Energy performance of buildings: modeling for better efficicency

Sanda Lefteriu, a researcher at IMT Lille-Douai, is working on developing predictive and control models designed for buildings with the aim of improving energy management. A look at the work presented on April 28 at the IMT “Energy in the digital revolution” symposium.

Good things come to those who wait. Seven years after the Grenelle 2 law, a decree published on May 10 requires buildings (see insert) used for the private and public service sector to improve their energy performance. The text sets a requirement to reduce consumption by 25% by 2020 and by 40% by 2030.^[1] To do so, reliable, easy-to-use models must be established in order to predict the energy behavior of buildings in near-real-time. This is the goal of research being conducted by Balsam Ajib, a PhD student supervised by Sanda Lefteriu and Stéphane Lecoeuche of IMT Lille-Douai as well as by Antoine Caucheteux of Cerema.

A new approach for modeling thermal phenomena

State-of-the-art experimental models for evaluating energy performance of buildings use models with what are referred to as “linear” structures. This means that input variables for the model (weather, radiation, heating power etc.) are only linked to the output of this same model (temperature of a room etc.) through a linear equation. However, a number of phenomena which occur within a room, and therefore within a system, can temporarily disrupt its thermal equilibrium. For example, a large number of individuals inside a building will lead to a rise in temperature. The same is true when the sun shines on a building when its shutters are open.

Based on this observation, researchers propose using what is called a “commutation” model, which takes account of discrete events occurring at a given moment which influence the continuous behavior of the system being studied (change in temperature). “For a building, events like opening/closing windows or doors are commutations (0 or 1) which disrupt the dynamics of the system. But we can separate these actions from linear behavior in order to identify their impacts more clearly,” explains the researcher. To do so, she has developed several models, each of which correspond to a situation. “We estimate each configuration, for example a situation in which the door and windows are closed and heat is set at 20°C corresponds to one model. If we change the temperature to 22°C, we identify another and so on,” adds Sanda Lefteriu.

Objective: use these models for all types of buildings

To create these scenarios, researchers use real data collected inside buildings following measurement programs. Sensors were placed on the campus of IMT Lille-Douai and in passive houses which are part of the INCAS platform in Chambéry. These uninhabited residences offer a completely controlled site for experimenting since all the parameters related to the building (structure, materials) are known. These rare infrastructures make it possible to set up physical models, meaning models built according to the specific characteristics of the infrastructures being studied. “This information is rarely available so that’s why we are now working on mathematical modeling which is easier to implement,” explains Sanda Lefteriu.

“We’re only at the feasibility phase but these models could be used to estimate heating power and therefore energy performance of buildings in real time,” adds the researcher. Applications will be put in place in social housing as part of the ShINE European project in which IMT Lille-Douai is taking part. The goal of this project is to reduce carbon emissions from housing.

These tools will be used for existing buildings. Once the models are operational, control algorithms installed on robots will be placed in the infrastructures. Finally, another series of tools will be used to link physical conditions with observations in order to focus new research. “We still have to identify which physical parameters change when we observe a new dynamic,” says Sanda Lefteriu. These models remain to be built, just like the buildings which they will directly serve.

 ^[1] Buildings currently represent 40-45% of energy spending in France across all sectors. Find out more+ about key energy figures in France.

This article is part of our dossier Digital technology and energy: inseparable transitions!

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Energy performance of buildings:

The energy performance of a building includes its energy consumption and its impact in terms of greenhouse gas emissions. Consideration is given to the hot water supply system, heating, lighting and ventilation. Other building characteristics to be assessed include insulation, location and orientation. An energy performance certificate is a standardized way to measure how much energy is actually consumed or estimated to be consumed according to standard use of the infrastructure. [/box]