The six studies that provided some evaluation of water use found that high-performance or green buildings on average used 8 to 11 percent less water than conventional buildings.

Seven studies provided some analysis of the performance of buildings certified at different levels of LEED. They indicated that the majority of LEED-Silver, Gold, or Platinum buildings studied used significantly less energy and less water than conventional buildings.

The long-term cost savings that can be achieved through reductions in energy and water use over the life cycle of buildings will depend, in part, on local utility prices and on heating and cooling loads related to climate zones. Five studies focused on buildings in specific regions or states (Pacific Northwest [2], Massachusetts, Illinois, and Arizona). In these studies, energy use reductions attributed to green buildings when compared to conventional buildings ranged from 5 to 40 percent. During the 30 or more years a DOD building is in use, those differences could be significant. Across a portfolio of facilities, local price factors may be an important consideration for DOD in determining which investments in military construction or major renovations will be the most cost-effective over the long term.

Finding 6. Not every individual high-performance or green building achieved energy or water savings when compared to similar conventional buildings.

Although high-performance or green buildings saved energy and water, on average, across a sample of green buildings, some individual buildings had significantly greater reductions than the average, and some did not perform as well as conventional buildings. Similarly, there were LEED-Silver and LEED-Gold buildings that used more energy and more water than conventional buildings. The research studies speculated about reasons why this was so but did not provide sufficient evidence to draw generalizations regarding why some high-performance or green buildings significantly outperformed conventional buildings and why others did not, although building type was clearly a factor. Another factor was the type of technologies employed to reduce energy or water use.

Finding 7. In general, the quantities of energy and water used by a building once it is in operation are greater than the quantities of energy and water predicted by building design models, if these models are specifically created for compliance with LEED, Green Globes, or ASHRAE standards.

All building standards and green building certification systems require that a building design meet or surpass an energy efficiency standard. In the case of LEED, Green Globes, and ASHRAE 189.1, this standard is ASHRAE/IESNA 90.1. An energy model created to be compared with the ASHRAE/IESNA 90.1 standard necessarily underestimates the energy use and the energy cost of the building once it is constructed and in operation. This is because (1) such models assume perfection in manufacturing, installation, and operation of buildings and their systems; and (2) such models do not include certain heat losses, because they are too difficult to calculate.

Energy and water use should be predicted with an “actual use” model that takes into account factors not considered by the LEED, Green Building Initiative (GBI), or ASHRAE design models. An “actual use” model starts with the model created for compliance with LEED, Green Globes, or with ASHRAE 189.1, and then incorporates real-life assumptions of manufacturing, installation, and operation. It also incorporates the three-dimensional heat losses.

An “actual use” model created during design can be significantly improved in its predictive value if it is updated with as-built/as-operated conditions. Imperfections during construction can be observed and incorporated in the model, change orders can be modeled as well, and variations in occupancy captured

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