This work validates and demonstrates the potential of a methodology based on a continuous monitoring system with real time measurements, as a key support to make decisions on buildings energy systems based on quantitative data . For this work , a continuous loop -based monitoring methodology was designed and implemented to enhance the performance of Heating Ventilation and Air Conditio ning (HVAC) systems by improving the energy efficiency of u niversity buildings and the quality of life of the people who use them . The results from the case stud y, used to demonstrate the proposed methodology, can be extrapolated to the entire university in order to transform it into a smart campus . The case study also shows that the continuous measurement of temperatures allows to avoid excessive heating , reducing unnecessary energy consumption. Additionally, the case study shows the importance of monitor ing CO 2 concentration in rooms where occupancy is fluctuating, since it enables a control of the HVAC system based on the instantaneous CO 2 level (and predictive in the imm ediate aftermath ). This proposed measurement can save between 40% and 70% of HVAC energy co nsumption. The positive results obtained in this research show that implementing Internet of Things (IoT) smart ecosystems contribute to promote data -driven decisions in public tertiary buildings among decision -makers, politicians, and other stakeholders . Keyworks Building energy efficiency ; Heating Ventilation and Air Conditioning (HVAC) ; Internet of Things (IoT) monitoring ; smart campus ; Energy Performance Buildings Directive ( EPBD ) Results and Conclusions This study proposes a methodology to apply continuous monitoring of comfort parameters, such as temperature and CO 2 concentration, in public buildings, as a measure to ensure the energy optimization of HVAC systems. The analysis of these measures allows to predict and control in real time the operation mode of these equipment and reveals itself as a very powerful metho dology to ensure the reduction of energy consumption while maintaining optimal comfort conditions . This work shows, using the university buildings and their facilities as a research laboratory , the potential of continuous monitoring and measuring. As sensoriZAR harmonizes mechanisms to manage data through APIs for third -party, it contributes with an indispensable support methodology to make decisions based on quantitative data that help to optimize the operation of HVAC equipment and to improve the energy effici ency of buildings and the quality of life of the people who occupy them . The implementation of increasingly demanding regulations from an energy efficiency point of view is not enough on its own, but mu st be accompanied by procedures to ensure compliance through real measurements to determine the degree of compliance and to obtain conclusions based on quantitative data . Cover Letter Is IoT monitoring key to improve building energy efficiency? Case study of a smart campus in Spain Abstract This work validates and demonstrates the potential of a methodology based on a continuous monitoring system with real time measurements, as a key support to make decisions on buildings energy systems based on quantitative data . For this work , a continuous loop -based monitoring methodology was designed and implemented to enhance the performance of Heating Ventilation and Air Conditio ning (HVAC) systems by improving the energy efficiency of university buildings and the quality of life of the people who use them. The results from the case stud y, used to demonstrate the proposed methodology, can be extrapolated to the entire university in order to transform it into a smart campus . The case study also shows that the continuous measurement of temperatures allows to avoid excessive heating , reducing unnecessary energy consumption. Additionally, the case study shows the importance of monitor ing CO 2 concentration in rooms where occupancy is fluctuating, since it enables a control of the HVAC system based on the instantaneous CO 2 level (and predictive in the imm ediate aftermath ). This proposed measurement can save between 40% and 70% of HVAC energy co nsumption. The positive results obtained in this research show that implementing Internet of Things (IoT) smart ecosystems contribute to promote data -driven decisions in public tertiary buildings among decision -makers, politicians, and other stakeholders. Keyworks Building energy efficiency; Heating Ventilation and Air Conditioning (HVAC) ; Internet of Things (IoT) monitoring; smart campus; Energy Performance Buildings Directive ( EPBD ) 1. Introduction Nowadays, climate change [1] and environmental degradation are a serious global challenge. Energy efficiency is essential to contribute to decarbonization and to limit, as set in the Paris Agreement in 2015, to 1.5°C the increase of global temperature [2]. In this context, the United Nations (UN) ha ve established different Sustainable Development Goals (SDGs) for 2030 [3], including: affordable and clean energy; sustainable cities and communities; and climate action; with a commitment to save more than 32.5% of energy use by 2030 (compared to proje ctions of the expected energy use in 2030) [4]. In the European Union (EU) it is estimated that 75% of the EU building stock is inefficient [5]. Additionally , as p ointed out in the Energy Performance Buildings Directive (EPBD) [6], buildings are responsible for 40% of energy consumption and 36% of greenhouse gas emissions ; accordingly , EPBD proposes to incorporate Internet of Things (IoT) technologies and Artificial Intelligence (AI ) mechanisms into the Heating, Ventilation and Air Conditioning (HVAC) systems . Buildings are energy consumers and carbon producers throughout their entire life cycle, including their construction, use, demolition and end of life . The operation and construction phases are, in that order, the most important energy consumers. The use or operation phase includes the energy required for maintaining comfort conditions, being the most relevant the energy for running HVAC systems , domestic hot water, lighting, and domestic appliances. The share between the primary energy consumption of these two phases has been extensively studied, being greater that of the use phase. However , this share has been changing considerably in recent years and will continue to change due to the efforts made to re duce the energy consumption of th e operation phase in dwellings and tertiary sector buildings , e.g. through the nearly Zero Energy Buildings (nZEB) standard, and the forthcoming Z ero Energy Buildings (ZEB) and Positive Energy Buildings (PEB) ones towards the Life Cycle Zero Energy Building (LC -ZEB) concept [7]. Another factor that is balancing the share is the use of renewable energies, whether it is on site energy production or at national level, as national plans are being designed to transform the electricity mix into a les s polluting one. The share, in any case, also depends to a large extent, on the climatic conditions , the building design (its orientation, configuration, materials, etc.), and the use of the building, among other factors . Manuscript File Click here to view linked