That takes us to getting started with EnergyPlus. How does it work? I've already installed the EnergyPlus software. It's typically best to let it install in the default directory on the C drive. As you can see, I have version 7.0, 7.1, 7.2 and they're all in separate folders. When you get an updated version you don't need to delete the older version, but you can if you choose to. Most experienced modelers know that sometimes it's great to have an older version available, especially if you're working on several projects. In the EnergyPlus folder, there's a list of available files. Let's explain these one by one because they are very important for understanding this entire framework.
The DataSets folder is actually a database which is supplied within EnergyPlus. You can see that the data is already there. You just open any of these in notepad or any other note editor. Here you see all of the data that is available as far as construction and materials. You can use these things within EnergyPlus automatically. There are various other components for things such as boilers, chillers, Dx Cooling equipment and more. There are also examples available that are built into energyPlus. You'll also see the various schedules. I'm just opening the notepad right now. You'll also see the various different schedules available. These are custom schedules which you can use in specific files, like in any other simulation software that you generally use. If you are familiar with other software, like eQUEST, there are often default schedules as there are in EnergyPlus, these are validated and well researched schedules that you can directly use or use for reference.
You can also see here that California Title 24 definitions are available. As you can see, the light and electrical equipment, all of the standards that are used for simulation, are already here. This DataSets folder is something you'll need for doing professional simulation services. This is very important as far as the background of EnergyPlus is concerned. It's very important for you to know what is available at the install, as you can either use these datasets as they are or make modifications to them for your energy models.
Starting with the documentation folder, you'll see that a lot of PDF files are available. I'll be opening these within the EnergyPlus interface, but first we want to see what is available. This brings us to another very important aspect of using EnergyPlus: making use of pre-made examples. They are located in this example files folder. Here you will see various different kinds of simulation items. In fact, all of the objects inside energyplus are available within these files. There are two excel files provided which consolidate the information regarding these example files. Let's open this. You will see that it contains a hyperlink to the object. For example, you see the 1 zone evaporator cooler .IDF. It's obviously an IDF file. You can see that additional information is also provided in the excel file. If you scroll to the right, you'll eventually see a brief description of this IDF object.
If we scroll down, we can look at another example. Let's go to five zone ice storage. If I want to model ice storage, I would first look at this IDF file to see what object it uses. Once I have an understanding of various objects and what this ice storage object uses, I'll be able to use it in my own energy model. Similarly, we can look at the five zone night ventilation system and see all the objects used in this IDF file. These are all of the objects that are going to be used. This serves as a very good reference for you to understand items in your proposed model. The spreadsheet shows you what is generally required. It shows a very precise list of what individual objects you will need to have in your model to add any of the components listed here. It also gives you an idea of what would be added directly to your model if you imported any of the listed IDF files into your energy model.
Of course, this Excel file is just for understanding which example file is using what various objects. I think it is reasonably self-explanatory and contains the link to the example file plus the data if you would like to know exactly what objects are used in example files. The other excel file in the documentation directory gives you a list of objects in each of the example files.
Now that we can find example files, lets open a very basic EnergyPlus file and run it. We actually created some basic files utilizing the example files that are available. As soon as you double click it, you'll see this window. This is known as the EP Launch window. It's as simple as that-- you just have to provide a link to the IDF file which we assume is already created here and then hit simulate. As soon as you simulate this, it will generate more files.
Let's walk through an example. For simplicity, I'm copying exercise 1A into My Runs. This is my energy model. Consider that the geometries are already built and various assignments are already done. We are going to run in EnergyPlus for the first time. What you have to do is simply double click on your IDF file and you'll see that as soon as you double click, it will display the IDF path in EP-Launch. Then you can choose the weather file on which you want to run it. The source of these weather files can be found on the internet by searching "energyPlus weather data" --a lot of locations are available. I'm selecting San Francisco. Now, we can click simulate. It's a very small run and it is simulated very quickly. As soon as I completed the run, it gave me a message that this IDF file was run at this location and the run is completed with 0 warnings and 0 errors and we can click okay. If we look at the folder that previously contained 1 file, we now see the various output files which are created as a result of the input. The results in the output files and the number of output files vary based on certain settings in the IDF input. So if you want an hourly output of a certain variable, and you entered that in the inputs, then you would get another file or another column in this MTR file.
