A HVAC field device, HVAC system, method of operating an HVAC field device and a computer program product for regulating a differential pressure of a network section of a fluid transportation network

Abstract

A HVAC field device (10) for regulating a differential pressure (∆psection) of a network section (F) comprising a valve (PR), an actuator (12) drivingly connected to the valve (PR) and a controller (20). The controller (20) configured to receive a differential pressure (∆psection) between a supply side (LS) and a return side (LR) of the network section (F) and to receive a flow rate (Q) of the fluid through the valve (PR). The controller (20) is further configured to determine a flow coefficient (kv, section) of the network section (F) using the differential pressure (∆psection) and the flow rate (Q). The controller (20) is configured to control the actuator (12) to drive the valve (PR) to regulate the differential pressure (∆psection) using: the flow co-efficient (kv, section); the differential pressure (∆psection); a flow characteristic (kv,valve(u)) of the 10 valve (PR); and a differential pressure setpoint (∆psetp).

Description

[0001] A HVAC FIELD DEVICE, HVAC SYSTEM, METHOD OF OPERATING AN HVAC FIELD DEVICE AND A COMPUTER PROGRAM PRODUCT FOR REGULATING A DIFFERENTIAL PRESSURE OF A NETWORK SECTION OF A FLUID TRANSPORTATION NETWORK

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to a HVAC field device, a HVAC system, a method of operating an HVAC field device and a computer program product. Specifically, the present disclosure relates to a HVAC field device, a HVAC system, a method of operating an HVAC field device and a computer program product for regulating a differential pressure of a network section of a fluid transportation network.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] In the field of Heating, Ventilation and Air Conditioning, HVAC systems typically comprise a fluid transportation network comprising thermal energy exchanger(s) arranged such as to be able to transfer thermal energy to I extract thermal energy from the environment to be controlled (referred to hereafter as controlled environment) by means of a fluid circulating in said fluid transportation network. By regulating the flow of fluid through a thermal energy exchanger of an HVAC system, it is possible to adjust the amount of energy (respectively the amount of energy per unit of time, power) transferred by the thermal energy exchanger. For example, the energy exchange or the power transfer, correspondingly, is adjusted by regulating the amount of energy delivered to / extracted from the thermal energy exchanger to heat or cool a room in a building, or by regulating the amount of energy delivered to a chiller for cooling purposes. While the fluid transport through the fluid transportation circuit of the HVAC system is driven by one or more pumps or fans, the flow is typically regulated by varying the orifice (opening) or position of valves. In order to be able to regulate the flow of fluid to / from the thermal energy exchanger and hence the amount of thermal energy transferred, thermal energy exchanger(s) are connected to the fluid transportation network via one or more flow regulating devices such as valves and dampers. The regulating devices are mechanically controlled by HVAC field devices, in particular actuators, including motorized HVAC actuators coupled to the regulating device(s). In the field of HVAC, HVAC actuators typically comprise an electric motor, drivingly coupled (through gears and / or other mechanical coupling), to the actuated part, i.e. the regulating device. HVAC actuators are electrically controlled by HVAC controllers, in particular an electronic circuit thereof. In addition, various sensors are used to measure environmental variables such as humidity, temperature, CO2 or dust particle levels. Furthermore, HVAC sensors are used to determine operational parameters of various elements of an HVAC system, such as an actuated position of an actuated part, the operational state of an HVAC actuator.

[0006] Fluid transport networks often comprise one or more network sections, each network section being connected to a fluid transportation circuit through respective supply line(s) and return line(s). Due to different characteristics of the consumers of the different sections of fluid transportation network and / or of the flow regulating devices in the various zones, there are different requirements of operational parameters to be met for one or more of the network sections. A common requirement to be met within a network section of a fluid transportation network is the differential pressure being maintained within a specified differential pressure range. The specified differential pressure range to be maintained is defined by an operational range of the regulating device(s), the thermal energy consumer and / or any other element within the respective parallel zone, in particular an optimal operational range. For example, pressure invariant regulating valves have a specific pressure range within which they are capable of maintaining a specified flowrate irrespective of the fluid pressure. Hence, optimally, the fluid pressure in a parallel zone comprising such a pressure invariant regulating valve is to be maintained within the specific pressure range within which they are capable of maintaining a specified flowrate irrespective of the fluid pressure. Alternatively, or additionally, various com- ponents of a fluid transportation network have specific operational pressure ranges, or optimal operational pressure ranges, these ranges being determined such as to avoid the turbulences leading to excessive noise and / or wear, such as turbulences due to cavitation of the fluid. For example, cooling systems of datacenters comprise a multitude of heat exchangers (such as cool plates) hydraulically connected to a fluid transportation network having a plurality of network sections, the heat exchangers being arranged in thermal connection with computer chips. Since the number and / or arrangement and / or load of such computer chips in a datacenter is highly dynamic, there is a yet unmet need for maintaining the differential pressure of sections of such fluid transportation networks within prescribed operational ranges irrespective of addition, removal and / or reconfiguration of the heat exchangers (leading to changing flow characteristics of the fluid transportation network).

[0007] Conventional approaches typically employ linear controllers, such as Proportional-lntegral- Derivative (PID) controllers, to manage the differential pressure within network sections. However, these systems' nonlinear nature poses a substantial challenge, as linear controllers often fail to provide consistent control performance across a non-linear system's entire operating range. This inconsistency is primarily due to the nonlinearity of the network section and the variation of the non-linearity, which changes not only from one installation to another but also during operation, further complicating the control process.

[0008] A particular challenge arises in accurately controlling the differential pressure within a network section, given the unknown and time-variant flow coefficient of the network section, which is influenced by fluctuations, disturbances, and non-linearities that occur when valves within the zone open or close.

[0009] Moreover, existing differential pressure controllers may not function effectively under certain conditions, such as following initialization when all valves in a network section are closed, when a pump is switched off, or other scenarios where the system's flow controller does not operate as intended. SUMMARY OF THE DISCLOSURE

[0010] It is an object of this disclosure to provide an HVAC field device, a computer implemented method of operating an HVAC field device, a computer program product, and a system for regulating a differential pressure in a network section of a fluid transportation network which do not have at least some of the shortcomings, limitations and / or disadvantages of the prior art.

[0011] In particular, it is an object of this disclosure to provide an HVAC field device, a computer implemented method of operating an HVAC field device, a computer program product, and a system for regulating a differential pressure in a network section of a fluid transportation network which can adapt to a specific nonlinearity of the controlled system related to a position of the valve controlling the differential pressure in a network section to the differential pressure of the network section as controlled value, provide consistent performance across all operating conditions, and accurately account for variations of the flow coefficient of the controlled network section.

[0012] According to the present disclosure, these objects are addressed by the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description.

[0013] According to the present disclosure, the above-mentioned objects are particularly achieved by a HVAC field device for regulating a differential pressure of a network section of a fluid transportation network. The fluid transportation network may be a fluid transportation network of a Heating, Ventilation, and Air Conditioning system for influencing ambient conditions, such as a ambient temperature and / or humidity and / or air quality. Alternatively, the fluid transportation network may be part of a fluid transportation network of an industrial heating or cooling installation, such as a cooling system of a data center or other industrial installation. The HVAC field device comprises a valve, in particular a ball valve, and an actuator drivingly connected to the valve. The HVAC field device further comprises a controller configured to receive signals indicative of a differential pressure between a supply side and a return side of the network section. According to embodiments, the controller is configured to receive signals indicative of a differential pressure from a differential pressure sensor and / or an interface for communicatively connecting a differential pressure sensor.

[0014] The controller is configured to receive signals indicative of a flow rate of the fluid through the valve. According to embodiments, controller configured to receive signals indicative of a flow rate from a flow sensor and / or an interface for communicatively connecting a flow sensor.

[0015] The controller is configured to determine a flow coefficient of the network section using the differential pressure and the flow rate. The controller is configured to control, in a differential pressure regulating mode, the actuator to drive the valve to valve position(s) to regulate the differential pressure. The control is using the flow coefficient of the network section, the differential pressure and flow characteristic of the valve as a function of valve positions of the valve and a differential pressure setpoint.

[0016] In particular use cases, the flow coefficient of the network section may vary overtime, due to opening or closing of valves in a network section and also due to the addition or removal of a branch in the section (e.g. installing a cooling module in a data center). According to a particular embodiment, in order to be able to adapt to such changing environments, the controller is configured to determine the flow coefficient of the network section using the differential pressure and the flow rate repeatedly during operation, continuously, at set time intervals, upon occurrence of set events (e.g. start-up, restart, power failure, flow rate fluctuations, etc.).

[0017] According to an embodiment, the controller is further configured to determine - using a parameter estimator - a branch differential pressure between a supply side of the network section and an output side of the valve or between an input side of the valve and a return side of the network section. This determination uses the flow characteristic of the valve, the flow rate, the differential pressure, and an actual position of the valve.

[0018] According to an embodiment, the controller is configured to control the actuator further using a flow coefficient of a flow sensor generating the sensor signal indicative of the flow rate of the fluid through the valve.

