Operative temperature (previously known as resultant temperature or dry resultant temperature, but renamed to align with ASHRAE and ISO standards) is a simplified measure of human thermal comfort derived from air temperature, mean radiant temperature and air speed. It can be useful in assessing the likely thermal comfort of the occupants of a building.
Actual thermal comfort is dependent on environmental factors, such as air temperature, air velocity, relative humidity and the uniformity of conditions, as well as personal factors such as clothing, metabolic heat, acclimatisation, state of health, expectations, and even access to food and drink. However as empirical fits to these variables are very complex (see predicted mean vote), a simpler measure can be more useful in practice.
Operative temperature is defined as:
Operative temperature = (tr + (ta x √10v)) / (1+√10v)
ta = air temperature
v = air speed (m/s)
Operative temperature = (( hr x tr) + (hc x ta )) / ( hr + hc )
hc = convective heat transfer coefficient
hr = radiative heat transfer coefficient
Where the air speed is less than 0.1m/s, (as is typical in buildings) radiative and convective heat transfers may be similar, and so the equation can be simplified to:
Operative temperature = (ta + tr)/2
In many spaces, with low air velocity and where air temperature and mean radiant temperature may be similar, air temperature alone can be a reasonable indicator of thermal comfort. However, in spaces where surfaces may be heated or cooled, where there is significant thermal mass, or where solar radiation is present, air and radiant temperatures may be very different and so it is necessary to take account of radiant temperatures in assessing thermal comfort...
 Related articles on Designing Buildings Wiki
Featured articles and news
Have a look at this incredible Möbius strip-inspired media centre in Beijing.
OMA's plans for new arts centre to revitalise city's culture given planning approval.
Select committee criticises DEFRA for failing to take up its recommendations.
Nicola Sturgeon presents ICE's People's Choice Award to the Forth Road Bridge reopening.
Green paper published for consultation.
Mental health issues affect 80% of construction workers. Read our interview with the founders of a new wellbeing initiative.
Would Stephenson be disappointed by the lack of progress on the high speed transport of Hyperloop?
The immersive pop-up cinema experience that could revolutionise on-site health and safety training.
5 out of 10 filtering facepieces fail HSE tests.
Eleven Magazine announce the winner and runners-up in their Moontopia competition.
As January is the time for hitting the gym, Designing Buildings Wiki lists the best gym architecture in the world.