You can also see here that in exercise 1A, the dxf is already available. We have provided certain geometry to this IDF file using a different mechanism, but it has that converted the inputs into a DXF for us to view. Let's simply open this. As you can see, it gives you the north cardinal direction. You'll see this is the basic block which is what we modeled. There are multiple ways to look at it, but this is one way using TruView Dwg viewer (or you could use Free DWG viewer). EnergyPlus actually exports the DXF file based on the geometry input in the IDF file. This is the error file, but as you can see there are no errors so we know that it simulated correctly. Another important file is an IDD file. An IDD file actually defines a structure of EnergyPlus input. This is that IDD file. It's even possible for advanced users to edit the IDD file, which is way beyond anything a new user typically cares to do, but we can look at what it does.
For example, in this exercise 1A, as soon as I double clicked on this for running the simulation, I got a window, which is defined by the IDD file. It gives me two options-- either to open this in a text editor or to open it in the IDF editor. The choice of these two options is up to you but most new users will certainly use the IDF editor. The IDF editor is a more concise option. It is certainly less confusing to a new user because it has an automatically self-organized structure. A text editor can be much more powerful and faster for experienced users, but you will have to understand the entire EnergyPlus data structure itself before you can properly make use of it. Here we open the file in a text editor. In materials, you'll see that this is how a material is defined. It's similar to computer programming at this point which is why the text editor is recommended for advanced users only. But it's good for all users to know that this is what the EnergyPlus engine is going to read. If you are tech savvy, you will surely realize the power of being able to copy/paste parts of entire files.
But, let's just look at part of the text for now. Looking at a material, the name is given, roughness set to Medium smooth, thickness is given, conductivity is given, density is specified, thermal properties are given. These materials are going to be referred to somewhere else in the IDF as a construction type. These materials are used here-- outside layer one, two, three. Then, these constructions types are going to be used in zones of the building surfaces. Though this format may seem complicated at first it gives you a huge amount of flexibility and is reasonably easy to learn with some practice. Okay, I exaggerate, it's not that easy, but parts of it are very easy. For instance, you can create various materials and you can edit various layers to suit your needs, which is similar to other software.
There's a notable flexibility in EnergyPlus which we will cover now. If we open the IDF editor, we find that EnergyPlus gives you the option to play with the calculation algorithms as well.
Before we get too far ahead of ourselves, let's understand the IDF editor to become familiar with its structure. The objects listed on the left are referred to as classes and the class can contain a lot of objects. Take the time to understand the EnergyPlus framework. There are classes. Within the classes, there are objects which have various properties. When you click a property, you will see a detailed description in the upper right corner of the editor. For example, let's look through the hierarchy. If I go to "schedule compact", which is a class, and I select it, there are three objects in that class. These three objects have various properties which can be further edited or defined and you can create more objects as well. Similarly, the material that we just looked at in the text editor is defined here.
If we go to the material class, we have seven objects and you'll see the seven objects are also written here. The limitation of an IDF is that you cannot have more than 9,999 objects or else you can't open the file in the IDF editor. As we mentioned earlier, this is not a limitation of the EnergyPlus engine, but rather a limitation of the IDF editor. 9,999 sounds like a lot of objects, and it is, but it is not uncommon. For instance, in large buildings, you could have several thousand surfaces and you could approach 9,999 objects. In materials, however, it's unlikely to cause a problem because Materials cannot be more than 200 in the IDF editor - and it is pretty uncommon to reach more than 200 materials even when modeling a campus of buildings.
