Patent Publication Number: US-2021164693-A1

Title: Portable heating system

Description:
FIELD OF THE INVENTION 
     The present invention relates to a Portable Heating System (PHS). 
     BACKGROUND OF THE INVENTION 
     A variety of portable heating systems are available for mobile applications. Most appreciated is the use of electrical heaters where access to an electrical power source in form of a grid or a battery is available. However, since the availability of an electric grid or a high capacity battery is not always granted the heat source can also be a burner that utilizes a fluid fuel for producing heat. The heat can in both embodiments be transferred from the source to the consumer via an air- or liquid-based distribution system. 
     When it comes to larger mobile fuel-based heating systems, they can feature not only a burner for producing heat but also an engine coupled to a generator in order to additionally provide sufficient electrical energy in order to supply the transporting system for transporting the heat from the burner to the intended place that should be heated. For example, portable heating systems may have an integrated fuel tank and a power generator with the specific purpose of providing electrical power to the system. 
     The transporting system for transporting the heat, can be a tubing system with a blower fan or a circulation pump depending on the transportation media for transporting the heat being based on air or water. In the following the term “fluid” will be used which will cover both air and water based transporting systems as well as other suitable medias being glycol or oil based. 
     Portable heating systems require to be light weight so that can be easily transported and handled. Portable heating systems may be used for climate comfort or in extreme climate conditions where heat is needed, for example cabin of a vehicle, boat cabin, tents or engine of a vehicle in extreme cold climate. 
     Any application of fluid fuel based portable heating systems works following the same general concept. Means as a fan or pump for forcing a heat transporting media in form of a fluid through a heat generator are used so that the transporting media is heated. To power these transportation means and to facilitate the combustion of the fuel and produce heat, electrical power is needed. Thus, portable heating systems need to be connected to an electrical power source as a battery, power generator or grid power. 
     The main electrical consumption in these systems depends on the fuel injection system/fuel atomization pressure, spark system and the air fan/air blower. Because of the high electrical consumption, the commercial availability of these portable heating systems is rather limited. Due to the high electrical consumption it is not possible to operate a standard portable heating system using a car battery as power source since after few hours of use the battery becomes completely depleted. 
     Accurate use of vehicle batteries is particularly relevant in an electric vehicle. In these vehicles, cabin heating cannot be produced by electrical heating as this would cause complete depletion of the batteries within few hours. 
     For these reasons alternative solutions to keep small areas heated are currently used. For example, most of the truck drivers who stop their vehicles on resting areas during the night to get rest/sleep keep the vehicle engine running in order to use the heat from the engine to heat the cabin. 
     This solution causes pollution of the environment and reduces the total fuel efficiency as the use of the engine for heating is rather inefficient. 
     Furthermore, this solution is not possible in all-electric or battery electric vehicles (BEVs) where no internal combustion engine is present. 
     Additionally, combustion engines, being the engine of a truck or for powering a standalone electric generator, is rather noisy and thus not very environmentally friendly and acceptable. 
     Alternatively, a small fluid fuel-based heating system can be installed in the cabin of the vehicle avoiding running a noisy engine and getting a better heat efficiency, e.g. between 65-70% from the fuel. This solution has the drawback that a separate battery is needed to supply enough electrical power and avoid that the battery of the vehicle gets depleted. However, even in this case, after a couple of hours of use the separate battery for the portable heating system needs to be recharged. The recharging of the battery can be obtained at the expense of the vehicle battery. Indeed, under driving conditions the vehicle generator will have to use part of the power from the engine, i.e. more fuel consumption, to charge in turn the separate battery of the portable heating system. 
     U.S. Pat. No. 3,150,656 discloses a heater for use in a vehicle, including a burner, a heat exchanger and thermoelectric elements. A plurality of such thermoelectric elements is arranged in series on the outer surface of the heater combustion chamber to produce an electric current. Thermoelectric elements for sure can help the problem and maintain the full charge of the battery which can make the portable heater completely independent from external electrical supplies. 
