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468 p., This PhD thesis deals with the evaluation of energy renovations in buildings, facing the different parts involved in that process, such as data acquisition and monitoring, data treatment (by means of building models) and analysis of obtained results. The interest of the thesis was awoken by the current energy situation where the construction sector is responsible of over 40 % of the total energy consumption in the European Union. Besides, building energy consumption has kept rising in the recent years due to several factors, such as a growth in population, an increasing demand for healthy comfortable indoor environment and for higher comfort standards. Hence, reducing the need for energy sources is a key factor in the development towards a sustainable energy future. For that reason, energy efficiency in buildings is a priority goal for the European Union, and this energy and environmental situation requires improving the energy performance of buildings. Taking into account the age of the building stock in the European Union, and specially in Spain, and the low thermal requirements existed in the past, it can be stated that in order to reduce the energy consumption, the main effort must be focused on the challenges of improving the existing stock. This energy situation is closely related to global CO2 carbon emissions. A massive decarbonisation of the world economy needs to be achieved while improving the life standards of the global population. However, other aspects must be taken into account when energy issue is treated in buildings. In those areas or population sectors where immediate economic priorities override environmental concerns and climate change alone is often not sufficient, improving energy performance in buildings is also a way driven to alleviate the so called fuel poverty. Implications and benefits of energy renovations thus have consequences not only in the reduction of CO2 emissions and energy savings but also in financial and social aspects, closely connected amongst them, such as the reduction of mentioned fuel poverty. Thus, methodologies for evaluating in an accurate way the effect of different energy renovations are needed more and more by the different agents involved on building retrofits. For policy makers it is useful, on the one hand, to check whether a given energy renovation fulfils the conditions required by law; on the other hand, to check whether a given incentive has been invested in a suitable way or not. As for architects and engineers, to identify the most adequate energy renovations for a specific building and climatic area. Thus, the development of this thesis faces the different steps given in every analysis on building energy performance. It is started with the analysis of the building stock in this region. Afterwards, two kind of data acquisition are presented: in an empty dwelling, for obtaining data mainly from the passive characteristics of the building; and in several occupied dwellings, more led to obtain data about occupants’ behaviour and profiles. Obtained data from both studies are used afterwards to define two different building models. Finally, possibilities of evaluation of results obtained from mentioned building models are described. For presenting the development of mentioned work, this PhD thesis is divided into 4 different parts. The first one, which is the introduction, encompasses Chapter 1 and Chapter 2, where the state of art of the different aspects treated in this thesis are presented, and objectives and methodology are described, respectively. The second part exhibits the experimental research carried out in this thesis. Firstly, a field study of 10 social dwellings is reported in Chapter 3. Ten dwellings are selected to be representative of the different types of buildings built during the 20th century. This study provides a huge amount of data about the current situation of the social building stock. Indoor temperature and relative humidity is logged in each dwelling during a year, obtaining information not only about indoor comfort, but also about operating conditions of each dwelling and occupants' behaviour. Energy consumption information is gathered, by means of energy bills. Additionally, questionnaires are filled in by the occupants, complementing the information obtained by other sources. This study provides an overview of the real energy performance of the social apartments, as well as an important reference for defining later a representative operating condition profiles on social building sector. Analogously, Chapter 4 is focused on the description of a detailed monitoring of a representative dwelling, selected according to the previously carried out classification. This monitoring covers two scenarios: The first one, carried out in winter 2012, and a second one, carried out in winter 2013, after a thermal improving by means of a windows replacement is executed. Around 60 temperature sensors are placed within the vacant dwelling, obtaining data for characterizing in detail the thermal performance of the constructive elements of the dwelling. Afterwards, the treatment of the data obtained from this experimental part is carried out mainly using two kinds of simulation models. The development of mentioned models is dealt with in the third part. It embraces Chapter 5 (the white box model, TRNSYS) and Chapter 6 (grey box model). Data obtaining in the second monitoring (the detailed monitoring of the selected dwelling) are used for defining the RC Model, and validating and calibrating both the RC Model and TRNSYS model. Meanwhile, information obtained from the monitoring of the ten social apartments is used to define occupation and operating profiles representative of social building apartments. Finally, the last part of this thesis has focused on the simulation design and evaluation of results obtained from the above mentioned simulations. It is explained in two different chapters. Energy savings obtained as a result of improvements both on building envelope and heating systems, is presented and evaluated in Chapter 7, under economic, energy, environmental and comfort criteria. This study is carried out on a dwelling scale. The simulations show firstly the results of 64 possible combinations of energy savings measurements on the building envelope. After choosing one of the evaluated combinations, the impact of the different heating control strategies on the final energy consumption and indoor comfort are presented. Meanwhile, the exergy approach usefulness is evaluated in Chapter 8, where a brief literature review about this concept in buildings applications is presented, followed by two papers developed in the Faculty of Architecture of TU Delft. These papers explore the possibilities of this approach on the analysis of energy renovations on an entire building scale, using as base case the reference building of this PhD Thesis. Taking into account the work presented in this PhD Thesis, different aspects can be highlighted. The energy renovations in buildings present a great potential for reducing (in an important manner) the CO2 emissions of the construction sector, but also present significant social and economic benefits in the different scales. RC models and TRNSYS models can be a very useful and suitable tool in order to evaluate energy consumption in buildings. Finally, the importance of considering a holistic approach when energy consumption the of building stock is evaluated, has also been remarked in this thesis, and the role that aspects such as human behaviour, operating conditions (simulations in this thesis present differences of around 50% on energy consumption depending on the assumed operating conditions) and control strategies play in the global energy consumption is proved. In the close future, two different lines are identified to develop. The improvement and adjustment of the RC model must be developed, and later, the interaction of the RC model with the TRNSYS model, and both of them with the Energy System Plant (experimental plant for testing different building energy systems) must be explored. This way, a workflow starts on the field study of a given building which is used for defining the RC Model. Defined RC model calculates the energy demands, and that energy demands feeds the TRNSYS model, which is connected to the Energy Systems Plant. Thus, different energy systems are tested in laboratory under real conditions of energy demands. Moreover, the TRNSYS model calibrated in this PhD Thesis, as well as the first results obtained from it in the last part of this PhD Thesis must be the base to develop a building energy renovations handbook, useful for the different agents of the construction sector. This handbook, which can be developed with the support of the Laboratory for Quality Control in Buildings of the Basque Government (LCCE) will present economic, energy and environmental results of different energy renovation strategies, on different kind of existing buildings, in different climatic area, based on dynamic simulations and experimental data.