FIELD OF THE INVENTION

The present invention relates to a method of affecting the operation of a control valve by changing a system parameter in a fluid flow system when the control valve operates under a condition that would influence the overall operation of the fluid flow system. According to the invention, this is done by introducing a balancing system adapted to balance the fluid flow system to an adjustable setpoint, where the balancing system comprises a setting actuator capable of adjusting the setpoint in response to an operating value of the control valve. In the main, but not limiting, embodiment of the present invention, the fluid flow system is a heating system connected to a district heating supply, where the fluid flow is controlled by the control valve, and where a balancing system is a differential pressure controller comprising a differential pressure valve actuator. The setpoint is related to a differential pressure.

BACKGROUND OF THE INVENTION

It is well known that in heating systems, such as in heating systems for district heating where a remotely supplied heating fluid heats domestic water and water to be fed to heating devices, such as floor heating systems and radiators, one of the pre-conditions for a wellfunctioning (e.g. oscillation and noise free) control is the use of a differential pressure controller for the balancing of the differential pressure across the system, such as the heating system.

If the differential pressure is not chosen correctly, the risk is malfunctions, such as pressure oscillation and noise in the system. Differential pressure controllers are used to maintain differential pressure in a system, regardless of the variation of differential pressure in the supply net and consumption in the system. Differential pressure controllers are also used to create a hydraulic balance in a network.

Use of differential pressure controllers in substations and in the district heating network will maintain a hydraulic balance in the network which ensures a good distribution of water in the supply network, and that the desired pressure level in the network can be achieved, leading to an adequate heat supply in the network. The correct balancing ensures that the quantity of circulating water in the network can be limited, providing reduced costs for water circulation. Due to the balancing of the network, the pressure drop on, e.g., a substation or a control valve is always the designed one, and no excess energy is needed for pressure pumps. Most problems arise when the control valve is almost closed, leaving only a small through- flow where the control becomes difficult and may lead to oscillations.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide a method for balancing a heating system in such a manner that oscillations in the heating system are eliminated or significantly reduced.

The invention provides a method for balancing a heating system, the heating system comprising a heat exchanging unit, a pressure regulation unit, a main flow controller and at least one heat consuming device, where heat exchange takes place in the heat exchanging unit between a primary side fluid and a secondary side fluid, where secondary side fluid is supplied to the at least one heat consuming device, and where the pressure regulation unit is arranged to control a differential pressure in a part of the heating system, the method comprising the steps of:

- changing a differential pressure in a part of the heating system, by means of the pressure regulation unit, until a flow rate corresponding to a nominal flow rate is obtained in the part of the heating system, and

- selecting the differential pressure which results in the nominal flow rate as a differential pressure setting for the pressure regulation unit.

Thus, the invention provides a method for balancing a heating system. In the present context the term 'heating system' should be interpreted to mean a system which provides heating, e.g. in the form of room heating and/or heating of domestic water. The heating system could, e.g., be a domestic heating system.

In the present context the term 'balancing' should be interpreted to mean that differential pressures across the heating system are controlled in an appropriate manner which ensures a good distribution of fluid throughout the heating system, in order to ensure an energy efficient heating system.

The heating system comprises a heat exchanging unit, a pressure regulation unit, a main flow controller and at least one heat consuming device. In the heat exchanging unit, heat exchange takes place between a primary side fluid and a secondary side fluid, where the primary side of the heat exchanger may be connected a heating plant, e.g. in the form of a district heating network, a geothermal heating system, solar heating system, etc. The at least one heat consuming device is arranged at the secondary side of the heat exchanger, and thereby secondary side fluid is supplied to the at least one heat consuming device.

The pressure regulation unit is arranged to control a differential pressure in a part of the heating system. Accordingly, the pressure regulation unit is applied for performing the balancing of the heating system. The part of the heating system where the differential pressure is controlled by means of the pressure regulation unit may, e.g., be a primary side supply line, a primary side return line, a secondary side supply line or a secondary side return line.

The main flow controller is arranged to control a fluid flow in the heating system, e.g. in the same part of the heating system where the differential pressure is controlled by means of the pressure regulation unit. The main flow controller may, e.g., be in the form of a valve.

