U.S. patent application number 13/454371 was filed with the patent office on 2012-08-16 for sub-wet bulb evaporative water chiller with gradient chilling and air-to-air heat exchange.
Invention is credited to Eric Edward Jarvis.
Application Number | 20120204591 13/454371 |
Document ID | / |
Family ID | 38222942 |
Filed Date | 2012-08-16 |
United States Patent
Application |
20120204591 |
Kind Code |
A1 |
Jarvis; Eric Edward |
August 16, 2012 |
SUB-WET BULB EVAPORATIVE WATER CHILLER WITH GRADIENT CHILLING AND
AIR-TO-AIR HEAT EXCHANGE
Abstract
An evaporative chiller cooling water to below ambient wet bulb
temperature. Sub-wet bulb chilling is achieved by pre-cooling
incoming air upstream of the saturator. The incoming air is ambient
air at ambient air temperature that is cooled using the coolness of
the lower temperature outgoing air exiting the saturator. The
pre-cooling lowers the temperature of the incoming air and lowers
its wet bulb temperature below that of ambient air. The saturator
water is chilled to below the ambient wet bulb temperature. The air
in the saturator flows across the water as it gravity drips or
flows from the top to the bottom of the saturator. The pre-cooled
air flows across the saturator with the coolest air directed across
the bottom of the saturator where the coldest water is flowing and
with the hottest air directed across the top where the hottest
water is flowing to provide gradient chilling.
Inventors: |
Jarvis; Eric Edward;
(Boulder, CO) |
Family ID: |
38222942 |
Appl. No.: |
13/454371 |
Filed: |
April 24, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12722741 |
Mar 12, 2010 |
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13454371 |
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11616303 |
Dec 27, 2006 |
7698906 |
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12722741 |
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60755142 |
Dec 30, 2005 |
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60800682 |
May 16, 2006 |
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Current U.S.
Class: |
62/314 |
Current CPC
Class: |
F28D 5/00 20130101; Y02B
30/54 20130101; F24F 1/0007 20130101; Y02B 30/545 20130101; F24F
5/0035 20130101 |
Class at
Publication: |
62/314 |
International
Class: |
F28D 5/00 20060101
F28D005/00 |
Claims
1. An evaporative water chiller, comprising: a saturator with a
liquid inlet and a liquid outlet, wherein water to be cooled enters
the saturator through the liquid inlet and drains by gravity
through the saturator and exits through the liquid outlet; and an
air delivery assembly delivering a volume of air to the saturator
at temperatures below a temperature of ambient air entering the
chiller, wherein the air delivered to the saturator has a first
temperature near the liquid inlet of the saturator and a second
temperature near the liquid outlet of the saturator that is lower
than the first temperature, wherein the air delivery assembly
comprises an air-to-air heat exchanger including plates defining a
plurality of incoming passageways for the air delivered to the
saturator and a plurality of outgoing passageways interposed
between adjacent pairs of the incoming passageways for the
delivered air to exit the chiller after passing through the
saturator, and wherein the air-to-air heat exchanger defines the
incoming and outgoing passageways to maintain a vertical chilling
gradient in the air delivered to the saturator and the air exiting
the chiller after passing through the saturator.
2. The chiller of claim 1, wherein the air delivered to the
saturator is directed to flow through the saturator transverse to a
direction of flow of the liquid in the saturator.
3. The chiller of claim 1, wherein the plates are positioned to
extend parallel and vertically within the chiller.
4. The chiller of claim 3, wherein the heat exchanger further
comprises spacers defining at least two separate flow levels in
which the air delivered to the saturator is forced to flow in
horizontal channels without mixing with air in other ones of the
horizontal channels or with the air exiting the chiller.
5. The chiller of claim 1, wherein the plates are positioned to
extend horizontally and in a parallel manner within the
chiller.
6. The chiller of claim 5, wherein side-by-side pairs of the plates
have a W-shaped cross sectional shape or an S-shaped cross
sectional shape to enhance heat transfer.
7. The chiller of claim 1, wherein the air-to-air heat exchanger
defines the incoming and outgoing passageways such that the air
delivered to the saturator flows in a first direction and the air
exiting the chiller after passing through the saturator flows in a
second direction counter to the first direction.
8. The chiller of claim 1, wherein the plates are formed of plastic
sheets.
9. An evaporative chiller for cooling water to a temperature below
the ambient air wet-bulb temperature, comprising: a saturator in
which water is able to flow from a top portion to a bottom portion,
the saturator extending vertically within the chiller with a first
side and a second side both permeable to air flow; a fan for
drawing ambient air into the chiller as incoming air to flow
through the first and second sides of the saturator; and a heat
exchanger at least partially positioned upstream of the first side
of the saturator for first cooling the incoming air to a range of
temperatures below ambient temperature and for second directing the
cooled incoming air into the saturator along the first side with
portions at a higher end of the range of temperature provided near
the top portion and portions at a lower end of the range of
temperature provided near the bottom portion of the saturator.
10. The chiller of claim 9, wherein the heat exchanger comprises a
plurality of spaced apart sheets defining flow passageways for the
incoming air and flow passageways for outgoing air exiting the
saturator with each of the incoming air flow passageways being
adjacent at least one of the outgoing air flow passageways.
11. The chiller of claim 10, wherein the spaced apart sheets are
arranged to control air mixing to at least partially maintain
temperature stratification within the incoming air and within the
outgoing air.
12. The chiller of claim 10, wherein the heat exchanger controls
air flow to provide counter flow between the incoming air and the
outgoing air.
13. The chiller of claim 10, wherein the spaced apart sheets are
parallel and extend horizontally within the heat exchanger.
14. The chiller of claim 13, wherein the incoming air flows in a
cross flow pattern through the saturator and then reverses
direction and flows through the heat exchanger as the output
air.
15. The chiller of claim 10, wherein the spaced apart sheets are
parallel and extend vertically within the heat exchanger.
16. The chiller of claim 9, wherein the water flowing near the
bottom portion is at a temperature below the wet-bulb temperature
of the ambient air.
17. An evaporative cooling system, comprising: a chiller comprising
a saturator and an air-to-air heat exchanger generating a stream of
pre-cooled air at an air inlet to the saturator by cooling ambient
air to temperatures below ambient air temperature by transferring
heat from the ambient air to air exiting the saturator through an
air outlet, wherein the pre-cooled air temperatures range from a
higher temperature proximate to a top of the saturator and a lower
temperature proximate to a bottom of the saturator; a space cooling
system including a heat exchanger with a liquid side; and a water
circulation system pumping water exiting the bottom of the
saturator through the liquid side of the space cooling system heat
exchanger.
18. The system of claim 17, wherein the heat exchanger comprises a
plurality of sheets defining flow channels for the pre-cooled air
and for the air exiting the saturator such that no mixing of the
pre-cooled air and the air exiting the saturator occurs and such
that the pre-cooled air is input into the saturator to flow
transversely across water flowing downward through the
saturator.
19. The system of claim 18, wherein the sheets are arranged to
extend horizontally within the heat exchanger and are substantially
planar or have a W-shaped or S-shaped cross sectional shape and
wherein the water exiting the bottom of the saturator is at a
temperature at least about 5.degree. F. lower than a wet-bulb
temperature of the ambient air.
20. The system of claim 17, wherein the air-to-air heat exchanger
is configured for counter current flow between incoming flow of the
ambient air and flow of the air exiting the air outlet of the
saturator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/722,741, filed Mar. 12, 2010, which is a
divisional of U.S. patent application Ser. No. 11/616,303, filed
Dec. 27, 2006, now U.S. Pat. No. 7,698,906, which claims the
benefit of U.S. Provisional Applications No. 60/755,142 filed Dec.
30, 2005 and No. 60/800,682 filed May 16, 2006, all of which are
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to evaporative chillers and
evaporative cooling systems, and more particularly, to an
evaporative water chiller or evaporative fluid cooling system that
is operable to lower the temperature of water or other liquid
exiting the chiller or chiller system to below the ambient wet-bulb
temperature. This may be achieved by pre-cooling the incoming air
flow or airstream to a temperature below the ambient air
temperature such as by using the outgoing or exiting air flow or
airstream.
[0004] 2. Relevant Background
[0005] Today, a large fraction of the electrical energy used in the
United States and elsewhere in the world is used for cooling
interior spaces, such as habituated areas of residential and
commercial buildings, to desired or acceptable temperatures. In
some geographic regions, cooling costs may be more than half of the
annual energy cost for businesses and home owners. The electrical
energy used for space cooling is not only costly but causes
problems because it is concentrated into certain times of the day
when highest temperatures are experienced, and this high demand can
create high peaks in power demand that are difficult for power
companies to satisfy. Hence, there is an ongoing need for reducing
the amount of energy needed for cooling and for better distributing
the demand to reduce the size of spikes or peaks in demand.
Reducing demand for electricity is a vital and growing concern as
the human population increases, as more and more countries become
industrialized and more urban, as concerns heighten over global
warming from fossil fuel combustion, and as the availability of
fossil fuels dwindles and the associated prices rise. One way to
control electricity or power consumption is to develop
lower-energy, alternative cooling systems that have the potential
to reduce overall and peak electricity usage.
[0006] However, it has proven difficult to design cooling systems
and devices that can effectively compete with refrigerant-based air
conditioning (A/C) systems to significantly reduce overall power
consumption. Evaporative coolers are one approach, but a number of
disadvantages have blocked widespread use of these cooling systems.
Evaporative cooling involves evaporation of a liquid to cool an
object or a liquid in contact with an airstream. When considering
water evaporating into air, the web bulb temperature of the ambient
air (as compared with the dry bulb temperature) is a standard
measure for the potential for evaporative cooling systems, and the
greater the difference between the wet bulb and dry bulb
temperatures the greater the possible evaporative cooling effect.
Evaporative cooling is a fairly common form of cooling for
buildings for thermal comfort since it is relatively cheap and
requires less energy than many other forms of cooling. However,
evaporative cooling requires a water source as an evaporative and
is presently only efficient when the relative humidity is low,
which has restricted its use to geographic regions with dry
climates.
