California Building Research Articles

Reducing inter-unit pollutant transfer through multifamily unit compartmentalization

Compartmentalization, which refers to air sealing each unit within a building from the exterior and other interior spaces, has been proposed as a strategy to improve indoor air quality and energy efficiency in multifamily buildings. This study collected field data on air tightness and pollutant transfer in three new-construction multifamily buildings in California, which was used to develop a model in CONTAM that simulated the impact of leakage levels, ventilation strategies, and climate zones on inter-unit pollutant transfer in multifamily buildings. Air leakage testing found an average total unit leakage of 0.8 L/s50/m2, almost twice as tight as California’s current compartmentalization requirement (1.5 L/s50/m2). Two buildings designed with balanced ventilation systems were measured to have imbalanced continuous unit ventilation flows, which were further imbalanced by intermittent exhaust fan operation. Tracer gas testing in two buildings indicated that only about 1–3% of the total air entering a unit came from each neighbouring unit. Furthermore, all particles were apparently removed along the way, as there was no observable particle matter transfer at the tested air tightness levels (0.6–0.9 L/s50/m2). Modelling results indicated that leakier units led to greater dilution of pollutants generated within the unit but increased gaseous pollutant transfer from neighbouring units. The average concentration of benzene, a proxy gas for cigarette smoke, transferred into non-smoking units from neighbours who did smoke almost doubled, surpassing acceptable exposure levels, in the leaky simulation (2.3 L/s50/m2) compared to the tight simulation (0.8 L/s50/m2). Overall, this study suggests that stricter compartmentalization requirements should be adopted in multifamily building code updates, as tighter requirements appear to be manageable for builders and beneficial for indoor air quality when combined with mechanical ventilation.

Transit-oriented development: A case study of exterior-to-interior noise control for buildings near transit and highway noise sources

A case study of acoustical design for mixed-used, transit-oriented development is presented. The project is two, six-story mixed-used residential buildings near a rapid transit station and heavily traveled elevated highway in the San Francisco Bay Area. The buildings are metal frame construction over concrete podiums. The California Building Code requires the building shell to be designed to provide interior noise from exterior noise sources not to exceed 45 dBA Ldn. Exterior noise due to trains and buses serving the transit station, and traffic on the elevated highway, required high sound attenuating windows and acoustically rated walls and roofs. Initially, none of the exterior wall assemblies included batt insulation in the stud cavities, only continuous rigid insulation behind the façade. Modeling was done to compare the exterior wall assemblies with and without batt insulation in the stud cavities combined with various window configurations. Estimates of the building shell transmission loss are presented along with a summary of noise control recommendations for building roof, windows, and doors.

Examining the impact of energy efficiency retrofits and vegetation on energy performance of institutional buildings: An equity-driven analysis

Inequities in the built environment have long persisted in communities around the world. Prior studies have exposed that energy retrofit programs invest inequitably in residential buildings, leaving racial minorities with disproportionately less energy inefficient homes, regardless of income level. This inequity in energy performance and retrofit investments has yet to be studied for commercial and institutional buildings. Further research has shown that tree canopy coverage and vegetation is less dense in historically disadvantaged communities, contributing to a greater urban heat island effect and corresponding higher energy consumption for cooling compared to historically advantaged communities. Moreover, there is limited albeit emerging research that utilizes granular socioeconomic data with fine temporal scale energy consumption data to help identify energy inequalities among race and income groups. This paper examines the differential impact of energy efficiency retrofit installation on energy performance between advantaged vs. disadvantaged groups using data from U.S. public school buildings. Additionally, it studies how the effect of retrofits is compounded by the presence of vegetation surrounding the building. Utilizing hourly interval smart meter data from primary and secondary school buildings in California, the impact of retrofits are quantified using three energy metrics. Then the disparities in retrofit impact for advantaged vs. disadvantaged groups (as defined by three equity metrics) are evaluated using school-level demographic data. Lastly, regression on the percent change in monthly energy consumption from the pre-retrofit to post-retrofit period is used to quantify the incremental benefits of retrofits compounded by vegetation. Findings show that energy efficiency retrofits can improve energy performance and reduce energy inequities. Specifically, retrofits significantly increase energy efficiency and reduce the energy efficiency equity gap by up to 198%. Evidence shows that vegetation surrounding a building has a synergistic effect with mechanical retrofits for reducing energy consumption in respect to reduced cooling loads, even in cases where mechanical retrofits alone resulted in significant increases in energy consumption. Dense vegetation provides around 6% energy savings, similar in magnitude to savings from mechanical retrofit installation. This validates the effectiveness of retrofits for reducing energy consumption and improving energy equity, and demonstrates the ability of vegetation to provide additional energy savings beyond mechanical interventions.

