EP0091931A1 - Heating system for space heating and tap water heating - Google Patents

Abstract

Heating system for heating spaces and tap water with the same medium, comprising a regulator (5) which decreases, respectively increases, the flow of the heating medium to a space heating device (2) when a control device signals an increased, respectively reduced, demand for the heat of tap water and a heat exchanger (3) placed between the heating medium and tap water, where the relative control device controls the temperature of a wall which is in direct heat exchange relation with the cold water of the supply line of the heat exchanger and is arranged so as to be heated by the heating medium. The other side of this wall is also in a direct heat exchange relationship with the heating medium at such a point on its path that it flows along this point when it does not flow towards the heat exchanger for heating tap water. The regulator opens and closes the supply of the heating medium to the heat exchanger for heating the tap water to respectively lower and upper wall temperatures.

Description

Heating system for space heating and tap water heating.

The invention relates to a heating system for space heating and tap water heating by the same heating medium, comprising a regulator which decreases respectively increases the flow of the heating medium to a space heating device if a monitoring means signals an increased respectively decreased demand for tap water heat, and a heat exchanger between heating medium and tap water, said monitoring means monitors therefor the temperature of a wall, which is in direct heat exchanging relationship with the cold water in the supply conduit of the heat exchanger and is positioned such that it is heated by the heating medium.

Such a system is known in various embodiments. E.g.from the Dutch Patent Application 297,384 such a system is known, wherehy a flow-through water heater for tap water heating is connected to a boiler through open supply- and discharge connections, where by the monitoring means is mounted on said boiler such, that if no water is tapped said means are heated by the water heater through heat conduction. Said mondtoring means actuates at. circulation valve in the space heating system, such that when warm water is tapped the connection between the space heating system and the boiler is interrupted and a circulation can be maintained in said system.

The invention aims to improve known systems of this type such that also in a small scale configuration a high efficiency is achievable in a cheap embodiment.

For this purpose a system as mentioned above is according to the invention characterized in that said wall is furthermore at the other side in direct heat exchanging relationship with the heating medium at such a spot in the path thereof, that it flows along said spot if it flows to the heat exchanger for tap water heating, and that said regulator opens and closes the supply of the heating mediumn to the heat exchanger for tap water heating at respectively lower and higher temperature of said wall.

The system according to the invention has small dimensions, has associated with said dimensions low insulation losses and therefore a high efficiency, whereas the heat exchanger can advantageously be so configurated that at the main distant tap point, hot tap water of the right temperature is immediately available.

Thereby the regulator influences more directly the flow of the heating medium to the tap water heater and because the regulator tries, to maintain a constant temperature of said wall, along which the heating medium flows if it heats the tap water, it is possible to keep the temperature of the tap water constant within broad limits nearly independent of the tapped water volume and the temperature of the heating medium.

The invention further relates to a more specified realisation of this principle, both for installations with their own heating source (boiler) and for installations connected to a district heating system, which will become clear from the following description of some embodiments of ( parts of ) a system according to the invention, illustrated in the accompanying figures. In said figures is:

Fig. 1 a diagram of a system according to a preferred embodiment of the invention;

Fig. 2 a sectional view along line II-II in Fig.3 through the regulatd&j as used in said system; Fig. 3 a sectional view along line III-III in Fig.2 through said regulator; and

Fig. 4 a possible embodiment of a heat exchanger for the tap water heating; whereas

Figs. 5, 6 and 7 show possible embodiments of the tube respectively the tube system of this heat exchanger.

The system according to Fig. 1 comprises a boiler 1, a space heating device 2, such as a set of radiators, a heat exchanger 3 for tap water heating and tap points, of which one is shown and referenced by 4. A regulator 5 is mounted in the conduit 6, through which the heating medium arrives from boiler 1. The regulator connects said conduit 6 to a conduit 7 leading to said device 2 or to a conduit 8 leading to said tap water heat exchanger 3. Through a return conduit 9 the medium from device 2 or heat exchanger 3 returns back into the boiler, for which purpose the exchanger 3 is connected to conduit 9 by return conduit 12.

