EP2372260B1 - Method for heating water according to the circulation principle and water heating system - Google Patents

Description

The invention relates to a method for heating water of variable volume flow according to the flow principle according to the preamble of claim 1, wherein a heat generator heated by a pump in a circulating heating fluid, the heating fluid heated in a run water, at least one in a waterway arranged sensor measures an outlet temperature Tw and / or a volume flow Vw of the water, and at least one arranged in a Heizfluidweg sensor measures at least one Heizfluidtemperatur T _{H of} the heating fluid. Furthermore, the invention relates to a water heating system according to the flow principle according to the preamble of claim 7 with a heat generator, a heated by the heat generator heating fluid circuit, which is funded by a pump, heated by Heizfluidkreislauf water passage, at least one arranged in a waterway sensor for detecting an outlet temperature Tw , an inlet temperature T _K and / or a volumetric flow Vw of the water, as well as at least one arranged in a Heizfluidweg sensor for detecting at least one Heizfluidtemperatur T _{H of} the heating fluid.

These methods are used, for example, in so-called combination heaters. Combination heaters can solve two heating tasks, such as hot water heating for room heating and domestic hot water for applications in the kitchen and sanitary area. In general, a heater arranged in the heater (heat source) via a primary heat exchanger heats a circulating heating fluid (heating water), which is conveyed in a space heating mode by a pump (circulation pump) from the heater via flow and return lines to the rooms to be heated and there emits the heat, for example via space heaters (consumers, heat sink) to the room.

In a mode for domestic hot water preparation, a diverter valve directs the heating fluid to a secondary heat exchanger (eg, plate heat exchanger), often also located in the heater, where it transfers the heat to a flowing drinking water. The drinking water usually flows under the pressure prevailing in the supply line through the secondary heat exchanger is heated here by heat release from the side of the heating fluid and exits with a volume flow corresponding to an opening cross section at a downstream tap fitting for use.

The heat generator may be a burner fueled with fuel oil or natural gas, but also a heat generator operating with electrical energy. The heat generator can switch its heat output on and off and, as a rule, also modulate it between a minimum power different from zero and a maximum power (nominal power). In DHW mode, drinking water of different volume flows can be heated. For DHW heating, a set DHW temperature as well as minimum and maximum outflow temperatures can be set via a thermostat, a control unit and / or other components. The amount of a request made to the heat source heat demand to achieve the target hot water temperature results from the drinking water volume flow, the temperature of the incoming into the secondary heat exchanger cold drinking water (inlet temperature), the set temperature of expiring from the secondary heat exchanger warm drinking water (hot water, outlet setpoint temperature) and the efficiency chain for the heat transfer between heat generator and domestic hot water.

In condensing boilers, a burner operated with fuel oil or natural gas heats a heating fluid via a corrosion-resistant primary heat exchanger. The humidity of the fuel gas produced by the burner condenses in the primary heat exchanger, whereby the energy yield is increased by the condensation heat (condensing effect). For good condensation conditions, the primary heat exchanger must be well cooled, so it is a low Heizfluid-return temperature required. When the domestic hot water heating with modern combination heaters the Heizfluidvolumenstrom is unregulated, so not dependent on the drinking water volume flow, but constantly high, and it is for example at small drinking water flow rates significantly higher than the drinking water volume flow itself EP 0226246 A1 a heater is known in which the drinking water preparation, a heat exchanger is acted upon by a constant heating volume flow, the burner is modulated in certain areas. This results in relatively high Heizfluid-return temperatures, especially at low drinking water flow rates that reduce the gross calorific value by their height or completely destroyed.
In the mode for domestic hot water preparation, the heater can also be used to charge a domestic hot water tank with warm drinking water. The charging of a stratified charge accumulator is identical to the heating fluid circuit of a combination heater the Tnnkwarmwasserbetrieb. The heat absorbed by the primary heat exchanger is released via the secondary heat exchanger to the drinking water to be heated. In the heaters known today while the heat generator power is modulated so that the memory is loaded at target temperature. The cold water located in the lower part of the storage tank is conveyed through the secondary heat exchanger with a storage loading pump and heated by the heating fluid. After a drinking hot water tap, the temperature in the lower part of the store is just as cold as the inlet temperature of the drinking water in the combi appliance. Now, when the charge of the accumulator begins, the accumulator charge pump conveys the cold water from the lower part of the accumulator through the secondary heat exchanger into the upper part of the accumulator. The temperatures are the same as in the combination heater during direct tapping. However, a fixed set drinking water volume flow is conveyed by the storage loading pump through the secondary heat exchanger. This is usually set by a hydraulic throttle so that the heat generator is operated with a power just below the maximum power. This allows a quick recharge and a high degree of deployment. In addition to the high degree of deployment, the main advantage of the stratified storage tank is that until just before the end of the charge, the cold storage water allows a low return temperature in the heating fluid circuit. This increases the efficiency of the charging process for condensing appliances.