Nonlinear dynamic seismic analysis of a modern concrete core wall building in Los Angeles using the BTM‐shell methodology

AbstractThis paper discusses the nonlinear dynamic seismic response of a 14‐story reinforced concrete core wall building designed with the prescriptive requirements of the 2019 California Building Code for a near‐fault site in Los Angeles, California, simulated with a detailed nonlinear analysis of the complete structure and subjected to an ensemble of three‐component ground motion input. The study follows up on a recently published work by the authors, which examined the response of the specific building to static lateral loads. The nonlinear model of the building was developed in the software FE‐Multiphys using a shell‐element implementation of the beam–truss model (BTM). The BTM has been extensively validated through prior studies for planar, flanged, and coupled walls under static and dynamic loading. The building model was subjected to an ensemble of ground motions scaled at the design and risk‐targeted maximum considered earthquake levels. The vertical ground motion component and the out‐of‐plane shear degradation of wall piers were included in the simulations. The analyses elucidate the profound effect of nonlinear flexure–shear interaction and of the multidirectional behavior of the flanged coupled core wall on the evolution and localization of damage and on residual deformations. The coupling behavior between the core wall, the slabs, and the columns is also analyzed, and the importance of modeling the nonlinear behavior of all slabs for the residual damage evaluation is demonstrated. The aim of this study is to improve the understanding of issues arising from prescriptive design requirements as well as of issues associated with limitations of standard nonlinear seismic analysis.

Bayesian model selection considering model complexity using stochastic filtering

AbstractThis paper proposes a Bayesian model selection framework to determine optimal, parsimonious models for given building structures under ground motion excitation using stochastic filtering. Structural system identification at a regional scale after an earthquake is nominally a monumental task due to its inherently high computational cost. This challenge is currently addressed in the literature by using simplified structural models that bear analytical solutions, such as Timoshenko or shear beams, and shear building models. However, a low computational effort usually leads to an increased prediction error and consequently, a higher model uncertainty. This poses the dilemma of prediction accuracy versus model complexity when selecting a model class to represent a building structure. The proposed framework selects the model class that strikes the best balance between the two. To this end, the notion of cumulative evidence is introduced here as the integral of local evidence over the ground motion duration, which is then formulated as the difference between the cumulative likelihood of the observed measurements and the cumulative penalty. The likelihood measure promotes models whose predictions better match the observations. This is counteracted by the penalty, which is devised as an “Ockham factor,” and penalizes models with higher information gains due to their higher complexities, for example, a larger number of parameters. The proposed approach also yields the best tuning parameters of the stochastic filter for each model class and the best initial values of the identification parameters. The proposed framework is verified using a synthetic example, and validated using recorded data from the Millikan Library building in California and the ANX building in Japan.

Methods in open policy analysis: An application to California's building energy codes

AbstractHave building energy codes lowered energy consumption, and have their benefits outweighed costs? Using 2000 Census data, I estimate household energy expenditures by decade of home construction, controlling for household and home characteristics. I find homes built in the 1980s used $35 less in electricity and $46 less in natural gas, per year, compared to 1970s era homes. For Sacramento, energy codes pass a cost‐benefit test when low‐end policy costs are used, but fail with base‐case costs. This study also clarifies how a cost‐benefit analysis (CBA) for a representative household fits into a comprehensive CBA.

Transitioning from diesel backup generators to PV-plus-storage microgrids in California public buildings

Climate-related wildfires have caused significant power outages in California, including planned outages called Public Safety Power Shutoffs (PSPS). Consequently, concerns about grid reliability have increased public and private demands for backup generators, including diesel-fueled ones. However, diesel generators bear high environmental costs, emitting greenhouse gases and air pollutants that negatively impact public health. This research quantifies the economic value and environmental benefit of replacing diesel backup generators with PV-plus-storage microgrids for public buildings in California, which has a net zero carbon emissions target in the electricity sector by 2045. Using an energy integration and optimization model, REopt, and empirical data, this study demonstrates that replacing diesel backup generators in just one building would save almost $3M of public expenditures and reduce over 10,000 tons of CO2 emissions over a 20-year period. The resulting implication is that public buildings and critical facilities in the state's 22 air districts could save $31-385M annually by the same application. Also, this research develops a marginal resilience curve for the cost and environmental impact of extended outages, which demonstrates that increasing energy storage capacity greatly outweighs increasing PV or generator capacity to enhance resilience, while reducing costs and emissions.

