EP1261828B1

EP1261828B1 - A new concept, fast-acting water storage heater

Info

Publication number: EP1261828B1
Application number: EP01915301A
Authority: EP
Inventors: Andrea Manini
Original assignee: Merloni Termosanitari SpA
Current assignee: Merloni Termosanitari SpA
Priority date: 2000-03-03
Filing date: 2001-02-28
Publication date: 2006-01-04
Anticipated expiration: 2021-02-28
Also published as: ITAN20000006A0; ES2256218T3; PL365117A1; WO2001065186A1; IT1316723B1; DE60116473T2; DE60116473D1; ITAN20000006A1; AU2001242438A1; ATE315208T1; EP1261828A1; CZ20022816A3; HUP0301079A2

Abstract

This invention describes a method for heating water to be used for sanitary purposes in a storage tank (5) and certain pieces of equipment which implement this method. The invention's main feature is that when the cold water from the main water supply system enters the said storage tank (5), it is forced to pass across a portion (15.b) of a heat exchanger (15), which is sufficiently powerful to bring the said water immediately up to, or very close to, the usage temperature. The said heat exchanger (15) also heats up the water during the storage phases. The advantage of this invention is that the negative effects of the mixing of the cold incoming water with the already heated water in the storage tank (5) are either eliminated or significantly reduced.

Description

Technical field

The invention relates to a method for the heating and storage of water to be used for sanitary purposes and apparatus for implementing the said method, the said invention being particularly useful for the production of hot water to be used for sanitary purposes in small quantities such as for household use. An example of such a water storage is given in EP-A-0 870 993.

Background Art

The current, commonly known techniques, involving many ways of producing hot water, will now be described in a summary form, with the advantages and the disadvantages highlighted.
All the water storage heaters have the following features in common: a low level of installed thermal power, a relatively large water reserve and a storage temperature which is much higher than the usage temperature.
The main advantages of the water storage heaters are as follows:

the low level of heating power required, a feature which is particularly important for electric water heaters used in countries with limited amounts of electricity available for household use;
the potential for an extremely substantial water flow rate, which means the water can be used by several connected devices at the same time without causing any problems such as a reduction in flow rate or temperature;
the ease with which the usage temperature of the water can be adjusted, either manually or with a thermostatic mixer, since the temperature and the flow rate of the water dispensed are both independent of each other, which is not the case with the instant boilers.

On the other hand, water storage heaters have the following disadvantages:

the quantity of hot water is limited to the volume of the storage tank, so that , if the consumption levels are high, the use cannot be continuous;
the heating time required to restore the water reserve is a few hours, generally around 5 to 7 hours for an electric water heater, and generally half of that for gas water storage heaters;
while water is being taken from the storage tank, the cold water mixes with the hot water still in the tank, lowering its temperature to below the usage temperature, in general equal to 35-40°C; as a result, not all the water that has been heated to a temperature considerably higher than that required by the connected devices is immediately available for use.
In fact, that volume of water, which was sufficiently hot before the water was taken from the storage tank, but which has cooled because of the cold water mixed in during the drawing process, will need to be heated again before it can be brought up to at least the usage temperature.
The phenomenon is commonly known to technicians in the field and so it is measured using special procedures which have become standards, and consequently, it is only described here in a summary form.
If the temperature of the water from the water system is t.h2o and if the water stored V.acc is heated to an average temperature t.acc of about 70°C but which is higher than the usage temperature t.util, the maximum quantity of hot water theoretically available to the connected devices at the usage temperature t.util is V.util = V.acc x (t.acc-t.h2o)/(t.util- t.h2o) but the actual volume available V.util. eff can be obtained by drawing the water from the water stored, at the temperature desired t.util, mixing it manually or with a thermostatic mixer, with the cold water from the mains at the temperature t.h2o, gradually decreasing the temperature. However, drawing the water in this way stops as soon as the water comes from the stored reserve, albeit hot, but at a temperature below the t.util.
The ratio of V.util.eff to V.util is called the "mixing factor" is always less than 1. In practise, it is as if there were available, in fact, a storage tank which is smaller than the actual volume V.acc. This drawback is currently limited, but not eliminated, by designing the cold water input methods for the storage space suitably so that the mixing of the input water with the already heated water is limited. The smaller the storage tank is, the more fastidious the phenomenon becomes, as is the case of the water heaters with a capacity of 15-30 litres used for showers.

