scholarly journals Energetic efficiency and the first law: the California net energy system revisited

2018 ◽  
Author(s):  
Carl A Old ◽  
Heidi A Rossow ◽  
Ian J Lean ◽  
Thomas R Famula
Keyword(s):  
Energy System ◽  
Energetic Efficiency ◽  
Net Energy

scholarly journals Fiftieth Anniversary of the California Net Energy System Symposium: What are the energy coefficients for cows?1

2019 ◽  
Vol 3 (3) ◽  
pp. 969-975 ◽  
Author(s):  
Harvey C Freetly
Keyword(s):  
Energy Metabolism ◽  
Energy Use ◽  
Current Model ◽  
Energy System ◽  
Energy Utilization ◽  
Energetic Efficiency ◽  
Production Cycle ◽  
Net Energy ◽  
Support Functions ◽  
Animal Metabolism

Abstract The same model structure used to describe energy metabolism in the growing animal is often used to model energy metabolism in the cow. Energy requirements of the cow are modeled as the summation of energy required for maintenance and recovered energy, where recovered energy is the summation of energy for the conceptus, milk, and tissue energy. Energetic requirements of the cow fluctuate throughout the production cycle depending on whether they are pregnant, lactating, or both. The current model requires energy cost to be associated with either net energy of maintenance or the partial efficiencies of conceptus growth, milk production, and tissue energy change. Mathematically, they are not independent. Incorrectly estimating one will result in an erroneous estimate in the other. Most of the current models in production agriculture allocate energy use into maintenance, and synthesis of tissues making it difficult to assign energy utilization by tissues that provide support functions to pregnancy, lactation, and weight fluctuation. The consequence is the assignment of partial efficiencies that reflect whole animal efficiencies rather than tissue efficiencies. Historically, these models have been predictive of energy metabolism, but caution should be used when inferring the energetic efficiency at the tissue level. Alternative modeling approaches more thoroughly describe tissue energy metabolism and have been used to estimate whole animal metabolism. These models resolve the problems associated with developing coefficients that lack biological meaning but are more complex. There is a critical need for independent data sets to test new components of the model for cows.

scholarly journals Can net energy values be determined from animal performance measurements? A review of factors affecting application of the California Net Energy System1

2019 ◽  
Vol 3 (3) ◽  
pp. 929-944 ◽  
Author(s):  
Fredric N Owens ◽  
Robert B Hicks
Keyword(s):  
Average Daily Gain ◽  
Energy System ◽  
The United States ◽  
Feedlot Cattle ◽  
Feed Additives ◽  
Metabolizable Energy ◽  
Feed Ratio ◽  
Energetic Efficiency ◽  
Net Energy ◽  
Two Factors

Abstract The California Net Energy System (CNES) can reliably project performance of feedlot cattle based on three factors: expected dry matter intake (DMI), some index of degree of maturity of cattle linked to body composition (fat and protein content), and an estimate of the net energy (NE) content of the diet. The CNES allowed feedlot managers to monitor growth and efficiency of individual pens of cattle. Through assigning distinct values for net energy for maintenance (NEm) vs. net energy for gain (NEg) of the metabolizable energy (ME) present in feeds, the CNES enables valid economic comparisons among feedstuffs, an appraisal not feasible based on total digestible nutrients or digestible energy (DE) values. Because NEm and NEg are linked mathematically to ME, the CNES also allows performance-adjusted ME (paME) value of diets to be calculated from observed DMI and growth or carcass measurements. Compared with other productivity measures (e.g., average daily gain and gain-to-feed ratio) that are confounded with and affected by DMI, the CNES logically separates production responses by cattle into two factors—DMI and ME of the diet. This enables research scientists or cattle producers to appraise responses within these two factors independently. In feeding studies, means of paME values were related closely to ME values of diets calculated from the ME of diet ingredients. But unlike ME values projected from diet analyses, paME estimates are affected by environmental conditions (e.g., season, weather, animal interactions, stress, nutritional history and deficiencies, associative effects of feeds, imprecise feed management, and animal healthfulness and disorders). These factors typically overestimate ME intake or increase energy requirements, both of which decrease energetic efficiency. By comparing paME with ME values calculated from diet composition, logical reasons behind performance responses to and quantitative benefits from feed additives, grain processing, hormone implants, and animal management can be appraised. Considering the evolution in cattle types, management and marketing conditions, and changes in diet ingredients and processing that have occurred during the past 50 yr, updating by a skilled committee to correct certain anomalies within the CNES as currently being applied seems appropriate. Developing simplified spreadsheets could help users evaluate their own dietary and management conditions and assure that the CNES continues to be widely applied by the feedlot industry within the United States and worldwide.

