WO1993008428A1

WO1993008428A1 - Apparatus for heating water

Info

Publication number: WO1993008428A1
Application number: PCT/FI1992/000280
Authority: WO
Inventors: Hannu Koskela
Original assignee: Hannu Koskela
Priority date: 1991-10-25
Filing date: 1992-10-20
Publication date: 1993-04-29
Also published as: FI915035A0; AU2879592A; FI915035A

Abstract

The invention relates to an apparatus for heating water comprising a water tank (1), a cold water connection (2) for leading water into the tank, a hot water connection (3) for leading hot water out of the tank (1), a heating unit (4) for heating the water in the tank (1), and a channel assembly (7) for leading the water heated by the heating unit (4) essentially upward into an area wherefrom heated water is conducted out of the tank (1). The channel assembly (7) is provided with a control unit (12) for controlling the amount of water flowing in the channel assembly (7).

Description

Apparatus for heating water

The invention relates to an apparatus for heating water according the claim 1.

A conventional water heater i.e. a hot water boiler is generally provided with a vertical cylindrical tank having tube connections for supplying cold water into the tank on the one hand and for leading hot water out of the tank on the other hand. The cold water tube is generally led into the lower part of the tank and, respectively, the end of the hot water tube is placed in the upper part of the tank. This kind of disposition is natural since hot water is always bound to move upward. Water is heated by means of a heating unit which can be for e.g. an electric resistance, which transforms the through-going electric current into resistance heat which is transferred to the surrounding water.

As the water in the vicinity of the resistance gets warmer, it goes upward to the upper part of the tank. At the same time, cold water from the lower part of the tank moves near to the heating unit and starts getting warmer due to the effect of the heating unit. This causes a relatively strong circulation of water with a subsequent strong mixing of water. Therefore, in a conventional water heater all water heats simultaneously and the temperature difference between the upper and the lower part remains very small during the whole heating period. It is then obvious that use of this kind of water heater of prior art for heating water requires that the whole lot of water has to be heated to the desired temperature.

For example, if the volume of a water heater is 300 1 and the heating capacity is 3 kW and the initial temperature of water is 25°C_r it takes over three hours to heat the water to 55°C. However, there are often situations in households when large quantities of hot water are used and hot water runs out short. Also in summer cottages, where the boiler is switched off during the time of absence for saving energy, a small amount of hot water e.g. 10-20 1 would be quickly needed. Heating quickly such a small quantity of water is not possible by means of water heaters of known technique which have a volume of a few hundred litres. It is natural that small quantities of water could be heated quickly by using separate heaters with a sufficiently small size. So the problem with known water heaters is that they are not capable of heating quickly small amounts of water while they are heating large quantities of water for continuous use. In this respect their operation is not flexible.

A Swiss patent publication 524115 presents such a water heater which has a vertical flow tube and a resistance heater inside. The flow tube conducts heated water along the tube to the upper part of the tank. The tank is additionally provided with thermostats, the first one of which being situated in the upper part of the tank and the second one in the lower part thereof. Heating power of the heater can be alternatively controlled by either the upper or the lower thermostat. The apparatus is aimed at an operation wherein heating is controlled by the lower thermostat in night use and by the upper thermostat in day use, respectively. The apparatus is not capable of producing quickly hot water because water flows continuously through the flow tube having time to heat only a little while it passes the heating resistance. Furthermore, continuous flow causes mixing of the water in the tank.

It is the objective of the invention to present an apparatus which is capable of heating large quantities of water for the needs of a household but which is also capable of heating very quickly a small quantity of water in a situation when the tank is full of cold water. This objective is obtained by means of an apparatus according to the invention which is primarily characterized in what has been presented in the characterizing part of claim 1.

The invention relates to such a heater for water or other liquids wherein hot water, heated by the heating unit, is conducted through a channel to the upper part of the tank near to the hot water connection tube. Therefore, immediately after switching on the water heater, which is full of cold water, the heating unit starts heating water which is conducted straight to the hot water connection tube, more specificly to the proximity of the hot water tube in the upper part of the tank, wherefrom it can be immediately taken into use. The channel assembly and particulary the control unit therein prevents any significant mixing of hot water with the cold water in the lower and middle parts of the tank. The control unit controls flow and establishes such a flow with no essential mixing of hot and cold water in the upper part of the tank. The control unit functions according to a thermostat principle. This is beneficial in that water that goes through the flow channel has a temperature which is at least the set value given to the control unit. Therefore, the water that flows to the upper part of the tank has the desired temperature at the beginning of heating. This solution makes operation of the water heater very flexible.

