Patent Publication Number: US-11640096-B2

Title: Multipurpose controller for multistate windows

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     An Application Data Sheet is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in their entireties and for all purposes. 
     FIELD 
     The invention relates generally to electrochromic devices, more particularly to controllers for electrochromic windows. 
     BACKGROUND 
     Electrochromism is a phenomenon in which a material exhibits a reversible electrochemically-mediated change in an optical property when placed in a different electronic state, typically by being subjected to a voltage change. The optical property is typically one or more of color, transmittance, absorbance, and reflectance. One well known electrochromic material is tungsten oxide (WO 3 ). Tungsten oxide is a cathodic electrochromic material in which a coloration transition, transparent to blue, occurs by electrochemical reduction. 
     Electrochromic materials may be incorporated into, for example, windows for home, commercial and other uses. The color, transmittance, absorbance, and/or reflectance of such windows may be changed by inducing a change in the electrochromic material, that is, electrochromic windows are windows that can be darkened or lightened electronically. A small voltage applied to an electrochromic device (EC) of the window will cause them to darken; reversing the voltage causes them to lighten. This capability allows control of the amount of light that passes through the windows, and presents an opportunity for electrochromic windows to be used as energy-saving devices. 
     While electrochromism was discovered in the 1960&#39;s, EC devices, and particularly EC windows, still unfortunately suffer various problems and have not begun to realize their full commercial potential despite many recent advancements in EC technology, apparatus and related methods of making and/or using EC devices. 
     SUMMARY OF INVENTION 
     “Smart” controllers for EC windows are described. Controllers with multiple features can sense and adapt to local environmental conditions. Controllers described herein can be integrated with a building management system (BMS) to greatly enhance the BMS&#39;s effectiveness at managing local environments in a building. Controllers described herein may have functionality for providing one, two, three or more of the following features: (a) powering an EC device of an EC window; (b) determining percent transmittance of an EC window; (c) determining size of an EC window; (d) determining temperature of an EC device of an EC window; (e) determining damage to an EC device of an EC window; (f) determining wire length between the EC window controller and an EC window; (g) wireless communication between the EC window controller and a separate communication node; (h) storing and transmitting data relating to an EC window via an RFID tag that is actively or passively powered; (i) storing charge resulting from a transition of an EC device of the EC window and/or direct such charge to a power grid; (j) repairing short related defects of an EC device of an EC window; and (k) heating one or both electrodes of an EC device of an EC window. 
     In one disclosed aspect, a window controller for controlling one or more windows capable of undergoing reversible optical transitions is configured or designed to provide at least two functions. In certain embodiments may be any two of the following: (a) powering a reversible optical transition of at least one of the one or more windows; (b) determining transmittance of at least one of the one or more windows; (c) determining a size of at least one of the one or more windows; (d) determining temperature of at least one of the one or more windows; (e) determining damage to at least one of the one or more windows; (f) determining wire length between the window controller and at least one of the one or more windows; (g) wireless communication between the window controller and a separate communication node; (h) storing and transmitting data relating to at least one of the one or more windows via an RFID tag that is actively or passively powered; (i) storing charge resulting from a transition of at least one of the one or more windows and/or direct such charge to a power grid; (j) repairing short related defects of at least one of the one or more windows; and (k) heating one or both electrodes of an electrochromic device of at least one of the one or more windows. In various embodiments, the controller is configured or designed to provide at least functions (b), (c), (d) and (e). In other embodiments, the controller is configured or designed to provide at least functions (a), (b), (c), (d) and (e). In still other embodiments, the controller is configured or designed to provide at least functions (a), (b), (d), (g), and (h). 
     Some disclosed aspects concern a controller as described but provided as part of a larger combination of system of elements such as a building management system containing window controller as described. In another example, an apparatus includes (i) a Building Management System (BMS); (ii) the window controller as described above; and (iii) a multistate electrochromic window. In yet another example, an apparatus includes (i) the window controller as described above, and (ii) an electrochromic window. In various embodiments, the electrochromic window is entirely solid state and inorganic. 
     Other disclosed aspects pertain to methods of managing a building&#39;s systems. Such methods may make use of data collected by a window controller from one or more windows capable of undergoing reversible optical transitions in the building. This data is used as input for adjusting at least one other system of the building, such as HVAC, lighting, security, power, fire suppression and elevator control. In some related methods, the controller provides power to the one or more windows to drive the reversible optical transitions. In a specific embodiment, the method includes the following operations: (a) powering the reversible optical transition of at least one of the one or more windows; (b) determining transmittance of at least one of the one or more windows; (c) determining temperature of at least one of the one or more windows; (d) wireless communication between the window controller and a separate communication node; and (e) storing and transmitting data relating to at least one of the one or more windows via an RFID tag that is actively or passively powered. 
     In a specific example, the method further involves collecting one or more of the following types of data about the one or more windows: transmittance, size, temperature. In a different example, the method additionally involves storing data, in the controller, about the one or more windows. 
     Still other disclosed aspects pertain to window controllers for controlling one or more windows capable of undergoing reversible optical transitions, where the window controllers are configured or designed to provide the following functions: (a) powering a reversible optical transition of at least one of the one or more windows; (b) determining transmittance of at least one of the one or more windows; (c) determining temperature of at least one of the one or more windows; (d) communication between the window controller and a separate communication node; and (e) storing and transmitting data relating to at least one of the one or more windows. 
     In such controllers, the function of determining temperature of at least one of the one or more windows may be implemented by direct measurement from one or more sensors on the at least one window. Alternatively, the function of determining temperature of at least one of the one or more windows may be implemented by algorithmically inferring temperature from current and/or voltage information from the at least one window. 
     In such controllers, the function of powering the reversible optical transition may be implemented with pulse width amplifier rendered as an h-bridge or a buck converter. Additionally or alternatively, the function of determining transmittance of at least one of the one or more windows is implemented by direct measurement from one or more sensors on the at least one window. In certain embodiments, the function of storing and transmitting data relating to at least one of the one or more windows may involve reading data from a controller embedded in the at least one window. 
     These and other features and advantages will be described in further detail below, with reference to the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description can be more fully understood when considered in conjunction with the drawings in which: 
         FIG.  1    depicts a an EC window controller interfaced with a building management system. 
         FIG.  2    is a schematic representation of a charge storage mechanism of controllers described herein. 
         FIG.  3    is a schematic of an onboard window controller. 
         FIG.  4    depicts a different onboard window controller and associated user interface. 
         FIG.  5    is a cross section schematic of an all solid state and inorganic EC device on a substrate. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional EC window controllers have a number of pitfalls. For example, they typically need to be calibrated at the factory for a specific insulated glass unit (IGU) size and wire length—any mismatch at the time of installation can cause problems. Also, conventional window controllers must be hard wired to a building management system and commands to the controller are usually entered by hand at the controller or via a BMS. Sensors on such window controllers typically have separate sensors for providing data feedback for control of the window and for supplying a BMS with data. Conventional EC window controllers also are limited in the type of data they collect from the EC window environment and how they collect such data. Controllers described herein do not suffer from such issues. Multipurpose EC window controllers described herein include features that provide easier installation, improved user interfaces, wireless communication and control, higher and consistent performance under varying conditions and capability to enhance environmental conditions, for example, when integrated into a building management system. 
