U.S. patent application number 12/231716 was filed with the patent office on 2010-03-11 for thermoelectrically powered indirect evaporative cooling system with desiccant dehumidification.
Invention is credited to Mohinder S. Bhatti, John F. O'brien, Ilya Reyzin.
Application Number | 20100058778 12/231716 |
Document ID | / |
Family ID | 41798054 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100058778 |
Kind Code |
A1 |
Bhatti; Mohinder S. ; et
al. |
March 11, 2010 |
Thermoelectrically powered indirect evaporative cooling system with
desiccant dehumidification
Abstract
Disclosed is a system for cooling using indirect evaporative
cooling, dehumidification using desiccant, and a thermoelectrically
powered heat exchanger. The thermoelectric heat exchanger pulls
heat from the working air exiting the indirect evaporative cooler
and injects that heat energy into ambient air that is then forced
through a portion of the rotating desiccant wheel to regenerate the
desiccant by removing water molecules from the desiccant material.
Liquid water that is condensed by cooling the working air with the
thermoelectric heat exchanger is saved and provided to the indirect
evaporative cooler for use to cool via evaporation.
Inventors: |
Bhatti; Mohinder S.;
(Williamsville, NY) ; Reyzin; Ilya;
(Williamsville, NY) ; O'brien; John F.; (Lockport,
NY) |
Correspondence
Address: |
Delphi Technologies, Inc.
M/C 480-410-202, PO BOX 5052
Troy
MI
48007
US
|
Family ID: |
41798054 |
Appl. No.: |
12/231716 |
Filed: |
September 5, 2008 |
Current U.S.
Class: |
62/3.7 |
Current CPC
Class: |
Y02B 30/54 20130101;
F24F 5/0035 20130101; F24F 5/0014 20130101; F24F 3/1423 20130101;
F24F 5/0042 20130101 |
Class at
Publication: |
62/3.7 |
International
Class: |
F25B 21/02 20060101
F25B021/02 |
Claims
1. A method of indirect evaporative cooling a space, the method
comprising: cooling a flow of hot and humid working air via a cold
side of a thermoelectrically powered heat exchanger, to provide a
flow of cooled working air; mixing the cooled working air with a
first incoming flow of ambient air, to provide a combined flow of
air; dehumidifying the combined flow of air via a dry portion of a
rotating desiccant wheel, to provide a flow of cooled and
dehumidified working air; transferring thermal energy from a first
portion of the cooled and dehumidified working air to a second
portion of the flow of cooled and dehumidified working air via an
indirect evaporative cooler, so that the second portion becomes the
flow of hot and humid air, and so that the first portion becomes a
flow of conditioned air; distributing the flow of conditioned air
from the indirect evaporative cooler to the space to be cooled;
heating a second incoming flow of ambient air via a hot side of the
thermoelectrically powered heat exchanger, to provide a flow of
heated ambient air; regenerating the rotating desiccant wheel using
the flow of heated ambient air to drive moisture from a water laden
portion of the rotating desiccant wheel; recovering, at the cold
side of the thermoelectrically powered heat exchanger, water
condensed via cooling of the flow of hot and humid working air; and
supplying the recovered water to the indirect evaporative cooler
for use in evaporating into the second portion of cooled and
dehumidified working air.
2. An air conditioning system for conditioning air in an interior
space, the system comprising: a thermoelectric heat exchanger
module connected to receive a flow of hot and humid working air
into a cold side fluid passage so that a flow of cooled humid
working air emerges from the cold side fluid passage; a rotating
desiccant wheel connected to dry the flow of cooled humid working
air receive from the thermoelectric heat exchanger module so that a
flow of cooled dried working air emerges from the rotating
desiccant wheel; an indirect evaporative cooler having a wet
channel and a dry channel, the wet channel being connected to
receive a first portion of the flow of cooled dried working air
from the rotating desiccant wheel, the dry channel being connected
to receive a second portion of the flow of cooled dried working air
and to supply conditioned air for the interior space, and the wet
channel producing the hot and humid working air; a return conduit
connected to route the hot and humid working air emerging from the
wet channel of the indirect evaporative cooler to the cold side
fluid passage of the thermoelectric heat exchanger module; and a
regeneration conduit connected to provide heated ambient air
emerging from a hot side fluid passage of the thermoelectric heat
exchanger module to a moisture laden portion of the rotating
desiccant wheel to remove moisture from the desiccant wheel; and a
moisture recovery assembly connected to gather liquid water
condensed in the cold side fluid passage of the thermoelectric heat
exchanger and supply the gathered liquid water to the indirect
evaporative cooler to be evaporated in the wet channel.