[0007] Smaller scale evaporative coolers are often called swamp
coolers, and the typical swamp cooler passes an air stream from
outside of the building or interior space through the swamp cooler
to contact water or other liquid in the cooler. The air is cooled
by evaporation of the water, and the cooled air is directed by fans
into the building or interior space. Traditional evaporative or
swamp coolers have met with a fair degree of market acceptance
because they work well in arid and semi-arid regions and are
inexpensive to purchase and operate. While such coolers can often
provide most or all of the cooling needed for a home or business,
they suffer from several disadvantages. Swamp coolers are generally
incompatible for integration with compressor-based A/C because they
are "pass-through" systems in which conditioned air must be allowed
to flow out of the building. They also require large air flow
rates, and may be noisy. Further, evaporative coolers in which the
cooling air contacts the water may introduce mold and allergens
into the interior of the building and often unacceptably raise the
indoor humidity making it "muggy" in the building. Evaporative
coolers also can require significant maintenance and often require
winterization to avoid damage.
[0008] An alternative cooling system involves the use of an
evaporative cooling system that functions by cooling a volume of
liquid such as water by evaporating a portion of the cooling liquid
in a stream of ambient or outdoor air. Such systems are referred to
herein as "evaporative chillers." The cooled or chilled liquid is
then circulated through piping of an air-to-water heat exchanger to
cool the air blown or drawn through the exchanger. The air is
cooled as heat is transferred to the water in the pipes and does
not directly contact the water. The cooler air is returned to the
interior spaces of the building. Evaporative chillers, which are
also known as cooling towers, are more common in commercial
buildings and can provide a large portion of the required cooling.
Evaporative chillers are sometimes unable to lower the temperature
of the interior space or building to an acceptable level, and in
these cases, conventional compressor and refrigerant based air
conditioning may be used to supplement the cooling achieved by
evaporative cooling (however, this reduces the energy savings
provided by use of the evaporative cooling system). When compared
with swamp coolers and similar systems, evaporative chiller systems
are compatible with compressor-based A/C units, do not introduce
allergens or humidity to the cooling air (because there is no
direct contact between indoor air and the chilled water), and do
not require large air flow through the interior spaces of the
building. In addition, evaporative chillers integrate well with
typical HVAC practices in that the location of the chiller unit is
flexible and existing ductwork can be utilized. Evaporative
chillers are also compatible with radiant cooling technologies that
are gaining acceptance in some areas.
[0009] Even in light of these advantages, evaporative chillers have
not been widely used for cooling in the residential market. There
are at least two main reasons that evaporative chillers are not
attractive to home owners and residential builders. Depending on
the wet bulb temperature, evaporative chillers often will not be
able to cool the flowing coolant or water to a low enough
temperature to effectively cool a building or interior space.
Evaporative chillers may be seen as an unnecessary expense or an
expense that will require many years to recoup based on potential
energy savings. The costs associated with an evaporative chiller
may be particularly unpalatable if a backup A/C system is still
required to handle higher loads or to cool on hotter days. Thus,
the ability of an evaporative chiller to more effectively lower the
water temperature relative to the ambient wet bulb temperature is
key to the success of such cooling systems.
[0010] Two-stage evaporative coolers have also been developed.
These units combine both an indirect and a direct evaporative
cooling stage to generate air that can sometimes reach the ambient
wet bulb temperature or below. This is achieved by lowering the wet
bulb temperature of the ambient air by first passing it through the
indirect stage (in which no humidity is added). The second, direct
evaporative cooling stage adds humidity and further reduces the air
temperature. Lower air temperatures mean that these coolers can
provide the required level of cooling under a wider range of
ambient conditions and geographical areas than typical swamp
coolers. Unfortunately, because these two-stage coolers still
produce chilled air (rather than water) many of the disadvantages
of swamp coolers still apply. This, along with the complexity and
cost of two-stage coolers, has prevented their rapid market
penetration. In theory, the two-stage designs could be adapted to
produce water rather than air (by utilizing the water in the sump).
Besides the cost and complexity factors, this approach has at least
two disadvantages compared to the system described in the present
invention. First, the two-stage cooler used as a water chiller will
exhaust cooled air to the ambient environment, thus wasting cooling
power and increasing water consumption. Second, the theoretical
temperature to which water can be cooled is not as low as in the
present invention. That is because the first (indirect) stage can
only reduce the air temperature to the ambient wet bulb temperature
(and typically higher in practice), whereas in the present
invention the use of cooled exhaust air to cool the incoming air
makes possible pre-cooling air to below the wet bulb temperature.
Others have described chiller designs based on recycling exhaust
air from the chiller to pre-cool incoming air. However, those
designs do not take advantage of the "gradient chilling" concept of
the present invention (explained below) that allows further
reduction of water temperatures.
[0011] Hence, there remains a need for cooling systems that are
more energy efficient and preferably that more effectively
implement evaporative cooling to cool buildings or interior spaces
within a residence or commercial structure. Preferably, such
cooling systems would include an evaporative chiller that is
designed to provide improved levels of cooling with low energy
consumption and that would be adapted for use in the residential or
housing market as well as in commercial settings.
SUMMARY OF THE INVENTION
[0012] The invention provides an evaporative chiller (sometimes
referred to as a cooling tower even in smaller residential models)
that can cool water to temperatures below the ambient wet bulb
temperature. This ability sets the evaporative chillers of the
invention apart from traditional cooling towers that are limited to
cooling water to the wet bulb temperature of the ambient air.
Sub-wet bulb chilling is achieved by pre-cooling the air to be used
for cooling the water in the saturator (e.g., where water is
allowed to flow over packing, pads, or the like and be evaporated
to obtain chilling). This inlet or incoming air is typically the
air surrounding the chiller or ambient air at ambient air
temperature. The incoming air in some embodiments of the invention
is cooled using the coolness of the lower temperature outlet or
outgoing air that has passed through the saturator. The pre-cooling
acts to lower the temperature of the incoming air and, thus, to
lower its wet bulb temperature below that of the ambient air. As a
result, the water in the saturator can be chilled to a lower
temperature and, typically, a temperature below the ambient wet
bulb temperature. To further enhance the chilling effect, the air
in the saturator is directed to flow across the flow path of the
water as it gravity drips or flows from the top to the bottom of
the saturator or saturator column (e.g., to have a cross-flow path
rather than counter-current as is used typically in conventional
cooling towers). Yet further, the pre-cooled air is directed across
the saturator so as to have a range of temperatures with the
coolest air directed across the bottom of the saturator where the
coldest water is flowing and with the hottest air directed across
the top of the saturator where the hottest water is flowing. This
is achieved by maintaining the vertical temperature stratification
of the incoming and outgoing air streams such that the coldest
outgoing air at the bottom is used to pre-cool the incoming air at
the bottom of the device, and the hottest outgoing air at the top
is used to pre-cool the incoming air at the top of the device.
Thus, a temperature gradient is established which we will refer to
as "gradient chilling." Gradient chilling functions to chill the
water more effectively and to achieve a lower final water
temperature.
[0013] More particularly, an evaporative chiller is provided that
includes a saturator and a mechanism for delivering a volume of air
to the saturator at temperatures below the ambient air temperature
outside the chiller. The saturator includes a liquid inlet and a
liquid outlet (e.g., into a sump) and liquid to be cooled or
chilled enters through the liquid inlet and is fed by gravity
vertically downward to exit through the liquid outlet. To chill
this flowing liquid, the air delivered to the saturator is forced
to flow transversely across the flowing water and is provided with
a temperature gradient (i.e., at a first temperature near the water
inlet and at a second lower temperature near the water outlet and
increasing between the outlet and the inlet gradually). The air
delivery mechanism typically includes a fan or fans for forcing the
air into the chiller, through the saturator, and back out of the
chiller.
[0014] Six embodiments of the invention are presented that share
the basic principles of chilling water to sub-wet bulb
temperatures, transverse flow in the saturator, and gradient
chilling, but differ in the nature and design of the heat exchanger
that utilizes outgoing air to pre-cool the incoming air. In one
embodiment, a first thermal storage matrix is positioned along a
first side of the saturator, a second thermal storage matrix along
a second opposite side of the saturator, and the fan(s) has its
direction reversed periodically such that incoming ambient air
alternates between flowing over the first and second thermal
storage matrices prior to entering the saturator such that the
incoming air is pre-cooled as it flows through the matrices. In
another embodiment, the air delivering mechanism includes a first
air-to-liquid heat exchanger positioned upstream the saturator air
inlet, a second liquid-to-air heat exchanger positioned downstream
of the saturator air outlet, and a pump that circulates liquid
through the liquid side of these two heat exchangers, which results
in pre-cooling of the air fed to the saturator (again with
"gradient chilling").
[0015] In some preferred embodiments, the air delivering mechanism
is formed to provide an air-to-air heat exchanger upstream of the
saturator to use air exiting the saturator to pre-cool the incoming
ambient air. For example, the chiller may include a cabinet
defining an interior space and the saturator may be positioned at
one end of this interior space. The air delivering mechanism then
may include a plurality of spaced-apart, parallel tubes that extend
horizontally within the cabinet's interior space with one end
extending to or into the saturator but spaced apart from the
cabinet side wall to provide a space for incoming air to flow
through the space between the tubes, through the saturator, through
the gap between the tube ends and the cabinet side wall, and into
the tube ends to be directed out of the cabinet but first cooling
the incoming air. In other examples, vertical or horizontal,
parallel plates may be used to define side-by-side incoming and
outgoing airstream channels or passageways upstream of the
saturator (and sometimes the saturator material may be provided
within the outgoing (or incoming) passageways. In other
applications, plates are again used (such as thin metal sheets) but
in these cases the plates are wound about the saturator to define
spiral flow paths for the incoming and outgoing airstreams. In each
of these embodiments, the incoming and outgoing air generally does
not mix extensively in the vertical dimension (i.e., remains
stratified) and is provided to the saturator with a temperature
gradient with the cooler air being fed into the bottom of the
saturator to further cool the already chilled water and the hotter
air (but still pre-cooled to a temperature below ambient) fed to
the upper or inlet portions of the saturator in which the water is
also warmer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a functional block diagram of a cooling system
including a sub-wet bulb evaporative chiller according to the
present invention;
[0017] FIGS. 2A and 2B are sectional side views of one embodiment
of an evaporative chiller of the invention that is useful in
cooling systems such as the system of FIG. 1 and that shows the use
of reversible air flow and cooling storage matrices to obtain
sub-wet bulb temperature cooling;
[0018] FIGS. 3A and 3B are graphs showing theoretical examples of
the psychometrics of the air flowing at the top and bottom,
respectively, of an evaporative chiller of the invention that
utilizes gradient chilling;
[0019] FIG. 4 is a graph illustrating results of operation of the
chiller of FIGS. 2A and 2B under one set of operating conditions
and one exemplary chiller configuration including a particular
storage matrix material or filler used for storing "coolage" (i.e.,
being placed at a temperature below ambient) for use in pre-cooling
inlet air flow;
[0020] FIG. 5 is a sectional side view of another embodiment of an
evaporative chiller of the present invention that may be used in
cooling systems such as the system of FIG. 1;
[0021] FIG. 6 illustrates an end view of a fin and tube heat
exchanger useful in the chiller of FIG. 5 for providing efficient
air-to-liquid and liquid-to-air heat transfer while maintaining
gradient chilling;
[0022] FIG. 7 is a perspective view of yet another embodiment of an
evaporative chiller for use in cooling systems of the present
invention with the chiller utilizing tubing for return or exiting
air so as to provide an air-to-air heat exchanger that is of a tube
or tube-channel configuration;
[0023] FIG. 8 is a sectional side view of an embodiment of an
evaporative chiller of the invention that provides an air-to-air
heat exchanger for providing pre-cooling with a plate configuration
for providing flow channels for inlet and outlet/return air;
[0024] FIG. 9 is a top view of the chiller of FIG. 8 showing one
exemplary, but not limiting, example of a configuration for the
plate air-to-air heat exchanger;
[0025] FIG. 10 is a sectional or cutaway side view of another
embodiment of an evaporative chiller of the invention that
pre-cools incoming or inlet air upstream of the saturator or water
column using vertical plates and spacers to provide flow
channels;
[0026] FIG. 11 is a sectional side view of the chiller showing the
positioning of saturator pads/packing in return flow channels;
[0027] FIGS. 12 and 13 illustrate exemplary spacer designs for use
with the chiller of FIGS. 10 and 11; and
[0028] FIGS. 14A and 14B illustrate sectional top and side views,
respectively, of still another embodiment of an evaporative chiller
of the present invention that shows the use of side-by-side,
spirally wound plates for defining flow channels for inlet and
outlet/return air to provide pre-cooling of the inlet air prior to
its reaching a centrally positioned saturator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In the drawings, like reference numerals indicate like
features, and a reference numeral appearing in more than one figure
refers to the same element. The drawings and the following detailed
descriptions show specific embodiments of the invention with
numerous specific details including materials, dimensions, and
products being provided to facilitate explanation and understanding
of the invention. However, it will be obvious to one skilled in the
art that the present invention may be practiced without these
specific details and these broader embodiments of the invention are
considered within the breadth of the following claims.
