TECHNICAL FIELD

The present invention relates generally to household appliances, in particular to transfer of heat energy between household appliances utilizing peltier elements.

BACKGROUND

As public concerns more and more about the environment change due to global warming, rising fossil fuel prices and security of energy. Renewable energy is playing a vital role in producing local, clean, and inexhaustible energy to solve these problems. Among different renewable sources such as wind, hydropower, waves, solar, biomass and others, distribute generation from solar and wind turbine is increasing rapidly where each of these resources is intrinsically direct current (DC). Better compatibility with the DC energy storage technique such as battery and fuel cell has drawn recent interest to DC use. Moreover, a large number of appliances in households, offices, and industries that run on low voltage, direct current, converted inside the device from standard alternating current (AC) supply. By simply getting rid of the losses that come from AC to DC conversions, energy losses can be reduced. Easier incorporation of distributed generation and back up batteries can be used in an efficient way to supply the DC appliances directly. Mechanisms that are normally used for communication among devices within buildings that includes sensors, controllers, and status of other devices need to be low power and persistent. There are energy losses in power conversion when the electronic devices are in active use, losses when they are in low power modes, and losses when the product is disconnected but still the external supply remains plugged in. Low voltage DC usage provides key benefits which is that low voltages power needs not to be in balance and as a result disturbances do not propagate through the system and also it protects sensitive devices from many other power quality problems. Among other benefits of low voltage DC includes safety and fine scale control.

Recently developed household systems include houses run on DC only, where the power inlet into the house is DC from solar cell, wind power plants or other sources in addition to direct converted AC. One problem when implementing such a household system is how to provide home appliances that typically run on AC current, such as refrigerator, stove, dishwasher, laundry machine to a DC system. At the same time, it is an ongoing development to replace conventional cooling systems in e.g. refrigerators. Conventional cooling systems typically include refrigerants that are both hazardous for humans and to the environment. A conventional cooling system contains three fundamental parts, namely the evaporator, compressor, and condenser. The evaporator is the part where the pressurized refrigerant is allowed to expand, boil, and evaporate. Energy is absorbed during the change of state from liquid to gas. The compressor acts as the refrigerant pump and recompresses the gas to changes its phase to liquid. The heat absorbed at the evaporator and the heat produced during compression are expelled into the environment or ambient the condenser.

One possible technical field that has been explored in relation to heating or cooling techniques is the application of peltier elements. This will be described further in the detailed description, but in short, it entails utilizing peltier elements that provide a temperature gradient when fed with a direct current, and that provide a direct current when subjected to a temperature gradient. Examples of such applications have been presented in [1] which describes a refrigerator utilizing peltier elements for cooling, and [2] which describes a freezing/defrosting arrangement utilizing peltier elements. There is a need to find viable solutions to providing home appliances that are adapted to run on DC without any need for a converter. In addition, in order to combat variations in power supply and enable managing over consumption of available energy, it is necessary to provide means of efficiently storing and utilizing energy in or near the kitchen or household appliances.

SUMMARY The present disclosure obviates some of the problems of the above- mentioned solutions, and provides an energy efficient household appliance.

An aspect of the present disclosure presents a household system, which includes, a first cooling unit that is configured to be connectable to a heat/ energy reservoir via a first peltier system, and a heating unit that is configured to be connectable to the heat/ energy reservoir via a second peltier system, where the first peltier system is configured for transferring heat/ energy between the cooling unit and the energy reservoir, and the second peltier system is configured for transferring energy between the heat reservoir and the heating unit.

Advantages of the present disclosure include an energy efficient household system.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, together with further objects and advantages thereof, may best be understood by referring to the following description taken together with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a peltier element;

Fig. 2 is a block diagram of an embodiment of the present disclosure;

Fig. 3 is a block diagram of part of an embodiment according to the present disclosure;

Fig. 4 is a block diagram of a further embodiment according to the present disclosure;

Fig. 5 is a block diagram of yet a further embodiment according to the present disclosure; Fig. 6 is a block diagram of a further embodiment of the present disclosure,

Fig. 7 is an illustration of an embodiment of a household system according to the present disclosure.

DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

The present disclosure provides an energy efficient household system or appliance where energy is stored and exchanged between a cooling unit e.g. refrigerator and a heating unit e.g. stove by using peltier elements. There are existing known household appliances that utilize peltier elements to heat a stove or cool a refrigerator. However, the known appliances are unable to provide a temperature difference e.g. 60°C needed to simultaneously maintain a refrigerator and a stove at their respective operational temperatures. The inventors have identified a novel solution wherein two peltier systems are utilized in combination with a heat reservoir, whereby at least a cooling unit and a heating unit can be maintained at their respective operational temperatures. In order to further the understanding of the present disclosure, a brief discussion of peltier elements follows below.

