GB1597064A

GB1597064A - Hot water supply system for producing hot water by means of solar energy

Info

Publication number: GB1597064A
Application number: GB22397/78A
Authority: GB
Original assignee: Sachs Systemtechnik GmbH
Current assignee: Sachs Systemtechnik GmbH
Priority date: 1977-05-27
Filing date: 1978-05-25
Publication date: 1981-09-03
Also published as: JPS53148045A; IT7868203A0; NL7805451A; FR2392338A1; IT1107820B; BE867470A; DE2724011A1

Description

(54) HOT WATER SUPPLY SYSTEM FOR PRODUCING HOT WATER BY MEANS OF SOLAR ENERGY (71) We, SACHS-SYSTEMTECHNIK GMBH, a German Body Corporate, of 13 Johann-Georg-Gademann-Strasse, Schweinfurt, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a hot water supply system producing hot water, with non-exclusive use of solar energy from a solar energy collector.

It is generally known to heat up heat reservoirs by solar energy and in absence of solar energy to bring a conventional heating plant into use.

It is the problem of the present invention to produce a system for the exploitation of solar energy for the production of hot water for the household. which possesses an especially good efficiency and can be realised with minimum possibfe expense.

According to the invention we provide a hot water supply system comprising: a cold water supply line; a hot water line; a water tank serving as a heat reseroir connecting said cold water supply line to said hot water line; energy supply means for collecting radiant solar energy and for transmitting the collected energy to a heat transfer fluid circulating in a transfer fluid circuit; said circuit including first heat exchange means having a low heat storage capacity and being operatively connected to the cold water supply line, and a second heat exchange means in thermal contact with the content of said tank; first temperature sensing means for sensing the temperature of said heat transfer fluid at said energy supply means; second temperature sensing means for sensing the temperature of water in said tank; circulating means for controlling the flow of transfer fluid in said circuit in response to the temperatures measured by said first and second temperature sensing means; and auxiliary heating means operatively interposed between said cold water line and said line for supplying thermal energy to said water in the absence of sufficient collected solar energy.

Since now ordinarily mains water has a fairly regular and low temperature of the order of 10"C, it is possible to conduct heat from the collector through the further heat exchanger into the inflowing cold water even when - the temperature in the heat reservoir is higher than the temperature in the collector. Thus the collector can be exploited better than was known hitherto, and the overal efficiency is increased.

As an alternative to the above-described embodiment however the circuit arrangement can also be set up so that the further heat exchanger in the cofd water inlet is always connected into the circulation of the heat transport medium and only the heat exchanger arranged in the heat reservoir can additionally be connected into the heat transport medium circulation in dependence upon the temperature in the collector and in the heat reservoir, namely before the heat exchanger in the cold water inlet, in the direction of flow. With this arrangement the circulation of the heat transport medium is deliberately always conducted through the heat exchanger which precedes the heat reservoir.Heat can be supplied to this heat exchanger even when the temperature in the collector is higher than the temperature in the heat reservoir, accordingly the circulation for the heat transport medium is conducted firstly through the heat exchanger in the heat reservoir and then supplied to the heat exchanger in the cold water inlet, since in every case the cold water has a temperature lower than the temperature in the heat reservoir. Thus the overall efficiency of the installation is improved.

According to a further feature of the invention it is advantageous that a further heat reservoir having a heat exchanger is provided, which serves for the storage of heat when the first heat reservoir is filled, and which can be connected into the water transport medium circulation by the control arrangement in dependence upon the temperature of the first heat reservoir, and the collector temperature. The arrangement of a further heat reservoir brings with it inter alia the advantage that the temperature in the first heat reservoir, through which the mains water flow directly, can be kept at such a low temperature level that no lime deposits can occur.On the other hand in the further heat reservoir which can be filled with any desired storage medium, a substantially higher maximum temperature can be realised which is dependent only upon the maximum collector temperature and possibly the boiling point of the storage medium.

The heat exchangers may be connectable in series, by-passing the collector, for heat transport between the two heat reservoirs.

Such a connection arrangement is especially advantageous when as a result of the absence of solar radiation the temperature in the collector lies lower than in the more highly charged heat reservoir, so that the heat can exchange directly between the two heat reservoirs, by-passing the collector circulation.

