Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2000-06-28
2001-06-05
Tapolcai, William E. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S235100
Reexamination Certificate
active
06240737
ABSTRACT:
FIELD OF THE INVENTION
THIS INVENTION relates to a solar-powered refrigerator particularly suited for, but not limited to, use in remote locations.
BACKGROUND OF THE INVENTION
Refrigerators have become indispensable for the preservation of temperature-sensitive items such as food, drink, medicines, pharmaceuticals, vaccines and the like.
As defined herein, the term “refrigerator” includes refrigerators capable of cooling to temperatures below 4° C., and/or freezers which cool to −20° C. or below.
In simplest form, a refrigerator comprises a compressor in fluid communication with a coolant circuit (which includes a coolant such as R134a), the coolant circuit being in thermal communication with the interior of a cooling chamber, in which are stored items to be cooled or frozen.
The principle of operation is that the compressor pressurizes the coolant which circulates through the coolant circuit located in the walls of the cooling chamber, whereupon the coolant expands drawing heat from the cooling chamber and contents therein, resulting in cooling or freezing of the cooling chamber and contents.
The expanded coolant is then re-compressed and recirculated through the circuit. Usually, a thermostat is provided which assists maintenance of a desired temperature in the cooling chamber.
Typical refrigerator compressors are provided with induction motors which operate at a fixed speed with a fixed energy requirement, and as such are relatively wasteful in terms of energy consumption.
Recently, variable-speed compressors have been developed which can operate at variable speeds and hence with variable energy consumption, thereby providing enhanced energy efficiency. It will be appreciated that variable-speed compressor technology has progressed rapidly in recent years, such as may be found in International Application WO98/15790, Japanese Patent No. 10038439, Japanese Patent No. 9196535 and U.S. Pat. No. 5,711,159, for example. Of particular note are the TLV alternating current (AC) compressor and the BD35F and BD50F direct current (DC) compressors produced by Danfoss A/S.
Although in many cases refrigerators operate via mains powered AC electricity, an increasingly used alternative source of energy for refrigerators is solar energy. Usually, solar energy operation is achieved using solar panels which collect and convert incident solar radiation into electrical energy which is storable in batteries. When incident solar radiation is minimal, such as at night, early morning or late evening, or in overcast conditions, the batteries can be used to power the refrigerator compressor.
A disadvantage of this system is that typical refrigerator compressors require a threshold electrical current, often 5 Amps, to be operable. Thus, the refrigerator is only operable once the threshold current necessary to power the compressor has been reached.
A further disadvantage with such systems is that the current regulators between the solar panels and batteries are unreliable. If they fail, the batteries will either not be charged or be damaged by uncontrolled current input.
Also, existing solar-powered refrigerators are often not readily transportable. This creates a particular problem in remote regions where solar powered refrigeration is often used to prevent spoilage of medicines and vaccines. For example, it is common for vaccines to be transported from central storage locations to surrounding regions via couriers carrying vaccine containers equipped with freezer blocks A ready supply of these blocks must be maintained.
However, in conditions of low sunlight, it can be extremely difficult to maintain this supply as the typical solar-powered refrigerators used for this purpose become inoperable due to their requirement for a threshold current to be provided. Although batteries can provide power under conditions of low sunlight, they typically have the shortest lifespan of any of the components of the refrigeration system. Consequently, they tend to constitute the weakest “link” in the system. Furthermore, batteries can be stolen or otherwise become inoperable, and therefore require replacement. The high replacement costs and lack of ready availability of solar-chargeable batteries pose a particular problem in remote areas of poor countries.
OBJECT OF THE INVENTION
It is therefore an object of the invention to provide a solar-powered refrigerator with enhanced utilization of a variable supply of solar-generated electrical energy.
It is a further object of the invention to provide a solar-powered refrigerator which does not require a battery.
It is a preferred object of the invention to provide a solar-powered refrigerator which reduces the risk of refrigerated contents thawing and otherwise spoiling.
Other preferred embodiments will become apparent from the following description.
SUMMARY OF THE INVENTION
In a broad aspect, the present invention resides in a solar-powered refrigerator which includes:
(i) two or more variable-speed compressors in fluid communication with one or more coolant circuits in thermal communication with the interior of a cooling chamber; and
(ii) a switch;
whereby in use, said switch senses compressor motor current to thereby regulate supply of an available current to said two or more variable-speed compressors, so that each of said two or more variable-speed compressors is operable at a maximal speed attainable according to said available electric current.
It will be understood by the skilled addressee that solar panels are used as a source of electrical energy for the solar-powered refrigerator.
Preferably, at least two solar panels are provided per variable-speed compressor. However, it is envisaged that future advances to solar panel technology may provide solar panels of sufficient power output that only one panel may be required per variable-speed compressor.
It will be appreciated that as hereinbefore described, variable-speed compressor technology is rapidly expanding, with Danfoss A/S, Matsushita and General Electric producing a variety of such compressors, at least some of which may be suitable for the purposes of the present invention. Preferably, the variable-speed compressors are B D35F or BD50F DC compressors manufactured by Danfoss A/S Nordberg, Denmark.
More preferably, the variable-speed compressors are BD50F DC compressors.
The BD35F and BD50F variable-speed compressors are capable of speeds ranging from 2000 rpm up to a maximal speed of 3500 rpm.
Preferably, no more than three compressors are included in the solar-powered refrigerator. It is envisaged that if more than three compressors are required, a generator would be preferred to a solar power source.
Advantageously, two or three compressors are included in the solar-powered refrigerator.
Suitably, the switch senses compressor motor current. Preferably, the switch regulates compressor speed by varying an impressed reference signal (5 volt quadrangular) so that the compressor(s) operate(s) at a maximal speed attainable according to available current In use, to achieve this function, the switch varies the impressed reference signal in response to any fluctuations which are sensed in compressor motor current.
Preferably, the switch is capable of varying the impressed reference signal to thereby vary compressor speed from 2000 rpm to 3500 rpm.
Alternatively, the switch regulates supply of electric current to said compressors by varying electrical resistance.
Suitably, the coolant circuit comprises a conduit within which is located a coolant, preferably R600a or R134a coolant.
In one preferred form, the solar powered refrigerator includes a switch which regulates two variable-speed compressors, wherein a first compressor is in fluid communication with a first coolant circuit and a second compressor is in fluid communication with a second coolant circuit, each said circuit being in thermal communication with cooling panels and/or zones in the cooling chamber interior.
According to this and another preferred form to be described hereinafter, the cooling chamber is preferably cubic or box-like, the int
Albiez Robert Charles
Tapolcai William E.
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