Possibilities with Probabilistic Methods for Dynamic Building Energy Simulations using Stochastic Input Data: – Initial Analysis

As observed in earlier studies, there is evidently a performance gap between the predicted annual energy use from building performance simulations based on traditional deterministic methods compared to the monitored annual energy use of a building. The hypothesis is that using a probabilistic method makes it possible to consider the uncertainties in the input data and quantify the overall uncertainty of a building design using a probability distribution for the predicted energy performance of a building. Thus, reducing the performance gap between the predicted and monitored energy use. This paper aims to detail the advantages and disadvantages of both the deterministic and the probabilistic methods when determining the energy performance of a building and evaluate the differences based on a qualitative analysis. The differences between the methods are evaluated further based on the results from a previous case study where the probabilistic method has been implemented in two dynamic building performance simulation software. The conclusion from this study is that both methods have their specific advantages and disadvantages, however the main differentiating point is the scope of application. The deterministic method is a simpler alternative, needing a less amount of data and is performed in less time, thus making it advantageous in early phases when the basic design of a building is decided, and available information still is limited. However, this method must make use of an arbitrary margin of safety when used for code compliance. The perceived accuracy of the results, since the software reports the result to several decimals, are often misleading since the numerical value says nothing about the probability of fulfilling the requirements. The probabilistic method is more robust and requires more information, such as a larger quantity of data for each factor, and more advanced knowledge of both energy performance and statistics from the operator. Because of this, it also requires more computational power and is more time consuming. Thus, the method is more advantageous for analysis and determining the risks associated with not fulfilling the building regulations, since the method determines the probability of failure, instead of using an arbitrary margin of safety.