In the exemplary situation mentioned above, the water heater according to the invention is capable of heating approximately 50 1 water to a temperature of 55°C in the upper part of the tank in 35 minutes from the time the water heater is switched on. In this case the average temperature of the tank is only about 30^βC. Therefore, it is obvious that the water heater according to the invention presents a notable improvement for the user and operation of the water heater is much more flexible compared to water heaters of prior art. A water heater according to the invention, which had power of 3 kW, enabled a situation wherein hot water was continuously taken out of the tank at a rate of 0,85 1/min while temperature of hot water remained 55°C higher than that of cold water in the tank.

Structure and operation of the apparatus according to the invention will be described in more detail in the following referring to the enclosed drawings in which

fig. 1 shows an apparatus according to the invention partly cross-sectioned, fig. 2 and 3 present results from tests with the apparatus according to the invention.

The apparatus for heating water, which in the following will be called a water heater, comprises a cylindrical tank which is vertically mounted on its base. A cold water connection 2 and a hot water connection 3 lead into the tank from the lower part of the tank 1. The cold water connection 2 comprises a tube extending to the lower part of the tank 1 and, correspondingly, the hot water connection 3 comprises a tube extending to the upper part of the tank. A heating unit 4 is mounted in the lower part of the tank 1 preferrably in the middle of the tank. An immersion heater, which is in direct connection with the water in the tank and which operates according to the principle of a resistance heater, functions as the heating unit 4. In addition, a control thermostat 9 is provided in the lower part of the tank close to the heating unit 4 for controlling operation of the heating unit 4.

The tank accommodates a flow channel assembly which, in the examplary case, comprises an essentially vertical flow tube 7 having the same diameter from one end to the other. The flow tube 7 has such a diameter that it accommodates the heating unit 4 and the control thermostat 9. The diameter of the flow tube 7 depends on the power of the electric resistance. When a high power resistance is used, a flow tube with a larger diameter is needed than in case of a low power resistance. The flow tube 7 is made of a heat insulating material like e.g. a plastic.

The first end i.e. the lower end 5 of the flow tube 7 is open so that cold water in the lower part of the tank 1 can easily get into the flow tube 7. In the case presented in the figure, cold water flows under the flow tube 7 through openings 8 along the path indicated by arrows.

The second end i.e. the upper end 10 of the flow tube 7 extends to the upper part of the tank 1 so that the second end 10 of the flow tube 7 is close to the upper end 11 of the hot water tube. Then, the hot water going up along the flow tube 7 is carried, along the path indicated by arrows, close to the upper part 11 of the hot water tube wherefrom it can be immediately led out through the hot water tube 3. Part of the hot water which comes from the other end 10 of the flow tube 7 starts filling the upper part of the tank 1 displacing cold water in the upper part of the tank so that the boundary between cold and hot water starts lowering in the tank 1.

In the middle part of the flow tube 7, there is provided a control unit 12 whereby the flow through the flow tube 7 is controlled. In case of the figure, a thermostat valve serves as the control unit comprising e.g. a wax-filled bellows 14, a collar 15 attached to the flow tube 7 and provided with a gasket, and a moving disk 13 connected to the bellows. The valve is a so-called self adjusting valve.

In the beginning, when the water heater full of cold water is switched on, the thermostat valve 12 is fully closed preventing flow of water through the valve. As the water in the lower part of the flow tube 7 gets warmer, the wax in the bellows 14 of the thermostat 12 expands and the thermostat valve 12 opens and water starts flowing to the upper part of the flow tube 7 and further to the upper part of the tank l. Naturally, the flow of water in the flow tube 7 is the stronger the larger the flow opening 6 of the valve 12 is at each instant. As the flow in the beginning tends to get too strong, water in the flow tube 7 cools and the wax in the bellows 14 contracts so that the opening of the thermostat valve 12 becomes smaller and, at the same time, the flow gets smaller to correspond the power of the electric resistance. Therefore, position of the thermostat valve 12 depends on the temperature of the water flowing in the flow tube 7. The thermostat valve 12 can be e.g. of such a type that it is fully closed when the temperature is 53°C and fully open when the temperature is 57°C.

