Hydronic system and method for operating such hydronic system

Abstract

A hydronic system (HS) that comprises at least one hydronic circuit (HC) and a control (CT) for controlling the operation of said at least one hydronic circuit (HC) via a control path (CP), whereby said control (CT) comprises a feed forward controller (FFC). Operation of the system is improved by the hydronic system (HS) further comprising a control improvement path (CIP) running from the at least one hydronic circuit (HC) to the control (CT). Due to the control improvement path (CIP), the control (CT) can be improved in the case of the hydronic system (HS) becoming instable and/or showing poor system control.

Claims

1. A hydronic system (HS) comprising: at least one hydronic circuit (HC; 10; 20), a control (CT) for controlling the operation of said at least one hydronic circuit (HC; 10; 20) via a control path (CP) that communicates an exchange of control signals and operating parameters, whereby said control (CT) comprises a feed forward controller (FFC; 23) and an alternative controller (AC), and a control improvement path (CIP) running from said at least one hydronic circuit (HC; 10; 20) to said control (CT), wherein said alternative controller (AC) can replace the feed forward controller (FFC) and the feed forward controller (FFC) can replace the alternative controller (AC), whereby said control (CT) can be improved in the case of said hydronic system (HS) becoming instable and/or showing poor system control.

2. The hydronic system as claimed in claim 1, characterized in that said at least one hydronic circuit (10) comprises a control valve (12) as a variable flow resistance and a static flow resistance (13), which are connected in series by a piping (19, 19), whereby said control valve (12) is controlled by a valve control device (14), in that a flow sensor (18) is provided for measuring the flow () of a fluid flowing through said circuit, and in that a valve authority determining device (16) is associated with said hydronic circuit (10), whereby said valve authority determining device (16) is connected to said valve control device (14) in order to receive information about the actual opening position of said control valve (12), and whereby said valve authority determining device (16) is further connected to said flow sensor (18) in order to receive information about the actual fluid flow () flowing through said circuit.

3. The hydronic system as claimed in claim 2, characterized in that a storage (15) is associated with said valve authority determining device (16), which storage (15) contains and provides said valve authority determining device (16) with, information on a valve characteristic of said control valve (12).

4. The hydronic system as claimed in claim 2, characterized in that an outlet of said valve authority determining device (16) is connected to said feed forward controller (FFC).

5. The hydronic system as claimed in claim 1, characterized in that a frequency detector (31) for detecting oscillations is provided in said hydronic system, and that said frequency detector (31) is in operative connection with said control (CT).

6. The hydronic system as claimed in claim 5, characterized in that said control (CT) comprises oscillation suppressing means (32, 33, 35), and that said frequency detector (31) is in operative connection with said oscillation suppressing means (32, 33, 35).

7. The hydronic system as claimed in claim 6, characterized in that said feed forward controller (FFC) comprises a physical model (27) of said hydronic circuit, and that said oscillation suppressing means (32, 33, 35) has an effect on input and/or output signals of said physical model (27).

8. The hydronic system as claimed in claim 6, characterized in that said oscillation suppressing means comprises at least one filter (32, 33).

9. A method for operating a hydronic system according to claim 5, comprising the steps of: a. monitoring a flow through said hydronic system and/or a set point signal (F.sub.sv, PS.sub.sv) by means of said frequency detector (31); b. acting on said control (CT), when an oscillation is detected by said frequency detector.

10. The method as claimed in claim 9, characterized in that oscillation suppressing means (32, 33, 35) are activated in said control (CT), when an oscillation is detected by said frequency detector (31).

11. The method as claimed in claim 9, characterized in that said feed forward controller (FFC) is replaced by an alternative controller (AC), when an oscillation is detected by said frequency detector (31).

12. A hydronic system (HS) comprising: at least one hydronic circuit (HC; 10; 20); a control (CT) for controlling the operation of said at least one hydronic circuit (HC; 10; 20) via a control path (CP), whereby said control (CT) comprises a feed forward controller (FFC; 23); and a control improvement path (CIP) running from said at least one hydronic circuit (HC; 10; 20) to said control (CT), by means of which control improvement path (CIP) said control (CT) can be improved in the case of said hydronic system (HS) becoming instable and/or showing poor system control, wherein a frequency detector (31) for detecting oscillations is provided in said hydronic system, said frequency detector (31) being in operative connection with said control (CT), wherein said control (CT) comprises an alternative controller (AT), and wherein said frequency detector (31) is in operative connection with switching means for switching between said feed forward controller (FFC) and said alternative controller (AC).

