METHOD FOR CONTROLLING A CIRCULATION PUMP

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a United States National Phase Application of Inter-national Application PCT/EP2024/060246, filed Apr. 16, 2024, and claims the benefit of priority under 35 U.S.C. § 119 of Danish (DL) Application PA 2023 70348, filed Jun. 30, 2023, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

[0002]The present disclosure is directed to a method for controlling a circulation pump being installed in a system for heating or cooling, wherein the system is equipped with one or more temperature-controlled valves. For example, the system may be an ordinary household heating system with radiators that are equipped with temperature-controlled valves, e.g. thermostatic radiator valves (TRVs). Alternatively, or in addition, the temperature-controlled valves of the system may be “smart valves” being remotely temperature-controlled by a smart valve application.

BACKGROUND

[0003]A circulation pump is typically installed at a piping system as a standalone circulation pump assembly comprising a pump, an electric motor for driving the pump and an electronics housing with electronics for controlling the speed of the motor. The circulation pump may be operated in different selectable control modes, e.g. constant pressure control mode or proportional pressure control mode. Each control mode may include a certain number of selectable pump control curves. If the pump is operated to follow a certain pump control curve, the operating point of the pump sticks to the pump control curve if possible.

[0004]When the piping system comprises temperature-controlled valves, the valves gradually close when the demand for thermal energy decreases and they gradually open when the demand for thermal energy increases in order to achieve a target temperature. Typically, the circulation pump as a stand-alone pump assembly does not get any direct information about how much the valves are opened or closed. If the pump sticks to its set pump control curve, it may run with an unnecessary high speed when the valves close or with a too low speed when the valves open. A too high speed of the pump waists energy saving potential and leads to undesired flow noise. A too low speed of the pump has a negative impact on the user comfort, because the cooling or heating system does not achieve its target temperatures, at least not within a desired time frame.

[0005]It is known in the prior art to automatically adapt the pump control curve in a closed-loop control based on a pipe resistance value as a feedback value. For example, EP 0 726 396 B1 or EP 1 323 986 B1 describe such an automatic adaptation of the pump control curve in a closed-loop control.

[0006]It has shown that the known methods of automatic adaptation of the pump control curve successfully reduce the energy consumption and flow noise when the valves close. However, the known methods of automatic adaptation of the pump control curve have also shown to be too slow when the valves open during high thermal energy demand. The user thus experiences a lack of comfort, because the cooling or heating system does not achieve its target temperatures, at least not within a desired time frame.

[0007]It is therefore an object of the present disclosure to provide a method for controlling a circulation pump that on the one hand adapts the pump control curve quickly enough both when the proportional control valves in the system are closing and when they are opening. On the other hand, the energy consumption and the flow noise is still to be reduced as much as possible when the proportional control valves are closing.

SUMMARY

[0011]The term “common degree of openness” of the one or more temperature-controlled valves, i.e. in form of proportional control valves, is to be understood as an absolute or relative measure of how much open or closed all those temperature-controlled valves are through which the circulation pump pumps heating or cooling liquid, e.g. ranging from 0% to 100%. If only one valve exists in the system, the “common degree of openness” may simply be the opening degree of said valve. If there are two or more valves in the system, a weighted or unweighted average of the opening degrees of the valves may be considered as the “common degree of openness”. A stand-alone pump assembly has no information about the common degree of openness, but it “feels” a pipe resistance that scales with the common degree of openness of the valves. When all valves of the system are open to a maximum degree, the pump experiences the lowest pipe resistance. When all of the valves but one are closed, and the one open valve is nearly closed, the pump experiences the highest pipe resistance. It can be assumed that the pipe resistance is constant as long as the common degree of openness of the valves does not change.

[0012]The system characteristic curve varies with the pipe resistance, i.e. it varies with the common degree of openness of the valves. If the system characteristic curve changes, the pump characteristic curve is adapted by changing the pump speed to keep the operating point on the pump control curve. If the pump control curve, e.g. a proportional pressure control curve in form of a linear line in a head-flow-diagram, is fixed, undesirable situations occur in which the pump does not run at full speed when the valves are fully open for high thermal energy demand and in which the pump runs too quickly when the valves are nearly or fully closed for low or no thermal energy demand. In other words, it is most desirable to have the common degree of openness of the valves in a desired range between a minimum common degree of openness and a maximum common degree of openness. In that desired range, the temperature-controlled valves can react to a rise and fall of the thermal energy demand. Thus, the pump control curve is not fixed, but adjustable to keep the common degree of openness of the valves within the desired range as much as possible.