The volume of the more highly chargeable heat reservoir is here advantageously a multiple of the volume of the heat reservoir the temperature of which is kept lower. Thus a quite large volume of heat is available even over a lengthy period of time without solar radiation.

Especially for the accommodation of the arrangement it is advantageous that the two heat reservoirs spatially form one construction unit and are arranged insulated from one another. Both for accommodation and for installation, a spatial combining of the two heat reservoirs is especially advantageous.

The heat reservoir having the higher possible temperature level may be arranged to surround the other heat reservoir and is constructed as pressureless container.

Especially due to its large capacity the more highly chargeable heat reservoir when constructed as pressureless container is completely free from danger in operation, is simple to produce and moreover is independent of official acceptance procedures. Thus only the smaller heat reservoir which is not to be charged up so highly has to be formed as a pressure vessel and to withstand the pressure in the water mains system.

The control arragnement may consist of valves and/or pumps. Thus it is possible either to provide several valves and at least one pump for the control of the circulation of the heat transport medium or to dispense completely with valves and to provide several pumps which admittedly then when in the shut-off condition completely block the corresponding circulation or at least substantially increase the throughflow resistance.

The three heat exchangers designated in more detail above may be connected in parallel with one another and with the collector and to each heat exchanger a separate pump is allocated which in the shutoff condition acts as a closed valve or possesses a substantially higher throughflow resistance. Such an arrangement is especially simple in assembly and also easily comprehensible as regards the manner of operation. Each pump independently in action connects the heat exchanger associated with it with the collector. In the case of heat transport among the heat reservoirs by-passing the collector, two pumps are in action simultaneously, one contrarily of its normal direction of rotatian.

The two heat exchangers which are arranged in the two heat reservoirs may be connected in parallel with one another and with the collector, the heat exchanger in the cold water inlet is arranged behind the two heat exchangers, in the direction of flow, a short circuit conduit is provided for bypassing the two heat exchangers in the two heat reservoirs, having two corresponding valves, and a pump is arranged in the flow path behind the heat exchanger in the lowchargeable heat reservoir and a pump is arranged behind the heat exchanger in the cold water inlet. In this way it is possible with only two pumps and two valves to find a control arrangement which contains all the necessary circuits.

It is especially advantageous if the control arrangement consists of only one pump which is arranged directly behind the heat exchanger in the cold water inlet, in the direction of flow, and the controlling of the individual circuits takes place through valves. Thus minimum possible expense is involved as regards the pump.

The hot water appliance can advantageously here be designed so that, seen in the direction of flow, the two heat exchangers in the heat reservoirs are arranged in any desired sequence before the heat exchanger in the cold water inlet, and a by-pass conduit is provided for each of these two heat exchangers and for the collector. Thus it is ensured that the heat exchanger in the cold water inlet is inclined in every case into the heat transport medium circulation, irrespective of whether the collector is also connected, in the case of adequate temperature. Such an arrangement produces noticeable simplification in the assembly of the entire installation, and this simplification is not at the cost of the efficiency.

It is possible, for the controlling of the individual circuits of the heat transport medium, either to provide three 3/2-way valves, which in each case with the one inlet and the two outlets represent a very good solution, or in place of the three 3/2-way valves there are provided six 2/2-way valves which are actuated in each case by pairs.

This latter case is to be provided when the 2/2-way valves are especially moderately priced. However there is yet a third possibility which is especially moderately priced in production, and in fact in this case only three 2/2-way valves are provided which are arranged in each case in the corresponding by-pass conduits of the heat exchangers and of the collector, in which case however the flow resistance of the heat exchangers and of the collector must be considerably greater than that of the valves in the open position. If this is not guaranteed, then differential pressure nonreturn valves are to be arranged in the individual heat exchanger circuits and in the collector circuit, especially in the outlet conduits in each case to increase the flow resistances with the valves in the open position.These differential pressure nonreturn valves ensure that when the corresponding valve is in the open position the heat transport medium cannot flow through the corresponding heat exchanger, but they are also so designed that they represent only a low throughflow resistance in the throughflow direction.

