Patent Publication Number: US-2016237745-A1

Title: A window shading control system and method thereof based on decomposed direct and diffuse solar radiations

Description:
The invention generally relates to the control of lighting, and shading, and more specifically to a controller having a flexible architecture to control the same. 
     In modern buildings electric lights and window shades are electronically controlled to create comfortable lighting conditions. Electric lights may be controlled by wall switches, or may be automatically dimmed or turned off in response to daylight and/or occupancy status. Shading systems, such as venetian blinds and roller shades, are motorized systems that can be controlled responsive to daylight, glare and/or an occupant&#39;s preferences. 
     Specifically, window shading systems are used to block glaring direct sun and regulate the indoor daylight level. The control of shade deployment level and/or blind occlusion not only impacts the visual comfort of occupants, it also impacts energy consumption. That is, if the shade or blind blocks more daylight than necessary, additional electric lighting energy may be required to provide general illumination. On the other hand, additional cooling energy may be consumed to offset the cooling load due to solar heat gain resulting from shades/blinds that are not properly adjusted. The shade deployment level is the percentage of a window area occluded due to the shade. The shade deployment level differs for different buildings and façades. 
     Automated shading systems often utilize a sky sensor to control the deployment of shades or the occlusion of blinds. The sensor may be mounted horizontally on the roof facing the sky, or on the window wall interior, or on the exterior of the controlled space. The sensor may be sensitive to visible light for detecting illuminance (daylight) or sensitive to the entire solar spectrum for detecting irradiance (solar heat flux). Regardless of the sensor&#39;s location and sensitivity, the sensor only outputs the combined effect of direct and diffuse illuminance or irradiances, typically referred to as global illuminance/irradiance. 
     In order to correlate a sky sensor&#39;s output signal (global illuminance/irradiance) to the presence of direct sunlight or the overall interior daylight condition, certain heuristic or complex calibration procedures should be utilized. These procedures usually result in thresholds that are outside a range which causes a full deployment of the shades or closing of the blinds. In other words, the presence of direct sunlight or excessive daylight is merely an inference, but not an actual measurement. 
     In the related art there are number of solutions for measuring direct and diffuse solar radiation. For example, in weather stations the direct normal irradiance value is measured using a pyrheliometer mounted on a solar tracker, and horizontal irradiance is measured by a pyrometer with a solar shading ring or band. These types of sensors are very expensive, thereby cost-prohibitive for shading control applications. Moreover, the measurements performed by the pyrheliometer and pyrometer sensors do not provide any information about the actual solar and lighting conditions experienced at each window. 
     Another solution for measuring the direct and diffuse solar radiation includes six silicon solar cells arranged in three pairs on three mutually perpendicular planes. One cell of each pair is exposed to both the direct rays of the sun and the diffuse light radiation incidental from the same direction, depending upon the orientation of the device and the time of day. The other cells of each pair are exposed only to the diffuse radiation on their respective planes. The differences in the measured radiation on each plane are squared, summed, and the square root of the sum is then taken to determine the actual value of the direct rays of the sun. Thus, this solution is designed to detect the presence of sunlight in the sky as further discussed in U.S. Pat. No. 4,609,288. 
     Yet another solar radiation sensor, discussed in the related art, is based on a plurality of light sensitive detectors and a masking element. The masking element has a pattern of translucent and opaque areas which are disposed to ensure that at any given time at least one detector can be exposed to direct sunlight (if the sun is shining) through a translucent area and at least one detector is shaded from direct sunlight by an opaque area. The light sensitive detectors lie in a horizontal plane of the radiation sensor. An exemplary implementation of such a sensor can be found in U.S. Pat. No. 6,417,500. 
     This solar radiation sensor is designed however, to merely detect the presence of sunlight in the sky and cannot provide sufficient information about the direct solar radiation that hits a window on a particular façade or the amount of diffuse radiation falling on a window. Therefore, the radiation sensors disclosed in the related art cannot be utilized in shading controller applications. 
     The main challenge when using a radiation sensor to control shades and/or blinds of a window shading system is that presently there is no easy way to distinguish the contribution of direct radiation from that of diffuse radiation. Direct sunlight is often undesirable on a task surface as bright patches of sunlight on the work surface (e.g., a desk, a computer screen, etc.) causes disturbing or even disabling glare, thereby preventing occupants from performing visual tasks. Diffuse daylight, on the other hand, is usually desirable for providing evenly distributed natural light on the work surface as long as the overall level is not unacceptably high. 
     With a single global light or radiation sensor, direct sunlight in front of a window has to be inferred through some calibration procedures. When the sensor reading exceeds a certain threshold, it is assumed that direct sun is present or that the overall light has reached an unacceptable level. In this case, the shade will be deployed or the blind will be closed in response. However, this threshold value can be achieved by many combinations of direct and diffuse light/radiation. Therefore, the shade/blind may be deployed or closed on a relatively bright day even without direct sunshine, thus obstructing an occupant&#39;s view to the outside and also resulting in suboptimal utilization of daylight for illumination. 
     Therefore, in recognition of the deficiencies of the prior art, it would be advantageous to provide a solution for controlling shading systems based on the decomposed direct and diffuse solar radiations. 
     Certain embodiments disclosed herein include a window shading control system. The system includes a sensor configured to produce a global radiation measurement for each direction of at least four directions, wherein each global radiation measurement is a combined direct and diffuse component of at least one of illuminance and irradiance; a processor connected to the sensor and configured to compute a discrete direct component and a diffuse component for global radiation measurement; and a control circuit connected to the processor and configured to control a window shading system based on the discrete direct component and the diffuse component computed for at least one global radiation measurement. 
     Certain embodiments disclosed herein also include a method for controlling a window shading system. The method comprises measuring a global radiation measurement for each direction of at least four directions, wherein each global radiation measurement is a combined direct and diffuse component of at least one of illuminance and irradiance; computing a discrete direct component and a diffuse component for the global radiation measurement; and controlling a window shading system based on the discrete direct component and the diffuse component computed for at least one global radiation measurement. 
    