[0019] According to an embodiment, referred to as inversion-based control, the controller is further configured to compensate a non-linearity N(u) of a relationship between valve positions of the valve and values of the differential pressure. According to an embodiment, the compensation is using an inverse W-1(u) of an approximation N(u) of the non-linearity N u), (whereby N(u) denotes an approximation, a model of N), and a parameter estimator (configured to estimate the branch differential pressure and the flow coefficient of the network section), particularly an observer structure using a state estimator, a Least Squares estimator, or a machine learning algorithm, whereby:

[0020] According to an embodiment, referred to as inversion-based feedforward control, the controller is further configured to preemptively counteract the non-linearity / V(u) (of the relationship between valve positions of the valve and values of the differential pressure) using a feedforward component based on an inverse W-1(u) of an approximation / V(u) of the nonlinearity / V(u) and a parameter estimator (configured to estimate the branch differential pressure and the flow coefficient of the network section), particularly an observer structure using a state estimator, a Least Squares estimator, or a machine learning algorithm, particularly an observer structure using a state estimator, a Least Squares estimator, or a machine learning algorithm. It shall be noted that this approach based on feedforward control can be combined with any feedback-based control. According to embodiments, the parameter estimator comprises a model of the network section. In particular, the model of the network section comprising an estimation of the relationship between valve positions of the valve and values of the differential pressure. According to embodiments, linear time-invariant dynamics are also considered in the feedforward controller. Feedforward control is advantageous since changes in the system (e.g. due to disturbances), such as changes of the flow coefficient of the network section and / or of the differential pressure, are compensated faster than with a pure feedback controller. Furthermore, changes in the differential pressure setpoint are also tracked faster.

[0021] According to an embodiment, referred to as gain-scheduling control, the controller is further configured to compensate variations of a local gain (across the operating range) due to a non-linearity N(u) of a relationship between valve positions of the valve and values of the differential pressure and / or due to disturbances impacting the local gain. This compensation uses in particular a reciprocal of a local derivative / V'(u) of an approximation N u) of the non-linearity N(u) and a parameter estimator (configured to estimate the flow coefficient of the network section), particularly an observer structure using a parameter estimator, a Least Squares estimator, or a machine learning algorithm, whereby

[0022] According to an embodiment, referred to as gain-scheduling control with inversion-based feedforward control, the controller is configured to: compensate, in a process referred to as gain-scheduling, variations of a local gain due to a non-linearity N(u) of a relationship between valve positions of the valve and values of the differential pressure. This compensation uses in particular a reciprocal of a local derivative N'(u) of an approximation N(u) of the non-linearity N(u) and a parameter estimator (configured to estimate the flow coefficient of the network section), particularly an observer structure using a state estimator, a Least Squares estimator, or a machine learning algorithm; and preemptively counteract the non-linearity N(u) (of the relationship between valve positions of the valve and values of the differential pressure) using a feedforward component based on an inverse / V-1(u) of an approximation N(u) of the non-linearity N(u) and a parameter estimator (configured to estimate the branch differential pressure and the flow coefficient of the network section), particularly an observer structure using a parameter estimator, a Least Squares estimator, or a machine learning algorithm), particularly an observer structure using a parameter estimator, a Least Squares estimator, or a machine learning algorithm.

[0023] The Gain-Scheduling control combined with Inversion-Based Feedforward Control is a powerful technique for handling non-linearities, leveraging the strengths of each approach to provide robust control of the non-linear system. This embodiment is advantageous as it dynamically adjusts the controller gain based on the current operating conditions and uses feedforward control to preemptively counteract the effects of non-linearities.

[0024] In order to account for limitations of the actuator (electro-mechanical and / or limitations set by configuration) and / or the mechanical connection between the actuator and valve, according to embodiments, the controller is configured to consider actuator dynamics when controlling the actuator, in particular to consider a limitation of the rate of change the actuator can exert on the valve. For example, the controller, in controlling the differential pressure, considers the limitation that an actuator has an actuator rate limitation of around 1 second per degree in the rotational displacement of the valve, i.e. it requires around 90 seconds to drive the valve from a full closed to a fully open position.

[0025] According to an embodiment, the controller is configured to determine the flow coefficient of the network section and / or branch and / or the flow characteristic of the valve using and a parameter estimator, particularly an observer structure using a state estimator, a Least Squares estimator, or a machine learning algorithm.

[0026] According to an embodiment, the controller is further configured to control the actuator in one or more of the following alternative operating modes: a valve position regulating mode comprising a start-up position regulating mode and / or a freeze position regulating mode, an alternative differential pressure regulating mode, a flow regulating mode, and / or a power regulating mode. The selection is a function of one or more of the flow rate, the differential pressure setpoint, a deviation of the differential pressure from the differential pressure setpoint, the valve position, an event signal, detecting an erroneous flow rate signal, detecting an erroneous differential pressure signal, a condition of an external device such as a pump, and / or a timer signal.

[0027] The power regulating mode is advantageous as it enables an energetic balancing of the entire fluid transportation network, avoiding one network section being supplied with the whole or an over-proportional amount of the available heating I cooling power.

[0028] The flow regulating mode is advantageous as it enables a hydronic balancing of the network section controlled by the control valve.

[0029] According to an embodiment, in the start-up position regulating mode, the controller is configured to control the actuator to drive the valve and maintain a start-up valve position (the start-up valve position is different from a fully sealed valve position of the valve). The startup position regulating mode is switched into in one or more of the following conditions: after the HVAC field device has been restarted; after a power failure; after switching into differential pressure regulating mode, in particular after switching from flow regulating mode and valve position regulating mode; if the differential pressure is below a minimum differential pressure threshold; if the flow rate is below a minimum flow threshold, such as 0.2 % of a nominal flow rate (e.g. when a pump supplying fluid pressure is off); and / or after actuator synchronization.

[0030] The start-up position regulating mode according to embodiments aims at avoiding noise (e.g. whistling sound) or other issues such as damage that would otherwise occur due to overpressure that would arise if the controller would drive the valve to a fully open position (as there would be no measurable pressure differential) instead of the start-up valve position is different from a fully sealed valve position of the valve and the source of fluid pressure, such as a pump would be started.

[0031] When valves within network section(s) are slowly closed more and more, the valve for controlling differential pressure also needs to close more and more to maintain the differential pressure setpoint. However, if the valve for controlling differential pressure would fully close, the flow rate would drop to zero, potentially leading to valves in network section(s) to open again. The measured differential pressure would then be 0 which would lead to the valve for controlling differential pressure to also start opening, which could lead to an oscillating system. Therefore, the valve for controlling differential pressure needs to stop closing before it's actually fully closed but as close to the closing point as possible in order to enable differential pressure control also if only a valve in a network section is demanding a little bit of flow. Hence, according to an embodiment, in the valve position regulating mode, the controller is configured to control the actuator in a freeze position regulating mode, maintaining the valve at its current position, referred to as a freeze position when the flow rate falls below a minimum flow rate threshold, the freeze position being different from a fully closed position. Maintaining the freeze position when the flow rate falls below a minimum flow rate threshold allows controlling the differential pressure in a wider flow rate range. In order to reduce oscillations between the freeze position regulating mode and the differential pressure regulating mode, according to an embodiment, the minimum flow rate threshold is adapted.

[0032] According to an embodiment, the controller is configured to control the actuator to drive the valve to a valve position to regulate the differential pressure in the alternative differential pressure regulating mode upon detecting an erroneous flow rate signal. This alternative differential pressure regulating mode uses a constant flow coefficient of the network section. Alternatively, or additionally, alternative differential pressure regulating mode may implement a feedback-based regulation (e.g. a proportional regulation) using a difference between the differential pressure setpoint and the differential pressure. Alternative, or additionally, in order to avoid fully closing the valve in the absence of a valid flow rate signal, the controller is configured to control the actuator to drive the valve to a valve setpoint position.

[0033] According to an embodiment, the controller is configured to switch from the alternative differential pressure regulating mode to the differential pressure regulating mode upon detection of a valid sensor signal indicative of the flow rate. Optionally, the switch from the alternative differential pressure regulating mode to the differential pressure regulating mode implements a hysteresis to allow sensor signals to stabilize and to avoid the risk of toggling between the operating modes.

[0034] According to an embodiment, the controller is further configured to switch from the start-up position regulating mode to the differential pressure regulating mode if the sectional differential pressure falls below a fraction of the differential pressure setpoint which indicates the zones are significantly opened. This switch also occurs if the flow rate is higher than the absolute minimum flow rate threshold and the differential pressure is less than a fraction of the differential pressure setpoint. Additionally, the controller is further configured to switch from the start-up position regulating mode to the differential pressure regulating mode if the flow rate is higher than a minimal flow rate threshold, which is higher than the absolute minimal flow rate threshold. In other words, the controller is configured to monitor each of the above conditions and switch regulating modes if any one of the conditions are met.

[0035] Advantageously, the minimum flow rate threshold rate is chosen as low as possible, ensuring that the controller switches into the differential pressure regulating mode even at low flow rates in relatively small network sections, hence avoiding whistling sounds that would occur if the pressure drop over the network section is too big due to the dp-control valve which doesn’t create sufficient pressure drop due to the start-up position.

[0036] According to an embodiment, the controller is further configured to switch from the freeze position regulating mode to the differential pressure regulating mode or to the alternative differential pressure regulating mode if the flow rate is higher than a second minimum flow rate threshold. The second minimum flow rate threshold is higher than the minimal flow rate threshold. This switch also occurs if the differential pressure is less than a minimum differential pressure threshold (may be dependent on the setpoint differential pressure), and the flow rate is higher than an absolute minimal flow rate threshold, which is lower than the minimal flow rate threshold. In other words, the controller is configured to monitor each of the above conditions and switch regulating modes if any one of the conditions are met. Advantageously, a hysteresis in flow rate or a time-out is implemented in the controller between entering and leaving freeze position regulating mode, to avoid the system toggling between regulating modes.

