Dear Colleagues,

The retrofitting of the existing building stock is a priority for current energy policies that aims to achieve climate neutrality by 2050. Until recently, the main challenge of retrofitting strategies was to face the consequences of progressive climate change. However, the health crisis of the COVID-19 pandemic has highlighted the need to include users’ well-being as a priority. Due to this pandemic, the use of homes has been intensified and air quality requirements in schools, offices, and public buildings are in the spotlight. Is the building stock qualified to be comfortable and healthy for users under these new challenges?

Retrofitting proposals must necessarily be linked to indoor environmental quality (IEQ), also taking into account future climate emergency conditions. It is essential to previously characterize the environmental and energy behavior of the building stock under real conditions of use. These use patterns should meet the new requirements derived from health crisis (homes become working spaces, schools increase the need for air renewal, etc.). We are now more aware that deficiencies in indoor air quality, thermal comfort, or lighting conditions become health risk factors. Therefore, the quantitative diagnosis of these deficiencies is essential for decision-making in renovation procedures.

This Special Issue of Sustainability focuses on, but is not limited to, evaluating the environmental behavior of existing buildings under real conditions in order to propose measures to improve their energy efficiency and IEQ, facing future health and climatic challenges. Therefore, this Issue aims to collect research works related to the building monitoring of occupied buildings in order to avoid performance gap, user behavior, adaptive thermal comfort, the effects of climate change on the built environment, the influence of the COVID-19 pandemic on environmental comfort and IAQ, and retrofitting proposals for IEQ improvement.

Dr. Rocío Escandón Ramírez
Dr. Alicia Alonso Carrillo
Guest Editors

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• indoor environmental quality
• climate change
• COVID-19 pandemic
• building retrofitting
• ventilation
• building monitoring
• occupant comfort
• healthy buildings
• user behavior building-in-use evaluation

Title: Application of solar renewable energy in a HVAC system in order to promote occupants thermal comfort and indoor air quality in winter conditions
Authors: Eusébio Conceição, Rocio Escandón, João Gomes and Hazim Awbi
Affiliation: 1. FCT-Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; 2. Instituto Universitario de Arquitectura y Ciencias de la Construcción, Escuela Técnica Superior de Ar-quitectura, Universidad de Sevilla, Av. Reina Mercedes 2, 41012 Seville, Spain; 3. CINTAL, Campus de Gambelas, 8005-139 Faro, Portugal; 4. School of Built Environment, University of Reading, RG6 6AW Reading, United Kingdom;
Abstract: This paper is focused on the application of solar renewable energy in a Heating, Ventilation and Air-Conditioned (HVAC) system in order to promote occupants thermal comfort and indoor air quality in buildings in winter conditions. In this numerical work, an occupied virtual chamber, a mixing ventilating system and a virtual solar collector system are considered. The performed simulations link numerical models for simulate building thermal response and human thermal physiology response is applied. The building thermal response model calculates the temperatures of the opaque and transparent surfaces, the indoor air chamber and the internal water ducts. The human thermal-physiology response model calculates the human thermal comfort and the tissue and clothing temperatures. The results show that the application of this HVAC system in a Mediterranean-type climate is able to guarantee acceptable thermal comfort conditions in the late morning and early afternoon in winter conditions. However, acceptable indoor air quality conditions can be achieved during all day in winter conditions.