EP0038318B1 - Control system for controlling the heating of domestic water for a storage tank - Google Patents

Description

The invention relates to a temperature control device for the water in a water storage tank, which is heated using a heat exchanger equipped with a primary and a secondary circuit, arranged outside the storage tank and supplied with heat energy on the primary side by a heat source, the water to be heated being in the secondary circuit at the bottom of the storage tank removed and returned by a thermostatically controlled charge pump via the heat exchanger in the heated state on the cover side.

In conventional domestic water heaters, there is e.g. cylindrical, upright and with appropriate thermal insulation storage tank attached a heat exchanger, which is acted upon by the heating circuit - usually a central heating system. In such systems, this gives e.g. from the central heating boiler coming part of the heat contained in it to the water in the storage tank, which, due to the convection, heats up evenly. However, the higher the temperature of the water in the tank rises, the higher the temperature of the water flowing back from the heat exchanger. However, this means that the temperature difference between the contents of the storage container and the e.g. water coming from the boiler ("flow") becomes lower and consequently less and less heat is released into the domestic water; the performance or the efficiency of the heat exchanger therefore decreases with increasing temperature of the domestic water.

In the case of hot water preparation using solar energy, the arrangement is essentially the same as that described above, in which case the heat exchanger is connected to the heating circuit of the solar system.

This efficiency of the heat exchanger described above, which decreases with increasing temperature of the hot water, leads to problems when using heat pumps for hot water preparation, because the heat pump has only a small power range and switches off when the power output decreases. As a result, the duty cycle of the pump decreases with increasing temperature of the domestic water and the pump starts to work intermittently. Due to the necessary cooling times before the heat pump is switched on again, the time until the water heater is completely heated is increased accordingly or the maximum possible temperature is reached.

On the other hand, a memory with a separate heat exchanger is known from DT-A-2 508 135, which is connected on the primary side to a heating system. A thermostatically controlled pump is provided on the secondary side, which takes the water to be heated from the storage tank at the bottom, passes it through the heat exchanger, and returns it to the storage tank at the top. As a characteristic feature, an electrical heater is provided in the heat exchanger, which enables additional heat supply and thus a certain adaptation to fluctuating operating conditions. A combination of such a heat exchanger with a heat pump requires the use of expensive electrical energy and can therefore not be considered for economic reasons.

Devices for temperature control for hot water storage tanks are also known, which are connected to heat pumps or solar systems. For example, DE-B-1 019 792 relates to a heat pump system with a hot water pressure accumulator, the condenser or condenser of the heat pump being designed as a heat exchanger. The water is removed from the bottom of the pressure accumulator by heat convection, passed through the heat exchanger and returned in the upper third of the pressure accumulator. The refrigerant flowing back to the expansion valve heats the incoming fresh water in a further heat exchanger. The characteristic feature is a drain valve controlled by the coolant pressure for the water flowing from the storage tank to the heat exchanger.

DE-A-2432893 also describes a heat pump system for a pressure accumulator with a heat exchanger, which is also directly connected to the heat pump on the primary side. This means that the heat exchanger serves as a condenser for the heat pump. A first thermostat is arranged at the outlet of the coolant from the heat exchanger, which controls a thermostatic valve which is arranged in the line between the outlet of the store and the lower inlet to the heat exchanger and which controls this as a function of the outlet temperature of the refrigerant. A second thermostat is provided when the cold water enters the storage tank and switches off the heat pump when a limit temperature is exceeded. The heat exchanger is divided into two chambers, with the water being removed from the center of the storage tank and being returned on the bottom and lid side.

US-A-4142 379 also describes a memory with a heat exchanger through which the coolant flows directly on the primary side. When the coolant enters the heat exchanger, a pressure switch is provided which switches off the electrical heating element in the memory at a predetermined pressure of the coolant. A thermostat is provided in the line from the outlet of the water to be heated from the heat exchanger and the cover-side entry to the storage tank, which controls a circulation pump as a function of the outlet temperature of the water from the heat exchanger, i.e. the circulation pump is switched off from a predetermined temperature value.

US-A-4 141 222 also describes a memory with a heat exchanger through which the coolant flows directly on the primary side. A temperature-dependent three-way valve, which forms a bypass to the heat exchanger, is arranged between the circulation pump arranged on the bottom and the entry of the water into the heat exchanger. bridging the latter from a predetermined temperature. In addition, a temperature-controlled check valve is provided in the line from the heat exchanger to the cover of the storage tank, which prevents cold water from being fed to the storage tank.

