Advances in performance evaluation of residential ventilation systems

Introduction

On 9-10 October 2024, the AIVC – TightVent - venticool 2024 joint Conference "Retrofitting the Building Stock: Challenges and Opportunities for Indoor Environmental Quality", was organised by the International Network on Ventilation and Energy Performance (INIVE) on behalf of the Air Infiltration and Ventilation Centre (AIVC), the Building and Ductwork Airtightness Platform (TightVent Europe) and the international platform for ventilative cooling (venticool). The University of Galway, the Maynooth University and the Sustainable Energy Authority Of Ireland (SEAI) were also key organisers.

The conference programme featured three parallel tracks with approximately 150 presentations across the key themes of Smart Ventilation, Indoor Air Quality (IAQ) and Health, Building & Ductwork Airtightness, and Ventilative and Resilient Cooling. One of the conference sessions offered a number of interesting presentations discussing various aspects of performance evaluation of ventilation systems [1-5]. This article gives a summary of the advances achieved in this session.

Investigated problems

In many countries, existing houses are being retrofitted to achieve better energy efficiency levels. In this process, the building envelope's airtightness is usually improved, and a ventilation system becomes necessary to create and sustain a healthy indoor air quality (IAQ). However, standard ventilation system designs developed for new dwellings, are not always easy to integrate in existing houses. As a result, dedicated systems need to be developed with a potential for house retrofitting, and their performance need to be evaluated. This was the motivation for simulation studies on the performance of residential ventilation systems in France [1] and Chile [4].

Furthermore, ventilation standards in many countries use a prescriptive approach based on ventilation rates, while health issues relate to exposure of inhabitants to indoor pollutants of concern, with as most important one particulate matter (PM2.5). A performance-based approach, predicting pollutant concentrations through simulations, is more adequate for assessing IAQ. This was the subject of a French simulation study, analysing the performance of ventilation systems in a multifamily building located in an urban location characterised by high PM2.5 levels [2]. Another French study used measurements to evaluate the long-term performance of mechanical extract ventilation systems in multifamily buildings 15 years after construction [3]. A Dutch simulation study investigated the opportunities of a combined operation of effective range hoods and balanced mechanical ventilation with improved filtering, on the interior particulate matter concentration from indoor and outdoor sources [5]. The latter study also investigated the effect of window use.

Methodology

The different studies used a performance-based approach to predict or monitor the exposure to pollutant concentrations in dwellings. Performance was assessed by means of different sets of IAQ performance indicators:

·         Cumulative or average exposure to PM2.5 [1, 2, 3, 5]

·         Cumulative exposure to CO₂ above reference concentration [1, 2, 3, 4]

·         Cumulative exposure to formaldehyde [1, 2, 3]

·         TVOC-concentrations (P70) [3]

·         Percentage of time in which relative humidity is outside a reference range [1, 2, 4]

·         Ventilation heat loss [1, 2, 4]

·         Fan energy use [1, 2]

·         Mean air flow rate extracted or supplied [1]

The simulation studies used multizone software CONTAM [1, 4], COMIS [5] and HEAVENLY (Holistic Evaluation tool for Air VENtiLation sYstems) based on a TRNSYS-CONTAM [2]. The latter study mainly applies concentrations in bedrooms for performance assessment. In the monitoring study [3] continuous measurements over a two-year period were conducted in buildings located in Lyon and Paris.

Results

In general, according to the simulations, none of the different ventilation systems studied was superior to all others for all indicators. However, balanced ventilation systems with constant air volume and PM2.5 supply filter (E65) presented good results overall for single-family dwellings [1].

The simulation study on multifamily buildings obtained a similar conclusion: a dual-flow ventilation system with 60% filtration effectively maintained CO₂ levels between 500 and 1000 ppm, significantly reduced peak PM2.5 levels, and demonstrated superior energy efficiency, particularly with heat recovery system [2].

The Dutch study [5] showed that good cooking extraction in combination with balanced mechanical ventilation and better filtering (F7) in the supply can significantly reduce exposure to particulate matter in homes, even when windows are open in the bedrooms for a large part of the year. This was mainly due to the much lower exposure in the living room. The use of better filters than F7 only had a limited effect as a result of the assumption that windows were open during part of the year.

Even though improved IAQ was obtained with balanced mechanical ventilation, these are typically systems which represent more difficulties to integrate in existing dwellings [1].

The Chilean study therefore investigated how humidity controlled decentralized mechanical exhaust systems typically installed in kitchens and bathrooms in existing social houses in Chile may be optimized in terms of IAQ and energy use. Optimized systems were based on the extended cascade ventilation principle, or included the addition of an exhaust system specific to bedrooms.

Also, the monitoring study [3] focused on the performance of humidity controlled mechanical exhaust systems in social multifamily buildings, 15 years after construction. Overall, the CO₂ concentrations were acceptable within the limits considered (800 ppm, 1000 ppm and 1500 ppm). The PM2.5 measurements revealed significant concentrations primarily in dwellings occupied by smokers. Here the PM2.5 concentrations regularly exceeded the WHO short-term guide value 15 µg/m³. In non-smoking apartments, the indoor particle levels were generally lower than outdoor levels.

References

[1]     Boulier L., D. Mortari, B. Moujalled et al. 2024. Numerical performance evaluation of ventilation systems for energy-efficient retrofitting of existing houses in France, 44th AIVC, 12th Tightvent, 10th Venticool Conference Proceedings, Dublin, 165-175.

[2]     Kiani Z., A. Nour Eddine, K. Taurines et al. 2024. Evaluating the IAQ and energy performance of two types of ventilation systems in multifamily buildings, 44th AIVC, 12th Tightvent, 10th Venticool Conference Proceedings, Dublin, 284-287.

[3]     Mélois A., A. Marchand Mouri, J. Rios et al. 2024. Performance 2 project - Analysis of the interactions between the Humidity-based DCV systems and IAQ in homes 15 years after their construction, 44th AIVC, 12th Tightvent, 10th Venticool Conference Proceedings, Dublin, 577-586.

[4]     Flamant G., W. Bustamante, A. Janssens and J. Laverge. 2024. Performance evaluation of humidity-based decentralized ventilation systems in social housing in Chile, 44th AIVC, 12th Tightvent, 10th Venticool Conference Proceedings, Dublin, 209-219.

[5]     Jacobs P., W. Kornaat, W. Borsboom. 2024. Balanced ventilation - energy efficient and healthy, 44th AIVC, 12th Tightvent, 10th Venticool Conference Proceedings, Dublin, 707-713.