Method of controlling a motorized window treatment
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Solution Overview
Problem
Existing load control systems for motorized window treatments struggle to accurately distinguish between sunny and cloudy days, leading to potential glare issues around sunrise and sunset on sunny days due to incorrect threshold settings.
Innovation Solution
The system measures total light intensity and computes its rate of change, enabling or disabling sunlight penetration limiting modes based on thresholds that vary with solar elevation angle, particularly around sunrise and sunset to prevent direct sunlight penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant threshold is used to detect cloudy conditions, then the system can operate simply, but it fails to accurately distinguish between sunny and cloudy days around sunrise and sunset, causing glare issues
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant threshold to a dynamic threshold that varies with solar elevation angle. The threshold is adjusted based on the calculated solar elevation angle, allowing the system to adapt to changing lighting conditions throughout the day, particularly around sunrise and sunset when glare is most problematic.
Solution Approach 2:
The patent changes the parameter of the detection threshold from a fixed constant value to a variable value that depends on solar elevation angle. By calculating the solar elevation angle and using it to determine an appropriate threshold, the system achieves more accurate differentiation between sunny and cloudy conditions at different times of day.
2Object-affected harmful factors
If the system controls window treatments to limit sunlight penetration on sunny days, then occupant comfort is improved, but incorrect control around sunrise and sunset causes direct sun glare
Solution Approach 1:
The patent implements feedback by continuously monitoring the solar elevation angle and using this information to adjust the detection threshold and control decisions. The system calculates the solar elevation angle, compares it with predetermined values, and adjusts the cloudy-day threshold accordingly, creating a closed-loop control system that responds to changing environmental conditions.
Solution Approach 2:
The patent applies preliminary action by calculating the solar elevation angle in advance and using this information to proactively adjust the detection threshold before glare conditions occur. The system determines whether to enable or disable sunlight penetration limiting mode based on the calculated solar elevation angle and light intensity measurements, preventing glare before it happens.
3Measurement precision
If the cloudy-day threshold varies with solar elevation angle, then accurate sunny/cloudy day differentiation is achieved, but the control system becomes more complex
Solution Approach 1:
The patent introduces an intermediary element - the solar elevation angle calculation - that mediates between the simple light intensity measurement and the complex control decision. By using the solar elevation angle as an intermediate parameter, the system achieves accurate sunny/cloudy day differentiation without requiring direct complex analysis of light patterns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents sun glare by accurately differentiating between sunny and cloudy days, ensuring optimal sunlight control and occupant comfort by adjusting motorized window treatments accordingly.
Implementation Method 1
The load control system may comprise a photosensor (i.e., a daylight sensor or a radiometer) mounted to a window or to the outside of the building for detecting a cloudy condition. The load control system may detect the cloudy condition, for example, if a total light level measured by the photosensor is below a constant threshold THCONST.
Data Source
AI summary
A method comprises measuring a light intensity at a window; determining if the light intensity exceeds a cloudy-day threshold; operating in a sunlight penetration limiting mode to control the motorized window treatment to control the sunlight penetration distance in the space; enabling the sunlight penetration limiting mode if the light intensity is greater than the cloudy-day threshold; and disabling the sunlight penetration limiting mode if the total lighting intensity is less than the cloudy-day threshold. The cloudy-day threshold is maintained at a constant threshold if a calculated solar elevation angle is greater than a predetermined solar elevation angle, and the cloudy-day threshold varies with time if the calculated solar elevation angle is less than the predetermined solar elevation angle. The cloudy-day threshold is a function of the calculated solar elevation angle if the calculated solar elevation angle is less than the predetermined solar elevation angle.