This paper presents the design-optimization and economic viability analysis of a carbon dioxide power cycle integrated with a parabolic trough collector solar-thermal plant. CO2 cycles are the subject of ongoing research due to their potential advantages as compared to traditional steam cycles for power generation. Small-to- medium-scale combined heat and power application scenarios were investigated. A thermodynamic analysis helped identify the different power cycle configurations that were of interest due to applicability and potential economic benefits, namely: transcritical, recompression, and supercritical cycle configurations. First, a baseline transcritical plant was designed (presented in Part 1 of this study) and subjected to sensitivity analysis and empirical modeling validation. Then, four alternative designs with different power cycle configurations were developed: A, B, C, and D, with Alternative A being the baseline design. Alternative B achieved the lowest Levelized Cost of Energy (LCOE) of $ 0.2613/kWh. Sensitivity analysis results and alternative designs comparison enabled quantifying the impact on economic viability of key factors such as cycle temperatures, efficiencies, annual hours of operation, and capital costs. For instance, for every 10 % increase in the turbine efficiency, the LCOE is reduced by 9.5 %, while reductions in the largest capital costs of the power plant, i.e., the solar field and the power block, could potentially reduce the LCOE by 20 %. The supercritical cycle was found to be advantageous over the other cycle configurations for the applications studied. It was concluded that benefits in terms of performance, footprint and cost can make this technology increasingly competitive for cogeneration applications.

This study comprises the engineering design and economic assessment of a novel trans-critical-point Carbon Dioxide cycle integrated with a solar Parabolic Trough Collector (PTC) power plant. A 1-MW facility with a Rankine transcritical CO2 cycle providing combined heat and power for a small industrial facility in Texas was proposed as the baseline power plant to perform the analysis. A design and modeling effort was performed in Engineering Equation Solver (EES) for the many systems and components of the power plant, including the solar field, the power block, and sub-components such as turbomachinery and heat exchangers. The model created enabled the simulation of plant performance for the median day of each month in the year by inputting meteorological TMY3 data, and results were extrapolated to estimate the annual energy and monetary income yield. Data processing was performed with MATLAB. Economic analysis included estimation of capital and O&M costs for the baseline plant. Results were verified through empirical performance simulation, using System Advisor Model (SAM), a software provided by NREL. The levelized cost of energy (LCOE) for the modeled plant was $0.2915/kWh, as calculated with EES/MATLAB, and $0.305/kWh, as calculated with SAM, resulting in a difference of less than 5%, between the two different simulation approaches. The design and simulation work presented herein provides the means to perform an optimization analysis, which reveals important clues as to how the energy cost could be reduced so as to make this technology a competitive alternative within the energy market.

Recovering abandoned energy, global warming and CO2 utilization are important technological challenges of today. This study examines the performance of different hydrocarbon/CO2-based zeotropic mixtures as working fluids for a supercritical organic Rankine cycle. Four hydrocarbons, i.e., dimethyl ether, R1234yf, diethyl ether, and isobutane, were considered for the mixture based on their environmental characteristics, such as global warming potential, ozone depletion potential, flammability, and toxicity. The fractional molar concentration for each working fluid was varied from 20% to 80% hydrocarbon. The performance of the cycle operating on a low-grade waste heat source was investigated based on four different performance indicators of cycle efficiency, volumetric power coefficient, exergy efficiency, and exergy destruction. For each working fluid, the performance indicators were analyzed for different cycle operating pressures and different heat-source inlet temperatures from 400 K to 500 K. After detailed energy and exergy analyses, the zeotropic mixture of dimethyl ether and CO2, at a fractional molar concentration of 80%, was found to be the optimal working fluid for the operating conditions considered. The maximum cycle and exergy efficiency for the zeotropic mixture was calculated to be 15% and 39%, respectively, at a fractional molar concentration of 0.8 when operating at 500 K.

