Experimental and numerical investigation on thermal comfort and energy efficiency in indoor environments with radiant systems and mechanical ventilation

The thesis focuses on the configuration of a radiant system coupled with mechanical ventilation. This research aims to investigate the implications in global and local thermal perception and evaluation for the analyzed HVAC solution and the impacts caused by the presence of faults. Due to its subjectivity, the experimental part is crucial in the thermal comfort evaluation. In contrast, the numerical approach allows validating models that can be used to perform sensitivity analysis, predict scenarios, and consider the energy use and efficiency of the systems. The methodology used in this work exploits the strengths of both approaches to provide a comprehensive analysis. The first activity performed in this work is setting up a dynamic model of the test rooms using DigiThon. The models have been validated with data collected in tests in different conditions (winter or summer seasons, heating, cooling and passive modes). The importance of a validated model of a test room lies in the possibility of predicting indoor conditions and contributing to the tests’ setting, especially when the boundary conditions cannot be set. The results showed that both the test rooms could be precisely represented by the model, which also helped deduce the air volume and surface response time to the given impulses. The differences between the test rooms and the greater difficulty in the modeling activity with aleatory boundary conditions were highlighted. The activity deepened the knowledge of the equipment and its dynamic behavior, but also allowed to conclude about the end-use of both the test rooms and some precautions to take when performing tests. The second activity was mainly based on the experimental approach of the analyzed HVAC system solution. The comfort issue was investigated with tests to study how people could perceive global and local comfort within a controlled environment. The comparison with Fanger’s tests was performed to explore whether the participants’ feedback could be affected by the difference in the HVAC system and the room control: the tests in the CORE-CARE laboratory were planned with a different air change per hour, closer to a real one, and with hydronic radiant systems. The room was used to reproduce realistic indoor environments, testing the global comfort in heating and cooling in five different thermal conditions and the perception of the asymmetric radiant field caused by a hot ceiling in a thermally neutral environment. In the global thermal comfort evaluation tests, people showed that their perception was close to the expected, but a relevant time effect was noticed in the answers, with the ratings of the environment changing consistently along with the test duration. In the tests for the radiant asymmetry effect evaluation, participants could not perceive the increase in radiant asymmetry; despite the neutral environment, a prevalence of the cold localized sensation was noticed despite not being correlated with the asymmetry value. The final part of the thesis deals with investigating the faults’ impact on the analyzed configuration. As the radiant system is unlikely affected by faults, which are mostly found in production systems, it was decided to focus only on the air handling unit for the Fault Impact Analysis activity. A case study of a Danish residential building was studied with dynamic simulations in Modelica, and the effects of faults’ presence and their intensity were investigated using different indicators, which shows the impacts on thermal and electrical energy consumption, thermal comfort and indoor air quality. The output of the activity showed the importance of ordinary and extraordinary maintenance, as single faults were found to have a strong effect, especially on energy waste; this also highlights the importance of the research about fault modeling, detection and diagnosis in future installations.