Field of the Invention

This invention relates to refrigerator and freezer units and refers particularly to improving the energy efficiency of refrigerator and freezer units.

Background of the Invention

Normal refrigerators and freezers are powered by electricity. Whenever the internal temperature rises above a preset value, the compressor is switched on to initiate a refrigerating cycle so that the internal temperature is sufficiently lowered. With heat ingress through the door, door seals, and walls, this is not infrequent. Almost every time the door is opened the compressor is switched on. The continual stopping and starting of the refrigeration compressor causes the continual use of electric power. The more frequently the compressor is required to start, the more inefficient it becomes in the use of energy. Part of this problem is also that the only

store of "cold" in a normal refrigerator or freezer is the contents.

It is therefore the principal object of the present invention to improve the efficiency of a refrigerator or freezer unit.

Summary of the Invention

With the above and other objects in mind, the present invention provides a refrigerator unit having an evaporator coil, a tank in which said evaporator coil is located, said tank being arranged to contain solute to at least substantially submerge said evaporator coil, said solute being adapted to be cooled when said refrigerator is in its ON cycle. The placing of the evaporator coil in a tank of solute creates a reserve of "cold" . This reserve of cold can be generated by a number of means, e.g.: solar accumulated energy, off peak mains electricity, wind generated electricity, or even normal mains power that is not supplied on a constant basis or only provided for a few hours per day. None of these forms of energy are suitable to power a normal type refrigerator because if power is not available "on call" they simply will not function satisfactorily.

One feature of the present invention is that "cold" can be generated when power or energy is available. The "cold" is stored and then called for when required at a later time.

The cold storage bank contains a "storage medium" that is refrigerated during the "on cycle". The storage bank then absorbs heat from the cabinet, etc, during the off cycle. The mix of the "storage medium" is calculated in conjunction with the calculation of the size of the storage bank so as to provide adequate cooling to meet

desired refrigeration standards for an off cycle period of 18 hours in every 24 hour period, for domestic refrigerators.

Throughout this specification, the use of "refrigerator" is taken as including "freezer".

The invention described above is particularly useful in the design of small portable fridges that can be battery powered or coupled to a 12 volt DC supply.

Description of the Drawings

Preferred embodiments of the invention will now be described by way of non-limitative example only and with reference to the accompanying illustrative drawings. In the drawings: Figure 1 is a rear view of a conventional refrigerator illustrating the major components of a compression refrigerator cycle;

Figure 2 is a vertical cross-sectional view of the rear half of a refrigerator fitted with one embodiment of the present invention;

Figure 3 is a view in the direction of arrow A of Figure 2 after removing the insulating panel;

Figure 4 is a view corresponding to that of Figure 2, but for a freezer unit; Figure 5 is a view of the rear of the refrigerator modified in accordance with a second embodiment of the invention;

Figure 6 is a side elevational view of a portable refrigerator; and Figure 7 is a plan view of the refrigerator of

Figure 6.

Description of the Preferred Embodiments

As shown in Figure 1, a conventional compression

refrigerator comprises an outer casing A that includes an insulated enclosure B which defines the cool compartment of the refrigerator. A closed cycle refrigeration plant comprises a compressor C that is coupled to a condenser D which is in turn coupled through an expansion valve E to evaporator coils F. The evaporator coils are positioned within the insulated enclosure and return to form a closed circuit with the compressor. The refrigerant which is under low pressure is evaporated in the evaporator F. The coiled pipe of the evaporator has the effect of lowering the temperature in the refrigerating compartment. The compressor C draws away the vapour, compresses it and passes it to the condenser D. The condenser allows escape of heat and this loss of heat coupled with the increase in pressure causes the refrigerant to condense. The liquid refrigerant is expanded to the lower pressure and then returned to the evaporator. A thermostat is positioned within the insulated housing compartment of the refrigerator and operates to switch the compressor on and off as dictated by the temperature within the refrigeration compartment. The compressor is usually driven by an electric motor. The refrigerant may be any one of a number of liquids with low boiling points or liquefied gases, such as ammonia, ethyl chloride, freon, and other CFCs. In Figures 2 and 3, there is shown a refrigerator

10 of the subject invention having a cabinet with top 12, base 14 and rear wall 16. The remainder of the cabinet and the refrigerator is not shown as this componentry is considered standard. In conventional refrigerators the evaporator coil or tubing would normally be immediately below the top 12 or behind the rear wall 16.

In contrast, with the refrigerator of this invention, the rear wall 16 has a hollow portion 18 into which a tank 20 is placed. The tank 20 is filled with

solute 21. The evaporator coil (not shown) is also positioned in the tank 20. An insulated cover 22 is provided to protect the tank 20 from the rear, and an insulated panel 24 provided to protect the front of the tank 20. The evaporator coil is coupled to the condenser coils 6 positioned outside the rear of the refrigerator. A solenoid operated valve 7 controls flow of refrigerant to and from the evaporator and condenser.