[0013]The inventive idea is now to speed up the adjustment of the pump control curve by determining a system variable that is susceptible to system characteristic curve changes and by using the system variable as an input to provide a feed forward signal to automatically adjust the pump control curve in a feed forward control.

[0014]For example, the system variable may be the flow factor, also denoted as kv-value. The kv-value is, for example, defined in “Fluidic characteristic quantities of control valves and their determination”, VDI, VDE, September 2007, 2173, retrieved 17 Apr. 2020. The kv-value expresses the amount of water flow in units of m³/h through the system at a given common degree of openness with a pressure drop of 1 bar across the valves. It should be noted that the complete definition says that the flow medium must have a specific gravity of 1000 kg/m³ and a kinematic viscosity of 10⁻⁶ m²/s, e.g. water. The kv-value is generally defined as

$k_v=q\sqrt{\frac{\mathrm{SG}}{\Delta p}},$

wherein q is the flow in units of m³/h, Dp is the pressure drop across the valves in units of bar, and SG is the specific gravity of the flow medium (SG=1 for water).

[0015]The pump is able to determine or estimate the system variable based on its current operating point and performance indicators, such as its provided head and/or flow, its current pump speed, power consumption and/or the electric current currently drawn by the pump drive motor. The determined or estimated system variable is then used as an input to provide a feed forward signal to automatically adjust the pump control curve in a feed forward control.

[0016]Optionally, the method may further comprise continuously or regularly monitoring a head value h indicative of the head currently provided by the circulation pump and a flow value q indicative of the flow currently provided by the circulation pump, wherein the head value h and the flow value q are used to determine the system variable, e.g. the kv-value. In order to avoid the need for a pressure sensor and/or a flow sensor, it is beneficial to derive the head value and the flow value from electric performance indicators of the pump moto, e.g. motor speed and power consumption.

[0020]The maximum and minimum kv-values may be used to estimate over time the kv-values for the highest common degree of opening of the valves and the lowest common degree of opening of the valves, respectively.

[0021]Optionally, automatically adjusting the pump control curve may further comprise using a stored adaptable mapping between the system variable and the feed forward signal to be applied for the feed forward control. This is beneficial to account for deviations from the target opening degree as indicated by a PI controller. The mapping used for the feed forward may be adapted to keep the deviation from the target opening degree at a minimum.

[0022]Optionally, a deviation of the determined common degree of openness value from a pre-determined reference common degree of openness may be used as a further input in addition to the system variable to provide the feed forward signal, and wherein said deviation is used to update the stored adaptable mapping. It should be noted that this further input is, under normal operation, much smaller than the contribution of the system variable to the feed forward control. The contribution of the deviation of the opening degree from the target opening degree is rather a minor correction, e.g. in the range of +/−5%, to the feed forward control.

[0023]Optionally, the stored adaptable mapping may comprise a list of relative values defining which pump control curve is applied within a total range of applicable pump control curves at pre-determined system variable points, wherein the relative values are interpolated between the pre-determined system variable points. For example, the applicable pump control curves may range between a lowest proportional pressure curve PP1 and a highest proportional pressure curve PP3. The stored adaptable mapping may comprise a list of relative values in terms of percentage ranging from 0% for the lowest proportional pressure curve PP1 and 100% for the highest proportional pressure curve PP3.

[0027]The mapping between the system variable and the feed forward signal to be applied for the feed forward control must not have a negative gradient, because the pump must not reduce the pump control curve when the valves open, i.e. the kv-value rises. Similarly, the pump control curve must not increased when the valves close.

[0028]Optionally, the adjustable pump control curve may be a proportional pressure curve. This is particularly beneficial if the valves are installed at heating radiators.

[0029]Optionally, the system may comprise one or more thermal energy consumers and the one or more temperature-controlled valves may be automatically and/or thermostatically actuated valves installed at said thermal energy consumers. Preferably, the thermal energy consumers are radiators of a heating system.

