Iñigo Rodríguez-Vidal

Overheating in buildings is a growing challenge in temperate climates, even in those where the traditional design focus was on protecting from cold and winter energy savings. This paper addresses a collateral problem that arose during the study of overheating in a residential Passivhaus building in Bilbao, northern Spain. Specifically, the local climate of three laundry spaces was investigated, where high daytime and nighttime temperatures were recorded. An extensive monitoring campaign was carried out with different durations up to more than 21,000 h over four years, and the collected data were compared with outdoor climatic conditions. The results allowed for characterizing the thermal behavior of these semi-outdoor spaces and show the magnitude of the problem, quantifying it. Laundry spaces were confirmed to be hotter and dryer than the outdoor climate almost always. The mean average difference between the monitored rooms and the exterior was quantified to be around positive 5 °C during both daytime and nighttime. Extreme heat events were documented, with maximum temperatures above 50 °C and temperature differentials of up to 15.85 °C. In addition, this article comments on the impact of overheating these laundry spaces on the interior of the dwellings, pointing out the differences between the assumptions made during the design phase of the project and the observed or measured reality. Questions were raised about the possible implications of the peculiar performance of these semi-outdoor spaces on the mechanical heat recovery ventilation system (MHRV). The data presented in this article revealed and quantified a design flaw that went unnoticed by all agents involved in the planning, design, and construction of the 361-apartment project. The inability to predict the behavior of the studied spaces has had a negative impact on building performance during the summer months and has prevented the implementation of strategies that could have been beneficial in other periods. A thorough analysis of the thermal behavior of similar spaces becomes essential to prevent performance gaps in future projects and to inform adequate building modeling in the design stages.

This study presents a detailed analysis of thermal comfort and energy consumption in a Passivhaus-certified apartment in Bolueta Tower, Bilbao, Spain, over a period of three years (2020–2022). Utilizing a comprehensive, long-term monitoring approach, the research investigates the effectiveness of the Passivhaus standard in achieving both energy efficiency and occupant comfort in a temperate climate. Using calibrated data loggers to record indoor temperature, humidity, and CO2 levels were used alongside the collection of utility bills to assess energy consumption and thermal comfort, as well as IAQ, against several international standards. Significant issues with overheating were confirmed, in line with previous research. During the warmer months, indoor temperatures frequently exceeded the Passivhaus comfort threshold of 25 °C, reaching as high as 31.3 °C, particularly in the living room and bedroom. This resulted in discomfort during summer, with the percentage of hours above 25 °C reaching 23.21% in 2022. Nighttime temperatures often surpassed 24 °C, impacting sleep quality. Conversely, heating consumption was minimal, corroborating the building’s energy efficiency in colder months. The findings highlight a critical gap in the Passivhaus standard when applied in milder climates, where overheating becomes a significant issue. This study suggests the need for an integrated approach in sustainable building design, one that balances energy efficiency with adaptive strategies to mitigate overheating, such as improved natural ventilation and thermal mass. These insights contribute to the ongoing discourse on optimizing energy-efficient buildings for occupant comfort in various climatic conditions.