Ventilation conditions and their influence on thermal comfort in examination classrooms in times of COVID-19. A case study in a Spanish area with Mediterranean climate.

Current evidence and recent publications have led to the recognition that aerosol-borne transmission of COVID-19 is possible in indoor areas such as educational centers. A crucial measure to reduce the risk of infection in high occupancy indoors is ventilation. In this global pandemic context of SARS-CoV-2 virus infection, a study has been carried out with the main objective of analyzing the effects of natural ventilation conditions through windows on indoor air quality and thermal comfort during on-site examinations in higher education centers during the winter season, as this implies situations of unusual occupation and the impossibility in many cases of taking breaks or leaving classrooms, as well as the existence of unfavorable outdoor weather conditions in terms of low temperatures. For this purpose, in situ measurements of the environmental variables were taken during different evaluation tests. As the main results of the study, ventilation conditions were generally adequate in all the tests carried out, regardless of the ventilation strategy used, with average CO2 concentration levels of between 450 and 670 ppm. The maximum CO2 concentration value recorded in one of the tests was 808 ppm. On this basis, the limit for category IDA 2 buildings, corresponding to educational establishments, was not exceeded in any case. However, these measures affected the thermal comfort of the occupants, especially when the outside temperature was below 6 °C, with a dissatisfaction rate of between 25 and 72%. Examinations carried out with outside temperatures above 12 °C were conducted in acceptable comfort conditions regardless of outside air supply and classroom occupancy. In these cases, the dissatisfaction rate was less than 10%. The results obtained have made it possible to establish strategies for ventilation in the implementation of future exams, depending on the climatic conditions outside.

Analysis of pelletizing from corn cob waste.

In recent years, biomass market has constantly increased. Pellet industry has started looking for new products with the potential to be used as biofuels. Among them are agricultural wastes, such as corn cob waste, which presents some characteristics that make its direct use in industrial facilities possible. However, these properties are not enough for its use in domestic stoves and boilers, where higher quality of fuel is needed. For this reason, densification is used. In the present research work a technical and energy analysis of corn cob waste pelletizing was carried out in a semi-industrial pelletizer. Some relationships between variables, such as moisture, bulk density and mechanical durability, were analyzed, as well as their influence on energy use and final productivity. The results were satisfactory, as the pellets manufactured fulfilled with most specifications that were consulted, with higher values than those recorded for similar kinds of pellets. Concerning the energy study, the increase in production justified a higher energy consumption of the process in order to get a higher productivity ratio.