[0030]Optionally, the feed forward signal may be low-pass filtered with a predetermined time constant before it is used to automatically adjust the pump control curve in the feed forward control if the determined system variable is smaller than the previously determined system variable. This is particularly beneficial to avoid undesired rapid oscillations between the control curves. Such oscillations have shown to occur at households with low variations of the kv-value, where small changes of the opening degree of the valves may lead to larger changes of the pump head which the valves try to compensate. Preferably, in order to avoid such oscillations, a first order filter, for instance with a time constant of 1200 seconds, may be applied if the kv-value is dropping. A rising kv-value, however, may be used unfiltered as input into the feed forward control.

[0031]Optionally, the pump control curve may be adjustable without steps within a total range of applicable pump characteristic curves.

[0032]Optionally, the method may further comprise operating the pump in a first boost mode and/or in a second boost mode, wherein a gain factor is applied in the first boost mode for stronger adjusting the pump control curve as long as a determined common degree of openness value indicative of the common degree of openness of the one or more temperature-controlled valves is within a pre-determined low boost area adjacent to a minimum common degree of openness or within a pre-determined high boost area adjacent to a maximum common degree of openness, and wherein the pump is operated at maximum speed in the second boost mode if the system variable is within a pre-determined speed boost area adjacent to a logged maximum of the system variable, and a maximum pump control curve is currently applied, and a pre-determined period of maximum boosting time has not lapsed.

[0033]The first boost mode may be referred to as a PI controller boost. It is preferably applied as a first stage boosting when the kv-value and/or the opening degree is close to a maximum or minimum value, i.e. in a boost area. If the first boost mode is not successful to get the system out of the high boost area within a given time period, the second boost mode is activated to run the pump at maximum speed for a certain maximum boosting time.

[0034]According to another aspect of the present disclosure, a computer program is provided with instructions which, when the program is executed by a computer, cause the computer to carry out the previously described method.

[0035]According to another aspect of the present disclosure, a circulation pump is provided for being installed in a system for heating or cooling, wherein the circulation pump comprises control electronics being configured to carry out the previously described method or to execute the above-mentioned program.

[0036]Optionally, the circulation pump may be automatically programmed at a manufacturing site of the circulation pump to carry out the previously described method or to execute the previously described program. Thereby, the fully assembled circulation pump may leave the manufacturing site fully programmed for shipping to customers, such that there is no need for customers to program the circulation pump.

[0037]The method disclosed herein may be implemented in form of compiled or uncompiled software code that is stored on a computer readable medium with instructions for executing the method. Preferably, the software is installed on control electronics within the circulation pump according to the present invention. Alternatively, or in addition, the method may be executed by software in a cloud-based system and/or a building management system (BMS).

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]Embodiments of the present disclosure will now be described by way of example with reference to the following figures of which:

[0039]FIG. 1 is a schematic view showing an example of a system for heating or cooling described herein;

[0040]FIG. 2 is a perspective view showing an example of a circulation pump described herein;

[0041]FIG. 3 is a schematic view showing an example how the pump control curve is automatically adjusted according to the present disclosure;

[0042]FIG. 4 is a schematic flow diagram view showing an example how the common degree of openness is determined according to the present disclosure;

[0043]FIG. 5 is a diagram showing a determined kv-value of a time for logging maximum and minimum kv-values according to the present disclosure;

[0044]FIG. 6 is a schematic flow diagram view showing an example how the valve position is controlled according to the present disclosure;

[0045]FIG. 7 is a head-flow-diagram with indicated boost areas for the valve position control according to the present disclosure;

[0046]FIG. 8a is a diagram showing an example of an initial mapping between the kv-value and the feed forward signal according to the present disclosure;

[0047]FIG. 8b is a diagram showing an example of a control curve in a head-flow-diagram after it has been adapted to a heating system;

[0048]FIG. 9 is a schematic flow diagram showing an example how the mapping between the kv-value and the feed forward signal is updated according to the present disclosure; and

[0049]FIG. 10 is a diagram showing an example of the mapping before an update, after an update, and with the restriction to avoid a negative gradient.

