U.S. patent application number 10/351936 was filed with the patent office on 2003-07-17 for heat pump using phase change materials.
Invention is credited to Suppes, Galen J..
Application Number | 20030131623 10/351936 |
Document ID | / |
Family ID | 27541231 |
Filed Date | 2003-07-17 |
United States Patent
Application |
20030131623 |
Kind Code |
A1 |
Suppes, Galen J. |
July 17, 2003 |
Heat pump using phase change materials
Abstract
The present invention is directed toward compositions of phase
change materials derived from fats and oils, and the utilization of
such phase change materials in heating, venting, and air
conditioning (HVAC) systems. More particularly, the utilization of
such phase change materials in a heat pump or air conditioner to
significantly increase the efficiency of heat exchange with the
surrounding environment. Various embodiments are disclosed
including energy storage devices having phase change materials
encapsulated between sheets of material to reduce stresses
associated with freezing and thawing of the phase change material.
A preferred heat pump apparatus utilizes the phase change material
in the evaporator, and a smart fan mode of operation to circulate
outside air through the evaporator based on approach temperature
rather than compressor operation.
Inventors: |
Suppes, Galen J.; (Columbia,
MO) |
Correspondence
Address: |
Galen J. Suppes
The University Of Missouri
W2028 Engineering Bldg, East
The Department Of Chemical Engineering
Columbia
MO
65211
US
|
Family ID: |
27541231 |
Appl. No.: |
10/351936 |
Filed: |
January 27, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10351936 |
Jan 27, 2003 |
|
|
|
09945682 |
Sep 5, 2001 |
|
|
|
60351506 |
Jan 28, 2002 |
|
|
|
60364466 |
Mar 18, 2002 |
|
|
|
60410325 |
Sep 13, 2002 |
|
|
|
60426595 |
Nov 18, 2002 |
|
|
|
Current U.S.
Class: |
62/324.1 ;
62/434 |
Current CPC
Class: |
C09K 5/063 20130101;
Y02P 20/123 20151101; Y02P 20/124 20151101; Y02P 20/10 20151101;
Y02E 60/14 20130101; F28D 20/02 20130101; Y02E 60/145 20130101;
F25B 30/02 20130101; F25B 2400/24 20130101 |
Class at
Publication: |
62/324.1 ;
62/434 |
International
Class: |
F25B 013/00; F25D
017/02 |
Claims
I claim:
1. A heat pump apparatus utilizing a phase change material chemical
for heating a building, comprising: a condenser that functionally
releases thermal energy into a building; a compressor that
compresses a working fluid; an evaporator that takes in thermal
energy, and a fan that directs air through the evaporator; said
evaporator having at least one conduit for flow of the working
fluid through the evaporator, at least one sealed cavity containing
a phase change material chemical, and at least one air path through
which surrounding air can flow and transfer heat to said
evaporator.
2. The heat pump apparatus according to claim 1, wherein said at
least one conduit has an outer perimeter with a cumulative area, at
least 10% of which is in direct contact with said phase change
material chemical.
3. The heat pump apparatus according to claim 1, wherein the mass
of phase change material chemical contained in said sealed cavity
of said evaporator is at least 10 times greater than the mass of
working fluid flowing through said evaporator.
4. The heat pump apparatus according to claim 1, wherein said at
least one conduit has a mean internal hydraulic radius of from
about 0.02 inches to about 1 inch that is defined by the conduit
wall; and heat flows from outside the conduit wall to said working
fluid inside said conduit, and the ratio of the cumulative thermal
resistance between said working fluid and said phase change
material chemical is from about 0.1 to about 10 times the
cumulative thermal resistance between said working fluid and the
air in said air path.
5. The heat pump apparatus according to claim 1, wherein said at
least one conduit has an outer perimeter with a cumulative area, at
least 20% of which is in direct contact with said phase change
material chemical; and at least 10% of which is in direct contact
with the air in said air path.
6. The heat pump apparatus according to claim 1, further
comprising: a housing that contains and connects said evaporator
and fan; said housing having an outer surface with a surface area,
at least 50% of which functions to provide insulation resistant to
heat flow, and as a sealing surface resistant to air flow.
7. The heat pump apparatus according to claim 6, wherein said fan
directs air through said housing; and further comprising: shutter
means for blocking air from flowing through said housing when said
fan is not running.
8. An apparatus utilizing a phase change material chemical for
exchanging heat between a fluid and the phase change material
chemical, comprising: a phase change material chemical encapsulated
between sheets of thermally conductive material.
9. The apparatus according to claim 8, wherein said sheets are
laminated to seal said phase change material chemical
therebetween.
10. The apparatus according to claim 8, wherein said phase change
material chemical comprises multiple pouches of said phase change
material chemical.
11. The apparatus according to claim 8, further comprising: a
container having an entrance and exit for fluid flow; and said
sheets having said phase change material chemical encapsulated
therebetween are suspended in said container the path of fluid
flowing between said entrance and said exit.
12. The apparatus according to claim 11, wherein said sheets are
suspended from an upper end thereof in said container and disposed
vertically therein.
13. The apparatus according to claim 11, wherein said fluid flowing
through said container is air.
14. The apparatus according to claim 8, further comprising: a sheet
of porous material disposed between said sheets to facilitate even
fluid flow and improved heat transfer between the fluid and said
phase change material chemical.
15. The apparatus according to claim 8, further comprising: at
least one conduit disposed between said sheets for conducting a
working fluid therethrough having an exterior surface in contact
with said phase change material chemical in heat exchanging
relation to function as an evaporator.
16. A method of exchanging heat with outside air in an outdoor heat
pump unit having an evaporator/condenser and at least one conduit
for conducting a flow of working fluid through the
evaporator/condenser, and a fan that directs air through the
evaporator/condenser, comprising the steps of: providing a mass of
material having a heat capacity greater than 30 kJ/.degree. C. in
contact with the working fluid conduit in thermal exchange
relation, said mass of material absorbs heat and releases heat; and
operating said fan based on the temperature difference between the
average temperature of said at least one conduit and the outside
ambient temperature; whereby said evaporator/condenser serves as an
evaporator in a heating mode of operation, and as a condenser in a
cooling mode of operation.
17. The method according to claim 16, wherein in said cooling mode,
said fan is switched on when the outside ambient temperature is at
least 3.degree. F. cooler than the average temperature of said at
least one conduit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-In-Part of U.S. patent
application Ser. No. 09/945,682, filed Sep. 5, 2001, now pending,
and claims priority of the following U.S. Provisional Patent
Applications: Serial No. 60/351,506, filed Jan. 28, 2002; Serial
No. 60/364,466, filed Mar. 18, 2002; Serial No. 60/410,325, filed
Sep. 13, 2002; and Serial No. 60/426,595 filed Nov. 18, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention relates generally to phase change materials
and apparatus utilizing phase change materials and, more
particularly, to phase change materials produced from fats and
oils, and HVAC apparatus utilizing phase change materials,
including heat pumps.
[0004] 2. Description of Prior Art
[0005] The present invention relates to phase change material (PCM)
chemicals used in PCM devices to store or remove thermal energy.
Applications include (1) walls, flooring, and tank devices used to
moderate climates in buildings (2) food storage coolers or other
types of coolers, (3) devices used to keep food warm, and (4)
essentially any device used to keep a substance at a relatively
constant temperature between -20.degree. C. and 150.degree. C. More
specifically, this invention is directed toward a composition of
PCM chemicals largely comprised of fatty acid derivatives, a method
for producing these PCM chemicals, and a method for using these PCM
chemicals.
[0006] The term "phase change material" or PCM is known in the
science as that class of materials that uses phase changes to
absorb or release heat at a relatively constant temperature.
Typically the phase changes are fusion (or melting) with an
associated latent heat.
[0007] Advantages of PCM in climate control include:
[0008] 1. Eliminating need of air conditioner or heater
requirements during substantial portions of the year.
[0009] 2. Shift electricity usage from prime time to non-prime
time.
[0010] 3. Reducing the size of air conditioners needed to provide
cooling requirement.
[0011] 4. Substantially expanding regions in which heat pumps are
practical for heating in wintertime.
[0012] Commonly used PCMs include hydrated salts, eutectic salts,
and paraffins. Similar prior art on use of phase change materials
with the outside units of heat pumps has not been located.
SUMMARY OF INVENTION
[0013] The present invention is directed toward a composition of
phase change material and method for high yields of phase change
materials from fats and oils, the use of phase change materials in
the area of heating, venting, and air conditioning (HVAC) systems.
Another aspect of the present invention is an improvement on that
component of a heat pump or air conditioner that exchanges heat
with the surrounding environment. More specifically, a heat pump or
air conditioning coil that is designed to maximize the intake of
solar energy onto the coil. Similar technology for high yields of
products from fats and oils has not been located.
BRIEF DESCRIPTIONS OF DRAWINGS
[0014] FIG. 1 is a schematic illustration showing two methods of
integrating the tubing of a heat pump coil onto a surface.
[0015] FIG. 2 is a schematic drawing illustrating a method of
integrating the tubing of a heat pump coil with phase change
material wherein part of the surface in contact with air contacts
the phase change material and part of the surface in contact with
air contacts the working fluid.
[0016] FIG. 3 is a schematic drawing illustrating a method of
integrating the tubing of a heat pump coil with phase change
material.
[0017] FIG. 4 is an exploded isometric view of a solar coil
comprised of two heat transfer plates, a cavity, and a back plate
wherein the heat pump fluid flows between the two plates and the
cavity is filled with a phase change material.
[0018] FIG. 5 is a side view, top view, and front view of preferred
heat pump coil.
[0019] FIG. 6 is a schematic drawing illustrating methods of
integrating the tubing of a heat pump coil onto a surface by RIM
attachment of the tubing to a panel with air channels through
cavity, and a perspective view showing the path of air flow
directed through the panel with a fan.
[0020] FIG. 7 is a schematic drawing illustrating how the shield
does not block sunlight during winter and with the sun low to the
southern horizon (Northern hemisphere application).
[0021] FIG. 8 is a schematic drawing illustrating how the shield
blocks and reflects sunlight during summer and with the sun low to
high in the sky (Northern hemisphere application).
[0022] FIG. 9 is a schematic drawing illustrating an outside heat
transfer device for a heat pump with a fan controlling air flow and
insulation preventing heat flow when the fan is off.
[0023] FIG. 10 is a schematic drawing illustrating a modulated
central air unit for easy house installation.
[0024] FIG. 11 is a schematic drawing illustrating an
evaporator/condenser design using thin rectangular PCM
containers.