Investing in community power building to increase civic engagement through voting: lessons from the Building Healthy Communities initiative

ABSTRACT The objective of this study was to examine the impact of investments in community organizing made as part of a 10-year comprehensive community initiative focused on community power building in California. Data from multiple sources were used to examine the relationship between investments and one measure of civic engagement, voter turnout. Comparisons were made over time (2010–2019) and between intervention and propensity-weighted comparison sites. Analyses determined that investments by the funder were positively associated with turnout; this effect differed across elections and was largest in 2012. Broad investments to support community engagement, organizing, and base building had a positive impact on voting, an important indicator of civic engagement. In historically marginalized or underserved communities, investing in power building can yield benefits despite structural barriers that result in inequities. As restrictive electoral reforms grow across the country in the wake of the 2020 election, initiatives designed to build power may support proactively organizing against these changes or provide the infrastructure to understand and navigate them. Investing in community power building is a promising strategy for philanthropic organizations, organizers, and policy makers.

Financial Failure and Depositor Quality: Evidence from Building and Loan Associations in California

Flightiness, or depositor sensitivity to liquidity needs, can be an important determinant of financial distress. I leverage institutional differences—that attract depositors with varying flightiness—across building and loan associations in California during the Great Depression. A new type of plan, the Dayton plan, involved less restrictive savings plans and lower withdrawal penalties. Dayton plans in California were more likely to close during the Great Depression. Archival evidence on lending rates and returns supports the flightiness mechanism.

Structural and modal analysis of gas insulated switchgear structure made up of glass-epoxy and carbon-epoxy composite materials for seismic application

Earthquakes cause significant loss of life and infrastructure damage. As a result, there has been a huge increase in the development of technologies and materials to mitigate the effects of earthquakes in the infrastructure sector. Along with the infrastructure industry, the electrical sector is working to design structures that can withstand the effect of an earthquake. The purpose of this study is to develop lightweight frame structure for Gas Insulated Switchgear (GIS) for seismic applications. In the proposed study, GIS frame structure incorporates composite materials such as carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) in addition to traditional materials such as steel. These composite materials are subjected to experimental testing in order to determine their mechanical properties. To select optimal material for the frame structure, the structural and modal performance of these materials is evaluated using finite element simulations for the GIS frame structure under seismic loading as per California Building Code (CBC) and International Building Code (IBC) code.

Financial Failure and Depositor Quality: Evidence from Building and Loan Associations in California

Flightiness, or depositor sensitivity to liquidity needs, can be an important determinant of financial distress. I leverage institutional differences that attract depositors with varying flightiness across building and loan associations in California during the Great Depression. A new type of plan, the Dayton plan, involved less restrictive savings plans and lower withdrawal penalties. Dayton plans in California were more likely to close during the Great Depression. Archival evidence on lending rates and returns supports the flightiness mechanism.

Evaluating Deck Fire Performance—Limitations of the Test Methods Currently Used in California’s Building Codes

Combustible decks are identified as vulnerable components of buildings in wildfire-prone areas. In California, combustible deck boards can comply with the requirements of Chapter 7A of the California Building Code if they pass an under-deck flame-impingement exposure test. It is desirable if standard test methods can simplify procedures while not adversely affecting the reliability of the test. The test methods should also be able to discriminate the fire performance between products on the market. In this research, the specified conditions in the under-deck flame-impingement test, SFM 12-7A-4A and ASTM E2632, were evaluated. Different deck assemblies were exposed to above-deck ember and under-deck flame-impingement exposures. During the above-deck ember exposure tests, it was observed that embers accumulated in the gaps between deck boards, on top of the support joists, and, when ignition occurred, ignited in this area. Flames spread by burning into unburned areas of the deck boards and joists, thereby providing a pathway to the building. During the under-deck flame-impingement tests, the three assumptions in the standard test method were evaluated, namely, (1) a small deck size can adequately represent the performance of larger decks, (2) the absence of wind will not noticeably influence performance, and (3) differences in joist material would not noticeably change the performance of the deck boards. Results of experiments suggested that the current Chapter 7A compliant deck boards burned intensely and exposed the cladding of the test building, resulting in an elevated temperature at the wall. It is argued that the current assumptions are an oversimplification of real-world fire performance and a change in the current California’s building code is necessary. This research demonstrated the necessity of evaluating an entire deck assembly rather than only the walking surfaces.

Progress of Local Health Department Planning Actions for Climate Change: Perspectives from California, USA.