     EC Devices 
     Controllers described herein are used to control EC devices, particularly in EC windows. Virtually any EC device will work with multipurpose controllers described herein. Additionally, non-electrochromic optically switchable devices such liquid crystal devices and suspended particle devices. For context, EC device technology is described below in relation to all solid state and inorganic EC devices, particularly low-defectivity all solid state and inorganic EC devices. See the discussion associated with  FIG.  5   . Because of their low defectivity and robust nature, these devices are particularly well suited for multipurpose controllers described herein. One embodiment is any controller described herein where the controller includes one or more EC devices selected from those described herein. 
     EC Windows 
     Electrochromic windows may use one or more EC devices and for those that use more than one EC device, more than one type of EC device can used in a window unit (IGU plus frame and/or accompanying structural support). An EC window will typically have wires or leads that extend from the bus bars of the EC device(s) through a seal in the IGU. These leads may also pass through a window frame. A window controller is wired to the leads, for example, near the EC window or not. EC windows are described in the patent applications incorporated by reference herein. Although not limited to such use, multipurpose controllers described herein find particular use with multistate EC windows, that is, windows that can transition not only between disparate states of coloring and bleaching, but also can transition to one or more intermediate colored states. Particular examples of multistate windows, having two or more EC panes, are described in U.S. patent application Ser. No. 12/851,514, filed on Aug. 5, 2010, and entitled “Multipane Electrochromic Windows,” which is incorporated by reference herein for all purposes. One advantage to such multipane EC windows is that the likelihood of defects in each of the EC panes aligning perfectly, and thus being observable to the end user, is quite small. This advantage is accentuated when low-defectivity panes are used. Controllers described herein are well suited for controlling and coordinating the function of one or more EC devices, for example, in a single window. 
     When used in combination with EC windows that have superior performance characteristics, for example short transition times, low-defectivity, long life, uniform transitions and the like, for example, all solid state and inorganic EC windows, the window controllers described herein significantly augment environmental control in a building. This is particularly true when window controllers are integrated with a BMS. Interrelationships between window performance, microclimate sensing, and environmental control are described in more detail below. 
     Building Management Systems 
     Although not limited to this context, multipurpose controllers described herein are well suited for integration with a BMS. A BMS is a computer based control system installed in a building that monitors and controls the building&#39;s mechanical and electrical equipment such as ventilation, lighting, power systems, elevators, fire systems, and security systems including automatic door locks, alarms, turnstiles and the like. A BMS consists of hardware and associated software for maintaining conditions in the building according to preferences set by the occupants and or building manager. The software can be based on, for example, internet protocols and/or open standards. 
     A BMS is most common in a large building, and typically functions at least to control the environment within the building. For example, a BMS may control temperature, carbon dioxide levels and humidity within a building. Typically there are many mechanical devices that are controlled by a BMS such as heaters, air conditioners, blowers, vents, and the like. To control the building environment, a BMS may turn on and off these various devices under defined conditions. A core function of a typical modern BMS is to maintain a comfortable environment for the building&#39;s occupants while minimizing heating and cooling losses. Thus a modern BMS is used not only to monitor and control, but also to optimize the synergy between various systems, for example to conserve energy and lower building operation costs. One embodiment is a multipurpose controller as described herein, integrated with a BMS, where the multipurpose controller is configured to control one or more EC windows. In one embodiment, the one or more EC windows include at least one all solid state and inorganic EC device. In one embodiment, the one or more EC windows include only all solid state and inorganic windows. In one embodiment, the EC windows are multistate EC windows as described in U.S. patent application Ser. No. 12/851,514, filed on Aug. 5, 2010, and entitled “Multipane Electrochromic Windows.” 
       FIG.  1    is a schematic of a BMS,  100 , that manages a number of systems of a building,  101 , including security systems, heating/ventilation/air conditioning (HVAC), lighting of the building, power systems, elevators, fire systems and the like. Security systems may include magnetic card access, turnstiles, solenoid driven door locks, surveillance cameras, burglar alarms, metal detectors and the like. Fire systems may include fire alarms, fire suppression systems including water plumbing control. Lighting systems may include interior lighting, exterior lighting, emergency warning lights, emergency exit signs, and emergency floor egress lighting. Power systems may include main power, backup power generators, and uninterrupted power source (UPS) grids. 
     Also, BMS  100  manages a window controller,  102 . In this example, window controller  102  is depicted as a distributed network of window controllers including a master controller,  103 , intermediate controllers,  105 , and end or leaf controllers,  110 . For example, master controller  103  may be in proximity to the BMS, and each floor of building  101  may have one or more intermediate controllers  105 , while each window of the building has its own end controller  110 . In this example, each of controllers  110  controls a specific EC window of building  101 . 
     Each of controllers  110  can be in a separate location from the EC window that it controls, or be integrated into the EC window. For simplicity, only ten EC windows of building  101  are depicted as controlled by window controller  102 . In a typical setting there may be a very large number of EC windows in a building controlled by window controller  102 . Window controller  102  need not be a distributed network of window controllers, for example, a single end controller which controls the functions of a single EC window also falls within the scope of the invention. Advantages and features of incorporating multipurpose EC window controllers as described herein with BMS&#39;s are described below in more detail and in relation to  FIG.  1    where appropriate. 
     One aspect of the invention is a BMS including a multipurpose EC window controller as described herein. By incorporating feedback from a multipurpose EC window controller, a BMS can provide, for example, enhanced: 1) environmental control, 2) energy savings, 3) security, 4) flexibility in control options, 5) improved reliability and usable life of other systems due to less reliance thereon and therefore less maintenance thereof, 6) information availability and diagnostics, 7) effective use of staff, and various combinations of these, because the EC windows can be automatically controlled. Such multipurpose controllers are described in more detail below, for example, in the context of being integrated into a BMS, however, the invention is not limited in this way. Multipurpose controllers of the invention may be stand alone controllers, for example, configured to control the functions of a single window or a plurality of EC windows, without integration into a BMS. 
     Multipurpose Controllers for EC Windows 
     Window controllers described herein have a microprocessor that controls one or more functions of one or more EC devices of an EC window. In one example, the controller regulates the potential applied to the EC device of the window and may optionally control other functions (alone or combined with other microprocessors) such as recharging a battery used to function the window, wirelessly communicating with a remote control, such as a hand held (“clicker”) and/or a BMS. 