[0037] When the controller is in the freeze position regulating mode and there is no pressure from the fluid transportation network (e.g. because the corresponding pump is switched off), in order to enable the system to start-up again, according to an embodiment, the controller is further configured to switch from the freeze position regulating mode to the start-up position regulating mode if the differential pressure setpoint is lower than an absolute minimum differential pressure threshold, e.g. a fraction of the absolute minimum differential pressure threshold. This switch also occurs if the flow rate is lower than the absolute minimum flow rate threshold, and the differential pressure is less than a fraction of the differential pressure setpoint to reduce the time it takes for the flow rate to rise. Otherwise, it could happen, that the flow rate is so low (because the control valve is almost closed), that the flow rate would not exceed the required limit in order to start actually controlling the pressure.

[0038] In cases where the system is in the freeze position regulating mode, but the valve is close to a closed position, e.g. when the pump speed is reduced. In such situation a very high freeze position is to be avoided. Hence, according to an embodiment, the controller is configured to limit the freeze position of the valve to the start-up valve position.

[0039] According to an embodiment, the controller is further configured to control, in the differential pressure regulating mode, the actuator to drive the valve to limit the flow rate to a maximum flow rate. The controller is also configured to limit a rate of thermal energy transfer to a maximum rate of thermal energy transfer. The rate of thermal energy transfer is determined using the flow rate and a signal indicative of a temperature differential between the supply side and return side of the network section. It can also be determined using the flow rate and a defined flow rate to delta-T mapping.

[0040] The present disclosure further relates to an HVAC system. The HVAC system comprises a fluid transportation network comprising a network section. The HVAC system further comprises an HVAC field device according to one of the embodiments disclosed herein. According to a particular embodiment, the valve is a ball valve, enabling a complete closure of the valve, i.e. a complete blockage of fluid flow therethrough. The valve of the HVAC field device is fluidically connected to the supply side orthe return side of the network section. The HVAC system further comprises a differential pressure sensor configured and arranged for measuring a differential pressure between a supply side and a return side of the network section. The HVAC system further comprises a flow sensor configured and arranged for measuring a flow rate of a fluid through the valve.

[0041] According to the present disclosure, the above-mentioned objects are particularly achieved by a method of operating an HVAC field device. In a step, the controller receives signals indicative of a differential pressure between a supply side and a return side of the network section. In a step, the controller receives signals indicative of a flow rate of the fluid through the valve. In a step, the controller determines a flow coefficient of the network section using the differential pressure and the flow rate. In a step, the controller controls, in a differential pressure regulating mode, the actuator to drive the valve to valve position(s) to regulate the differential pressure using the flow coefficient of the network section, the differential pressure, a flow characteristic) of the valve as a function of valve positions of the valve, and a differential pressure setpoint.

[0042] In a step, according to an embodiment of the method, the controller determines a branch differential pressure between a supply side of the network section and an output side of the valve or between an input side of the valve and a return side of the network section using the flow characteristic of the valve, the flow rate, the differential pressure, and an actual position of the valve.

[0043] In a step, according to an embodiment of the method, the controller controls the actuator further using a flow coefficient of a flow sensor generating the sensor signal indicative of the flow rate of the fluid through the valve.

[0044] In a step, according to an embodiment of the method, the controller compensates non-linearity N(u) of a relationship between valve positions of the valve and values of the differential pressure, in particular using an inverse of an approximation N(u) of the non-linearity N(u), whereby:

[0045] According to embodiments where the controller controls the actuator further using a flow coefficient of a flow sensor generating the sensor signal indicative of the flow rate of the fluid through the valve:

[0046] In a step, according to an embodiment of the method, the controller compensates variations of a local gain due to a non-linearity N(u) of a relationship between valve positions of the valve and values of the differential pressure, in particular using a reciprocal of a local derivative N' (u) of an approximation N(u) of the non-linearity N(u), whereby

[0047] According to embodiments where the controller controls the actuator further using a flow coefficient of a flow sensor generating the sensor signal indicative of the flow rate of the fluid through the valve:

[0048] In a step, according to an embodiment of the method, the controller determines the flow coefficient of the network section and / or the flow characteristic) of the valve using one or more of an algorithm using an observer structure, particularly an observer structure using a parameter estimator, a Least Squares estimator, or a machine learning algorithm.

[0049] In a step, according to an embodiment of the method, the controller controls the actuator in one or more of the following alternative operating modes: a valve position regulating mode comprising a start-up position regulating mode and / or a freeze position regulating mode, an alternative differential pressure regulating mode, a flow regulating mode, and / or a power regulating mode. The selection is made as a function of one or more of the flow rate, the differential pressure setpoint, a deviation of the differential pressure from the differential pressure setpoint, an event signal, detecting an erroneous flow rate signal, detecting an erroneous differential pressure signal, a condition of an external device, and / or a timer signal.

[0050] In a step, according to an embodiment of the method, the controller in the start-up position regulating mode, controls the actuator to drive the valve and maintain a start-up valve position. The start-up valve position is different from a fully sealed valve position of the valve after the HVAC field device has been restarted, after a power failure, after switching into differential pressure regulating mode, in particular after switching from flow regulating mode and valve position regulating mode, if the differential pressure is below a minimum differential pressure threshold, and / or if the flow rate is below a minimum flow threshold.

[0051] In a step, according to an embodiment of the method, the controller in the valve position regulating mode, controls the actuator to maintain the valve at a freeze position when the flow rate is below a minimum flow rate threshold.

[0052] In a step, according to an embodiment of the method, the controller controls the actuator in the alternative differential pressure regulating mode upon detecting an erroneous flow rate signal. The actuator is driven to adjust the valve to a valve position to regulate the differential pressure in the alternative differential pressure regulating mode using a constant flow coefficient of the network section, such as an estimated constant flow coefficient.

[0053] In a step, the controller switches from the alternative differential pressure regulating mode to the differential pressure regulating mode upon detection of a valid sensor signal indicative of the flow rate. In a step, according to an embodiment of the method, the controller switches from the startup position regulating mode to the differential pressure regulating mode under several conditions. One condition is if the sectional differential pressure falls below a fraction of the differential pressure setpoint. Another condition is if the flow rate is higher than the minimum flow rate threshold or the differential pressure is less than a fraction of the differential pressure setpoint. A further condition is if the flow rate is higher than an absolute minimal flow rate threshold, which is lower than the minimal flow rate threshold.

[0054] In a step, according to an embodiment of the method, the controller switches from the freeze position regulating mode to the differential pressure regulating mode or to the alternative differential pressure regulating mode if specific criteria are met. The controller switches from the freeze position regulating mode to the differential pressure regulating mode or to the alternative differential pressure regulating mode if the flow rate is higher than a second minimum flow rate threshold, where this second threshold is higher than the minimal flow rate threshold. The switch also occurs if the differential pressure is less than a minimum differential pressure threshold, and the flow rate is higher than an absolute minimal flow rate threshold, which is lower than the minimal flow rate threshold.

[0055] In a step, according to an embodiment of the method, the controller switches from the freeze position regulating mode to the start-up position regulating mode under certain conditions. One condition is if the differential pressure setpoint is lower than an absolute minimum differential pressure threshold. Another alternative condition is if the flow rate is lower than the absolute minimum flow rate threshold, and the differential pressure is less than a fraction of the differential pressure setpoint.

[0056] In a step, according to an embodiment of the method, the controller in the differential pressure regulating mode controls the actuator to drive the valve. The controller drives the valve to limit the flow rate to a maximum flow rate. Additionally, or alternatively, the controller limits a rate of thermal energy transfer to a maximum rate of thermal energy transfer. The rate of thermal energy transfer is determined using the flow rate and a signal indicative of a temperature differential between the supply side and return side of the network section. It can also be determined using the flow rate and a defined flow rate to delta-T mapping.

[0057] According to the present disclosure, the above-mentioned objects are particularly achieved by a computer program product comprising instructions, which when executed by a controller of an HVAC field device comprising a valve and an actuator drivingly connected to the valve, cause the HVAC field device to carry out the method according to one of the embodiments disclosed herein.

[0058] Embodiments disclosed herein provide one or more of the following benefits:

[0059] The operation of the HVAC field device in a differential pressure regulating mode leads to a reduction of noise in valves due to the maintenance of a constant differential pressure.

[0060] The control stability of pressure-dependent valves is enhanced through the method of determining and using flow coefficients and flow characteristics of the network section.

[0061] The adjustment of differential pressure setpoints is simplified through the method steps carried out by the controller, as opposed to mechanical solutions.

[0062] Consistent differential pressure values are maintained, ensuring stable heating or cooling output across the network section.

[0063] The method optimizes power consumption by controlling the actuator in various modes, contributing to optimized energy use.

[0064] Full transparency of the connected network section is achieved through the controller’s determination of flow characteristics of the network section, allowing for a comprehensive understanding and optimization of the network section. The method facilitates pump optimization and positively impacts the system's supplying pump by reducing hydraulic system oscillations, contributing to lower energy consumption.

[0065] Malfunctions in the hydronic system are indicated through the method of measuring values, such as differential pressure and flow rate, by the controller.

[0066] The HVAC field device decouples the network section from influences of other components of the HVAC system.

[0067] It is a further, additional or alternative object of the present disclosure to provide a HVAC field device, a computer implemented method of operating an HVAC field device, a computer program product, and a system for regulating a fluid flow through a valve which is able to compensate non-linearities of the valve’s flow characteristics and / or compensate variations in a network section’s flow coefficient and / or compensate variations of the differential pressure of a network section. According to embodiments disclosed herein, this object is addressed by an HVAC field device according to claim 18, a method according to claim 41 , and a computer program product according to claim 45.

