Building energy models (BEM) are essential tools in modern architecture and engineering for optimizing energy efficiency and reducing the environmental impact of buildings. These models simulate a building’s energy performance, helping professionals understand how design choices, materials, systems, and occupant behavior affect overall energy consumption. By using BEM, architects and engineers can predict heating and cooling loads, lighting needs, and energy usage for ventilation and other building systems. This allows them to design more sustainable structures and comply with regulations like the European Union’s Energy Performance of Buildings Directive (EPBD).
What means the “Buildings energy model”
Energy modeling is the virtual or computerized simulation of a building or complex that focuses on energy consumption, utility bills, and life cycle costs of various energy-related items such as air conditioning, lights, and hot water.
It is also useful for evaluating the payback of renewable energy solutions like solar energy systems, wind turbines and high-efficiency appliances. To understand energy modeling, it’s important to understand building simulation.
Building simulation is the process of using a computer to build a virtual replica of a building. In other terms, the building is built from its parts on a computer, and a simulation is performed by taking that building through the weather conditions of an entire year. In a way, building simulation is a way to quantitatively predict the future and thus has considerable value. There are two main categories of building simulation: Load Design, and Energy-Analysis. But it’s not the topic of this article.
Utility of energy modelling for buildings
A study by the American Institute of Architects (AIA) found that buildings with energy modeling saved a considerable amount of energy as compared to buildings without energy modeling. Moreover, The study found that without energy modeling, the buildings achieved 37% energy savings comparatively to 52% energy for buildings with energy modeling. In other words, energy efficiency projects in buildings based on energy modeling may save up to 15%.
Types of building energy models
To understand the energy models, let’s look at the 3 main types depending on how each model processes information.
- White Box – This model is based on the modeling of physics and the properties of systems.
- Black Box – This model is based on historical data and statistical analysis.
- Grey Box – This model uses a combination of simplified physics and historical data.
White Box: Energy Modeling with Physics
Physics-based energy models are the most accurate ones and software like TRNSYS and EnergyPlus use this approach. Since the creation of physics-based models requires all the necessary data and equations, white box energy models are quite challenging. With the right engineering expertise and computing power, white box energy models can provide valuable insights and information for the project owners and developers.
Black Box: Energy Modeling with Data
White box models that are entirely physics-based for predicting behavior. However black box models use reverse engineering with already existing data. Since the data required for black box models is already available, the calibrations are easy and can be processed much faster. Some of the known examples are Artificial Neural Networks (ANN), Support Vector Machines (SVM), and Statistical Regression.
The dependency of pre-existing data can also be one of the main limitations at times. Creating a black box model for a non-existing building is impossible.
We use black boxes for existing buildings in the purpose of managing energy efficiency measures: the impact of these measures can be simulated even before implementing them. It allows an analysis of the building issues by pinpointing the causes.
Grey Box: Hybrid Energy Modeling
Grey Box has the design elements of both white box and black box models since they use physics equations like white box to represent the building behavior, but these equations are simpler. Hence, a good calibrated grey box model allows faster building model simulation. However, a simplified physics equation results in lower accuracy than a white box. To compensate for this, grey box models use historical data for calibration. Thus, the grey box energy model offers a balance between both, accuracy and speed as well.
For the calibration process, black box and grey box energy models are often referred to as “training” the models, since the parameters of the simulation are adjusted till the model’s results match the behavior of the system being modeled.
Conclusion
Depending upon the building requirements, the efficacité énergétique measures can vary to meet the required optimal conditions. Thus, we can consider neither of the above models as the best. When there is no data available for the energy consumption profile of a building, a white box model is the only option possible.
On the other hand, available data from the existing buildings can provide some valuable insights for the building owners when opting for the required energy modeling measures. By integrating building energy models “BEM” into the design process, building professionals can contribute to more sustainable urban environments while reducing both energy bills and carbon footprints.
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