     Thermoelectric elements when arranged between the combustion chamber being heated by the burner and the heat exchanger makes a very compact system. However, a disadvantage is seen in that the thermoelectric elements can be damaged if the temperature on the hot side exceeds the specifications of the specific thermoelectric element. More specifically the soldering&#39;s of the thermoelectric elements will melt and damage the thermoelectric element. If this happens the thermoelectric elements will have to be exchanged. One root cause for the damage is if the combustion process is not controlled and excess temperatures are reached. Another cause can be if the produced heat is not sufficiently transferred from the combustion chamber through the thermoelectric elements and absorbed by the heat transporting media. In other words when the heat generated in the combustion chamber is not removed by the heat exchanger. 
     Hence, an improved portable heating system would be advantageous, which in a better way controls the production of heat and the exchange of heat from the heat exchanger in order to safeguard the thermoelectric modules. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to provide a PHS featuring thermoelectric elements where the thermoelectric elements in a better way is safeguarded against excess heating. 
     SUMMARY OF THE INVENTION 
     As earlier stated investigations on the failure of thermoelectric elements integrated in a PHS has shown that excess heating is the major reason for failure. Thermoelectric elements are produced in a variety of types each having its own specification when it comes to the use conditions. Some are specifically developed for power generation and other for cooling purposes. Specific design choices when it comes to semiconductor material choice and doping, form and thickness of the material brings advantages and disadvantages that must be taken into consideration in the specific application. However, they all have one disadvantage in common that is solved by the solution presented hereby. The bunching of the individual PN semiconductors in thermoelectric elements are assembled to elements using a soldering technique where the soldering in general are not stable when a temperature over 320 degrees Celsius is reached. More specifically, it has been found that even though there is still a high demand for transfer of heat to the heat transporting media from the combustion chamber, the heat transfer ratio is decreasing because the heat cannot be transferred between the combustion chamber and the heat exchanger where the thermoelectric modules are arranged in-between. This is due to the specific semiconductor nature of the thermoelectric elements and the utilization of those. The heat conducting qualities of a thermoelectric element is highly influenced by the utilization of the component. Thus, when the thermoelectric element is not supplying a current, the thermal conductivity will be low and the thermoelectrical element will with its glass-like semiconductor crystal build up appear like a thermal isolating part for the forwarding of the heat to the heat transporting media. The problem is seen when the battery is fully charged and where the thermoelectric element is delivering more electric energy than absorbable by all the electrical consumers in the PHS. The electrical consumers include the electrical control, the combustion blower, the fuel pump and the means for forcing the heat transporting media, being a fan or a pump. However, if the thermoelectrical element is utilized in a way where a current is drawn, it serves like a heat pump, transferring heat between the hot and cold side proportional to the number of electrons that run or the current draw through the thermoelectric module. 
     Thus, the object of the invention is obtained in a first aspect of the invention by providing: a portable heating system (PHS), comprising a PHS air inlet, a combustion chamber for combustion of fuel, a burner connected to said air inlet, said burner comprising a fuel inlet for introducing fuel to said burner, a combustion blower for blowing air from the air inlet into said combustion chamber thereby allowing for production of heat by combustion of said fuel and an outlet for releasing exhaust from the combustion chamber, a heat exchanger, interfacing the combustion chamber and exchanging heat with a heat transporting media, wherein said heat exchanger is having a first side, arranged in such a way as to absorb heat from the combustion chamber and a second side for releasing heat into the heat transporting media wherein the heat exchanger further comprises at least one thermoelectric module arranged in-between the first side and second side of said heat exchanger for producing electrical effect, a rechargeable battery for absorbing the electrical power generated by the at least one thermoelectrical module where the PHS further comprises a control that monitors the electrical effect generated by the at least one thermoelectric module and regulates the current draw from the at least one thermoelectric module to a level within a preset range of current draw corresponding to a preset range of thermal conductivity of the at least one thermoelectrical module by distribution of the generated electrical effect into selected electrical power consumers arranged with the PHS. 
     In an embodiment, the PHS further includes at least one electrical consumer wherein the control is adapted as to monitor the charging of a battery connected to be supplied with electrical energy from the at least one thermoelectric module and further to switch off the charging when a threshold voltage level on the battery defining a state of full charge has been reached and subsequently connect the thermoelectric module with one or more electrical consumers that consumes at least an amount of electrical energy that provides a good thermal conductivity of the at least one thermoelectrical module. 