The heat transport medium flowing through the collector at the same time may constitute the heat storage medium in the highly chargeable heat reservoir. In this simple way it is possible to dispense completely with one heat exchanger without detriment to the operation.

The invention will be explained in greater detail below by reference to examples.

Individually: Figure 1 shows a basic circuit diagram of a hot water appliance; Figures 2 and 3 show illustrations of the individual circuits using one pump each; Figure 4 shows an illustration of the individual circuits using two valves and two pumps; Figure 5 shows an illustration of the individual circuits using four valves and one pump; Figure 6 shows an illustration of the individual circuits using one pump and three 3/2-way valves Figure 7 shows a circuit diagram for the individual valves and for the pump according to the temperature conditions; Figure 8 show an illustration of the four possible circuits a, b, c, d; Figure 9 shows an illustration of the individual circuits withy six 2/2-way valves; Figure 10 shows an illustration of the circuits with three 2/2-way valves;; Figure 11 shows a basic illustration of a circuit with one 2/2-way valve and a differential pressure non-return valve; Figure 12 shows a diagrammatic representation of one arrangement of the two heat reservoirs.

Figure 1 shows the illustration of the principle of the hot water appliance with a solar energy collector 1, the inlet 12 and outlet 11 of which are connected with a control arrangement 2, this control arrangement being connected through three pairs of conduits 5, 6, 7, 8, 9, 10 with the heat exchangers W1, W2 and W3. The heat exchanger W2 is situated in the heat reservoir WS2, which contains the water to be heated. The heat reservoir WS2 has an inlet 3 for the cold water and an outlet 4 for the hot water. Moreover in the heat reservoir WS2 there is arranged a heat exchanger W6 which is connected for example to an ordinary central heating system or is provided in the form of an electric immersion heater.Moreover a heat reservoir WS3 is provided in which the heat exchanger W3 is situated, while for the direct transmission of heat between the heat reservoir WS3 and the heat reservoir WS2 the two heat exchangers W4 and W5 are also provided, with corresponding connection conduits.

Thus according to the illustration of principle in Figure 1 it is possible to cause the heat transport medium which flows through the collector 1, with appropriate position of the control arrangement 2, to flow through the heat exchanger W3, the heat exchanger W2 or the heat exchanger W1. The decision for the setting of the necessary circuit to be derived in each case from the individual temperatures, namely from the temperature in the collector 1, the temperature in the heat reservoir WS2, the temperature in the heat reservoir WS3 and the temperature in the heat exchanger W1.

It is possible either to conduct the heat transport medium alternatively through the heat exchanger W2 or to heat exchanger W1 or to ensure that the heat exchanger W1 is always connected into the circulation and the heat exchanger W2 is included likewise only when necessary. The improvement of efficiency of the entire system already mentioned in the introduction to the description is achieved due to the fact that the heat exchanger W1 is arranged in the cold water inlet 3 for the heat reservoir WS2.Due to the relatively constant and fairly low temperature of about +10"C of mains water in our latitudes, it is possible at least over the day in most cases to realise higher temperatures in the collector 1 and thus to obtain heat transport through the conduits 5, 6, 11 and 12 into the heat exchanger W1. Thus the cold water coming from the inlet 3 can already be pre-warmed at entry into the heat reservoir WS2. The quantity of heat introduced in this way then no longer has to be produced elsewhere or brought in. Either the heat exchanger W2 or the heat exchanger W1 is connected into the heat transport medium circulation alternatively, namely according to whether the temperature in the collector 1 lies just above the temperature in the heat reservoir WS2 or not.If it lies lower then the circuit is to be passed through the heat exchanger Wl. If the temperature in the collector 1 lies above the temperature in the heat reservoir WS2, then it is possible either to conduct the heat transport medium only through the heat exchanger W2, or to connect the return conduit 9 from the heat exchanger W2 directly with the inflow conduit 6 for the heat exchanger W1, so that the heat transport medium after flowing back from the reservoir WS2 still delivers its excess energy to the heat exchanger W1. In both cases energy can be supplied to the heat exchanger W1 guaranteeing a low temperature of -the heat transport medium in the return conduit 5, from which again heat can be taken from the collector 1 as a result of this low temperature.Since with regard to possible lime deposits from the heated water the temperature in the heat reservoir WS2 can be limited to the order of 45-500C, it is advantageous in the case of a higher presentation of heat to provide an additional heat reservoir WS3. In volume this heat reservoir WS3 can be a multiple of the heat reservoir WS2. Since it has no connection with the circulation of the water to he heated, the maximum temperature achieved in it has no effect as regards lime deposits. The temperature therein can thus readily lie for example at 900 C. When a heat transport medium is used having a boiling point higher than 1000C, this temperature can even be shifted upwards.

