State-of-the art on the use of performance-based approaches for residential ventilation in 2024

Keywords: Ventilation, indoor air quality, energy, performance, residential buildings, smart ventilation

Introduction – towards an innovative basis of thought for building ventilation

The context of climate change and the need of saving energy has required rethinking the ventilation and the air change rates in buildings, because of their increased impact on thermal losses. Indeed, ventilation plays a crucial role estimated around 30-50% of the energy delivered to buildings, becoming an even higher part in high-efficient buildings (Liddament and Orme, 1998, AIVC FAQ).

Indoor air quality (IAQ) is another major area of concern in buildings which is influenced by ventilation. Because people spend most of the time in residential buildings (Klepeis et al., 2001) and 60-90% of their life in indoor environments (homes, offices, schools, etc.) (Klepeis et al., 2001; European Commission, 2003; Brasche and Bischof, 2005; Zeghnoun et al., 2010; Jantunen et al., 2011), indoor air quality is a major factor affecting public health. Logue et al. (2011b) estimated that the current damage to public health from all sources attributable to IAQ, excluding second-hand smoke (SHS) and radon, was in the range of 4,000–11,000 μDALYs (disability-adjusted life years) per person per year. By way of comparison, this means the damage attributable to indoor air is somewhere between the health effects of road traffic accidents (4,000 μDALYs/p/yr) and heart disease from all causes (11,000 μDALYs/p/yr). According to the World Health Organization (WHO, 2014), 99,000 deaths in Europe and 81,000 in the Americas were attributable to household (indoor) air pollution in 2012.

Thus, by optimizing airflows where and when needs are higher, a smart ventilation system can truly improve IAQ while significantly minimizing energy consumption (Durier et al., 2018; Guyot et al., 2018a).

An innovative basis of thought in order to conciliate energy and IAQ in buildings can be proposed for buildings, in the following order:

1.    Sufficiency: the best L·s-1 (airflow) is the one we do not need (because the pollutant sources have been reduced and strictly limited)

2.    Aeraulic efficiency: the right L·s-1 is the one renewed at the best time and at the best location (smart ventilation)

3.    Air cleaning & filtration: if the two first steps don’t meet IAQ objectives, filtration of air inlet and/or air cleaning are needed.

A majority of PRESCRIPTIVE ventilation regulations & associated issues

IAQ performance-based approaches are seldom used for the design of ventilation system in buildings. Instead, prescribed ventilation rates have been used. As a result, standards and regulations, such as ASHRAE 62.2-2016, EN 16798-1 and others in Europe (Dimitroulopoulou, 2012), often prescribe ventilation strategies requiring three constraints on airflow rates:

1.    A constant airflow based on a rough estimation of the emissions of the buildings, for instance one that considers size of the home, the number and type of occupants, or combinations thereof;

2.    Minimum airflows (for instance during unoccupied periods);

3.    Sometimes also provisions for short-term forced airflows to dilute and remove a source pollutant generated by activities as cooking, showering, house cleaning, etc.

Several issues can be highlighted with prescriptive regulations, notably in our global context towards energy efficient buildings and the three axes proposed in the innovative basis of thought for ventilation:

·         With the same level of ventilation airflows, you can reach a wide range of IAQ performance indicators, as shown by instance in (Guyot et al., 2019). In this article, the authors calculated that just by changing the assumptions concerning the distribution of air leakage with the same ventilation air flow rates, a 40% difference could be obtained in the average concentration of formaldehyde inside certain bedrooms over the course of a heating season.

·         With a lower average ventilation airflow, you can even improve the level of IAQ, this is exactly the principle of smart ventilation in general. A recent literature review reporting the performance of smart ventilation strategies gives a range of energy savings of 10-40% (associated to the reduced ventilation airflows) nearly always associated with an improved IEQ (Wang et al., 2024). It confirms results from another review performed in 2018 (Guyot et al., 2018a).

Performance-based approaches for smart ventilation & barriers

In order to conciliate energy saving and indoor air quality issues, interest for smart ventilation systems has been growing thanks to performance-based approaches. Such systems must often be compared either to constant-airflow systems (“equivalence approaches”) or to fixed IAQ metrics thresholds.

A paper published in 2018 offers a review of performance-based approaches for residential ventilation, which had only been found in use in four countries (France, Spain, Belgium and The Netherlands) and one ASHRAE standard around the world, often for the assessment of smart ventilation strategies (G. Guyot et al., 2019; Guyot et al., 2018b). At this time, most of these approaches were based on CO₂ and/or humidity-based performance indicators, or a fictive pollutant.

Poirier et al. (2021b) explain the three different steps of a performance-based approaches: 1) Definition of all the inputs needed for their computation; 2) Definition of the process and assumptions for the modelling stage; 3) Definition of a relevant set of performance indicators (Figure 1).

Figure 1. Schematic diagram illustrating a performance-based approach for ventilation at the design stage of a residential building. (Source: Poirier et al., 2021).

Associated scientific barriers (lack of data) can be listed below:

·         What is the smallest set of relevant performance indicators?

·         What are the levels of requirements (thresholds values)?