    
     
       The disclosed subject matter is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic diagram of a window shading controller constructed according to one embodiment; 
         FIG. 2  is a schematic block diagram of a sensor designed to measure the direct and diffuse components of the solar radiation according to one embodiment; 
         FIG. 3  is a schematic block diagram of a sensor designed to measure the direct and diffuse components of the solar radiation according to another embodiment; 
         FIG. 4  is a schematic block diagram illustrating how global radiation measurements are obtained by the sensor of  FIGS. 2 and 3 . 
         FIG. 5  is a flowchart illustrating a process for computing the diffuse and direct components of the solar radiation according to one embodiment; and 
         FIG. 6  is a flowchart illustrating a process for controlling of the shade/blind system using the diffuse and direct components of the solar radiation. 
     
    
    
     It is important to note that the embodiments disclosed are only examples of the many advantageous uses of the innovative techniques herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views. 
     Certain exemplary embodiments include a shading control system that controls a window shading system based on direct and diffuse solar radiation data decomposed from photosensitive elements. Also disclosed is a sensor comprised of a plurality of photosensitive elements arranged to allow obtaining the direct and diffuse components of at least one of illuminance (i.e., light) and irradiance (i.e., solar heat flux). In one embodiment, the sensor is mounted on a window wall, and hence “feels” the same amount of solar radiation as that which actually hits the window. Therefore, controlling the shades and blinds of the shading system, according to certain disclosed embodiments, facilitates accurate detection and prevention of direct sunlight as well as a better estimation of incoming daylight or solar heat gain. As a result, in certain embodiments the disclosed controller can actuate the shade or blind to optimize the indoor daylight and solar heat gain conditions. 
       FIG. 1  shows an exemplary and non-limiting block diagram of a window shading controller  100  constructed according to one embodiment. The integrated controller  100  includes a sensor  110 , a processor  120 , a control circuit  130 , and a driver  140  driving the shades and blinds of a window shading system  150 . The sensor  110  includes a plurality of photosensitive elements that are configured to measure direct and diffuse components of the illuminance, direct and diffuse components of the irradiance, or direct and diffuse components of both the illuminance and irradiance. The structure and configuration of the photosensitive elements of the sensor  110  are discussed in greater detail below. 
     The processor  120  is configured to compute the direct and diffuse components of the solar radiations measured by the sensor  110 . Each photosensitive element in the sensor  110  returns a global radiation measurement of illuminance or irradiance, depending on the type of the photosensitive element. The global radiation measurement provided by a photosensitive element contains a combination of direct and diffuse components measured at the direction to which the photosensitive element is facing. The process for computing the direct and diffuse components is discussed in greater detail below. 
     The control circuit  130  is configured to adjust or set the shade deployment level and the blinds occlusion level in the system  150  based on the input provided by the processor  120 , i.e., the computed direct and diffuse components. As will be discussed below, according to one embodiment, the control circuit  130  can iteratively adjust the deployment and occlusion levels of the shade and blinds until achieving comfortable lighting conditions for the occupant. 
     The driver  140  is configured to power and control the electrical components of the window shading system  150 . For example, the driver  140  is configured to control the motors (not shown) controlling the movement of the shades and blinds in the system  150 . 
