U.S. patent application number 12/135120 was filed with the patent office on 2009-12-10 for solar-powered air conditioning system using a mixture of glycerin and water to store energy.
Invention is credited to Chengjun Julian Chen.
Application Number | 20090301118 12/135120 |
Document ID | / |
Family ID | 41399058 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090301118 |
Kind Code |
A1 |
Chen; Chengjun Julian |
December 10, 2009 |
Solar-Powered Air Conditioning System Using a Mixture of Glycerin
and Water to Store Energy
Abstract
A solar-powered air conditioning system comprising an
energy-storage medium of 5%-10% glycerin and 90%-95% water in a
thermally insulated container, a solar photovoltaic panel, a
vapor-compression refrigeration unit driven by a DC motor powered
directly by the solar photovoltaic panel, a heat-exchange coil to
cool a stream of air by the energy-storage medium, and a
ventilation apparatus to circulate the cooled air. In the presence
of sunlight, the electrical current generated by the solar panels
drives the vapor-compression refrigeration unit to freeze the
mixture of glycerin and water. In the absence of sunlight, the
frozen mixture of glycerin and water keeps temperature low. The
flowing air cooled by heat-exchange coils through the
energy-storage medium circulates in the room or the entire building
to keep the space cool.
Inventors: |
Chen; Chengjun Julian;
(White Plains, NY) |
Correspondence
Address: |
AMSTER, ROTHSTEIN & EBENSTEIN LLP
90 PARK AVENUE
NEW YORK
NY
10016
US
|
Family ID: |
41399058 |
Appl. No.: |
12/135120 |
Filed: |
June 6, 2008 |
Current U.S.
Class: |
62/235.1 |
Current CPC
Class: |
F24F 2005/0064 20130101;
F25B 2400/24 20130101; F24F 5/0007 20130101; Y02B 10/20 20130101;
F25D 16/00 20130101; F25B 27/005 20130101; Y02B 10/24 20130101 |
Class at
Publication: |
62/235.1 |
International
Class: |
F25B 27/00 20060101
F25B027/00 |
Claims
1. A solar-powered air-conditioning system comprising: an
energy-storage medium of 5%-10% glycerin and 90%-95% water in an
insulated container; a solar photovoltaic panel facing the Sun; a
vapor-compression refrigeration unit driven by a DC motor powered
directly by solar photovoltaic panel to freeze the energy-storage
medium; a heat-exchange coil to cool a stream of air through the
frozen energy-storage medium; a ventilation apparatus to circulate
the cooled air.
2. The system of claim 1 wherein the ventilation system is
controlled by a thermostat to keep the room temperature near the
preset value.
3. The system of claim 1 wherein the solar power is turned off if
the temperature of the energy-storage medium is below a preset
value.
4. The system of claim 1 wherein the ventilation system is attached
to the energy-storage container to directly circulate the cooled
air in a room.
5. The system of claim 1 wherein the ventilation system is a set of
ducts running through a building or part of a building with fans or
blowers to circulate air into the rooms of the building.
6. The system of claim 1 wherein the electrical current from the
solar panel is controlled by a switch such that if the temperature
of the energy-storage medium is lower than a preset value then the
electrical current is turned off.
Description
BACKGROUND OF THE INVENTION
[0001] Cooling of buildings consumes a huge amount of energy
worldwide. For example, in southeast and southwest regions of the
US, air conditioning is the dominant end user of energy and the
single leading cause of peak demand for electricity. From economics
point of view, reducing electricity demand for space cooling could
save a lot for consumers. From utility-infrastructure point of
view, reducing air-conditioning electricity loads can lower demand
for annual power generation and peak capacity. Coincidentally, in
regions where air conditioning is needed the most, solar energy is
also abundant. Especially, from day to day, the stronger the
sunlight, the more air conditioning power is needed. Therefore, to
utilize sunlight to power air conditioning is a logical
solution.
[0002] A basic problem of solar-powered air conditioning is energy
storage. Solar energy is only available in sunny days, not in
evenings and nights. By directly using the solar electricity to
drive an air-conditioning unit to cool the rooms, 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 solar power 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). In the
evenings and nights, although air conditioning is still needed,
there is no sunlight. Sunlight is also absent in cloudy and raining
hours. To resolve this problem, an established method is to use
solar energy to generate hot water, and then to drive an adsorption
refrigerator using the stored hot water. Using a good
thermal-insulated tank, hot water can be stored for a day or two.
However, the efficiency of the adsorption refrigerator is low, and
the stored hot water would radiate heat into the building and to
increase the demand for cooling. Thus, the approach has not been
widely implemented.
[0003] A method to store cooling power using ice has been proposed
in the 1980s, with the purpose of taking advantage of the price
difference of electricity in peak time and night, mostly for large
commercial buildings. The problem with that approach is that when
water is frozen to ice, the volume is increased, and the expanding
ice could damage the container and the heat-exchange coils. That
method has not been widely implemented also.
[0004] The recent advancements of renewable energy technology have
opened new possibilities for a practical solar-powered air
conditioning system. The first is the rapid reduction of the price
of solar cells, which is approaching one dollar per watt, and the
price will continue to drop. Consequently, the cost of generating
DC electricity using solar cells per watt is only a fraction of the
cost for construction, maintenance and management of electricity
transmitting facilities. To drive appliances directly from solar
electricity is economically advantageous. The second one is the
availability of inexpensive crude glycerin as a byproduct of
biodiesel. To produce each gallon of biodiesel, 0.15 gallon of
surplus crude glycerin is generated. Although high-purity glycerin
has applications, purification from crude glycerin is expensive.
The limited market for pure glycerin does not always justify the
cost to construct glycerin purification plants, which leaves about
one million metric tons of crude glycerin for disposal
annually.
[0005] The present invention is related to a design of a
solar-powered air conditioning system which utilizes the DC current
directly from the solar cells to drive a vapor-compression
refrigeration unit to freeze a mixture of glycerin and water
(typically 5%-10% of glycerol and 90%-95% of water), then use the
stored cooling power of the partially frozen glycerin-water mixture
to cool the building. Because the low cost of crude glycerin, the
elimination of the inverter and power distribution facilities, and
the simplicity of the entire apparatus, the solar-powered air
conditioning system is economically advantageous.
BRIEF SUMMARY OF THE INVENTION
[0006] The current invention is a solar-powered air conditioning
apparatus with a safe and inexpensive medium to store cooling
energy. It utilizes the DC current from solar cells to drive a
vapor-compression refrigeration unit directly, bypassing the
inverter and power grid. It utilizes a mixture of glycerin and
water to store cooling energy. The cooling coil of the
refrigeration unit is placed in a container filled with a mixture
of glycerin and water, thus to freeze it into slurry of small
pieces of ice embedded in an aqueous solution of glycerin.
Experiments showed that with a mixture of 5% glycerin and 95%
water, the frozen substance resembles wet snow. With a mixture of
10% glycerin and 90% water, the frozen substance is a fluid filled
with small ice sheets. With a mixture of 7.5% glycerin and 92.5%
water, the frozen substance is a viscous fluid packed with ice
sheets and pellets. Because it is fluid, it would not damage the
container and the heat exchange coils. On the other hand, the
latent heat of the ice sheets and pellets is as large as regular
ice, which is 80 calorie per gram, or 335 kilojoules per kilogram.
The temperature is a few degrees below the freezing point of water.
A stream of air is passing through a set of heat exchange tubes in
the frozen mixture of glycerin and water, and then circulates by a
fan or a blower to cool the space. Using a thermostat, the
temperature can be regulated through the fan or the blower, similar
to ordinary air conditioning units.
[0007] As an apparatus in a residential home or an office, safety
is a major consideration. Glycerin is a popular food ingredient and
a commonly used skin-care lotion, therefore it is very safe.
[0008] Cost is an important factor for the viability of a product.
Decades ago, glycerin was fairly expensive. In recent years, a glut
of crude glycerin exists as a byproduct of biodiesel. The market
price of crude glycerin is $0 to $150 per metric ton. The
impurities in crude glycerin are mainly rock salt, water, alcohol
and residual fat, which are not toxic. Therefore, crude glycerin
can be directly used without purification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a solar-powered stand-alone air-conditioning
system.
[0010] FIG. 2 shows the basic components of a solar-powered central
air-conditioning system.
DETAILED DESCRIPTION OF THE INVENTION
[0011] FIG. 1 shows a solar-powered stand-alone air-conditioning
system for a single room, which is very popular in Asia. Solar
panel 101 is installed either on a south-facing roof or a
south-facing awning. Through cable 102, the electrical current from
the solar panel 101 drives a vapor-compression refrigeration unit,
103 through 109. The compressor 103 compresses the refrigerant
through pipe 104 into condenser 105. Here, a fan 106 disperses the
heat of the compressed refrigerant into air. Both the compressor
103 and the fan 106 are driven by a DC motor 107, powered by the
solar panel 101. After condensing, through pipe 108, the
refrigerant is let to expand by the expansion valve 109. The
expanded refrigerant is going through a thermally insulated pipe
110 into a heat-exchange coil 111 to freeze the energy-storing
medium 112, a mixture of glycerin and water, in a thermally
insulated container 113. The air in the room flows through the
heat-exchange tubes 114, and cooled by the energy-storing medium
112. The air is set to motion by fan 115, driven by a motor 116.
Fins 117 can be used to change the direction of wind. The A-A cross
section diagram further clarifies the relation among the
heat-exchange coil 111, the energy-storage medium 112, the
insulated container 113 and the heat-exchange tubes 114. Because
the frozen mixture of glycerin and water is fluid slurry, it would
not damage the container and the heat-exchange coils.
[0012] FIG. 2 shows the basic components of a solar-powered central
air-conditioning system. Solar panel 201 is installed either on a
south-facing roof or a south-facing awning. Through cable 202, the
electrical current generated by the solar panel 201 is used to
drive a vapor-compression refrigeration unit, 203 through 209. The
compressor 203 compresses the refrigerant through pipe 204 into
condenser 205. Here, a fan 206 disperses the heat of the compressed
refrigerant into air. Both the compressor 203 and the fan 206 are
driven by a DC motor 207, powered by the solar panel 201. After
condensing, through pipe 208, the refrigerant is let to expand by
the expansion valve 209. The expanded refrigerant is going through
a thermally insulated pipe 210 into a heat-exchange coil 211 to
freeze the energy-storing medium 212, a mixture of glycerin and
water, contained in a thermally insulated tank 213. The air is
flowing through the heat-exchange tubes 214, and cooled by the
energy-storing medium 212, into the duct system 215. As in the
conventional central air conditioning systems, the duct system
comprises a blower, a thermostat, and fins to control the
temperature and the intensity of air flow to the rooms. The
returning air from the rooms is going through duct 216 and then
cooled again by the heat-exchange tubes 214. The A-A cross section
diagram further clarifies the heat-exchange coil 211, the
energy-storage medium 212, the insulated container 213 and the
heat-exchange tubes 214. Again, because the frozen mixture of
glycerin and water is fluid slurry, it would not damage the
container and the heat-exchange coils.
[0013] For practical reasons, here we make an estimate of how much
energy-storage medium is required. For the case of a relatively
large single room, using standard insulation, if the outside
temperature is 30.degree. C., to maintain a room temperature of
20.degree. C., the rate of heat loss is 200 W. Each hour, the
energy loss is 720 kJ. If the mass of the thermal-storage medium is
100 kg, assuming one half of the mass is frozen to ice, the latent
heat is 1.67.times.10.sup.4 kJ, and the thermal-storage medium can
maintain the temperature for 24 hours. For an entire house, for
example, equivalent to five relatively large rooms, a 500 kg
thermal-storage medium could maintain the temperature for 24
hours.
[0014] For financial reasons, the size of solar panels is estimated
as follows. Suppose the coefficient of performance (COP) of the
refrigerator is 3-5, to freeze one half of the 100 kg
glycerin-water mixture in 5 hours, a power of 180 W to 300 W is
required. If the price of solar cells is one dollar per watt, the
cost of solar cells is $180 to $300. Assuming that the efficiency
of solar panel is 10%, the area of solar cells is 1.8 square meters
to 3 square meters. For a central air conditioning system, the cost
of solar cells is five times higher: 0.9 kW to 1.5 kW with a cost
of $900 to $1500 and an area of 9 to 15 square meters. Comparing
with the savings of electricity, the cost and the roof area is
reasonable.
[0015] An important issue is transportation and installation of the
thermal-storage medium. Because water is available anywhere, the
factory could supply an empty container and crude glycerin (for
example 80%). For a single room, the required quantity of crude
glycerin is less than 10 kg, which can be shipped in two one-gallon
plastic bottles. At the site, crude glycerin and water is mixed in
the container. For an entire house, the required quantity of crude
glycerin is less than 50 kg. Since on the open market, the price of
each ton of crude glycerin is less than $150, the cost of crude
glycerin for a single room is less than $1.50 and cost of crude
glycerin for a central air conditioning system is less than
$7.50.
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