The invention relates to an electrically heated sauna stove or the like space heating device, in accordance with the intro¬ ductory portion of the appended claims. Correspondingly, the invention also relates to a method for heating the heat storing means, e.g. the open-topped container for stones and stone material, over which water is thrown to produce steam, hereinafter referred to as the "stone pocket" in a sauna stove.

Such electrical sauna stoves are earlier known which comprise a body to be installed on a wall or on the floor, said body having electrical resistance means arranged therein. At the upper portion of said body a stone pocket usually is arranged, said stone pocket acting as a heat storing means.

Such electrical sauna stoves are also known which are essentially flat devices to be fastened to a wall, in which devices a said heat storing means is an essentially vertically extending flat panel which often is made of potstone or the like material, behind which said electrical resistance means are arranged.

During the sauna bath the heat storing capacity of the stove is used both as a heat equalizing means in the sauna steam room and especially as an evaporating means for the water thrown thereon, hereinafter referred to as the "bathing water" . For the latter function the surfaces of the stones should have a temperature above 100°C, and the stones should be able to deliver, through their surfaces, as much heat as possible.

A problem with hitherto known electrical sauna stoves has especially been the size of the structures and the relatively low efficiency especially in that the heating up of the stove takes a relatively long time. A large stone pocket needs a

high electrical power output in order to heat up sufficiently quickly. In a small stone pocket the quantity of heat which can be used for the bathing water will remain small, in which case the sauna bath will have weak heat generation. Further, the electrical resistor's liability to failures and the difficult replacement of them have been a special problem in electrical sauna stoves. Especially in vertically arranged stoves any unevaporated water flowing through the stone pocket *2 will quickly and unevenly cool down the electrical resistance means, in which case said resistors will break down in the course of time. If, on the other hand, said resistors are located in such a manner that the water cannot reach them there will simultaneously rise an overheating problem due to poor heat escape, in which case said resistors also will break down. In flat sauna stoves intended to be installed at a wall there has also occurred the problem of i.a. the structural complexity which partly depends on the demand to protect the wall lying behind.

In known electrical sauna stove solutions the control of the heating has essentially been based on a thermostat which has switched a current to said resistors when the space has been colder than a set temperature value, and, correspondingly, switched off the current when said set value has been reached. Such a control system is quite slow to react to changes in temperature, especially if the specific mass of the heating elements of the sauna stove is large. In this respect the purpose of the invention is to show such a sauna stove wherein the heating resistors of the stove react quicker than the present ones both during the initial heating stage and during the temperature regulation stage.

In kitchen technology one knows flat cooking plates wherein lamp like infrared radiators are used as heating elements. As an example Finnish patent No. 77109 can be mentioned here, wherein a heater is based on a special halogen lamp. In such cooking plates one utilizes the quick regulativity of the

lamp, in which case the layer of protective material between the cooking vessel must be very thin so that its specific mass would be small. Such cooking plates cannot successfully be used as sauna stoves.

Thus, the starting point for the invention is to provide a new kind of sauna stove which combines a small size, a quick and efficient heating and good steam giving properties, a good temperature regulativity and further a flexible and simple replacement of the heating elements.

The characteristics of the invention are evident from the appended claims. Thus the invention is characterized in that incandescent lamps, known per se, are used as heating elements, said lamps producing, besides light, also infrared radiation which, in the use for illuminating purposes, is considered to be waste heat.

Herein the definition incandescent lamp comprises devices having one or several resistance wires enclosed in an essentially gas tight closed space, the walls of said closed space being at least partly transparent to light. A typical feature of regular lamps is further that filament environments is made such that said filament will stand a rather high temperature without the risk of "burning" . In lamps this is usually achieved by removing air and especially oxygen from the space surrounding the glowing filament, and, correspondingly, filling said space preferably with such gases which prevent such material which due to the heat is released from said filament, i.e. mainly metal vapors, from being transferred from said filament.

With respect to the invention i.a. such known lamps are considered to be suitable, which usually are used in illuminators . Usual halogen lamps have proven to be especially favourable in this respect, the surplus heat from such lamps being used for heating the stone pocket of the sauna stove,

where further the stray light obtained from said lamps favorably can be used, in some embodiments of the invention, for illuminating the sauna space. The advantage of halogen lamps is especially based on the fact that the operating temperature of the glowing filament in such lamps can be remarkably high due to the favorable effects of the halogen gas. With respect to the invention other lamps may, however, also be considered, the suitability of the lamp with respect to the invention mainly depending on the relative amount of heat production and especially its rate.