scholarly journals Optimal Planning and Operation of a Residential Energy Community under Shared Electricity Incentives

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2045
Author(s):  
Pierpaolo Garavaso ◽  
Fabio Bignucolo ◽  
Jacopo Vivian ◽  
Giulia Alessio ◽  
Michele De Carli
Keyword(s):  
Renewable Energy ◽  
Power Distribution ◽  
Energy Demand ◽  
Renewable Energy Sources ◽  
Energy System ◽  
Distribution Networks ◽  
Building Envelope ◽  
Net Energy ◽  
Technical Equipment ◽  
Optimal Planning

Energy communities (ECs) are becoming increasingly common entities in power distribution networks. To promote local consumption of renewable energy sources, governments are supporting members of ECs with strong incentives on shared electricity. This policy encourages investments in the residential sector for building retrofit interventions and technical equipment renovations. In this paper, a general EC is modeled as an energy hub, which is deemed as a multi-energy system where different energy carriers are converted or stored to meet the building energy needs. Following the standardized matrix modeling approach, this paper introduces a novel methodology that aims at jointly identifying both optimal investments (planning) and optimal management strategies (operation) to supply the EC’s energy demand in the most convenient way under the current economic framework and policies. Optimal planning and operating results of five refurbishment cases for a real multi-family building are found and discussed, both in terms of overall cost and environmental impact. Simulation results verify that investing in building thermal efficiency leads to progressive electrification of end uses. It is demonstrated that the combination of improvements on building envelope thermal performances, photovoltaic (PV) generation, and heat pump results to be the most convenient refurbishment investment, allowing a 28% overall cost reduction compared to the benchmark scenario. Furthermore, incentives on shared electricity prove to stimulate higher renewable energy source (RES) penetration, reaching a significant reduction of emissions due to decreased net energy import.

Evaluation of Energy Efficiency for a CCHP System With Available Microturbine

2007 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang
Keyword(s):  
Gas Turbine ◽  
Waste Heat ◽  
Energy System ◽  
Primary Energy ◽  
Economic Benefits ◽  
Optimal Operation ◽  
Energy Utilization ◽  
Utilization Efficiency ◽  
Energetic Efficiency ◽  
Efficiency Evaluation

This paper deals with the problem of energy utilization efficiency evaluation of a microturbine system for Combined Cooling, Heating and Power production (CCHP). The CCHP system integrates power generation, cooling and heating, which is a type of total energy system on the basis of energy cascade utilization principle, and has a large potential of energy saving and economical efficiency. A typical CCHP system has several options to fulfill energy requirements of its application, the electrical energy can be produced by a gas turbine, the heat can be generated by the waste heat of a gas turbine, and the cooling load can be satisfied by an absorption chiller driven by the waste heat of a gas turbine. The energy problem of the CCHP system is so large and complex that the existing engineering cannot provide satisfactory solutions. The decisive values for energetic efficiency evaluation of such systems are the primary energy generation cost. In this paper, in order to reveal internal essence of CCHP, we have analyzed typical CCHP systems and compared them with individual systems. The optimal operation of this system is dependent upon load conditions to be satisfied. The results indicate that CCHP brings 38.7 percent decrease in energy consumption comparing with the individual systems. A CCHP system saves fuel resources and has the assurance of economic benefits. Moreover, two basic CCHP models are presented for determining the optimum energy combination for the CCHP system with 100kW microturbine, and the more practical performances of various units are introduced, then Primary Energy Ratio (PER) and exergy efficiency (α) of various types and sizes systems are analyzed. Through exergy comparison performed for two kinds of CCHP systems, we have identified the essential principle for high performance of the CCHP system, and consequently pointed out the promising features for further development.

scholarly journals Relationships of retained energy and retained protein that influence the determination of cattle requirements of energy and protein using the California Net Energy System

