U.S. patent application number 09/819530 was filed with the patent office on 2001-08-16 for liquid desiccant air conditioner.
Invention is credited to Baumann, Robert, Gurley, Kevin, Laurent, Robert L. JR., McKittrick, Phillip T., Potnis, Shailesh V., Rao, Srikant Ram.
Application Number | 20010013226 09/819530 |
Document ID | / |
Family ID | 25530813 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013226 |
Kind Code |
A1 |
Potnis, Shailesh V. ; et
al. |
August 16, 2001 |
Liquid desiccant air conditioner
Abstract
The present invention provides a liquid desiccant air
conditioner including an absorption air conditioner and a liquid
desiccant dehumidifier. The dehumidifier includes a liquid
desiccant absorber for absorbing moisture contained in ambient air
entering the dehumidifier and passing through the desiccant
absorber. A boiler is provided for boiling partially preheated
dilute liquid desiccant to evaporate moisture to reconstitute the
liquid desiccant into concentrated liquid desiccant. In a preferred
embodiment, a first heat exchanger fluidly communicates with the
desiccant absorber and a second heat exchanger. The first heat
exchanger is operable to transfer heat from the concentrated liquid
desiccant to the dilute liquid desiccant directed to the first heat
exchanger from the desiccant absorber to raise the temperature of
the dilute liquid desiccant to a first temperature. A condenser
fluidly communicates with the boiler to receive steam generated by
boiling the liquid desiccant in the boiler, and with the first heat
exchanger to receive partially heated dilute liquid desiccant from
the first heat exchanger at the first temperature. The condenser is
operable to sensibly heat the dilute liquid desiccant therein to a
second temperature by recovering the latent heat of condensation as
steam delivered from the boiler is condensed. The second heat
exchanger fluidly communicates with the condenser, the boiler and
the first heat exchanger. The second heat exchanger is operable to
transfer heat from concentrated liquid desiccant directed to the
second heat exchanger from the boiler to the dilute liquid
desiccant directed to the second heat exchanger from the condenser
at the second temperature to raise the temperature of the dilute
liquid desiccant to a third temperature. The dilute liquid
desiccant at the third temperature is directed to the boiler and
the concentrated liquid desiccant from the second heat exchanger is
directed to the first heat exchanger. The second heat exchanger is
disposed with respect to the boiler to recover waste heat from the
boiler. A pump is provided for pumping concentrated liquid
desiccant into the absorber. A fraction of the steam from the
boiler is used to regenerate the refrigerant in the absorption air
conditioner.
Inventors: |
Potnis, Shailesh V.;
(Effingham, IL) ; Gurley, Kevin; (Watson, IL)
; McKittrick, Phillip T.; (Effingham, IL) ;
Baumann, Robert; (Effingham, IL) ; Rao, Srikant
Ram; (Newton, PA) ; Laurent, Robert L. JR.;
(Martinsville, NJ) |
Correspondence
Address: |
Welsh & Katz, Ltd.
Richard L. Wood
22nd Floor
120 South Riverside Plaza
Chicago
IL
60606
US
|
Family ID: |
25530813 |
Appl. No.: |
09/819530 |
Filed: |
March 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09819530 |
Mar 28, 2001 |
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09131287 |
Aug 7, 1998 |
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6216483 |
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09131287 |
Aug 7, 1998 |
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08984741 |
Dec 4, 1997 |
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6138470 |
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Current U.S.
Class: |
62/271 ;
62/238.3; 62/332; 62/94 |
Current CPC
Class: |
F28D 7/106 20130101;
F24F 3/1411 20130101; F24F 3/1417 20130101; F24F 5/0014 20130101;
F28B 1/02 20130101; F28F 1/08 20130101; B01D 53/263 20130101; Y02E
30/10 20130101; F24F 2003/144 20130101 |
Class at
Publication: |
62/271 ; 62/94;
62/238.3; 62/332 |
International
Class: |
F25D 023/00; F25D
017/06; F25B 027/00; F25B 025/00 |
Claims
1. A liquid desiccant air conditioner, comprising: a liquid
desiccant absorber for absorbing moisture contained in ambient air
entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for
receiving concentrated liquid desiccant and dispensing dilute
liquid desiccant; a boiler for boiling partially preheated dilute
liquid desiccant to evaporate moisture to reconstitute the liquid
desiccant into concentrated liquid desiccant; a first condenser
fluidly communicating with said boiler to receive steam generated
by boiling liquid desiccant in said boiler, said first condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said first condenser being
operable to sensibly heat the dilute liquid desiccant therein by
recovering the latent heat of condensation as steam delivered from
said boiler is condensed, to preheat said dilute liquid desiccant
prior to delivery to said boiler; a second condenser; an evaporator
through which a refrigerant is passed to effect cooling of
dehumidified ambient air from said desiccant absorber passing
through said evaporator; an expansion valve disposed between said
condenser and said evaporator; a refrigerant absorber fluidly
communicating with said evaporator to receive vaporized refrigerant
from said evaporator, said refrigerant absorber containing an
absorbent for absorbing the vaporized refrigerant; a regenerator
for separating refrigerant from the absorbent, said regenerator
fluidly communicating with said second condenser to supply
separated refrigerant to said second condenser, said regenerator
fluidly communicating with said refrigerant absorber to receive a
solution of absorbent and refrigerant from said refrigerant
absorber and return absorbent from said regenerator to said
refrigerant absorber, said regenerator fluidly communicating with
said boiler to receive steam from said boiler as a heat input; and
a pump for pumping the solution of absorbent and refrigerant from
said refrigerant absorber to said regenerator.
2. The liquid desiccant air conditioner recited in claim 1, further
comprising a heat exchanger fluidly communicating with said
desiccant absorber, said condenser and said boiler, said heat
exchanger operable to transfer heat from the concentrated liquid
desiccant directed to said heat exchanger from said boiler to the
dilute liquid desiccant directed to said heat exchanger from said
desiccant absorber, and to deliver preheated dilute liquid
desiccant to said condenser, wherein said condenser further
preheats said dilute liquid desiccant prior to delivery to said
boiler.
3. The liquid desiccant air conditioner recited in claim 1, further
comprising a heat exchanger fluidly communicating with said
condenser, said boiler and said desiccant absorber, said heat
exchanger operable to transfer heat from concentrated liquid
desiccant directed to said heat exchanger from said boiler to the
preheated dilute liquid desiccant directed to said heat exchanger
from said condenser to further preheat the dilute liquid desiccant
prior to delivery to said boiler, said heat exchanger being
disposed with respect to said boiler to recover waste heat from
said boiler.
4. The liquid desiccant air conditioner recited in claim 1, wherein
said desiccant absorber includes a top and a bottom and comprises:
a plurality of horizontally and vertically disposed interconnected
microglass fiber plates; a distributor disposed above said fiber
plates at said top of said desiccant absorber for introducing the
concentrated desiccant into said desiccant absorber; and a drain
pan for collecting the dilute desiccant disposed at said bottom of
said desiccant absorber.
5. The liquid desiccant air conditioner recited in claim 1, wherein
said desiccant absorber includes a plurality of absorber pads
bonded together and disposed side-by-side, said desiccant absorber
further comprising a top distributor pan for distributing liquid
desiccant to a top side of said pads, and a drain pan for
collecting dilute liquid desiccant from a bottom side of said
pads.
6. The liquid desiccant air conditioner recited in claim 1, wherein
said boiler includes an inner vessel and an outer vessel, a heating
element disposed in said inner vessel, and a pipe communicating
heated liquid desiccant from said inner vessel and disposed within
said outer vessel, whereby liquid desiccant is returned to said
outer vessel from said condenser and is heated in said outer vessel
by hot liquid desiccant passing through said pipe prior to entering
said inner vessel.
7. The liquid desiccant air conditioner recited in claim 2, wherein
said heat exchanger comprises at least one tube assembly including
an inner tube concentrically disposed within an outer tube to
define an annulus therebetween.