Only those heat requirements that lie in the range between the minimum power and the maximum power of the heat generator can be fulfilled continuously and reliably. If the heat requirement is greater than the maximum heat output, then either the setpoint temperature or the volume flow of the domestic hot water is not reached (undershot). If the heat demand is less than the minimum heat output, the heat generator remain switched off permanently or must clock, so that the set temperature or a maximum allowable outlet temperature is not exceeded. Clocking means that the heat generator repeatedly switches on and off at short intervals with the circulating pump running, thus providing on average average heat outputs that are smaller than the minimum heat output.

In the case of heat requirements for heating water, which lie between a minimum and a maximum heat generator heat output, the setpoint temperature can be achieved in continuous operation and without cycles from the heat generator and the circulation pump. For changes in the heat demand, such as those resulting from a change in the water volume flow, the water inlet temperature or the setpoint temperature, must to the same extent change the heat generation energy output. As a rule, however, sudden changes in the heat demand can not be fulfilled immediately, but only with a time delay. This is due to the thermal inertia of the heat transfer system consisting of heat generator, primary heat exchanger, heating fluid circuit and secondary heat exchanger. The time delay can lead to overshoots and undershoots in the outlet temperature and the DHW comfort is negatively affected.

Some heat generators have a predetermined, unchangeable rate of change (speed), with which the power modulation can be changed. Due to their mass and geometry as well as the specific heat capacity and the thermal conductivity of the material, the heat exchangers have a thermal inertia, which acts like a heat accumulator. The Heizfluidkreislauf has its thermal inertia due to its water volume and the mass and the material of the pipe elements used. Only two flow states are known for the heating fluid circuit according to the current state of the art for domestic hot water preparation: circulation at a nominal circulation volume (heating fluid volume) or nominal pump speed and zero circulation when the pump is switched off.

Deviation of the outlet temperature from the outlet bottom temperature may result due to changed water volume flows or changed cold water inlet temperatures and affect as a changed heat demand to the heat generator. An arranged in the outlet waterway temperature sensor detects the deviation, then a temperature controller causes an adjustment of the heat generator heat output to the new heat demand, which also changes the Heizfluid-flow temperature.

If a heat requirement for domestic hot water production changes (eg by leaps and bounds), the heat output transferred to the water is adjusted only with a time delay and the setpoint temperature is only reached with a time delay. For example, in the event of a sudden increase in the water volume flow, the heat generator heat output and the heating fluid flow temperature will increase and the heat transfer system will adjust to the new heat demand until the outlet temperature returns to the setpoint temperature after an initial undershooting of the setpoint temperature and / or minimum outlet temperature. In the event of a sudden decrease in the water volume flow, on the other hand, the outlet temperature becomes the setpoint temperature (and possibly even the maximum in the short term) permissible outlet temperature) initially exceed, until such time as the heat output and the Heizfluidvorlauftemperatur correspondingly reduced and the heat transfer system have adapted to the new heat demand. By poorly adapted to the thermal inertia of the heat transfer system parameters of the temperature control underlying control algorithm 'it may also come to several overshoot and undershoot the outlet temperature to the setpoint temperature.

