Rising to New Challenges: Connecting IEQ to a Sustainable Future

This special REHVA Journal issue presents selected contributions from the IEQ 2025 conference (co‑organised by ASHRAE and AIVC in Montreal, alongside the 45th AIVC, 13th TightVent and 11th venticool), with a strong emphasis on what designers and operators can apply today. The conference contributions are complemented with articles related to the ongoing revision of the Energy Performance of Buildings Directive (EPBD) and the parallel update of standards such as EN 16798‑1. The conference emphasised the growing understanding of occupant response to indoor environment (thermal, air quality, lighting and acoustics) while enhancing resilience in a changing climate. Taken together, the papers offer timely insights into how comfort, health, energy performance and climate resilience can be better aligned.

Several contributions remind us that indoor environments cannot be reduced to general prescriptive IEQ design values. One paper shows how thermal comfort is shaped by socio‑cultural expectations, organisational norms, and the usability of controls, making it clear that achieving comfort requires more than simply meeting modelled temperatures. Another argues that discomfort is inseparable from health‑induced stress, urging designers to adopt an explicitly health‑protective mindset rather than a compliance‑driven one. These themes resonate with evidence from Ireland, where field monitoring of heat‑pump‑equipped homes reveals deviations from asset‑rating assumptions – bedrooms warmer than expected, living rooms cooler, and heating patterns far more variable. Such findings challenge the HVAC community to design systems that adapt to lived behaviour rather than idealised schedules.

Other contributions strengthen the case for integrating new IAQ metrics and evaluation methods into design practice, supporting designers in selecting strategies that align with both occupant health, energy performance and building durability. A comprehensive DALY‑based analysis quantifies the health and monetary burden of 44 indoor air contaminants in offices, with particulate matter overwhelmingly dominating the harm. This provides designers with a clear hierarchy of pollutants and a basis for cost‑effective intervention. A complementary framework extends DALY metrics to indoor heat exposure, demonstrating that overheating in social housing can be systematically translated into health burden – especially for older adults. Another study evaluates smart ventilation using multi‑pollutant indices, illustrating how pollutant‑responsive modulation can improve both IAQ and energy efficiency – provided minimum flow rates are maintained to prevent moisture‑related damage. A performance‑based comparison of single‑ and dual‑flow systems shows that systems with heat recovery deliver better IAQ and lower energy use, based on a holistic approach to evaluate ventilation system performance.

Measurement reliability also emerges as a crucial design foundation. Work on airtightness testing uncertainty demonstrates how repeatability, operator effects and wind influence results, while recommending weighted regression methods to improve robustness. For acoustics, a study identifies the Speech Privacy Class as the most reliable cross‑context metric, offering designers a clearer basis for specifying privacy in both open and closed offices. Finally, an integrated residential retrofit case study shows that deep renovation, paired with electrification via heat pumps, can reduce primary energy and operational carbon dramatically – yet highlights that comfort performance still hinges on coordinated control of heating and ventilation.

Collectively, the papers in this issue make the case for holistic thinking: indoor air quality, thermal comfort, acoustics, and lighting can no longer be addressed in isolation; neither can energy performance be separated from occupant satisfaction. Smart technologies offer new opportunities – yet technology must serve human needs, not override them.

We hope these contributions inspire HVAC professionals, researchers and policymakers to continue shaping indoor environments where people can thrive – comfortably, safely, and sustainably.