FR-A-2 443 029 (published on June 27, 1980) describes a solar-heated storage tank which has an additional heater which is controlled by a thermostat in the upper area of the storage tank. A second thermostat in the area of the bottom of the storage tank and a third thermostat at the solar collector control a circulating pump, which takes the water from the bottom and returns it on the cover side. A complicated ventilation system and an expansion tank complete this solar system.

All of the plants mentioned above relate to the field of the invention. However, they differ in the task and their solution from the object of the invention, which task essentially consists in creating a temperature control device of the type specified at the outset, which, particularly when using a heat pump as a heat source, is intended to avoid intermittent working of the heat pump .

According to the invention, this is achieved in that a first thermostat in the store, preferably in the area of the center of the store, and a second thermostat connected in series with the first thermostat in the area between the cold water zone at the bottom of the store tank and the entry point of the secondary circuit into the Heat exchangers are arranged, wherein the first thermostat switches on the charging pump for the charging process, and the second thermostat switches off the charging pump to end the charging process, the first thermostat being closed at a predetermined lower hot water temperature and the second thermostat being open at a predetermined upper hot water temperature , so that the hot water to be heated is circulated only once, and that an actuator for adjusting or controlling the flow rate is provided in the secondary circuit.

According to a further feature of the invention, it is provided that a third thermostat is arranged at the entry of the primary circuit into the heat exchanger, which is connected in series with the circuit for the charge pump and thereby enables the charge pump to be switched on by the first thermostat, the third Thermostat is closed at a predetermined upper temperature of the primary circuit medium.

An additional feature of the invention provides that an adjustable throttle valve is provided in series with the charge pump, the flow rate in the secondary circuit depending on the heat transfer performance of the heat exchanger being set or regulated by the throttle valve such that a maximum possible final temperature of the water to be heated during the one-time circulation is guaranteed.

The primary circuit is preferably connected to a heat pump, the heat transfer capacity of the heat exchanger being coordinated with the heat pump in such a way that the maximum amount of heat given off is transferred to the domestic water at the highest temperature.

The temperature control device according to the invention, in conjunction with the coordinated heat transfer capacity of the heat exchanger and the flow rate of the secondary circuit set by means of the throttle valve, ensures that the temperature of the cold service water drawn at the lowest possible point is increased to the maximum possible final temperature with a maximum of one pass of the service water to be heated. The storage tank is loaded from above and the separating layer between hot and cold process water moves downwards until the storage tank is no longer charged. There is therefore no undesirable mixing of hot and cold water, as is the case with conventional turbulence due to convection.

• Fig. 1 eine schematische Darstellung eines Beispiels der erfindungsgemässen Temperaturregeleinrichtung für einen Speicher mit einem getrennten Wärmetauscher, welcher primärseitig an eine Wärmepumpe angeschlossen ist,
• Fig. 2 ein weiteres Beispiel einer Variante des Beispiels nach Fig. 1 und
• Fig. 3 ein Beispiel nach Fig. 2 für zwei Speicher.

Further details and features of the invention are explained below with reference to the drawing. Show it

• 1 is a schematic representation of an example of the temperature control device according to the invention for a storage tank with a separate heat exchanger which is connected on the primary side to a heat pump,
• Fig. 2 shows another example of a variant of the example of Fig. 1 and
• Fig. 3 shows an example of FIG. 2 for two memories.

In Fig. 1, the pressure-resistant storage container is denoted by 1 and preferably has the shape of a standing cylinder with a curved bottom 2 and a likewise curved lid 3.

A cold water supply pipe 4 leads into the bottom 2, the inner end of which lies opposite a baffle plate 5. In the cover 3 there is the extraction line 6 for the domestic water. A distributor plate 7 is also located in the upper part of the storage container 1, near the cover 3. The secondary circuit is constructed by the pipe sections 8a, 8b and 8c. The pipe section 8a comes from the heat exchanger, generally designated 9, and opens into the cover 3. The pipe section 8b extends from the base 2 to a charge pump 10, an adjustable throttle valve 11 and a thermal flow preventer 12, which prevents circulation without the charge pump running. The pipe section 8c leads from the thermal flow preventer 12 back to the heat exchanger 9. For the scheme are The thermostats T1 and T2 are provided in the secondary circuit, the thermostat T1 being arranged approximately in the center of the accumulator 1 and the thermostat T2 when the pipe section 8c enters the heat exchanger 9.

