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Title:
THERMOSTAT FOR CONTROLLING THE TEMPERATURE OF HOT WATER TANKS SUPPLYING HOT-WATER
Document Type and Number:
WIPO Patent Application WO/2017/187213
Kind Code:
A1
Abstract:
Thermostat for controlling the temperature of hot water tanks supplying hot water. The thermostat can be placed in the tube (3) of the tanks (2). The thermostat (1) comprises a capillary tube (4), a membrane (5) and preferably a container (6). The membrane (5) is connected to the switch unit (9). The capillary tube (4) is arranged in the protecting tube (10). Protruding into the end of the protecting tube (10) a sensing tube (12) is installed coaxially which is able to deviate from the axis of the protecting tube (10) at most at an angle (11) of 10 degrees. The sensing tube (12) is hermetically connected to the internal space of the capillary tube (4). The outer diameter of the sensing tube (12) is smaller than the inner diameter of the protecting tube (10). The portion of the sensing tube (12) is enlarged. The end of the sensing tube (12) is flattened.

Inventors:
HORVÁTH TAMÁS (HU)
Application Number:
PCT/HU2017/050012
Publication Date:
November 02, 2017
Filing Date:
April 24, 2017
Export Citation:
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Assignee:
MMG AUTÓ- ÉS DOMOTECHNIKAI KERESKEDELMI ÉS SZOLGÁLTATÓ KFT (HU)
International Classes:
G01K5/32; F24H9/20; G01K11/04; G05D23/12
Foreign References:
US3251228A1966-05-17
US2418150A1947-04-01
US2366091A1944-12-26
Attorney, Agent or Firm:
JUREX IPARJOGVÉDELMI IRODA (HU)
Download PDF:
Claims:
Claims

1 . Thermostat for controlling the temperature of hot water tanks containing/supplying hot water, the thermostat (1 ) can be placed in the pocket tube (3) of the tanks (2), said thermostat (1 ) comprises a capillary tube (4) at least partially filled with liquid and/or gas, a membrane (5) hermetically connected to the inner space of said capillary tube (4) and advantageously a container (6) hermetically connected to the inner space of said capillary tube (4); said membrane (5) is arranged in a casing (7) and is connected to a switch unit (9) also arranged in said casing (7) for switching the heating element (8) of said tank (2) on and off; characterized in that the portion of said capillary tube (4) outside said casing (7) is arranged in a protecting tube (10) connected to said casing (7); protruding into the end of said protecting tube (10) opposite its end connected to said membrane (5) a sensing tube (12) is installed coaxially which is able to deviate from the axis of said protecting tube (10) at most at an angle (1 1 ) of 10 degrees, said sensing tube (12) is hermetically connected to the inner space of said capillary tube (4) the outer diameter of said sensing tube (12) is smaller than the inner diameter of said protecting tube (10); the portion of said sensing tube (12) or a part of it outside said protecting tube (10) is axially symmetrically enlarged at least to the size of the outer diameter of said protecting tube (10); the end of said sensing tube (12) opposite its end connected to said capillary tube (4) is flattened to form a heat receiving surface (16).

2. Thermostat according to claim 1 characterized in that said sensing tube (12) and said capillary tube (4) are connected to each other in such a manner that they have a common internal volume.

3. Thermostat according to claims 1 or 2 characterized in that a temperature limiting unit (13) is also arranged in said casing (7) in order to prevent overheating.

4. Thermostat according to any of claims 1 - 3 characterized in that said thermostat (1 ) is compatible with the known invar-rod type thermostats.

5. Thermostat according to any of claims 1 - 4 characterized in that said sensing tube (12) or a portion of it is formed as a container (6).

Description:
THERMOSTAT FOR CONTROLLING THE TEMPERATURE OF HOT WATER TANKS SUPPLYING HOT-WATER

The invention relates to a thermostat for controlling the temperature of hot water tanks containing/supplying hot water. The thermostat can be placed in the pocket tube of the tanks. The thermostat comprises a capillary tube at least partially filled with liquid and/or gas, a membrane hermetically connected to the inner space of the capillary tube and a container hermetically connected to the inner space of the capillary tube. The membrane is arranged in the casing and is connected to the switch unit also arranged in the casing for switching the heating element of the tank on and off.

