Is 22ºC the optimum office temperature?

AUSTRALIA: An Australian survey challenges long-held beliefs that 22°C is the optimum temperature to maintain the output of workers.

Setting the temperature at 22°C has become standard practice in office environments the world over with ASHRAE and REHVA claiming that office performance peaks at that temperature.

Now a team from Australia’s Griffith’s School of Engineering and Built Environment and Cities Research Institute challenges that view. Following what is described as an extensive review of research literature on the relation of moderate thermal environment to cognitive performance, they  found no evidence to support the view that 22°C is the optimum temperature to maintain the output of workers.  

Dr Fan Zhang and the team, which included researchers from the University of Sydney and the University of Central Florida, specifically examined two prevailing conceptual models pertaining to temperature effects on cognitive performance – the inverted-U model and the extended-U model.  

The team found that there is not a single optimum temperature featured by the inverted-U model, which psychologists use to establish the ideal conditions for cognitive performance. 

Instead, human response efficiency follows an extended-U relationship with indoor temperatures, the team maintains. In other words, human performance remains relatively stable across a broad range of acceptable temperatures, but it rapidly deteriorates at the boundaries of thermal acceptability.  

Dr Zhang said that guidebooks such as those produced by ASHRAE and REHVA claim office performance follows an inverted-U function with indoor temperature and peaks at 22°C.  

“Since REHVA and ASHRAE exert a strong influence on air conditioning practices, HVAC-related energy use, and greenhouse gas emissions well beyond their European and North American jurisdictions, it behooves us to critically review the scientific evidence put forward in support of temperature effects on cognitive performance and productivity. 

“In our paper, we have critically reviewed nearly 300 scientific evidences from multiple research disciplines – built environment, psychology, physiology, ergonomics, neuroscience, sports science, medical science, learning and instructional design, and human-technology interaction – on the cognitive performance research theme.”  

And the weight of research evidence reviewed does not favour the inverted-U function, but the extended-U relationship instead, Dr Zhang said.  

No evidence

Dr Zhang told the Cooling Post: “From the research point of view, there is no empirical evidence that this temperature [22ºC] should be maintained. In effect, it is inconsistent with the already-established comfort benchmarks such as ASHRAE 55-2017, which recommends a summer time thermal comfort zone of 23-26ºC. I would say 23-26 is a safe summer temperature set point range for western developed countries.”

Dr Zhang argues that implemention of the extended-U in indoor climate control could lead to substantial reductions in building energy demand, since it permits the heating and cooling set-point dead band to expand across the full width of the thermal comfort zone. Use of personal comfort systems can further extend the thermostat setpoint range beyond the comfort zone.

The team also questioned the cost-benefit analysis and what they say is the so-called productivity loss due to adverse temperatures.  

“Arithmetic relationships have been proposed by different researchers to quantify the productivity decrement in percentage terms as room temperature (or thermal sensation) deviates from the temperature optimum,” Dr Zhang said.  

“These functions have then often been subjected to cost-benefit analyses that trade off the costs of lost productivity from the building’s workforce against the costs of variations in building and building services design, retrofits, and operational facilities’ management practices.  

“However, temperature effects on productivity cannot be readily quantified, particularly with simulated performance tests,” she maintains.  

“For one reason, simulated performance tasks do not accurately represent the nature of real work carried out in actual workplaces.  

“For another, the effects of other factors of productivity beyond environmental factors cannot be eliminated from the research design.”  

Dr Zhang said the practical implications of temperature effects on performance or productivity relates to how we manage and control our buildings.  

“The inverted-U model encourages facility managers to specify heating and cooling set points as close together as technology permits; however, according to the extended-U model, indoor thermal environments can be controlled much less stringently than is currently practiced,” she said.  

“Contrary to the inverted-U function that has incurred horrendous waste of energy, the extended-U relationship has huge potentials in building energy conservation.  

“Therefore, facility managers and building service engineers need to recognise that indoor temperatures spanning the full range of thermal comfort zone are serviceable instead of blindly pursuing a speciously defined single-temperature optimum.”  

The study – Effects of moderate thermal environments on cognitive performance: A multidisciplinary review – has been published in Applied Energy.