       FIG. 2  is an exemplary and non-limiting diagram of the sensor  110  designed to measure the direct and diffuse components of the illuminance and/or irradiance according to one embodiment. The sensor  110  in the embodiment illustrated in  FIG. 2  includes a plurality photosensitive elements, collectivity labeled as  210 , a housing  220  to enclose the photosensitive elements  210  as well as any auxiliary circuitry (not shown), and reflection blockers collectivity labeled as  230 . The sensor  110  is designed to be mounted on the same side of a façade as the window shades/blinds. The sensor  110  can be mounted by means of glue, screws, or any other fastening means. 
     Each photosensitive element  210  can be either sensitive to visible light and/or the entire spectrum of solar radiation. In one embodiment, an element  210  can comprise two photodiodes, where one has the spectral response of visible light and the other has the spectral response of solar radiation. 
     As noted above the sensor  110  can be configured to measure the visible daylight level (illuminance), the solar radiation level (irradiance), or both. In any configuration, both the diffuse and direct components may be measured. In order to measure the visible daylight level, i.e., illuminance, all the photosensitive elements  210  have the spectral response of a Commission Internationale de l&#39;Éclairage (CIE) luminosity function with a similar sensitivity to that of human eyes. 
     To measure the heat flux from the solar radiation level, i.e., irradiance, the sensor  110  is configured to include photosensitive elements  210  with a spectral response that is relatively flat across all wavelengths. In the case where both illuminance and irradiance are required, for example, for simultaneously estimating daylight level and solar heat gain, the sensor  110  is configured to include two different types of photosensitive elements  210  installed on each of the four faces of the sensor housing  220 . An exemplary diagram of such a sensor is provided in  FIG. 3 . 
     In the exemplary  FIG. 3 , the photosensitive elements  310  measure the direct and diffuse components of the illuminance and have a response function as described above. The photosensitive elements  320  measure the direct and diffuse components of the irradiance and have a response function as described above. It should be noted that in  FIGS. 2 and 3 , only 3 faces of the 6 faces of the sensor housing  220  are shown. It should be further noted that a typical sensor  110  includes 4 (or 4 pairs) of photosensitive elements. 
     Referring back to  FIG. 2 , in one embodiment the enclosure of the sensor housing holds the photosensitive elements  210  in their predefined positions and seals the auxiliary circuitry within the housing. The auxiliary circuitry is used for amplifying the signals produced by the photosensitive elements  210 , to allow proper reading of such signals by the processor  120 . It should be noted that as the photosensitive elements  210  can be standard photodiodes, the dimensions of the sensor  110  can be relatively compact in size. The reflection blockers  230  are flanges designed to absorb light and/or radiation to prevent the photosensitive elements  210  from seeing the light and/or radiation reflected from the building surface. 
     The operation of the sensor  110  will now be described with reference to  FIG. 4 . Four photosensitive elements  411 ,  412 ,  413 , and  414  are included in the sensor  110  providing a global radiation measurement I 1 , I 2 , I 3 , and I 4  respective of illuminance or irradiance. The sensor  110  is mounted on a façade surface in such a way that element  411  is facing out of the building (i.e. perpendicular to the façade) and measures incident radiation normal to the façade. The photosensitive elements  412  and  413  measure radiation projected onto the horizontal plane and are parallel to the façade. The photosensitive element  414  measures radiation from sky zenith. Each measurement I 1 , I 2 , I 3 , and I 4  includes both the combined direct and diffuse components of either the illuminance or irradiance. The vector I b  shown in  FIG. 4 , is the direct normal solar radiation. The angles β and γ are the solar altitude and the solar elevation azimuth angles respectively, that is, the angle between the sun and the façade surface normally projected onto the horizontal plan. The angles β and γ can be computed using location and time information. For example, the solar altitude angle β and the solar elevation azimuth angle γ can be computed as follows: 
     