In order to limit the construction expense of the hot water appliance it is possible to replace the two heat exchangers W4 and W5 in that the heat transport between the two heat reservoirs WS2 and WS3 takes place by way of the heat transport medium of the heat exchangers W1, W2 and W3, namely by an appropriate setting of the control arrangement 2 so that flow takes place successively through the two heat exchangers W2 and W3 in any desired sequence. In the case of such a necessary heat transport between WS2 and WS3 the control arrangement 2 has to ensure that the collector 1 is not connected into this circulation. Since the heat reservoir WS3 should always possess priority in heating and since the maximum permissible temperature of the heat reservoir WS3 lies substantially higher, thus heat transport only from WS3 to WS2 is sensible.Thus the control arrangement 2 logically has to set the circulation between these two heat reservoirs in action when the temperature in the heat reservoir WS2 has not yet reached the desired maximum value, but the temperature in the heat reservoir WS3 lies thereabove. Here again it is possible for reasons of simplicity to connect the heat exchanger W1 into the circuit following the heat exchanger W2, since as a result of its low heat capacity no additional losses occur even if the cold water contained therein from the inlet 3 is already warmed.

In principle it is naturally possible at any time in the case of low temperatures in the collector circuit or in the heat reservoir WS3 to connect the pumps WP1 or WP2 into the corresponding conduits.

Figure 2 shows the basic circuit arrangement in which the control arrangement 2 according to Figure 1 consists of three pumps P1, P2 and P3. By alternative operation of one of these pumps it is possible to connect each of the heat exchangers W1, W2 and W3 alternatively into the circuit with the collector 1. In this case the inlet conduit 12 and the outlet conduit 11 respectively of the collector will be used. Admittedly for operation it is a prerequisite that all three pumps in their rest position represent a great throughflow resistance, so that flow does not take place through the heat exchangers of the pumps which are not in operation. For heat transport between the two heat exchangers W2 and W3 it is necessary that the direction of operation of at least one of the two pumps P2 or P3 is reversible.

An arrangement according to Figure 3 in which again three pumps are used is the same as regards construction expense. In this case however these pumps lie in each case in the inlet conduit 12 to the collector 1, and for heat transport between the two heat exchangers W2 and W3 the use of the pump P3 alone is necessary.

Figure 4 shows a form of embodiment in which under certain preconditions all necessary circuits can be constituted with two pumps P1 and P2 and two valves V1 and V2. The collector 1 comprises the inlet conduit 12 and the return conduit 11, while for the closure of the circuit between conduits 11 and 12 the valve V1, the shortcircuit conduit K, the valve V2, the heat exchanger W1 and the pump P1 are arranged in series. The two heat exchangers W2 and W3 are arranged parallel with the short-circuit conduit K, and in fact the pump P2 is also situated in the possible circuit between the heat exchanger W2 and the short-circuit conduit K.By appropriate setting of the valves Vl and V2 and appropriate use of the pumps Pl and P2 now it is possible to maintain all necessary circulations. The heat transport between W2 and W3 takes place through the pump P2, without flow through the heat exchanger Wi. In the filling up of the heat exchangers W2 and W3 through the collector, in each case the heat exchanger Wl is connected after one of the two heat exchangers W2 or W3, in the direction of throughflow.

Now Figure 5 shows an arrangement in which one single pump Pl is used. For the distribution of the individual circulations the valves V3, V4, V5 and V6 are here provided. The pump P1 is connected directly into the outlet 18 of the heat exchanger W1. Before the heat exchanger Wl the two heat exchangers W2 and W3 are provided, their sequence being immaterial. In the present case W2 is arranged before W1 and W3 before W2.

