Why Thermal Comfort is an Ergonomics Issue, not Just an Engineering Concern.
Updated: Sep 23
Figure 1: UFAD flexibility when setting out reconfigured layout in a control room
Thermal comfort can have a significant influence on how people experience their workplace. When conditions are too warm, too cold, draughty or stagnant, the effects can extend beyond simple discomfort — affecting concentration, wellbeing and satisfaction with the working environment. Yet achieving thermal comfort is not simply a matter of setting the thermostat to the ‘right’ temperature.
Thermal comfort is often the most challenging aspect of workspace environments, with a complex set of parameters to consider in support of the human bodies thermal balance. The British Standard for thermal ergonomics (7730) defines measurement techniques for indoor environments using various thermal comfort models. HAM have developed an ergonomics survey tool HUSI™, that defines a quantitative measure of reported user satisfaction. This approach is easy to deploy and yields a rich data set to understand the impact workspace environments as a starting point for improvement projects.
Our cover image shows the senior ergonomist completing the setting out of control room furniture and underfloor air distribution outlets, to optimise staff thermal comfort.
1.0 Designing for people not just temperature.
Thermal comfort is influenced by a combination of environmental and personal factors. These include air temperature, radiant temperature, air movement and humidity, together with factors such as clothing, activity levels and individual preference.
Standards and established methods provide useful ways of predicting whether environmental conditions are likely to be acceptable to a population of users. Measures such as Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD), for example, can help designers assess likely thermal comfort.
But predicted comfort and experienced comfort are not necessarily the same thing.
People vary considerably in their thermal preferences. The same environment can feel comfortable to one person, too warm to another and too cold to someone sitting only a few metres away.
This is where ergonomics adds another dimension to the engineering assessment.
Ask the people using the workspace
Post-occupancy surveys provide an opportunity to compare the intended performance of a workplace with the experience of the people actually using it.
At HAM Associates we use our Human User Satisfaction Index (HUSI) methodology to examine a range of workplace factors, including thermal comfort, lighting, noise, workstation design and other aspects of the working environment.
This can be particularly useful when comparing existing and new facilities, or when assessing a workplace following refurbishment.
The results can reveal issues that would not necessarily be identified through environmental measurements alone. They can also help project teams understand which aspects of the environment are having the greatest effect on users.
This combination of objective measurement and subjective user feedback provides a much richer picture of workplace performance..
Thermal comfort in critical workspaces
The challenge can be particularly important in control rooms and other continuously occupied workplaces.
These environments may operate 24 hours a day, accommodate significant equipment heat loads and bring together people performing demanding tasks for extended periods. Operators may also have relatively limited opportunities to move away from their workstation when conditions become uncomfortable.
A single environmental setting therefore has to accommodate people with different clothing, activity levels and thermal preferences, often across different shifts and seasons.
Providing some degree of personal or local control can consequently be valuable. Even relatively small opportunities for users to influence their immediate environment can affect perceptions of comfort and satisfaction.
Several studies have shown that the less the perceived control, the more occupants will say their productivity is reduced. Wyon also showed that control over temperature yields the best productivity gains; control over ventilation is next in importance, then control over lighting (See Figure 3 below) [Wyon 1996].
A lack of control over the thermal environment particularly temperature, can act as a significant additional stressor in the workplace. When individuals feel unable to regulate their comfort, they may adopt a range of coping strategies. These can include taking more frequent breaks, adjusting their clothing layers, relocating within the room, using personal heating or cooling devices, reducing physical or cognitive effort, or withdrawing socially. If these efforts fail to alleviate the discomfort, prolonged exposure can contribute to increased stress levels, decreased productivity, and in some cases, longer-term health consequences such as fatigue, headaches, or musculoskeletal strain [Murphy 2001]
2.0 Underfloor Air Distribution Systems UFAD
Can air-distribution strategy make a difference?
The way conditioned air is delivered into a workspace is one part of this wider ergonomics picture. Conventional systems typically distribute conditioned air from ceiling level. An alternative approach is underfloor air distribution (UFAD), where conditioned air is introduced into the occupied zone through floor-level outlets.
UFAD can offer potential advantages in appropriate applications, including flexibility in the positioning of outlets and opportunities to provide more localised control. It may therefore be worth considering where the building, occupancy pattern and engineering strategy support its use.
However, no particular air-distribution technology guarantees thermal comfort.
System design, air velocities, temperature gradients, equipment heat loads, workstation layout, occupancy and user behaviour all influence the eventual experience of the people occupying the space.
The important question is therefore not simply “Does the HVAC system meet its specification?”, but “Does the completed workplace provide an environment in which people can work comfortably and effectively?”
3.0 Conclusions
The cost of getting thermal comfort wrong
Building-services costs are relatively easy to identify during the design process. The organisational consequences of an uncomfortable working environment can be much harder to see.
Persistent discomfort may contribute to complaints, local heaters and fans appearing around the workplace, disagreement over temperature settings and dissatisfaction with otherwise well-designed facilities.
In critical environments, where organisations invest substantially in buildings, technology and specialist workstations, environmental ergonomics should therefore be considered as part of the overall user-centred design process rather than as a separate engineering issue.
Early user involvement can help establish requirements. Ergonomics input during design can help identify potential problems, while post-occupancy evaluation can determine whether the intended benefits have actually been achieved.
Closing the loop
Good workplace design requires more than compliance with individual technical specifications. It requires an understanding of how people, process, technology and the physical environment interact.
Thermal comfort provides a very good example. Although engineering analysis can predict performance and environmental measurements can tell us what conditions exist it is asking users about their experience that ultimately helps establish whether the workplace is actually delivering the right conditions.
For organisations developing control rooms and other critical workspaces, combining these approaches can help move the discussion from simply providing heating and cooling to creating environments that genuinely support the people working within them.
HAM Associates provides independent ergonomics and human factors support for the design and evaluation of control rooms and other critical workspaces, including environmental ergonomics, user consultation and post-occupancy evaluation.
HAM Associates Ltd. China Works, Black Prince Road, London SE1 7SJ.
www.ham.co.uk email: jh@ham.co.uk
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