2018 ◽  
Vol 3 (3) ◽  
pp. 1029-1039 ◽  
Author(s):  
Luis O Tedeschi
Keyword(s):  
Body Fat ◽  
Energy System ◽  
The Body ◽  
Metabolizable Energy ◽  
Net Energy ◽  
Body Protein ◽  
Protein Requirements ◽  
Growing Cattle ◽  
Lower Correlation

Abstract Interrelationships between retained energy (RE) and retained protein (RP) that are essential in determining the efficiency of use of feeds and the assessment of energy and protein requirements of growing cattle were analyzed. Two concerns were identified. The first concern was the conundrum of a satisfactory correlation between observed and predicted RE (r = 0.93) or between observed and predicted RP when using predicted RE to estimate RP (r = 0.939), but a much lower correlation between observed and predicted RP when using observed RE to estimate RP (r = 0.679). The higher correlation when using predicted vs. observed RE is a concern because it indicates an interdependency between predicted RP and predicted RE that is needed to predict RP with a higher precision. These internal offsetting errors create an apparent overall adequacy of nutrition modeling that is elusive, thus potentially destabilizing the predictability of nutrition models when submodels are changed independently. In part, the unsatisfactory prediction of RP from observed RE might be related to the fact that body fat has a caloric value that is 1.65 times greater than body protein and the body deposition of fat increases exponentially as an animal matures, whereas body deposition of protein tends to plateau. Thus, body fat is more influential than body protein in determining RE, and inaccuracies in measuring body protein will be reflected in the RP comparison but suppressed in the RE calculation. The second concern is related to the disconnection when predicting partial efficiency of use of metabolizable energy for growth (kG) using the proportion of RE deposited as protein—carcass approach—vs. using the concentration of metabolizable energy of the diet—diet approach. The culprit of this disconnection might be related to how energy losses that are associated with supporting energy-expending processes (HiEv) are allocated between these approaches. When computing kG, the diet approach likely assigns the HiEv to the RE pool, whereas the carcass approach ignores the HiEV, assigning it to the overall heat production that is used to support the tissue metabolism. Opportunities exist for improving the California Net Energy System regarding the relationships of RE and RP in computing the requirements for energy and protein by growing cattle, but procedural changes might be needed such as increased accuracy in the determination of body composition and better partitioning of energy.

The use of temporal factors for improved CO2 emissions accounting in buildings

2018 ◽  
Vol 39 (2) ◽  
pp. 196-210 ◽  
Author(s):  
Barny Evans ◽  
Sabbir Sidat
Keyword(s):  
Air Quality ◽  
Energy Demand ◽  
Energy System ◽  
Net Energy ◽  
Electricity Grid ◽  
Electrical Grid ◽  
Significant Difference ◽  
Emissions Factor ◽  
Single Number ◽  
The Impact

This paper is an investigation into the issues around how we calculate CO2 emissions in the built environment. At present, in Building Regulations and GHG Protocol calculations used for buildings and corporate CO2 emissions calculations, it is standard to use a single number for the CO2 emission factor of each source. This paper considers how energy demand, particularly electricity at different times of the day, season and even year can differ in terms of its CO2 emissions. This paper models three different building types (retail, office and home) using standard software to estimate a profile of energy demand. It then considers how CO2 emissions calculations differ between using the single standard emissions factor and using an hourly emissions factor based on real electrical grid generation over a year. The paper also examines the impact of considering lifetime emissions factors rather than one-year factors using UK government projections. The results show that there is a significant difference to the analysis of benefit in terms of CO2 emissions from different measures – both intra- and inter-year – due to the varying CO2 emissions intensity, even when they deliver the same amount of net energy saving. Other factors not considered in this paper, such as impact on peak generation and air quality, are likely to be important when considering whole-system impacts. In line with this, it is recommended that moves are made to incorporate intra- and inter-year emissions factor changes in methodologies for calculating CO2 emissions. (This is particularly important as demand side response and energy storage, although generally accepted as important in the decarbonisation of the energy system at present will show as an increase in CO2 emissions when using a single number.) Further work quantifying the impact on air quality and peak generation capacity should also be considered. Practical application: This paper aims to help practitioners to understand the performance gap between how systems need to be designed in order to meet regulations compared to how buildings perform in reality – both today and in the future. In particular, it considers the use of ‘real-time’ carbon factors in order to attain long-term CO2 reductions. This methodology enables decision makers to understand the impacts of different energy reduction technologies, considering each of their unique characteristics and usage profiles. If implemented, the result is a simple-to-use dataset which can be embedded into the software packages already available onto the market which mirrors the complexity of the electricity grid that is under-represented through the use of a static carbon figure.

