Letter to the Editor

The Adaptive Thermal Comfort model may not always predict

thermal effects on performance

The recent article by de Dear et al. (2013) misrepre-sents our interpretation of the available evidence onthermal comfort and thermal effects on performance.We have never stated the view that performance andthermal comfort are not compatible, merely thatperformance is not necessarily optimum under themost thermally comfortable conditions. We holdthat if, to conserve energy, indoor temperatures areallowed to change according to the adaptive thermalcomfort model (ATC), performance will not neces-sarily be maintained at those temperatures. Wemade this point most recently when reporting thephysiological changes that take place at temperaturesabove thermal neutrality (Lan et al., 2011, 2013),changes that are usually associated with reduced per-formance and so would be expected to reduce per-formance.

In attempting to refute the view that they incor-rectly impute to us, de Dear et al. cite Pepler andWarner (1968) and accept these authors’ own interpre-tation of their results, which supports the claim thatthe ATC might predict performance. This misinterpre-tation of a series of experiments that is highly relevantto the present disagreement was refuted almost imme-diately by one of us 44 years ago (Wyon, 1970), asfollows:

‘Pepler and Warner (1968) have also reported areversal of the temperature effect on performance. Itoccurred at precisely the same air temperature,27°C, as for the Swedish schoolchildren. Americanstudents were shown to work more slowly througha programmed text at this temperature than at tem-peratures 3° and 6°C above or below. This is whatwe found for reading speed and comprehension.However, the American subjects were wearing only0.5 clo, instead of the c. 1 clo in our field experi-ments, and they were optimally comfortable at27°C. They also estimated that they exerted leasteffort at this temperature, which accords well withtheir slower performance. Percentage errors werenot affected. Surprisingly, Pepler and Warner con-cluded that 27°C was the optimum temperature,reasoning that they worked with effortless efficiencyat this temperature, and were comfortable. The

question arises – optimum for whom? For the indi-vidual subjects, perhaps not very highly motivatedin an experiment of six three-hour exposures, theoptimum was quite possibly that temperature atwhich they could comfortably relax and be comfort-able. An employer might take a different view, rea-soning that the effort they reported was merely theeffort they felt inclined to exert, not the effortrequired to maintain performance, because they didnot in fact maintain their performance at the com-fortable temperatures. The optimum temperature forthe total system and for an employer would surelybe 20°C.’

The crucial point that de Dear et al. and the origi-nal authors missed is that percentage errors, whichare defined to be independent of rate of working, didnot change with temperature, while rate of workingwas lowest at the temperature subjects found mostcomfortable (27°C). They therefore made fewer errorsper hour, and this was the rather odd metric selectedby the original authors as an indicator of perfor-mance. It is difficult to imagine that any employerwould instruct employees to minimize the number oferrors they made per hour. Standard instructions areto work as fast as possible while maintaining anacceptable error percentage, so performance was notoptimum at 27°C, as de Dear et al. would have usbelieve: It did in fact reach its minimum value at 27°C– the temperature at which subjects were most ther-mally comfortable. Optimizing thermal comfort andconserving energy by applying the ATC model couldtherefore prove prohibitively expensive in terms oflost productivity. We should pursue energy conserva-tion by other means, and we should take care to opti-mize the indoor environment for performance so asto be able to afford the increased cost that this willoften entail.

D. P. Wyon, P. Wargocki

International Centre for Indoor Environment andEnergy, Department of Civil Engineering, TechnicalUniversity of Denmark (DTU), Lyngby, Denmark

E-mail: paw@byg.dtu.dk

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Indoor Air 2014; 24: 552–553 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltdwileyonlinelibrary.com/journal/inaPrinted in Singapore. All rights reserved INDOOR AIR

doi:10.1111/ina.12098

References

de Dear, R.J., Akimoto, T., Arens, E.A.,Brager, G., Candido, C., Cheong, W.D.,Li, B., Nishihara, N., Sekhar, S.C., Tana-be, S., Toftum, J., Zhang, H. and Zhu, Y.(2013) Progress in thermal comfortresearch over the last twenty years,Indoor Air, 23, 442–461.

Lan, L., Wargocki, P., Wyon, D.P. andLian, Z. (2011) Effects of thermal

discomfort in an office on perceived airquality, SBS symptoms, physiologicalresponses, and human performance,Indoor Air, 21, 376–390.

Lan, L., Wargocki, P., Wyon, D.P. andLian, Z. (2013) Warmth and perfor-mance: reply to the letter from Leytenand Kurvers (2013), Indoor Air, 23,437–438.

Pepler, R.D. and Warner, R.E. (1968) Tem-perature and learning: an experimentalstudy, ASHRAE Trans., 74, 211–219.

Wyon, D.P. (1970) Studies of children underimposed noise and heat stress, Ergonom-ics, 13, 598–612.

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Letter to the Editor