Each heat exchanger possesses an inlet 13, 15, 17 and an outlet 14, 16, 18 moreover a by-pass conduit 21 and 22 is provided for each of the heat exchangers W2 and W3 likewise a by-pass conduit 20 for the collector 1. This by-pass conduit 20 connects the inlet 12 after the pump Pl directly with the valve V3 in the outlet 11 of the collector 1. The by-pass conduit 22 for the heat exchanger W3 is arranged between the valve V3 and the valve V4 and the by pass conduit 21 for the heat exchanger W2 is arranged between the valve V4 and the valve V5. Thus it is possible according to the temperature at the individual measure ment points, to exclude the heat exchangers W2 or W3 from the circulation, also the collector 1.The heat exchanger Wl is automatically included in all circuits, namely always after the other heat exchangers in the direction of throughflow.

Figure 6 shows a possible form of embodiment using three 3/2-way valves V6, V7 and V8. Using only three valves of this ordinary construction type and one pump Pl it is possible to realise all the necessary circuits. The collector 1 is provided with an outlet 11 and an inlet 12. The entry of the valve V6 is connected both with the outlet ii and with the by-pass conduit 20 for the collector 1. The two exits of V6 are connected on the one hand with the inlet 13 to the heat exchanger W3 and on the other with the by-pass conduit 22 for the same heat exchanger. The entry of the valve V7 is connected with the outlet 14 of W3 and with the by-pass conduit 22 of W3, its two exits are connected on the one hand with the inlet 15 for the heat exchanger W2 and with the by-pass conduit 21 for the same heat exchanger.The inlet 17 of the heat exchanger Wl is connected directly with the outlet 16 of the heat exchanger W2 and with the by-pass conduit 21 and its outlet 18 leads to the suction side of the pump P1. On the delivery side the pump Pl is connected with the entry of the valve V8, the two exits of which are connected on the one hand with the by-pass conduit 20 for the. collector I and on the other with the inlet 12 for fhe collector 1. All three valves are illustrated in their basic position in Figure 6, but this basic position is not to be regarded absolutely as a logical setting.

With reference to a Figures 7 and 8 the manner of operation of a circuit according to Figure 6 will now be described.

Figure 7 here shows the decisive criteria for the setting of the valves and the pump according to the individual temperatures to be examined. The significances are here: TKf Collector temperature T1= Temperature in the heat exchanger Vlrl T2= Temperature in the heat reservoir WS2w10--450C T3= Temperature in the heat reservoir WS310--900C T3max 90 C T20 45"C As may be seen from the plan in the Figure, in the exploration of the different temperatures decisions are produced for circuit arrangements a, b, c, and d corresponding to the Figures 8a, 8b, Sc and 8d, and twice the decision for shutting off the pump and once for re-heating in the heat reservoir WS2 by outside energy.The individual cases will be listed below: 1. TK greater then T2; T2 less than T20 produces setting a.

2. TK greater than T2; T2 greater than T20; T3 less than T3m; TK greater than T3; produces setting b.

3. TK less than T2; T3 less than T2; T2 greater than T20; TK greater than T3; likewise produces setting b.

4. TK greater than T2; T2 greater than T20; T3 less than T3maX; TK less than T3; TK greater than T1; produces setting c.

5. TK less than T2; T3 less than T2; T2 greater than T20; TK less than T3; TK greater than T1; likewise produces setting c.

6. TK less than T2; T3 greater than T2; produces setting d.

7. TK less than T2; T3 less than T2; T2 less than T20; produces heating with an additional energy.

8. TK greater than T2; T2 greater than T20; T3 greater than T3rnax; produces pump off.

9. TK greater than T2; T2 greater than T20; T3 less than T3meX; TK less than T3; TK less than T1; produces pump off.

10. TK less than T2; T3 less than T2; T2 greater than T20; TK less than T3; TK less than T1 produces pump off.

Regarding the possible settings a to d it should also be remarked that the setting a is maintained until T2=450C; that the setting b is maintained until T3=900C; that the setting c is maintained until Tl=TK and the setting d is maintained until T2=T3 and T2=45 C.