In this paper, several hydrocarbons' performance as a working fluid for a supercritical Organic Rankine Cycle are studied. Energy, exergy, and exergoeconomic analysis are conducted for the cycle operating with a low-grade waste heat source. Initially, fifteen different working fluids, primarily hydrocarbons, were considered based on their environmental characteristics, global warming potential, ozone depletion potential, flammability, and toxicity. The cycle efficiency for each working fluid was analyzed for different cycle operating pressures and different inlet heat source temperatures from 400 K to 500 K for a constant turbine work output. Three different trends of cycle performance characteristics were observed for various working fluids with the cycle operating at different evaporator pressures and source inlet temperatures. The working fluids that exhibited similar characteristic trends were then categorized into families for further analysis. Three hydrocarbons, i.e., Dimethyl Ether, R1234yf, and Diethyl Ether, were each selected as the representative of their respective family, along with Isobutane as the reference working fluid for comparison. After detailed energy and exergy analyses, Dimethyl Ether and Isobutane were found to be promising working fluids for the range of pressure and source inlet temperatures considered. Finally, the exergoeconomic analysis showed Dimethyl Ether to be the optimal working fluid based on the unit cost of net work produced and the total cost of exergy destruction, which were calculated to be (59.18 +/- 0.49) $/MWh and (8.92 +/- 0.48) $/h, respectively, when operating at 450 K.

A new test procedure for determining capture efficiency (CE) of domestic range hoods (ASTM-E3087.18) was used to investigate how the range hood mounting height above a stove influences CE. Previous studies on CE utilized only two heights for a single range hood and a test procedure that did not strictly adhere to ASTM-E3087.18. In the study reported herein, testing was performed in accordance with ASTM-E3087.18 on six range hoods of similar design at three heights. The measured CE values ranged from 42.8–96.2%CE with CE changing by 8.2%CE at worst when varying the height for a specific fan. The influence of mounting height on CE uncertainty, repeatability, reproducibility and variability were also investigated. Lower mounting heights were found to increase CE and reduce uncertainty at the cost of increased variability between repeat tests. In contrast, intermediate mounting heights typically improved variability performance and repeatability/reproducibility. One range hood with vents for re-circulation showed higher uncertainty and more variability, indicating that flow exhausting from these vents can influence CE performance. Thus, it is possible that future ASHRAE/HVI certification standards be written with re-circulating vents sealed off during testing and a specified mounting height to minimize variations in CE caused by varying mounting heights.

In this study a test procedure for determining capture efficiency (CE) of domestic range hoods, namely ASTM-E3087.18, was used to investigate how changing the exhaust orientation of residential range hoods influences CE. Previous studies on residential range hood CE only utilized vertical discharge orientation and do not strictly adhere to ASTM-E3087.18. Furthermore, many range hoods are installed in households using horizontal discharge. In the study reported herein, testing was performed on five range hoods of similar design using both vertical and horizontal exhaust orientations and at a fixed mounting height. Resulting CE values ranged from 50.9 to 94.1%CE with CE varying by as much as 10.6%CE and uncertainty (δ) varying less than 1.0%CE when changing discharge orientation for a specific case. No consistent trend was observed among all range hoods when changing from vertical to horizontal orientation with 30% of cases showing an increase in CE, 30% showing a decrease and 40% showing no change. Exhaust orientation was found not to have a significant influence on CE uncertainty, but had varying effects on repeatability, reproducibility and variability. Additionally, inconsistent exhaust duct design, which may lead to the development of “CO2 Pockets,” can result in worsened variability performance when comparing exhaust orientations.