[0030] The present invention is generally directed at evaporative
chillers and cooling systems that include such evaporative chillers
(such as residential and commercial cooling systems). The
evaporative chillers of the present invention are unique for at
least two reasons. First, the chillers are designed to pre-cool the
incoming air flow from the ambient temperature to a lower
temperature prior to its entering the saturator and contacting the
liquid to be chilled (e.g., water in many embodiments but other
liquids may be utilized to practice the invention). This
pre-cooling phase is generally achieved with a heat exchanger in
which the hot gas is the incoming or inlet ambient air (or other
gas in some embodiments) and the cold gas is the outlet or return
air that has passed through and been cooled in the saturator.
Second, the chillers are designed to provide gradient chilling in
the saturator, e.g., the highest temperature water toward the top
of the saturator is cooled by air at a first temperature and the
coolest temperature water toward the bottom of the saturator is
cooled by air at a second temperature, with the second temperature
being significantly lower than the first temperature and water or
liquid flowing between the top and bottom of the saturator or water
column will generally decrease in temperature from the top to the
bottom to provide a desired gradient (or, more accurately, the
higher enthalpy water enters at the top and the lower enthalpy
water exits at the bottom with an enthalpy gradient between).
Generally, the cooling air is also directed transversely and, in
many cases, orthogonally across the path of the flowing water in
the saturator to establish a cross-flow pattern rather than a
counter-current flow as is used in many conventional chillers.
[0031] Before discussing specific implementations of chillers and
cooling systems, it may be useful to provide further general
discussion of these two features of the invention. In most versions
of the invention, saturator cross-flow and gradient chilling are
provided. The water in the saturator moves vertically downward
under the force of gravity while the air stream is moved by one or
more fans or blowers horizontally through the saturator (e.g., in
cross-flow or transverse direction relative to the water stream or
water flow direction). This is unlike many cooling towers in which
the water and air flows are directly opposite or counter-current.
The cross-flow pattern allows chillers of the invention to
establish and maintain a vertical temperature gradient (e.g., to
provide gradient chilling). The water stream or inlet water enters
the top of the saturator at an elevated temperature because, for
example, the water has gained enthalpy after passing through a heat
exchanger in a residential or commercial building or interior space
that is being cooled by use of the chiller (or a system including
the chiller). As the water passes down through the saturator over
packing and/or pads, the enthalpy of the water decreases as heat is
given up as latent heat in the passing airstream through
evaporative cooling (e.g., an enthalpy gradient exists in the water
in the saturator that decreases from the top to the bottom of the
saturator).
[0032] The air passing through the saturator is also cooled by the
evaporative cooling in the saturator, and the air passing through
the saturator near the bottom of the saturator is cooled to a lower
temperature than the air passing through near the top of the
saturator because of the range or gradient of the temperature and
enthalpy of the water in the saturator (e.g., due to the higher
temperature of the water near the inlet to the saturator as
compared to the temperature of the water near the outlet of the
saturator). The air being drawn into or blown into the chiller or
incoming air is pre-cooled indirectly (or without direct contact)
by the outgoing air (e.g., in a heat exchanger and, in some cases,
in the saturator itself). An important part of each heat exchanger
design, as described below, is that the air mixes relatively little
in the vertical direction or dimension. This lack of mixing is
typically maintained for both the incoming air and the outgoing
air, and it is used and maintained so that the warmest (or highest
enthalpy) water and incoming/outgoing airstreams (i.e., after
pre-cooling) are located at the top of the chiller and saturator
while the coolest (or lowest enthalpy) water and incoming/outgoing
airstreams are located at the bottom of the chiller and saturator.
In this description, this variation of temperatures vertically in
the chiller and saturator is labeled "gradient chilling" or
"vertical chilling gradient" or the like.
[0033] Pre-cooling of the incoming air is an important aspect of
the invention, and this is achieved generally with a heat exchanger
that is placed between the inlet of the ambient air and the
saturator (or is provided in part in the saturator in some cases
such as the plate arrangement of FIGS. 10 and 11). Generally, the
heat exchanger is an air-to-air configuration in which the incoming
ambient air transfers some amount of heat to the outgoing air but
at least one embodiment involves using the air exiting the
saturator to cool a different medium (such as a liquid flowing in
piping or tubes or material in a cooling matrix) that is positioned
in the path of the incoming air (e.g., upstream of the saturator
air inlet). The heat exchange in air-to-air embodiments is
typically achieved in a counter-current manner so as to maximize
the efficiency and completeness of the heat transfer. The heat
exchanger configurations may vary as is shown in the supporting
figures and described herein but the designs are all generally
adapted to reduce the wet bulb temperature of the air being fed
into the saturator when compared with the ambient air being blown
or drawn through the chiller. As a result, all or most designs of
chillers described in the following paragraphs may be thought of as
a sub-wet bulb temperature evaporative chiller. In addition to
being able to produce chilled water at a temperature below the
ambient wet bulb temperature, the chiller designs are typically
selected to provide efficient heat exchange, to be relatively
compact, and to be inexpensive to fabricate, install, and
maintain.
[0034] FIG. 1 illustrates one embodiment of a cooling system 100
that may be used to cool or condition an interior space or building
(residential or commercial) 140. The system 100 is shown to include
an evaporative chiller 110 that may be configured as described
above as a sub-wet bulb temperature evaporative chiller. In this
regard, the chiller 110 includes a fan or fans 112 for moving
ambient air 113 into the chiller 110. The fan(s) 112 may be
positioned as shown to blow or force the air 113 through the
components of the chiller or, in some cases, it may be positioned
to draw the air 113 through the chiller 110 (e.g., be positioned at
the outlet of the chiller 110) or be positioned within the chiller
110 (or fans may be positioned in any combination of these
positions).
[0035] The chiller 110 includes a heat exchanger 114 and a
saturator 120 with the heat exchanger 114 being positioned upstream
of the saturator inlet. As a result, the ambient air 113 is cooled
to produce pre-cooled air 115 that is fed to the inlet of the
saturator 120. Generally, this "pre-cooling" is achieved by using
the cool return air 116 exiting the outlet of the saturator 120
after passing over and/or through the pads/packing 124 of the
saturator 120. Thus, the exiting air 116 is typically at a lower
temperature than the ambient air 113 and the heat exchanger 114
makes use of this temperature differential to obtain efficient heat
transfer. The exchanger 114 outputs the pre-cooled air 115 that has
a lower temperature and lower wet bulb temperature than the ambient
air 113 fed into the chiller 110 and outputs air 118 after it has
passed through the heat exchanger 114. The heat exchanger 114 may
take many forms to practice the invention as shown in FIGS. 2A-14B,
with the air-to-air heat exchanger shown being one useful example
that is explained in more detail with reference to FIGS. 7-14B.
[0036] Water to be cooled 126 (e.g., that has a raised enthalpy due
to its use for cooling the building 140) is fed into a water inlet
of the saturator 120. The inlet is generally at the top of the
saturator 120 and the water 126 is allowed to gravity feed or drain
over the pads/packing 124 where it is contacted by pre-cooled air
115 from the heat exchanger 114. The saturator 120 is configured
for gradient chilling as described above with the highest
temperature/enthalpy water 126 being at the top of the saturator
120 along with the highest temperature portion of the pre-cooled
air in 115 and the chilled or cooler water (e.g., lower enthalpy
water) 128 being near the bottom of the saturator 120 or near the
water outlet of the saturator 120 along with the coolest portion of
the pre-cooled air 115. The gradient for the water in the saturator
120 is obtained due to feeding the hot water 126 in at the top of
the saturator 120 and using gravity for flow, but the gradient in
the pre-cooled air 115 fed into the saturator 120 is achieved by
the special configuration of the heat exchanger 114 (and, in some
cases, positioning or arrangement of the saturator 120). The
particular configuration of heat exchangers, such as exchanger 114,
to obtain the chilling gradient with the pre-cooled air 115 is
described in detailed with reference to FIGS. 2A-14B.
[0037] Returning to the system 100 of FIG. 1, the chilled or cooled
water 128 is fed into a sump or to a chilled water storage 130. A
level control 132 may be used to determine when water from a fill
source 134 should be added to maintain a preset volume of water in
the system 100 (or simply in the sump or storage tank 130). One or
more pumps 138 and associated piping, valves, and other plumbing
components are provided to allow the chilled water in the storage
or sump 130 to be used to cool or condition the building or
interior space 140. In some applications, it may be desirable to
further reduce the temperature of the water 128 exiting the chiller
120 such as when the wet bulb temperature of the pre-cooled air 115
is not low enough to provide desired cooling to the building 140.
