Energy Use:

We now have 24 months of data since the home was completed in November 2013. According to Rob Hammon, our energy consultant for the project, the home did in fact achieve source-ZNE based on its first year of use as a model home. However, it has been a model home since completion so the data isn’t necessarily “real world”.
In addition, it’s important to note that even with real occupant data the results would vary greatly depending upon the family living in the home. We recently did a study looking at real-world consumption of our homes compared to the energy model for each floor plan used and found that the largest deviation above the model estimate of electric consumption was 41% and the largest deviation below the model estimate of electric consumption was 81%. A pretty astounding amount of deviation from the energy models!
I bring this point up because, as a production home builder, we’re never really going to be too concerned with how any one individual home actually performs relative to the energy model, or ZNE goal. Rather, it will generally be more important for us to look at the average of a group of homes we’ve built and see how that compares to our energy models and ZNE goals, since individual occupant consumption varies so greatly. Luckily, the same study I referenced above also showed, on average, our real-world homeowner consumption to be pretty consistent with our energy model predictions.
This definitely begs the question of how to market a ZNE home the best way since we won’t be able to guarantee every home will meet the ZNE model, and we’re working very diligently on this very important issue. Ultimately, we feel it will come down to the need for a very clear disclosure, perhaps like the fine print car companies use when listing gas mileage (“your mileage may vary”).