To enable the passage of air past the tank 20, the hollow portion 18 is larger than the tank 20 thus providing an upper air space 26, a lower air space 28 and side spaces 27. Air can enter the upper air space 26 through inlet louvres 30 at the top of insulated panel 24, and can leave lower air space 28 through outlet louvres 32 at the bottom of insulated panel 24. The outlet louvres 32 are preferably adjustable so that the rate of air flow can be controlled.

When the refrigerator cycle commences, chilled refrigerant passes through the evaporator coil to thus chill the solute 21. The solute 21 may eventually freeze. When the refrigerator cycle concludes, the frozen or highly chilled solute 21 absorbs any heat inside the refrigerator to thus maintain the interior of the refrigerator at its normal, lowered temperature. This, naturally, causes the solute 21 to melt and/or for its temperature to rise slowly. The next refrigeration cycle lowers the temperature of the solute 21.

As any warmer air would rise towards the top 12, it will enter through the inlet louvres 30 into upper air space 26, pass down past the front and rear but principally the sides 27 of tank 20 (see Figure 3), into the lower air space 28, and out through the outlet louvres 32.

The solute 21 may be methylated spirits/water, glycol/water, calcium chloride/water, or any other suitable

liquid. The preferred feature is that the liquid solute should solidify at about -20°C.

With refrigerators currently in use, heat is introduced into the cabinet through the evaporator immediately after an "on cycle" and heat continues to flow into the cabinet throughout the "off cycle" . Therefore with a standard refrigerator that cycles continuously, heat is continually being re-introduced into the cabinet from two different sources, namely: a) the balancing of system pressures, and therefore transferring hot refrigerant from the condenser into the evaporator, and b) when these pressures are balanced, a "heat pipe" circulation effect is created between the condenser and the evaporator drawing ambient heat into the cabinet. In refrigerators of the subject invention, a solenoid operated valve is positioned at the capillary entry point, to prevent flow of refrigerant and thereby halting the heat transfer in both situations.

The use of the above system aids energy efficiency. It also makes the refrigerator ideal for use with inconsistent energy sources, such as solar energy. With the refrigeration cycle ON during sunlight hours, the solute 21 would chill sufficiently to act as a heat sink during the night. This also provides a naturally inbuilt balance, as during the warmer months the need for cooling is far greater, but this is offset by the availability of more sunlight to run the compressor for much longer periods to thus provide the additional refrigeration capacity.

Figure 4 illustrates one way of utilising the system in a deep freeze cabinet, in this instance a vertical cabinet. In a normal deep freeze cabinet the evaporator coils are located under some or all of the

shelves. If each of the evaporator coils are placed in a tank 320 filled with solute 321, the same effect as that described in relation to Figures 2 and 3 can be achieved. However, no control of circulation is required in a freezer because frozen food deteriorates far slower at lower temperatures, and it is preferable to operate cabinets of this type at temperatures as low as possible, within the safe limits or capabilities of the cabinet. A solenoid operated valve 325 is positioned between the evaporator and condenser to prevent flow of refrigerant when the compressor is not operating.

Furthermore, the rear wall 316 of the cabinet has no hollow portion. The top 312 and base 314, as well as the rest of the cabinet and its refrigeration system, are standard.

The invention is a modification to a domestic refrigerator as shown with reference to Figure 5 which illustrates a domestic refrigerator having an inner cabinet skin 4 and an outer cabinet skin 5, horizontal internal shelves 2. The evaporator coils would usually be positioned adjacent the top rear of the cabinet with a thermostat sensor 16 positioned beneath the coils and is coupled to a cabinet sensor 15. The condenser coil 3 is shown in dotted profile at the rear of the refrigerator. In this embodiment, an insulated rectangular cover 70 is adapted to be secured to the rear face of the refrigerator. A large rectangular evaporator tank 9 is mounted on the rear of the refrigerator to extend substantially across the width and along the height of the refrigerator. The evaporator coils 14 are positioned within the tank 9 and the tank is filled with solute of the kind described earlier. The rear of the refrigerator is also provided with air baffles 11 and 12 at the top and bottom of the refrigerator communicating with the interior of the

refrigerator. The air baffles allow flow of air around the evaporator tank 9. A mechanically actuated thermostat 10 is positioned adjacent the base of the rear wall of the refrigerator and acts to operate a blade 13 that closes the outlet baffle 12 at the base of the unit. The suction and feed tubing for the evaporator coils 14 extend through the base of the tank and the existing condenser coils 3 remain at the rear of the refrigerator external of the cover 70, but a solenoid operated valve 7 is positioned between the evaporator and condenser to be operable to cut off flow of refrigerant when the compressor is not working. The cover 70 is fitted to the rear of the refrigerator to insulate the tank 9 from the atmosphere and to prevent heat leakage. An air space is provided all around the tank to allow for circulation of refrigerated air to the interior of the cabinet. The amount of refrigerated air is controlled by the mechanically operated thermostat blade 13 that maintains constant temperature inside the refrigerator cabinet. The compressor cycling is controlled by a thermostat sensor 17 at the storage tank. When the solute in the tank freezes solid at around -8°C, this thermostat cuts off the compressor. As the solute in the tank warms due to the heat being absorb out of the cabinet, the thermostat 17 switches the compressor on and it runs until the heat is removed from the solute storage tank.

