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Open Access Publications from the University of California


The Center for the Built Environment's mission is to improve the design, operation, and environmental quality of buildings by providing timely, unbiased information on building technologies and design techniques. Our research falls into two broad program areas: (1) Tools for improving building performance, designed to serve those who manage buildings, as well as assist those who plan and design buildings; and (2) New technologies that make buildings more environmentally friendly, more productive to work in, and more economical to operate. These technologies are designed to help develop and target new product offerings, and allow facility management and designers to select and apply state of the art technologies effectively. CBE is a National Science Foundation Industry/University Cooperative Research Center.

Center for the Built Environment

There are 584 publications in this collection, published between 1980 and 2024.
Controls and Information Technology (56)

Towards utilizing internet of things (IoT) devices for understanding individual occupants' energy usage of personal and shared appliances in office buildings

Energy consumption in office buildings highly depends on occupant energy-use behaviors and intervening these behaviors could function as a cost-effective approach to enhance energy savings. Current behavior-intervention techniques extensively rely on occupant-specific energy-use information at the workstation level and often ignore shared appliances. It is because an occupant typically has full responsibility for her workstation appliances energy consumption and shares the responsibility of the shared appliances energy consumption. However, understanding energy-use behavior of both workstation and shared appliances is necessary for applying appropriate behavior-intervention techniques. Despite this importance, there is still no practical and scalable method to capture personalized energy-use information of workstation and shared appliances since the conventional methods use plug-in power meters that are extremely expensive and difficult to maintain over long period of time. To address this gap, we propose a comprehensive occupant-level energy-usage approach which utilizes the data from the internet of things devices in office buildings to provide information related to energy-use behavior of workstation and shared appliances of each occupant in an economical and feasible manner. In particular, we introduce an energy behavior index which quantitatively compares individual occupants’ energy-consuming data to identify high energy consumers and inefficient behaviors. Results from an experiment conducted in an office building equipped with internet of things devices demonstrate the feasibility of the proposed approach to classify occupants to different energy-usage categories. Our proposed approach along with appropriate behavior-intervention techniques could be used to impact occupant energy-use behaviors.

53 more worksshow all
Envelope Systems (41)

Human Behavior Meets Building Intelligence: How Occupants Respond to “Open Window” Signals

Designs for low-energy buildings increasingly incorporate operable windows for the benefits of personal control, environmental quality, and architectural value. In practice, however,there are unresolved debates about whether operable windows can be integrated with mechanical systems to optimize both comfort and energy efficiency. Signals that inform occupants about when to open and close their windows (usually red/green lights) have become a popular solution. These systems essentially propose a compromise between manual and automatic control philosophies, asserting that information from the building can influence behavior while retaining the fundamental benefit of personal control. Results from interviews, site visits and surveys of 16 U.S. case studiesshow mixed results. Signals play a role in window use behavior for only a minority of occupants under normative management/education practices. However, greater participation is possible given efforts to communicate the tangible benefits of the devices. Office type (shared or private), visibility of the signals from workstations, reliability of the signal modes, and a range of personal circumstances (noise, wind, window hardware) also influence participation.If conceived as reinforcement to an internal policy rather than as an element of the building controls, this technology holds promise for a wide range of building and user types, and the programming can be flexible and adaptable as circumstances change in our rapidly changing built environment. 

The impact of a view from a window on thermal comfort, emotion, and cognitive performance

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.

Building envelope impact on human performance and well-being: experimental study on view clarity

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.

38 more worksshow all
HVAC Systems (146)

Mixed-mode ventilation: HVAC meets mother nature.

Although more complex to design, combining operable windows with traditional systems can reduce energy use. It can also increase individual climate control, which has multiple benefits of its own. Europe and Japan are implementing mixedmode already, and it may be coming to an office building near you in the future.

Field Study of Capitol Area East End Complex (CAEEC) Sacramento, California

The energy and comfort performance of buildings using underfloor air distribution (UFAD) has been of interest, with some contention, in the building industry for many years. It is not often that an opportunity to address that question directly appears. This project represented such an opportunity to compare and contrast two similarly designed buildings in the same climate and co-located near one another, both occupied by California state employees, one with a UFAD system (B225) and the other with an overhead (OH) variable air volume (VAV) system (B172). At the outset there was hope that we could settle the question definitively due to the highly instrumented systems in these buildings that afforded an opportunity to use measured data for the comparison. This report contains a detailed description of the measured data and simulated analyses used to compare the energy performance of UFAD vs. OH systems, and a summary of the post occupancy evaluations (POE) used to study and compare the occupant satisfaction and indoor environmental quality (IEQ) of both buildings. In addition, we report on field measurements conducted in B225 to investigate two key performance issues with UFAD systems: (1) room air stratification and (2) temperature gain in underfloor plenums. The key findings from the study are listed here: • The measured energy performance data indicates improved efficiency for the UFAD system (B225) vs. the OH system (B172), as annual cooling energy is 31% higher and total annual fan energy is 50% higher for B172 compared to B225. • To account for all major design and operating differences between the buildings, we developed an alternative analysis method based on estimating the impact on B172 energy performance as if it was configured and equipped with central system equipment similar to B225; aka “apples to apples” comparison. When this “apples to apples” comparison method was applied, the total annual HVAC energy use (including cooling, heating, and fans) for OH (B172) is 20% higher than UFAD (B225) and total annual whole building energy use for B172 is 8% higher than B225. • Based on the calculated Energy Star ratings, both B225 and B172 demonstrate excellent energy performance overall. B225 showed a very high site Energy Star rating of 98 and the Energy Star rating for the B171-174 complex (B172 could not be calculated separately) was 91, both well above the 75 required to receive the Energy Star label. • The final POE surveys conducted during October 2007 in the two buildings found that the satisfaction ratings were generally positive and very nearly the same for most of the categories. An important lesson learned from the repeated surveys in B225 between 2003 and 2007 was the value of continuous commissioning of a building’s HVAC system. Efforts by building operations staff and the research team led to an improved understanding of the unique features of the UFAD system, and as a result, greater occupant satisfaction with the quality of the indoor environment in B225.