DETAILED DESCRIPTION

[0050]FIG. 1 shows a system 1 for heating or cooling as it is typically installed in a household. For the sake of simplicity, the system 1 is referred to in the following as a heating system, but it could equally be a cooling system without departing from the spirit of the present disclosure. The system 1 comprises a thermal energy source 3, e.g. a gas boiler, a heat exchanger, a heating coil or a heat reservoir. The thermal energy source 3 is connected to a piping system 4 filled with a fluid, e.g. water, for transferring thermal energy to one or more thermal energy consumers 5, e.g. radiators, underfloor heating, or heat exchangers. At least one circulation pump 7 is installed in the system 1 to circulate the fluid for thermal energy transfer from the thermal energy source 3 to the one or more thermal consumers 5.

[0051]The system 1 is further equipped with one more temperature-controlled valves 9, e.g. thermostatic radiator valves (TRVs), smart valves or other kinds of temperature-controlled valves. Each of the temperature-controlled valves 9 may be installed in the vicinity of one of the thermal consumers 5 to control the fluid flow through that respective thermal energy consumer 5. The thermal energy consumers 5 are installed in parallel in the system 1, such that each of the thermal energy consumers 5 has a fluid inlet connected to a feed line of the system 1 and a fluid outlet to a return line of the system 1. The associated temperature-controlled valve 9 is preferably installed at a fluid inlet of the thermal energy consumer 5.

[0052]Usually, there is no direct control connection between the circulation pump 7 and the temperature-controlled valves 9. The temperature-controlled valves 9 are each controlled by a closed-loop control using a thermostat, wherein a temperature sensor is used to determine the current temperature and a target temperature can be set for the thermostat. In case of a heating system, for example, the valves 9 open when the measured temperature is below a target temperature in order to increase the flow of the heating fluid through the respective thermal energy consumer 5. Analogously, the valve 9 closes when the measured temperature is above a target temperature in order to reduce the flow of the heating fluid through the thermal energy consumer 5.

[0053]It is in principle known that it is useful to adapt the speed of the circulation pump 7 depending on the common degree of openness of the temperature-controlled valves 9. As the circulation pump 7 is a stand-alone device without direct knowledge of the opening degree of the temperature-controlled valves 9, it would in principle run too fast when the common degree of openness of the valves 9 is low or too slow when the common degree of openness of the valves 9 is high. This would lead to the undesirable situation that the circulation pump 7 consumes unnecessary power and produces unnecessary flow noise when the valves 9 are nearly closed. Furthermore, the circulation pump 7 may not provide sufficient flow when the valves 9 are open to a maximum degree during times of high thermal energy demand. Therefore, there may be a lack of comfort during times of high thermal energy demand, because it takes too long to reach the target temperature. It has shown that known “auto adapt”—algorithms do not react quickly enough to provide the required thermal energy flow in situations of high thermal energy demand.

[0054]FIG. 2 shows a circulation pump 7 as it is installed in a heating or cooling system 1 as shown in FIG. 1. The hardware of the circulation pump 7 as shown in FIG. 2 may not differ from a circulation pump as known in the prior art. However, it differs in the way it is programmed and thus controlled to operate. The circulation pump 7 comprises a pump housing 11 with a suction inlet 13 and pressure outlet 14. The section inlet 13 and the pressure outlet 14 comprise coaxially aligned flanges directed into opposite directions in order to be installed in a piping system 4 of a cooling or heating system 1 as shown in FIG. 1. The pump housing 11 accommodates an impeller (not visible) that is rotatable around a rotor axis R in order to drive a fluid flow (e.g. water flow) from the suction inlet 13 to the pressure outlet 14. The circulation pump 7 is a wet-running circulation pump with an integrated permanent magnet synchronous motor (PMSM) within a motor housing 15.

[0055]Furthermore, the circulation pump 7 comprises control electronics (not visible) within the motor housing 15 in order to control the speed of the circulation pump 7. A lid 17 of the motor housing 15 comprises a front face 19 with human-machine-interface elements, such as a display, LED indicators, one or more buttons or switchers. A user may manually set the circulation pump 7 to follow a fixed control curve or to run in an “auto adapt” control mode to automatically adapt the applied control curve. For example, in case of a heating system 1 with radiators as thermal energy consumers 5, the circulation pump 7 may be set to one of three fixed proportional pressure curves PP1, PP2 and PP3. For example, FIG. 8b shows an example of three fixed control curves as linear lines in a head(h)-flow(q)-diagram.

