HEATING SYSTEM

Description

[0001] The invention relates to a heating system with a heat circuit connected to a heat source and a consumer, comprising a circulation pump, the flow and return of which are connected to each other by a bypass, and with a control device for controlling the circulation pump depending on the heat circuit temperature.

[0002] From EP2 275 748 A2, a heating system is known that includes a boiler and a heat storage tank connected to the boiler via a flow and return line. A charging pump is provided in the return line to charge the heat storage tank; its speed or power can be controlled depending on the flow temperature. To operate the boiler at its optimum efficiency, a return temperature within a predetermined range must be maintained. For temperature control, the return line is connected to the flow line via a bypass, so that heated heat transfer fluid can be supplied to the return line from the flow line when needed. For this purpose, the bypass is connected to the return line by means of a three-way valve. The three-way valve is controlled depending on the return temperature.In the return line, a differential pressure control valve is also installed downstream of the three-way valve. This valve ensures a constant pressure drop that is as independent as possible from the flow rate, but it has no influence on the control of the bypass. A disadvantage is the increased design complexity resulting from the three-way valve and its control system.

[0003] In a heating circuit with parallel-connected radiators connected to a flow and a return, it is known (DE 10 2009 007 053 A1) to connect the flow to the return via a pressure-controlled bypass valve in order to ensure a pressure difference between the flow and the return and thus a corresponding flow through the radiators.

[0004] To regulate the mass flow through a heating circuit depending on the heating circuit's heat demand, EP 0 681 148 A2 proposes, among other things, the installation of a pressurized switching valve in the bypass between the heating supply and return lines. This valve opens when a minimum differential pressure is exceeded, thus exposing a temperature sensor in the return section of the bypass to hot heat transfer fluid from the supply line. The resulting temperature difference between the temperature measured by the sensor in the bypass section and the return temperature measured by a sensor upstream of the bypass is used to throttle the mass flow of the supply line by means of a control valve. Therefore, the mass flow through the heating circuit is controlled, but not the temperature of the heating circuit itself.

[0005] The invention is therefore based on the objective of designing a heating system of the type in question in such a way that advantageous control of the heating circuit temperature is made possible with comparatively simple design means.

[0006] Starting from a heating system of the type described above, the invention solves the problem by providing the heating circuit with a switching valve that opens when a minimum pressure difference is applied, and which can be subjected to a pressure difference by means of the circulation pump, which is above or below the minimum pressure difference depending on the heating circuit temperature.

[0007] As a result of these measures, controlling the circulation pump alone is sufficient to maintain the heating circuit temperature within a desired range, because the switching valve located in the heating circuit switches depending on the pressure differential created by the circulation pump and the heating circuit temperature. When the minimum pressure differential is exceeded, the switching valve opens, thus connecting the heat consumer to the heating circuit. If the pressure differential falls below the predefined minimum value, the switching valve closes, causing the heat transfer fluid to flow through the bypass. By opening and closing the switching valve accordingly, the heating circuit temperature can therefore be influenced without the need for a three-way valve to control the bypass. Only the speed or power of the circulation pump is controlled by the control unit, depending on the heating circuit temperature.

[0008] If a boiler is used as the heat source, the return temperature is typically adjusted to the boiler's requirements using a bypass. In this case, the switching valve is located upstream of the bypass in the return line, with the control unit activating the circulation pump located downstream of the bypass in the return line depending on the return temperature. If the switching valve is subjected to a pressure differential above the minimum pressure differential due to the control by the circulation pump, the consumer, for example, a heat storage tank, is connected to the boiler via the return line. Due to the flow conditions, essentially no heat transfer fluid flows from the supply to the return line via the bypass.If the return temperature needs to be raised, for example when starting up the boiler, the switching valve is actuated with a pressure differential below the minimum pressure differential due to the control of the circulation pump depending on the return temperature, so that the flow and return are short-circuited via the bypass with the effect that the return temperature is raised.

[0009] For example, if a consumer connected to a non-controllable heat source is to be supplied with a heat transfer fluid whose flow temperature can be controlled, the switching valve, which switches depending on the applied pressure differential, must be located downstream of the bypass. The control device must then activate the circulation pump located in the heating circuit section on the consumer side of the bypass, depending on the flow temperature. When the switching valve closes, the heat transfer fluid from the consumer is fed into the flow, which is accompanied by a corresponding reduction in the flow temperature.

[0010] Due to the flow conditions when the switching valve is open, any residual flow between the supply and return lines via the bypass can be accepted. If such residual flow is to be prevented, the bypass can be equipped with a switching valve that closes when a minimum pressure differential is present. This switching valve therefore behaves in the opposite way to the switching valve in the heating circuit and closes the bypass when the consumer is supplied with heat from the heat source.

[0011] If a speed-controlled circulation pump is used, this pump can also be operated at low speeds, which is necessary in the event of an increase in the return temperature of a boiler to ensure a corresponding boiler circuit via the bypass in order to avoid local boiling of the heat transfer fluid in the boiler area.

[0012] To easily control the alternating opening and closing of the switching valve in the heating circuit via the speed or power of the circulation pump, the pump can advantageously be controlled using pulse width modulation (PWM). With PWM, the pump switches between two operating states, and the cycle ratio and cycle duration can be adjusted. Since one operating state is characterized by a low speed or power and the other by a correspondingly higher speed or power, and the pump switches between these states in pulses, PWM allows the mixing ratio between the flow and return lines, which controls the heating circuit temperature, to be precisely defined.