Increased environmental regulations mean that stricter standards and regulations regarding the current consumption and thermal efficiency of heating appliances can be expected. Therefore, in the space heating mode, so-called high-efficiency pumps have recently been applied. In addition to a significantly lower electrical power consumption, they are characterized by a considerably higher modutation range with regard to the heating fluid delivery capacity and can promote heating fluid volume flows of very different sizes. From the EP 0886110A2 a method for domestic hot water supply in a combined system according to the preamble of claim 1 is known, in which the rotational speed of a circulation pump is regulated as a function of the temperature of the heating or service water.

The invention has for its object to provide a method for heating water by the flow principle and a water heating system, which provide the basis for a high utilization of the condensing effect in domestic hot water and react quickly and accurately to changing water flow rates.

This is achieved by the objects with the features of claims 1 and 7 according to the invention. Advantageous developments can be found in the dependent claims.

The method according to the invention for heating water of variable volume flow according to the continuous flow principle in which a heat generator heats a heating fluid conveyed by a pump in a circulation, the heating fluid heats a flow-guided water, at least one sensor arranged in a water flow has an outlet temperature T _W and / or measures a volume flow Vw of the water, and at least one arranged in a Heizfluidweg sensor measures at least one Heizfluidtemperatur T _{H of} the heating fluid, aims to regulate the outlet temperature Tw of the water to a predetermined target outlet temperature Two.

In the case of a deviation of the outlet temperature T _W from the outlet setpoint temperature Two, the outlet temperature T _W is regulated by means of a change of a modulatable volume flow V _{H of} the heating fluid to the outlet setpoint temperature T _W0 .

In the case of a deviation of a heating fluid temperature T _H from a predefinable heating fluid setpoint temperature T _H0 , the heating fluid temperature T _H is regulated by means of a change in a modulated heat output Q of the heat generator to target heating fluid temperature T _H0 .

For a quick reaction, for example, to changes in water tapping volumes Vw or altered inlet temperatures is even possible T _K, which always accompanied by the prior art with temperature overshoots and undershoots temperature. The change in the Heizfluidvolumenstroms V _H by means of an adjustment of the pump delivery rate (circulation), which is very fast and almost instantaneous. As a result, more or less heat is supplied to the secondary heat exchanger and the outlet temperature is kept constant in accordance with the changed tap conditions. As soon as the changed heat loss on the water side in the heating fluid temperature T _H becomes noticeable by a deviation from the desired heating fluid temperature T _H0 , the comparatively slow heat transfer system also reacts with an adaptation of the heat generator heat conduction Q.

On the other hand, an adjustment of the heating fluid volume flow V _{H is given} to the Wasserzapfmenge V _W with the inventive method. A reduction in the tap quantity therefore does not lead to an increase in the heating fluid return temperature and thus improves the efficiency of the primary heat exchanger in condensing operation.

A suitable embodiment of the method is characterized in that if the outlet setpoint temperature T _{W0 is} exceeded by the outlet temperature T _W , as may result, for example, with a reduced tap water quantity Vw or at an increased inlet temperature T _K , the heating fluid volume flow V _{H is} reduced , And that when falling below the outlet target temperature Two, as may arise, for example, at an increased Wasserzapfmenge Vw or at a reduced inlet temperature T _K , the Heizfluidvolumenstrom V _{H is} increased. With the reduced or increased Heizfluidvolumenstrom V _H is accompanied by a reduced or increased heat output to the tap water.

A further suitable embodiment of the method is characterized in that when the heating fluid target temperature T _{H0 is} exceeded by the heating fluid temperature T _H , as it results, for example, with reduced heat output to the tapping water, the heat source heat output Q is reduced, and if the temperature falls below the Heating fluid target temperature T _H0, as it results, for example, with increased heat output to the tap water, the heat source heat output Q is increased.

