Buildings are one of the largest contributors to global energy consumption. In 2025 they accounted for around 30% of total global energy demand, 70% of which came from residential buildings. But as cities grow and standards of comfort rise, many nations are faced with mounting housing and energy crises.
This is especially important in light of increasingly frequent extreme weather events driven by climate change, which further increase the use of heating, ventilation, and air-conditioning (HVAC) systems. Without serious action to improve building performance, this rising demand will put added pressure on our energy systems, amplify social issues like energy poverty, and increase fuel consumption and greenhouse gas emissions.
Despite the urgency of the challenge, many buildings perform far below their potential. Poor insulation, ageing or inefficient HVAC systems, and lack of flexible control often lead to needless energy waste. Many buildings consume much more energy than they were designed to and still fail to provide comfort to their occupants.
Improving energy efficiency in buildings is therefore 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. But efficiency improvements are only effective if they are applied judiciously. This is where monitorisation comes in.
You can’t improve what you don’t measure
First and foremost, we need to understand how buildings operate in the real world and how their different systems interact with each other. Any building’s thermal and energy balance is complex and subject to multiple variables and parameters.
In a building, monitorisation refers to the continuous tracking of variables such as temperature, ventilation and air quality. This measurement and verification is the foundation of any serious energy efficiency strategy. It provides real-time insights into how buildings operate, and allows building operators, stakeholders, owners, occupants and policy makers to make evidence-based decisions.
In recent years, sensors have become much more affordable, and the use of Internet of Things elements has become widespread. It is now easier than ever to design and deploy monitorisation arrays to evaluate a building’s indoor behaviour and energy performance.
In some cases it is even possible to make use of the sensor arrays already in a building – usually as part of the building management system (BMS) – to track different key variables. BMS sensors are the primary interface between the building behaviour and its HVAC response, but modern buildings typically contain extensive BMS installations capable of measuring much more than temperature. Many can also monitor humidity, CO₂, electricity, heat and 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. This means not all buildings can provide the same amount of data, at least not without further intervention.
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A digital twin of your house
While monitoring provides valuable data, 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 data-driven virtual representation of a real building. It can take various forms, including a purely mathematical “black box” model or a physical “white box” rendering.
A building’s digital twin combines monitorisation input and control data alongside physical information such as geometry, constructions, HVAC systems, loads and operation schedules. It aims to describe the different interactions that occur inside the building and is used to calibrate the model minimising its performance gap. It uses monitorisation in conjunction with simulation to reveal – and predict – a building’s behaviour.
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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 behaviour, 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 usable knowledge, data-driven digital twins can also act as a powerful optimisation tool to evaluate new control strategies, operation schedules, system setpoints, or envelope renovation. And this is all done inside a safe virtual environment, without risking resources in real application.
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By using forecasts as input data, digital twins can also assess a building’s future response to weather, occupancy, and energy prices, adjusting HVAC operation in advance to produce lower energy peaks and a smoother operation.
But the search for energy efficiency should always prioritise the wellbeing and comfort of occupants. Proper monitorisation through digital twins achieves this by evaluating multiple results (temperature, humidity, air quality) whenever a new energy-saving strategy is being analysed.
In doing so, they enable informed decision making for policies and energy saving strategies, establishing a robust framework to achieve the goals of smarter, more sustainable building design.
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