The phenomenon of the mixing apart, the water stored is stratified with the higher t.acc temperatures at the top, consequently, the output temperature is not constant, which means that, in the absence of a thermostatic mixer, it becomes necessary to regulate the temperature with the tap handle to keep the water at a constant usage temperature t.util. Technicians in the field also know that when the average temperatures are equal, the less uniform the distribution of the temperature is in a storage tank, the greater the heat loss is.
The instant water heaters generally have the opposite features to the storage heaters: a high level of installed thermal power, no water reserve and heating to the usage temperature.
The main advantages of the instant water heaters are as follows:

an unlimited quantity of hot water since the energy dispensed heats the water which passes across the apparatus continuously;
hot water immediately available at any moment.

One disadvantage which is common to all kinds of instant heaters is the fact that the heated water flow-rate is limited by the amount of installed power, consequently it is difficult for the heater to serve several connected devices at once. There are also other disadvantages depending on the type of apparatus concerned.
Instant electrical heaters:

to have a sufficient water flow rate, 10-30kW of power are required, which means the market is limited to those few countries where the household electricity supply is such;
the power is regulated by steps, by inserting or not inserting the resistor units: it is impossible, or extremely difficult, to adjust the temperature and the flow rate separately, so the temperature t. util is only pleasant with certain flow rates.

The instant gas heaters with the gas capacity adjusted depending on the water capacity or the temperature of the output water:

the temperature should be constant regardless of the flow rates, but in reality, the lower flow rates produce water with too high a temperature, or the going out of the flame. In fact, the burner cannot bear combustion at a power which is much lower than the maximum. If the control is run on the output temperature, hunting is noted with extremely low, but normal, flow rates.

In gas water heaters, used for producing hot water for sanitary purposes, the water is generally heated indirectly by the primary heating circuit. If the heating involves storage, the adjustment of the flame power can be an ON-OFF type. Instant heating, on the other hand, is only possible for boilers with a modulating flame, so that the usage temperature t.util remains constant regardless of the flow rate. In fact, the heating is not really instant: the presence of a primary circuit between the flame and the water supply mains can lead to a time of 20-40 seconds for the temperature required to be reached. For the rest, the two alternatives have the same merits and faults as those just described for the water heaters.
There are also models of boilers which have an instant heating option for water to be used for sanitary purposes using an exchanger with suitable power but, in addition, either up or downstream of the exchanger, there is a small storage tank (4-5 litres) designed to supply hot water immediately until the instant exchanger is brought up to temperature. Although an improvement, it remains difficult to regulate the usage temperature t. util.