13. A method for operating a hydronic system according to claim 12, comprising the steps of: a. monitoring a flow through said hydronic system and/or a set point signal (F.sub.sv, PS.sub.sv) by means of said frequency detector (31); b. replacing said alternative controller (AC) by said feed forward controller (FFC), when an oscillation is detected by said frequency detector (31).

14. The hydronic system as claimed in claim 12, wherein switching between the feed forward controller (FFC; 23) and the alternative controller (AC) is done by a selector switch (34).

15. A method for operating a hydronic system (HS), the hydronic system comprising at least one hydronic circuit (HC; 10; 20) and a control (CT) for controlling the operation of said at least one hydronic circuit (HC; 10; 20) via a control path (CP), whereby said control (CT) comprises a feed forward controller (FFC; 23), and a control improvement path (CIP) running from said at least one hydronic circuit (HC; 10; 20) to said control (CT), by means of which control improvement path (CIP) said control (CT) can be improved in the case of said hydronic system (HS) becoming instable and/or showing poor system control, wherein said at least one hydronic circuit (10) comprises a control valve (12) as a variable flow resistance and a static flow resistance (13), which are connected in series by a piping (19, 19), whereby said control valve (12) is controlled by a valve control device (14), in that a flow sensor (18) is provided for measuring the flow () of a fluid flowing through said circuit, and wherein a valve authority determining device (16) is associated with said hydronic circuit (10), whereby said valve authority determining device (16) is connected to said valve control device (14) in order to receive information about the actual opening position of said control valve (12), and whereby said valve authority determining device (16) is further connected to said flow sensor (18) in order to receive information about the actual fluid flow () flowing through said circuit, said method comprising the steps of a. providing a valve characteristic of said control valve (12), which comprises the dependency of the flow coefficient (kv) of said valve on the opening position of said valve; b. moving said control valve (12) into a first opening position having a first flow coefficient (kv.sub.valve,1); c. measuring the flow (.sub.1) of said circulating fluid through said control valve (12) in said first opening position; d. moving said control valve (12) into a second opening position having a second flow coefficient (kv.sub.valve,2); e. measuring the flow (.sub.2) of said circulating fluid through said control valve (12) in said second opening position; f. determining from said measured flows (.sub.1, .sub.2) and the respective flow coefficients (kv.sub.valve,1, kv.sub.valve,2) the valve authority (N) using the formula $N=\frac{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2}{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2+{\left({\mathrm{kvs}}_{\mathrm{valve}}\right)}^2}\mathrm{with}{\mathrm{kv}}_{\mathrm{circuit}}=\sqrt{\frac{\left({}_2^2-{}_1^2\right)}{\frac{{}_1^2}{{\mathrm{kv}}_{\mathrm{valve},1}^2}-\frac{{}_2^2}{{\mathrm{kv}}_{\mathrm{valve},2}^2}}}$ and kvs.sub.valve being the flow coefficient of the fully opened valve.

16. The method as claimed in claim 15, characterized in that said valve authority (N) is determined at predetermined times during the lifetime of said hydronic system (10).

17. The method as claimed in claim 16, characterized in that said valve authority (N) is determined during a commissioning of said hydronic system (10).

18. The method as claimed in claim 17, characterized in that said valve authority (N) is determined at least a second time during the lifetime of said hydronic system (10).

19. The method as claimed in claim 16, characterized in that said valve control device (14) comprises a feed-forward part (23), and that said determined valve authority (N) is used as a parameter in said feed-forward part (23) of said valve control device (14).

20. A method for operating a hydronic system (HS), the system comprising at least one hydronic circuit (HC; 10; 20) and a control (CT) for controlling the operation of said at least one hydronic circuit (HC; 10; 20) via a control path (CP), whereby said control (CT) comprises a feed forward controller (FFC; 23), and a control improvement path (CIP) running from said at least one hydronic circuit (HC; 10; 20) to said control (CT), by means of which control improvement path (CIP) said control (CT) can be improved in the case of said hydronic system (HS) becoming instable and/or showing poor system control, wherein said at least one hydronic circuit (10) comprises a control valve (12) as a variable flow resistance and a static flow resistance (13), which are connected in series by a piping (19, 19), whereby said control valve (12) is controlled by a valve control device (14), in that a flow sensor (18) is provided for measuring the flow () of a fluid flowing through said circuit, and wherein a valve authority determining device (16) is associated with said hydronic circuit (10), whereby said valve authority determining device (16) is connected to said valve control device (14) in order to receive information about the actual opening position of said control valve (12), and whereby said valve authority determining device (16) is further connected to said flow sensor (18) in order to receive information about the actual fluid flow () flowing through said circuit, said method comprising the steps of: a. providing a shape of a valve characteristic of said control valve (12), which comprises the principal dependency of the flow coefficient (kv) of said valve on the opening position of said valve; b. moving said control valve (12) into a first opening position; c. measuring the flow (.sub.1) of said circulating fluid through said control valve (12) in said first opening position; d. moving said control valve (12) into a second opening position different from said first position; e. measuring the flow (.sub.2) of said circulating fluid through said control valve (12) in said second opening position; f. moving said control valve (12) into a third opening position different from said first and second opening position; g. measuring the flow (.sub.3) of said circulating fluid through said control valve (12) in said third opening position; h. determining from the three measured flows (.sub.1, .sub.2, .sub.3) the flow coefficients of the circuit, kv.sub.circuit, and the fully opened control valve (12), kvs.sub.valve; and i. determining the valve authority (N) of said control valve (12) using the formula $N=\frac{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2}{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2+{\left({\mathrm{kvs}}_{\mathrm{valve}}\right)}^2}.$