scholarly journals 4E Analysis of a Fuel Cell and Gas Turbine Hybrid Energy System

2020 ◽  
Vol 11 (1) ◽  
pp. 7568-7579
Keyword(s):  
Fuel Cell ◽  
Cell Voltage ◽  
Energy System ◽  
High Energy ◽  
Exergy Efficiency ◽  
Combined Cycle ◽  
Net Energy ◽  
Exergy Destruction ◽  
Molten Carbonate ◽  
Ambient Temperatures

Exergy analysis of the expansion turbine hybrid cycle of integrated molten carbonate fuel cells is presented in this study. The proposed cycle was used as a sustainable energy curriculum to provide a small hybrid power plant with high energy efficiency. To generate electricity with the system mentioned above, and externally repaired fusion carbon fuel cell was used located at the top of the combined cycle. Moreover, the turbine and steam turbine systems are considered as complementary and bottom layers for co-generation, respectively. The results showed that the proposed system could reach net energy of up to 1125 kilowatts, while the total exergy efficiency (including electricity and heat) for this system is more than 68%. Moreover, the energy supplied and exergy efficiency derived from the proposed cycle are stable versus changes in ambient temperatures. Besides, the effect of increasing the current density on the cell voltage and the total exergy destruction was considered. Also, the new approaches of the exergoeconomics and exergoenvironmental analysis are implemented in this system. The results show that the hybrid system can decrease the exergy destruction costs more than 16%, and the environmental footprint of the system more than 23.4%.

scholarly journals Mathematical absurdities in the California net energy system

2019 ◽  
Vol 3 (3) ◽  
pp. 1018-1028
Author(s):  
Carl A Old ◽  
Ian J Lean ◽  
Heidi A Rossow
Keyword(s):  
Linear Models ◽  
Energy System ◽  
High Energy ◽  
Ordinary Least Squares ◽  
Mitochondrial Metabolism ◽  
Energy Utilization ◽  
Parameter Estimates ◽  
Net Energy ◽  
High Energy Phosphate ◽  
Laws Of Thermodynamics

Abstract Net energy systems, such as the California Net Energy System (CNES), are useful for prediction of input:output relationships not because of fidelity to the laws of thermodynamics, but because they were designed to predict well. Unless model descriptions of input:output relationships are consistent with the laws of thermodynamics, conclusions regarding those relationships may be incorrect. Heat energy (HE) + recovered energy (RE) = ME intake (MEI) is basic to descriptions of energy utilization found in the CNES and is consistent with the laws of thermodynamics; it may be the only relationship described in the CNES consistent with the first law of thermodynamics. In the CNES, efficiencies of ME utilization for maintenance (km) and gain (kg) were estimated using ordinary least squares (OLS) equations. Efficiencies thus estimated using static linear models are often inconsistent with the biochemistry of processes underlying maintenance and gain. Reactions in support of oxidative mitochondrial metabolism are thermodynamically favorable and irreversible; these reactions yield ATP, or other high-energy phosphate bonds, used for what is generally termed maintenance. Synthesis of biomass (gain) is less thermodynamically favorable; reactions do not proceed unless coupled with hydrolysis of high-energy phosphate bonds and lie closer to equilibrium than those in support of oxidative mitochondrial metabolism. The opposite is described in the CNES (km > kg) due to failure of partitioning of HE; insufficient HE is accounted for in maintenance. Efficiencies of ME utilization (km and kg) as described in the CNES are variable. Further neither km nor kg are uniformly monotonic f (ME, Mcal/kg); for ME (Mcal/kg) <0.512 or >4.26, km are inconsistent with thermodynamically allowed values for efficiencies (>1.0); kg are a monotonically positive f (ME) concentration (Mcal/kg) for ME <3.27 Mcal/kg. For ME <1.42 Mcal/kg, kg are not in the range of thermodynamically allowed values for efficiencies (0 to 1.0). Variable efficiencies of ME utilization require that the first law may not be observed in all cases. The CNES is an excellent empirical tool for prediction of input:output relationship, but many CNES parameter estimates evaluated in this study lack consistency with biology and the laws of thermodynamics.

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