LEED Rotations in EnergyPlus

At this point, we have now covered a brief overview of how simulation parameters work. Let's move on to the very important topic of Compliance objects. This is a simple Appendix G rotation option, which is relevant to LEED energy modeling. You just have to enter the degree here. This is basically used by a group of functions which are known as parametric values. These parametric values are used in cases where you want to evaluate different variables in multivariate runs. You actually enter a certain value in a text script by entering a text using the dollar sign. We will enter $Var. It might have a value of 2, 2.1, 2.0, or something like that. You can put a lot of values here. Then, you use this suffix right here as it's equal to $Var.

I'm going to run the same building for a different rotation. So what I enter here is $Angle Appendix G we generally run at 0, 90, 180, and 270. I'm now going to give suffixes so that I will be able to identify the various runs in the output file, G000, G090, G180, and G270. The same model will be rotated now in 4 directions, with these values. As soon as you run this, you'll see these 4 simultaneous windows. This file is going to be remade for all these three directions and run simultaneously. I'm running it now. Now, there's a problem here in the input file and anyone who was paying careful attention hopefully caught the mistake. I changed the variable name to $Angle, and now I need to reference the name of the variable as $Angle under the compliance building. While we are here, I also want to note that we left the simulation to run at 1 thread, but EnergyPlus will automatically run each rotation on a separate processor. But remember, It cannot run more than 1 processor per shell because as we discussed before, it can only use 1 thread unless we have shading implemented. Now, as we know, exercise 1A is only one file. But, when we click run, there are four different shells that will run immediately, and energyplus is running each rotation as a separate simulation. Also, you'll see that these exercises are running separately within the 4 separate process folders. Each run is also running on a single thread. We will get the message that the run is complete. You will see that there are various outputs available and that they each have the corresponding suffixes that we just entered. Now one quick thing, just for confirming the rotation that it did-- we can open the newly generated DXF files and make note that it indeed rotated the building. This is how you run a parametric simulation. I did it for the building angle but you can do it for insulation or various glazings, reflectivity, and much more. We will go back into the IDF editor at this point to look at additional features.

Design Days

We just looked at compliance building, Now I want to come to site- location, climate, etc. Generally the sequence of simulation is that you first design the HVAC system based on certain climate data. This is the design day simulation that you generally do in other software packages as well. In EnergyPlus, in the weather folder, there's a DDY file available, which is in an IDF editor format itself. It gives you 18 various design conditions. You can use any of these conditions, but for appendix G we use 99.6 for heating, and 1% for cooling. This is what you use as design conditions. In this existing case, we are using .4 cooling and 99.6 heating for Chicago's design conditions. Once we run it, it first runs the simulation for design day and it will compute the equipment sizes, which will then be used for the annual run. The system sizing calculation is edited under simulation parameters, simulation control.

This is system sizing calculation, and I just have to say yes. I can say yes to zone sizing, and since there's no plant in this, I can just leave it “no” or I could also say “yes.” This is saved, and I'm going to run it, but first I'll be deleting the compliance objects so that we'll see only one calculation window. Now you'll see how design simulations are done in the process window: This calculates the Chicago .4% cooling, 99.6% heating design conditions - which determine equipment size and airflows. These numbers are used during this annual simulation. In fact, all of the sizing values which are calculated in the design simulation are used in your annual run to determine energy. This forms your sequence of calculations here and we get 3 warnings but they are insignificant at this point.

Going back into the IDF editor, we can see the design day, and we can even use certain days from the weather file to size our equipment - if we so choose. We can even enter height variation and surface temperature of the ground. Given this surface temperature of the ground, these design days, and site location, there are other utilities which are provided within EnergyPlus to handle these. Within this main window, where we generally run the simulation, there are additional capabilities. For instance, you can actually put a group of input files to run simultaneously, we can locate and select them in their folder locations, and then check all boxes, and then click next. We can then verify the weather file locations, which are all the same here and essentially we have setup a batch run, which we can perform from within EP-launch.

Built in Utilities

You can also see here that there is a tab for utilities here. These are pre-process utilities that you sometimes want to complete before doing an energy model. Here you'll see that you have an availability for various programs: soil surface temperature, coefficient check, Coefficient Convection and various other utilities.

Let's look at one of these: CalcSoil-Surface temperature. This program basically evaluates the temperature of the first 10-15 meters of soil for your annual program runs. You generally have to estimate your ground temperature that you actually enter here in the building surface temperature in the IDF editor, but to be more accurate, these temperatures can be picked up from various sources. One of these sources is the EnergyPlus utility.