Ten questions concerning the application of adaptive thermal comfort in mixed-mode buildings

The recently completed IEA Annex 69 (Strategy and Practice of Adaptive Thermal Comfort in Low Energy Buildings) identified mixed-mode (MM) building design and operation as key strategies for the buildings sector in its transition towards a low-carbon mode. Mixed-mode is short-hand for naturally ventilated designs with supplemental air-conditioning that can be called upon whenever and wherever external climatic loads and/or internal loads dictate. Success of the MM strategy requires shifting the sector’s concept of thermal comfort away from a static comfort zone towards an adaptive approach in which the indoor comfort zone drifts in the same direction as external weather and seasonal trends. The potential for mixed-mode design arises from its applicability in both new construction and existing building stock. The objective of this paper is to elevate awareness of the mixed-mode design concept within the building sector and related research communities. Furthermore, it aspires to influence international thermal comfort standards and guidelines, advocating for a more explicit endorsement of adaptive thermal comfort in mixed-mode applications. Towards this end, we address ten critical questions concerning the application of adaptive thermal comfort in mixed-mode buildings. The questions elucidate the fundamental aspects of MM buildings, the role of adaptive thermal comfort, and the broader implications for building design and operation.