GB2360571A

GB2360571A - Recirculation circuit and cold water connection arrangement for a water heater

Info

Publication number: GB2360571A
Application number: GB0004270A
Authority: GB
Inventors: Johannes Albertus He Willemsen
Original assignee: Heatex BV
Current assignee: Heatex BV
Priority date: 2000-02-07
Filing date: 2000-02-23
Publication date: 2001-09-26
Also published as: NL1014303C2; GB0004270D0; DE20003556U1

Abstract

The water heater comprises a tank (1) for storing a volume of heated water (2), a furnace (3), a burner (4) and a heating element made up of a furnace wall (5) and a helical flue gas discharge channel (7). The recirculation and cold water connection arrangement includes a channel (20) including a pump (11), connected between a tapping channel (17) and a cold water supply channel (9). When hot water is required it is drawn through the tapping channel (17) via a space formed between the furnace wall (5) and a further wall (12) the water used is replaced via the cold water supply channel (9). A controller (30) switches the pump (11) on, when flow is detected by sensor (21) in the cold water supply channel (9) or when the temperature detected by sensor (23) of the water in the space (2) or in the tapping channel (17) is below a predetermined minimum. This arrangement requires a smaller pump than previously, as it does not have to pass the full flow of water drawn through the tapping channel (17) when water is demanded. Also cold water is not able to bypass the heating element as previously.

Description

2360571 Boiler The invention relates to a boiler according to the preamble

of claim 1.

Such a boiler is known from applicants' Dutch patent application 1004086.

In such a boiler, during the tapping operation and during recirculation to heat water in the tank, water is passed along the heating element and heated by heat exchange with the heating element. When water is tapped, cold water taking the place of the tapped hot water f lows via the pump to the tank. This boiler has the drawback that when a hotwater tap is opened water can flow to the tapping channel via the recirculation circuit, instead of via the pump, until the pump gives a throughout which is at least equal to the tapping throughput. This leads to a cold water pulse shortly is after the beginning of the tapping of hot water, especially when a large tapping throughput is attained very rapidly.

It must further be ensured that during the tapping of water at a specific throughput the pump always gives at least the same throughput, because otherwise, then too, a part of the water flows via the recirculation circuit and is tapped without having passed along the heating element. Furthermore, in case of power failure, hot water is no longer available nearly immediately, because then, too, during the tapping operation, cold water can flow via the recirculation circuit and can be tapped without having passed along the heating element.

It is an aim of the invention to provide a boiler in which these drawbacks have been removed.

According to the present invention, this aim is achieved by carrying out a boiler in accordance with claim 1.

Because the pump is placed upstream of the cold water supply line, the tapping of heated water and the supply of cold water in replacement of the tapped heated water can take place independently of whether the pump is in operation or not. Accordingly, the required pumping capacity is not 2 dependent on the desired tapping throughput. Moreover, becaug-e the pump need not pump the water supplied in replacement of tapped hot water, energy is saved and wear of the pump is limited. Furthermore, the pump also prevents the tapping of cold water flowing via the short-circuit channel without having passed along the heating element.

Special advantageous embodiments of the pump according to the invention are laid down in the dependent claims.

Further aims, practical aspects, effects and details of the invention will hereinafter be described and explained in more detail with reference to the drawing, in which: - Fig. 1 is a cutaway side elevation of a boiler according to a first practical example of the invention, and Fig. 2 is a schematic partial elevation in crosssection taken on the line II-II in Fig. 1.

The boiler according to the example shown has a tank 1 with an inner space 2 f or storing water. The tank has an inner wall 23 and a layer of insulating material 24 which is disposed around this inner wall, and which, in turn, is enclosed by a housing 25. To directly heat water, the boiler is provided with a furnace 3 with a burner 4 and a furnace wall 5 which forms a boundary surface between a burner chamber 6 containing the burner 4 and the inner space 2 of the tank 1.

Connected to the burner chamber 6 is a flue gas discharge channel 7 for discharging flue gases in a direction indicated by an arrow 8. The flue gas discharge channel 7 extends helically through the tank 1, so as to promote, in use, heat transfer from the flue gases to the water in the tank 1. Connected to the burner 4 are also channels 26, 27 for supplying fuel and ambient air, while a ventilator 28 serves to generate a controlled air supply. To meter the fuel supply in relation to the amount of air sucked in, a control block 29 is provided.

