Patent Publication Number: US-9846261-B2

Title: Method and apparatus for determining an icing condition status of an environment

Description:
FIELD 
     The improvements generally relate to the field of ice mitigation systems such as de-icing and anti-icing systems, and more particularly to intelligent control thereof to reduce energy consumption. 
     BACKGROUND 
     Some known ice mitigation systems are switched on or off manually, which requires human intervention. In other cases, when the icing condition status cannot readily be determined by human intervention, ice mitigation systems are left active more than actually required, or even sometimes permanently, which is a cause of energy waste. Energy waste is a concern in itself, and is particularly a concern in situations of limited energy resources, such as where the ice mitigation system is battery powered for instance. 
     There thus remained room for improvement. 
     SUMMARY 
     A system or method to automatically determine an icing condition status of an environment such as described below can be used in automating the control of an ice mitigation system, for instance, or for other purposes. 
     In accordance with one aspect, there is provided a method for determining an icing condition status of an environment, the method comprising: receiving a value of a quantity of heat applied to at least a portion of a structure, said structure having a sensor surface exposed to the environment, receiving a temperature measurement of the sensor surface, receiving a wind speed measurement of the environment, receiving an ambient temperature measurement of the environment, determining a temperature projection of the sensor area using the value of the quantity of heat applied, the wind speed measurement, and the ambient temperature measurement, comparing the temperature projection to the temperature measurement of the sensor surface, and generating a signal indicating the icing condition status based on the comparison. 
     In accordance with another aspect, there is provided an apparatus for determining an icing condition status of an environment, the sensor comprising: a structure having a sensor surface exposed to the environment, a heater positioned to apply a quantity of heat to at least a portion of the structure, a temperature sensor positioned to obtain a temperature measurement of the sensor surface, a controller to receive a wind speed measurement of the environment and an ambient temperature measurement of the environment, a function to determine a heat transfer projection of the sensor area using at least the wind speed measurement, the ambient temperature measurement, and one of the value of a quantity of heat and a target temperature of the sensor surface and a function to compare the heat transfer projection to an associated heat transfer value. 
     In accordance with another aspect, there is provided a method for determining an icing condition status of an environment, the method comprising: receiving a value of a quantity of heat applied to at least a portion of a structure, said structure having a sensor surface exposed to the environment, receiving a temperature measurement of the sensor surface, receiving a wind speed measurement of the environment, receiving an ambient temperature measurement of the environment, determining a heat transfer projection of the sensor area using at least the wind speed measurement, the ambient temperature measurement, and one of the value of a quantity of heat and a target temperature of the sensor surface; comparing the heat transfer projection to an associated heat transfer value, and generating a signal indicating the icing condition status based on the comparison. 
     As demonstrated below, the temperature projection can be computed based on the laws of thermodynamics and other measured or predictable parameters. The temperature projection can be compared with the corresponding measured temperature and the likelihood of icing can then be evaluated. If used as an input of or as part of a controller in an ice mitigation system for an anemometer or a windmill, for instance, this method can reduce significantly the amount of energy needed. Moreover, if icing is likely to occur, different actions can be taken such generating a signal indicative of the likelihood of icing. Such a signal can be recorded by a data recording device such as a data logger, for instance. 
     When icing is likely to occur, actions can be triggered such as activating an ice mitigation system, activating a bearing heating system, storing data in a data recording device such as a data logger, transmitting the signal to a remote location, etc. Henceforth, information on weather conditions with potential risk of icing can be provided and used as desired. 
     Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       In the figures, 
         FIG. 1  is a schematic elevation view showing an anemometer including an apparatus for determining an icing condition status of an environment, in accordance with one embodiment. 
         FIG. 2  is a bloc diagram of main components of the apparatus of  FIG. 1 ; 
         FIG. 3  is a bloc diagram showing an alternative to the apparatus of  FIG. 1 ; 
         FIG. 4  is a bloc diagram showing another alternative of the apparatus of  FIG. 1 ; 
         FIG. 5  is an elevation view showing a variant to the apparatus of  FIG. 1 ; 
