Energy Technologies

Burners and cooking activities are both major sources of air pollutants in many residences. Mechanical kitchen ventilation can effectively reduce cooking- related indoor air pollution but the knowledge about kitchen ventilation device performance and usage in real homes remains limited. We reviewed recent lab, field and survey studies that investigated the performance and occupant use patterns for mechanical kitchen ventilation devices. We have found the following three major issues. Firstly, in-home performance is lower than what was certificated in laboratory testing. In several recent field studies, researchers investigated 125 US single family homes and 23 apartments and found 82 homes had range hoods or over-the-range microwaves (OTR) certificated by Home Ventilating Institute (HVI) that had working airflows greater than 100 cfm. However, the field measurements showed only 44 of them had installed airflow that matched the rated, with the average ratio of installed versus rated flow of 0.76. The lower installed airflows were due to high air flow resistance of duct venting systems, incorrect installation and dirty hood inlets. Second, the knowledge of range hood performance for pollutant removal before mixing into the room (i.e. capture efficiency) is very limited. We found the capture efficiency was only measured for 57 hoods in 9 studies in the US, either in the lab or in the field. The measured capture efficiency ranged from 10% to 100%, generally increasing with the airflows. The capture efficiency can be influenced by the burner location, hood airflow, range hood geometry and test conditions. The main reason for limited capture efficiency data was the difficulty in conducting field measurements. Third was that the actual usage of the kitchen ventilation during cooking is low. Occupants often do not use their range hood due to the lack of awareness of the benefits of kitchen ventilation. A large survey study in Canadian homes showed that 30% of households reported regularly using their range hood. After being informed of the benefits of kitchen ventilation, the overall willingness to use the range hood was significantly higher. Field data from California showed range hoods were only used for 36% of cooking events in houses and 28% in apartments, though the occupants claimed they used them more frequently.

Embodied emissions from the production of building materials account for 17% of Chinas carbon dioxide (CO2) emissions and are important to focus on as China aims to achieve its carbon neutrality goals. However, there is a lack of systematic assessments on embodied emissions reduction potential of building materials that consider both the heterogeneous industrial characteristics as well as the Chinese buildings sector context. Here, we developed an integrated model that combines future demand of building materials in China with the strategies to reduce CO2 emissions associated with their production, using, and recycling. We found that measures to improve material efficiency in the value-chain has the largest CO2 mitigation potential before 2030 in both Low Carbon and Carbon Neutrality Scenarios, and continues to be significant through 2060. Policies to accelerate material efficiency practices, such as incorporating embodied emissions in building codes and conducting robust research, development, and demonstration (RD&D) in carbon removal are critical.

In the transition from fossil fuel to electrified heating, a concerning trend is emerging in certain regions of the US. Owners of buildings with gas-based systems leave them in place after adding heat pumps (HPs). Existing control solutions for these hybrid (dual fuel) systems are rudimentary and fall short of realizing the full carbon reduction potential of these systems. Model predictive control (MPC) is often regarded as the benchmark for achieving optimal control in integrated systems. However, in the case of small-medium commercial buildings (SMCBs), the control and communication infrastructure required to facilitate the implementation of such advanced controls is often lacking. This paper presents a field implementation of easy-to-deploy MPC for a dual fuel heating system consisting of HPs and a gas-fired furnace (GF) for SMCBs. The control system is deployed on an open-source middleware platform and utilizes low-cost sensor devices to be used for real SMCBs without major retrofits. We demonstrated this MPC in a real office building with 5 HPs and 1 GF for 2 months. The test results showed that MPC reduced 27% of cost while completely eliminating GF usage by shifting 23% of the thermal load from occupied-peak time to non-occupied-non-peak times.

Roughly, 50% of primary energy worldwide is rejected as waste heat over a wide range of temperatures. Waste heat above 573 K has the highest Carnot potential ( > 50 % ) to be converted to electricity due to higher Carnot efficiency. Thermoelectric (TE) materials have gained significant attention as potential candidates for efficient thermal energy conversion devices. Silicon nanowires (SiNWs) are promising materials for TE devices due to their unique electrical and thermal properties. In this study, we report the successful fabrication of high-quality double-sided SiNW arrays using advanced techniques. We engineered the double-sided structure to increase the surface area and the number of TE junctions, enhancing TE energy conversion efficiency. We also employed non-agglomeration wire tip engineering to ensure uniformity of the SiNWs and designed effective Ohmic contacts to improve overall TE efficiency. Additionally, we post-doped the double-sided SiNW arrays to achieve high electrical conductivity. Our results showed a significant improvement in the TE performance of the SiNW array devices, with a maximum figure-of-merit (ZT) value of 0.24 at 700 K, fabricated from the single SiNW with ZT of 0.71 at 700 K in our previous work [Yang et al., Nat. Commun. 12(1), 3926(2021)].

This report details modeled energy performance and savings from retrofit packages in prototypical school buildings in climate zones throughout the U.S. The information herein serves as a reference for elementary and secondary schools interested in implementing retrofit packages in their facilities for energy savings as well as health and safety benefits. School models developed for simulating package performance differentiated between rural and urban environments. Simulations were run for 10 distinct climate zones covering a range of climate conditions throughout the U.S. Results include savings estimates for electricity, natural gas, CO2 emissions, and annual utility costs for nine different retrofit packages that combine energy conservation measures, including HVAC controls and equipment upgrades, lighting efficiency upgrades, and electrification technologies such as heat pumps for space conditioning and domestic hot water. Nine additional retrofit packages were also developed for elementary schools and modeled in two climate zones. Appendix B describes the additional retrofit packages and presents savings estimates.

