from a hot tank or hot water storage tank into the system for
increasing the efficiency and rate of evaporation from the desiccant
material surfaces and regeneration of the desiccant bed.
When the first heat exchanging desiccant bed operating in the adsorption
phase is saturated with moisture and the second heat exchanging
desiccant bed has been recharged by drying during the desorption
phase, the function of the HXDB's is switched and the first HXDB
commences operation in the desorption phase for recharging and drying
while the second HXDB commences operation in the adsorption phase
for removing moisture and conditioning the building air. This is
accomplished as fully set forth in U.S. Ser. No. 750932 by the
switching of valves in the respective circulating lines so that
hot water or other heating liquid from the hot tank circulates through
the first heat exchanging desiccant bed now in the desorption phase
while the cold water or liquid coolant from the cold tank circulates
in the second heat exchanging desiccant bed now in the adsorption
phase. At the same time shutters or louvers are reversed so that
building air to be conditioned flows through the second HXDB for
adsorption in the desiccant bed air passageways while heated recharging
air flows through the air passageways of the first HXDB for recharging.
According to the present invention, to this pair of parallel, complementary,
alternate cycling non-change of phase heat transfer liquid circulating
heat exchanging desiccant beds, is added a heat pump having an evaporator
coil immersed in the cold tank or in heat exchange relationship
with the circulating cold water, and a condenser coil immersed in
the hot tank or in heat exchange relationship with the circulating
hot water tank. By this arrangement, according to the present invention,
heat energy returning to the cold tank in water or other heat transfer
fluid circulating in the return line from the adsorption phase heat
exchanging desiccant bed is continuously pumped out of the cold
tank through the evaporator coil in the latent heat of vaporization
of the refrigerant vapor and transferred to the hot tank through
the condenser coil by the heat of condensation from the liquid refrigerant.
As a result, the coolant liquid or cold water in the cold tank remains
cold for efficient removal of heat from the adsorption desiccant
bed increasing the efficiency of adsorption. At the same time the
heating liquid or heat water in the hot tank remains hot for efficient
recharging and drying of the desorbing desiccant bed in the desorption
phase.
This is accomplished by what is effectively enthalpic matching
and enthalpic pumping of both latent and sensible heat energy. The
latent heat of condensation in the adsorption desiccant bed is carried
away by the coolant liquid or cold water to the cold tank. It is
then pumped or transferred in the latent heat of vaporization of
the refrigerant and delivered to the hot tank as latent heat of
condensation. This heat is then transferred to the desorption desiccant
bed to provide the latent heat of evaporation of moisture desorbed
from the desiccant material surfaces. Sensible heat is combined
with the latent heat transfer throughout the cycle. Effectively,
the latent heat and sensible heat associated with adsorption and
condensation of moisture in the adsorption desiccant bed is ultimately
delivered up as the latent and sensible heat of desorption and evaporation
of moisture from the desorption desiccant bed.
Referring to FIG. 12 hot refrigerant gas is pumped from compressor
150 through a coaxial coil heat exchanger condenser 142 through
which also circulates the hot water or other heat transfer liquid
from the hot tank of a non-change-of-phase heat exchanging desiccant
air conditioning system (not shown) of the type described in U.S.
Ser. No. 750932. The refrigerant condenses giving up its heat to
the circulating water, then passes through expansion valve 144 expanding
through coaxial coil heat exchanger evaporator 145. The refrigerant
evaporates and picks up heat from the circulating cold water from
the cold tank of the heat exchanging desiccant air conditioning
system of U. S. Ser. No. 750932 (not shown). The evaporated refrigerant
returns to compressor 140 through accumulator 146.
The difference between this embodiment of the invention and the
systems of FIGS. 1-11 is that in the systems FIGS. 1-11 the change
of phase refrigerant circulates directly in the channels of the
heat exchanging desiccant beds while in the latter embodiment the
change of phase refrigerant circulates between the cold tank and
hot tank circulating lines, one step removed from the heat exchanging
desiccant beds. A non-change of phase heat transfer liquid circulating
loop or link is therefore provided between the adsorption heat exchanging
desiccant bed and the cold tank or cold water circulating line and
between the desorption heat exchanging desiccant bed and the hot
tank or hot water circulating line. The heat pump circuit is therefore
one step removed from the air conditioning heat exchanging desiccant
beds and a non-change of phase heat transfer fluid circulating link
or loop is provided in each direction to complete the enthalpic
impedance matching latent heat and sensible heat energy transfer
between the reverse cycling heat exchanging desiccant beds.
The system of FIG. 12 provides substantial energy savings over
conventional air conditioners. In addition to the 30% saving of
energy by use of the condenser heat and heat of compression, the
system permits load management by use of non-peak load energy with
insulated hot and cold tanks.
The COP or coefficient of performance for this system is approximately
3.5 compared to the COP of 2.14 for conventional air conditioners.
The SEER or seasonal energy efficiency ratio is 11.9 compared to
the conventional SEER of 7.3. With solar heating of the hot water,
the present invention achieves a COP of 5.3 and a SEER of 18.1.
The peak load savings are substantial affording 30% to 80% reduction
in use of peak energy.
While the invention has been described with reference to particular
example embodiments, it is intended to cover all modifications and
equivalents within the scope of the following claims. |