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==Introduction/Preface==
==Introduction/Preface==
The implementation of the .net version of Greet required us to model the data in Greet excel. This includes the ETOH sheet of Greet excel. The ETOH data sheet contains many calculations that are not done in other portions of Greet. The purpose of this document is to summarize these differences, and explain our execution of this portion of our .net model in further detail.
The implementation of the .net version of GREET required us to track the data and calculations in the ETOH sheet of the Excel version of GREET. The ETOH data sheet contains some calculations that are specific to the corn ethanol production and not common with other fuel production pathways in GREET. This includes fuel yield, land use changes, and co-product types and handling. The purpose of this document is to summarize these differences, and explain in details the execution of this portion in the .net model.
 
 
For the most part the ETOH data is implemented in the same manner as all the other data. However, their are some topics that need clarification for users and scientists alike. The main points to focus on are feed & fuel, main input, yields, and co-products.


==Feed & Fuel==
==Feed & Fuel==
[[File:FeedFuelExcel.png|thumb|right|300px|Feed and Fuel in Greet Excel 2011 ETOH Sheet cell C255]]
[[File:FeedFuelExcel.png|thumb|right|300px|Feed and Fuel in Greet Excel 2011 ETOH Sheet cell C255]]


In Greet excel their is a split in the data results between feed & fuel. Fuel refer to the fuel being fuel being produced. This is a final product such as Ethanol, Fisher Tropsh Diesel, Conventional Gasoline etc. The feed, or feed stock, refers to the main resource used to produce this fuel. For example for Ethanol it can be corn. In the case of Conventional Gasoline it will be crude. In Greet excel the results are split between these two categories. For example in ETOH they will show emission output and energy consumption for the corn used to make the Ethanol, and then in a separate column show the energy and emissions corresponding to Ethanol. Examples of feed and fuel in Greet excel are shown the right.
In GREET excel, The energy and emissions results are split between "feed" & "fuel" in the summary tables for the fuel pathways at the bottom of each fuel recpective sheet. The energy and emissions allocated to the "fuel" in the summary tables refer to the energy and emissions associated with process fuels use in the production process (excluding the amount of the feed with energy equivalent to the energy in the produced fuel). The energy and emissions allocated to the "feed", or feedstock, refer to the energy and emissions associated with extracting, processing and transporting an amount of the feed (with energy content equivalent to the energy in the produced fuel) to the fuel production plant. In the case of Conventional Gasoline, crude is the feed. Examples of feed and fuel in GREET excel are shown in the table to the right.




In our implementation of Greet .net we do not formally split fuel from feed. We total all our data on a life cycle basis. The final results we generated encompass the total life of the fuel not just the feed half and the fuel half, but both. However, a user can easily obtain the energy and emission data pertaining to a certain step of the fuels life.  
In our implementation of GREET.net we do not split fuel from feed. We sum all our data on a life cycle basis. The final results we generate encompass both feed and fuel. However, a user of the GREET.net can easily obtain the energy and emission data pertaining to a certain process in the fuel life cycle. The upstream energy use and emissions are also provided in conjunction with each process results.  




The best way this can be shown is by example. Below is a screen shot of Corn Stover to Ethanol from Greet .net. The results shown to the left are for the final process, the transportation process. Since this is the final process the results shown are for the entire life cycle for the fuel as described above. If a user wishes to obtain the data for the fuels life right before the transportation process they can press the "Corn Stover to Ethanol via Fermentation" process, and greet will show data for the fuels life up to that point.
Below is a screen shot of Corn Stover to Ethanol pathway in GREET.net. The results shown to the left are for the final process in the pathway, which is the transportation process. Since this is the final process the results shown are for the entire life cycle for the ethanol fuel product. If a user is interested in the data up to the process immediately before the transportation process, the user can simply select that process (by pressing its icon), and GREET will show the results for the selected process, including the upstream processes all the way to the primary source of energy (main feedstock).




In addition it should be noted that at the beginning of this pathway their is a "Feed" of Corn Stover. This is analogous to the fuel & feed split in Greet excel. By hovering your mouse over the "Feed" it expands reveling the data as shown below. By click the "Feed: Corn Stover" hyperlink Greet will open up the Corn stover mix and reveal the pathways and processes that generate this data. Once again a user can click on these to view the energies and emissions corresponding to different stages of the fuels life.
In addition it should be noted that at the beginning of the pathway their is a "Feed", representing Corn Stover in the above example. By hovering your mouse over the "Feed" it expands revealing the energy and emissions data associated with extracting, processing and transporting the amount of feed required for the production process (see screen shot below). By click the hyperlink in the "Feed: Corn Stover" frame, the pathways and processes associated with extracting, processing and transporting corn stover to the ethanol plant will be shown. Once again a user can click on any of these processes to view the energy use and emissions associated with these processes.