An embodiment of the method is characterized in that a heating fluid target temperature T _HV0 in the flow of Heizfluidkreislaufes by a constant difference amount is greater than the outlet target temperature Two of the water. This temperature increase ensures that even with finitely small secondary heat exchanger, the outlet setpoint temperature Two is safely reached.

A particularly suitable embodiment of the method is characterized in that a heating fluid target temperature T _HV0 in the flow of Heizfluidkreislaufes by a difference is greater than the outlet setpoint temperature of the water, the difference being from a water volume flow V _W and / or from an inlet temperature T _{K of} the water yields. This adapted temperature increase ensures that the heating fluid temperatures are as low as possible and thereby favor the condensation conditions for the utilization of the condensing effect in the primary heat exchanger.

A further embodiment of the method is characterized in that, in the case of a deviation of the outlet temperature Tw from the outlet setpoint temperature Two, in addition to the change in the heating fluid volume flow V _H and before the heating fluid temperature T _H deviates from the desired heating fluid temperature T _H0 , then Heat generator heat output Q is changed. This serves to adapt the thermally inert heat transfer system at an early stage to the changing tapping conditions and to further reduce temperature overshoots and temperature undershoots. For this purpose, a module pump controller via a signal transmission path corresponding control signals to a module heat controller in a controller.

The inventive method can be realized for example by two control modules, wherein a first module ("pump controller") for controlling the Heizfluidvolumenstroms and a second module ("heat controller") is used to control the heat generator heat output. When a deviation of the outlet temperature from the outlet setpoint temperature occurs First, the pump controller changes the Heizfluidvolumenstrom so that the temperature deviation is compensated. This results in a change in the Heizfluidvorlauftemperatur because yes from the heat source initially still the same heat output is introduced. However, the change in the heating fluid volume flow changes the heat output that is released to the drinking water. The resulting change in the heating fluid flow temperature is compensated by the heat controller and regulated to the setpoint for the Heizfluidvorlauftemperatur. If the heat controller to achieve the heating fluid target temperature changes the heat generator capacity and thus also the Heizfluidvorlauftemperatur, this change also affects the drinking water outlet temperature. However, the deviation is compensated by the pump controller by means of a change in the Heizfluidvolumenstroms. The pump regulator, the pump and the heating fluid circuit can react quickly and have no trouble balancing the slow change (thermal inertia) of the heating fluid flow temperature. However, because, for example, if the drinking water volume flow is reduced, the heat controller reduces the heat generator output until the heating fluid setpoint temperature has been reached, then the pump regulator must inevitably adapt to this change. If both temperatures have reached their setpoint by means of the two controllers, the volume flow in the heating fluid circuit is automatically adjusted to the volume flow in the drinking water circuit. This results in a noticeable improvement in the heater efficiency, because with the decrease in the drinking water volume flow and the volume flow in the heating circuit decreases and thus the return temperature decreases.

If a large volume of drinking water is abruptly stopped, the heat generator will be switched off immediately. Nevertheless, the heat stored in the primary heat exchanger leads to overheating of the heating fluid circuit. If a short time thereafter a renewed tapping, arises in the conventional method, a strong temperature increase compared to the outlet set temperature. This is greatly reduced by the method according to the invention.

The inventive method is similar to changes in the water outlet temperature, which arise when the heat generator in the clock mode, automatically from. If the heating fluid supply temperature exceeds a maximum value, the heat generator must switch off until it drops below a minimum value again. Resulting temperature deviations of the DHW outlet temperature are compensated by the pump controller by changing the Heizfluidvolumenstroms.

The inventive method is particularly advantageous in heaters in which the primary heat exchanger has a large thermally inert mass, the secondary heat exchanger but a small mass. This is the case, for example, with primary heat exchangers made of cast materials for utilizing condensing technology. As a rule, these have a plate heat exchanger as a secondary heat exchanger with low mass.

