Buildings Guide

Thermal Comfort

Key Message

Defining the level of indoor comfort for a building in accordance with the climatic conditions found on site, has enormous potential for saving energy at absolutely no cost. Adjusting the thermostat in hot climates from 24°C to 28°C results in energy savings of 50 to 65 %, while maintaining good thermal comfort for the occupants. In cooler climates, reducing the thermostat temperature by 5-8°C for 8 hours a day (e.g., at night), will result in energy savings of up to 15%.


Humans can tolerate a wide range of climatic conditions. However, they prefer a condition where the optimum conditions of thermal comfort are maintained. The thermal comfort zone has been defined as the condition under which man succeeds in arriving at “the point at which minimum expenditure of energy is needed to adjust himself to his environment" (Olgay, 1963). It is thus a description of the thermal relationship between man and his immediate surroundings.

Heat exchanges of the human body
(Szokolay, 2008)

Cd = conduction
E = evaporation
Rd = net radiation exchange
Cv = convection (including respiration)



These can be divided into two types, the Heat Balance Approach and the Adaptive Thermal Approach. The most widely used and internationally accepted are the ISO 7730 (2005) which is a heat balance approach and the ASHRAE 55 (2004) and CEN 15251 (2011) which are adaptive approaches. Although each model can be used in all conditions norms such as the EN 15251 recommend that the heat bal-ance approach (Fanger Model) be used in actively controlled buildings whereas the adaptive approach is used in open buildings and non-mechanically ventilated buildings.


Thermal comfort in a space can be enhanced by passive measures such as increasing the air speed, by minimizing local discomfort factors such as radiant asymmetry, draft and thermal stratification. Each of these factors is influenced by the design architectural, interior design and air conditioning systems. Some of the measures are further described below.


  • Johanna Knaak
  • Sriraj Gokarakonda 
  • Christopher Moore 


  • BIS, (2005). National building code of India, 2005. 2nd ed. New Delhi: Bureau of Indian Standards, pp.8-1-36.
  • de Dear, R. and Brager, G. (1998). Developing an adaptive model of thermal comfort and preference. ASHRAE Transactions, 104(1).
  • Fanger, P. (1972). Thermal comfort: analysis and applications in environmental engineering. New York: McGraw-Hill.
  • Griffiths, I. (1988). Field-Based Research on Thermal Comfort in Passive Solar Buildings. In: T. Steemers, ed., Solar Energy Applications to Buildings and Solar Radiation Data: Proceedings of the EC Contrac-tors’ Meeting held in Brussels, Belgium, 1 and 2 October 1987, 1st ed. Dordrecht: Kluwer Academic Pub-lishers., pp.110-114.
  • Harvey, L. (2010). Energy and the new reality. London: Earthscan.
  • Lin, Z. and Deng, S. (2004). A study on the characteristics of nighttime bedroom cooling load in tropics and subtropics. Building and Environment, 39(9), pp.1101-1114.
  • Nicol, J. and Humphreys, M. (2002). Adaptive thermal comfort and sustainable thermal standards for buildings. Energy and Buildings, [online] 34(6). Available at: http://www.sciencedirect.com/science/article/pii/S0378778802000063 [Accessed 31 Aug. 2016].
  • Olgyay, V. (1963). Design with climate. [S.l.]: Princeton Univ Press.
  • Szokolay, S. (2008). Introduction to architectural science. Oxford [etc.]: Architectural Press, p.17.

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