Public health departments are on the frontlines of protecting vulnerable groups and working to eliminate health disparities through prevention interventions, disease surveillance and community education. Exploration of the roles national, state and local health departments (LHDs) play in advancing climate change planning and actions to protect public health is a developing arena of research. This paper presents insights from local public health departments in California, USA on how they addressed the barriers to climate adaptation planning with support from the California Department of Public Health’s Office of Health Equity Climate Change and Health Equity Section (OHE), which administers the California Building Resilience Against Climate Effects Project (CalBRACE). With support from the U.S. Centers for Disease Control and Prevention (CDC) Climate-Ready States and Cities Initiative (CRSCI), CalBRACE initiated an adaptation project to seed climate planning and actions in county health departments. In this study, we compared the barriers and strategies of twenty-two urban and rural LHDs and explored potential options for climate change adaptation in the public health framework. Using key informant interviews and document reviews, the results showed how engagement with CalBRACE’s Local Health Department Partnership on Climate Change influenced the county departments’ ability to overcome barriers to adaptation through the diversification of funding sources, the leveraging strategic collaborations, extensive public education and communication campaigns, and the development of political capital and champions. The lessons learned and recommendations from this research may provide pathways and practices for national, state and local level health departments to collaborate in developing protocols and integrating systems to respond to health-related climate change impacts, adaptation and implementation.

Response Study of a Tall San Diego, California Building Inferred from the M7.1 July 5, 2019 Ridgecrest, California Earthquake Motions

The shaking of a new 24-story tall building in San Diego, California, was recorded by its seismic monitoring array during the M7.1 Ridgecrest, California earthquake of July 5, 2019. The building is located ~340 km from the epicenter of the event. The building is a special moment framed (SMF) steel structure with reduced beam sections (RBS) and viscous damper systems (DS). Peak accelerations recorded by the array indicate 0.007 g at the basement level and 0.044 g at the roof level. Spectral analyses and system identification methods indicate coupled NS, EW, and torsinal fundamental modes at ~ 0.30 Hz frequency and critical damping percentages < 5%. For the EW and fundamental torsional modes, critical damping percentages are < 2.5%. At the low-level shaking, the computed largest average drift ratio is ~ 0.065%, less than 0.5% of the value considered to be the starting threshold of nonlinear behavior or damage.

Real time side-by-side experimental validation of energy and comfort performance of a zero net energy retrofit package for small commercial buildings

Making buildings zero-net energy (ZNE) is one of the major strategies for achieving carbon emission reduction goals. For this strategy to be successful, it entails a very significant reduction in energy use – 50% or more. In small commercial buildings, however, owners and building management teams usually have limited resources for identifying, analyzing, and procuring appropriate retrofit measures for reducing such use. An approach to overcome this limitation is the development of bundles of energy efficiency measures that can be presented to building owners/operators as a comprehensive package. The research presented in this paper focuses on an experimental evaluation of the impacts of a retrofit package developed for small office buildings in California. Performing this evaluation in a full-scale whole-building integrated systems test facility allowed a side-by-side evaluation in real time, against a reference case, of the impact of the retrofit package not only on energy use but also on visual and thermal comfort. The retrofit package evaluated is comprised of a combination of HVAC, lighting (including daylighting), and plug load measures. The evaluation occurred at different times of the year in order to account for seasonal variations in environmental conditions, including solar angles and weather. The experimental facility allowed testing for two different façade orientations: south and west. Results show that the proposed ZNE retrofit package can save significant amounts of energy for small commercial buildings. During cooling-prevalent periods, total energy savings were 65% for south orientation and 68% for west orientation; during heating-prevalent periods total energy savings were 22% for south orientation and 25% for west orientation. Measurements indicate that the ZNE retrofit package resulted in small but not very significant changes in comfort levels for building occupants.

The occupational safety implications of the California residential rooftop solar photovoltaic systems mandate

Introduction: A 2018 change to the California building code mandates that new residential construction in the state include rooftop solar photovoltaic power systems beginning in 2020. As residential construction (especially work on rooftops) is among the more dangerous occupations in the United States, this paper seeks to quantify the increased risks to workers as a result of this mandate. Method: An analysis of the trends by occupation of nonfatal safety incident rates in the United States combined with a Monte Carlo simulation provide an estimate of the uncertain impact of this new mandate. Results: Recordable safety incidents are anticipated to increase by a total of 16.6 incidents (standard deviation = 1.0 incidents) over the 2020–2029 time period as a result of this policy change. However, lessons from Germany and other industries offer potential avenues to reduce the negative social impact of this mandate. Conclusions: While it is not possible to increase employment in any sector without increasing the expected number of occupational injuries to some degree, these results indicate that risks could be considerably reduced by making solar PV system design decisions that increase worker productivity and reduce roof exposure time. Practical Applications: Changes such as eliminating work on roofs could decrease the expected number of recordable injuries over the 10-year period by 0.30 incidents per year (a reduction of 18%).