[0056]The circulation pump 7 may further comprise a wireless interface or a connector via which the control electronics within the circulation pump 7 can be programmed, reprogrammed or updated. The circulation pump 7 may thus be programmed at the time of manufacturing and assembly and/or when it is already installed in a cooling or heating system 1.

[0057]FIG. 3 shows how the circulation pump 7 of FIG. 2 is programmed to be controlled. As already mentioned above, it is known in the prior art, for example from EP 0 726 396 B1 or EP 1 323 986 B1, to automatically adapt the pump control curve in a closed loop control based on a pipe resistance value as a feedback value. So, the circulation pump 7 is known to react to a change of the opening degree of the valves 9 and to set the pump control curve accordingly. As this has shown to be too slow to provide sufficient comfort in situations of high thermal energy demand, the idea of the present invention to use a system variable, e.g. a pipe resistance or a kv-value, as an input to provide a feed forward signal to automatically adjust the control curve in a feed forward control. In other words, the circulation pump 7 is more proactively used to indirectly control the valve position. It should be noted that there is no direct control communication between the circulation pump 7 and the valves 9. The circulation pump 7, however, knows that the valves 9 open when they do not get sufficient thermal energy flow and that they close when they get too much thermal energy flow.

[0058]Therefore, the control schematics shown in FIG. 3 comprise a valve position control 21 and an opening degree estimation 23. It is the goal of the valve position control 21 to automatically adjust the control curve when the pipe resistance changes in order to keep the common degree of openness OD of the valves 9 in a desired range between a minimum common degree of openness OD_min and a maximum common degree of openness OD_max. Here, the common degree of openness OD in kept as close as possible to a predetermined fixed reference or target opening degree OD_ref, e.g. OD_ref=0.55, wherein OD_min=0 and OD_max=1. A central range of the common degree of openness is desirable, because it leaves upward and downward control room to adjust the valve position to the current thermal energy demand.

[0060]FIG. 4 shows the opening degree estimation 23 in more detail. It starts with calculating a kv-value based on the monitored head value h and monitored flow value {circumflex over (q)}. The kv-value, also denoted as flow factor, is used as system variable to express the amount of water flow in units of cubic meters per hour through the system 1 at a given common degree of openness OD of the valves 9 with a pressure drop of one bar across the valves 9. So, the kv-value is calculated as

$\mathrm{kv}=\frac{\hat{q}}{\sqrt{\hat{h}}},$

$k_{v,\Delta }=\max \left(k_{\mathrm{vhigh}}-k_{\mathrm{vlow}},k_{\mathrm{vBandMin}}\right)\widehat{\mathrm{OD}}=❘\begin{array}{cc}{\mathrm{OD}}_{\mathrm{ref}}& \mathrm{if}{k}_{v,\Delta }<k_{v,\mathrm{dynband},\min }\\ \frac{k_v-k_{\mathrm{vlow}}}{k_{v,\Delta }}& \mathrm{else}\end{array}0<=\widehat{\mathrm{OD}}<=1$

[0067]FIG. 7 shows a head(h)-flow(q)-diagram with a pump characteristic curve 31 of maximum pump speed and three displayed system characteristic curves 33a-c. The system characteristic curve 33a represents the situation when the valves 9 have a minimum degree of openness (OD=0) and the kv-value is at its minimum kv_min. The system characteristic curve 33b represents the situation in which the common degree of openness OD of the valves 9 is at the reference value OD_ref, e.g. OD_ref=0.55. It is the goal of the valve position control 21 to operate the circulation pump 7 in such a way that the common degree of openness of the valves 9 is at or around the reference value OD_ref. The system characteristic curve 33c represents a situation in which the common degree of openness OD is at a maximum (OD=1) and the kv-value is at its maximum kv_max. The boost areas for applying the first boost mode of the PI controller 25 are the bands close to the extreme system characteristic curves 33a and 33c.

[0068]FIG. 8a shows an initial mapping of 26 kv-values between zero and 2.5 m³/h to the relative proportional pressure curve to be applied in terms of percent. A relative proportional pressure curve value of 100% may represent the highest proportional pressure curve PP3. A relative proportional pressure curve value of 0% may represent the lowest proportional pressure curve PP1. The feed forward signal Out_ff as the output 27 of the feed forward control 29 is an interpolation between the mapping points in FIG. 8a. The mapping of FIG. 8a is then stored in the control electronics of the circulation pump 7.

