Operative temperature

Operative temperature (t_o) is defined as a uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment.^[1] Some references also use the terms 'equivalent temperature" or 'effective temperature' to describe combined effects of convective and radiant heat transfer.^[2] In design, operative temperature can be defined as the average of the mean radiant and ambient air temperatures, weighted by their respective heat transfer coefficients.^[3] The instrument used for assessing environmental thermal comfort in terms of operative temperature is called a eupatheoscope and was invented by A. F. Dufton in 1929.^[4] Mathematically, operative temperature can be shown as;

$t_o = \frac{(h_r t_{mr} + h_c t_a)}{ h_r + h_c}$

where,

h_c = convective heat transfer coefficient

h_r = linear radiative heat transfer coefficient

t_a = air temperature

t_mr = mean radiant temperature

Application

Operative temperature is used in heat transfer and thermal comfort analysis in transportation and buildings.^[5] Most psychrometric charts used in HVAC design only show the dry bulb temperature on the x-axis(abscissa), however, it is the operative temperature which is specified on the x-axis of the psychrometric chart illustrated in ANSI/ASHRAE Standard 55 – Thermal Environmental Conditions for Human occupancy.

See also

• HVAC
• Psychrometrics
• Underfloor heating
• ASHRAE

References

1. ^ ASHRAE Terminology, ASHRAE Handbook CD, 1999-2002
2. ^ Nilsson, H.O., Comfort Climate Evaluation with Thermal Manikin Methods and Computer Simulation Models, National Institute for Working Life, 2004, pg. 37
3. ^ Thermal Comfort, ASHRAE Handbook, Fundamentals, Ch. 9, pg.3, 2009
4. ^ Glossary of Meteorology, American Meteorological Society, < http://amsglossary.allenpress.com/glossary/browse?s=e&p=42>, accessed Sept 2010
5. ^ Dufton, A. F. The Equivalent Temperature of a room and its Measurement, Building Research Technical Paper No. 13. London, 1932