Based on the EU Erp directive it is important for the OEM manufacturers to produce energy efficient, good quality, easy to repair devices. In fact, all the manufacturers have started developing new products which fit into the application system for 'smart home'. Hungarian Patent Application HU 145558 describes a safety mechanism for thermostats utilizing dilatation of fluids. The device comprises a heat sensor operated with dilatational fluid, a capillary tube and a throttle valve. In the housing a wavy tubular membrane and a spring are arranged and are placed on the heat sensor.

This is an out-of-date solution, it is operated manually and basically it does not control heating. Instead, its aim is to prevent damages caused by a possible overheat.

Hungarian Patent Application HU 149840 describes a thermostat operating on the principle of tension of liquids. The rotating axle of the temperature adjusting unit of the thermostat is bordered by arcs and flat surfaces. A correspondingly dimensioned threaded pulley is placed on it. The pulley is connected by means of a cogged wheel which communicates with a drum-like body on a common pivot. On the cylindrical outer surface of the drum-like body a temperature scale is presented which can be fixed on the cogged wheel by means of a screw. This solution is not suitable for controlling the temperature of the water in the boilers used these days.

Patent Application GB 565309 teaches a temperature control system with the use of known invar rods.

Patent Application US 2418150 relates to a thermal responsive element which can be inserted in a well of a water tank. The thermal responsive element comprises a capillary tube at least partially filled with liquid and/or gas, a membrane connected to the inner space of the tube, a casing for receiving the membrane and a switch unit operated by means of the membrane. The capillary tube is provided with a long stem portion and a short resilient end portion which is formed by two oppositely disposed spaced hairpin bends. The most distant end of the capillary tube is flattened. The aim of this solution is to improve the heat transfer of the sensing unit of the heat sensing systems using capillary tubes (i.e. a better thermal contact between the liquid in the tank and the resilient portion is provided).

Patent Application US 3251228 describes a temperature sensitive pressure system containing a capillary tube at least partially filled with liquid and/or gas, a membrane connected to the inner space of the tube, a casing for receiving the membrane and a switch unit or pointer operated by means of the membrane, a protective tube surrounding the tube in its entire length. The capillary tube has a terminating tube fixed to its end opposite the end connected to the membrane. This terminating tube is not able to deviate from the axis line of the protective tube. There is a direct connection between the terminating tube and the medium to be measured so heat transmission is ensured on the entire surface. The novelty of this solution resides in the application of the plastic protective tube. Earlier, a kind of helical material was used as the material of the protective tube which was expensive, installation of it was complicated and the tubing became thicker and rigid. Moreover, it could damage the capillary because of its sharp ends. Plastic is cheaper, it can be extruded directly on the tube, it is instrumental in electric insulation, it makes the whole method inexpensive.

The aim of the aforementioned documents is to improve the component parts of the already existing capillary systems, however, the operating principle and mechanism of the whole temperature sensing and switching system is not affected. They do not teach an embodiment by which replacement of the invar-rode type thermostats could be ensured.

According to the document by Miklos Danas titled Hotermelo berendezesek szerkezeti elemei (Nemzeti Szakkepzesi es Felnottkepzesi Intezet 2008) (hUp://www epzesevo!ucioia.hu/dmdocuments/4ap/6 1398 tartalomelem 007 munkaanvag 100331.pdf) the following thermostats are known and used in these days: Expansion-tube thermostat in which a copper expansion tube senses the changes of temperature and its length changes as a function of the sensed temperature. As the length of the invar-rod fixed inside the tube at its one end does not change significantly, the change in the length of the expanding tube operates a micro-switch whose switching temperature can be set by means of an adjusting screw. Thermostats filled with gas and fluid are used in apparatuses where the sensing point and the handling facility are distant (~ 0.5 ... 1 .5 m) from each other e.g. automatic washing machines. The structure and the principle of operation of gas-filled and vapour pressure thermostats are essentially the same. The sensitive tank arranged at the point of detection contains gas in case of gas-filled thermostats and in case of vapour pressure thermostats it contains a few drops of liquid. The sensitive tank and the membrane are connected by means of a capillary tube. There are thermostats which do not have a separate tank in this case the capillary tube also functions as a tank. With the temperature rise the pressure of the gas or vapour increases, the membrane expands and operates a micro-switch and heating is switched off. In case of temperature drop the operation is reversed.