In these cases, an optional supplemental cooler 142 may be provided
to further cool the water 128 prior to its use for cooling the
building 140. Alternatively, a cooling coil or other technique may
be used to reduce the temperature of the water in the storage or
sump 130 to lower the temperature of the chilled water supply
143.
[0038] The chilled water supply 143 is then used to cool the space
140 such as by passing the chilled water supply 143 through the
liquid or tube side of air-to-water heat exchanger 144 as shown.
The hot recirculation water 139 is then returned via piping to the
chiller 110 as shown at 126. A fan 150 is used to provide air 146
that flows through the exchanger 144 and is cooled by the chilled
water 143. The cooled air 147 is recirculated via a ventilation
system 148 to the interior space 140. In some cases, the heat
exchanger 144 may not provide adequate cooling capacity for the
space 140, and a conventional or other cooler such as a
compressor-based A/C unit 160 may be used to supplement the heat
exchanger 144. Conventional thermostat(s) and/or controller(s) 170
typically are provided as part of the cooling system 100 to control
operation of the exchanger 144 (such as by controlling the
ventilation system and fan 150 and/or by controlling the volume of
chilled water supply 143 and operation of the optional supplemental
cooler 142). Although not shown, control equipment often is
provided with the chiller 110 to control its operation such as by
selectively operating the fan (e.g., on/off, direction, speed, and
the like), operating refill pumps associated with source 134 and
level control 132, controlling flow of water 126 into the saturator
120, or operating louvers or other devices limiting flow through
fan 112 to set volume and/or rate of air in and out 113, 118.
[0039] Alternative configurations of pumps and piping may be
advantageous. For example, it may be desirable to separate the
water loop used in the chiller 110 from the water used in the
cooling system of the interior space 140, so as to reduce oxygen
and contaminant levels in the interior water and thereby slow the
rate of corrosion in the air-to-water heat exchanger 144. This can
be achieved by pumping chilled water with pump 138 into one side of
a counter-current water-to-water heat exchanger and into pipe 126
to the top of the saturator 120. A second pump is placed to pump
water from the air-to-water heat exchanger 144 into the second side
of the water-to-water heat exchanger and back to the optional
supplemental cooler 142, thus creating two separate water flow
loops. A second alternative configuration would place the optional
supplemental cooler 142 within the chiller 110 rather than in the
interior space 140. A third alternative configuration would
separate the water flow through the saturator 120 from the water
flow through the interior space 140. This would be particularly
useful, for example, when a large volume of chilled water storage
130 is employed. One pump moves water from the top of the storage
vessel 130 to the top of the saturator pad/packing 124, the chilled
water then being allowed to drain 128 or be pumped through a pipe
leading to the bottom of the storage vessel 130. Chilled water for
cooling the interior space 140 is pumped from the bottom of the
storage vessel 130, and hot water returning from the air-to-water
heat exchanger 144 is piped to the top of the storage vessel 130.
Thus, a thermal gradient will form in the storage vessel 130 such
that the warmer water is at the top. Separating the saturator loop
from the interior space cooling loop allows the chiller 110 to
operate and accumulate chilled water independent of the demand for
cooling in the interior space 140. This would facilitate chilling
of stored water at night to utilize off-peak power, utilize cooler
nighttime wet-bulb temperatures, and allow downsizing of the
chiller 110. Many other configurations of the system components are
possible and would be apparent to those skilled in the art.
[0040] In one preferred embodiment, pre-cooling of incoming air is
achieved through the use of a thermal storage medium to indirectly
cool the ambient incoming air using the air exiting the saturator.
For example, the heat exchanger 114 of FIG. 1 may be formed to
include a thermal storage medium that is cooled by the exiting air
and then the incoming air is passed over/through the storage medium
(e.g., the exiting air is used to cool the thermal storage medium
which is, in turn, used to cool the incoming air rather than
utilizing a more direct heat exchange as found in air-to-air
exchangers). FIG. 2A illustrates one embodiment of an evaporative
chiller 200 utilizing thermal storage media to pre-cool inlet air
before it is fed to a saturator. The chiller 200 is also adapted to
maintain a chilling gradient to enhance heat transfer
efficiency.
[0041] The chiller 200 is typically placed in a frame or outer
structure 204 that may, for example, include a floor, side walls,
and a rooftop that are formed from metal (e.g., sheet metal),
plastic, or wood and includes louvers or other openings to allow
air to flow into the sides or sidewalls. Additionally, insulation
may be provided in some or all the sides or walls of the structure
204 to reduce the amount of heat that enters the chiller 200. The
structure 204 is shown to define a sump 208 in which chilled water
210 is stored (e.g., a storage tank or basin for receiving chilled
water 219 that has flowed through the saturator 214). In other
embodiments, the chilled water 219 may be directed via the sump 208
and/or piping to a storage tank for storing larger volumes of
chilled water 219 for use in a cooling system.
[0042] The chiller 200 includes a saturator 214 defined by a side
wall 213 and packing or pads 216. For example, the side wall 213
may be a porous sheet of metal, plastic, or the like or a wire or
mesh sheet in which packing or one or more saturator pads 216 are
positioned or supported. During operation, hot or higher enthalpy
water 218 enters the top 215 of the saturator 214 and flows down
over the pad/packing 216 to the bottom 217 of the saturator where
the chilled or lower enthalpy water 219 exits the saturator and is
discharged into the sump 208. The saturator walls 213 and pads 216
may define a rectangular volume as shown or may have differing
shapes and/or cross sections (e.g., side facing incoming air 234).
The chiller 200 further includes one or more fans 230 that are
selected to be reversible so as to draw ambient air 234 into the
chiller 200 from the right side of the chiller 200 as shown and
discharge hot air 238 out the left side of the chiller 200 as shown
in FIG. 2A in a first operating mode. In a second operating mode
shown in FIG. 2B, the fans draw ambient air 244 into the chiller
from the left side of the chiller 200 to flow through the saturator
walls 213 and pads 216 to be discharged as hotter air 248 from the
right side of the chiller 200. The chiller 200 includes two or more
thermal storage matrices 224, 220 defined by side walls (e.g.,
screen, mesh, or other retaining structure that also allows air to
flow through the matrix) and a storage medium 222, 226 that is
positioned within the side walls. As shown, a single matrix 220 is
provided on one side of the saturator and a single matrix 224 is
provided on the second or other side of the saturator such that air
flowing horizontally or cross-current through the saturator is
forced to flow through a matrix 220, 224 on the inlet and on the
outlet sides of the saturator. Of course, the number of matrices
and their sizes, shapes, and materials may be varied to practice
the invention with one example being shown for simplicity of
explanation and as one useful but only exemplary embodiment of the
invention.
[0043] As can be seen in FIGS. 2A and 2B, the chiller 200 in
general includes four components: (a) a bank 224 of thermal storage
material or media 226 that is chosen to be or is arranged to be
permeable to air flow; (b) a set (one or more) of reversible and,
typically, low power fans 230; (c) a saturator 214 in which water
218, 219 flows from top 215 to bottom 217 through a medium 216 such
as a conventional saturator pad or fibrous packing; and (d) a
second bank 220 of thermal storage material or media 222. The banks
220, 224 may have the same or differing configurations, e.g., cross
sectional shape, thickness, wall material, and the like, and the
media 222, 226 may be similar or identical, but in other
embodiments, the two thermal storage banks or matrices may differ
such as by using different thermal storage material or the
like.
[0044] With reference to FIGS. 2A and 2B, the principle of
operation of the chiller 200 is a temporal separation of thermal
capture and removal from each thermal storage bank 220, 224
mediated by periodic reversal of the fans 230. For example, during
operation of the chiller 200, the fans 230 may first operate as
shown in FIG. 2B to force ambient air 244 from the left side of the
structure 204 through the left (or first) storage bank 224 and its
storage material 226. The air would then flow through the saturator
pad(s) 216 where the air gains humidity and is cooled, and this
cooled and exiting air 248 is forced through the storage material
222 of the right or second storage bank 220 prior to exiting the
chiller structure 204. The air 248 exiting the saturator 214 is
cooled resulting from passing through the saturator pad 216 and
water 218, 219, and at least a portion of the "coolness" of this
air 248 decreases the temperature of the storage material 222 of
the right side matrix or bank 220, i.e., a heat transfer occurs due
to a temperature difference between the material 222 and the air
248. The chiller 200 may be operated for a period of time in the
direction shown in FIG. 2B so as to lower the temperature of the
material 222 in the matrix or bank 220.
[0045] Then, after a period of time (e.g., a few minutes or more
depending upon the thermal capacity of the storage matrix 220, the
heat transfer rate, and other factors), the fans 230 are reversed
to the mode shown in FIG. 2A. As shown, the ambient air 234 is
drawn in on the right-hand side of the structure 204. The incoming
ambient air 234 is first cooled or pre-cooled as it passes through
the storage matrix 220 and contacts the thermal storage media or
material 222. Generally, this heat exchange occurs without adding
moisture to the ambient air 234. This reduction in the ambient air
234 temperature results in air leaving the bank 220 and entering
the saturator 214 that is at a lower temperature (e.g., at a
temperature below ambient temperature). Thus, the wet bulb
temperature of the air entering the saturator 214 and pad/packing
216 is lower than the ambient wet bulb temperature. During heat
transfer in the saturator 214, moisture is added to the air, and
its temperature drops even further to a temperature that may
ideally be below the wet bulb temperature of the ambient air 234.
The temperature of the water 218, 219 stream flowing in/over the
saturator pad/packing 216 drops from the top 215 to the bottom 217
and typically to a point below the ambient wet bulb temperature.
The water in the sump 210 is then distributed to air-to-water or
other heat exchangers in a cooling system to cool a residence or
other space as discussed with reference to FIG. 1. The cooled air
is then passed through the left-hand bank 224 and its thermal
storage media or material 226, cooling the temperature of this
material 226 prior to exiting at 238 through the outlet of the
structure 204. The material 226 is placed at a temperature below
ambient air temperatures such that when the fans 230 are again
reversed the material 226 is useful for pre-cooling the incoming
ambient air 244 shown in FIG. 2B.