In the method according to the invention, a differential pressure is initially changed in a part of the heating system, by means of the pressure regulation unit. The differential pressure is changed until a flow rate corresponding to a nominal flow rate is obtained in the part of the heating system. In the present context, the term 'nominal flow rate' should be interpreted to mean a flow rate at which the heating system operates appropriately at steady state. The nominal flow rate is sometimes referred to as 'design flow rate'. The flow rate may, e.g., be a flow rate through the main flow controller.

Accordingly, the differential pressure regulation unit is operated in such a manner that the differential pressure in a certain part of the heating system is changed or adjusted.

Meanwhile, the flow rate in that part of the heating system is monitored and compared to the nominal flow rate.

When the nominal flow rate is reached, the differential pressure is registered, and it can be concluded that this differential pressure will result in the nominal flow rate, under the prevailing operating conditions. Therefore, this differential pressure is selected as a differential pressure setting for the pressure regulation unit. Thus, when the differential pressure regulation unit is subsequently operated in accordance with this setting value, it will also be operated in a manner which seeks to obtain the nominal flow rate in the part of the heating system. Thereby appropriate fluid flow throughout the heating system, with no or only limited oscillations in the fluid flow, is also obtained.

The method may further comprise the step of setting a flow rate in the part of the heating system at a maximum flow rate, prior to the step of changing a differential pressure. According to this embodiment, the method described above is performed while the fluid flow through the part of the heating system where the differential pressure is controlled is as high as possible. This could, e.g., be obtained by fully opening one or more valves, e.g. including the main flow controller. The differential pressure is then changed in order to cause the flow rate through the part of the heating system to gradually approach the nominal flow rate, which will normally be lower than the maximum flow rate.

The step of changing a differential pressure may comprise initially setting the pressure regulation unit at a start setting differential pressure. According to this embodiment, a starting point is selected for the differential pressure before the method described above is initiated. The start setting differential pressure may, e.g., be the lowest possible setting or another predefined setting. Alternatively, the start setting differential pressure may simply be the present differential pressure setting at the time where the method is initiated, or a measured differential pressure value.

The step of changing a differential pressure may be performed by changing a setting of the pressure regulation unit. According to this embodiment, the differential pressure is changed by gradually or stepwise changing a setting which is provided to the pressure regulation unit. When the setting of the pressure regulation unit is changed, the pressure regulation unit will subsequently operate in such a manner that it attempts to reach an actual differential pressure which is equal to the setting value. Thereby the actual differential pressure changes in accordance with the changes in setting value. This is an easy, accurate and reliable manner of changing the differential pressure.

The step of changing a differential pressure may be performed in a stepwise manner, and the method may further comprise the step of, for each stepwise change in differential pressure, measuring the flow rate in the part of the heating system after a waiting period, dt, in time.

According to this embodiment, the step of changing a differential pressure is performed in the following manner. The differential pressure is changed in a step, and subsequently a waiting period, dt, is allowed to lapse, in order to allow the system to reach an equilibrium state. When the waiting period, dt, has lapsed, the flow rate in the part of the heating system, where the differential pressure is changed, is measured. The measured flow rate can then be compared to the nominal flow rate, in order to determine whether or not the nominal flow rate has been reached. By allowing the waiting period, dt, to lapse before measuring the flow rate, it is ensured that the measured flow rate actually corresponds to set differential pressure. If the nominal flow rate has not yet been reached, the process described above is repeated, starting by changing the differential pressure in a step. The waiting period, dt, may be a constant time period. As an alternative, the waiting period, dt, may be dependant on the differential pressure setting. As another alternative, the waiting period, dt, may be dependant on a difference between a measured flow rate and the nominal flow rate in the part of the heating system, e.g. with a long waiting period when the difference between the measured flow rate and the nominal flow rate is large, and decreasing the waiting period as the measured flow rate approaches the nominal flow rate.

The step of changing a differential pressure may comprise ramping up the differential pressure at a constant rate. According to this embodiment, the differential pressure is initially at a low level, and the differential pressure is gradually increased when performing the method described above. This may be done in a stepwise or in a continuous manner.