A peltier element is a device that utilizes the peltier effect to pump heat from one surface to another surface. It typically consists of two plates, one is a cold plate, and the other is a hot plate. The plates are electrically connected to a power supply. If voltage is applied to the peltier element, heat will be pumped from the cold surface to the hot surface and will make one plate cool and one plate hot. It does not generate heat or cold by itself, rather transfers heat from one plate to the other. It is also called a thermo electric cooler (TEC) or thermo electric module (TEM). It is also important to know- that this phenomenon may be reversed when the polarity of the applied DC voltage is changed and it will cause heat to move in the opposite direction. A thermoelectric module may be used for both heating and cooling purpose; in addition, it is very suitable e for precise temperature control applications. If a temperature difference is applied across the module, it will generate a voltage and thus the module can be used for power generation.

The present disclosure exploits the functionality provided by a so-called peltier element. The peltier effect is a thermoelectric phenomenon, which occurs when a direct current is conducted by a combination of metals and semiconductors and establishes a temperature gradient between the two sides of the element, see Fig. 1. The effect can be used in order to provide a direct current by applying a temperature gradient to the peltier element. The corresponding Seebeck effect causes a transport of heat between the two sides by providing a direct current to the peltier element. In essence, the charge carriers e.g. electrons and holes transport thermal energy from the cold side to the hot side of the peltier element. Thereby it is possible to use a peltier element as either a provider of a current, or as a means of transferring heat from one object to another. By heating one side of the peltier element, the opposing side will become cooler and vice versa. With reference to Fig. 2, a basic embodiment of a household system according to the present disclosure will be described. The system 1 includes a first cooling unit 10, which is connected to a heat reservoir 30 via a first peltier system 1 1. A heating unit 20 is connected to the same heat reservoir 30 via a second peltier system 21. Thereby, the first peltier system 1 1 is configured to transfer energy in the form of heat energy between the cooling unit 10 and the heat reservoir 30, and similarly the second peltier system 21 is configured to transfer energy in the form of heat between the heat reservoir 30 and the heating unit 20. The peltier systems can preferably be configured to be powered by a DC system e.g. 48 V DC system.

In a further embodiment, the cooling unit 10 is a refrigerator and the heating unit 20 is a stove. According to an additional embodiment, the heat reservoir 30 comprises a hot water reservoir to which a water consuming 40 units e.g. dishwasher or laundry machine can be connected. Thereby, the household system 1 provides a refrigerator 10, a stove 20, and a hot water reservoir 30. The present disclosure presents a novel combined refrigerator 10 and stove 20 unit 1 configured to be powered mainly by a DC supply. A thermoelectric module (TEM) 1 1 creates temperature differences on both sides of it by extracting heat from one side to another side when it is supplied to electric power. This concept is used for the refrigerator 10 to work. Both the extracted heat from the refrigerator 10 and the heat created due to the power supplied to the TEM 1 1 appear as heat on the other side of the TEM 1 1. This heat is collected by a water reservoir 30 and circulated by a pump to the cold side of a second TEM 21. This heat is used to increase the cold side temperature of the second TEM 21 so that the temperature at the hot side of the module can be increased easily to 100°C by connecting the module to a 48 V DC supply. To store heat in the stove 20, paraffin is used which has a capability of latent heat storage by changing its phase from solid to liquid at 100°C. The water of the hot water reservoir 30 can have a temperature of up to 60°C, which can be used in a dishwasher or a laundry machine and thus reducing the power consumption of the dishwasher or laundry machine. An additional small (cylindrical) aluminum water tank 23 can be placed inside the paraffin of the stove to provide boiling water.

According to a particular embodiment, the current disclosure concerns a household system with a refrigerator 10 and a stove 20 connected via two peltier elements 1 1 , 2 1 or peltier systems and a hot water reservoir 30. The system 1 comprises a cooled unit (refrigerator) 10 connected to a reservoir 30 of hot water via an air/ liquid peltier system 1 1. A heated unit (stove) 20 is also connected to the hot water reservoir 30 via a liquid/ solid peltier system 21. The peltier systems are preferably powered by a 48V DC system. Each peltier system can comprise a plurality of individual peltier elements. The peltier systems 1 1, 21 or TEM operate in an analogous way as conventional cooling systems. Thermal energy is absorbed at the cold junction by electrons as they pass from a low energy level in the p-type semiconductor element, to a higher energy level in the n-type semiconductor element acting as the evaporator. Thermal energy is expelled to the hot junction when the electrons are moving from a high energy level of n-type element to a lower energy level p-type element acting as the condenser. Thermoelectric Coolers acts as a heat pump and a solid-state device without moving parts, fluids, or gasses. The electrical power that is supplied to the module provides the energy to move the electrons through the system as the compressor.