[0025] FIG. 12 is a schematic drawing illustrating a hot water
heater using PCM as a stored source of heat to provide sufficient
capacity to heat rapid flow of water.
[0026] FIG. 13 is a schematic drawing illustrating a tube and shell
configuration using segregated PCM chemicals and a refrigerant coil
to heat water.
[0027] FIG. 14 is a schematic drawing illustrating a laminated
pouch array using two sheets to encapsulate the PCM chemical.
[0028] FIG. 15 is a schematic drawing illustrating a vessel
configuration for hanging laminated pouch arrays.
[0029] FIG. 16 is a schematic expanded front view of a laminated
pouch array embodiment with a refrigerant tube and packing sheet to
provide 3-way heat transfer.
[0030] FIG. 17 is a schematic expanded side view of the laminated
pouch array embodiment with a refrigerant tube and packing sheet to
provide 3-way heat transfer.
[0031] FIG. 18. is a schematic side view in cross section of a
vessel containing the laminated pouch array embodiment with a
refrigerant tube and packing sheet to provide 3-way heat
transfer.
[0032] FIG. 19a is a schematic front view in cross section of the
vessel containing the laminated pouch array embodiment with a
refrigerant tube and packing sheet to provide 3-way heat transfer
illustrating the air flow pattern forcing air to enter on the sides
of the hanging laminated pouch array.
[0033] FIG. 19b is a schematic front view in cross section of the
vessel containing the laminated pouch array embodiment showing the
pouches arranged to provide even air flow.
[0034] FIG. 20a and FIG. 20b are block air flow diagrams of systems
using PCM to enhance the performance of desiccant with evaporative
cooling follow-up, and with AC cooling follow-up, respectively.
[0035] FIG. 21 is a block flow diagram of a process for producing
PCM chemicals from fats and oils using reversible reaction and a
solid-liquid separation process.
[0036] FIG. 22 is a block flow diagram of a process for producing
PCM chemicals from fats and oils using two solid-liquid separation
processes.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] Three-Way Heat Transfer Embodiment
[0038] The improved heat transfer devices in accordance with the
present invention may serve as either the evaporator or condenser
of a heat pump, and alternative embodiments, as described
hereinafter are effective for replacing conventional hot water
heaters. The present apparatus and method incorporates a phase
change material into the heat transfer device such that efficient
heat transfer occurs between; a) air and the working fluid of the
heat pump, b) the phase change material and the working fluid of
the heat pump, and c) air and the phase change material. A
significant advantage of the present invention over other apparatus
and methods of the prior art is that all three heat transfer
processes (a, b, and c) occur efficiently and in one integrated
device. Incorporation of the phase change material into the
evaporator or condenser can improve efficiency, extend heat pump
operation into colder temperatures where it would otherwise not be
the preferred option, and reduce the needs for deicing the heat
pump evaporator.
[0039] The improved heat transfer device contains a passage for the
flow of a heat pump fluid (also referred to as working fluid) such
that heat transfer occurs through the surface of at least part of
that passage. FIG. 1 and FIG. 2 illustrate alternative
configurations for this heat transfer means--the working fluid is
the fluid of the heat pump or refrigerant cycle.
[0040] Heat transfer to or from the passage is through a surface
preferably comprised of metal or polymer or two or more surfaces in
contact so as to function as a single surface for heat transfer.
The inside of this surface is defined as being in contact with the
working fluid (such as a FREON refrigerant). 10% to 90% of the
outside of this surface contacts a gas comprised primarily of air,
and 10% to 90% of the outside of this surface contacts a phase
change material. More preferably, 30% to 80% of the surface outer
side contacts air, and 20% to 70% of the surface outer side
contacts a phase change material. Most preferably, 50 to 70% of the
surface outer side contacts air, and 30% to 50% of the surface
outer side contacts a phase change material.
[0041] In this embodiment, a heat pump uses a PCM chemical to
improve the efficiency for heating a building, the heat pump
includes a condenser that functionally releases thermal energy into
a building, a compressor that compresses a working fluid, an
evaporator that takes in thermal energy, and a fan that directs air
through the evaporator. The evaporator includes at least one
conduit for flow of said working fluid through the evaporator, at
least one sealed cavity containing a PCM chemical, and at least one
air path through which surrounding air can flow. At least 10% of
the cumulative area of the outer perimeter(s) of the conduit(s) is
(are) functionally in direct contact with the PMC chemical. Here,
"functionally in direct contact" means that the outside (working
fluid is inside) of the conduit wall is in direct contact with the
PCM chemical or the conduit wall is in direct contact with the PCM
chemical container.
[0042] The amount of phase change material in the heat transfer
device is greater than the amount of working fluid in the heat
transfer device. The ratio of phase change material mass to working
fluid mass is greater than 10, more preferably greater than 25, and
most preferably about 100. The total volume of phase change
material is preferably between 1 and 500 gallons and more
preferably between 10 and 100 gallons for every 2500 square feet of
space being heated by the heat pump. The ratio decrease for larger,
commercial buildings.
[0043] The phase change material is itself isolated from
surrounding air in a cavity that would generally be considered a
passage or container, and the volume of this cavity is greater than
volume of the working fluid passage per the mass ratios previously
specified. Consistent with heat pump operation, the working fluid
passage allows the working fluid to flow through the heat transfer
device. The working fluid flow is typically caused by a pump or
compressor (not shown in the diagrams).
[0044] The phase change material is contained within the heat
transfer device and does not leave the heat transfer device during
normal operation. Air flows through the heat transfer device to
facilitate heat transfer. Air flow is caused by a blower, a fan, or
natural convection cause by wind or solar heating/expansion of
air.
[0045] By way of example, FIG. 1 illustrates an embodiment in which
the working fluid passage is a tube. The tube is attached to the
phase change material's containing surface. About 50% of the outer
tube circumference is in contact with air and about 50% of the
outer circumference is in contact with a phase change material. The
phase change material may be either a continuous phase or an
encapsulated phase. Sheet metal is depicted in FIG. 1, by way of
example, as a means to contain the phase change material. The
surface of the sheet metal extends beyond contact with the working
fluid tube to include contact with air therein providing efficient
heat transfer between the air and the phase change material.
[0046] Three-Way Heat Transfer Device
[0047] The embodiment of FIG. 1 illustrates the use of tubes for
flow of the working fluid. Here, two surfaces separate the working
fluid from the phase change material. In these embodiments the two
metal surfaces are at least in part in close contact so as to
function as one thicker wall having relatively high thermal
conductivity. The first illustration of FIG. 1 illustrates the use
of a tube next to a thin sheet of thermally conductive material
such as aluminum foil. Subsequently, the foil contains and protects
a phase change material that in the bulk is not fluid. An example
of a phase change material that in bulk is not fluid is a polymer
undergoing a glass transition at the temperature of interest.
Another example of a phase change material that in bulk is not
fluid is a solid-liquid transition phase change material that is
encapsulated in a polymer such as epoxy resin. The second
illustration of FIG. 1 is a tube connected to a rigid sheet that is
thermally conductive. An example of such a sheet is sheet metal.
Here, the sheet serves three purposes: (1) it contains the phase
change material and (2) it acts as a fin to increase the heat
transfer area of the tube, and (3) it increases the surface
available to absorb the radiant energy of sunlight or enthalpy of
air.
[0048] By way of example, FIG. 2 illustrates an embodiment in which
the working fluid passage is a conduit formed by two sheets. One
sheet separates the working fluid from the air. Another sheet
separates the working fluid from the phase change material. The two
sheets are welded, brazed, or otherwise continuously joined so as
to form a passage for the working fluid. About 50% of the outer
tube circumference is in contact with air and about 50% of the
outer circumference is in contact with a phase change material.
Sheets extend to fully contain the phase change material and
provide a heat transfer area between the phase change material and
surrounding air. Methods known in the science can be used to
identify the material and thickness of the sheet to provide both
heat transfer and structure. Metals containing varying amounts of
copper, iron, and zinc are commonly used for similar applications
requiring both efficient heat transfer and structure, but the
embodiments of this invention are not limited to a particular
material of construction.
[0049] FIGS. 3, 4 and 5 further illustrate examples of various
embodiments of the invention. The example embodiment of FIG. 5
allows orientation to absorb solar radiation during the winter
months. The rectangular configuration is represented by a length
(L), width (W), and thickness (T) as illustrated by FIG. 5. The
preferred size of the device is such that the thickness is less
than 20% of the length. More preferably, the thickness is less than
10% of the length. In a more absolute sense, the length is
preferably between 1 and 30 feet. More preferably, the length is
between 2 and 15 feet. Most preferably, the length is between 3 and
10 feet. As compared to conventional heat pump coils, conventional
coils are typically arranged in a cylindrical or box pattern
surrounding a fan.
[0050] The back face of the cavity of FIGS. 3, 4, and 5 are
primarily containing walls that optionally exchange heat with air.
The front face of the cavity is that face contains the integrated
working fluid passage and in FIG. 5 is positioned to receive
incidental sunlight. The working fluid is separated from the
surrounding air by an air-side wall. In this embodiment, the
working fluid flows through a tube, or alternatively, it flows
generally between two plates.
[0051] In the embodiment of FIG. 4, a corrugated plate separates
the air from the working fluid, a second separation plate separates
the working fluid from the phase change material, and a back plate
contains the phase change material. An enlarged cavity is
optionally created by a perimeter around the cavity that increases
the space between the separation plate and back plate. The
corrugated plate forces spaces between the separation plate and the
corrugated plate to allow flow by the working fluid. Ports at the
upper and lower end of the corrugated plate allow the working fluid
to be introduced and removed. Optional ports in the phase change
material cavity allow the phase change material to be introduced or
removed from the cavity. The plates are fastened by methods known
in the science to create a seal on the perimeters and to provide
structural reinforcement as necessary along the large flat
surfaces.
[0052] FIGS. 2 and 3 illustrate in greater detail the separation of
the working fluid from air and from the phase change material.
[0053] Methods known in the art are used to configure the heat
transfer fluid passage so as to allow evaporation or condensation
consistent with proper heat pump operation, and to enhance the
configurations to improve heat transfer with the air adjacent to
the working fluid passage and adjacent to the surface that contains
the phase change material. A conductive packing in the cavity
increases heat transfer throughout the phase change material.
[0054] The heat transfer embodiments may be used to transfer heat
to/from outside air (for example, as an evaporator for a heat pump)
or to/from inside air (for example, as a condenser for a heat
pump). It should be understood that the heat transfer embodiments
are not limited to heat pumps. For example, the heat transfer
embodiments may be used with air conditioners.