3 Connected to the tank 1 is a supply line 9 for suppl7-ing water to be heated in a direction indicated by.-an arrow 10.

The tank 1 further includes a screening cap 12 which screens the furnace 3 at a small distance therefrom and defines a space 13 between the screening cap 12 and the furnace wall 5. The screening cap 12 is provided with passages 14, 15 for letting in and out water in the interspace 13. A number of the passages 14 are distributed over the screening cap. Via these distributed passages 14 the interspace 13 directly communicates with the remaining interspace 2 of the tank 1.

In use, water is admitted to the interspace 13 between-the screening cap 12 and the furnace wall 5 via the distributed passages 14 in the screening cap 12 in places distributed over the interspace 13. The water is then passed through the screening cap 12 along the furnace wall 5, which effects an intensive cooling flow along the outer surface of the furnace wall 3. Consequently, the temperature of the furnace wall 5 remains relatively low during the burning of the burner 4, which prevents boiling effects and scale on the furnace wall 5.

Because the interspace 13 between the screening cap 12 and the furnace wall 5 directly communicates with the remaining inner space 2 of the tank 1 via the distributed passages 14, water is admitted, in use, to the interspace 13 via places distributed over the screening cap 12. The water admitted in places distributed over the surface of the screening cap forms a flow through the interspace 13, which is uniformly distributed over the outer surface of the furnace wall 5, and which cools the furnace wall 5 accordingly uniformly. Another central passage 15 forms a discharge opening for discharging water from the interspace 13. 35 Connected to the central discharge. passage 15 is a tapping channel 17 for tapping water from the tank 1 in a 4 direction indicated by arrows 18. Consequently, in use, the water'displacements generated when tapping water are also utilised to allow water to be heated to flow through the' interspace 13.

Pre-heating the water in the tank 1 by heat exchange with the f lue gas channel 7 inhibits scale in the area of the burner which occurs in many regions when heating mains water in a specific temperature range. Thus, scale on the furnace wall is inhibited and chipping of scale owing to boiling effects along the furnace wall 5 is therefore inhibited as well.

Scale on the furnace wall is particularly inhibited effectively, because the furnace 3 is located above at least the most important parts of the heat exchanger 19 and the is flue gas channel 7 in the tank 1. Freshly supplied cold water, which is still relatively rich in calcium, collects, owing to the relatively high specific weight thereof, especially in subjacent parts of the tank 1. Only after the water has been heated by heat transfer and the calcium content has decreased accordingly, and after, in addition, colder water has been supplied to the tank, does the slightly heated water rise in the tank 1 and is it given the opportunity to reach the interspace between the screening cap 12 and the furnace wall 5 via the supply passages 14.

Because a pump 11 is included in a channel 10 between the central passage 15 and the inner space 2 of the tank 1, a flow can be maintained therewith in the interspace 13, also while no water is tapped from the tank. The furnace 3 can therefore also be fired when no water is tapped. The heated water then f lows back again into the inner space 2 of the tank 1.

Because the pump 11 is placed upstream of the part of a recirculation circuit 9, 20 formed by the cold water supply line 9, the tapping of heated water and the supply of cold water in replacement of the tapped heated water can take place independently of whether the pump 11 is in operation or not. Accordingly, the required pumping capacity is not depenjent on the desired tapping throughput. Moreover, because the pump 11 need not pump the water supplied in replacement of tapped heated water, energy is saved and wear 5 of the pump 11 is limited.

The part of the recirculation circuit 9, 20 in which the pump 11 is included forms a short-circuit channel 20. The short-circuit channel 20, on its side remote from the tapping channel 17, communicates via a part of the supply channel 9 with the inner space 2 of the tank 1. via this short-circuit channel 20, when no water is tapped, water pas"sed through the interspace 13 can be returned to the inner space 2 of the tank 1.

-Included in the supply line 9 is a current switch 21 which switches in reaction to a tapping of water from the boiler. The current switch 21 is coupled via a control unit 30 with the pump 11 to switch on the pump 11 in reaction to the detection of a specific current through the current switch 21. The current switch could, in principle, also be included in the tapping line 17, but there it is exposed to greater thermal stresses. By switching on the pump already in reaction to the detection of any or a specific minimum of water flow, the boiler can react more rapidly to a heat demand following the tapping of heated water than when it would react to a decrease of temperature of the heated water. Once the pump operates, the burner can immediately start, so that delay by waiting for the start-up of pump 11 is prevented. Because the pump 11 is placed upstream of the part of a recirculation circuit 9, 20 formed by the cold water supply line 9 and therefore without any problem the tapping flow can start up with some delay when compared to the startup of the supply, the sensitivity of the current switch and the accuracy of this current switch are of relatively little importance. Therefore, a simple current switch produced at a low cost price may be used.

