Roderick K Jackson

Specific contact resistance at metal/carbon nanotube interfaces

In this report, the specific contact resistance between a thin film single wall carbon nanotube electrode and a deposited silver contact was measured. The specific contact resistance was found to be 20 mΩ cm2, which is an order of magnitude higher than typically observed in standard Si photovoltaic technology. We demonstrate that when utilized as the transparent anode in organic photovoltaics, the specific contact resistance has the potential to induce non-negligible resistive power losses. Thus, specific contact resistance will adversely affect the performance of these systems and should therefore be addressed.

Evaluation of transparent carbon nanotube networks of homogeneous electronic type

In this report, we present a description of the optical and electronic properties of as-deposited, annealed, and chemically treated single-walled carbon nanotube (SWNT) films showing metallic or semiconducting behavior. As-deposited and annealed semiconducting SWNT films were significantly less conductive than metallic SWNT films; however, chemical treatment of semiconducting SWNT films resulted in sheet resistance values as low as 60 Omega x sq(-1) in comparison to 76 Omega x sq(-1) for similarly processed metallic SWNT films. We conclude that the greater improvement of electrical conductivity observed in the semiconducting SWNT film results from the difference in the density of available electronic states between metallic and semiconducting SWNTs. A corroborative investigation of the change in surface work function and the chemical composition of SWNT films, as revealed by X-ray photoelectron spectroscopy, is provided to support these conclusions and to give new perspective to the formation of electronically homogeneous SWNT networks.

A method for modeling household occupant behavior to simulate residential energy consumption

This paper presents a statistical method for modeling the behavior of household occupants to estimate residential energy consumption. Using data gathered by the U.S. Census Bureau in the American Time Use Survey (ATUS), actions carried out by survey respondents are categorized into ten distinct activities. These activities are defined to correspond to the major energy consuming loads commonly found within the residential sector. Next, time varying minute resolution Markov chain based statistical models of different occupant types are developed. Using these behavioral models, individual occupants are simulated to show how an occupant interacts with the major residential energy consuming loads throughout the day. From these simulations, the minimum number of occupants, and consequently the minimum number of multiple occupant households, needing to be simulated to produce a statistically accurate representation of aggregate residential behavior can be determined. Finally, future work will involve the use of these occupant models along side residential load models to produce a high-resolution energy consumption profile and estimate the potential for demand response from residential loads.

A Review of Carbon Nanotube Ensembles as Flexible Electronics and Advanced Packaging Materials

The exceptional electronic, thermal, mechanical, and optical characteristics of carbon nanotubes offer significant improvement in diverse applications such as flexible electronics, energy conversion, and thermal management. We present an overview of recent research on the fabrication, characterization and modeling of carbon nanotube (CNT) networks or ensembles for three emerging applications: thin-film transistors for flexible electronics, interface materials for thermal management and transparent electrodes for organic photovoltaics or light emitting diodes. Results from experimental measurements and numerical simulations to determine the electrical and thermal transport properties and characteristics of carbon nanotube networks and arrays used in the above applications are presented. The roles heterogeneous networks of semiconducting and metallic CNTs play in defining electrical, thermal, and optical characteristics of CNT ensembles are presented. We conclude with discussions on future research directions for electronics and packaging materials based on CNT ensembles.

A MATLAB based occupant driven dynamic model for predicting residential power demand

This paper presents a MATLAB based dynamic model for predicting residential power demand. Markov chain based occupant behavior models developed using data gathered by the U.S. Census Bureau in the American Time Use Survey (ATUS) are used in conjunction with models of the most common residential loads to predict residential power demand on a one-second time scale. First, the methods utilized for the modeling of each residential load are presented. Next, an explanation of how these load models are combined with occupant behavior models to predict residential power demand is given. Simulation results showing the overall contribution of each load to the overall residential sector power demand are shown for both winter and summer cases. Finally, future work will involve the use of this high-resolution dynamic residential model to estimate the potential for demand response from residential loads.

