Center for the Built Environment

Thermochromic windows have been widely studied as a technology that can potentially offer increases in energy conservation and provide a desirable luminous environment inside buildings. However, there has been little attention placed on how the tinted states of thermochromic glazing influence occupant behaviour and visual perception. An experiment under controlled conditions was designed to test the influence of different thermochromic tint states on human response. By using a controllable artificial window, five typical luminous conditions were set up, including clear (no tint) and two different levels of blue and bronze tint states, respectively, which produced different room colour temperatures. Thirty-one subjects were recruited who completed three visual tasks, including a visual acuity and a colour naming tasks using the coloured Landolt ring chart and a sustained attention test using the d2 test. Subjective assessments were also collected using questionnaires. Statistical analyses showed the across the thermochromic window conditions, no significant differences in performance were found for the visual acuity and d2 tests. However, there was a significant effect for the colour naming task from the Landolt ring test. Under blue tint conditions, subjects reported higher alertness and produced fewer errors. More natural and acceptable lighting conditions were found under the bronze-tinted conditions. Therefore, when developing innovative thermochromic windows applied in buildings, it is also important to cater for the visual requirements of the occupants in the space, not only energy efficiency goals.

Visual connection to nature has been demonstrated to have a positive impact on attention restoration, stress reduction, and overall health and well-being. Inside buildings, windows are the primary means of providing a connection to the outdoors, and nature views even through a window may have similar effects on the occupants. Given that humans recognize environments through multi-sensory integration, a window view may also affect occupants’ thermal perception. We assessed the influence of having a window with a view on thermal and emotional responses as well as on cognitive performance. We conducted a randomized crossover laboratory experiment with 86 participants, in spaces with and without windows. The chamber kept the air and window surface temperature at 28 °C, a slightly warm condition. The outcome measures consisted of subjective evaluations (e.g., thermal perception, emotion), skin temperature measurements and cognitive performance tests. In the space with versus without windows, the thermal sensation was significantly cooler (0.3 thermal sensation vote; equivalent to 0.74 °C lower), and 12 % more participants were thermally comfortable. Positive emotions (e.g., happy, satisfied) were higher and negative emotions (e.g., sad, drowsy) were lower for the participants in the window versus the windowless condition. Working memory and the ability to concentrate were higher for participants in the space with versus without windows, but there were no significant differences in short-term memory, planning, and creativity performance. Considering the multiple effects of window access, providing a window with a view in a workplace is important for the comfort, emotion, and working memory and concentration of occupants.

One of the drivers of sustainable design is to maximize daylight across the floor plan in order to decrease electric energy consumption and create more productive and healthy working spaces. However, uncontrolled incoming solar radiation can lead to significant visual and thermal comfort issues. In particular, solar radiation landing on occupants can create thermal discomfort that the HVAC system cannot compensate for, thereby causing intolerable conditions for users close to the façade. We aim to present a new climate-based annual framework, based on ASHRAE 55 appendix C (2017), to assess radiant discomfort across a space due to direct solar radiation. The framework is calculated using the hourly effective radiant field (ERF) and delta Mean Radiant Temperature (ΔMRT) across the indoor space. The Radiance-based framework coupled with the proposed Annual Radiation Discomfort metric (ARD) provides designers a robust method to assess the performance of complex fenestration systems (CFS) at reducing potential thermal discomfort caused by incoming shortwave radiation.

This paper proposes and evaluates an integrated workflow that simultaneously uses ventilation, thermal, and luminous autonomy for the assessment of passive design strategies, introducing a potential way to integrate these three metrics in the design process. We developed a new metric, ventilation autonomy, and assessed the advantages and limitations of applying the three autonomy metrics with building performance simulations in two climates. We developed a novel visualization to display the hourly and yearly environmental autonomy values. The results show that when we consider the three metrics together, designers may have contradicting design directions if trying to both mitigate the solar radiation and to utilize natural ventilation. The visualizations that categorize nine combinations of thermal and visual comfort along with ventilation autonomy are effective in showing the trade-offs among ventilation, thermal, and visual performance.