The step of changing a differential pressure may be performed based on whether the flow rate in the part of the heating system is above or below the nominal flow rate. For instance, if the flow rate is below the nominal flow rate, the flow rate should increase as a consequence of changing the differential pressure, in order to cause the nominal flow rate to be reached. Therefore, in this case the differential pressure should be changed in such a manner that an increase in flow rate may be expected. Similarly, if the flow rate is above the nominal flow rate, the differential pressure should be changed in such a manner that a decrease in flow rate may be expected.

The method may further comprise the step of a remote controller communicating a differential pressure setting signal to a setting actuator of the differential pressure regulation unit. According to this embodiment, the differential pressure regulation unit is controlled by means of the remote controller, in the sense that the remote controller defines a desired differential pressure setting, and communicates a setting signal which is indicative of this desired differential pressure to the differential pressure regulation unit. The setting actuator of the differential pressure regulation unit then actuates an appropriate pressure regulating element of the differential pressure regulation unit in accordance with the received differential pressure setting signal, i.e. in order to attempt to reach the desired differential pressure.

As an alternative, the differential pressure regulation unit may be controlled by means of a local or internal controller.

The step of changing a differential pressure may be performed in dependence of a present differential pressure setting. According to this embodiment, the present or current differential pressure setting dictates the manner in which the change in differential pressure is to be performed, e.g. in terms of whether the differential pressure should be increased or decreased, at which rate, etc.

The heating system may further comprise a flow measuring device. The flow measuring device may, e.g., be applied for measuring the flow rate in the part of the heating system where the differential pressure is changed, in order to determine whether or not the nominal flow rate has been reached.

The present invention further provides a controller adapted to perform the method described above. The controller may be a remote controller, or it may be a local controller, such as an internal controller of the differential pressure regulation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Fig. 1 shows an example heating system, where the method according to the present invention could be implemented,

Fig. 2 shows an example differential pressure controller composed of a valve connected to a pressure responsive actuator, adjustable biasing means and setting actuator, and

Fig. 3 is a flow chart illustrating automatic differential pressure setting in a substation in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from the detailed description.

Fig. 1 illustrates an example heating system 1 to supply a heating fluid to one or more heat consuming devices 4. Heating fluid is supplied at a primary side to a heat exchanging unit 2 at a primary side supply temperature Tn by a primary side supply line 6 and returned at a primary side return temperature T12 by a primary side return line 7. This heating fluid is also referred to as the primary side fluid. The primary side main lines 6, 7 are connected to a heating plant of any kind, such as a district heating network, a geothermal heating system, solar heating system etc., or a combination thereof.

In the illustrated embodiment, the heat exchanger unit 2 connects to a secondary side heating system by a secondary side supply line 8 and secondary side return line 9. In the heat exchanger unit 2 heat is exchanged between the secondary side fluid passing the heat exchanger unit 2 and the primary side fluid. This provides a secondary fluid supplied at a local supply temperature T22 to the secondary side supply line 8 and returned to the heat exchanger 2 with a secondary side return temperature T21 by the secondary side return line 9.

The secondary side heating system includes one or more heat consuming devices 4, such as radiators, floor heating systems, use-water tapping, etc., and any needed flow controllers 10, such as valves and/or thermostats.

The heating system 1 further comprises a pressure regulation unit 3, which in the illustrated embodiment is positioned at the primary side supply line 6 and is adapted to maintain a substantially constant pressure in the heating system 1. This allows a hydraulic balancing of the primary side fluid flow which is independent of pressure fluctuations. The same advantage can be obtained by alternatively positioning the pressure regulation unit 3 at the primary side return line 7.

Alternatively or additionally, the pressure regulation unit 3 could be adapted to make a hydraulic balancing of the secondary side fluid and could therefore be positioned at the secondary side supply 8 or the secondary side return line 9.

A controller 5 may be positioned in data exchange communication with the pressure regulation unit 3, where the data exchange communication could be of any kind, such as wireless, wired, digital, analogue, etc. The controller 5 may, e.g., be adapted to provide a setpoint differential pressure signal to the pressure regulation unit 3.

