A method and apparatus for conditioning air for an enclosure is
disclosed in which a stream of outside ambient air is dried in a
desiccant core and cooled; thereafter the air stream is further
cooled by passing the same over a cooling element whose surface
temperature under normal operating conditions is higher than the
dew point of the cooled and dried air leaving the heat exchanger.
The thus cooled outside air stream is supplied to the enclosure
while return air is withdrawn from the enclosure and supplied to
desiccant core to pass in heat and moisture exchange relation to
the outside air stream in order to remove moisture sorbed by the
desiccant material from the outside air stream.
What is claimed is:
1. The method of conditioning air for an enclosure which comprises
the steps of:
i) drying a first stream of outside ambient air in a fixed desiccant
core formed of a plurality of sheets of air impervious corrugated
material coated with a desiccant material and defined by two sets
of said sheets positioned at angles to each other to define first
and second sets of passages in the core positioned at angles to
each other, said drying step comprises the steps of passing said
first stream of outside ambient air through said first set of passages
wherein the desiccant material removes water from said outside ambient
air and cooling the dried outside air stream in said first set of
passages in the desiccant core;
ii) further cooling the cooled and dried outside air stream by
passing the same over a cooling element whose surface temperature
under normal operating conditions is higher than the dew point of
the cooled and dried first outside air stream leaving the desiccant
iii) supplying the cooled outside air stream to said enclosure
without further drying in the desiccant core;
iv) passing enclosure return air in heat and moisture exchange
relation to said outside air stream in the second set of passages
in the fixed desiccant core to remove moisture from the core and
to reduce the temperature of the outside air stream, while increasing
the temperature of said enclosure return air; and
v) exhausting the heated enclosure return air to the atmosphere.
2. Apparatus for conditioning air for an enclosure comprising means
for supplying outside ambient air in a first outside air stream
to an enclosure; a fixed desiccant core for reducing the moisture
content and temperature of said first outside air stream; said desiccant
core being formed of first and second sets of air impervious corrugated
sheets coated with a desiccant material, said sheets in said first
and second sets being positioned at angles to each other, and a
third set of flat sheets selectively positioned between sheets of
said first and second sets to define independent first and second
sets of passageways in said core positioned at angles to each other;
air conditioning means downstream of said desiccant core for further
cooling of said first outside air stream; said air conditioning
means having a cooling element whose surface temperature at normal
operating conditions is greater than the dew point of the first
outside air stream leaving the heat exchanger; and means for supplying
return air from the enclosure to the desiccant core for removing
moisture from the core while increasing the temperature of said
enclosure return air and for discharging the humidified and heated
return air from the core to the atmosphere.
3. Apparatus as defined in claim 2 wherein the corrugations of
said first and second sets are positioned at right angles to each
4. Apparatus as defined in claim 3 wherein said flat sheets are
positioned between each of the sheets in said first and second sets.
5. Apparatus as defined in claim 4 wherein said desiccant material
comprises a silica gel desiccant.
6. A desiccant core comprising first and second sets of air impervious
corrugated sheet material coated with a desiccant material, said
sheets in the first and second sets being positioned at an angle
to each other, and a third set of flat sheets of air impervious
material also coated with a desiccant material selectively positioned
between the sheets of the first and second sets to define first
and second sets of passageways in the core which extend at an angle
to each other.
7. Apparatus as defined in claim 6 wherein the corrugations of
the first and second sets of sheets are positioned at 90.degree.
to each other.
8. Apparatus as defined in claim 5 wherein the corrugations of
the first and second sets have the same dimensions.
9. Apparatus as defined in claim 5 wherein the corrugations of
one of said first and second sets are smaller than the corrugations
of the other set.
10. Apparatus as defined in claim 7 wherein one sheet of one of
said first and second sets of sheets is positioned between pairs
of sheets of the other of said first and second sets of sheets.
11. Apparatus as defined in claim 7 wherein one sheet of said third
set of sheets is positioned between each of the sheets of the first
and second sets.
12. Apparatus as defined in claim 11 wherein the sheets of said
first and second sets include a silica gel desiccant material.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to air conditioning systems
and more particularly to an air conditioning system which uses a
static desiccant core for humidity control and/or dehumidification.
2. The Background of the Invention
Air conditioning systems for cooling air in an enclosed space typically
must condense water vapor from an air stream to achieve adequate
dehumidification. The result is that the air conditioning system
works to maintain temperature control in the space (sensible load)
and also must have the capacity to remove the heat of condensation
from the water vapor which is extracted from the air stream to maintain
the desired level of humidity in the enclosed space (latent load).