[[File:FeedFuelDotNet.png|320px|Corn Stover Results as shown in Greet.net]]
[[File:FeedFuelDotNet.png|320px|Corn Stover Results as shown in GREET.net]]


==Main Input==
==Main Input==
The main input refers the energy content of the initial amount of resource put into a fuels production life. For example the main input of most Ethanol pathways would be corn. In the case of Compressed Natural Gas the main input would be some initial amount of natural gas. Both Greet Excel and Greet.net incorporate this input into their life cycle analyses. However, the way it is accounted for in each is different. In the .net model of Greet is always added to the results. However, this is not the case for Greet excel.  
The "main" input in GREET refers to the initial amount of primary resource (main feedstock) used in the fuel's production pathway. For example the main input of corn-ethanol pathways would be corn. In the case of Compressed Natural Gas the main input would be natural gas in the well. More precisely, the main input represents the amount of main feedstock with energy equal to the energy in the unit fuel produced. The functional unit is typically 1 mmBtu of the fuel in GREET Excel. Both GREET Excel and GREET.net incorporate the "main" input into their life cycle calculations. However, the stage in which it is accounted for in each model is different. In the .net model, the energy in the main input is always added to the energy use by the first process in the pathway (the recovery of the main feed from its primary source in nature). However, this is not the case for GREET Excel. In GREET Excel, this energy in the main input (e.g., 1 mmBtu) is added in the vehcile operation stage of the life cycle of the fuel. The difference in accounting stage is a subtle issue since both models produce the same life-cycle results.
 
 
In the ETOH sheet of Greet excel it is not accounted for in the final results. This can easily be noted by comparing results between the two models. To compare Greet Excel ETOH data to Greet.net one must add the results of the Fuel and the Feed because as described above Greet .net does not make that division. Once added together one will notice that the emissions (VOC, CO, NOx, PM10, SOx, etc.) are relatively close in value. However, the energy is off by a factor of a million btu. This is because in Greet.net we include the initial one million but from the main input, but in Greet Excel they do not. To compare the results simply add a million to excel or subtract a million for the .net results.
 
 
In the case of sugar cane ethanol and corn acetone the main input is not one million btu, so one must subtract the portion of the energy represented by the main input. This will be specified as sugar cane or corn respectively in the Greet.net results. It must be stressed that in regards to the main input what is done in Greet Excel or what is done in Greet .net are both right. It is simply two different ways to interpret the same data.


==Yields==
==Yields==
[[File:YieldsExcel.png|thumb|300px|]]
[[File:YieldsExcel.png|thumb|300px|]]
The ETOH sheet utilizes yields to indicate the amount of product that can be produced from a certain amount of feed. For example they will indicate how much corn it takes to create a single gallon of Ethanol, or how much switch grass is needed to create a single gallon of ethanol fuel. Throughout the ETOH sheet corn, herbaceous and etc. data are calculated at a per bushel basis. They show how much energy is consumed and how many emissions are produced per bushel of feed harvested. However, they calculate the ethanol production in a per gallon basis. In other words how much energy and how many emissions per gallon of Ethanol produced. The yields fills the gap between these two ways of calculated results, so that a totaled result can be calculated in a per one million btu basis. Screen shots of the yields shown in Greet Excel are shown. They are primarily found in two tables. In the screenshot they are highlighted in green so they can be easily identified.  
The ETOH sheet utilizes yields to indicate the amount of product that can be produced from a certain amount of feed. For example it indicates how much corn is used to produce a single gallon of Ethanol, or how much switchgrass is needed to produce a single gallon of ethanol fuel. Throughout the ETOH sheet corn, switchgrass, etc., data are calculated on a per bushel basis for corn and per ton of for other feedstock sources. GREET Excel shows how much energy is consumed and emissions are produced per bushel of feed harvested. However, in the subsequent process (i.e., ethanol production), the energy and emissions are calculated on a per gallon basis. The yield provides the conversion factor between these two functional units (i.e., per bushel of corn, and per gallon of ethanol). Screen shots of the ethanol yield from different feed sources in GREET Excel are shown below. They are primarily found in two tables. In the shown screenshot they are highlighted in green so that they can be easily identified.  