[0069]FIG. 8b shows an example of a control curve in a head(h)-flow(q)-diagram after it has been adapted to the heating system 1. The lowest proportional pressure curve PP1 is only followed for a flow below or 0.1 m³/h. For flows between 0.1 and 0.2 m³/h, the proportional pressure curve is gradually increased to apply the proportional pressure curve PP3 for flow values between 0.2 and 0.9 m³/h. Above 0.9 m³/h, the circulation pump 7 reaches in the shown example its maximum and follows its maximum pump characteristic curve 31 for flow values above 0.9 m³/h. As the pump has reached its maximum speed limit, the head drops with an increase of flow above 0.9 m³/h.

[0070]FIG. 9 shows how the mapping of FIG. 8a as used by the feed forward control 29 is adapted based on the output 28 Out_PI of the PI controller 25. The output 28 Out_PI of the PI controller 25 is used as an indicator to decide whether the feed forward signal 27 Out_ff is too high or too low. If the current feed forward signal 27 Out_ff is perfect for the current thermal energy demand, the output 28 Out_PI of the PI controller 25 is zero. If the output of PI controller 25 is positive, there is a need to increase the feed forward signal 27 Out_ff. Likewise, a negative output 28 Out_PI of the PI controller 25 suggests a decrease of the feed forward signal 27 Out_ff. The stored mapping is adapted by changing the mapping points located closest to the current kv-value. Over time, the mapping is adapted to give the appropriate relative proportional pressure curve value href needed for a certain kv-value.

[0071]The adaptation of the feed forward control 29 is only performed if the variation of the kv-value is above a noise level, i.e. k_v,Δ≥k_{v,dynband,min} and there is no kv-spike currently detected. A limitation of the output 28 Out_PI of the PI controller 25 based on a PI controller limiting parameter prevents a too aggressive adaptation when the PI controller 25 is operated in the first boost mode. A non-zero output 28 Out_PI of the PI controller 25 shows as a deviation of the current kv-value from the interpolated mapping and triggers a correction of the closest two mapping points in proportion to the output 28 Out_PI of the PI controller 25 such that the interpolation between those two corrected mapping points lies on the current kv-value. If the current kv-value is outside of the mapped range of kv-values, only the lowest or highest mapping point is adapted accordingly. The adapted mapping points are limited to relative proportional pressure curve values between 0% and 100%.

[0072]In order to avoid a negative gradient in the mapping, the mapping points at all kv-values above the adapted higher closest mapping point are shifted upward by the minimum amount that is needed to avoid the updated mapping from having a negative gradient. Similarly, in case of a downward adaptation of the lower closest mapping point, all mapping points with kv-values below said downward adapted closest lower mapping point are shifted downward by an amount that is needed to avoid the updated mapping from having a negative gradient. Finally, the updated mapping is stored for the subsequent iteration of the feed forward control 29.

[0073]FIG. 10 shows an example how the mapping may look like before an update (on the left), after an update (in the middle) and after the mapping is adapted to avoid a negative gradient (on the right). FIG. 10 shows on the left the mapping as it is stored before it is updated. A positive output 28 Out_PI of the PI controller, however, suggests that the mapping around the current kv-value should be increased. Therefore, the neighbouring mapping points are shifted upward accordingly. The shifting is weighted according to the distance of the current kv-value to the mapping point. In the shown case, the closest higher neighbouring mapping point is shifted more upward than the closest lower neighbouring mapping point. As this would lead to a negative gradient in the mapping between the closest higher neighbouring mapping point and the next-to-closest higher mapping point, all mapping points with kv-values above the closest higher neighbouring mapping point are shifted upward by the least amount A that is necessary to avoid a negative gradient.

[0074]Where, in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as optional, preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

[0075]The above embodiments are to be understood as illustrative examples of the disclosure. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. While at least one exemplary embodiment has been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art and may be changed without departing from the scope of the subject matter described herein, and this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0076]In addition, “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, characteristics or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments described above. Method steps may be applied in any order or in parallel or may constitute a part or a more detailed version of another method step. It should be understood that there should be embodied within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of the contribution to the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the disclosure, which should be determined from the appended claims and their legal equivalents.

LIST OF REFERENCE NUMERALS