No reference to the solution of the present invention can be found in this document. Not even the theory for embodying the present invention is implied in the documents known in the art. Not even the combined knowledge of the thermostats operating on the basis of gas/vapour or liquid tension, the known helical tube forms and the invar- rod type solutions presents satisfactory teaching to a person skilled in the art for realization of the present invention.

Knowing the requirements of the industry in relation to thermostats and safety restrictions we have come to the conclusion that a solution which is not based on the conventional invar-rod method would meet the current requirements of the users as products provided with the thermostats of the present invention may reach a higher- level ErP category.

As opposed to the known solutions the present invention is a rod-like, lengthwise placed device which combines the controlling-limiting function. Its most important mechanical element is the thermostat operating with capillary temperature sensor. The operating principle of the sensitive switch system used earlier is laid on new foundations resulting in a new solution. The basic principle of the earlier solutions used for electric boilers is based on the different dilatation motion of two different kind of metal (brass, steel). The temperature controller of the device comprises a heat conducting element made from two kinds of material pressed to each other (invar-rod) which due to the above mentioned different dilatational modulus will become deformed when the temperature changes, and as it moves it turns the switch on. It is also connected to the bimetal safety limiter which when a certain temperature is reached will switch off (if the temperature controller accidentally fails to switch off). In this case both of the electric poles are switched off, the current supply is terminated and overheat is prevented. Accuracy of this structure gradually decreases during its normal operation due to metal fatigue. After 2-3 years it becomes unreliable.

The novel feature of the present invention is that the principle of mechanical dilation is replaced by the principle of liquid expansion. The present invention uses a construction based on capillary tubes in the longitudinally placed controlling-limiting devices which earlier were constructed exclusively on the basis of the principle of invar-rods. The outer form and measurement of thermostat according to the present invention correspond to the measurements of a device using the invar-rod. In this manner compatibility is ensured during its practical use. The present invention is not only a theoretical innovation but a product which directly can be put into practice by both the manufacturers and the service technicians. The thermostat according to the present invention also allows for the safety regulations: the device is also provided with a mechanical limiter, its operation is ensured by the pocket tube having excellent heat conductive features. Heat is transferred to the bimetal limiting element by means of the pocket tube. The heat adjusting part ensures accurate switching for several years due to the practical application of the above described principle.

The present invention makes introduction of an already existing and developed technology (capillary heat sensors and adjusters) to an entirely new application field (rod thermostats) in such a way that it requires minimal investment on the manufacturers side and minimal expenses on the users side due to the simple structure and compatibility. In this manner besides the technical innovation it meets the requirements of the economic rationality and market.

The aim of the present invention is to provide a more accurate and more economical thermostat which is compatible with the invar-rode type thermostats.

It has been realized that if a properly stable capillary tube filled with liquid or gas is formed similarly to the invar-rode type solution then a more accurate and more economical temperature control can be performed.

Accordingly, the present invention is a thermostat for controlling the temperature of hot water tanks containing/supplying hot water. The thermostat can be placed in the pocket tube of the tanks. The thermostat comprises a capillary tube at least partially filled with liquid and/or gas, a membrane hermetically connected to the inner space of the capillary tube and a container hermetically connected to the inner space of the capillary tube. The membrane is arranged in the casing and is connected to the switch unit also arranged in the casing for switching the heating element of the tank on and off. The portion of the capillary tube outside the casing is arranged in the protecting tube connected to the casing. Protruding into the end of the protecting tube opposite its end connected to the membrane a sensing tube is installed coaxially which is able to deviate from the axis of the protecting tube at most at an angle of 10 degrees. The sensing tube is hermetically connected to the inner space of the capillary tube. The outer diameter of the sensing tube is smaller than the inner diameter of the protecting tube. The portion of the sensing tube or a part of it outside the protecting tube is axially symmetrically enlarged at least to the size of the outer diameter of the protecting tube. The end of the sensing tube opposite its end connected to the capillary tube is flattened to form a heat receiving surface.

Preferred embodiments of the invention will be defined by the appended claims and the following description.

Detailed description of the thermostat of the invention will be given with reference to the accompanying drawings in which:

Figure 1 is a partial cross-section of the thermostat as viewed from the side;

Figure 2 is a partial cross-section of an embodiment of the thermostat as viewed from the side in which a portion of the sensing tube is formed as a container and the capillary tube is introduced into the membrane through the upper surface of the membrane; and Figure 3 is the cross-section of the tank containing the heating element and provided with the installed thermostat as viewed from the side.