3. A thermoelectric heat exchanger module comprising: plural
thermoelectric devices, each of the devices having a hot plate, a
cold plate, a positive electrode, and a negative electrode; a cold
side fluid passage having plural cold side lumens, each of the cold
side lumens being in thermal contact with the cold plate of at
least one of the thermoelectric devices; a hot side fluid passage
having plural hot side lumens, each of the hot side lumens being in
thermal contact with the hot plate of at least one of the
thermoelectric devices; wherein the plural thermoelectric devices
are connected electrically in a parallel circuit with one another
and are physically disposed so that adjacent pairs of the
thermoelectric devices either sandwich one of the cold side lumens
between their respective cold plates, or sandwich one of the hot
side lumens between their respective hot plates.
4. The thermoelectric heat exchanger module of claim 3, wherein
each thermoelectric device comprises a solid-state active heat pump
which transfers heat from the cold plate to the hot plate.
5. The thermoelectric heat exchanger module of claim 3, wherein
each thermoelectric device comprises a Peltier effect cell.
Description
TECHNICAL FIELD
[0001] This invention relates generally to evaporative cooling and,
more particularly, to an evaporative cooling system that is
indirectly powered via thermoelectric effect.
BACKGROUND INFORMATION
[0002] The subject invention pertains to an indirect evaporative
cooling system to abstract heat from the ambient air. Examples of
an indirect evaporative cooler can be found in the U.S. Pat. Nos.
6,497,107; 4,977,753 and 4,976,113. In an indirect evaporative
cooler, the dry and wet air streams do not come in direct contact
with each other and as such the absolute humidity of the dry air
does not change during its passage through the dry channels of the
evaporative cooler. However, its dry bulb temperature drops, which
is the desired effect in summer time. For proper comfort cooling,
the absolute humidity of the cold air stream exiting the dry
channels of the evaporative cooler must remain low. Thus an
indirect evaporative cooler is superior to a direct evaporative
cooler (colloquially referred to as "swamp" or "sump" cooler) since
in the latter the dry and wet air streams mix resulting in higher
absolute humidity of the conditioned air, which often is
characterized by an unpleasant odor like that prevailing in a
swamp. Direct evaporative coolers are effective for building
cooling in environments where the prevailing relative humidity is
quite low. They are very popular in the desert southwest of the
United States and in Iran, for example.
[0003] An indirect evaporative cooler is incapable of dehumidifying
the air and as such a desiccant wheel is incorporated in the air
conditioning system to dehumidify the ambient air preparatory to
its entry into the evaporative cooler. Examples of the air
conditioning systems incorporating desiccant wheels to dehumidify
the ambient air can be found in the U.S. Pat. Nos. 5,660,048;
5,727,394; 5,758,508; 5,860,284; 5,890,372; 6,003,327; 6,018,953;
and 6,050,100.
[0004] A shortcoming of the desiccant-assisted evaporative cooler
system is that it consumes excess amount of water to effect
evaporative cooling. Moreover, it requires large amount of thermal
energy to regenerate the desiccant material. What is needed is an
evaporative cooler that can provide substantial cooling in a humid
ambient environment with minimum consumption of water and thermal
energy.
SUMMARY OF THE INVENTION
[0005] In general terms, this invention provides an indirect
evaporative cooler that pre-treats working air by first
thermoelectrically cooling it and then dehumidifying it before it
is input to an indirect evaporative cooler. Moisture laden working
air is looped back from the wet side of the evaporative cooler to
start the pre-treat process over again. Ambient air is
thermoelectrically heated and the heated air is used to dehumidify
a desiccant wheel that becomes water laden when being used to
dehumidify the working air preparatory to entering the evaporative
cooler. The thermoelectric cooling for pre-treating the working air
produces condensate, which is gathered and sent to the indirect
evaporative cooler to be used for evaporation. Heat rejected via
the thermoelectric cooling for pre-treating the working air
returned from the wet side of the evaporative cooler is reused to
heat the ambient air that is used to dehumidify the desiccant
wheel.