Disclosure of Invention

The aim of this invention is to indicate a method for heating water to be used for sanitary purposes and an apparatus to implement this method so as to eliminate the problems described earlier with regards to both the storage heating apparatus and methods and the instant ones, maintaining the merits of both kinds.
In particular, the main aim of the present invention is to produce a water storage heater whose mixing factor, as described above, is one.
A further aim of the present invention is to obtain an unlimited quantity of water, continuously, from a water storage heater.
A still further aim of the present invention is to guarantee an accuracy in the regulation of the temperature of the water dispensed which is at least equal to that of the storage heaters.
These and other aims are achieved through a heating method for the water contained in a storage tank using a heat generator with identical power to that of instant water heaters and according to the methods outlined in the description and the claims that follow.
These aims and advantages of-the invention will better emerge in the description of the heating method for water to be used for sanitary purposes according to the invention and of certain apparatus which enables the application of this method and which is provided in the form of a nonlimiting example.
Figure 1 shows, schematically, a gas boiler for household use fitted with a storage tank for hot water to be used for sanitary purposes.
Figure 2 shows, schematically, the aforementioned storage tank in the heating mode with no water being drawn.
Figure 3 shows, schematically, the storage tank in figure 2 in the instant heating mode during the hot water dispensing phase.
Figure 4 shows, in a perspective view, a part of the boiler in figure 1.
Figure 5 shows a lateral section of the storage tank in the previous figure.
Figure 6 shows, schematically, an electric water heater according to the invention.
With reference to figure 1, number 1 denotes the heat exchanger between the flame and the primary circuit of the room heating; 2 indicates the burner, 3 the regulator valve for the gas at the point at which it reaches the burner; 4 denotes the primary circuit of the room heating; 5 is the storage tank for water to be used for sanitary purposes, the said tank, in its turn, being divided into two zones: 5a outlet and 5b inlet; 6 indicates the temperature check probe for the stored water; 7 denotes the valve for switching the primary circuit 4 between the room heating function and the heating function for the water to be used for sanitary purposes; 8 indicates the thermostatic mixer for regulating the temperature of the water to be used for sanitary purposes; 9 denotes the collection area within the storage tank 5 for the water to be used for sanitary purposes which will go to the connected devices, 10 indicates the distribution zone within the storage tank 5, for the water for sanitary purposes coming from the main water system; 11 indicates the flow switch which detects when water for sanitary purposes is being drawn from the tank; 12 denotes the circulation pump for the primary circuit 4; 13 indicates a baffle, in a vertical position, which partially divides the storage tank 5 into a first and second zone, 5a and 5b respectively; 14 denotes other partial division baffles in a vertical position; 15 is the heat exchanger, 15a indicates a first part of the exchanger 15 above the collection area 9 for the water for sanitary purposes which will go to the connected devices; 15b a second part of the heat exchanger 15 above the distribution zone 10 for the water coming from the main water system; 16 indicates the inlet point of the primary circuit 4 in the heat exchanger 15; 17 indicates the outlet point of the primary circuit 4 from the heat exchanger 15; 18 denotes an opening for the primary circuit 4 to pass through from the first part 15a to the second part 15 b of the heat exchanger 15. MR indicates the delivery flow of the heating circuit; RR the return flow of the heating circuit; IS denotes the inlet of water from the main water system to the storage tank 5; US indicates the outlet of hot water to be used for sanitary purposes from the boiler going towards the connected devices; GAS denotes the connection to the gas supply system.
With reference to figure 2, in addition to the areas or elements already indicated in the previous figure, there are also arrows which represent the convective motions of the water through the natural circulation in the stored water.
With reference to figure 3, in addition to the areas or elements already indicated in the previous figures, there are arrows which represent the direction of the flow of water while hot water is being drawn from the tank.
Figure 4 shows only elements that have already been described.
Figure 5 shows only elements that have already been described.