     Because electrochromic windows offer enhanced control of not only the amount of light that enters the interior of a building, but also can serve, for example, to keep heat in, or out, of a building by providing a superior thermal barrier, the benefits of EC windows are enhanced by multipurpose controllers described herein. This is especially true when the controllers are integrated with a BMS, for example, in a building having many EC windows. The benefits are multiplied even more when the multipurpose controllers are not only integrated into a BMS, but also are used to control the functions of multistate EC windows. 
     In one embodiment, the EC window controller is a multipurpose controller, that is, it can control and/or monitor a number of functions and/or characteristics of one or more EC windows. One way to enhance the capabilities of a BMS which includes an EC window controller into its systems is to have a window controller with such enhanced capabilities providing feedback to the BMS, particularly where the feedback includes a number of parameters and on a more granular, window-by-window basis. These capabilities and/or functions allow synergistic control of, for example, a building&#39;s energy requirements and thus can save money above and beyond installing EC windows in a building, with or without conventional automatic control of the windows. The more efficient and versatile the EC windows employed in such a system, the greater energy savings and environmental control. Multistate EC windows are an exemplary choice for BMS&#39;s configured with multipurpose controllers. 
     Embodiments described herein include multipurpose controllers that can control one or more EC devices of an EC window and also one or more functions of each EC device of the associated window. One aspect of the invention is an EC window controller that includes one, two, three or more of the following functions: (a) powering an EC device of the EC window; (b) determining percent transmittance of an EC window; (c) determining size of the EC window; (d) determining temperature of an EC device of the EC window; (e) determining damage to an EC device of the EC window; (f) determining wire length between the EC window controller and the EC window; (g) wireless communication between the EC window controller and a separate communication node; (h) storing and transmitting data relating to an EC window via an RFID tag that is actively or passively powered; (i) storing charge resulting from a transition of an EC device of the EC window and/or direct such charge to a power grid; (j) repairing short related defects of an EC device of the EC window; and (k) heating one or both electrodes of an EC device of the EC window. Each of these capabilities and functions is described in more detail below. 
     Powering an EC Device 
     In some embodiments, the multipurpose controller can power one or more EC devices in an EC window. Typically, this function of the controller is augmented with one or more other functions described in more detail below. Controllers described herein are not limited to those that have the function of powering an EC device to which it is associated for the purposes of control. That is, the power source for the EC window may be separate from the controller, where the controller has its own power source and directs application of power from the window power source to the window. However, it is convenient to include a power source to the controller and configure the controller to power the window directly, because it obviates the need for separate wiring for powering the EC window. 
     One embodiment is a window controller with one, two, three or more capabilities described herein, where at least one of the capabilities is to control the optical state of an EC window. In various embodiments, there are certain conditions in which current and voltage may to be individually limited, and there is an optimum sequence by which the window is controlled with current limits and/or voltage limits to ensure reasonably quick and non-damaging optical transitions (such as coloring and bleaching an electrochromic window). Examples of such sequences are disclosed in U.S. patent application Ser. No. 13/049,623, naming Pradhan, Mehtani, and Jack as inventors, titled “Controlling Transitions In Optically Switchable Devices” and filed on Mar. 16, 2011, which is incorporated herein by reference in its entirety. As part of the window control process, the controller may receive measurements of current and/or voltage on a window. Once such measurements are made the “control” function may impose appropriate current and/or voltage limits to allow the window to reliability change state. 
     An example of powering an electrochromic window involves use of a controller having a pulse width modulated amplifier (see  FIG.  3   ) rendered as an “h-bridge” which allows the load to float, be grounded, or be set to any voltage or polarity between the input voltage to the controller and ground. In other embodiments, an EC controller is implemented using a “buck converter” and a separate polarity switch allowing the load to set to any voltage or polarity between the input voltage to the controller and ground. Control may also include current limits during all or part of the transition from one state to another. 
     Percent Transmittance (% T) 
     Electrochromic windows have at least one EC device deposited on a glass or other transparent substrate and may have other coatings and panes that are part of an IGU in a window unit. The percent transmittance (% T) of an EC window, typically the integrated transmittance across the visible spectrum for an IGU of an EC window, is an important parameter because it is a measure of how much light is entering a room where the window is installed. When using windows with multistate capability, that is having intermediate states as well as end states of colored and bleached, it may be important to have feedback on the % T in order to maintain a particular state of transition and/or move to a new color transition according to the desire of the end user. Controllers described herein can measure % T by use of sensors and/or by using current/voltage (I/V) parameters to calculate % T. 
     Determining the % T can be inferred algorithmically or measured directly using a sensor (e.g. a photometric sensor such as a silicon photodiode) wired to a controller&#39;s analog input (AI-Transmittance). See  FIGS.  3  and  4   , discussed below. Another acceptable sensor is a pyranometer which measures solar irradiance across a larger spectrum of solar radiation. 
     In one embodiment, the controller includes a sensor on the outside of the building (or window side which will face outside when installed), which serves one or more EC windows and measures the solar spectrum that is entering the window or windows, and one more internal sensors which measure solar irradiance transmitted through the window of each window&#39;s IGU. These two energy values are compared in logic in the controller to provide a measure of % T of the window. When one sensor on the outside of the building (or window) is used to serve more than one window, the controller will typically sample solar irradiance on the exterior for use in calculating (effective) % T of each window unit. Sensors are calibrated to their respective IGU&#39;s, for example, when installed or replaced in the field. 
     In one embodiment, the controller employs an outside and an inside sensor for % T for each window. This embodiment is particularly well suited for obtaining more granular feedback on % T for adjusting individual windows&#39; transmissivities accordingly, or for example when the window controller is integrated into a BMS, for adjusting a number of parameters of a building such as HVAC and the like. For example, referring again to  FIG.  1   , window controller  102  controls five EC windows on side A of building  101 , and five windows on side B of building  101 . These windows are depicted as being on the top floor of building  101 . In this example, intermediate controller  105   a  controls three windows of one room of building  101 , and intermediate controller  105   b  controls seven windows in another room, two on side A of building  101  and five on side B of building  101 . In this example, there is a shadow of a cloud on side B of building  101  because a cloud is obscuring part of the sun&#39;s rays. Assuming all the EC windows are of the same size and type, each of the two windows controlled by intermediate controller  105   b  on side A of building  101  will have the same approximate % T, while each of the five windows controlled by intermediate controller  105   b  on side B of building  101  will have different % T values because each has a different percent area covered by the shadow from the cloud. 
     This granularity in data feedback is highly valuable in controlling the environment, for example light, heat, etc., in the room having these seven windows. Intermediate controller  105   b  uses the % T feedback to maintain the desired environment in the room having these seven windows. Master controller  103  uses the data from intermediate controller  105   a  and  105   b  to control the environment of both rooms. For example if the room having the EC windows controlled by intermediate controller  105   b  is a conference room with many people, the drop in % T due to the cloud&#39;s shadow will make the room easier to cool, or for example, lessen the power requirements for darkening the window during a slide presentation in the conference room. 