         FIG. 6  is an elevation view showing another variant to the apparatus of  FIG. 1 ; and 
         FIG. 7  is an elevation view showing yet another variant to the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment shown in  FIG. 1 , an anemometer of the rotary cup type is shown. The anemometer generally has a rotor having a plurality of rotary cups circumferentially interspaced around an axis and rotatably mounted to a base via an elongated shaft. The configuration of the shaft is intended to provide a small disturbance to air flow. 
     In this embodiment, the shaft forms a structure to which heat is applied and of which an sensor area is exposed to the environment. In this particular embodiment, the shaft is hollow, having a cylindrical wall, and a coiled electrical wire forming a resistor  1  is provided inside the cylindrical wall, placed in contact with an inner face of the cylindrical wall—the outer face being exposed to the environment. Heat is applied to the cylindrical wall by the Joule effect, when a measurable electrical current is circulated through the resistor. The cylindrical wall can be formed of a high electrical conductivity material, such as a metal for instance, to favour uniformity of the temperature of the cylindrical wall. The quantity of heat applied to the cylindrical wall, or heat transfer rate q meas , can be determined, by measuring the voltage drop and the current flowing into the resistor and multiplying these two values together, for instance. The heated portion can extend to rotor bearings, for instance, to keep them warm and maintain the predictability of the instrument&#39;s calibration curve which is likely to be affected by temperature variations, such as from increased friction which can result from temperature decrease. 
     The temperature of the sensor surface of the cylindrical wall, which is exposed to the environment can be measured with one or more temperature sensor(s), and will be referred to as T s   _   meas . In the embodiment illustrated in  FIG. 1 , thermistors  2  were selected as temperature sensors. If the cylindrical wall is highly conductive, positioning the thermistors against the internal surface of the cylindrical wall, or in apertures provided inside the cylindrical walls for instance, can allow to measure the temperature of the sensor area since the temperature of the outer wall will by very close to the temperature of the inner wall. Alternately, the sensor area temperature T s   _   meas  can be measured by an external device, such as an infrared sensor  6  for instance. It will be understood that in alternate embodiments, the sensor area can be located on another structure portion, examples of which can include the cups, a portion of the base, or even a portion which does not form part of the anemometer itself as will be detailed below. Further, as will be seen below, more than one sensor area can be used. The ambient temperature of the environment will be referred to as T ∞ , and can be measured by any suitable temperature sensor, such as a thermistor  13  for instance. The wind speed of the environment, which will be referred to as U meas , can be obtained from the anemometer itself in this embodiment. A controller  5  which can include a microprocessor and can be provided separately from the anemometer or conveniently embedded in the base thereof, for instance, can receive signals representative of U meas , T meas , T ∞ , q meas , etc. 
     The conditions of the environment will affect the surface temperature T s   _   meas  of the sensor area. For instance, if the ambient temperature T ∞  decreases, while every other parameter remains constant, the surface temperature will decrease as well. In the same way, if the wind speed U meas  increases, the surface temperature T s   _   meas  will decrease since the convection coefficient will increase and more heat will be removed from the heated surface. If the heat transfer rate q is increased, while all other parameters remain constant, the surface temperature T s   _   meas  will increase. Given necessary obedience to the laws of physics and given apparatus features, a relationship can be established between the surface temperature T s   _   meas , and the outside conditions, namely the measured wind speed U meas , the ambient temperature T ∞  and the measured heat transfer rate q meas , which can allow to determine a temperature projection of the sensor area. Environment conditions such as precipitation or icing for instance, can cause the measured temperature of the sensor area T s   _   meas  to differ from the temperature projection. Henceforth, comparing the temperature projection to the measured temperature of the sensor area, which can be done by the controller for instance, can allow to determine an icing condition status. An associated signal can then be generated, such as by the controller for instance. The signal can be in any suitable form such as frequency-based, voltage-based, and/or current-based, for instance. 
     In one embodiment, the temperature of the sensor area is controlled in order to maintain it constant independently of external conditions. Henceforth, a target temperature can be set. 
     The theoretical heat transfer rate required a q theo  to keep the surface at a given temperature T s   _   meas  can be expressed as equation 1.
 
