U.S. patent application number 12/017407 was filed with the patent office on 2009-07-23 for solar-powered cooling and heating system using a structured water wall.
Invention is credited to Chengjun Julian Chen.
Application Number | 20090183853 12/017407 |
Document ID | / |
Family ID | 40875514 |
Filed Date | 2009-07-23 |
United States Patent
Application |
20090183853 |
Kind Code |
A1 |
Chen; Chengjun Julian |
July 23, 2009 |
Solar-Powered Cooling and Heating System Using a Structured Water
Wall
Abstract
A solar-powered cooling and heating system comprising one or
more vertical water containers of special design as the thermal
storage device (the structured water wall), a compressor driven by
a DC motor powered directly by solar photovoltaic panel(s) for
cooling, and a south-faced window for direct solar heating. The
solar photovoltaic panel(s) is placed on an awning above the
south-facing window; the said awning is designed to allow full
sunlight in the winter but no direct sunlight in the summer through
the window. The thermal inertia of the structured water wall allows
optimum heating and cooling day and night for all seasons of a
year. It allows an automatic self-adjustment utilizing the natural
annual and diurnal cycles to achieve maximum comfort and
efficiency.
Inventors: |
Chen; Chengjun Julian;
(White Plains, NY) |
Correspondence
Address: |
Chengjun Julian Chen
19 Denim Place
White Plains
NY
10603
US
|
Family ID: |
40875514 |
Appl. No.: |
12/017407 |
Filed: |
January 22, 2008 |
Current U.S.
Class: |
165/48.2 ;
237/56; 62/467 |
Current CPC
Class: |
F24D 2220/006 20130101;
F24D 2200/123 20130101; F25B 2400/01 20130101; F24D 2200/12
20130101; Y02E 10/44 20130101; Y02B 10/20 20130101; Y02A 30/272
20180101; Y02E 10/40 20130101; F24D 2200/02 20130101; F24D 11/0264
20130101; F25B 27/005 20130101; F24D 11/0221 20130101; Y02B 30/13
20180501; F24S 20/63 20180501; F24D 11/007 20130101; F24D 2200/14
20130101; F24S 60/30 20180501; Y02B 10/70 20130101; F24D 11/003
20130101 |
Class at
Publication: |
165/48.2 ;
62/467; 237/56 |
International
Class: |
F25B 13/00 20060101
F25B013/00; F25B 27/00 20060101 F25B027/00; F25B 29/00 20060101
F25B029/00 |
Claims
1. A solar-energized cooling-and-heating system for a room in a
building comprising: a solar photovoltaic panel installed as an
awning above a south-facing window for generating electric power in
the summer; a DC motor directly driven by the electricity generated
by the solar photovoltaic panel; a vapor-compression refrigeration
unit driven by the DC motor; a structured water wall placed in the
room near a south-facing window cooled by a heat-exchange coil from
the refrigeration unit in the summer and heated by direct sunlight
through the window in the winter.
2. The system of claim 1 wherein the cooling coil of a
refrigeration unit is placed near the top of the structured water
wall.
3. The system of claim 1 wherein the structured water wall
comprises a plural of component water containers connected by
flanges and pumps.
4. The system of claim 1 wherein each component water container is
made of two identical parts preferably made of fiber-reinforced
plastics.
5. The system of claim 1 wherein the side of the structured water
wall facing the window is colored black to maximize the absorption
of sunlight for effective heating in the winter.
6. The system of claim 1 wherein the window side of the structured
water wall is covered by a shutter system made of insulating
material to allow maximum sunlight to come in the day time and to
prevent heat loss in the night.
7. The system of claim 1 wherein the heat generated by the
compressed refrigerant is dissipated to the environment air.
8. The system of claim 1 wherein the heat generated by the
compressed refrigerant is dissipated to a geothermal heat trap.
9. The system of claim 1 wherein the electrical current from the
solar panel is controlled by a switch which is turned off when the
temperature of the structured water wall is lower than a
predetermined value, for example, 17.degree. C. or 63.degree.
F.
10. The system of claim 1 wherein the insulating shutter is
controlled by a mechanism which is closed when the temperature of
the structured water wall is higher than a predetermined value, for
example, 23.degree. C. or 75.degree. F.
11. The system of claim 1 wherein a heating element is installed
through a flange near the bottom of the structured water wall, to
heat up the water wall with external electrical power in cold and
cloudy winter time.
12. The system of claim 1 wherein the structured water wall is
placed at any place in the room, and the solar photovoltaic panel
is placed in any external location to generate electricity, such
that the system is for solar-powered cooling only.