[0006] A thermoelectric module is configured as a heat exchanger
that pulls heat from the working air exiting the wet side of the
indirect evaporative cooler and injects that heat energy into
ambient air that is then forced through a portion of the rotating
desiccant wheel to regenerate the desiccant by removing water
molecules from the desiccant material. The thermoelectric module is
configured as plural Peltier cells with the hot plates of the cells
in thermal communication with the hot side of the exchanger and the
cold plates in thermal communication with the cold side of the
exchanger. Water that is condensed in the thermoelectric module
heat exchanger is gathered and plumbed to be provided for use in
wetting absorbent media lining the interior of the wet side of the
indirect evaporative cooler.
[0007] One aspect of the indirect evaporative cooler is the
recovery of spent water in the thermoelectrically powered heat
exchanger.
[0008] Another aspect of the indirect evaporative cooler is the use
of the thermoelectrically powered heat exchanger to effect the dual
goals of condensing water vapor from the working air returned from
the wet side of the indirect evaporative cooler and regenerating a
desiccant wheel.
[0009] These and other features and advantages of this invention
will become more apparent to those skilled in the art from the
detailed description of a preferred embodiment. The drawings that
accompany the detailed description are described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a schematic view of an indirect evaporative
cooling system according to an embodiment of the present
invention.
[0011] FIG. 2 shows a cross sectional schematic view of a
thermoelectrically powered heat exchanger assembly for use in the
indirect evaporative cooling system of FIG. 1.
[0012] FIG. 3 shows a flow chart of operation of an indirect
evaporative cooler.
DETAILED DESCRIPTION
[0013] Evaporative cooling is used to condition air of an enclosed
space. Evaporative coolers lower the dry bulb temperature of air by
using latent heat of evaporation, changing liquid water to water
vapor. In this process, the overall energy in the air remains
substantially constant. Heat in the air is used to evaporate water.
In evaporative coolers of the indirect type, some kind of heat
exchanger is used to isolate working air on the wet side from
conditioned air on the dry side; the cooled moist air on the wet
side never comes in direct contact with the conditioned air on the
dry side.
[0014] Referring to FIG. 1, an indirect evaporative cooling system
100 according to an embodiment of the present invention is
schematically illustrated. In the mixing valve 110, fresh ambient
air is blended with cool, dry air from the thermoelectric heat
exchanger 120 and the blended air is sent to the desiccant wheel
130 where it is dehumidified with elevation in its dry bulb
temperature.
[0015] The working air is passed through the desiccant wheel 130 to
remove moisture therefrom to provide a moisture-depleted stream of
working air exiting the rotating desiccant wheel 130. The desiccant
wheel 130 is regenerated by passing hot gases therethrough to
remove moisture from the desiccant wheel 130.
[0016] An indirect evaporative cooler 140 is provided having a dry
side and a wet side separated by a moisture-impervious wall wherein
heat is extracted from said dry side through an internal heat
exchange process on the wet side. Cooling in the dry side is
achieved by evaporation of water into air passing through the wet
side. The evaporating water is provided to the absorbent media
lining the interior of the wet side.
[0017] The dehumidified blend air then enters the indirect
evaporative cooler 140 where it is split into two streams.
Approximately 20 to 40 percent of air enters the wet side of the
evaporative cooler as the working air and the remaining 60 to 80
percent of the air enters the dry side of the evaporative cooler
140 emerging as the conditioned air 150 for providing comfort
cooling in the conditioned space 154.
[0018] The moisture-laden working air 142 exiting the wet side of
the evaporative cooler 120 is sent to the cold side 122 of the
thermoelectrically energized heat exchanger 120 where the moisture
is condensed from the working air 142. Relatively cool dry air from
the thermoelectrically energized heat exchanger 120 is sent to the
mixing valve 110 for blending with the make up ambient air for
supply to the dehumidification portion of the desiccant wheel
130.