The primary circuit consists of a heat pump 13, a circulation pump 14, a priority valve (electromagnetically operable three-way valve) 15, which in the application case shown supplies the heater 16 outside the charging time of the water heater. Furthermore, the thermostat T3 is arranged in the primary circuit, specifically at the entry point of the primary circuit medium into the heat exchanger 9.

This system is controlled in the following way: A switching device is designated 17 and contains a relay with a coil 18 and with contacts 19, 20a and 29b open in the idle state. The coil 18 is in series with the contacts of the thermostats T1 and T2, which are also in series, at a supply voltage (for example mains voltage). If the temperature of the hot water in the storage tank 1 is sufficiently high, the contact of the thermostat T1 is open. The contact of the thermostat T2 is closed because cold service water is present in the secondary circuit from the bottom of the storage tank. If hot service water is withdrawn via the extraction line 6, cold water flows in via the feed pipe 4. As soon as the temperature at the point of the thermostat T1 falls below a predetermined value, the contact of the thermostat T1 closes and thus closes the circuit for the coil 18, so that the contacts 19, 20a and 20b close. The contact 19 serves as a hold contact, i. H. it bridges the contact of the thermostat T1. Through the closed contacts 20a and 20b, on the one hand, the electromagnetically actuated priority valve 15 is directly connected, and on the other hand, the charging pump 10 is connected to the supply voltage via the contact of the thermostat T3. The contact of the thermostat T3 is opened below a predetermined temperature of the primary circuit medium, i. H. the charge pump only starts to work until the flow temperature of the thermostat T3 is reached.

The heat transfer capacity of the heat exchanger 9 and the flow rate of the secondary circuit set by means of a throttle valve 11 now ensure a temperature increase in the cold service water drawn off at the lowest possible point and a temperature increase to the maximum possible final temperature with a single pass of the service water to be heated. The store 1 is loaded from above and the separating layer between hot and cold process water moves downward until the store 1 has finished charging and the thermostat T2 breaks the circuit for the coil 18, so that the contacts 19, 20a and 20b break and thus the priority valve 15 is switched back to heating mode.

If the heater 16 is not in operation, in addition to the switching operations described above, the thermostat T1 additionally switches on the heat pump 13 and switches on the primary circuit. After the maximum flow temperature has been reached, the thermostat T3 switches on the charge pump 10 again, which ensures that the secondary circuit is only started when the primary circuit has full power. The thermostat T1 can be arranged at any height of the storage container, the location is usually determined by the desired discharge state of the storage until the heating process begins.

Of course, other embodiments are also possible, e.g. B. the heat pump can only be used for domestic water preparation or the primary circuit can be flowed through by an intermediate medium or coolant. Other elements with the same effect are also possible in the control, e.g. the thermostat T3 can be replaced by a time relay, i.e. the charge pump is switched on after the contacts 20a, 20b are closed after a predetermined time interval.

Of course, instead of a heat pump for energy supply, e.g. a central heating boiler or a solar system can also be used. With these heating systems, too, the constant heat transfer performance throughout the entire charging process ensures a consistently high level of system efficiency.

An advantageous embodiment of the invention provides that the flow rate of the secondary circuit of the heat exchanger is regulated as a function of the outlet temperature of the water from the heat exchanger.

A device for this purpose contains in the secondary circuit an actuator for regulating the flow rate, which is regulated as a function of the outlet temperature of the water from the heat exchanger determined by means of an additional temperature sensor (FIGS. 2 and 3).

The flow rate can be controlled continuously or discontinuously, i.e. for example as a two-point control.

In FIGS. 2 and 3, the elements that are the same as in FIG. 1 are provided with the same reference numerals, so that their description is unnecessary. As in the example according to FIG. 1, the pipe section 8b goes from the bottom 2 to a charge pump 10, an adjustable throttle valve 11. Parallel to the throttle valve 11, a solenoid valve 21 is in series with an additional throttle valve 22. The pipe section 8c leads from the throttle valve 11 back to the heat exchanger 9.

A thermostat T4 is arranged as an additional temperature sensor when the secondary circuit emerges from the heat exchanger 9.