Description
BACKGROUND OF THE INVENTION
[0001] Cooling and heating of buildings, especially residential
houses, consume a huge amount of energy worldwide. Because solar
energy is directly accessible to a large percentage of the
residential houses, using solar energy to cool and heat the houses
is highly desirable. For many decades, concepts of cooling and
heating systems based on solar energy have been proposed. However,
none of those designs has been widely used.
[0002] Several combined solar cooling and heating systems have been
disclosed that comprise a solar collector, typically on the roof,
to generate hot water (or other liquid) for the storage of thermal
energy; then use the stored thermal energy for heating, or for
cooling using the heat-pump principle. For example, Worthington in
U.S. Pat. No. 4,128,124 (1978); Adcock in U.S. Pat. No. 4,129,177
(1978); Ruder in U.S. Pat. No. 4,153,104; Hiser in U.S. Pat. No.
4,173,994; Yukimachi et al. in U.S. Pat. No. 4,269,263 (1979);
Wilson in U.S. Pat. No. 4,674,476 (1987); and Tracy in U.S. Pat.
No. 5,941,238 (1999). Those systems are complicated and bulky,
having low efficiency because of thermal-storage loss and indirect
heating and cooling, requiring dedicated design for new houses
substantially different from ordinary houses, and almost impossible
to retrofit into existing houses. Those systems have not been
widely used in practice.
[0003] A simple idea for solar heating of houses has been practiced
using a thermal storage medium, as summarized in E. Marzia's "The
Passive Solar Energy Book" (Rodale Press, Emmaus, Pa. 1979); and in
D. Chiras's "The Solar House" (Chelsea Green Publishing Company,
White River Junction, VM 2002). Typically, masonry thermal storage
walls (made of adobe, bricks or concrete) are used as the thermal
storage medium. In a sunny winter day, direct sunlight is allowed
to come through windows to heat up the masonry wall. The heat
stored in the wall is then gradually released after sunset. The
temperature of the house or room can be maintained within a
comfortable range day and night. However, a masonry wall with
sufficient thermal mass is very bulky and heavy which requires a
large space and a strong foundation. Therefore, it is not widely
used.
[0004] Solar cooling has a similar thermal-storage problem. By
directly using the solar energy to drive an air-conditioning unit
for cooling the room, it does not provide a relatively constant
temperature throughout the entire day and night. Right after
sunset, when the environment is still very hot, the cooling effect
disappears. And the maximum cooling effect from direct sunlight is
at noon time, which is not the hottest time of the day (the hottest
time in a day is about 3-5 pm). This problem can be resolved by
using a thermal storage medium to store the cooling power generated
by solar energy with 4 to 8 hours of delay or inertia. Because
generally speaking, the stronger the sunlight in the day time, the
more cooling power is required, it can be self-sufficient from day
to day.
[0005] However, to store cooling power, a proper design of the
thermal storage system must be provided. Masonry walls are not
useful as a thermal storage for cooling because of the difficulty
to cool it down. It is well known that water is a much better
thermal storage medium, as shown in Table 1. To achieve the same
thermal mass, the weight of water is only one tenth of that for
brick or concrete. Moreover, water has great advantage as storage
medium of cooling because of natural convection: once a source of
cooling is accessed to the top of a water container, cooling
spreads quickly to the entire volume. Although it is well known
that water is much more advantageous even for solar heating, the
technology and design of reliable and affordable water storage
systems does not yet exist. In the field of passive solar heating,
most applications utilizing water as thermal storage medium have
been using either stacked 55-gallon drums or freestanding metal and
plastic cylinders; see the above cited books of E. Marzia and D. D.
Chiras. Those systems are cumbersome. Therefore, to date, water
storage systems for passive solar heating are not publicly
accepted. For solar cooling, to date, water as a cooling storage
medium has not been explored.
