Patent Publication Number: US-2010112499-A1

Title: Sauna stove heating method and stove

Description:
The invention relates to a method for heating a sauna stove as claimed in the preamble of claim  1 , and a sauna stove according to the method. 
     Known methods for heating a sauna stove are based on the use of wood or electricity as a heat source and transmission of heat produced by this method by conducting it through contact surfaces to sauna stones. The efficiency of heat transmission based on conduction is poor, wherefore it takes a long time, usually about an hour, to heat the sauna stove. In addition, stoves that are based on the above-mentioned method have a heavy structure and are thus unsuitable for camping or travelling purposes, for example. 
     Many sauna enthusiasts have, however, provided their boat or caravan with sauna facilities. In these cases the stoves are, almost without exception, heated with wood, which means that wood needed for heating must be carried along, which takes space and is laborious. 
     From an ecological point of view, a wood stove produces a high amount of fine particles and hydrocarbon emissions, whereas the use of electricity is problematic because of great losses in production and transmission. 
     Sauna stoves have been built for dozens of years based on this philosophy, and no significant progress has happened in the field, except for the inventions described in patents FI108213B and FI115114B, for instance. 
     In some cases it is necessary that the sauna stove is transportable. A typical source of energy used by caravanners and sailors in cookers and grills is bottled gas, i.e. propane. A gas-fired stove heating method would thus be the most natural solution in these purposes, but a working solution has not been found for heating a gas stove. The biggest problem has been a typical characteristic of gas when it is burnt with a free flame. A gas flame lacks almost entirely the free carbon particles, the glowing of which would produce flame radiation essential for forming infrared heat radiation. The most common method of utilizing the heat energy of gas combustion is thus based on convection, i.e. heat transmission, as a hot low-density substance rises upwards in the gravitational field. 
     Due to the above facts, the development of a heating method for gas stoves cannot be based on known heating methods for wood or electric stoves. 
     A chance of utilizing a gas stove has long existed in camping as well as in regions where natural gas is generally available. In addition, emission standards, which become stricter in the future, will probably limit the use of traditional wood stoves particularly in densely populated countries. Gas would thus provide a good foundation for using a clean heating method, especially as the combustion products of gas are heat, water and carbon dioxide. 
     The above disadvantages can be eliminated and the aforementioned objects are achieved by a method of the invention for heating a sauna stove and a sauna stove according to the method, characterized by what is defined in the characterizing part of the claims. 
     One of the most significant qualities of the invention is the high efficiency of the sauna stove. In few minutes the stove is heated and is ready for use, which significantly reduces the energy consumption. This is based, first of all, on infrared heat radiation produced in the stove by gas energy and its large area as well as on the quickly achieved temperature of 1000 degrees. Secondly, it is based on the large area of reception elements (vaporizer surface/sauna stones) and their good capability of infrared heat radiation absorption and, thirdly, on unrestricted infrared heat radiation as well as the distance between the infrared radiant heater and the reception elements. 
     The sauna stove according to the invention may be manufactured cost-efficiently from known components and raw materials that have been in use for a long time and, if required, it can be made lighter than the traditional stoves. It is thus clear that due to the above facts, economic benefit is achieved and that there is an obvious demand for such a stove. 
     A substantial advantage of the invention is also the ecological significance of the stove, when compared with other corresponding methods. The ecological efficiency of natural gas is 65 to 70%, whereas that of electricity is 45 to 50% and that of oil 55 to 60%. 
     It can also be mentioned that the new method for heating a sauna stove and the sauna stove of the method opens up entirely new markets for a new type of sauna solutions, the key factors of which are transportability, easy manageability and quick heating. The invention creates new businesses and does not compete with already existing market players. 
    
    
     
       In the following, the invention will be described in greater detail with reference to the attached figures, in which 
         FIG. 1  schematically shows an embodiment of the invention cut from the middle at the stage of heating a sauna stove, 
         FIG. 2  schematically shows an embodiment of the invention cut from the middle at the stage of using the sauna stove for bathing, 
         FIG. 3  schematically shows an embodiment of the invention cut from the middle at the heating and bathing stages of the sauna stove, 
         FIG. 4  shows an embodiment of the invention obliquely from behind. 
     
    
    