8. The liquid desiccant air conditioner recited in claim 7, wherein
dilute liquid desiccant from said desiccant absorber is passed
through said inner tube, and concentrated liquid desiccant is
passed through said annulus.
9. The liquid desiccant air conditioner recited in claim 7, wherein
dilute liquid desiccant from said desiccant absorber is passed
through said annulus, and concentrated liquid desiccant is passed
through said inner tube.
10. The liquid desiccant air conditioner recited in claim 7,
wherein said inner tube is fabricated from Teflon, and said outer
tube is fabricated from silicone rubber.
11. The liquid desiccant air conditioner recited in claim 2,
wherein said heat exchanger comprises at least one tube assembly
including an inner tube fabricated from Teflon concentrically
disposed within an outer tube fabricated from silicone rubber to
define an annulus therebetween.
12. The liquid desiccant air conditioner recited in claim 3,
wherein said heat exchanger comprises at least one tube assembly
including an inner tube concentrically disposed within an outer
tube to define an annulus therebetween, said at least one tube
assembly being coiled around said boiler to recover said waste
heat.
13. The liquid desiccant air conditioner recited in claim 12,
wherein dilute liquid desiccant from said condenser is passed
through said inner tube, and concentrated liquid desiccant from
said boiler is passed through said annulus.
14. The liquid desiccant air conditioner recited in claim 12,
wherein dilute liquid desiccant from said condenser is passed
through said annulus, and concentrated liquid desiccant from said
boiler is passed through said inner tube.
15. The liquid desiccant air conditioner recited in claim 12,
wherein said inner tube is fabricated from Teflon, and said outer
tube is fabricated from silicone rubber.
16. The liquid desiccant air conditioner recited in claim 3,
wherein said heat exchanger comprises at least one tube assembly
including an inner tube fabricated from Teflon concentrically
disposed within an outer tube fabricated from silicone rubber to
define an annulus therebetween.
17. The liquid desiccant air conditioner recited in claim 1,
wherein said condenser comprises an inner shell disposed within an
outer housing defining at least one chamber between said inner
shell and said housing.
18. The liquid desiccant air conditioner recited in claim 17,
wherein said inner shell is fabricated from materials selected from
the group of inconel, monel, titanium, Teflon, Teflon-coated
copper, Teflon-coated aluminum, and Teflon-coated stainless steel;
and said outer shell is fabricated from materials selected from the
group of Teflon, polycarbonate, polyvinylidene fluoride,
polypropylene, silicone rubber, polyethylene, and polystyrene.
19. The liquid desiccant air conditioner recited in claim 17,
wherein said condenser further comprises at least one steam inlet
communicating steam from said boiler with said at least one chamber
and at least one solution inlet communicating dilute liquid
desiccant with said inner shell.
20. The liquid desiccant air conditioner recited in claim 17,
wherein said condenser further comprises at least one steam inlet
communicating steam from said boiler with said inner shell and at
least one solution inlet communicating dilute liquid desiccant with
said at least one chamber.
21. The liquid desiccant air conditioner recited in claim 1,
wherein said condenser comprises a housing and a plurality of
tubes, said tubes being supported by opposing support plates, said
tubes communicating with a steam inlet to receive steam from said
boiler, said housing including a solution inlet to receive dilute
liquid desiccant.
22. The liquid desiccant air conditioner recited in claim 21,
wherein said tubes are at least one of convoluted and
corrugated.
23. The liquid desiccant air conditioner recited in claim 21,
wherein said tubes are fabricated from Teflon, and said support
plates include at least one silicone rubber sheet attached
thereto.
24. The liquid desiccant air conditioner recited in claim 17,
wherein said inner shell divides said housing into two separate
compartments, each compartment having a steam inlet and a
condensate outlet, said housing further comprising a plurality of
baffles to prevent short circuiting from said steam inlets to said
condensate outlets.
25. The liquid desiccant air conditioner recited in claim 1,
wherein said condenser comprises at least one tube assembly
including an inner tube defining a first flow passageway and an
outer tube, said inner tube being disposed within said outer tube
to define an annular second flow passageway therebetween, wherein
liquid desiccant is communicated through a first of said flow
passageways and steam is communicated through a second of said flow
passageways.
26. The liquid desiccant air conditioner recited in claim 25,
wherein said inner tube is at least one of convoluted and
corrugated.
27. The liquid desiccant air conditioner recited in claim 25,
wherein said tube assembly is coiled.
28. The liquid desiccant air conditioner recited in claim 1,
further comprising a frame fabricated from materials selected from
the group of polypropylene, polyethylene, Teflon, polyvinylidene
fluoride, polycarbonate, PVC and polystyrene.
29. The liquid desiccant air conditioner recited in claim 1,
wherein said liquid desiccant is selected from the group of aqueous
LiCl, LiBr and CaCl.sub.2.
30. The liquid desiccant air conditioner recited in claim 29,
wherein said liquid desiccant is a mixture of at least two of
aqueous LiCl, LiBr and CaCl.sub.2.
31. The liquid desiccant air conditioner recited in claim 1,
wherein said boiler includes a vessel fabricated from plastic.
32. The liquid desiccant air conditioner recited in claim 31,
wherein said plastic is selected from the group of Teflon,
polycarbonate, fiber glass and polyvinylidene fluoride.
33. The liquid desiccant air conditioner recited in claim 1,
further comprising means for pumping concentrated liquid desiccant
into said desiccant absorber.
34. The liquid desiccant air conditioner recited in claim 1,
further comprising an indirect evaporative cooler for cooling the
incoming ambient air with exhaust air prior to passing the incoming
air through said desiccant absorber.
35. The liquid desiccant air conditioner recited in claim 1,
further comprising a direct evaporative cooler for further cooling
the air cooled by said evaporator.
36. The liquid desiccant air conditioner recited in claim 34,
further comprising a direct evaporative cooler for further cooling
the air cooled by said evaporator.
37. The liquid desiccant air conditioner recited in claim 1,
further comprising an indirect evaporative cooler for cooling
dehumidified air from said desiccant absorber with exhaust air
prior to passing the dehumidified air through said evaporator.
38. A liquid desiccant air conditioner, comprising: a liquid
desiccant absorber for absorbing moisture contained in ambient air
entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for
receiving concentrated liquid desiccant and dispensing dilute
liquid desiccant; a boiler for boiling partially preheated dilute
liquid desiccant to evaporate moisture to reconstitute the liquid
desiccant into concentrated liquid desiccant; a condenser fluidly
communicating with said boiler to receive steam generated by
boiling liquid desiccant in said boiler, said condenser further
fluidly communicating with said absorber to receive dilute liquid
desiccant from said absorber, said condenser being operable to
sensibly heat the dilute liquid desiccant therein by recovering the
latent heat of condensation as steam delivered from said boiler is
condensed, to preheat said dilute liquid desiccant prior to
delivery to said boiler; an indirect evaporative cooler for cooling
the incoming ambient air with exhaust air prior to passing the
incoming air through said desiccant absorber; and a direct
evaporative cooler for further cooling the exiting said desiccant
absorber.
39. A liquid desiccant air conditioner, comprising: a liquid
desiccant absorber for absorbing moisture contained in ambient air
entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for
receiving concentrated liquid desiccant and dispensing dilute
liquid desiccant; a boiler for boiling partially preheated dilute
liquid desiccant to evaporate moisture to reconstitute the liquid
desiccant into concentrated liquid desiccant; a condenser fluidly
communicating with said boiler to receive steam generated by
boiling liquid desiccant in said boiler, said condenser further
fluidly communicating with said absorber to receive dilute liquid
desiccant from said absorber, said condenser being operable to
sensibly heat the dilute liquid desiccant therein by recovering the
latent heat of condensation as steam delivered from said boiler is
condensed, to preheat said dilute liquid desiccant prior to
delivery to said boiler; an indirect evaporative cooler for cooling
air from said desiccant absorber with exhaust air; and a direct
evaporative cooler for further cooling air exiting said indirect
evaporative cooler.
