Thermal comfort is a complex issue that is often misunderstood in building design
Thermal comfort is one of the biggest challenges facing building owners—and the source of countless occupant complaints in modern buildings. There are many for reasons for this. It’s technically difficult, frankly, to make buildings thermally comfortable for everyone. There is a myriad of thermodynamic and physiological factors impacting occupants in any space, resulting in what we all know intuitively to be true: some people are always too hot, while some people are always too cold. The result is frustration and discomfort that detracts from people’s health, well-being, focus and performance.
Facility operators recognize that thermal comfort is a tough issue and they know a lot of people in their buildings aren’t comfortable. But the conventional wisdom is to manage the issue by tightly controlling the space—one temperature, at all times, in all seasons, for all occupants.
Research and our experience clearly indicates this is the wrong approach. In fact, the conventional approach generally leads to more complaints and higher energy use.
A better method to address variable comfort expectations is to let the building relax and float a bit, while giving the occupants the ability to control their personal thermal conditions through a variety of means. Allowing some thermal variability in spaces leads to both more satisfied occupants and lower energy bills.
As building designers, the question is: how do we provide a thermally comfort environment when you’ve got people in the same space with different metabolic rates, different clothing and fundamentally different preferences? There is simply no one set of conditions that is going to make everyone happy.
There are conditions that, statistically, the majority of people find acceptable. But why should we strive for merely acceptable spaces? Do we just want people to tolerate their conditions? Of course not. We want people to work in an environment that makes them happy and productive.
LPA is an industry partner with the Center for the Built Environment (CBE), a university-industry collaborative research group based at the University of California, Berkeley, that studies indoor environments and develops tools to help designers and building owners. CBE’s research overwhelmingly indicates that providing occupants an amount of variability and control over thermal conditions produces improved results. Simple intuitive thermal controls such as ceiling fans, operable windows, desk fans and personal heaters make a big difference in going from unacceptable to exceptional comfort.
For some, personal thermal control devices are derided as a waste of energy and problematic in office dynamics. And yet, the best research demonstrates that these solutions are necessary to provide an environment where everyone’s working optimally, satisfying both the people who are otherwise too hot and those who are otherwise cold.
Comfort issues are complex (and not just based in thermodynamics), including wardrobe and gender issues. In many office environments, you will find men wearing suits and closed-toed shoes and women wearing lighter clothing and open-toed shoes. How do you provide a thermal environment that doesn’t make one person hot and sweaty and another person cold and miserable?
And there’s quite a bit of data to demonstrate that, in general, we overcool our buildings. The traditional rule of thumb, especially with Class-A office buildings, is the office needs to be 70 degrees, maybe 72 max. But research shows cooling to 75 or 76 is more to people’s liking, especially in an era when attire is generally getting more casual and many workplace tasks are fairly sedentary.
This is also true of education environments. High school and college students are coming to class in shorts and flip flops and tank tops. If they’re sitting in a 72-degree classroom they’re cold and that makes it harder for them to learn. And the school is increasing its energy bill in order to make these students uncomfortable.
It’s a myth to believe that people who are colder are more alert and active. Being cold doesn’t make people want to learn or be productive. Being cold makes it harder to focus.
Letting occupants have some control over the thermostat setpoints also produces better comfort outcomes. That doesn’t mean unlimited control, but occupants should be able to respond to changing conditions.
At LPA, we are proponents of providing operable windows whenever we can. No one would rent an apartment where the windows were fixed shut. But in commercial spaces we accept that we have fixed windows that can’t be opened, even when the weather outside is great and the air inside is stuffy. Operable windows are a simple, intuitive control that gives people the ability to connect with the outdoors while increasing air movement and ventilation.
Ceiling fans are another traditional building element that we are specifying more and more, providing increased air movement when the space becomes warm or stuffy. The CBE’s research on ceiling fans confirms they are an efficient way to generate air movement and enhance comfort, as opposed to, “let’s crank up the air conditioning.”
Our job as engineers is to think critically and evaluate the different options for meeting our clients’ needs. We evaluate system performance, cost, constructability and operations issues, keeping in mind there are strengths and limitations to every design strategy. There are always fads and “innovative” HVAC systems that come into vogue. But the reality is every building is different and there’s no one approach that’s appropriate for all conditions. And generally, the simplest measures provide the best thermal comfort results.
When it’s done right, we’re making the building operator’s life simpler and better. Occupants won’t be calling the facility operator to say, “I’m miserable, you’ve got to do something about the AC system.” Instead, we’re striving to provide people the ability to address their own thermal comfort conditions, recognizing that there is not one answer that is right for all buildings or all occupants.
Erik Ring is Principal and Director of Engineering at LPA.