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows in a generalized configuration a hydronic system according to an embodiment of the invention comprising a hydronic circuit and a control interacting by means of a control path and a control improvement path;

(3) FIG. 2 shows a basic hydronic circuit comprising a pump, a control valve and a heat exchanger;

(4) FIG. 3 shows a learning hydronic system according to an embodiment of the invention based on the circuit of FIG. 2 and further comprising control means capable of reacting to changes of certain parameters of the hydronic circuit by valve authority learning;

(5) FIG. 4 shows a diagram related to a first method of authority learning used in the present invention;

(6) FIG. 5 shows a diagram related to a second method of authority learning used in the present invention;

(7) FIG. 6 shows a learning hydronic system according to another embodiment of the invention;

(8) FIG. 7 shows a feed forward control scheme, which may be used to implement the valve authority learning method according to the present application;

(9) FIG. 8 shows a modified feed forward control scheme, which may be used to suppress unwanted oscillations of the system; and

(10) FIG. 9 shows another way of dealing with unwanted oscillations of the system by switching between different controllers.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

(11) FIG. 1 shows in a generalized configuration a hydronic system HS according to an embodiment of the invention. Hydronic system HS comprises a hydronic circuit HC, which is usually associated with a building and includes piping, valves, heat exchangers, pumps, and the like, and a control CT interacting by means of a control path CP and a control improvement path CIP. Control path CP is related to the communication between control CT and hydronic circuit, and is the path for exchanging control signals from control CT to hydronic circuit HC, and operating parameters from hydronic circuit HC to control CT. Control CT comprises a feed forward controller FFC, which contains a physical model of hydronic circuit HC. Control CT may further comprise an alternative controller AC, which may replace feed forward controller FFC, and vice versa. The switching between the two controllers FFC and AC is symbolized in FIG. 1 by a selector switch.

(12) An improvement of the control may be achieved in different ways, depending on the situation in the hydronic circuit: During commissioning of the system it may be necessary and/or advantageous to adapt the control CT to certain parameters of the system, which were unknown prior to commissioning. Operation of the system for a longer time may result in a change of important system parameters and/or a degradation, which may lead to poor system control and instability.

(13) There are especially two cases, which are of concern with regard to the controllability of the hydronic system: 1) As long as control valves are part of the hydronic circuit, the so-called valve authority is an important parameter: Poor valve authority leads to poor system control and instability 2) Sometimes hydronic systems are prone to undesirable oscillations, so-called hunting: Hunting signals, too, lead to poor system control and instability.

(14) According to the invention, negative implications of a change of valve authority over time or an insufficient knowledge of the actual valve authority will be avoided by a respective improvement of the control.

(15) As has been already described in the introductory part FIG. 2 shows a hydronic system 20 in its most general form, which comprises in a closed circuit a pump 11, a two-port control valve 12 and a terminal unit, in this case a heat exchanger 13. Pump 11, control valve 12 and terminal unit 13 are connected in series. When pump 11 pumps the fluid through the circuit with a certain pressure, there are pressure drops p in the various sections of the system. These pressure drops or differential pressures can be divided into a first differential pressure p.sub.valve at the control valve 12 and a second differential pressure p.sub.circuit at the rest of the circuit.

(16) In such a circuit the valve authority N is the pressure drop across the fully open valve in relation to the pressure drop across the whole system. Valve authority N, which is defined by equations (1) to (4) above, indicates how good the hydronic system is controllable (the higher the valve authority N, the better the hydronic system can be controlled). However, valve authority N is not a parameter, which is constant through the lifetime of the system. When valve authority N changes as a result of changes in the system, it will be advantageous to have a valve authority learning capability of the system in order to adapt the control mechanism of the system to the changing system environment.