40. A liquid desiccant air conditioner, comprising: a liquid
desiccant absorber for absorbing moisture contained in ambient air
entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for
receiving concentrated liquid desiccant and dispensing dilute
liquid desiccant, a boiler for boiling partially preheated dilute
liquid desiccant to evaporate moisture to reconstitute the liquid
desiccant into concentrated liquid desiccant; a first heat
exchanger operable to transfer heat from the concentrated liquid
desiccant to the dilute liquid desiccant directed to said first
heat exchanger from said desiccant absorber to raise the
temperature of the dilute liquid desiccant to a first temperature;
a first condenser fluidly communicating with said boiler to receive
steam generated by boiling liquid desiccant in said boiler, said
first condenser further fluidly communicating with said first heat
exchanger to receive partially heated dilute liquid desiccant from
said first heat exchanger at said first temperature, said first
condenser being operable to sensibly heat the dilute liquid
desiccant therein to a second temperature by recovering the latent
heat of condensation as steam delivered from said boiler is
condensed; a second heat exchanger fluidly communicating with said
first condenser, said boiler and said first heat exchanger, said
second heat exchanger operable to transfer heat from concentrated
liquid desiccant directed to said second heat exchanger from said
boiler to the dilute liquid desiccant directed to said second heat
exchanger from said first condenser at said second temperature to
raise the temperature of the dilute liquid desiccant to a third
temperature, said dilute liquid desiccant at the third temperature
being directed to said boiler and said concentrated liquid
desiccant being directed to said first heat exchanger, said second
heat exchanger being disposed with respect to said boiler to
recover waste heat from said boiler; and a pump for pumping
concentrated liquid desiccant into said absorber; a second
condenser; an evaporator through which a refrigerant is passed to
effect cooling of dehumidified ambient air from said desiccant
absorber passing through said evaporator; an expansion valve
disposed between said condenser and said evaporator; a refrigerant
absorber fluidly communicating with said evaporator to receive
vaporized refrigerant from said evaporator, said refrigerant
absorber containing an absorbent for absorbing the vaporized
refrigerant; a regenerator for separating refrigerant from the
absorbent, said regenerator fluidly communicating with said second
condenser to supply separated refrigerant to said second condenser,
said regenerator fluidly communicating with said refrigerant
absorber to receive a solution of absorbent and refrigerant from
said refrigerant absorber and return absorbent from said
regenerator to said refrigerant absorber, said regenerator fluidly
communicating with said boiler to receive steam from said boiler as
a heat input; and a pump for pumping the solution of absorbent and
refrigerant from said refrigerant absorber to said regenerator.
41. The liquid desiccant air conditioner recited in claim 25,
further comprising an air vent.
42. The liquid desiccant air conditioner recited in claim 41,
wherein said air vent comprises Teflon tape.
43. The liquid desiccant air conditioner recited in claim 41,
wherein said air vent is a float-type air vent.
44. The liquid desiccant air conditioner recited in claim 1,
wherein a fraction of the liquid desiccant leaving said first
condenser is recirculated to said liquid desiccant absorber.
45. The liquid desiccant air conditioner recited in claim 34,
wherein at least a fraction of water supplied to said indirect
evaporative cooler is obtained from condensate produced in at least
one of said first condenser and said regenerator.
46. The liquid desiccant air conditioner recited in claim 35,
wherein at least a fraction of water supplied to said direct
evaporative cooler is obtained from condensate produced in at least
one of said first condenser and said regenerator.
Description
[0001] This application is a continuation-in-part application of
Appl. Ser. No. 08/984,741, filed Dec. 4, 1997.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates generally to room air cooling
and dehumidification, and more particularly, to a liquid desiccant
air conditioner which is energy efficient, corrosion resistant, and
capable of operation with low energy usage.
[0004] 2. Description of the Prior Art
[0005] Typical air conditioning units operate on a vapor
compression cycle. Over recent years, the phase out of CFC based
air conditioning units has been dictated by environmental concerns.
One alterative to vapor compression units, is the absorption
system. The basic elements include an evaporator, condenser,
absorber, pump, heat exchanger, throttle valve and regenerator. In
the absorption cycle, an "absorbent" is used to absorb the
refrigerant in the vaporized state after leaving the evaporator.
The vaporized refrigerant is converted back into the liquid phase
in the absorber. Heat released in the absorption process is
rejected to cooling water passed through the absorber. A solution
of absorbent and refrigerant is pumped to a regenerator, where heat
is added and the more volatile refrigerant is separated from the
absorbent through distillation. The refrigerant is then
communicated to the condenser, expansion valve and evaporator in a
conventional manner. A heat exchanger may be used for heat recovery
between the absorbent returned to the absorber and the
absorbent-refrigerant solution delivered to the regenerator.
[0006] Absorption systems currently represent only a small
percentage of commercial refrigeration systems because they are
generally bulky and inefficient.
[0007] However, with concerns over CFCs and ever increasing energy
costs, the absorption unit has potential to provide efficient
cooling by taking advantage of waste heat. This may be provided by
combining such an absorption unit with a liquid desiccant
dehumidifier.
[0008] It is known in the art to dehumidify ambient air using
liquid desiccant systems. These devices typically utilize
hygroscopic liquids such as lithium bromide (LiBr), lithium
chloride (LiCl) or calcium chloride (CaCl.sub.2) as the desiccant
solution. In a desiccant system, the desiccant solution absorbs
moisture from ambient air exposed to the solution. As the desiccant
solution continues to absorb moisture, it becomes dilute and must
be regenerated. In the regeneration process, the desiccant solution
is heated to evaporate the excess moisture or the desiccant
solution is brought into contact with a hot gas to desorb the
excess moisture. In some expedients, air regenerators are used to
regenerate the desiccant. These arrangements have relatively high
operating costs as energy is required to provide a source of heat
and to generate a suitable flow of air. In others, boiler-type
regenerators are employed. However, boiler embodiments are
expensive, as the corrosive nature of liquid desiccant solutions
necessitates the use of costly corrosion resistant metals.
[0009] A liquid desiccant dehumidification system in which a liquid
desiccant is regenerated with a boiler is described in U.S. Pat.
No. 4,939,906 ("the '906 Patent"). The '906 Patent discloses a
gas-fired desiccant boiler and a combined desiccant
regenerator/interchange heat exchanger, in which the combined
regenerator/heat exchanger utilizes steam produced from the boiler
to provide heat for partial regeneration. The desiccant boiler has
a liquid/vapor separator chamber and thermosyphon recirculation to
reduce scale and corrosion of the boiler. Specifically, the overall
system is shown in FIG. 1, wherein outdoor air is drawn into the
system through an inlet duct 22, and is evaporatively cooled by a
water spray 24. The cooled air is directed to a desiccant
conditioner 26 to which return air is also directed through a duct
30. In the desiccant conditioner 26, the return air is contacted
with a liquid desiccant solution from a sprayer 28. The desiccant
liquid is disclosed as lithium calcium chloride.
[0010] This dehumidified air is then supplied to the space to be
dehumidified, or it can be sensibly cooled through an evaporative
cooler 32. The desiccant dehumidifies the air stream, and in the
process its moisture-absorbing capability is reduced; this
capability is regenerated by passing a portion of the dilute
desiccant from the conditioner 26 to a first interchange heat
exchanger 44, wherein the temperature of the desiccant is raised.
The weakened desiccant is partially concentrated in an
air-desiccant regenerator 46, in which heated air from a
regeneration air heater 48 contacts the liquid desiccant. This
desiccant is pumped through a second interchange heat exchanger 52
and thereafter to a desiccant boiler 56, in which regeneration of
the desiccant is completed. The water vapor generated in the
desiccant boiler 56 raises the temperature of the air passing
through the regeneration air preheater 48. The interchange heat
exchangers 44, 52 reduce the temperature of the regenerated
desiccant as it returns along the pipe 60 to the conditioner
26.