[0046] The cycling of the fans 230 may be performed on some pre-set
periodic basis (e.g., a number of minutes selected from the range
of 2 to 30 or more minutes) or may be controlled based on
temperature sensors placed in the air stream (e.g., outlet of a
matrix 220, 224) and/or in or on the storage material 222, 226
(e.g., to determine when a previously determined temperature below
ambient is achieved or other control parameter is determined).
Electronic controls provided for the chiller 200 typically would
include those useful for periodically alternating the direction of
fans 230, which may be achieved via reversible motors or a
mechanism for physically rotating the fans 230 to alter their
direction. For example, the motors of the fans 230 may be
electronically commutated motors that typically have good
efficiencies. The ability to control the speed of the fans 230 (and
other fans of other chiller embodiments) may be provided for in the
electronic controls to maximize or at least improve the efficient
operation of the chiller 200 such as adjusting speed based on
cooling load/demand. The power of the fans 230 generally is
selected based on the size of the chiller 200, the pressure drop
through the storage banks 220, 224 and saturator, and the desired
air flow. It is anticipated that relatively low power or low
wattage fans will be adequate for many chiller 200
configurations.
[0047] The gradient cooling of the incoming airstreams 234, 244 to
pre-cool the air input to the saturator in the chiller 200 is
similar to counter-current air-to-air heat exchangers of the
invention. This gradient cooling of the incoming streams 234, 244
in the matrices 220, 224 results in enhanced heat transfer in the
saturator, which contains water that decreases in temperature
(and/or enthalpy) from the water 218 near the top or water inlet
215 of the saturator column to the water 219 near the bottom or
water outlet 217 of the saturator column. This combination provided
gradient chilling in the chiller 200.
[0048] With reference to FIGS. 3A and 3B, the gradient is the
result of the psychometrics changing from the top to the bottom of
the chiller 200. FIG. 3A provides a graph 300 of a hypothetical
example of the psychometrics of the air flowing at or near the top
of the chiller 200. FIG. 3B provides a graph 310 of a hypothetical
example of the psychometrics of the air flowing at the bottom of
the chiller 200. In the graphs 300 and 310, ambient air enters the
chiller at point A such as at 100.degree. F. and 15 percent
humidity in the illustrated example (with it being understood that
the particular operating conditions will vary widely while the
overarching concepts are applicable in many inlet or ambient air
conditions). The air is cooled indirectly or without moisture
addition from point A to point B as it passes through the thermal
storage matrix between the chiller air inlet and the saturator
inlet (or in an air-to-air heat exchanger or other heat exchanger
configuration in other embodiments of the invention). The air is
then passed through the saturator as shown from point B to point C
in FIGS. 3A and 3B where it gains moisture and its relative
humidity increases to 85 percent. The air also gains enthalpy in
the saturator from the water stream as is shown by the upward slope
of the line between points B and C. The air is used to pre-cool
incoming air or a second thermal storage matrix (or liquid in a
heat exchanger as shown in FIGS. 5 and 6) as it is passed out of
the chiller, and the psychometric effects are shown from point C to
point D where the air gains heat or enthalpy from the incoming
airstream, which is being pre-cooled to a lower temperature. In
operation of a chiller, water at the top of the saturator has
higher enthalpy than at the bottom, and this can be seen as the
line from point B to point C having a steeper slope in graph 300
compared with the line from point B to point C in graph 310.
[0049] At equilibrium, a gradient is established such that the
airstreams (and, therefore, the water in the saturator) reach lower
temperatures at the bottom of the chiller than at the top of the
chiller (e.g., 59.degree. F. versus 64.degree. F., respectively, as
shown in the example of FIGS. 3A and 3B). The overall outcome of
providing gradient chilling in the chillers of the invention is
that lower temperatures for the output chilled water are achieved
by the chillers in a single pass of the water through the saturator
than in chillers that do not include such gradient chilling. As
will be appreciated, lower temperatures of the pre-cooled air at
the saturator inlet and the resulting lower temperatures of the
output chilled water expand the number of days and the geographical
range for which chillers such as those described herein may be used
to satisfy all or much of the cooling load for a particular
application, building, or interior space. In the use of storage
matrices as shown in FIGS. 2A and 2B, as the airstream is cooled,
it will experience the coldest media on the side of the bank or
matrix proximate to the saturator, thereby affecting a
counter-current-like heat exchange. The gradient chilling is
achieved because as the warmer water enters the top of the
saturator, a vertical temperature gradient is set up in the
saturator and in the thermal storage banks or matrices such that
the coldest temperatures of both will be at or near the bottom of
the chiller (e.g., as viewed with a vertical cross section of such
components).
[0050] The saturators used in the chillers of the present invention
may be of the types found in conventional evaporative coolers or
use similar pads, packing, or other materials over and through
which air and water flow (e.g., in a cross or transverse pattern as
discussed above). For example, the saturator may use aspen fibers
or other similar materials and/or use a rigid medium. Generally,
any material giving ample surface area, good wetability properties,
and relatively easy passage of air may be suitable for use in the
saturator. During operation, water from an insulated sump or from a
return line from a building or interior space heat exchanger is
pumped to the top of the media and dispersed to thoroughly wet the
saturator media. Water flows down through the saturator typically
unaided under the effect of gravity. The functional goal is to
saturate the airstreams flowing through this media in the saturator
with water as completely as practical (e.g., up to about 85 percent
relative humidity or more in some cases) as the air passes through
the saturator. The saturator media, pads, or packing are selected
and arranged to reduce the rate of downward flow of the water being
chilled and also to disperse the flow such as into small channels
or droplets so as to increase the time the water spends exposed to
cooling air and the surface area of the water available for
evaporation. In theory, the water in the saturator may simply be
dripped downward from a top to a bottom of a saturator without or
with little media, pads, or packing being utilized. It is generally
preferred that a relatively small amount of non-evaporated water be
carried from the saturator (e.g., into the thermal storage
matrices) by the airstream or by capillary action. Hence, in some
embodiments, a space or gap and/or a screen/filter are provided
between the saturator and a heat exchanger such as a thermal
storage matrix. In any case, it is typically useful to include a
water level control device in the chiller or the associated cooling
system, such as a float-based refill mechanism, float valve, or the
like, to replenish water periodically to account for evaporation
and other losses of water from the chiller and/or cooling
system.
[0051] Again, suitable material for use in the saturator may be the
same as is used in conventional evaporative coolers and may
include, but is not limited to, wood or paper fibers, wood,
plastic, ceramic or metal media such as a honeycomb arrangement,
particles, or the like, plastic mesh, glass fibers, metal fibers,
or any other useful material. In the thermal storage matrix
embodiments, the saturator may include media similar or the same as
used in the storage matrices. The storage material or media
preferably is chosen to provide sufficient thermal storing capacity
and to have rapid thermal conduction or heat transfer from its
surfaces that contact the air to its internal or subsurface mass
but yet provide relatively non-restrictive flow paths for (e.g., to
be permeable to) the air flowing through the matrix or bank so as
to not create an unacceptable pressure drop or to require high
power or large fans. In some preferred embodiments, high efficiency
heat transfer is achieved with relatively thin matrices (i.e., the
air flow path across the matrix is short because the matrix is less
than about 3 feet thick and more typically less than about 1 foot
thick). In the preferred embodiments, the pressure drop is not
significant (e.g., less than about 0.4 inches WC for each bank and
more typically less than about 0.2 inches WC) so as to not add
unacceptable fan energy and capital costs (e.g., require larger,
more expensive fans).
[0052] As discussed, a wide variety of materials may be used for
the media or material in the thermal storage matrices. Examples
include stone (e.g., gravel, rocks, pebbles, or some combination
thereof), glass, metals including aluminum, steel, and the like,
plastics, wood, and concrete. The material may be provided in a
number of forms, such as particles that when placed in a column or
array provide air gaps, but in some cases the material may be
provided as one or more larger pieces with air paths provided such
as honeycomb or porous blocks or chunks (e.g., a cast block with
perforations). When particles are used, the geometry of these
storage media particles may also widely vary and may include any
one or more than one of the following: spherical shapes; irregular
shapes (e.g., aggregate, rocks, or the like); toroidal shapes;
strip shapes (e.g., shredded material such as shreds of plastic or
metal); fibers or fibrous shapes; and complex shapes. Materials and
configurations that create convoluted air flow paths may in some
cases be desirable to increase thermal transfer efficiency. The
material may be chosen to control fabrication costs, for its ready
availability, and because it exhibits a good ratio of heat capacity
to mass. To further increase heat capacity, an alternative would be
to use encapsulated phase change material (e.g., material that
changes between liquid and solid phases at a temperature within the
range normally experienced by the material in storage matrices).
The thermal storage banks may be uniform in the distribution and/or
density of the storage media and in their cross section or they may
be varied across one or more cross sections. For example, it may be
useful to have the bank be thicker in certain portions to obtain a
desired heat transfer or it may be useful to vary particle sizes in
some areas or otherwise provide smaller air passages in some
portions (such as directly in front of the fans) to balance air
flow (e.g., with larger passages or less dense material packing
provided more distal to the fans or their centerline or central
axis). Rather than rectangular, the storage banks may be "V", "W",
"S", or otherwise configured in cross section so as to allow a
greater area for air flow. Spacing of loose objects or particles
such as pebbles or metal/plastic/glass spheres or the like may be
controlled by selecting differing object sizes and/or interleaving
plastic or wire mesh in the matrix or bank.
[0053] An implementation or embodiment of the chiller 200 was
constructed and tested. A cabinet was constructed of wood and 0.5
inch foil-faced foam insulation to create an interior chamber (with
open ends) measuring 17.5 inches high by 15.5 inches deep and an
overall length of about 5 feet. Storage banks were constructed at
either end using metal supports and wire mesh (hardware cloth) to
contain the heat storage media, which consisted of highly
irregularly shaped gravel (stones) with average diameters of about
0.5 inch. Spacing between the stones was increased by layering the
gravel on sheets of wire mesh such that the overall density of the
storage banks was approximately 52 pounds of stone per cubic foot.
