Window treatment control using bright override
A system includes a window treatment adjacent to a window of a room. At least one motor drive unit is associated with the window treatment, for varying the position of the window treatment. A sensor measures a light level (e.g., an outdoor light level) at the window. A controller provides signals to the motor drive unit to automatically adjust the position of the window treatment so as to control a penetration distance of sunlight into the room when the window treatment is partially opened. The controller is configured to position the window treatment in a bright override position if the measured light level is at least a bright threshold value. The controller is configured to select the bright threshold value from among at least two predetermined values. The selection depends on an angle of incidence between light rays from the sun and a surface normal of the window.
1. An apparatus comprising:
a controller having a processor; and
a memory having instructions stored thereon that when executed by the processor of the controller direct the controller to:
provide signals to a motor drive unit of a window treatment to adjust a position of the window treatment so as to control a penetration distance of sunlight into a room when the window treatment is partially opened;
position the window treatment in a bright override position when a measured light level is at least one of greater than or equal to a bright threshold value; and
calculate the bright threshold value as a function of at least one of an altitude angle of the sun or an incident angle between rays from the sun and a surface normal to the window.
2. The apparatus of claim 1 , wherein the instructions, when executed by the processor of the controller, further direct the controller to calculate the bright threshold value as a function of the altitude angle and the incident angle.
3. The apparatus of claim 2 , wherein the instructions, when executed by the processor of the controller, further direct the controller to calculate the bright threshold value periodically during a day.
4. The apparatus of claim 3 , wherein the instructions, when executed by the processor of the controller, further direct the controller to calculate the bright threshold value as a function of the altitude angle and the incident angle.
5. The apparatus of claim 4 , wherein the instructions, when executed by the processor of the controller, further direct the controller to calculate the bright threshold value according to the equation:
E max=( E sun/0.8)* C alt* C inc,
where: Emax is the bright threshold value;
Esun is a predetermined maximum bright threshold value;
Calt is a function of the altitude angle; and
Cinc is a function of the incident angle.
6. The apparatus of claim 5 , wherein Calt is given by the equation:
C alt=1−0.75*[1−exp(−0.21/sin At )/0.81],
where At is the altitude angle.
7. The apparatus of claim 6 , wherein Cinc is given by the equation:
C inc=[1−cos Ai ]*[1 −E shade/ E sun]
where Ai is the incident angle; and
Eshade is a predetermined minimum bright threshold value.
8. The apparatus of claim 7 ,
where the predetermined maximum bright threshold value is approximately 6,000 foot-candles, and
where the predetermined minimum bright threshold value is approximately 2,500 foot-candles.
9. The apparatus of claim 1 , wherein the instructions, when executed by the processor of the controller, further direct the controller to select a bright threshold value from at least two predetermined values.
10. The apparatus of claim 1 , wherein the instructions, when executed by the processor of the controller, further direct the controller to position a plurality of window treatments in the bright override position when the measured light level is at least one of greater than or equal to a bright threshold value.
11. A method of controlling a motorized window treatment by a controller having a processor configured to execute instructions stored in a memory, the method comprising:
calculating, by the controller, a bright threshold value as a function of at least one of an altitude angle of a sun or an incident angle between rays from the sun and a surface normal to a window; and
providing, by the controller, signals to a motor drive unit to:
adjust a position of the motorized window treatment to control a penetration distance of sunlight into a room when the motorized window treatment is partially opened; and
position the motorized window treatment in a bright override position when a measured light level is at least one of greater than or equal to the bright threshold value.
12. The method of claim 11 , further comprising receiving, by the controller, the measured light level from a sensor disposed adjacent to the window.
13. The method of claim 11 , wherein calculating the bright threshold value includes calculating the bright threshold value periodically during a day.
14. The method of claim 11 , wherein calculating the bright threshold value includes calculating the bright threshold value as a function of the altitude angle of the sun and the incident angle between rays from the sun and the surface normal to the window.
15. The method of claim 14 , wherein calculating the bright threshold value includes calculating the bright threshold value according to the equation:
E max=( E sun/0.8)* C alt* C inc,
where:
Emax is the bright threshold value;
Esun is a predetermined maximum bright threshold value;
Calt is a function of the altitude angle; and
Cinc is a function of the incident angle.
16. The method of claim 15 , wherein Calt is given by the equation:
C alt=1−0.75*[1−exp(−0.21/sin At )/0.81],
where At is the altitude angle.
17. The method of claim 15 , wherein Cinc is given by the equation:
C inc=[1−cos Ai ]*[1 −E shade/ E sun]
where:
Ai is the incident angle; and
Eshade is a predetermined minimum bright threshold value.
18. The method of claim 17 , wherein the predetermined maximum bright threshold value is approximately 6,000 foot-candles, and wherein the predetermined minimum bright threshold value is approximately 2,500 foot-candles.
19. The method of claim 11 , wherein the method includes selecting the threshold value from at least two predetermined values.
20. The method of claim 11 , wherein providing signals to the drive motor unit to position the window treatment in the bright override position includes providing signals to a plurality of drive motor units to position a plurality of window treatments in the bright override position.