Thermoelectric modules can be compared with thermocouples that are made by connecting two wires of different metal, typically copper or constantan, in such a manner so that two junctions are formed. After that, one junction is kept at some reference temperature, while the other junction is attached to the object being measured. When the circuit is opened at some point then the generated voltage is measured. By considering a pair of fixed junctions into which electrical energy is applied cause one junction to become cold while the other becomes hot in an opposite manner. Several thermocouples are used between two plates of peltier element and they are connected in series. Peltier elements are mainly made of semi conductive materials. It has several PN junctions that are connected in series electrically and thermally in parallel. They are heavily doped which indicates special additives that will increase the excess or lack of electrons. The thermoelectric elements and electrical interconnects are mounted between two ceramic substrates. The substrates are used to hold the overall structure together mechanically and to insulate the individual elements electrically from one another and from external mounting surfaces. The peltier elements normally generate a lot of heat on the hot surface, which is more than the heat they dissipate. It is because the TEC itself draws a lot of current, which generates heat itself due to heat losses. The most commonly used cooling method for peltier modules is the air-cooling. A heat sink that carries a cooling fan is mounted on the hot side of the peltier module to transport the heat away from the body. Heat transfer paste is used to transfer the heat efficiently. At the hot side, energy is expelled to a heat sink as electrons move from a high energy level element (n-type) to a lower energy level element (p-type).The heat sink should be chosen in a way so that it would be able to draw all the heat power that comes from the hot side of the peltier module.

Different types of cooling/ heating systems can be used for peltier modules, for example air/air, air/liquid, and liquid /liquid, and liquid/solid cooling systems. Air/ air has a fan mounted on both sides of the module. Each fan spreads the air to the surroundings. The fan that is attached on the cold side spreads cold air and the fan that is connected to the hot side, spreads hot air. An air/ liquid is used between the refrigerator compartment and the water tank compartment. A fan connected to the cold side of the peltier module to spread the cold air and the tube is connected to the hot side of the peltier module to flow liquid that will carry out the heat from the hot side of the module. The fan of the air cooling system is supplied by low DC voltage and it takes less power, as illustrated in Fig, 3. The peltier module extracts heat from the cold side of the module to the hot side of the module and the water that is used for cooling, circulated by a pump through the pipe and serves to take away the heat from the hot side of the peltier module to the tank water. The cooling fan spreads the cooling air inside the refrigerator compartment.

Another system with liquid circulation through the pipe on both sides of the thermo electric module can also be used. Usually high temperature thermoelectric module use the liquid system on the cold side to reach at a certain temperature and then to get high temperature on the hot side of the module by maintaining a certain temperature difference. A liquid cooling system on the hot side is normally used to take out heat from the hot side.

According to the embodiment disclosed in Fig. 4, the first peltier system 11 typically is an air/ liquid peltier system in which the air from the refrigerator 10 is transported to the cool side of the peltier system 11 or TEM by means of a fan, and the hot side of the peltier system 1 1 is in direct contact with the water of the hot water reservoir 30. The second peltier system 21 is typically a liquid/ solid peltier system, in which the cool side of the peltier system 21 is subjected to the water of the hot water reservoir 30 and the hot side is in direct contact with the stove 20 e.g. hot surface of the stove. In practical terms, the hot water is circulated from the first peltier system 1 1 , to the second peltier system 21 , and through the hot water reservoir, before being reintroduced at the hot side of the first peltier system 11 again.

In the combined refrigerator-stove system 1 of the present disclosure, the refrigerator side thermoelectric module or peltier system 1 1 operates both in a refrigerator mode and in the heating mode. On the refrigerator side, it pumps the heat from the refrigerator to cool it and on the hot side; it is heating the water simultaneously for later use.

The power coefficient of a thermoelectric module depends on the temperature difference between the hot side and the cold side. For low temperature difference, the maximum amount of pumped energy is high.

High temperature is necessary for the heating unit or stove 20. It is not possible to achieve a high temperature (> 100°C) using a single thermoelectric module or peltier system when the refrigerator temperature is 0-5°C. Consequently, a two-stage operation according to the present disclosure is required to get high temperatures. The purpose of the stove side module is to get high temperature and the energy from this module is stored in the phase change material. Paraffin is used to store the energy.

The two peltier systems each typically include a plurality of peltier elements connected in series, in the embodiment in Fig. 4 both peltier systems 1 1 , 12 include four 12 V DC peltier elements connected in series. However, any number of peltier elements can be connected in series to form the two peltier systems. Each thermoelectric module or peltier system 1 1 , 21 consist of at least one peltier element with a rated input voltage of 12 volt DC. In the embodiment of Fig. 4, four peltier elements are connected in series to form each of the two peltier systems 1 1 , 21. Total input voltage for the system is 48 volt DC. The cooling system of the refrigerator side thermoelectric module is air-to-liquid system. Inside the refrigerator, it is air-cooling and a fan is used to reduce thermal resistance of the heat sink inside the refrigerator. Liquid cooling system is used at the hot side of the refrigerator. The temperature inside the refrigerator is maintained between 0°C to 5°C and the hot side temperature of the module is maintained at almost 50 to 60°C as the maximum temperature difference of the module is 60°C. In the stove side, the temperature must be greater than 100°C. To increase the temperature on the stove side two-step operation has done. Another thermoelectric module with four series connected peltier element is used that rises the temperature up to 120°C. The input voltage of the module is also 48 volt DC. The cooling system used in this system is a liquid/ solid system. A liquid cooling system is used on the cold side of the module and the other side is typically a metal plate attached to the hot side of peltier elements.

According to a particular embodiment, also with reference to Fig. 5, the heating unit 20 further includes an internal heat reservoir 22 configured for storing thermal energy in the form of e.g. latent heat within the heating unit 20. According to a preferred embodiment, the internal heat reservoir 22 comprises paraffin. A tank e.g. aluminum or similar is used inside the stove compartment that contains paraffin for storing the thermal energy in the form of latent heat. A heat sink attached with hot side of the peltier module is used to give large surface area to the paraffin for heating up quickly. A radiator is placed inside the paraffin and connected between the water supply tap and the dishwasher or laundry machine water compartment via water tank compartment. The purpose of the radiator is to take the preheated water from the water tank to supply very hot water if needed in a dishwasher or laundry machine by absorbing heat from the paraffin. A small cylindrical water tank 23 can also be placed inside the paraffin, to provide boiling water.

Latent heat refers to the amount of energy released or absorbed by a chemical substance during its state change which occurs without changing its temperature, implies a phase transition such as the melting of ice or the boiling of water. A latent heat storage device contains a phase change material. Normally solid-liquid phase change materials are used as these stages are manageable compared to gas. Different types of phase change materials are used to store the heat energy such as Organic Phase Change material for example Paraffin (C _n H2n+2) and Fatty acids (CH3(CH2)2nCOOH) , Inorganic Phase Change material for example Salt hydrates (M11H2O) . Paraffin can be used as a phase change material. It is good for storing thermal energy as it has a high specific heat capacity and it is relatively cheap.

Solid liquid phase change materials such as paraffin, changes their state at a certain temperature without increasing its own temperature significantly at that point. It absorbs huge amount of thermal energy during this change of state from solid to liquid and the amount of the stored thermal energy depends on the volume and heat storage capacity of the phase change material. The stored thermal energy is released when the ambient temperature around the liquid decreases and the phase is changed to its previous stage. Paraffin absorbs a certain amount of heat at a relatively constant temperature during phase change from solid to liquid. During the reverse phase change process that means from liquid to solid, the previously stored latent heat is released at almost constant temperature. Paraffin shows crystalline characteristics due to higher purity and special composition and it gives high heat storage capacity. It is chemically inert, can store and release heat at almost constant temperature. Performance is stable during phase change cycle. It is non-toxic, ecologically harmless, easy to handle and has large melting temperature range.

With reference, once again to Fig. 2 and Fig. 6, a further embodiment of a household system according to the present disclosure will be described. The embodiment includes, in addition to the previously described units, a second cooling unit 50 configured to be connectable to said first cooling unit 10 via a third peltier system 51. The second cooling unit 50 comprises a freezer 50 connected to the first cooling unit 10 e.g. refrigerator via an air/ air peltier system. In the same manner as the first and second peltier systems 1 1 , 21, the third peltier system 51 can include a plurality of series connected peltier elements.