 q   theo   =f ( T   ∞   ,U   meas   ,T   s   _   meas )  eq. 1
 
     If precipitations are occurring, the heat transfer rate theoretically required q theo  will be lower than the heat transfer rate actually required because water will contribute to extract more heat from the sensor surface. The control of the heat transfer rate can be done by the controller for instance, to ensure that the surface temperature remains constant at a given value by adjusting the heat transfer rate q meas  of the heating element. A difference, which can be referred to as an error, can be obtained by comparing the measured heat transfer rate q meas  to the heat transfer rate theoretically required q theo  to maintain the surface at a given temperature T s   _   meas  under given meteorological conditions U meas  and T ∞ . It will be understood by those skilled in the art that this is equivalent to and indirectly involves comparing a temperature projection to the measured temperature of the sensor area, because the actual measured heat transfer rate q meas  is obtained from a measure of the temperature of the sensor area. The reference value (equation 1), the heat transfer rate theoretically required q theo , is obtained from a previous calibration and stored in the anemometer&#39;s controller  5 . If the difference is greater than a given threshold, it can indicate that precipitations are occurring. If the ambient temperature T ∞  is below the freezing point, it is likely that the precipitations would lead to icing, and a signal indicating icing condition status as a presence of icing or a quantitative indication of a likelihood of icing can then be generated. 
     The generation of the signal can trigger activation of an icing mitigation system, such as heating of the anemometer rotor and bearings, for instance, to prevent biased wind measurements, as well as any suitable alternate action such as transmitting data, or recording data in a data recording device such as a data logger for instance. 
     In such an embodiment, the theoretical heat transfer rate can be considered to be a heat transfer projection which is then compared with an associated heat transfer value, the actual measured quantity of heat value, to form a basis for the signal generation. 
       FIG. 2  presents an example control scheme, based on the heat transfer rate theoretically required q theo  and the measured heat transfer rate q meas , used for the ice detection method to control the activation of the anemometer heating system and/or the heating of other equipment and/or triggering an ice mitigation system such as anti-icing or de-icing mechanisms installed on equipment and/or generating a signal indicative of the presence or likelihood of icing that can be recorded by a data recording device. 
     In another embodiment, the temperature projection T s   _   theo  can be theoretically modeled using the expression presented in equation 2.
 
 T   s   _   theo   =f ( T   ∞   ,U   meas   ,q   meas )  eq. 2
 
     In this embodiment, the quantity of heat applied to the sensor area q meas  can be constant for instance, rather than being varied to maintain the temperature of the sensor area constant. If precipitations are occurring, the measured surface temperature T s   _   meas  will be lower than the temperature projection T s   _   theo  because water will contribute to extract additional heat from the heated zone. The temperature projection for the measured wind velocity U meas  and ambient temperature T ∞  is obtained from a previous calibration and stored in the anemometer&#39;s controller  5  for instance. The temperature projection can be directly compared to the measured surface temperature to determine a difference, or error, therebetween. If the difference is greater than a given threshold, it can indicate that precipitations are occurring. If the ambient temperature T ∞  is below the freezing point, it is likely that the precipitations would lead to icing, and a signal indicating icing condition status as a presence of icing or a quantitative indication of a likelihood of icing can then be generated. 
     In such an embodiment, the temperature projection can be considered to be a heat transfer projection which is then compared with an associated heat transfer value, the actual measured temperature of the sensor area, to form a basis for the signal generation. 
       FIG. 3  presents the control scheme, based on the surface temperature measured/modeled, used with the control probe and the thermal model to control the activation of the anemometer heating system and/or an ice mitigation system and/or generating a signal indicative of the likelihood of icing. 
     The total heat transfer rate from the sensor area can be express by equation 3, the usual convective heat transfer equation also known as Newton&#39;s law of cooling, where q is the heat transfer rate,  h  is the average convection coefficient, A s  is the area of the probe, T s  is the surface temperature and T ∞  is the ambient temperature.
 
 q= h A   s ( T   s   −T   ∞ )  eq. 3
 
     The average convection coefficient can be approximated by a function, for example but not limited to, a second order polynomial equation, such as the one presented in equation 4, where coefficients a, b and c are obtained empirically through calibration. An analytical expression or one obtained through numerical simulations or a look-up table could also be used to describe the average convection coefficient.
 
   h =a·U   meas   2   +b·U   meas   +c   eq. 4
 
     In one embodiment, the heat transfer rate theoretically needed q theo  to keep the surface of a heated volume at a given temperature is obtained using equation 5, which is derived from equations 3 and 4. The heat transfer rate theoretically needed q theo  can be calculated according to, but not limited to, equation 5 or an equivalent expression.
 
 q   theo =( a·U   meas   2   +b·U   meas   +c ) A   s ( T   s   _   meas   −T   ∞ )  eq. 5
 
     The heat transfer rate q meas  is measured at any given time and compared with the heat transfer rate theoretically needed q theo . 
     In another embodiment, the temperature projection T s   _   theo  can be calculated based on equation 6, which is derived from equations 3 and 4, and directly compared to the measured temperature of the sensor area. 
     
