A Net-Zero Energy Residential Test Facility has been constructed at the National Institute of Standards and Technology to demonstrate that a home similar in size, aesthetics, and amenities to those in the surrounding communities can achieve net-zero while meeting the needs of a four member family. The home incorporates a vast array of renewable energy and energy efficient technologies, a subset of which was used during the first year of operation, including an air-to-air heat pump system, a solar photovoltaic system, a solar thermal hot water system, and a heat recovery ventilation system (HRV). The solar photovoltaic system generated 13,523 kWh of energy, exceeding the home's annual energy consumption by 484 kWh during the 12-month test interval. The solar thermal hot water system provided 54% of the energy required to meet the hot water load. Use of the heat recovery ventilator, used to provide ventilation air to the home, resulted in 1965 kWh of energy consumption, 514 kW h to power the HRV and 1451 of energy used by the heat pump system to meet the additional sensible and thermal loads. This paper describes the facility and presents performance data for the first year of operation. Published by Elsevier B.V.

This article extends the Institutional Analysis and Development Framework's seminal research on common pool resource (CPR) management in new directions by exploring how the design principles of robust and enduring CPR management, initially proposed by Elinor Ostrom in 1990, can be used to measure and assess cross‐scale institutional linkages. This study examines data from 14 interstate river basin compacts in the western United States to identify the types of linkages established in these interstate settings, the factors that contribute to the emergence of diverse types of linkages around these shared resources, and how different types of linkages perform. Using Ostrom's CPR design principles to operationalize and measure linkages, the study shows that diverse types of cross‐scale linkages were created under the 14 interstate compacts, with linkages related to monitoring found to be particularly prevalent. The types and diversity of linkages can largely be explained by the conditions under which compacts emerged and the water management issues states jointly face. In applying the evaluative criteria operationalized by the CPR design principles, this research further shows that the monitoring and collective choice linkages created by compacts tend to be of higher quality, while enforcement and conflict resolution linkages appeared to be of the lowest quality. In addition to developing the IAD literature on CPR management, these findings offer critical insights for assessing the capacity of interstate river basin compacts in the western United States to manage shared resources successfully, as well as insights for what types of institutional investments may be needed for enhanced resource governance.

Understanding how to alter people's behavior to mitigate GHG emissions in cities is a challenge for both researchers and practitioners. The problem encompasses comprehending variation in behavior among thousands to millions of people living in cities, as well as their contributions to the cities' GHG footprint. To help simplify this challenge, this article seeks to define and justify the partitioning of people into three categories of actors for understanding and mitigating GHGs at the city-scale. The three actor categories are policy actors, designers and operators of infrastructure and individual infrastructure users. By linking theories from across the social sciences, this article provides specific illustrations of the three actor categories and intertwines them with the goal of developing better GHG mitigation strategies. This paper concludes with a discussion of the need for meta-theoretical approaches toward describing and explaining the interactions among the social actor categories and GHG mitigation in cities.

Driven by increasing demands for increased safety and reduced operational costs, advanced Health and Usage Monitoring System (HUMS) technologies and applications are emerging/maturing that can be used to introduce structural Usage Based Maintenance (UBM) credits. FAA Advisory Circular AC-29-2C, Section MG 15 addresses airworthiness approval of rotorcraft HUMS and HUMS-based maintenance credits. The AC provides general guidance for achieving airworthiness approval for installation, credit validation, and instructions for continued airworthiness. This paper describes an FAA funded R&D effort to assess and validate existing regime recognition algorithms and establish a viable end-to-end UBM process that would be compliant with the FAA AC and therefore certifiable. This is accomplished by two sets of tasks. First, a proposed end-to-end UBM process is shown to exploit the capability of currently available HUMS, while mitigating any deficiencies, to enable near-term benefit of regime recognition technology. Second, existing HUMS regime recognition algorithms are evaluated against both flight test and HUMS fleet data. A new technique is presented to post-process available HUMS output to make it compatible with the established dynamic component life assessment process and credit validation guidelines. The UBM process is demonstrated to be compliant to the FAA AC as one but not the only means of complying.

