Controlling transitions in optically switchable devices

A method of limiting energy consumption in a facility having at least one tintable window between an interior and exterior of the facility, wherein the level of tinting in the tintable window can be controlled automatically, the method comprising:

• (a) receiving output signals from an exterior photosensor and any one or more sensors selected from the group consisting of an interior photosensor, an occupancy sensor, an exterior temperature sensor, and a transmissivity sensor which detects light passing through the tintable window from the exterior;
• (b) determining a level of tint for said tintable window using a relationship between the received output signals and the level of tint;
• and
• (c) providing instructions to change the tint of the tintable window to the level of tint determined in (b),
• wherein the relationship employed in (b) requires (i) transitioning from a first lighter tint level to a second darker tint level when the output signal from the exterior photosensor passes a first threshold and (ii) transitioning from the second darker tint level to the first lighter tint level when the output signal from the exterior photosensor passes a second threshold, and wherein the first and second thresholds are different, and
• wherein the first threshold is reached at a first value of irradiance and the second threshold is reached at a second value of irradiance, and the first value is greater than the second value.

A method of limiting energy consumption in a facility having at least one tintable window between an interior and exterior of the facility, wherein the level of tinting in the tintable window can be controlled automatically, the method comprising:

• (a) receiving output signals from any two or more sensors selected from the group consisting of an exterior photosensor, an interior photosensor, an occupancy sensor, an exterior temperature sensor, and a transmissivity sensor which detects light passing through the tintable window from the exterior;
• (b) determining a level of tint for said tintable window using a relationship between the received output signals and the level of tint;
• and
• (c) providing instructions to change the tint of the tintable window to the level of tint determined in (b),
• wherein the output signals comprise a signal from the exterior photosensor and a signal from the interior photosensor, and wherein the relationship employed in (b) is an expression or look up table in which the level of tint is the dependent variable and the signals from the exterior photosensor and the interior photosensor are independent variables.

A controller for a tintable window for a facility having at least one tintable window between an interior and exterior of the facility, the controller comprising:

• (a) a processor or control circuit;
• (b) at least one input for receiving output signals from one or more sensors;
• (c) instructions for causing the processor or control circuit to determine a level of tint in said tintable window by using a relationship between the received output signals and the level of tint, wherein the relationship employs output signals from any two or more sensors selected from the group consisting of an exterior photosensor, an interior photosensor, an occupancy sensor, an exterior temperature sensor, and a transmissivity sensor which detects light passing through the tintable window from the exterior;
• (d) at least one output for controlling, directly or indirectly, the level of tint in the tintable window;
• (e) logic for receiving one or more of the output signals from a building management system, a lighting control panel, or a security system for the facility;
• and further comprising logic for receiving an energy or power consumption signal indicating energy or power consumption by a heating system, a cooling system, and/or lighting in the facility.

A system for controlling energy consumption in a facility that contains a tintable window between an interior and exterior of the facility, the system comprising:

• (a) a building management system;
• (b) a lighting control panel;
• (c) a network over which the building management system and the lighting control panel communicate;
• (d) a controller for the tintable window, the controller comprising (i) instructions for determining a level of tint in said tintable window by using a relationship between received output signals and the level of tint, wherein the relationship employs output signals from any two or more sensors selected from the group consisting of an exterior photosensor, an interior photosensor, an occupancy sensor, an exterior temperature sensor, and a transmissivity sensor which detects light passing through the tintable window from the exterior, and (ii) at least one output for controlling, directly or indirectly, the level of tint in the tintable window;
• and wherein the lighting control panel provides occupancy information derived from the occupancy sensor, and wherein the relationship between received output signals and the level of tint employs the occupancy information from the lighting control panel.

A controller for a tintable window for a facility having at least one tintable window between an interior and exterior of the facility, the controller comprising:

• (a) a processor or control circuit;
• (b) at least one input for receiving output signals from one or more sensors;
• (c) instructions for causing the processor or control circuit to determine a level of tint in said tintable window by using a relationship between the received output signals and the level of tint, wherein the relationship employs output signals from an exterior photosensor, an interior photosensor, an outside temperature sensor, and a tint command;
• (d) at least one output for controlling, directly or indirectly, the level of tint in the tintable window;
• and
• (e) a network interface for communicating with a network containing a building management system for the facility, a lighting control panel for the facility, and/or a security system for the facility.