Electrochromic Window Controller for Energy Efficiency

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1 Electrochromic Window Controller for Energy Efficiency Design Team Malek Ben Ayed, Ghali Laghrari, Ahmed Nowilati Joseph Pang, Behic Pektas, Justin Prosser, Chris Vittoria Design Advisors Prof. Sagar Kamarthi, and Prof. Yiannis Levendis Abstract The implementation of electrochromic (EC) smart windows results in significant energy savings when compared to traditional glass pane windows that use manual shades or no shades at all. Although smart window technology has proved to be efficient in energy savings, it has failed to satisfy the occupant s personal preferences, such as desired inside brightness levels and temperature. The focus of this project is to provide a preliminary control interface that will have the capability to take into account the occupant s preferences, while minimizing the energy consumed by the heating, lighting and cooling systems that are integrated into the room. This project uses energy consumption data from an energy test bed that simulates an office room with an EC window, to develop an energy consumption model based on various real-world conditions. This model, using a neural network model and response surface methods, allows the smart window controller to consider the occupant s preferences to determine an optimal EC window tint level. This allows the occupant to set their desired preferences while maintaining the energy savings provided by the EC window. With an increase in occupant satisfaction, electrochromic smart windows can be further implemented in large scale office buildings saving energy and improving the environment and comfort of the occupants. For more information, please contact s.kamarthi@neu.edu, or y.levendis@neu.edu 44

2 The Need for Project Electrochromic window installations on office buildings have a low occupant satisfaction rating. Electrochromic (EC) windows can provide significant energy savings, but have no integrated control system that accounts for the occupant s preferences for natural light. Occupants in these office spaces must use blinds in cases where it is too bright or are completely unable to do anything to allow more light in. While overall energy usage by the building is reduced, the occupants are dissatisfied which discourages the installation of the EC windows. Therefore to promote the overall acceptance of EC windows, there is a need for an automatic controller that is set with the occupant s preferences and automatically finds the optimal middle ground between the highest energy savings and the occupants preferences. An NREL (National Renewable Energy Laboratory) study reports that a broad installation of high performance, color-changing windows could save about 5 percent of the nation s total energy budget. With a budget of 27.2 billion (FY 2013) the savings would amount to $1.36 billion dollars. Even if 20% of the commercial and residential buildings are fitted with smart windows, the total U.S. energy budget could be reduced by approximately $272 million. The Design Objectives and Requirements The objective of the design is to create a controller that considers both occupant preferences and energy consumption data to reduce energy consumption while satisfying the occupant s preferences. Design Objectives The main objective of this project is to develop an optimized control algorithm that will regulate the occupant s working environment to provide a comfortable working atmosphere for the user while minimizing energy consumption. To achieve this comfortable environment a constant temperature within the range of F will be maintained. Integrating both neural networks and response surface methods the capstone team will simulate and generate a model that will determine the optimal tint level needed that satisfies the occupant s preferences (indoor brightness and temperature) while minimizing energy consumption. This energy algorithm will then be used to control the electrochromic window s control interface to regulate the window s tint level satisfying the user. 45

3 Design Requirements For the design requirements, the capstone team identified some elements that are crucial for the project success. The test bed must produce data that matches the expected results, such that when simulating summer conditions the HVAC unit should consume less energy as the window becomes more tinted and the opposite should hold true for winter conditions. When implementing the controller it must consider occupant preferences while also reducing energy consumption by the HVAC unit. Design Concepts Considered Analysis of existing test bed This project is currently in its third phase; the first two phases both design was performed to designed the test bed and performed data collection to verify its determine possible flaws. The operation. Since the data collected did not meet the expected results the control method was limited in goal was to first investigate the test bed for possible design flaws. scope to only control the Troubleshooting steps that had taken place upon first investigating the window. test bed were to verify the construction of the office simulation chamber. This included verifying it was properly insulated from the capstone lab environment and the HVAC system was isolated from the capstone lab. The outside simulation chamber was also investigated to reduce the temperature fluctuation and verify that the light array accurately simulated light levels for both winter and summer conditions in Boston. The last design concept was the implementation of the control system. Previous phases had already purchased an Arduino microcontroller to begin the controller implementation. Due to past experience with the Arduino platform this was the hardware that was decided upon for implementation. The controller concept considered was to have it control the HVAC unit, tint level, and inside light. 46

4 Recommended Design Concept The test bed HVAC unit was modified to interface with the outside environment chamber and the Arduino controller was limited in scope to only control the EC window After performing investigative testing on the test bed, it was found that the HVAC system condenser was interfacing with the capstone lab rather than the outside simulation chamber. The heat pump and refrigeration efficiency was therefore much higher than what would be observed in a real world situation. The HVAC system ducting was modified to interface with the outside environment on the condenser side. On the evaporator side it was further insulated so that no air could leak in from the capstone lab. A sample of the data collected showing energy consumption of the simulated office HVAC system during simulated winter conditions, with pre-modification results (in red) and post-modification results (in blue), is shown on the left. The postmodification results show that allowing more solar radiation into the office by reducing tint levels decreases energy consumed by the office HVAC system in simulated winter conditions, which matches our The Arduino controller only interfaces with the EC window to control tint level, based on outside temperature, inside temperature, and inside brightness. This allowed all the appropriate data to be collected so the given occupant s preferences could be met while also keeping energy consumption low. In order to quickly implement this controller with minimal electrical design, the existing EC window controller was used to adjust the tint levels. The Arduino platform communicates with the existing EC window controller using a serial connection to set tint values in the EC window controller s firmware. Using the energy consumption data from the electrochromic window simulation bed, neural network weights were generated which were then used to calculate energy consumption levels for simulated parameters. This simulation integrated with response surface methods allows the algorithm to find the optimized window tint level that minimizes energy consumption. 47

5 Financial Issues The primary financial concern is with the installation of the EC windows. The modifications required to the existing controller to implement this system would be inexpensive. The primary financial burden of the EC window installation is purchasing the windows themselves, which are more expensive than standard glass pane windows. The primary financial burden would be to modify the circuitry of the existing EC window controller to accommodate thermocouples for reading inside and outside temperature. This would be a relatively inexpensive change to the existing controller. Recommended Improvements Going forward it would be beneficial if the Arduino controller represented a total building control system which included all building environment controls. Finally, there are a few improvements that we are suggesting for the next group to work on the project to consider. It would be beneficial if the Arduino controller was able to be an all-encompassing building control system, which controls indoor lighting, HVAC units, and EC window tint levels. This would allow a total building solution that saves energy as well as meets the occupants needs. In addition, implementing the response surface algorithm within Arduino would allow the control interface to regulate all the building s control systems automatically and optimize energy consumption at all times, creating a more seamless system that meets the occupant s preferences. 48