There are no ASHRAE/HVI standards for characterizing or specifying acceptable values of capture efficiency (CE) (i.e. percentage of cooking-contaminants captured/exhausted by a household rangehood). A test method, ASTM-E3087.18, was recently published describing a facility/procedure for attaining consistent CE measurements. This study presents the design, construction and operation of the first CE test-facility assembled from the ground-up following this ASTM standard. Aside from this facility, there is one other nonproprietary test-facility for standardized testing of rangehoods in accordance with ASTM-E3087.18, namely Lawrence Berkeley National Laboratory (LBNL) where a chamber was designed and built for the purpose of developing ASTM-E3087.18. Additionally, several CE tests were performed using the described test-facility to compare results with previously published data. Similar to LBNL results, 93% of CE-tests had standard deviations less than 2.0% during a test, with non-conformances attributed to inadequate steady-state times prescribed by ASTM-E3087.18 and inlet design. Using the precision/bias procedure in ASTM-E3087.18, CE-uncertainties ranged from 0.7-3.3%, with 89% of tests having 2% uncertainty or less. A preliminary repeatability analysis showed 91% of cases repeated more than once were repeatable within 10% (i.e. +/- 5%) and 77% of cases repeatable within 6%(i.e. +/- 3%). Preliminary results showed CE increasing with flowrate, though uncertainty/repeatability appear unaffected by flowrate.

Continuously tightening Particulate Matter (PM) and Particulate Number (PN) regulations make Gasoline Particulate Filters (GPFs) with high filtration efficiency and low pressure drop highly desir- able as Gasoline Direct Injection (GDI) engines increase in market share. Due to packaging constraints, GPFs are often coated with three-way catalyst (TWC) materials to achieve four-way functionality. Therefore, it is critical to investigate the effects of various washcoating strategies on GPF performance. A three-dimensional (3D) Computational Fluid Dynamics (CFD) model, along with an analytical filtration model was created. A User Defined Function (UDF) was implemented to define the heterogeneous properties of the GPF wall due to washcoating or ash membrane application. The model demonstrated the ability to predict transient filtration efficiency and pressure drop of uncoated and washcoated GPFs. Simulation results showed the evenly coated GPF yielded the best performance compared to other washcoating profiles. The model-predicted results indicated that the sample GPF with a 2.6 g/L ash loading was able to achieve a balance between high initial filtration efficiency and low pressure drop.

In this study a test procedure for determining capture efficiency (CE) of wall-mounted range hoods, namely ASTM-E3087.18, was used to investigate how the temperature of the simulated cook-top influences CE. ASTM-E3087.18 was initially released in 2017 and revised within one year to modify the temperature requirements of the cook-top from 200 degrees C to 160 degrees C; however, there is no evidence of a detailed study being performed to quantify the effects of this temperature change on CE. The study reported herein performed testing at 200 degrees C, 160 degrees C and 130 degrees C for five range hoods with three different design types. CE ranged from 60.3-92.9%CE with CE variations as high as 9.2%CE when varying temperature, and uncertainty (delta) always varying by less than 1.0%CE. The influence of cook-top temperature on CE repeatability, reproducibility and variability was also investigated, with each metric varying by a maximum of 1.2%CE, 1.5%CE and 1.1%, respectively, with varying temperatures. Range hoods with poor burner coverage (i.e. over-the-range microwaves) showed higher variability/uncertainty, indicating temperature effects are more dominant when range hoods have less burner coverage. It is possible that future HVI/ASHRAE certifications specify different acceptability/test requirements for CE, as well as the CE uncertainty/repeatability, of range hoods with poor burner coverage.

This paper covers a basic model for analyzing the performance of the Claridge-Culp-Liu dehumidification process. The fundamental process efficiency limit for dehumidification is close to COPCarnot, but for the eight dehumidification cases examined, the limiting or ideal energy use required is 26% to 56% that of a Carnot condensing system as shown in an earlier paper. The model presented in this paper is used to show the membrane system performance reduction caused by finite membrane area, finite water vapor permeance, non-zero air permeance, non-zero system air pressure drop, non-ideal compressors, vacuum pumps, and condensers. The performance of a “conservative” membrane system based on the use of existing components is computed for eight specific conditions along with that of a “target” system that assumes expected component performance after additional future component development. The “conservative” membrane system would use 36% to 66% as much energy as a system with a COP=7 chiller to produce the same dehumidification for the eight cases examined while the “target” system would use 15% to 40% the energy of a system with a COP=7 chiller. In addition to the significant energy reduction over conventional technology, the membrane system offers the advantages of: 1) no HFC refrigerant use; 2) direct isothermal control over humidity ratio setpoint; 3) maximum capacity occurs at design conditions; and 4) system generates pure water extracted from air as a by-product.