Temperature sensors 11 may be positioned to measure the temperatures of the fluids in the heating system 1, such as positioned to measure the primary side and secondary side inlet and outlet temperatures (Tn, T12, T21, T22) of the heat exchanger 2. Temperature sensors (not shown) may also be positioned in connection to the individual heat consuming devices 4, for measuring any or all of the inlet and outlet temperatures of the passing secondary fluid(s) and/or the ambient temperature(s). The consumer of the heat consuming device(s) 4 may request a certain temperature of a space accommodating a certain heat consuming device, such as a living room, which will be reflected in the measured ambient temperature and/or the inlet and outlet temperatures of the heat consuming device 4. For instance, it may be reflected in the difference between inlet and outlet temperature(s) of the heat consuming device 4.

In many heating systems 1 the separation between the primary and secondary side heating systems is formed by a substation 12 comprising the heat exchanging unit 2. In addition, it could include other devices, such as temperature sensors 11, flow controllers such as valves and/or thermostats, a main flow controller 10a, a pressure regulation unit 3, and optionally the controller 5. The substation 12 may, thus, be installed and connected as the link between the primary 6, 7 and secondary 8, 9 side flow systems and lines with the associated heat consuming devices 4 and other components.

In general, many of the devices in the heating system 1, such as the flow controlling devices 10, 10a, e.g. in the form of valves and/or thermostats, the pressure regulation unit 3, the heat exchanging unit 2, and thus also the substation 12, observe non-linear and dynamic behavior. When, e.g., the secondary side flow rate changes, this affects the outputted secondary side supply temperature T22 of the heat exchanging unit 2 in a non-linear manner. Similarly, changes in the pressure at the primary side would also affect the secondary side supply temperature T22.

The controller 5 is adapted to control and regulate the operation of the heating system 1, such as the flows, pressures and temperatures of the fluids entering and leaving the heat exchanging unit 2. The controller 5 may include a processor and operates as, e.g., a PI or PID controller, this part being referred to as a PI or PID controller. The controller 5 could further include a memory storing required parameters, such as data regarding operating point, operational data and nominal data or settings.

In the present context, an operating point refers to the actual values at steady state of the heating system 1 and possible of the substation 12.

The operating points of the substation 12 may be defined by several variables, such as primary side flow rate, secondary side flow rate, the inlet temperatures Tn and T21 of the heat exchanging unit 2 (i.e. the temperatures of the fluids which are supplied to the heat exchanging unit 2, being the primary side supply temperature Tn and the secondary side return temperature T21), the differential pressure over the main flow controller 10a, etc. For the heating system 1 itself, the operating point may in addition include the inlet and/or outlet temperatures of the heat consuming device(s) 4, etc. In the present invention a selected number of such variables could be used as data input. In the present disclosure, the operational data refers to the actual data as being measured or operating in the heating system 1 in general, or the substation 12 more specifically. These data include measured data, such as the heat exchanger primary inlet temperature Tn, heat exchanger primary outlet temperature T12, heat exchanger secondary inlet temperature T22, heat exchanger secondary outlet temperature T21, and respectively the primary side flow rate and secondary side flow rate. This may include the latest data or a number of actually measured and known data, possibly stored in the memory of the controller 5 or in the cloud, such as the latest N measurements, N being any natural number.

By nominal data or setting values are in general referred to the set operational data, such as the primary inlet temperature Tn, primary outlet temperature T12, secondary inlet temperature T22, secondary outlet temperature T21, of the heat exchanger 2, and respectively the primary side flow rate and secondary side flow rate. These are the values which the controller 5 aims to obtain in the heating system 1 by the control. Often 'nominal data' are also referred to as 'design data', such as design flow rate and design pressure.

The nominal data or setting values need not be the same as the data of the operation point, since the dynamic requirements of the heating system 1 may 'move' set operation away from steady state. In this case, the controller 5 operates in order to keep the operational values stable and at least close to the nominal or setting values. The controller 5 aims to keep T22 at the desired setpoint, regardless of the change of operating points, such as secondary flow, or primary inlet temperature Tn.