[0055] Performance benefits in air conditioning can be achieved by
using two evaporators, one containing a phase change material and
one not containing a phase change material. Flow of working fluid
to the heat transfer device(evaporator) may be controlled by a
valve where, in an example of an air conditioner evaporator, flow
to the heat transfer device during the night time stores coolness
in the phase change material while during the day time flow is
diverted to a second evaporator that does not contain a phase
change material. In this alternative embodiment, load shifting is
achieved by having return air contact that heat transfer device
containing the phase change material prior to contacting the heat
transfer device that does not contain the phase change
material.
[0056] As previously indicated, the heat transfer device of this
invention is designed to provide efficient heat transfer between a)
air and the working fluid of the heat pump, b) the phase change
material and the working fluid of the heat pump, and c) air and the
phase change material. In addition, the heat transfer must be
controllable. Heat transfer with the working fluid is controlled by
controlling the flow of working fluid to the heat transfer device.
When working fluid flow stops (such as when the compressor is
switched off), the working fluid will approach the temperature of
the air. Independent control of heat transfer between the phase
change material and air requires an auxiliary control means.
[0057] The heat transfer device is generally designed such that
when air flows through the device, heat is readily transferred
between the working fluid and air, and when air does not flow
through the device the phase change material is insulated from heat
transfer between the phase change material and air. Methods known
in the art incorporating baffles and ducts to direct air flow and
insulation to enclose the heat transfer device can generally be
used to achieve these desired heat flow characteristics. Heat
transfer between surrounding air and the heat transfer device is
thus controlled by controlling the air flow through the device.
[0058] By way of example, FIG. 6 illustrates an alternative
embodiment for integrating a fan with the heat transfer device.
FIG. 6 illustrates how the generally rectangular embodiment of FIG.
4 and FIG. 1 can be incorporated with a fan. The overall
rectangular embodiment is comprised of a series of smaller
rectangular embodiments with gaps between the smaller rectangular
embodiments to facilitate air flow. A fan pulls or pushes air
through these gaps. Ducting of air between the generally
rectangular embodiment and the fan is such to allow good
integration of the generally rectangular embodiment with its
location. The embodiment of FIG. 6 illustrates this ducting where
the generally rectangular embodiment is oriented at a different
angle than the surface where it is mounted. The preferred method
for manufacturing the embodiment of FIG. 6 is by reaction injection
molding. When this embodiment is placed on the roof or wall, the
roof/wall insulates one side.
[0059] FIGS. 7 and 8 illustrate how the heat transfer device of
FIG. 6 can be designed to receive solar radiation in the winter
while reflecting away this radiation during the summer.
[0060] Insulated Outside Evaporator Embodiment
[0061] By way of example, FIG. 9 illustrates the preferred outside
evaporator of a heat pump of this invention. Interconnected
vertical panels contain the phase change material with the working
fluid passages on one side of these panels. Air spaces between the
panels allow upward air flow. The four sides are comprised of
insulate panels. Air enters the bottom and is forced through the
system by a fan located at the top. When the fan is not
operational, convective air flow largely ceases and the insulating
side panels largely eliminate heat transfer with the outside
air.
[0062] In the preferred outside unit illustrated by FIG. 9, the
functionality of the housing is particularly important. In a heat
pump using a PCM chemical to improve the efficiency for heating a
building, the heat pump includes a condenser that functionally
releases thermal energy into a building, a compressor that
compresses a working fluid, an evaporator that takes in thermal
energy, a fan that directs air through the evaporator, and a
housing that contains and connects said evaporator and fan. The
housing has an outer surface with a respective surface area.
Preferably, at least 50% of the said housing surface area provides
insulation resistant to heat flow and also seals that surface
against air flow. Preferably, a fan directs air through the said
housing methods known in design are incorporated in the design to
minimize air flow with the fan is not on. Use of a shutter that
blocks air from flowing through the housing when the fan is not
running is an example of one design option. This insulated housing
serves the important purpose of preserving the stored heat in the
PCM chemical until such time it is needed to provide heat to the
building served by the heat pump. FIG. 9 illustrates an embodiment
with insulation on the sides and a fan on top. Air is preferable
pulled in the top and forced out the bottom. A screen and other
methods known in the science are used to prevent plugging of the
air path ways through the evaporator.
[0063] Whether the PCM panel of FIG. 4, 6, or 9, the preferred
thickness of these panels are between 0.25 and 5 inches and more
preferably between 0.5 and 3 inches. Most preferably, the thickness
is about 2 inches, which provides an optimum between storage
capacity and good access for heat transfer.
[0064] Within the scope of this invention, the use of phase change
materials in the exterior component (outside house) of the heat
pump is not limited to phase change materials based on fatty acid
derivatives. Essentially any phase change material can be used in
the preferred embodiment of FIG. 1. The preferred embodiment of
FIG. 1. is in the structure of FIG. 4; however, the incorporation
of phase change materials into the embodiment of FIG. 1 can be in a
variety of larger geometries including but not limited to flat
surfaces, curved surfaces, or cylindrical surfaces.
[0065] An alternative phase change material for use in the exterior
component of a heat pump (the evaporator in the case of the heating
cycle of the heat pump) is water. The advantage of water is that it
can readily be melted during the warm winter days for use during
the night. Since the economic viability of using the heat pump with
a conventional evaporator alternative to electrical or natural gas
heating is typically favored until temperatures go below about
30.degree. F. Water is a good, example phase change material for
this application since it is a good heat storage media at
32.degree. F.--a low temperature point where the heat pump is
favored over natural gas. Salts or antifreeze can be added to the
water to create freezing at temperatures lower than 32.degree. F.,
as desired.
[0066] Proper use of convection heating created by the fan-induced
air flow over the evaporator is important. The value of water is
realized when the highest temperature of the day is above
32.degree. F. while the lowest temperature of the day is below
32.degree. F. When temperatures are below 32.degree. F., the
outside convection fan is not used in favor of conducting heat from
water(the phase change material in the evaporator) that can freeze
therein releasing its latent heat. During that part of the day when
the outside temperature is above 32.degree. F. (more preferably
above 33.degree. F.), the outside fan is turned on until such time
that the temperature of water is above 32.degree. F. as an
indication that the water has melted.
[0067] Smart Fan Embodiment
[0068] When used for residential heating, the preferred means for
controlling fan operation in the evaporator of the heat pump is to
operate the fan when the exterior air temperature is warmer than
the evaporator coil by an incremental temperature difference. This
incremental temperature difference is preferably between 1.degree.
F. and 5.degree. F. During those days when the heat pump is not
used for heating, control of the fan to store energy in the phase
change material is not required. This mode of operating the fan of
an outside evaporator unit based on the outside temperature being
warmer than the evaporator coils is hereafter referred to as a
"Smart Fan" method of operation.
[0069] The advantage of operating a heat pump in this manner is
that the heat pump can operate a nighttime with efficiencies
similar to those realized during the warmer daytime hours. An
additional advantage of operating a heat pump in this manner is
that the phase change material moderates the temperature extremes
that otherwise occur in the heat pump. For example, a heat pump
will readily generate evaporator temperatures 5.degree. F. to
20.degree. F. lower than ambient temperatures to cause the flow of
heat from the surroundings into the working fluid of the heat pump.
By example, if the outside temperature is 20.degree. F., this
translates to a working fluid temperature of about 10.degree. F.
The good thermal conductivity of the phase change material reduces
the temperature driving force and stores energy creating a working
fluid temperature of about 29.degree. F. for the same outside
conditions. The higher working fluid temperature provides the
following advantages: a) higher heat pump efficiency, b) high
outlet air temperatures in the house, and c) reduced or eliminated
icing of the exterior evaporator. All of these advantages are most
significant. By reducing or eliminating icing, the heat pump will
allow operation at even lower temperatures than would otherwise be
possible. Reducing or eliminating icing is realized at all
subfreezing outside temperatures since icing is caused by the
temperature difference between the evaporator coils and the outside
air temperature--this temperature difference is reduced by the heat
capacity of the phase change material provided the heat pump is
only operated intermittently (as is usually the case).
[0070] Phase change materials used with heat pump evaporators are
preferably water or mixtures containing water. In general and for
either heating or cooling applications, the phase change material
preferably has substantial latent heat capabilities between
20.degree. F. and 100.degree. F. The optimal phase change material
will depend upon location.
[0071] In the most preferred residential heating embodiments,
convection heating of the exterior coils is supplemented with solar
heating. As previously described, solar heating can be on a flat
evaporator embodiment. Alternatively, air can be heated by the
solar heating embodiment (such as SOLARWALL) and directed over the
exterior component of the heat pump. Allowing solar heating
elements to function independent of the heat pump has the
operational advantage of allowing the solar heating element to
directly heat the house when the outside temperatures are warm
enough, and then, using the solar heating element to enhance heat
pump performance when outside temperatures are too cool to directly
use the solar heating element to directly warm the house.
[0072] Preferably, the solar heating embodiment is on the roof with
air flow under the upper, hot surface. Preferably, the solar
heating embodiment provides both heated air and roofing therein
avoiding shingling costs. Preferably, in the summer water is
sprayed on the roof, preferably in an automated manner with methods
known in the science, so that the large heat transfer surface
provides a cooling heat transfer during summer nights. Drainage
should be periodically complete to avoid microscopic growth.
Preferably, the air cooled under the heat transfer surface is drawn
from a source that is not itself laden with moisture. The cooled
air could be directed for ventilation or contacted with water for
further cooling and used to cool the exterior air conditioning
coils.
[0073] The embodiments of FIGS. 5, 7, and 8 are designed to
selectively receive solar radiation during winter months. When in
position, the large face of the rectangular configuration is
preferably oriented such that the top edge of the plane is level.
The end of the plane is at an angle from vertical such that the
sunlight hits the plane at a perpendicular angle at a time during
that half of the year when heating is required. For areas like
Arkansas where the heating season is short, it is preferred to have
the sunlight hit the plane at a vertical angle during the longest
day of the year. Further north, it is too ambitious to pursue heat
pump use during the shortest day of the year, and so, the angle is
such that sun light hits the plane at a vertical angle at 1 to 2
months prior (and accordingly after) the shortest day of the
year.
[0074] The advantage of this configuration is that solar energy is
used to improve the efficiency of the heat pump. This advantage is
realized in the wintertime; however, in the summer the incidental
angle of the sun is such that it does not induce much radiation
onto the surface and reduce the cooling efficiency of the heat
pump.
[0075] It should be understood that the embodiments of the present
invention may essentially be of any geometry that generally fits in
the space of the rectangular plane described herein.