The wide application of Gasoline Direct Injection (GDI) engines and the increasingly stringent Particulate Matter (PM) and Particulate Number (PN) regulations make Gasoline Particulate Filters (GPFs) with high filtration efficiency and low pressure drop highly desirable. However, due to the specifics of GDI operation and GDI PM, the design of these filters is even more challenging as compared to their diesel counterparts. Computational Fluid Dynamics (CFD) studies have been shown to be an effective way to investigate filter performance. In particular, our previous two-dimensional (2D) CFD study explicated the pore size and pore-size distribution effects on GPF filtration efficiency and pressure drop. The "throat unit collector" model developed in this study furthers this work in order to characterize the GPF wall microstructure more precisely. Throat unit collectors with different diameter ratios were created and simulated in ANSYS FLUENT to calculate the size-dependent particle filtration efficiency. The simulation results indicated a nonlinear change of single-collector efficiency, as the efficiency first decreased and then increased with a decreasing throat unit collector diameter ratio. The simulation results also showed the total wall filtration efficiency increased as the throat unit collector diameter ratio decreased. The throat unit collector model was also used to simulate the wall filtration efficiency change during particulates loading. The decrease of pore size in throat unit collector was used to mimic the pore-bridging process during loading. This study showed that the throat unit collector model is able to predict the GPF filtration performance at initial or loading state by only requiring the principle properties of the GPF (mean pore size, porosity, wall thickness) without model tuning.

The objective of this study is to investigate the field performance, economic benefits, and environmental impact of ground source heat pumps (GSHPs) for residential space heating compared with conventional natural gas furnaces in a severely cold climate. A total of 32 residential houses with 16 vertical and 16 horizontal loop GSHPs in Iowa, U.S. were included in this study. The required heating energy in each house was estimated by using the heating degree-day (HDD) method and the building characteristics obtained during the on-site energy audits. The monthly GSHP electricity use in each house was collected over two consecutive heating seasons. Based on the estimated heating energy and the monthly GSHP electricity consumption, the coefficient of performance (COP) was derived for each unit on a monthly basis over the dominant heating period. Results showed that the median values in the calculated COP were 2.8 for both horizontal and vertical loop systems. The calculated COPs were found to be 30%–124% of the nominal values for horizontal systems and 46%–110% for vertical systems, with an average being 80% of the nominal value for both horizontal and vertical systems. In addition, 28 out of 32 GSHPs showed lower calculated COPs compared with the nominal values. The economic analysis showed 44–86% savings in energy expenses as a result of using GSHPs in place of conventional natural gas furnaces, with median savings being 70–77% depending on the electricity rates. The environmental analysis showed 23%–61% CO2 emission reduction with a median of 45% compared with natural gas furnaces. These results quantified the economic and environmental benefits of using GSHPs in Iowa, U.S., which provided essential information for policy making and incentive program development. Also, the developed analytical approach to determining the field performance of GSHPs is suitable for large-scale, long-term GSHP performance evaluation given its minimum requirement on field measurements and readily available utility data.

The Claridge-Culp-Liu Dehumidification Process is a novel and efficient approach to removing water vapor from air using a combination of membrane separation, vacuum compression and sub-atmospheric condensation. The basic theory of this process is to separate water vapor from moist air flowing across one side of a membrane by applying a partial vacuum to the opposite side of the membrane and then compressing the water vapor to its saturation pressure at the wet-bulb temperature of the ambient air so as to facilitate condensation. This process has a fundamental efficiency limit that approximates the Carnot limit, but for eight different ideal dehumidification-only cases examined herein, the process requires only 26–56% the energy required by a Carnot vapor-compression system. Furthermore, the limiting energy required by an ideal 5-stage membrane system is 16–31% that of a Carnot system for the same cases. Of special importance, the ideal Claridge-Culp-Liu Dehumidification Process requires less than 5% of the energy required by an ideal desiccant process for all cases treated. The Claridge-Culp-Liu Dehumidification Process can also be combined with evaporative cooling to provide dehumidification and sensible cooling with the temperature and humidity controlled independently. Of special importance, this system uses no HFC refrigerants, and it generates pure water as a by-product.

