Energy Modeling and Building Simulation-- The Big Picture
This video explains some of the key differences between load design and energy. New users often struggle with these two unique but related concepts. Don't just watch the video! Make sure you understand the analogies as they are key to your future success in Trace 700, as well as any other energy modeling software.
Load Design VS Energy Analysis
Moving from building loads to building energy adds several things to our TRACE 700 model. But before we start in TRACE 700 it is important to understand the differences between Load Design and Energy Analysis. In this picture we see load design as an RPM meter and energy analysis as a fuel meter.
Let’s say you were buying a semi-truck based on the amount of weight you needed to haul. That would be the equivalent of Load Design-- it's essentially a maximum capacity. Energy Analysis would consider how long, how often, how far you are driving the semi, and at what horse power. All of these factors tell you how much fuel you consume. In the same way, load design determines the size of your air conditioner while energy analysis simulates that air conditioner.
Now let's take a real life example. Let’s say you go out to pick out an air conditioner. What is the first question that you need to answer? A lot of people immediately say efficiency, but that is because they have already assumed that load design has been completed. The first thing we really need to know is how big of an air conditioner we are looking for. Are we looking at the local hardware store to find an air conditioner to cool grandma’s tiny apartment? Or are we talking to our local air conditioning representative to find a monster air conditioner to cool great uncle Jim's giant Rockefeller mansion? You see, the capacity of the unit is the first thing we need to know-- that is what is determined when calculating building design. When entering energy information, we are selecting unit efficiency. When we calculate energy, it is the equivalent of installing the equipment and running it for one year. This is the key element to understand for successful energy models.
In summary, the load design portion calculates the size of the equipment, which is done before it is ever even purchased. The energy analysis is done after a specific piece of equipment is selected. So it’s important to note that these simulations are done separately, and even more important to understand that they are done with different conditions.
Design Assumptions:
Let's take a look at Design Assumptions. If we calculate the capacity of Uncle Jim's air conditioner, we are going to have to make several conservative assumptions. We assume that the worst case day is well above average temperature. It is sunny, all of the people are there, all of the equipment is on, and all of the lights are on. Don't calculate the size of the air conditioner using mild weather. We have to use above average summer conditions so we have a bit of a safety factor. However, if we used above average summer weather and below average winter weather to calculate the building energy, the result would be an energy model that used way too much energy.
Analysis Assumptions:
To calculate the annual energy, TRACE 700 uses typical data instead of design data because energy calculations require regular run-of-the-mill data in order to accurately depict energy consumption. While TRACE 700 uses ASHRAE design weather to calculate building design modes, it uses Typical Mean Year or TMY weather to determine a building's energy. This is not average data, but real weather data from a particular year, say from 1993. So the weather used is typical weather, in this case there are clouds included. When running energy, the people, while they may reach a maximum at one or two hours, are typically at a reduced role, as well as equipment such as computers and lights. If you think about it, this makes sense because taking any given building on any given day makes it unlikely that everything will be fully operational.