This paper presents new results on the link between energy factors and commercial mortgage default. First, we summarize results from an empirical analysis of the impact of source energy use intensity (EUI) and electricity prices on mortgage default. We used a unique data set that merges building-level energy use data from city benchmarking ordinances and financial data for commercial mortgages on the same buildings. We found that building source EUI and electricity price are statistically and economically associated with commercial mortgage defaults. Next, we present five case studies on the impact of energy use and price variations on default risk: three office buildings, a hotel, and a multi-family residential building. We use the empirical model coefficients to compute the default risk impacts due to variations in source EUI and electricity price over the course of the mortgage term. We found that variations in source EUI could raise or lower the default rates in these properties by between 5% and 40%, depending on the property type and geography. Electricity pricing has an even greater effect – roughly 60% change in default rate in the Denver area and nearly 90% in northern California. Finally, we propose an energy risk score that lenders can use to assess energy risk and inform mortgage terms. The score is being developed and piloted in collaboration with three mortgage lenders. We conclude with implications of this score as a market signal and mechanism for incentivizing energy efficiency investments through the commercial mortgage channel.

Most existing buildings have sub-optimal heating, ventilation, and air conditioning (HVAC) controls, resulting in wasted energy and occupant discomfort. Retro-commissioning (RCx) addresses many of these issues, but it is a lengthy and highly customized process. Limited capabilities of existing building automation system hardware restricts the scope of most RCx projects. Incentive programs consider building automation system (BAS) hardware retrofits to be high-capital investments and do not allow them in typical RCx programs. This paper describes work that the authors are leading to facilitate technical and market innovation in the BAS industry to unlock large savings in existing commercial buildings through deep retrofits of BAS hardware and software. California and New York research projects are demonstrating BAS retrofits leveraging the American Society of Heating, Refrigeration, and Air Conditioning Engineers’ (ASHRAE) new Guideline 36 high performance sequences of operation to achieve greater than 20 percent whole building energy savings, while saving costs and reducing risk through streamlined processes and standardization across BAS manufacturer product lines and across implementation practices. This paper describes market barriers that impede achieving deep savings from BAS retrofits in custom incentive and traditional RCx programs and presents a new maximum potential BAS retrofit model that addresses these barriers. The new model leverages the authors’ efforts in market enablement through open standards, BAS industry partnerships, and tools for cost-effective scaling that includes tools for project screening, savings calculations, and measurement and verification (M&V). This approach is widely applicable and will be ready for at-scale implementation within two years.

Substantial energy is used to condition the air that enters California homes through leaks in the building envelope and ductwork - typically about a third of all heating and cooling. Reducing this through air sealing is essential to California achieving zero energy homes. However, this outdoor air also dilutes pollutants emitted inside homes and contributes to a healthy indoor environment and acceptable indoor air quality (IAQ). To address this IAQ issue, California’s Title 24 Building Standards have required mechanical ventilation in new homes since 2008. This report presents a comprehensive study of the impacts of these requirements in recently constructed homes with natural gas appliances. The study included a survey about satisfaction and activities that impact IAQ; a field study of homes built to 2008 or later; and simulations assessing how various ventilation rates would impact chronic exposures to an indoor emitted pollutant as air tightness improves in California. The report focuses on the field study; the webbased survey and simulation elements are described in appendices. The field study characterized 70 homes built between 2011 and 2017. Each home was monitored over roughly one week with the dwelling unit mechanical ventilation system operating and windows closed. Pollutant measurements included time-resolved fine particulate matter (PM2.5) indoors and outdoors, and formaldehyde, nitrogen dioxide (NO2), and carbon dioxide (CO2) indoors. Time-integrated measurements were made for formaldehyde, NO2 and nitrogen oxides (NOX) indoors and outdoors at all homes. Activity monitoring devices were installed on the cooktop, range hood and other exhaust fans, and the heating and cooling system. The field study found that most homes met most ventilation requirements and the dwelling unit ventilation fans on average moved 50% more airflow than the minimum specified in Title 24. Air pollutant concentrations were similar or lower than those reported in a study of recent construction California new homes conducted in 2007-08. Notably, the median formaldehyde level was 38% lower than in the prior study. Measured concentrations were below health guidelines for most pollutants, indicating that IAQ is acceptable in new California homes when dwelling unit mechanical ventilation is used. However, the dwelling unit mechanical ventilation fans were only operating in one quarter of the homes when first visited and the control switches in many homes did not have informative labels as required by the standards. Corrective action needs to be taken to improve labeling and controls for ventilation systems.

Most building retrofit projects are still component-based in that they typically address only one piece or type of equipment at a time. Systems-based retrofits that seek to address multiple components in an integrated manner have the potential to provide significantly greater energy savings. Lawrence Berkeley National Laboratory (LBNL) partnered with several utilities to develop and evaluate three different integrated retrofit packages involving lighting systems: automated shading with daylight dimming controls, workstation-specific lighting with daylight controls, and task/ambient lighting with plug load occupancy controls. Specifically, our analysis sought to quantify the marginal benefits of these systems (energy savings as well as lighting performance and visual comfort) relative to component based approaches. The analysis was based on a combination of measured performance data from LBNL’s FLEXLAB® test facility and energy simulations. All three systems were compared to a simple fluorescent-to-LED retrofit, which represents the component-based approach. While the simple LED upgrade provides significant lighting energy savings of 63%, the systems yielded energy savings of 81-93%, which equates to additional savings of 49-82% over the simple LED upgrade (Table A-1).1 All systems tested provided satisfactory visual comfort as well, indicating good potential for market acceptance.