6 Furthermore, a temperature sensor 23 is provided to monitor a water temperature in the boiler, which tempe'rature sensor 23 is coupled - in this example also via t>IE control unit 30 with the pump 11 to switch on the pump 11 in reaction to the detection of a temperature below a specific minimum value. The pump 11 can thus be automatically switched on both in reaction to a tapping of water and in reaction to a decreased temperature.

optionally, the temperature sensor 23 may be located in the tapping channel 17, which enables an accurate control of the temperature in the area of the furnace'wall 5 as well as of the tapping temperature. To this end, the pumping throughput and and/or the burner capacity may be controlled in dependence on the detected temperature. Besides, it is also possible to use the pump 11 for admixing cold water from the supply line 9 to the tapping line 17 during the tapping operation, e. g. to limit the tapping water temperature to a maximum of 601C at a maximum water temperature in the boiler of 600C. 20 The temperature sensor 23 is located within the tank 1. Consequently, the water temperature in the tank 1 can be measured so as to start up the pump and subsequently the burner in reaction to cooling below a specific temperature. The heating element 3 is located at the top of the tank 1, while the flue gas channel 7 extends downwards through the tank and the tapping channel 17 extends substantially vertically from a superjacent part of the tank 1 to a subjacent part of the tank 1. This has the advantage that the water at the bottom of the tank 1 is relatively little heated and therefore remains relatively cold. This, in turn, promotes condensation of water vapour in the flue gas channel 7. By promoting this condensation, a substantially higher efficiency is attained. Furthermore, during the tapping of heated water the tapping water which delivers heat to the water at the bottom of the tank for a relatively short time cools relatively little. To attain a specific 7 temperature, the water therefore needs to be heated by the heating element 3 to a less high temperature, which is also favourable to the efficiency of the boiler. That the water in the area of the heating element needs to be heated to a less high temperature is especially advantageous in combination with the position of the pump 11 upstream of the cold water supply line 9, so that during the tapping operation a relatively large throughput is attained along the heating element 3, but also is an essential advantage when the pump would be placed downstream of the intermediate channel 10 in the cold water supply line 9.

The maintenance of a relatively cool zone in the area of the flue gas channel 7 is further promoted because the flue gas channel 7 extends in a tubular outside zone of the tank and the tapping channel 17 extends in a central zone of the tank and at a distance from this tubular outside zone. The tapping channel 17 thereby heats in particular water in a central columnar area of the boiler, which heated water rises to the heating element and thereby has a very low heating effect on the water in the outer area of the inner space of the tank where the flue gas channel 7 is situated. Conversely, the rising column of hot water ensures that the cooling within the tank of water that is tapped is further limited. The temperature to which the water must be heate by the heating element 3 to attain a specific delivery temperature is thereby further limited, which further increases the efficiency of the boiler. Here, too, the reduction of the required water temperature in the area of the heating element is especially advantageous in combination with the position of the pump 11 upstream of the cold water supply line 9, so that during the tapping a relatively large throughput is attained along the heating element 3, but is also advantageous when the pump would be placed downstream of the intermediate channel 10 in the cold water supply line 9.

8

Claims

1. A boiler for heating water and storing a volume of heated water, comprising:

a tank with an inner space for storing water, a heating element.

a tapping channel for tapping water from the tank, which tapping channel connects to said heating element, a recirculation circuit between said heating element and the inner space of the tank., comprising a part of a supply channel for supplying water to be heated and a shortcircuit channel between the tapping channel and the supply channel., of which short-circuit channel a downstream end connects to the supply channel. and is a pump in said recirculation circuit, characterised in that the pump is included in said recirculation circuit upstream of the supply channel.

2. A boiler according to claim 1, further comprising a current switch in a supply line or a tapping line for switching in reaction to a tapping of water from the boiler, which current switch is coupled with said pump for switching on said pump in reaction to the detection of a specific flow.

3. A boiler according to claim 1 or 2, further comprising a temperature sensor for monitoring a water temperature in said tank,. which temperature sensor is coupled with said pump for switching on said pump in reaction to the detection of a temperature below a specific minimum value.

4. A boiler according to claim 3, in which said temperature sensor is located in said tapping channel.

9

5. A boiler according to any of the preceding claims, in which said temperature sensor is located within said tank.

6. A boiler according to any of the preceding claims, in which the heating element is located at the top of the tank., further comprising a flue gas channel extending downwards through the tank., in which the tapping channel extends substantially vertically from a superjacent part of the tank to a subjacent part of the tank.

7. A boiler according to claim 6, in which the f lue gas channel extends in a tubular out side 'Zone of the tank and the tapping channel extends in a central zone of the tank,

8. A boiler substantially as hereinbefore described with reference to the accompanying drawings.