     In a further embodiment, the PHS further includes at least one electrical consumer, wherein the control is adapted as to monitor the charging of a battery connected to be supplied with electrical energy from the at least one thermoelectric module and to provide a pulse width modulated (PWM) signal for distribution of electrical energy generated by the at least one thermoelectric module so as to by switching means provide electrical energy to the battery during a first period of the pulse width modulated signal and to by switching means provide electrical energy to an electrical consumer during a second period of the pulse width modulated signal and where the PWM ratio of the PWM signal is adjusted in response to the monitored charging level of the battery so as to absorb in total at least an amount of electrical energy that provides a good thermal conductivity of the at least one thermoelectrical module. The PWM signal thus with the pulse-pause ratio determine the charging time and the dissipation time of the electrical energy generated by the at least one thermoelectric module where it of choice can be the pulse or the pause interval that controls the charging or dissipation time. The pulse-pause length of the PWM is in an embodiment configured to be in the interval from 1 microsecond to 10 minutes. However, the specific measures depend on the design of the electronics. If the switching means is a relay, the PWM will be in the range of minutes. If the switching means is transistor based, it can be in the interval from 1 microsecond and up, depending on the slew rate of the transistor used since high frequency switching and a slow transistor will lead to high dissipation and possible destruction of the switching transistor. In an embodiment featuring transistors, the PWM pulse-pause length is configured to be between 1 (one) millisecond to 1000 milliseconds. The transistor is in an embodiment a bi-polar transistor. In an embodiment, the transistor is a Field Effect Transistor (FET). In an embodiment, the transistor is a MOSFET transistor. FET type transistors feature a high slew rate and low on-resistance which avoid dissipation and destructive heat buildup in the transistor itself. Additionally, the impedance of the gate pin is high thus rendering the FET easy to control with a control signal from the controller. 
     In an embodiment, a thermo sensor is arranged with the rechargeable battery in order to determine the temperature of the battery. 
     The control is configured to determine a value of the PWM as to provide a charging current to the rechargeable battery based on the temperature of the battery and corresponding preconfigured safe charge values mapped to the temperature of the battery, the safe charge values being stored with the control. 
     More specifically, in embodiments of the PHS the electrical consumer is one or more resistive heating elements for dissipation of electrical power and converting the electrical power into heat. 
     In embodiments of the PHS, the resistive heating element is arranged in position within the PHS for heating one of the following: the air inlet; the fuel tank; the fuel pump; the fuel inlet to the fuel pump; the motor for the combustion blower; the circulation pump (if transportation media of heat is liquid based); a buffer water tank for heated water (if transportation media of heat is liquid based); the motor for the air-blower (if transportation media of heat is air based) or with the rechargeable battery. 
     Since the performance of especially a rechargeable battery is very temperature dependent, a temperature regulation is foreseen that only dissipates electric energy into heat in position with the described components when the supply of heat will keep the component in its ideal temperature conditions. As an example, a rechargeable battery will perform best when the temperature is between plus ten to plus 50 degrees Celsius. For a rechargeable battery dissipation of electrical energy as heat in proximity of the component should only be done when the temperature is within the ideal temperature range in order to prolong lifetime and enhance performance of the rechargeable battery. Thus, in an embodiment, the control is adapted to monitor the temperature of the rechargeable battery and in case the temperature of the rechargeable battery exceeds a predetermined value disconnect a heating element arranged with the battery to avoid excess heating of the battery. 
     In a special embodiment of the PHS, the electrical consumer is a clamp that serves to electrically short circuit the at least one thermoelectric module and dissipate the electrical power generated by the at least one thermoelectric module in the inner resistance of the thermoelectric module itself. 
     In yet another embodiment of the PHS, the control is configured to provide the motor for 1) the electric fuel pump, 2) the combustion air-blower or 3) the air-blower or 4) the circulation pump with a supply current that varies in amplitude and polarization so as to regulate the motor to inefficiency but keeping the intended velocity so as to burn electric power generated by the at least one thermoelectric module in the motor and provide heat. In this way there is no need for extra components in the form of heating elements or power resistors which helps to build a compact and cheaper PHS. A normal DC motor with brushes can be controlled in this way as well as will be the case with a brushless DC motor or a Stepper motor. 