[0068] In particular, this further object is addressed by a HVAC field device comprising a valve, in particular a ball valve, an actuator drivingly connected to the valve and a controller configured to receive signals indicative of a flow rate of the fluid through the valve. The controller is configured to model - in particular using a Valve Characteristic Modeler - the flow characteristic) of the valve comprising a plurality of segments. The controller is further configured to control the actuator to drive the valve to compensate non-linearities of the flow characteristic) of the valve in accordance with each of the plurality of segments of the flow characteristic).

[0069] According to embodiments, modeling the flow characteristic of the valve - using the Valve Characteristic Modeler - comprises dividing the flow characteristic into two or more different segments of the list comprising: a no flow segment, characterized by a lack of fluid flow through the valve; a linear segment, characterized by a linear relationship between the valve positions and the flow rate; an exponential segment, characterized by an exponential relationship between the valve positions and the flow rate; and a parabolic segment, characterized by a parabolic relationship between the valve positions and the flow rate.

[0070] According to embodiments, dividing the flow characteristic) into two or more different segments comprises detecting transition positions of the valve positions between the two or more segments of the flow characteristic), in particular detecting the transition positions based on repeated measurement of the flow rate of the fluid through the valve and recording of corresponding actuator and / or valve positions.

[0071] According to embodiments, detecting transition positions of the valve positions between the two or more segments of the flow characteristic) comprises one or more of: identifying a flow entry position as the valve position below which the flow rate is zero or below an absolute minimal flow rate threshold; identifying a linear-to-exponential position as the valve position above which the flow rate has an exponential relationship with the valve position and below which the flow rate has a linear relationship with the valve position; identifying an exponential-to-parabolic position as the valve position above which the flow rate has parabolic relationship with the valve position and be-low which the flow rate has an exponential relationship with the valve position.

[0072] According to embodiments, transitions between two or more segments of the flow characteristic kv,vaive(u) are detected using derivative analysis, for example by calculating and analyzing a first derivative of the flow characteristic curve. Linear segments will have a constant first derivative, exponential segments will show an increasing or decreasing slope, and parabolic segments will show a linear trend in the first derivative.

[0073] The two or more segments can be described as follows: no flow segment: exponential segment: parabolic segment (of degree n):

[0074] {ue-p< u < 1} : 1 — a (1 — u)n

[0075] According to embodiments, modeling the flow characteristic of the valve comprises determining parameters of formulas describing one or more of the sections, e.g. through repeated measurements of the flow rate of the fluid through the valve and recording of corresponding actuator and / or valve positions.

[0076] According to embodiments, the controller is configured to control the actuator to drive the valve for one or more of: regulating a differential pressure of a network section of a fluid transportation network; regulating a flow rate of the fluid through the valve; regulating a rate of thermal energy transfer, the rate of thermal energy transfer being determined using the flow rate and a signal indicative of a temperature differential and / or determined using the flow rate and a defined flow rate to delta-T mapping.

[0077] Embodiments whereby the flow characteristic is modeled by dividing into segments are advantageous as compensating of non-linearities - by inversion-based control, inversion-based feedforward control, gain-scheduling control or gain-scheduling with inversion-based feedforward control - are more accurate as all these are provided with more appropriate models of the non-linearities in accordance with the actual valve position. The segmented modeling is by far superior to a uniform modelling of the flow characteristic across the entire valve position range (from fully closed to fully open). Furthermore, the transition positions between segments may vary between different valves. Nevertheless, the linear-to-exponential position and the exponential-to-parabolic position can be calculated / adapted once the flow entry position is determined based on measurement.

[0078] Alternatively, or additionally, the flow characteristic is recorded during operation of the valve, e.g. by repeated measurement of the flow rate of the fluid through the valve and recording of the flow rate Q measurements and corresponding actuator and / or valve positions.

[0079] It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the PRjnciples and operation of the concepts disclosed.

[0080] BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The present disclosure will be explained in more detail, by way of example, with reference to the drawings in which: Figure 1 shows a highly schematic block diagram illustrating an HVAC field device according to an embodiment of the present disclosure;

[0082] Figure 2 shows a highly schematic block diagram illustrating an HVAC field device according to a further embodiment of the present disclosure;

[0083] Figure 3 illustrates the valve characteristics of a valve of an HVAC field device according to an embodiment of the present disclosure;

[0084] Figure 4 illustrates the relationship between a differential pressure of a network section and a valve position of a valve of an HVAC field device according to an embodiment of the present disclosure for two different values of the flow coefficient of the network section;

[0085] Figure 5 illustrates the relationship between a derivative of the differential pressure of a network section and a valve position of a valve of an HVAC field device according to an embodiment of the present disclosure for two different values of the flow coefficient of the network section

[0086] Figure 6 illustrates a mathematical model of a network branch of a fluid transportation network;

[0087] Figure 7 a schematical illustration of a first embodiment of a differential pressure regulating mode of differential pressure of a network section of a fluid transportation network;

[0088] Figure 8 a schematical illustration of a further embodiment of a differential pressure regulating mode of differential pressure of a network section of a fluid transportation network; Figure 9 a schematical illustration of a further embodiment of a differential pressure regulating mode of differential pressure of a network section of a fluid transportation network;

[0089] Figure 10 shows a state diagram corresponding to various regulating modes of a further embodiment of the controller of the HVAC field device;

[0090] Figure 11 illustrates steps of a first embodiment of the method of operating an HVAC field device;

[0091] Figure 12 illustrates steps of a further embodiment of the method of operating an HVAC field device, comprising compensating a non-linearity of a relationship between valve positions u of the valve and values of the differential pressure;

[0092] Figure 13 illustrates steps of a further embodiment of the method of operating an HVAC field device comprising compensating variations of a local gain due to a nonlinearity of a relationship between valve positions u of the valve and values of the differential pressure;

[0093] Figure 14 illustrates steps of a further embodiment of the method of operating an HVAC field device combining gain-scheduling with feedforward control;

[0094] Figure 15 illustrates steps of a further embodiment of the method of operating an HVAC field device comprising alternative operating modes;

[0095] Figure 16 depicts a diagram of the relationship between a flow rate of a fluid and the differential pressure of a network section, illustrating various flow rate values associated with different regulating modes; and

[0096] Figure 17 illustrates flow characteristics of a valve, modelled as a plurality of segments. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0097] Figure 1 shows a highly schematic block diagram illustrating an HVAC field device 10 according to an embodiment of the present disclosure as part of an HVAC system 1 . The HVAC system 1 comprises a fluid transportation network N having one or more network branches B, a network branch B comprising a network section F and a HVAC field device 10 fluidically connected between a return side LR of the network section F and a return line BR of the fluid transportation network N. Alternatively (not shown on the figures), the HVAC field device may be fluidically connected between a supply line BS of the fluid transportation network N and the supply side LS of the network section F.

[0098] The HVAC field device 10 comprises a valve PR and an actuator 12 drivingly connected to the valve PR. The HVAC field device 10 further comprises a controller 20 configured to receive signals, from a differential pressure sensor 30, indicative of a differential pressure Apsec- tion between the supply side LS and the return side LR of the network section F. The controller 20 is further configured to receive signals, from a flow sensor 52 (such as an ultrasonic flow sensor), indicative of a flow rate Q of the fluid through the valve PR.

[0099] The network section F may comprise various components, such as valves FVi.n, sensors FSi-nor heat exchangers (not shown), each potentially having an impact on the flow coefficient kv, section of the network section F.

[0100] The controller 20 is configured to determine a flow coefficient kv, section of the network section F using the differential pressure Apsection and the flow rate Q. The controller 20 is configured to control, in a differential pressure regulating mode I, the actuator 12 to drive the valve PR to valve position(s) u to regulate the differential pressure Apsection. The controller 20 is using the flow coefficient kv, section of the network section F, the differential pressure Apsection and flow characteristic kv,vaive(u) of the valve PR as a function of valve positions u of the valve PR and a differential pressure setpoint ApsetP. According to an embodiment, the controller 20 is further configured to determine - using a parameter estimator - a branch differential pressure Apbranch between a supply side LS of the network section F and an output side PR0Ut of the valve PR or between an input side PRjnof the valve PR and a return side LR of the network section F. This determination uses the flow characteristic kv, valve of the valve PR, the flow rate Q, the differential pressure Apsection, and an actual position u of the valve PR.

[0101] Figure 2 shows a highly schematic block diagram illustrating an HVAC field device 10 according to a further embodiment of the present disclosure, the HVAC field device 10 further comprising the differential pressure sensor 30 and the flow sensor 52.

[0102] Figure 3 illustrates the valve characteristics of a valve PR of an HVAC field device 10 according to an embodiment of the present disclosure, i.e. The relationship kv,vaive(u) between the flow rate Q and valve positions u of the valve PR at 1 bar. According to embodiments, the valve characteristics are stored in a memory comprised by or communicatively connected to the controller 20, as a function and / or in the form of a look-up table.

[0103] It shall be noted that while figures depict the valve positions u as angular values (between 0° and 90° typical for a ball valve), the valve positions u may be also represented as percentages between 0% and 100% whereby 0% corresponds to a fully closed position and 100% corresponds to a fully open position of an orifice of the valve PR (e.g. of a ball valve). Accordingly valve positions of globe valves could be represented as percentages between 0% and 100% or by a linear position, e.g. in mm.

