Energy Modeling Comparisons in High Performance Buildings

The lure is compelling for high performance buildings. Improved interior environments, better working conditions, and lower energy bills to boot! But many building owners and facilities managers are realizing that achieving the modeled energy performance is easier modeled than done. As more high performance buildings come online, some owners and architects, probably many more than would like to admit it, are seeing energy consumption is not as low as modeled, and in some cases is even higher than the building being replaced. With this realization comes several reactions, including disbelief, disappointment, finger-pointing and confusion, and a degree of resignation that sometimes things are not what they hoped for.

The typical questions and hoped-for explanations include the following: Why is there such a disconnect? Are the energy models accurate? Are the systems and monitoring systems properly commissioned and functioning? Are the building occupants using the building correctly? Was it just a harsh winter or hot summer? Are the energy gods meting out punishment for trying to shortchange them?

While every high performance building is unique, there are several points that are consistently overlooked that begin to account for discrepancies in modeled and actual energy consumption. About half are quantifiable and measurable. The others are less intuitive and often overlooked. The quantifiable reasons for higher energy consumption include but are not limited to the following:

1. Incomplete or ongoing commissioning

2. Lighting controls not functioning properly (See 1)

3. Mechanical systems not fully automated and lacking control routines (See 1)

4. Longer building occupied more hours or days than anticipated

5. Program changes during design but after modeling has been completed

6. Comparison of gas/electricity utilities vs. new building with different mix of gas/electric consumption across different systems.

7. Comparison of old building to new building with different program, SF, and site

These lists are not complete, but they do begin to get at the complex interaction and built-in nature of much of the energy consumption in new buildings. The simple and low-energy building systems in older buildings often require accommodation on the part of users who have all adapted accordingly. The same users therefore expect a 'perfect' environment inside the new facility - 74.0 degrees year round. After all, it's new and high performance, right?

AGB 7/2005