Colour as a psychological agent to manipulate perceived indoor thermal environment for low energy design; cases implemented in Sri Lanka

Achieving indoor thermal comfort via innovative, sustainable, energy efficient approaches is a contemporary research mission world-wide. Colour, being a characteristic property of any indoor environment, has rarely been considered for its thermal impacts in this regard, especially in distinguishing a dichotomy of colour perception in thermal terms. The current paper examines the potential of Colour associated Thermal Perception (CTP) to psychologically manipulate perceived indoor thermal environment of inhabitants against the 'real' thermal conditions of indoor environments. If done correctly, this may enable the inhabitants to reach comfort levels consuming comparatively less energy leading to a potential hybrid method of energy conservation. Based on a series of empirical studies in Sri Lanka, the paper reveals CTP to be a psychological response and confirms the common perception of red colour as warm against blue as cool irrespective of the fact that the subjects are normal sighted, colour bind or even blind. Further work revealed that incorporating red colour in interiors of cool tropical uplands (Thalawakele, Sri Lanka, Altitude = 3,930 ft, 6.9388° N, 80.6632° E) is supportive of psychologically inducing a comparatively warmer thermal perception against the real (cold) thermal condition, resulting in reduced heating costs. The reverse was true in hot, humid coastal areas (Panadura, Sri Lanka, Altitude= 3ft, 6.7202° N, 79.9305° E) where factory workers demanded increased ceiling fan speeds to achieve thermal comfort in red coloured interiors whereas lower fan speeds were sufficient for thermal comfort when exposed to blue colour. Accordingly, integrating the shades of cool colours (blue, green, purple) in the interiors of a hot humid climate and warm colours (red, yellow, orange) in cold climate is recommended as a highly supportive low cost solution in reducing the heating and cooling costs respectively, leading to energy conservation.