[0011] The boiler 56 is depicted in FIG. 2, and operates on natural
circulation, with the density of the fluid (part liquid, part
vapor) in the "fired" tubes 70 being less than the density of the
liquid in the outer "unfired" tube 74.
[0012] A porous ceramic burner 80 facilitates combustion to provide
a heat source and hot combustion gases are blown through a
combustion chamber formed by a housing 88 enclosing the fired tubes
70, and flow across fins 90 of the fired tubes 70. Weak desiccant
is pumped into the fired tubes 70 through a manifold 94 which
causes water in the desiccant to be vaporized. Accordingly, a
density differential is created between the fluid in the fired
tubes 70 and the unfired tubes 74 connected between the manifold 94
and a liquid/vapor separator 98 outside the combustion chamber
housing 88. This density differential induces a natural flow of
desiccant solution up the fired tubes 70 and down the unfired tubes
72. In this manner, the natural circulation of desiccant keeps the
inside walls of the fired tubes 70 coated with desiccant to thereby
reduce or prevent "hot spots" from forming on the inside of the
fired tubes 70 to reduce corrosion and scale build up in the fired
tubes 70.
[0013] The liquid vapor separator 98 at the top of the boiler 56
separates water vapor from the concentrated liquid desiccant. A
portion of the concentrated desiccant is withdrawn from the bottom
of the liquid/vapor separator 98 and is returned to the desiccant
conditioner 26. Water vapor flowing out of the top of the
liquid/vapor separator 98 is subsequently condensed to heat air for
use in an earlier regeneration step shown in FIGS. 3 and 4.
[0014] The combined regenerator/interchange heat exchanger,
depicted in FIGS. 3 and 4, comprises two (2) interchange heat
exchangers 44, 52, the desiccant regenerator 46 and the
regeneration air heater 48. The combined desiccant
regenerator/interchange heat exchanger is identified by the
reference numeral 102, and is constructed by alternately stacking
two (2) different corrugated plates (see FIG. 4) to define
alternating flow channels. Water vapor or steam from the desiccant
boiler 56 is introduced near the top of the regenerator/exchanger
102 in alternate channels (plate A). This water vapor is condensed,
thereby transferring heat to the air and weak desiccant entering
adjacent channels near the top of the regenerator/heat exchanger
102 (plate B).
[0015] The upper portion of each plate corresponds to the desiccant
regenerator 46 and regeneration air heater 48. As the water vapor
condenses, the weak desiccant and air mixture is heated and the
desiccant is partially regenerated. Warm air and moisture are
exhausted by fan 106 to the outdoors. An entrainer 108 is provided
to prevent desiccant from escaping the combined
regenerator/exchanger 102. The partially regenerated desiccant
flows into the middle of a channel plate B, and is further heated
by the hot concentrated desiccant removed from the liquid/vapor
separator 98. Hot concentrated desiccant from the boiler 56 is
introduced at the middle of plate A while the partially regenerated
desiccant is removed from the middle of plate B. The partially
regenerated desiccant is then pumped to the desiccant boiler 56.
Diluted desiccant from the regenerator/heat exchanger 102 is
introduced at the bottom of the plate A and is heated by the hot
desiccant from the boiler 56. The heated dilute desiccant from the
regenerator/heat exchanger 102 is then removed from the center of
plate B and pumped to the top of plate B.
[0016] The apparatus shown and described in the '906 Patent suffers
from several disadvantages. The regeneration process described
therein requires the flow of hot air through the system in order to
operate. This necessitates the use of additional components such as
fans, air preheaters, and liquid/vapor separators, which adds
system complexity. Furthermore, the multiple stacked plate
interchange heat exchanger configuration is complex and takes up a
relatively large amount of space.
[0017] The present invention provides an improved air cooling
system comprising an absorption air conditioner operating in
conjunction with a liquid desiccant dehumidifier.
SUMMARY OF THE INVENTION
[0018] It is an object of the present invention to provide a liquid
desiccant air conditioner which dehumidifies and cools ambient air
in a combined liquid desiccant-refrigerant absorption cycle.
[0019] It is another object of the present invention to provide a
liquid desiccant air conditioner which does not require CFCs.
[0020] It is a further object of the present invention to provide a
liquid desiccant air conditioner which is energy efficient.
[0021] It is still another object of the present invention to
provide a liquid desiccant air conditioner which does not require a
compressor.
[0022] It is yet another object of the present invention to provide
a liquid desiccant air conditioner which does not require any
external heat input to effect regeneration of the refrigerant
absorbent.
[0023] It is an object of the present invention to provide a liquid
desiccant air conditioner which efficiently regenerates the liquid
desiccant using a simple arrangement having a minimum number of
components.
[0024] It is still another object of the present invention to
provide a liquid desiccant air conditioner which utilizes primarily
plastic components to prevent corrosion.
[0025] It is yet another object of the present invention to provide
a liquid desiccant air conditioner in which steam to desiccant heat
recovery takes place in a condenser.
[0026] It is a further object of the present invention to provide a
liquid desiccant air conditioner in which plastic components are
used for the interchange heat exchangers.
[0027] It is yet another object of the present invention to provide
a liquid desiccant air conditioner in which the waste heat
radiating from the boiler is utilized in an interchange heat
exchanger for desiccant regeneration.
[0028] It is still another object of the present invention to
provide a liquid desiccant air conditioner having a boiler which is
primarily elongated in a horizontal orientation to minimize the
temperature gradient and consequent concentration differential in
the liquid desiccant.
[0029] It is yet another object of the present invention to provide
a liquid desiccant air conditioner which is lightweight, energy
efficient, and inexpensive to manufacture.
[0030] In accordance with the foregoing objects and additional
objects that will become apparent hereinafter, the present
invention provides a liquid desiccant air conditioner, including a
liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through the
desiccant absorber, the desiccant absorber constructed and arranged
for receiving concentrated liquid desiccant and dispensing dilute
liquid desiccant. A boiler is provided for boiling partially
preheated dilute liquid desiccant to evaporate moisture to
reconstitute the liquid desiccant into concentrated liquid
desiccant. A condenser fluidly communicates with the boiler to
receive steam generated by boiling liquid desiccant in the boiler,
and with the absorber to receive dilute liquid desiccant from the
absorber. The condenser is operable to sensibly heat the dilute
liquid desiccant therein by recovering the latent heat of
condensation as steam delivered from the boiler is condensed, to
preheat the dilute liquid desiccant prior to delivery to the boiler
to increase operating efficiency. An evaporator effects cooling of
dehumidified air delivered from the desiccant absorber. A
refrigerant is vaporized in the evaporator and passed to a
refrigerant absorber which contains an absorbent solution such as,
for example, ammonia-water or water-lithium bromide. The
refrigerant-absorber solution is pumped to a regenerator in which
the refrigerant is separated from the absorbent. The regenerator
fluidly communicates with the boiler to receive steam from the
boiler as a heat input to effect regeneration. A second condenser
receives the reconstituted refrigerant from the regenerator. The
refrigerant passes through the second condenser, and from there
through an expansion valve and into the evaporator in a
conventional manner. A heat exchanger may be used to recover heat
from the absorbent as it is returned to the refrigerant absorber to
preheat the refrigerant-absorbent solution prior to introduction of
the solution into the regenerator.