[0104] Figure 4 depicts the relationship between a differential pressure of a network section Apsection and a valve position u of the valve PR for two different values (0.8 m3 / bar respectively 3.0 m3 / bar) of the flow coefficient kv, section of the network section F. Figure 4 illustrates the nonlinearity N(u) of the relationship between valve positions u of the valve PR and values of the differential pressure Apsection. Figure 5 illustrates the relationship between a derivative N'(u) of simulated values of the differential pressure of a network section F and the valve position u of the valve PR for two different values 0.8 m3 / bar respectively 3.0 m3 / bar of the flow coefficient kv, section of the network section F.

[0105] Figure 6 illustrates a mathematical model of a network section F comprising a static nonlinearity N(u) and a linear time invariant component (s).

[0106] Illustrated on figures 7 to 9 conceptually as a block “Valve Characteristic Modeler”, according to embodiments, the flow characteristic kv,vaive(u) of the valve PR is modelled, in particular using a Valve Characteristic Modeler. Modeling of the flow characteristic kv,vaive(u) of the valve PR using a Valve Characteristic Modeler shall be described in detail with reference to figure 17.

[0107] Furthermore, illustrated on figures 7 to 9 conceptually as a block “Parameter Estimator”, according to embodiments, the controller 20 is configured to estimate the branch differential pressure Apbranch and the flow coefficient of the network section kv, section using a Parameter Estimator on the basis of the valve position u, the flow rate Q, the differential pressure Apsection and the flow characteristic kv,vaive(u) of the valve PR.

[0108] Figure 7 illustrates conceptually a first embodiment of a differential pressure regulating mode I of differential pressure Apsection of the network section F of the fluid transportation network N.

[0109] As illustrated, the non-linearity N(u) of the relationship between valve positions u of the valve PR and values of the differential pressure Apsection are compensated e.g. using an inverse of an approximation N(u) of the non-linearity N(u)

[0110] The mathematical model of the static nonlinearity N(u) has two unknown parameters: The (time-varying) branch pressure p_branch (t) and time-varying flow coefficient of the section / fv, section <t)—determined using the Parameter Estimator. These parameters are determined by the controller 20 online, i.e. during operation of the HVAC system 1 using the flow characteristic kv,vaive(u) of the valve PR. According to a particular embodiment, the controller 20 is configured to determine the flow coefficient kv, section of the network section F using the differential pressure Apsection, the valve position u, the flow characteristic kv,vaive(u) of the valve PR and the measured flow rate Q repeatedly during operation, at set time intervals, upon occurrence of set events (e.g. start-up, restart, power failure, flow rate fluctuations, etc.).

[0111] Figure 8 illustrates a further embodiment of a differential pressure regulating mode I of the differential pressure Apsection of the network section F of a fluid transportation network N. According to this embodiment, variations of a local gain due to the non-linearity N(u) of the relationship between valve positions u of the valve PR and values of the differential pressure Apsection are compensated using a reciprocal of a local derivative N'(u) of an approxima tion N(u) of the non-linearity N(u)

[0112] The local derivative N'(u) of an approximation N(u) of the non-linearity N(u) has one unknown parameter: the time-varying flow coefficient of the section kv,secnon(t). This parameter is determined by the controller 20 online using the Parameter Estimator, i.e. during operation of the HVAC system 1. According to a particular embodiment, the controller 20 is configured to determine the flow coefficient kv, section of the network section F using the differential pressure Apsection, the valve position u, the flow characteristic kv,vaive(u) of the valve PR and the measured flow rate Q repeatedly during operation, at set time intervals, upon occurrence of set events (e.g. start-up, restart, power failure, flow rate fluctuations, etc.)

[0113] Figure 9 illustrates a further embodiment of a differential pressure regulating mode I of the differential pressure Apsection of the network section F of a fluid transportation network N. According to this embodiment, gain-scheduling control is combined with an inversion-based feedforward control. As shown in the illustration of figure 9, the controller is configured to: compensate, in a process referred to as gain-scheduling, variations of a local gain due to a non-linearity N(u) of a relationship between valve positions of the valve u and values of the differential pressure Apsection. This compensation uses in particular a reciprocal of a local derivative N'(u) of an approximation N(u) of the non-line arity W(u); and preemptively counteract the non-linearity N(u) (of the relationship between valve positions of the valve u and values of the differential pressure Apsection) using a feedforward component based on an inverse W-1(u) of an approximation N(u) of the nonlinearity N(u) and a parameter estimator.

[0114] Figure 10 shows a state diagram corresponding to various regulating modes of a further embodiment of the controller of the HVAC field device.

[0115] In the start-up position regulating mode 0, the controller 20 is configured to control the actuator 12 to drive the valve PR and maintain a start-up valve position ustart (the start-up valve position Ustart is different from a fully sealed valve position of the valve PR).

[0116] In the freeze position regulating mode II, the controller 20 is configured to control the actuator 12 to maintain the valve PR at a freeze position utreeze.

[0117] The controller 20 is configured to switch a) from the start-up position regulating mode 0 to the differential pressure regulating mode I if the sectional differential pressure Apsection falls below a fraction of the differential pressure setpoint ApsetP. This switch also occurs if the flow rate Q is higher than the minimum flow rate threshold Qmin or the differential pressure Apsection is less than a fraction of the differential pressure setpoint ApsetP. Additionally, this switch occurs if the flow rate Q is higher than an absolute minimal flow rate threshold Qmin.abs, which is lower than the minimal flow rate threshold Qmin.

[0118] The controller 20 is further configured to switch b) from the freeze position regulating mode II to the differential pressure regulating mode I if the flow rate Q is higher than a second minimum flow rate threshold Qmin, 2. The second minimum flow rate threshold Qmin, 2 is higher than the minimal flow rate threshold Qmin. This switch also occurs if the differential pressure Apsection is less than a minimum differential pressure threshold Apsection,min, and the flow rate Q is higher than an absolute minimal flow rate threshold Qmin.abs, which is lower than the minimal flow rate threshold Qmin. This switch also occurs if the differential pressure Apsection is less than a fraction of the differential pressure setpoint ApsetP(e.g. 50%).

[0119] The controller 20 is further configured to switch c) from the freeze position regulating mode II or the differential pressure regulating mode I into the start-up position regulating mode 0 if the differential pressure setpoint Apsetp is lower than an absolute minimum differential pressure threshold Apsection, min, abs. This switch also occurs if the flow rate Q is lower than the absolute minimum flow rate threshold Qmin.abs, and the differential pressure is less than a fraction of the differential pressure Apsection setpoint.

[0120] The controller 20 is configured to switch d) from the differential pressure regulating mode I to the freeze position regulating mode II when the flow rate Q is below a minimum flow rate threshold Qmin. This mode allows to control differential pressure Apsection in a wide range up to a minimum flow Qmin. In the following paragraphs, steps of various embodiments of the method of operating an HVAC field device shall be described in detail.

[0121] Figure 11 illustrates steps of a first embodiment of the method of operating an HVAC field device 10. In a step SO, the controller 20 receives signals indicative of a differential pressure Apsection between a supply side and a return side of the network section F. In a step S2, the controller 20 receives signals indicative of a flow rate Q of the fluid through the valve PR. In a step S4, the controller 20 determines a flow coefficient kv, section of the network section F using the differential pressure Apsection and the flow rate Q. In step S4, according to an embodiment of the method, the controller 20 determines the flow coefficient kv, section of the network section F and / or the flow characteristic kv,vaive(u) of the valve PR using one or more of an algorithm using an observer structure, particularly an observer structure using a parameter estimator, a Least Squares estimator, or a machine learning algorithm.

[0122] In a step S6, the controller 20 controls, in a differential pressure regulating mode I, the actuator 12 to drive the valve PR to valve position(s) u to regulate the differential pressure Apsection using the flow coefficient kv, section of the network section F, the differential pressure Apsection, the flow characteristic kv,vaive(u) of the valve PR as a function of valve positions u of the valve PR, and a differential pressure setpoint ApsetP.

[0123] In a step S8, according to an embodiment of the method, the controller 20 determines a branch differential pressure Apbranch between a supply side LS of the network section F and an output side PR0Ut of the valve PR or between an input side PRinof the valve PR and a return side LR of the network section F using the flow characteristic kv,vaive(u) of the valve PR, the flow rate Q, the differential pressure Apsection, and an actual position u of the valve PR.

[0124] In a step S10, according to an embodiment of the method, the controller 20 controls the actuator 12 further using a flow coefficient of a flow sensor 52 generating the sensor signal indicative of the flow rate Q of the fluid through the valve PR. Figure 12 illustrates steps of a further embodiment of the method of operating an HVAC field device 10, whereby in a step S12, the controller 20 compensates a non-linearity N(u) of a relationship between valve positions u of the valve PR and values of the differential pressure Apsection using an inverse (V-1(u) of an approximation N(u) of the non-linearity N(u) , whereby:

[0125] Figure 13 illustrates steps of a further embodiment of the method of operating an HVAC field device 10, whereby in a step S14, the controller 20 compensates variations of a local gain due to a non-linearity N(u) of a relationship between valve positions u of the valve PR and values of the differential pressure Apsection, in particular using a reciprocal of a local de rivative N' u) of an approximation (V(u) of the non-linearity N(u), whereby

[0126] Figure 14 illustrates steps of a further embodiment of the method of operating an HVAC field device 10, whereby in a step S19A, the controller compensates, in a process referred to as gain-scheduling, variations of a local gain due to a non-linearity N u) of a relationship between valve positions of the valve u and values of the differential pressure Apsection using a reciprocal of a local derivative N'(u) of an approximation N(u) of the non-linearity N(u).