TABLE-US-00001 TABLE 1 Thermal mass per unit weight of different
materials Specific heat Density Thermal mass per unit Material
(water = 1) (water = 1) weight (water = 1) Water 1 1 1 Oak 0.57
0.742 0.768 Adobe 0.24 1.67 0.143 Brick 0.2 1.94 0.103 Concrete
0.156 2.27 0.068
BRIEF SUMMARY OF THE INVENTION
[0006] The current invention discloses a novel apparatus for
solar-powered cooling and heating, which comprises one or more
water containers of special design to form a structured water wall,
placed near a south-faced window in a room as the thermal mass for
solar cooling and heating. Using proper design parameters, it could
have a thermal inertial delay time of 4 to 8 hours. A solar
photovoltaic panel is installed on an awning above the south-faced
window. The output of the solar photovoltaic panel is connected
directly to a DC motor to drive a compressor of a vapor-compression
refrigeration unit. For the principles of vapor-compression
refrigeration, see for example W. P. Jones "Air Conditioning
Engineering" (Edward Arnold, London 1994). The heat generated by
the compressed refrigerant (for example, R22) is dissipated to the
surrounding air, and the liquefied refrigerant is then letting into
a copper coil through an expansion valve. The copper coil is
located near the top of a water container to cool down the water.
In a sunny summer day, the electricity generated by the sunlight
drives the compressor and cools the water. By natural convection,
the entire water wall is being cooled. The temperature of the water
wall reaches minimum in the late afternoon, typically 3 pm to 6 pm,
which matches the hottest time of the day. Because the structured
water wall is located in the room, it cools down the entire room.
After sunset, the temperature of the structured water wall
gradually increases. Because the environment temperature is also
decreasing, the warming up of the water wall is slowing down. The
cooling effect persists throughout the night. Such a system has a
self-adjusting effect according to the weather: The stronger the
sunlight in the day time, the more cooling is generated by the
water wall. On the other hand, sunlight could fall on the water
wall directly through the window. However, in the summer, the
sunlight is blocked by the awnings (which support the solar
photovoltaic panels) from coming directly through the window, and
the insulating shutters are closed. No heating effect is caused by
direct sunlight. In the day time of the winter, by opening the
insulating shutters, full sunlight comes through the window and
heats up the water wall. In the night, by closing the shutters, the
heat is releasing slowly to keep the room warm. In cold and cloudy
days, an auxiliary heating system is required. However, substantial
savings of the heating cost can be achieved. The said
solar-energized cooling-and-heating apparatus can be installed into
new houses of standard design, can be retrofit into existing
houses, can be decorated as a good-looking furniture (screen,
bookshelf, entertainment system, picture-displaying wall, etc.) and
can be mass-produced with low cost. The operation of the apparatus
is simple and virtually maintenance free.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows the solar cooling-and-heating system with a
structured water wall.
[0008] FIG. 2 shows the design of the water container.
[0009] FIG. 3 shows an external view of a house with the solar
cooling-and-heating system.
[0010] FIG. 4 shows the design of the vapor compression
refrigeration system driven directly by solar power through a DC
motor and directly connected to a water wall.
[0011] FIG. 5 shows the typical temperature variation of the water
wall and the environment in summer time.
[0012] FIG. 6 shows the typical temperature variation of the water
wall and the environment in winter time.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 shows a design of the apparatus in a residential
building. The wooden beams, 101, typically 2 by 10 with 12 to 18
inch spacing, support the floor 102. The external wall 103 is
insulated and with a window 104. In the room, about 1 ft from the
window, is a structured water wall 105. In this example, the
structured water wall comprises two vertical water containers. A
cooling coil 106 directs the expanding refrigerant through the
pipes 107 from the refrigerating unit 108, which is driven by a DC
motor connected through wire 109 to the solar photovoltaic panel
110, located outside the wall 103 on an awning above the window
104. The two water containers are connected from the top through a
pump 111, which is also driven by a DC motor powered by the solar
photovoltaic panel 110. An optional heating element 112 is
installed through a flange to heat up the water wall if needed.
Near the bottom of the two water containers, a flange 113 connects
them to provide water flow. The structured water wall is installed
on a base, typically made of wood, through the bolts 114. A valve
115 is connected to one of the water containers for draining the
water if necessary.
[0014] In front of the structured water wall 105, insulating
shutters 116 are installed. The shutters are preferably made of
plastic foam, about one inch thick, and covered by aluminum foil or
colored white. During the summer, the shutters are closed to become
a continuous thermal insulating panel to the water wall, to avoid
thermal loss through the window. During the day time of winter, the
shutters are opened to an angle approximately equal to the
inclination angle of the sunlight. The surface of the structured
water wall is colored black to ensure good absorption of heat.
After sunset, the shutters are closed. This can be controlled by a
timing device or a light-sensing device. The back side of the water
wall is protected by a panel 117, which is decorated as a screen in
this case. Also in the room, a bed 118 is placed nearby. The panel
117 can also be decorated as an entertainment center or a bookcase
as appropriate.