Due to the combination of the hot water reservoir and the three peltier elements or peltier systems, it is possible to provide a system with a high efficiency. In addition, one single system can provide a freezer, a refrigerator, a stove, and supply of hot water to a household. Prior art peltier elements are only able to function with a temperature differential of 50 degrees, maximum 60°C. Based on the present disclosure it is possible to attain at least the -45°C, 5°C, 55°C, and 105°C that are necessary for freezer, refrigerator, hot water, and stove respectively (max -60°C, 0°C, 60°C, 120°C). Although very specific temperatures and intervals are presented, it is evident that also temperatures near or around those specific values are possible to attain. Energy can be stored as cooling energy in the freezer down to -45 C and can slowly rise to - 18 C before activating the peltier element. Energy can also be stored in the stove as latent heat. With reference to Fig. 6, the household system is typically configured to be connectable to a DC or AC providing network 100. The network 100 can comprise a low voltage e.g. 48 V DC or a high voltage DC providing network 100, or a 230 V AC network, or a combination. In addition, it is desirable to utilize control electronics to control the power balance between the individual peltier elements. Therefore the system is, according to a particular embodiment, configured to be connected to a control unit 200 and with temperature sensors in each unit 10, 20, 30, 50 for controlling the power distributed to the respective units of the household system 1 from the DC providing network 100.

Also, in case other appliances e.g. a microwave oven, are connected to the DC system, the control electronics can be utilized to momentarily shut off the power to the peltier elements in order to enable additional power to the other appliance during a short period of time. In the case of a microwave oven being connected to the DC system, the power to the peltier elements can be reduced or completely shut off during the time the magnetron in the microwave is activated. As soon as the magnetron is inactive, the power to the peltier elements is supplied again.

Due to the combination of the hot water reservoir and the two peltier elements or peltier systems, it is possible to provide a system with a high efficiency. In addition, one system can provide a refrigerator, a stove, and an ample supply of hot water to a household. Prior art peltier elements are only able to function with a temperature differential of 50 degrees. Based on the present disclosure it is possible to attain 5, 55, and 105 degrees Celsius that are necessary for refrigerators, hot water, and stoves respectively. According to a particular embodiment, the household system 1 is implemented as a single combined household appliance with three separate compartments, one for the refrigerator, one for the water reservoir and one for the stove. In the case of the addition of a freezer, an additional compartment is provided, as indicated in Fig. 7.

In summary, the present disclosure provides a solution for household appliances to run with 48 V DC supply instead of normal 230 V AC voltage. Any DC house e.g., with solar panel that produces DC can be used for different household appliances at different regulated voltage level. The Energy that comes from the solar panel can also be stored in the battery as DC voltage. This stored energy from the battery can be used to run different household appliances at different regulated DC voltage level during night. The losses for AC to DC and DC to AC conversion inside the home appliances can be reduced by using home appliances that runs on DC voltage. Refrigerator and Stove normally runs on AC voltage. This work proposed a solution for refrigerator and stove to run on low voltage DC instead of normal 230 V AC supply. Two separate thermoelectric modules are used to cool down the refrigerator and to store the heat in phase change material inside the stove by creating at least a 100 °C temperature difference between these two modules. The efficiency of the thermoelectric module intended to increase by storing the extracted heat from the refrigerator and also the heat that is appearing on the TEM from the input electrical power. By storing the extracted heat from the refrigerator, hot water of around 60 °C temperature can be stored in a tank placed between the refrigerator and the stove module. This hot water can be used in the dishwasher or shower or laundry machine or for other devices where hot water is required. The hot water from the tank is used for the dishwasher during its cycle of hot water replacement. The dishwasher can be configured to take 10L hot water from the water tank during its hot water replacement cycle. By using a pump, hot water circulation can be maintained between the stove and the dishwasher water tank. If very hot water is needed, circulating water takes heat energy from the paraffin while it passes through the radiator placed inside the tank of paraffin i.e., stove.

The proposed model of refrigerator and stove might be used in DC house to run on 48 V DC voltage. These appliances will be more efficient due to waste energy storage and reduction of conversion losses. Most of the electronic appliances are already designed for low voltage DC supply. New solution of refrigerator and stove might give hope to build DC houses and as a result, society might be benefited for increased use of renewable energy sources of DC. The increased use of DC voltage for every appliance will give hope to make a revolution of DC voltage use from renewable energy sources and which in turn will give benefit to the whole world from an environmental perspective. Although the embodiments of the present disclosure are presented with reference to a low voltage DC supply network, it is equally applicable to a high voltage DC supply network or even to a regular AC supply network.

The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

REFERENCES

[1] GB935679, Improvements in or relating to cooling devices;

[2] US patent 6,038,865, Temperature-controlled appliance.