A 14 inch reversible fan in a shroud was placed to the right of the
left-hand storage bank. A saturator was placed between the fan and
the right-hand storage bank with dimensions 17.5 inches high by
15.5 inches deep by 3.5 inches wide and composed of layers of
commercial plastic swamp cooler pads. Water was pumped from a sump
beneath the saturator and delivered across the top of the saturator
using tubing with perforations at a delivery rate of about 2.5
gallons per minute. The fan moved air through the device at an
average rate of about 160 cubic feet per minute. Dimensions and
rates of water and air flow were not optimized. The graph 400 of
FIG. 4 illustrates results of a sample run for this particular
embodiment of the chiller 200. Line 410 illustrates the sump water
temperature over the course of the experiment. Line 412 illustrates
the dry bulb temperature of the ambient air available at the air
inlet of the chiller 200. The wet bulb temperature of the ambient
air is shown at 414 along with error bars. Also, line 418 is
included to show the dewpoint of the ambient air. At the start of
the test run, the sump was filled with 6 gallons of warm water (at
approximately 85.degree. F.), the recirculating pump was started,
and the fan was run in one direction for the time period shown as
period A. The temperature of the sump water 410, which was being
recirculated through the saturator without having its enthalpy
increased in a building heat exchanger as would be more typical,
reached a steady state at approximately 55.degree. F. This
temperature of the sump water was approximately the wet bulb
temperature of the ambient air as shown as an overlap of 414 and
line 410 in period A, and represents what can be achieved at
equilibrium without pre-cooling the inlet air to the saturator.
During period B, the fan direction was cycled periodically (e.g., a
10-minute cycling period in this case) to run in opposite or
alternating directions. For example, at the beginning of period B,
the fan was run in a direction opposite that used in initialization
period A, and after 10 minutes, the fan direction was reversed,
with this process then being repeated. As shown with line 410, the
temperature of the sump water dropped approximately 5.degree. F. or
to below the temperature achieved using only ambient air (i.e., the
outlet water of the saturator was dropped below the wet bulb
temperature of the ambient air by about 5.degree. F.). In time
period C, the fan was again fixed in one direction, and, as a
result, the sump water temperature 410 returned to about the wet
bulb temperature of the ambient air. The test run illustrated with
graph 400 clearly demonstrates the effectiveness of chillers with
the design of chiller 200 of FIG. 2 for achieving sub-wet bulb
temperature chilling using thermal storage matrices in the air
inlet and outlet of a saturator, with cross-flow of the air through
the saturator.
[0054] There are numerous other techniques for pre-cooling the
incoming air using the exiting air. FIG. 5 illustrates another
chiller 500 of the present invention that provides an air-fluid-air
heat exchanger configuration to achieve pre-cooling. As shown, the
chiller 500 includes a frame or structure 504 with a sump 508 with
an upper plate 509 for storing chilled water 510 for use in a
cooling system (such as a building or interior space heat exchanger
as shown in FIG. 1). The frame or structure 504 is adapted with air
inlets on a first side for allowing ambient air 515 to be drawn
into the chiller interior by operation of one or more fans or
blowers 514. The air passes through side walls 540 of a saturator
and the saturator medium 542 (e.g., one or more pads or the like)
to chill the water 518 flowing downward through the medium 542, and
then the air 516 exits the second or opposite side of the chiller
structure 504.
[0055] To pre-cool the incoming air 515, the chiller 500 includes
an air-to-fluid heat exchanger that is positioned upstream of the
saturator inlet. The upstream exchanger includes, in this
embodiment, a pair of finned-tube heat exchangers 520 and 530 with
an example shown in FIG. 6 to include a serpentine tube 624 for
containing a liquid such as water or the like and fins 628 attached
to the tubes 624 to enhance heat transfer rates between the air 515
and the tubes 624 and the liquid contained therein. The upstream
exchangers 520, 530 contain water or other liquid at a temperature
below the ambient air temperature, and as a result, the air
entering the saturator wall 540 (e.g., its air inlet) is below the
ambient air temperature. At the air outlet of the saturator, air
exiting the saturator 516, which is cooler due to evaporation in
the saturator medium 542, is used to lower the temperature of the
liquid in upstream heat exchangers 520, 530. This is achieved by
routing the liquid 528, 538 used for pre-cooling in exchangers 520,
530 as shown at 522, 532 to the downstream or outlet exchangers
524, 534 via piping 521, 531 (which may also include pumps), and
cooled water 528, 538 is then returned to the inlet exchangers 520,
530 via piping 526, 536. The outlet exchangers 524, 534 may be
configured as finned-tube heat exchangers as shown for exchanger
520 in FIG. 6 to provide increased heat transfer area for
liquid-to-air heat transfer between the liquid in the exchangers
524, 534 and the exiting air 516. Two exchangers are shown at both
the air inlet and the air outlet of the saturator, but one or more
exchangers may be used at one or both of these positions.
[0056] In this manner, the heat exchange between the incoming and
outgoing airstreams 515, 516 is affected by using a combination of
air-to-fluid and fluid-to-air heat exchangers. As shown in the
chiller shown in FIG. 5, heat in the liquid 522, 532 can be pumped
from one side of the saturator to the other using, for example,
finned heat exchange units 520, 524, 530, 534. Such units, which
are well know in the HVAC arts, can be fabricated from metal fins
(e.g., aluminum or the like) attached to metallic tubes (such as
copper or other metal tubes). Additionally, the pre-cooling may be
achieved with many other air-to-fluid heat exchanger designs, which
are considered within the breadth of this description, for
achieving high surface area and heat conduction with the air and/or
fluid/liquid streams. The liquid or heat transfer fluid may be
water, a glycol solution, or any other suitable heat transfer
fluid. As shown, the fluid is pumped downward in the air outlet
exchangers 524, 534. The fluid is chilled in these heat exchangers
524, 534 by contact with the exiting airstream 516 from the
saturator. The fluid is then piped to heat exchangers 520, 530
upstream of the air inlet to the saturator. The cold fluid 528, 538
enters at these exchangers 520, 530 at their bottom (or lower
vertical portion) and is warmed as it is pumped upward toward the
top or higher vertical portion of the exchangers 520, 530 due to
heat transfer from the incoming air 515 to the fluid. Thus, the air
entering the saturator is pre-cooled, and the air entering at the
bottom of the saturator will be cooler than air entering at the top
of the saturator because it contacts the cooler fluid in the
exchangers 520, 530. This not only provides the desired pre-cooling
of the incoming air 515 to a temperature below the ambient air
temperature but also maintains the desired gradient chilling in the
chiller 500. The chiller 500 optionally includes multiple inlet and
outlet heat exchangers, and as discussed with reference to chiller
200, the saturator pad or filler 542 is selected to be a material,
a configuration, and size to provide adequate surface area to
achieve a desired level of chilling/evaporation of the chilled
water 510. The chiller 500 is designed to provide compact unit
dimensions and relatively low pressure drops for the fans 514.
Saturation of the airstream 515 in the saturator may be enhanced by
introducing makeup water using misters placed upstream of the air
inlet of the saturator.
[0057] Rather than air-to-fluid or air-to-storage matrices, the
pre-cooling may be achieved with an air-to-air heat exchanger
positioned in the chiller cabinet generally upstream of the
saturator. For example, the chiller 700 of FIG. 7 utilizes a
plurality of tubes to define channels or pathways for incoming air
718 and outgoing air 750 from the chiller to cause the two air
streams to flow in a counter-current manner and to achieve
cross-current flow of the air and water in the saturator 730. As
shown, the chiller 700 includes a frame or cabinet 710 that defines
an interior space in which a plurality of tubes 720 (e.g., metal,
thin plastic or other materials having high heat transfer
coefficients) are arranged in a spaced apart manner and with their
elongate axis transverse or orthogonal to the vertical axis or
plane of the chiller 700. Incoming air 718 is drawn into the
chiller cabinet 710 by one or more fans 714 and flows in channels
or passageways 724, 728 defined by the outer surfaces of the tubes.
The incoming air is cooled in layers or gradients from the top to
the bottom by outgoing air 741, 743, 747 in the tubes with this air
being warmer in the top tubes (such as stream 747) and cooler as it
approaches the bottom of the chiller (such as streams 743 and even
cooler in stream 741). The pre-cooled air 724, 728 passes through
saturator medium 734 (such as one or more pads or the like) and
returns at 740, 742, 746 by entering the tubes 720. Water to be
chilled 761 (e.g., water with increased enthalpy from a building
heat exchanger or other cooling system device) enters the top of
the saturator 730 and is cooled by evaporation via contact with the
pre-cooled air 724, 728, and the chilled water 762 drains by
gravity to the sump 760.
[0058] As shown, the tubes 720 are a set of parallel and relatively
closely spaced tubes that allow the incoming ambient air 718 to
pass between them as shown at 724, 728. The air 724, 728 gives up
heat to the outgoing or exiting air 747, 743, 741 that is flowing
within the tubes 720 before the air exits at 750. The saturator 730
in some embodiments is made up of material 734 interposed between
the tubes 720 and/or that is provided at the end of tubes 720 where
return or recirculated air 740, 742, 746 is shown in FIG. 7 as
reversing its direction. Suitable material for pads, packing,
filler, or the like 734 includes high wettable paper, wood fiber,
plastic, or any other material that creates or provides a large
surface for water flow 761 to sump 760. The tubes 720 typically are
thin-wall tubes formed from plastic and more typically metal or
other thermally conductive material.
[0059] In other preferred embodiments, the pre-cooling is achieved
with air-to-air heat exchangers such as plate heat exchangers or
the like. FIGS. 8 and 9 illustrate side and top views,
respectively, of a chiller 800 that includes a counter-current
air-to-air heat exchanger 830 upstream of a saturator. Again, a
cabinet or frame 810 is provided with an air inlet and air exit and
a water inlet/return. As shown, the incoming air 904 enters the
heat exchanger 830 at the top of the cabinet 810 and passes through
the passageway adjacent the heat exchanger plates, and the outgoing
air 918 exits the heat exchanger 830 at the front left of the
cabinet 810. The heat exchanger 830 is shown to be made up of a
plurality of horizontally extending plates 834 (e.g., thin metallic
plates or other plates with relatively high heat transfer
coefficients or rates). The plates 834 may be planar as shown or be
textured or have a "W", "S", or other cross section to obtain
additional heat transfer between incoming air 904 and outgoing air
918 from the saturator. The incoming air 904 and outgoing air 918
is caused to flow in the space or channel between alternating pairs
of the plates 834 so as to allow the incoming air 904 to give up
heat to the cooler outgoing air 918 as is shown at 910 to represent
incoming air below the top plate 834 and at 914 showing outgoing
air flowing above the top plate 834. The air 910 becomes pre-cooled
air or air at a temperature below the temperature of the incoming
ambient air 904 and passes through the saturator media 824 as shown
at 912 where it (i.e., the recirculating air) loses further heat
during the evaporation process and is returned as air 914 where it
is used to cool the incoming air 910. Spacers 920 and 924 are used
between the plates 834 to control the flow of the incoming and
outgoing air or to define the flow paths for the incoming air 904
and the recirculated air 912 such that the airstreams 910, 914
remain in adjacent and alternating airflow passages between the
plates 834. Generally, the heat exchanger 830 is constructed of
alternating layers of conductive "plates" 834 and spacers 920, 924.