This paper presents an economic analysis of stationary and dual-axis tracking photovoltaic (PV) systems installed in the US Upper Midwest in terms of life-cycle costs, payback period, internal rate of return, and the incremental cost of solar energy. The first-year performance and energy savings were experimentally found along with documented initial cost. Future PV performance, savings, and operating and maintenance costs were estimated over 25-year assumed life. Under the given assumptions and discount rates, the life-cycle savings were found to be negative. Neither system was found to have payback periods less than the assumed system life. The lifetime average incremental costs of energy generated by the stationary and dual-axis tracking systems were estimated to be $0.31 and $0.37 per kWh generated, respectively. Economic analyses of different scenarios, each having a unique set of assumptions for costs and metering, showed a potential for economic feasibility under certain conditions when compared to alternative investments with assumed yields.

This article presents methodologies that can be used to evaluate the impact of unsteady background noise for standard acoustic tests. When sound or noise emitted by a unit-under-test is measured according to acoustical test standards in the presence of background noise, background corrections are necessary. However, the use of a background correction factor is valid only when the signal-to-noise ratio (SNR) of the sound source is above a lower-limit specified in acoustic test standards. Therefore, the testing of increasingly quiet devices is becoming problematic because low SNRs are significantly affected by background noise variations (i.e., unsteadiness, defined as a background with change, variation, or interruption). This study investigates and introduces two methodologies that address effects of background variations. As the first methodology, the uncertainty in the background correction is evaluated and discussed. The second methodology is a different SNR metric, zero loudness SNR, in order to provide acceptable tolerances during standard acoustic tests that use loudness as a rating method. The two above methodologies are presented with 200 real-world ventilation device testing conforming to ISO, ANSI, and AMCA standards. It is shown that the combined use of the zero loudness SNR and the uncertainty of the SNR enables to assess both background unsteadiness and the impact of low SNRs. The method is found out to be useful acoustical tests of devices such as ventilating fans suffering from low SNRs. (C) 2018 Institute of Noise Control Engineering.

This study is to comprehensively evaluate energy impacts and life cycle costs of duct designs for residential central HVAC systems. Building energy simulations were performed under two different climates (Chicago, IL and Austin, TX) to predict the heating and cooling energy use in systems with blowers of different types of motors, namely electronically commutated motors (ECMs) and permanent split capacitor (PSC) motors, paired with ductworks of varying flow resistance and duct materials. In addition to the energy use, the life cycle cost of each duct design was determined over a 15-year lifetime. Depending on the specific duct design, the annual energy cost in the Chicago home decreased by 11-17% for systems with ECM blowers and 3-8% for systems with PSC blowers as the flow resistance decreased from 0.8 to 0.3 in. w.g. (200-75 Pa). In the Austin home for the same flow resistance decreases, the annual energy costs decreased by 16-18% for systems with ECM blowers and 7-8% for systems with PSC blowers. Although the cost-effectiveness of a specific duct design is shown to be heavily dependent on initial duct fabrication and installation costs, the use of lower flow resistance ductworks generally leads to lifetime savings in the presence of 10% supply and return leakage. Specifically, the lifetime saving is achieved in 6 out of 8 simulated cases for the Chicago home and all simulated cases for the Austin home.