[0031] In a preferred embodiment, the invention provides a liquid
desiccant air conditioner including a liquid desiccant absorber for
absorbing moisture contained in ambient air entering the
dehumidifier and passing through the desiccant absorber, the
desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid
desiccant. A boiler is provided for boiling partially preheated
dilute liquid desiccant to evaporate moisture to reconstitute the
liquid desiccant into concentrated liquid desiccant. A first heat
exchanger fluidly communicates with the desiccant absorber and a
second heat exchanger. The first heat exchanger is operable to
transfer heat from the concentrated liquid desiccant to the dilute
liquid desiccant directed to the first heat exchanger from the
desiccant absorber to raise the temperature of the dilute liquid
desiccant to a first temperature. A condenser fluidly communicates
with the boiler to receive steam generated by boiling the liquid
desiccant in the boiler, and with the first heat exchanger to
receive partially heated dilute liquid desiccant from the first
heat exchanger at the first temperature. The condenser is operable
to sensibly heat the dilute liquid desiccant therein to a second
temperature by recovering the latent heat of condensation as steam
delivered from the boiler is condensed. The second heat exchanger
fluidly communicates with the condenser, the boiler and the first
heat exchanger. The second heat exchanger is operable to transfer
heat from concentrated liquid desiccant directed to the second heat
exchanger from the boiler to the dilute liquid desiccant directed
to the second heat exchanger from the condenser at the second
temperature to raise the temperature of the dilute liquid desiccant
to a third temperature. The dilute liquid desiccant at the third
temperature is directed to the boiler and the concentrated liquid
desiccant from the second heat exchanger is directed to the first
heat exchanger. The second heat exchanger is disposed with respect
to the boiler to recover waste heat from the boiler. A pump is
provided for pumping concentrated liquid desiccant into the
absorber. An evaporator effects cooling of dehumidified air
delivered from the desiccant absorber. A refrigerant is vaporized
in the evaporator and passed to a refrigerant absorber which
contains an absorbent solution such as, for example, ammonia-water
or water-lithium bromide. The refrigerant-absorber solution is
pumped to a regenerator in which the refrigerant is separated from
the absorbent. The regenerator fluidly communicates with the boiler
to receive steam from the boiler as a heat input to effect
regeneration. A second condenser receives the reconstituted
refrigerant from the regenerator. The refrigerant passes through
the second condenser, and from there through an expansion valve and
into the evaporator in a conventional manner. A heat exchanger may
be used to recover heat from the absorbent as it is returned to the
refrigerant absorber to preheat the refrigerant-absorbent solution
prior to introduction of the solution into the regenerator.
[0032] In a preferred embodiment, the desiccant absorber includes a
top and a bottom and comprises: a plurality of horizontally and
vertically disposed interconnected microglass fiber plates; a
distributor disposed above the fiber plates at the top of the
desiccant absorber for introducing the concentrated desiccant into
the desiccant absorber; and a drain pan for collecting the dilute
desiccant disposed at the bottom of the desiccant absorber.
[0033] The first heat exchanger comprises at least one tube
assembly including an inner tube concentrically disposed within an
outer tube to define an annulus therebetween. The dilute liquid
desiccant from the desiccant absorber is passed through the inner
tube, and the concentrated liquid desiccant is passed through the
annulus, or vice-a-versa.
[0034] The second heat exchanger comprises at least one tube
assembly including an inner tube concentrically disposed within an
outer tube to define an annulus therebetween. The tube assembly is
coiled around the boiler to recover waste heat passing through the
walls of the boiler. The concentrated liquid desiccant from the
boiler is passed through the annulus and the partially heated
dilute liquid desiccant from the condenser is passed through the
inner tube, or vice-a-versa.
[0035] In a preferred embodiment, the inner tubes of the heat
exchangers are fabricated from Teflon and the outer tubes are
fabricated from silicone rubber.
[0036] The inner tubes may be convoluted or corrugated to increase
the available heat transfer area.
[0037] In a preferred embodiment, the condenser comprises an inner
shell disposed within an outer housing defining at least one
chamber between the inner shell and the housing. Steam is directed
to the inner shell from the boiler through a steam inlet. The
housing includes a solution inlet to direct partially heated dilute
liquid desiccant from the first heat exchanger into the at least
one chamber. A solution outlet communicates with the chamber and
directs partially heated dilute desiccant at the second temperature
to the second heat exchanger. The inner shell is fabricated from
materials including inconel, monel, titanium, Teflon, Teflon-coated
copper, Teflon-coated aluminum, and Teflon-coated stainless steel;
and the outer shell is fabricated from materials including Teflon,
polycarbonate, polyvinylidene fluoride, polypropylene, silicone
rubber, polyethylene, and polystyrene.
[0038] In an alternative embodiment, the condenser comprises at
least one steam inlet communicating steam from the boiler with the
at least one chamber and at least one solution inlet communicating
partially heated dilute liquid desiccant from the first heat
exchanger with the inner shell.
[0039] The condenser may incorporate a plurality of fins associated
with the inner shell and a plurality of fins associated with the
housing. The inner shell may be provided with a plurality of
baffles to prevent short circuiting from the steam inlet to the
condensate outlet.
[0040] In another embodiment, the condenser comprises a housing and
a plurality of convoluted tubes. The tubes are supported by
opposing support plates, and communicate with a steam inlet to
receive steam from the boiler. The housing includes a solution
inlet to receive partially heated dilute liquid desiccant from the
first heat exchanger, and a solution outlet through which partially
heated dilute liquid desiccant is delivered to the second heat
exchanger. The tubes are fabricated from Teflon, and the support
plates include at least one silicone rubber sheet attached
thereto.
[0041] In a preferred embodiment, the respective components are
disposed with respect to one another to take advantage of gravity
feed to communicate the liquid desiccant from the absorber to the
boiler via the first and second heat exchangers and the condenser,
thereby eliminating the need for multiple pumps in the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] In accordance with the above, the present invention will now
be described in detail with particular reference to the
accompanying drawings.
[0043] FIG. 1 is a schematic of a first embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0044] FIG. 2 is a schematic of a second embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0045] FIG. 3 is a schematic of a third embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0046] FIG. 4 is a schematic of a fourth embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0047] FIG. 5 is a schematic of a fifth embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0048] FIG. 6 is a schematic of a sixth embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0049] FIG. 7 is a schematic of a seventh embodiment of a liquid
desiccant air conditioner in accordance with the present
invention;
[0050] FIG. 8 is an exploded isometric view of the portable liquid
desiccant dehumidifier in accordance with the present
invention;
[0051] FIG. 8A is a block diagram depicting the general operation
of the liquid desiccant dehumidifier;
[0052] FIG. 9 is an exploded isometric view of a desiccant absorber
assembly;
[0053] FIG. 9A is a detail view of the microglass fiber plates in
the absorber;
[0054] FIG. 9B is a side elevational view of a desiccant absorber
in another embodiment;
[0055] FIG. 9C is a detail view of the absorber pads;
[0056] FIG. 9D is an isometric view of the desiccant absorber of
FIG. 9B;
[0057] FIG. 10 is an isometric view of a boiler;
[0058] FIG. 11 is an isometric view of a coiled interchange heat
exchanger and the boiler;
[0059] FIG. 11A is an isometric view of a boiler in an alternative
embodiment;
[0060] FIG. 12 is an isometric view of a split interchange heat
exchanger;
[0061] FIG. 12A is a plan view of an inner tube for an interchange
heat exchanger having a convoluted profile;
[0062] FIG. 12B is a plan view of an inner tube for an interchange
heat exchanger having a corrugated profile;
[0063] FIG. 13 is an isometric cut-away view of a condenser in a
first embodiment;
[0064] FIG. 14 is an isometric cut-away view of an inner shell of
the condenser shown in FIG. 13;
[0065] FIG. 15 is an isometric cut-away view of a condenser in a
second embodiment;
[0066] FIG. 16 is an isometric cut-away view of a condenser in a
third embodiment;
[0067] FIG. 17 is an isometric view of a condenser in a fourth
embodiment;
[0068] FIG. 18 is an isometric view of a condenser is a fifth
embodiment;
[0069] FIG. 19 is an isometric cut-away view of a frame for housing
the respective components of the system; and
[0070] FIG. 20 is an isometric cut-away view depicting the frame
and some of the components installed therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Referring to the several views of the drawings, there is
shown a liquid desiccant air conditioner ("LDA"), generally
characterized by the reference numeral 10.
[0072] FIG. 1 is a schematic of the LDA 10 in a first embodiment.