The shape of the plates 834 at the ends used to define the inlet
and outlet passageways for the air 904, 918 may be triangular as
shown, circular (e.g., a semi-circle or the like), or any other
useful configuration for defining the air passageways (or may even
include piping or the like to define an inlet and outlet manifold
or similar arrangement).
[0060] The chiller 800 further includes the saturator that is
defined by porous sidewalls 820 and the inner side of the frame or
cabinet 810 and by the pads or saturator medium 824. Return or
higher temperature water is input at the top of the saturator
(e.g., through a water inlet or return pipe outlet at the top of
the cabinet 810). The higher enthalpy water 825 flows by gravity
through the pad or medium 824 where it contacts the pre-cooled air
912 and becomes chilled as it flows downward in the chiller from
825 to point 826 to the bottom of the saturator at 828. The medium
824 may be a single large saturator pad provided at the right end
of the chiller cabinet 810 as shown or multiple pads or media may
be used. Alternatively, a thinner pad or pads could be applied
flush against the right end of the heat exchanger stack 830,
leaving an open space for air reversal 912 at the right end of the
cabinet 810. The chilled water 816 is stored in the sump 814 (or a
storage tank in some cases), and the sump 814 is typically
connected to a cooling system such as a residential or commercial
building heat exchanger (air-to-water or the like), which results
in the water increasing in enthalpy and/or temperature at which
point it is returned to the top of the saturator for chilling. The
use of horizontal plates 834 and the cross-flow of the air 912
relative to the water 825, 826, 828 results in the chilling
gradient being maintained (as discussed in detail for other chiller
embodiments). Of course, although not shown, a fan or other
mechanism for forcing the air to flow through the heat exchanger
and saturator would be provided in the chiller 800 such as at the
air inlet or outlet or adjacent to the heat exchanger 830.
[0061] FIGS. 10-13 illustrate another embodiment of a chiller 1000
that uses an air-to-air heat exchanger to pre-cool incoming air
1015 with outgoing air 1037, 1039, 1041. The chiller 1000 includes
a cabinet or frame 1010 with a solid sidewall 1012 and a sidewall
1050 with openings to allow the outgoing air 1037, 1039, 1041 to
exit from its flow or return channels in the heat exchanger. One or
more fans 1014 are provided at the air inlet of the cabinet 1010 to
draw ambient air 1015 at the ambient air temperature and humidity.
As shown in FIG. 11, the heat exchanger is achieved with
side-by-side vertical plates (e.g., heat conductive metal plates)
1120 with spacers 1018 that are configured to define flow paths for
the incoming air 1015 and control flow of the exiting air 1037,
1039, 1041 in layers or non-mixing gradients (with three layers
being shown but two layers or more than three layers may be used).
The spacers 1018 provide openings 1022, 1026, 1029 through which
portions 1020, 1024, 1028 of the incoming air 1015 flow in the
channels or passageways 1110 between the plates 1120.
[0062] This pre-cooled air in channels 1110 reverses direction
1036, 1038, 1040 and flows through saturator pads or media 1030
that is positioned between the plates 1120 at one end of the
outgoing air passages or passageways/channels 1030 (with an opening
or space typically provided between the end of the incoming air
passage 1110 and the wall 1012). The frame 1010 further includes
front and back sidewalls 1102, 1104. Incoming water 1034 enters the
chiller at the top of the saturator pads 1030 and is cooled by
evaporation of water in the pre-cooled air 1036, 1038, 1040 before
it is returned to the sump 1060 as chilled water 1062 (e.g., water
at or near the wet bulb temperature of the pre-cooled air 1036,
1038, 1040 (such as at or near the wet bulb temperature of the air
1036 due to gradient chilling in the saturator)). FIGS. 12 and 13
illustrate a representative spacer assembly 1200 for defining
incoming air passages and a representative spacer assembly 1300 for
defining outgoing passages. A water distribution pipe 1310 is
include in the outgoing spacer assembly 1300 as are perforations
1314 for water flow at one end (e.g., the saturator end) for water
flowing in the saturator pad(s).
[0063] In the chiller 1000 the incoming airstream is pre-cooled by
passing counter-current to the outgoing airstream in a flat or
other cross section plate-based air-to-air heat exchanger
positioned upstream of the saturator. As shown in FIGS. 10 and 11,
vertical and parallel sheets of thin, conductive material are used
to separate the incoming and outgoing airstreams but place them in
adjacent heat transfer passages or channels. Several layers of
alternating incoming and outgoing passages are employed in most
preferred embodiments. These heat transfer sheets or heat exchange
plates are separated using spacers such as those shown in FIGS.
11-13 in alternating layers of spacers. A fan is placed at the top
of the unit to force ambient air down between the plates as shown.
This air then passes to the right (in this example) until it
reaches an open chamber at the right end of the device or cabinet
in which the air can reverse direction to flow and enter the
outgoing passages. In the outgoing passages, material or saturator
media is placed that is wetted during operation of the chiller 1000
by a vertically flowing stream of water (e.g., this portion of the
chiller is considered the saturator). This may take the form of
water passing down the walls of the heat exchanger passages but
more typically includes some wettable material that is interposed
between the walls or in the outgoing or return air passages.
[0064] For example, a zigzag shaped, thin, wettable "pad" could be
used as shown in FIG. 11. The saturator material preferably does
not occupy a significant amount of the passage space to control
pressure drop of the pre-cooled air but is adequate to allow
sufficient saturation of the passing air with water. The heated
water from the building interior is typically pumped to the top of
the saturator pads by a pump (not shown) and flows downward over
the pads by the force of gravity. Below the saturator, an insulated
sump is provided for receiving and storing the draining chilled
water. The airstream then exits at the left-hand side of the device
as shown in this example. The number of heat exchange plates and
the dimensions of the passages may be varied to practice the
invention, and may be determined to obtain a desired efficiency of
heat transfer, to suit fan power limits, and to control or based on
fabrication costs. Air and water flows are typically determined by
the amount of cooling (e.g., desired tonnage) required and
anticipated temperature differentials where the chiller is
installed for use. The surface area of the saturator pads
preferably is sufficient to accommodate the required total water
flow while maintaining thin film flow over the surfaces. The
saturator pads can occupy the full length of the outgoing air
passages in some embodiments or, as shown, only a portion on one
side/end of the passage. Water can be distributed evenly along the
tops of the saturator pads or unevenly (e.g., a higher flow rate
may be desirable on the end of the saturator pads nearer the inlet
to the pre-cooled air into the saturator region of the chiller). A
mechanism may also be provided to maintain the water level in the
sump, such as a float valve that allows water to be added or to
flow into the sump when the level drops below a preset level.
Additionally, an anti-scale filter on the incoming fresh water or
fill water may be useful in some implementations. For added
saturation of the airstream, the water entering the saturator may
be introduced using misters or fill water entering the sump may be
added by spraying with misters or the like in the opening or gap at
the edge of the cabinet between the pads and the cabinet end or
side wall.
[0065] Fabrication of the chiller 1000 involves engineering
different spacer sets such as those shown in FIGS. 12 and 13 for
the incoming and outgoing air channels/passageways. The heat
exchanger stack is composed of alternating layers of spacers and
plates. The heat exchanger plates or material is typically thin and
formed of thermally conductive materials such as metal but plastic
and other materials may be used. The sheets may be relatively rigid
or can be formed from thin relatively flexible material that is
pulled or tensioned to be taught or planar. The spacers can be
formed from metal, plastic, foam, rubber, wood, or other materials.
To ease fabrication and provide support, the "open" regions of
spacer sets may also be of material configured with perforations or
with an open, corrugated, or honeycomb design to allow air to flow
through. The saturators may be made of a material such as wood or
paper fibers, plastic mesh, fabric, glass fibers, metal fibers, a
honeycomb arrangement of such materials, or the like and preferably
is configured to be highly wettable. Note, in the chiller 1000 and
similar designs, the gradient chilling effect is maintained by the
horizontal partitions included in the spacer configurations shown
in FIGS. 10-13, and the spacers are preferably formed of a
nonporous material and are arranged to block or limit vertical
mixing (i.e., maintain temperature stratification) of both the
incoming and outgoing air such that the incoming ambient air is
effectively and efficiently pre-cooled by the outgoing, cooler
air.
[0066] The complete assembly of the heat exchanger and saturator
(and sump) is preferably located within some type of cabinet or
frame such as metal, plastic, wood, or the like sheets, walls, and
support structures. The cabinet provides improved aesthetics for
the chiller for use near commercial and residential buildings and
also protects the heat exchanger from damage from elements or the
like. In addition, the cabinet helps to seal the edges of the heat
exchanger and the chamber at the side or end of the saturator to
prevent or limit air leakage that may bypass the saturator or
pre-cooling heat exchanger. Preferred dimensions of the cabinet are
such that the chiller 1000 can be mounted against or adjacent an
exterior building wall while not protruding very far outward. For
example, a 3-ton (or 36,000 BTU/hour) chiller could theoretically
be housed in a cabinet measuring less than 5 feet wide by 6 feet
tall by 2 feet deep. These dimensions allow the chiller to be
mounted up against the side of a building of a residence or a
commercial building, even in areas with small setbacks from
property lines. Because the outer facing side of the cabinet (e.g.,
one of the larger side walls rather than the smaller end walls or
the top/roof) has no air inlets or outlets, it is sometimes covered
with material such as siding to match the facade of the adjacent
building.
[0067] In other embodiments of the invention, a heat exchanger that
interleaves the incoming and outgoing airstreams in a spiral,
counter-current configuration is utilized to achieve pre-cooling of
the incoming airstream and to maintain a chilling gradient. One
useful embodiment of such a chiller 1400 is shown in FIGS. 14A and
14B in top and side views, respectively. The chiller 1400 includes
a cabinet or frame 1410 in which a fan 1412 is provided to draw
ambient air 1414 into the cabinet 1410 and to force the air 1414
into an inlet channel or passageway 1418 for incoming, ambient
temperature air. Two sheets 1416, 1420 of metal or other thermally
conductive materials are used to define the inlet passageway 1418
and an adjacent outlet channel or passageway 1422 for outgoing air
1448 that has passed through the saturator media, pad, or the like
1434 retained by a saturator side wall 1430 (e.g., the saturator of
the chiller 1410). In FIGS. 14A and 14B, spiral solid and dashed
lines are used to indicate the two interleaved sheets of heat
exchange material with arrows provided to indicate direction of air
movement in the chiller 1400.
