Electrochromic glass thermal comfort: proposals for improving existing workflow

Windows, as one of the least energy efficient components of a building, are responsible for up to 40 percent of the total energy cost including heating, cooling and lighting, and over 30 percent of this energy is lost through poor efficient building components. Electrochromic glass (EC) is one of the state-of-art technologies and can substantially reduce the energy consumptions of buildings. Unlike traditional glass, EC glass dynamically changes its tinting states based on occupant needs. When the glass tint level changes, the glass properties (e.g. Tv, SHGC) change accordingly. Previous studies have been done on electrochromic glass energy simulations. However, most of the existing softwares don’t have the capability of adding the four tinting states to the EC glass or applying a specific tinting schedule, which makes the simulation result inaccurate and not reliable. ❧ The research objective is to find a better way to conduct thermal comfort simulations for EC glass windows. Occupant comfort is a critical condition that may eventually be a market driver for new energy-saving technologies. EC glass manufactures, designers and building owners can get a better understanding of how the occupants feel in a space with EC glass installed. Also by comparing the thermal comfort results with traditional glass installed in the same space, they can see how EC glass can help to improve occupants comfort level. ❧ Workflows have been developed in COMFEN, DesignBuilder, CBE Thermal Comfort Model, and Grasshopper (with Ladybug and Honeybee plugins). The 71T lab at National Lawrence Berkeley Lab (NLBL) was chosen to serve as the simulation prototype. The lab is modeled in software as two identical rooms with the same configurations except for window types: the test case with EC glass and the reference room with low-e glass. The EC control strategy used in the simulation process is automatic daylighting control. Simulation process and results are evaluated and compared, and the workflows in CBE Comfort Model and Grasshopper seem to indicate more reliable results than the workflows in COMFEN, DesignBuilder. ❧ As a supplementary part of the thesis, a full size unit with two pieces of electrochromic glass was assembled in the shop of Arcadia Inc. (an aluminum window and façade system manufacturer and re-seller). Learning the fabrication process is an important approach to understanding the glass system because it involves installation details and wire works which are all different from conventional glass.

门窗作为建筑能源效率最低的组成部分之一，其消耗的能源占建筑总能耗（包括采暖、制冷与照明）的比例高达40%，其中超过30%的能源损耗源于低效建筑构件。电致变色玻璃（Electrochromic Glass, EC）是当前前沿技术之一，可大幅降低建筑能耗。与传统玻璃不同，EC玻璃可根据使用者需求动态调节着色状态。随着玻璃着色程度改变，其性能（例如可见光透射比Tv、太阳得热系数SHGC）也会相应变化。此前已有多项针对电致变色玻璃的能耗模拟研究，但当前主流软件大多无法为EC玻璃设置四种着色状态，或无法应用特定的着色调度方案，导致模拟结果精度不足、可靠性欠佳。

本研究的目标是探索更适配EC玻璃窗的热舒适模拟方法。使用者热舒适是影响新型节能技术市场推广的关键因素。EC玻璃制造商、设计师与建筑业主可借此更直观地了解安装EC玻璃的空间内使用者的感受；同时，通过对比同一空间分别安装EC玻璃与传统玻璃的热舒适模拟结果，可明晰EC玻璃对提升使用者热舒适水平的作用。

研究团队已在COMFEN、DesignBuilder、CBE热舒适模型（CBE Thermal Comfort Model）以及Grasshopper（搭配Ladybug与Honeybee插件）中开发了相应的模拟工作流。选取劳伦斯伯克利国家实验室（NLBL）的71T实验室作为模拟原型。该实验室被建模为两间配置完全一致的房间，仅窗型存在差异：试验房间安装EC玻璃，对照房间安装低辐射（low-e）玻璃。模拟过程中采用的EC玻璃控制策略为自动采光控制。随后对模拟流程与结果进行评估与对比，结果显示，CBE热舒适模型与Grasshopper的工作流所得到的结果，相较COMFEN与DesignBuilder的工作流更为可靠。

作为本论文的补充部分，研究团队在阿尔卡迪亚公司（Arcadia Inc.，一家铝门窗与外立面系统制造商及经销商）的车间内组装了一套搭载两块电致变色玻璃的全尺寸窗单元。了解制造流程是理解该玻璃系统的重要途径，因为其涉及的安装细节与布线工作均与传统玻璃存在显著差异。