[0076] To further reduce incidental radiation during the summer,
shields are preferably attached to the rectangular embodiment such
that sunlight largely does not hit the shield (see FIG. 7) during
the season when the heat pump provides heating. During the heating
season, the face of the rectangle is largely perpendicular to the
incidental radiation. As the year progresses to summer, the greater
the incidental sunlight angle is from vertical. The shield is
designed such that during the air conditioning season the sunlight
hits the shield (rather than the face of the rectangle) and is
preferably reflected away from the plane. During the hottest three
months of the year, essentially no light hits the tubing or
interconnected metal for heat transfer--essentially all sunlight
being reflected away from the tubing (see FIG. 8). The preferred
shield consists of one or more surfaces that are generally
perpendicular to the plane of finned coils. More specifically, the
shield is a series corrugated surfaces such as that illustrated by
the insert of FIG. 8.
[0077] The preferred location for the flat rectangular embodiment
of this invention is on a roof with exposure to the winter sun.
Operating as a solar energy receiver, fan convection is not
necessary with the solar energy received is greater than or equal
to the energy taken from the evaporator to heat the building.
Operation without a fan is preferred. In such an application, no
exterior fan is used to force air over the coil and the heat pump
operation is regulated to provide a lower, steady heat flow rather
than typical operation where the heat pump runs at full capacity
for several minutes and then shuts off for several minutes. During
the summer, nighttime operation, radiant heat losses will at times
be sufficient to alleviate the need for fan use. Preferably, in the
summer a spray of water on the face of the condenser will reduce
the need for fan use. Reducing fan use saves on electricity and
reduces noise.
[0078] Referring to FIG. 6, optionally, to assist airflow through
the coil, a fan under the coil pulls air down and into the coil.
Ducting surrounds the bottom surface of the flat coil embodiment
and directs air flow to the fan--forcing essentially all air that
flow through the coils to also go through the fanning area.
[0079] Preferably, the fan is reversible. When providing heat to
the house, the fan pulls air down through the coils. When providing
cooling, the fan pushes air up through the coils. Glass or other
transparent material is optionally placed above the coil to trap in
heat during the winter--in this embodiment air preferably flows in
under the glass and above the soil plane at the lowest part of the
glass surface. The preferred color of the coil fins is black. The
preferred color of the shields is any reflective metallic
color.
[0080] Optionally, water is sprayed in the air during cooling
months (summer) such that the water mixes with air prior to
contacting the coil. This provides evaporative cooling and lowers
the coil temperature more than would otherwise be achievable.
[0081] Alternative to positioning on a roof, the rectangular
embodiment is at ground level with a Southern exposure (for use in
the Northern hemisphere). Alternatively, the rectangular embodiment
is set with the face at a near-vertical orientation next to a
building's siding or in place of the building's siding.
[0082] The preferred use of the coil of this embodiment is with a
heat pump. The heat pump preferably can operate at different
condenser/evaporator pressures so as to increase the COP values
when the ambient temperatures are similar to inside set point
temperatures. With solar heating of the coil during the heating
season, the coil will at times reach temperatures several degrees
warmer than inside temperatures (Likewise, with evaporative cooling
the coil temperature will often be cooler than set point
temperatures during the cooling season.). In these instances,
heating (cooling) can be achieved by merely circulating the heat
pump fluid. The preferred mode of operation under these
circumstances is to circulate the cooling fluid with the least
energy-intensive means available to the system when such
circulation alone provides sufficient heating (cooling).
[0083] The preferred method to circulate the heat pump fluid when
circulation alone is sufficient is to open or bypass all throttling
devices in the cycle by methods known in the science including but
not limited to opening a throttling valve or by-passing a
throttling valve through a parallel tube that is activated by
opening a solenoid valve. Circulation can be induced by compressing
the heat pump fluid at the minimum pressure ratio that will allow
circulation. Alternatively, the compressor can be by-passed by
methods known in the science with pump being used to move liquid at
a location parallel to the throttle.
[0084] The rectangular condenser/evaporator embodiment may function
with or without significant heat storage capacity. When designed
without significant heat storage capacity, heat transfer fins are
preferably attached to the tubing as is conventional in air
conditioner coils. In such embodiments, the fins surface is
preferably perpendicular to the face of the rectangular embodiment
in an arrangement known in the science such that gravity would
assist the flow of condensed liquids to the bottom of the
embodiment.
[0085] FIG. 10 illustrates how a heat pump system can be integrated
into a sheet of plywood for prefabrication. The prefabrication
reduces installation costs. Integration the outside unit on the
wall further reduces installation costs and specifically eliminates
the cost of the concrete slab where the outside unit is typically
mounted.
[0086] Alternative Embodiments and Chemicals
[0087] While in the preferred embodiment, 10% to 90% of the outside
of the surface contacts a gas comprised primarily of air, and 10%
to 90% of the outside of this surface contacts a phase change
material; an alternative embodiment has the tube containing the
working fluid (typically a refrigerant) substantially enclosed in
the phase change material container.
[0088] By way of example, the working fluid could be in a 0.25 inch
tube that is located in a 4 inch pipe containing the phase change
material. The 0.25 inch tube is substantially in the 4 inch pipe;
however, it is outside the pipe at locations adjacent to where it
enters/exits the pipe and is manifolded by methods commonly used in
evaporator/condenser design.
[0089] In this alternative embodiment and specifically in the heat
pump mode, the 0.25 inch tube and phase change material (PCM) alone
reach temperatures lower that the temperature at the PCM container
to air interface. This is important since the low temperatures at
the air interface can induce condensation and freezing that
requires an energy-intensive thawing cycle. By operating the fan to
warm the PCM essentially continuously during the warm part of the
day, the container-air interface will not reach temperatures as low
as those reached in the PCM and the cycle will be more efficient
and require lower maintenance.
[0090] The preferred PCM for the outside, evaporator coil of the
heat pump is a water-salt mixture that freezes between about
-8.degree. C. and 0.degree. C. More preferred, the salt-water
mixture freezes between about -6.degree. C. and -2.degree. C.
Several salts and water-salt compositions that are capable of
operating at these conditions are summarized in Lang's Handbook of
Chemistry.
[0091] For summer operation as an air conditioner, it is preferred
to have the PCM in the outside condenser to be a material having a
melting point between 80.degree. F. and 100.degree. F. It is
preferred to spray water over the cooler during the nighttime hours
to cool and freeze the PCM for use as a cool temperature reservoir
during the daytime. Devices could be made with both types of PCM
materials(type for use with cooling and type for use with heating)
present or where the PCM can be changed twice a year.
[0092] Thin Container/Pouch Design
[0093] It is highly desirable to reduce the resistance to air flow
and travel path of air in the outside evaporator unit during
heating and the outside condenser unit during cooling.
[0094] FIG. 11 illustrates an alternative design of a
PCM-containing device wherein the PCM is located in thin containers
1, for example, a container that is 2 inches thick, 2 feet wide,
and 3 feet long. Tubing 2 containing the working fluid is located
adjacent to the container 2. By way of example, the tubing is 0.25
inch copper tubing that is glued to the container. A heat transfer
enhancer 3 is placed above the tubing 2. By way of example, this
heat transfer enhancer is a series of thin aluminum fins that
direct flow over the tubing 2. By alternative example, the heat
transfer enhancer is an aluminum mesh resembling steel wool in
appearance. A spacing plate 4 is located above the heat transfer
enhancer. This plate 4, by example, divides an air travel path of 8
inches into an air travel path of 4 inches through a heat transfer
enhancer followed by a travel path of 4 inches through a
low-resistance space. This plate 4 allows two such paths parallel
paths to be located between containers 1. The advantage created by
this plate is that it creates travel paths similar to those
encountered with conventional air conditioner heat exchangers while
allowing for larger containers. Above the plate, a second heat
transfer enhancer 3 is located in contact with a different PCM
container such that it is located on a different location of the
container. Tubing 2 is located between the heat transfer enhancer 3
and container 1.
[0095] This configuration allows the stacking of functional
assemblies as indicated by FIG. 11. Air flows in from three sides
through the open portion at the middle of the spacing plate 4 and
out the fourth side. Preferably the fourth side is upward-facing
(placed as the top) with a fan mounted (similar to FIG. 9) to pull
air through the evaporator/condenser.
[0096] In the embodiment of FIG. 11, the containers, tubing, heat
transfer enhancers, and plates can be stacked as illustrated by
FIG. 11. This stacking can increase the weight on the bottom units.
This weight can increase stresses during freezing and thawing and
lead to leaks. To reduce the stresses, the containers can be
supported from their perimeters; however, for this to be effective
at least one of the stacked elements (containers, tubing, heat
transfer enhancers, or plates) must have a structural strength. The
Hanging Laminated Pouch Embodiment overcomes the problems with
weight accumulating on the bottom of a series of containers.
[0097] Water Heating Embodiment
[0098] A water heating embodiment of the present invention
incorporates a working fluid conduit next to the energy storage of
a PCM heats water rather than air. In this embodiment, the PCM
stores enough thermal energy to heat water as it flows through the
system. The PCM preferably melts over a temperature range from
70.degree. F. to 140.degree. F. A working fluid melts the PCM,
which stores energy. The stored energy delivers heat to the water
at a rate greater than the capacity of the heat pump system for
short periods of time such as during a shower. The advantage of
this system is that the efficiency of the heat pump is used to heat
hot water. In addition to the heat provided by the heat pump,
electrical heating devices are used to increase the water
temperature to values greater than 140.degree. F. The cool water
source flows through the PCM-based hot water heater in a flow path
such that it contacts (through the container wall) the PCM with the
lowest melting point first. Unlike air systems, this water heater
system is preferably designed such that water has longer flow paths
next to the PCM allowing for greater heat transfer. FIG. 12 shows
this embodiment where the PCM modules are not stacked, but rather
end-on-end to provide greater flow paths and heat exchange to the
water. The advantage of this unit is that the stored heat can be
delivered at a rate fast enough to heat the water while the heat
pump or electrical resistance alone would not be able to supply the
heat fast enough. Also, the heat pump as enhanced with the PCM
operates at greater efficiency than is possible without the PCM.
Also, when this is a controllable dump of heat from a heat pump,
the heat can actually be pumped from the house into the hot water
therein providing both cooling and hot water with little or no
additional heating beyond that used/required for air
conditioning.
[0099] Hot Water Heater Embodiments
[0100] The preferred means for heating the PCM in a hot water
heater (or hot water preheater) is with the hot compressor effluent
of a vapor-compression air conditioner or heat pump. In the
vapor-compression cycle, the compressor exit is the hottest
temperature reached by the working fluid in the cycle. This highest
temperature is best utilized to heat water exiting a flow-through
hot water heater. FIG. 12 shows a hot water heater using
containerized PCM, a counter/cross flow of the refrigerant through
the system, and a packing element that enhances heat transfer. FIG.