[0127] In addition, in a step S19B, the controller preemptively counteracts the non-linearity N(u) (of the relationship between valve positions of the valve u and values of the differential pressure Apsection) using a feedforward component based on an inverse W-1(u) of an approximation N(u) of the non-linearity N(u). Figure 15 illustrates steps of a further embodiment of the method of operating an HVAC field device 10, whereby in a step S18, the controller 20 controls the actuator 12 in one or more of the following alternative operating modes: a valve position regulating mode comprising a start-up position regulating mode 0 and / or a freeze position regulating mode II, an alternative differential pressure regulating mode, a flow regulating mode, and / or a power regulating mode. The selection is made as a function of one or more of the flow rate Q, the differential pressure setpoint ApsetP, a deviation of the differential pressure Apsection from the differential pressure setpoint ApsetP, an event signal, detecting an erroneous flow rate Q signal, detecting an erroneous differential pressure Apsection signal, a condition of an external device pump, and / or a timer signal.

[0128] In a step S20, the controller 20 in the start-up position regulating mode 0, controls the actuator 12 to drive the valve PR and maintain a start-up valve position ustart. The start-up valve position Ustart is different from a fully sealed valve position of the valve PR. after the HVAC field device 10 has been restarted. The start-up position regulating mode 0 is selected after a power failure, after switching into differential pressure regulating mode, in particular after switching from flow regulating mode and valve position regulating mode, if the differential pressure Apsection is below a minimum differential pressure threshold Apsection,min, and / or if the flow rate Q is below a minimum flow threshold Qmin.

[0129] In a step S22, the controller 20 in the valve position regulating mode, controls the actuator 12 to drive the valve PR to a valve setpoint position, such as start-up valve position or freeze position Ufreeze (when the flow rate Q is below a minimum flow rate threshold Qmin).

[0130] In a step S24, the controller 20 controls the actuator 12 in the alternative differential pressure regulating mode upon detecting an erroneous flow rate Q signal. The actuator 12 is driven to adjust the valve PR to a valve position u to regulate the differential pressure Apsection in the alternative differential pressure regulating mode using a constant flow coefficient kv, section of the network section F such as an estimated constant flow coefficient kv, section. In a step S26, the controller 20 switches between the various regulating modes as described above. In a step S28, the controller 20 controls the actuator 12 in a freeze position regulating mode, maintaining the valve PR at its current position.

[0131] In a step S34, the controller 20 controls the actuator 12 to drive the valve PR to limit the flow rate Q to a maximum flow rate Qmax. Additionally, or alternatively in a step S36, the controller 20 limits a rate of thermal energy transfer P to a maximum rate of thermal energy transfer Pmax. The rate of thermal energy transfer P is determined using the flow rate Q and a signal indicative of a temperature differential At between the supply side LS and return side LR of the network section F. It can also be determined using the flow rate Q and a defined flow rate to delta-T mapping.

[0132] Figure 16 depicts a diagram of the relationship between the flow rate Q of the fluid and the differential pressure Apsection, illustrating various flow rate values associated with different regulating modes. According to this embodiment, the controller 20 is further configured to control the actuator 12 in one or more of the following alternative operating modes: a startup position regulating mode 0 and / or a freeze position regulating mode II - in addition to the differential pressure regulating mode I. The selection between the regulating modes is a function of one or more of the flow rate Q, the differential pressure setpoint ApsetP, a deviation of the differential pressure Apsection from the differential pressure setpoint ApsetP, an event signal, detecting an erroneous flow rate Q signal, detecting an erroneous differential pressure Apsection signal, a condition of an external device (pump), and / or a timer signal.

[0133] Figure 17 illustrates flow characteristics of the valve PR, modelled as a plurality of segments as a function of the valve position u, comprising: a no flow segment, characterized by a lack of fluid flow through the valve PR;

[0134] {0 < u < u0_ a linear segment, characterized by a linear relationship between the valve positions u and the flow rate Q;

[0135] 1Z UO-1 1 (1 - )

[0136] {u0_( < u < u; - e}: - expui-e u100 ~u0-lul-e an exponential segment, characterized by an exponential relationship between the valve positions u and the flow rate Q; and a parabolic segment (of degree n), characterized by a parabolic relationship between the valve positions u and the flow rate Q. dividing the flow characteristic kv,vaive(u) into two or more different segments comprises detecting transition positions uo-i, ui-e, uxe-Pof the valve positions u between the two or more segments of the flow characteristic kv,vaive(u), in particular detecting the transition positions based on repeated measurement of the flow rate Q of the fluid through the valve PR and recording of corresponding actuator and / or valve positions uo-i, ui-e, uxe-P.

[0137] Detecting transition positions uo-i, ui-e, uxe.pof the valve positions u between the two or more segments of the flow characteristic kv,vaive(u) comprises one or more of: identifying a flow entry position uo-i as the valve position u below which the flow rate Q is zero or below an absolute minimal flow rate threshold Qmin.abs; identifying a linear-to-exponential position ui-eas the valve position u above which the flow rate Q has an exponential relationship with the valve position u and below which the flow rate Q has a linear relationship with the valve position u; identifying an exponential-to-parabolic position ue.pas the valve position u above which the flow rate Q has parabolic relationship with the valve position u and below which the flow rate Q has an exponential relationship with the valve position u.

[0138] Alternatively, or additionally, according to an embodiment, the flow characteristic of the valve PR is represented as a look-up table indicative of the plurality of segments.

[0139] It should be noted that, in the description, the sequence of the steps has been presented in a specific order, one skilled in the art will understand, however, that the order of at least some of the steps could be altered, without deviating from the scope of the disclosure.

[0140] REFERENCE LIST

[0141] A HVAC field device 10 differential pressure Apsection minimum differential pressure threshold Apsection,min absolute minimum differential pressure threshold Apsection, min, abs branch differential pressure Apbranch differential pressure setpoint ApsetPmaximum differential pressure Apmax network section F fluid transportation network N supply line (of the fluid transportation network) BS return line (of the fluid transportation network) BR valve PR actuator 12 controller 20 supply side (of the network section) LS return side (of the network section) LR flow rate Q minimum flow threshold Qmin absolute minimal flow rate threshold Qmin.abs second minimum flow rate threshold Qmin, 2 maximum flow rate Qmax valve position(s) u freeze position Ufreeze flow entry position uo-i linear-to-exponential position ui-eexponential-to-parabolic position ue.pflow characteristic of the valve kv,vaive(u) flow coefficient of network section kv, section flow coefficient of network branch kv, branch start-up position regulating mode 0 differential pressure regulating mode I freeze position regulating mode II start-up time tstart

Claims

CLAIMS1 . A HVAC field device (10) for regulating a differential pressure (Apsection) of a network section (F) of a fluid transportation network (N), the HVAC field device (10) comprising: a valve (PR); an actuator (12) drivingly connected to the valve (PR); a controller (20) configured to: receive signals indicative of: a differential pressure (Apsection) between a supply side (LS) and a return side (LR) of the network section (F); and a flow rate (Q) of the fluid through the valve (PR); determine a flow coefficient (kv, section) of the network section (F) using the differential pressure (Apsection) and the flow rate (Q); control, in a differential pressure regulating mode (I), the actuator (12) to drive the valve (PR) to valve position(s) (u) to regulate the differential pressure (Apsection) using: the flow coefficient (kv, section) of the network section (F); the differential pressure (Apsection) ; a flow characteristic (kv,vaive(u)) of the valve (PR); and a differential pressure setpoint (ApsetP).

2. The HVAC field device (10) according to claim 1 , wherein the flow characteristic (kv,vaive(u)) of the valve (PR) is provided as a function of valve positions (u) of the valve (PR).

3. The HVAC field device (10) according to claim 1 or 2, wherein the controller (20) is further configured to determine a branch differential pressure (Apbranch) - between a supply side (LS) of the network section (F) and an output side (PR0Ut) of the valve (PR) or between an input side (PRjn) of the valve (PR) and a return side (LR) of the network section (F) - using the flow characteristic (kv,vaive) of the valve (PR), the flow rate (Q), the differential pressure (Apsection) and an actual position (u) of the valve (PR).

4. The HVAC field device (10) according to one of the claims 1 to 3, wherein the controller (20) is configured to control the actuator (12) further using a flow coefficient of a flow sensor (52) generating the sensor signal indicative of the flow rate (Q) of the fluid through the valve (PR).

5. The HVAC field device (10) according to one of the claims 1 to 4, wherein the controller (20) is further configured to compensate a non-linearity of a relationship between valve positions (u) of the valve (PR) and values of the differential pressure (Apsection), in particular using an inverse of an approximation of the non-linearity and a parameter estimator, in particular a parameter estimator configured to estimate the branch differential pressure (Apbranch) and the flow coefficient (kv, section) of the network section (F).

6. The HVAC field device (10) according to claim 5, wherein the controller is further configured to preemptively counteract the non-linearity of the relationship between valve positions of the valve and values of the differential pressure using a feedforward component based on an inverse of an approximation of the non-linearity and the parameter estimator.

7. The HVAC field device (10) according to one of the claims 1 to 6, wherein the controller (20) is further configured to compensate variation(s) of a local gain due to a non-linearity of a relationship between valve positions (u) of the valve (PR) and valuesof the differential pressure (Apsection), in particular using a reciprocal of a local derivative of an approximation of the non-linearity and a parameter estimator, in particular a parameter estimator configured to estimate the flow coefficient (kv, section) of the network section (F).