The most common HVAC device in a residence, or in most other buildings for that matter, is the bathroom ventilation fan. Because these devices operate in close proximity to humans, the concept of loudness is particularly relevant to the acoustic performance of fans. In this regard, acoustic performance is an important component of indoor environmental quality, and the use of loudness as a method of achieving an acoustic rating is now widely accepted in codes and standards. Therefore, a long-term comparative study investigating changes in acoustic performances was performed for bathroom ventilation fans of the alternating current (AC) motor type, with a focus on fan loudness over an 11-year period from 2005 to 2015. Because of difference in performances and designs along with divisions created by testing standards and codes, the 1400 fans tested and analyzed were divided into low- and high-volume flow rate groups, namely below and above 42.5 L/s. In addition to specific conclusions reached from analyzing 11 years of fan performance measurements, major overall conclusions are that (1) the fan noise in terms of loudness has decreased, even to the point of being lower than typical human conversations in many cases, and (2) fan loudness has a weak relationship with volume flow rate and a more noticeable linear relationship with fan rotating speed. This study proves that acoustic performance improvements in bathroom ventilation fans have advanced acoustic-indoor environmental quality over the decade-long period of this study.

Pressures on water resource availability are a global concern and escalations in water prices and mandatory water rationing make alternate water sources, such as rainwater, more attractive as options to handle increasing water demands and drought conditions. Water system efficiency and lifecycle impacts are factors in building sustainability, and this study investigated the performance and economics of a rainwater collection system and underground cistern in a single-family residential setting, focusing on rainfall, rainwater collection, and lifecycle costs. This study reports on an expanded investigation of the hydraulic and economic performance of residential rainwater harvesting (RWH) systems, including model details, model sensitivity analysis, and a Monte Carlo simulation. Daily water demand averages of 1.39 m(3)/day were used in the simulation with a 30% variation. Hydraulic inputs, outputs, and economics were evaluated over a 50-year lifecycle. Sensitivity and stochastic analyses were performed with below average, average, and above average estimates of input parameters to assess contributions, and to assess a probabilistic interpretation of the lifecycle results. Using 30-year rainfall normals and Monte Carlo stochastic methods, there was a 45-48% probability of 73% of the annual demand being harvested. (C) 2017 American Society of Civil Engineers.

The usage of loudness in standards and rating programs promoted by ASHRAE, HVI, and Energy Star is supported by the fact that occupants in buildings are exposed to noise from ventilating fans that are in close operational proximity to people. The current loudness calculation procedure, which is based on ANSI S3.4-1980 following a model by Stevens, is widely considered to be outdated because of its limited accuracy on equal-loudness contours, loudness-level-to-loudness conversions, and tonal components. Therefore, the study presented herein utilizes an extensive database consisting of 394 fan testing results to perform a detailed comparative analysis of this conventional Stevens loudness model and a revised loudness model developed by Moore et al. Although loudness results from each model were close to each other, a majority of fans under 2 sone show an overall larger loudness when the revised model is used for the noise calculation while there was no clear trend of noise differences for fans over 3 sone. These loudness differences between the two models are significant and would result in more fans failing certification if a revised loudness model is integrated into ventilation rating and certification programs. This effect on certification is more easily understood if one notes that less than a 0.5 sone difference in the certification limit would result in the same number of certified ventilating products presently conforming to Energy Star V4.0, at least for the large database evaluated in this study. (C) 2017 Elsevier Ltd. All rights reserved.

A grid-connected dual-axis tracking photovoltaic (PV) system was installed in the Upper Midwest of the U.S., defined as a cold region, and then evaluated and monitored for a 1 year period. This system serves as a real-world application of PV for electricity generation in a region long overlooked for PV research studies. Additionally, the system provides an opportunity for research, demonstration, and education of dual-axis tracking PV, again not commonly studied in cold regions. In this regard, experimental data for the system were collected and analyzed over a 1year period. During the year of operation, the PV system collected a total of 2173 kWh/m(2), which equates to 5.95 kWh/m(2) on average per day, of solar insolation and generated a total of 1815 kWh, which equates to an energy to rated power ratio of 1779 kWh/kW(p) of usable AC electrical energy. The system operated at an annual average conversion efficiency and performance ratio of 11% and 0.82%, respectively, while the annual-average conversion efficiency of the inverter was 92%. The tracking system performance is also compared to a stationary PV system, which is located in close proximity to the tracking PV system. The tracking system's conversion efficiency was 0.3% higher than the stationary system while the energy generation per capacity was 40% higher although the PV module conversion efficiencies were not significantly different for the two systems.