Tap water enters at 10 and is guided to conduit 11 through the regulator 5 and is supplied from the heat exchanger 3 to tap points such as 4. Shown in dash lines is a heat exchanger 13 in the return conduit 12, in which the tap water entering through 10 can be preheated by the return flow of the heating medium. This option should be considered in particular if not a boiler 1 is used as heating source, but an external source such as in a district heating system, whereby it is important and often required that the return flow has a low temperature. The boiler 1 is then substituted by a supply conduit 15, which supplies external heated medium at high temperature, and a return conduit 16, which returns medium after withdrawing a part of the heat therefrom.

Now the regulator 5 will be described more detailed with reference to Figs. 2 and 3. A shaft 17 is journalled in appropriate guidances in the housing of the regulator to be movable in axial direction in said housing and said shaft supports a valve body 18, movable between an upper seat 19 and a lower seat 20. At the port 21 the conduit 6 (Fig. 1) is connected, which supplies heating medium from the boiler. This port is communicating via a passage along seat 19 and through space 22 to conduit 7 leading to the space heating device 2 and via a passage along seat 20 and through space 23 to conduit 11 leading to the tap water heater (exchanger 3).

Space 23 contains a tubular body 24, which is mounted with sealing rings 25 in holding rings 26 of heat insulating material, for instance a temperatureproof hard plastic, porcelain or the like, which are sealingly mounted in the house of regulator 5. This body can, as shown, be configurated as a simple short tubelet, for instance of copper alloy.

The interior of the tubular body 24 is communicating with conduit 10 via a port 27, which conduit 10 supplies cold tap water. Tap water flowing through the tubelet 24, and can thereafter leave the housing of the regulator at 28 (Fig.3), flowing to conduit 11, which leads to heat exchanger 3.

It will be clear from Fig. 3 that the tubular body 24 is provided with a temperature sensor 29 , mounted in a tubelet which is thermally insulated from the regulator housing, such that also a medium tight passage through the wall of the housing for a sensor line connected to said sensor is provided. Above the housing, as viewed in Fig. 2, a control amplifier is installed, with a drive motor for shaft 17, which is actuated dependent of the signals of said sensor, whereby an overload protection can be realised based on signaling of the fact that valve body 18 has reached one of its seats. Such control amplifiers are known and commercially available. A by-pass conduit 14 shown in dashlines can be mounted between the conduits 7 and 9 as will be described later.

The operation of this device is as follows: If there is no demand for warm tap water the boiler 1 will provide the space heating device 2 with heating medium in the usual way through conduit 6 and regulator 5, in which situation the valve body 18 is In the lowest position in Fig. 2 onto seat 20, such that the medium which enters at 21 leaves the regulator through 22 to conduit 7. Through the return conduit 9 the cooled medium returns to the boiler. In a district heating system this heated medium enters through 15 and flows, cooled down, back through 16. The whole housing of regulator 5 is now hot and the hot heating medium which earlier flowed for tap water heating through seat 20 to space 23, as well as the initially cold tap water in the tubelet 24, have also reached approximately the temperature ofcthe housing 5 after a sufficient long stand still. However, after a considerable period of time without any demand for space heating or tap water, the situation is different as will be described below.

If now warm tap water has to be supplied, for instance by opening a tap 4, cold tap water flows through conduit 10, port 27 and tubular body 24 via 28 to the heat exchanger 3. The temperature of the wall of the tubular body 24 so decreases sharply and this is monitored by sensor 29 delivering a signal to the control amplifier, which actuates the engine to displace the regulator rod 17, such that the valve body 18 moves upwardly to the position shown in Fig. 2. The heating medium now does not flow at all or only for a part to space heating means 2, but flows In stead completely or at least partly to the heat exchanger 3 to heat the cold tap water and from there to conduit 9 via conduit 12 and so back to boiler 1 (or to return conduit 16 in a district heating system). The distances between the isolating rings 26 and space 23 around the tubular body are chosen relative to the inner diameter of the tubular body 24, such that the surfaces of the passages for the heating medium and the tap water have a certain relationship to each other. This relationship is such that the flow rates of the heating medium and the tap water are equal at average entering temperature of the heating medium and of the (cold) tap water and at the desired final temperature of the tap water ( which is approximately equal to the temperature of the heating medium at the output of exchanger 3).

