The Theory of Thermal Comfort in Naturally Ventilated Indoor Environments - "The Pleasure Principle"

Designing for natural ventilation became permissible across an extended range of climate zones in 2004 with the incorporation of an adaptive model into ASHRAE's comfort standard (ASHRAE, 2004). This mainstreaming of adaptive comfort was further reinforced with the introduction in 2007 of a European standard (EN, 2007) that mirrored ASHRAE's precedent. Despite broad international acceptance and application of the concept, there remains a gap in the fundamental theoretical underpinnings of the adaptive comfort approach. The biggest question left begging is: "How can a single set of thermal environmental conditions deemed unacceptable in a conventional HVAC setting be regarded as acceptable and even pleasant in a naturally ventilated setting?" A related question is directed specifically at the role of air movement: "How can a single level of air speed be experienced as an unpleasant draught under one set of conditions, and yet induce pleasant sensations in different conditions?" In this paper the physiological phenomenon of alliesthesia is applied to the specific context of thermal comfort to provide a deeper understanding of why adaptive comfort actually works in naturally ventilated situations.