8. The HVAC field device (10) according to one of the claims 1 to 7, wherein the controller (20) is configured to determine the flow coefficient (kv, section) of the network section (F) and / or the flow characteristic (kv,vaive(u)) of the valve (PR) using one or more of: an algorithm using an observer structure, in particular an observer structure using a state estimator; a Least Squares estimator; a machine learning algorithm.

9. The HVAC field device (10) according to one of the claims 1 to 8, wherein the controller (20) is further configured to control the actuator (12) in one or more of the following alternative operating modes: a valve position regulating mode comprising a start-up position regulating mode (0) and / or a freeze position regulating mode (II); an alternative differential pressure regulating mode; a flow regulating mode; a power regulating mode; and / or a fully open mode selected as a function of one or more of: the flow rate (Q); the differential pressure setpoint (ApsetP);a deviation of the differential pressure (Apsection) from the differential pressure setpoint (ApsetP) , the valve position(s) (u); an event signal; detecting an erroneous flow rate (Q) signal; detecting an erroneous differential pressure (Apsection) signal; a condition of an external device (pump); and / or a timer signal.

10. The HVAC field device (10) according to claim 9, wherein, in the start-up position regulating mode (0), the controller (20) is configured to control the actuator (12) to drive the valve (PR) and maintain a start-up valve position (ustart), the start-up valve position (u^art) being different from a fully sealed valve position of the valve (PR) in one or more of the following conditions: after the HVAC field device (10) has been restarted; after a power failure; after switching into differential pressure regulating mode, in particular after switching from flow regulating mode and valve position regulating mode; if the differential pressure (Apsection) is below a minimum differential pressure threshold (Apsection, min) , and / OT if the flow rate (Q) is below a minimum flow threshold (Qmin).

11. The HVAC field device (10) according to claim 9 or 10, wherein, in the valve position regulating mode, the controller (20) is configured to control the actuator (12) to switch into the freeze position regulating mode (II) to maintain the valve (PR) at a freeze position (ufreeze) if:the flow rate (Q) is below a minimum flow rate threshold (Qmin) and the differential pressure (Apsection) meets or exceeds the differential pressure setpoint (Apsetp) and the flow rate (Q) exceeds an absolute minimum flow rate threshold (Qmin.abs) or the differential pressure (Apsection) exceeds a maximum differential pressure (Apmax) for a predefined amount of time.

12. The HVAC field device (10) according to one of the claims 9 to 11 , wherein the controller (20) is configured to control the actuator (12) to drive the valve (PR) to a valve position (u) to regulate the differential pressure (Apsection) in the alternative differential pressure regulating mode upon detecting an erroneous flow rate (Q) signal, using a constant flow coefficient (kv, section) of the network section (F).

13. The HVAC field device (10) according to claim 12, wherein the controller (20) is configured to switch from the alternative differential pressure regulating mode to the differential pressure regulating mode (I) upon detection of a valid sensor signal indicative of the flow rate (Q).

14. The HVAC field device (10) according to one of the claims 9 to 13, wherein the controller (20) is further configured to switch from the start-up position regulating mode (0) to the differential pressure regulating mode (I) after a predetermined amount of time, if the differential pressure setpoint (ApsetP) is greater than 0 and: if the flow rate (Q) is higher than the minimum flow rate threshold (Qmin) or the differential pressure (Apsection) is less than a fraction of the differential pressure setpoint (ApsetP) and the flow rate (Q) is higher than an absolute minimal flow rate threshold (Qmin.abs), which is lower than the minimal flow rate threshold (Qmin).15 The HVAC field device (10) according to one of the claims 9 to 14, wherein the controller (20) is further configured to switch from the freeze position regulating mode(II) to the differential pressure regulating mode (I) or to the alternative differential pressure regulating mode if the differential pressure setpoint (ApsetP) is greater than 0 and if: the flow rate (Q) is higher than a second minimum flow rate threshold (Qmin, 2), the second minimum flow rate threshold (Qmin, 2) being higher than the minimal flow rate threshold (Qmin); or the differential pressure (Apsection) is less than a minimum differential pressure threshold (Apsection.min), and the flow rate (Q) is higher than an absolute minimal flow rate threshold (Qmin.abs), which is lower than the minimal flow rate threshold (Qmin).

16. The HVAC field device (10) according to one of the claims 9 to 15, wherein the controller (20) is further configured to switch from the freeze position regulating mode (II) to the start-up position regulating mode (0) if: the differential pressure setpoint (ApsetP) is lower than an absolute minimum differential pressure threshold (Apsection, min, abs); or the flow rate (Q) is lower than the absolute minimum flow rate threshold (Qmin.abs), and the differential pressure is less than a fraction of the differential pressure (Apsection) setpoint.

17. The HVAC field device (10) according to one of the claims 1 to 16, wherein the controller (20) is further configured to control, in the differential pressure regulating mode (I), the actuator (12) to drive the valve (PR) to: limit the flow rate (Q) to a maximum flow rate (Qmax); and / or limit a rate of thermal energy transfer (P) to a maximum rate thermal energy transfer (Pmax), the rate of thermal energy transfer (P) being determined using the flow rate (Q) and a signal indicative of a temperature differential (At) between the supply side (LS) and return side (LR) of the network section (F) and / or determined using the flow rate (Q) and a defined flow rate to delta-T mapping.

18. The HVAC field device (10) according to one of the claims 1 to 17, wherein the controller (20) is further configured to: model the flow characteristic (kv,vaive(u)) of the valve (PR) comprising a plurality of segments; and control the actuator (12) to drive the valve (PR) to compensate non-linearities of the flow characteristic (kv,vaive(u)) of the valve (PR) in accordance with each of the plurality of segments of the flow characteristic (kv,vaive(u)).

19. The HVAC field device (10) according to claim 18, wherein modeling the flow characteristic (kv,vaive(u)) of the valve (PR) comprises dividing the flow characteristic (kv,vaive(u)) into two or more different segments of the list comprising: a no flow segment, characterized by a lack of fluid flow through the valve (PR); a linear segment, characterized by a linear relationship between the valve positions (u) and the flow rate (Q); an exponential segment, characterized by an exponential relationship between the valve positions (u) and the flow rate (Q); and a parabolic segment, characterized by a parabolic relationship between the valve positions (u) and the flow rate (Q).

20. The HVAC field device (10) according to claim 19, wherein dividing the flow characteristic (kv,vaive(u)) into two or more different segments comprises detecting transition positions (uo-i, ui-e, uxe-P) of the valve positions (u) between the two or more segments of the flow characteristic (kv,vaive(u)), in particular detecting the transition positions based on repeated measurement of the flow rate (Q) of the fluid through the valve (PR) and corresponding valve positions (u).

21. The HVAC field device (10) according to claim 19 or 20, wherein dividing the flow characteristic (kv,vaive(u)) into two or more different segments comprises:detecting a first transition position (uo-i, ui-e, uxe-P) of the valve positions (u) between a first segment and a second segment of the two or more segments of the flow characteristic (kv,vaive(u)); and determining one or more further transition position(s) (uo-i, ui-e, uxe-P) of the valve positions (u) between two or more segments of the flow characteristic (kv,vaive(u)), different from the first segment and the second segment, at least partially based on the detected first transition position (uo-i, ui-e, uxe.p).

22. The HVAC field device (10) according to claim 20 or 21 , wherein detecting transition positions (uo-i, ui-e, uxe.p) of the valve positions (u) between the two or more segments of the flow characteristic (kv,vaive(u)) comprises one or more of: identifying a flow entry position (uo-i) as the valve position (u) below which the flow rate (Q) is zero or below an absolute minimal flow rate threshold (Qmin.abs); identifying a linear-to-exponential position (ui-e) as the valve position (u) above which the flow rate (Q) has an exponential relationship with the valve position (u) and below which the flow rate (Q) has a linear relationship with the valve position (u); identifying an exponential-to-parabolic position (ue.p) as the valve position (u) above which the flow rate (Q) has parabolic relationship with the valve position (u) and below which the flow rate (Q) has an exponential relationship with the valve position (u).

23. An HVAC system (1) comprising: a fluid transportation network (N) comprising a network section (F); an HVAC field device (10) according to one of the claims 1 to 22, the valve (PR) of the HVAC field device (10) being fluidically connected to the supply side (LS) or the return side (LR) of the network section (F); a differential pressure sensor (30) configured and arranged for measuring a differential pressure (Apsection) between a supply side and a return side of the network section (F); anda flow sensor (52) configured and arranged for measuring a flow rate (Q) of a fluid through the valve (PR).

24. A method of operating an HVAC field device (10) comprising a valve (PR), an actuator (12) drivingly connected to the valve (PR) and a controller (20), the method comprising the steps carried out by the controller (20): receiving signals indicative of: a differential pressure (Apsection) between a supply side and a return side of the network section (F); and a flow rate (Q) of the fluid through the valve (PR); determining a flow coefficient (kv, section) of the network section (F) using the differential pressure (Apsection) and the flow rate (Q); controlling, in a differential pressure regulating mode (I), the actuator (12) to drive the valve (PR) to ) to valve position(s) (u) to regulate the differential pressure (Apsection) using: the flow coefficient (kv, section) of the network section (F); the differential pressure (Apsection); a flow characteristic (kv,vaive(u)) of the valve (PR); and a differential pressure setpoint (ApsetP).

25. The method of operating an HVAC field device (10) according to claim 24, further comprising providing the flow characteristic (kv,vaive(u)) of the valve (PR) as a function of valve positions (u) of the valve (PR).

