This page is intended to introduce users to some of the ways that GHGenius can be used. It is not an in depth user guide, but an introduction to some of the concepts and methods that are prominent in the model.
- Installing and Running GHGenius
- Input Sheet
- Output Sheets
- Advanced Model Use
Installing and Running GHGenius
The GHGenius model was originally developed in Lotus 123 for Apple users. Levelton Engineering Ltd. upgraded the model to the ‘97 Windows version of Lotus 123 in 1999. Version 3.0 of GHGenius and later have been developed as an Excel spreadsheet model by (S&T)2. Current model development is done in Excel 2010 and saved as a legacy .xls file, the newer .xlsm or .xlsb formats are not used due to slower calculation speed and larger compressed file size. This should provide forward and backward compatibility from Excel 97 to current day, with exception of Mac Excel 2008 and any other versions that do not support macros.
The model is downloaded from www.ghgenius.ca as a zipped file. It must be unzipped prior to use. If your OS does not have a built in unzipping tool, there are many free options available online such as 7zip.
Checking Excel Settings
GHGenius relies on macros to do many calculations and provide extra tools for users to understand the data. The Excel security settings need to not be at the most restrictive setting to allow macros to run. Upon first opening the model you may be prompted to allow macros. If macros are enabled and working you should be on the Index sheet, and after pressing the accept button you will be sent to the Input sheet and now be able to see all the other sheets in the model. If this is not true double check your macro settings.
In addition to macros, it is necessary that excel is set up for iterative calculations. Under File > Options > Formulas check that Enable Iterative Calculations is checked and set Maximum Iterations to 25. It is recommended, but not necessary, to set Workbook Calculation to Manual. This will prevent the model from pausing to recalculate with every change or value input.
GHGenius, as downloaded, comes set up for Canada with a full set of working default values. It is possible to open up GHGenius, navigate to an output sheet, and start getting immediate results.
If a user wants to start making changes, the Input sheet is the place to start. The model, as of GHGenius 5.x, is set up using colours to help with flow of data. Headings of new sections are a darker green, and white space is used to separate distinct tables. The other important colours are orange and yellow cells signifying the two types of input cells.
Orange cells are drop downs, with a selection of possible values for the user to choose from. You can see this on the Input sheet in cell B11, which allows a user to choose how the global warming potential, or GWP, is applied. These are based on the IPCC GWP scenarios.
Yellow cells are usually numeric input cells. These cells make up the majority of the Input sheet and can also be found scattered throughout the model. It is possible to make changes to cells that don't have a yellow background, but there may be unexpected effects or no effects at all.
There are plenty of macros used in GHGenius that can be roughly divided into three types: default macros, calculation macros, and tool macros.
Default macros include the regional defaults, and section specific defaults. Mostly found on the Input and Input Costs sheets, these macros input best estimates of regional and industry wide average values. One of them, Regional Defaults, is discussed below.
Calculation macros include Run Program, Separate Gases, and EV Regions. They do the work of calculating specific types of output values in the model. While using F9/Calculate is always faster, making use of the appropriate calculation macro will produce a larger set of output data than is possible with just F9/Calculate.
Tool macros include analysis tools such as the sensitivity solvers and Monte Carlo, as well as the helper macro Fix Circular. The analysis tools allow a user to better understand and visualize trends around changing input values. Each analysis tool has its own separate sheet, placed after the output sheets. The Fix Circular macro is intended to help a user recover a model that was given invalid input. If the invalid input is corrected, then using the Fix Circular macro may return the model to a state with no #DIV/0 or other errors.
Found at the top of the Input sheet, this macro has been rewritten and expanded in GHGenius 5. It now operates as a combination of a drop down menu, in cell B4 on the Input sheet, and a button to the right of the drop down. To use the macro choose a different region from the drop down then press the button. There will be a brief moment while Excel executes the macro, often less than a second, and then the model will have a set of default values specific to that region.
If you intend to make changes to the model, this is the first thing that should be done. It sets the region, supplies new default values for many of the crop and fuel transportation distances, and makes many changes to farming practices. If you wanted to check exactly what the inputs are, they can be seen on the sheet Regional Defaults which is the last sheet in the model. Blank cells are ignored, and everything else is copied into the labelled sheet (column B) and cell (column C).
Found both at the top of the Input sheet and at the top of the Output Summary sheet. The most important of the calculation macros, this makes multiple model runs in sequence to populate the output pages. Run program can be slow, but it is the most comprehensive way to run the model.
The first thing it does is set heavy duty vehicles to be trucks and run the Separate Gases macro, which will repeatedly recalculate the model to populate all the individual gases. Without separate gases, for example when just pressing F9 to recalculate cells, the model will only keep the CO2e up to date. The results of separate gases can be seen in many places throughout the model, some examples are on Upstream Results, Freight Emissions, and LDV Summary.
After the separate gases are calculated, the model will be run two more times. The first run will be setting the heavy duty vehicles to be buses and the second to a combination of buses and trucks. This vehicle breakout can be seen on output sheets with heavy duty vehicles such as Lifecycle Results, HDV Summary, and Exhaust Emissions.
Not all of the macros are accessed from the Input sheet. The sensitivity solver is a tool on its own separate sheet. This is the simpler of three analysis tools added to GHGenius, the others being a two dimensional sensitivity solver, and a Monte Carlo tool. It will iterate a single input across a range and track four outputs to create an output table and graph.
This macro requires several inputs to run. On the Sensitivity Solver sheet, B7 and C7 are used to choose the input cell; this is the cell that will be given 11 different values. The range of those values is input in D7 and E7. It's important to be careful when setting your range that all the values will be valid. One way to cause a problem would be setting a span of years that is not divisible by ten, the model would experience issues if it were to try to run on a non-integer year.