In Figure 8 the individual settings a to d are reproduced. The settings a to c each comprise a circulation with inclusion of the collector 1, the different combinations with the heat exchangers W2 and W3 being possible and the heat exchanger W I automatically being included in each case.

The setting d renders possible heat transport between the two heat reservoirs WS2 and WS3, by-passing the collector 1.

Figure 9 shows a variant of Figure 6 using six 2/2-way valves. Such an arrangement can be selected if this type of valves can be purchased at more moderate prices than the more expensive three 3/2-way valves according to Figure 6. The illustration shows the valves V61, V62, V71, V72, V81 and V82 in the basic position. This position in the present case produces no sensible setting as regards the problem of the invention. The individual settings are however transferable simply by reference to Figure 8. V61 here lies in the by-pass conduit 22 of the heat exchanger W3. W.62 lies in the feed conduit 13 to W3. V71 lies in the feed conduit 15 to W2 and V72 lies in the by-pass conduit 21 of W2. V81 lies in the bypass conduit 20 for the collector I and V82 lies in the feed conduit 12 between the pump Pl and the collector 1.

Figure 10 shows a further- substantial simplification of the arrangements according to Figures 6 and 9. Here only three 2/2-way valves V9, V10 and V11 are used. These three valves are connected one each into the by-pass conduits 22, 21 and 20.

For the operational capacity of such an arrangement it is admittedly a prerequisite that the flow resistance through the individual heat exchangers Wi, W2 and W3 is substantially greater than that through the valves V9, V10 and V11 in the forward direction. If however for other considerations these throughfiow resistances cannot be kept as low as in the present desired case, then in accordance with Figure 11 it is possible to insert differential pressure nonreturn valves RV into the respective circuits. The arrangement of such a differential pressure non-return valve RV will be described with reference to the example of the circuit for the heat exchanger W3. A 2/2-way valve V9 is connected into the by-pass conduit 22 for the heat exchanger W3.When this valve V9 is in the position as illustrated the circulation is to be conducted past the heat exchanger W3. So that a part of the heat transport medium does not nevertheless flow through W3, a differential pressure nonreturn valve RV is installed in the outlet conduit 14 between W3 and the exit of the valve V9. This differential pressure nonreturn valve is designed so that it keeps the return 14 blocked at least up to the differential pressure between entry and exit of the valve V9. In the case of higher pressures occurring in the blocking position of the valve V9 this valve opens and then has a low throughflow resistance. Due to its connection as differential pressure nonreturn valve, the valve RV can be equipped with a very low initial stress force for its closure mechanism.

Figure 12 shows a space-saving arrangement of the heat reservoirs WS2 and WS3, where the heat reservoir WS3 encloses the heat reservoir WS2, being separated therefrom by a thermally insulating wall 23. All conduits leading through the heat reservoir WS3 to and from the heat reservoir WS2 are to be thermally insulated from the heat reservoir WS3. The principle of the arrangement of the heat exchangers in Figure 12 and their connection with the circuit arrangement 2 correspond to the nossibilities as illustrated in Figures 1 to 11.