A main flow controller 10a in the illustration is positioned at the primary side supply line 6, but could alternatively, similarly to the pressure regulation unit 3, be positioned at the primary side return line 7, at the secondary side supply line 8, or at the secondary side return line 9. The main flow controller 10a could optionally be integrated into the pressure regulation unit 3, thus forming a shared pressure and flow controlling unit. The main flow controller 10a may be connected to an actuator to adjust its valve opening, where the actuator may be remotely controlled, e.g. by the controller 5. In the illustration of Fig. 1 the main flow controller 10a, in the form of a valve, and the pressure regulation unit 3 are indicated to be a part of the substation 12.

By an improper commissioning of, e.g., the substation 12, it can be observed that primary side nominal flow (the setpoint flow rate in the primary side lines 6, 7) is never reached, thus not offering the required energy to the heat consuming devices 4 to be sufficiently powered, at the discomfort for the consumer. In case of higher demand, this causes the secondary side supply temperature T22 to fall below a desired setpoint. Focusing on the control of the temperature on the secondary side and assuming stable pressure on the primary side of the heat transfer unit 2, one cause of oscillations in the flow of in the heating system 1 can be attributed to the operating point of the substation 12.

When the substation 12 operates away from its nominal operating point (the operational settings like flow rates, temperatures, etc.), the non-linearity of, e.g., the main flow controller 10a in combination with a non-linear heat exchanger unit 2, the PI controller 5 may cause oscillatory responses of the main flow controller 10a. This, in turn, causes oscillations in the flow which inherently propagate through the non-linear heat exchanger unit 2. Due to phase shift between temperature and flow, the oscillations, which are caused by poor control, may influence the energy measurement, increase wear, etc.

It is well known that in heating systems 1, one of the pre-conditions for a well-functioning (e.g. oscillation and noise free) control is the use of a differential pressure controller, such as a pressure regulation unit 3, for the control of the differential pressure across the system 1, and thus hydraulic balancing ensuring a hydraulic balance in a network, such as the heating system 1.

Such differential pressure controllers 3 are used to maintain differential pressure in a system regardless of the variation of differential pressure in the supply net and consumption in the system.

The pressure regulation unit 3 according to the present invention may comprise a pressure regulation valve of any kind adapted to control the differential pressure of the fluid in general, or in a part of the heating system 1, and may thus be in pressure communication to two positions at the heating system 1, the pressure difference between the two positions being the differential pressure. In the illustrated embodiment of Fig. 1 the two positions are over the main flow controller 10a at respectively the inlet and outlet side. The pressure regulation unit 3 is, thus, positioned to maintain a constant differential pressure over the main flow controller 10a to a given setpoint differential pressure which may be adjustable. One such example pressure regulation valve is to be found in, e.g., European Patent publication 3093729.

Fig. 2 illustrates an example differential pressure controller, or differential pressure regulation unit 3, including a valve 10b connected to a pressure responsive actuator 3a. The pressure responsive actuator 3a may be formed as a diaphragm connected to a valve stem for changing the valve opening of the valve 10b. The two sides of the diaphragm are in pressure communication to the two positions in the heating system 1, such as at over the main flow controller 10a illustrated in Fig. 1. The pressure setting can be changed by adjustable biasing means 3b in the form of a spring element acting on the diaphragm. A setting actuator 3c is connected to the adjustable biasing means 3b to change the tension of the adjustable biasing means 3b. The setting actuator 3c may comprise a processor and memory and may be in data exchange communication with external devices, such as the controller 5 illustrated in Fig. 1. In one embodiment the controller 5 may form part of the setting actuator 3c.

Use of differential pressure regulation units 3 in substations 12 and in heating systems 1 maintains a hydraulic balance to ensure a good distribution of fluid to ensure an energy efficient heating system 1.

Problems arise, e.g., when the main flow controller 10a is almost closed, leaving only a small through-flow where the control becomes difficult and may lead to oscillations.

To ensure an energy efficient balance of the heating system 1, the differential pressure setting according to the present invention therefore is being adjusted according to a differential pressure setting algorithm over the main flow controller 10a. In particular, it is directed to find a setpoint differential pressure for the differential pressure regulation unit 3 as it is being regulated according to a differential pressure setting signal related to the setpoint, to maintain this pressure difference independent of static disturbances of the supply network connected by the primary side lines 6, 7.