       
         
           
             y 
             = 
             
               α 
               - 
               e 
             
           
         
       
       
         
           
             
               tan 
                
               
                 ( 
                 α 
                 ) 
               
             
             = 
             
               
                 
                   - 
                   
                     
                       sin 
                        
                       
                         ( 
                         H 
                         ) 
                       
                     
                     * 
                   
                 
                  
                 
                   cos 
                    
                   
                     ( 
                     D 
                     ) 
                   
                 
               
               
                 - 
                 
                   ( 
                   
                     
                       
                         
                           cos 
                            
                           
                             ( 
                             L 
                             ) 
                           
                         
                         * 
                       
                        
                       
                         sin 
                          
                         
                           ( 
                           D 
                           ) 
                         
                       
                     
                     + 
                     
                       
                         
                           sin 
                            
                           
                             ( 
                             L 
                             ) 
                           
                         
                         * 
                       
                        
                       
                         
                           cos 
                            
                           
                             ( 
                             D 
                             ) 
                           
                         
                         * 
                       
                        
                       
                         cos 
                          
                         
                           ( 
                           H 
                           ) 
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 sin 
                  
                 
                   ( 
                   β 
                   ) 
                 
               
               = 
               
                 
                   [ 
                   
                     
                       
                         sin 
                          
                         
                           ( 
                           L 
                           ) 
                         
                       
                       * 
                     
                      
                     
                       sin 
                        
                       
                         ( 
                         D 
                         ) 
                       
                     
                   
                   ] 
                 
                 - 
                 
                   [ 
                   
                     
                       
                         cos 
                          
                         
                           ( 
                           L 
                           ) 
                         
                       
                       * 
                     
                      
                     
                       
                         cos 
                          
                         
                           ( 
                           D 
                           ) 
                         
                       
                       * 
                     
                      
                     
                       cos 
                        
                       
                         ( 
                         H 
                         ) 
                       
                     
                   
                   ] 
                 
               
             
             ; 
           
         
       
     
     where, α is the solar azimuth angle; e is the elevation azimuth angle (i.e., the angle between façade normal and true south); L is the latitude (negative for Southern Hemisphere); D is the declination (negative for Southern Hemisphere); and H is the hour angle. The values of L and D are determined by the geographical location, while H is determined by the hour of the day. 
     The process performed by the processor  120  computes and outputs the discrete values of the direct and diffuse components of the solar radiation. The relation between each global measurement (I 1 , I 2 , I 3 , and I 4 ) and the direct and diffuse solar radiations as measured by the photosensitive elements  411 ,  412 ,  413 , and  414  are as follows: 
         I   1   =I   1   b   +I   1   d   =I   b ·cos β·cos γ+ I   1   d  
 