WHAT WE CLAIM IS: 1. A hot water supply system comprising: a cold water supply line; a hot water line; a water tank serving as a heat reservoir connecting said cold water supply line to said hot water line; energy supply means for collecting radiant solar energy and for transmitting the collected energy to a heat transfer fluid circulating in a transfer fluid circuit; said circuit including first heat exchange means having a low heat storage capacity and being operatively connected to the cold water supply line, and a second heat exchange means in thermal contact with the content of said tank; first temperature sensing means for sensing the temperature of said heat transfer fluid at said energy supply means; second temperature sensing means for sensing the temperature of water in said tank circulating means for controlling the flow of transfer fluid in siad circuit in response to the temperatures measured by said first and second temperature sensing means; and auxiliary heating means operatively interposed between said cold water line and said line for supplying thermal energy to said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. T20; T3 greater than T3rnax; produces pump off. 9. TK greater than T2; T2 greater than T20; T3 less than T3meX; TK less than T3; TK less than T1; produces pump off. 10. TK less than T2; T3 less than T2; T2 greater than T20; TK less than T3; TK less than T1 produces pump off. Regarding the possible settings a to d it should also be remarked that the setting a is maintained until T2=450C; that the setting b is maintained until T3=900C; that the setting c is maintained until Tl=TK and the setting d is maintained until T2=T3 and T2=45 C. In Figure 8 the individual settings a to d are reproduced. The settings a to c each comprise a circulation with inclusion of the collector 1, the different combinations with the heat exchangers W2 and W3 being possible and the heat exchanger W I automatically being included in each case. The setting d renders possible heat transport between the two heat reservoirs WS2 and WS3, by-passing the collector 1. Figure 9 shows a variant of Figure 6 using six 2/2-way valves. Such an arrangement can be selected if this type of valves can be purchased at more moderate prices than the more expensive three 3/2-way valves according to Figure 6. The illustration shows the valves V61, V62, V71, V72, V81 and V82 in the basic position. This position in the present case produces no sensible setting as regards the problem of the invention. The individual settings are however transferable simply by reference to Figure 8. V61 here lies in the by-pass conduit 22 of the heat exchanger W3. W.62 lies in the feed conduit 13 to W3. V71 lies in the feed conduit 15 to W2 and V72 lies in the by-pass conduit 21 of W2. V81 lies in the bypass conduit 20 for the collector I and V82 lies in the feed conduit 12 between the pump Pl and the collector 1. Figure 10 shows a further- substantial simplification of the arrangements according to Figures 6 and 9. Here only three 2/2-way valves V9, V10 and V11 are used. These three valves are connected one each into the by-pass conduits 22, 21 and 20. For the operational capacity of such an arrangement it is admittedly a prerequisite that the flow resistance through the individual heat exchangers Wi, W2 and W3 is substantially greater than that through the valves V9, V10 and V11 in the forward direction. If however for other considerations these throughfiow resistances cannot be kept as low as in the present desired case, then in accordance with Figure 11 it is possible to insert differential pressure nonreturn valves RV into the respective circuits. The arrangement of such a differential pressure non-return valve RV will be described with reference to the example of the circuit for the heat exchanger W3. A 2/2-way valve V9 is connected into the by-pass conduit 22 for the heat exchanger W3.When this valve V9 is in the position as illustrated the circulation is to be conducted past the heat exchanger W3. So that a part of the heat transport medium does not nevertheless flow through W3, a differential pressure nonreturn valve RV is installed in the outlet conduit 14 between W3 and the exit of the valve V9. This differential pressure nonreturn valve is designed so that it keeps the return 14 blocked at least up to the differential pressure between entry and exit of the valve V9. In the case of higher pressures occurring in the blocking position of the valve V9 this valve opens and then has a low throughflow resistance. Due to its connection as differential pressure nonreturn valve, the valve RV can be equipped with a very low initial stress force for its closure mechanism. Figure 12 shows a space-saving arrangement of the heat reservoirs WS2 and WS3, where the heat reservoir WS3 encloses the heat reservoir WS2, being separated therefrom by a thermally insulating wall 23. All conduits leading through the heat reservoir WS3 to and from the heat reservoir WS2 are to be thermally insulated from the heat reservoir WS3. The principle of the arrangement of the heat exchangers in Figure 12 and their connection with the circuit arrangement 2 correspond to the nossibilities as illustrated in Figures 1 to 11. WHAT WE CLAIM IS:

1. A hot water supply system comprising: a cold water supply line; a hot water line; a water tank serving as a heat reservoir connecting said cold water supply line to said hot water line; energy supply means for collecting radiant solar energy and for transmitting the collected energy to a heat transfer fluid circulating in a transfer fluid circuit; said circuit including first heat exchange means having a low heat storage capacity and being operatively connected to the cold water supply line, and a second heat exchange means in thermal contact with the content of said tank; first temperature sensing means for sensing the temperature of said heat transfer fluid at said energy supply means; second temperature sensing means for sensing the temperature of water in said tank circulating means for controlling the flow of transfer fluid in siad circuit in response to the temperatures measured by said first and second temperature sensing means; and auxiliary heating means operatively interposed between said cold water line and said line for supplying thermal energy to said

water in the absence of sufficient collected solar energy.