[0068] The sheets 1416, 1420 are arranged to create side-by-side
spiral paths for the airstreams 1414, 1448 to provide
counter-current heat transfer between the two airstreams 1414, 1448
to pre-cool the air 1414 prior to its reaching the saturator pad
1434 at 1438. The pre-cooled air 1438 passes through the saturator
pad 1434 where it contacts water that is input at 1456 at the top
of the chiller 1400 such as via a mister, sprayer, or drip line or
the like and chills the water 1470 via evaporation. The chilled
water 1464 is stored in a sump 1460 at the bottom of the cabinet
1410 (and/or in an insulated storage tank (not shown)). A pump 1450
may be used to recirculate the water 1464 via the return piping
1452 to the saturator at 1456 and/or to another heat exchanger such
as an air-to-fluid exchanger used to cool a residence or commercial
space (as shown in FIG. 1). The air 1438, 1440 in the saturator is
cross-flow (e.g., transverse or orthogonal) to the vertical flow of
the water 1456, 1470 and is allowed to enter and exit along the
entire or most of the sides of the saturator wall 1430. Gradient
chilling is maintained by minimizing vertical mixing in the heat
exchanger, an effect that can be enhanced by interposing one or
more sets of horizontal spacers 1458 between the sheets.
[0069] More generally, the spiral formed by the sheets 1416, 1420
may be circular, ovoid, or other configurations to define desirable
adjacent flow paths for the two airstreams, with one exemplary but
not limiting configuration being shown in FIGS. 14A and 14B. The
material of construction for the heat exchanger is chosen to allow
efficient conduction of heat from one channel to the other, and
some preferred materials include thin sheet metal such as steel,
aluminum, or copper, thin plastic sheeting, or other materials. The
thickness of the sheets or separating/heat transfer walls of the
heat exchanger should be such that it provides adequate structural
support to the heat exchanger while conducting heat rapidly between
the airstreams. The dimensions (width and height) of the airflow
channels and the number of turns of the spiral (e.g., length of the
pre-cooling run) may vary to practice the invention and can be
chosen to match or suit the fan or to obtain a desired flow with a
selected fan(s) and/or to obtain particular heat transfer
properties.
[0070] In some embodiments, the heat exchanger spiral is composed
of multiple channels rather than one inlet and one outlet channels
as shown in FIGS. 14A and 14B. For example, embodiments with two or
more channels for incoming air and for outgoing air may be useful
in some implementations to achieve higher air flow and are
considered within the breadth of this disclosure. The inlets of all
embodiments of the invention may utilize one fan as shown in the
figures such as by clustering the inlets in multi-channel
embodiments. The outgoing air may be vented along a vertical side
wall of the cabinet or otherwise such as vertically out of the heat
exchanger and out the top or roof of the cabinet (e.g., an exhaust
stack or vent pipe).
[0071] Located at the center or core of the heat exchanger and
chiller is the saturator 1434 through which the water stream that
is being cooled passes. The pre-cooled air enters the core on one
side and exits on the opposite side or in another region of the
core. The water stream enters at or near the top of the saturator,
flows downward under the force of gravity, and drains out the
bottom into a sump. The sump is typically insulated so that the
chilled water does not as quickly regain heat from the outside
environment around the chiller cabinet. The water flowing through
the core region is broken down into smaller channels or droplets to
increase the surface area available for evaporation. This can be
facilitated by using media as in traditional evaporative coolers
and as described above for other embodiments. Such media could
include but is not limited to wood or paper fibers, plastic mesh,
glass fibers, metal fibers, and any other materials useful for
saturator media. Alternatively, or in addition to such media, the
water can be broken into droplets using sprinkler heads, misters,
atomizers, motorized blades, or other mechanisms. Such water
delivery devices could be located only in the core as shown or also
in the outgoing channel of the air-to-air heat exchanger to further
facilitate indirect cooling of the incoming airstream.
[0072] The water stream introduced into the core or saturator is
cooled by evaporative cooling via the pre-cooled air stream that is
flowing cross-current (or transverse) and then drains into the sump
located below the core or saturator. The water is moved through the
chiller via a recirculating pump or pumps. The air flow through the
spiral heat exchanger and saturator is maintained by a fan or fans
located at any useful position within or outside the chiller
cabinet. In one embodiment, the fan is located at the point where
the outside ambient air enters the heat exchanger as is shown in
the figures. As with other chiller designs, a mechanism typically
would be provided to maintain the water volume in the chiller or
sump such as a float valve that allows fresh water to flow into the
sump when the level drops below a preset point. Also, an anti-scale
filter may be provided to filter incoming water to limit
scaling.
[0073] The complete chiller assembly may be positioned within some
type of cabinet with walls (e.g., metal, plastic, wood, or other
material) that physically support and protect the heat exchanger
and saturator and increase its aesthetic appeal. The cabinet may
also be designed to "seal" the heat exchanger, saturator, and sump
such that air generally does not leak in or out to bypass the heat
exchanger or saturator. The cabinet may take numerous shapes and
sizes to practice the invention such as cylindrical, oval,
rectangular, or other cross sectional shapes with dimensions
selected to suit the size and shape of the heat exchanger, fan,
saturator, and sump.
[0074] Fabrication of the chiller may be achieved in a number of
fashions. For example, long sheets of heat exchanger material with
a width selected to match the "height" of the assembled exchanger
are attached to a frame. Spacers with thickness selected to provide
desired channel widths are interposed between the sheets such as by
attachment to the upper and/or lower edge of the sheets. Spacer
material is desired to be resilient so as to maintain the spacing
and to block air flow but yet be bendable for assembly. Hence, a
rubber, closed-cell foam, or similar material may be used for the
spacers. The sheets are then rolled up such that the spacers
maintain the spacing between the sheets, and the ends of the sheets
are then secured to the cabinet or a structure within the cabinet
at their edges. The frame may be used to support the saturator
materials or pads and/or in some cases, the frame is replaced with
a saturator or core that is designed for attachment to the sides of
the heat exchanger sheets.
[0075] A modification of this assembly technique would be to use
removable spacers, and in this case, the edges of the heat
exchanger spiral may be embedded into a layer of material on a
receptacle that holds the edges in place (for example, tar, molten
plastic, cement, adhesive, or the like). The spacers can then be
removed and a similar layer of material can be applied on the lid
surface to hold the upper edges of the heat exchanger in place. The
inventor constructed a prototype spiral heat exchanger using the
fanner construction techniques, and effective heat transfer between
the incoming and outgoing air streams was successfully
demonstrated.
[0076] Fabrication of other chillers such as those with thermal
storage matrices as shown in FIGS. 2A and 2B may also be completed
relatively inexpensively and without high assembly costs. For
example, the chiller 200 may use cabinet dimensions and shapes as
discussed for the cabinet of chiller 1000 or other chillers
discussed herein. However, the fabrication would be less
complicated because no complex heat exchanger is used, which
results in lower costs of construction. The cabinet 204 may be
designed to accept or receive modular units or components. For
example, a cabinet 204 may be designed to receive four modular
components including two thermal storage banks or matrices, one set
of fans, and one saturator unit. The storage banks may also be
constructed simply as "cages" that are filled with the storage
media 222, 226 or with cast blocks with perforations or other
storage bank configurations. Maintenance of the chiller 200 would
be minimal and may include seasonal draining, rinsing of dust and
dirt from the storage banks 220, 224, and occasional replacement of
the saturator media or pads 216.
[0077] For all six designs, the efficiency of cooling of the
chilled water is very high. The only electrical requirements are
for the relatively low power fan(s), one or two small pumps, and
control circuits. Further, in some residential and smaller
commercial embodiments, the movement of the water from the sump to
the top of the saturators is achieved using a small recirculation
pump (submersible in the sump or non-submersible located adjacent
to the sump). As described for the system 100 of FIG. 1 above, one
pump could be used to move water into the building with the return
water entering the device at the top of the saturator or two or
more separate pumps could be used. The total electricity usage is
very low relative to compressor-based air conditioning, resulting
in higher EER or SEER ratings than conventional A/C systems. Each
chiller of the invention is designed to chill water to below the
ambient wet-bulb temperature. Each chiller also establishes a
gradient such that the coolest air and water temperatures are found
at the bottom of the cooler (i.e., the gradient chilling
principle). Each of these chillers also can be designed to fit
inside a cabinet that integrates well with a residential or
commercial building, perhaps having a depth of two feet or
less.
[0078] The chiller embodiments of the invention are also compatible
with chilled water storage. In one embodiment, this is achieved by
increasing the volume of the sump; i.e., the chiller is placed over
an underground, insulated tank into which the chilled water can
flow. A volume of several hundred or thousands of gallons,
depending on the application, allows storage of substantial cooling
power for use during the hottest parts of the day. This could defer
electric loads to off-peak (e.g., nighttime and morning) hours
and/or allow the equipment to be down-sized so that the chiller
runs for a large fraction of the day even though cooling may only
be required during a small fraction of the day. This application
also benefits from the use of cooler nighttime ambient dry bulb and
wet bulb temperatures for chilling the water. Both efficiency of
cooling and the temperature achieved likely benefit from the lower
temperatures at night, and water usage would be lower as a
result.
[0079] The chillers described are also generally compatible with
backup air conditioning (A/C). One application or embodiment for
using any of the chiller designs would be to have the chiller and
A/C as independent systems with the thermostats set such that the
A/C only comes on if the chiller system is unable to keep up with
the cooling demand. An alternative application would be to pass the
water stream from the chiller through a backup compressor-based
chiller unit as in FIG. 1 such that the unit could further cool the
water when necessary. This would eliminate the need for redundant
heat exchangers in the building. The heat from the compressor unit
could be dumped to ambient air, to the water stream coming from the
house and going to the chiller, or to another sink. The A/C
efficiency would be enhanced by using the relatively cool (e.g.,
around 75.degree. F.) water stream to remove heat. Another
embodiment or application for the chillers presents itself with the
chilled water storage option. In this embodiment, an A/C coil in
the cool water storage tank further chills the water in the morning
hours (for example, from 5:00 AM to 10:00 AM) when and if the
chiller is unable to reach the desired tank temperature during the
night. This defers the backup A/C electric load to off-peak hours
as well.
[0080] Although the invention has been described and illustrated
with a certain degree of particularity, it is understood that the
present disclosure has been made only by way of example, and that
numerous changes in the combination and arrangement of parts can be
resorted to by those skilled in the art without departing from the
spirit and scope of the invention, as hereinafter claimed.
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