     Multipurpose controllers described herein include logic for using this type of feedback for adjusting parameters of the building, via a BMS, for maximizing energy savings. In this example, the energy saved in the conference room due to the shadow&#39;s cooling and darkening effects can be used for transitioning windows in the room controlled by intermediate window controller  105   a , or, for example, the energy can be stored for later use in the windows in the conference room (see “Charge Storage” below). 
     In one embodiment, % T is inferred from the I/V characteristics of an EC device of the IGU. An IGU or a window can be characterized by the relationship between an electrical pulse sent through the device and how the device behaves before and after the pulse. For example, a direct current (DC) pulse is sent through an EC device of an IGU, and the DC voltage measured across the electrodes (TCO&#39;s) of the device as a result provides an UV characteristic of the device. Environmental factors such as temperature or material characteristics of the device can produce non-linear I/V relationships (and cause hysteresis). Thus EC devices are tested at varying temperatures in order to create data for programming into the logic of controllers of the invention for reference when determining various characteristics of the IGU installed with the controller. In one embodiment, % T is measured in this way. For example, upon power up, the controller sends a pre-determined signal to the IGU of a window and based on the IGU&#39;s response to the signal, the % T is calculated by knowing the hysteresis curve of the EC device of the IGU. % T may also be inferred as a function of “ionic current,” which can be calculated by measuring the applied current and subtracting the leakage current. 
     In one embodiment, the open circuit voltage (V oc ) of the EC device is measured, then an electrical pulse is applied, followed by measuring the V oc  again. The change in the V oc  as a result of the electrical pulse allows calculation of % T based on, for example, prior characterization of the device. In one example, the temperature of the device is measured along with V oc  and the % T calculated based on the EC device&#39;s behavior to such pulses in previous characterization tests. 
     Size and Temperature of the IGU 
     The “temperature of an electrochromic device can be inferred algorithmically or measured directly using a sensor (e.g. a thermocouple, thermister, or RTD (resistive thermal device)). In various embodiments, such device is wired or otherwise communicatively coupled to a controller analog input (AI-EC Temperature). See  FIGS.  3  and  4   . 
     Using I/V measurements as described above, along with characterization data of the IGU, the size and temperature of the IGU can be determined by controllers described herein. For example, for each of a 20″ by 20″ window, a 40″ by 40″ window and a 60″ by 60″ window, data is collected based on I/V measurements at a number of temperatures. This data is programmed into a window controller which has distinct capabilities and functions with respect to these three window sizes. In the field, during installation, an installer connects the window controller so programmed with an EC window. The controller sends an electrical pulse through the IGU of the window and from the current response, and correlating with the programmed data, the controller can determine the size and temperature of the window. This information is used, for example, to program the controller&#39;s logic according to the appropriate window size so that, for example, the appropriate power is used to transition the window during operation. 
     Damage to the EC Device 
     In one embodiment, window controllers described herein use I/V characteristics such as those described above to determine damage to an EC device in an IGU of an EC. For example, given the characterized leakage current of the EC device programmed into the controller&#39;s logic, when the controller pings the IGU for I/V feedback, this data can be compared to the data for that IGU from the factory and/or when installed. If the leakage current is greater than it was at installation, then damage to the IGU is likely. The larger the change in UV characteristics, the more likely damage has occurred to the EC device of the IGU. For example, if the window is damaged by an object hitting the window, controllers described herein would detect the damage (for example a large electrical short) as described and, for example, alert the appropriate repair or security personnel via a BMS. In another example, over time, a number of defects arise in the EC device of an IGU which results in a change in UV characteristics of the window. This data is fed back to an end user and/or a BMS to inform the appropriate personnel that the IGU needs to be replaced or repaired (see “In Field Short-Related Defect Repair” below). 
     Wire Length: Ranging 
     Controllers described herein may have the logic and associated hardware to determine the length of wire between a window and the controller. For example, the controller may apply an electrical signal to the wiring that leads to the one or more ICU&#39;s that they control and then measure the change in frequency in the line transmission of the signal. This change in frequency is used to determine the length of the wiring or “range” between the controller and the IGU. Knowing the length of the wiring can be important because the amount of power provided by the source is dependent on how much wiring the power must traverse, as there is a power drop off associated with resistance in the wire. The power source may need to adjust the amount of power it sends to power windows separated from it by differing lengths of wire. 
     Ranging is typically done between an end controller and an associated IGU in a window. Ranging can be done either actively or passively. In active ranging, the EC device of the IGU is active and can reply to a signal from the controller. In passive ranging, the EC device is switched out of the circuit while ranging is performed. 
     In certain implementations, a relay is provided at the IGU end of the wire, typically embedded in the IGU secondary seal. The controller sends a message down IGU power lines (using, e.g., MAXIM&#39;s OneWire interface, see www.maxim-ic.com/products/1-wire/flash/overview/index.cfm (incorporated by reference)), and the IGU then switches itself out of the circuit for a finite time period to allow the controller to conduct a ranging test. At some predefined time interval the IGU would then switch itself back into the circuit and allow normal control of the IGU to resume. 
     In some embodiments, the controller is located in or very near the window frame, and thus ranging is not necessary as all end controllers have the same length of wiring between them and their respective IGU&#39;s. 
     Wireless or Wired Communication 
     In some embodiments, window controllers described herein include components for wired or wireless communication between the window controller and separate communication node. Wireless or wired communications may be accomplished with a communication interface that interfaces directly with the window controller. Such interface could be native to the microprocessor or provided via additional circuitry enabling these functions. 
     A separate communication node for wireless communications can be, for example, another wireless window controller, an end, intermediate or master window controller, a remote control device, or a BMS. Wireless communication is used in the window controller for at least one of the following operations: programming and/or operating the EC window, collecting data from the EC window from the various sensors and protocols described herein, and using the EC window as a relay point for wireless communication. Data collected from EC windows also may include count data such as number of times an EC device has been activated, efficiency of the EC device over time, and the like. Each of these wireless communication features is described in more detail below. 
     In one embodiment, wireless communication is used to operate the associated EC windows, for example, via an infrared (IR), and/or radio frequency (Rf) signal. In certain embodiments, the controller will include a wireless protocol chip, such as Bluetooth, EnOcean, WiFi, Zigbee, and the like. Window controllers may also have wireless communication via a network. Input to the window controller can be manually input by a user, either directly or via wireless communication, or the input can be from a BMS of a building of which the EC window is a component. 
     In one embodiment, when the window controller is part of a distributed network of controllers, wireless communication is used to transfer data to and from each of a plurality of EC windows via the distributed network of controllers, each having wireless communication components. For example, referring again to  FIG.  1   , master window controller  103 , communicates wirelessly with each of intermediate controllers  105 , which in turn communicate wirelessly with end controllers  110 , each associated with an EC window. Master controller  103  may also communicate wirelessly with the BMS. In one embodiment, at least one level of communication in the window controller is performed wirelessly. 
