METHOD AND SYSTEM FOR COOLING BY USING SOLAR

ENERGY

Field of the Invention

The present invention relates to cooling systems. More particularly, the invention relates to a method and system for cooling by using solar energy, and especially for providing solar air-conditioning of residence buildings, and by utilizing flexible heat (loop) pipes and Thermal-Driven Cooling Machines (TDCMs - for example, absorption, adsorption, desiccant based, ejector cycle based, Rankine cycle based, Stirling cycle based machines, etc.)

Background of the Invention

Using solar energy for cooling purposes has good prospects compared to conventional air conditioning systems. The replacement of compressor cooling systems by solar driven desiccant cooling systems is an important contribution to environmental protection. Especially, the combination of solar cooling/heating and solar collectors, which are used for heating purposes, is more economical.

According to the prior art, the following types of solar collectors are usually used: a) a parabolic trough; b) a parabolic dish; c) a flat-plate Fresnel lense; and d) an asymmetric concentrator.

The parabolic trough has mirrors that are parabolic in only one dimension and form a long parabolic shaped trough. Although the trough arrangement is mechanically simpler than two-dimensional dish systems, which require more complex tracking systems, the concentrating factor is lower. Mechanisms that allow the parabolic concentrator to follow the sun

(tracking system) are required to ensure that the maximum amount of sunlight enters the concentrating system. Parabolic trough systems can be orientated either horizontally (in long rows) or vertically. Horizontally orientated systems are usually positioned in an east-west direction to reduce the amount of tracking required, and hence the cost. Alternatively, vertically mounted systems follow the motion of the sun throughout the day, by rotating the direction of the trough.

On the other hand, a practical application of a parabolic dish is a flashlight lens, which is used to transform a point source of light into a parallel beam. However, the reverse is true. Since sunlight radiation is essentially parallel, it may be concentrated at the focal point of the lens. A tiny flashlight lens may be used as a cigarette lighter by substituting a cigarette for the bulb and by pointing the lens in the direction of the sun. A type of solar reflector dish concentrator may also be made by lining the inside of a cardboard box with aluminum foil. Large experimental parabolic dishes, known as heliodynes, are capable of melting steel, but they operate at a low efficiency, and therefore must be aligned to be of any practical value.

Flat-plate thermal solar collectors are the most commonly used type of solar collector. Their construction and operation are relatively simple. A large plate of blackened material is oriented in such a manner that the solar energy that falls on the plate is absorbed and converted to thermal energy, thereby heating the plate. Flat plate collectors have the advantage of absorbing not only the energy coming directly from the disc of the sun (beam normal insulation), but also the solar energy that has been diffused into the sky and that is reflected from the ground.

Asymmetric non-imaging concentrators, as an alternative to symmetric compound parabolic concentrators, have the following advantages: - increased design flexibility;

- increased operational flexibility; and

- significant collection of diffuse radiation.

The utilization of non-imaging optics allows direct and diffuse insulation to be concentrated while not tracking the solar motion. In the asymmetric nonimaging concentrators, optical efficiency of over 90% is achieved for incidence angles of solar radiation between 0° and 65°.

According to the prior art, the heat can be transferred from one place to another by means of a heat pipe that is a device designed to transport heat with a very small temperature difference between a heat source (evaporator section of the heat pipe) and a heat sink (condenser section of the heat pipe). In terms of thermal conduction, a heat pipe is designed to have very high thermal conductance. However, conventional heat pipes have relatively low output power, and they are mainly used in electronic systems and circuits. In heat pipes, the heat is transported from the heat source to the heat sink by means of a condensable fluid contained in a sealed chamber. Liquid is vaporized, absorbing heat in the evaporator section. Then the vapor flows to the condenser section, where it condenses and releases its latent heat. The liquid is drawn back to the evaporator section by capillary action, where it is re-vaporized to continue the cycle. The temperature gradient, along the length of pipe, is minimized by designing for a very small vapor pressure drop as the vapor flows from the evaporator section to the condenser section. Thus, the saturation temperatures (temperatures at which evaporation and condensation takes place) are very nearly the same in both sections. The spectrum of heat pipe working fluids extends from cryogens to Ii quid metals, the choice of fluid being such that its saturation temperature, at the heat pipe operating pressure, is compatible with the heat pipe's application. In addition, the fluid is chosen to be chemically inert when wetting the pipe and capillary wick. Ideally, the fluid would have a high thermal conductivity and latent heat. It should have a high surface tension and low viscosity.

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The more advanced way to transport the heat is by means of a loop heat pipe (LHP) that is robust, self- starting, and has passive two-phase thermal transport devices; and by means of a siphon contour pipe (SCP). The loop heat pipe utilizes the latent heat of vaporization of a working fluid to transfer heat, and the surface tension forces that are formed in a fine-pore wick to circulate the working fluid. Loop heat pipes are used to transport excess heat from a heat source, such as payload instruments in a spacecraft, to a low temperature heat sink, while maintaining the temperature within specified limits. However, in spite of the relatively long (some decades) history of using these pipes for heat transfer, they are not applied to the transfer of more than 1 kW, because it has recently become possible to produce flexible LHP and SCP. Using flexible LHP and/or SCP allows significantly decreasing the cost and expenses for heat transfer, thus decreasing the total energy consumption of an air-conditioning system.

The decreased global warming and the environmental impact of chlorofluorocarbon and other similar refrigerants in the atmosphere ozone layer have stimulated an interest in developing environmentally-friendly air conditioning systems. However, the most important factor in intensifying the development of solar air-conditioners is the continuous growth in energy usage and the continuous growth of energy cost. For example, according to the US Department of Energy, the residential energy use in the United States can be increased by 25 percents by the year 2025. According to the prior art, the use of solar energy for air-conditioning purposes is mainly implemented by the following:

- Liquid desiccant solar air-conditioner; and

Solar power cooling systems with a solar module.

In Liquid desiccant solar air-conditioner, a cross-flow type Plate Heat Exchanger (PHE) is used as a dehumidifier, offering an environmentally friendly air conditioning system. It removes moisture form the air and

provides 100% fresh air without the application of Chlorofluorocarbon (CFC). Low-grade energy such as waste heat, heat from co-generation or solar energy could be used for the liquid desiccant regeneration. The liquid desiccant solar air conditioner is usually considered for commercial applications due to its relatively high cost. It should be noted that the conditioner dimensions depend on the component sizes to be included inside the system. Consequently, the dimensions of all the unit components, such as the PHE, fans, pumps, cooling pads, etc. have to be identified prior to system design. In addition, an important component of this system is the solar hot water system that is waiting for installation on the roof of the site building. This provides the hot water at necessary temperature and flow rate from flat plate solar collectors to regenerate the weak desiccant solution, obtained from the dehumidifier, using gas or electrical energy as the back up. The regeneration process is done by heating the solution up to about 85 °C in a regenerator (typically a liquid-liquid heat exchanger) using hot water from the flat plate solar collectors. To facilitate the boning of the weak liquid desiccant and removing the water vapor, a vacuum pump can be used to produce vacuum over the solution. Subsequently, the produced vapor has to be separated from the liquid by using a vapor separator device.

The practical realization of the usage of heat for the production of cold, which is the basis of all known techniques in refrigeration and air- conditioning, demands that a heat-carrier be used. Such a carrier is usually water or another volatile liquid. The pumping of the heat carrier is relatively easy in the one-level house scale, but it becomes an essential consumer of energy when a high multi-level building is in question. Pioneered by NASA to provide power for satellites and spacecraft, photovoltaic is a viable source of energy used to bight over 1 million rural homes around the world. Photovoltaic cells directly convert sunlight into electricity, without having to utilize limited fossil fuel resources. PV energy contributes to improved air quality and aids in the reduction of greenhouse

gases that play a role in global warming. For example, when it displaces coal-fired generation, a common source of electricity among power plants, harmful sulfur dioxide and nitrous oxide emissions are eliminated. Most homes running on PV energy, however, employ simplistic lighting systems that are incapable of providing refrigeration. This can be especially troublesome for areas in which no conventional power source exists, including remote automated weather stations, forest stations, and Third World villages.

An example of a prior art solar power cooling system using a solar module, can be a PV direct-drive (or "PV direct") portable solar refrigerator of the SunDanzer™ company, located in the United States, that is designed to function in arid to semi- arid regions with at least 5 sun-hours per day. It comprises a chest-type cabinet with a 105-liter (3.7 cubic feet) internal volume, a lockable top-opening door, a corrosion-resistant coated steel exterior, and a patented low-frost system. It uses thermal storage for cooling efficiency, with a direct connection between the vapor compression cooling system and the PV module. This is accomplished by integrating a phase- change material into a well-insulated refrigerator cabinet and developing a microprocessor-based control system that permits the direct connection of a PV module to a variable-speed compressor. The integration allows for peak power-point tracking and the elimination of batteries (thus, the environmental threat of improper battery disposal is eliminated). However, the "PV direct" portable solar refrigerator has low output cooling power, and cannot replace a conventional home refrigerator.

JP 8,082,492 discloses a heat pump type air conditioner comprising a loop- like heat pipe for circulating heating medium to connect an outdoor heat exchanger; and a solar heat collector for collecting solar heat, wherein the heat collected by the collector is radiated by moving heating medium in the pipe and conveying it to the heat exchanger of the conditioner. However, JP

8,082,492 does not teach utilizing an abortion-cooling machine that receives heat from a solar collector by means of flexible heat pipes. In addition, the air conditioner of JP 8,082,492 does not eliminate the need for electrical energy (besides solar energy), and the electrical energy is still required for operating a compressor of said air conditioner. Further, JP 8,082,492, utilizes heat exchangers for exchanging the heat with the heat pipe, wherein for exchanging a large amount of the heat, said heat exchangers must have relatively large dimensions.

The most typical representatives TDCM are absorption cooling machine and Adsorption-cooling machine. The absorption cooling machine corresponds to a vapor-compression refrigerator, in which the compressor is usually substituted by four elements:

- a vapor absorber based on another liquid,

- a pump for the liquid solution,

- a generator or boiler to release the vapor from solution, and

- a valve to recycle the absorbent liquid.

The advantages of using the absorption cooling machine are: (a) lowering or eliminating electrical consumption besides a heat source; (b) possibility of heat recovery or co- generation synergies; (c) low environmental impact working fluids; and (d) low vibrations.

An adsorption-cooling machine (also called a solid- sorption cycle based machine) is a preferential partitioning of substances from a gaseous or liquid phase onto a surface of a solid substrate. This process involves the separation of a substance from one phase to accumulate or concentrate on a surface of another substance. The adsorption process is caused by the Van der Vaals force between adsorbents and atoms or molecules at the adsorbent surface. In the adsorption refrigeration cycle, refrigerant vapor is not being compressed to a higher temperature and pressure by the compressor but it is adsorbed by a solid with a very high microscopic porosity. This process

requires only thermal energy, with no need for mechanical energy. The principles of the adsorption process provide two main processes, adsorption or refrigeration and desorption or regeneration. The advantages of using the adsorption-cooling machine are: (a) no moving part; (b) low operating temperature that can be achieved.

It is an object of the present invention to provide a method and system for cooling by using solar energy, and particularly for providing solar air conditioning of residence buildings by utilizing flexible heat pipes and TDCMs.

It is another object of the present invention to provide a method and system, which utilizes solar energy only, and does not require an additional source of energy.

It is still another object of the present invention to provide a method and system for providing solar air conditioning of residential buildings, wherein each inhabitant of the building can control the air conditioning within his apartment.

It is a further object of the present invention to provide a method and system, which utilizes the existing solar boilers/tanks infrastructure.

It is still a further object of the present invention to provide a method and system, in which the conventional water boilers/tanks are used as heat accumulators.

It is still a further object of the present invention to provide a method and system, which is relatively inexpensive.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

The present invention relates to a method and system for cooling by using solar energy, and especially for providing solar air-conditioning of residence buildings, and by utilizing flexible heat pipes and TDCMs.

The system for cooling by using solar energy comprises: (a) a solar energy collector for collecting solar energy and converting it to heat energy; (b) one or more heat pipes connected to said solar energy collector for receiving said heat energy from said solar energy collector and passing it to a TDCM, said TDCM used for performing cooling by means of said heat energy; and (c) a control unit for controlling the operation of said TDCM.

According to another preferred embodiment of the present invention, the system further comprises a heat accumulator, connected to the solar energy collector, for accumulating the heat energy provided by said solar energy collector.

According to a particular preferred embodiment of the present invention, the heat accumulator is a water boiler or a water tank.

According to still another preferred embodiment of the present invention, the one or more heat pipes are connected between them by means of a connector.

According to a further preferred embodiment of the present invention, the system is a solar air-conditioner.

According to still a further preferred embodiment of the present invention, the system is a refrigerator.

According to still a further preferred embodiment of the present invention, the system is a cooler.

According to still a further preferred embodiment of the present invention, the heat pipe is a loop heat pipe.

According to still a further preferred embodiment of the present invention, the heat pipe is flexible.

According to still a further preferred embodiment of the present invention, the operation of the TDCM is controlled by means of a remote control.

According to still a further preferred embodiment of the present invention, the operation of the TDCM is cyclic.

According to still a further preferred embodiment of the present invention, the operation of the TDCM is continuous (uninterruptible).

According to still a further preferred embodiment of the present invention, instead of the solar energy collector, a solar energy concentrator is used.

The method for cooling by using solar energy comprises: (a) collecting solar energy be means of a solar energy collector, and then converting said solar energy to heat energy; (b) receiving said heat energy from said solar energy collector by means of one or more heat pipes that are connected to said solar energy collector, and then passing said heat energy to a TDCM by means of said one or more heat pipes; (c) performing cooling by means of said TDCM

by using the passed heat energy; and (d) controlling the operation of said TDCM by means of a control unit.

Brief Description of the Drawings

In the drawings:

Fig. 1 is a schematic illustration of providing solar air-conditioning to a plurality of apartments within a residence building by utilizing heat pipes and TDCM, according to a preferred embodiment of the present invention; and

- Fig. 2 is a schematic block-diagram of a system for providing solar air-conditioning by utilizing a heat pipe(s) and a TDCM, according to a preferred embodiment of the present invention.

Detailed Description of the Preferred Embodiments

Although the following description will be provided with a particular reference to an "air-conditioner", it will be appreciated by the skilled person that any type of a cooling device or cooling system, such as a refrigerator, cooler, etc. benefits from the present invention and is encompassed within it.

In addition, although the following description will be provided with a particular reference to a " residence building", it will be appreciated by the skilled person that the method and system of the present invention for providing solar air-conditioning can be implemented within any building, house, home, structure, construction and the like.

Fig. 1 is a schematic illustration of providing solar air-conditioning to a plurality of apartments within a residence building 150 by utilizing heat

pipes and TDCM, according to a preferred embodiment of the present invention. It is supposed, for example, that residence building 150 comprises three apartments (apartment 1, apartment 2 and apartment 3), wherein each apartment can have its own air-conditioning system 100. The air- conditioning system 100 comprises: a solar energy collector 105 for collecting the solar energy from the sun and converting it to the heat energy; one or more heat pipes 115, connected to said solar energy collector 105 via connector/adaptor 140, for transferring (passing) the heat from said solar energy collector 105 to TDCM 120 that is provided within each apartment, wherein said TDCM 120 is used for receving (absorbing) the heat energy from one or more heat pipes 115, and in turn, for cooling the air within each apartment by using the passed heat energy; and a control unit 125, provided within each apartment, for controlling the operation of said TDCM 120 (e.g., by means of a remote control).

Solar energy collectors 105 are usually located on the roof of building 150, where they are the most accessible by the sun light. The solar energy is collected by means of each solar energy collector 105, which converts it to the heat energy. Solar energy collector 105 can be connected to heat pipe 115 by means of a connector/adaptor 140 for transferring the heat energy to said heat pipe. Heat pipe 115, in turn, passes the received heat energy to TDCM 120 within the corresponding apartment. TDCM 120 cools the air by performing a conventional cooling process by using said heat energy. The inhabitant (user) of each apartment can fully control the operation of said TDCM 120, and in turn, can fully control the cooling process. For example, the user can make all required settings (similarly to operating a conventional air-onditioner), such as setting a temperature, setting a timer, setting a cooling power, etc.

It should be noted that heat pipes 115 can be conventional heat pipes and/or loop heat pipes (LHP). Further, the heat pipes can be flexible in order to

transfer the heat to each apartment within the residence building 150, in a convenient way. The flexibility can allow the heat pipes to be transferred within the walls of the building to any location of each apartment. Further, it can allow the inhabitants of each apartment to easily change the location of the heat pipes, if required.

According to a preferred embodiment of the present invention, heat pipe 115 can be divided onto several portions (e.g., portions 115', 115", 115'" and the tike), wherein each portion of said heat pipe 115 can have a predefined length (e.g., 6-6.5 meters) in order to be able to transfer the heat from each solar energy collector 105 to corresponding TDCM 120 in a relatively efficient way. Thus, portion 115' of heat pipe 115 can be, for example, 6.5 meters long, portion 115" of said heat pipe 115 can be, for example, 4 meters long and portion 115'" of said heat pipe 115 can be, for example, 3 meters long. One portion is connected to another by means of a connector/adaptor 130. Connector 130 enables one heat pipe to transfer the heat energy from it to another heat pipe in an efficient manner. Thus, the overall length of heat pipe 115 can be, for example, 20-25 meters. The heat energy is further transferred by said another heat pipe to TDCM 120. In this way, the heat energy can be transferred from solar energy collector 105 to long distances (e.g., tens of meters).

According to another preferred embodiment of the present invention, the solar energy can be accumulated by means of conventional water boilers/tanks 110, which are usually provided on the roof of the building. Such water boilers/ tanks 110 can function as heat accumulators, and the accumulated energy can be used at night or in cloudy weather (when there is no sun heat) for cooling apartments within the building. Said water boilers/tanks 110 can be connected to both solar energy collectors 105 and heat pipes 115 via connectors/adaptors 140.

Fig. 2 is a schematic block-diagram of a system 100 for providing solar air- conditioning by utilizing a heat pipe(s) 115 and a TDCM 120, according to a preferred embodiment of the present invention. The air-conditioning system 100 comprises: a solar energy collector 105 for collecting the solar energy from the sun and converting it to the heat energy; one or more heat pipes 115, connected to said solar energy collector 105 via connector/adaptor 140, for transferring (passing) the heat from said solar energy collector 105 to TDCM 120 that is provided within each apartment, wherein said TDCM 120 is used for receving (absorbing) the heat energy from one or more heat pipes 115, and in turn, for cooling the air within each apartment by using the passed heat energy; and a control unit 125, provided within each apartment, for controlling the operation of said TDCM 120 (e.g., by means of a remote control). Further, the solar energy can be accumulated by means of heat accumulator 110, which can be a conventional water boiler/tank 110 (Fig. 1), usually provided on the roof of building 150 (Fig. 1).

It should be noted that according to another preferred embodiment of the present invention, TDCM 120 can be connected to a conventional electrical power supply. Thus, when there is a cloudy weather or at the night time (when there is no sun light) and when there is no heat accumulated by means of heat accumulator 110, said TDCM 120 can consume the electrical power from said conventional electrical power supply for providing solar air- conditioning (for cooling).

According to still another preferred embodiment of the present invention, instead of a solar energy collector 105, a solar energy concentrator (of any type) is used.

According to a further preferred embodiment of the present invention, the operation of TDCM 120 is cyclic and/or continuous (uninterruptible).

While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be put into practice with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.