The method solves or improves all fundamental problems that occur in domestic hot water. The various states of the system (heat generator clocks, repeated taps, tap start at very high heat fluid temperature, etc.) are resolved without the need to set the control algorithm controlling the method to a particular state or to change parameters. Also, the failure of the interface to the pump controller (the pump then goes to maximum capacity) does not lead to system failure, because the heat controller still regulates to a constant Heizfluidvorlauftemperatur. This reduces the comfort for the customer, but the drinking water operation is still possible. The modulating pump operation improves not only the increase in the heater efficiency because of the almost delay-free response pump and the control quality of the process. Furthermore, the power consumption of the pump is lower because of the more frequent partial load operation. As expected, there will be no cost disadvantage, since the modulating high-efficiency pumps will presumably be prescribed in the foreseeable future in the important European countries.

The invention comprises a water heating system according to the continuous flow principle with a heat generator, a heated by the heat generator, pumped by a pump heating fluid, a heated by the heating fluid, conveyed in the flow, at least one arranged in a waterway sensor for detecting an outlet temperature T _W , a Inlet temperature T _K and / or a volume flow V _{W of} the water, as well as at least one arranged in a Heizfluidweg sensor for detecting at least one Heizfluidtemperatur T _{H of} the heating fluid, wherein for controlling the outlet temperature Tw to a predetermined outlet target temperature T _W0, the flow rate V _H of Heizfluidkreislaufs and the heat output Q of the heat generator can be modulated.

An embodiment of the water heating system is characterized by a control device connected to the heat generator, the pump and the sensors, which has an input device for setting desired values and / or constants, a control module for Control of the pump and a control module for controlling the heat generator comprises, wherein the control device influences the operation of the connected components and thus controls the outlet temperature T _W.

Fig. 1

ein der Erfindung zugrundeliegendes Wassererwärmungssystem,

Fig. 2

einen Signalflussplan eines Regelkreises zur Trinkwarmwasserbereitung nach dem Stand der Technik,

Fig. 3

einen Signalflussplan eines Regelkreises zur Trinkwarmwasserbereitung nach der vorliegenden Erfindung,

The drawings illustrate various aspects of embodiments of the invention and show in the figures:

Fig. 1

a water heating system on which the invention is based,

Fig. 2

a signal flow plan of a control loop for domestic hot water preparation according to the prior art,

Fig. 3

a signal flow diagram of a loop for domestic hot water according to the present invention,

Fig. 1 schematically shows a combination heater for room heating and domestic hot water. The heater comprises a heat generator 1 (heat source), a heated by the heat generator 1 via a primary heat exchanger 2 Heizfluidkreislauf 3, which is promoted (circulated) by a pump 4, and a connected to the heater heat consumer 5, for example, a space heater 5. The circulating heating fluid (Heat transfer medium) transports the heat from the heat source 1 to the heat consumer 5. For domestic hot water, the heater comprises a working according to the flow principle water heating system with a heated by Heizfluidkreislauf 3 via a secondary heat exchanger 6 water flow 7, at least one arranged in a waterway 7 sensor 8, 9 10 for detecting an outlet temperature T _W and / or an inlet temperature T _K and / or a volumetric flow V _{W of} the water, and at least one arranged in a Heizfluidweg 3 sensor 11, 12 for detecting a flow temperature T _HV and / or a Rückl temperature T _{HR of} the heating fluid. For regulating the outlet temperature T _W to a predefinable setpoint temperature T _W0 , the heat output Q of the heat generator 1 and the volume flow V _{H of} the heating fluid circuit 3 are modulated. The two heating tasks room heating and DHW heating are usually not fulfilled simultaneously, but individually. For this purpose, the heating fluid circuit 3 between the two heat consumers space heater 5 and secondary heat exchanger 6 is switched by means of a switching valve 13.