     In some embodiments, more than one mode of wireless communication is used in the window controller distributed network. For example, a master window controller may communicate wirelessly to intermediate controllers via WiFi or Zigbee, while the intermediate controllers communicate with end controllers via Bluetooth, Zigbee, EnOcean or other protocol. In another example, window controllers have redundant wireless communication systems for flexibility in end user choices for wireless communication. 
     Wireless communication between, for example, master and/or intermediate window controllers and end window controllers offers the advantage of obviating the installation of hard communication lines. This is also true for wireless communication between window controllers and BMS. In one aspect, wireless communication in these roles is useful for data transfer to and from EC windows for operating the window and providing data to, for example, a BMS for optimizing the environment and energy savings in a building. Window location data as well as feedback from sensors are synergized for such optimization. For example, granular level (window-by-window) microclimate information is fed to a BMS in order to optimize the building&#39;s various environments. 
     A BMS may also collect data on how many times an EC device is powered and the like for higher level feedback to vendors, for example, on quality control and reliability of the windows installed in the building. However, there are other advantages for such wireless communications. For example, since EC window control and data transfer does not require a large amount of bandwidth, having a distributed network of wirelessly linked windows and controllers offers a very useful opportunity to use the network for other purposes. In one embodiment, the wireless window controller network is used for relaying other, non-EC window related information within a building. Zigbee, for example, uses the window controller to build a mesh network, with other window controllers or other devices like dimmable ballasts, alarm systems, etc. that also employ Zigbee. As such network traffic passing through the window controller may not be related to window control at all, the window controller is simply improving the mesh reliability. 
     Radio Frequency Identification 
     Radio-frequency identification (RFID) involves interrogators (or readers), and tags (or labels). RFID tags use communication via electromagnetic waves (typically radio frequency) to exchange data between a terminal and an object, for example, for the purpose of identification and tracking of the object. Some RFID tags can be read from several meters away and beyond the line of sight of the reader. 
     Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (Rf) signal, and other specialized functions. The other is an antenna for receiving and transmitting the signal. 
     There are three types of conventional RFID tags: passive RFID tags, which have no power source and require an external electromagnetic field to initiate a signal transmission, active RFID tags, which contain a battery and can transmit signals once a reader has been successfully identified, and battery assisted passive (BAP) RFID tags, which require an external source to wake up but have significant higher forward link capability providing greater range. RFID has many applications; for example, it may be used in enterprise supply chain management to improve the efficiency of EC device inventory tracking and management. 
     One embodiment is a window controller as described herein including an RFID tag. In one embodiment, the window controller is an end controller associated with a particular IGU. In one embodiment, the RFID tag may be installed on the IGU prior to installation of the window controller, that is, after the IGU and window controller are wired together, the RFID tag is considered part of the window controller. The RFID tag may be active, passive or BAP, depending on the controller&#39;s capability to power the RFID. An RFID tag in a window controller as described herein may contain at least one of the following types of data: warranty information, installation information, vendor information, batch/inventory information, EC device/IGU characteristics, customer information, manufactured date, window size, and specific parameters to be used for a particular window 
     Such RFID tags obviate the need for stickers on IGU&#39;s or windows with such information and some RFID&#39;s have rudimentary processing capability such as keeping track of how many times an associated EC device has been activated. An unsophisticated BMS can use such information for environmental control, for example, based on known performance of EC devices as a function of usage. In another example, an installer can use a portable reader to decide which end controller to install in a particular window and/or the controller itself may read the RFID tag and program itself prior to, or upon wiring, to the IGU. 
     In related embodiments, a controller could also read data from the IGU that has an embedded (e.g. part of a wiring harness, or encapsulated by the secondary seal, etc.) but physically separate RFID tag, EEPROM or FLASH memory chip that would allow various details of the window to be stored with one of these storage devices. Examples of information that may be stored on the tag or memory device embedded in the IGU include warranty information, installation information, vendor information, batch/inventory information, EC device/IGU characteristics, an EC device cycle count, customer information, manufactured date, and window size. 
     Charge Storage 
     The amount of ions held in the counter electrode layer during the bleached state (and correspondingly in the EC layer during the colored state) and available to drive the EC transition depends on the composition of the layers as well as the thickness of the layers and the fabrication method. Both the EC layer and the counter electrode layer are capable of supplying charge (in the form of lithium ions and electrons) in the neighborhood of several tens of millicoulombs per square centimeter of layer surface area. The charge capacity of an EC film is the amount of charge that can be loaded and unloaded reversibly per unit area and unit thickness of the film by applying an external voltage or potential. In some embodiments, window controllers have the capability of storing charge that is produced when an associated EC device undergoes a transition that produces a charge. In other embodiments, the charged produced by the EC window transitions is diverted to a power grid. The charge is then reused, for example, for further transitions of EC windows or, for example where a BMS is integrated with the window controller, for other needs in a building where appropriate. Although the charge produced by an EC window&#39;s reverse transition is not large, the charge can be stored in, for example, a battery or sent to a grid where collectively they can be reused, for example, for further window operations including transitions. 
       FIG.  2    depicts a circuit,  200 , where an IGU,  205 , including an EC device, is powered via a source,  210 . In accord with embodiments described herein, source  210  could be part of the window controller, or not. In this example, when power is supplied to the EC device of IGU  205 , the EC device transitions to a colored state as depicted in the top portion of  FIG.  2   . Circuit  200  also includes a charge storage device,  215 . Device  215  may be a capacitor or battery, for example. As depicted at the bottom of  FIG.  2   , when the EC device transitions from colored to bleached, upon discontinuing application of power from source  210 , the circuit is reconfigured, for example using double pole switches, to send the resultant charge that the EC device creates into charge storage device  215 . This stored charge may be used to power further transitions of the EC device in IGU  205 , or to power other aspects of the window controller such as electrical pulses for I/V measurements, ranging pulses and the like. In one embodiment, charge from an EC device&#39;s transition is sent to a power grid for combination with other charge from other window&#39;s transitions for use in the EC window system or for other purposes. By reusing charge created from the transition of EC windows, the energy efficiency of the windows is enhanced because this charge is not simply wasted by discharging it to ground. 
     In Field Short-Related Defect Repair (“AC Zap”) 
     As discussed above, EC devices can develop short circuit defects between oppositely charged conductive layers, for example, when a conductive particle makes contact with each of two conductive and electrically charged layers. When a short circuit occurs, electrons rather than ions migrate between the EC layer and the counter electrode, typically resulting in bright spots or halos at the location of, and surrounding, the electrical short when the EC device is otherwise in the colored state. Over time, some EC windows can develop many such electrical shorts and thus degrade in performance due to a significant increase in the leakage current and the appearance of many such bright spots. In certain embodiments, multipurpose window controllers have the capability to repair short related defects in associated EC devices. This has the great advantage of repairing the IGU rather than replacing it, and repairing the IGU without removing it from the window unit. 
