WO2001067001A1

WO2001067001A1 - Storage vessel assembly for hot water

Info

Publication number: WO2001067001A1
Application number: PCT/NL2001/000195
Authority: WO
Inventors: Leonardus Wouter Koot
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-03-10
Filing date: 2001-03-09
Publication date: 2001-09-13
Anticipated expiration: 2002-09-10
Also published as: NL1014612C2; AU4285701A

Abstract

Storage vessel assembly for storing hot water at low temperature and method for storing hot water. In order to prevent legionella and other undesired microorganisms that could cause disease, it is proposed, while maintaining the relatively low temperature in the storage vessel, continuously to subject a fraction of the water present in said vessel temporarily to such a high temperature that such microorganisms are rendered harmless.

Description

Storage vessel assembly for hot water

The present invention relates to storing hot water at

temperature, comprising a storage vessel for hot water provided with a feed and a discharge for water. A storage vessel assembly of this type is disclosed in European Application 0557994A1. This

Application describes a vessel that is provided in the interior with a partition, by means of which two compartments are delimited. Water circulates between these two compartments even when water is not withdrawn. With this arrangement one of the two compartments can be brought to a relatively high temperature. Heating water to a relatively high temperature is important in order to prevent the multiplication of microrganisms as far as possible. By this means it is possible to counteract the occurrence of diseases and other harmful effects. One of the best known examples is the occurrence of legionella infection. If hot water is stored at a relatively low temperature there is a risk that such microorganisms multiply very rapidly, with all of the associated harmful consequences.

On the other hand, the aim is to lower the temperature of hot water for domestic use and other applications as much as possible in order to restrict energy losses as far as possible.

With the construction according to European Application 0557994 it is indeed possible to preclude the risk of legionella if one of the compartments is adequately heated, but this is associated with an appreciable input of energy.

The aim of the present invention is to avoid this disadvantage and to provide a relatively simple storage vessel assembly with which, on the one hand, the formation of harmful microorganisms is prevented in a guaranteed manner and with which, on the other hand, the consumption of energy is restricted as far as possible.

A further aim of the present invention is to be able to implement this improvement both in the case of new installations to be constructed and in the case of existing installations without this incurring high additional costs.

This aim is achieved with a storage vessel assembly as described above, in that there is an auxiliary heating unit, located outside the storage vessel, for heating said water to a temperature above the temperature in said vessel, which auxiliary heating unit is provided with an inlet line and outlet line for water, which lines are connected to said storage vessel via a pump. According to the invention, a small quantity of water is continuously withdrawn from the storage vessel and heated in an auxiliary heat exchanger, which is located outside the vessel, to a temperature at which microorganisms become harmless. That is to say, only a small fraction of the water present in the storage vessel has to be heated. The energy consumption of the auxiliary heating unit is relatively low as a result. In practice it has been found that this circulation can be relatively restricted. The various aspects are, of course, dependent on the conditions in the storage vessel. If a relatively lower temperature prevails in said vessel, for example because cold water is added as a result of hot water consumption, a higher circulation will be needed than if a higher temperature prevails in such a storage vessel. Complete treatment of the water in the storage vessel once or a few times per day may be mentioned as an example.

Because the auxiliary heating unit consumes only little energy, it is possible to obtain this energy in an environmentally friendly manner. Solar energy can be used, either directly via a so-called solar collector or indirectly via photovoltaic elements. It is also possible to use a heat pump, on its own or in combination with other energy sources. Different energy sources can be used for the main heating system and the auxiliary heating unit.

The temperature in the auxiliary heating unit must be substantially higher than 60 °C. In order further to restrict the energy requirement of the auxiliary heating unit, according to an advantageous embodiment of the invention a heat exchanger is installed between the inlet line and outlet line of this auxiliary heating unit. That is to say, the water from the auxiliary heating unit that has been heated to a higher temperature is re-cooled to the temperature in the inlet line before it enters the vessel. It is relatively simple to construct a heat exchanger with an efficiency such that the temperature jump over such a heat exchanger is less than 3 °C. As a result, the water that is returned to the vessel is only 3 °C hotter, compared with the temperature in the vessel. Because, moreover, the quantity concerned is relatively small, the energy requirement of the auxiliary heating unit will be relatively low.

Especially if such a heat exchanger is used, it is possible not to withdraw the water from the vessel but to pass the feed of cold water through the auxiliary heating unit first. After all, because the inlet and outlet temperatures are essentially the same, the additional amount of energy that is needed for the additional heating of the relatively cold water is negligibly small. In this way it is possible to guarantee that the water entering the vessel is essentially free from microorganisms.

Especially in the case of vertical vessels of appreciable hight, it is possible to achieve further limitation of the risk of contamination of the water by arranging a horizontal separation in these vessels. This results in a bottom section containing relatively cold water and a top section containing relatively hot water. The separation can be implemented by means of a relatively restricted opening.

Such a separation can be implemented by fitting a plate, but it is equally well possible to place two separate vessels on top of one another and to connect these to one another. The invention also relates to a method for storing water in a vessel at a relatively low temperature, that is to say at a temperature lower than 60 °C. As described above, small amounts of water are withdrawn from the vessel and heated to a temperature substantially above 60 °C. The construction according to the present invention can be used with simple systems with a single hot water line. The system according to the present invention can also be used with systems which have an indirect heating coil where heated water is circulated continuously. In this case the return water can be externally heated. This heating system must be differentiated from the auxiliary heating unit according to the invention.

