Simple uncertainty budget and assessment with the Kragten method: Examples for building physics

Abstract

The aim of this lecture note is to present and exemplify the Kragten method to calculate the combined uncertainty (uncertainty budget) of a measurand from the standard uncertainty estimates of individual inputs of that measurand, and the mathematical formulation of that measurand. If these two elements are not available, the Kragten method cannot be applied. The method also provides sensitivity (significance) assessment of the different components (inputs) in the combined uncertainty budget. The Kragten method for uncertainty calculation is very simple yet a robust and accurate alternative to the more complex GUM or Monte Carlo simulation methods. It can be performed with a simple spreadsheet tool (e.g., MS Excel) with minimum risks of mistakes. This method is adequate for the field of building physics, energy in buildings and indoor environmental engineering. This lecture note also provides examples of uncertainty calculations (budgets) for common measurands and metrics in the field of building physics, energy in buildings and indoor environmental engineering. These examples are attached to the present lecture note document (Excel spreadsheet documents). One should note that this lecture note does not cover the process of estimating the standard uncertainty of the individual inputs of the measurand. Those standard uncertainties should be obtained from technical documentation, models, or estimates from measurements (e.g., 1σ standard deviation of a set of repeated measurements on measurand that is assumed to remain constant over the monitoring period), and converted into standard uncertainties (1σ confidence interval assuming a normal probability distribution or the errors).