Value Beyond Cost Savings - Green Building Finance Consortium

Value Beyond Cost Savings: How to Underwrite Sustainable Properties1. Energy forecasting models, while generally considered fairly accurate, aresubject to some level of intrinsic error ranging from 10% to 20%. Thisforecasting error is interpreted as the percentage error between actual energyconsumption and forecasted energy use based on a building’s actual designcharacteristics and use profile, including actual energy used.2. The accuracy of the forecasts closely depends upon the skill level of the modeler.Skilled modelers can tweak or trick the model to adjust for factors that mightotherwise be outside the capabilities of the model.3. Given the proliferation of new building technologies, it has been increasinglydifficult for modeling software to keep up.4. The design parameters of the building fall outside of the range that the model canadequately handle.5. The model or modeler does not adequately address property type issues thatarise, for example, in big-box retail, laboratories, hospitals or other specializedproperty types, nor addresses unusual design features such as building arms,wings or projections.6. There are design flaws in energy efficiency components that may be relativelynew and/or untested. The components do not perform as expected.7. Thermal massing causes cooling loads to be greater than anticipated.8. The building is not built to the original design specifications: energy efficientfeatures have been omitted or improperly installed.9. The building is not built to the original design specifications: space design haschanged, adding lunchrooms, additional copy rooms, etc.10. The building is not operated in the same manner as the assumptions used in thedesign phase.11. Sustainable O&M techniques are not employed.12. Sufficient time was not allowed for the building to “settle down” after being putin service and before measuring energy consumption. A rule of thumb is that ittakes about one year for a newly constructed building to settle down or stabilizein terms of its energy consumption.13. Fundamental commissioning was not performed. If energy efficient systems havenot been commissioned to operate as designed, expected performance levels willnot be obtained.167