13 shows a more-conventional arrangement in a tube-and-shell
configuration. The end cap section of the shell 61 of the
embodiment of FIG. 13 directs water flow to and through the pipes
62. On the shell side of the pipes, a refrigerant tube 63 coils
around the bundle of tubes. The shell side of the tubes is divided
into multiple sections along the longitudinal direction by
shell-side dividers 64. PCM chemicals are static in the shell side
cavity 65 with lower-melting PCM chemicals on the water entrance
side and higher-melting PCM chemicals on the water exit side. The
water in the tubes joins at the exit-side cap 66 to exit at a hot
temperature suitable for use as hot water or suitable for heating
to higher temperatures. Lower-temperature PCM chemicals typically
have latent heat storage between about 20 and 40.degree. C.
Higher-temperature PCM chemicals typically have latent heat storage
between about 60 and 110.degree. C.
[0101] Methods known in the art to avoid pinch-point-related heat
transfer limitations may be used to maximize the utilization of
available heat and minimize the creation of entropy. The entering
refrigerant tubing 63 preferable comes directly from the compressor
and proceeds in a countercurrent coiling configuration to exit the
hot water heater at the water entrance side. The advantage of this
heat pump configuration is that it stores the hottest temperature
of the vapor-compression cycle for use to heat water and allows the
water consumption and heat pump operation to be largely
independent. However, it would be advantageous to operate the heat
pump and charge the hot water heater on an as-needed basis. Using
the heat pump or air conditioner to provide hot water can reduce
the electrical consumption by about 50% to 80% as compared to
electrical hot water heating. The highest energy savings are
reached during the summer when the heat pump under this
configuration takes heat from the house air and puts that heat into
the water--thus providing both air conditioning and hot-water
heating.
[0102] Hanging Laminated Pouch Embodiments
[0103] An alternative configuration to the PCM container 1 of FIG.
11 is illustrated in FIG. 14. The PCM container of FIG. 14 consists
of at least two sheets 41 that are laminated to create sealed
pouches 42 containing PCM chemical. The sheets could be any of a
range of materials used to contain liquids including but not
limited to such materials as flexible plastics, rubbers, or
aluminum. Plastics such as polyethylene or PET would work well as
would aluminum foil coated with a puncture-resistant plastic.
Laminating to create and seal the pouches 42 can be performed by a
number of methods known in the science, including but not limited
to the use of an adhesive or heating of thermoplastic sheets to
create a bond. These laminates are preferably prepared to create
multiple pouches in one sheet such as that illustrated by FIG.
14.
[0104] If the envelope-like pouches created by flexible sheets were
laid on-upon-the-other, the bottom pouches would be under
considerable pressure and related stresses. In addition, air would
not readily flow between pouches. To overcome these problems, the
embodiment of FIG. 15 places the laminated pouch array in a vessel
43. The load-supporting bar 45 is placed on the top end of the
laminated pouch array and this load-supporting bar is supported 44
by the vessel 43 such that air is directed and flows about evenly
between the multiple laminated pouch arrays in the vessel 43. This
configuration allows each laminated pouch array to be supported
without its weight adding to the stresses on other laminated pouch
arrays and creates longitudinal air flow pattern that takes air
across the entire laminated pouch array and is referred to as the
"Hanging Laminated Pouch Configuration". The pouches 42 of PCM are
supported by a tensile load on the sheets rather than compressive
loads of stacked sheets--the needed tensile strength is much less
expensive to design into devices. In the hanging position, the
vertical dimensions of the pouches preferably do not exceed three
feet, more preferably do not exceed one and a half feet, and most
preferably are between two and fifteen inches. The longer vertical
dimensions of the pouches 42 are to be avoided because the increase
the pressure of the fluids at the bottom of the pouches and cause
bulging. The pouches 42 are preferably arranged to create an even
air flow distribution over all pouches. The configuration of FIG.
15 is an alternative to more-costly tube-and-shell configurations
and sphere or cylinder encapsulations that are used to store PCM
chemicals and provide contact with air for thermal energy
storage.
[0105] Although the Hanging Laminated Pouch Configuration of FIG.
15 illustrates air entering at the top and exiting at the bottom of
the vessel 43, the embodiments of the Hanging Laminated Pouch
Configuration are not limited to an particular direction of air
flow or location of air entrances and exits to the vessel 43.
[0106] In the configuration of FIG. 15, cold air is introduced into
the vessel 43 to charge (freeze) the PCM chemical and warmer air is
passed through the vessel to use the stored coolness (charge).
Alternatively, refrigerant tubing can be passed through the vessel
and placed in direct contact with the PCM pouches. Preferably, a
3-way heat exchange is established such as that illustrated by
FIGS. 1 and 2. FIG. 16 illustrates an embodiment where refrigerant
tubes 46 are placed next to the laminated pouch array. A packing
sheet 47 is then placed next to the refrigerant tubes 46. The
packing material 47 serves substantially the same purpose and is
substantially the same as the heat transfer enhancer 3 of FIG. 11.
The packing sheet 47 can be any of a variety of materials that
allows air to freely flow through the packing material while
providing resistance to compression (compression that would choke
air flow between the PCM containers). In addition, the preferred
packing material enhances heat transfer by creating turbulence in
the air flow and by conducting heat from air to the tubing 46 or
laminate 41. A mesh of aluminum wool is a suitable packing sheet 47
while other materials that are less likely to puncture the laminate
41 are preferred. FIGS. 16 and 17 show the expanded front and side
views illustrating the preferred arrangement of laminate 41, tubing
46, and packing 47.
[0107] FIG. 18 illustrates how multiple laminated pouch arrays,
tubing 46, and packing 47 are hung in a vessel 48 to provide
contact between the tubing 46 and laminate 41 where the packing 47
keeps the tubing and laminates in close contact while allowing air
flow. In this configuration, the refrigerant tubing 46 is networked
by methods known in the design of evaporators and condensers for
heat pumps--this includes at least one refrigerant tube entrance
into the vessel 48 and at least one refrigerant tube exit from the
vessel. The embodiment of FIGS. 18 and 19 may be used as either the
evaporator or condenser of a heat pump and may be used for either
heat exchange with inside air or outside air in these
capacities.
[0108] When used with inside air, longer air contact paths/times
are preferred as compared to uses with outside air. This is because
the goal of heat exchange with inside air is to change the air
temperature--typically by more than 10.degree. F. and preferably
more than 15.degree. F. When used with inside air, air is
preferably directed along the entire longitudinal length of the
laminated pouch arrays.
[0109] When used with outside air, the purpose is not to change the
outside air temperature, but rather to change the refrigerant
temperature; therefore, higher air throughputs are pursued with
shorter laminate 41 contact times/paths. FIGS. 18 and 19a show the
preferred configuration for creating shorter contact times with the
air. In this configuration, a plate 49 prevents the air from
entering at the top of the laminated pouch array and directs the
air to the sides of the array. Air enters the sides and exits down
the middle of laminated pouch array and out the bottom. Since air
will tend to follow the path of least resistance, packing 50 is
placed at locations along the laminated pouch array that are not
naturally filled by the packing sheet 7. This packing 50 may be any
of a number of materials capable of filling empty spaces and
thereby significantly increasing the resistance to air flow to
locations where air flow is not desired such as an PCM-void
location on the laminated pouch array. In addition, plates/dividers
51 are placed at the bottom of the vessel in a manner that allows
flow out the middle of the laminated pouch arrays but not along the
perimeter at the bottom of the laminated pouch arrays. The
preferred means of sealing between the hanging laminated pouch
arrays and the lower divider 51 is with packing that fills in void
spaces.
[0110] The vessel of FIG. 16 containing the PCM chemical without
refrigerant tubing is useful to provide air conditioning at
locations where evaporative coolers provide marginal performance.
In these locations, the cooler nighttime air can be evaporatively
cooled and used to freeze the PCM chemical during the night by
directing the evaporatively-cooled air through the PCM vessel
during the night. During the day, building air can be circulated
through the PCM vessel to chill the air. The embodiment of FIG. 16
is also effective for peak load shifting.
[0111] Pouch Defined Air Flow Embodiment
[0112] The preferred hanging laminated pouch configuration is
illustrated in FIG. 19b. The sealed pouches 42 containing PCM serve
two purposes: 1) they contain the PCM chemical, and 2) their
arrangement assists in directly air flow in the desired pattern.
Typically, the desired air flow pattern is one of equal
distribution of air flow over all of the PCM materials. In the
embodiment of FIG. 19b, an absence of pouches 42 at the top and
sides of the container provides for air access throughout the
length of the hanging pouch. As air progresses down the sides of
the hanging pouch, a lower cross sectional area is encountered and
air the path of least resistance is for an even flow of air over
the pouches 42 toward the inside of the hanging laminated pouch
configuration. A progressively larger section in the downward
direction along the middle section of the configuration further
facilitates the cumulative path of least resistance to air being
one of equal distribution over the pouches 42. Multiple
configurations are possible, all based on locating pouches 42 on
the sheet 41 in a manner that provides even air flow across the
pouches.
[0113] This hanging laminated pouch configuration is a means for
encapsulating a PCM chemical in a configuration for exchanging heat
between air and the PCM chemical, wherein the PCM chemical is
encapsulated by two sheets wherein the two sheets are laminated to
seal the PCM chemical between the two sheets. In practice, the
laminated sheets contain multiple pouches of PCM chemical and
multiple laminated sheets are fastened in a container to hang
vertically from a support at the top of the top of the laminated
sheets. The vessel has an entrance and exit for air flow.
[0114] Desiccant Embodiments
[0115] To further enhance the cooling ability, desiccants can be
used to remove moisture from the air. In this moisture removal
process, the air and desiccant heat in response to the heat of
adsorption of the water. Cooling of the warm air with PCM is
preferred since this PCM can store the coolness of night. Depending
upon the specifics of the application, this dehumidification and
cooling will be sufficient to provide the needed building air
conditioning. To provide further cooling, the cool air can be
evaporatively cooled as illustrated by FIG. 20a. If evaporative
cooling alone is insufficient, the final cooling can be provided by
a conventional air conditioner as illustrated by FIG. 20b.
[0116] In this configuration, the desiccant must be periodically
dried. The preferred means for drying the desiccant is with the
heat of the condenser coils of the air conditioner where the coils
are in the same vessel as the desiccant and outside air is
circulated through the desiccant container during the drying.