[[File:YieldsExcel1.png|400px|]]
[[File:YieldsExcel1.png|400px|]]




In Greet.net these yield are used in a very similar fashion. The "Feed" portion of our data would be calculated in a per bushel basis, and then it is imputed into a fuel production pathway designed for a per gallon basis. This is shown in the screenshot below. The yield value is in a text box highlighted in blue:  
In GREET.net these yields are used in a similar way. The "Feed" portion of data would be calculated on a per bushel basis, and then it is used as an input into a fuel production process which is based on a per gallon output. This is shown in the screenshot below. The yield value is in a text box highlighted in blue:  


[[File:YieldsDotNet.png|400px|Yields Utilized in Greet.net]]
[[File:YieldsDotNet.png|400px|Yields Utilized in Greet.net]]
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==Co-Products==
==Co-Products==


In both Greet.net and Greet Excel Co-Products are a form of credit. A Co-product is something that is produced along side the main product. The energy content of this co-product and emissions saved by otherwise producing it from scratch are credited back to the process. To calculate this credit we specify different resources that are displaced. Their are many co-products in the ETOH spread sheet. The calculation for a Co-production are very straight forward. Below they are shown for energy, but the calculation is exactly the same for emissions:
A co-product is something that is produced along side the main product. In both GREET.net and GREET Excel a co-product can provide energy and emissions credit if it displaces a product that conusmes energy and produces emissions. To calculate this credit the user selects the displaced product and the pathway for its production if the pathway is in GREET. Alternatively, the life cycle energy use and emissions associated with the displaced product can be specified to calculate the energy and emissions credits. If the co-product and displaced product are not the same, a displacement ratio has to be specified. For example, DGS can displace corn as an animal feed but the ratio is not necessary 1:1. It should be noted that the displacement calculations done in GREET.net accounts for the energy in the displaced material. The calculations for a co-product energy and credits are relatively straight forward. Below the credit calculations are shown for energy, but similar calculations can be done for emissions:
 
<math>Energy Credit for Co Production= Energy to Produce Displaced Resource \cdot Displacement Ratio\,</math>
 
The "Energy to Produce Displaced Resource Normaly" is provided from that resources specific mix and the displacement ratios are calculated in the ETOH sheet. For more information on how Co-Products are implemented in Greet.net refer to the [[Co-Products]] section of the wiki.
 
 
 


It should be noted that in excel the co production formula for Corn has to be adjusted to match Greet .net. The adjustment is shown below:
<math>Enem_{credit}(f_p)=\,</math> Energy and emissions credited to the co-product <math>f_p</math>


<math>Energy Credit for Co Production= (Energy to Produce Displaced Resource + Energy Content of Corn) \cdot Displacement Ratio\,</math>
<math>Enem(d)=\,</math> Energy and emissions associated with the production of the displaced product <math>d</math>
<center>
<math>Enem_{credit}(f_p) = Enem(d) \cdot Displacement Ratio\,</math>
</center>


This is because in the case of other resources being displaced such as Urea the heating value is zero. However, corn has a heating value. It has energy and the Greet.net model accounts this. For that reason the energy content of corn itself must be displaced as well.
The <math> Enem (f_p)</math> is provided from the displaced product life cycle calculations and the displacement ratio is provided in GREET but can be changed by the user. For more information on how Co-Products are implemented in GREET.net refer to the [[Co-Products]] section of the wiki.

Latest revision as of 22:06, March 21, 2012

Introduction/Preface

The implementation of the .net version of GREET required us to track the data and calculations in the ETOH sheet of the Excel version of GREET. The ETOH data sheet contains some calculations that are specific to the corn ethanol production and not common with other fuel production pathways in GREET. This includes fuel yield, land use changes, and co-product types and handling. The purpose of this document is to summarize these differences, and explain in details the execution of this portion in the .net model.

Feed & Fuel

Feed and Fuel in Greet Excel 2011 ETOH Sheet cell C255

In GREET excel, The energy and emissions results are split between "feed" & "fuel" in the summary tables for the fuel pathways at the bottom of each fuel recpective sheet. The energy and emissions allocated to the "fuel" in the summary tables refer to the energy and emissions associated with process fuels use in the production process (excluding the amount of the feed with energy equivalent to the energy in the produced fuel). The energy and emissions allocated to the "feed", or feedstock, refer to the energy and emissions associated with extracting, processing and transporting an amount of the feed (with energy content equivalent to the energy in the produced fuel) to the fuel production plant. In the case of Conventional Gasoline, crude is the feed. Examples of feed and fuel in GREET excel are shown in the table to the right.