The control amplifier is configurated such that it tries to maintain a fixed set temperature of the tubular body 24 by increasing or decreasing the opening between the valve body 18 and the seat 20. The heat flow from the heating medium via the wall of the tubular body 24 to the (still cold) tap water, and associated therewith the temperature of the tubular body 24, which is measured by the temperature sensor 29, is defined by the flow rate of the heating medium and of the cold tap water, by the temperature of the heating medium and the tap water respectively, and by the surfaces of the tubular body 24, respectievely in contact with the heating medium and the tap water. The relationship between both said surfaces is chosen such that the final temperature of the tap water remains for the present purpose sufficiently constant within broad limits. The device is insensitive for pressure variations in the heating medium and tap water because only the flow speed in and around the trubular body 24 has any influence.

A speed variation caused by pressure differences for instance along the seat 20 is compensated by another setting of valve body 18. As soon as the tapping of the tap water from the tap 4 changes or stops, the speed of the tap water in the tubular body 24 will also change or reduce to zero as result of which the temperature measured by sensor 29 changes and the opening between the valve body 18 and the seat is changed or completely closed. With particular reference to Fig. 4, 5, 6 and 7 the heat exchanger 3 will.be described now. As is already indicated in Fig. 1, such a heat exchanger can be configurated as a long double walled tube, which ends preferably near one of the tap points (e.g. 4). One can thereby save a lot of space although of course a return conduit 12 to 9 has to be applied, but said conduit can be very short at favourable lay out of heat exchanger 3 and return conduit 9. The heat exchanger 3 needs of course a external insulation 30, but the assembly can be maintained relatively thin. If the main tap point is placed so near to the regulator 5 that the shortest distance therebetween is smaller than the preferred length of heat exchanger 3, embodied tubular, then this tube can have a meandering shape along some distance or along the entire distance, i.e. partitially folded back, with some insulation therebetween, as is shown in Fig. 4. Preferably the three tube sections are not in a same plane but situated in a triangular pattern to maintain a small external diameter.

If a heat exchanger 13 is applied one can build this together with the exchanger 3 as two adjacent double walled tubes in the same insulation, with inputs 8 and 11, a tap water conduit 10 to the regulator and the return conduit 12 at the end of this assembly near the regulator 5. The cold tap water Is thereby supplied through conduit 10, the warm water is tapped at 4 and the heating medium is conducted to the other end.

To keep the internal tube at desired distance from the external tube, Fig. 5 shows how the external tube can be pinched locally to contact and so support the internal tube, which pinching can be done for instance with a simple pair of pliers at uniform intervals of for instance 30 cm. Also a helically extending wire, for instance of metal, could be positioned between the internal and external tube. Fig. 6 shows a ribbed tube, at which tube ribs are extending straight or helically. A smooth tube can be externally mounted to form the double walled heat exchanger. Fig. 7 shows a double walled tube, made integrally with bridges 31 for the connection between the internal and external tube. This tube can be used as internal tube, by which an almost complete "double barrier" is created between tap water and (possibly polluted) heating medium. Heat exchangers according Fig. 5 and therefrom derivated can be fairly easily bent at site.

For further explanation the following may be useful: if a heat exchanger 13 is used, the quantity of heat medium has to be smaller and the internal dimensions of the regulator have to be adapted. Mostly the boiler comprises in a known way an own return (by-pass) conduit to maintain circulation, and normally also comprises a circulation pump. One can apply in stead of this a by-pass conduit 14 or a by-pass conduit for each radiator or the like. Thereby the regulator 5 and also the tubular body 24 are kept at a higher temperature so that the valve body 18 also remains pressed onto the seat 20. Nowadays a circulation pump, as described above, is often switched off in time periods during which no space heating is required. One has to switch said pump on if tap water is wanted and the signal therefor can be derived from regulator 5 for instance because the energizing of the engine of the regulator to lift valve 18 from seat 20 results into the generation of an appropriate signal. If the valve 18 turns again onto seat 20, one can derive (i.e. preferably also from the engine of the regulator) a signal to stop the pump preferably delayed.

Because the tubular body 24 will become in such time periods so cold that the valve 18 is lifted from seat 20, some heating medium will flow every time to heat exchanger 3 although no tap water is withdrawn.

One also can, particularly if the pump is not switched off, allow constantly some leakage loss through valve 18 along seat 20. The heat brought into the regulator 3 in this way compensates the insulation losses.