Figure 6 shows, in addition to the elements already described in the previous figures, the section of a heat exchanger 15.1, as an alternative to the exchanger 15. The exchanger 15.1 could be made of a pipes band or a battery of armoured electrical resistors.
There will now follow a detailed description of the functioning modes and the advantages of the heating method and a piece of apparatus designed to use the method according to the invention.
For the sake of an example, the water heating methods according to the present invention are now described as applied to a boiler for room heating and production of hot water for sanitary purposes fitted with a storage tank according to one possible embodiment of the invention.
As shown above all in figure 4, in the first example examined, the storage tank 5 is a 'rucksack' kind, substantially prismatic in shape, and crossed with baffles 13 and 14 whose structural functions are known: the baffle 13 is also an element of the embodiment of the invention being described now.
With reference to figure 1, supposing there is a period in which no hot water is drawn: using the probe 6 the temperature of the water in the storage tank 5 is checked. If this temperature is less than a pre-set value t.acc, e.g. 70°C, the deviator valve 7 switches its position so that the primary circuit 4 closes through the heat exchanger 15. Then the fluid in the primary circuit 4 enters the heat exchanger 15 through the inlet 16, it runs through the first part 15a, passes over the partial division baffle 13 of the heat exchanger, through the opening 18, through the second part 15b of the exchanger 15 from which it exits thought the outlet 17 to return to the heat exchanger 1. Naturally the heating of the fluid circulating in the primary circuit 4 can be achieved with any known method.
In the exchanger 15, the containment sleeve for the secondary fluid, i.e. the containment fluid for the water to be used for sanitary purposes, is composed of the storage tank cover 5; in other words, the water for sanitary purposes must be allowed to circulate freely around all the surfaces of the heat exchanger 15 that are in contact with the primary fluid. With regards to the dimensions and the minimum power exchange of the said exchanger 15, these will be indicated later on.
With reference to figure 2, it is easy to see, how, in this functioning mode, the convective motions indicated by the arrows are activated, the said motions enabling the water contained within the storage tank 5 to be heated in a substantially uniform way until it reaches the temperature required t.acc, which, when exceeded, will cause the heating of the primary circuit 4 to be deactivated.
With reference to figure 3, there will now follow a description of the functioning mode while the water to be used for sanitary purposes is being drawn. In this situation, water from the main water system enters the tank 5 through the inlet IS, then it is distributed through the zone 10, passes through the second part 15b of the exchanger 15 and rises up into the tank 5, along the second zone 5.b. It then moves over the top of the baffle 13, goes back down into the tank 5, along the first zone 5.a, through the first part 15.a of the exchanger 15 and it is then collected in the zone 9, from where it goes to the connected devices via the hot water outlet US, where, after being suitably mixed in the mixer 8 with cold water it is brought to the usage temperature t.util.
While the water is being drawn, the flow switch 11 detects the passing of the water and, consequently, with known methods, ensures that, through the exchanger 15 and according to the methods described above, the primary heating fluid circulates.
The exchanger 15 must occupy all the section of the passage from zone 10 to 5.b and from zone 5.a. to 9. This is to prevent part of the water to be used for sanitary purposes by-passing the first and the second part 15.a and 15.b of the exchanger 15 while being drawn.
The baffle 13 is designed to force the water for sanitary purposes to run along the whole tank 5 so that there are no stagnant areas in the water in the higher part of the tank, nor air pockets which cannot be removed by the tow of the water in transit.
It is clear that the thermal power of the heat exchanger 15, in its entirety, must be sufficient to guarantee the dispensing of the thermal energy required to ensure the hot water for sanitary purposes reaches the connected devices for an unlimited time and at the maximum usage temperature t.util envisaged, regardless of whether or not there is enough water at the temperature t.acc. in the storage tank. But the minimum requisite for the heat exchanger 15 in the embodiment in this invention is that its second part 15.b has enough exchanging power alone to guarantee the water from the main water system which is passing across it during the drawing phases can be heated to a temperature not less than the usage temperature t. util.