Alternatively, solar heat can be directed to the desiccant
container during drying. The preferred means to cool the desiccant
after drying is to circulate air between the PCM vessel and the
desiccant vessel until the desiccant is chilled to about 4.degree.
F.-10.degree. F. of the PCM vessel temperature. In this operation,
the PCM vessel may be cooled/charged twice--preferably during the
night. One time to provide cooling for the desiccant and the second
time to cool air after it flows from the desiccant and prior to
release to the house. Air circulation to provide these cooling and
drying options are known in the art.
[0117] Preferred Smart Fan Embodiments
[0118] The utility of the smart fan operation described herein is
not limited to use with phase change materials nor is it limited to
use with outside evaporators. For the smart fan mode of operation
to provide benefit, the outside unit (either outside evaporator for
heat pump heating or outside condenser for heat pump cooling) must
have a heat capacity sufficiently large to provide the needed
thermal energy to moderate temperatures changes in the outside
unit.
[0119] The benefit of smart fan operation is that the smart fan in
combination with a high heat capacity in the outside unit reduces
the extremes in temperature (moderates temperature changes) of the
outside unit. For air conditioning, the outside unit (condenser)
does not get as hot, and therefore, the coefficient of performance
of the air conditioner (heat pump) is increased. For heating, the
outside unit (evaporator) does not get as cold, and therefore, the
heat pump efficiency is increased. It should be noted that in the
limit of the heat pump operating continuously for times of about
one half hour or more at a time (undersized unit), the benefits of
the smart fan diminish. However, there are always times of the year
where even an undersized heat pump unit does not operate
continuously for more than one half hour at a time.
[0120] The necessary components of a smart fan are 1) a
sufficiently high heat capacity built into the coil system of the
outside unit, and 2) a control strategy operating the fan based on
measured or anticipated temperatures (coil temperature and outside
temperature).
[0121] A sufficient heat capacity can be built into the coil system
of the outside unit by a number of methods known in the art. Use of
thicker working fluid tubing increases the heat capacity. Use of
phase change materials per the other embodiments of this invention
increases the heat capacity. Placement of the coil tube inside a
larger tube filled with a fluid increases the heat capacity.
Contacting the fins that surround the coil directly with an object
having the necessary heat capacity will increase the heat capacity.
Placement of the coil tube inside a plastic sheath filled with a
fluid increases the heat capacity.
[0122] A control strategy for operating the fan (hence the name
"Smart Fan") can be based on measured temperatures, an algorithm
based on anticipated temperatures, or any combination of these.
Control strategies based on measured temperatures would operate the
fan: 1) preferably at any time the average temperature of the
outside evaporator coil is more than about 3.degree. F. cooler than
the outside temperature, 2) preferably at any time the average
temperature of the outside condenser coil is more than about
3.degree. F. warmer than the outside temperature, 3) more
preferably at any time the average temperature of the outside
evaporator coil is more than about 1.degree. F. cooler than the
outside temperature, and 4) preferably at any time the average
temperature of the outside condenser coil is more than about
1.degree. F. warmer than the outside temperature. Here, the
1.degree. F. and 3.degree. F. are referred to as targeted approach
temperatures. Statistically, the times necessary to reach these
temperature constraints can be correlated with the temperature
constraints. The times would be the times allowed after the heat
pump's compressor is turned off. Thus methods known in the science
can be used to developed control strategies based on these
estimated times rather than measured temperatures. The times will
be specific to the heat pump (or air conditioner) models.
[0123] In a fundamental sense, control strategies based on measured
temperatures are substantially independent of the said heat
capacities while control strategies based on times are dependent
both on the said heat capacities and the targeted approach
temperatures. The temperature-based control strategy is preferred
for embodiments of this invention based on phase change materials
designed to store sufficient heat to allow operation without
outside fan operation during night time heating.
[0124] For alternative embodiments that use a Smart Fan and energy
storage to moderate temperature changes between heat pump operating
cycles (cycles refer to times when the compressor is operating and
are typically 3 to 30 minutes), the heat capacity requirements of
the outside unit are obviously less than nighttime storage units.
The "Smart Fan Moderating System" is based on recharging the heat
capacity between the typical 3 to 30 minute compressor operation
times. The "24-hour Cycle PCM Embodiments" are based on recharging
the heat capacity (preferably a containerized PCM chemical) on
24-hour cycles.
[0125] The amount of PCM chemical and corresponding heat storage
capacity for a 24-hour Cycle PCM Embodiment is about what is
required to provide heat for a typical winter night. This quantity
is thus substantially dependent upon where the heat pump is being
used geographically. More preferably, the optimal thermal
characteristics and amount of PCM chemical in a 24-hour Cycle PCM
Embodiment is based on averaged calculations dependent upon
geographic location, cost of PCM chemical, and cost of
electricity--these economic optimizations can be performed by
methods known in the science.
[0126] The optimal amount of heat capacity in a Smart Fan
Moderating System is preferably sufficient to provide 2 to 30
minutes of heat pump operation resulting in an outside average coil
temperature change of less than 10.degree. F. (absolute) without
the outside fan operating. In a heating mode this translates to the
average temperature of the coil being no more than 10.degree. F.
cooler than the average temperature of the coil prior to starting
the heat pump. In a cooling mode this translates to the average
temperature of the coil being no more than 10.degree. F. warmer
than the average temperature of the coil prior to starting the heat
pump. More preferably, the optimal amount of heat capacity in a
Smart Fan Moderating System is sufficient to provide 5 to 20
minutes of heat pump operation resulting in an outside average coil
temperature change of less than 10.degree. F. (absolute) without
the outside fan operating.
[0127] In the Smart Fan Moderating System, the fan may be switched
off when the approach temperature is reached. Alternatively, the
fan may be turned off when a time, previously correlated with
approach temperature, is reached after the compressor has switched
off. In the approach temperature mode, the fan is preferably turned
on based when the approach temperature is exceeded shortly after
the compressor is switched on. In the time mode of operation, the
fan is preferably automatically switched on when the compressor is
switched on.
[0128] This Smart Fan Moderating system is a method of operating
the fan of the outside unit of a heat pump. To work well, the
working fluid conduit of the outside unit must be in contact with
mass of material where the primary purpose of the mass of material
is to absorb and release heat thereby moderating temperature
fluctuations. To a first approximation, the heat capacity of the
said mass of material should be at least five times greater than
the copper tubing in the outside component of a typical house heat
pump. A typical house heat pump contains about 200 feet of copper
tubing with a mass near 17 kg. Five times the heat capacity of this
copper tubing is approximately 30 kJ/.degree. C.; therefore, the
said mass of material should have a heat capacity of at least 30
kJ/.degree. C., and preferably of a mass identified by temperature
rise criteria without fan operation as previously described.
[0129] Most Preferred Embodiment
[0130] The most preferred embodiment of this invention utilizes the
hanging bag configuration of FIG. 18 in the evaporator housing
illustrated in FIG. 9 with heat flow controlled by the Smart Fan
method. The general concepts and design of the evaporator and
condenser units described herein may be incorporated into the
outside or inside evaporator/condenser of a heat pump (or air
conditioner system). When used inside the house for exchange with
internal air, the preferred melting temperatures for the PCM for
air conditioning are between 50.degree. F. and 75.degree. F. When
used inside the house for exchange with internal air, the preferred
melting temperatures for the PCM for air heat pump heating are
between 75.degree. F. and 105.degree. F.
[0131] My previous patent, Ser. No. 09/945,682, which is hereby
incorporated by reference to the same extent as if fully set forth
herein, discloses a method for producing a composition of fatty
acid derivatives for use as phase change material (PCM) chemicals
and a method of using PCM chemicals. The value of the production
method lies in the ability of a simple process to provide high
conversions of feed stocks to useful PCM chemicals. The thermal
storage ability of these chemicals can be used to both eliminate
the need for air conditioning and to shift air conditioning load to
non-peak-demand times.
[0132] Method of Manufacturing PCM Chemicals from Triglyceride Feed
stocks
[0133] FIG. 21 illustrates a preferred method for manufacturing a
triglyceride-based PCM chemical. The process consists of mixing a
triglyceride that largely solidifies above the temperature of PCM
chemical use with a triglyceride that largely solidifies below the
temperature of PCM chemical use. After mixing, the mixture is
heated to a temperature suitable for transesterification reaction.
Subsequent to transesterification, the mixture is cooled and that
solid fraction with a suitable melting point temperature is
separated as product with the remaining triglyceride returned to
the feed for mixing and further reaction. For purposes of
terminology in this invention, a triglyceride is a fatty acid
glyceride. Solvents improve separation. The solvent is preferably
largely recycled internally with makeup solvent added as
needed.
[0134] Solvents are preferably more volatile than the PCM product.
The solvent does not react with the other reactants as compared to
a co-reactant that can both react and serve many of the same
purposes as a solvent. Common solvents include but are not limited
to acetone, volatile ethers, and volatile hydrocarbons. The solvent
is preferably removed from the final product by flashing the
more-volatile solvent from the product.
[0135] To provide high yields of product, the reaction occurring in
the reactor of FIG. 21 as well as the reactor of FIG. 22 must be a
reversible reaction whereby a reversible reaction is defined as
having an equilibrium constant between 0.02 and 50 for reactions
where the liquid concentrations in the equilibrium constant cancel
to produce a dimensionless equilibrium constant. For reactions
where concentrations do not cancel in the equilibrium constant, the
reaction is determined to be reversible if, when reactants are
reacted in stoichiometric amounts relative to the desired product,
the ratio of initial reactant concentration to reaction after the
mixture has reacted to equilibrium is between 0.02 and 50. The
embodiments of this invention are not limited to specific feed
streams to the process. Rather, the embodiments of this invention
include a process for the production of phase change material (PCM)
chemicals wherein a reactant is reacted in a reaction mixture to
yield a PCM chemical, the improvement which comprises the steps of
carrying out said reaction in a reactor generating a reactor output
stream, cooling said reactor output stream generating a stream
containing solid reactor product suspended in liquid reactor
product, separating the solid product from the liquid product
generating a concentrated solid product and a mostly liquid
product, recirculating either the concentrated solid product or the
mostly liquid product as a feed to the reactor, and reacting of the
recirculated chemical in a reversible reaction.
[0136] While the solid-liquid separation processes of FIGS. 21 and
22 are preferred to vapor-liquid separation processes, the
embodiments of this invention can be practiced with vapor-liquid
separation processes in place of the solid-liquid separation
processes of FIGS. 21 and 22.
