Last edited 08 Jul 2014

Running mean temperature

When people are dissatisfied with their thermal environment, not only is it a potential health hazard, it also impacts on their ability to function effectively, their satisfaction at work, the likelihood they will remain a customer and so on.

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.

In the 1970s the existing, ‘steady-state’ theory of comfort was challenged by an adaptive comfort theory which suggested that comfort was time dependent, as the occupants of a building would adapt to their environment over time, adjusting clothing, modifying behaviour and so on. This suggested that the occupants of a building might actually accept conditions that would otherwise have been predicted to be unsatisfactory.

It was proposed that an exponentially-weighted outside running mean temperature could account for this time-dependency.

The equation for the exponentially-weighted running mean temperature for time T is:

Trm = (1-α){T(t-1) + αT(t-2) + α²T(t-3)…..}

Were Tn is the temperature at each time interval, and α is a constant between 0 and 1. The temperatures Tn become less significant as time progresses, with the speed of decay depending on the value of the constant α. The lower the value of α, the less significant the weighting of past temperatures.