Computer simulation models to accurately predict the electrical performance of photovoltaic modules are essential. Without such models, potential purchasers of photovoltaic systems have insufficient information to judge the relative merits and cost effectiveness of photovoltaic systems. The purpose of this paper is to compare the predictions of a simulation model, developed by Sandia National Laboratories, to measurements from photovoltaic modules installed in a vertical wall fac¸ade in Gaithersburg, MD. The photovoltaic modules were fabricated using monocrystalline, polycrystalline, tandem-junction amorphous, and copper-indium diselenide cells. Polycrystalline modules were constructed using three different glazing materials — 6 mm low-iron glass, 2 mm ethylene-tetrafluoroethylene copolymer (ETFE), and 2 mm polyvinylidene fluoride (PVDF). In order to only assess the simulation model’s ability to predict photovoltaic module performance, measured solar radiation data in the plane of the modules is initially used. Additional comparisons are made using horizontal radiation measurements. The ability of the model to accurately predict the temperature of the photovoltaic cells is investigated by comparing predicted energy production using measured versus predicted photovoltaic cell temperatures. The model was able to predict the measured annual energy production of the photovoltaic modules, with the exception of the tandem-junction amorphous modules, to within 6% using vertical irradiance measurements. The model overpredicted the annual energy production by approximately 14% for the tandem-junction amorphous panels. Using measured horizontal irradiance as input to the simulation model, the agreement between measured and predicted annual energy predictions varied between 1% and 8%, again with the exception of the tandem-junction amorphous silicon modules. The large difference between measured and predicted results for the tandem-junction modules is attributed to performance degradation. Power measurements of the tandem-junction amorphous modules at standard reporting conditions prior to and after exposure revealed a 12% decline. Supplying post-exposure module parameters to the model resulting in energy predictions within 5% of measured values.

Definitions and Nomenclature DefinitionsCirculating fluid -mixture of anti-freeze (specified here to be propylene glycol) and water that circulates between the RFCS and external heat exchangers and that is used to transfer thermal energy from the RFCS to an external load.Constant power RFCS -a residential fuel cell system that supplies power at a constant rate regardless of the electrical or thermal loads of the residence.Electrical load following RFCS -a residential fuel cell system that is designed to vary its electrical output in response to the changing electrical energy needs of the residence.Grid independent RFCS -a residential fuel cell system that incorporates power management systems and/or electrical storage systems to meet the transient residential electrical loads so that interconnection with the utility grid is not necessary.Grid interconnected RFCS -a residential fuel cell system that must be connected to the utility grid.Grid interconnected systems must meet all applicable codes for interconnection with the utility grid.Residential fuel cell system (RFCS) -a packaged system that includes a fuel reformer, air compressor, humidifiers, power conditioner, heat rejection devices, heat exchangers for heat delivery systems, and all other necessary devices and controls to operate as a stand-alone system.Residential fuel cell systems receive a hydrocarbon fuel and supply alternating current electricity to a residence.In addition, thermal energy may be supplied to the residence and excess electricity may be supplied the utility grid.Domestic hot water simulated-use test -a test in which water is withdrawn in specified quantities and at specified times from the preheat tank connected to the RFCS.The draws are scheduled in accordance with a standard procedure and designed to simulate a residential hot water use pattern.Steady-state test -a test in which the operating conditions including ambient conditions, fuel supply, and energy loads remain constant for the duration of the test.Thermal load following RFCS -a residential fuel cell system that is designed to vary its thermal output in response to the changing thermal energy needs of the residence.Real power -time average of the instantaneous product of voltage and current. NomenclatureAE annual net electrical energy supplied by the RFCS to the residence, kW⋅h (Btu) AF annual natural gas usage by the RFCS, kW⋅h (Btu) AG annual net electrical energy supplied by the RFCS to the utility grid, kW⋅h AQ wh annual thermal energy supplied by the RFCS for water heating, kW⋅h (Btu) AQ sh annual thermal energy supplied by the RFCS for space heating, kW⋅h (Btu) AW annual domestic water usage by the RFCS, L (gal) c h the specific heat of the heat transfer fluid used to transfer thermal energy from the RFCS to an external load, evaluated at the average of the RFCS inlet and outlet temperatures, kJ/kg⋅ºC (Btu/lb m ⋅ºF)water used by the RFCS as a result of meeting the water heating load during hour i at ambient temperature T I (for an indoor unit), L (gal) V w,whH,i water used by the RFCS as a result of meeting the water heating load during hour i at ambient temperature T H (for an outdoor unit), L (gal) V w,whL,i water used by the RFCS as a result of meeting the water heating load during hour i at ambient temperature T L (for an outdoor unit), L (gal)