[0137] In the configuration of FIG. 21 the recycled liquid freezes
at a lower-than-desired temperature (on a solvent-free basis) and
has a relatively high concentration of unsaturated fatty acids
derivatives. An oil/fat having a lower unsaturated fatty acid
content is added prior to interesterification reaction in an amount
of 0.01 to 1.0 times the mass of the recycled fatty acid
derivatives and preferably between 0.05 and 0.2. The low
concentration of saturated fatty acids substantially limits the
amount of high-freezing-point derivatives that are formed with very
high yields of the preferred-freezing-point derivatives being
formed and frozen out of solution.
[0138] Alternative to a solvent that is largely soluble with the
PCM product, an anti-solvent that is substantially not soluble with
the feed stock may be used. In addition to reducing viscosity, the
solvent serves the purpose of displacing liquid fat/oil derivatives
from solid fat/oil derivatives during solid-liquid separation
processes.
[0139] Optionally, a solid-liquid separation may be performed prior
to the solid-liquid process that produces product (see FIG. 22);
this optional solid-liquid separation process is useful for
reaction products in which a fraction of the products melts above
the targeted PCM application temperature. Counter-current heat
exchange is preferred but optional and applicable by methods known
in the science.
[0140] Feed stocks other than triglycerides provide an alternative
embodiment and additional degrees of freedom to control melting
point temperatures of the transesterification products. When feed
stocks in addition to triglycerides are used, the process consists
of mixing a triglyceride derivative that largely solidifies above
the application temperature with a triglyceride derivative that
largely solidified below room temperature. After mixing, the
mixture is heated to a temperature suitable for reversible
reaction. Subsequent to reaction, the mixture is cooled and that
solid fraction with a suitable melting point temperature is
separated as product with the remaining product returned to the
feed for mixing and further reaction. Solvent technology would
facilitate separation.
[0141] During the reaction processes of FIGS. 21 and 22,
irreversible reactions may parallel the reversible reactions.
Provided these irreversible reactions are slow relative to the
reversible reactions, the irreversible reactions can enhance
product quality and/or product yields. Here, slow is defined as
having a reactive triglyceride half-life less than 20% of the
dominant reversible reactions.
[0142] The reactions of FIGS. 21 and 22 are not limited to
particular catalysts or temperatures. Heterogeneous catalysts are
preferred. When homogeneous catalysts are used, a separation
process needs to be performed to remove the homogeneous catalyst
from the product. Typically the reaction temperatures will be
between 25 and 325.degree. C. The pressure of the reaction may be a
function of temperature and can be optimized by methods known in
design to maintain a liquid phase. Catalysts and reactions known in
the science may be used including but not limited to catalysts
promoting transesterification, alcoholysis, inter-esterification,
hydrogenation, cis-trans isomerization, and other chemistry of
ester bonds including nitrogen, phosphorous, sulfur, and group 1a
metal derivatives. Preferred feed stocks include animal fat,
soybean oil, palm oil, animal greases, and used cooking oils since
these are the most abundant and least costly of fat and oil feed
stocks. For example, a preferred feed stock is 60% to 90% (by mass)
beef tallow and 10% to 40% soybean oil reacted in a
transesterification reaction over 10-20 mesh calcium carbonate
catalyst in a packed-bed reactor operated at a temperature between
200 and 280.degree. C. For the process of FIG. 22, the feed stock
stream labeled "other" is any chemical that reversibly reacts with
the fatty acids of the triglyceride feeds. Examples include
methanol, ethanol and diethylene glycol but are not limited to
alcohols.
[0143] The fractionation processes may be solid-liquid separation
processes or vapor-liquid separation processes. Preferably,
solid-liquid separation is used. For any given product, the choice
of solvent can impact the temperature at which separation is
performed. Typically, the solid-liquid separation processes are
conducted at temperatures between 10.degree. C. and 35.degree.
C.
[0144] The natural fats and oils may be fed to the processes of
FIG. 21 or 22 after the reaction or prior to the reaction. If the
naturally occurring fat/oil has a higher fraction of product having
the desired latent heat properties as compared to the natural
fat/oil after reaction, the natural fat/oil is preferably fed to
the process after the reaction.
[0145] The process of FIG. 21 can be used to produce a variety of
fats and acids with an emphasis on ester bond chemistry. The
preferred PCM chemicals of this process are comprised mostly of
triglycerides since these triglycerides provide the largest variety
of chemical species with the largest number of chemical species
falling within the targeted PCM chemical temperature range.
[0146] For use in building climate control, compositions of these
chemicals are preferably >50% triglycerides with >10% but
<50% of the fatty acid content of said triglycerides being
saturated fatty acids. More preferably, >70% triglycerides with
>20% but <40% of the fatty acid content of said triglycerides
being saturated fatty acids.
[0147] For triglycerides or esters terminating in alkyl groups,
emulsions can be formed with water. The formation of stable
emulsions with water can be used in PCM device applications were
fire-retardant materials are desired.
[0148] Preferred Method of Using Charged PCM Chemicals
[0149] PCM chemicals are considered charged when they are frozen,
if the intended use is to cool the contents of a house, and when
they are unfrozen, when the intended use is to heat a house. The
preferred method of using the PCM chemicals is to charge the
chemical and consume the charge in 24-hour cycles. The preferred
form of the PCM chemical is in an isolated form where heat
transfers through the isolating surface to air. This surface
prevents odors, oxidation, and biological growth in the PCM
chemical.
[0150] For air-cooling operations the preferred method comprises
having air contact the encapsulated PCM chemicals prior to
contacting the evaporator coils of an air conditioning system by
locating the evaporator coils downstream from the PCM device. The
evaporator coils of the air conditioning system are only operated
when additional cooling is needed beyond that supplied by the PCM
chemicals. The preferred method to determine if additional cooling
is need by the coils is to use a two-temperature control
system--one temperature higher than the other. When inside air
temperature rises above the lower temperature set point, inside air
flow is directed next to the encapsulated PCM chemicals with the
evaporator coils not operational. When the inside air temperature
rises above the higher set point temperature, the evaporator coils
are activated to provide additional cooling.
[0151] For heating operations the preferred method comprises having
air contact the encapsulated PCM chemicals prior to contacting the
auxiliary heating means. Auxiliary heating means include but are
not limited to heat pumps and furnaces. The auxiliary heating means
is only operated when additional heating is needed. The preferred
method to determine if additional heating is need by the coils is
to use a two-temperature control system--one temperature higher
than the other. When inside air temperature falls below the higher
temperature set point, inside air flow is directed next to the
encapsulated PCM chemicals with the auxiliary heating means not
operational. When the inside air temperature falls below the lower
set point temperature, the auxiliary heating means is activated to
provide additional heating.
[0152] One skilled in the art could readily set up the control
system described in the previous two paragraphs, therefore that
operation is not described in detail.
[0153] Preferred Method of Charging PCM Chemicals
[0154] PCM chemicals are charged during the night when the PCM
chemicals are used to provide cooling. The chemicals are charged
during the day when providing heating.
[0155] For typical building cooling applications, two sources are
available to directly or indirectly charge PCM chemicals: (1) use
of outside air or (2) use of a chiller (normally a
vapor-compression air conditioner). When the outside air has a
wet-bulb temperature that is less than approximately 5.degree. F.
lower than the desired indoor air temperature, the use of outside
air is preferred to use of a chiller. Preferably, the outside air
is contacted with water to cool the air to its wet-bulb
temperature. Unlike direct use of evaporative cooling in a
building, when cooling PCM devices, maximum cooling of ambient air
is preferably achieved by cooling the outside air to 100% relative
humidity (i.e. the wet-bulb temperature of the ambient air). When
outside air cannot be sufficiently cooled, evaporatively cooled air
is further cooled with a chiller prior to use in cooling the PCM
devices. When the wet-bulb temperature of the outside air is warmer
than about 5.degree. F. less than the set point temperature in the
building, the chiller is preferably used without supplemental
cooling from evaporatively cooled outside air.
[0156] For this method of recharging the encapsulated PCM chemical
used to cool a building, water that accumulated in the system is
drained from the system, contacting of the said air with water is
terminated by terminating the water supply for at least 8
consecutive hours for each 24 hours of system utilization, and all
surfaces contacted by the said air are present without water on the
said surfaces for at least 6 consecutive hours for each 24 hours of
system utilization.
[0157] Preferred Method and Embodiment for Using PCM Chemicals
[0158] The preferred method and embodiment for using PCMs in
moderating climates in a building consists of an apparatus with the
following features:
[0159] 1. A device containing PCM chemical with at least one
surface over which air can travel with a heat flux through the
surface to or from the PCM chemical;
[0160] 2. A means of connecting the said device with air external
to the building;
[0161] 3. A fan or other means for conveying air from outside the
building, across the said surface to charge the PCM chemicals, and
then back to outside the building;
[0162] 4. A control means that uses external air temperature or
time of day to start and stop flow of air across the PCM; and
[0163] 5. A surface and air-flow means through which heat is
transferred from air inside the building to the PCM chemical to
provide cooling for the building, or alternatively, through which
heat is transferred from the PCM chemical to the air inside the
building to provide heating.
[0164] The surface that separates the PCM chemical from air
preferably totally encapsulates the PCM chemical, said surface
preferably being a plastic or metal. The encapsulated PCM devices
are preferably contained in a tank through which air flows therein
contacting the outside surfaces of the PCM devices. In the
preferred embodiment the means of connecting the said tank with air
external to the building is an air duct.
[0165] In the preferred embodiment operated in an air conditioning
mode, the first step (charging step) of the method of operation
includes directing air from outside the building through a first
duct to the PCM device then over the PCM heat exchange surface(s)
and then through a second duct and back outside the building. The
location of the said fan or other means for conveying air is
preferably next to or in one of the ducts. This first step is
preferably performed at night when the external temperature is
below the temperature at which the PCM chemical undergoes a phase
transition. The temperature for the latent heat transformation is
preferably between 50.degree. F. and 100.degree. F. For summer
cooling, said temperatures are more preferably between 65.degree.
F. and 75.degree. F. and most preferably between 68.degree. F. and
73.degree. F. A second step of the method of operation includes
directing air from inside the building through a duct to the PCM
device then over the PCM heat exchange surface(s) and then through
a different duct and back inside the building. Optionally, an
auxiliary cooling means is located downstream of the PCM device.
This second step is preferably performed when the temperature of
air in the building is above the temperature at which the PCM
undergoes a process through which it absorbs a significant latent
heat.
[0166] The use of evaporative cooling during the night and not
during the day has the distinct advantage of allowing the equipment
to undergo a drying cycle during the day. This drying cycle will
substantially prevent fungal and other growth on the equipment.