It has frequently been found that with previously proposed air
conditioning systems the temperature required to condense water
vapor in order to maintain the desired humidity in an enclosure
is lower than the temperature needed to be maintained within the
space itself. Accordingly, it is often necessary to reheat the dehumidified
air in order to maintain desired comfort levels. In addition, contemporary
indoor air quality requirements have created a demand for large
quantities of outside air to be supplied continuously to the enclosed
space. This typically means that a greater load is placed on the
air conditioning system than was required in the past, making the
initial size or capacity of the air conditioning unit greater with
attending increased capital and operating costs.
To avoid these excess expenses, air conditioning systems using
rotary enthalpy wheels have been previously proposed. Such systems
generally reduce the load imposed by outside air on the air conditioning
unit by utilizing exhaust air from the enclosed space as a driving
force for temperature and moisture transfer from the make-up air
to the rotary wheel and then finally to the exhaust air discharge.
Such systems have not been found to be satisfactory in practice
because of cross-contamination between air streams and because of
the complexity of the system. As a result these systems have a poor
reputation for reliability and suffer from bearing, drive system
and metal fatigue.
In accordance with the present invention an air conditioning system
is disclosed in which the return air in the enclosure is exhausted
into the atmosphere, but is used first in the process in order to
treat outside air being introduced into the enclosure for air exchange
purposes. The return air is passed in counter current relationship
to the outside air in a fixed desiccant core unit having no moving
It is an object of the present invention to provide an improved
air conditioning system based upon desiccant technology.
Another object of the present invention is to provide an improved
air conditioning system which is less expensive to construct and
to operate as compared to prior art systems.
Yet another object of the present invention is to provide a desiccant
based air conditioning system which has greater mechanical reliability
and lower risk of cross circuit air contamination due to leakage.
A still further object of the invention is to provide a desiccant
based air conditioning system which allows for independent control
of temperature and humidity.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention an air conditioning
system for an enclosure such as a room or the like is provided in
which outside air is supplied to an exchange device which is constructed
of a desiccant material. The exchange device is formed of corrugated
sheets which, in one embodiment, are positioned alternately in crossing
relation with flat sheets between them to define first and second
perpendicularly arranged sets of passages in the device or core.
The desiccant material forming the walls of the exchange device
attracts water vapor from a warm and humid air stream (e.g. outside
air) while allowing transfer of the sorbed water through the material
to an exhaust air stream (e.g. exhaust room air). The exchanger
simultaneously transfers thermal energy between the two air streams
to reduce the heating or cooling loads imposed on the air conditioning
In use, outside air is supplied to one set of passages in the device
for humidity and temperature exchange with exhaust room air supplied
to the other set of passages. The cooled and dried outside air is
then supplied to an air conditioner device which further cools the
outside air by passing it over a cooling element whose surface temperature,
under normal operation conditions, is higher than the dew point
of the outside air from the heat exchanger. As a result of the use
of the desiccant core, the air supplied to the air conditioner is
relatively dry so the air conditioner can be operated at higher
temperatures while avoiding condensation in the air conditioner.
It thus operates in its most efficient mode. The exhaust air supplied
to the core or exchanger provides a temperature sink for the exchange
of thermal energy between the two air streams. The room air from
the core or exchanger then may be exhausted to the atmosphere.
Applicant has found that an air conditioner system constructed
in accordance with the present invention is less expensive to construct,
operate and maintain than an air conditioning system using only
an air conditioner device or a combination of an air conditioner
device and a rotary enthalpy wheel. By this system the initial capacity
of the air conditioner unit can be substantially reduced because
of the temperature and moisture exchange through the desiccant core
which removes energy from the outside air before it is supplied
to the air conditioner. The static nature of the desiccant core
eliminates the problems associated with the drive systems, sealing
mechanisms and failure of rotating components found in the prior
art. The walls of the desiccant exchanger core of the invention
allow moisture transfer via internal diffusion while remaining highly
impermeable to air flow. The present invention therefore has a very
low amount of cross circuit air contamination compared to the prior
art wherein seals rub against sliding surfaces to prevent air mixing
and wherein purge air streams are required to extract contaminants
from the volume of the exchanger rotating between air streams.
In one example, a conventional air conditioning system for cooling
outside air may require a 59 ton air conditioner. With the present
invention, using a desiccant exchange, the required air conditioner
need only be 31 tons. Thus the size of the air conditioner and the
power consumption of the system is reduced by almost 50%.