The storage vessel according to the invention can itself be provided with a main heating system, but it is also possible to supply the vessel with water heated in some way or other.

The invention will be explained in more detail below with reference to an illustrative embodiment shown in the drawing. A storage vessel assembly according to the invention is shown diagrammatically in this drawing.

In the drawing the storage vessel for storing hot water is indicated by 1. According to an advantageous embodiment, the hot water inside this storage vessel is at a temperature of approximately 60 °C in the top section thereof. The temperature in the bottom section is approximately 40 °C. Cold water is supplied via line 2 and hot water is discharged with the aid of line 3. Downstream of one or more tapping points, line 3 is provided with a return system so that continuous circulation of hot water can be achieved. The main heating system 4 provides for heating hot water. Alternatively, or in addition, a central heating boiler 20 can be used for this purpose. Water issuing from discharge 3 is supplied to the users, shown diagrammatically, and fed back.

According to the present invention, there is an auxiliary heating unit 9. This can be powered in any manner known in the state of the art. A heat exchanger 13 is connected upstream of this auxiliary heating unit 9. Line 11 is connected to a pump 10 and opens into a bottom region of the storage vessel 1, whilst line 12, the outlet line, opens into the vessel at a higher point. Circulation takes place from inlet line 11 through auxiliary heating unit 9 to outlet line 12. As a result of the presence of heat exchanger 13, the heat introduced into the water in auxiliary heating unit 9 can be essentially completely discharged from outlet line 12 to inlet line 11. That is to say there is only a small temperature jump of, for example, less than 3 °C over heat exchanger 13. If the auxiliary heating unit 9 heats the water to approximately 75 °C only a very small amount of energy will be required. After all, only a very restricted fraction of the quantity of water in the storage vessel 1 is heated, whilst, moreover, the major proportion of the heat from heating is recovered in heat exchanger 13. According to a variant of the invention, inlet line 11 is connected directly to feed line 2. That is to say the water entering the system is always subjected to a heat treatment in an auxiliary heating unit 9. At the temperature prevailing in the storage vessel 1 there is a risk that microorganisms will multiply rapidly. Legionella may be mentioned as an example in this context. This risk can be limited or even excluded by, in accordance with the invention, continuously or intermittently heating a fraction of the water present in the storage vessel to a temperature at which the effect of these microorganisms is largely destroyed. The speed of circulation through the auxiliary heating unit 9 is dependent on the temperature in the storage vessel. Under adverse conditions, the contents of the storage vessel can be heated every hour, but under favourable conditions this can take place once a day.

With the installation according to the present invention it is, on the one hand, possible to render such microorganisms harmless in a controlled manner and, on the other hand, the temperature in the storage vessel can be kept relatively low. Furthermore, the energy requirement for the temporary heating of the water to render such microorganisms harmless is very restricted.

Although the invention has been described above with reference to a preferred embodiment, those skilled in the art will understand that numerous modifications can be made which are obvious following the above, without going beyond the scope of the present invention. For instance, it is possible to arrange the main heating system outside the vessel and heating of return water can be implemented in another way or can be omitted.

Claims

1. Storage vessel assembly for storing hot water at low temperature, comprising a storage vessel (1) for hot water provided with a feed and a discharge for water, characterised in that there is an auxiliary heating unit (9), located outside the storage vessel, for heating said water to a temperature above the temperature in said vessel, which auxiliary heating unit is provided with an inlet line (11) and outlet line (12) for water, which lines are connected to said storage vessel via a pump (10).

2. Storage vessel assembly according to Claim 1, wherein a heat exchanger (13) is arranged between said auxiliary heating unit and said vessel, the water from the outlet line releasing heat to the water from the inlet line.

3. Storage vessel assembly according to one of the preceding claims, wherein the control of the pump is designed in such a way that the contents of the vessel are fed through said auxiliary heating means at least once a day.

4. Storage vessel assembly according to one of the preceding claims, wherein said auxiliary heating unit is powered by solar energy.

5. Storage vessel assembly according to one of the preceding claims, wherein said auxiliary heating unit comprises a heat pump.

6. Storage vessel assembly according to one of the preceding claims, wherein said feed comprises the outlet line from said heat exchanger and wherein the inlet line of said heat exchanger is designed for connection to the mains water supply.

7. Method for storing water in a vessel, wherein said water is at a storage temperature of less than 65 °C, comprising removing a relatively small quantity of said water from said vessel, heating said relatively small quantity of water to above 65 °C and returning it to the vessel.

8. Method according to Claim 7, wherein said relatively small quantity comprises at least the entire volume of said vessel per day.

9. Method according to Claim 7 or 8, wherein, after heating, the water to be returned to the vessel is re-cooled with the aid of the water to be subjected to said heating.

10. Method according to Claim 9, wherein said re-cooling of said water is carried out in such a way that the temperature difference between leaving the vessel and entering said vessel again is at most 3 °C.

1. Method according to one of Claims 7 - 10, wherein water fed to said storage vessel is subjected to said heating before it enters said vessel.