The LDA 10 is principally comprised of a liquid desiccant
dehumidifier 200 and an absorption air conditioner 202. The details
of the liquid desiccant dehumidifier 200 are described in detail
below and are the same as disclosed in U.S. Appl. Ser. No.
08/984,741 to the same assignee, filed Dec. 4, 1997. The liquid
desiccant dehumidifier 200 primarily includes an absorber 12,
condenser, 86, and boiler 34. An interchange heat exchanger 58 is
disposed between boiler 34 and condenser 86, and a split
interchange heat exchanger 66 is located between condenser 86 and
absorber 12. These components are described below. Specifically,
the LDA 10 dehumidifies incoming ambient air prior to effecting
sensible cooling of the air in the air conditioner 202. The
absorption cycle employs waste heat generated by the boiler 34 of
liquid desiccant dehumidifier 200 for energy efficient cooling and
dehumidification. The air conditioner 202 employs the known
absorption cycle, and includes an absorber 204, a pump 206, a heat
exchanger 208, at throttle valve 210, a regenerator 212, an
evaporator 214, a condenser 216, and an expansion valve 218. In the
absorption cycle, an absorbent, such as aqueous ammonia or aqueous
lithium bromide, is used to absorb refrigerant in the vaporized
state after leaving evaporator 214. The vaporized refrigerant is
absorbed back into the liquid phase in absorber 204. Heat released
in the absorption process is rejected to cooling water or air
passed through absorber 204. A solution of absorbent and
refrigerant is pumped to regenerator 212, where heat is added and
the more volatile refrigerant is separated from the absorbent. The
refrigerant is then communicated to condenser 216, through
expansion valve 218 and into the evaporator 214 in a conventional
manner. A heat exchanger 208 may be used for heat recovery between
the warm absorbent returned to the absorber 204 through throttle
valve 210, and the absorbent-refrigerant solution delivered from
the absorber 204 to the regenerator 212 via pump 206. The
regenerator 212 fluidly communicates with boiler 34 to receive
steam generated in reconstituting the liquid desiccant as described
below. In this manner, no external heat input is required to
regenerate the refrigerant. The heat exchanger 208 can configured
as described below with respect to interchange heat exchanger 66 of
the liquid desiccant dehumidifier 200.
[0073] FIG. 2 is a schematic of a second embodiment of the LDA 10,
which adds an indirect evaporative cooler 220 for cooling the
incoming air with exhaust air from the residence prior to passing
the incoming air through the desiccant absorber 12. The indirect
evaporator cooler 20 receives a water supply from condenser 86 and
regenerator 212. Fresh air is directed into the cooler 220 from the
ambient, cooled, and thereafter delivered to desiccant absorber 12.
The remainder of the cycle operates as described above.
[0074] FIG. 3 is a schematic of a third embodiment of the LDA 10,
which adds a direct evaporative cooler 222 to the embodiment of
FIG. 2. The direct evaporative cooler 222 is operable to further
cool the air prior to delivery to the ambient. Water is supplied to
cooler 222 from condenser 86 and regenerator 212. FIG. 4 is a
schematic of a fourth embodiment of the LDA 10, in which the
ambient air is first directed into the absorber 12 for
dehumidification, and then into the indirect evaporative cooler 220
for cooling. FIG. 5 is a schematic of a fifth embodiment of the LDA
10, which is similar to that shown in FIG. 1, but adds the direct
evaporative cooler 222.
[0075] FIG. 6 is a schematic of a sixth embodiment of the LDA 10
which does not utilize a refrigerant. In this expedient, the LDA 10
cooperates with an indirect evaporative cooler 220 and a direct
evaporative cooler 222 to cool and dehumidify the incoming air. The
air is directed through indirect evaporative cooler 220, cooled,
and thereafter delivered to the desiccant absorber 12. The
dehumidified air is then passed through the direct evaporative
cooler 222, where it is further cooled by sensible cooling, and
exhausted to the ambient. The principle of operation is generally
the same as described above. Water from condenser 86 is delivered
to indirect evaporative cooler 220 and direct evaporative cooler
222. Exhaust air from the residence is communicated to the indirect
evaporative cooler 220. FIG. 7 is a schematic of a seventh
embodiment of the LDA 10, which is similar to that shown in FIG. 6
and described above, but here the incoming ambient air is first
dehumidified in the desiccant absorber 12, and thereafter cooled in
the indirect evaporative cooler 220.
[0076] Referring now to FIGS. 8 and 8A, the desiccant dehumidifier
section 100 includes liquid desiccant absorber 12 for absorbing
moisture contained in air entering air conditioner 10 and passing
through desiccant absorber 12. The desiccant absorber 12 is
constructed and arranged for receiving concentrated liquid
desiccant at the top of desiccant absorber 12 and dispensing dilute
liquid desiccant from the bottom of desiccant absorber 12. The
desiccant solution may be any one of several conventional
solutions, including aqueous LiBr, LiCl or CaCl.sub.2, as described
above, or any mixture of these solutions. Referring now to FIGS. 9
and 9A, desiccant absorber 12 includes a distributor 14 disposed at
the top of desiccant absorber 12 which receives concentrated liquid
desiccant and delivers the liquid desiccant through a plurality of
"spaghetti" tubes 16 extending radially outward from a central hub
18. The desiccant absorber 12 includes a plurality of horizontally
and vertically disposed interconnected microglass fiber plates. The
vertical plates are identified by the reference numeral 20, and are
supported by horizontal interconnecting fiber plates 22 as shown.
The top plate 22 is referred to as a distribution sheet. The
concentrated desiccant wicks into the distribution sheet 22 and
down the vertical plates 20. The vertical plates 20 contain beads
21 which separate and support contiguous vertical plates 20.
Ambient air is drawn into the unit and forced through the
microglass fiber plates by a fan 23 (see FIG. 8), where the
moisture in the air is removed as the air makes contact with the
liquid desiccant. As the desiccant dehumidifies the air stream, the
moisture-absorbing capability of the desiccant is reduced and the
desiccant must be regenerated. This dilute desiccant is collected
in a drain pan 24 disposed at the bottom of desiccant absorber 12.
The drain pan 24 includes an intermediate support plate 26 defining
at least one drain hole 28 which enables the dilute desiccant to
flow into a bottom chamber defined between support plate 26 and a
bottom wall 30 of drain pan 24. A drain tube 32 including a one-way
or check valve 33 extends from the bottom chamber to direct the
dilute desiccant out of absorber 12. The absorber components are
disposed within a frame 35 as shown in FIG. 19, which can be
fabricated from materials including, but not limited to,
polypropylene, polyethylene, Teflon, polyvinylidene fluoride,
polycarbonate, PVC or polystyrene. The frame 35 includes a
plurality of shelves 37a, 37b, and 37c for supporting the
respective components of the unit described below.
[0077] In an alternative embodiment shown in FIGS. 9B-9D, a
plurality of absorber pads 20a are stacked side-by-side and bonded
together at the ends with an adhesive "A" (or taped) so that the
gaps between the pads 20a are completely sealed to force the liquid
desiccant to wick through the pads 20a. The pads 20a are received
in an aperture or slots in a top tray or distributor pan 25 and a
bottom tray or drain pan 27. Any gaps between the pads 20a and the
pans 25, 27 may be filled with an RTV silicone sealant or like
material. Liquid desiccant is communicated into the distributor pan
25 through an inlet 29. This configuration prevents the liquid
desiccant from just flowing over the surface of the pads, and
consequently increases absorber efficiency. The trays 25, 27
effectively prevent spillage of liquid desiccant from the absorber
12 in the event of tilting. In addition, the liquid desiccant
supplied to the distributor pan 25 forms a thin film on the pan
surfaces to reach every distributor pad 20a to improve desiccant
distribution.