     For safeguarding the at least one thermoelectrical module against heating and damage a special embodiment of the PHS is further comprising means for measuring the temperature on the hot side of the at least one thermoelectrical module where the control is adapted to monitor the temperature level on the hot side of the at least one thermoelectrical module and in case the temperature level exceeds a temperature threshold value, the control responds by increasing the current draw from the at least one thermoelectrical module until the temperature level on the hot side is beyond the temperature threshold value and in case a maximum threshold value for the current draw is reached and the temperature level still exceeds the temperature threshold value, the control further controls the fuel pump in order to decrease the amount of fluid supplied to the burner until a state is reached where the temperature level on the hot side of the at least one thermoelectrical module is not exceeding the temperature threshold value. It is understood that the regulation will need to have an inbuild latency as such as to allow the process to regulate before any further adjustment is needed. In an embodiment, the latency of regulations can be configured in the range of 1 to 60 seconds. However, the regulation latency will depend on the physical build of the PHS in order to secure that the PHS is not damaged. Thus, the threshold values for temperature values has to be chosen to match the specific type of thermoelectric module and can be maintained from consulting a data sheet. 
     In an embodiment that is within the scope of the invention the control is configured to, in case the temperature on the hot side of the at least one thermoelectrical module is below another threshold temperature and there is still a demand for producing heat, the control reacts by increasing the supply of fuel to the burner and thus producing more heat. The control will in such case lower the current draw to match a threshold level for current draw that has been found to give the best or a wanted efficiency of the system. 
     However, if there is a need for charging the battery it will be appreciated if the charging current is not limited but is optimized to the current value and waveform that will in the best way charge the battery. 
     In yet another embodiment the PHS further comprises means for measuring the temperature in a motor for at least one of the combustion air-blower, the fuel pump (centrifugal or solenoid pump) or the heat transporting media pump (air-blower or circulation pump) and where the control is adapted to monitor the temperature level and in case the measured temperature level is below a predefined temperature threshold the control avoids the startup procedure of the PHS and supply a current from the battery to heat up the motor itself or the motor environment by dissipation of electrical energy in a heating element or by dissipation of electrical energy in the coils of the motor or the solenoid without or with limited angular rotation of the motor shaft or forth and back movements of the solenoid activation member. 
     For the sake of producing an efficient and environmentally friendly PHS when it comes to submission of noise the PHS is in an embodiment adapted for having multiple settings for production of heat implemented in the control. The control can be adapted for setting a specific production level of heat and for regulating the PHS to continuously keep that production level. The control can in another embodiment be adapted for regulating the PHS from feedback from a wired or wirelessly connected temperature sensor in order to provide and maintain a constant temperature at the position that is intended to be heated. The regulation can be seamless or in steps. The regulation of the produced heat will involve regulation of both the fuel pump, the combustion blower and the heat transporting media pump to mutually providing an efficient link for transferring heat from the combustion of fuel to the heat transporting media. This is done in such a way that the thermoelectrical elements are always electrically utilized in order for providing effective heat pumps for transferring the heat and producing electrical power. 
     The thermoelectric modules may be any commercial thermoelectric modules, i.e. commercially available components such as thermoelectric p- and n-type semiconductor legs, slices, elements or discs of any shape, or any commercially available modules with integrated p- and n-type semiconductor legs. 
     The first and other aspects and embodiments of the present invention may each be combined with any of the other aspects and embodiments. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The PHS according to the invention will now be described in more detail with regard to the accompanying figures. 
       The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. 
         FIG. 1 , is a schematic drawing of a PAHS according to some embodiments of the invention, 
         FIG. 2 , is a top view of a PAHS according to some embodiments of the invention, 
         FIG. 3 , is a schematic drawing showing a PAHS  1  according to some embodiments of the invention with focus on the electrical features and 
         FIG. 4 , is a schematic drawing showing various scenarios for distribution of the by the TEG produced electrical energy controlled by the controller, for which the individual embodiments are shown in  FIG. 4 a   - FIG. 4   d.    
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     For the sake of easy explanation of the inventive concept, a portable heating system (PHS) of the type using air as the heat transportation media is hereby demonstrated. For mobile applications a portable air heating system (PAHS) is practical. However, for the use in caravans, cottages and for many other applications a liquid-based system is preferred. Thus, it is appreciated if all types of PHS is recognized to fall within the scope of the invention. 