2. A hot water supply system as claimed in claim 1, wherein the first heat exchanger is connected constantly into the circuit of the heat transport medium and the second heat exchanger is connectible into the circuit, before the first heat exchanger, in the direction of flow.

3. A hot water supply system as claimed in claim 1 or 2, wherein a further heat reservoir having a third heat exchanger is provided which serves for heat storage when the heat reservoir is filled and is connectible into the circuit of the heat transfer medium by the circulating control means in dependence upon the temperature of the heat reservoir and upon the collector temperature.

4. A hot water supply system as claimed in claim 3, wherein for heat transfer between the second heat reservoir and the first heat reservoir, the third and second heat exchangers are connectible in series, by-passing the energy supply means.

5. A hot water supply system as claimed in claim 3 or 4, wherein the volume of the second heat reservoir amounts to a multiple of the volume of the first heat reservoir.

6. A hot water supply system as claimed in claim 5, wherfin both heat reservoirs form one construction unit spatially and are arranged insulated from one another.

7. A hot water supply system as claimed in claim 5 or 6, wherein the second heat reservoir surrounds the first heat reservoir and is made as pressureless container.

8. A hot water supply system as claimed in any one of claims 1 to 7, wherein the circuit arrangement includes valves and/or pumps.

9. A hot water supply system as claimed in claim 8 when appended to any one of claims 3 to 7, wherein a third heat exchanger is provided, the three heat exchangers being connected parallel with one another and with the energy supply means and with each heat exchanger there Is associated a separate pump which in the shut-off condition acts as a closed valve or possesses a substantially higher throughflow resistance.

10. A hot water supply system as claimed in claim 8, wherein the second and third heat exchangers are connected parallel with one another and with the collector, the first heat exchanger is arranged behind the other two heat exchangers in the direction of flow, a short-circuit conduit is provided to by-pass the other two heat exchangers with two corresponding valves and in the flow path a pump is arranged behind the second heat exchanger and a pump is arranged behind the first heat exchanger.

I I. A hot water supply system as claimed in claim 8, wherein the circuit arrangement comprises only one pump which is arranged directly in the direction of flow behind the first heat exchanger and the controlling of the individual circuits takes place through valves.

12. A hot water supply system as claimed in claim 11, wherein, considered in the direction of flow, the second and third heat exchangers are arranged in any desired sequence before the first heat exchanger and a by-pass conduit is provided for each of the two first-mentioned heat exchangers and for the collector.

13. A hot water supply system as claimed in claim 12, wherein three 3/2-way valves are provided of which the first is connected by its entry with the collector outlet and the collector by-pass conduit and by its two exits with the inlet to the third heat exchanger and the by-pass conduit of the third heat exchanger, the entry of the second valve is connected with the outlet from the third heat exchanger and the bypass conduit of the third heat exchanger and by its exits with the inlet to the second heat exchanger, and the by-pass conduit of the second heat exchanger, while the outlet of the second heat exchanger and the by-pass conduit of the second heat exchanger at the same time form the inlet to the first heat exchanger and the outlet of the first heat exchanger is connected with the suction side of the pump, and the third valve is connected on the entry side with the delivery side of the pump and on the exit side with the inlet to the collector and the collector by-pass conduit.

14. A hot water supply system as claimed in claim 13, wherein in place of the three 3/2-way valves there are provided correspondingly six 2/2-way valves.

15. A hot water supply system as claimed in claim 12, wherein three 2/2-way valves are provided which are arranged each in the corresponding by-pass conduits of the second and third heat exchanger and of the collector, and the flow resistance of the said heat exchangers and of the collector is considerably higher than that of the valves in the open position.

16. A hot water supply system as claimed in claim 15, wherein differential pressure non-return valves are arranged in the individual heat exchanger circuits and the collector circuit, especially in the outlet conduits, to increase the flow resistances in the open position of the valves.

17. A hot water supply system as claimed in any one of claims 3 to 16, wherein the heat transfer fluid flowing through the collector at the same time constitutes the heat storage medium in the second heat reservoir.

18. A hot water supply system substantially as described with reference to the accompanying drawings.