• Ist die Temperatur des Brauchwassers in Speicher 1 genügend hoch, so ist der Kontakt des Thermostates T1 offen. Der Kontakt des Thermostates T2 ist geschlossen, da kaltes Brauchwasser von der Bodenseite des Speichers her ansteht. Wird warmes Brauchwasser über die Entnahmeleitung 6 entnommen, so fliesst kaltes Wasser über das Zuführrohr 4 zu. Sobald die Temperatur an der Stelle des Thermostates T1 einen vorbestimmten Wert unterschreitet, schliesst der Kontakt des Thermostates T1 und schliesset damit den Stromkreis für die Spule 18, so dass die Kontakte 19, 20a und 20b schliessen. Der Kontakt 19 dient als Selbsthaltekontakt, d. h. er überbrückt den Kontakt des Thermostaten T1. Durch die geschlossenen Kontakte 20a und 20b werden einerseits das elektromagnetisch betätigte Vorrangventil 15 direkt und anderseits über den Kontakt des Thermostaten T3 die Ladepumpe, sowie das Magnetventil 21 über den Kontakt des Thermostaten T4 an die Versorgungsspannung gelegt. Der Kontakt des Thermostaten T3 ist unterhalb einer vorbestimmten Temperatur des Primärkreislaufmediums geöffnet, d.h. die Ladepumpe beginnt erst dann zu arbeiten, bis beim Thermostat T3 die Vorlauftemperatur erreicht ist. Der Kontakt des Thermostaten T4 ist oberhalb einer vorbestimmten Temperatur von vorzugsweise 50°C geschlossen, so dass das Magnetventil 21 geöffnet ist und die Durchflussmenge ein Maximum ist. Sinkt die Temperatur beim Thermostaten T4, so öffnet der Kontakt des Thermostaten T4 bedingt durch dessen Hysterese bei ca. 45°C und das Magnetventil 21 schliesst, so dass die Durchflussmenge ein Minimum ist. Die maximale bzw. minimale Durchflussmenge wird durch die Drosselventile 11 bzw. 22 festgelegt und gewährleisten nun eine Temperaturerhöhung des an der tiefstmöglichen Stelle entnommenen kalten Brauchwassers und eine Temperaturerhöhung auf die maximale Endtemperatur bei einmaligem Durchlauf des zu erwärmenden Brauchwassers. Der Speicher 1 wird von oben geladen und die Trennschicht zwischen warmem und kaltem Brauchwasser wandert nach unten, bis die Ladung des Speichers 1 beendet ist und der Thermostat T2 den Stromkreis für die Spule 18 unterbricht, so dass die Kontakte 19, 20a, 20b unterbrochen und somit das Vorrangventi) 15 wieder auf Heizbetrieb umgestellt wird.

The regulation according to the example according to FIG. 2 takes place in the following way:

• If the temperature of the hot water in storage tank 1 is sufficiently high, the contact of thermostat T1 is open. The contact of the thermostat T2 is closed because cold water is available from the bottom of the storage tank. Is hot domestic water about the withdrawal Line 6 removed, so cold water flows through the feed pipe 4. As soon as the temperature at the point of the thermostat T1 falls below a predetermined value, the contact of the thermostat T1 closes and thus closes the circuit for the coil 18, so that the contacts 19, 20a and 20b close. The contact 19 serves as a self-holding contact, ie it bridges the contact of the thermostat T1. Through the closed contacts 20a and 20b, on the one hand, the electromagnetically actuated priority valve 15 is connected directly and, on the other hand, the charging pump is connected via the contact of the thermostat T3, and the solenoid valve 21 is connected to the supply voltage via the contact of the thermostat T4. The contact of the thermostat T3 is open below a predetermined temperature of the primary circuit medium, ie the charge pump only begins to work until the flow temperature is reached in the thermostat T3. The contact of the thermostat T4 is closed above a predetermined temperature of preferably 50 ° C., so that the solenoid valve 21 is open and the flow rate is a maximum. If the temperature of the thermostat T4 drops, the contact of the thermostat T4 opens due to its hysteresis at approx. 45 ° C. and the solenoid valve 21 closes, so that the flow rate is a minimum. The maximum or minimum flow rate is determined by the throttle valves 11 and 22 and now ensure a temperature increase of the cold service water drawn off at the lowest possible point and a temperature increase to the maximum final temperature with a single pass of the service water to be heated. The store 1 is loaded from above and the separating layer between hot and cold process water moves downward until the store 1 has finished charging and the thermostat T2 interrupts the circuit for the coil 18, so that the contacts 19, 20a, 20b are interrupted and thus the priority valve) 15 is switched back to heating mode.

Fig. 3 shows the application of the invention in the combination of a heat pump 13 with a memory 1 for the production of hot water and a memory 1 'for heating water production, the elements associated with the memory 1' having the same reference numerals as for the memory 1, but with Apostrophe (') are provided. In this case, a further contact 20c is provided in the relay of the control device 17, which interrupts the circuit for starting the charge pump 10 'as soon as the coil 18 of the relay is energized, so that the circuit for hot water generation is operated primarily. The function of this arrangement is otherwise the same as that of the previous exemplary embodiment, so that its description is unnecessary.

