Understanding the Three Types of Building Energy ModelsUnderstanding the Three Types of Building Energy ModelsUnderstanding the three types of Energy modeling
Understanding the Three Types of Building Energy ModelsUnderstanding the Three Types of Building Energy ModelsUnderstanding the three types of Energy modeling
Blog Article
The energy consumption of building systems can be estimated from their nameplate data and operating schedule. However, this is a very rough estimate that does not consider the local climate and the interaction between different building systems. When deciding between energy efficiency measures for a building project, energy modeling is a powerful tool.
White-Box: Energy Modeling with Physics
Physics-based energy models are the most accurate, and this is the approach used by software like DOE-2 and EnergyPlus. However, the creation of white-box models is demanding, since they must include all the necessary equations and data. Due to their complexity, white-box models are also the most demanding in computer power, which makes their simulation slow.
Black-Box: Energy Modeling with Data
Black-box modeling is a completely different approach: while a white-box models tries to predict behavior based on physics, a black-box models is reverse engineered with existing data. These models can be calibrated easily with the available data, and they can be processed much faster than white-box models. Some examples of data-based modeling methods are artificial neural networks (ANN), support vector machines (SVM) and statistical regression.
The main limitation if black-box models is dependence on historical data. In energy efficiency applications, these models are only valid for the building that produced the data, or other buildings with very similar properties. Creating a black-box model for a building that doesn’t exist is impossible, since there is no data to calibrate the model.
Grey-Box: Hybrid Energy Modeling
Grey-box models have elements of white-box and black-box models. They use physics equations to represent building behavior, but these are simpler equations than those used in white-box models. As a result, a grey-box model can be simulated faster once it has been calibrated.
However, simplified physics lead to a loss of accuracy. To compensate for this, grey-box models are calibrated with historical data, just like black-box models. A grey-box energy model offers a balance between the accuracy of a white-box model and the speed of a black-box model.
Using Energy Modeling Effectively
Neither of the energy modeling approaches can be considered better than the others, since all have applications in the building sector. White-box models are the only option when no data is available. However, they can also be used to compare the real behavior of a building with its ideal behavior according to physics principles. On the other hand, black-box and grey-box models can be used to represent an existing building and predict its energy consumption.
Energy modeling can be very useful for NYC building owners, since Local Law 97 of 2019 stringent emission limits starting from 2024. With so many different options to upgrade buildings, owners must make sure they find the best mix to cut emissions. Ideally, a building retrofit should maximize the energy savings and avoided emissions per dollar invested upfront.