     
       
      
       I 
       2 
       =I 
       2 
       b 
       +I 
       2 
       d 
       =I 
       2 
       d  
      
     
         I   3   =I   3   b   +I   3   d   =I   b ·cos β·cos γ+ I   3   d  
 
         I   4   =I   4   b   +I   4   d   =I   b ·sin β+ I   4   d   (1)
 
     where, I x   b  and I x   d  x (x=1, 2, 3 or 4) are the direct and diffuse components of solar radiations, respectively, sensed by each of the photosensitive elements; and I b , β, and γ are as defined above. 
       FIG. 5  shows an exemplary and non-limiting flowchart  500  describing the process for computing discrete values of the direct and diffuse components of the solar radiation according to one embodiment. At S 510 , the global measurements (I 1 , I 2 , I 3 , and I 4 ) are received from the sensor  110 . In addition, the values of the angles β and γ are received as input. Alternatively, the values of the angles β and γ are computed, for example, as discussed above. 
     At S 520 , a check is made to determine if the sun is astronomically positioned in front of the façade to which the sensor  110  is mounted. In one embodiment, S 520  includes a check if the value of the angle β is greater than 0° (β&gt;0) and the value of γ is between −90° and 90° (−90&lt;γ&lt;90). If not, at S 530 , the direct component (I direct ) is set to 0 and consequently, I 1   b , I 2   b , I 3   b  and I 4   b  are all 0. In addition, the diffuse component (I diffuse ) of the solar radiation perpendicularly projected onto the façade, i.e., the window, is set to I 1 . It should be noted that if, from the sensor  110  readings it can be determined that the sun is not seen on the façade, then there is no direct radiation on the façade, hence, I b =I 1   b =0. Consequently, the element  411  senses only the diffuse radiation on the façade, i.e. I d =I 1 . 
     If S 520  results with a Yes answer, the execution continues with S 540  where another check is made to determine if the sky is overcast. Specifically, it is checked if the values I 1 , I 2  and I 3  are approximately equal. For example, a difference of up to 5% between the values I 1 , I 2  and I 3  will be considered as approximately equal. If so, execution continues with S 530 ; otherwise, execution proceeds to S 550 . 
     At S 550 , the sky&#39;s luminous distribution and the proportional diffuse components I x   d  of I x  (x=1, 2, 3, and 4) are computed. There are known techniques in the related art for computing the sky&#39;s luminous distribution under the dome of sky using a zenith luminance measurement, which is proportional to the global measurement I 4 . In one embodiment, the zenith luminance is normalized to 1, and any location under the dome of sky, particularly locations at elements  411 ,  412 , and  413 , can be calculated relative to 1. Specifically, the luminous distribution is the ratio between respective measurements (L 1 :L 2 :L 3 :L 4 , where L 4  is 1). Then, the ratio is multiplied by the global measurement I 4  to obtain the diffuse components I x   d  (x=1, 2, 3, and 4) that fall on each photosensitive element  411 ,  412 ,  413 , or  414 . 
     At S 560 , the values of the direct components I x   b  (x=1, 2, 3, and 4) for each global measurement I x  are computed using equation (1) defined above and the diffuse components I 1   d :I 2   d :I 3   d :I 4   d  computed at S 550 . At S 570 , the computed values of the direct and diffuse components are input to the control circuit  130 . The computed values may be saved for future use in a memory (not shown). It should be noted that the direct and diffuse components can be computed for either the illuminance or irradiance depending on the type of the photosensitive elements. 
       FIG. 6  shows an exemplary and non-limiting flowchart  600  describing a process for controlling the window shading system using one or more computed direct and diffuse components. In the embodiment depicted in  FIG. 6 , the control circuit  130  receives the direct and diffuse illuminance components E 1   b  and E 1   d  of the perpendicular solar radiation (as measured by element  411 ) and computed by the processor  120 . 
     At S 610 , a direct illuminance threshold value E THD  as well as upper bound E UPPER  and lower bound E LOWER  values of the user-specified lighting levels are set. The E THD  value determines a level that is strong enough to cause glare and may be set by a user or according to a preconfigured value. At S 620 , a check is made to determine if the sun shines directly in front of the façade. That is, if the direct illuminance value E 1   b  is greater than the threshold value E THD . If so, at S 625 , the blind/shade of the window shading system  150  is deployed to a level that blocks direct sun at the specified depth into the room. That is, the deployment level (H S ) of the window shading system is set to H THD  which is a percentage value (0-100%) of a window area that would be occluded due to the deployment operation. 
     At S 630 , the resulting daylight level E TASK  at a task surface (e.g., a desk) is estimated. In one embodiment, the estimation is performed using a function ƒ( ) for predicting interior horizontal illuminance on the task surface using the values of E 1   b  and E 1   d , H S , and θ S . The parameter θ S  is the slat angle that controls blind occlusion (if a venetian blind instead of a shade is used). That is, 
         E   TASK =ƒ( E   1   b   ,E   1   d   ,H   S ,θ S )
 