2 and 3, the bypassing of the first throttle valve 11, 11 'in the secondary circuit by the solenoid valve 21, 21' or the combination of the solenoid valve 21, 21 'with the second throttle valve 22, 22' causes one Increasing the flow rate of the water through the heat exchangers 9, 9 ', so that an increased supply of heat from the heat pump causes the thermostats T4 or T4' to be switched on and can advantageously be used for faster filling of the store.

According to the invention, the actuator for regulating the flow rate can also be designed as a continuously adjustable valve, which e.g. is adjustable by a servomotor and also depending on the water temperature at the exit point of the secondary circuit from the heat exchanger, the z. B. measured by means of a thermocouple, the temperature corresponding voltage (actual value) is amplified and compared with a selectable setpoint, the differential voltage between the setpoint and actual value is supplied to the servomotor via a power amplifier. With such a control loop, the drive motor for the charge pump 10, 10 'can also be controlled, i.e. act as an actuator, the flow rate being adapted to the respective heat supply by changing the number of revolutions depending on the above differential voltage. In this case the drive motor is connected to the output of the power amplifier.

Claims (10)

1. Apparatus for an automatic temperature control of the water which is contained in a water storage container (1) and is heated by means of a heat exchanger (9), which is disposed outside the storage container and provided with primary and secondary circuits and is supplied on its primary side with heat energy from a heat source, wherein the water to be heated flows through the secondary circuit and is withdrawn from the storage vessel near its bottom and by a thermostat-controlled charging pump (10) is pumped through the neat exchanger and returned in a heated state near the cover, characterized in that a first thermostat (T1) is disposed in the storage container (1), preferably adjacent to the middle of the storage container, a second thermostat (T2) is connected in series with the first thermostat (T1) and disposed in the region between the cold water zone atthe bottom of the storage container (1) and the entrance of the secondary circuit to the heat exchanger (9), the first thermostat (T1) energizing the charging pump (10) for the charging operation, and the second thermostat (T2) deenergizing the charging pump for terminating the charging operation, the first thermostat (T1) being closed at a predetermined first temperature of the water for consumption and the second thermostat (T2) being opened at a predetermined upper temperature of the water for consumption so that the water for consumption which is to be heated is circulated only once, and a final control element adjusting or automatically controlling the flow rate is provided in the secondary circuit.

2. Apparatus for an automatic temperature control according to claim 1, characterized in that a third thermostat (T3) is provided at the entrance of the primary circuit to the heat exchanger (9) and is connected in series with the circuit for the charging pump (10) to enable the first thermostat (T1) to energize the charging pump (10), and the third thermostat (T3) is closed when the fluid in the primary circuit is at a predetermined upper temperature.

3. Apparatus for an automatic temperature control according to claim 1, characterized in that the final control element consists of an adjustable throttle valve (11), which is connected in series with the charging pump (10), and the flow rate in the secondary circuit is so adjusted or automatically controlled by the throttle valve in dependence on the heat transfer rate of the heat exchanger (9) that the highest possible final temperature of the water is ensured by single circulation.

4. Apparatus for an automatic temperature control according to claim 1, characterized in that the final control element is automatically controlled in dependence on the temperature at which the water exits from the heat exchanger (9), which temperature is detected by a temperature sensor.

5. Apparatus according to claim 4, characterized in that the final control element comprises a solenoid valve (21), which is connected in parallel to a first throttle valve (11) in the secondary circuit.

6. Apparatus according to claim 5, characterized in that a second throttle valve (11) is connected in series with the solenoid valve (21).

7. Apparatus according to claims 4 and 6, characterized in that the temperature sensor consists of a thermostat (T4), which is disposed at the exit of the secondary circuit from the heat exchanger (9) and is closed above a predetermined water temperature of preferabyl 50°C to open the solenoid valve (21) when the charging pump is operating.

8. Apparatus according to claim 4, charaterized in that the final control element consists of an infinitely adjustable valve.

9. Apparatus according to claim 8, characterized in that the infinitely adjustable valve is adjustable by a servomotor and the temperature detector consists of a thermocouple, the voltage of which is amplified and as an actual value is compared with a selectable desired value, and the difference between the desired and actuel values is applied via an end amplifier to the servomotor for the infinitely adjustable valve.

10. Apparatus according to claims 4 and 9, characterized in that the final control element consists of a charging pump (10, 10') and the motor for driving the charging pump is connected to the output of the final amplifier.

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