Previous studies have demonstrated a potential reduction in cooling load and improvement in comfort from the implementation of night ventilation. This paper describes the performance, in terms of indoor environmental conditions, of three buildings from both the U.S. and India that use night ventilation as their primary cooling method. The research methods used the following approach: (1) Assess the cooling strategy in relation to the adaptive comfort model; (2) Develop a hybrid model, using both first principle equations and the collected data, to predict the instantaneous air and mass temperatures within each building and use the model to assess performance of the cooling strategy; (3) Determine an optimized ventilation control strategy for each building to minimize energy and maintain comfortable temperatures. (4) Develop a statistical model using collected data to predict the window opening pattern for occupants of a building using natural night ventilation. The study yielded the following results: (1) The buildings in the mild climate are successfully keeping the indoor temperature low, but also tend to be overcooling; (2) The night ventilation strategy has very little impact on indoor conditions of the buildings in the mild climate; (3) The impact of night ventilation is less significant when there is low internal loads and heavy mass; (4) The building in the hot and humid climate is keeping the indoor temperature within the comfort bounds for 88% of the year; (5) The night ventilation strategy has advantageous impact on indoor conditons of the building in the hot and humid climate, but not enough to cool the space on its own; (6) Model predictive control has the potential to further improve the performance of night ventilation. (7) Window opening behavior for the building using natural night ventilation is most heavily dependent on indoor air temperature and mass temperature.

The goal of this project was to assess the visual effect of selected aspects of the building envelope on human performance and perception, first broadly, and then focused on view clarity. The initial literature review examined human factors that could be explicitly considered in building envelope design, operation and current daylight metrics. We found that debate remains on the practical applicability of these metrics, and gaps exist between daylight and other building envelope-related aspects such as view. Following the literature review, we narrowed down our research question to experimentally investigate the visual performance of fabric shading systems and electrochromic windows under both diffuse and direct sunlight conditions, and develop a view clarity rating method. We introduce and show results from an experimental study done at Lawrence Berkeley National Laboratory’s Windows Testbeds. We tested High Dynamic Range (HDR) photography techniques to capture the different view clarity through the selected building envelope layers (shades and electrochromic glass) under various sky conditions. The experimental study reveals that light fabric shades restrict the view compared to dark fabric shades, and that view clarity through a blind can be significantly reduced when there is direct sun in the field of view (at certain sun angles). The direct sun caused white-spotted visual noise at the partial area of the fabric shade. Hence, the view was more obscured by the effect of the direct sun even though in this case there was a greater vertical illuminance than the others. The study also shows the potential of HDR photography techniques to be used for a standard view clarity rating method, while noting that further support is needed from human subject testing and advanced computational image analysis algorithms.

This paper proposes and evaluates a novel approach that simultaneously uses thermal and luminous autonomy for the assessment of human-centered passive design strategies, introducing a potential way to integrate these two metrics in the design process. In this study, we assessed the advantages and limitations of applying the two autonomy metrics with energy and lighting simulations in two climates. We developed a novel visualization to display the hourly thermal and luminous autonomy values for an entire year. The results showed that when we consider the two metrics together, designers may have contradicting design directions to mitigate the solar radiation; for example, the space is overly cool, but it is overlit at the same time, or the space is overly warm, but the daylight metrics predicts it is underlit. The visualization categorizes thermal and visual comfort in nine combinations allowing the designers to understand the trade-off relationships between thermal and visual aspects of the space.

Signalling systems that tell building occupants when to open and close windows have become a popular strategy for balancing the comfort benefits of manual windows with the efficiency benefits of automation in mixed-mode buildings. Data from surveys, interviews and site observations in 16 US buildings reveal a diversity of design objectives, control sequences and circumstances to anticipate when designing buildings with window signalling systems. The signals had the strongest influence on occupants’ use of windows when they were visible, the logic behind the controls algorithms was clearly understood, and they were seen as an informational device linked to an explicit internal policy that has to do with efficient and comfortable building operation. Lower levels of participation occurred when occupants tend not to pay attention to their windows, or the signals, unless they are uncomfortable, at which point it matters little what the signals indicate. However, occupants who do discover value in the signals are more likely to be more satisfied with their personal control. Occupants’ reasons for opening windows may include the desire for fresh air or air movement, which is as important to them as temperature adjustment, but admittedly difficult to program into the controls’ algorithms.