The water heating method just described obviously achieves the aims described earlier with the following advantages.
During the heating phase when no water is drawn, since the exchanger 15 has the thermal power typical of the instant heaters for household use, i.e. at least 10 - 11kW, the natural circulation due to the convective heat exchanges is extremely active, so much so that it causes very little stratification of the water, in other words, the temperature increases very uniformly throughout the whole tank 5. A first advantage is that there is less heat loss than with storage tanks with the same average temperature, but the distribution of the heat loss is less uniform. During the drawing phases, since the cold water entering the tank 5 has already been preheated, according to this preferred embodiment of the invention, at least to the usage temperature t.util, the mixing factor cannot be lower than 1, i.e. all the water contained in the tank 5 can be used since it has been preheated by the second part 15.b of the exchanger 15 regardless of any further heating of the outgoing water by the first part 15.a of the said exchanger 15. To be precise, using the symbols defined above, the quantity of water immediately available V.util.eff is equal to V.acc x (t.acc - t.h2o) / (t.util -t.h2o). When the water contained in the storage tank 5 has been used up, the water heater continues to function according to the methods typical of an instant heater, supplying for an unlimited amount of time and at the usage temperature t.util, the flow permitted by the power available.
However, even if the heating method just described used a heat generator with a moderate power, i.e. not enough to be able to bring the incoming water at the temperature of the main water system up to the usage temperature t.util, its benefits with regards to the mixing factor would be equally noticeable: in this case the water heater produced would not be capable of functioning also as an instant heater, however it would still have an excellent mixing factor.
The low level of stratification and the pre-heating of the incoming water ensure the temperature of the outgoing hot water to be used for sanitary purposes is more uniform than in the storage tanks which do not follow the teachings of the present invention. Consequently, it is much easier to keep the temperature of the hot water to be used by the connected devices constant, by means of a thermostatic mixer or, even more so, by manual mixing.
The heating method just described in a preferred embodiment, in which the method is applied to a boiler which produces hot water and stores it, can undergo a number of application variations, some examples of which now follow:
According to the essential features of the invention, the heat exchanger 15 could be composed of a different kind of heat generator than the one described above and the storage tank could also have a more traditional form.
Above all it is not essential for the storage tank 5 to be formed with two zones 5a (outlet) and 5b (inlet) as well as the first part 15a of the exchanger 15; the first part 15.a is necessary for the heating phase while no water is being drawn, in the particular embodiment of the tank 5 just described it is particularly beneficial when installed in a heating boiler, but otherwise, according to the essence of the present invention, the heater 15 could just as well be composed exclusively of one part, i.e. the part defined in this report as the second part 15.b, while the hot water outlet US from the storage tank 5, as just mentioned, could be positioned above, according to the traditional form illustrated schematically in figure 6.
In fact, a gas water storage heater with great benefits could be designed with a combustion chamber and a fume shaft positioned horizontally in relation to the lower part of the storage tank 5. The construction methods for the said combustion chamber with the relative shaft are described sufficiently in Italian patents n° 1 182 951 granted on 05.10.1987 and n° 1 178 296 granted on 09.09.1987. Equally advantageous is an electric combined instant - storage water heater with a high power level (at least 10-11kW) in which, with reference to figure 6, there is a band of electrical resistors 15.1 in position with the inlet for the water from the main water system. The implementation of the heating methods according to the present invention in this kind of hot water generator actually eliminates the adjustment difficulties for the outgoing water completely since, as it is clear to any technician in the field, although the regulation of the electrical power supplied remains stepped, the storage tank 5 acts as a thermal stabilizer, enabling the temperature of the outgoing water US to be adjusted easily by means of thermostatic mixer.

