1) Why energy efficiency in buildings matters

The building sector remains one of the largest contributors to global energy consumption, with approximately 30% of global energy demand. In 2025 alone, the residential sector accounted for around 70% of the total energy demand in buildings. As cities grow and standards of comfort rise, various nations continue to face an increasingly difficult housing and energy challenge.  

Especially when we consider that currently climate change is driving a growing trend of extreme weather events, which further increases the consumption of heating, ventilation, and air-conditioning (HVAC) systems. Without serious action to improve the performance of buildings, this rising demand will continue to put pressure on different energy systems, amplify social issues like energy poverty, increase fuel consumption and greenhouse-gas emissions.

At the same time, many buildings perform far below their potential. Poor envelope design, aging or inefficient HVAC systems, and lack of flexible operational control, can lead to unnecessary energy waste, and in many cases, buildings can consume much more energy than they were designed to and still fail to provide comfort to their occupants.

Therefore, improving energy efficiency in this sector is not just a technical challenge, but also an economic and environmental one. Addressing a building’s energy performance improves indoor conditions, lowers operating and living costs, and cuts greenhouse gas emissions.

2) You cannot improve what you do not measure

First and foremost, we must understand how buildings operate in the real world and how their different systems interact with each other. The fact is that a building’s thermal and energy balance is inherently a complex undetermined system subject of multiple variables and parameters.

In this regard, monitorization can provide insights into real-time operation of the buildings and help address this issue. After all, measurement and verification are the foundation of any serious energy efficiency strategy; it allows building operators, stakeholders, owners, and policy makers to undertake evidence-based decisions.

As sensor prices drop, and the use of IoT elements become widespread, it is becoming easier to deploy monitorization arrays to evaluate building indoor behavior and energy performance. Furthermore, in some cases it is even possible to make use of multiple sensor arrays already deployed in the building as part of the building management system (BMS) to track different key variables. BMS sensors constitute the primary interface between the building behavior and its HVAC response. While modern buildings typically contain extensive BMS installations capable of measuring: temperature, humidity, CO₂, electricity, heat, ventilation flows, valve positions, equipment status, and sometimes occupancy; many older or smaller buildings have only limited sensor arrays, restricted to basic thermostats, on/off signals, and energy meters. Meaning that not all buildings can provide the same level of data availability, without requiring a certain degree of intervention.

3) The smart move, a data driven digital twin.

While monitoring provides valuable data, that once cleaned, validated, and contextualized, can be clustered as input data used to dictate the operation constraints of the building, or as control data which states the effects produced by such operation, numbers alone do not explain why a building behaves the way it does. This is where digital twins play a central role. In plain terms, a digital twin is a virtual representation of a real building and depending on the nature of its simulation environment it can be labelled as black-box, white-box, or gray-box.

A data driven digital twin combines monitorization input and control data alongside the building’s physical information, such as geometry, constructions, HVAC, loads and operation schedules. It aims to describe the different interactions that occur inside the building and is used to calibrate the model minimizing its performance gap. This way, monitorization is used in conjunction with simulation to reveal the building’s behavior.

4) Towards wellbeing, comfort, and energy savings

One of the greatest advantages of data-driven digital twins is their ability to act as baseline or referential models. By comparing the simulated results against real measured behavior, it becomes possible to identify different building inefficiencies and system flaws exposing energy waste that would otherwise remain hidden.

Furthermore, by turning raw data into actionable knowledge, data-driven digital twins can also act as a powerful optimization tool to evaluate new control strategies, operation schedules, system setpoints, or envelope renovation; all inside a safe virtual environment before risking resources in real application. The employment of forecasts as input data, digital twins can assess the building’s future response to weather, occupancy, and energy prices, adjusting HVAC operation in advance to achieve lower energy peaks and a smoother operation.

The search for energy efficiency should always consider occupancy wellbeing and comfort. Proper monitorization linked with digital twins addresses this issue by evaluating results in multiple levels (temperature, humidity, air quality) at the same time and resolution whenever a new energy saving strategy is being analyzed. In doing so, data-driven digital twins promote informed decision making for policies and energy saving strategies, establishing a robust framework to achieve the goals of a smarter and sustainable building design.

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José Pachano
Escuela de Arquitectura de la Universidad de Navarra

25.02.2026