The next thing to set is the outputs to record. There can be up to four outputs, but they must be on the same sheet. The sheet is set in B8 and the individual cells are set in C8 through F8. It is okay to have blank cells in order to track less than four outputs. This is an improvement from previous versions of the model that tracked only a single output.
The last two inputs alter how the macro runs. The dropdown labelled as Sep Gases toggles whether or not the Separate Gases macro, discussed above under Run Program, will be run. If set to No then the sensitivity solver will be run by updating the model with F9/calculate. Setting to No is faster and should be used if the results you're tracking are only CO2e. The Fix Circular option will run an additional macro after each step of the sensitivity solver. This should be set to No unless it is suspected that some, but not all, of the input values will break the model. After each step the Fix Circular macro, available on the Input sheet, will be run in an attempt to fix any problems that were caused with invalid inputs.
Below the inputs are the outputs. A table of the outputs followed by a line graph of the results.
The first sheets seen after Input and Input Costs are the many different output sheets available in GHGenius. They represent different endpoints of fuel pathways, different units, or different ways to visualize the results. Some of the more significant output sheets are discussed below.
Upstream Results HHV
Upstream Results HHV is one of the most fundamental output sheets that most of the others are built on. Presenting results in g/GJ, the fuel pathways here are taken from field or well right up to the end user. What's not included are the emissions that involve the end use vehicle, tailpipe emissions and vehicle construction. The macro Separate Gases acts on this sheet, the results of which are below the main CO2e results.
There is a second sheet called Upstream Results LHV that gives the same results presented with lower heating values.
Lifecycle Results presents results in g/km. For most of the results on this sheet the different units are simply the product of a value from Upstream Results HHV times the active vehicle's GJ/km efficiency. The bigger difference from Upstream Results HHV is that the results on Lifecycle results take into account the full lifecycle of a fuel from field or well up to burning it in an end user's vehicle and retirement of that vehicle. The values that can be found on Lifecycle Results but not Upstream Results are the exhaust emissions, vehicle assembly, and the materials included in the vehicle.
There is a second sheet called Lifecycle Results 2 that gives the same results presented on a g/litre or g/kilogram basis.
Output Summary is quite different from other output sheets in three key ways. It is interactive, it makes no attempt to encompass all the pathways, and it presents results at different points in a pathway's lifecycle. Output summary is designed as a comparison tool, for quickly contrasting different fuels under specific scenarios. It has the light and heavy duty vehicle pathways that are present on many other output sheets, and adds to this ways to compare fuels being used for power generation, residential heating, or industrial use.
For the transportation fuels and power generation the user can choose the fuels they want to look at from drop down menus. For power generation, residential use, and industrial use the user can set the efficiency of converting the fuel to electricity or heat. After making selections and using the Run Program macro from the top of the sheet, the user is presented with both comparison tables and graphs showing the results.
Advanced Model Use
The above is intended as a surface look at some of the ways a new user might use GHGenius. It will be enough for many users. However GHGenius is capable of much more. By making use of the formula tracing tools it is possible to trace through and understand any cell in the model. Because the code is not locked down an advanced user can audit all of our code with the Visual Basic editor, or write their own if they have a specific case to automate.
Below are some possible avenues to delve into more advanced use of GHGenius.
Sheets as Independent Systems
The most important part of becoming a power user is knowing when you can safely ignore parts of the model. Due to the iterative nature of life cycle analysis, tracing formulas can quickly become overwhelming. One way to counter this is to take the LCA idea of system boundaries, and apply it to each individual sheet. GHGenius strives to give each street a self contained purpose, where values come in, get transformed in some way, then go out. Any sheet that you're not working on can be considered a black box.
For example the Biomass Production sheet takes input values for crops, multiples them by energy and emission intensities calculated elsewhere, and calculates crop specific energy and emission intensities to be used elsewhere in the model. This is a common setup for sheets. If a user wanted to change the Biomass Production sheet, they would want to find the outputs from the sheet and work backwards from there to find where their changes can be inserted. If done in this way, it won't matter to the rest of the model that changes were made, because the outputs are still in the same place and with the same units.
For example, rows 23 through 30 are calculated values that go off sheet. As long as those rows don't change units, they could be calculated in a different way without worrying about what happens to them on the Energy Use or Fertilizer sheets.
Alt Fuel Prod as Advanced Input
It is mentioned above that input cells exist throughout the model. One of the more prominent sheets with input cells is Alt Fuel Prod. This sheet takes, from the Input sheet, energy inputs for each alternative fuel pathway and calculates how much energy is involved. Included in that energy calculation are the chemical inputs, which a user may set on Alt Fuel Prod rather than the Input sheet. Starting in row 29 are many chemical inputs, ranging from simple nitrogen to complex enzymes. Most are on a kilogram per unit of fuel bases, but a few are in litres.
In addition to adding the amount of chemicals, there are inputs related to the production of those chemicals. Attempts have been made to have reasonable industry average energy intensities for every possible chemical input. In some cases the chemicals are dependent on electricity, which is quite regionalized. For every chemical there is a drop down option to choose between using the average American grid, the average Canadian grid, or the regional electricity grid that is currently active in the model.
Further advanced tweaking of chemical inputs is possible. There are three placeholder chemicals at the bottom of the list of chemicals. If a user wanted to, they could add a new chemical to their model by simply adding the energy inputs in columns C through G. Name the chemical and start adding it to fuels, no further steps required. Several placeholder rows are included for this purpose.
There are many ways to make use of GHGenius. Ranging from referring to default values, to modelling specific facilities or fuel systems. The model also has GHG output data for feedstocks and regional power grids.
The model is expandable and new feedstocks, production systems, vehicles, and regions can be added to the model.