Now that we have seen how classes, objects, and properties are linked, we will look deeper at how they operate because this is a very important aspect. Classes are basically a bunch of various functions that are built into EnergyPlus, but the objects are items that we add. For instance, I can access a material, which is located in a group called "Surface construction Elements". The first class is Materials, the first of which is "Material: Nomass" As the name suggests, it will contain materials which have no mass and you really don't have any possibility to put specifications apart from resistance. Then you have "Material:InfraredTransparent", and you can actually model a thermal resistance of an "air gap". Then you have "Material: RoofVegetation". This is how you can model a green roof and you can see the various properties associated with green roofs. You'll see that there are many ways to enter a glazing into the system. A typical way is to enter "WindowMaterial:Glazing" This is a simple way to model basic windows. As soon as I add an object here, I can just name the glazing-- I'll call it Glass 1. I can give it a U-factor, which we will give 5.1 arbitrarily, and also give it a Solar heat gain coefficient which can be .25, and then the visible transmittance also needs to be set and we will simply set it to the manufacturer specifications, for instance .7 or .3.
Now we have a simple definition of glass material. This glass material can be used somewhere else in the IDF editor. The Key point here is that everything works on references. You define an object here and then you use it somewhere else. The building is made out of various components, and this entire structure file structure follows that. If you were to correlate, you'd see that in the beginning, the group "Simulation Parameters" only references the simulation controls, building, shadow calculation algorithms, and surface convectional algorithm inside and outside.
The point that I made earlier was that the basic difference between EnergyPlus with other software is that you have an option to select various algorithms for your computation. For the Inside and Outside you can use these various algorithms. Similarly, under heat balance you can use various algorithms such as the conduction transfer function which is a DOE2 type of Algorithm. And then certain other advanced algorithms are there as well. The differences of these go beyond the scope of this course and I can simply say that all of these algorithms are well researched. When you first start with EnergyPlus, you might ask which of these is best. My advice is, they are all well tested and you should probably just leave the defaults and not really look into it. I am simply illustrating this because it is important you know that there are options which can be utilized at the later date.
Now, similarly to choosing algorithms, but probably more important for new users, it is important to know that you can use time steps. For example, Time step one is an hourly simulation. Precisely speaking, this means the calculations will occur for each hour. Time step two means half hour simulation. At maximum you can do a minute-by-minute simulation in EnergyPlus. Unlike many mainstream simulation programs, Energyplus is a sub-hourly program. This means that you can more accurately solve heavy mass and certain high heat capacitance structures by choosing a high time step. In the case of erratic weather and high mass materials, certain algorithms can fail at what's called a convergence test. The time steps make sure that what is called "convergence" happens in a smoother way, more similar to reality. This is an option that EnergyPlus gives you to evaluate certain structures with a realistic approach. Smaller timesteps are more important for certain algorithms, such as conduction-finite-difference, but that is beyond the scope of this course. Generally, you'll like to leave it as it is-- the default. The default timestep is 6. It is important to remember, this time step directly impacts simulation time. A time step of 60 is going to take approximately 60 times longer than a time step of 1.
Let's look at the next field down. There's a recent capability which has been added to EnergyPlus which is quite different from other programs that are currently available for energy modeling. This is for the parsing of the calculation-- to solve processes in parallel. Here, under "ProgramControl", what is allowed is that you can actually control the number of computer processors that EnergyPlus is allowed to use.
I want to demonstrate how it works. I'm using the same file, but I'm just going to change one thing here, which is the run period. I'm just adding a small object here to give you an idea of how it works. Enter a start month of 1 and an end month of 12; this makes it an annual simulation which you can see here. Just to test the limitations of EnergyPlus, I'm going to run it at a start year of 3 instead of 2013 and we are going to run it for 1 year, which is noted by the "Number of times the run period will be repeated". Now, we are going to save the file. One more thing that I will change here is the “run simulation for weather periods” which I will set to Yes.
Open this file in EP-launch and you'll see that this file is edited in my run. I'm going to run it at year 3 for a single year period. You will see it run quickly. What it did is it has given one warning here. It appears when the calculation completes. The warning is actually that the weather file that we have used is not matching with San Francisco. I used San Francisco as the weather file but the file was built on Chicago, so the latitude/longitude difference is noted and recorded as an error. It's just a warning so the model will still run, but the warning is telling us that the results might not make sense because it used weather data from San Francisco but the geographical location and timezone from Chicago. The inaccuracies this will cause are quite interesting but they require a detailed knowledge of how energyplus works. I mainly wanted to illustrate the advanced warning system in Energyplus.
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