The algorithm manipulates several components 3, 10a of, e.g., the substation 12 to reach nominal flow through the main flow controller 10a. The flow can be measured in any suitable manner and by any suitable means, such as by a flow measuring device 13, such as a heat meter or a flow meter, etc., where this could be connected permanently as a part of the substation 12 or heating system 1, or be connected when required. As illustrated in Fig. 1, the flow measuring device 13 may be positioned on the primary side of the heat exchanging unit 2 either on the primary side supply line 6 or on the primary side return line 7.

The basic method includes 130 changing the differential pressure until a flow rate is measured corresponding to a nominal flow rate. The change of differential pressure may be done by changing the differential pressure setting of the differential pressure regulation unit 3.

Fig. 3 illustrates the process, including a first step 100A of setting the main flow controller 10a at a setting, such as to fully open position or another defined setting, before starting to change 130 the differential pressure. Another step 100B includes setting the differential pressure regulation unit 3 to a start setting differential pressure. This could be at the lowest possible setting, at another predefined setting, or could simply be the one present setting at the time of starting the algorithm, or even a measured actual differential pressure if this does not correspond to the setting.

A waiting period, 110, then can be introduced before checking 120A, 120B if respectively the main flow controller 10a and the differential pressure regulation unit 3 is at the requested settings. If not, then wait for another time period 110. In one embodiment a maximum aggregated time period is included, or number of time periods. If something is wrong in the heating system 1, substation 12, the main flow controller 10a, or the differential pressure regulation unit 3, so that the settings may never be obtained, the algorithm will not continue, but halt and possibly indicate an error.

For every change 130 of the differential pressure, the flow rate is measured after a waiting period, dt, in time. The waiting period, dt, in time may be a constant, depend on the differential pressure setting, depend on the difference of the measured flow rate to the nominal flow rate, for example starting with a large waiting period, dt, and then decreasing it as they approach each other.

In one embodiment, the change in differential pressure may be a ramp up at a constant rate. This could be the case if the differential pressure setting (step 100B) was set at the minimum. An alternative could be a ramp down at a constant rate if the differential pressure setting (step 100B) was set at a maximum.

The change in differential pressure may be based on whether the measured flow rate is smaller or larger than the nominal flow rate. For example, if the setting of the differential pressure (step 100B) is chosen according to the setting at the time of starting the algorithm, the change may depend on which is largest of the measured flow rate and the nominal flow rate.

The step of change of differential pressure may also be related to the difference between the measured flow rate and the nominal flow rate.

The differential pressure signal may be communicated by a remote controller 5 communicating with the setting actuator 3c. When the measured flow rate 140 corresponds to the nominal flow rate the present setting is set as the system setting differential pressure, and the algorithm is stopped 150. The heating system 1 is returned to normal operation of the heating system 1.

The new system setting differential pressure may be stored in the controller 5 and/or the setting actuator 3c.

The algorithm may be started with the input of the operational data 200, including, e.g., the present differential pressure and the present setting differential pressure.

The algorithm may be processed by the controller 5, or possibly in the setting actuator 3c, each comprising the required means, such as a processor and memory.

References

1 - Heating system

2 - Heat exchanging unit

3 - Pressure regulation unit

3a - Adjustable pressure response actuator

3b - Adjustable biasing means

3c - Setting Actuator

4 - Heat consuming device

5 - Controller

6 - Primary side supply line

7 - Primary side return line

8 - Secondary side supply line

9 - Secondary side return line

10 - Flow controllers

10a - Main flow controller

10b - Valve

11 - Temperature sensors

12 - Substation

13 - Flow measuring device

100A - Setting the main flow controller 10a at the fully open position before starting to ramp up the differential pressure

100B - Setting the pressure regulation unit 3 to be set at a start setting differential pressure. 110 - Waiting a time period

120A - Check if the main flow controller 10a is at the requested settings

120B - Check if the differential regulating unit 3 is at the requested settings 130 - Change of differential pressure

140 - When the measured flow rate corresponds to the nominal flow rate the present setting is set as the system differential pressure

150 - Exit of algorithm and return to normal operation of the heating system 1 200 - Operational data

Tn - Primary side supply temperature

T12 - Primary side return temperature

T21 - Secondary side return temperature

T22 - Secondary side supply temperature