Claims

A heating method for water to be used for sanitary purposes and to be stored in a storage tank (5) at a determined storage temperature (t.acc) and to be distributed to connected devices at a determined usage temperature (t.util) which is less than the storage temperature (t.acc.), comprising the following steps:
- while water is being drawn, all the incoming water from the main water system is forced to pass across a heat exchanger (15, 15.b) to be heated to a higher temperature than that of the main water system (t.H₂O); and

- during the heating phase when no water is drawn, the outgoing water from a heat exchanger (1) which is positioned between a burner (2) and a primary circuit (4) of the room heating is forced to pass across the heat exchanger (15) positioned inside the storage tank (5) and then comes back to said heat exchanger (1) after above mentioned crossing; this crossing of the heat exchanger (15) from the water of the primary circuit (4) heating the body of water contained in said storage tank through convective motions,
characterized in that a sufficient amount of the power is supplied to the water by the heat exchanger (15, 15.b) to heat all the flow required to a temperature higher than or equal to the usage temperature (t.util),).
A heating method for water to be used for sanitary purposes according to claim 1, wherein, while the water is being drawn, further supplementary power is supplied to the water from the storage tank (5) by the heat exchanger (15, 15.a).
A heating method for water to be used for sanitary purposes, according to any of the previous claims 1, 2 and 3, wherein, before being sent to the connected devices, the water is mixed at the usage temperature (t.util) with suitable automatic means (8).
Equipment for heating water to be used for sanitary purposes, comprising:
- a storage tank (5) equipped, with an inlet for water from the main water system (IS);

- a heat exchanger (15) positioned above the distribution zone (10), said heat exchanger being able to be passed across by the incoming water in the storage tank (5) through an inlet (IS) in order to reach an outlet (US) when water is being drawn,
characterized in that a baffle (13), is positioned in a vertical position above the said heat exchanger, said baffle partially dividing the storage tank (5) into a first and second zone (5a and 5b) respectively, said zones being positioned above the heat exchanger (15, 15.a, 15. b); the baffle (13) being able to facilitate the crossing of the sanitary water in the whole said storage tank so that there are no stagnant areas nor air pockets in the water in the higher part of the tank.
Equipment for heating water to be used for sanitary purposes, according to the previous claim, wherein the said equipment comprises in addition:
- a so-called first zone 5.a positioned above the exchanger (15, 15.a),

- a heat exchanger (15, 15.a) positioned below the said first zone (5.a),

- a collection area for the water (9) below the said exchanger (15, 15.a), the said heat exchanger (15, 15.a) being formed in such a way as to force the outgoing water, while it is being drawn, to pass across it before reaching the outlet (US),

- lastly, a baffle 13 that divides the storage tank 5 into the so-called first and second zones (5.a, 5.b), the said zones being formed in such a way as to force the water, when water is being

- drawn, to circulate in the upper part of the storage tank (5).
Equipment for heating water to be used for sanitary purposes, according to the previous claim, wherein both the inlet IS and the outlet US for the water to be used for sanitary purposes are positioned in the lower part of the tank (5).
Equipment for heating water to-be used for sanitary purposes, according to any of the claims from 4 to 6, wherein
- the said heat exchanger (15, 15.a, 15.b) is composed of a heating body across which a primary heating fluid passes,

- there are means envisaged (4, 7, 16, 18, 17, 12) which enable the said primary fluid to circulate inside the said exchanger (15, 15.a, 15.b).
Equipment for heating water to be used for sanitary purposes, according to any of the claims from 4 to 7, wherein there are checking means (6, 12) envisaged to decide what thermal power should be supplied to the water for sanitary purposes during the heating phases, both when water is being drawn and not.
Equipment for heating water to be used for sanitary purposes, according to any of the claims from 4 to 8, wherein there are means (8) envisaged for the automatic mixing of the water for sanitary purposes with water from the main water system before it is sent on to the connected devices.
Equipment for heating water to be used for sanitary purposes, according to any of the claims from 4 to 9, wherein the storage tank 5 has a substantially prismatic shape and there are baffles (13, 14) envisaged which have the dual function of strengthening the structure and guiding the flow of water.
A boiler for heating rooms with the production of hot water to be used for sanitary purposes according to the previous claim, wherein any of the equipment according to one of the claims 4 to 10 is used.
A gas water storage heater according to the previous claim wherein any of the equipment according to one of the claims 4 to 10 is used.
A gas water storage heater according to claim 12 wherein the heat exchanger (15, 15.a, 15.b) is composed of a combustion chamber and a fume shaft positioned substantially horizontally.
An electric water storage heater wherein any of the equipment according to one of the claims 4 to 10 is used, whereby the heat exchanger (15.1) is composed of a band of electrical resistors.