Modeling, controls, and applications of community energy storage systems with used EV/PHEV batteries

This study presents the modeling and controls of a community energy storage system composed of repurposed used electric or plug-in hybrid electric vehicle (EV/PHEV) battery packs. The expectation is that the vehicular batteries will be replaced with a fresh battery pack by the original equipment manufacturers (OEMs) once their performance (storage capacity and peak power capability) decrease to its 80% of the initial performance. Community energy storage (CES) systems can be a feasible application of these after vehicle batteries due to economic and environmental reasons. These batteries, if their power electronic interfaces are controlled properly, can perform many grid support applications or provide grid ancillary services as will be detailed in this study.

Advancing Residential Retrofits in Atlanta

This report will summarize the home energy improvements performed in the Atlanta, GA area. In total, nine homes were retrofitted with eight of the homes having predicted source energy savings of approximately 30% or greater based on simulated energy consumption.

A dynamic simulation tool for estimating demand response potential from residential loads

This paper presents a MATLAB based dynamic simulation tool for estimating demand response potential from residential loads. First, a review of residential demand response strategies is conducted. Next, the modeling approach used during the development of this tool is described. Markov chain based occupant behavior models constructed using data gathered by the U.S. Census Bureau in the American Time Use Survey (ATUS) are used in conjunction with models of the most common residential loads to predict the dynamic changes in residential power demand on a one-minute time scale. Separate control schemes are used along with these models to simulate different demand response strategies. Finally, simulation results showing the benefits and trade-offs associated with residential demand response programs are presented. Future work will involve using this tool to examine specific utility areas and the development of real-time pricing and incentive program components.

A rule-based expert system applied to moisture durability of building envelopes

The moisture durability of an envelope component such as a wall or roof is difficult to predict. Moisture durability depends on all the construction materials used, as well as the climate, orientation, air tightness, and indoor conditions. Modern building codes require more insulation and tighter construction but provide little guidance about how to ensure these energy-efficient assemblies remain moisture durable. Furthermore, as new products and materials are introduced, builders are increasingly uncertain about the long-term durability of their building envelope designs. Oak Ridge National Laboratory and the US Department of Energy’s Building America Program are applying a rule-based expert system methodology in a web tool to help designers determine whether a given wall design is likely to be moisture durable and provide expert guidance on moisture risk management specific to a wall design and climate. The expert system is populated with knowledge from both expert judgment and probabilistic hygrothermal simulation results.

Investigation of the proposed solar-driven moisture phenomenon in asphalt shingle roofs:

Unvented attics are an energy-efficiency measure to reduce the thermal load of the conditioned space and decrease the space conditioning energy consumption by about 10%. This retrofit is usually done by spraying polyurethane foam underneath the roof sheathing, and on the gables and soffits of an attic to provide an air barrier and a thermal control layer. Unvented attics perform well from this perspective, but from a moisture perspective sometimes homes with unvented attics have high interior humidity or moisture damage to the roof. As homes become more air tight and energy efficient, a better understanding of the hygrothermal dynamics of homes with energy-efficient envelopes becomes more important. One proposed reason for high unvented attic humidity has been that moisture can come through the asphalt shingle roof system and increase the moisture content of the roof sheathing and attic air. This has been called “solar-driven moisture.” Oak Ridge National Laboratory investigated this proposed phenomenon by examining the physical properties of a roof and the physics required for the phenomenon. Results showed that there are not favorable conditions for solar-driven moisture to occur. Oak Ridge National Laboratory also conducted an experimental study in a home with an unvented attic and compared the humidity below the roof sheathing before and after a vapor impermeable underlayment was installed. There was no statistically significant difference in absolute humidity before and after the impermeable underlayment was installed. The outcomes of the theoretical and experimental studies suggest that solar-driven moisture does not occur in any significant amount.