When possible, the equipment undergoing drying is preferably placed
in direct sunlight to facilitate drying and to allow radiation to
also inhibit fungal growth. Methods of water introduction are known
and practiced in the science and art of water coolers (also called
evaporative coolers or swamp coolers).
[0167] For air conditioning, preferably at least part of the
air-flow patterns includes the first step during the cooler
nighttime hours and the second step during the warmer daytime
hours. Wet-bulb temperatures are lower at nighttime and provide a
better driving force for cooling the house. The system that uses
the coolest web-bulb temperatures within a 24 hour period to chill
the PCM chemicals is referred to as the "PCM-LW24" system.
[0168] Optionally, during the cooler nighttime hours, evaporatively
cooled external air can be used to freeze the PCM chemical during
the night followed by using the PCM to chill external air that is
not evaporatively cooled and is subsequently put inside the
building. To prevent accumulation of air in the building, a means
is needed to vent warmer air from inside the building as it is
displaced by cooled air being conveyed into the building.
[0169] For heating during the winter, the preferred embodiment has
a third step of the method of operation directing air from outside
the building through a first duct to the PCM device then over the
PCM heat exchange surface(s) and then through a second duct and
back outside the building. This first step preferably performed
during the day when the external temperature is above the
temperature at which the PCM undergoes a process through which it
releases a significant latent heat. The temperature for the latent
heat transformation is preferably between 60.degree. F. and
100.degree. F., more preferably between 75.degree. F. and
85.degree. F. and most preferably between 77.degree. F. and
83.degree. F. A fourth step of the method of operation includes
directing air from inside the building through a duct to the PCM
device then over the PCM heat exchange surface(s) and then through
a different duct and back inside the building. This fourth step is
preferably performed when the temperature of air in the building is
below the temperature at which the PCM undergoes a phase
transition.
[0170] When used in combination with a heat pump (for heating the
building), the PCM provides a higher temperature heat sink than is
possible during the nighttime. In this embodiment, heat is removed
from the PCM chemical during the nighttime and pumped into the
house. Alternatively, heat can be taken from outside air during the
day with a heat pump and stored in a higher-temperature PCM.
[0171] Maintenance costs associated with organism growth on the
contact elements of evaporative coolers can be substantial. To
reduce or eliminate these costs, the preferred method of using
evaporative coolers with PCM devices is to keep the evaporative
coolers dry and warm during substantial parts of the day. Warm is
preferably >80 F therein inhibiting bacterial growth--such modes
of operation can diminish performance of evaporative coolers used
in conventional applications but do not diminish performances of
the embodiments of this invention. To further inhibit growth of
organisms, the evaporative cooler is preferable directly exposed to
sunlight and respective ultra-violet radiation with designs
configured to maximize the effectiveness of this exposure to
minimize organism growth.
[0172] The preferred means for evaporatively cooling the air is to
spray a fine mist of water into the air followed by flow through a
demisting pad. After the demisting pad, the water that does not
evaporate accumulates and leaves by a water drain. The system is
designed to allow no water to accumulate and for the system to be
entirely dried each 24 hour cycle with the exception of water
located at least six inches down the drain pipe.
[0173] Combinations with Air Cycle
[0174] As an alternative to the conventional vapor-compression
chiller to enhance cooling, an open air-cycle refrigerator is
well-suited to supplement cooling for PCM devices. When wet-bulb
temperatures are too high and/or moisture should be removed from
interior air to meet comfort standards, the PCM-LW24 system needs
to be enhanced with an auxiliary air conditioning system. One
embodiment of this invention uses an air cycle to enhance the
capabilities of the PCM-LW24 system. The air cycle is used to
either; chill nighttime air to lower temperatures and assist
cooling of the PCM or, alternatively, the air cycle is used to
lower the temperature of the air by expansion after the air
contacts PCM device during daytime cooling of interior air.
[0175] The preferred air cycle (also referred to as reverse Brayton
cycle) includes an embodiment that can route/duct air differently,
depending upon the purpose of the interaction between the air cycle
and the PCM-LW24 system. To assist nighttime air in cooling the
PCM, the following procedure is preferred: (1) outside air is
routed to an expander that expands air to a lower pressure with
associated cooling, (2) the expanded air is routed to and contacts
the PCM devices, (3) after cooling the PCM devices, the warmed air
is routed to a compressor that compresses the air to ambient
pressure, and (4) the ambient pressure air is released to the
outside. The expansion work is used to power the compressor. This
method has utility for cooling the PCM chemicals when the outside
nighttime air is too warm to perform this otherwise.
[0176] Preferred pressure ratios for expansion are 0.98 to 0.7 and
most preferably between 0.98 and 0.85. Preferably, the pressure
ratio of the reverse Brayton cycle is variable with preferred
pressure ratios identified to optimize overall coefficients of
performance. The preferred PCM devices are encapsulated PCM placed
in a vessel that can handle the low pressures. The size of the
encapsulated PCM devices can be identified by methods known in the
art.
[0177] The reverse Brayton cycle operated in this method where the
air is at less than atmospheric pressure when contacting the PCM
device has a non-obvious advantage in that all the cooling provided
by expansion results in additional cooling. In the conventional
reverse Brayton cycle, some of the cooling is lost as the driving
force temperature difference needed for heat transfer. This
advantage substantially increases the efficiency of this cycle.
[0178] Preferably the same compressors and expanders are also
capable of moving air for circulation, for chilling the PCM, and
for chilling air beyond the capabilities of the PCM.
[0179] To assist the cooling capabilities of the PCM during the
daytime, the following procedure is preferred: (1) inside air is
routed to the compressor that compresses air to a higher pressure
with associated warming, (2) the compressed air is routed to and
contacts the PCM devices, (3) after the air is cooled by the PCM
devices, the cooled air is routed to the expander that expands the
air to ambient pressure with associated further chilling, and (4)
the ambient pressure air is released to the outside. Preferably the
expansion work is used, in part, to power the compressor. This
method has utility for cooling the inside air when additional
cooling is needed than can be required by the PCM devices. Methods
known in the art will allow condensed water to be removed from the
PCM devices.
[0180] The preferred configuration for the reverse Brayton cycle
heating and cooling consists of 1) a PCM surface heat exchange
area, 2) a large expander, 3) a large compressor connect to the
large expander, and 4) a driving compressor powered by auxiliary
means. The heat exchange area is at a higher pressure when
providing heating and at a lower pressure when providing cooling.
The only power applied to the system for heating or cooling
purposes is to the driving compressor. The simple design of the
large expander/compressor leads to low cost and high efficiency.
The driving compressor/expander could be in parallel or series with
the large compressors/expanders and is preferably connected in
parallel.
[0181] During operation of the reverse Brayton cycle as a cooler,
outside air first enters the expander expanding to a lower
pressure. During expansion, shaft work from the expander physically
drives the compressor. The expanded air is cooled proportionally to
the shaft work transferred from the expander to the compressor. The
cooled air next contacts the PCM devices therein cooling the PCM
devices. In the preferred embodiment, most of the air is then
compressed by the large compressor to atmospheric pressure and
released. The air not compressed by the large compressor is
compressed by the driving compressor and released. To both increase
flow through the cycle and provide greater cooling, the volume of
air sent through the driving compressor is increased by increasing
the speed of the driving compressor.
[0182] During operation of the cycle as a heater, outside air first
enters the compressor compressing to a higher pressure. Shaft work
compression is provided by physical connection to the larger
expander. The compressed air is heated proportionally to the shaft
work transferred from the expander to the compressor. The heated
air next contacts the PCM devices therein heating the PCM devices.
In the preferred embodiment, the air is then expanded by the large
expander to atmospheric pressure and released. The air not
compressed by the large compressor is compressed by the driving
compressor and diverted into the containing of PCM devices. To both
increase flow through the cycle and provide greater heating, the
volume of air sent through the driving compressor is increased by
increasing the speed of the driving compressor.
[0183] Independent of the PCM chemical application, an evaporative
cooler can be used in combination with a vapor-compression air
conditioning system to provide the needed cooling. Unless humidity
levels are extremely high, evaporative coolers can be used in place
of vapor-compression cycles for much of the air conditioning needs.
Preferred methods of operation use an evaporative cooler at all
times when the cooler provides sufficient cooling. For most
locations that require vapor compression cycle air conditioners
this translates to using the vapor compression cycle with the
evaporative cooler in insufficient to meet cooling standards.
[0184] Combinations with Adsorption (or Absorption) Cycle
[0185] One embodiment of this invention uses an adsorption or
absorption system to enhance the capabilities of the PCM-LW24
system. In this embodiment, air is contacted with a material
capable of removing moisture from the air (adsorbent or absorbent).
As a result of removing moisture from the air, the temperature of
the air is increased. The warmer air is then contacted with the PCM
devices to cool the air. The air can either be directly circulated
back into the house, or water can be sprayed into the air producing
evaporative cooling to further chill the air prior to circulation
back into the house.
[0186] When used to remove moisture for air to be released into the
house, this process can be used at night or day. Methods known in
the science can be used to remove the moisture from the adsorbent
or absorbent. In some instances, the warm daytime air is sufficient
to remove the moisture from the adsorbent/absorbent. In other
instance, heat must be supplied to air that is used to regenerate
the adsorbent/absorbent. Preferably, if hot air is produced to
regenerate the adsorbent/absorbent, the hot air is used to heat
water in a hot water heater. Regeneration of adsorbent/absorbent
can be timed to coincide with needs to generate hot water in the
hot water heater.
[0187] The most preferred embodiment of this invention is the
PCM-LW24 system enhanced with adsorption (or absorption) to remove
water from air and where the heat produced during the regeneration
of adsorbent/absorbent is used to heat water in a hot water
heater.
[0188] Further Details on Method of Manufacturing PCM Chemicals
from Triglyceride Feed Stocks
[0189] A preferred method for producing phase change materials from
fats and oil is to hydrogenate the fat or oil therein converting
the bound fatty acids to a composition consisting mostly of
palmitic and stearic acids when using common tallow, lard, or
vegetable oil feed stocks. For some applications, the saturated
triglyceride is useful. For other applications, the alkyl esters of
the saturated fatty acids is useful. To produce the alkyl esters of
the saturated fatty acids, the order of reaction is not important,
either hydrogenation may be performed first or alcoholysis may be
performed first. When using catalysts like palladium, hydrogenation
and alcoholysis may be performed simultaneously in the same
reactor.
[0190] While this invention has been described fully and completely
with special emphasis upon preferred embodiments, it should be
understood that within the scope of the appended claims the
invention may be practiced otherwise than as specifically described
herein.
* * * * *