     In one embodiment, the window controller repairs short related defects in the EC device by sending a high voltage alternating current (AC) through the EC device for a period of time. While not wishing to be bound to theory, it is believed that this repairs the short related defects because during application of the AC current, the frequency of the AC current does not allow ions to move across the EC stack materials, but current does flow, especially through the short related defects. The device does not transition during the application of AC current and therefore is protected from damage, while the high AC current “overloads” the shorts and burns them out, effectively sealing the short related defect areas from further current leakage. This method of in situ repair of short related defects is described in U.S. patent application Ser. No. 12/336,455, naming McMeeking et al. as inventors, and filed on May 2, 2008, which is incorporated herein by reference in its entirety. 
     Window (Resistive) Heating 
     The electrode layers of EC devices can be used for resistive heating, for example, by passing a current through one of the electrodes and thus using it as a resistive heating element. In one embodiment, the window controller includes the function of heating one or both electrodes of an EC device of the EC window for resistive heating. Resistive heating is useful for controlling the temperature of IGU for thermal barrier, to defrost the IGU and to control the temperature of the EC device to aid transitions. In one embodiment, window controllers described herein can alternate between transitioning the device and heating the device to aid in transitions. One embodiment is an apparatus including a multipurpose EC window controller as described herein and an EC window where at least one transparent conductive oxide layer of an electrochromic device of the EC window is configured to be heated independently of operation of the EC device. 
     Examples of Smart Controllers 
     The above described features of a smart controller may used alone or in combination with one another. A few specific embodiments will now be described. In one embodiment, the following functions are combined in a single smart controller: (i) powering one or more smart windows, (ii) determining a percent transmittance of the one or more smart windows (at any particular instance in time), (iii) determining the temperature of the one or more smart windows (at any particular instance in time), (iv) providing a communications interface for communicating with the one or more smart windows, and (v) reading data from physically separate memory devices or tags embedded in IGUs associated with the one or more smart windows. 
     In the embodiment just outlined, the powering a smart window may be accomplished using pulse width modulated amplifier rendered as, for example, an “h-bridge” allowing the window load to float, be grounded, or be set to any voltage or polarity between the input voltage to the controller and ground. The powering function could also be realized using a “buck converter” and a separate polarity switch allowing the load to set to any voltage or polarity between the input voltage to the controller and ground. Control may also include current limits during all or part of the transition from one state to another. 
     Determining the “percent transmittance” can be could be inferred algorithmically or measured directly using a sensor (e.g. a silicon photo diode) communicating by a wired or wireless interface to an analog input (AI-Transmittance) of the controller. See  FIGS.  3  and  4   , for example. Determining the “temperature of an electrochromic device” can be inferred algorithmically or measured directly using a sensor (e.g. a thermocouple, thermister, or RTD) communicating by wireless or wired interface to an analog input (AI-EC Temperature) of the controller. See  FIGS.  3  and  4   , for example. Wireless and/or wired communications may be accomplished using a communication interface that interfaces directly with the smart controller. This may be native to the controller&#39;s microprocessor or additional circuitry enabling these functions. Finally, the exemplary smart controller may read data from an embedded memory devices or tags in the smart windows. Such devices or tags may be part of a wiring harness, encapsulated by the secondary seal, etc. but physically separate from the smart controller. Examples of such devices or tags include RFID tag, EEPROM or FLASH memory chips that would allow all storage of various information about the windows including temperature, number of cycles, manufacturing date, etc. 
     In another embodiment, the following functions are combined in a single smart controller: (i) powering one or more smart windows, (ii) determining a percent transmittance of the one or more smart windows (at any particular instance in time), (iii) determining the size of one or more windows, (iv) measuring the temperature of the one or more smart windows (at any particular instance in time), (v) determining if damage to the window has occurred (evolved defects), (vi) providing a communications interface for communicating with the one or more smart windows, and (vii) reading data from physically separate memory devices or tags embedded in IGUs associated with the one or more smart windows. 
     In the embodiment just outlined, the powering a smart window may be accomplished using pulse width modulated amplifier (either h-bridge or buck) as outlined in the previous embodiment but now combined with sensors to simultaneously measure current and voltage delivered to the EC window. Transmittance may be determined algorithmically using a single photo sensor, knowledge of the real-time voltage and current values as the window transitions state and measuring the actual EC window temperature with a sensor in direct contact with the EC coating. Furthermore, direct knowledge of the voltage and current profiles together with measurement of the EC window temperature allows algorithmic determination of the window dimensions. The voltage and current sensing capability allows the controller to compare the current readings against historic values stored in the controller, or conveyed and retrieved via communication with the BMS, to determine if damage to the EC coating has occurred. 
     In yet another embodiment, a controller is designed or configured to perform the following functions: (i) powering a reversible optical transition of one or more windows; (ii) determining the transmittance of the one or more windows; (iii) determining the temperature of the one or more windows; and (iv) storing and transmitting data relating to the one or more windows via an RFID tag or via memory. A separate implementation provides a controller designed or configured to perform the following functions: (i) powering a reversible optical transition of one or more windows; (ii) determining the size(s) of the one or more windows; (iii) determining the temperature of the one or more windows; (iv) communicating between the controller and a separate communication node; and (v) storing and transmitting data relating to the one or more windows via an RFID tag or via memory. Yet another controller is designed or configured to perform the following combination of functions: (i) powering a reversible optical transition of one or more windows; (ii) determining the transmittance of the one or more windows; (iii) determining the size(s) of the one or more windows; (iv) determining the temperature of the one or more windows; (v) determining damage to the one or more windows; (vi) determining a wire length between the window controller and the one or more windows; (vii) communicating between the window controller and a separate communication node; (viii) storing and transmitting data relating to the one or more windows via an RFID tag or via memory; and (ix) repairing short related defects of the one or more windows. In these examples, as well as others given herein, when a controller interfaces with more than one window, the recited functions can apply to any one of the controlled windows, or any combination of these windows, or all of the windows. 
     Another controller is designed or configured to perform the following functions: (i) powering a reversible optical transition of one or more windows; (ii) determining temperature of the one or more windows; and (iii) heating a device on the one or more windows. The heated device may be the electrochromic devices themselves or a separate device formed on the windows. This embodiment is particularly appropriate for cold weather climates when it is desirable to include relatively large windows. It permits the windows to operate in a relatively untinted state when the flux of solar radiation is sufficient. The additional heating permitted by function (iii) permits use of larger window panes in areas where insulated walls are typically expected in place of large windows. 