The operation of thermostat 1 according to the invention is based on the principle of liquid expansion as opposed to the invar-rod type solution where the deformation of the brass tube is utilized. By means of the technology using capillary tube 4 and by means of switch unit 9 provided with a known switch mechanism the thermostat 1 can be operated steadily and reliably. For operation of switch unit 9 a closed sensor is used and the motion of the membrane is pre-set.

The thermostat 1 according to the invention can be used for controlling the temperature of tanks 2 containing/supplying hot water e.g. boilers. The known invar-rod type thermostats which were positioned in the pocket tube 3 of tanks 2 can be replaced by it.

Switch unit 9 of the thermostat 1 according to the invention is operated by means of membrane 5. The inner space of capillary tube 4 and the inner space of membrane 5 are connected hermetically and are at least partially filled with liquid and/or gas. Capillary tube 4 is placed in a protecting tube 10. A sensing tube 12 is connected hermetically to the inner space of capillary tube 4. At the connecting point the outer diameter of sensing tube 12 is smaller than the inner diameter of the protecting tube 10 so that sensing tube 12 is able to deviate from the axis of the protecting tube 10 at most at an angle of 10 degrees. Further, the portion of the sensing tube outside the protecting tube 10 is enlarged at least to the size of the outer diameter of the protecting tube 10 so forming a container 6 (Figure 2). Protecting tube 10 extends from the temperature limiting unit 13 of casing 7 at most to the meeting point of container 6 and sensing tube 12. Container 6 is hermetically connected to the inner space of capillary tube 4 (Figure 2). In fact, container 6 is the enlarged inner space of sensing tube 12. Membrane 5 arranged in casing 7 operates switch unit 9 which controls heating element 8. The switching point of switch unit 9 - which basically may be an operating plate - operated by membrane 5 can be set in a known manner by means of control unit 14 connected to intervening unit 17 communicating with membrane 5. For example control unit 14 may be provided with threads formed axially by means of which its position can be adjusted. The thread may fit into a corresponding threaded seat (not shown in the Figures). A temperature limiting unit 13 is also arranged in casing 7 by means of which control of heating element 8 can be switched off in case of failure of thermostat 1. Temperature limiting unit 13 may be realized e.g. by bimetal. If the bimetal of the temperature limiting unit 13 tilts over, it can be reset by means of reset button 15. The portion of the capillary tube 4 outside the casing 7 is arranged in the protecting tube 10 connected to casing 7. Protecting tube 10 ensures the proper position of capillary tube 4 and the required stable form of thermostat 1 for the sake of compatibility with the invar-rod type thermostats. In addition, due to its good thermal conductivity protecting tube 10 serves as a safety switch in case of incidental failure, leakage of the capillary system. Though in this case the system switches off 10 - 15°C later it is still within the safety limit. As it has already been mentioned, protruding into the end of the protecting tube 10 opposite its end connected to the membrane 5 a sensing tube 12 is installed coaxially. The sensing tube 12 is able to deviate from the axis of the protecting tube 10 at most at an angle 1 1 of 10 degrees. The other end of the sensing tube 12 is flattened i.e. it forms a heat receiving surface 16 (Figure 1 ). The heat receiving surface 16 of the sensing tube 12 deviate from the axis line of the protecting tube 10 (which is essentially connected to the base of casing 7) to such an extent that it can communicate with the inner wall of pocket tube 3. After placing the thermostat 1 into the pocket tube 3 of tank 2 the heat receiving surface 16 leans against the inner surface of pocket tube 3 which directly communicates with the water present in tank 2. In this manner a more exact temperature sensation is ensured (Figure 3). Thermostat 1 of the present invention operates similarly to the known thermostats. According to the solution of the present invention expansion of gas/steam forces membrane 5 to expand which makes intervening unit 17 communicating with membrane 5 move upwards similarly to the operation of thermostats comprising helical tube filled with gas or utilizing steam tension. At the temperature pre-set by control unit 14 the intervening unit 17 placed on membrane 5 presses the controlled switching element and the power supply of heating element 8 is terminated. After the heated medium e.g. water is cooled down the internal volume of membrane 5 decreases, it shrinks, the pressure exerted on the switching element by intervening unit 17 is terminated and power supply of heating element 8 is switched on.