[0015] To facilitate mass production, the preferred design of the
water container comprises two identical halves, as shown in FIG. 2.
It can be made of cast aluminum or glass-fiber reinforced plastics.
It can be formed using a pair of simple moulds. To reduce weight
and manufacturing cost, the body 201 has non-uniform thickness: the
container wall is thicker near the bottom and thinner near the top.
In the middle of the container, four or more through holes 202
facilitates the use of steel bolts to reinforce the structure. At
the edges, 10 holes 203 are made for bolts. On the top of the
container, there are two small flanges 204 for interconnection
through the pump 111 or filling with water, and one large flange
205 for the cooling elements 106. Near the bottom, there are two
small flanges 209 for interconnecting the containers and for the
drainage of water. After the two halves are bonded together with
water-resistant glue and bolts, the flanges are further covered by
caps 207, 208, and 209. To ensure good absorption of sunlight in
the winter, the front side is painted black.
[0016] FIG. 3 shows the external view of the house with such an
apparatus. The solar photovoltaic panel 301 is installed as an
awning facing south on supports 303. The refrigeration unit 302
(see FIG. 4 for details) is located in a cool location. The
geometry of the awning 301 is designed such that it allows full
sunlight to enter the window 304 in the winter, 305; and prevents
any direct sunlight to enter window 304 in the summer, 306.
[0017] FIG. 4 shows the details of the vapor-compression
refrigeration system driven by solar power through a DC motor. For
a general description of the vapor-compression refrigeration
system, see W. P. Jones 1994. In FIG. 4, 401 is the wall of the
house. The refrigeration unit 402 is mounted on the external of the
house. A cable 403 leads the electric current from of the solar
photovoltaic cells to a DC motor 404. The motor drives both the
compressor 405 and the fan 406. Compressor 405 compresses the
refrigerant vapor into the condenser 407. After the heat is
released into the air by fan 406, the refrigerant is liquidized
then flows to an expansion valve 409 through pipe 408. The vapor of
the refrigerant flows through an insulated pipe 401 into the heat
exchange coil 411. Directly from the factory, the pipe 410 is
straight. During the installation of the apparatus, the pipe is let
through the hole of the wall 410 into the interior of the house.
Then the pipe is bent such that the heat exchange coil 411 reaches
the top of the water in the container through the flange 205.
[0018] The operation of the apparatus is as follows. In a sunny day
of summer, the solar photovoltaic panels 110 receive plenty of
sunlight to generate electricity. Through the DC motor 404, it
directly drives the compressor 405 of the refrigerating unit. The
refrigerant, for example R22, is compressed, and the heat generated
is dissipated to the environment by the fan 406. The refrigerant is
then liquefied. It passes through an expansion valve 409 to become
vapor, and then flows through pipe 410 to the heat exchange coil
411 near the top of the water wall 105. If there is a single water
container, the cooling effect spreads quickly to the entire volume
by convection. For systems having two or more water containers, see
FIG. 1, a pump driven by the electricity from the solar panel 111
provides circulation of the water, and the cooling effect spreads
to all the water containers. In a sunny day, the temperature of the
water wall could be lowered by 2.degree. C. or 3.degree. C. from
the average temperature of the water wall, for example, 20.degree.
C. See the thermodynamic calculations below. The cooled water wall
provides extraordinary comfort to the room. After sunset, the
temperature of the water wall gradually rises. Because of the large
thermal mass of the water wall, if the room is properly insulated,
comfortable temperature could be maintained throughout the night.
In the day time of winter, sunlight enters directly through the
window 104 to heat up the water wall, where the insulating shutters
116 are opened to expose the black surface of the water wall 105.
With a conventional window, for example, two windows of 3 ft wide
and 4.5 ft high, more than 1 kW of heating power can be obtained.
For an entire day, the water wall can be heated up a few degrees
from its average temperature, for example 20.degree. C. The warm
water wall provides extraordinary comfort to the room. After
sunset, the insulating shutters 116 are closed to prevent heat loss
through the window. Owing to the large thermal mass of the water
wall, comfortable temperature can be maintained continuously
throughout the night.
[0019] A typical temperature profile in the summer is shown in FIG.
5. Curve 501 shows the variation of solar power on the solar
photovoltaic panel with time. Curve 502 represents the variation of
external temperature with time. As shown, it has 3-6 hours of delay
from the variation of the solar power. In late afternoon, between 3
pm and 6 pm, the external temperature reaches maximum. The
temperature of the structured water wall 503 shows a similar
behavior. Between 3 pm and 6 pm, the temperature of the structured
water wall reaches minimum. And it increases slowly after
sunset.