       FIG. 1  is a schematic drawing of a PAHS according to some embodiments of the invention. The PAHS  1  comprises one or more cabin air inlet  2 , one or more combustion air inlet  3 , a burner  4  connected to the combustion air inlet  3  via an air inlet chamber  5 ; a first heat exchanger  6  for producing electricity; a second heat exchanger  7  for increasing the temperature of the air entering the PAHS  1 ; one of more air outlet  8  to diffuse warm air in the vicinity of the PAHS  1 ; an exhaust outlet  9  to allow the release of the exhaust from the burner to the outside environment or towards a third heat exchanger. 
     When in operation fuel is pumped towards the burner  4  though piping (not shown) and air is allowed to enter the PAHS via air inlet  2 . Part of this air is directed towards the burner  4  via a burner air blower  11  (not shown in  FIG. 1  but shown in  FIG. 2 ). Most of the air entering the air inlet  2  is blown towards the first heat exchanger  6  by a main air fan  10 . The main air fan  10  and the burner air blower  11  may be mechanically independent as well as independently powered. This configuration has the great advantage that the air flux can be optimized depending on the need of the PAHS. For example, at start the main air fan  10  does not need to blow air to be heated by the first and second heat exchanger as these exchangers are not hot as the burner has not started yet or have been just started. The burner air blower  11  on the contrary needs to blow air inside the burner so as to start the burner and produce heat. Thus, the speed and the need of the main air fan  10  and the burner air blower are quite different, and the detachment of their operability optimizes their function and reduces the electricity and fuel consumption. For example, when the heat exchangers  6 , 7  are hot, the burner  4  can be stopped, i.e. the burner air blower  11  can also stop, while the main air fan  10  needs to blow continuously so as to take advantage of the hot heat exchangers and thus producing hot air that is released via hot air outlet  8 . The fuel used may be in the liquid, gas or solid form. 
       FIG. 2  is a top view of a PAHS  1  according to some embodiments of the invention.  FIG. 2  shows PAHS  1  comprising a cabin air inlet  2  allowing air to enter an air intake chamber  12 . When in operation, the air in the air intake chamber  12  is blown via the main air fan  10  inside the PAHS  1  from the air intake chamber  12  towards the first heat exchanger  6  and towards the second heat exchanger  7  so as to produce hot air to be released into the vicinity of the PAHS  1  via air outlet duct  8 . From the combustion air inlet  3  air is forwarded via the air inlet chamber  5  to the burner  4  via the burner air blower  11   
     A flue pump (not shown) ensures that fuel from a fuel tank is pumped into the burner  4  via internal piping. Heated air and exhaust from the burner exchange heat with the first heat exchanger  6  and the second heat exchanger  7  and leaves the PAHS  1  via exhaust outlet  9 . 
     Programmed control electronics may control the burner under operation. 
     The burner is controlled by a flame sensor (not shown), fuel pump/metering pump (not shown), a temperature sensor (not shown) and the combustion air blower  11 . 
     In operation by liquid fuel the burner  4  is firstly started: the electric glow wire mesh receives electrical power and start to glow. The fuel is injected onto the glowing wire mesh and also dropped partly onto the glass wool. The burner air blower  11  begins to add the necessary volume of air for combustion. The fuel over the glow wire mesh and dropped on glass wool ignites. The flame sensor senses the glowing from the flame and switch off the electric power to the glowing wire mesh. The flame from dropped fuel on glass wool superheats and evaporates the fuel in the fuel evaporator. Evaporated hot gas injects in the start flame and burns in the present of air, so that the burner 4  will run continuously. 
     In operation by LPG gas fuel the burner the burner  4  is firstly started: the spark plug receives high voltage electrical power from the electronic ignition system and start to ignite. The LPG fuel will be mixed with air in the primary gas-air mixer  135 . The burner air blower  11  begins to add the necessary volume of air for combustion and the burner  4  will run continuously. The flame sensor works as mentioned before. 