Risk-constrained multi-period investment model for Distributed Energy Resources considering technology costs and regulatory uncertainties

One of the reasons for the emerging adoption of behind-the-meter distributed energy resources (DERs), particularly photovoltaic (PV) and storage, is the impressive decrease in technology costs over the last years together with favorable policy and regulatory environments that created early-stage incentives to the proliferation of these assets. However, when looking at the next decade, the evolution of the regulatory framework and the trajectory of technology costs are difficult to predict. This uncertainty poses a new challenge to prosumers and microgrid owners who are trying to find the best moment to invest in these DERs. In particular, unpredictable changes in the conditions of the investments may translate into economic risks to potential DER adopters, which raises the need for new risk-mitigation methods to support their investment decisions. To address this issue, this paper proposes a multi-period DER investment model with economic risk constraints, considering technology costs and regulatory uncertainties. A case study, involving a large building in California, is used to show that different types of economic risk constraints can affect not only the size, but also the optimal timing of these investments in a multi-year planning horizon with significant DER technology costs and regulatory uncertainties.

Data-Driven Examination of the Impact Energy Efficiency has on Demand Response Capabilities in Institutional Buildings

Abstract Growing concerns over climate change and grid reliability have led to widespread adoption of energy efficiency (EE) and demand response (DR) programs at utilities. Despite such adoption, numerous questions exist regarding the interactions between EE and DR, including whether EE diminishes a building’s DR potential. In this brief, we empirically examine the impact a building’s EE level (quantified by traditional EE benchmarking metrics) has on its DR capabilities (quantified by a building’s normalized load shed) for 194 K-12 institutional school buildings in California, USA. We found inconclusive statistical evidence that a building’s EE level has an impact on its DR load shed capabilities. We provide initial evidence countering concerns that EE diminishes DR potential and thus pave the path for future work than can further support synergistic EE and DR strategies which can enhance demand-side management programs.

Seismic analysis of a modern 14‐story reinforced concrete core wall building system using the BTM‐shell methodology

AbstractThis paper uses computational simulation to investigate the lateral load‐displacement behavior and failure modes of a modern 14‐story reinforced concrete (RC) core wall building. The design complies with the minimum code requirements of the current California Building Code, which is based on ASCE 7–16 and ACI 318–14. The computational representation of the building, which accounts for the material nonlinearities of all structural components, employs the beam‐truss model (BTM) for the walls and floor slabs. Analyses of the building model are conducted for static monotonic and cyclic lateral loads using the program FE‐MultiPhys, which provides a user‐friendly implementation of the BTM as an assemblage of rectangular shell macroelements. Two different load patterns, that is, lateral load distributions along the building height, are considered. The analyses provide insights into the evolution of damage and lateral strength degradation and their dependence on the load pattern, while also elucidating the complex interaction between the webs and flanges of the core wall and the system effects associated with coupling between the walls, beams, slabs, and columns. The presentation of the analytical results is accompanied by a discussion on the advantages of the BTM over seismic analysis methods used in current code‐minimum and performance‐based seismic design (PBSD) practice.

Predicting airborne pollutant concentrations and events in a commercial building using low-cost pollutant sensors and machine learning: A case study

Prediction of indoor airborne pollutant concentrations can enable a smart indoor air quality control strategy that potentially reduces building energy use and improves occupant comfort. In service of this overarching goal, this work pursues four objectives: 1) Determine which low-cost airborne pollutant sensors are useful for prediction of indoor air quality variables of interest, investigating whether a few commercially available sensors held value for making such predictions. 2) Investigate which algorithms are most useful for making these predictions. 3) Develop an understanding of how far into the future we can conceivably predict indoor concentrations based on low-cost airborne pollutant signals. 4) Investigate methods for predicting elevated concentration events from historical data. Four different methods (Rolling Average, Random Forest, Gradient Boosting, and Long-Short Term Memory) for predicting eight indoor pollutant concentrations (carbon dioxide, nitrogen dioxide, ozone, PM 1, PM 2.5, PM 10, formaldehyde, total volatile organic compounds) are compared for their ability to predict future sensor signals in a single commercial building in California. Long-Short Term Memory was consistently the best method for predicting indoor pollutants, though the best combinations of input variables differed depending on pollutant of interest. To predict elevated concentration events, results show that indirect classification through a regression prediction that was then compared to a threshold performed marginally better than a direct classification prediction for all pollutants except PM1.