[0078] The dilute liquid desiccant is regenerated into concentrated
desiccant by boiling the liquid desiccant in a boiler 34 at a
temperature in the range of from approximately 260.degree. F. to
320.degree. F. An improvement over prior art systems resides in the
use of steam to desiccant heat recovery to directly preheat the
dilute liquid desiccant. The dilute liquid desiccant is thus passed
through a condenser and preheated using the latent heat of
condensation of the steam produced by boiling the liquid desiccant.
Preferably, a series of interchange heat exchangers are employed to
further preheat the dilute liquid desiccant entering the boiler 34
by recovering heat from the concentrated liquid desiccant delivered
to absorber 12 from boiler 34 to further increase operating
efficiency. These components are described in more detail
below.
[0079] The boiler 34 is shown in FIG. 10, and is configured in the
shape of a tub or vessel having an elongated horizontal dimension.
The horizontal elongation provides a uniform temperature gradient,
and thus a uniform concentration level of the liquid desiccant
solution, as compared to a vertically elongated boiler. The boiler
34 includes side walls 36, a bottom wall 38, a top wall 40, and a
peripheral support flange 42. The boiler 34 is constructed from
materials including, but not limited to, polycarbonate,
polyvinylidene fluoride, Teflon, fiber glass and the like. A
heating element 44 is coiled proximal to the bottom wall 40 as
shown, and is connected to a pair of leads 46 in a conventional
manner. A thermocouple 48 extends into boiler 34 to monitor the
internal temperature. The leads 46 and thermocouple 48 extend
through top wall 40. The heating element 44 and thermocouple 48 are
operably associated with a controller (not shown) for maintaining
boiler 34 at the optimum temperature. A pair of steam outlets 50
extend through top wall 40 to deliver steam generated by boiling
the liquid desiccant to a condenser described in more detail
below.
[0080] Referring now to FIG. 11, a drain tube 51 is coupled to one
of the side walls 36 to enable boiler 34 to be emptied as required.
A U-fitting 52 is coupled to the upper region of one of the side
walls 36 to receive preheated dilute liquid desiccant from the
condenser through an inlet port 54, and to dispense concentrated
liquid desiccant through an outlet port 56. The U-fitting 52
communicates with a coiled interchange heat exchanger 58, which
comprises at least one tube assembly including an inner tube 60
concentrically disposed within an outer tube 62 to define an
annulus 64 therebetween. The tube assembly is coiled around boiler
34 to recover the waste heat radiating through side walls 36. This
arrangement is exemplary, as the tube assembly could be embedded
within the side walls 36, or disposed in contact with top wall 40.
The concentrated liquid desiccant from boiler 34 enters the annulus
64 through side wall 36 and is directed to outlet port 56. The
partially heated dilute liquid desiccant from the condenser is
passed through the inner tube 60 in a direction counter to the
concentrated liquid desiccant and enters boiler 34 through side
wall 36.
[0081] Alternatively, the concentrated liquid desiccant is passed
through inner tube 60 and the dilute liquid desiccant is passed
through annulus 64. In a preferred embodiment, inner tube 60 is
fabricated from Teflon, and outer tube 62 is constructed from
silicone rubber. The Teflon inner tube 60 has relatively high heat
conductivity, while the outer silicone rubber tube 62 has a
relatively low thermal conductivity, and is a good insulator. These
components can withstand relatively high temperatures
(.about.400.degree. F.), and are not corroded by the desiccant
solution. To improve efficiency, inner tube 60 may be convoluted as
shown in FIG. 12A or corrugated as shown in FIG. 12B. It is to be
understood that the use of this type of Teflon/silicone rubber
tube-in-tube heat exchanger is not limited to a liquid desiccant
system. There are many applications in which this arrangement may
be employed. The particular operation of the coiled interchange
heat exchanger 58 will be described in more detail below.
[0082] Referring now to FIG. 11A, there is shown an isometric view
of an boiler 34a in an alternative embodiment, having a double-wall
configuration including an inner wall 400 and an outer wall 402
which define an inner vessel 404 and an outer vessel 406. A heating
element 408 extends into the inner vessel 404 and around the floor
as shown. The incoming liquid desiccant from condenser 86 enters
the outer vessel 406 of the boiler at inlet 410. Hot liquid
desiccant from the inner vessel 404 is communicated into pipe 412
which coils through the outer vessel 406 to effect heat transfer
with the incoming liquid desiccant. The desiccant puddle contained
in the outer vessel 406 is heated and the hottest portion of the
liquid is forced to rise to the top of the vessel 406. It is then
fed into the inner vessel 404 via an inlet 414. A thermocouple 416
is disposed in the inner vessel 404 as described above to control
the boiler temperature. This arrangement forces any heat radiated
or conducted from the inner vessel 404 to flow through the
desiccant puddle in the outer vessel 406, thereby reducing thermal
losses, and pressure losses attributable to long flow paths. The
heating element 408 is disposed below the pump suction or inner
vessel boiler outlet 415a so that heating element 408 is always
immersed in a pool of liquid desiccant within the inner vessel 404.
In this manner, the pump 80 stops drawing liquid desiccant from
inner vessel 404 before it is reduced to a level beneath the
heating element 408. Hot liquid desiccant leaves the boiler through
outlet 415b. This arrangement eliminates the need for a low-level
control switch. High level control in the boiler is necessary to
provide consistent dehumidification and to prevent excess liquid
buildup. A high level control switch can be eliminated by sizing
the inner vessel 404 with an internal volume equal to approximately
twice the volume of pooled liquid desiccant accumulation. This
takes advantage of the inherent desiccant properties to make the
system flexible to adapt to varying weather conditions without
compromising performance.
[0083] Referring now to FIG. 12, there is depicted a split
interchange heat exchanger 66, which includes a pair of tube
assemblies 68. Each tube assembly 68 comprises an inner tube 70
concentrically disposed within an outer tube 72 to define an
annulus 74 therebetween. The dilute liquid desiccant from desiccant
absorber 12 is gravity fed to the interchange heat exchanger 66,
where it is directed through a manifold 76 and into the inner tubes
70. Concentrated liquid desiccant from boiler 34 is first delivered
through coiled interchange heat exchanger 58 and thereafter
directed through a U-fitting 78 coupled to the respective outer
tubes 72 and into the annuli 74. Alternatively, dilute liquid
desiccant is passed through annuli 74 and concentrated liquid
desiccant is passed through inner tubes 70. In this manner, heat is
transferred from the concentrated liquid desiccant to the dilute
liquid desiccant within split interchange heat exchanger 66. The
concentrated liquid desiccant is thereafter drawn into a pump 80
(see FIGS. 8 and 8A) through a U-fitting 82 coupled to the
respective outer tubes 72. The pump 80 delivers the concentrated
liquid desiccant to distributor 14 of absorber 12. The partially
heated dilute liquid desiccant flows through a manifold 84 to the
condenser. During this stage, the dilute liquid desiccant dispensed
from absorber 12 is raised to a first temperature. As discussed
above with respect to coiled interchange heat exchanger 58, the
inner tubes 70 may be fabricated from Teflon and the outer tubes 72
may be constructed from silicone rubber. Likewise, the inner tubes
may be provided with a convoluted or corrugated profile as shown in
FIGS. 12A and 12B, respectively.
[0084] The partially heated liquid desiccant at the first
temperature is delivered to a condenser 86 from split interchange
heat exchanger 66 as shown in FIGS. 8 and 8A. Referring now to
FIGS. 13 and 14, there is depicted a first embodiment of condenser
86, which is comprised of an inner shell 88 disposed within an
outer housing 90 defining at least one chamber 92 between inner
shell 88 and housing 90. The housing 90 includes a plurality of
side walls 94, a top wall 96 and a bottom wall 98. A pair of steam
tubes 100 communicate with inner shell 88 through top wall 96 to
deliver steam from boiler 34. A pair of air vents 102 likewise
communicate with chamber 92 through top wall 96 to evacuate excess
air therefrom. A condensate tube 104 communicates with inner shell
88 through bottom wall 98 to drain condensate into a condensate pan
106 (see FIG. 8A). An inlet tube 108 communicates with chamber 92
through one of the side walls 94 to deliver partially heated dilute
desiccant to condenser 86 from split interchange heat exchanger 66.