26. The method of operating an HVAC field device (10) according to claim 24 or 25, further comprising determining, by the controller (20), a branch differential pressure (Apbranch) - between a supply side (LS) of the network section (F) and an output side(PRout) of the valve (PR) or between an input side (PRjn) of the valve (PR) and a return side (LR) of the network section (F) - using the flow characteristic (kv,vaive) of the valve (PR), the flow rate (Q), the differential pressure (Apsection) and an actual position (u) of the valve (PR).

27. The method of operating an HVAC field device (10) according to one of the claims 24 to 26, further comprising controlling, by the controller (20), the actuator (12) further using a flow coefficient of a flow sensor (52) generating the sensor signal indicative of the flow rate (Q) of the fluid through the valve (PR).

28. The method of operating an HVAC field device (10) according to one of the claims 24 to 27, further comprising compensating, by the controller (20), a non-linearity of a relationship between valve positions (u) of the valve (PR) and values of the differential pressure (Apsection), in particular using an inverse of an approximation of the non-linearity.

29. The method of operating an HVAC field device (10) according to claim 28, further comprising preemptively counteracting, by the controller (20), the non-linearity of the relationship between valve positions of the valve and values of the differential pressure using a feedforward component based on an inverse of an approximation of the non-linearity and a parameter estimator, in particular a parameter estimator configured to estimate the branch differential pressure (Apbranch) and the flow coefficient (kv, section) of the network section (F).

30. The method of operating an HVAC field device (10) according to one of the claims 24 to 29, further comprising compensating, by the controller (20), variation(s) of a local gain due to a non-linearity of a relationship between valve positions (u) of the valve (PR) and values of the differential pressure (Apsection), in particular using a reciprocalof a local derivative of an approximation of the non-linearity and a parameter estimator, in particular a parameter estimator configured to estimate the flow coefficient (kv, section) of the network section (F)..

31. The method of operating an HVAC field device (10) according to one of the claims 24 to 30, further comprising determining, by the controller (20), the flow coefficient (kv, section) of the network section (F) and / or the flow characteristic (kv,vaive(u)) of the valve (PR) using one or more of: an algorithm using an observer structure in particular an observer structure using a state estimator; a Least Squares estimator; a machine learning algorithm.

32. The method of operating an HVAC field device (10) according to one of the claims 24 to 31 , further comprising controlling, by the controller (20), the actuator (12) in one or more of the following alternative operating modes: a valve position regulating mode comprising a start-up position regulating mode (0) and / or a freeze position regulating mode (II); an alternative differential pressure regulating mode; a flow regulating mode; a power regulating mode; and / or a fully open mode selected as a function of one or more of: the flow rate (Q); the differential pressure setpoint (ApsetP);a deviation of the differential pressure (Apsection) from the differential pressure setpoint (ApsetP), the valve position(s) (u); an event signal; detecting an erroneous flow rate (Q) signal; detecting an erroneous differential pressure (Apsection) signal; a condition of an external device (pump); and / or a timer signal.

33. The method of operating an HVAC field device (10) according to claim 32, further comprising controlling, by the controller (20) in the start-up position regulating mode (0), the actuator (12) to drive the valve (PR) and maintain a start-up valve position (Ustart), the start-up valve position (ustart) being different from a fully sealed valve position of the valve (PR): after the HVAC field device (10) has been restarted; after a power failure; after switching into differential pressure regulating mode, in particular after switching from flow regulating mode and valve position regulating mode; if the differential pressure (Apsection) is below a minimum differential pressure threshold (Apsection, min), and / OT if the flow rate (Q) is below a minimum flow threshold (Qmin).

34. The method of operating an HVAC field device (10) according to claim 32 or 33, further comprising controlling, by the controller (20) in the valve position regulating mode, the actuator (12) to switch into the freeze position regulating mode (II) to maintain the valve (PR) at a freeze position (Ufreeze) if:Qminthe flow rate (Q) is below a minimum flow rate threshold (Qmin) and the differential pressure (Apsection) meets or exceeds the differential pressure setpoint (Apsetp) and the flow rate (Q) exceeds an absolute minimum flow rate threshold (Qmin.abs) or the differential pressure (Apsection) exceeds a maximum differential pressure (Apmax) for a predefined amount of time.

35. The method of operating an HVAC field device (10) according to one of the claims 32 to 34, further comprising controlling, by the controller (20) in the alternative differential pressure regulating mode upon detecting an erroneous flow rate (Q) signal, the actuator (12) to drive the valve (PR) to a valve position (u) to regulate the differential pressure (Apsection), using a constant flow coefficient (kv, section) of the network section (F).

36. The method of operating an HVAC field device (10) according to claim 35, further comprising switching, by the controller (20) from the alternative differential pressure regulating mode to the differential pressure regulating mode (I) upon detection of a valid sensor signal indicative of the flow rate (Q).

37. The method of operating an HVAC field device (10) according to one of the claims 32 to 36, further comprising switching, by the controller (20), from the start-up position regulating mode (0) to the differential pressure regulating mode (I) after a predetermined amount of time, if the differential pressure setpoint (ApsetP) is greater than 0 and: if the flow rate (Q) is higher than the minimum flow rate threshold (Qmin) or the differential pressure (Apsection) is less than a fraction of the differential pressure setpoint (ApsetP) and the flow rate (Q) is higher than an absolute minimal flow rate threshold (Qmin.abs), which is lower than the minimal flow rate threshold (Qmin).

38. The method of operating an HVAC field device (10) according to one of the claims32 to 37, further comprising switching, by the controller (20), from the freeze position regulating mode (II) to the differential pressure regulating mode (I) or to the alternative differential pressure regulating mode if the differential pressure setpoint (Apsetp) is greater than 0 and if: the flow rate (Q) is higher than a second minimum flow rate threshold (Qmin, 2), the second minimum flow rate threshold (Qmin, 2) being higher than the minimal flow rate threshold (Qmin); or the differential pressure (Apsection) is less than a minimum differential pressure threshold (Apsection,min), and the flow rate (Q) is higher than an absolute minimal flow rate threshold (Qmin.abs), which is lower than the minimal flow rate threshold (Qmin).

39. The method of operating an HVAC field device (10) according to one of the claims 24 to 38, further comprising switching, by the controller (20), from the freeze position regulating mode (II) to the start-up position regulating mode (0) if: the differential pressure setpoint (ApsetP) is lower than an absolute minimum differential pressure threshold (Apsection, min, abs); or the flow rate (Q) is lower than the absolute minimum flow rate threshold (Qmin.abs), and the differential pressure is less than a fraction of the differential pressure (Apsection) setpoint.

40. The method of operating an HVAC field device (10) according to one of the claims 24 to 39, further comprising controlling, by the controller (20) in the differential pressure regulating mode (I), the actuator (12) to drive the valve (PR) to: limit the flow rate (Q) to a maximum flow rate (Qmax); and / orlimit a rate of thermal energy transfer (P) to a maximum rate thermal energy transfer (Pmax), the rate of thermal energy transfer (P) being determined using the flow rate (Q) and a signal indicative of a temperature differential (At) between the supply side (LS) and return side (LR) of the network section (F) and / or determined using the flow rate (Q) and a defined flow rate to delta-T mapping.

41. The method of operating an HVAC field device (10) according to one of the claims 24 to 40, further comprising: modeling, by the controller (20), the flow characteristic (kv,vaive(u)) of the valve (PR) comprising a plurality of segments; and controlling, by the controller (20), the actuator (12) to drive the valve (PR) to compensate non-linearities of the flow characteristic (kv,vaive(u)) of the valve (PR) in accordance with each of the plurality of segments of the flow characteristic (kv,vaive(u)).

42. The method of operating an HVAC field device (10) according to claim 41 , wherein modeling the flow characteristic (kv,vaive(u)) of the valve (PR) comprises dividing the flow characteristic (kv,vaive(u)) into two or more different segments of the list comprising: a no flow segment, characterized by a lack of fluid flow through the valve (PR); a linear segment, characterized by a linear relationship between the valve positions (u) and the flow rate (Q); an exponential segment, characterized by an exponential relationship between the valve positions (u) and the flow rate (Q); and a parabolic segment, characterized by a parabolic relationship between the valve positions (u) and the flow rate (Q).

43. The method of operating an HVAC field device (10) according to claim 42, wherein dividing the flow characteristic (kv,vaive(u)) into two or more different segments comprises detecting transition positions (uo-i, ui-e, uxe-P) of the valve positions (u) between the two or more segments of the flow characteristic (kv,vaive(u)), in particular detecting the transition positions based on repeated measurement of the flow rate (Q) of the fluid through the valve (PR).

44. The method of operating an HVAC field device (10) according to claim 43, wherein detecting transition positions (uo-i, ui-e, uxe-P) of the valve positions (u) between the two or more segments of the flow characteristic (kv,vaive(u)) comprises one or more of: identifying a flow entry position (uo-i) as the valve position (u) below which the flow rate (Q) is zero or below an absolute minimal flow rate threshold (Qmin.abs); identifying a linear-to-exponential position (ui-e) as the valve position (u) above which the flow rate (Q) has an exponential relationship with the valve position (u) and below which the flow rate (Q) has a linear relationship with the valve position (u); identifying an exponential-to-parabolic position (ue.p) as the valve position (u) above which the flow rate (Q) has parabolic relationship with the valve position (u) and below which the flow rate (Q) has an exponential relationship with the valve position (u).

45. A computer program product, comprising instructions, which, when executed by a controller of an HVAC field device (10) comprising a valve (PR) and an actuator (12) drivingly connected to the valve (PR), cause the HVAC field device (10) to carry out the method according to one of the claims 24 to 44.

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