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Air-change effectiveness: theory and calculation

This paper reports the development of methods for calculating a ventilation performance metric that is a measure of the airflow pattern in a room or zone of a multi-zone ventilation system. Temporal mixing theory is used as the basis for these methods. The methods are applicable to all ventilated systems that can be modeled as a set of interconnected chambers. Relations between the ventilation performance metric defined in this paper and those defined previously are derived. The theoretical results of this paper are consistent with published experimental findings. They also illustrate that the conclusions in some experimental studies about the airflow patterns in working buildings may be incorrect. Re-analysis of previously published detail illustrates how common features of mechanically ventilated buildings, such as recirculation of return air and multiple chambers, confound information about airflow patterns in tracer gas data. The calculation methods developed in this paper can be used to undo this confounding.

143 more worksshow all
Indoor Environmental Quality (IEQ) (303)

Nudging the adaptive thermal comfort model

The recent release of the largest database of thermal comfort field studies (ASHRAE Global Thermal Comfort Database II) presents an opportunity to perform a quality assurance exercise on the first generation adaptive comfort standards (ASHRAE 55 and EN15251). The analytical procedure used to develop the ASHRAE 55 adaptive standard was replicated on 60,321 comfort questionnaire records with accompanying measurement data. Results validated the standard's current adaptive comfort model for naturally ventilated buildings, while suggesting several potential nudges relating to the adaptive comfort standards, adaptive comfort theory, and building operational strategies. Adaptive comfort effects were observed in all regions represented in the new global database, but the neutral (comfort) temperatures in the Asian subset trended 1–2°C higher than in Western countries. Moreover, sufficient data allowed the development of an adaptive model for mixed-mode buildings that closely aligned to the naturally ventilated counterpart. We present evidence that adaptive comfort processes are relevant to the occupants of all buildings, including those that are air conditioned, as the thermal environmental exposures driving adaptation occur indoors where we spend most of our time. This suggests significant opportunity to transition air conditioning practice into the adaptive framework by programming synoptic- and seasonal-scale set-point nudging into building automation systems.

Why is the Indian Sari an all-weather gear? Clothing insulation of Sari, Salwar-Kurti, Pancha, Lungi, and Dhoti

Barring a few reports on the clothing insulation of sari and salwar-Kurti, little is known about the other traditional ensembles men use in South Asia and beyond. To accurately account for the thermal insulation on the human body, simulation studies necessitate insulation on various body parts. This study reports the segmental level insulation of 52 traditional ensembles of both genders recorded in a climate chamber.


Indian garments are worn as ensembles. We focused on the drape, as traditional ensembles offer great opportunities for thermal adaptation through changing drape. We researched on 41 sari ensembles, four salwar-kurti and seven men’s’ ensembles, such as dhoti, pancha and lungi. More than the material, drape has a significant effect on the clothing insulation. For the same pieces of garments, the clo value of the ensemble varied by as much as 3.1 to 32 %, through changing drape in saris, the lower values being associated with lighter saris. A similar trend but somewhat lower variation was noticed in men’s’ ensembles. This makes the sari an all weather ensemble. Interestingly in the pancha ensemble, men can achieve 47% reduction in the clo value with minor variations. The adaptation possibility in traditional ensembles is enormous.

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Sustainability, Whole Building Energy and Other Topics (40)

A tenant interface for energy and maintenance systems

We describe the design of a user interface for energy and maintenance systems in commercial buildings. The user interface is for use by occupants (tenants) of commercial buildings. Our hypothesis is that by allowing tenants access to information from the energy and maintenance systems and by giving them some control over these systems, energy and maintenance performance can be improved. We used interviews with potential users and existing energy and maintenance databases to guide the design.

We describe the design of a user interface for energy and maintenance systems in commercial buildings. The user interface is for use by occupants (tenants) of commercial buildings. Our hypothesis is that by allowing tenants access to information from the energy and maintenance systems and by giving them some control over these systems, energy and maintenance performance can be improved. We used interviews with potential users and existing energy and maintenance databases to guide the design.

Wind and building energy consumption: an overview

The environment around a building affects its energy consumption primarily by influencing its requirement for space heating and cooling. The environmental variables influencing the amount of energy needed for heating and cooling are outside temperature, humidity, solar radiation, and wind.

Wind influences building energy consumption by affecting the following:

1. Air infiltration and exfiltration from conditioned spaces, resulting from pressure gradients and the resulting mass transfer through surface.

2. The rate of heat transmission to or from external surfaces, partially determined by the turbulent mixing of air close to the building surface.

3. Mechanical systems efficiency. Air circulation around buildings affects the thermal efficiency of air-conditioning cooling towers, and can increase fan power requirements when ventilation inlets and exhausts are poorly located.

4. The necessity for enclosing and conditioning outdoor space. Buildings commonly have uncomfortable surroundings, and architects have responded to this by enclosing the surrounding in atria or malls which need to be heated or cooled. Such enclosures might not be necessary if the site and building were designed to control air movement to an acceptable level.

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