Spring is here—it’s feeling more and more comfortable!
Yes, it’s getting much more pleasant.
By the way, what do you think determines comfort?
Well… I guess temperature and maybe humidity?
Comfort—or thermal sensation—is said to be determined not only by temperature and humidity but also by the temperature of walls and ceilings, wind speed, human activity levels, and the amount of clothing worn. (*1)
There are also various indices that use these factors to measure comfort. (*2)
Exactly. Our bodies exchange heat with the environment in many ways.
And we exchange heat with the air touching our skin (convection).
We constantly generate heat depending on our activity level (metabolism).
Sweating removes heat when it evaporates (evaporation).
We both receive and emit radiant heat from surrounding surfaces (radiation).
Humans are warm-blooded animals, so we must keep our body temperature constant.
This requires a balance of all heat gains and losses.
We adjust by raising metabolism to warm up or sweating to cool down—even clothing adds another layer of control.
A comfortable environment exists when this balance is maintained without stress. If not, it becomes uncomfortable.
This diagram summarizes the heat balance.
Right. The heat balance depends on many factors—not just air temperature.
But in building design, air temperature alone still gets most of the attention.
Most people rely on air conditioning to control just the air temperature.
But for true comfort, we must consider many factors.
This next diagram shows the relationship between human exergy consumption (the load on the body), air temperature, and average wall temperature in winter.
Comparing two cases with the same total temperature (air + wall):
(A) Air 23°C + Walls 20°C → 2.75 W/m² load
(B) Air 18°C + Walls 25°C → 2.5 W/m² load
Even though (A) feels warmer by air temperature alone, (B) actually puts less strain on the body.
In summer, cooler wall surfaces also make us feel more comfortable.
I see. So even if we heat the air, poor insulation means cold walls—and that keeps things uncomfortable.
Exactly. We must consider conduction, convection, and radiation together.
Before air conditioning, people relied on ingenuity and experience to stay comfortable.
Personal differences and psychology also matter. Studies show that places like stations or atriums often feel fine even with minimal air conditioning (*3).
Maybe being closer to the outdoors makes us less sensitive to discomfort.
Even bare feet on a cool floor or the sound of wind chimes can create comfort.
Interesting. I’ve always felt that just adjusting air temperature alone isn’t enough.
And constant temperature feels strange compared to my childhood environment.
Some argue that growing up without daily or seasonal temperature changes weakens our adaptability (*4).
For adaptable species like us, an unchanging environment may not always be ideal.
Even mild stress can be essential for health and happiness.
There’s also the idea of two types of comfort:
“Tekki” (適): comfort in stable environments
“Kai” (快): comfort from changes or contrasts
Experts in engineering tend to value stability (Tekki), while designers often value variation (Kai).
But for health and happiness, we probably need both.
I guess it varies a lot from person to person.
The question “What is comfort?” is profound.
My conclusion is: don’t just focus on temperature—pay attention to many small things, and layer them to create comfort.
That leads to spaces with depth and richness.
Right. I’ll work harder to create more comfortable spaces too.
What is comfort?
It seems possible to express it numerically in engineering terms, but it is difficult to capture it by numbers alone. It may look like a simple problem, but it is actually quite profound.
Old wisdom can be helpful here, and thinking you fully understand it might actually take you further away from true comfort.
That is why I believe it is a fascinating and thought-provoking theme in architectural design.