(17) The present invention deals with such valve authority learning.

(18) Within the scope of the present invention at least two different procedures of valve authority learning are possible. Both of them include active measurements at the valve in the hydraulic circuit, meaning the valve is actively moved between different valve positions.

(19) A first of these at least two different procedures is chosen, when the whole valve characteristic is known. In this case the curve kv vs. valve position shown in FIG. 4(a) is known. Further, as a primary assumption, there shall be a constant pressure across the relevant zone of the system.

(20) To evaluate the actual valve authority of control valve 12, the valve is moved to two different positions. These positions are in FIG. 4 characterized through two respective kv-values, namely kv.sub.valve,1(for position 1) and kv.sub.valve,2(for position 2). In each of these two positions the related flow is measured (FIG. 4(b)) and stored together with its associated kv-value, thus giving pairs of values .sub.1, kv.sub.valve,1 and .sub.2, kv.sub.valve,2.

(21) Based on these pairs of values, the actual valve authority N can be calculated by means of the following formulas:

(22) $\begin{array}{cc}N=\frac{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2}{{\left({\mathrm{kv}}_{\mathrm{circuit}}\right)}^2+{\left({\mathrm{kvs}}_{\mathrm{valve}}\right)}^2}& \left(5\right)\\ {\mathrm{kv}}_{\mathrm{circuit}}=\sqrt{\frac{\left({}_2^2-{}_1^2\right)}{\frac{{}_1^2}{{\mathrm{kv}}_{\mathrm{valve},1}^2}-\frac{{}_2^2}{{\mathrm{kv}}_{\mathrm{valve},2}^2}}}& \left(6\right)\end{array}$

(23) A second of these at least two different procedures is chosen, when only the shape of the valve characteristic is known, but no scaling is available. In this case the curve kv vs. valve position (shown in FIG. 5(a)) is a function F(kvs, n.sub.gl) of the value kvs and a parameter n.sub.gl, which is a measure of how sharply the characteristic curve is curved. For example, when the curve represents a valve with an equal percentage characteristic, n.sub.gl=3. Curves with other values of n.sub.gl are shown in FIG. 5(a) with dash and dot-and-dash lines.

(24) Again, as a primary assumption, there shall be a constant pressure across the relevant zone of the system.

(25) Now, the valve is moved to three (different) positions (FIG. 5(b)). The respective flows .sub.1, .sub.2 and .sub.3 are measured at these positions and stored.

(26) Finally, an equation system with 3 unknowns kv.sub.circuit, kvs.sub.valve and p can be solved using the stored flows.

(27) To move control valve 12 into the different positions and measure the respective flow circulating through piping 19 and said valve a valve control device 14 and a flow sensor 18 are provided in a hydronic system 10 in accordance with FIG. 3. Both devices are connected to a valve authority determining device 16, which controls the measuring action of control valve 12 and flow sensor 18. Storage 15 may be used to store certain parameters of the valve characteristic, which are necessary for a valve authority calculation, as explained above. The valve authority measured and calculated by valve authority determining device 16 from time to time may be transferred to a valve authority using unit 17, as indicated. Valve authority unit 17 then may control valve control device 14, accordingly.

(28) Valve authority N may be determined at predetermined times during the lifetime of hydronic system 10. Furthermore, valve authority N may be determined during a commissioning of hydronic system 10, and, preferably, at least a second time during the lifetime of said hydronic system.

(29) As valve control device 14 comprises (besides a possible feedback) a feed-forward part 23, as shown in FIG. 6, said determined valve authority N may be used as a parameter in feed-forward part 23 of valve control device 14.

(30) Hydronic circuit 10, as shown in FIG. 6, may be a simple circuit with a pump 11, a control valve 12 and a heat exchanger 13. However, there may be further circuit elements 21 and branches comprising further piping 19 and circuit elements 22.

(31) Finally, the arrangement of control valve 12, valve control device (or actuator) 14, flow sensor 18 and valve authority determining device 16 and storage 15 may be combined in one unit, which is known as energy valve EV (see for example EP 2 896 899 A1).