     The figures show the following parts of a sauna stove: a reception element  2   a,    2   b  as well a radiator  3   a  and a gas energy infrared heat radiation distance  3   c  between them. A frame  6   a  provided with an operating means  10   a,    10   b,  lifting means  16  and openings  7   a,    7   c,  which, for their part, are provided with channels  5   a,    5   b  and a closing flap  8 . A sauna furnace  4   a,  at which there is an opening  7   b  with its edges  18 , and a lid  4   c  arranged thereon as well as a cavity  12  and an inclined upper surface  6   b.  Inside the frame  6   a  there are also an oxygen sensor  14  and a flame detector  15 . 
     In the sauna stove of the invention, one or more reception elements  2   a,    2   b  are heated by means of gas energy infrared heat radiation  3   b.  The reception element  2   a  comprises at least one radiator  3   a  arranged essentially at a gas energy infrared heat radiation distance  3   c  from the reception element  2   a,    2   b.    
     Gas energy infrared heat radiation  3   b  is prior art, and is used most commonly in small local heaters and, for instance, in various processes of the paper industry because of its efficiency, easy controllability and non-polluting properties. The burners of known gas energy infrared radiant heaters are most commonly based on utilization of a 3D ceramic tile mesh or catalytic wool in flameless gas combustion. This prior art is also used in the present invention to produce gas energy infrared radiation  3   b  for the stove and to heat the reception elements  2   a,    2   b.    
       FIG. 1  shows a structure solution of the invention schematically, in which the radiator  3   a  converts the energy contained in the gas into gas energy infrared heat radiation  3   b.  The radiator  3   a  is arranged to radiate unrestrictedly at a gas energy infrared heat radiation distance  3   c  from the reception element  2   a  in order to heat it up as efficiently as possible. The thickness of the reception element  2   a  affects the heating properties of the sauna stove and its purpose of use. The figures show a convection flow  9   b  caused by gas combustion and arranged in such a manner that the upper surface  6   b  of the frame part  6   a  is arranged to be inclined, the frame part  6   a  comprising one or more openings  7   a,    7   c,  which are provided with a channel  5   a,    5   b  with a closing flap  8  for closing the channel  5   a,    5   b.  The convection flow  9   b  may thus be utilized, firstly, for heating the reception elements  2   b  by leading the convection flow  9   b  through the lower part  4   b  of the sauna furnace  4   a  into the channel  5   a  and from there to outside air  11   b  and, secondly, for bringing in the outside air  11   b  through the channel  5   b.    
       FIG. 2  shows a structure solution of the invention schematically, in which the radiator  3   a  heats the reception elements  2   b  directly. In this solution, the hot radiating surfaces of the radiator  3   a  must be protected with some method in order to prevent harmful effects of splashes of sauna water. For instance, glass surfaces that tolerate heat variations may be used for this protection. The frame part  6   a  is at the sauna furnace  4   a  provided with an opening  7   b,  to which sauna water is thrown. To speed up the heating, the opening  7   b  is provided with a lid  4   c.  On the side of the sauna furnace  4   a  the edges  18  of the opening  7   b  are arranged to extend substantially lower than the upper edge of the radiator  3   a,  and so exhaust gases  9   a  are not discharged from the opening  7   b  into a sauna room  11   a  when the lid  4   c  is open. 
       FIG. 3  shows a structure solution of the invention schematically, in which the reception element  2   a  comprises at least one radiator  3   a  arranged to radiate unrestrictedly substantially at a gas energy infrared heat radiation distance  3   c  from the reception element  2   a  in order to heat it up as efficiently as possible. 
     In the figure the convection flow  9   b  is arranged in such a manner that the upper surface  6   b  of the reception element  2   a  is inclined and the reception element  2   a  comprises one or more openings  7   a  provided with a channel  5   a,  through which exhaust gases  9   a  flow into the outside air  11   b.  The radiator  3   a  takes the air required for gas burning from the sauna room  11   a  from below the lower edge of the reception element  2   a.  This sauna stove model could be used most preferably in saunas where it is easy to arrange sufficient ventilation, such as in tent saunas. 
     At the reception element  2   a  there is arranged a cavity  12  with reception elements  2   b,  and a bowl  13  with a lid for an odorizer, such as alder chips. A warm steam flow  1  is shown in the figure by an arrow. A flame detector  15  is arranged inside the reception element  2   a.    
       FIG. 4  shows a structure solution of the sauna stove of the invention, in which the frame part  6   a  comprises at least one radiator  3   a  arranged to radiate unrestrictedly substantially at a gas energy infrared heat radiation distance  3   c  from the reception element  2   a  in such a manner that it would heat up as efficiently as possible. 
     The outer surface of the frame part  6   a  is provided with an operating means  10   a  for gas flow and an operating means  10   b  for a spark igniter, which are used for switching the stove on and off and controlling the power of the stove. The outer surface of the frame  6   a  is provided with lifting means  16 , and inside the frame  6   a  there is an oxygen sensor  14 , which turns off the gas supply if the oxygen level of the sauna room  11   a  decreases too much. 
     The frame part  6   a,  the lid  4   c,  the channels  5   a,    5   b  and the flap  8  are most preferably made of stainless steel or other metal and formed as solutions having a shape of a plate, a cylinder or a casing. The reception element  2   a  is most preferably made of a heat-resistant stone-based or ceramic raw material, such as soapstone or a heat-resistant castable, and shaped as planar or like a cylinder, a casing or a bowl. Other shapes are also possible. The reception elements  2   b  are most preferably previously known, typical sauna stones. 
     All parts of the sauna stove of the invention may be made of known raw materials and with known manufacturing methods and machines. Other generally known fuels that are in liquid form at standard atmospheric pressure, such as paraffin oil, may also be used, whereby gassing occurs with known techniques by utilizing heat and pressure. 
     The method of the present invention mainly describes the sauna stove according to the method by means of a few structural alternatives only. It is obvious to a person skilled in the art that the invention is not restricted to the above alternatives only, but many variations are feasible within the inventive idea defined by the appended claims.