       
         
           
             
               
                 
                   
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     In still another embodiment, the surface area of the sensor surface to which the heat is being generated is modified so that the exposed surface area A s  can be changed. This embodiment requires to obtain a measurement of the surface area of the sensor area A s   _   meas  contrary to the embodiments described above where the surface area of the sensor area can be treated as a constant. This can be achieved by changing the surface area of a flexible polymer membrane for instance. The theoretical area needed A s   _   theo  is calculated according to the surface temperature T s   _   meas , the measured heat transfer rate from the volume q meas , the measured flow velocity U meas  and the ambient temperature T ∞ , using equation 7, which is derived from equations 3 and 4. The theoretical needed area A s   _   theo  can be calculated according to, but not limited to, equation 7 or an equivalent expression. 
     
       
         
           
             
               
                 
                   
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     The surface area of the heated zones A s   _   meas  is measured at any given time and compared with the theoretical area needed A s   _   theo . If the theoretical area A s   _   theo  is larger than that of the measured area A s   _   meas , it is a sign of precipitations. 
     In such an embodiment, the surface area required can be considered to be a heat transfer projection which is then compared with an associated heat transfer value—the actual measured surface area of the sensor area, to form a basis for the signal generation. 
       FIG. 4  presents the control scheme, based on the surface area measured/modeled, used to generate a signal indicative of the likelihood of icing which can be used to control the activation of the anemometer heating system and/or an ice mitigation system. 
     In the embodiment shown in  FIG. 1 , the anemometer is provided with an ice mitigation system which, in this embodiment, is provided in the form of a heating system for the rotor  4 . The heating of the rotor is activated only when a risk of icing is detected while the sensor area can be permanently heated using any suitable strategy which can be based on constant temperature control or a constant power control for instance. Using an intelligent heating strategy for the rotor can allow to minimize the amount of energy consumed by the instrument. In alternate embodiments, the ice mitigation system which can be intelligently controlled based on the signal indicative of icing conditions can be provided on other equipments such as wind turbine components or other ice-sensitive equipment for instance. 
       FIG. 5  shows another embodiment where the sensor area is provided externally to the anemometer, but exposed to the same environment. Such a configuration can pose less stringent heating requirements for the bearings of the anemometer, and/or facilitate retro-fitting with an existing anemometer. However, some measuring instruments such as sonic anemometers, do not have moving parts. The functioning of such an alternate embodiment can be similar to that disclosed above in relation with the embodiment shown in  FIG. 1 . 
     An other alternate embodiment is shown in  FIG. 6  in which case the sensor area  7  forms part of a windmill. 
     A still other alternate embodiment is shown in  FIG. 7  which uses two sensor areas. A first sensor area  11  is provided as detailed above with reference to  FIG. 1 , whereas a second sensor area  12  is provided as part of a cylinder that is positioned adjacent the anemometer. The second sensor area can be kept below the freezing point and the first sensor area can be kept above the freezing point by independently controlling the quantity of heat provided, for instance. The sensor area kept below the freezing point can be used in quantifying the persistence of icing. The persistence of icing, also known as instrumental icing, is an important data since it indicates the total length of an icing event. The sensor area kept at a temperature above the freezing point provides information on the meteorological icing, i.e. the duration of the meteorological event. This data can be useful during wind resource assessment to justify or not the implementation of ice mitigation mechanisms for wind turbines (i.e. anti-icing and/or deicing) at a future given site. Moreover, the zone kept below the freezing point can allow differentiating between a snow event and an icing event. In the case of a snow event, snow will not stick to the surface and will simply make its way around the zone. During an icing event, the ice will grow on the zone affecting its thermal behaviour and icing will be detected. Alternate embodiments can have two sensor area provided in different form, such as both being external to the anemometer or both being part of the anemometer, for instance, or more than two sensor areas. 
     It will be understood that ice mitigation systems which can be triggered upon an indication of an icing condition status can be de-icing, anti-icing, can be battery powered, grid powered, can be vibratory, heat based, etc. Ice mitigation systems can be used on wind powered devices such as windmills and anemometers, but can also be used on other structures such as on ocean-based platforms, ships, buildings, etc. 
     As can be seen therefore, the examples described above and illustrated are intended to be exemplary only. The scope is indicated by the appended claims.