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Literature Review of Uncertainty of Analysis Methods (Inverse Model Toolkit), Report to the Texas Commission on Environmental Quality
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This report reviews the reported uncertainty of ASHRAE’s Inverse Model Toolkit (IMT) analysis method and the linear, and change-point linear algorithms that it uses by reviewing the published literature on the related accuracy of IMT and its algorithms versus other well-accepted statistical analysis tools, such as SAS. This report begins with a review of the history of the IMT, and the linear and change-point linear models. Then it reviews the published comparisons of the IMT and other analysis software, relying heavily on the accuracy testing that was performed as part of ASHRAE’s Research Project 1050-RP. It also includes a detailed description of the basic algorithms and an example of the IMT weather-normalization analysis. In summary, from the literature it was found that the algorithms in the IMT almost exactly reproduce the same regression analysis one would get by running any one of the programs that it was compared against (i.e., usually to several significant digits). Therefore, it can be concluded that the IMT is accurate, when it is called upon to perform weather normalized regressions for modeling building energy use.
DescriptionASHRAE’s Guideline 14 has identified three methods for measuring energy savings, including component isolation, before-after measurements, and calibrated simulation (ASHRAE 2002). These methods are intended to be guidelines that will serve as a foundation for the development of reliable and accurate measurement of energy and demand savings from energy conservation retrofits. Guideline 14 describes linear, change-point linear, variable-based degree-day, and multivariable linear regression models as the modt used models for calculating before-after savings from energy conservation retrofits. ASHRAE’s Inverse Model Toolkit (IMT) is a FORTRAN 90 application for calculating linear, change-point linear, variable-based degree-day, multi-linear, and combined regression models (Kissock et al. 2002). The development of the IMT was sponsored by ASHRAE research project RP-1050 under the guidance of Technical Committee 4.7, Energy Calculations.
Inverse Model Toolkit
weather normalized regressions
modeling building energy use
- Technical Reports 
Haberl, J. S.; Cho, S. (2004). Literature Review of Uncertainty of Analysis Methods (Inverse Model Toolkit), Report to the Texas Commission on Environmental Quality. Energy Systems Laboratory (http://esl.tamu.edu), Texas A&M University. Available electronically from