In the preferred embodiment of the invention, as described hereinafter,
a cross flow desiccant exchanger is used, however other exchanger
configurations, such as counter flow arrangements, could also be
used. It is believed that the cross flow configuration provides
the best combination of design flexibility, ease of manufacture,
and mechanical strength to resist internal air pressure while maintaining
high transfer efficiencies.
The above and other objects, features and advantages of this invention
will be apparent in the following detailed description of illustrative
embodiments thereof, which is to be read in conjunction with the
accompanying drawing wherein:
BRIEF DESCRIPTION OF DRAWING
FIG. 1 is the schematic view of an air conditioning system constructed
in accordance with the present invention;
FIG. 2 is a chart showing an example of operating conditions within
the system of the present invention wherein outside air temperature
is 90.degree. Fahrenheit and enclosure return air is at 75.degree.
FIG. 3 is a perspective view of a desiccant core for the air conditioning
system constructed in accordance with one embodiment of the invention
wherein the corrugations of both sets of sheets are of the same
FIG. 4 is a perspective view of another embodiment of exchanger
core wherein one set of sheets has smaller corrugations of greater
frequency than the other set;
FIG. 5 is a perspective view of yet another embodiment or desiccant
core of the invention wherein one set of passages is formed of pairs
of sheets of desiccant material arranged parallel to each other;
FIG. 6 is a schematic side view of a core pack illustrating another
way of forming the core pack; and
FIG. 7 is a schematic illustration of yet another form of core
Referring now to the drawing in detail, and initially to FIG. 1
thereof, an air conditioning system 10 constructed in accordance
with the present invention is illustrated. This system includes
a desiccant exchanger core 12 which has no moving parts. The core
is formed of desiccant sheet material, such as, for example, desiccant
sheet material previously used to form desiccant wheels as sold
by Cargocaire Engineering Corporation and by Munters Corporation.
Such sheet material can be formed with a silica gel coating, as
is known in the art, e.g. U.S. Pat. No. 4871607 or with a lithium
chloride or other desiccant materials in a known manner. The sheets
are preferably formed with a substantially air impervious base material
which could, for example, be formed of material sold under the trademarks
TYVEK and GORTEX or other known supporting materials. Such materials
however permit water vapor transfer between desiccant material on
opposite sides thereof.
In one embodiment of the invention core 12 is formed of two sets
of corrugated sheets 14 and 16 (see FIG. 5) wherein the sheets of
each set are alternated with one another with the corrugations of
each adjacent sheet positioned at 90.degree. to each other. A third
set of flat sheets 18 of the desiccant material are provided with
one flat sheet positioned between each adjacent pair of sheets 14
16. This arrangement provides first and second sets of perpendicularly
related air flow passages 20 22 in the core to allow two separate
air streams to pass through the core in cross flow relationship
to one another.
The edges of each sheet of material in sets 14 16 may be closed
by flat sheet sections 15 if desired to completely isolate the two
air streams. The sheets are bonded together at their contact points
in any known or convenient manner.
In accordance with one embodiment of the present invention ambient
or outside air is supplied to the system 10 through an intake duct
24 or the like under the influence of a blower 26 to one set of
passages 20 in core 12.
The outside air in this stream is preferably passed through a conventional
dust filter 28 or the like before entering the desiccant core 12.
As the air passes through the passages 20 of desiccant core 12 moisture
is removed from the air.
At the same time enclosure or room return air is withdrawn from
the room through a conventional dust filter system 29 by a blower
30 and passes through the passageways 22 of core 12. This return
air is cooler and drier than the outside air. It removes moisture
sorbed by the desiccant material and also decreases the temperature
of the outside air.
The temperature conditions of various stages of the process are
depicted on the graph of FIG. 2 for one embodiment of the invention
wherein the air flow induced by the blower 26 is 10000 standard
cubic feet per minute, with outside air temperature being 90.degree.
Fahrenheit and having a humidity ratio of 110 grains per pound.
These are the conditions of the ambient air stream at point A in
FIG. 1. As seen from the chart in FIG. 2 after the air passes through
the desiccant core, at point B, its temperature has been lowered
to 78.5.degree. Fahrenheit and its humidity ratio has been decreased
to 80 gr/lb. At the same time the room return air, which is preferably
passed first through the dust filter 29 has its temperature raised
from 70.degree. F. to 86.3.degree. F. and 70 gr/lb to 100 gr/lb.