In an arrangement according to the invention the traditional special resistance elements are replaced by lamps, especially such usual suitably tubular lamps which are extremely common in the market. In this respect lamps based on halogen or the like gases are especially favorable, the operation temperature of such lamps being essentially higher than the temperature of traditional sauna stove resistors. An especially favorable embodiment of the invention is partly based on the feature found in lamps that the heated mass in a lamp is very small in relation to the lamp power output, in which case a very rapid heating will be achieved with lamps in spite of the fact that the main purpose of lamps is usually the production of light, where the production of heat traditionally has been considered as a secondary and even adverse factor.

In this connection it should be observed that even if such stove plates and ovens are known in the household equipment field, which are intended for food cooking purposes and wherein the heating is based on the function of halogen lamps, in said cases there is no question of quickly heating a relatively large space and especially not a stone pocket. In said household equipment the special problem has been that the even distribution of heat usually has called for the use of a special glass ceramic plate which in most cases has considerably raised the costs. In said oven solutions one has also usually used specially manufactured halogen tubes, in

which case the manufactured quantities have remained small. In all kitchen stove or the like solutions the heat produced has been directed to a space which is essentially closed to the user and wherein the food to be cooked has been positioned. The inventive solution, on the other hand, concerns a sauna stove or the like space ^' heating device where the object of the heating in the first place is a stone plate or the like heat storing element which is arranged to be the device ' s outermost portion which extends towards the user.

The invention will now be described with reference to the appended drawing, wherein

Figure 1 shows the inventive sauna stove as seen from above, where the stone plate is shown partially cut open in order to improve the illustrativeness,

Figure 2 shows the sauna stove according to Figure 1, at section A-A,

Figure 3 shows the sauna stove according to Figure 1, at section B-B, and

Figures 4a to 4c show some alternative stone plate structures in a sauna stove according to the invention.

In accordance with Figure 1 the heating arrangement for a stone plate 1 in accordance with the invention comprises one or several conventional halogen lamps 4. The halogen lamps 4 shown in the drawing are straight tube like halogen lamps of a standard size, said lamps having, at each end, a standard type halogen lamp bracket 5. In a tube shaped halogen lamp 4 of standard type there is a glowing filament 6 arranged centrally in a tube of special glass, said filament being held by usually several holding means 7. Said tube is filled with a gas having a suitable composition which due to halogens incorporated therein in a known manner facilitates an

extremely high operating temperature for said glowing filament 6, without said filament burning through as an effect of uneven material transfer. Due to the very high operating temperature a halogen lamp 4 is excellent as a heat producer, even regardless the fact that the main purpose of a halogen lamp is to produce light and not heat . Due to its high temperature a halogen lamp is able to heat a stone plate considerably quicker than a traditional electrical resistance.

The light which as such in a sauna application will be generated as a by-product can be utilized for illuminating the sauna steam room. For this purpose a sauna stove in accordance with the invention can comprise suitably located light apertures . Said apertures are usually covered by a glass so that bathing water cannot directly hit the halogen lamps . In one favourable embodiment said glass is tinted in order to give a romantic atmosphere.

In order to have the heat power output emanating from the halogen lamps directed to said stone plate in the most effective manner a favorable embodiment of the invention comprises mirrors or background reflectors 8 located behind said halogen lamps. as can be seen in Figures 2 and 3. Behind said background reflectors there is suitably one or several further casings 9, 10 preventing the heat from passing to the backside of the sauna stove.

Even though the transfer of heat from said halogen lamps 4 to said stone plate 1, on one hand, and directly to the air space of the sauna steam room, on the other hand, is usually sufficient without any special arrangements some of the embodiments of the invention further comprise a design of the back surface of said stone plate 1 in order to increase the surface area thereof. In other embodiments also a separate ceramic plate 11 is arranged between said halogen lamps 4 and said stone plate, said ceramic plate for making the heat from said halogen lamps more even. In one embodiment a transparent

ceramic plate 11 is further utilized in order to change the rather bright light from said halogen lamps into a more romantic one. Since said ceramic plate 11 in the embodiments mentioned last as such will protect said halogen lamps from splashing water said solutions may even comprise rather large slits in said stone plate 1, in which case e.g. a reddish light may be seen between individual stones.

A typical halogen lamp for a sauna stove in accordance with the invention will be a tube shaped lamp of standard type and suitably having a power of about 1000 to 1500 W at a voltage of 230 V, in which case the sauna stove usually comprises several tubular halogen lamps arranged in a parallel disposition. Other lamp arrangements are also possible, and instead of standard type tubular halogen lamps one can also in certain special embodiments of the invention use even halogen lamps of other shapes. It is, however, clear that the inter- changeability which can be obtained due to the standard type of the lamps constitutes an especially considerable advantage.

In the embodiment disclosed in the drawing the traditional stone pocket of a sauna stove has been replaced with a stone plate 1 of a special design. Favourably said stone plate comprises a bottom portion 2 and suitably pyramid shaped protrusions 3 which extend outwards from said bottom portion, in which case the stone plate area which can be exposed to the sauna bathing water will be considerably enlarged while the size of the sauna stove remains essentially smaller than the size of traditional sauna stoves. Thus the transfer of heat from said stone plate 1 to the water poured thereupon is efficient and the bath steam "good" . Even though the surface of the stone plate 1 disclosed in the drawing is shown to be fairly smooth except for said pyramids 3 the surface of said stone plate 1 can, within the scope of the invention, also be designed to be small-scale uneven e.g. so that further channels, bulges or the like formations are provided in order to increase the surface area.

As such said stone plate 1 can be designed as an entity or alternatively as assembled of several pieces. Especially in the latter case waste pieces from the stone industry can in an efficient manner, be utilized in a structure according to the invention, in which case one simultaneously achieves a large effective area and durability against temperature fluctuations. Especially potstone is considered to be a favour¬ able manufacturing material for said stone plate, but also another natural material can be considered. In certain cases said stone plate can be made of some artificial material, e.g. a refractory mortar-like shedding material or a corresponding material .

Figure 4a discloses an example of a stone plate structure according to one embodiment of the invention, wherein the stone plate 1 is constituted of separate rod-like stone pieces 12, 12a which are arranged in an adjacent manner, said pieces comprising ridge-like protrusions 13 in order to increase the stone material volume and especially the stone surface area. In some embodiments said protrusions 13 can further comprise a transverse grooving or the like, in which case the surface area acted upon by the water will be even larger. Figures 4b and 4c disclose some alternatives of this embodiment.

Since said stone plate in this embodiment is assembled of separate rods 12, 12a above-mentioned waste pieces from the stone material industry can be especially effectively utilized. An expansion joint 14 is formed between the separate stone pieces 12, 12a and thus the stone plate's 1 durability against temperature variations is remarkably good. Simultaneously subsequent stones, however, also lock each other in position so that said stone plate will remain well coherent. In an alternative embodiment of the invention such expansion joints are also arranged in the transversal direction, in which case the structure seen from above is like the one disclosed in Figure 1.

Contrary to the traditional sauna stoves the sauna stove according to the invention is very small in relation to its size, due to its compact structure, and thus said sauna stove can be located in an essentially arbitrary manner. Thus a wall design, which today is considered fashionable, is also possible, besides the traditional horizontal installation. The stone plate of the sauna stove according to the invention is as such favourably replaceable so that the surface structure of the stone plate is chosen in accordance with the way of installation or e.g. the user's own taste or preferences, in which case the surface configuration of the stone plate can be even very special, varying from the above described pyramidal configuration or a completely smooth surface to very complicated surface configurations. The design of a sauna stove according to the invention can thus be accomplished within remarkably wide borders. It is also obvious that an arrangement according to the invention can be accomplished also more generally for rapid heating of small spaces.

Among the other advantages of the inventive sauna stove one can especially mention the heating speed which e.g. appears in that said halogen lamps immediately deliver their full power output to the stone plates without the delay which is typical for electrical sauna stoves . A sauna stove according to the invention can be ready for use in less than 10 minutes. Since the sauna stove according to the invention widely is based on the use of standard formed components in a new application the manufacture and service of the sauna stove is especially simple, which feature will be even more evident since also the number of components is rather low. As such the very hot lamps do not withstand the strains of temperature changes due to the sauna bathing water, and thus the inventive structure favour¬ ably realized so that said lamps 4 are protected by either an unbroken stone plate 1 or by a separate ceramic plate. Since the heating elements according to the invention have a surface completely made of glass they have also the advantage over

conventional electrical sauna stoves that the sauna bathing water can never directly hit metal surface resistors, which prevents the occurrence of the "rusty" sauna bathing steam which is typical for older electrical sauna stoves.

One essential advantage with the sauna stove structure according to the invention is further the good possibilities to control the temperature. Since the operational temperature is very high a small rate of relative power control will function efficiently. For a satisfactory function the halogen lamps need a base power which is at about 50 % of the maximum power. In the area between said base power and said maximum power the power can be controlled rather easily and using conventional electric or electronic means, favorably a very exact and quick regulation by using e.g. thyristor means, which in traditional sauna stoves has been impossible. Generally it is appropriate for the control means not to be located in the actual sauna stove where, in use, they are near hot surfaces and further exposed to splashing water. In one embodiment of the invention the control means are actually arranged so that they like other household devices can be remote-controlled by using a infra-red transmitter or the like device.

Also the fact must be considered to be an advantage that the apparatus according to the invention is extensively based on a modular concept and standard components in the electric field, and thus a wide scope of variation possibilities are guaranteed in the implementation of the sauna stove or spade heater, with respect to size, power output or equipment, and further a secure availability of spare parts.

Above some favorable embodiments of the invention have been disclosed, but for the expert it is clear that the invention can be varied in many other ways within the scope of the claims.