Guest editorial: Ventilation challenges in a changing world - Selected papers from the 42^nd AIVC Conference, 5–6 October 2022

More than ever in the past, climate change and the transition to carbon neutrality are at the centre of many countries´ policies and research programmes. The building sector plays a crucial role in achieving these goals, considering the carbon emissions attributed to buildings’ construction and operation, and its potential for better energy performance. At the same time the COVID-19 crisis has emphasized the need to improve indoor air quality (IAQ) and ventilation in our buildings to reduce the risks of airborne virus transmission. All these challenges require a transformation of the existing building stock that at the same time achieves better IAQ and lowers environmental impact.

In 2022 the Air Infiltration and Ventilation Centre (AIVC) organized its first international conference since the beginning of the COVID-19 crisis. Therefore, the conference organizers wanted to pay specific attention to the role of ventilation and infiltration in building decarbonisation, and improvement of indoor air quality including epidemic preparedness. How can design, construction and renovation practices, innovative and digital technologies help in today’s challenges? For these reasons, “Ventilation Challenges in a Changing World”, was defined as the core theme of the joint 42^nd AIVC, 10^th TightVent and 8^th venticool Conference, organized in Rotterdam, the Netherlands, in collaboration with TNO.

Over 70 scientific papers were submitted and, after abstract review, selected for the conference following a call for abstracts on topics of smart ventilation in relation to indoor air quality and health, building and ductwork airtightness, and ventilative and resilient cooling. There were two separate calls for abstracts and papers depending on whether the authors were interested in the peer review of their papers or not. This special issue of the International Journal of Ventilation presents a selection of eight papers from the peer reviewed track, addressing issues raised by the conference topics.

In order to improve IAQ and epidemic preparedness in buildings there is a need for adequate health-centred metrics, and for a better understanding of the exposure to various pollutants in buildings, and how ventilation system design influences this. Morantes et al. address the need to develop health-centred IAQ metrics as alternative to metrics based on limit values for indoor air contaminant concentrations. Their approach is based on the computation of Disability Adjusted Life Years (DALYs) and corresponding uncertainty intervals. They performed an extensive literature review to collect information on the various input parameters needed to implement and strengthen the approach. The updated methodology may be used to assess cumulative health impacts. The study by Verniers et al. is an experimental investigation on the prevalence of two specific groups of contaminants of interest in various rooms of a dwelling. They analysed measurements of particulate matter (PM) and volatile organic compounds (VOC) indoors for a series of household activities, to contribute to a better understanding of health risks. They compared the influence of different ventilation methods, including window ventilation, cooker hoods and dedicated mechanical ventilation systems. A third paper that investigates how ventilation design may reduce health risks is by a Dutch research team (de Haas et al.). They discuss a climate chamber experiment to analyse the effectiveness of personalized ventilation (PV) on infection risk reduction as a potential application in long-term care facilities. The outcomes indicated that operating the PV system can reduce infection risk up to 50%, depending on various design parameter settings.

Three other papers relate to the on-going transition towards nearly zero-energy buildings with at the same time adequate ventilation. Rojas et al. address the lack of specifications for residential ventilation in Austrian building regulations, by investigating whether sufficient ventilation can be ensured with window airing only. They present a stochastic calculation method to estimate the risk of mould growth and the window airing interval necessary to ensure acceptable IAQ. The results suggest the need for mechanical ventilation concepts to prevent mould growth independent of occupant behaviour. A French simulation study by Filis et al. compares the energy and IEQ performance of three residential ventilation systems: room ventilation units with heat recovery (RVU), humidity controlled mechanical exhaust ventilation, and mechanical exhaust ventilation with constant flow rate. The results demonstrated significant energy savings with similar or improved IEQ for RVUs. In zero-energy buildings with energy-efficient ventilation systems a good building airtightness is a prerequisite. Therefore, a fast and reliable detection of leaks is crucial for improving energy-efficiency. For this purpose Kölsch et al. proposed a new approach which combines infrared thermography and periodic excitation by a blower door system. The approach was explored through a series of field measurements of a building façade. The measurements showed higher detection quality and less impact from varying ambient conditions than state-of-the-art methods.

Airtight and highly insulated buildings are subject to overheating risks, also in moderate climates. However, as a result of climate change, overheating risks further increase, also due to unexpected events like severe heatwaves and power outages. There is a need for suitable metrics to quantify the resilience of buildings to overheating and investigate how ventilation concepts may contribute to improve resilience. This is the subject of the two final papers in this special issue. Sengupta et al. define thermal resilience as the ability of the building to withstand thermal disruptions. They present a simulation approach and a set of indicators to assess resilience, which is applied to lecture rooms equipped with different systems for ventilative cooling. Ziarani et al. address one specific concept for ventilative cooling, single-sided ventilation, which is present in many existing buildings for intensive ventilation and can contribute to resilient cooling. They used CFD-simulations to investigate the influence of adding airflow guiding components like louvers to enhance the effectiveness of the wind-driven flow and provided guidance on optimizing louver design for this purpose.

We would like to thank the authors for their efforts to contribute to this special issue, the members of the scientific committee of the 42^nd AIVC conference for their valuable comments in reviewing the papers, and the previous and current editor-in-chief of the Journal, Ben Hughes and Jensen Zhang, for the opportunity and support to organize this special issue.

Content

1. Morantes, G., B. Jones, M. Sherman, C. Molina, A preliminary assessment of the health impacts of indoor air contaminants determined using the DALY metric

2. Verniers, K., F. Losfeld, I. Pollet, J. Laverge, Impact of Ventilation Type on Indoor Generated PM and VOC Levels for Different Indoor Activities.

3. de Haas, M., M. Loomans, M. te Kulve, A. Boerstra, H. Kort, Effectiveness of personalized ventilation in reducing airborne infection risk for long-term care facilities

4. Rojas, G., A. Greml, R. Pfluger, P. Tappler, Assessing the “sufficient ventilation” requirement for Austrian buildings - Development of a Monte Carlo based spreadsheet calculation to estimate airing intervals and mould risk in window ventilated buildings.

5. Filis, V. K. Smith, J. Kolarik, F. Kuznik, L. Merlier, The indoor environmental quality and energy savings potential of room ventilation units compared to exhaust-only ventilation systems in France.

6. Kölsch, B., J. Pernpeintner, B. Schiricke, E. Lüpfert, Air Leakage Detection in Building Façades by Combining Lock-In Thermography with Blower Excitation.

7. Sengupta, A., H. Breesch, D. Al Assaad, M. Steeman, Evaluation of thermal resilience to overheating for an educational building in future heatwave scenarios.

8. Najafi Ziarani, N., M. Cook, P. O’Sullivan, The effect of airflow guiding components on effective ventilation rates in single-sided ventilation applications.