[0020] A typical temperature profile in the winter is shown in FIG.
6. Curve 601 shows the variation of solar power on the window.
Curve 602 represents the variation of external temperature with
time with a time lag of 3-6 hours. The behavior of the temperature
of the structured water wall 603 is similar. Between 3 pm and 6 pm,
the temperature of the structured water wall reaches maximum. And
it decreases slowly after sunset.
[0021] Following is a thermodynamic calculation for estimating the
proper sizes of the elements to achieve maximum comfort.
[0022] First, a moderately sized structured water wall can provide
extraordinary comfort for a typical room of 12 ft wide and 16 ft
long and 8 ft high in a residential building. Suppose that two
sides of the room have walls towards the exterior of the house. In
SI units, the area of the walls is approximately 20 m.sup.2 and the
area of the windows is 4 m.sup.2. For modern houses, the typical
U-value of the insulated walls is 0.3 W/.degree. C.m.sup.2 (Watts
per degree Celsius per square meter), and the typical U value of
the window is 1.4 W/.degree. C.m.sup.2. The total rate of heat loss
is 11.6 W/.degree. C. Suppose that the average external temperature
is 30.degree. C., and the average temperature of the water wall is
20.degree. C., the temperature difference is 10.degree. C., and the
rate of heat loss is 116 W. Each hour, the heat loss is 417,000
Joule, or about 500 BTU.
[0023] On the other hand, suppose the size of the water wall is 5
ft high 7 ft wide and 6 inch thick. The volume of water is about
0.5 cubic meters. The heat capacity of the water is
4.19.times.500,000=2,100,000 Joule/.degree. C. Each hour, the
temperature drop is 0.2.degree. C. For 10 hours, the temperature
drop is 2.degree. C. Therefore, one half metric ton (or
approximately one half English ton) of water is enough to keep the
temperature of an average-sized, well-insulated room comfortably
constant. It is important to note that a 0.5 metric ton water wall,
comparable with the weight of a grand piano, is not ax
extraordinary burden for an average house. Especially, the water
wall is located near the wall, not near the center.
[0024] Next, we estimate how much solar power is required to cool
the water wall down by at least 2.degree. C. during the day time.
We assume that the external temperature is 10.degree. C. higher
than the temperature of the water wall. Using a refrigerating unit
with a coefficient of performance (COP) of 6 (see for example W. P.
Jones 1994), to bring the temperature of the water wall with heat
capacity of 2,100,000 Joule/.degree. C. down by 1.degree. C., an
input energy of 2,100,000.times.10/6=3,500,000 Joule is required to
operate the compressor. If the process takes 8 hours, the average
power required is 3,500,000/(8.times.3600)=121 W. To cool down the
water wall by 2.degree. C., 242 W of average power is required.
Therefore, a 500 W peak power is sufficient. The size of a typical
200 W solar photovoltaic panel is 1 m.times.2 m. Two 200 W solar
photovoltaic panels is of a perfect size to function as an awning
for a pair of 3-ft times 4.5-ft windows.
[0025] Finally, we estimate the solar power required to heat up the
water wall during the winter. The solar constant is roughly 1 kW
per m.sup.2. The area of two standard windows (3 ft times 4.5 ft)
is 2.5 m.sup.2. Suppose that the transmissibility of atmosphere and
the glass is 60% and the absorbance of the (black) water wall is
80%, the solar power received by the structured water wall is about
1 kW. If the average solar exposure is 6 hours with a sinusoidal
profile, the heat absorbed is 10,800,000 Joule, which can heat up
the water wall by about 5.degree. C. However, at the same time,
there is heat loss though the walls and the windows. The net rise
of the temperature of the water wall is about 2-3.degree. C. During
the night, the temperature of the structured water wall gradually
decreases by about 2-3.degree. C.
[0026] The maximum cooling power and heating power by design is
preferred to be greater than for maintaining a comfortable
temperature. To avoid excess cooling or excess heating, the
operation is regulated by a thermostat. In case of cooling, when
the temperature of the structured water wall is lower than a
predetermined value, for example, 17.degree. C. or 63.degree. F.,
the refrigeration unit is turned off. In case of heating, when the
temperature of the structured water wall is higher than a
predetermined value, for example, 23.degree. C. or 75.degree. F.,
the insulating shutters are closed. In a cool and cloudy winter
day, if the temperature of the structured water wall is too low, an
external heater can be tuned on.
* * * * *