·         What is the level of performance of reference (constant airflow) systems? And must this level be used for fixing thresholds values?

·         What are the scenarios to be used as input data: occupancy patterns – emission scenarios – exposure profiles at the room scale?

·         What is the proper level of details of the modelling to require at the design stage of a building, notably on air leakage distributions, on deposition/resuspension phenomena, chemical reactions and dependencies, etc.?

·         How assumptions made on input data and modelling can influence the output? Some answers have been provided with sensitivity analysis works (Poirier et al., 2024a, 2024b).

·         How to balance IAQ and energy (or other non IAQ) in outputs results aggregation from performance-based approach for design and/or decision making?

What is new in 2024?

This paper gives an updated overview of how the performance-based concept has been used and developed in research projects since 2018, and how it has been transposed in standards and some regulations since. In order to update the knowledge published in 2018 (G. Guyot et al., 2019; Guyot et al., 2018b) highlighting only four countries (France, Spain, Belgium and The Netherlands) and one ASHRAE standard.

Since 2018, new research has been published and collected, notably in the context of the IEA-EBC Annex 86 - Energy Efficient Indoor Air Quality Management in Residential Buildings (2022-2025) with a series of deliverables to be published shortly. In this Annex, the preliminary scheme developed by (Poirier et al., 2021b) based on five indicators based on relative humidity, CO₂, formaldehyde and PM2.5 with associated input data on emission scenarios (Poirier et al., 2021a) has been extended and tested in a common exercise performed in five countries (France, Denmark, Belgium, Brazil, Austria).

In our international context in 2024, IAQ and energy are still an issue of interest. Nevertheless, other aspects should be included in the performance indicators. An efficient ventilation system should ensure the exchange of stale indoor air with fresh outdoor air, thus improving indoor environmental quality (IEQ), preventing the build-up of pollutants and excessive moisture or pathogens/viruses, without needlessly wasting energy heating or cooling incoming air, considering environmental and climate changes (heatwaves, pollution peaks, pandemics, …).

In the revised European standard prEN 15665:2024 – Ventilation for buildings – Ventilation systems in residential buildings – design, the section 11 is dedicated to describe the “Performance assessment method” into 11.1-General approach; 11.2-Primary ventilation requirements and performance indicators; 11.3-Calculation method and assumptions.

A new addendum was proposed to the standard ANSI/ASHRAE 62.2- Ventilation and Acceptable Indoor Air Quality in Residential Buildings (Jones, 2023; Jones et al., 2024). A new metric named “harm intensity” is proposed with an associated requirement: the “harm budget”. This proposal is based on the choice of three contaminants of concern: PM2.5, formaldehyde, and nitrogen dioxide. Indeed, the harm caused by those three pollutant accounts for ~83% of all harm caused by each of the 45 contaminants in residential dwellings. This proposal has not been voted yet.

The existing performance-based regulation in Spain has been quite updated and interesting feedbacks since 2018 are now available (García-Ortega and Linares-Alemparte, 2024; Linares-Alemparte and García-Ortega, 2024). Two indicators based on CO₂ are still used. Associated energy savings have been estimated between 20 and 100%.

In France, although a performance-based method was already in use since the 80’s for humidity-based ventilation, which equips over 90% of new residential buildings, the concept is going to be extended to all types of ventilation with the recent ESSOC law (Leprince et al., 2023; Leprince and Poirier, 2024), based on the following statement “Air renewal, shall be such as, in normal condition of use, the indoor air pollution does not endanger health and security of occupants and that condensation is avoided, except temporarily”. Twelve Performance indicators could be used in this future performance-based approach: two based on CO₂, three based on relative humidity, two based on a fictitious pollutant representing constant emissions, two based on another fictitious pollutant representing cooking emissions and three based on air renewal, which remains an intermediate indicator that can be assessed more affordably in most cases and is independent of sources.

In Poland, the use of smart ventilation is still rare in 2024 despite some humidity-based ventilation, same type of the French ones. In the regulation, ventilation requirements can have exception for a given building if it is proven than energy savings can be obtained. The calculation method and the whole procedure have been established procedure by WUT and NAPE (Sorwa et al., 2013).

In Ireland, new regulations for building including ventilation aspects were published in 2019 and 2022, with requirements on air leakage and ventilation performance. The first NSAI (National standard Authority of Ireland) Agreement Certificate for ventilation systems was awarded in 2021 for AERECO humidity-based ventilation systems.

Conclusion

This is not a new topic, but it's not going away any time soon either. A number of scientific hurdles are still in place, despite the research carried out as part of the IEA-EBC Annex 86 project. Secondly, as regards the national standards and regulations that are responsible for transferring this research into the real world, feedback from Spain and France highlights all the remaining barriers: political barriers, as well as technical barriers such as the issue of regular inspections to check that the expected performance is achieved throughout the life of the ventilation system.

Acknowledgements

The authors would like to thank you the experts below who helped reporting the updates in 2024: Jerzy Sorwa, WUT, Poland; Simon Jones, Air quality matters, Ireland; Christoffer Plesner, VELUX, Denmark; All experts from the IEA-EBC Annex 86.

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