If it is desired to heat the tank e.g. to 80°C and, at the same time, a small amount of water of e.g. 55°C is quickly required, the control thermostat 9 is given a set value of 80°C and the thermostat valve 12 is given that of 55°C. Then water in the tank first warms to a temperature of 55°C from the top to the bottom and then, as the thermostat valve 12 is now fully open, water warms from 55°C to 80°C. As the whole volume of water in the tank 1 has reached a sufficiently high temperature, the control thermostat 9 in the vicinity of the heating unit 4 switches off the heating unit 4. The set value for the control thermostat is generally 55-80"C but lower and also a little higher set values can be used. In connection with the control thermostat, there is provided a safety guard for overheating which switches off the current if temperature for some reason rises too high e.g. over 95°C.

The water heater according to the invention functions in the following way. As the water heater is switched on, there will be an electric current through the heating unit 4 having the effect that the heating unit 4 gets hot.

Then, water in the neighborhood of the heating unit 4 gets hotter and starts flowing upward along the flow tube 7. Mixing of hot and cold water during the flow upward in the tank is prevented by virtue of the flow tube 7.

Hot water discharges from the other end 10 of the flow tube 7 to the proximity of the upper part 11 of the hot water tube 3 and starts filling the upper part of tank 1 simultaneously displacing cold water in the tank.

As hot water flows upward in the flow tube 7, the same amount of cold water flows from the lower part of tank l to the vicinity of the heating unit 4. This leads to a situation in the tank l wherein there is hot water in the upper part of the tank which can immediately be conducted out through the hot water tube 3 for use whereas the water elsewhere in the tank is relatively cold. The boundary surface between hot and cold water gradually moves downward from the upper part of the tank and at the final stage all the water in the tank is heated to the desired set value.

When there is a control unit 12 installed inside the flow tube 7, water in the tank 1 first heats to the temperature which equals the set value of the control unit 12 and then water heats to the higher temperature of the control thermostat.

Example 1

In order to test the operation of a water heater according to the invention, tests were performed using a water heater with a volume of 250 1 and with an electric resistance having a nominal power of 3 kW. The resistance was surrounded by a tube which had the same diameter from one end to the other and which was made of a poorly heat conducting plastic and to which a thermostat valve was installed as the temperature controller. The opening temperature of the thermostat was 55°C. The reference values were measured when the flow tube of the water heater was removed.

Figure 2 shows the measured curves from a heating test which lasted 7 hours altogether. The uppermost curve was measured in the upper part of the tank and the lowest curve, respectively, in the lower part of the tank when a flow tube and a thermostat valve was used in the water heater. The middle curve is the temperature of the upper part from a reference test in which there was no flow tube according to the invention nor a thermostat valve therein. Figure 2 shows that the temperature of the water in the upper part of the tank, the temperature being about 12°C at the beginning of the test, rose in 10 minutes to a temperature of 45-50 °C. Correspondingly, the temperature in the lower part of the tank remained almost the same nearly for 6 hours. This test clearly showed clearly that there is no mixing of hot and cold water in a water heater that is provided with a flow tube and a thermostat valve. It was not until after 6 hours that also the water temperature in the lower part of the tank started to approach the temperature of the upper part. When a flow tube without a thermostat valve was used, the water heater worked essentially in the same way as a conventional water heater. There was a strong flow in the flow tube which caused efficient mixing throughout the tank. Therefore, the advantage gained by using the flow tube only was small. The tests showed that, in this case, the temperature difference between the upper and lower part was only about 5°C. According to figure 2 the corresponding temperature difference, when a flow tube with a thermostat valve was used, was about 30-40"C on the average.

Example 2

In a second test which was performed using the water heater of example 1, the water heater was compared to a corresponding water heater which had no flow tube and no thermostat valve. Tests showed that the water heater according to the invention was able to produce water that was ready for use (35°C) into the cooled tank about 14 times faster than the water heater used as a reference. Correspondingly, when cold (15°C) water was heated, a heater according to the invention produced 62 litres of water of 35°C after a starting period of 42 minutes while the water heater was loaded for 100 seconds with a flow of 10 liters a minute at 5 minutes intervals. It took about 4 hours to reach the same capacity with the reference water heater. The tests therefore showed that a considerably higher heating rate is obtained with a water heater according to the invention because formation of disadvantageous thermal circulating flows is prevented.