[0013] The invention is illustrated in the drawing as an example. It shows Fig. 1 a heating system according to the invention in a schematic block diagram, Fig. 2 one of the Fig. 1 corresponding representation of an embodiment of a heating system according to the invention and Fig. 3 the time-dependent power curve of a circulating pump designed as a pulse width modulation pump.

[0014] A heating system according to the invention comprises a heat source 1 which is connected to a consumer 4 via a flow line 2 and a return line 3. A bypass 5 is provided between the flow line 2 and the return line 3, which divides the heating circuit, equipped with a circulation pump 6, into a heating circuit section 7 assigned to the heat source 1 and a heating circuit section 8 assigned to the consumer 4. Preferably, a switching valve 9 is provided in the return line 3, which switches between a closed and an open switching state depending on the applied pressure differential. The minimum pressure differential required for opening is preferably determined by a spring, so that the pressure differential threshold required for switching can also be adjusted by changing the spring preload.

[0015] The circulation pump 6 is controlled by a control unit 10, depending on the temperature of the heat transfer fluid detected by a temperature sensor 11.

[0016] According to the embodiment according to the Fig. 1 The switching valve 9 is located upstream of the bypass 5, while the circulation pump 6 is located downstream of the bypass 5. The control unit 10 receives information about the return temperature via the temperature sensor 11. If the return temperature is to be increased, the switching valve 9 is closed by the control unit 10 through a corresponding control of the circulation pump 6, because the pressure differential at the switching valve 9 is reduced below the set minimum pressure differential due to the reduced pump output. This means that the heat transfer fluid circulates within the heating circuit section 7, which leads to an increase in the return temperature. When the switching valve 9 opens, the flow conditions change, so that the heat transfer fluid flow via the bypass 5 is interrupted.

[0017] The embodiment according to the Fig. 2 The main difference is that the circulation pump 6 is located in the heating circuit section 8 and is controlled by the control unit 10 depending on the flow temperature. The switching valve 9 is located downstream of the bypass 5. When the switching valve 9 is closed, the heat transfer fluid flows through the heating circuit section 8 via the bypass 5, whereby the flow temperature is reduced due to the connection of the return 3 with the flow 2. This heating circuit configuration can be particularly advantageous in cases where a heat source 1 that is not sufficiently controllable is available and the consumer 4 is to be supplied with a heat transfer fluid temperature adapted to the consumer conditions, as is the case, for example, with underfloor heating connected to a heat storage tank.

[0018] The circulation pump 6 is advantageously speed-controlled and can be configured according to the Fig. 3 The system switches between two power levels, P1 and P2, with different rotational speeds in a pulsed manner. The pressure differential at switching valve 9, resulting from power level P1, is below the minimum pressure differential of this switching valve 9. Therefore, switching valve 9 only opens in operating state P2, which results in a pressure differential at switching valve 9 above the minimum pressure differential. As shown in the temporal power profile of the Fig. 3The opening and closing times of the switching valve 9 can be coordinated by pulse width modulation to achieve a specific mixing ratio between the heat transfer fluid in the supply line 2 and the return line 3. By controlling the pulse width based on the actual temperature in the return line 3 or supply line 2 as measured by the temperature sensor 11, the actual temperature can be adjusted according to a predetermined target temperature via the control unit 10 by controlling the circulation pump 6, without requiring a complex control of the bypass 5 using a three-way valve.

[0019] To prevent any residual flow between the supply line 2 and the return line 3 via the bypass 5 when the switching valve 9 is open, a switching valve 12 can be provided in the bypass 5. Unlike the switching valve 9, this valve closes when a minimum pressure differential is exceeded. Since the pressure differential at the switching valve 12 depends on the operating state of the circulation pump 6, this switching valve 12 is also controlled by the circulation pump 6.

[0020] In order to deliver the full power of the heat source 1 to the consumer 4, the speed of the circulation pump 6 can be increased beyond power level 2.

Claims

1. Heating system comprising a heat source (1), a consumer (4), and a heating circuit connected to the heat source (1) and to the consumer (4), having a circulation pump (6), the flow line (2) and the return line (3) of which heating circuit being connected to one another by a bypass (5), and comprising a control device (10) for actuating the circulation pump (6) as a function of the heating circuit temperature, wherein the heating circuit has a valve (9), characterized in that the valve (9) is a switching valve (9) opening at an applied minimum pressure difference, which can be subjected, with the aid of the circulation pump (6), to a pressure difference which lies above or below the minimum pressure difference as a function of the heating circuit temperature.

2. Heating system according to claim 1, characterized in that the switching valve (9) is arranged in the return line (3) upstream of the bypass (5), and in that the control device (10) actuates the circulation pump (6), provided in the return line (3) downstream of the bypass (5), as a function of the return line temperature.

3. Heating system according to claim 1, characterized in that the switching valve (9) is arranged in the return line (3) downstream of the bypass (5), and in that the control device (10) actuates the circulation pump (6), provided in the heating circuit section (8) on the side of the bypass (5) facing the consumer (4), as a function of the flow line temperature.

4. Heating system according to one of claims 1 to 3, characterized in that the bypass (5) has a switching valve (12) closing at an applied minimum pressure difference.

5. Heating system according to one of claims 1 to 4, characterized in that the rotational speed of the circulation pump (6) is controllable.