     The burner is designed so that most of the hot gases will be burned at the flame outlet, which means that most of the hot gases will be burned in the first heat exchanger, i.e. the power generator. An electronic control system (not shown) adjusts the volume of the combustion air and the metering of the fuel in any condition. 
     Programmed control electronics may control the burner  4  under operation. 
     By operation with liquid fuel the burner  4  is controlled by the flame sensor, fuel pump/metering pump, temperature sensors and the combustion air blower  11 . 
     By operation with LPG gas fuel the burner is controlled by the flame sensor, Fuel solenoid valve, self-acting thermostatic safety valve and overheat sensor. 
       FIG. 3  is a schematic drawing showing a PAHS  1  according to some embodiments of the invention with focus on the electrical features. More expediently, the first heat exchanger  6  for producing electricity features at least one thermoelectric module (TEG)  13  for producing an electric current. From the electric power outlet  14  the electric current produced is led to the controller  15  which monitors the electrical effect generated by the at least one TEG  13  and regulates the current draw from the at least one TEG  13  to a level within a preset range of current draw corresponding to a preset range of thermal conductivity of the at least one TEG  13  by distribution of the generated electrical effect into selected electrical power consumers arranged with the PAHS  1 . The controller  15  monitors the battery  16  and do a recharge when needed to keep the battery  16  fully charged. When the electrical current supplied to the battery  16  decreases as the state of full charge is achieved the controller  15  distributes the surplus generated electrical energy to electrical power burners or consumers  17  arranged with the PAHS. Arranged with the PAHS does not necessarily mean fully integrated with the PAHS but also that the power consumer  17  can be arranged external to the PAHS housing. As an example, the battery  16  itself can be arranged inside or outside the PAHS housing free of choice and so as well will it be the case for other electrical power consumers  17 . The reason for the controller  15  to distribute the generated electrical power and put a load on the TEG  13  is as earlier described to enable the TEG  13  to act as a thermo pump for transferring heat generated by the burner  4  through the heat exchanger  6  in order to heat the air stream from the cabin air inlet  2  forced through the PAHS with means of the main air fan  10  producing hot air that is released via hot air outlet  8 . For the sake of completion, the battery can be any suitable type of battery that satisfies the specifications. The battery type should be chosen carefully with regard to the environment when it comes to performance under low temperature conditions where the battery should still be in a condition as to supply sufficient electrical energy as to start up the PAHS. 
       FIG. 4  is a schematic drawing showing four different scenarios a-d for distribution of the by the TEG produced electrical energy controlled by the controller. 
     In the first embodiment showed in  FIG. 4 a   , the controller  15  has closed the switch  18  in order to forward the total produced amount of electrical energy from the TEG  13  for recharging the battery  16 . 
     The second embodiment showed in  FIG. 4 b   , shows the condition where the battery  16  is fully charged and where charging is stopped by the controller  15  by opening the switch  18 . This open loop influences the PAHS heavily since the TEG  13  will not be able to work as a thermo pump using the Seebeck effect since the flow of electrons has been stopped. Thus, the thermal conductivity of the semiconductor of the TEG  13  will be lowered and provide a lower transfer ratio of heat from the burner to the heat exchanger fins. This situation should be avoided since overheating in the burner section will be subject to the TEG  13  being damaged. 
     In the third embodiment showed in  FIG. 4 c   , the controller  15  upon completion of charging the battery  16  the switch  18  has a third position where in the closed position it connects a power consumer  17 . The power consumer is designed to take up sufficient electrical power as to enable the TEG  13  to work as a thermo pump. Referring to  FIG. 2  a power consumer  17  in form of a power resistor is arranged in the PAHS. Thus, the surplus electrical power generated is converted into heat which is within the spirit of the invention having the aim of producing heated air. The physical arrangement of the power consumer, here a power resistor, can as shown in  FIG. 2  be for heating the combustion air or the cabin air. However, power resistors can be arranged various places as e.g. for heating or evaporating the fuel, for heating the motor or fan environment, for heating the battery and will still be within the scope of the invention. 
     In the fourth embodiment showed in  FIG. 4 d   , the switch  18  has by the controller been put in a position to short circuit the TEG  13 . Thus, the Seebeck effect is maintained and the heat produced by the TEG is dissipated in the inner resistance of the TEG itself and forwarded to the airstream.