Performance-Based Evaluation of Residential Ventilation Systems

Summary of a paper presented at the joint 45th AIVC conference and ASHRAE 2025 IEQ conference “IEQ 2025: “Rising to New Challenges: Connecting IEQ to a Sustainable Future” will be held on September 24-26, 2025, in Montreal, Quebec together with the 13th TightVent and the 11th venticool conferences.

This article presents a performance-based approach to evaluate indoor air quality (IAQ) and energy performance of single-flow and dual-flow ventilation systems in residential buildings.

Introduction

Indoor environments account for 60% to 95% of total lifetime exposure to airborne pollutants, making indoor air quality (IAQ) a major public health concern. Proper ventilation can improve occupant health by over 20%, yet higher airflow rates often increase energy consumption for heating, cooling, and fan operation.

Despite advances in energy‑performance regulations, ventilation rules still rely largely on prescriptive airflow requirements, which do not reflect real operating conditions. A performance‑based approach is now emerging to better integrate IAQ and energy efficiency.

Central to this shift is the selection of key pollutants. International guidelines—such as IEA Annex 68 and WHO—identify CO₂, formaldehyde (HCHO), and PM2.5 as priority indicators for evaluating ventilation performance and exposure risks in residential buildings.

Study Design and Tools

Two distinct case studies were evaluated under identical external climate and pollution conditions, using complementary tools:

·         Case Study 1 — Individual Houses (MATHIS): two single-family houses, one with single-flow exhaust, one with dual-flow with heat recovery and filtration.

·         Case Study 2 — Multifamily Building (HEAVENLY TRNSYS–CONTAM): a nine-apartment building, comparing collective single-flow versus collective dual-flow at equal airflow.

Performance Indicators

·         CO₂ stuffiness index

·         Formaldehyde (short-term and long-term)

·         PM2.5 exposure (with/without filtration)

·         Relative humidity

·         Intrinsic (fans) and induced (thermal losses) energy consumption

Case Study 1: Individual Houses (MATHIS)

Two otherwise identical houses were simulated. The dual-flow system delivered better IAQ across CO₂, HCHO and humidity, and a higher Final IAQ index, compared to single-flow. Figure 1 summarises these indices.

Figure 1. IAQ Performance (4‑axis Radar, Individual Systems).

Case Study 2: Multifamily Building (HEAVENLY TRNSYS–CONTAM)

With equal airflow for single-flow and dual-flow systems, CO₂ and HCHO were similar (indoor-generated pollutants driven by dilution). Dual-flow improved PM2.5 due to filtration and reduced heat-loss energy via heat recovery. Figure 2 shows IAQ indices; Figure 3 shows energy.

Figure 2. IAQ Performance (5‑axis Radar, Multifamily Building).

Figure 3. Annual Energy Use from Ventilation (Stacked) Invidual house (top) and Multifamily building (bottom).

Energy Performance

Dual-flow systems consumed roughly half the ventilation-related energy compared with single-flow in the individual houses; in the building, heat-loss induced by air renewal decreased from 162.1 to 78.7 kWh/(m²·year).

Practical Implications

Across both case studies and tools, dual‑flow systems provided better IAQ (including PM2.5 when filtration is present) and significantly reduced energy losses due to heat recovery. Single‑flow can maintain acceptable IAQ but at higher energy cost and without filtration benefits.

Conclusion

Selecting an appropriate ventilation strategy is essential for achieving a balance between energy efficiency and healthy indoor environments. The dual‑flow system, equipped with heat recovery and filtration, delivers substantial energy savings while reliably maintaining good IAQ. These findings support the broader adoption of performance‑based approaches in ventilation system design—approaches that more accurately reflect real‑world conditions and encourage sustainable, health‑focused building practices.