An outlet tube 110 is similarly disposed to communicate with
chamber 92 on an opposite side of condenser 86 to deliver dilute
desiccant which is sensibly heated to a second temperature by the
latent heat of condensation as the steam condenses in the inner
shell 88, to the coiled interchange heat exchanger 58 via the inlet
port 54 of U-fitting 52 shown in FIGS. 8 and 11. A fraction of the
desiccant flow leaving the condenser may be recirculated to the
desiccant absorber 12. This reduces the flow rate to the boiler 34
to lower heat loss and increase energy efficiency. In addition,
this maintains a relatively high flow through the absorber 12 and
condenser 86 to yield a higher absorption and condensation
capacity. To facilitate heat transfer, inner shell 88 is fabricated
from materials including inconel, monel, titanium, Teflon,
Teflon-coated copper, Teflon-coated aluminum, and Teflon-coated
stainless steel. The housing 90 is fabricated from materials
including Teflon, polycarbonate, polyvinylidene fluoride,
polypropylene, silicone rubber, polyethylene, and polystyrene. If a
plastic such as Teflon is used for the housing 90, the wall
thickness is made suitably thick to provide the necessary
insulating properties.
[0085] The condenser 86 may incorporate a plurality of fins 112
located on the exterior of inner shell 88 and a plurality of fins
114 disposed on bottom wall 98 of housing 90. The inner shell 88
may be provided with a plurality of baffles 116 to prevent short
circuiting from steam inlets 100 to condensate outlet 104.
[0086] Although depicted with the steam being directed into the
inner shell 88 and the liquid desiccant being directed into the
chamber 92, the opposite arrangement may be employed with the
liquid desiccant directed into the inner shell 88 and the steam
delivered to the chamber 92. Referring now to FIG. 15, there is
shown an alternative embodiment of a condenser 86a, including a
housing 90a and inner shell 88a, where the inner shell 88a
segregates housing 90a into two compartments 92a, 92b,
respectively. A steam inlet tube 100a communicates with compartment
92a, and a steam inlet tube 100b communicates with compartment 92b.
Partially heated dilute desiccant solution is delivered to inner
shell 88a through solution inlet 108a, and is sensibly heated by
the latent heat of condensation as the steam condenses in the
respective chambers 92a, 92b.
[0087] Condensate flows out of chambers 92a, 92b, via condensate
outlets 104a, 104b, respectively. Partially heated dilute desiccant
at the second temperature flows out of inner shell 88a through
solution outlet 110a to coiled interchange heat exchanger 58.
Baffles 112a, 112b are provided in chambers 92a, 92b,
respectively.
[0088] Referring now to FIG. 16, there is shown a third embodiment
of a condenser 86b, comprising a housing 90b and a plurality of
tubes 118, which may be convoluted or corrugated as described above
with regard to the interchange heat exchangers and shown in FIGS.
12A and 12B. The tubes 118 are supported by opposing support plates
120 and communicate with respective steam inlets 100c, 100d through
which steam is delivered from boiler 34. The housing 90b includes a
liquid desiccant solution inlet 108b to receive dilute liquid
desiccant from split interchange heat exchanger 66, and an outlet
110b to deliver partially heated liquid desiccant at the second
temperature to the coiled 10 interchange heat exchanger 58. The
tubes 118 are fabricated from Teflon, and the support plates 120
include at least one silicone rubber sheet attached thereto.
[0089] Referring now to FIG. 17, there is shown another embodiment
of a condenser 86c, utilizing multiple double-pipe heat exchangers.
Each double-pipe heat exchanger comprises an outer straight tube
300 and an inner convoluted tube 302 concentrically disposed within
the outer tube. A small annular gap is defined between the outer
and inner tubes 300, 302 which forces the fluid to follow a
"screw-like" tortuous path through the convolutions at high
velocity. This arrangement provides high heat transfer coefficients
and condensation capacity. The components can be fabricated from
plastics such as polypropylene, Teflon, PVDF or silicone rubber.
Dilute liquid desiccant from split Interchange heat exchanger 66 is
directed into a manifold 304. Similarly, steam from boiler 34 flows
into a manifold 306 through inlet ports 308. Manifold 304
communicates with the inner convoluted tubes 302. Steam flows
through the annuli formed between outer tubes 308 and inner tubes
302, causing the dilute liquid desiccant entering the heat
exchangers from manifold 304 to be partially heated to the second
temperature. This heated liquid desiccant is delivered to the
coiled interchange heat exchanger 58 from exit manifold 310.
Condensate is collected in manifold 312, and is then delivered to
pan 106. Air vents are utilized to ensure reliable gravity assisted
drain flow of the liquid desiccant from the absorber 12 to the
boiler 34. In a preferred embodiment, small pieces of Teflon tape
having a micro-pore structure can be used in the vent assembly. The
Teflon material is hydrophobic and has a micro-pore structure which
enables the free passage of air while preventing steam or desiccant
leakage. The air vent 314 comprises a tube 316 extending upwardly
from manifold 310. The tube 316 includes a polypropylene mesh 318
and a piece of Teflon tape 320 in a laminated structure.
Alternatively, conventional float-based air vents, such as air
vents manufactured by Honeywell, can be utilized to vent air from
the system.
[0090] Referring now to FIG. 18, in another embodiment the
condenser 86d comprises multiple coiled double pipe heat
exchangers. Each double pipe heat exchanger includes an outer
straight tube 300a and inner convoluted tube 302a concentrically
disposed within the outer tube 300a. Steam from boiler 34 enters a
manifold 306a, from where it is communicated into the annuli formed
between outer tubes 300a and inner tubes 302a. Dilute liquid
desiccant is delivered to manifold 304a and thence into the inner
tubes 302a. Partially heated liquid desiccant exits into manifold
310a, and is delivered to coiled Interchange heat exchanger 58.
Condensate flows through outlets 312a to pan 106. This condenser
86d, operates on the same principles and offers the same advantages
as the double-pipe condenser 86c described above.
[0091] Referring now to FIG. 20, the respective components of the
LDA 10 are shown stacked within frame 35 (the components of the
absorption air conditioner 202 are not shown).
[0092] During the operating cycle, ambient air is drawn into the
unit, through absorber 12 and exhausted to the room by fan 23. The
moisture in the air is extracted as the air makes contact with the
liquid desiccant wicking across the microglass fiber wick plates
20, 22. Dilute liquid desiccant is gravity fed from drain pan 24 of
absorber 12 to manifold 76 of split interchange heat exchanger 66,
wherein it is raised to a first temperature through heat transfer
from concentrated liquid desiccant flowing through annuli 74. The
dilute liquid desiccant at the first temperature is then delivered
to the condenser 86, in which the latent heat of condensation as
the steam condenses sensibly heats the liquid desiccant to the
second temperature. The liquid desiccant at the second temperature
is thereafter delivered to the coiled interchange heat exchanger 58
in which it is further heated to a third temperature prior to
introduction into boiler 34 for regeneration. The coiled
interchange heat exchanger 58 recovers waste heat radiating from
the walls 36 of boiler 34. The concentrated liquid desiccant
solution produced by boiling the liquid desiccant is drawn through
the coiled interchange heat exchanger 58 and split interchange heat
exchanger 66, and thereafter delivered to distributor 14 of
absorber 12 by pump 80. The stacking of the respective components
as shown in FIG. 8 provides for the gravity feed of dilute liquid
desiccant from absorber 12 to boiler 34 through the first and
second heat exchangers and the condenser, thereby eliminating the
need for multiple pumps in the system.
[0093] The present invention has been shown and described in what
are considered to be the most practical and preferred embodiments.
It is anticipated, however, that departures can be made therefrom
and that obvious modifications will be implemented by persons
skilled in the art.
* * * * *