In our implementation of GREET.net we do not split fuel from feed. We sum all our data on a life cycle basis. The final results we generate encompass both feed and fuel. However, a user of the GREET.net can easily obtain the energy and emission data pertaining to a certain process in the fuel life cycle. The upstream energy use and emissions are also provided in conjunction with each process results.


Below is a screen shot of Corn Stover to Ethanol pathway in GREET.net. The results shown to the left are for the final process in the pathway, which is the transportation process. Since this is the final process the results shown are for the entire life cycle for the ethanol fuel product. If a user is interested in the data up to the process immediately before the transportation process, the user can simply select that process (by pressing its icon), and GREET will show the results for the selected process, including the upstream processes all the way to the primary source of energy (main feedstock).


In addition it should be noted that at the beginning of the pathway their is a "Feed", representing Corn Stover in the above example. By hovering your mouse over the "Feed" it expands revealing the energy and emissions data associated with extracting, processing and transporting the amount of feed required for the production process (see screen shot below). By click the hyperlink in the "Feed: Corn Stover" frame, the pathways and processes associated with extracting, processing and transporting corn stover to the ethanol plant will be shown. Once again a user can click on any of these processes to view the energy use and emissions associated with these processes.

Corn Stover Results as shown in GREET.net

Main Input

The "main" input in GREET refers to the initial amount of primary resource (main feedstock) used in the fuel's production pathway. For example the main input of corn-ethanol pathways would be corn. In the case of Compressed Natural Gas the main input would be natural gas in the well. More precisely, the main input represents the amount of main feedstock with energy equal to the energy in the unit fuel produced. The functional unit is typically 1 mmBtu of the fuel in GREET Excel. Both GREET Excel and GREET.net incorporate the "main" input into their life cycle calculations. However, the stage in which it is accounted for in each model is different. In the .net model, the energy in the main input is always added to the energy use by the first process in the pathway (the recovery of the main feed from its primary source in nature). However, this is not the case for GREET Excel. In GREET Excel, this energy in the main input (e.g., 1 mmBtu) is added in the vehcile operation stage of the life cycle of the fuel. The difference in accounting stage is a subtle issue since both models produce the same life-cycle results.

Yields

YieldsExcel.png

The ETOH sheet utilizes yields to indicate the amount of product that can be produced from a certain amount of feed. For example it indicates how much corn is used to produce a single gallon of Ethanol, or how much switchgrass is needed to produce a single gallon of ethanol fuel. Throughout the ETOH sheet corn, switchgrass, etc., data are calculated on a per bushel basis for corn and per ton of for other feedstock sources. GREET Excel shows how much energy is consumed and emissions are produced per bushel of feed harvested. However, in the subsequent process (i.e., ethanol production), the energy and emissions are calculated on a per gallon basis. The yield provides the conversion factor between these two functional units (i.e., per bushel of corn, and per gallon of ethanol). Screen shots of the ethanol yield from different feed sources in GREET Excel are shown below. They are primarily found in two tables. In the shown screenshot they are highlighted in green so that they can be easily identified.

YieldsExcel1.png


In GREET.net these yields are used in a similar way. The "Feed" portion of data would be calculated on a per bushel basis, and then it is used as an input into a fuel production process which is based on a per gallon output. This is shown in the screenshot below. The yield value is in a text box highlighted in blue:

Yields Utilized in Greet.net

Co-Products

A co-product is something that is produced along side the main product. In both GREET.net and GREET Excel a co-product can provide energy and emissions credit if it displaces a product that conusmes energy and produces emissions. To calculate this credit the user selects the displaced product and the pathway for its production if the pathway is in GREET. Alternatively, the life cycle energy use and emissions associated with the displaced product can be specified to calculate the energy and emissions credits. If the co-product and displaced product are not the same, a displacement ratio has to be specified. For example, DGS can displace corn as an animal feed but the ratio is not necessary 1:1. It should be noted that the displacement calculations done in GREET.net accounts for the energy in the displaced material. The calculations for a co-product energy and credits are relatively straight forward. Below the credit calculations are shown for energy, but similar calculations can be done for emissions:

Energy and emissions credited to the co-product

Energy and emissions associated with the production of the displaced product

The is provided from the displaced product life cycle calculations and the displacement ratio is provided in GREET but can be changed by the user. For more information on how Co-Products are implemented in GREET.net refer to the Co-Products section of the wiki.