Simulation programs are useful tools for predicting different parameters connected with buildings’ functioning, such as energy use for heating and cooling, internal temperature, solar gains, heat losses, etc. They are becoming necessary and irreplaceable elements of buildings’ design process, allowing for optimal choices concerning opaque and glazed partitions as well as installation systems.

The key problem, however, is the reliability and creditability of simulation results. Building modeling should be foregone by validation or calibration procedures, helping to adjust the model’s parameters in such a way, that the simulation outcomes are as close to reality as possible.

The paper presents three cases of validation and calibration on a commercially available simulation program based on a control volume method. They used different reference objects and weather datasets, which caused different modeling problems and various sources of uncertainties and errors.

The first case was a validation according to a relatively simple setup included in one of the European standards. A single zone enclosing one room with a window was modeled there, and the analyzed parameters were heating and cooling demands simulated in several configurations of partitions and installation systems. Main validation problems were connected with a lack of data or program capability to simulate processes described in the standard.

The second case was a calibration based on measurements in a climatic chamber belonging to Rzeszów University of Technology. The measurements here were made in summer, when the chamber was in a “free-running mode”, meaning that the internal temperature was mainly a product of heat losses and gains between the room and the external environment. Modeling a relatively small space required including thermal bridges in all of the connections, as it turned out that they had an important influence on the heat transfer ability.

In the third case, an apartment in a multi-family building was modeled. The internal temperature was monitored there during the absence of the user, being the reference point for the calibration of a model. The major difficulty here lies in the lack of information about some of the thermal properties of building materials used in construction.

Despite the uncertainties, the validation and calibration procedures allowed to produce more reliable calculation results and improved the knowledge of the simulation tool used by the modeler.

EPC has converted itself in an instrument to guide the European Renovation wave and lead to decarbonisation of its building stock. To efficiently prioritize investments, it is key to have reliable EPCs that are representative of the true thermal performance of buildings and their systems. One of the sources of unreliability of EPC comes from the inputs used for the energy model.

EPC’s inputs can be divided in two categories. First, geometrical data, linked with surfaces and volumes, have a big influence on the results of thermal models, therefore ensuring their adequate measurements is important. Second, thermos-physical and system performance inputs generally use standard assumptions that do not reflect the reality of the building, as little information is available. Even if technical information is available, it does not reflect the quality of the constructive process. Using real energy consumption in realistic use conditions (weather, occupancy) to calibrate the thermal energy model can improve the reliability of the EPC results.

Based on a study on 15 residential dwellings located in the northern Spain, the influence of different geometric measurement technics on EPC results has been studied, and recommendations to improve their accuracy are proposed. In addition, a methodology to calibrate thermos-physical inputs of EPC models has been developed. It is based on automating the generation of detailed thermal model from inspection data, especially regarding HVAC systems. The study shows that differences in input can lead to up to two EPC category difference for the same residential building.

Based on a study on 15 residential dwellings located in the northern Spain, the influ-ence of different geometric measurement technics on EPC results has been studied, and recommendations to improve their accuracy are proposed. In addition, a method-ology to calibrate thermos-physical inputs of EPC models has been developed. It is based on automating the generation of detailed thermal model from inspection data, especially regarding HVAC systems. The study shows that differences in input can lead to up to two EPC category difference for the same residential building.

The building sector accounts for over one-third of global energy consumption and approximately 26% of energy-related CO₂ emissions. Renovating exist-ing buildings to improve their energy performance is a key strategy for low-ering operational energy demand and achieving global climate targets. In this context, accurate energy simulations are essential, enabling reliable evaluation and optimization of new products and solutions.

This study is conducted within the EU-funded EASI ZERo project, which aims to develop easy-to-install building envelope components for energy-efficient renovations, targeting near-zero energy balance and minimal CO₂ emissions. The components under development integrate bio-sourced insula-tion, low-carbon paints and plasters, and lightweight frames for windows and doors. As part of the project, a dedicated laboratory facility was modelled us-ing both IDA ICE and EnergyPlus to evaluate a novel wall component (test wall). The simulation results are validated against measurements collected over a 16-day period, including operative temperature, surface temperatures, and heat fluxes through the test wall.

The results demonstrate good overall agreement between simulations and measurements. EnergyPlus showed slightly better performance than IDA ICE in predicting operative temperature (Normalized Root Mean Square Er-ror, NRMSE: 0.25 vs. 0.32), glazing surface temperature (NRMSE: 0.098 vs. 0.114), and heat flux (NRMSE: 0.16 vs. 0.18), while IDA ICE provided better predictions for the test wall surface temperature (NRMSE: 0.12 vs. 0.16).

