EZ Sim Demo

Review Building Operations

Our workhorse is the "tuning graph". Here we plot the average energy use against the average temperature. The actual bills are the blue points and the model's estimates are shown as a red line.

For electrically heated buildings (as in the example), expect to see a U-shaped plot. The bottom of the U is the same regardless of season -- it tells us something about the amount of baseloads -- that is, lights and plug loads. The right side of the U increases with hot weather -- it tells us something about the amount of air conditioning. The left side of the U increases with cold weather -- it tells us about the amount used for space heating.

This technique of matching the seasonal shape is very powerful, despite its apparent simplicity. For a model to match all of the billing points means that we must have done a reasonable job of assigning the end uses.

The model keeps track of the different end uses and interactions for us. If we increase the amount of lighting energy, for example, it changes the internal loads within the building. The model figures out how that will affect the demand for heating and cooling. It computes the BTUs of thermal load (both heating and cooling), figures out how many cfm of air were involved to move those BTUs and then how much fan energy was needed to move that much air. This is the value of a simulation model based on building physics!

Based on these calculations, the model has computed an end use breakdown for us. Here is what that looks like --  plotted against average monthly temperature the same way as the tuning graph.

Take a look at this plot and think about what it means. This customer is using a lot of energy for Heating and little for Interior Loads (lights and plugs). That is one clue that something is wrong!