     At S 635 , a check is made to determine if the resulting task lighting exceeds the upper boundaries of the user-defined lighting level, i.e., E TASK &gt;E UPPER . If S 635  results with a negative answer execution continues with S 660 ; otherwise, at S 640 , another check is made to determine if the shade/blind is fully deployed, that is, if H S =100% (where, 0% is fully retracted and 100% is fully deployed). If so, execution continues with S 645 ; otherwise, at S 650 , the shade/blind deployment level H S  is lowered by a predefined increment (e.g., 10%). Then, execution continues with S 690 . 
     Optionally and also when the blinds are of a venetian type, at S 645 , it is determined if the slats are completely closed, i.e., if θ S =100% (i.e., the slat angle is 90°) where a 0% slat angle is fully opened (i.e., the slat angle is at 0°) and a 100% slat angle is fully occluded (i.e., the slat angle is at 90°). If the slat angle is different than 100%, then at S 655 , the blinds are closed by a predefined increment, e.g., 5%. Otherwise, execution continues with S 690 . 
     If S 635  results with a No answer, then at S 660  a check is made to determine if the resulting task lighting is below a lower boundary of the user-specified lighting level, i.e., if E TASK &lt;E LOWER . If S 660  results with a No answer execution returns to S 620 ; otherwise, at S 665 , another check is made to determine if the shade/blind is fully retracted, that is, if H S =0%. If so, execution continues with S 670 ; otherwise, at S 675 , the shade/blind deployment level H S  is retracted by a predefined increment, e.g., the value H S  is decremented by 10%. 
     Optionally and also when the blinds are of a venetian type, at S 670 , it is determined if the slats are completely opened, i.e., if θ S =0%. If not, at S 680 , the blinds are opened by predefined increment, e.g., incrementing θ S  by 5%. Otherwise, execution continues with S 690 . 
     At S 690 , it is checked if at least one exit condition is satisfied. An example for such a condition may be, for example, if it is nighttime, if the room is vacant, and the like. If the process should end, execution terminates; otherwise, at S 695 , the controller waits a predefined time period and returns to S 630  where another iteration is performed. 
     The various embodiments disclosed herein can be implemented as hardware, firmware, software or any combination thereof. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage unit, a non-transitory computer readable medium, or a non-transitory machine-readable storage medium that can be in a form of a digital circuit, an analog circuit, a magnetic medium, or combination thereof. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (“CPUs”), a memory, and input/output interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the application program, or any combination thereof, which may be executed by a CPU, whether or not such computer or processor is explicitly shown. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit. 
     While several embodiments have been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in view of the prior art and, therefore, to effectively encompass the intended scope of the invention. Furthermore, the foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto.