FI90724B - electric heater - Google Patents

Description

90724

ELECTRIC HEATER

The invention relates to an electric heater comprising a thermally insulated outer jacket surrounding a rock space containing heat-storing mass 5 and one or more electric resistors arranged in the rock space to heat the heat-storing mass. these to heat the charging mass from each other.

Often, electric heaters have poor steam properties. The sauna has to be heated too hot, because at a lower temperature the steam output is not enough. On the other hand, the warm-up time may be too long.

Finnish patent application 875786 discloses an electric heater with a charging mass and a thermally insulated outer sheath, which is a so-called "Ready" sauna stove. In such a heater, a low-power resistor is able to heat the stone space so hot that when the lid belonging to the heater is opened, creating an air flow connection between the stone space and the sauna space, the sauna space can be heated quickly to sauna room temperature.

25

Despite its stone mass of 100 kg, such a stove is equipped with high-power resistors, because the low-power resistor mentioned in connection with the sauna is not enough to keep the temperature of the stones high enough and the stone mass can no longer be increased.

30 The stove is already quite large. The so-called resistance for heating the stone space. the "roughing resistance" can only be, for example, 300 W, when the normal thermostatically controlled resistors of the heater total 6 kW.

35 The normal resistors in these heaters require a three-phase power supply with fuses of at least 10 amps and often fuses of 16 amps. If we wanted to make the stove a traditional stove, similar to a wood-heated, storage stove, the stone space would have to be significantly increased from the current one. It is clear that a quantity of stones of 200 to 500 kg would be able to store the energy required for 2 normal saunas, but such a quantity of stones is no longer practical in current electric heaters.

All known types of electric heaters require the aforementioned more than 5 man kilowatts of power. The power supply to the entire house must be designed according to the high instantaneous power demand of the electric heater. Main fuses, house supply lines and transformers have to be dimensioned to withstand this short-term peak load. Often, electrical switchboards have to be fitted with an alternating system of electric heating, which switches off some other load when the stove is switched on.

Bathing with an electric heater is timed for most users at the same time of day. There are more than 500,000 electric saunas in Finland. Every 100 nights there are about 100,000 saunas on site at the same time. The energy requirement for one sauna is about 8 kWh. In the two-hour period, approximately 800,000 kWh will thus be taken from the national grid. The power demand due to the load on the electric heaters greatly increases the power output in the evening to an unfavorable level.

20

From the above shortcomings of the known electric heaters, the characteristics of the new good heater can be deduced: - immediately after bathing 25 - low power consumption good steam properties at low temperatures simple connection to the mains - power consumption takes place mainly at night

- a reasonably sized SO

The object of the present invention is to provide a new type of charging electric heater in which the above-mentioned objects are achieved. The characteristic features of the electric heater according to the invention are set out in claim 1. Typically, the phase-changing mass is a meltable mass, preferably aluminum, which stores in its melting heat the thermal energy required for saunaing. Phase change thermal energy associated with various changes in crystal structures or reversible chemical reaction may also be involved. By means of the invention, a small heater can accommodate a huge storage of thermal energy compared to previous charging heaters. The heat content of the charging mass is made so large by practical dimensions that the high-power resistor can be completely dispensed with and only a small continuously on resistor can be left. In contrast to the prior art, a low-power resistor connected in a single phase is sufficient for such a heater. Preferably, the aluminum used as the molten mass is placed in a steel vessel, the inner surface of which is lined with a dissolution-preventing material. These include a high temperature resistant fiber sock, a glass tube or a ceramic liner. In practice, after the sauna has taken place, the charging of the mass that takes place in the evening takes place largely at night.

Other advantages and embodiments of the invention will become apparent below.

15

In the following, the invention will be described with reference to the accompanying figures, which show some embodiments of the invention.

Figure 1 shows an electric heater storing heat in a meltable mass.

Figure 2 is a cross-section of point II-II in Figure 1.

Figure 3 shows another arrangement of the melting mass in the heater.

Figure 1 shows a cross-section of a heater according to the invention with the lid open. It comprises an outer jacket 1 which is substantially thermally insulated. This outer casing includes a lid 2 which can be opened as part of it. The thermally insulated outer casing 1 surrounds the stone space 3 substantially tightly also on the sides and partly on the bottom. In the middle of the space 3 of the stone-30 there is a cylindrical vessel 5 in a vertical position, inside which there is an inner cylindrical channel 10 with electrical resistors 4. The vessel 5 consists of a space between the cylinders filled with aluminum 6. The stone space 3 around the vessel 5 is filled with with a mass such as 35, for example stove stones 8. Synthetic, for example ceramic stove stones can also be used here.

At the lower end of the air duct 10 there is a valve 9 with which the air flow can be adjusted and which can be connected to thermostat means 4. Above the air flow channel, at a distance from its upper end, a protective plate 13 is provided, which prevents the thrown steam water from entering this channel. The lower part of the heater includes a switch housing for electrical connections and thermostatic switches.

5

The cross-section of Fig. 2 shows the structure of the heater consisting of nested cylinders, in which the ilro flow channel 10 and the resistor 4 contained therein are in the inner part.

10 The above-mentioned aluminum or its alloy is quite an ideal substance for heat storage. The heat of fusion of aluminum is high (Qs * 400 kJ / kg). In addition, the specific heat capacity of aluminum is quite high (Cp = 900 J / kgC). The melting point of aluminum is also very advantageous. Depending on the alloy, 550 to 660 ° C. The specific gravity of aluminum 15 is 2.7 kg / l. These good features are utilized in a heater like the one described above. The aluminum is melted with a low power resistor and kept molten at a constant temperature. When heating and sowing a sauna, molten aluminum releases energy as it solidifies and continues to cool.

20

Some of the thermal energy contained in the aluminum tank is used to raise the basic temperature of the sauna to the desired level. The amount of energy remaining in the tank is used to maintain the temperature of the stove stones in order to throw the desired amount of steam. 25 Due to this efficient method of heat storage, it is possible to build a small stove (10 kWh »36 MJ) that stores a large enough amount of thermal energy for one sauna session. The common volume of the masses charging the stove can be 30 for example: a tank filled with aluminum 10 1 = 27 kg aluminum stone space 23 1 * 30 kg stove stones.

The total volume is thus 33 l when it is about 70 l in the above-mentioned known "ready-to-use" heater.

35

Figure 3 shows a modification of the embodiment of Figures 1 and 2. Similarly, the corresponding parts are denoted by the same reference numerals as the outer jacket 1, the stone space 3, the electrical resistor 4 and the aluminum groove 6. The air duct 14 is denoted herein by reference numeral 90724 5 14. A plurality of circumferential vessels 12 4 is again set to this channel. The vessels 12 are formed completely sealed and a small expansion space 5 is left in them, although experiments show that possible thermal expansion serums do not cause problems. Instead, it is important to line the inner surface of the steel vessel appropriately to prevent molten aluminum from dissolving in the steel vessel.

10 The total charging capacity of the sample heater is obtained as follows. In accordance with the above, a 10 l or 27 kg aluminum tank is placed inside the thermally insulated outer jacket among a 30 kg stone mass. In this case, the heat of fusion of aluminum is 3 kWh and its heat of cooling from 700 * to 200 * is about 3.4 kWh. The cooling of the Kivi-15 mass from 600 * to 200 * (on average) gives a thermal energy of about 2.7 kWh and the structures 1 kWh, whereby the total charge heat of the heater is about 10 kWh. In addition to this, the stove is preferably equipped with a resistor of 1000 W, which thermal power is also obtained during the sauna. Thus, about 12 kWh of thermal energy is available in two 20 hours, which is well enough for a sauna for an ordinary family. If necessary, the resistor is equipped with overheating protection. This is also the case with thermostatic means, which aim to keep the vessel 5 or the stone space 3 at a constant temperature.

25

In a standard 7 m3 sauna, a 6 kW stove is normally used. In such a state, the charging stove according to the invention is able to maintain normal sauna conditions as described above for two hours, even if the stove is loaded with a continuous steam discharge. Usually, however, the heater is not loaded so much, which allows the heater to provide normal sauna conditions for several hours.

After the sauna, a 1000 w resistor in connection with the heater starts 3.5 to reheat the charging mass and melt the solidified aluminum mass. It takes 11 to 12 hours to fully charge such a stove from a completely empty space. The power of the resistor can be further reduced. 500 W of heating power would still allow daily sauna use.

6

In Journal of Engineering for Industry, 8/1975 p. 893-896, "Thermal Energy Storage and Control"; Schröder introduces various salts and mixtures thereof. For example, LiF / MgF2 alloys offer some alternatives to aluminum. With these, it is possible to achieve a better heat storage capacity than with aluminum.

Claims (10)

1. Electric sauna oven, son consists of a heat insulated outer shell (1) which surrounds the rock space (3) son contains 5 heat storage mass and one or more electrically resistive son is placed in the stone space to heat the heat stored mass (6, 8). electric sauna furnace includes means (2, 9) for providing an air flow connection between the stone space and the space where the furnace is located to transfer heat from the stone space (3) to the space where the furnace is located or alternatively to insulate them from one another heated the storing mass (6, 8), characterized in that a part of the storing mass (6) is a mass which, under the influence of said heating, changes its phase during the bonding and release of the energy used in the sauna bath using fasförändringsvärme. Electric sauna oven according to claim 1, characterized in that the mass (6) which changes its phase is placed in one or more vessels (5, 12). Electric sauna oven according to claim 2, characterized in that at least one vessel (12) consists of the space between two inside tubes and the electrical resistor (4) is located inside the inner tube. Electric electric oven according to claim 2, characterized in that the oven contains several cylindrical vessels (12) which are placed in a circle and that the electrical resistor (4) is placed in the center of the circle. Electric sauna oven according to claims 1-4, characterized in that the resistance space is formed as part of the air flow duct (10) and that it is placed in a vertical direction. Electric sauna oven according to claims 2 - 4, characterized in that the vessel (5, 12) is completely closed and that a small expansion space has been left in this. 10 Electric sauna oven according to claims 2 - 4, characterized in that the vessel (5, 12) comprises an inner liner (11) to prevent the vessel's material from being released into the molten mass. 5 8. An electric sauna oven according to claim 7, characterized in that the inner lining (11) of the vessel consists of any of the following: fiber stocking, glass tube, ceramic lining. 9. An electric sauna oven according to claims 1-8, characterized in that the storage mass (6) contains one or more of the following materials: pure aluminum, aluminum alloy, salt mixture. Electric sauna oven according to claims 1 to 9, characterized in that the heat-insulated outer shell (1) includes an openable cover (2), which in the open position creates the said air-flow connection from the stone space (3) to the space where the oven is located. . II