Example 3

Figure 3 shows results of measurements during the first 10 minutes from a heating test according to example 1. Temperatures were measured below the thermostat valve and in the upper part of the tank. The upper curve, resembling a saw tooth, shows how a thermostat valve operates. When the thermostat valve is closed and the temperature rises to the set value of 55°C, the thermostat valve opens and hot water flows into the upper part of the tank and, respectively, cold water flows to the thermostat valve which then closes. After this, water below the thermostat valve starts to warm again and within a minute it warms to 55"C whereupon the thermostat valve opens and so on. It is already after a few minutes that the temperature in the upper part of the tank starts to rise and in 10 minutes it has already reached a temperature of 50 °C. It can be deduced from the curves of measurement of figure 3 that flows inside the flow tube are very slow so that disadvantageous thermal circulating flows are not generated. A flow tube was used in the test which was made of polypropylene with a diameter of about 75 mm and a wall thickness of 6,5 mm.

Example 4

In one test, a small bypass opening was made to the thermostat valve through which water was able to flow at a rate of about 0,85 1/minute. This corresponded a 6 mm diameter hole in the disk 13 of the thermostat valve of figure 1. The test showed that this kind of bypass opening reduced fluctuation of the water temperature in the flow tube (the saw tooth curve of figure 3) and, therefore, improved the performance of the thermostat valve. There was a small flow of hot water through the opening also when the thermostat valve was closed. Diameter of the opening was less than 10% of the diameter of the flow tube. Furthermore, in case of disturbances, air or steam is able to discharge through the bypass opening upward which, in addition to the safety guard of overheating, prevents the electric resistance from getting too hot. It is obvious that a small bypass flow can be realized also e.g. by means of suitable grooves in the collar 15. The invention is not limited to the embodiment presented above but it can be varied within the limits of the enclosed claims. For example, the flow channel is not necessarily a wide vertical tube but it can be shaped to another form e.g. having a multi-branched tube channel assembly at the lower end. This solution comes into question when more than one heating units are used. Also, location of the heating unit and the flow tube, respectively, in the tank can be freely chosen. The flow tube can be e.g. attached close to the wall of the tank or even outside of the tank to form a separate tube branch.

The invention can be used in single tariff water heaters as well as in double tariff water heaters. In the latter case, a second control thermostat is installed to the wall of tank 1 to a height of e.g. 3/4, this thermostat also controlling operation of the heating unit 4. The second thermostat switches off the current of the heating unit when the boundary between cold and hot water reaches up to the second thermostat. Therefore, higher tariff energy is used only for heating small quantities of water. It is to be noted that in a water heater according to the invention which uses the double tariff principle, there is no need for another heating unit as in conventional water heaters. It is also obvious that other liquids than water can also be heated with a heater according to the invention

Claims

1. Apparatus for heating water comprising a water tank (1) , a cold water connection (2) for leading water into the tank, a hot water connection (3) for leading hot water out of the tank (1) , a heating unit (4) for heating the water in the tank (1) , and a channel assembly (7) for leading the water heated by the heating unit (4) essentially upward into an area wherefrom heated water is conducted out of the tank (1) characterized in that the channel assembly (7) is provided with a control unit (12) for controlling the amount of water flowing in the channel assembly (7) .

2. Apparatus according to claim 1 characterized in that the control unit (12) is a so-called self-adjusting valve like a thermostat valve.

3. Apparatus according to claim 2 characterized in that the control unit (12) comprises an opening for enabling a flow through or past the control unit (12) when the control unit (12) is in a position that essentially closes the flow.

4. Apparatus according to claim 2 characterized in that the channel assembly (7) is made of a heat insulating material like e.g. a plastic.

5. Apparatus according to claim 1 wherein the heating unit (4) is placed in the lower part of the tank (1) , at the first end of the channel assembly (7) essentially inside the channel assembly (7) , the first end of the channel assembly (7) comprising an inlet arrangement like an opening (8) for leading the water to be heated into the channel assembly (7) , characterized in that the control unit (12) is^' fitted in the channel assembly (7) above the heating unit (4) , preferrably to an area which is situated at a height of 1/2 - 1/3 in the vertical direction of the tank (1) .

^'6. Apparatus according to claim 5 characterized in that the channel assembly is essentially comprised of a vertical flow tube (7) .

7. Apparatus according to claim 6 characterized in that the flow tube (7) essentially extends to the whole height of the tank (1) .