(32) FIG. 7 shows a feed forward control scheme, which may be used to implement the valve authority learning strategy explained so far. Central part of forward control scheme 24 of FIG. 7 is a physical model 27 of the hydronic system in question. When a flow set value F.sub.sv is given, the physical model 27 generates a feed forward position set value PS.sub.Fsv by using flow set value F.sub.sv, the measured actual flow, F, valve authority 28 and other input parameters 29, e.g. the valve characteristic. Added to said feed forward position set value PS.sub.Fsv is a deviation of valve position set value, PS.sub.sv, which is determined by deviation part 30 from the difference between flow set value F.sub.sv and measured actual flow F. Deviation part 30 comes up for small deviations due to a mismatch of physical model 27 and reality. The sum of PS.sub.Fsv and PS.sub.sv is finally used as valve position set value PS.sub.sv for controlling the controlled system flow 25. The resulting actual flow F is measured by flow sensor 26.

(33) The valve authority 28 put into the physical model 27 is the valve authority determined by the methods explained above. In this way the feed forward control can react to changes of this relevant system parameter in order to improve system control and stability.

(34) However, as already mentioned above, other characteristics of the system than valve authority may trigger an action on the feed forward control scheme. For example, document WO 2006/105677 A2 discloses a method and a device for suppressing vibrations in an installation comprising an actuator for actuating a flap or a valve used for metering a gas or liquid volume flow, especially in the area of HVAC, fire protection, or smoke protection. Vibrations of the flap or valve caused by an unfavorable or wrong adjustment or configuration of the controller and/or by disruptive influences are detected and dampened or suppressed by means of an algorithm that is stored in a microprocessor. Said algorithm is preferably based on the components recognition of vibrations, adaptive filtering, and recognition of sudden load variations.

(35) Specifically, according to the document, a regulating variable from the regulating path is provided, whereby said regulating variable corresponding to the effective liquid volume flow. Further, a predefined control signal corresponding to the required liquid volume flow is provided. The predefined control signal and the regulating variable are compared and a regulator output variable is calculated therefrom. The regulator output variable is monitored by a vibration detection algorithm. If the vibration detection algorithm does not detect vibrations of the regulator output variable, the regulator output variable is fed to an actuating device which is actuating a flap or a valve in the pipe for dosing the gas or liquid volume flow. If, on the other hand, the vibration detection algorithm detects vibrations of the regulator output variable, the regulator output variable is fed to an adaptive filter and the adaptive filter suppresses the vibration and generates a control signal with suppressed or damped vibrations of the regulator output variable, which is then used at the actuating device instead of the regulator output variable.

(36) In the present case of a feed forward control scheme the situation is different: As shown in FIG. 8, a modified feed forward control scheme 24a may be used to suppress unwanted oscillations of the system. To detect unwanted oscillations of the system, a frequency detector 31 may be connected to flow sensor 26. When frequency detector 31 detects unwanted oscillations in the system, appropriate input or output signals of the physical model 27 will be compensated or filtered (e.g. with lead or lag filters or a combination thereof). As an example, FIG. 8 shows two filters 32 and 33 (dashed lines) at the input of the flow set value F.sub.sv and the output of floe signal F of flow sensor 26. A further filtering means 35 may be used to filter the valve position set value (PS.sub.sv). Other locations of filtering and/or compensating are possible.

(37) In addition, setpoint signals flow set value F.sub.sv and/or position set value PS.sub.sv may be monitored by frequency detector 31.

(38) Another way of dealing with unwanted oscillations of the system is shown in FIG. 9: When unwanted oscillations are detected by frequency detector 31 of feed forward control scheme 24b, it actuates a disabling means 34 (e.g. a switch) to shut down the actual feed forward control and replace it with an alternative, more suitable and oscillation-free controller AC. The switching may be reversed in other situations, so that the system switches from an alternative controller AC to a feed forward controller to improve stability and control.

LIST OF REFERENCE NUMERALS

(39) 10, 20 hydronic circuit 11 pump 12 control valve 13 heat exchanger 14 valve control device (or actuator) 15 storage 16 valve authority determining device 17 valve authority using unit 18 flow sensor 19, 19 piping 21,22 circuit element 23 feed-forward part (valve control device) 24 feed forward control scheme 24a,b feed forward control scheme 25 controlled system flow 26 flow sensor 27 physical model 28 valve authority 29 other input parameters (e.g. valve characteristic) 30 deviation part 31 frequency detector 32, 33 filter 34 disabling means (e.g. switch) 35 filtering means AC alternative controller CIP control improvement path CP control path CT control EV energy valve F flow F.sub.sv flow set value FFC feed forward controller HC hydronic circuit HS hydronic system PS.sub.sv deviation of valve position set value PS.sub.sv valve position set value PS.sub.Fsv feed forward valve position set value kv.sub.valve flow coefficent of control valve flow through control valve p.sub.valve pressure drop at control valve p.sub.circuit pressure drop at circuit outside control valve .diamond-solid.