The National Institute of Standards and Technology (NIST), in conjunction with Virginia Tech, has developed a rating methodology for residential-scale stationary fuel cell systems. The methodology predicts the cumulative electrical production, thermal energy delivery, and fuel consumption on an annual basis. The annual performance is estimated by representing the entire year of climate and load data into representative winter, spring/fall, and summer days for six different U.S. climatic zones. It prescribes a minimal number of steady state and simulated use tests, which provide the necessary performance data for the calculation procedure that predicts the annual performance. The procedure accounts for the changes in performance resulting from changes in ambient temperature, electrical load, and, if the unit provides thermal as well as electrical power, thermal load. The rating methodology addresses four different types of fuel cell systems: grid-independent electrical load following, grid-connected constant power, grid-connected thermal load following, and grid-connected water heating.This paper will describe a partial validation of the rating methodology for a grid-connected thermal load following fuel cell system. The rating methodology was validated using measured data from tests that subjected the fuel cell system to domestic hot water and space heating thermal loads for each of the three representative days. The simplification of a full year's load and climate data into three representative days was then validated by comparing the rating methodology predictions with the prediction of each hour over the full year in each of the six cities.

Computer simulation tools used to predict the energy production of photovoltaic systems are needed in order to make informed economic decisions. These tools require input parameters that characterize module performance under various operational and environmental conditions. Depending upon the complexity of the simulation model, the required input parameters can vary from the limited information found on labels affixed to photovoltaic modules to an extensive set of parameters. The required input parameters are normally obtained indoors using a solar simulator or flash tester, or measured outdoors under natural sunlight. This paper compares measured performance parameters for three photovoltaic modules tested outdoors at the National Institute of Standards and Technology (NIST) and Sandia National Laboratories (SNL). Two of the three modules were custom fabricated using monocrystalline and silicon film cells. The third, a commercially available module, utilized triple-junction amorphous silicon cells. The resulting data allow a comparison to be made between performance parameters measured at two laboratories with differing geographical locations and apparatus. This paper describes the apparatus used to collect the experimental data, test procedures utilized, and resulting performance parameters for each of the three modules. Using a computer simulation model, the impact that differences in measured parameters have on predicted energy production is quantified. Data presented for each module includes power output at standard rating conditions and the influence of incident angle, air mass, and module temperature on each module’s electrical performance. Measurements from the two laboratories are in excellent agreement. The power at standard rating conditions is within 1% for all three modules. Although the magnitude of the individual temperature coefficients varied as much as 17% between the two laboratories, the impact on predicted performance at various temperature levels was minimal, less than 2%. The influence of air mass on the performance of the three modules measured at the laboratories was in excellent agreement. The largest difference in measured results between the two laboratories was noted in the response of the modules to incident angles that exceed 75deg.

Researchers at the National Institute of Standards and Technology (NIST) have measured the performance of a residential fuel cell system when subjected to various environmental and load conditions. The system, which uses natural gas as its source fuel, is capable of generating electrical power at three nominal power levels (2.5 kW, 4.0 kW, and 5.0 kW) while providing thermal energy for user-supplied loads. Testing was conducted to determine the influence of ambient temperature, relative humidity, electrical load, and thermal load on system performance. Steady-state and transient tests were conducted. The steady-state tests were performed in accordance with the American Society of Mechanical Engineering (ASME) Fuel Cell Power Systems Performance Test Code (PTC-50) for fuel cell power systems. The results of the investigation are being used to develop a proposed rating procedure for residential fuel cell units.

Fuel cell systems for residential applications are an emerging technology for which specific consumer-oriented performance standards are not well defined. This paper presents a proposed experimental procedure and rating methodology for evaluating residential fuel cell systems. In the proposed procedure, residential applications are classified as grid independent load following; grid connected constant power; grid connected thermal load following; and grid connected water heating. An experimental apparatus and procedures for steady state and simulated use tests are described for each type of system. A rating methodology is presented that uses data from these experiments in conjunction with standard residential load profiles to quantify the net effect of a fuel cell system on residential utility use. The experiments and rating procedure are illustrated using data obtained from a currently available grid connected thermally load following system.