Fig. 2 shows the schematic signal flow plan of a control loop for domestic hot water preparation with the input variable (setpoint) T _W0 , the output (outlet temperature) Tw, the controller R, the actuator (heat generator 1) and the manipulated variable Q. The heat generator 1 is the Outlet temperature T _W influenced. Fig. 3 shows the schematic signal flow plan of a control circuit for domestic hot water generation according to the present invention with the input value (setpoint) Two, the output (outlet temperature) T _W , the controller R with module W (heat controller), module P (pump controller) and signal transmission path S between the two controllers , the actuators (heat generator 1 and pump 4) and the manipulated variables Q and V _H. With the heat generator 1 and the pump 4, the outlet temperature Tw is influenced.

Claims (8)

1. Method for heating water of variable volume flow according to the continuous flow principle, in which a heat generator (1) heats heating fluid conveyed by a pump (4) in a circuit, the heating fluid heats water carried in continuous flow, at least one measuring sensor (8, 9, 10) arranged in a water path (7) measures an outlet temperature T_W and/or a volume flow V_W of the water, and at least one measuring sensor (11, 12) arranged in a heating fluid path (3) measures at least one heating fluid temperature T_H of the heating fluid, the outlet temperature Tw of the water being controlled to a predefinable outlet temperature set point Two, in the event of a deviation of the outlet temperature Tw from the outlet temperature set point Two the outlet temperature Tw being controlled to the outlet temperature set point Two by means of a change to a volume flow V_H of the heating fluid that can be modulated,
   characterized in that

   - in the event of a deviation of a heating fluid temperature T_H from a predefinable heating fluid temperature set point T_H0, the heating fluid temperature T_H is controlled to the heating fluid temperature set point T_H0 by means of a change to a heat output Q from the heat generator that can be modulated.
2. Method according to Claim 1, characterized in that if the outlet temperature set point is overshot, the heating fluid volume flow V_H is reduced, and if the outlet temperature set point is undershot, the heating fluid volume flow V_H is increased.
3. Method according to Claim 1 or 2, characterized in that if the heating fluid temperature set point T_H0 is overshot, the heat generator heat output Q is reduced, and in that if the heating fluid temperature set point T_H0 is undershot, the heat generator heat output Q is increased.
4. Method according to one of Claims 1 to 3, characterized in that a heating fluid temperature set point T_HV0 in the flow of the heating fluid circuit is greater by a constant differential amount than the outlet temperature set point Two of the water.
5. Method according to one of Claims 1 to 3, characterized in that a heating fluid temperature set point T_HV0 in the flow of the heating fluid circuit is greater by a differential amount than the outlet temperature set point Two of the water, wherein the differential amount is given by a water volume flow Vw and/or an inlet temperature T_K of the water.
6. Method according to one of the preceding claims, characterized in that, in the event of a deviation of the outlet temperature Tw from the outlet temperature set point Two, in addition to changing the heating fluid volume flow V_H and even before the heating fluid temperature T_H deviates from the heating fluid temperature set point T_H0, the heat generator heat output Q is also changed, by a pump controller module (P) outputting appropriate actuating signals via a signal transmission path (S) to a thermostat (W) module in a controller (R).
7. Water heating system according to the continuous flow principle having a heat generator (1), a heating fluid heated by the heat generator (1) and conveyed by a pump (4) in circulation, water heated by the heating fluid and conveyed in continuous flow, at least one measuring sensor (8, 9, 10) arranged in a water path (7) to measure an outlet temperature Tw and/or an inlet temperature T_K and/or a volume flow V_W of the water, and at least one measuring sensor (11, 12) arranged in a heating fluid path (3) to measure at least one heating fluid temperature T_H of the heating fluid, wherein, to control the outlet temperature Tw to a predefinable outlet temperature set point Two, the volume flow V_H of the heating fluid circuit and the heat output Q from the heat generator (1) can be modulated.
8. Water heating system according to Claim 7, characterized by a control device connected to the heat generator (1), the pump (4) and the measuring sensors (8, 9, 10, 11, 12), comprising an input device for setting set points and/or constants, a control module for controlling the pump and a control module for controlling the heat generator, wherein the control device influences the operation of the connected components and thus controls the outlet temperature Tw.

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