     Examples of Controller Architectures 
       FIG.  3    is a schematic depiction of a window controller configuration,  300 , including an interface for integrating smart windows into, for example, a residential system or a building management system. Such controller may serve as a smart controller of the type herein described or it may serve to provide “local” information from a smart window indirectly controlled by a smart controller. The disclosed embodiment may be implemented in a controller embedded in an IGU, for example. Such controllers are sometimes referred to as “onboard” controllers and are described in more detail in U.S. patent application Ser. No. 13/049,750, titled “Onboard Controller for Multistate Windows” and filed on Mar. 16, 2011, which is incorporated herein by reference in its entirety. 
     In the depiction of  FIG.  3   , a voltage regulator accepts power from a standard 24 v AC/DC source. The voltage regulator is used to power a microprocessor (g) as well as a pulse width modulated (PWM) amplifier which can generate current at high and low output levels, for example, to power an associated smart window. A communications interface allows, for example, wireless communication with the controller&#39;s microprocessor. In one embodiment, the communication interface is based on established interface standards, for example, in one embodiment the controller&#39;s communication interface uses a serial communication bus which may be the CAN 2.0 physical layer standard introduced by Bosch and widely used today in automotive and industrial applications. “CAN” is a linear bus topology allowing for 64 nodes (window controllers) per network, with data rates of 10 kbps to 1 Mbps, and distances of up to 2500 m. Other hard wired embodiments include MODBUS, LonWorks™, power over Ethernet, BACnet MS/TP, etc. The bus could also employ wireless technology (e.g. Zigbee, Bluetooth, etc.). 
     In the depicted embodiment, the controller includes a discrete input/output (DIO) function, where a number of inputs, digital and/or analog, are received, for example, tint levels, temperature of EC device(s), % transmittance, device temperature (for example from a thermistor), light intensity (for example from a LUX sensor) and the like. Output includes tint levels for the EC device(s). The configuration depicted in  FIG.  3    is particularly useful for automated systems, for example, where an advanced BMS is used in conjunction with EC windows having EC controllers as described herein. For example, the bus can be used for communication between a BMS gateway and the EC window controller communication interface. The BMS gateway also communicates with a BMS server. 
     Some of the functions of the discrete I/O will now be described. 
     DI-TINT Level bit  0  and DI-TINT Level bit  1 : These two inputs together make a binary input (2 bits or 2 2 =4 combinations; 00, 01, 10 and 11) to allow an external device (switch or relay contacts) to select one of the four discrete tint states for each EC window pane of an IGU. In other words, this embodiment assumes that the EC device on a window pane has four separate tint states that can be set. For IGUs containing two window panes, each with its own four-state TINT Level, there may be as many as eight combinations of binary input. See U.S. patent application Ser. No. 12/851,514, filed on Aug. 5, 2010 and previously incorporated by reference. In some embodiments, these inputs allow users to override the BMS controls (e.g. untint a window for more light even though the BMS wants it tinted to reduce heat gain). 
     AI-EC Temperature: This analog input allows a sensor (thermocouple, thermister, RTD) to be connected directly to the controller for the purpose of determining the temperature of the EC coating. Thus temperature can be determined directly without measuring current and/or voltage at the window. This allows the controller to set the voltage and current parameters of the controller output, as appropriate for the temperature. 
     AI-Transmittance: This analog input allows the controller to measure percent transmittance of the EC coating directly. This is useful for the purpose of matching multiple windows that might be adjacent to each other to ensure consistent visual appearance, or it can be used to determine the actual state of the window when the control algorithm needs to make a correction or state change. Using this analog input, the transmittance can be measured directly without inferring transmittance using voltage and current feedback. 
     AI-Temp/Light Intensity: This analog input is connected to an interior room or exterior (to the building) light level or temperature sensor. This input may be used to control the desired state of the EC coating several ways including the following: using exterior light levels, tint the window (e.g. bright outside, tint the window or vice versa); using and exterior temperature sensor, tint the window (e.g. cold outside day in Minneapolis, untint the window to induce heat gain into the room or vice versa, warm day in Phoenix, tint the widow to lower heat gain and reduce air conditioning load). 
     AI-% Tint: This analog input may be used to interface to legacy BMS or other devices using 0-10 volt signaling to tell the window controller what tint level it should take. The controller may choose to attempt to continuously tint the window (shades of tint proportionate to the 0-10 volt signal, zero volts being fully untinted, 10 volts being fully tinted) or to quantize the signal (0-0.99 volt means untint the window, 1-2.99 volts means tint the window 5%, 3-4.99 volts equals 40% tint, and above 5 volts is fully tinted). When a signal is present on this interface it can still be overridden by a command on the serial communication bus instructing a different value. 
     DO-TINT LEVEL bit  0  and bit  1 : This digital input is similar to DI-TINT Level bit  0  and DI-TINT Level bit  1 . Above, these are digital outputs indicating which of the four states of tint a window is in, or being commanded to. For example if a window were fully tinted and a user walks into a room and wants them clear, the user could depress one of the switches mentioned and cause the controller to begin untinting the window. Since this transition is not instantaneous these digital outputs will be alternately turned on and off signaling a change in process and then held at a fixed state when the window reaches its commanded value. 
       FIG.  4    depicts a controller configuration  402  having a user interface. For example where automation is not required, the EC window controller, for example as depicted in  FIG.  3   , can be populated without the PWM components and function as I/O controller for an end user where, for example, a keypad,  404 , or other user controlled interface is available to the end user to control the EC window functions. The EC window controller and optionally I/O controllers can be daisy chained together to create networks of EC windows, for automated and non-automated EC window applications. 
     In certain embodiments, the controller  402  does not directly control a window but may indirectly control one or more windows. The controller may direct or coordinate the operation of one or more other controllers such as controllers  103  and/or  105  in  FIG.  1   . 
     Solid-State and Inorganic EC Devices 
     A description of EC devices is provided for context, because window controllers described herein include functions that use features of EC devices, for example, in order to measure parameters such as temperature, window size, percent transmission and the like, as well as using EC devices in a non-conventional sense, for example, using an electrode of an EC device for resistive heating. Thus structure and function of EC devices is described in the context of solid-state and inorganic EC devices, although controllers described herein can control any EC device. Further, as noted above, such controllers may be used with windows having non-electrochromic optically switchable devices such as liquid crystal devices and suspended particle devices. 
       FIG.  5    depicts a schematic cross-section of an EC device,  500 . Electrochromic device  500  includes a substrate,  502 , a conductive layer (CL),  504 , an EC layer (EC),  506 , an ion conducting layer (IC),  508 , a counter electrode layer (CE),  510 , and a conductive layer (CL),  514 . Layers  504 ,  506 ,  508 ,  510 , and  514  are collectively referred to as an EC stack,  520 . A voltage source,  516 , operable to apply an electric potential across EC stack  520 , effects the transition of the EC device from, for example, a bleached state to a colored state (depicted). The order of layers can be reversed with respect to the substrate. The EC device  500  may include one or more additional layers (not shown) such as one or more passive layers. Passive layers used to improve certain optical properties may be included in EC device  500 . Passive layers for providing moisture or scratch resistance may also be included in the EC device  500 . For example, the conductive layers may be treated with anti-reflective or protective oxide or nitride layers. Other passive layers may serve to hermetically seal the EC device  500 . 