The invention described above has particular advantages in situations where supply of energy is intermittent such as by use of solar power or wind power or in remote areas where electricity has to be generated during darkness hours only. The invention also considerably improves the energy efficiency of conventional domestic refrigerators. Refrigerators use less power and can be adapted to use power at off peak rates thereby

substantially reducing the annual cost involved in running refrigerators.

The embodiment discussed above aims to improve the energy efficiency of the compressor by reducing the compressor "on cycles" to preferably one cycle per 24 hour period, whilst still producing the desired refrigeration, and to reduce the average suction pressure at which the compressor can successfully operate by between 5psi and 20psi, to reduce evaporator reheat by up to 75%, to store the cold to an appropriate level so as to maintain desired cabinet temperatures during the period the compressor does not cycle, and therefore by reducing the energy requirement by up to 70% to improve the energy efficiency of the refrigerator or freezer unit. The invention described above has particular advantages in the design of small portable refrigerators designed to run on solar power or 12 volt DC supply, i.e. from a motor vehicle. With portable refrigerators for use in outdoor environments it is assumed that power is not always available. In the embodiment shown in Figures 6 and 7 a small portable refrigerator 50 comprises a rectangular insulated cabinet 51 having a removable insulated lid 52. One side of the cabinet 51 is lined on its interior by a narrow long tank 53 which houses the evaporator coils 62 and is filled with solute. The remainder of the refrigerator componentry is housed at the rear 59 of the cabinet 51 and comprises a small compressor 55, a battery charger 56, a dry battery 57 and condenser coil 58. A solenoid operated valve 61 is positioned between the evaporator coils 62 and condenser 58 to be operable to cut off flow of refrigerant when the compressor 55 is not working.

The tank 53 is designed to contain a pre- calculated amount of phase change solute to provide

adequate cooling within the cabinet for at least 6 hours in an ambient temperature of 25°C. The refrigerator operates on 12 volt DC power supplied from the battery 57 that is self-contained within the unit compartment. This battery is capable of running the refrigeration system for at least one complete refrigeration or cooling cycle and provide a 6 hour hold over period. The battery can be recharged by: a) an inbuilt battery charging system 56 that is connected into the 240 volt mains or a solar accumulation panel, b) plugging a supplied lead into a car cigarette lighter for around 30 minutes per cycle, or c) connecting to an outside 12 volt DC supply. It is estimated that if the refrigerator is connected to an outside power source and turned on for about 90 minutes the cooling tank 53 would be activated and therefore provide refrigeration to the cabinet for 6 hours, after which the compressor 55 would re-start and run from the self-contained battery 57 to provide a further 6 hours of refrigeration, thus effectively cooling the cabinet for a minimum of 12 hours without any additional outside power requirement. This period could be further extended in lower ambient conditions. With the use of a solar accumulation panel to re¬ charge the battery the system will effectively provide a refrigerator that could be continually operated without the need for any outside power and at a "zero cost" to the user. The system of immersing the evaporator coils in a tank of solute, improving the energy efficiency of the compressor and reducing reheat cycles could be also adapted to a small upright cabinet similar to that used in caravans, and if used in conjunction with solar panels

mounted within the van roof could provide permanent no cost refrigeration.

In the case of solar accumulation the operation is almost self-regulatory. Higher ambient temperatures are usually associated with increased intensities of sunlight and therefore the potential of accumulation is proportionately increased.

By placing the evaporator coils in a tank of solute an additional source of "cold" is provided which means that the compressor can be operated less frequently than in conventional refrigerators. Intermittent lengthy use of a compressor is much more energy efficient than frequent use in short bursts. The energy efficiency of the compressor can be improved by up to 70% by reducing evaporator reheat from the evaporator back into the refrigerator cabinet, by reducing the operating pressure of the compressor by between 5psi and 20psi (depending on refrigerant) and the introduction of a cold storage bank. Whilst there has been described in the foregoing description a refrigerator unit incorporating the principal features of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the essence of the present invention.

In particular it is also envisaged that by incorporating the changes to provide for the increased energy efficiency of the compressor, the dramatic reduction of evaporator reheat and the use of the cold storage bank as embodies in this invention, it is also possible to provide refrigeration and freezing units for commercial application that operate with significant advantages in energy efficiency.