In a preferred embodiment of thermostat 1 according to the invention when it 1 is placed in pocket tube 3 of tank 2 the heat receiving surface 16 provided at the end of capillary tube 4 and sensing tube 12 opposite the casing 7 comes in contact with the inner wall of pocket tube 3 which directly communicates with the controlled medium, e.g. water. Since pocket tube 3 and capillary tube 4 as well as the sensor of sensing tube 12 are (typically) made of brass with high thermal conductivity and there is direct contact between them, heat transmission is more rapid, temperature control is more reliable.

Should thermostat 1 fail to switch off the heating for some reason, then temperature limiting unit 13 interferes. If it comprises bimetal, the bimetal tilts over and power supply of heating element 8 is terminated by breaking the secondary contacts (forming a component part of the switch unit) which are installed in the current path supplying power for heating element 8. After fixing thermostat 1 when the heated medium is cooled down the bimetal can be reset by means of the reset button 15. Thus the usual safety function is effected in the same manner as in case of the conventional solutions and it meets all the requirements and specifications.

Applying capillary tube 4 guarantees that the life span of thermostat 1 according to the invention equals to the life span of the built-in capillary components i.e. it endures 50,000 switch cycles specified by ENEC and certified by TL)V. Life span tests proved that the thermostat 1 according to the invention completed 100,000 cycles without failures. In fact, the test had to be terminated after 101 ,826 cycles only because the capacity of the test laboratory had to be cleared.

The thermostat 1 according to the present invention operates more accurately than the invar-rod type thermostats. According to the new EU ErP directive energy efficiency ranking and marking of boilers depends on the efficiency of the apparatus. The efficiency of thermostat 1 according to the present invention is higher due to the narrower hysteresis loop of switching so it can be included even in class 'C. In this manner the profit of the manufacturer can be increased.

The advantage of the present invention is that the thermostat realized with capillary tube operates on the principle of liquid expansion as opposed to the invar-rod type solution where the deformation of the brass tube is utilized. Due to the capillary technology the switching mechanism is stable and reliable with a closed sensor and the pre-set motion of the membrane. Thereby a higher quality and component integrity can be achieved while the accuracy of the invar-rod type apparatus continually decreases because of the negative features of the used materials. The life span of the invar-rod type apparatus is shorter, so it must be repaired or replaced more often consequently the image of the given boiler is diminished and it has a negative marketing message. The capillary structure guarantees that the life span of the thermostat according to the present invention equals to the life span of the built-in capillary components. In this manner the number of the switch cycles specified by ENEC is more than two times exceeded. While the number of the switches in case of an invar-rod type apparatus is 5 - 10,000, the switch number in the solution according to the present invention can be more than 50,000 proved by laboratory tests. The solution of the present invention makes a higher grading possible for the thermostat as compared to the known invar-rode type thermostats. For boiler manufacturers applying the thermostat according to the present invention an opportunity for additional income is provided which may be maintained for a long term. The capillary thermostat operates much more accurately than the invar-rode type apparatus. Hysteresis of 4 +/- 2K means that the required water temperature can be set accurately at any time and wearing out of the component parts before time due to the frequent switching on/off can be avoided. The accuracy in case of the invar-rod type apparatus is +/- 4C°, while with the thermostat according to the present invention an accuracy of +/- 2C°can be achieved. This results in a higher efficiency since the accurate temperature switch optimizes the energy consumption. This is why boilers provided with the thermostat according to the present invention can be classified in one class higher in terms of energy efficiency than the boilers using invar-rods. This was proved by measurements performed in laboratories. As the dimensions of the thermostats according to the invention equal to the dimensions of the invar-rod type thermostats present on the market they can be installed simply and rapidly even in existing boilers which currently use invar-rods. In this manner the manufacturers can save costs (there is no need for changing technology), the technicians can replace it easily. In case of the conventional invar-rod type thermostats instead of contact there is an air-gap between the pocket tube and the sensing invar rod. Thus inaccuracy of the apparatus is increased since the thermal conductivity of the air is very low (it is almost heat insulating) which makes the apparatus more inaccurate and may enlarge the so called ΔΤ value. According to the solution of the present invention there is a direct contact with the pocket tube therefore direct heat transmission is ensured.