     Such all solid-state and inorganic EC devices, methods of fabricating them, and defectivity criterion are described in more detail in U.S. patent application Ser. No. 12/645,111, entitled, “Fabrication of Low-Defectivity Electrochromic Devices,” filed on Dec. 22, 2009 and naming Mark Kozlowski et al. as inventors, and in U.S. patent application Ser. No. 12/645,159, entitled, “Electrochromic Devices,” filed on Dec. 22, 2009 and naming Zhongchun Wang et al. as inventors, both of which are incorporated by reference herein for all purposes. In accordance with certain embodiments, EC devices where the counter electrode and EC electrodes are formed immediately adjacent one another, sometimes in direct contact, without separately depositing an ionically conducting layer, are used with controllers described herein. Such devices, and methods of fabricating them, are described in U.S. patent application Ser. Nos. 12/772,055 and 12/772,075, each filed on Apr. 30, 2010, and in U.S. patent application Ser. Nos. 12/814,277 and 12/814,279, each filed on Jun. 11, 2010—each of the four applications is entitled “Electrochromic Devices,” each names Zhongchun Wang et al. as inventors, and each is incorporated by reference herein in their entireties. These devices do not have an IC layer per se, but function as if they do. 
     It should be understood that the reference to a transition between a bleached state and colored state is non-limiting and suggests only one example, among many, of an EC transition that may be implemented. The term “bleached” refers to an optically neutral state, for example, uncolored, transparent or translucent. Still further, unless specified otherwise herein, the “color” of an EC transition is not limited to any particular wavelength or range of wavelengths. In the bleached state, a potential is applied to the EC stack  520  such that available ions in the stack that can cause the EC material  506  to be in the colored state reside primarily in the counter electrode  510 . When the potential on the EC stack is reversed, the ions are transported across the ion conducting layer  508  to the EC material  506  and cause the material to enter the colored state. 
     In this example, the materials making up EC stack  520  are both inorganic and solid state. Because organic materials tend to degrade over time, inorganic materials offer the advantage of a reliable EC stack that can function for extended periods of time. Materials in the solid state also offer the advantage of not having containment and leakage issues, as materials in the liquid state often do. One embodiment is an apparatus including a controller as described herein and an EC device that is all solid state and inorganic. 
     Referring again to  FIG.  5   , voltage source  516  is typically a low voltage electrical source and may be configured in multipurpose controllers to operate in conjunction with other components such as sensors, RFID tags, and the like. In certain embodiments, multipurpose controllers described herein include the capability to supply power to an EC device, for example, as voltage source  516 . 
     A typical substrate  502  is glass. Suitable glasses include either clear or tinted soda lime glass, including soda lime float glass. Typically, there is a sodium diffusion barrier layer (not shown) between substrate  502  and conductive layer  504  to prevent the diffusion of sodium ions from the glass into conductive layer  504 . 
     On top of substrate  502  is conductive layer  504 . Conductive layers  504  and  514  may be made from a number of different materials, including conductive oxides, thin metallic coatings, conductive metal nitrides, and composite conductors. Typically, conductive layers  504  and  514  are transparent at least in the range of wavelengths where electrochromism is exhibited by the EC layer. Transparent conductive oxides include metal oxides and metal oxides doped with one or more metals. Since oxides are often used for these layers, they are sometimes referred to as “transparent conductive oxide” (TCO) layers. 
     The function of the TCO layers is to spread an electric potential provided by voltage source  516  over surfaces of the EC stack  520  to interior regions of the stack, with very little ohmic potential drop. The electric potential is transferred to the conductive layers though electrical connections to the conductive layers. Typically, bus bars, one in contact with conductive layer  504  and one in contact with conductive layer  514 , provide the electric connection between the voltage source  516  and the conductive layers  504  and  514 . Generally, various thicknesses of the layers of the conductive material may be employed so long as they provide the necessary electrical properties (for example, conductivity) and optical properties (for example, transmittance). Typically, the conductive layers  504  and  514  are as thin as possible to increase transparency and to reduce cost. Preferably, the thickness of the each conductive layer  504  and  514  is also substantially uniform. 
     The sheet resistance (R s ) of the conductive layers is also important because of the relatively large area spanned by the layers, for example, when the device is part of an electrochromic window. The sheet resistance of conductive layers  504  and  514  may be between about 5 Ohms per square to about 30 Ohms per square. In general, it is desirable that the sheet resistance of each of the two conductive layers be about the same. The conductive layers can be exploited for resistive heating of the device, by virtue of their sheet resistance, rather than for functioning the EC device of which they are a part. In one embodiment, multipurpose controllers described include the function of resistive heating using one or more conductive layers of an EC device. Such resistive heating as described in more detail below. 
     Overlaying conductive layer  504  is EC layer  506 . The EC layer may contain any one or more of a number of different EC materials, including metal oxides. An EC layer  506  including a metal oxide is capable of receiving ions transferred from counter electrode layer  510 . The thickness of the EC layer  506  depends on the EC material selected for the EC layer. The EC layer  506  may be about 50 nm to 2,000 nm thick. 
     An ion conducting layer  508  overlays EC layer  506 . Any suitable material may be used for the ion conducting layer  508  provided it allows for the passage of ions between the counter electrode layer  510  to the EC layer  506  while substantially preventing the passage of electrons. 
     On top of ion conducting layer  508  is counter electrode layer  510 . The counter electrode layer may include one or more of a number of different materials that are capable of serving as reservoirs of ions when the EC device is in the bleached state. During an EC transition initiated by, for example, application of an appropriate electric potential, the counter electrode layer transfers some or all of the ions it holds to the EC layer, via the IC layer, changing the EC layer to the colored state. Concurrently, in the case of nickel tungsten oxide (NiWO), the counter electrode layer colors with the loss of ions. Because counter electrode layer  510  contains the ions used to produce the EC phenomenon in the EC material when the EC material is in the bleached state, the counter electrode preferably has high transmittance and a neutral color when it holds significant quantities of these ions. When charge is removed from a counter electrode  510  made of NiWO (that is, ions are transported from the counter electrode  510  to the EC layer  506 ), the counter electrode layer will turn from a transparent state to a brown colored state. Thus when potential is applied to an electrochromic device, an optical transition occurs. Likewise, when an EC device transitions in the other direction, it behaves as a battery, and produces an electrical charge by virtue of the ions traversing the IC layer in the opposite direction, current flows from the EC device. Multipurpose controllers described herein exploit this phenomenon by capturing and/or diverting this charge to a power grid for reuse. 
     Although the foregoing invention has been described in some detail to facilitate understanding, the described embodiments are to be considered illustrative and not limiting. It will be apparent to one of ordinary skill in the art that certain changes and modifications can be practiced within the scope of the appended claims.