[0019] The heat extracted from the working air 142 is carried away
by the ambient air supplied to the hot side 124 of the
thermoelectrically energized heat exchanger 120. Relatively hot air
from the hot side 124 of the thermoelectrically energized heat
exchanger 120 is sent to the regeneration portion of the desiccant
wheel 130 where it is utilized to drive the moisture from the
desiccant wheel 130 thereby regenerating the slowly turning wheel.
The desiccant wheel 130 revolves at a rate of about 3 to 4
revolutions per minute. The liquid water condensed from the
moisture laden working air 142 in the thermoelectrically energized
heat exchanger 120 is gathered by a moisture recovery assembly
(160) and supplied (as indicated by the broken line) to a water
reservoir of the indirect evaporative cooler.
[0020] FIG. 2 shows detailed construction of the thermoelectrically
powered heat exchanger 120. Thermoelectric modules (TEM's) 210,
212, 214, 216, 218, 220, for example Peltier cells, are arranged in
a stack as plural opposed pairs with their respective hot plates
222, 224 and cold plates 226, 228 facing one another. Sandwiched in
between each pair of facing opposed cold plates 226, 228 (or
attached to a single cold plate at the ends of the stack) is a heat
transfer conduit 230 divided into plural lumens by convoluted
louvered fins 232. The convoluted louvered fins 232 help guide the
working air as it flows through the cold side of the heat exchanger
120 and, importantly, serves to provide abundant surface area for
easy transfer of heat energy from the working air to the TEM cold
plates 226, 228.
[0021] Sandwiched in between each pair of facing opposed hot plates
222, 224 is a flat tube 240 heat transfer conduit. Ambient air is
drawn into the hot side inlet tank 242 flows through the flat tubes
240, drawing heat energy from the TEM hot plates 222, 224. The
heated ambient air flows from the ends of the flat tubes 240 into
the outlet tank 244 and is drawn out of the heat exchanger by a
pump 250 to sent onward to regenerate the desiccant wheel.
[0022] A switch 260 and a DC power supply 262 are connected to the
stack of TEM's in a parallel circuit according to the appropriate
polarities to cause each cold plate to draw in heat and each hot
plate to emit heat.
[0023] Referring to FIG. 3, a flow diagram illustrates operation of
the thermoelectrically power indirect evaporative cooler with
desiccant dehumidification. This method of conditioning a space
using indirect evaporative cooling has aspects that save energy and
save water. A flow of hot and humid working air is cooled 310 by
being passed through a cold side of a thermoelectrically powered
heat exchanger. This provides a flow of cooled partially dry
working air 320. The cooled working air is mixed 330 with a first
incoming flow of ambient air, providing 340 a blended flow of air.
The blended flow of air is dehumidified 350 by flowing through a
dry portion of a rotating desiccant wheel, resulting in a flow 360
of dry air. Thermal energy is transferred from a first portion of
the dry air selected for conditioning to the remaining second
portion of the dry air using an indirect evaporative cooler. The
first portion of the dry air becomes the flow 370 of hot and humid
working air that is returned to the thermoelectrically powered heat
exchanger. The second portion of the dry air becomes a flow 380 of
conditioned air distributed 390 to the space to be conditioned. A
second incoming flow of ambient air is heated 400 using a hot side
of the thermoelectrically powered heat exchanger, to yield a flow
410 of heated ambient air. The rotating desiccant wheel is
regenerated 420 using the flow of heated ambient air to drive
moisture from a water laden portion of the rotating desiccant
wheel. Water condensate is recovered 430 from cooling of the flow
of hot and humid working air at the cold side of the
thermoelectrically powered heat exchanger. The recovered water is
supplied 440 to the indirect evaporative cooler for use in
evaporating into the working air.
[0024] The foregoing invention has been described in accordance
with the relevant legal standards, thus the description is
exemplary rather than limiting in nature. Variations and
modifications to the disclosed embodiment may become apparent to
those skilled in the art and do come within the scope of the
invention. Accordingly, the scope of legal protection afforded this
invention can only be determined by studying the following
claims.
* * * * *