This study provides valuable guidance for selecting appropriate simulation tools and contributes to enhancing the accuracy of thermal performance pre-dictions, which is crucial for optimizing energy use in renovation projects and supporting sustainability goals.

This study presents the results of the analysis of climate change effect on the energy performance of urban buildings located in two different LCZ (Local Climate Zone) areas in Athens, Greece. To thoroughly assess the potential impacts of climate change, the analysis concerns 3 different periods: the reference period of 1980–2000, a mid-century future period of 2040–2060, and a late-century future period of 2080–2099. In each case study area, two different buildings are studied, having southern and northern orientation respectively. Both buildings are considered to be located in similar urban complexes and have a typical multifamily building form, while dynamic energy performance simulations are conducted with the Energy Plus tool.

By comparing the performance of buildings across these different climate and emissions scenarios (RCP4.5 and RCP8.5), valuable insights can be gained regarding long-term thermal behavior and resilience. The findings reveal a significant shift in energy demand patterns due to climate change. More specifically, heating demand is consistently declining in all scenarios and buildings. Hence, reductions reach up to 37% during the late-century period and for the RCP 8.5 scenario, reflecting the expectation of milder winters in the future. In addition, cooling demand shows a large increase, with projections ranging from 75% to 145% by the late-century period. This outcome is highlighting the urgent need for cooling solutions due to prolonged heatwaves and rising outdoor temperatures, that are accessible by vulnerable household, energy efficient and ensure high thermal comfort conditions during the cooling period.

In addition, the indoor thermal comfort analysis, based on the Fanger PMV index, demonstrates a clear degradation of comfort levels under future climatic scenarios. Higher PMV values are observed during summer, particularly on upper building floors due to increased solar heat gains. Under RCP 8.5, the discomfort levels rise significantly, with PMV values exceeding acceptable limits during peak summer periods. These results emphasize the urgent need for adaptive thermal comfort strategies, such as improved building insulation, reflective surfaces, and passive cooling techniques, to mitigate the adverse impacts of rising temperatures on occupant wellbeing.

HVAC equipment accounts for one of the largest uses of energy con-sumption in buildings. While numerous studies have been directed to-ward standalone systems such as heat pumps or ventilation systems, ad-dressing these separately has revealed several limitations, particularly in energy recovery as well as coordination. This has created the demand for compact multifunctional systems (MCS) integrating HVAC and DHW functions. However, the lack of standardized Key Performance Indicators (KPIs) to evaluate such integrated solutions remains a serious barrier. Therefore, it appears to be essential to identify an approach to evaluate these systems through a global KPI framework. This paper provides a de-tailed description of a new MCS combining heating, cooling, ventilation, and domestic hot water production (DHW), including its components. It proposes a KPI framework based on a review of key performance indica-tors commonly used to evaluate conventional systems that compose the multifunctional unit, including heat pumps, ventilation systems, and DHW modules. These KPIs were selected according to their relevance for assessing: (i) the overall energy performance of the integrated system, (ii) thermal comfort when coupled with the building, and (iii) indoor air quality under real operating conditions. This initial qualitative selection focused on identifying measurable, and functionally significant indica-tors from scientific literature and professional practice. Therefore, this study will serve as a guideline to evaluate and optimize the performance of such a multifunctional compact system in literature, as well as assist-ing in improving the existing HVAC and DHW standards.

Thermal comfort in buildings is one of the most important architectural design parameters to consider. The building envelope is an important building component that affects the energy efficiency of residential buildings. The building envelope component is the building element that separates the internal and external environments of the building, provides the necessary comfort conditions for the internal environment of the building, and is used to control environmental factors such as heat, light, and sound in order to create the indoor comfort required by the occupants. One of the main ways to reduce the cooling and heating energy expenditure to provide thermal comfort in buildings is to make the right decisions regarding the building envelope, where the heat transfer in the building takes place, and to control the heat transfer in the building envelope. The aim of this study is to show the effect of envelope alternatives with similar thermal transmittance values but different thermal properties, using different building elements, on energy efficiency under different climatic conditions and with future climate scenarios.For this purpose, the thermal design of the building envelope is evaluated by energy simulation in three different climate zones with different temperature and humidity levels in Turkey using a prediction model enriched with machine learning algorithms over future climate scenarios.First, we build a prediction model by clustering the building envelope alternatives with machine learning algorithms. In the analytical evaluation, building envelope alternatives with different indoor thermal capacities and similar U-values (total thermal transmittance values) were analyzed in terms of heating and cooling energy loads in the summer and winter periods with current, 2050 and 2080 climate scenarios. We compare the annual changes in heating and cooling loads for different building envelopes in terms of their dynamic thermal heat capacity, based on simulations.