WELL Buildings: The Thermal Comfort Challenge

“You can please some of the people all of the time, you can please all of the people some of the time, but you can’t please all of the people all of the time.”

The poet John Lydgate probably wasn’t referring to workplace temperature control, but there may be no better way of describing the challenge of maintaining a perfect environment in modern buildings.

Everyone experiences thermal conditions differently and there is no simple definition of what is ‘too hot’ or ‘too cold’. The aim, when taking a holistic approach to building design, is to consider all the factors that affect thermal comfort, and apply that knowledge to make the majority of people comfortable for the majority of the time. In the second of a series of articles exploring the WELL Building standard, we look at how thermal conditions affect performance, and what we can do to find a better balance in every indoor environment.

Too Hot or Too Cold?

Buildings in the UK are designed to retain heat, because we experience cold winters. Many are made of brick, which can store heat and gradually release it over a period of days or weeks. But our summers are getting warmer and our buildings are increasingly failing to keep us comfortable during and after heatwaves.

A study conducted at Shanghai Jiao Tong University found there is a 4% drop in staff performance when an office is too cold. The impact is even greater if it is too hot, when there is a 6% drop in performance.

But the effects go further, as uncomfortable conditions can lead to health risks. Apart from the risk of sick building syndrome, people might take shortcuts to avoid areas that are too cold. They may not wear appropriate personal protective equipment (PPE) if they are too hot, and the likelihood of mistakes increases when concentration is affected by the environment.

Perceiving Thermal Comfort

The Health and Safety Executive outlines six basic factors that affect thermal comfort and it is the combination of these factors that affects a person’s perception of their individual comfort level.

  • Air temperature: This describes the temperature of the air surrounding the body, usually in degrees Celsius, and is the most common measurement. However, it does not give enough information on its own to indicate how comfortable a space is.

  • Radiant temperature: This can have a greater effect than air temperature because it directly affects the body, rather than the air. Think about how the sun will heat you up on a winter’s day. The air temperature doesn’t change, but the direct impact of radiant heat on your body can prompt you to remove your coat. The effect is the same indoors, when radiant heat sources cause you to feel warmer than a thermometer measuring air temperature will show.

  • Air velocity: When it comes to maintaining comfort, air velocity is one of the most important factors. We’ve all experienced draughts at some point and know how distracting and disconcerting they can be. There is no point in cooling a space to ‘ideal’ level if the method involves pumping uncomfortable blasts of cold air at your staff.

  • Humidity: High humidity levels can limit the body’s ability to cool down through sweating, while low humidity contributes to a spread of viruses and causes irritation of the eyes, skin and throat.

  • Clothing insulation: Along with the four environmental factors above, two personal factors contribute to thermal comfort. The first can be affected by policies, as company uniforms or PPE requirements may limit an individual’s ability to adapt their clothing to their environment.

  • Metabolic heat: The second is affected by physical attributes such as age, size and fitness level, while the amount of heat produced by the body in the course of physical work should also be borne in mind.

Meeting the Standard

The WELL Building approach to making the majority of people comfortable for the majority of the time is to use these parameters to create a model for predicting whether people will be satisfied. Once these satisfactory conditions are established, they need to be met for 98% of the building’s occupied hours of the year.

If a project is to meet the standard, it must demonstrate through historic weather data that the sort of extremes the building wouldn’t cope with are not expected for more than 2% of the year.

More advanced criteria of the standard assess the likes of humidity control, while the ability of individuals to adjust their own environment plays a major role. Control of air speed, air temperature and radiant temperature can drastically improve comfort levels, and something as simple as a flexible dress code can have a significant effect by granting more control over the personal factors.

Ultimately, the key to achieving thermal comfort is having the right equipment, in the right place, for the right purpose. That’s why an experienced designer is vital. Putting a fan in a hotspot because you think it will blow enough cold air will not solve a problem.

Instead, we need to consider the interaction of the different factors, how a space is used and what the people who occupy that space need to stay comfortable. By taking this holistic approach, we can get much closer than we ever thought possible to pleasing all of the people, all of the time.

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