From the desiccant core the now slightly cooled and dried stream
of outside air is passed to an air conditioner 32 which is of known
construction. The air conditioner may be a conventional electrically
operated refrigerant based air conditioner having cooling coils
over which the air is passed in heat exchange relationship. Because
the air has been dried in the desiccant core it is possible to operate
the air conditioner unit at higher temperatures than have been previously
used in the art because the air conditioner does not have to produce
as much dehumidification. Indeed, the air conditioner may operate
at a temperature which is higher than the dew point temperature
of the air being treated thereby avoiding formation of condensation
on the condensation coils. Condensation on the coils would decrease
the efficiency of the air conditioner and its ability to cool the
air. It also produces undesirable sites for bacterial growth. Of
course, while the air conditioner operates at the desired temperature
above the dew point of the air flowing from the core during normal
on-line operating conditions, it will be understood by those skilled
in the art that during initial start up of the air conditioner,
before it reaches a steady state condition, there may be some temperature
As a result of the passage of the air through air conditioner 30
its temperature is decreased (point C) to 55.degree. Fahrenheit
and its moisture content is also reduced to 64 gr/lb. Blower 26
then supplies the thus cooled air to the room enclosure.
In the illustrative embodiment of FIG. 1 a gas burner or furnace
38 is provided in the air stream between air conditioner 32 and
blower 26. This burner is not used in the air conditioning mode
of operation of the apparatus of FIG. 1. The burner is used when
heated air is required and the air conditioning system is not operating.
When operating in the normal air conditioning mode of the present
invention the air passes untreated through the burner system. From
blower 26 the cooled and dehumidified air is supplied to the room
or enclosure where it mixes with air in the enclosure and/or recirculated
filtered room air to maintain desired temperature and humidity levels
By this arrangement of the present invention an improved air conditioning
system is provided which has fewer moving parts that are subject
to failure and which is more efficient in operation. The use of
the corrugated desiccant core material provides for efficient heat
and humidity transfer by a very simple structure wherein the corrugations
of the sheets provide ample air flow through a plurality of separated
passageways. The core itself has great structural integrity because
of the alternate crossing of the corrugated sheets which is reinforced
by the intermediate flat sheets and the bonding of the sheets together.
The air conditioner system of the present invention represents
an improved desiccant material based system with substantial efficiencies
both in original installation expenses and in operation. As a result
the size of the air conditioner needed in the system is reduced.
As described above these systems are used for cooling air supplied
to the enclosure. If it is necessary supply heated air to the enclosure,
the system operates as described except that instead of the air
conditioner 26 being operative, the gas burner is operative. It
should be noted that in winter operation the desiccant core helps
maintain heat and humidity levels in the enclosed space. This also
allows the heater to be reduced on a first cost and operating cost
In the embodiment of the core shown in FIG. 3 the corrugations
of sheets 14 and 16 have the same amplitude (or height) and frequency.
However, the operating characteristics of the core may be varied
by changing the size or configurations of the sheets, thereby to
modify the relative volume of air flow in the air passageways 20
For example, in the embodiment shown in FIG. 4 the sheets 16 are
formed with corrugations that have a smaller amplitude and higher
frequency than that of sheets 14. Thus the volume of air at a given
pressure which can pass through the air passageways 22 formed by
sheets 16 will be less than can pass through passages 20.
In the embodiment of FIG. 5 two sheets 14 are placed between each
pair of sheets 16 thus doubling the air flow capacity of the air
passages 20 formed by sheets 14 as compared to passageways 22.
In the embodiments of FIGS. 3 to 5 the cores 12 are formed as rectangular
blocks with the air passageways extending perpendicularly to the
edges of the core. With this construction the air ducts carrying
the outside and room air streams to the core are arranged to extend
perpendicularly to the core. In some situations it may be desirable
to have unbalanced air flow circuits in the core. In those cases
the core may take an elongated rectangular form, as shown in FIG.
6 so that one face 50 has a larger inlet area for its air stream
than the other face 51.
An alternative method of creating unequal air flows is to initially
form the core with flow paths at 90.degree. angles to the core faces,
as seen in FIG. 3 for example, and then re-cutting the core material
on one or both pairs of opposed faces at different angles to the
flow paths to form a diamond shaped core whose air inlet faces have
different areas, as seen in FIG. 7.
Although illustrative embodiments of the present invention have
been described herein with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those
precise embodiments, but that various changes in modifications can
be effected therein by those skilled in the art without departing
from the scope or spirit of this invention.