In the case of boilers which are intermittenary switched on and off, for instance controlled by a room thermostat, it can take a little time before the tap water is sufficiently heated, but further the system can also successfully be applied to those boilers.

It is Intended that in time periods in which no warm water is tapped, the heat exchanger 3 adapts the final temperature of the tap water. This is possible by correctly selecting the volume of the tap water and that of the heating medium in the exchanger 3 without counting for insulation losses, in other words by using appropriate tube diameters.

The insulation losses have to be compensated by extra supply of heating medium, as is indicated. A more elegant solution comprises of course that the temperature of the exchanger 3 is measured at a convenient place and that at a deviating (lower) temperature a signal is delivered to the regulator 5 to let the heating medium flow to the exchanger 3, without withdrawing tap water. After adaption, this second signal can be easily processed together with the signal of the temperature sensor 29 in the control amplifier. In this way the temperature of the exchanger 3 can be much better maintained constant in time periods in which no tap water is withdrawn, than with the described process in which a volume of heating medium is supplied depending onto the circumstances.

Claims

C L A I M S. 1. Heating system for space heating and tap water heating by the same heating medium, comprising a regulator, which decreases respectively increases the flow at the heating medium to a space heating device if a monitoring means signals an increased repectively a decreased demand for tap water heat, and a heat exchanger between heating medium and tap water, said monitoring means monitors therefor the temperature of a wall, which is in direct heat exchanging relationship with the cold water in the supply conduit of the heat exchanger and is positioned such that it is heated by the heating medium, characterized in that said wall is furthermore at the other side in direct heat exchanging relationship with the heating medium at such a spot in the path thereof, that it flows along said spot if it flows to the heat exchanger for the tap water heating, and said regulator opens and closes the supply of heating medium to the heat exchanger for the tap water heating at respectively lower and higher temperature of said wall.

2. System according to claim 1, characterized in that said wall is a short tubelet and said media are flowing around said tubelet internally and externally.

3. System according to claim 2, characterized in that said tubelet is supported by heat insulating supports in its housing.

4. System according to claim 2 or 3, characterized in that the passages through which the heating medium and the tap water flow along the tubelet, are chosen such that the rates of the media which flow at both sides along said tubelet are approximately equal.

5. System according to one of the preceding claims, characterized in that the tap water heat exchanger is a uniflow exchanger.

6. System according one of the preceding claims, characterized in that the tap water heat exchanger is configurated like a long eventually helicaly and/or spirally wound double walled tube.

7. System according to claim 6, characterized in that the tube ends near a tap point, from which end the heated medium flows back to a heat source.

8. System according to claim 6 and eventually 7, characterized in that the tap water heat exchanger has means to support the internal tube on the external tube.

9. System according to claim 8, characterized in that the external tube Is locally pinched from the cylindrical sectioned configuration until or almost until in contact with the internal tube.

10. System according to one of the preceding claims, comprising a circulation pump in the heating system, and means to switch said pump off if at least during a considerable period of time no space heating is required, characterized in that the system comprises monitoring means, which when monitoring the withdrawal of tap water, will switch on the circulation pump and stop it, preferably delayed, if no drain water is withdrawn anymore.

11. System according to claims 2 and 10, characterized in that said monitoring means monitor the opening and closing of the valve in the supply conduit of the heating medium to the tap water-heat exchanger.

12. System according to one of the preceding claims for district heating systems, i.e. with heating medium as a heat source, supplied by external means, characterized in that in the flow of the medium beyond the regulator for the tap water heating downstream the heat exchanger for said tap water, a heat exchanger is installed, in which said medium exchanges heat with the entering cold tap water on its way to the regulator.

13. System according to claims 7 and 12, characterized in that also said exchanger for the entering tap water is configurated like a long double walled tube.

14. System according to claim 13, characterized in that the heat exchangers for the tap water are built together into a structural unit with adjacent tubes within a common insulation.

15. System according to one of the preceding claims, characterized in that said regulator is configurated and set such, that it tries to maintain a fixed set temperature of the temperature monitoring means and not only can fully open and close the supply of heating medium to the tap water-heat exchanger for that purpose, but also can increase or decrease the supply in intermediate positions.